Instruction Manual
Model 194
High Speed Voltmeter
01985, Keithley Instruments, Inc.
Instrument Division
Cleveland, Ohio, U.S.A.
Document Number: 194-901-01 Rev. A
SAFETY PRECAUTIONS
The following safety precautions should be observed before using the Model 194.
This instrument is intended for use by qualified personnel who recognize shock hazards and arc famili.lr
with the safety precautions required to avoid possible injury. Read over this manual carefully before operating
the instrument.
Exercise extreme caution when a shock hazard is present at the instrument’s input. The American National
Standards Institute (ANSI) states that a shock hazard exists when voltage levels greater than 3OV RMS 01
42.4V peak are present. A good safety practice is to expect that a hazardous voltage is present in any unknown
circuit before measurement.
Do not exceed 3OV RMS between input low and earth ground.
Inspect your test leads for possible wear, cracks, or breaks before coach use.
For maximum safety, do not touch the test leads or the instrument while power is applied to the circuit undrr
test. Turn the power off and discharge all capacitors before connecting or disconnecting the instrument.
Do not touch any object which could provide a current path to the common side of thr circuit under test
or power line (earth) ground. Always make measurements with dry hands while standing on ‘1 dry, insulated
surface capable of withstanding the voltage being measured.
Do not exceed the instrument’s maximum allowable input as defined in the specifications and operation
section of this manual.
CHANNEL 1
-- ~..l..y.~.I...u..~u
SPECIFICATIONS
MATH FUNCTIONS
INPUT IMPEDANCE: l.lMt, (I.OMll on 200” range) shunted by
<47pF.
MAXIMUM ALLOWABLE INPUT: 250” peak, 2xlO’V*Hz.
MAXIMUM COMMON MODE VOLTAGE: 30” rms, 42V Peak,
SxlO~“.Hz.
COMMON MODE RE,ECTfON RATIO: >6OdS at dc to IkHz, IkR
unbalance.
DIFFERENTIAL NONLINEARITY: Ih-Bit: 52 LSD. 8 bit: 50.5 LSB.
TEMPERATURE COEFFlClENT (Of’-18T & **^-5o”c,: < -t(O.l Y
applicable accuracy specification)i”C.
DYNAMIC CHARACTERISTICS
16 BIT 8 BIT
Minimum
Maximum Sample Rate IS
Sample Rate Resolution
Number of Samples
Sample interval Accuracy
(typical, excluding time base
accuracy,
SIGNALINOISE RATIO: 5OdB for full range IOOkHz sine input.
SLEW RATE: 13”lps minimum.
SETTLING TIME: 1 gs to 0.1% of final value.
CHANNEL CROSSTALK: <6OdB at SOOkHz.
INPUT CO”PI.ING: Ac, dc, ground.
FREQUENCY RBSPONSE (Filter Off,:
dc (15Hz) 20kHz dc @Hz) 20OkHz dc (2Hz) 750kt tz
( ) indicates ac coupled performance.
LOW PASS FILTER: 50kHz, 500kHz, single pole.
Sample Rate
O.ZdB IdlJ
10,s (;;ktfz)
lOOX
1 to 32k 1 t” 65k
0.4”s
1ps (IMHz)
3dB
loons
2ns
TRIGGER CHARACTERISTICS
DELAY:
Pm-Trigger: -Zk<n<-1,Mbitmode; -@kc”<-1.8.bitmod
In/ samples are stored prior to triggering.
Past-Trigger: 1 <n < 1 x 10’. Storage begins “n” samples after tri
gWi”g.
TRIGGER:
SOURCE DESCRlPTlON
Input Signal Slope: + or
External:
Front Pane,:
IEEE-488 Interface:
Other Channel: ,nterna,,y generated.
TIMESASE: Internal: IOMHZ *o.o*%.
Extenta,: IOMHZ nominal, Tn..
Level: Selectable over input voltage
range and resolution.
Negative TTL edge.
Manual pushbutton.
16 programmable trigger modes.
e.
6.
I
A”ERAGE: ~1%
PEAK TO PEAK: Difference between maximum and minimum v.,,ws
of samples.
PLUS PEAK: Maximum va,w of samples.
MINUS PEAK: Minimum value of samplcs~
= v...,
”
II I
z: (V, -TV...,’
STANDARD DE”,AT,ON:
TRUE
ROOT MEAN SQUARE:
INTEGRAL: (‘I*“.+%“..,+ ,F, V.) 1,
DIFFERENCE: Channel 1 Channrl 2,
RATIO: Channel 1 / Chnnncl 2.
v,: Voltage of sanlple i,
n: Total number of samples,
i: Locn,ion of individual ssmplc.
t,: Sample intewa,.
n 2
ANALOG OUTPUT
MODES 0”TPuTS USED
CRT x, y, z (blanking)
Oscilloscope y, % (trigger)
Slow Plot
Strip Chart y
x OurPUT: O-10” I”,, scale. 2.44mV rfS”I”ti0”.
Y OUTPIJT: 0.,ov full scale, 2.44mV rCSO,“ti”n
z 0”TP”T: 0”. 5v or 15”.
ZOOM MAGNIFICATION: O.,:, to 1O”O:l
PAN: Across entire memory.
x, y, z (pen upidown)
REAL TIME (DMA) OUTPUT
FORMAT: Binary, I&bit or S-bit.
RATE: Same as Sample Rate.
CONTROL LINES: End of Sample, Overrun, tligh Byte. I.ow t,yW
s-u
II
II
1 FRONT PANEL PROGRAMS 1 1 GENERAL
0 IEEE ADDRESS: Set IEEE address.
1 SELF TEST: Performs internal RAM and ROM check.
2 DIGITAL CALIBRATION: Executes calibration procedure.
3 CALlBRATlON STORAGE: Stores calibration constants in
NVRAM.
4 x an-PUT FULL SCALE: Sets full scale x output voltage.
5 Y OUTPUT FULL SCALE: sets full scale Y output voltage.
6 Z OUTPUT BLANKING LEVEL: Sets high or law blanking level.
[
IEEE-488 BUS IMPLEMENTATION
M”LTH.INE COMMANDS: DCL, LLO, SDC, GET, GIL “NT,
“NL, SPE, SPD, MIA, Mm
“NILINE COMMANDS: IFC, REN, EOI, SRQ, ATN.
INTERFACE FIJNCTIONS: SH1, AHI, T6, no, Lb, LEO, Slu, RLI,
PPO, DC1, DTI, CO, El.
PROGRAMMABLE PARAMETERS: Range, Math Functions, Zero,
Delay, Sample Rate, Number of Samples, Trigger, Calibration, Output Format. Self Test, Display, Status, Service Request, Storage,
Filter, Terminator, fnput Coupling, Buffer Size, Channc,, Saw and
Recall Setups, Front l’anel Frograms 1.6, key Sequence, Slope,
Analog Outputs, EOI.
BINARY TRANSFER RATE: 90k bytesisecond.
DISPLAY: Fourteen-digit alphanumeric LED display. Function and
IEEE bus status also displayed.
RANGING: Manual or autoranging.
WARMUP: One hour to rated accuracy.
OPERATING ENVIRONMENT: 0” to 50°C, 0% to 80% relative
humidity up to 35°C.
STORAGE EN”IRONMENT: -25” to 65°C.
POWER: 105.125” or 210.250” (internal switch selectable), 50117. or
6OHz. 12O”A maximum. 90-110” and 180-220” version available
upon request.
CONNECTORS: All Ii0 connectors are BNC except Real Time Out-
put (“B-25, and IEEE-488 connectors.
DIMENSIONS, WEIGHT: 89mm high x 435mm wide x 448mm
deep (3% in. x 17% in. x 17% in.). Net weight 9.Ikg (20 Ibs.), Dual
Channel unit.
ACCESSORIES AVAILABLE:
Model 1938: Fixed Rack Mounting Kit
Model 1939: Slide Rack Mounting Kit
Model 1944: Channel 2
Model 7007-I: Shielded IEEE-488 Cable, Im (3.2 ft.)
Model 7007-Z: Shielded IEEE-488 Cable, 2m (6.5 ft.)
Model 7051.2: BNC Interconnect Cable, 2 ft.
Model 7051-5: BNC lntcrconnect Cable, 5 ft.
Model 7754.3: BNC to Alligator Cable, 3 ft.
Model 7755: 5On Feed-Through Terminator
Model 8573A: IEEE-488 Interface for IBM PC, PC-AT
Model 194 High Speed Voltmeter
Specificafi~ns subject to chrn,qe withuut notice.
Contains an overview of the instrument including
features, unpacking instructions, as well as available
accessories.
Includes an overview of front panel controls, rear
panel configuration, and fundamental measurement
procedures. Use this section to get your instrument
up and running as quickly as possible.
This section contains detailed operating information
for the Model 194, and the Model 1944 A/D Module.
Use this section as a reference on all front panel
operating aspects of the instrument.
SECTION 1
General Information
SECTION 2
Getting Started
SECTION 3
Operation
Contains information on connecting the Model 194
to the IEEE-488 bus and programming the instrument from a computer.
Outlines procedures necessary to verify that the instrument is operating within stated specifications.
A complete description of operating principles for
the instrument is located in this section. Analog,
digital, microcomputer, and power supply circuits
are described, as is the IEEE-488 interface.
Details maintenance procedures including fuse replacement, option installation, line voltage selection,
calibration, and troubleshooting.
SECTION
4
~
IEEE-488 Programming
SECTION 5 i
Performance Verification ~
SECTION 6
Principles of Operation ~
SECTION 7
Maintenance
Includes replacement parts information, schematic
diagrams, and component location drawings for the
Models 194 and 1944.
SECTION 8
Replaceable Parts
TABLE OF CONTENTS
SECTION l-GENERAL INFORMATION
1.1
1.2
1.3
1.4
1.5
1.6
1.6.1
1.6.2
1.6.3
1.6.4
1.6.5
1.6.6
1.6.7
1.6.8
1.7
1.8
1.9
1.10
INTRODUCTION ............................................................................. l-l
FEATURES............................................................................~
WARRANTYINFORMATION ................................................................... 1-l
MANUAL ADDENDA..
SAFETY PRECAUTIONS AND TERMS
SPECIFICATIONS
Resolution.. ................................................................................ l-2
Differential Non-Linearity .................................................................... l-2
Slew Rate
Input Impedance and Coupling,
Common-Mode Considerations
Crosstalk
DC Voltage Accuracy and Dynamic Characteristics.
Settling Time ................................................................................ I-4
UNPACKING AND INSPECTION
PREPARATION FOR USE.. .................................................................... ~1-5
REPACKINGFORSHIPMENT ..................................................................
ACCESSORIES
...................................................................................
...................................................................................
................................................................................
.......................................................................
.............................................................................
SECTION 2-GETTING STARTED
2.1
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.3
2.4
2.4.1
2.4.2
2.5
2.5.1
2.5.2
2.5.3
2.5.4
2.6
2.6.1
2.6.2
2.7
INTRODUCTION
FRONT PANEL FAMILIARIZATION
Controls ....................................................................................
Display
IEEE-488 Status Indicators ....................................................................
TiltBail .....................................................................................
REAR PANEL FAMILIARIZATION ..............................................................
POWERUPPROCEDURE .....................................................................
Power Line Connections
Power Up Self Test and Display Messages
BASIC MEASUREMENT TECHNIQUES
Warmup Period
Input Connections
Fundamental Control Selection
Measurement Procedure .....................................................................
SAMPLES, MEASUREMENTS AND READINGS
Definitions
Sampling Discussion
TYPICAL OPERATING MODES
.....................................................................................
............................................................................. 2-l
.....................................................................
............................................................................ 2.14
.......................................................................... 2-14
.................................................................................
........................................................................
.......
..........................................................
..............................................................
...............................................................
.............................................
..............................................................
............................................................ 2-l
....................................................
........................................................
..............................................................
................................................
............................................................... 2-16
i-1
l-2
l-2
l-2
~1-2
l-2
1-3
I-4
l-4
l-5
l-5
l-5
2-1
2-8
2-Y
2-Y
2-Y
2-12
2-12
2-13
2.14
2:14
2.35
2.15
2-15
2-X
SECTION 3-OPERATION
3.1
3.2
3.3
3.3.1
3.3.2
3.3.3
3.3.4
3.4
3.4.1
INTRODUCTION
GENERAL DISPLAY MESSAGES ...............................................................
RANGE SELECTION
Autoranging
Uprange
....................................................................................
Downrange .................................................................................
Range Selection Considerations.
DATA ENTRY .................................................................................
DataKeys ..................................................................................
.............................................................................
................................................................................
..........................................................................
..............................................................
3;l
3-2
3-2
3-2
3-2
3-3
3-3
3-3
3-3
I
3.4.2
3.4.3
3.4.3
3.4.5
3.4.6
3.5
3.5.1
3.5.2
3.5.3
3.6
3.6.1
3.6.2
3.6.3
3.6.4
3.6.5
3.6.6
3.6.7
3.7
3.8
3.9
3.9.3
3.9.2
3.9.3
3.9.4
3.10
3.10.1
3.10.2
3.10.3
3.11
3:12
3.12.1
3.12.2
3.12.3
3.12.4
3.12.5
3.12.6
3.12.7
3.w
3.13.1
3.13.2
3.13.3
3.33.4
3.13.5
3.13.6
3.13.7
3.14
3.14.1
3.14.2
3.15
3.16
3.16.1
3.16.2
3.17
3.18
3.19
3.20
3.20.1
3.20.2
3.20.3
ENTER ..................................................................................... 3.4
CANCEL....................................................; .............................. 3.4
FREQiTIME .................................................................................
Using the Cursor Keys .......................................................................
3.4
3.4
Data-Entry Examples ........................................................................ 3.5
RATE AND SAMPLES PROGRAMMING ....................................................... 3-5
Programming Sampling Rate ................................................................. 3-6
Programming the Number of Samples ........................................................ 3-6
Samples and Rate Selection Considerations. ................................................... 3-8
TRIGGERING ................................................................................
3-9
Trigger Source .............................................................................. 3-10
Single/Continuous Arming Modes
TRIGGER Button Operation
Trigger Delay
...............................................................................
...........................................................
.................................................................
3-10
3-10
3-11
Trigger Slope ............................................................................... 3-13
Trigger Level ...............................................................................
3-W
External Triggering .......................................................................... 3-14
1NPLJT COUPLING ..................................................... .................... 3-14
RECALLING DATA.. ......................................................................... 3-15
DLJALCHANNEI. OPERATION ............................................................... 3-16
Channel 2 Connections ..................................................................... 3-16
Channel Selection .......................................................................... 3.16
Speed Considerations ....................................................................... 3-17
Cross Channel Triggering .................................................................... 3-17
USING ZERO ................................................................................ 3-17
Zeroing From an Applied Signal ............................................................. 3~18
Keying In the Zero Value .................................................................... 3-18
Zero Mode Considerations .................................................................. 3-18
FILTERING .................................................................................. 3-19
USING THE ANALOG OUTPUT .............................................................. 3-21
Analog Output Connections ................................................................. 3.21
Entering the XY Mode (XY MODE)
3-22
Analog Output Data Source (XY DATA) ..................................................... : 3.23
Triggering the Analog Output (XY TRIG). .................................................... 3.24
Scaling the Analog Output (XY ZOOM). ..................................................... 3.24
Controlling the Analog Output Viewed Data (XV PAN) ........................................ 3.25
Setting Maximum Analog Output Levels ..................................................... 3-27
MATHEMATICAL FUNCTIONS ............................................................... 3-29
Average ................................................................................... 3-30
True RMS ................................................................................. 3.30
Peak ...................................................................................... 3.31
Peak-to-Peak ............................................................................... 3-31
Standard Deviation. ........................................................................
3.32
Integral .................................................................................... 3.32
WaveformMode ............................................................................
3.33
RATIOANDDIFFERENCE ................................................................... 3.33
DifferenceMode ........................................................................... 3.33
RatioMode ................................................................................
3.34
STATUS ..................................................................................... 3.34
SETUP MODE ............................................................................... 3-35
RecallinaSetuus ...........................................................................
Saving SYetups'. .............................................
FRONT PANEL PROGRAMS (OTHER KEY OPERATION) ........
RESET .......................................................
EXTERNAL CLOCK ...........................................
REAL TIME OUTPUT .........................................
Signal Lines.. ..............................................
Reading Real Time Data ......................................
Computer Interfacing.. ......................................
.............
.............
.............
.............
.............
.............
......
......
......
......
......
......
......
......
......
......
......
......
......
3.35
3.35
3-36
3-36
3-37
3-38
3-38
3-39
3.40
ii
3.21
3.21.1
3.21.2
3.21.3
321.4
3.21.5
3.22
3.22.1
3.22.2
3.22.3
3.22.4
3.22.5
3.22.6
3.22.7
MEASUREMENT CONSIDERATIONS ...
Ground Loops .......................
RF1 .................................
Instrument Loading Effects. ...........
Input Capacitance Effects ......... ...
AC Frequency Response Considerations
TYPICAL APPLICATIONS ..............
Periodic Waveform Analysis ...........
Long Term Measurements .............
Digital Storage Oscilloscope ...........
Dual-Channel V&meter ..............
Catch a Falling Pulse .................
Reducing Noise in the Measured Signal
Mechanical Vibration Testing ..........
SECTION 4-IEEE-488 PROGRAMMING
._....
,.....
......
......
......
..........
...... ...
...... ...
..........
,.....~...
,.........
,.........
..........
..........
..........
..........
..,...
......
......
......
......
......
......
......
......
......
......
......
......
.....
,....,
......
......
..,...
......
......
3-43
3-43
3-43
344
3-44
3-45
3-40
3-46
3-47
3.47
3.48
?-4X
3-x
3-5 I
4.1
4.2
4.3
4.4
4.5
4.6
4.6.1
4.6.2
4.6.3
4.7
4.7.1
4.7.2
4.7.3
4.8
4.8.1
4.8.2
4.8.3
4.8.4
48.5
4.8.6
4.8.7
4.8.8
4.9
4.9.1
4.9.2
4.9.3
4.9.4
4.9.5
4.9.6
4.9.7
4.9.8
4.9.9
4.9.10
4.9.11
4.9.12
4.9.13
4.9.14
4.9.15
14.9.16
4.9.17
4.9.18
4.9.19
INTRODUCTION ............................................................................. 4-l
A SHORTCUT TO IEEE488 OPERATION .................... ................................. 4-I
BUS CONNECTIONS .........................................................................
INTERFACE FUNCTION CODES ....................... ................................... ...
PRIMARY ADDRESS SELECTION .............. ................................... ...... ...
1-3
J-6
4-h
CONTROLLER PROGRAMMING ........................ ........................ ......... 4-7
LunIrOlier tlanaier
BASIC Interface Programming Statements.
Model 8573 Software Configuration ................ .......... ...... ...... ...... ........
sorrware
............................ ................. ...... ...... .. -t-i
............... .......... ...... ...... ..........
4-i
4-H
FRONT PANEL ASPECTS OF IEEE-488 OPERATION .. .......... ...... ...... ................. 4-8
Front Panel Error Messages
IEEE-488 Status Indicators
............... .......
.....................................
IX)CALKey.....................................................................~
GENERAL BUS COMMAtiD PROGRAMMING
................
........................
REN(Remote Enable) .......................................................................
IFC(Interface Clear) ........................................................................
LLO(LocalLockout).............................................................~ ..........
GTL(GoTo Local) ..........................................................................
DCL (Device Clear) .........................................................................
SDC (Selective Device Clear)
GET (Group Execute Trigger) ..........
Serial Polling (SI’E, SPD) ....
DEVICE-DEPENDENT COMMAND PROGRAI\?MING
Execute (X)
.......
........................................................................
..................................................... ......... 4-14
.......... ...... .......... ...... ...... ......... 4-14
..................................................... ......... 4-15
...... .......... ...................... 4-15
Function(F) ...............................................................................
Range(R)
Rate(S)
Number of Samples(N)
Trigger Mode (T)
..................................................................................
...................................................................................
....................................................................
...........................................................................
Delay(W) .................................................................................
Data Format(G)
............................................................................
........................ 4-N
.......... 4-10
..........
4mlU
...... &lO
4.11
412
4-12
4.12
4.13
4.20
4.20
4-21
4.22
4-22
4-23
4-25
4.26
Analog Output(O) ......................................................................... 4-30
BufferPointer Control(B).....................................................~
Reading Buffer Control (Q).
.......................................................... ......
Filter(P) ...................................................................................
Zero (Z)
Input Coupling(I)
status (U)
SRQ Mode (M) and Status Byte Format
................................................................................ .. 4-34
......................................................................
................................................................................. 4-35
..................................... ................ 4-40
Channel (C) ...............................................................................
EOI and Bus Hold-off Modes (K) ............................................................
Terminator (Y)
................................................................
.............
............
..
4-31
4-32
4.34
4-35
4-43
444
4-45
iii
4.9.20
4.9.21 Recall(A)
4.9.22
4.9.23
4.9.24
4.10
4.10.1
4.10.2
4.10.3
4.10.4
4.10.5
4.11
Save (L) ......................................................
.....................................................
Hit Button (II) .............. ............ ....................
Display (D)
...................................................
Self Test(J) ...................................................
TRANSLATOR MODE ............................ ...... ......
Defining Translator Words (ALIAS) .............................
Enabling and Disabling the Translator Mode (KNEW and OLD)
Combining Translator Words
............................ ......
Reading Back Translator Words (LIST). ..........................
Purging Translator Words (FORGET) ............................
BUS DATA TRANSMISSIOX TIMES.
.............................
SECTION 5-PERFORMANCE VERIFICATION
,...,
......
......
......
......
......
......
......
......
......
......
......
......
.,....
4-46
4-47
4-47
4-48
4-49
4-50
4-50
4-52
4-53
4-53
4-54
4-54
3.1
5.2
5.3
5.4
5.5
5.6
5.7
5.71
5.72
5.8
1NTRODUCTION
ENVIRONMENTALCONDITIONS ............................................................. 5-l
INITIAL CONDITIONS
RECOMMENDED TEST EQUIPMENT .................
TEST EQUIPMENT CO1
VERIFICATION PROCEDI JR1
COMPUTERIZED VERIFICATION ......................
HP-85 Verification Program
IBh? PC/Model 8573 Verification Program
AC FREQUENCY RESPONSE
.............................................................................
‘JNECTIONS ...................
SECTION 6-PRINCIPLES OF OPERATION
6.1
6.2
6.3
6.3.1
6.3.2
6.4
6.4.1
6.4.2
6.4.3
6.4.4
6.4.5
6.5
6.5.1
6.5.2
6.5.3
6.5.4
6.5.5
6.5.6
6.5.7
6.5.8
6.5.9
6.6
6.6.1
6.6.2
6.6.3
6.6.4
6.6.5
6.6.6
6.6.7
6.6.8
INTRODUCTION .............................................................................
FUNCTIONALDESCRIPTION
.................................................................
ANAU)GCIRCU~RY .........................................................................
BlockDiagram ..............................................................................
Circuit Description .......................................................................... 6-3
A!D CONVERTER ............................................................................ 6-4
Converter Block Diagram .................................................................... 6-4
C onverter MDdule ........................................................................... 6-6
FaraIlel-to-Serial
Data Conversion ............................................................. 6-8
Data Transmission Control ................................................................... 6-8
Serial Control ............................................................................... 6-8
DIGITAL CONTROL CIRCUITRY. .............................................................. 6-9
Block Diagram of Digital Circ~uitry ...................................................... ..... 6-9
Isolator Data Transmission, ................. ................................................ 6-11
Serial-to-Parallel Data Conversion ... ..............................
Sample
Counter ..................................................
Digital Trigger Comparator Circuits. ................................
Trigger Period Control Logic .......................................
64K Byte Dual-Port Memory .......................................
Digital Control-to-Microprocessor Interfacing Circuits ................
Non-Volatile Memory Circuits (NVRAM) ............................
MlCROCOMI’UTER ................................................
Microcomputer Block Diagram .....................................
68008 Microprocessor .............................................
Clock and Reset Circuits ..........................................
Address
Decoder .................................................
Control Circuits .......................... .......................
Memory Circuits ..................................................
Buffers ..........................................................
IEEE-488 Interfacing ...............................................
5-l
... 5-l
....................................... 5-l
....................................... 5-2
....................................... 5-2
....................................... 5-3
....................................... 5-3
....................................... 5-5
....................................... 5-6
6-l
6-l
6-3
6-3
.... ...................
........................
6-12
6-12
6-12
6-13
6-13
6-14
6-N
6-14
6-14
6-16
6-16
6-17
6-U
h-18
6.la
6-E
iv
6.7
6.7.1
6.7.2
6.7.3
6.7.4
6.75
6.8
6.8.1
6.8.2
6.8.3
6.8.4
6.9
6.9.1
6.9.2
I/O (Input/Output) Circuitry.
I/O Block Diagram.
Bus Buffering
Display and Keyboard Interface
Serial and NVRAM Control
Analog Output Interfacing
POWER SUPPLIES..
Power Supply Block Diagram.
Power LineInput .......................................
Digital Supplies
Analog Supplies
DISPLAYBOARD ........................................
Block Diagram of Display Board
Circuit Description
....................................
..........................................
.....................................
........................................
.......................................
.....................................
SECTION -/-MAINTENANCE
.............................
..........................
.............................
..............................
...........................
.........................
.................
.................
.................
.................
.................
.................
.................
.................
.................
.................
.....
.....
......
......
......
......
......
......
......
6-l’)
6.1Y
6-21
h-21
6-21
h-21
6.2~1
b-21
h-22
h-23
h-23
h-21
6-24
h-25
7.1
7.2
7.3
7.3.1
7.3.2
7.4
7.4.1
7.4.2
7.5
ix.1
7.5.2
7.5.3
7.5.4
7.5.5
7.5.6
7.6
7.7
7.7.1
7.7.2
7.7.3
7.7.4
7.7.5
7.8
7.8.1
7.8.2
7.8.3
7.8.4
7.8.5
7.8.6
7.8.7
7.8.8
7.8.9
7.8.10
7.9
7.10
7.11
INTRODUCTION
LINE VOLTAGE SELECTION
FUSE REPLACEMENT
Line Fuse Replacement
Digital Supply Fuse Replacement
OPTION INSTALLATION.. ....................................................................
Installation Procedures .......................................................................
Module Recognition Programming
CALIBRATION
Recommended Calibration Equipment
Environmental Conditions,
Warm-up Period
Front Panel Calibration
IEEE-488 Bus Calibration .....................................................................
Input Amplifier Frequency Compensation Adjustment
SPECIAL HANDLING OR STATIC-SENSITIVE DEVICES
DISASSEMBLY ...............................................................................
Top and Bottom Cover Removal
Circuit Board Removal and Replacement
Case Disassembly
Rear Panel Disassembly
Front Panel Disassembly
TROUBLESHOOTING ........................................................................
Recommended Test Equipment
SelfTest ...................................................................................
Troubleshooting Sequence.
Power Supply Checks .......................................................................
Microcomputer
Display Board..
l/O Board ..................................................................................
Analog Circuitry Checks ....................................................................
A/D Converter Checks
A/D Board Digital Circuitry Checks
FAN FILTER CLEANING/REPLACEMENT
Z OUTPUT HIGH LEVEL MODIFICATION
CIRCUITBOARDJUMPERLOCATIONS
..............................................................................
...................................................................
.........................................................................
.......................................................................
............................................................. 7-2
............................................................ 7-6
........................................................................... ...
......................................................... 7-h
......................................................... ......... 7-0
.............................................................................
.......................................................................
.........................................
........................................
..............................................................
................................................... ..
..........................................................................
.....................................................................
....................................................................
..............................................................
..................................................................
.............................................................................
............................................................................
......................................................................
.......................................................... 7-33
...................................................... 7-38
................................................. .. 7-38
.......................................................
7.1
7-l
7-2
7-2
7-2
7.2
7-h
7-i
7-7
7-X
7-10
7-12
7-13
7-13
7-15
7-20
7-20
7-20
7.25
7-2.5
7-25
7-27
7-27
7.27
7-27
7-27
7~33
7~3.1
7-38
SECTION 8--REPLACEABLE PARTS
8.1
8.2
INTRODUCTION .,,....,...........,...........,,,........................
ELECTRICAL PARTS LIST ,..........,,,.......,...,.........,,........,....
:::::::::::::::::: HH::
8.3
8.4 ORDERING INFORMATION.. .................................................................
8.5
8.6 COMPONENT LOCATION DRAWINGS AND SCHEMATIC DIAGRAMS ..........................
MECHANICAL PARTS
FACTORY SERVICE
........................................................................... 8-l
........................................................................
APPENDICES
8-l
8-l
8-l
AI’PENDIXA .........................................................................................
APPENDIX B .........................................................................................
APPENDIX C .........................................................................................
APPENDIX D ........................................................................................
APPENDIX E.. .......................................................................................
AI’PENDIX F .........................................................................................
APPENDIX G-IEEE-488 BUS OVERVIEW
APPENDIX H ........................................................................................
..............................................................
A-l
B-l
C-l
D-l
E-l
F-l
G-l
FL-1
LIST OF ILLUSTRATIONS
.............................................................................................................................................................................................
SECTION l-GENERAL INFORMATION
l-l Equivalent Input Impedance
l-2 Methods of Input Coupling
l-3
l-4
Common Mode Voltage.. ......................................................................
SettlingTime .................................................................................
...................................................................
....................................................................
SECTION 2-GETTING STARTED
2-l
2-2
2-3
2-4
2-5
2-6 Rear Panel A/D Module Connectors.,
2-7
2-8
2-9
Model194 Front Panel .........................................................................
Front Panel Controls ..........................................................................
Front Panel Controls
Display Format ...............................................................................
Model194RearPanel .........................................................................
Rear Panel Connectors, Fuse and Fan
Basic Input Connections
Basic Sampling ...............................................................................
.......................................................................... 2-h
......................................................................
SECTION 3-OPERATION
3-l
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-13
3-14
3-15
3-16
3-17
3-u
3-19
3-20
3-21
3-22
3-23
3-24
3-25
3-26
3-27
3-28
3-29
3-30
3-31
Trigger Delay
Level and Slope Triggering
TRIGGER IN Pulse Specifications
TRIGGER OUT Pulse Specifications
Rear Panel Showing Channel 2 Installed
Typical Filter Response Curves
Rear Panel Showing ANALOG OUTPUT Jacks
Typical Plotter Connections
Typical Oscilloscope Connections
Typical CRT Connections
How Scaling Factor Affects Viewed Data
Moving Analog Output Viewed Data with XY PAN
Output Blanking Levels .......................................................................
Integration by Approximate Area Summation.
Synchronous Operation
Synchronizing Five Units by Daisy Chaining
Real Time Output Connector.
Real Time Output Timing
Flow Chart for Reading Real Time Data
Simplified Block Diagram of Real Time Computer Interface
Multiple Ground Points Create a Ground Loop
Eliminating Ground Loop.
LoadingEffects ..............................................................................
Input Capacitance Effects
Periodic Waveform Analysis
Transient Waveform
Typical Digital Oscilloscope Connections
DuaIChanneIOperation
Pulse Rwe and Fall Tomes
Noise Superimposed on DC Signal
Vibration Testing .............................................................................
................................................................................
....................................................................
..............................................................
................................................................
...................................................................
..............................................................
.....................................................................
......................................................................
.................................................................
.....................................................................
.................................................................... 3-43
.....................................................................
.............................................................................................................................................
.....
..........................................................
.......................................................... 2-12
............................................................
........................................................
..................................................
.......................................................
.............................................
..................................................
................................................... 3-38
........................................................ 3-40
......................................
.................................................
............................................................
l-2
l-3
~I-3
I-4
2-2
2-J
2-X
Z-10
2.11
2-15
2-K
3-12
3.13
3-14
3-14
3.16
3.20
3~21
3.21
3-22
3-22
3-25
3-26
3-28
3-33
3-37
3-38
3-39
3-41
3-43
3-44
3-45
“3%;
3-48
iI+%;
3-50
3-5~1
vii
SECTION 4-IEEE-488 PROGRAMMING
4-l Typical Program Flow Chart
4-2 IEEE-488 Connector
4-3 IEEE-488 Connections
4-4
4-5
4-6 ASCII Data Format (GO to c-5)
4-7
4-8 Circular Buffer
4-9 UO Status Word
4.IO LJl Status Word Format
4.11 Data (U2) Status Word Format.
4-12
4.13 SRQ Mask and Status Byte Format
IEEE-488 Connector Location..
Contact Assignments
Binary Data Formats
U3-Ull Status Word Format
...........................................................................
..........................................................................
..........................................................................
...............................................................................
..............................................................................
...................................................................
.........................................................................
.................................................................
................................................................
.......................................................................
................................................................
...................................................................
............................................................
SECTION 5-PERFORMANCE VERIFICATION
5-l
5-2
s-3 AC Verification Connections
DC Verification Connections
Flow Chart
...................................................................................
...................................................................
....................................................................
SECTION 8-PRINCIPLES OF OPERATION
64
6-2
6-3
6-4 A/D Converter Timing
6-5 Digital Control Block Diagram
6-6
6-7 Memory Map.. ..............................................................................
h-8
6-9
6.10
Simplified Block Diagraln
Simplified Block Diagram of Analog Circuitry
Block Diagram of AID Converter
Microcomputer Block Diagram
110BlockDiagram
Power Supply Block Diagram
Display Board Block Diagram
...........................................................................
......................................................................
...................................................
...............................................................
.........................................................................
.................................................................
.................................................................
.................................................................
.................................................................
4-2
4-3
4-S
4-5
4-6
4.27
4-28
4-33
4.37
4.38
4.39
4-39
4.41
5-2
5-2
5-6
h-2
6-3
6-S
6-7
h-10
h-15
6.17
h-20
h-22
6.24
SECTION 7-MAINTENANCE
7-1
7-2
7-3
7-4
7-5
7-6
7-7
7-8
7-9
7-10
7-11
7-12
7-13
7-14
7-15
7-16
7-17
7-18
Line Voltage Switch and Digital Supply Fuse Locations
Model 1944 A/D Module Installation
Calibration Procedure Flow Chart. ..............................................................
Calibration Connections
Frequency Compensation Adjustment Locations
AC Frequency Response Calibration Connections ................................................
Top and Bottom Cover Removal ................................................................
Circuit BoardRemoval
Cable Connections
Case Assembly
Rear Panel Disassembly
Front Panel Disassembly
Ul Status Word Format
Troubleshooting Flow Chart
Troubleshooting Block Diagram
Fan Filter Removal
Z Output Blanking Level Programming. ........................................................
MovableJumper Locations ....................................................................
............................................................................
...............................................................................
............................................................................
...........................................
............................................................
........................................................................
.................................................
........................................................................
.......................................................................
......................................................................
.......................................................................
...................................................................
................................................................
7-4
7-5
7-8
7-S
7.11
7.12
7.14
7-17
7-19
7.21
7-23
7-24
7-26
7-28
7-29
7-39
7-39
7.40
SECTION 843EPLACEABLE PARTS
8-l
8-2
8-3 Mother Board, Schematic Diagram, Dwg. No. 194-106.
8-4 Display Board, Component Location Drawing, Dwg. No. 194-110
8-5 Display Board, Schematic Diagram, Dwg. No. 194-116
8-6 A/D Board, Component Location Drawing, Dwg. No. 194.120
8-7 A/D Board, Schematic Diagram, Dwg. No. 194-126
8-8 I/O Board, Component Location Drawing, Dwg. No. 194-160
8-9 I/O Board, Schematic Diagram, Dwg. No. 194-166
8-10 Sample Rate Board, Component Location Drawing, Dwg. No. 194-170. ............................
8.11
MechanicalPartsLocation
Mother Board, Component Location Drawing, Dwg. No. 194-100. .................................
Sample Rate Board Schematic Diagram, Dwg. No. 194.176
...................................................................... 8-3
...........................................
.................................
...........................................
....................................
..............................................
.....................................
...............................................
.......................................
APPENDIX G
G-l
G-2
G-3
IEEE Bus Configuration
IEEE Handshake Sequence
Command Codes .............................................................................
.......................................................................
....................................................................
S-10
8-11
8-20
8-21
8-30
8-31
8-42
8-43
8-45
8-46
G-l
CT-3
Gh
ix
SECTION 2-GETTING STARTED
LIST OF TABLES
24
2-2
2-3 Rear Panel Summary
2-4 Factory Default Power Up Conditions
2-s
Front Panel Control Summary
Limits and Resolution for Programmable Parameters.
..........................................................................
Recommended Operating Modes For Typical Waveforms
..................................................................
SECTION 3-OPERATION
3-l
3-2 Range Summary..
3-3 Trigger Source Display Messages
3-4 Display Format
3-5 Filter Display Messages
3-6
3-7 XY Mode Display Messages
3-8
3-Y
3.10
3-11
3.12
3-13
3-14
3-15
3-16
3-17
General Display Messages
............................................................................
...............................................................................
Filter Response Times
XY Mode Level Programming
Math Function Display Messages
Data For Mathematical Function Examples.
Ratio and Difference Display Messages
Typical Status Mode Display Messages
Setup Mode Display Messages
Front Panel rrograms
Factory Default (RESET (SETUP 1) Conditions
Synchronizing Five Units by Daisy Chaining
Voltage and Percent Error For Various Time Constants
.....................................................................
...............................................................
.......................................................................
.........................................................................
...................................................................
.................................................................
..............................................................
................................................................
.........................................................................
.............................................
..........................................................
.........................................
.....................................................
.........................................................
.........................................................
..................................................
...................................................
...........................................
2-3
2-7
2-9
2.13
2-17
3-2
3-2
3-10
3.17
3.19
3.19
3-22
3.27
3.29
3-31
3-33
3.35
3.35
3-36
3.37
3-38
3.45
SECTION 4-IEEE-488 PROGRAMMING
4-l
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4.11
4.12
4-13
4-14
4-15
4-16
4-17
4-18
4-19
4-20
4-21
4-22
4-23
4-24
Summary of Most Often Used IEEE-488 Commands
IEEE Contact Designations
Model 194 Interface Function Codes
BASIC Statements Necessary to Send Bus Commands
Front PanelIEEE-488 Messages
General Bus Commands and Associated BASIC Statements
Power on, DCL, or SDC Default Conditions
Device-Dependent Command Summary
Function Commands
RangeCommands
Rate Commands
Number of Samples Commands ...............................................................
Trigger Commands
Delay Commands
Data Format Commands
Buffer Pointer Select Commands.
Reading Buffer Control Commands
Filter Commands
Zero Mode Commands..
Input Coupling Commands
Status Commands
Values Returned to UO Status for Last Button Pressed
SRQ Commands
Channel Control Commands
............................................................................
.............................................................................
...........................................................................
............................................................................
............................................................................
...........................................................................
.............................................................................
.....................................................................
............................................................
................................................................. 4-8
......................................................................... 4-21
......................................................................
..............................................................
............................................................
.....................................................................
................................................................... 4.35
..................................................................
.............................................
............................................
......................................
....................................................
........................................................
...........................................
4-4
4-5
4-6
4-8
4-11
4-13
4-17
4-21
4-22
4.22
4.23
4.25
4.26
4.31
4.32
4.34
4.34
4-36
4-36
4.41
4-43
x
4-25 EOI and Bus Hold-Off Commands ............
.................................................................................................................................................................................................................
4-26
4-27
4-28 Save Command Summary
4-29
4-30
4-31
4-32
4-33
4-34
4-35
Typical NRFD Hold-Off Times ................
Terminator Commands .......................
....................
Modes Stored By Save Command .............
Recall Commands ............................
Hit Commands ..............................
Display Commands ..........................
UO Self Test Error Codes
Translator Reserved Words and Character ......
Bus Data Transmission Times .................
......................
SECTION 5-PERFORMANCE VERIFICATION
......
......
......
......
......
......
......
......
......
......
......
......
......
......
......
.....
......
......
......
......
......
......
....... 4-44
....... 4-45
....... 4-45
....... 4-46
....... 4-46
....... 4-47
... 4-4x
... 4-48
... 4.49
.......
.......
4-M
4.ss
5-l
5-2
5-3 AC Frequency Response Verification
Performance Verification Equipment.
Performance Verification Limits
.........................
...............................
..........................
SECTION 8-PRINCIPLES OF OPERATION
6-l Attenuator and Gain Values.
6-2 Memory Mapping
................................
.......................
SECTION 7-MAINTENANCE
7-l
7-2
7-3
7-4
7-s
7-6
7-7
7-8
7-9
7-10
7-11
F-12
7-13
7-14
7-15
7-16
7-17
Line Voltage Selection
Line Fuse Selection
Recommended Calibration Equipment
Calibration S urnmary ..........................................................................
AC Response Adjustment Procedure.
Static Sensltwe Dewces
Recommended Troubleshooting Equipment
Self Test Display Messages
Power Supply Checks
MicrocomputerChecks ........................................................................
Display Board Checks
I/O BoardChecks
Input Amplifier Checks
Input Amplifier Gain Values
A/D Converter Checks
A/D Module Digital Circuitry Checks
Z Output Resistor Values
....................................................................
.......................................................................
...........................................................
...............................................................................................................
..
....................................................................
........................................................................
........................................................................
............................................................................
.......................................................... 7-37
.....................................................................
.....................................................
5-1
5.3
.%6
h-4
h-17
7-2
....
7-2
....
7-7
7-7
7.10
................. 7-L?
7-25
7-25
7-30
7.31
7-31
7-32
7-34
7-34
7-35
7-38
SECTION 8-REPLACEABLE PARTS
8-l
8-2
8-3
8-4 I/O Board, Parts List
8-5 Sample Rate Board, Parts List
8-6 Case Assembly, Parts List
8-7
Mother Board, Parts List
Display Board, Parts List
A/D Board, Parts List,
Miscellaneous Mechanical, Parts List.
..........................
.........................
............................
.............................
.....................
.........................
..............
............................
............................
............................
............................
........
,.....
......
......
........ R-6
........ 8-18
....... 8-24
....... 8.40
... 8-45
....... 8-47
....... 8-48
xi
APPENDICES
G-l
G-2
G-3
G-4
G-S
IEEE-488 Bus Command Summary.
Hexadecimal and Decimal Command Codes
Typical Addressed Command Sequence
Typical Device-Dependent Command Sequence
IEEE Command Group
........................................................................
............................................................
....................................................
........................................................
.................................................
G-3
G-7
G-7
G-7
G-7
xii
SECTION 1
GENERAL INFORMATION
1.1 INTRODUCTION
This section contains information on Model 194 features,
warranty, manual addenda, safety terms and symbols, and
specifications. Also included are procedures for unpacking and inspecting the instrument, as well as available
accessories.
The information in Section 1 is divided into the following
major paragraphs:
1.2 Features
Warranty Information
1.3
Manual Addenda
1.4
Safety Symbols and Terms
1.5
Specifications
1.6
Unpacking and Inspection
1.7
Preparation For Use
1.9
Repacking For Shipment
1.9
1.10 Accessories
1.2 FEATURES
The Model 194 High Speed Voltmeter is a high speed DC
voltage sampling instrument suitable for a wide variety of
applications, including the analysis of laboratory
phenomenon, as well as the characterization of transient
and periodic waveforms.
The Model 194 can sample at rates up to lMHr with 2%
digit, a-bit usable resolution, or up to 1OOkHz with 4%
digit, 16-bit resolution. Each A/D channel has 64K bytes
of memory allowing up to 65,535 samples to be stored for
later analysis with one of the many Model 194 mathematical
functions.
l Filtering-Internal analog filtering with sclcctablc poles
of 50kHz or 500kHz is available to reduce the effects of
noise.
l Math Functions-A number of mathematical functions
including average, integral, standard deviation, true
RMS, peak, and peak-to-peak arc included with the in-
strument software.
l Dual-channel Operation-Two separate, isolated AID
channels are available with the optional Model 1944 AiD
Module installed.
l IEEE-488 Interface-A standard feature of the Model 194
that allows the instrument to be controlled from rl
computer.
l Real Time Output-This port allows instrument data to
be transmitted to a computer or similar device at the
sampling rate via a user-supplied interface.
l Programmable Sampling Rates-The instrument CA” bc
programmed to sample data as fast as ‘IMHz, or as slw
as 1Hz.
l Programmable Number of Samples-The number oi sam
pies per measurement sequence Cd” bc prw
grammed to any value between I and 32,767 (~16.bit rc’solution) or 1 and 65,535 (X-bit resolution).
l I’rogramtnable Triggering-The instrument ca” bc trig-
gered from the input signal, an external triger signal,
from the other channel (when the Model 1944 option is
installed), or over the IEEE-488 bus. Programmable triggering parameters include single or continuous modes,
delay, slope, and level.
l XY Mode-Allows the instrument to drive external
display devices such as oscilloscopes and plotters. Internal software allows easy generation of graphs from
sampled data.
l Translator Mode-Simplifies IEEE-488 programming by
allowing the use of English-like syntax.
1.3 WARRANTY INFORMATION
Key Model 194 features include:
l Autoranging-Autoranging allows the instrument to
measure a wide dynamic range of input signals.
l Zero-A zero feature allows a baseline signal level to be
subtracted from subsequent readings. The baseline can
either be taken from a” applied signal, or keyed in from
the front panel or programmed over the IEEE-488 bus.
Warranty information for your Model 194 may be found
inside the front cover of this manual. Should it become
necessary to use the warranty, contact your Keithley
representative or the factory for inform&&xl 011 obtaining
warranty service. Keithley Instruments, Inc. maintains service facilities in the United States, West Germany, France,
the Netherlands, Switzerland, and Australia. Information
concerning the operation, application, or service of the
Model 194 may be obtained by contacting an applications
engineer at any of these locations.
l-l
GENERAL INFOHMATION
1.4 MANUAL ADDENDA
Information concerning improvements or changes to the
instrument which occur after this manual is printed will
be found on an addendum sheet included with the instru-
ment.
Please
attempting to operate or service your instrument.
be
sure that
you read this information before
1.5 SAFETY SYMBOLS AND TERMS
The following safety terms and symbols are used in this
manual or found on the instrument.
The A
should refer to
for further details.
The WARNING heading as used in this manual explains
dangers that could result in personal injury or death.
Always read the associated information very carefully
before performing the indicated procedure.
symbol on the instrument indicates that the user
the
operating instructions in this manual
For example, in the lh-bit mode, the 32OmV range is actually capable of displaying values in the range of -327.68
to + 32.7.67mV, for a total range of 655.35mV. Dividing this
figure by the total number of quantized steps (65,535)
yields the 1OpV resolution figure given in the specifications.
1.6.2 Differential Non-Linearity
The differential non-linearity specification defines the maximum deviation of a quantized step width from the ideal
quantization step width, FSRI(Z”-l), where FSR is the full
scale range of the A/D converter (1OV) and n is the number
of bits (8 or 16) depending on the sampling rate.
1.6.3 Slew Rate
The slew rate specification applies to the sample and hold
portion of the A/D converter and is usually defined as the
maximum rate at which a capacitor can charge expressed
in volts per microsecond. Generally, it is desirable to have
as high a slew rate as possible in order to minimize
response time.
The CAUTION heading used in this manual explains
hazards that could damage the instrument. Such damage
may invalidate the warranty.
1.6 SPECIFICATIONS
Detailed Model 194 specifications are located at the front
of this manual. Some terms used in the specifications are
discussed in the following paragraphs.
1.6.1 Resolution
The resolution of an A/D converter is generally defined
as the number of output states expressed in bits. The
number of output states of a binary quantizing A/D converter is Zn, where n represents the number of bits. The
AID converter in the Model 394 operates with either a-bit
or 16.bit resolution, depending on the sampling rate. Thus,
the AID converter has either 256 (28) or 65,536 (216) output
states.
The resolution figures given in the specifications are derived by dividing the full scale displayable range by the
number of steps for that particular converter resolution.
1.6.4 Input Impedance and Coupling
The input impedance is simply the equivalent resistance
appearing between input high and input low shunted by
(in parallel with) the stated capacitance value. Figure 1-l
shows an equivalent circuit of the input impedance appearing at the VOLTAGE INPUT jack. Input impedance can
become especially important when measuring voltage
sources with high internal resistance: the resistive component can load the source, degrading measurement accuracy, and the capacitive element can increase response
time to rapidly-changing signals
Figure l-l. Equivalent Input Impedance
I-2
GENERAL INFORMATION
Input coupling defines the method used to apply the signal
voltage to the input amplifier. Figure l-2 demonstrates the
three forms of coupling used: AC, DC, and ground. With
the DC coupling method in (a), a straight-through path
is established. Figure 1-2(b) shows the AC coupling
method, in which a capacitor is inserted in series with the
high input signal path. In the case of ground coupling
[Figure 1-2(c)], the input signal is effectively removed from
the input terminals of the input amplifier by shorting the
high and low terminals of the input amplifier together.
1.6.5 Common-Mode Considerations
The low input terminal of the Model 194 can be floated
up to 30V RMS, 42.4V peak above chassis ground. This
voltage is known as the common mode voltage and is
shown on the diagram in Figure l-3. The advantage of
floating the input is that you can measure many sources
that are not referenced to power line ground. The 30V RMS
limitation given in the specifications is defined by ANSI
safety standards; since the shield of any cable connected
to the instrument will also be at common mode potential,
it is imnortant that the 30V limitation be observed to avoid
a possjble shock hazard
Figure 1-2. Methods of Input Coupling
The common mode rejection ratio (CMRR) defines how
much of a common mode signal in the specified frequen-
cy range will appear in the final reading, exclusive of other
factors such as selected math function. Note that this
specification is given is dB and can be converted to an
equivalent noise voltage as follows:
where: V, is the resulting noise voltage.
V,, is the common mode voltage.
CMRR is the common mode rejection ratio in dB.
1-3
GENERAL INFORMATION
As an example, assume that the common mode voltage
is 3OV, and that the CMRR is 60dB. The amount of the
noise signal can be calculated as follows:
3ov
v, = ~
103
v, = 3omv
1.6.6 Crosstalk
The crosstalk specification defines how much of a signal
applied to one A/D module will leak through to the other
A/D module. This signal can be considered as an error or
noise signal that could degrade measurement accuracy.
Thus, crosstalk can be particularly important when
measuring a low level signal on one channel with a high
level signal on another channel.
Like
the CMRR specification, crosstalk is given in dB, with
the higher figure the better. The formula given above for
CMRR can be used to determine how much noise voltage
will appear in a given channel as the result of a signal applied to an alternate channel. For example, assume that
ZOOV is applied to the channel 2 AID converter. With a 60dB
crosstalk figure, the noise voltage in channel 1 is:
Note that the accuracy figures given assume that the instrument has been properly zeroed. To zero the instrument, simply select ground coupling and press the ZERO
button.
1.6.8 Settling Time
The settling time figure defines the length of time the in-
strument response takes to rise to and stay within certain
limits. This specification includes the input amplifier and
sample and hold circuitry, but excludes the A/D converter
itself.
Figure l-4 demonstrates how to interpret the settling time
figure. Assume that the idealized step function shown in
Figure 1-4(a) is applied to the instrument. A hypothetical
response curve is shown
instrument response rises to within stated limits, but, due
to overshoot, continues to rise to point C. Because of ringing, the response drops slightly under the limit at point
D, then rises to within the final limits and stays there at
point E. Thus, the settling time would be interpreted to
be the time period between the initial stimulus (point A)
and the time the response reaches the stated limits (point
El.
in
Figure 1-4(b). At point B, the
VN = 2oomv
1.6.7 DC Voltage Accuracy and Dynamic
Characteristics
The accuracy figures given in the specifications are for DC
voltages, and do not necessarily apply to AC signals. Certain dynamic characteristics may affect overall accuracy
when measuring rapidly-changing signals. In particular,
slew rate and settling time could degrade accuracy for
signals with rapid rise and fall times. Slew rate and settling time are discussed elsewhere in this section.
Basic DC accuracy is specified as *(percent of reading +
an offset). Since the offset on a given range is constant,
better accuracy will be achieved when measuring signals
near full range than when measuring lower-level signals.
Thus, for best accuracy, you should use the most sensitive
range possible for the signal being measured.
1-4
Figure 1-4. Settling Time
GENERAL INFORMATION
1.7 UNPACKING AND INSPECTION
The Model 194 was carefully inspected and packed before
shipment. Upon receiving the instrument, carefully unpack all items from the shipping carton and check for any
obvious signs of physical damage that might have occurred during shipment. Report any damage to the shipping
agent at once. Retain the original packing material in case
reshipment becomes necessary.
The following items are included with every Model 194
shipment:
Model 194 High Speed Voltmeter
Model 194 Instruction Manual
Additional accessories as ordered.
If the Model 1944 A/D Module was ordered with the instrument, it will be shipped already installed.
If an additional instruction manual is required, order the
manual package, Keithley Part Number 194-901-00. The
manual package includes an instruction manual and all
pertinent addenda.
1.9 REPACKING FOR SHIPMENT
Before shipment, the instrument should be repacked in
its original shipping carton.
If the instrument is to be returned to Keithley Instruments
for repair, include the following:
Write ATTENTION REPAIR DEPARTME:NT on the shipping label.
Include the warranty status of the instrument.
Complete the service form at the back of this manual.
1.10 ACCESSORIES
The following accessories are available from Kcithlry Instruments, Inc to enhance Model 194 capabilities.
Model 1938 Rack Mount Kit-The Model 1938 allows the
stationary mounting of the Model 194 in a standard ~14.inch
rack.
Model 1939 Rack Mount Kit-The Model l93Y is similar tu
the Model 1938 except that a sliding-mount configuration
is used.
1.8 PREPARATION FOR USE
Line Power-The Model 194 is designed to operate from
105~125V or 2%250V AC power sources. A special power
transformer may be installed for 90-1lOV and 180.220V
ranges. The factory set range is marked on a label near the
rear panel of the instrument.
CAUTION
Do
not attempt to operate the instrument on a
line voltage outside the indicated range, or in-
strument damage may occur.
Line Voltage Selection-The operating voltage is internally selectable. Refer to Section 7 for the procedure to change
or verify the line voltage setting.
Line Frequency-The Model 194 may be operated from
either 50 or 6OHz power sources.
IEEE-488 Primary Address-If the Model 194 is to be con-
trolled over the IEEE-488 bus, it must be set to the correct
primary address. The primary address is set to 9 at the
factory, but it can be programmed from the front panel,
as described in Section 4.
Model 1944 AID Module-& Model 1Yu giws the Modrl
194 dual-channel AID capability.
7007 Shielded IEEE-488 Cables-The Model 7007 cables in-
clude a shielded metric IEEE-488 connector on each end,
the Model 7007-l is lm (3.3 ft.) long, while the Model 70077
is 2m (6.6 ft.) in length. These cables are shielded to
minimize electrical interference.
7051 BNC Cables-The Models 7051.2 and 705~1-5 are sin&r
cables made up of RG-58C and xe equipped with ankle
BNC connectors on each end. The Model 7051-2 is two irct
in length, while the Model 7051-S is five feet long.
Model 7754 BNC-to-Alligator Cable-The Model 7754 has
a male BNC connector on one end, and a pair of alligator
clips on the other end.
Model 7755 500 Input Terminator-The Model 7755 is J
feed-through BNC terminator that allows the proper tw
mination of 500 cables.
Model 8573 IEEE-486 Interface for the IBM PC-The Model
8573 allows the Model 194 to be connected to and controlled from the IBM PC computer via the IEEE-488 bus.
The Model 8573 installs within the IBM PC and includes
the necessary software to control the IEEE-488 bus from
interpretive BASIC. A Model 7007 cable will bc necessary
to connect the Model 194 to the 8573 interface.
SECTION 2
GETTING STARTED
2.1 INTRODUCTION
This section contains introductory information on
operating your instrument and is intended to help you get
your Model 194 up and running as quickly as possible. It
includes a brief description of operating controls, as well
as fundamental measurement procedures. Once you are
thoroughly familiar with the material presented here, refer
to Section 3 for more detailed information.
Section 2 is organized as follows:
2.2 Front Panel Familiarization:
front panel control, outlines display operation, and
lists where to find more detailed information in Section 3.
2.3 Rear Panel Familiarization:
the Model 194 rear panel including connectors.
,2.4 Power-Up Procedure:
instrument to line power and the type of display
messages to be expected during the power-up cycle.
2.5 Basic Measurement Techniques:
nections and gives the basic instrument configuration
for making measurements.
2.6 Samples, Measurements, and Readings:
these terms as used in this manual.
Describes how to connect the
Briefly describes each
Describes each aspect of
Outlines input con-
Defines
2.2 FRONT PANEL FAMILIARIZATION
An overview of the Model ‘194 is given in the following
paragraphs. The front panel of the instrument is shown
in Figure 2-l. The panel consists of a Ncharacter alpha
numeric display, 38 momentary-contact switches (many <)f
which include display annunciators), and three I.El1s that
indicate IEEE-488 status.
2.2.1 Controls
All front panel controls except POWER arc momentar)
contact switches. To augment the controls, many displ+
annunciators are included. Many of the control buttons
have secondary functions that are invoked with the Stllf;[
key. Primary (not shifted) functions arc indicated above
the corresponding keys, while secondary (shifted) funcCons are marked in yellow below the respective keys (c.xcept for the secondary modes associatecl bvith the Mll~,
kHz, and Hz keys, which arc’ controlled by the. IXEC):‘l~I.Llli
button).
All controls are logically arranged and color coded into
functional groups for east of operation.
Table 2-l summarizes these control functions and also lists
the location in the manual where more detailed inform+
tion concerning these functions may be found. In the
following descriptions, shifted functions are placed in
parentheses.
2-1
GETTING STARTED
2-2
Figure 2-1. Model 194 Front Panel
CO”ttd
POWER
ZERO
(ZERO VAL)
FILTER
TRIGGER
(XY TRIG)
SGLiCONT
(XY MODE)
SOURCE
(XY DATA)
DELAY
(XY PAN)
SLOPE
LEVEL
(XY ZOOM)
SCAN
CPLG
SAMPLES
RATE
LOCAL
CHANNEL
AUTO
UPRANGE
I
IOWNRANGE
SHIFT
RECALL
STATUS
(RESET)
ENTER
CANCEL
FREQiTIME
Data Keys
(CHI + CHZ)
(CHl - CH2)
(OTHER)
(WAVEFORM)
(PK TO PK)
(STD DEV)
(INTEGRAL)
(SETUP)
Table 2-1. Front Panel Control Summary
I
Description
F
,
zontrol AC power to the instrument.
I
?nable/disable zero mode (subtract baseline value from subsequent readings).
I
<ey in zero value with data entry keys.
I
3nableidisable 50kHz or 500kHz analog filter.
1
.nitiate measurement sequence when immediate triggering is enabled. Arm
c
xternal, input signal, and other channel triggering.
start/stop XY analog output data.
Select single or continuous A/D arming.
jelect XY mode to allow data plotting: CRT, oscilloscope, plotter, or strip chart.
Select external triger pulse, immediate, input signal, or other channel as trigger
wurce. (Use uprange or downrange to scroll through sources).
jelect data source for XY analog output: measurement buffer, RAM, readings, or
1
[EEE buffer.
I
Program trigger delay (post or pre-trigger).
1
Program window for XY analog output.
Select positive or negative edge for triggering from input signal.
Program trigger threshold when triggering from input signal.
1
1
Program XY output horizontal scaling factor.
,
Control future scanner module.
Set AC, DC or ground input signal coupling.
1
Program number of samples or measurement duration.
Program sampling frequency or interval between samples.
,
Cancel IEEE-488 remote status, restore front panel operation, return display to
normal.
Select channels 1 or 2, dual channel display, or scanner channels.
Enable/disable autoranging.
Move uprange, mow cursor right (data entry), increment sample number
(RECALL), move viewed data right (XY PAN), increment scaling factor (XY
ZOOM), select front panel program (OTHER), scroll through modes (FILTER,
SOURCE, XY MODE, XY DATA).
Move downrange, move cursor left (data entry), move viewed data left (XY I’AN),
decrement buffer location (RECALL), select front panel program (OTHER), scroll
through modes (FILTER, SOURCE, XY MODE, XY DATA).
Add second function to front panel keys (shifted modes marked in yellow).
Recall stored samples from measurement buffer.
Obtain information on programmed operating modes.
Reset instrument to power-on conditions (same as SETUP 1).
Enter data into memory during data entry process.
Cancel data entered into display during data entry.
Enter data as reciprocal frequency or time.
Enter numeric data and time, frequency, or voltage units.
Divide channel 1 by channel 2 (dual A/D module units only).
Subtract channel 2 from channel 1 (dual A/D module units only).
Access IEEE address, self-test, NVRAM storage, digital calibration, X output full.
scale value, Y output full scale value, Z output blanking level.
Display sample at trigger point.
Display peak-to-peak value of measurement.
Display standard deviation of measurement.
Display integral of measurement in volt-seconds.
Save, recall instrument configurations.
GETTING STARTED
?aragraph
2.4
3.~10
3.10
3.11
3.6
3.12
3.6
3.12
3.6
3.12
3.6
3.12
3.6
3.6
3. I2
3.7
35
3.5
4.7
3.‘)
3.3
3.3
3.3
3.x
3. IS
3. I8
3.4
3.‘1
3.4
3.4
3.14
3.1-I
3. I7
3. I3
3.13
3.13
3.13
3.~16
2-3
GETTING STARTED
Table 2-1. Front Panel Control Summary (Cont.)
.-
Control
(AW
(TRMS) Display true RMS value of measurement.
(PEAK) Display peak value of measurement.
NOTE: Functions in parentheses ( ) are accessed by pressing SHIFT first. Math function keys need not use SHIFT unless
data entry mode is in effect
Description
Display average of measurement.
Paragraph
3.13
3.w
3.13
Figure 2-2. Front Panel Controls
The following controls are indicated in Figure 2-2.
@ POWER-The POWER switch controls the AC power
to the instrument. On and off positions are marked on the
front panel. The instrument should be operated only on
a line voltage in the range marked on the rear of the
instrument.
@ ZERO-The ZERO button enables and disables the
zero mode, which allows a baseline reading to be subtracted from subsequent readings. The baseline value can
either be obtained from an applied input signal, or it can
be keyed in from the front panel. When the zero mode
is enabled, the indicator to the right of the ZERO button
will be on.
@ (ZERO VAL)-Th’
used with the zero mode to be viewed or entered from the
front panel by using the data entry keys.
0
3 FILTER-The
single-pole analog filters. These filters can be used to
reduced the effects of high frequency noise. Filter modes
IS mode allows the baseline value
FILTER button selects 50kHz or 500kHz
are then selected with uprange or downrange. The light
next to the FILTER button will be on when either filter is
enabled.
@ TRIGGER-This key initiates a continuous or single
series of measurements, when immediate triggering has
been selected with the SOURCE key. TRIGGER is also
used to arm the A/D converter with other trigger sources.
@ (XV TRIG)-Used with the XY mode to start and stop
data transmission through the analog output, which is
used to graph data with external devices.
@ SGLICONT-Selects
ing modes. In the single mode, the A/D must be manually rearmed with TRIGGER. In the continuous mode, the
A/D converter is automatically re-armed after each
measurement. Annunciators adjacent to the SGLiCONT
key indicate the selected mode.
0
5 (XV MODE)-This key is used to select the XY mode,
which can be used to drive various display devices such
as plotters and oscilloscopes via the analog output.
single or continuous A/D arm-
2-4
GETTING STARTED
@ SOURCE-Selects the trigger source. The trigger
stimulus can come from an external trigger, the input
signal, the other channel (for dual-channel instruments),
or with the TRIGGER button. Sources are selected with
uprange and downrange. The instrument may also be triggered with IEEE-488 commands, as discussed in Section 4.
@ (XV DATA)-Selects the data source for the analog
output. Available sources include instrument displayed
readings, the measurement buffers or 64k RAM for either
channels 1 or 2 (channel 2 is available only with the Model
1944 option installed), or the IEEE reading buffer.
@ DELAY-The DELAY key is used to program the
beginning point of a measurement sequence relative to the
applied trigger stimulus. Both post- and pre-trigger modes
are available. With post trigger, the instrument waits the
programmed period before beginning sample storage; with
pre-trigger, the instrument begins storing samples at the
programmed interval before the trigger point. Both are
available with all trigger sources.
@ (XV PAN)-Th’ k y II IS e a ows you to select which group
of samples located in the measurement buffer will be applied to the analog output. XY PAN effectively moves the
analog output viewed data left or right.
@ SLOPE-The SLOPE button selects whether the in-
strument is triggered on the positive or negative edge of
the input waveform. The two annunciators adjacent to the
SLOPE button indicate the selected mode. Slope selection
is applicable only when triggering from the input signal.
@ LEVEL-The LEVEL button permits you to program
the signal voltage level at which the instrument is triggered
only when triggering from the input signal. Trigger level
values are keyed in with the data entry keys.
0
g (XV ZOOM)-Applies a magnification or reduction
factor to the horizontal axis on plots. XY ZOOM works in
conjunction with XY PAN to sweep and expand areas of
interest, or to get an overall view of collected data.
0
‘0 SCAN-The SCAN kev is intended for use with a
scanner module to become~available in the near future.
0
” CPLG-CPLG selects AC, DC, or ground coupling
modes analogous to those found on an oscilloscope. AC
and DC coupling are indicated by the respective indicators.
Ground coupling is selected when both indicators xc off.
0
I2 SAMPLES-Allows selection of the amount oi data
taken by programming the number of s.m~plcs to t&x during a measurement cycle, ur the tinw duration of a
measurement. The number of samples or the duration oi
the measurement cycle are keyed in with the data en+
keys. Time duration or number of samples is selected xvith
the FREQiTlME key.
0
l3 RATE-Allows the sclcction of thr spwd uf data
taken by programming sampling frequency or the time iw
terval between individual samples. Time or frequency iw
formation (controlled by FREQITIME) is keyed in with the
data entry keys.
0
‘4 LOCAL-The LOCAL key is used to wmwc’ tht. iw
strumcnt from the remote mode when it is being used owl
the IEEE-488 bus. Note that all front panel controls erccpt
LOCAL and I’OWER will be inoperative when the instrw
ment is in remote (REMOTE indicator on). LOCAL \\-ill
also be inoperative if the IEEE-488 LLO (Local Lockoul)
command is in effect, as discussed in Section 4.
0
I5 CHANNEL-When the instrument is equipped with
the optional Model ‘I944 module, the CHANNEL button
is used to select which channel is to be displayed. ‘Three
basic modes are available: channel 1, channel 2, and duachannel display. For the two single-channel modes, the
display mode also dictates which channel is affected b!
the other front panel buttons. Most of the other buttons
are inoperative when the dual channel display mode is
selected. CHANNEL is also used to return the display to
the previous operating mode when using many Model 194
functions.
2-5
GETTING STARTED
Figure 2-3. Front Panel Controls
The following controls are indicated in Figure 2-3.
0
l6 AUTO-The AUTO button enables or disables the
autoranging mode. The annunciator to the right of the button will be on when the autoranging mode is enabled.
While in this mode, the instrument will choose the best
range to measure the applied signal. Note that a separate
trigger may be required for each range change even if in
auto. Autoranging may be cancelled by pressing AUTO a
second time, or by pressing either the uprange or
downrange keys.
0 Uprange (
The most obvious is to move the instrument uprange once
each time it is pressed until the highest range is reached.
Once the maximum range is established, pressing uprange
will have no further effect. In the data entry mode, this
key moves the display cursor one place to the right each
time it is pressed. In the XY pan mode, the uprange key
moves the viewed data to the right. Uprange is used to
increment the buffer location being accessed when the in-
strument is in the data recall mode. Finally, this key is used to scroll through front panel programs, trigger sources,
and filter and XY modes.
@
Downrange
range has a number of functions: to move the instrument
down one range each time it is pressed, to move the
display cursor ti the left in the data entry mode, to decre-
A
b)-This key. serves several functions.
(4.)-Like the uprange key, down-
ment the scaling factor in the XV zoom mode, to move the
viewed data to the left in the XY pan mode, to decrement
the buffer location in the data recall mode, and to scroll
through front panel programs, trigger sources, and filter
and XY modes.
@ SHIFT-The
functions. Shifted modes are marked in yellow below the
respective keys. When the shift mode is enabled, the
yellow annunciator to the right of the key will be on. The
shift mode can be cancelled by pressing the SHIFT key
a second time. If a key with no shifted mode is pressed
(for example, RECALL), a SHIFTLESS KEY error message
will be displayed.
0
0 RECALL-This key is used to recall data from the
measurement buffer. Once in this mode, the buffer location to be accessed can be keyed in with the data entry
keys, or decremented or incremented with the downrange
or uprange keys. The RECALL annunciator will be on
while the instrument is in the recall mode. To cancel this
mode, press RECALL or CANCEL.
0
1 STATUS-Returns
ment configuration, including A/D and scanner module
parameters, if installed. The instrument will scroll through
various operating parameters.
0
(RESET)-The RESET key returns the unit to power-
on configuration determined by the setup 1 configuration.
SHIFT key allows selection of secondary
information on present instru-
2-6
* ENTER-The
0
the data entry process. Once the desired data appears on
the display, pressing ENTER will store the data in memory
for use by the mode in question. Modes requiring data entry are summarized in Table 2-2.
3 CANCEL-This
0
try mode to cancel keyed in data without actually entering it into memory.
0 4 FREQ/TIME-FREQITIME is used to enter reciprocal
frequency or time information while programming sample rate, scan rate, samples per measurement, or trigger
delay.
ENTER key performs the final step in
key can be used during the data en-
GETTING STARTED
5 (CHi+CH2)-This key programs the instrument to
0
display the ratio of the channel 1 reading to the channel
2 reading. It is operational only if the Model 1944 option
is installed in the CARD 2 location.
0 6 (CHl-CH2)-This button programs the Model 194 to
display the algebraic difference between channels I and
2. It also is operational only if the Model 1944 option is
installed in CARD 2.
7 (OTHER)-This key gives access to various front
0
panel programs, including IEEE-488 address, self test,
digital calibration, NVRAM programming, X output full
scale value, Y output full scale value, and Z output blanks
ing level.
5 sg Data Entry
Q-O
include 0 through 9, +/-, ., MHz (cs), kHz (ms,mV), and
Hz (s,V), are used to enter data into the instrument for
those modes that require data entry, such as samples, rate,
level, delay, and so on. The type of units will depend on
the entry mode. For example, time or frequency would be
in effect when entering sampling rate, while voltage units
(mV or V) would apply when entering a trigger level. The
mode of the MHz (ps), kHz (ms), and Hz (s) keys is determined by the FREQiTIME key-- not by the shift key. Table
2-2 lists modes, limits, and resolution values for the various
modes programmed with the data entry keys. The MHz,
kHz, and Hz keys implicitly perform an ENTER.
Keys-The data entry keys, which
Table 2-2. Limits and Resolution for
Programmable Parameters
1
Mode
RATE
SAMPLES No: l-65,535*
DELAY
LEVEL
ZERO VAL 12OOV
x Output
Full Scale**
Y output**
Full Scale
Limits
Time @sec.lsec
Frequency lHz-lMHz
Time: Orsec-65,534sec*
No: Samples -65,536 to 10’
Time: -65,536 to +lO’sec
*zoov
l-1OV nominal
l-1OV nominal
&3olution
I
O.lpSK
Samples
O.l@C
Samples
O.l@seC
i
HZ
P’v
F’v
PV
0 B (WAVEFORM)-Pressing this key displ.~ys the ~a”>~
pie at the trigger point.
30 (PK TO PK)-l’ak-to-peak values of the nlrasurr-
0
ment can be displayed by pressing I’K TO I’K. I’eak-twpr,lk
values are calculated by subtracting the most negative salw
pie from the most positive sample.
3’ (STD DEV):-The standard deviation of the mel~surc~
0
ment samples can be displayed by pressing this button.
The standard deviation gives a measure of thr spread <of
sample data in comparison to the weragc of the
measurement.
32 (INTEGRAL)-The integral of the measurement
0
samples is obtained with the INTEGRAL button. The iw
tegral function returns the area under a curve (in vo11seconds), which is bounded by the amplitude of the
samples and the measurement duration.
@ (SETUP)-T
operating modes may be stored and recalled through ust’
of the SETUP key. Stored configurations arc retained whrn
power is removed. Setup can also be used to restore factory default configuration.
@ (AVG)-Display
ing a measurement sequence. The average \,rlluC is simply the sum of the samples divided by the numbtv of
samples in the measurement.
wo different combinations of instrument
s the average of samples taken dur-
*32,768 in 16.bit mode
**Accessed with OTHER key.
2-7
GETTING STARTED
8 (TRMS)-Displays the calculated RMS value of the
samples taken in a measurement sequence. The TRMS
value of a waveform is equivaltint to a DC voltage with the
same heating value.
@ (PEAK)-Displays the most positive or most negative
samples taken during a measurement. Positive and
negative values may be obtained by repeatedly pressing
PEAK.
..^__
NUllI
Kevs 25-37 do not reauire uressiw SHIFT if the
Model 194 is in a stat; wh&e data&try is mean-
“NITS
RANGE
32OWl”
3.2 v
32 ”
200 ”
FORMAT
.xxxxx
x.xxxx
xx.xxx
xXx.xX
w VOLTS
VS=“OLTS SECOND
READING
ingless. For example, if channel 1 is being
displayed, you can press SHIFT AVG or just AVG
to enter the average function.
2.2.2 Display
The Model 194 display consists of fourteen 14.segment LED
display units. The display shows not only instrument
readings, but, in many cases, messages to augment the
various operating modes. The general display format is
shown in Figure 2-4
DC-WAVEFORM
P~P=PEAKrO~PEAK
STD=STANDARO DEVlATlON
INTEGRAL lNDlCATED BY vs “NlTS
AVG-AVERAGE
RMS=TRMS
PK+= +PEAK
PK-= -PEAK
T IN THlS POSITION
INDICATES TRIGGER POlNT
CHANNEL NUMBER
2-S
AID AhMED I
‘ND’CATCIR IEEE~GS STATUS
INDICATORS
Figure 2-4. Display Format
GETTING STARTED
‘When reading normal instrument data, the display can
take on one of three formats: channel 1 data, channel 2
data, and dual-channel display (the 1944 option must be
installed for channel 2 or dual channel operation). For the
single channel modes, the display mode also determines
which channel is affected by most of the remaining control buttons. In the dual channel mode, many of the rcmaining front panel controls are locked out. The desired
display mode is selected with the CHANNEL button.
The display normally shows 4% digits regardless of
whether the A/D converter is operating in the 8. or 16.bit
mode. For sampling rates above 1OOkHz (or for more than
32,768 samples), the converter operates in the &bit mode.
Thus, the usable display resolution is only 2% digits under
these conditions, even though 4% digits are shown. For
example, the usable resolution on the 32OmV range at 16
bits is lOpV, but only 2.56mV in the S-bit mode.
The display update rate is indicated by the flashing decimal
point.
Channel 1 Example-The example below demonstrates the
basic format for the display when reading channel 1. Note
that units are specified, as is the channel number which
appears at the extreme right.
2.2.3 IEEE-488 Status Indicators
The TALK, LISTEN, and REMOTE I.EDs (shown in Figure
2-4) indicate the instrument’s status when it is being cow
trolled over the IEEE-488 bus. Section 4 contains complctca
information on IEEE-488 operation. Note that all front
panel controls except LOCAL and POWER will be it?operative when the REMOTE indicator is on.
2.2.4 Tilt Bail
A tilt bail is available on the bottom of the instrument to
elevate the front panel to II con\wlient viwving lhcight. Tcr
extend the bail, pull out each bail extension (c)n the hottom near each front corner) until it locks into place. .To
retract the bail, rotate each extension until it is flush with
the bottom cover.
2.3 REAR PANEL FAMILIARIZATION
The rear panel of the Model 194 is shmvn in Figure Z-.5
The rear panel includes all input and output signal con-
nections, as well as a line fuse and AC receptacle. Each
of these items is briefly described below and summ.trizcd
in Table 2-3
-1.2345 V DC I
Channel 2 Example-The example below shows the basic
channel 2 display format. It is identical to the channel 1
format except for the channel number in the right digit.
2.5902 V DC 2
Dual-Channel Example--The example below demonstrates
the basic dual channel display format. Note that channel
numbers are not displayed in this mode.
-1.2345 2.5902
Note that channel 1 appears on the left in the dual channel mode.
NOTE
A decimal point between the second and third
digits from the right will indicate when the AID
converter is armed and waiting for a trigger. See
paragraph 3.6.
Table 2-3. Rear Panel Summary
Item
VOLTAGE INPUT
REAL TIME
OUTPUT
TRIGGER OUT
TRIGGER IN
ANALOG OUTl’Ul
CLK
IEEE-488 Interface
AC Receptacle
Line Fuse
instruments.
Initiate measurement sequence.
Graph data on plot- ! 3.13
ter or oscilloscope. j
Synchronize several
194s.
Connect 194 to
IEEE-488 bus.
Apply power to
instrument.
Protect instrument 73
from overload. 1
3.6
3.20
4.5
2.4
2-9
GETTING STARTED
2-10
Figure 2-5. Model 194 Rear Panel
GETTING STARTED
Figure 2-6. Rear Panel AID Module Connectors
The following connectors are shown in Figure 2-h.
0
WJ CARD l-CARD 1 is the standard input channel for
the instrument. It includes a signal input, as well as trig-
gering connections and a real time output.
0
4’
CARD
the CARD 2 location. The Model 1944 is functionally
equivalent to the module in CARD 1.
0
42 VOLTAGE INPUT-The
isolated female BNC connector that is used to apply input signals to the instrument.
2-The Model 1944 option can be installed in
VOLTAGE INPUT jack is an
0
43 REAL TIME OUTPUT-This
used to transmit A/D data in byte or word parallel form
to other equipment, such as a computer. Data can be
transmitted at the programmed sample rate, up to the
maximum conversion rate (1MHz) of the instrument. A
user-supplied interface on the computer end is required
to make the necessary connections.
0
44 TRIGGER
apply an external trigger pulse to initiate a mcas~~rcnwnt
sequence. External triggering is available only when the
instrument is properly programmed with the SOURCE
key.
0
45 TRIGGER
ger output pulse when the Model 194 is itself trigRcrcd.
It can be used to trigger other instrumentation.
IN-This BNC connector can be used to
OUT-This BNC connector provides a trig-
DB-25 connector i’,
2-11
GETTING STARTED
Figure 2-7. Rear Panel Connectors, Fuse and Fan
The following connectors are indicated in Figure 2-7
@ ANALOG OUTPUT-The
which include the X, Y, and Z outputs, are used with the
XY mode to plot data with external devices such as plotters, CRTs, or oscilloscopes. The X output provides time
or interval information, while the Y output provides signal
amplitude information. The Z output provides a blanking signal, trigger pulse, or pen lift signal, depending on
the type of graphing device. The ANALOG OUTPUT jacks
are standard BNC connectors.
0 - 47
two or more Model 194s together for synchronous opera-
tion. CLK IN can also be used to operate the instrument
from an external time base. Standard BNC connectors are
used.
0
48 IEEE-488 Connector--This
nect the Model 194 to the IEEE-488 bus. IEEE-488 function
codes are marked above the connector.
@
plied 3-wire power cord to the AC receptacle. The operating
voltage is marked on a label adjacent to the rear panel.
If necessary, the operating voltage can be changed, as
described in Section 7.
CLK IN and OUT can be used are to connect
CLK
AC Receptacle-Power
ANALOG OUTPUT jacks,
connector is used to con-
is applied through the sup-
0 50
Lme
Fuse-The line fuse protects the power line input of the instrument from overloads. If the instrument
repeatedly blows fuses, the problem must be rectified
before continuing operation. Section 7 contains fuse
replacement and troubleshooting procedures.
0 - 5’
Fan
The fan provides a continuous flow of cooling
air over the various components within the instrument.
To ensure proper cooling, the air flow path must be kept
free of obstructions, including the exhaust vents on the
opposite side of the rear panel. Also, the fan filter must
be kept clean.
2.4 POWER UP PROCEDURE
Use the following procedure to connect the Model 194 to
the power sowce and turn the instrument on.
2.4.1 Power Line Connections
Connect the instrument to line power as follows:
1. Connect the female end of the supplied line cord to the
AC receptacle on the rear panel of the instrument. Connect the other end of the line cord to a grounded AC
outlet.
2-12
GETTING STARTED
WARNING
The Model 194 is equipped with a 3-wire power
cord that contains a separate ground wire and
is designed to be used with grounded outlets.
When proper connections are made, instrument
chassis is connected to power line ground.
Failure to use a grounded outlet may result in
personal injury or death because of electric
shock.
CAUTION
Be sure that the instrument is being operated
on the correct line voltage. Failure to observe
this precaution may result in instrument
damage. If necessary, the operating voltage can
be changed, as discussed in Section 7.
2. Turn on the power by pressing in the front panel
POWER switch. The switch will be at the inner position when the instrument is on.
3. The instrument will then begin performing a self test
as described in the following paragraph.
2.4.2 Power Up Self Test and Display
Messages
When power is first applied to the instrument, it will perform a self test procedure to determine if any internal faults
exist. The self test sequence consists of a ROM checksum
test, a RAM test, and various hardware tests. During the
self test period, all LEDs and display segments will be on,
giving you an opportunity to check for proper display
operation. Immediately preceding the self test, the following message will be displayed:
Following this display, the instrument will display the programmed IEEE-488 address and software revision level, ‘1s
in the example below.
REV. D2.2 IEEE=09
In this example, the IEEE-488 address is the factory def~~ult
value (9), and the software revision level is D2.2. The software revision level of your instrument may be different and
should be recorded for future reference should it ever
become necessary to replacc the internal ROM memory.
After this message, the instrument will C’ntcr the uper;~
tional mode. Table 2-4 lists the factory default values for
the instrument when it is first turned on. N<>te that vc1u
can press SHIFT RESET to return the instrument to thaw
default conditions, if desired (assuming you haven’t altered
the SETUP I configuration).
If any errors are found during the self test srquenw, the
instrument will not begin normal operation, but \vill ins
stead display appropriate error messages as an aid in deter-
mining the fault. These error messages are discussed in
Section 7.
NOTE
If the instrument is still under warranty (less than
one war from date of shiDmcntJ. it should bc
returned to Keithley Instruments for repair. See
paragraph 1.10 for details on returning the
instrument.
Table 2-4. Factory Default Power Up Conditions
SELF ‘TESTING
Assuming all tests are passed successfully, the instrument
will display the following:
SELFTEST PASS
Followed by:
KEITHLEY 194
NOTE
If an NVRAM fault occurs in one of the modules,
the instrument will not be able to recognize that
module. If such an error occurs, the unit will
display a CAN’T IDENTIFY error message for the
appropriate channel. In this case, it will be
necessary to program module recognition, as
described in paragraph 7.4.2.
Filter
Trigger Mode
Trigger Source
Trigger Delay
Trigger Slope
Trigger Level
Sample Rate
Input Coupling
Measurement Size
Reading Function
IEEE Address
Immediate (TRIGGER button)
Disabled
Continuous
0
Off
ov
166.7+zec
DC
101 samples
Average
09
NOTE: These modes will differ if the SETUP ~1 cunfiguration is changed.
2-13
GETTING STARTED
2.5 BASIC MEASUREMENT TECHNIQUES
The following paragraphs describe the basic procedure to
make basic measurements. More detailed information on
various aspects of Model 194 operation is located in Section 3.
2.51 Warm Up Period
The Model 194 is usable immediately when it is first turned
on. However, the instrument should be allowed to warm
up for at least one hour to achieve rated accuracy.
2.5.2 Input Connections
The VOLTAGE INPUT jack is intended for all signal inputs
to the instrument. This jack is an isolated BNC connector,
with the outer shell connected to input low, and the center
connector connected to input high.
WARNING
The maximum common-mode voltage (voltage
between input low and chassis ground) is 30V
RMS, 42.4V peak. Exceeding this value may
create a shock hazard.
CAUTION
The maximum input voltage
lO’V*Hz. Exceeding this value may cause
damage to the instrument.
NOTE
is
250V peak, 2 x
Shielded cable should be used for all input and
output connections to minimize the possibility of
EMI radiation.
2.5.3 Fundamental Control Selection
Before making measurements with your Model 194, you
will probably want to select the following operating modes,
as described below.
Step 2: Set the Range
Press uprange or downrange to select the measurement
range (32OmV, 3.W 32V, or ZOOV), or press AUTO and let
the instrument choose the best range for the applied
signal.
Step 3: Program the Sampling Rate
Press RATE followed by the desired data entry sequence.
For example, to program a 1Omsec sampling interval, press
the following in order: RATE, 1, 0, ms. Press FREQiTIME
immediately after RATE to change between time and frequency units.
Step 4: Program the Number of Samples
Press SAMPLES followed by the desired numeric keys. For
example, to program 1000 samples, press the following in
order: SAMPLES, 1, 0, 0, 0, ENTER. Press FREQiTIME immediately after SAMPLES to toggle between measurement
duration and number of samples.
Step 5: Select a Trigger Source
Press SOURCE and then uprangeidownrange repeatedly
to scroll through available trigger sources: IMMEDIATE,
(TRIGGER button), INPUT SIGNAL, EXTERNAL,
OTHER CHANNEL. Press CHANNEL to return to the
normal display mode. (the trigger source is selected as
soon as it appears on the display).
Step 6: Choose the Single/Continuous Trigger Arming
Mode
To arm the A/D converter (only once), press SGLKONT
until the SGL indicator is on. To automatically re-arm the
A/D converter, press SGLKONT until the CONT indicator
is on. Once the desired mode is selected, apply the appropriate trigger, as selected by the SOURCE key, to begin
the measurement sequence or sequences (TRIGGER must
be pressed to arm the A/D converter for all modes except
immediate).
Step 7: Select Input Coupling
Step 1: Select the Channel
If your instrument is equipped with two A/D modules,
select the channel you wish to use by pressing the CHANNEL button. The selected channel is displayed in the right
most digit of the display. A dual channel display mode is
also available with dual-channel units.
2-14
Press the CPLG key to select the desired input coupling.
Ground coupling is in effect when both AC and DC are off.
Step 8: Choose Your Math Function
Press the desired math key. For example, to select the
average function, press AVG. (If you are already in a mode
requiring data entry, you must press SHIFT first.)
2.54 Measurement Procedure
Use the following basic procedure to connect the instru-
ment to a voltage source and display readings on the front
p3”d.
1. Turn on the instrument power and allow a one-hour
warm up period for rated accuracy. Verify that the instrument goes through its normal power up procedure,
as described in paragraph 2.4.
2. Press SHIFT RESET to make certain that the factory
default configuration is placed in effect, or program your
own operating modes, as discussed in paragraph 2.5.3.
3. If your instrument is equipped for dual channel operation, select either channel 1 or channel 2 by pressing
the CHANNEL button. The selected channel number
will appear in the right most digit of the display for
either of the sin&-channel modes.
Select a range that is consistent with the anticipated
4.
measurement by using the uprange or downrange buttons, or use autoranging and allow the instrument to
select the best range.
Connect a suitable BNC cable to the VOLTAGE INPUT
5.
jack for the selected channel.
Connect the other end of the cable to the voltage source
6.
to be measured, as shown in Figure 2-8. Remember that
the cable shield is connected to input common, and
must not be floated more than 30V RMS above chassis
ground.
Place the unit in the continuous trigger mode (CONT
7.
indicator on) and then press TRIGGER to ensure that
the unit is processing readings.
At this point, the instrument should display the voltage
8.
level being measured. An OFLO error message will be
displayed if the input signal is above the selected range,
in which case the instrument should be moved uprangc.
GETTING STARTED
BNC CABLE
WARNlNG: MAXIMUM COMMON MODE VOLTAGE
CAUTION: MAXIMUM iNP”T
Figure
2-8.
Basic Input Connections
250” PCAK, 2 ,O~“.HZ
1””
2.6 SAMPLES, MEASUREMENTS AND
READINGS
Throughout this manual you will encounter references to
samples, measurements, and readings. .I‘he follo\ving
paragraphs define and discuss these terms in order t<>
clarify them.
2.6.1 Definitions
Sample-an individual AID cmwersion resulting in d single
unit of digitized binary data.
2-15
GETTING STARTED
Measurement-a series of samples stored in internal
memory. You can control the number of samples and how
fast they are taken with the SAMPLES and RATE keys.
Reading-a measurement that is mathematically processed
in some way and then displayed on the front panel
transmitted over the IEEE-488 bus. Typical processes include waveform (display a single sample), average (average
the samples in the measurement and display the result),
and standard deviation (take the standard deviation of the
measurement and display it).
OI
2.6.2 Sampling Discussion
Using the procedure discussed in paragraph 2.5, the Model
194 appears to operate much like an ordinary DMM, in
that a reading immediately appears on the display. Actually, the instrument is taking a number of samples, digitizing the analog value, and storing the result in its internal
memory. The resulting sequence of samples is called a
measurement. While in the continuous trigger mode (as
in this example), the display is continuously updated with
the sample stored in the memory location at the trigger
point (assuming the waveform mode is in effect). Samples
stored in the remaining locations can be accessed by us-
ing the RECALL button.
Figure 2-9 demonstrates the basic idea behind signal
sampling. Here, a time-varying signal with the amplitude
shown is being sampled at specific intervals. As each sam-
ple is taken, it is digitized into an S-bit or 16.bit binary value
(depending on the sampling rate and number of samples
in the measurement) and stored in memory. The complete
sampling sequence is a measurement, as defined above.
Once the measurement sequence is performed, a reading
can be generated by processing the block of samples in
s”me way. For example, to obtain the true RMS value of
the measurement (remember a measurement is a series
of samples), you would use the TRMS function. By using
the instrument in a single trigger mode, you could apply
a variety of different mathematical functions to a single
measurement. Conversely, a single mathematical process
could be applied to a variety of different signals by using
the instrument in the continuous trigger mode. A single
sample can be displayed by using the waveform mode (in
which case the sample at the trigger point is displayed),
or by using the RECALL button to display individual
SCl”lpleS.
v
Figure 2-9. Basic Sampling
2.7 TYPICAL OPERATING MODES
The following information will help you t” select the
various operating modes for commonly encountered
voltages and waveforms. Keep in mind that these are in-
tended only as a starting point. Some experimentation may
be required to determine the optimum instrument configuration for a particular measuring situation based on
your particular waveform analysis requirements.
Table 2-5 summarizes recommended mode selection for
four c”mm”n voltages or waveforms: a DC voltage of 3Ov;
a 60Hz, 2.82V RMS sine wave; a ZV, lkHz symmetrical rec-
tangular waveform; and a 50V peak, 15.734kHz sawtooth
waveform.
When selecting operating modes, the following points
should be kept in mind:
1. The selected range should be high enough to handle
the peak value of the waveform you are measuring. For
example, the peak value of a 30V RMS sine wave is
42.4V. Thus, you would have to place the instrument
on the ZOOV range to properly measure this waveform.
Keep in mind that the instrument will normally display
the OFLO (overrange) err”r message even if only one
sample is overrange.
2-16
GETTING STARTED
2. When measuring sinusodial waveforms, the sampling
frequency must be greater than twice the frequency you
are measuring, or aliasing will occur. For example, with
a 6OHz sine wave you might choose a sampling frequency of 150 or 200Hz. Since non-sinusodial waveforms are
generally rich in harmonics, a good rule of thumb is to
select a sampling frequency of at least 20 times the frequency of the periodic waveform. For example, with a
2kHz rectangular wave, a sampling frequency of at least
40kHz should be chosen.
3. The programmed number of samples will depend on
the frequency of the signal you are measuring, the
sampling rate, as well as how many cycles of the
waveform you wish to capture. You can dctcrminc the
required number of samples required to measure one
complete cycle by dividing the period of the waveform
Table 2-5. Recommended Operating Modes For Typical Waveforms
Waveform
-~
Range
32V
by the sampling interval. Fur example, the period of a
IkHz signal is l/lOOO=lmsec. With a 50~s~ sampling
interval, the required number of samples is ~lmseci
5O~sec=20 samples.
4. The type of coupling will depend on whether or not you
wish to remwe the DC component from a waveform.
To measure a pure DC signal, you \wuld <>bviousl\
select DC coupling. For d synumctrical sine \vInr. ,\i
coupling could be used to removt‘ JIIY SIIUII DC uffwt
that might be present in thr wa\wfo;m.
5. The m.~thematical function you USC‘ ~vill depend on \CU!
analysis requirements. For DC voltages the .wrr.lg’ ilmc~
tion (along with the default 166.7~wc, 101 samples) is
recommended to minimize 601Hz AC noise eifects on the
measurcmcnt. (If operating the unit on 5tlt Iz puwer, the
sampling interval should be 200,rscc.).
ampling
hItend
# Samples
COllpling
DC
Math Function’
Aver‘lgr
32v
3.2V
2oov
~=15734Hz
SAWTOOTH WAVEFORM
*Math function depends on required waveform analysis
lmsec
50rsec
3LLsec
100
20
25
AC
DC
DC
TRMS
Peak
SECTION 3
OPERATION
3.1 INTRODUCTION
This section contains complete and detailed information
on most operating aspects of the Model 194, including a
complete description of each front panel operating mode,
as well as pertinent information on rear panel functions
such as triggering and real time output.
Section 3 is organized in the following manner:
3.2
General Display Messages:
of general front panel display messages associated
with front panel operation.
3.3
Range Selection:
Describes the operatio” of the
ranging buttons, and how to
range from the display.
3.4
Data Entry:
Outlines the data entry sequence used
by many front panel operating modes.
Rate and Samples Programming:
3.5
tion on programming the number of samples per
measurement, as well as how fast those samples are
taken.
3.6
Triggering:
Gives
complete information on all
of instrument triggering modes and functions, including how to select the trigger source, how to initiate a measurement sequence, and how to program
trigger level and delay values.
3.7
Input Coupling:
Covers instrument input signal
coupling modes, and outlines how to select AC, DC,
or ground coupling.
Recalling Data:
3.9
Describes how to recall data stored
in the measurement buffer during OT after a measurement sequence.
Dual Channel Operation:
3.9
information on using a Model 194 that is equipped
with the optional Model 1944 Module in the channel
2 location.
Gives a brief description
determine
the selected
Contains informa-
aspects
Gives important operating
3.10 Using Zero:
Describes how t” USC the ZC’T” mode, in-
cluding how to program baseline values from the front
panel.
3.11 Filtering:
Outlines “per&ion “I the 50kf Iz and
500kHz single pole analog filters.
3.12 Using the Analog Output:
Describes how to use the
analog output to drive graphing devices such as plotters, CRTs, and oscilloscopes.
3.13 Mathematical Functions:
Describes the man!
available Model 194 math functions, including integral, average, peak to peak, and TRMS.
3.14 Ratio and Difference: Describes IWM.
to display the
ratio and difference bctwecn the two channels.
3.15 Status:
Tells how to recall instrument status and
determine the configuration “f various operating
modes.
3.16 Setup Mode:
Outlines how t” store and rccaII twu
different instrument configurations in non-volatile
“lt3”Wy.
3.17 Front Panel Programs:
Summarizes I~ccc1ss to such
miscellaneous functions as IEEE-488 address pnlgramming and digital calibration thmugh ,151’ ~,f the
OTHER key.
3.18
Reset:
Tells how to quickly reset the instrument to
its power up default conditions.
3.19 External Clock:
Outlines methods fw connecting two
or more Model ~194s together for synchronw
operatkm
3.20Real Time Output:
Dcscribcs how to use the real tinw
output to transmit data t” other equipnwnt.
3.21 Measurement Considerations:
Details sonw impw
tant considerations when using the Model 194.
3.22Typical Applications:
Gives some typical uses for the
unit.
3-1
OPERATION
3.2 GENERAL DISPLAY MESSAGES
General display messages that may be encountered when
using the Model 194 are summarized in Table 3-1. Many
operating modes have additional display messages that are
described in paragraphs pertaining to those modes.
Table 3-1. General Display Messages
Message
OFLO
NMBR TOO LARGE
NMBR TOO SMALL Parameter too small entered
SHIFTLESS KEY Key without shift mode
NO A/D IN CH2 CHl+CH2 or CHl-CH2
NO SCANNER SCAN button pressed with
Description
Overrange input applied, or
stored in at least one buffer
location.
No valid reading after A/D
configuration was changed.
Parameter too large entered
during data entry.
during data entry.
pressed after pressing SHIFT.
pressed with no channel 2
A/D module installed.
no scanner module* installed.
RANGE BUTTONS
Y
AUTO
3.3.1 Autorsnging
The AUTO button enables and disables the autoranging
mode. The associated indicator will be on when the
autoranging mode is enabled. While in this mode, the instrument will automatically select the best range to
measure the applied signal. Autoranging may be cancelled
either by pressing ALIT0 a second time, or by pressing the
uprange or downrange keys. When autorange is cancelled,
with the AUTO key, the unit will remain on the range that
was previously selected.
*Future option of the Model 194
3.3 RANGE SELECTION
The Model 194 has four ranges, as summarized in Table
3-2. Note that the resolution of each range depends on the
selected sampling rate and number of samples because of
differences in A/D converter resolution. The operation of
the various range modes is described in the following
paragraphs.
Table 3-2. Range Summary
Resolution G~*Wll
Range 16-Bit*
320 mV 10 pv 2.56mV .xxxxx
3.2 V 100 FV
32 V 1mv 256 mV
200 v
*lOOkHz and lower sampling rate and #samples ~32,768.
**Above 100kHz sampling rate or #samples >32,768.
1omv 2.56 V xxx.xx
E-Bit*
25.6 mV
Display Format
x.xxxx
xx.xxx
NOTE
A separate trigger will still be required for each
range change except in the continuous front panel
mode.
Upranging occurs at 100% of range, while downranging
takes place at 8% of range.
If the instrument is in the dual-channel mode, the AUTO
button is locked out; however, if either channel was placed
in autoranging before entering the dual-channel mode, it
will remain in the autoranging mode, although the AUTO
indicator will remain off under these conditions.
3.3.2 Uprange
The Uprange key is one of the two manual ranging but-
tons on the instrument. Each time this key is pressed, the
instrument will move up one range. Once the instrument
reaches the highest range, pressing this key will have no
further effect. Pressing Uprange will also cancel the
autorange mode, if enabled.
3-2
OPERATION
The Uprange key is also used with many other front panel
operations such as data entry and various XY modes.
These aspects are covered in the respective paragraphs.
3.3.3 Downrange
The Downrange key operates much like the Uprange key,
except, of course, for the fact that the instrument is moved
downrange. Once the lowest range is reached, this key has
no further effect. Pressing downrange, will also cancel
autoranging, if that mode was previously selected.
Like the Uprange key, Downrange is used with other
modes including data entry and various XY modes.
3.3.4 Range Selection Considerations
Generally, the lowest range that can be used without overranging the instrument is the best one for most situations
(the instrument will display the “OFLO” error message
if an overrange signal is applied). Doing so will generally
result in the best overall accuracy. However, because the
instrument operates a little differently than an ordinary
DMM, there are some key points to keep in mind when
selecting a range.
measurement and, if necessary, change range; it will repeat
measurements until a satisfactory range is found.
3.4 DATA ENTRY
Many front panel modes such as zero value, delay, trigger
level, rate, and samples require that numeric data bc
entered from the front panel. Model 194 data is cntrred
by using the ENTER, CANCEL, FREQITIME, 0 through
9, +/-, ., MHz, kHz, and IIz keys. The operation of these
kevs or kev uoutx is discussed in the follm\Gg
p&graphs.’ ” ’
DATA ENTRY KEYS
When the instrument is measuring a signal, it is actually
taking a series of samples at pre-programmed intervals.
As these samples are taken, the resulting data arc stored
in memory as a complete measurement. If the signal
amplitude varies with time, it is possible that one or more
of these samples is an overrange value. Under these conditions, the unit will still display the “OFLO” message even
if most samples are on range. If this condition exists, it is
still possible to go back and access the good samples by
using the RECALL button.
When the instrument is in the continuous trigger and
autorange mode, it continuously samples the signal at the
selected rate and attempts to choose the best range based
on the maximum buffer sample amplitude. However, there
could be some situations where an occasional overrange
reading occurs because the instrument was unable to move
uprange fast enough to keep up with the applied signal.
While autoranging, the instrument will take a complete
3.4.1 Data Keys
The data keys, 0 through 9, +/-, ., MHz (,,s), kHz (ms,
mV), and Hz (s,V) are used to enter a numeric quantity
into those modes requiring data entry. These keys are
operational only when the instrument has been placed into
the data entry mode by pressing another mode button re-
quiring data entry. For example, pressing RATF will enter
this mode and allow you to program a rate.
During the data entry process, a flashing digit or segment
(the cursor) on the display will indicate which digit \vill
be affected by a numeric key press. The 0 through 9, ., or
+/-- keys can be pressed at the appropriate times to enter
the desired data. During the numeric entry pnxcss, the
cursor can be moved to the right or left by pressing
Uprange or Downrange respectively, and ‘1 single-digit
change can be made at that point.
3-3
OPERATION
If a numeric key is pressed instead of a cursor key immediately upon entering the data entry mode, the current
value is blanked out and the new value must be keyed in
completely.
The type of units that will be entered will depend on the
selected mode-some modes require voltage units, while
others require time/frequency information. For example,
a trigger level is entered as a voltage, thus appropriate units
(mV or V) are automatically selected by pressing one of
those two keys. In a mode such as samples, frequency
(MHz, kHz, or Hz) or time interval (ps, ms, or s) units arc
selected with the aid of the FREQiTIME key, as discussed
below.
NOTE
Pressing a units key automatically enters data. +/may be pressed at any time during the numeric
input sequence.
3.4.2 ENTER
The ENTER key performs the last step in the data entry
process. Once you have keyed in the desired numeric data,
pressing ENTER will store the parameter in question in
memory for use by the instrument, unless an invalid
parameter was entered. If data is not valid, the instrument
will display one of the following error messages:
NMBR TOO LARGE
the data entry keys. When CANCEL is pressed, the display
will return to the previous value. If no cursor or data entry keys were pressed, the unit will return to the previous
mode.
Pressing CANCEL after pressing ENTER has no effect
since the value is already stored in memory.
3.4.4 FREWTIME
FREQiTIME is used in the data entry mode to toggle between reciprocal frequency time units when programming the following modes: sample rate, number of samples
per measurement and delay.
When FREQiTlME is used to program sample rate, it toggles the displayed value between samples (or scan sequence, for the scanner) per second in Hz, kHr, or MHz,
and time interval between samples in xc, msec, or psec.
When programming samples per
FREQiTlME toggles units between elapsed time for the entire measurement in set, msec, or usec, and the number
of samples per measurement.
When programming trigger delay, the FREQiTlME key toggles data entry units between time in set, msec, or psec,
and the total number of samples.
measurement,
Or,
NMBR TOO SMALL
The instrument will then return to the data entry mode.
If the data is valid, pressing ENTER will cause the instrument to momentarily display the entered value, and then
return to the previous operating mode. If a units key is
pressed during the data entry process, ENTER need not
be used.
ENTER is also used to store instrument configurations
when using the setup mode, as discussed in paragraph
3.16.
3.4.3 CANCEL
The CANCEL key can be used during the data entry process to
3-4
cancel
data previously entered into the display with
NOTE
Once the data
entry
keystroke sequence has
begun, FREQiTIME will have no effect.
3.4.5 Using the Cursor Keys
During the numeric entry process, the left (4.) and right
(A
)) cursor keys can be used to move the cursor (flashing
digit or segment) to the desired display digit location. Once
the cursor is on the desired digit, a new value can be typed
in; the change will affect only the location where the
change is made. In this manner, a one or two digit change
can be made easily without having to type in the new value
completely.
If a numeric key is pressed first during the entry process
without pressing a cursor key first, the current value is
blanked out and the complete number must be keyed in.
OPERATION
3.4.6 Data Entry Examples
The examples below will help demonstrate the basic procedure for entering instrument data. The various operating
modes that are used here as a demonstration aid are
covered in more detail in subsequent paragraphs of this
section.
Example 1: Entering voltage units.
1. Press LEVEL to enter the trigger level entry mode. The
instrument will then display the presently programmed trigger level. For example, the display might
show:
o.,v
2. To key in a trigger level of -1.675V, press: +/-, 1, ., 6,
7, 5. The display will show the numbers as they are
keyed in.
3. Press V to store the new trigger level in memory. The
instrument will briefy display the new value and then
return to the previous operating mode.
Example 2: Entering frequency/time units.
1. Press the RATE key to enter the sampling rate entry
mode. The instrument will then display the presently
programmed value, for example:
166.7~
2. At this point, you can toggle between reciprocal time
and frequency units by pressing the FREQiTIME key.
3. Press FREQiTIME until time units are entered (for example, Ins)
4. To key in an interval of 23.4msec, press: 2, 3, ., 4, ms.
5. Press RATE to get back into the rate entry mode.
6. Press the FREQiTIME key and note that you can toggle
the display between frequency and time units. With a
programmed interval of 23.4msec, the corresponding frequency is 42.73504Hz.
Example 3: Demonstrating a NMBR TOO SMALL error.
1. Press RATE to enter the sampling rate entry mode.
2. Press FREQlTIME (if necessary) to display time interval units.
3. To attempt to program a Oms (invalid) rate, press: 0, ms.
4.Note that the instrument displays the NMBR TOO
SMALL error message, and then returns to the previously programmed value.
Example 4: Demonstrating the use of the CANCEL key.
1. Press RATE to enter the sample entry mode. Note that
the instrument displays the presently programmed
value.
2. Press: 3, 5.
3. Press CANCEL, and note that the display returns to the
previous value.
4. press: 5, 0, ms; note that the last valrx is entered into
“W”“KY.
Example 5: Using the cursor keys.
1. Press RATE to enter the sampling rate entry mode and
note that the presently programmed value is displayed.
2. Use the right cursor (Uprange) key to move the flashing
cursor to the right. You can stop on any digit and make
a change, if desired. If you move off the display to the
right, the cursor will wrap around to the first digit on
the left.
3. Using the left cursor (Downrange key), mow the
flashing display cursor to the left. Again, you can stop
on any digit and make a change, if necessary. Once the
cursor reaches the extreme left, it will wrap around to
the right most digit.
4. Once all changes have been made by using the cursor
keys, press ENTER to store the new parameter in
mem0*y.
3.5 RATE AND SAMPLES PROGRAMMING
A measurement sequence is made up of a number of iw
dividual samples taken at predetermined intervals.
Through the use of the RATE and SAMPLES keys, you
have precise control over how many samples to take, and
the time period between individual samples. I’rogramming of each of these modes is performed by pressing the
appropriate key (RATE or SAMPLES) and then using the
data entry keys to enter the desired value. During the entry process, the display can be returned to the prwious
value by pressing the CANCEL key. If an incorrect
parameter is entered, the instrument will display an error
message (NMBR TOO SMALL or NMBR TOO LARGE,
as the case may be).
3-5
OPERATION
RATE AND SAMPLES BUTTONS
SAMPLES
El
RATE
cJ” 0
3.51 Programming Sampling Rate
The RATE key is used to program either the sampling frequency, or the time interval between individual samples.
When programming frequency, values between 1Hz and
IMHz may be entered. When entering frequency, the unit
will automatically adjust the frequency value to correspond
to the resolution of the sampling interval (O.l@ec).
For rates abovc lOOkHz, the usable display resolution is
reduced to 2% digits (although 4% digits are displayed)
because the A/D converter operates with S-bit resolution
above lDOkHz, or when 32,768 or more samples are
programmed.
When programming time intervals, values between l@sec
and 1st~ may be entered. If a value below the allowable
resolution (O.lpec) is entered, the instrument will
automatically adjust the entered parameter to the closest
valid value.
The FREQiTIME key can be -rsed when entering rate
parameters to toggle the instrument between the time and
frequency entry modes. The display will show the type
of units currently in effect. When new data is being
entered, it will be entered in the same mode as the display
currently shows unless FREQiTIME has been pressed to
change to reciprocal units.
50kHz and 20~s~ because one value is the reciprocal
of the other (f = l/T).
3. Press: 3,5, ps to program the new value. The instrument
will then return to the previous operating mode.
Example 2: Program a 1OOkHz rate.
1. Press RATE to enter the rate entry mode. The unit will
then display the programmed value.
2. Press FREQITIME, if necessary, to display time interval information. If the instrument is still programmed
with the 35psec sampling rate from Example 1, the
display will show:
28.57142 kHz
3. Press: 1, 0, 0, kHz The new rate will be programmed, and the instrument will return to the
previous operating mode.
Example 3: Automatic recalculation of frequency units.
The resolution of the programmed sampling interval is
O.lflec. When entering sampling rate as a frequency,
however, it is quite possible for you to enter a frequency
parameter that results in an interval below the 0.1~~
resolution limit. For example, with a 35kHz sampling rate,
the resulting interval would be 28.57l@ec. In this instance,
the unit would adjust the frequency to result in the nearest
whole interval-28.6psec in this case. Thus, if a value of
35kHz were entered, the unit would actually program a
value of 34.96503kHz.
1. Press the RATE key in order to enter the rate mode.
2. If necessary, press FREQiTIME to place the instrument
in the frequency entry mode.
3. Program a 35kHz rate with the following sequence: 3,
5, kHz.
4. Note that the unit adjusts the frequency value to
34.96503kHz.
5. Press RATE and then FREQiTIME to display sampling
interval. Note that a value of 28.6psec is programmed.
3.52 Programming the Number of Samples
Example 1: Program a 35@ec sampling interval.
1. Press RATE to allow entry of rate data. The display will
show the currently programmed value. For example, the
display might show:
50.00000 kHz
2. Press the FREQiTIME key several times and note that
the display alternates between time and frequency. With
a 50kHz rate, the display would alternate between
3-6
The number of samples to take in a given measurement
sequence is programmed through use of the SAMPLES
key, as you might expect. The input parameter for this
mode may be entered either as the number of samples
(l-65,535), or as a time duration for the measurement sequence (0.65,534s). As is the case when entering sampling rate, the FREQiTIME key is used to toggle the instrument between these two modes. If you enter a time dura-
tion shorter than the programmed sampling rate, the unit
will automatically round the input to the nearest valid
value.
OPERATION
NOTE
When the programmed number of samples is
>32,768 the A/D converter operates in the S-bit
mode.
When entering time units, it is possible that you could key
in a number that is not an integer multiple of the time interval between samples. In this case, the instrument will
automatically convert your input to the closest valid value.
For example, assume you have previously programmed a
12msec sampling rate and enter a sampling duration of
603msec. The instrument will automatically change this
value to bOOmsec, which is the closest integer multiple of
a 12msec sampling rate.
Note that the measurement duration is n-l times the
sampling interval. For example, with 100 samples programmed and a lmsec interval, the measurement duration is 99mscc.
When programming the number of samples, the unit
“remembers” whether you previously entered this
parameter in number of samples or elapsed time, and it
will automatically display the value in those units when
the SAMPLES key is pressed. Also, if the number of
samples is programmed in elapsed time, and you then
change the sampling rate, the unit will automatically
recalculate the number of samples to keep the total elapsed
time the same. If this value is entered as a number of
samples rather than as elapsed time, no such recalculation is performed. The end result is that the number you
programmed remains the same.
The two display formats for the samples mode differ slightly depending on whether number of samples or elapsed
time is entered. If time duration is specified, the display
will include time units, as in the example below:
250.0,e
presently programmed value. For example, the display
might show:
~10~1 SAMPLES
In this case, the factory default value is displ.lycd
Press FREQITIMII and note that )‘ou can tog& the
display between elapsed time and number ~,f samples.
For the purposes of this demonstration, leave the displ.l!
in the number of samples mode.
Press: 7, 5, 0, ENTER. ‘The unit is now programnwd fo!
a 750.sample measurement scqucncc.
Example
2: Program a 56Omsec sampling duration
[II the example below, it will be necessary to enter r&t’ illformation as part of the demonstration sequence to make
sure that the sampling duration is an even multiple of the
sampling rate.
1. Press RATE to enter the rate entry mode.
2. Press: FREQiTIME (if necessary to display rate in timt’
interval rather than frequency units). I, ms. ,\ lms<~
sampling interval has now been programmed.
3. Press SAMPLES to enter the sample cntrv mode. ‘I’hc
unit will display the previouslv progrClmmc~d vhttps://manualmachine.com/LII.~ It
you entered the value from tixamplc I, the displ.l!
should show:
750 SAMPLES
4. Press FREQITIME to display the samples parameter in
time units. Since a lms interval has been selected \vith
the number of samples set to 750, the time duration will
be 749mscc.
.’ tion interval.
6. Press SAMPLES, FREQiTIME and note that 561 samples
are displayed -- a value that is one more than you might
expect.
In this example, a time duration of 250psec is specified.
The number of samples are specified, as in this example:
7200 SAMPLES
In this case, 1200 samples are to be taken during the
measurement sequence.
Example 1: Program 750 samples.
1. Press the SAMPLES key. The unit will then display the
Example 3: Automatic rounding of sample duration
As pointed out earlier, the instrument will automaticall!
convert a programmed time duration to the nearest integer
multiple of the sampling rate. The example below will
demonstrate this process.
1. Press RATE, FREQiTIME (if necessary to enter
parameters as time interval information), ~1, 2, ms. This
keystroke sequence programs a 12msec sanpling rate.
3-7
OPERATION
2. Press: SAMPLES, FREQiTIME (if necessary to enter
data as time duration), 6, 0, 2, ms.
3. Note that the 602msec programmed value has changed to 600msec, which is the nearest integer multiple of
the l2msec sampling interval.
Example 4: Setting the sampling duration smaller than
the sampling interval.
The sampling duration cannot be smaller than the sam-
pling interval, as discussed previously. The instrument will
round off the value if you attempt to program the instru-
ment in this manner, as in the example below.
1. Press RATE, FREQiTIME (if necessary to place the
display in the time interval mode), 1, 0, 0, ms, ENTER.
This keystroke sequence programs a 10011~ sampling
interval.
2. Press SAMPLES, FREQiTIME (if necessary to display
and enter time units), 2, 0, ms.
3. Note that the measurement duration is changed to Opsec
(1 sample) because it is rounded down.
Example 5: Automatic recalculation of number of samples.
If the sampling rate is changed after programming
measurement duration, the instrument will automatically recalculate the number of samples to keep the measurement duration the same, as in the example below.
1. Press RATE, FREQ/TIME (if necessary to enter time interval information), 1, ms. At this point a lmsec sampling interval has been programmed.
2. Press SAMPLES, FREQiTIME (if necessary to enter
duration as time information), 5, 0, 0, ms, ENTER. This
sequence enters a 500msec sampling duration.
3. Press SAMPLES and FREQiTIMlZ to display the number
of samples. The display should indicate that the programmed number of samples is 501 because the sampling duration is 500msec, and the sampling interval is
1lllSeC.
4. Change the sampling interval to 5msec as follows.Press:
RATE, 5, ms.
5. Press SAMPLES and FREQiTIME to display the programmed number of samples. Note that the number
of samples has been changed to 101 because of the
change in sampling interval, although the sampling
duration remains at 500msec, as previously programmed (you can verify these values by pressing the
FREQiTlME key while in the samples mode).
3.5.3 Samples and Rate Selection
Considerations
Because the Model 194 can sample input signals at rates
as high as lMHz, it is ideal for many applications involving the analysis of many time-varying signals, both of the
periodic and transient variety. To ensure optimum accuracy
when measuring such signals, care must be taken when
selecting both the sampling rate and the number of
samples. In the following paragraphs, we will discuss some
of these considerations that should be taken into account
when choosing sampling rates and measurement
durations.
Input signals to the Model 194 are in analog form. Internally, however, the Model 194 operates in the digital world.
Thus, the analog signal must be converted into digital information by the A/D (Analog-to-Digital) converter of the
instrument. This conversion process is not continuous, but
rather is done at discrete intervals, determined by the
entered rate parameter. If the sampling rate is too slow,
considerable information about the original analog signal
will be lost, and errors can creep into the resulting data.
For example, assume that a sinusoidal waveform is being
sampled at regular intervals, and the result digitized and
stored internally.
Once the data is sampled and stored, we can attempt to
reconstruct the original waveform from the data. However,
the result is no longer a smooth, continuous waveform,
but is instead made up of discrete steps. Thus, as the result
of this digitization process, we may have lost much important information about the original signal.
To make the steps in the reconstructed data smaller, we
can increase the sampling rate. At the same time, we will
have to increase the number of samples per measurement
if we still wish to measure at least one cycle of the applied
signal.
It is clear then, that we should make the sampling rate sufficiently high so as not to loose important information present in the original input signal. Information theory states
that, for sinusoidal waveforms, the sampling frequency
must be at least twice as high as the highest frequency
component in the measured sienal. Thus. if a 1OOkHz
signal is to be sampled, the sampling frequency must be
at least 200kHz.
3-8
OPERATION
If the sampling frequency is not at least twice the frequency
being sampled, a phenomenon known as &sing results.
When aliasing occurs, the sampled information will not
contain data on the original waveform, but instead a new
signal with a frequency equal to the difference between
the sampling frequency and the original applied signal.
For example, if a 1OOkHz signal is sampled at a 1lOkHz rate,
a new signal of 1OkHz will be the one actually seen in the
resulting data. If the signal and sampling frequencies are
exactly the same, a DC signal level will result, since the
difference between the two signals is zero. Thus, it is imperative that the minimum 2:l ratio of sampling frequen-
cy to measured frequency be maintained if accurate results
are to be expected.
Once we have established our minimum sampling frequency based on the above criteria, we can then go ahead
and choose the correct sample and rate parameters for a
given situation. For example, assume that we are measuring a 20kHz sine wave. We would then press the RATE
key and then key in the desired sampling frequency.
Although a 40kHz frequency sampling frequency would
be adequate, we might want to play it safe and choose a
50kHz sampling frequency for this measurement. Once
the rate parameter is established, we can choose a sam-
pling duration or number of samples to measure based on
how many cycles, or how much of a single cycle WC wish
to sample. For example, if we wished to sample one com-
plete cycle of the 20kHz waveform, the measurement duration would be li20kHz = 50~s~. Aside from which range
to use, the only other consideration for a basic measurement would be the trigger method, as described in
paragraph 3.6.
Another consideration when selecting the sampling rate
is the overall resolution and accuracy of the measurement.
For sampling rates 1OOkHz and below,, the AID converter
operates with &bit resolution (assuming the number of
samples is ~32,768), meaning that it digitizes the signal
into 21L, or 65,536 steps. Above lOOkHz, the A/D converter
has only R-bit resolution, so it can resolve only 2”, or 256
steps. The A/D resolution has a direct effect on display
resolution as well as the ultimate accuracy of the measure-
ment. At 1OOkHz and below, display resolution is 4% digits,
while the usable resolution is reduced to 2?0 digits ,~bow
lOOkfIr (the unit will still display 4% digits, howc\~r, ab<~vt~
100kHr). Consequently, instrument accuracy is not a go<~l
with sampling rates above 1OOkHz as it is below that valw
(refer to the specifications at the front of this manuI~l iol
actual figures). Thus, if accuracy is ot paramount impw
tance, you should select a sxnpling rate of 1OOkHz or less
and ~32,768 samples, unless other factors such 1)s
measurement speed override this consideration
3.6 TRIGGERING
A triger stimulus is used to initiate .) M~~lel I’ll mel~suw
ment sequence. The duration of that seqwnc~’ dnd the
number of samples taken during the sequence will depend
on previously selected rate and sample parameters.
TRIGGER BUTTONS
Thus far in our discussion, we have assumed that all
signals arc sinusoidal in nature. In the real world, of
course, many complex waveforms exist. These complex
waveforms can be broken down into a fundamental
sinusoidal waveform and a number of harmonics in accordance with the Fourier series. While detailed Fourier
analysis is beyond the scope of this discussion, you should
be aware that such harmonics do exist.
From this discussion, we can see that it may necessary to
choose a sampling frequency substantially above the fun-
damental frequency of a non-sinusoidal waveform to ensure good results. For example, when sampling a 10kHz
rectangular waveform it would be a good idea to choose
a sampling frequency of 200kHz since a substantial por-
tion of the ninth harmonic (YOkHz) is present, and the
sampling rate must be at least twice as high as the highest
frequency.
The unit can be triggered with the front panel ‘I‘l~I~~C~ER
button, the input signal, from a pulse applied to the ex-
ternal trigger input jack, or from the other channel (the
instrument can also be triggered over the IEEE-488 bus,
as discussed in Section 4). When triggering from the ill-
put signal, you can define slope and triger level
parameters. From the front panel, these modes xc’ prw
grammed with the various trigger buttons. as described
in the following paragraphs.
3-9
OPERATION
3.6.1 Trigger Source
The trigger source is selected by pressing the SOURCE key.
The instrument will display one of the trigger sources, as
summarized in Table 3-3. To select a different source, press
uprange or downrange repeatedly until the desired trigger source is displayed. The new trigger source is saved
once the source is displayed. To return to the previous
mode, press SOURCE.
Note that the SOURCE key is inoperative when the instru-
ment is in the dual-channel display mode.
NOTE
When you select external, input signal, or other
channel triggering, you must first arm the AID
converter by pressing the TRIGGER button. The
measurement sequence will then begin when the
appropriate trigger stimulus occurs.
Table 3-3. Trigger Source Display Messages
Message
LMMEDIATE
EXTERNAL
INPUT SIGNAL Input signal, depending on
OTHER CHANNEL Second channel when 1944 opTRIG ON TALK
TRIG ON X
TRIG ON GET
Selected Trigger Source
TRlGGER button or IEEE trig-
gcr (X, GET, etc.)
Pulse applied to TRIGGER IN
jack.
selected slope and levels.
tion installed.
IEEE talk command
IEEE X command
IEEE GET command
3.62 Single/Continuous Arming Modes
A/D arming can be set up to operate in two different ways:
in continuous or single modes. In a continuous mode, the
unit will automatically rearm the A/D converter after each
measurement sequence. The unit will then perform
another measurement sequence when it receives the appropriate trigger stimulus (as selected with the SOURCE
key). In the single mode, however, the A/D converter must
be manually re-armed after each measurement (the A/D
converter can be re-armed from the front panel by press-
ing TRIGGER).
Single/continuous arming selection is performed by pressing the SGLiCONT button to select the desired mode; the
appropriate indicator will then display the selected mode.
When the instrument is in the dual-channel display mode,
the SGLiCONT button and associated indicators are
inoperative.
NOTES:
I. If the instrument is in the immediate (TRIGGER button),
continuous mode, it will process measurements continuously without requiring additional triggers.
2. If the selected trigger source is the input signal, external trigger, or other channel, the unit will require a
separate trigger stimulus for each measurement
regardless of whether the unit is in the single or continuous armed modes.
3. When going from the single, immediate mode to the
continuous, immediate mode, it will be necessary fol
you to press the TRIGGER button to begin processing
measurements.
4. The decimal point in the display (between second and
third digits from the right) will turn on to indicate that
the A/D converter is armed and waiting for a trigger.
Discussion
Basically, there are two steps needed for initiating a
measurement sequence. First, the A/D converter must be
armed, so that it is running and processing data. Secondly, the unit must be triggered by the appropriate trigger
stimulus (determined by the selected source) before it will
perform a measurement sequence. The only exception to
this two-step process is when the immediate, front panel
mode is selected. In this situation, pressing TRIGGER performs both steps simultaneously so that the A/D converter
is armed and the measurement is initiated with a single
action.
There are two fundamental reasons why the A/D converter
must be running before a measurement sequence takes
place. First, when input signal triggering is in effect, the
A/D converter must supply input signal amplitude data
to the digital comparator circuits so that they can trigger
a measurement when the programmed trigger threshold
is reached. Secondly, when using pre- or post-trigger, the
unit must continuously store data so that it can later flag
the beginning of the measurement relative to the programmed trigger point.
3.6.3 TRIGGER Button Operation
The Model 194 can be triggered by the front panel TRIG-
GER button, if the immediate mode has been selected as
the trigger source (paragraph 3.6.1). Once activated, pressing TRIGGER will initiate a single or continuous sequence
of measurements, depending which of those two modes
was selected with the SGLiCONT button.
3-10
OPERATION
The TRIGGER button is also used to arm the remaining
trigger modes. For example, suppose you select input
signal triggering with the SOURCE key. You must then
press TRIGGER to start the AID converter so it can process samples to determine when the input signal has
crossed the programmed trigger threshold. Once the trigger occurs, the instrument will begin the measurement sequence in the usual manner.
NOTE
Pressing TRIGGER will alternately arm and
diliiey the A/D converter when in the continuous
Note that TRIGGER is operational in the dual-channel
display mode, as well as in the CHl-CH2 and CHlKH2
modes.
3.6.4 Trigger Delay
The DELAY key can be used to program the location of
the beginning of a measurement relative to the trigger
point. The delay value can be entered either in units of
time, or in number of samples. The limits for the delay
parameter are -65,536 to +lO’ seconds or -65,536 to +lO’
samples. The input data is alternated between time and
sample units by pressing the FREQITIME key.
When negative values are entered, pre-triggering is in ef-
fect. Post-triggering is in effect when positive delay values
are entered. Both post- and pre-triggering arc available
with all trigger sources.
NOTE
If pre-triggering is selected, and the A/D converter
is armed, any previous stored measurements will
be overwritten even if the next measurement sequence has yet to be triggered.
The basic keystroke sequence to enter a trigger delay is:
DELAY, data, ENTER or time units. If an incorrect
parameter is entered, an appropriate error message will
be displayed. During the entry process, you can press
CANCEL to restore the display to the previous value.
When entering the delay parameter in time units, it is
possible that you might enter a value that is not an integer
multiple of the sampling interval. Under these conditions,
the instrument will automatically adjust the entered delay
to the nearest valid value.
Whether delay is entered in time or sample units, the illstrument will “remember” which units were previously
in effect. Thus, pressing DELAY will give you a display
of the delay parameter in previously programmed units.
Also, if you enter the delay in time units, and then change
the sampling rate, the instrument will maintain the same
delay time by recalculating the number of samples to delay.
However, no such recalculation is pcrformcd if you enter
the delay parameter as a number of samples.
Example 1: Program a 50msec positive delay.
1. Program a lms sample interval as follows. Press RAlX.
FREQ/TlME (if necessary to display time units), I, ms.
2. Press DELAY to cntw the delay entry mode. The instrument will display the presently programned v~luc, ior
example: 0 DELAY.
3. If necessary, press FREQITIME to display the delay \.dlw
in time units.
4. Press: 5, 0, i-I- (only nccessall-y if ncgativc value is cur-
rently displayed), ms. The new trigger dclq period is
now programmed.
Example 2: Program a 25msec negative delay period.
1. Press DELAY to place the instrument in the delay cntr).
mode. The unit will display the previously pmgr.m~mrd
VdW.
2. Press: +/-, 2, 5, “IS. The new delay \,alue is n,,\\
programmed.
Example 3: Program an 80 sample positive delay.
1. Press DELAY to enter the delay entry mode.
2. Press FREY/TIME to change the displw tu sh(1\x
number of samples.
3. Press 8, 0, +/-, ENTER. The ne\\’ value is nc>\\
programmed.
Example 4: Automatic recalculation of delay number of
SiW+?S.
If the sampling interval is changed after pwgramming the
delay, the instrument will automatically recalculate the
delay number of samples, as in the following rxamplc.
‘I. Press DELAY to enter the delay entry mode.
2. Press FREQiTIME to display the delay in time units.
3. Program a 50msec positive delay as follows. Press S, (I,
+/- (only necessary if a negative value is displayed), ms.
4. Press DELAY then FREY/TIME and note that the delay
is programmed as 50 samples.
-
3-11
5. Change the sampling interval to 5msec as follows. Press
RATE, FREQiTIME (if necessary to display time units),
5, ms. The sampling interval has now been changed to
5msec.
6.
Press DELAY to program delay period. If necessary, use
the FREQiTIME key to display the number of samples.
Note that the number samples to delay has been
changed from 50 to 10 because of the change in sampling interval from lmsec to 5msec.
Discussion
The trigger delay parameter tells the instrument where to
begin storing readings relative to the trigger point. If the
parameter is zero, no delay occurs, and the trigger point
is assumed to be the same as the first buffer sample.
However, if the delay parameter is non-zero, the first sample location will be moved in accordance with the programmed delay parameter.
Figure 3-l will help to demonstrate the basic concept
behind delayed triggering. In Figure 3:1(A), the delay is
zero, so the measurement begins at the trigger point. In
(B), which shows a positive delay, the measurement se-
quence begins some time after the trigger occurs. That time
period is, of course, determined by the programmed delay
value.
In Figure 3-l(C), a negative delay is shown, with the first
measurement occuring ahead of the trigger stimulus. The
amount of delay is again determined by the programmed
delay parameter.
Figure 3-1. Trigger Delay
3-12
OPERATION
3.6.5 Trigger Slope
The SLOPE key can be used to program the instrument
to trigger either on the positive or negative-going edge of
the input signal. The instrument can be toggled between
these two modes by repeatedly pressing SLOPE. The active mode is indicated by the indicators adjacent to the
SLOPE key.
If the instrument is in the dual-channel display mode, or
if the selected trigger source is not the input signal, the
SLOPE button and associated indicators are inoperative.
3.6.6 Trigger Level
The programmed trigger level can be entered into the unit
by using the LEVEL key. 7’ ’
the selected trigger source is the input signal. When LEVEL
is first pressed, the instrument will display the currently
txoarammed tri%er level. A new level can then be pro-
‘gr&med with tlh6 data entry keys.
The allowable range for the trigger level is i2OOV. Program-
ming values above or below this range will result in an ap-
propriate error message. If the programmed value is below
the resolution of the A/D converter (lOpV), the unit will
round the value to the nearest allowed value.
:his teature
applies c mly when
Discussion
The level and slope operating modes determine when the
instrument is triggered from the applied input signal. If
a positive slope is selected, triggering will take place when
the input signal rises to the preset level that was prw
grammed with the LEVEL key. If a negative slope is
selected, triggering will occur when the signal lwel drops
to that preset level.
Figure 3-2 will help to demonstrate slope and level triggering. In (A), the instrument is programmed for a positive
slope with a level of +2.5V. When the input signal rcachcs
the 2.5V threshold going in a positive direction, the instrument is trigered to begin the measurement sequence.
In (B), a similar situation exists, except that the unit is non
programmed for a negative slope with a level of +I..iV
In this case, the unit is triggered once the input signal
drops to the 1.5V level.
Note that PV levels can be programmed with the ps key.
When the instrument is in the dual-channel display mode,
the LEVEL button is inoperative.
Example 1: Program a +5V trigger level.
1. Press LEVEL to enter the level entry mode. The instrument will display the presently programmed trigger
level. For example, the display might show:
2.55V.
2. Press: 5, V. The unit will now briefly display the programmed value and return to the previous display mode
with a 5V trigger level programmed.
Example 2: Program a -300&V trigger level.
1. Press LEVEL and note that the presently programmed
trigger level is displayed.
2. Press: ., 3, +/-, mV. Thr new trigger level of -3OO&’ is
now prograqmed~
Figure 3-2. Level
and Slope Triggering
3-13
OPERATION
3.6.7 External Triggering
The TRIGGER IN jack can be used to apply a trigger pulse
to
the
instrument to initiate a reading sequence. In a similar
manner, the instrument will feed an output pulse out the
TRIGGER OUT jack when it is triggered by some other
stimulus.
TRIGGER JACKS
TRIGGER IN is a BNC connector that requires a negative
going pulse to trigger the instrument. The specifications
for the trigger pulse are shown in Figure 3-3. Before external triggering is active, the instrument trigger sourcf must
be programmed for that mode with the SOURCE key.
Whenever the instrument is triggered, it will generate an
output pulse via the TRIGGER OUT jack, with the
specifications shown in Figure 3-4. The trigger pulse will
be generated regardless of the selected trigger source, including input signal, external trigger input, other channel, or immediate modes (TRIGGER button or IEEE bus
triggers).
Figure 3-4. TRIGGER OUT Pulse Specifications
3.7 INPUT COUPLING
Figure 3-3. TRIGGER IN Pulse Specifications
CAUTION
The outer rings of both TRIGGER jacks are
connected to chassis ground and cannot be
floated.
NOTE
Shielded cable should be used for TRIGGER
signal connections to minimize the possibility of
EM1 radiation.
The CPLG key allows you to select AC, DC, or ground
coupling modes that are analogous to those found on an
oscilloscope. The LEDs associated with the CPLG key in-
dicate AC and DC coupling modes, while ground coupling
is indicated by both LEDs being off. You can toggle the
instrument between these three modes by repeatedly
pressing the CPLG key.
CPLG KEY
3-14
OPERATION
When DC coupling is selected, a straight-through DC
signal path is established to the input section of the instrument. When AC coupling is in effect, the instrument
low-frequency response rolls off (see specifications). Thus,
DC coupling would be used when measuring DC signals
or very low frequency AC signals, while AC coupling is
useful for removing the DC component of the input signal.
When ground coupling is selected, the signal voltage is
disconnected from the input amplifier, and the input
amplifier terminals are shorted.
3.8 RECALLING DATA
The RECALL key allows you to recall any of the individual
samples that are stored within the measurement buffer.
Naturally, the number of buffer locations that contain valid
data will depend on the programmed number of samples.
RECALL KEY
SHIFT
While in the recall mode, you can random access data ‘It
any of the buffer locations by keying in the desired buffer
location and then pressing the ENTER key. If an incurrcct
location is entered, an ernx message will bc displayed.
hrr example, if you program a sample location higher than
the programmed number, a NMBR ‘IWO LARGE message
will be displayed.
Alternately, you can increment or d~rernent buffer Ior+
tions by using the Uprange or Dwvnrangr keys, rcspc’c~
tively. If either of these buttons is held down for one se-
cond, the button will autorepeat.
Depending on whether the instrument is in the single or
continuous mode, the samples in the various buffer Iocd-
tions may or may not be changing as you access thenl. In
the single trigger mode, the samples will be updated ml>
when the instrument is triggered. In the continuous trig-
ger mode, however, buffer samples will be updated at a
rate dependent on the selected sa~~pling rate and intcr\.r~l.
When recalling data, the trigger point is indicated by the
letter “T” in the display as in the example below:
ID El
RECALL
OD El
When the recall mode is enabled, the RECALL indicator
will be on, and the display will show the data at the
selected location, the buffer location and the channel, as
in the example below.
25.000 0 1
In this example, a value of 25V is being read from the first
(0) buffer location of channel 1.
25.000 47x Tl
In this example, buffer location 478, which is the trigw
point for the measurement sequence, is bring displayed.
For quicker access to the trigger point you can use the
waveform mode, as discussed in paragraph 3.14.
To return the instrument to the normal display mode,
simply press the RECALL button a second time. The unit
will then return to the previous display mode.
Example: Random and sequential buffer access.
Use the example below to demonstrate buffer .ICCC’SS.
Before using this example, program the instrument for a
lms sampling interval and 1000 samples with the RATE
and SAMPLES keys. Set the instrument for the single trigger mode and apply a time-varying signal such as a 60Hz
sine wave to the VOLTAGE INPUT jack on the war pnnel.
Select AC coupling with the CI’LG key.
1. Press the RECALL button. The display will enter the
recall mode and display the sample at the selected buffer location (0).
3-15
OPERATION
2. Select a random buffer location by keying in a value with
the data entry keys and then pressing ENTER. For example to view the 56th location, press: 5, 6, ENTER. The
data at that location, along with the buffer location will
then be displayed. For example, the display might show:
16.17 56 1
3. Use the Uprange and Downrange keys to sequentially
increment and decrement buffer locations. Note that the
buttons will autorepeat after being held down briefly.
4. Press the RECALL key to return to the normal operating
mode.
3.9 DUAL CHANNEL OPERATION
When the optional Model 1944 A/D Converter Module is
installed in the CARD 2 location, the Model 194 is
equipped with two identical channels that operate virtually
independently of one another. Aside from sharing the
display and control buttons, each channel can be in-
dependently programmed for various operating modes.
The following paragraphs describe dual-channel operation
of the Model 194.
CAUTION
The maximum input voltage is 250V peak, 2 x
10’ V*Hz. The unit mav be damaoed if this value
is exceeded.
WARNING
The maximum common-mode voltage is 30V.
Exceeding this value may create a shock
hazard.
REAL TIME OUTPUT-Provides binary data from the A/D
converter at the sampling rate (paragraph 3.20).
TRIGGER OUT-Provides an output pulse to trigger other
instrumentation when channel 2 is triggered for a measure-
ment sequence (paragraph 3.6).
TRIGGER IN--Allows channel 2 to be triggered from an
external sowce. This mode is available only when properly
programmed with the SOURCE key (paragraph 3.6).
CAUTION
Digital common is internally connected to
chassis ground and cannot be floated.
3.9.1 Channel 2 Connections
As shown in Figure 3-5, the connections for the CARD 2
module are identical to those for CARD 1. The purpose
of each connector is briefly described below. The paragraph
where more detailed information may be found is also
indicated
Figure 3-5. Rear Panel
VOLTAGE INPUT-All analog input signals are applied to
this isolated BNC connector (paragraph 2.5).
Showing Channel 2 Installed
NOTE
Shielded cable should be used for all input and
output connections to minimize the possibility of
EM1 radiation.
3.9.2 Channel Selection
The channel to be accessed is selected by using the CHANNEL button.
CHANNEL BUTTON
CHANNEL
I
3-16
OPERATION
Pressing CHANNEL does two things:
1. It toggles the display between channel 1, channel 2, and
the dual-channel display mode. Table 3-4 shows typical
displays for each of the three formats. For the two singlechannel formats, the channel number appears in the
right most digit. In the dual channel display mode, channel 1 is on the left, and channel 2 is on the right.
2. It allows you to access a particular channel for programming remaining parameters. To change channel
operating modes, the display must be in the single channel mode of that particular channel. For example, to pro-
gram the rate on channel 1, you must first use the
CHANNEL button to display only that channel. Similarly, if you wish to change the range on channel 2, you
must first display channel 2 by pressing CHANNEL and
then use the appropriate range button to change the
range.
Table 3-4. Display Format
3. Press the CHANNEL button, as required, to select the
channel 1 display mode.
4. Select input signal triggering with the SOURCE and
uprangc keys.
5. Using the SLOPE button, program channel 1 to tripp
on the positive-going edge.
6. Press the LEVEL button and key in a trigger level of
+4.6V. To do so, press: 4, ,6 , V.
7. Arm both channels by pressing TRIGGER in the dualchannel display mode.
8. With this programming, channel ~1 will be triggered
when the input signal rises above 4.6V. Channel 2 will
in turn be triggered by channel 7.
3.10 USING ZERO
The zero mode allows a stored offset value to be subtracted
from subsequent readings. The stored offset can be obtained from an applied signal, or directly keyed in \vith
the data entry keys. Once the baseline is stored, the zero
mode can be enabled or disabled by pressing the ZERO
button. When the zero mode is enabled, the ZERO in-
dicator will be on.
3.9.3 Speed Considerations
Each channel has its own A/D converter, 64K bytes of
memory, and clocking circuits. As a result, each channel
can be independently programmed for the maximum
@MHz) sampling rate without affecting sampling rate of
the other channel. However, the overall reading rate will
be reduced if both channels are sampling simultaneously.
3.9.4 Cross Channel Triggering
Either channel can be triggered by the other channel to
begin its measurement sequence. To do so, program each
channel for the appropriate trigger mode, as required.
Paragraph 3.6 covers triggering in detail.
As an example, assume that channel 2 is to be triggered
by channel 1, and that channel 1 is to be triggered by a
positive-going input signal at a threshold of 4.6V.
1. Using the CHANNEL button, select the channel 2
display mode.
2. Press the SOURCE button and then uprange or
downrange repeatedly until the following message is
displayed: OTHER CHANNEL.
ZERO KEYS
f
When the instrument is in the dua-channel display mode,
the ZERO button and associated indicator are inoperative,
although the instrument will remain in the selected zen~
mode if already so programmed when entering the dual-
channel mode. The unit must be in a single-channel
display mode to change or indicate the mode presently in
effect.
The zeroed reading can be as small as the resolution of
the instrument (lOl,V), or as large as full range. Somr
typical examples include:
Zeroed Reading
+10.5oov +18.6OOV
+2.566V +1.8OOOV
-12.6OOV +4.5ooov
ZERO
Applied Signal
-
>
D+ayed Value
1~8,lOOV
-0.756OV
+‘17.1oov
3-17
OPERATION
3.10.1 Zeroing From an Applied Signal
To store the zero offset value from a” applied signal, per
form the following procedure.
1. Select the desired channel.
2. Cancel the zero mode if presently enabled.
3. Select a range that is consistent with the anticipated
measurement.
4. Connect the signal that is to be used as a” offset value
to the VOLTAGE INPUT jack of the selected channel.
5. Press the ZERO button to enable the zero mode. If there
is no valid reading on the display, the zero mode cannot be enabled.
6. Disconnect the offset signal from the instrument and
connect the signal to be measured in its place. Subsequent measurements will be the difference between the
suppressed value and the applied signal.
WARNING
The voltage on the input terminals may be
larger than the displayed value. For example, if
a 175V zero offset is stored, an applied voltage
of 200V will result in a displayed reading of on-
ly 25v.
in the appropriate
emv message. Also, the instrument will
display a NMBR TOO SMALL error if you attempt to program a zero value smaller than the resolution of the AID
converter (1OpV).
As with the ZERO key, ZERO VAI. is inoperative when the
instrument is in the dual-channel display mode.
Program a zero value from the front panel as follows:
1. Press SHIFT ZERO VAL to enter the front panel zero
mode. The instrument will prompt with the presently
programmed value.
2. Using the data keys, key in the desired value. For example, program a zero value of 255mV as follows. Press
: 2, 5, 5, mv.
3. The new zero value will be programmed, and the ZERO
indicator will be on.
4. To cancel the programmed zero mode, simply press the
ZERO key. The presently programmed zero value will
be retained for use when ZERO VAL is pressed again.
3.10.3 Zero Mode Considerations
7. To cancel the zero mode, simply press ZERO a second
time. The stored v&c will be retained for use by the
zem value mode discussed below.
3.10.2 Keying In the Zero Value
The zero feature may also be used by keying in the zero
offset from the front panel. This mode is entered by pressing SHIFT ZERO VAL and then using the data entry keys
to key in a new value. Once the value is entered, the zero
mode will remain in effect until zero is disabled with the
ZERO key. The ZERO indicator will be on when the zero
mode is enabled.
The allowable range for the entered zero parameter is between -200 and +2OOV. Exceeding these values will result
The display can show up to +99999 counts in the zero
mode, unlike a normal “on zeroed reading, which is
limited to -32,768, +32,767 counts. For example, if a zeroed
value is -6OOmV, and the applied signal is +3OO.OOmV, the
display will show .ROOOOV.
If the instrument is in the autorange mode, it will move
up range If the *99,999 count limit is exceeded. Once zero
is enabled, setting the range lower than the zeroed value
will create a” overrange condition. The Model 194 will
display the OFLO message in this case. Note that the in-
strument must be triggered to effect a range change.
When using zero with a mathematical function, the zeroed
value is subtracted from the reading after the mathematical
operation is performed.
3.18
OPERATION
3.11 FILTERING
The Model 194 has two single-pole, low-pass analog filters
with appropriate -3dB points of 5OkHz and 500kHz. These
filters are useful in situations requiring attentuation of high
frequency noise or interference. The filters can be accessed by pressing the front panel FILTER button. Each time
uprange or downrange is pressed, the display will indicate
the selected filter mode, as summarized in Table 3-5. The
filter mode is selected as soon as the appropriate message
is displayed. If either the 50kHz or 500kHz filters are enabled, the FILTER indicator will be on. To return to the
previous mode, press FILTER a second time.
Table 3-5. Filter Display Messages
Message
FILTER OFF
FILTER 500KHZ
FILTER 50KHZ
Description
Both filters disabled.
Filter with -3dB point of 5OOkHz
enabled.
Filter with -3dB point of 50kHz
enabled.
FILTER BUTTON
Typical curves for the two filters are shwvn in Figure 3-h.
Although filtering can be beneficial in the form of
creased noise, it does increase the response tinw to
changes in input signal. Table 3-6 summarizes response
times to within lo%, l%, O.l%, and 0.01% of final wluc
for each of the two available filters.
dc-
Table 3-6. Filter Response Times
Response to Within:
3-19
3-20
Figure 3-6. Typical Filter Response Curves
3.12 USING THE ANALOG OUTPUT
The analog output of the instrument can be used to drive
display devices such as oscilloscopes, CRTs, plotters and
strip chart recorders. The Y output provides the amplitude
information, while the X output provides horizontal position information for the graphing devices requiring such
information. The Z output provides a blanking or pen lift
signal, depending on the type of graphing device.
The following paragraphs describe the various operating
modes of the analog output, including programming and
output connections.
XY BUTTONS
OPERATION
Figure 3-7. Rear Panel Showing ANALOG OUTPUT
Jacks
Typical connections for using the analog ~mtput in the plotter mode are shown in Figure 3-X. In this instance, the illstrument is driving a plotter. Note that the X output is corv
netted to the X input of the plotter, the Y output is cow
netted to the Y plotter input, while the % output is connected to the pen up input of the plotter. Typical COIIIWCtions for using the analog output in the oscilloscope ,~nd
CRT modes are shown in Figures 3-9 and 340
3.12.1 Analog Output Connections
‘The analog output has three jacks, which are shown in
Figure 3-7. The X output provides position or time information in the CRT or plotter modes, the Y output provides
amplitude information in all three modes, and the Z out-
put provides a blanking signal in the CRT mode, a pen
up signal in the plotter mode, and a trigger signal in the
oscilloscope mode.
The Y output is unipolar, with the amplitude varying between 0 and the programmed full scale value (default,
1OV). The minimum Y output (OV) corresponds to a minus
full range input, while the maximum Y output is equal
to a plus full range input. For example, on the 32OmV
range, a -327.68mV input voltage will yield a Y output
value of approximately OV, while a +327.68mV input will
give the full scale value.
CAUTION
Analog output common (outer
nected to chassis
ground and cannot be
ring) is con-
floated.
NOTE
Shielded cable should be used for analog c,utput
connections to minimize the possibility of EMI
radiation
The X output is also unipolar with OV corresponding to
the position of the first sample, and the programmed full
scale value corresponding to the position of the last
SiXllpl~.
The Z output is factory programmed so that low is OV and
high is 5V. The high level can be changed to +15V as
discussed in paragraph 7.10.
Figure 3-8. Typical Plotter Connections
3-21
OPERATION
3.12.2 Entering the XY Mode (XV MODE)
The XY MODE key is used to place the instrument in the
XY mode (SHIFT must be pressed before pressing XY
MODE). Repeated pressing of uprange or downrange
causes the instrument to scroll through the various modes,
as indicated by the display messages summarized in Table
3-7. When the associated message is displayed, the instrument immediately goes intb that mode. Pressing XY
MODE a second time will return the unit to the previous
mode.
Table 3-7. XY Mode Display Messages
Figure 3-9. Typical Oscilloscope Connections
1
F
I(Y DATA
I:
YY ZOOM
ZY PAN
XY CRT
XY SCOPE
XY SLOW PLOT
XY STRIP CHT
MEASMNT BUFFER
MEASMNT RAM
READINGS
IEEE-488 BUF
XYZOOM = l.O*
XYPAN = 1*
Description
XY Mode
Disable
CRT Mode
Selected
Oscilloscope
Mode
Selected
Plotter Mode
Selected
Strip Chart
Mode
Selected
Channel
Measurement
Buffer
64K Measurement Buffer
Readings
from Selected
Channel
IEEE Output
Buffer
Scaling Factor
Window
Location
Figure 3-10. Typical CRT connections
3-22
*Depends on programmed value.
vpes of graphing devices include:
CRT: In the CRT mode, the X output drives the horizontal axis of the CRT while the Y output is used to drive the
vertical axis. The Z output is used to provide a blanking
OPERATION
signal during the CRT retrace period. In the CRT mode,
only 100 points will be graphed. However, all samples in
the measurement will be scaled. The output rate is lmsec
per point.
Oscilloscope: The Y axis is used to drive the vertical input while the Z output is used to trigger the oscilloscope.
Only 100 points are displayed in the oscilloscope mode;
a measurement will be scaled in accordance with the scaling factor. Again, the output rate is lmsec per point.
Plotter: The Y and X output are used to drive the Y and
X inputs of the plotter, while the Z output acts as a pen
lift signal. A maximum of 4096 points are graphed in the
plotter mode. If more than 4096 samples are in the
measurement, the instrument will automatically scale it.
Strip Chart: Only the Y output is used in this mode. Each
time a reading is completed, the value will appear at the
Y output and remain at that level until a new reading is
ready. The number of points that can be graphed is equal
to the number of samples in the measurement. Thus, this
mode will give you the best resolution.
NOTES:
The analog output should be left disabled (XY OFF)
when not in use, in order to allow other functions ample microprocessor time to operate normally,
The Model 194 should be placed in the single trigger
mode when using the analog output in order to speed
up XY processing.
In the CRT and oscilloscope modes, analog output aliasing can occur if the measurement contains substantially mnre than 100 samples (the number of points plotted in these two modes). To avoid such aliasing, program the unit for no more than 100 samples per
measurement.
3.12.3 Analog Output Data Source (XV DATA)
By using the XY DATA key, you can select the data source
for the analog output. To select the source, you need only
press XY DATA (remember to press SHIFT first) once and
then press uprange or downrange until the appropriate
message is displayed (Table 3-7). The displayed data source
is placed into effect immediate. Press XY DATA again to
return to the previous mode.
Available data sources include:
1. Measurement buffer for the currently selected channel.
2. Readings from the presently selected channel.
3. Entire 64K sampling buffer regardless of measurement
size.
4. IEEE Reading Output Buffer.
Each of these sources is further described below
Measurement Buffer: When this data source is selected,
the measurement for the selected channel will bc placed
in the analog output buffer. If the programmed number
of samples is larger than I’0 (the size of the analog output buffer), and the unit is in the CRT or scope mode, the
measurement will be automatically scaled so that II plot
or screen display reflects all the samples in the mcasurement. If no measurement is available, no data will bc
transmitted.
Channel Readings: Selection of this mode empties the
analog output buffer and allows new readings from the
selected channel to be stored in the buffer as they become
available. As readings become availablt?, tlwv will be
transmitted via the analog output to your graphing device.
In this manner, you could apply a variety of different m,lth
functions to a single measurement and then graph the
results on a single plot.
64K Measurement RAM: This mode graphs the entire 64K
RAM memory regardless of the programmed number of
samples. Thus, all samples plotted by this mode may not
be from the current meaurement. For example, eight XK
sample measurements could be displayed on a single plot.
This data could be from previous single-channel
measurements.
IEEE Reading Output Buffer: The ~100 reading IEEE-488
output buffer that is controlled with the Q command is
the source for the analog output in this mode. Each reading
will reflect the entire associated measurement except for
the waveform mode which only displays the trigger point.
NOTE
For dual A/D channel units, the selected AID channel is
the source for the analog output.
3-23
3.12.4 Triggering the Analog Output (XV TRIG)
Program a scaling factor by using the following procedure:
By using XY TRIG, you can start and stop the analog output. In this manner, you can stop the analog output, load
the plotter with paper, and then initiate the plotting sequence. In addition, you can halt the plotting process at
any time simply by pressing XY TRIG. When halting the
plot in this manner, the pen will lift and return to the home
position. XY TRIG is also used in other XY modes to update the analog output.
As with the remaining XY mode keys, you must press
SHIFT first to initiate the mode.
3.125 Scaling the Analog Output (XV ZOOM)
In most cases, a measurement buffer will be larger than
the analog output viewed data. In those cases, it may be
necessary to apply a scaling factor in order to get a better
resolution of the sampled measurement.
You can program a scaling factor to effectively increase the
magnification of the plot with the XY ZOOM key If the
scaling factor is 1, the complete measurement buffer will
be reflected in the analog output. If the scaling factor is
2, only half the measurement will appear, and so on.
_.
The minimum value for the scaling factor is 0.1, and the
maximum value is 1000. The resolution of the scaling factor is 0.1, thus it is possible to program a scaling factor of
1.4. For example, the total number of samples reflected in
the output would be N/,.,. With 900 samples, the number
of samples reflected in the output would be 90011.41642.
1. Press SHIFT XY ZOOM. The instrument will then
display the presently programmed scaling factor. For
example, the display might show:
XYZOOM = 1.0
2. You can change the scaling factor in one of two ways.
Either press the desired numeric key and then ENTER,
or use the Uprange or Downrange keys to increment
or decrement the displayed value. In this case, it is not
necessary to press ENTER, as the value is entered
automatically. During the entry process, you can press
the CANCEL key to return to the previous value.
3. If you enter an invalid parameter, the instrument will
display an error message.
Figure 3-11 demonstrates how using XY ZOOM can help
zoom in on a portion of a plotted waveform. In (A), a scal-
ing factor 4 is applied, with the result that only 100 of the
400 samples are reflected in the analog output sequence.
In (B), a scaling factor of 1 is applied, so the entire measure-
ment buffer is plotted. In this instance, only every fourth
sample is reflected in the final signal. Thus, an appropriate
scaling factor can be used to effectively increase resolution
in cases where only a portion of a measurement requires
graphing.
If the XY ZOOM parameter is less than 1, you will be effectively zooming out from your graph. In this case, other
portions of the 64k RAM buffer not associated with the
measurement will become visible in the plot.
3-24
OPERATION
3.12.6 Controlling the Analog Output Viewed
Data (XV PAN)
By using the XY PAN key, you can select the first nwasurement buffer sample to be placed in the analog output buffer, thus effectively moving the viewed data left or right.
For example, if the measurement buffer contains 400
readings, 300 readings will not be seen, assuming the scating factor set with XY ZOOM is 4. By using XY PAN, you
can control which of those 100 samples you wish to ser.
This key is active only if the XY data source is a measurement buffer, and is inactive otherwise.
The smallest permissible value is --65,535, and Ihc max.
imum value is: 65,535 (64k).
Program the analog output window JS follows:
1. Press SHIFT XY PAN. The instrument will prompt with
the presently programmed value of the first buffer Ior,v
tion to appear at the analog output. For example, the
display might show: XYI’AN = 100. Under these conditions, samples 100.199 will be transmitted out the analog
output, assuming a scaling factor of 1.
2. To change the value, key in the new digits \vith the
numeric keys and press ENTER, (v increment or decre-
ment the displayed value with the Uprange or
Downrange keys. If you use Uprange or Downrange, it
is not ncccssary to press ENTER to enter the neu v.llue.
3. If an invalid value is entered, the instrument will displa!
an error message.
Discussion
We can demonstrate how the XY PAN key can be used to
move the analog output viewed data with the help of
Figure 3-12. In all cases, the scaling factor is 4, and 400
samples xc stored in the buffer. These samples are
numbered O-399.
In Figure 3-12(A), the XY PAN parameter is zero, with the
result that samples O-99 arc included in the viewed data,
while samples loo-399 are excluded from the viewed data
and loo-399 do not appear at the analog output. In (B),
the window begins at sample 100 and extends through
sample 199. Figures 3-12(C) and 3-12(D) demonstrates
viewed data placement for XY I’AN parameters of 200 and
300, respectively.
3-25
OPERATION
3-26
Figure 3-12. Moving Analog Output Viewed Data with XY PAN
OPERATION
3.12.7 Setting Maximum Analog Output
The maximum output levels of the X and Y outputs can
be programmed to values between 1 and lOV, and the Z
output blanking level can be set to high or low by using
the OTHER key, as described in the following paragraphs.
The full scale values can be changed at any time without
affecting other operating modes. Table 3-8 summarizes
keystroke sequences and display messages for each of
these programming modes.
Levels
OTHER BUTTON
X Output Level Programming-The full scale X output can
be programmed to values between 1 and 1OV with 1pV
resolution. To program the X output lcvcl, perform the
following sequence.
1. Press: SHIFT, OTHER, 4, or SHIFT, OTHER, A, A, A,
Table 3-8. XY Mode Level Programming
Mode
x Output Full Scale Value
Y Output Full Scale Value
Z Output Manking Level
Range
lV-1ov
1VlOV
Low or
Hieh
SHIFT, OTHER, 5
SHIF’I; OTHER, 6
example, to progran, a WV value, pwss: 5, ., I
ENTER.
Display Message
x FS = 1o.oooooov
Y FS = ‘1O.OOOOOOV
% ISLANK = LOW
3-27
OPERATION
2 Output Blanking Level-The Z output blanking level can
be set to one of two levels: OV (LOW) or 5V (HIGH)
nominal (also, a provision is made on the I/O board for
15V nominal). The purpose of the blanking pulse will depend on whether the instrument is in the CRT, plotter, or
oscilloscope modes.
If the instrument is programmed for the CRT mode, the
blanking level is intended to blank the beam during the
beam retrace period. If the instrument is being used in the
plotter mode, the Z output blanking level can be used to
tell the plotter to lift the pen and return to the home position. In the oscilloscope mode, the Z output blanking pulse
can be used to triger the oscilloscope to begin the horizon-
tal sweep cycle.
Program the Z output blanking level as follows:
1. Press SHIFT, OTHER, 6. The unit will display the
presently programmed blanking level (HIGH or LOW)
as in this example:
Z BLANK = LOW
LOW blanking). After each transmission sequence, the Z
output assumes the programmed blanking level. Note that
the transmission sequence is recurrent in the CRT and
oscilloscope modes, but it occurs only once with each XY
trigger in the plotter mode.
BLANK BEAM CRT MODE,
PENUP ,PLOTTER MODE,
TRIGGER SCOPE ~OSCUOSCOPE MODE,
_illii f[NG
PLOTTER SEOUENCE
STARTS HERE
A. HlGH BLANKING LEVEL
r--
DATA TRANSMlSSlON
2. Use the Uprange or Downrange key to toggle the
display between LOW and HIGH levels.
3. The blanking level is placed into effect immediately.
4. Press CHANNEL to return to previous mode.
Discussion
Figure 3-13 demonstrates the operation of the blanking
pulse. In (A) a HIGH level is assumed, while (B) shows
a blanking pulse with a LOW level. Note that one pulse
is essentially the inverted form of the other.
During the transmission of data through the XY outputs,
the Z output is at the non-blanking level (OV when programmed for HIGH blanking, 5V when programmed for
DATA TRANSMISSION
:r :u-‘ir
PREVIOUS BLANKING
PULSE
B. LOW BLANKING LEVEL
BLANK BEAM ,CRT MODEl
PENUP iPLOTTER MODE,
TRIGGER SCOPE
,OSClLLOSCOPE MODE,
Figure 3-13. Output Blanking Levels
3-28
OPERATION
3.13 MATHEMATICAL FUNCTIONS
The Model 194 has a number of built in mathematical functions that can be used to analyze a measurement. These
functions include:
AVG (Average)
TRMS (True Root Mean Square)
PEAK (Positive and Negative Peak Values)
PK TO PK (Peak to Peak)
STD DEV (Standard Deviation)
INTEGRAL
WAVEFORM (Display sample at trigger point)
MATH BUTTONS
These mathematical functions operate on the samples CUTrently stored in the measurement buffer. Samples are
numbered 0 through n-l, where n is the programmed
number of samples in the measurement. If the instrument
is in the single-trigger mode, selecting a function will cause
that function to operate on the most recent measuremrnt
sequence. Thus, by taking a single measurement sequence,
you can apply a variety of differerent math functions to
a single measurement. Note, however, that only o”c’ function can be in operation at any given time; selecting a ne\\
mathematical function will cancel the previously selected
function. It is not possible, for example, to take the integral
of the standard deviation.
Once a function is selected, you can perform that particular
function a number of times for different mea~urenwnts
simply by triggering the instrument. Each time the unit
is triggered, the measurement buffer will bc updated, the
selected mathematical operation will be performed on th<a
new measurement, and the result will be shown on tht,
display.
If the zero mode is in effect for a particular channel. the
zero baseline value will be subtracted from the reading
after the function is performed. 1” every mode, the result
will be overrange if one or II~TC’ samples is overrange~
The keys associated with the mathematical functions are
operational only when the instrument is in the singlechannel display mode. However, either channel may be
programmed for a particular function before placing the
instrument in the dual-channel mode. To do so, use the
CHANNEL button to display the desired channel and
select the desired function. Once the function is selected,
place the unit in the dual-channel display mode with the
CHANNEL button.
Table 3-9. Math Function Display Messages
Function
AVG
TRMS
PEAK
PEAK
PK TO PK
STD DEV
INT
WAVEFORM 2.5931V DC T2
Display Message*
-1.2345V AVG 1
‘1.2345V RMS 2
1.2345V PK+2
1.2345V I’K-‘I
1.2345v P-P 1
O.lOlZV STD 1
4.0315EOOO VS 2
Display messages associated with the various math tunc~
tions are summarized in Table 3.9. The indicated \~alucs
are, of course, typical, and will depend on the measure-
ment on which the particular function is being performed
If a valid measurement is not present in the buffer, the
reading portion of the display will contain dashes.
NOTE
The display update rate may vary defending cjn
the selected math function.
Description
Average of Readings
True RMS of Readings
Display positive peak value.
Display negative peak value.
Peak-to-Peak Value.
Standard Deviation
Integral of Measurement
Display sample at trigger
point.
*Displayed value depends on applied signal
3-29
OPERATION
3.13.1 Average
The average of the samples in the measurement buffer can
be displayed by pressing SHIFT AVG (or simply AVG if
not in the data entry mode). The instrument will then
display the average of the samples in volts stored in the
measurement buffer in accordance with the following
formula:
n-1
c vi
i=O
V”“, = _____
n
Where: Vi = voltage amplitude of individual sample
i = individual sample number (0 through n-l)
II = number of samples in the measurement
Thus, the average is determined simply by adding up all
the samples and then dividing by the number of samples
in the measurement.
Typically, the display might show:
1.2235 V AVG 1
DC voltage. For a sine wave, the TRMS value equals 0.707
times the peak value.
To determine the true RMS value of the measurement,
press SHIFT TRMS (or simply TRMS if not in the data cntry mode). The instrument will respond by displaying the
TRMS value in volts of the samples in the measurement
buffer. Although TRMS can be applied to measurements
of any number of samples, it is usable only for
meaSurcme”tS of two or more samples.
A typical display in the TRMS mode is as follows:
2.Y875 V RMS 2
In this instance, the TRMS value of the channel 2 measurement buffer is being displayed.
TRMS values are calculated as follows:
“-1
c v;
i=O
VTM =
I--
”
In this case, the average of samples in channel 1 is being
displayed.
‘The average function can be applied to measurements “f
any sire, although taking the average of a single-sample
measurement sequence makes no sense because the
average is the same as the sample.
Example:
As an example, assume that the data listed in Table 3-10
has been taken during a measurement sequence. The
average value is simply the sum of the samples divided
by the number of samples (11). Thus, the average of this
measurement would be:
v,,,; = l30.65111
V rlVG = 11.877V
3.13.2 True RMS
The true RMS value of a voltage waveform is that value
which would produce the same heating effect as an equal
Where: Vi = voltage amplitude of individual sample
i = individual sample number (0 through n-l)
n = number of samples in measurement
Example:
As an example, let us determine the TRMS value of the
measurement with samples listed in Table 3-10. WC can first
determine the sum of the squares of all 11 samples as
follows:
i=n-1
E = 1576.5825
i=O
The TRMS value can then be easily calculated by using
the above value as follows:
1576.5825
vTM =
K,,, = 11.97V
F-
11
3-30
.-
OPERATION
Table 3-10. Data For Mathematical Function
3.13.3 Peak
The peak mode allows you to display positive and negative
peak values in volts for the selected channel. Again, this
function is only usable for readings with two or more
SX”pleS.
Example:
From our example measurement in Table 3-10, we can easily
determine the positive and negative peak values. The mat
positive sample is number 3, which has an amplitude “f
14.25V. The most negative (least positive) sample is number
10, with a signal level of 1OV.
3.13.4 Peak-to-Peak
The peak-to-peak value of the selected channel can bc
displayed by pressing SHIFT PK T0 PK (or I’K T0 I’K ii
not in data entry mode). A typical display fw this nwdc
might be:
12.503 V P-P 2
In this case, the peak-to-peak value of the channel 2
measurement is being displayed.
Rx&to-peak values arc calculated as follwvs:
Positive and negative peak values are defined as follows:
Positive Peak: the most positive sample stored in the
measurement buffer.
Negative Peak: the most negative sample stored in the
measurement buffer.
You can display positive and negative peak values as
f0110ws:
1. Press SHIFT PEAK (or PEAK if not in the data entry
mode). The instrument will then display the positive
peak value, as in this example:
1.2345 V PK+l
2. You can toggle the unit between the + PEAK and -PEAK
values by using the PEAK button. For example, the
negative peak value might be as follows:
-2.4451 V PK.1
3. To cancel the peak mode, select another mathematical
function.
Where: VF.p = peak-to-peak value in v”lts
V+I, = most positive sample in the measurement
V-1, = most negative sample in the measurement
This function is valid for measurements of any size, but
when selected for a single-sample measurement, a reading
of zero will be displayed.
Example:
As an example, assume the instrument is displaying the
peak-to-peak value of the measurement shmvn m Table
3-10. The most positive sample is number 3, which has an
amplitude of 14.25V. The most negative sample has an
amplitude of lO.OV (number 10). Thus, the instrument
would calculate and display the peak-to-peak value as
follows:
Vp.p = 14.25 10.0
Vp.p = 4.25V
3-31
OPERATION
3.13.5 Standard Deviation
Very often when dealing with a group of samples, it is
necessary to know how much the data varies from the
average of the measurement (group of samples). A common term used to describe this “spread” of data is the standard deviation. The Model 194 includes a standard deviation function to help you analyze data in this manner.
To obtain the standard deviation of the measurement,
simply press SHIFT STD DEV (or simply STD DEV if not
in the data entry mode). The instrument will then display
the standard deviation of the measurement, as in the example below:
1.0001 V STD I
This display would indicate that the standard deviation of
samples in channel 1 is being displayed.
The Model 194 calculates the standard deviation as follows:
n-l
c (vi-v,“,)~
i=O
v,,, =
n
1
Where: V,,,, = standard deviation of the measurement
in volts
i = the number of an individual sample (0
through n-l)
n = the number of samples in the measurement
V,, = the average of the samples in the
meaSl”-ement
3.13.6 Integral
Pressing SHIFT INTEGRAL (or simply INTEGRAL if not
in data entry mode) will display the integral of the
measurement in volt-seconds. A typical display in the integral mode might be:
4.0315EOOl VS 2
In this case the integral of the channel 2 measurement is
displayed. Note that the VS indication in the display
depicts that volt-second units are being shown. Note that
the exponent of the integral is included in the display (EOOl
in this example).
The integral function may be applied to measurements of
any sample size; however, usable readings are returned
only for readings of two or more samples.
The Model 194 calculates the integral by summing areas
associated with individual samples under a curve. Thus,
the value returned by the integral function is an approximation of the area under the entire curve. The boundaries
of this curve are defined by the measurement duration,
as well as the amplitude of the signal being measured, as
shown in Figure 3-14. Thus, the integral is calculated:
n-2
J
Vdt = [ % V, + % V.w, + ye%’ t,
Where: i Vdt = the integral of the signal with respect to
time
n = total number of samples in the measurement
Example:
For example, assume we can calculated the standard devia-
tion of our sample data from Table 3.10 as follows:
24.8165
vsrr, =
V ST” = 1.502v
3-32
11
I---
Because each calculated curve area is only an approximation, the resulting integration process is only approximate. For maximum accuracy, choose the largest number
of samples per measurement possible.
Example:
For example, using the formula above with the example
data from Table 3-10, we have:
n-2
J
Vdt = [ % V, + ‘12 V.m, + C Vi ] t,
i=l
OPERATION
J Vdt = [ 5.3V + 5V + 110.05V ] 0.001
J Vdt = 0.12035 VOLT SECONDS
RATIO & DIFFERENCE BUTTONS
Display messages associated with these modes are sum
marized in Table 3-11. Note that the instrument displays
the following message if one of these mode buttons is
pressed with no channel 2 module present:
NO A/D IN 012.
Most other front panel buttons are inoperative \vhcn in
the ratio or difference modes.
Table 3-11. Ratio and Difference Display Messages
Figure 3-14. Integration by Approximate Area
Summation
3.13.7 Waveform Mode
The waveform mode can be used to display the buffer sample that occurs at the trigger point. If it is not possible to
display the trigger point location, the instrument will
display the location as close as possible to the trigger point.
The RECALL button can be used to view samples stored
at other buffer locations.
A typical display in the waveform mode might bc:
1.5467V DC Tl
In this instance, the reading is 1.5467 and T indicates that
the trigger point is being displayed.
3.14 RATIO AND DIFFERENCE
When the optional Model 1944 is installed, the Model 194
can be programmed to display the ratio or difference between channels 1 and 2, as discussed in the following
paragraphs.
Message* Description
1.2345EO1 XX ‘1.2 Display diffwcncc between
channels 1 and 2 (see below 1~1
XX units).
1.2345E.3 XX 112 Display ratio of channel 1 to
channel 2 (see below for XX
units).
NO A/D IN CH2 1944 option not inst.tlled.
xx= Descri+on
blanks Dimensionless
VS Volt-seconds
V Volts
S
l/S Reciprocal seconds
??
L
*Displayed values depend on calculated result.
Seconds
Invalid units
3.14.1 Difference Mode
By pressing the CHl-CH2 key, you can display the difference between the channel 1 reading and the channel
2 reading. A typical display in this mode might bc:
1.2567Em3 V 1-2
3-33
OPERATION
This display indicates that the channel 2 reading is being
subtracted from the channel 1 reading. Note that the
displayed value has 4% digit resolution and includes an
exponent and appropriate units.
If one or both channels are programmed for mathematical
functions, those functions are performed prior to the
algebraic subtraction process. For example if channel 1 is
programmed for the average function, and channel 2 is
programmed for the TRMS function, the display will show
the difference between the channel 1 average and the chan-
nel 2 RMS value.
Any combination of math functions for the two channels
is valid, with the restriction that units must match. For example, you cannot subtract volts from volts seconds.
If either channel is in the waveform mode, the sample that
is normally displayed will be applied to the Civil-CHZ
mode. If either channel is in the overflow condition, the
result of the subtraction will be overflowed.
3.14.2 Ratio Mode
The Model 194 can be programmed to display the ratio of
channel 1 to channel 2 by pressing the CHltCH2 button.
The instrument will then display the ratio of the two than-
nels. A typical display might be:
2.3451EOI V 312.
Again, the displayed value has 4% digit resolution and in-
cludes an exponent along with appropriate units.
Any previously selected mathematical operations will be
performed before the division process is completed. When
in the waveform mode, the instrument will use the normally displayed waveform reading as input for the ratio
calculation. Any combination of math functions for the two
channels is valid.
If the channel 2 reading is zero, the OFLO message will
be displayed.
3.15 STATUS
the status of the channel 1 AID converter, as well as the
A/D converter in channel 2. To check status of a particular
channel, you must be in the single channel display mode
for that channel.
STATUS BUTTON
When STATUS is pressed, the instrument displays the
status of various operating parameters in the following
order:
Zero value
Filter mode
Trigger source
Trigger mode
Delay (in time or number of samples)
Trigger level (if source is the input signal)
Sample rate
Measurement size (in elapsed time or number of samples)
Maximum sampling rate for 16.bit resolution
Maximum sampling rate for &bit resolution
Once the status mode is entered, the unit will scroll
through and display the various status parameters at a rate
of one per second. Table 3-12 shows typical display
messages. To terminate the status mode, press any other
front panel key. For example, you might wish to press
CHANNEL, which will return the instrument to the
previous mode.
By pressing the STATUS key, you can obtain and display
3-34
OPERATION
Table 3-12. Typical Status Mode Display Messages
Mode
zero Value
Filter
Trigger Source
Trigger Delay
Trigger Level
Sampling Rate
Number of Samples
16.Bit Maximum Rate
B-Bit Maximum Rate
Typical Display Message
OFV
FILTER OFF
IMMEDIATE
ODELAY
O&V
166.7/1s
100 SAMPLES
16 BIT 100kHz
8 BIT 1MHz
3.16 SETUP MODE
Through use of the setup mode, you can store two different
instrument configurations in non-volatile RAM. These configurations will be retained for future recall cvcn if the
power has been turned off. Setup 0 also allows you to
return to factory default configuration.
SETUP BUTTON
f
nnnnEI
OOOc3~
SETUP
Display messages associated with the setup mode are sum
mar&d in Table 3-13. Note that the contents of the
measurement buffer arc not saved by the setup mode.
NOTE
If the unit is in the dual-channel display mude,
pressing SFKJP will result in a
message. At this point, you should use the Cl-IANNEL key to select which channel to recdll.
smir WI IICI I!
Table 3-13. Setup Mode Display Messages
Message / Description
RECALL SETUP n ’ <
STORE SETUP n
WHICH CHANNEL? Unit in dual-channel rn~~ic~.
1
> >
Setup parameter too large.
3.16.1 Recalling Setups
Three setup positions (O-2) may be rrcalled by using the,
basic procedure below. Setup position 0 is pcrmanrnt!)
programmed at the factory for the configuration sho\\,n in
Table 3-15, while the configurations stored in setup positions 1 and 2 can be programmed as discussed in
paragraph 3.16.2. Note that the instrument assumes the
SETUP1 configuration upon power up or when RESET is
used.
000011
Stored parameters include the following:
Zero Mode (if enabled or disabled, and zero value)
Filter (Enabled or disabled)
Trigger Arming Mode (single/continuous)
Trigger Source
Trigger Delay (samples or time)
Trigger Slope
Trigger Level
Selected Range
Autorange (on or off)
Sample Rate (interval or frequency)
Measurement Size (number of samples or duration)
Input Coupling
Mathematical Function
IEEE-488 Primary Address
1. For instruments equipped with two AiD modules, select
the desired channel to be recalled with the CkIANSEI.
button
2. Press SETUP to enter the setup mode. The instrument
will then display the
3. To recall the presently displayed setup, simply press
ENTER at this ooint.
4. ?b access a different setup than the ant’ displayed, kc!
in the new digit (O-2) and press
selected
RECALL SETUP 0
configuration, for cxamplc:
the
f:NTER key.
3.16.2 Saving Setups
Two different instrument configurations may be stored in
NVRAM by using the store aspect of the setup mode. Note
that you cannot store a setup at position 0 as that position
is permanently programmed with factory defwlts.
1. If your unit has tw” Ail1 modules, use the Cf IANh’fII.
button to select the channel to be configured.
3-35
OPERATION
2. Select the various operating modes for the configuration to be saved using the appropriate front panel
buttons.
3. Press SETUP twice in succession. The instrument will
then display the following message:
STORE SETUP 1
4. To store presently selected setup, simply press ENTER.
NOTE
The SETUP 1 configuration is used for power on
and RESET conditions.
5. To store the configuration at a new position, key in the
digit (1 or 2) and press ENTER. The unit will then store
the new configuration. To return to the previous
operating mode, press CHANNEL.
6. If you attempt to store a configuration at the SETUP D
position, the unit will display the following message:
CAN’T STORE 0
3.17 FRONT PANEL PROGRAMS
(OTHER KEY OPERATION)
mode). The instrument will then respond with the
message for the IEEE-488 address program:
0 IEEE- 488 ADR
At this point, you can key in a single digit number to select
the desired program, (in which case ENTER is not
necessary), or use the A or 7 key to scroll through
available modes. Once the desired program is displayed,
press the ENTER key to actually enter the selected
program.
The various programs associated with the OTHER key arc
covered in detail in appropriate paragraphs of this manual
as follows:
Program 0 (IEEE-488 address): paragraph 4.5.
Program 1 (self test): paragraph 7.8.
Programs 2 and 3 (digital calibration and NVRAM storage):
paragraph 7.5.
Programs 4, 5, and 6 (Analog output levels): paragraph
3.1~2.7
Table 3-14. Front Panel Programs
Miscellaneous modes include programming the IEEE-488
address, self test, digital calibration, NVRAM storage of
calibration constants, X output full scale value, Y output
full scale value, and Z output blanking level. These modes,
along with display messages are summarized in Table 3-14.
OTHER BUTTON
ä u 0 El 0
These various programs can be accessed by pressing
OTHER (SHIFT will be necessary if in the data entry
Progran
Description
0
IEEE-488 Address
1
Self Test
2
Digital Calibration
3
NVRAM Storage of
Calibration Constants
4
X Output Full Scale
Y Output Full Scale
5
Z Output Blanking Level
6
1 SELF TEST
2 DIGITAL CAL
4 X OUTPUT FS
5 Y OUTPUT FS
6 Z BLANK
3.18 RESET
Pressing SHIFT RESET returns the instrument to poweron default (SETUP 1) operating conditions. The factory
default reset conditions are listed in Table 3-15. Note that
these will be different if you modify the SETUP 1
configuration.
3-36
Table 3-15. Factory Default RESET (SETUP 1)
Conditions
Mode
Range
Zero
Filter
Trigger Mode
Trigger Source
Trigger Delay
Trigger Slope
Trigger Level
Sample Rate
Input Coupling
Measurement Size
Reading Function
Immediate (TRIGGER button)
Auto
Disabled
Disabled
Continuous
0
off
ov
166.7fisec
DC
101 samples
AVerage
OPERATION
Figure 3-15. Synchronous Operation
NOTE
These conditions are also restored by SETUP 0.
3.19 EXTERNAL CLOCK
The CLK IN and OUT jacks may be used to connect two
“r m”re Model 194s together for synchronous operation.
To do so, connect the CLK OUT jack of the master unit
to the CLK IN jack of the slave unit, as shown in Figure
3-15.
CAUTION
Digital common is internally connected to
chassis ground and cannot be floated.
NOTE
Shielded cable should be used for the clock input and output connections to minimize the
possibility of EM1 radiation.
Up to 16 units may be daisy chained together by tlsing the
same basic connecting scheme. Figurr 3-16 shows five such
units connected together: one master, and fwr slaws. fixternal clock operation is automatic; the instrument will
automatically switch to the external clock when the prw
per signal is detected.
CLK IN may also be used to apply an external time b.w
at TTI. levels (low, 0-0.W high 2.4-5V). Thr time base, c.111
be in the range of 1MHz t” 1OMllz; h~~.~vw, pr”grammed sampling rates assume that a IOMHz signal is trsed~
Thus, sampling rates must be adjusted accordinglv if ‘1
non-standard clock is applied. F”r ~~xamplr, if the .&xi,
rate is 5MHz, the instrument will sample at exactly cmchalf the programmed rate.
NOTE NOTE
Both A/D modules (dual-channel units) use the Both A/D modules (dual-channel units) use the
same time base. ‘Thus, any signal applied t” CLK same time base. ‘Thus, any signal applied t” CLK
IN will affect both A/D modules. IN will affect both A/D modules.
3-37
OPERATION
Figure 3-16. Synchronizing Five Units by Daisy Chaining
3.20 REAL TIME OUTPUT
Each A/D module has a real time output port that can
transmit A/D data to an external device such as a computer
on a real time basis.
Data can be taken a byte at a time (8 bits) or a word at a
time (16 bits). The transmission rate will, of course, depend on the selected sampling rate. For example, if you
program a 1OOkHz sampling rate, transmission will occur
at that frequency.
3.20.1 Signal Lines
The pin out diagram for the real time connector is shown
in Figure 3-17. Signal lines are listed in Table 3-16. Figure
3.18 shows a typical timing diagram for the real time
output
Table 3-16. Real Time Output Signals
Pin Number
1 Digital Common
2
3
4
5 HIGH BYTE
6
7 D9
8
9 Dll
10
11
12
13
14 Not Used
15
16
17 LOW BYTE
18 DO
19 Dl
20 D2
21
22
23 D5
24
25
Signal Line
MEASURING
OVERRUN
NEW CONVERSION
D8
DlO
D12
Dl3
D14
Dl5
Not Used
Not Used
D3
D4
D6
D7
Figure 3-17. Real Time Output Connector
3-38
OPERATION
CAUTION
Digital common is connected to chassis ground
and cannot be floated.
NOTE
Shielded cable should be used with the real time
output in order to minimize the possibility of EM1
radiation,
Real time output signal lines include:
Data lines (DO-D15)-These lines have non-inverted A/D
converter data. DO is the least significant bit, and IX5 is
the most significant bit. Note that converter data has 16
bits at sampling rates of 1OOkHz and lower (and if the programmed number of samples is ~32,768). Above 1OOkHz
(or if the number of samples is >32,768), the converter
operates in the R-bit mode. In this case, relevant data is
located only on DO through D7.
NEW CONVERSION-This signal line will go high when
converter data has been latched into the real time output
data latches and is ready for transfer.
LOW BYTE-This line should be set low to enable the
DO-D7 data lines. Note that the data lines DO-D7 will be
in the high-impedance state when LOWBYTE is high.
HIGH BYTE-This line should be set low to turn on the
De-D15 data lines. De-D15 will be in the higbimpedancc
state when HIGHBYTE is high.
OVERRUN-This flag bit will be set high if data made
available by a previous conversion was not taken. Ont, or
more data words will have been lost under these
conditions.
MEASURING-This line will be high when the instrument
is performing a measurement sequence; in other \vords.
the triggering condition has been met.
3.20.2 Reading Real Time Data
The exact method used to transmit data will depend on
the particular application; however, the pmcedurc belou
gives the basic sequence for transfer of data. The sequence
assumes the instrument is processing samples (MEASURING high). A flow chart of this stxlucnc~~ is sh<)\vn in
Figure 3-19.
1. Monitor the NEW CONVERSION line and observe
when it goes high. When NEW CONVERSION gws
high, the data byte or word has been latched into the
output data latches.
2. Test the state of the OVERRUN flag. If it has been set
high, you have missed one or more jvords of data. To
correct an overrun condition, either increase the reading
rate of the external equipment, or program a slwwr
sampling rate.
OVERRUN J
AS c
DATA ,00~0,5~ +t:x
VALID
A. EOC goes true, setting NEW CONVERSION
B. LOWBYTE andbr HIGHBYTE go true. clearing NEW CON”ERSlON
c. same as A
F. EOC goes true with NEW CONVERSION false, string NEW CONVERSION and clearing OVERRUN
G. same as B
H. EOC goes true while LOWBYTE and,or HlGHBYTE are still twe, setting OVERRUN. NEW CONVERSION does not Wt 5~1
I. EOC goes true after LOWBYTE and HlGHBYTE have gone false. clearing OVERRUN and setting NEW CONVERSION
Figure 3-18. Real Time Output Timing
0 E F
xx
VALID
G H
,~,,I,
VALID
3-39
3. If data is to be transferred in low byte, high byte fashion,
first pull LOW BYTE low and read the DO-D7 data lines.
Next, pull HIGH BYTE low and read the D&D15 data
lines.
4. If all 16 bits are to be transferred at the same time, simply
pull both LOW BYTE and HIGH BYTE low
simultaneously and read DO through D15 at the same
time.
5. Test the state of the MEASURING line. If it is high, the
instrument is still sampling, and steps l-4 above can be
repeated for the next sample. If MEASURING is low,
the sequence has been terminated and no new data will
be made available.
3.20.3 Computer Interfacing
The exact nature of the interface will, of course, depend
on the computer being used. In this paragraph we will
discuss computer interfacing in general terms.
Figure 3-20 shows a simplified block diagram of a typical
computer interface. At the left side of the diagram, typical
computer bus lines are shown, including the data bus
(DO-D7), the address bus, as well as bus clock and reset
lines. The interface itself is shown in the center part of the
diagram, while Model 194 components of note are shown
on the right.
The address decoding circuitry partitions the interface circuitry into three unique addresses as follows:
STATUS: A read-only location that allows you to determine
the conditions of the MEASURING, NEW CONVERSION
and OVERRUN flags in the Model 194.
LOW BYTE: A read-only location that returns the low byte
of instrument data.
HIGH BYTE: A read-only location that returns the high
byte of the real time data.
The tri-state buffer is the interface between a number of
interface and Model 194 status lines, including SHIFT
COMPLETE, OVERRUN, MEASURING, and NEW CONVERSION. Status of these lines can be checked bv readine
the STATUS location and then masking off the adpropriat;
bit to determine the state of that particular line.
Figure 3-19. Flow Chart for Reading Real Time
Data
3-40
OPERATION
r
-----
Figure 3-20. Simplified Block Diagram of Real Time Computer Interface
1
3-41
OPERATION
Reading Real Time Data
Real time data can be read by performing a read opera-
tion to the low and high byte locations in sequence. The
exact memory locations will, of course, depend on the address decoding scheme used. For example, assume that
the interface is located at four memory locations beginning at address 5DF00, with the three locations decoded
as follows:
STATUS: 5DFO0
LOWBYTE: 5DF02
HIGH BYTE: $DF03
Further assume that the three status signals are assigned
the following data bus lines:
OVERRUN: Dl
NEW CONVERSION: D2
MEASURING: D3
The following source code gives a simple example using
6502 assembly language on how to go about accessing real
time data and storing it in computer memory. The program
accesses 256 bytes (128 words) of instrument data and
stores them in a memory buffer beginning at location
$COOO.
SOURCE CODE
START
LOOP
PASS
LDX #$00
LDA $DFOO
AND #$04
BEQ LOOP
LDA $DF02
STA $COOO,X
INX
LDA $DF03
STA $COOO,X
LDA $DFOO
AND #$08
BEQ PASS
INX
BNE LOOP
RTS
COMMENTS
Clear memory pointer.
Load interface status
into accumulator.
Mask off NEW CONVERSION bit.
If no conversion,
branch back and wait.
Load low byte into
accumulator.
Put low byte in
memory location with
offset x.
Increment memory
pointer.
Load high byte into
accumulator.
Put high byte into
memory location with
offset x.
Get interface status.
Mask off MEASURING bit.
If no longer measuring, end routine.
Increment memory
location pointer.
Branch back for next
reading.
Return to calling
routine.
3-42
Speed Considerations
The interface discussed in this paragraph uses memorymapped I/O. Thus, the limiting factor for the rate of data
transfer lies in the speed of the processor involved. For
a 6502 running at lMHr, for example, we are looking at
a byte transfer rate of 20.25rsec per byte-a speed that is
much slower than the fastest [lMHz) sampling rate of the
Model 194. Even with a much faster 16-bit processor, it is
doubtful whether the MPU could keep up with the
available data at these extremely high rates
OPERATION
Thus, for more rapid data transfer, the interface discussed
here would have to be modified to incorporate a DMA
(Direct Memory Access) controller IC. This arrangement
would allow the interface to take data bytes as they come
from the instrument and dump them directly to computer
memory, bypassing the bottleneck of the MPU. Of course,
this added speed would come at the expense of both software and hardware complexity.
3.21 MEASUREMENT CONSIDERATIONS
The following paragraphs describe a number of considera-
tions to be taken into account when using the Model 194.
3.21.1 Ground Loops
Ground loops that occur in multiple-instrument test setups can create error signals that cause erratic or erroneous
measurements. The configuration shown in Figure 3-21 introduces errors in two ways. Large ground currents flowing in one of the wires will encounter small resistances,
either in the wires, or at the connecting points. This small
resistance results in voltage drops that can affect the
measurement. Even if the ground loop currents are small,
magnetic flux cutting across the large loops formed by the
test leads can induce sufficient noise voltages to disturb
sensitive measurements.
To prevent ground loops, instruments should be connected
to ground only at a single point, as shown in Figure 3-22.
Experimentation is the best way to determine an accep-
table arrangement. For this purpose, measuring in-
struments should be placed on the lowest ranges. The con-
figuration that results in the lowest noise signal is the one
that should be used.
L
Figure 3-21. Multiple Ground Points Create a
Ground Loop
Figure 3-22. Eliminating Ground Loop
3.21.2 RFI
Radio Frequency Interference (RFI) is a general term frcquently used to describe electromagnetic intcrfcrence over
a wide range of frequencies across the spectrum. RF1 can
be especially troublesome at low signal levels, but it may
also affect higher level measurements in extreme cases.
RF1 can be caused by steady-state sources such as ‘TV or
radio broadcast signals, or it can result from impulse
sources, as in the case of arcing in high volt.lge rw
vironments. In either case, the effect on instrument performance can be considerable if enough of the unwanted
signal is present. The effects of RF1 can be seen a ,m
unusually large offset, or, in the case of imp&c SOIIICC’S,
sudden, erratic variations in the displayed twding.
3-43
OPERATION
RF1 can be minimized by taking one or more of several
precautions when operating the Model 194 in such noisy
environments. The most obvious method is to keep the
instrument and measured source as far from the RF1 source
as possible. Shielding the instrument, source, and test
leads will often reduce RF1 to an acceptable level. In extreme cases, a specially constructed screen room may be
necessary to attenuate the troublesome signal.
In many cases, the internal 50kHz or 500kHz filters may
provide sufficient attentuation of any RF1 signals. In more
difficult situations, it may be necessary to use external
multiple-pole notch or band-stop filters, tuned to the offending frequency range. Keep in mind, however, that such
filtering may have detrimental effects (such as increased
response time) on the measurement.
3.21.3 Instrument Loading Effects
The input impedance of the Model 194 is l.lMO (lMn, 200V
range) in parallel with less than 47pE The resistive component of the input impedance is sufficiently high so as
to have a negligible loading effect on most ~iources. For
sources with high internal resistance, however, the finite
input resistance of the instrument can have a detrimental
effect on measurrme”t accuracy.
Rs and RI form a voltage divider that attenuates the input signal as follows:
Thus, if Rs has a value of lOOkQ, and Rt is SKI (the input resistance of the instrument), the actual voltage
measured by the Model 194 with a 1OV source will be:
10 x lMR
vj.J =
1MQ + 1OOkQ
VM = Y.OYV
Thus, we see that the effects of instrument loading with
high source resistances can be substantial, resulting in an
error of almost 10% in this case.
For any given source resistance, we can calculate the percent error in the measurement from the following formula:
%ERROR = ~
RS
RS + IMR
x ~100%
To SW how instrument loading can affect the measurement, let us review the equivalent circuit in Figure 3-23.
Es and Rs are the source voltage and source resistance
respectively, the instrument input resistance is RI, and the
voltage seen by the meter is VM.
r-------l
r-------l
r------ r------
1 1
ifi
iFT+$Q
I RI I RI
VM I VM I
Ir'; 1
@
I
I
L---_---J
L---_---J
Figure
I
3-23.
I
L------d
Loading Effects
For example, assume that Rs has a value of IkO. The error due t” instrument loading is:
lk0
%ERROI~ =
‘IkR + 1MO
%ERROR = 0.0999%
x100%
3.21.4 Input Capacitance Effects
Virtually
distributed capacitance that can slow down measurement
response time, especially if the Model 194 is being used
at very high sampling rates. Even if the circuit itself has
minimal capacitance, cable or instrument capacitance ef-
fects can be noticeable.
As an example, assume that the Model 194 is being used
to measure the circuit shown in Figure 3-24. The source
voltage and resistance are represented by ES and Rs, the
input capacitance is Ct, and the voltage is VM. For the p”rposes of this discussion, we will ignore the effects of the
input resistance.
any
circuit has at least a small amount of
3-44
L
1 ES
r
RS
wvv
I
-:- c
-y-
OPERATION
While input capacitance does increase response time, it
can help to filter out some of the higher frequency noise
present in the signal by effectively limiting instrument
bandwidth. If we assume that all input capacitance is
lumped into a single element, the half-power (-3dB) point
of the circuit in Figure 3-25 will be:
1
f-3db = ~
27%C1
Thus, if RS has a value of lkl2, and Cl has a value of
lOOOpF, the half-power point will be 159kHz.
Table 3-17. Voltage and Percent Error For Various
Time Constants
Figure
When ES is first applied, the voltage across the capacitance
(and thus, at the input of the instrument) does not rise
instantaneously to its final value. Instead, the capacitance
charges exponentially as follows:
Note that RS is given in ohms, C is in farads, while t is
in seconds.
Because of the charging action of CI, the input voltage
follows the exponential curve shown in Figure 3-24. At the
end of one time constant (R&), the voltage will reach approximately 63% of its final value. At the end of two time
constants (2R&), the voltage will reach 86% of its final
value, and so on. Table 3-17 summarizes voltage and percent error values for ten different time constants.
3-24. Input Capacitance Effects
VM = ES (l-e RC)
Time*
*T = RsC
VM
T 0.632 ES
27
37 0.95
41
57 0.993 Es
61
71
87
YT 0.9999 ES
107
0.86 Es
0.982 ES
0.9975 ES
0.999 Es
0.99966E,
0.99995Es
ES
%EIIor
36 %
14 %
5 %
1.8 %
0.674%
0.25 B
0.09 7’”
0.033%
0.0~12%
0.005%
3.215 AC Frequency Response
Considerations
The strength of the Model 194 lies in its ability to analyze
complex waveforms. The following paragraphs discuss a
number of considerations to keep in mind when measuring AC signals, including low frequency response limits,
as well as volt-hertz product considerations.
Low Frequency Response
The response time will, of course, depend on the relative
values of Rs and CI. For example, if Rs has a value of IkfI,
and CI has a value of IOOOpF, a time constant of lesec
results. Thus, to allow the reading to settle to within O.l%,
approximately 7pec must be allowed.
When DC coupling is in effect, the instrument measures
down to DC levels (OHz). Thus, no consideration as to the
reponse of the instrument at low frequencies need be given
when using DC coupling.
3-45
OPERATION
If AC coupling is in effect, however, the instrument
response rolls off at low frequencies. Thus AC coupling
should not be used in cases where this attenuation factor
might lead to significant errors in the measurement of low
frequency signals, unless AC coupling is necessary to
remove the DC component of a” applied signal.
Volt-Hertz Considerations
With almost any measuring instrument, there exists a limit
as to the maximum volt-hertz product that can be
measured. Simply stated, the volt-hertz product defines
the maximum peak voltage that can be measured at a give”
frequency.
For example, the maximum normal-mode input that can
be safely applied to the Model 194 is 2 x 10’ V*Hz. From
this value, you can easily determine the maximum fre-
quency at a given peak voltage by dividing the volt-hertz
product by that voltage. For example, the maximum fre-
quency at 20V peak would be:
2 x 107V’Hz
fMAX =
20
fMAX = lMHz
3.22 TYPICAL APPLICATIONS
3.22.1 Periodic Waveform Analysis
Probably one of the more obvious situations for the Model
194 is in cases calling for rapid sampling of the input signal,
as is the case when analyzing periodic waveforms. The
type of analysis, of course, will depend on the waveform
as well as your particular requirements.
For example, assume that a 50kHz sine wave like the one
shown in Figure 3-25 is to be analyzed. Our fit task would
be to set up the instrument to properly sample the
waveform at hand. Operating modes such as range, sampling rate and interval, and trigger mode would be set up
in accordance with our knowledge of the waveform being
sampled.
Since the nominal peak-to-peak value of the waveform is
+lOV, we could place the instrument on the 32V range.
With a frequency of 50kHz, the waveform has a period of
li50kHr = 20psec. Thus, to capture at least one complete
cycle
of the waveform, we would have to choose a sampling interval of 20ksec. The maximum number of samples
per cycle would then be 20 since the minimum sampling
interval is l@ec.
If the instrument is left in the continuous trigger mode,
the measurement sequence will be repeated on a continuous basis. The various mathematical functions could
then be used to provide important information such as the
peak-to-peak, RMS, and average values.
Applications for the Model 194 are many and varied and
will depend largely on your particular needs. Basically, the
Model 194 operates much like an ordinary DMM in that
it measures DC voltages. However, special characteristics
such as high sampling rates, a large measurement buffer,
and built in math functions allow application of the instrument to measurements not possible with more ordinary
units.
In the following paragraphs, we will discuss Some typical
applications for the Model 194 High Speed Voltmeter. Keep
in mind that these examples are only representative of
Model 194 capabilities, and by no means even begin to exhaust the possible uses for the unit.
3-46
10" -
tn
r
I
v
vpp-20"
VAVG=OV
VRMS-7.07”
“PEAK 4~ = +lO”
VPEAK- _ ~10”
t
Figure 3-25. Periodic Waveform Analysis
3.22.2 Long Term Measurements
Although the Model 194 is primarily designed for high
sampling rates, its large measurement buffer makes it
suitable for any application requiring a large number of
samples--even on a long term basis.
Long term drift analysis of power supplies is one area
where such measurements may be required. The Model
194 could be programmed to sample the power supply
voltage at specific intervals. Once the measurement cycle
is completed, the peak-to-peak variations as well as the
long-term average power supply voltage could then be easily obtained with the Model 194 mathematical functions.
For example, assume you desire to monitor the output
voltage of a power supply at one second intervals. You
would then program the instrument for this interval by
entering information with the RATE key. The number of
samples to be programmed would then depend on the
duration of the test. With a one-second interval, a total of
7,200 samples would be required for a two-hour measure-
ment period.
OPERATION
Figure 3-26. Transient Waveform
Once the waveform has been digitized and stored in the
buffer, the XY mode can be used to graph the data. ‘Three
basic graphing modes arc available: CRT. oscilloscope, and
plotter.
3.22.3 Digital Storage Oscilloscope
Oscilloscope analysis of recurrent or periodic waveforms
is fairly routine since the scope can be triggered repeatedly to generate the required trace. Transient waveforms are
another story, however, as it is generally difficult, if not
impossible, to view such waveforms on an ordinary
oscilloscope. The Model 194, however, can give you digital
storage oscilloscope capabilities when used with an exter-
nal display device such as a plotter, CRT, or a basic
oscilloscope.
Consider the transient waveform shown in Figure 3-26.
When the Model 194 is performing a measurement sequence, it will measure all or part of the waveform, as
determined by the sampling window. The relative size of
this sampling window depends on the programmed rate
and samples, as well as such trigger parameters as delay,
slope, and level. Since the measured waveform is transient
in nature, careful selection of these parameters is necessary
to ensure proper triggering and measurement.
The XY analog output is used to drive the graphing device
regardless of the plot mode selected. Figure 3-27 shows
typical connections for the oscilloscope and plotter modes.
With the oscilloscope mode in (A), the Y output is used
drive the vertical input of the scope, while the % output
is connected to the external trigger input. With the plotter
in (B), the X and Y outputs drive the X and Y inputs of
the plotter, while the 1. output provides a pen up signal
for the plotter.
3-47
OPERATION
3.22.4 Dual-Channel Voltmeter
The Model 194 can be equipped for dual-channel operation by adding an optional Model 1944 A/D Module. When
the instrument is equipped in this manner, each channel
operates independently from one another, with the excep-
tion of the display, front panel controls, and IEEE-488 bus.
Since each channel can be independently programmed,
the Model 194 can be set up to make two entirely different
types of measurements at the same time.
For example, assume a periodic waveform is to be sampled
and analyzed on channel 1, while a DC voltage is to be
monitored for drift with channel 2. Figure 3-28 shows the
basic configuration for this measurement. Each channel
could be programmed for appropriate rate, samples, and
trigger mode. With the periodic waveform, a rapid sampling rate would probably be required, while a much slower
rate would be required for long-term drift analysis.
Figure 3-27. Typical Digital Oscilloscope
Connections
3-48
Figure 3-28. Dual Channel
Once data is sampled and stored in the independent
nel buffers, mathematical functions could be performed
on each channel independently. For example, you may
wish to obtain the RMS value of the waveform sampled
on channel 1, and the average of the DC voltage measured
on channel 2.
OperatiOn
chan-
3.22.5 Catch a Falling Pulse
The Model 194 lends itself readily to pulse analysis due
to its high sampling rates. Its buffer storage capabilities
allows the instrument to catch rapid pulses and retain them
for additional analysis.
Common pulse measurements include pulse duration, as
well as rise and fall times. Generally, the rise time is defined as the period of time required for the pulse to rise
OPERATION
from 10% of maximum value to 90% of full value. Con-
versely, the fall time is defined as the time period required
to fall from 90% of maximum value to 10% of maximum
value.
Assume we wish to analyze the fall time of a typical pulse
like the one shown in Figure 3-29. This pulse has a peak
amplitude of lOV, and a duration of approximately 30msec.
To properly analyze the fall time, we must choose correct
operating parameters such as sampling interval and rate,
as well as such triggering parameters as slope, Icvel, and
single/continuous mode. For example, if we know that fall
time is approximately lOmsec, we might choose a saw
pling duration of 15msec, allowing a certain amount of
margin for error. With a Emsec duration, the maximum
number of samples we can take is 15,000, since the instrument can sample at rates up to IMHz. Above lOOkHz,
however, the A/D converter operates with A-bit resolution
instead of the lh-bit resolution in effect for sampling rates
of 1OOkHz and less. Thus, if accuracy is a requirement, wc
may wish to settle for 1,500 samples, which would give
us a IOfisec sampling interval.
Figure 3-29. Pulse Rise and Fall Times
3-49
OPERATION
Once the sampling rate and duration values are chose”,
the next thing we must consider is the triggering
parameters. Since we are in effect catching a single pulse,
these parameters must be chosen carefully to place the
sampling window on the appropriate segment of the
pulse--in this case, on the falling edge.
The first aspect we must determine is whether to trigger
on the negative or positive slope of the input waveform.
Since we are attempting to measure the falling edge, we
would obviously opt for negative slope triggering. The next
aspect to consider would be the trigger level. In the exam-
ple of Figure 3-29, we have chosen a trigger level of 9.5V.
Thus, the instrument measurement sequence will be trig-
gered when the pulse amplitude drops to 9.5V when go-
ing in the negative direction.
One final triggering aspect to be considered is whether to
place the instrument in the single or continuous trigger
mode. If a one-shot pulse is to be measured, naturally we
would use the single trigger mode. However, the con-
tinuous trigger mode could be used if a train of identical
pulses is to be measured.
Once the pulse has been captured, and the resulting data
is stored in the measurement buffer, we can then use the
recall mode to determine the 10% and 90% amplitude
points. In the case of the pulse in Figure 3-29, these are
simply 1V and 9V amplitude values. The fall time can the”
be determined from the relative buffer locations and the
programmed sampling interval as follows:
ti = (LlO% - L9w) x t,
Where:
tf= fall time
L1”% = buffer location number at 10% amplitude
Lqoyi = buffer location number at 90% amplitude
ts = sampling interval.
signal, resulting in erratic or erroneous readings. Such unwanted signals can be induced as normal mode noise (appearing between input high and input low), or common
mode noise (appearing between input low and chassis
ground). While the Model 194 has more than adequate
noise rejection for most situations, additional noise reduction may be required in more difficult cases.
Figure 3-30 shows a sinusoidal noise signal riding on a DC
level. If we assume that the noise signal waveform is sym-
metrical about the DC level, its average value will be zero;
thus, such noise can be effectively cancelled by taking a
number of samples and the” taking the average of the
samples.
For optimum noise rejection when using this method, the
sampling sequence duration should be exactly equal to (or
exact multiples of) the period of the noise waveform. The
period of a 60Hz noise signal is 16.667msec. Thus, we might
choose a sampling interval of IO~sec, and program the instrument for 1667 samples, resulting in a duration of
16.667msec per sampling sequence. The period of a 50Hz
waveform is 50msec, so a total of 2000 samples would be
programmed with a 10~s~ interval to obtain the required
20msec sampling sequence duration.
Once the signal is connected for measurement, use the
average function to display the average of the measurement. The degree of noise reduction will depend on the
symmetry of the noise signal, as stated earlier. If the
superimposed noise signal is not perfectly symmetrical,
its DC or average value will not be zero, resulting in a DC
level shift in the final reading. The amount of shift will
depend on the noise amplitude and the degree of
non-symmetry
For example assume that the 90% and 10% buffer location
points are 150 and 900 respectively, and that the sampling
interval is 1Opsec (100kHz sampling frequency). The fall
time under these conditions is:
tf = (900.150) x 10 x lo-6
tf = Z5msec
3.22.6 Reducing Noise in the Measured Signal
Very often 50 or 6OHz noise can creep into a DC input
3-50
_-- - -
w
v
DC LEVEL
t
Figure 3-30. Noise Superimposed on DC Signal
OPERATION
3.22.7 Noise Analysis
In s”me cases, it may be necessary to analyze noise, rather
than attempt to eliminate it. Peak-to-peak or RMS noise
values are the quantities most often required when analyzing noise. The Model 194 can be used to perform such
noise analysis in a manner similar to that described in the
last paragraph for noise reduction.
Once again, let us consider the AC noise signal riding on
a DC level (Figure 3-30). The first thing we must do is
separate the noise signal from the DC level for proper
analysis. By using AC coupling on the input, the DC signal
will be effectively eliminated.
Once the DC signal has been eliminated, the next considerations are the sampling duration and rate. The duration, of course, will depend on the length of the time span
required for the analysis in question. The sampling rate
depends on the expected noise spectrum. Again, a good
yardstick is to choose a sampling frequency at least twice
as high as the noise frequency, assuming that the noise
signal is basically sinusoidal in nature.
Once a measurement sequence has been initiated, peakto-peak or RMS values of the noise can be obtained by using the appropriate mathematical function. The instrument
will then calculate and display the corresponding noise
characteristic.
The basic instrument configuration for performing these
tests is shown in Figure 3-31. Additional equipment required besides the Model 194 include the vibration table
itself, an accelerometer, and the charge amplifier. The
charge amplifier is necessary to convert the output “f the
piezoelectric accelerometer into a DC voltage that can be
measured by the Model 194.
When the equipment is being tested, the xc&ration
measured at the table will be converted into rl voltage and
measured by the Model 194. The resulting data is then
stored in the buffer of the instrument f”r further .malvsis.
Data can be recalled as required to determine the acceicration at any instant of time.
The velocity can be found by integrating the accelcrati”n
as follows:
v = \ cl dt
The integral function of the Model lY4 cwld be used t”
perform the necessary conversion from acceleration t”
velocity. Specific transient waveforms could also be pl”tted using the analog output, if required.
3.22.6 Mechanical Vibration Testing
Most equipment manufacturers perform some sort of
vibration tests on their equipment in order to get some idea
as to how well it will hold up in the real word. As with
any test procedure, data is meaningful only if the test con-
ditions are precisely controlled. The parameters of note
with vibration testing are displacement, instantaneous
velocity, and acceleration. The Model 194 can be used with
external equipment to perform such tests with relative
simplicity.
Figure 3-31. Vibration Testing
3-5113-52
SECTION 4
IEEE-488 PROGRAMMING
4.1 INTRODUCTION
This section contains information on programming the
Model 194 over the IEEE-488 bus. Detailed instructions for
all programmable functions are included; however, information concerning operating modes presented elsewhere
is not repeated here. Refer to Sections 2 and 3 for information not found in this section.
A detailed overview of the IEEE-488 bus is located in Appendix G. Device-dependent commands are summarized
on pages 4-17 through 4-19 and in Appendix E.
Section 4 contains the following information:
4.2
4.3
4.4
A Short-cut to IEEE-488 Operation: Gives a
simple step-by-step procedure for getting on the
bus as quickly as possible.
Bus
Connections:
connecting the instrument to the
Interface Function Codes:
Shows typical methods for
bus.
Defines IEEE standard
codes that apply to the instrument.
4.11 Bus Data Transmission Times:
lists typic.11 times
when accessing instrument data over the bus.
4.2 A SHORT-CUT TO IEEE-488 OPERATION
Step 1: Connect Your Model 194 to the Controller
Step
2:
Select
the Primary Address
4.5
4.6
4.7
4.8
4.9
4.10
Primary Address Selection:
Tells how to program
the instrument for the correct primary address.
Controller Programming:
Demonstrates simple
programming techniques for typical IEEE-488
c”n~rollers.
Front Panel Aspects of IEEE-488 Operation:
Describes the operation of the LOCAL key and bus
status indicators, and summarizes front panel
messages that may occur during bus operation.
General Bus Command Programming:
Outlines
methods for sending general bus commands lo the
instrument.
Device-Dependent Commands:
Contains
descriptions of most of the programming commands used to control the instrument over the
bus.
Using the Translator Mode:
Describes an alternate programming method of using easily
recognized user-defined words in place of devicc-
dependent commands.
The primary address of your Model 194 is set to ‘J at thC
factory, but you can program other values betxwcn 0 and
30 by pressing SHIFT, OTHER, ENTER, and then using
the data entry keys to change the primary ‘Iddress. Once
the desired value is displayed, press ENTER to program
the value.
More detailed information on primary address selecti<>n
is located in paragraph 4.5.
Step 3: Write Your Program
Even the most basic operations will rcquirc that y<,u x\-rile
a simple program to send commands and read back dat,l
4-1
IEEE-488 PROGRAMMING
from the instrument. Figure 4-l shows a basic flow chart
that a typical simple program will follow. The two programming examples below follow this general sequence.
These programs will allow you to type in command strings
to program
the
instrument
and display data on the com-
puter CRT.
HP-85 Programming Example-Use the simple program
below to send programming commands to the Model 194
and display the data string on the computer CRT.
Model 8573 Programming Example-Add the lines below
to the modified declaration file (see Model 8573 lnstruction Manual or paragraph 46.3 of this manual) to program
instrument operating modes and display data on the computer CRT.
PROGRAM
1, $:j I.,! ::.; I: :I, I::: (1 L. L..
:I: E: Ti F-Y E
COMMENTS
Send remote enable.
Figure 4-1. Typical Program Flow Chart
Prompt for
command
string.
Type in EXIT to end
program.
Send command string to
194.
Define reading input
buffer.
Get reading string from
194.
Print reading string.
Close the board file.
4-2
IEEE-488 PROGRAMMING
Step 4: Program Model 194 Operating Modes
You can program instrument operating modes by sending
the appropriate command, which is made up of an ASCII
letter representing the command, followed by one or two
numeric parameters separated by commas for the command o$ion. Table 4-l summarizes the most often used
Model 194 commands.
A number of commands can be grouped together in one
string, if desired. Also, you must terminate the command
or command string with the X character in order for the
instrument to execute the commands in question.
If you are using the programming examples from Step 3
above, simply type in the command string when prompted
to do so. Some example strings are given below.
ClX: select channel I.
FOROX: program waveform function, autoranging.
FlN0,12OOX: program average function, 1200 samples per
measurement.
IlR3F7X: program AC coupling, 32V range, integral
function.
DCV shows the math function in effect (in this LISC’,
waveform),
-1.2345 is the mantissa of the reading data,
E+O represents the exponent.
011 is the channel number (1 or 2)
Note that a variety of both ASCII and binary data formats
are available, as discussed in paragraph 4.9.
4.3 BUS CONNECTIONS
The Model 194 is intended to bc connected tc> the IEL;li-4#
bus through a cable equipped with standard II+LlHH cow
nectars, an example of which is shown in Figure 4-2. The
connector is designed to be stacked to allwv a number of
parallel connections at one instrument. ‘Two screws are
located on each connector to ensure that connections re-
main secure. Current standards call for metric threads,
which arc identified with dark colored screws. Earlier vw
sions had different screws, which wcrc silver colored. Do
not attempt to use these type of connectors on the Model
194, which is designed for metric threads.
NOTE
Many controllers, including the HI-‘-85 and IBMPC, use commas to delimit their BASIC INPUT
statements. When using the above programs, use
different delimiter such as / or <space > in dual-
parameter commands. For example, use NOilOOX
instead of NO,lOOX.
Step 5: Get Readings from the Model 194
Usually, you will want to obtain one or more readings from
the Model 194. In the example programs above, a single
reading is requested and displayed after each command.
In other cases, you may wish to program the instrument
configuration at the beginning of your program, and then
obtain a whole series of measurements.
The basic reading string that the Model 194 sends over the
bus is in ASCII characters of the form:
NDCV-1.2345E+O, CHI
where: N indicates a normal reading (0 would indicate
an overflow),
Figure 4-2. IEEE-488 Connector
A typical connecting scheme for a multiple-instrument test
setup is shown in Figure 4-3. Although any number of ax)nectars can be stacked on one instrument, it is recommended that you stack no more than three connectors on
any one unit to avoid possible mechanical damage.
4-3
IEEE-488 PROGRAMMING
Table 4-I. Summary of Most Often Used IEEE-488 Commands
Mode
2xecutc
Function (Fn) FO
Range (Rn) RO
Command Description
c
Rate (Sn,m) SO,m
Sl,lll
Number of Samples
(Nn, 4
Trigger (Tn,m) To
Input Coupling (In) IO
Channel (Cn,m) Cl
NO,m
Nl,m
T20,m
T21,m
T22,m
T23,m
L
X
Fl
F2
F3
M
F5
F6
F7
F20
F21
Rl
1~2
R3 32V
R4 2oov
R12
Tl
T2
l-3
T4
T5
T6
T7
T24
T25
T2b
T27
TAO
T31
I1
I2
c2
Execute other device dependent commands.
Waveform (sample at trigger)
AVerage
TRMS
+Peak
-Peak
Peak to Peak
Standard deviation
Integral
CHl-CH2
CHlICH2
Auto
32OmV
3.2V
Cancel auto, stay on range.
Take 1 sample every m sec.
Take samples at m Hz frequency.
Take m samples per measurement.
Measurement duration=m sec.
Continuous, talk
Single, talk
Continuous, GET
Single, GET
Continuous, X
Single, X
Continuous, external
Single, external
Continuous, +Slope using trigger level m volts
Single, +Slope using trigger level m volts
Continuous, -Slope using trigger level m volts
Single,
Continuous, other channel
Single, other channel
Continuous, TRIGGER button
Single, TRIGGER button
Start plotting
Stop plotting
DC coupling
AC coupling
Ground coupling
Channel 1
Channel 2
-Slope using trigger level m volts
NOTES:
1. The following characters may be substituted for the comma delimiter. ! @ # $ % & * ( ) = / \ < >
? <space>
2. A complete table of device-dependent commands is located on pages 4-17 through 4.19.
4-4
IEEE-488 PROGRAMMING
NOTE
INSTRUMENT
i
INSTRUMENT INSTRUMENT
The IEEE-488 bus is limited to II maximum of 15
devices, including the controller. The maximum
cable length is 20 meters, or 2 meters times the
number of devices, which ever is less. Failure to
observe these limits may result i” erratic bus
operation.
Custom cables may be constructed by using the infomma-
tion in Table 4-2 and Figure 4-5. Table 4-2 lists the contact
assignments for the bus, and Figure 4-5 shows the contact
configuration.
Figure 4-3. IEEE-488 Connections
Connect the Model 194 to the IEEE-488 bus as follows:
1. Line up the cable connector with the connector located on the rear panel of the instrument. The connector
is designed so that it will fit only one way. Figure 4-4
shows the location of the IEEE-488 connector on the
instrument.
2. Tighten the screws securely, but do not overtighten
them.
3. Add additional connectors from other instruments, as
required.
4. Make certain that the other end of the cable is properly
connected to the controller. Most controllers are
equipped with an IEEE-488 style connector, but a few
may require a different type of connecting cable. Con-
sult the instruction manual for your controller for the
proper connecting method
CAUTION
IEEE-488 common is connected to chassis
ground and cannot be floated.
Table 4-2. IEEE Contact Designations
Contact
-, Number Designatiofim
1
2
3
4
5
6
7
8
9
10
11 ATN
12 SHIELD
13
14
‘IS D107
16 D108
17
18
19
20 Gnd, (8)’
21 Gnd, (9)’
22
23
24
IEEE-488
DlOl
DI02
D103
D104
EOI (24)*
DAV
NRFD
NDAC
IFC
SRQ
D105
DlOh
REN (24)
Gnd, (6)
Gnd, (7)
Gnd, (10)
Gnd, (ll)*
Gnd, LOGIC
LYF ~~~~
Dat.1
Data
Data
Data
M‘“lagc”lcnt
I Iandshdkc
Handshake
tlandshakc
Management
Management
Management
Ground
Data
Data
Data
Data
Management
Ground
Gn,und
Ground
Ground
Ground
G”lU”d
Ground
Figure 4-4. IEEE-488 Connector Location
*Numbers in parentheses refer to signal ground return
of referenced contact “umber. EOI and REN signal
lines return on contact 24.
4-5
IEEE-488 PROGRAMMING
Figure 4-5. Contact Assignments
L7T (Device Trigger)-The ability for the Model 194 to have
its readings triggered is defined by the tYI function.
C (Controller)-The Model 194 does not have controller
capabilities.
TE (Extended Talker)-The Model 194 does not have extended talker capabilities.
LE (Extended Listener)-The Model 194 does not have extended listener capabilities.
E (Bus Driver Type)-The Model 194 has open-collector bus
drivers.
4.4 INTERFACE FUNCTION CODES
The interface function codes, which are part of the
lEEE-488 standards, define an instrument’s ability to support various interface functions, and they should not be
confused with programming commands found elsewhere
in this manual. Interface function codes for the Model 194
are listed in Table 4.3 and are listed for convenience on the
rear panel adjacent to the IEEE-488 connector. The codes
define Model 194 capabilities as follows:
SH (Source Handshake)-SHl defines the ability of the
Model 194 to properly handshake data or command bytes
when the unit is acting as a source.
AH (Acceptor Handshake)-AH1 defines the ability of the
Model 194 to properly handshake the bus when it is ac-
ting as an acceptor of data or commands.
T (Talker)Jhe ability of the Model 194 to send data over
the bus to other devices is defined by the T function. Model
194 talker capabilities exist only after the instrument has
been addressed to talk.
L (Listener)-The L function defines the ability of the
Model 194 to receive device-dependent data over the bus.
Listener capabilities exist only after the instrument has
been addressed to listen.
SR (Service Request)-The SR function defines the ability
of the Model 194 to request service from the controller.
RL (Remote-Local)-The RL function defines the capability of the Model 194 to be placed in the remote or local
modes.
Table 4-3. Model 194 Interface Function Codes
Code Interface Function
SHl Source Handshake Capability
AH1 Acceptor Handshake Capability
T6 Talker (Basic Talker, Serial Poll, Unaddressed
To Talk On MLA)
L4 Listener (Basic Listener, Unaddressed To
Listen On MTA)
SRl
RLI
PPO
DC1 Device Clear Capability
Dll Device Trigger Capability
co No Controller Capability
El Open Collector Bus Drivers
TEO
LEO
Service Request Capability
Remote/Local Capability
No Parallel Poll Capability
No Extended Talker Capabilities
No Extended Listener Capabilities
4.5 PRIMARY ADDRESS SELECTION
The Model 194 must receive a listen command before it
will respond to addressed commands over the bus.
Similarly, the instrument must receive a talk command
before it will transmit its data. These listen and talk cornmands are derived from the primary address of the instrument, which is set to 9 at the factory. Until you become
more familiar with your instrument, it is recommended
that you leave the address at this value because the pro-
gramming examples in this manual assume the instrument
is programmed for that address.
PP (Parallel Poll)-The Model 194 does not have parallel
polling capabilities.
DC (Device Cl&x)-The DC function defines the ability of
the Model 194 to be cleared (initialized).
4-6
The primaly address can be programmed for any value
between 0 and 30. However, each device on the bus must
have a unique primary address-- a factor that should be
kept in mind when setting the primary address of the
IEEE-488 PROGRAMMING
Model 194. Most controllers also use a primary address;
consult the controller instruction manual for details.
Whatever address is used, it must be the same as the value
specified as part of the controller’s programming language.
To check the presently programmed primary address, or
to change to a new one, proceed as follows:
1. Press SHIFT, OTHER, ENTER. The instrument will respond with the presently programmed primary address:
IEEE ADDR = 09
2. In this example, the default value (Y) is being displayed.
3. To exit without changing the address at this point, simp-
ly press the CHANNEL key.
4. To modify the address, key in a new value (O-30) with
the numeric data keys.
5. Once the desired value is displayed, press the ENTER
key. The new address will be programmed, and the instrument will return to the previous operating mode.
If you key in an incorrect value, a NMBR TOO SMALL
or NMBR TOO LARGE error will be disolaved.
1 ,
6. To permanently store the new address, press the following: SETUP, SETUP, 1, ENTER
4.6 CONTROLLER PROGRAMMING
A number of IEEE-488 controllers are available, each of
which has its own programming language. In this section,
we will discuss programming languages for two typical
controllers: The Hewlett--Packard HP-Q and the IBM PC
equipped with a Keithley Model 8573 IEEE-488 interface.
interface programming may depend on the particular interface being used. Many times, little “tricks” xc necessaw
to obtain the desired results.
4.6.2 BASIC Interface Programming
Statements
Most of the programming instructions cowred in this se<tion include cxamples written both in I II’-% BASIC, and
IBM PC BASIC utilizing Model 8.573 programming
statements. Thcsc computers and interfaces ,\‘erc chosen
for these examples because of their versatility in cuntrolling the IEEE-488 bus. A partial list of statements for the
HP-85 and the Model 8573 is shown in TabIt, 4-J
I IF-85 statements have ii one or three digit .~rgumcnt that
must bc specified as part of the statement. ~I‘hc first digit
is the interface select code, tvhich is set to 7 it the fxtllrv.
The last twu digits of those statements requiring a 3.diiit
argument specify the primary address. In the cxamplcs
shown, the default Model 194 address (Y) is shown. fi,r
a different address, you would of coursc1 change the curresponding digits in the programming statement.
Some of the statements ha\fr two iorms, \vith the exdct cow
figuration depending on the command to br sent (,vcr the
bus. For example, CLEAR 7 sends a DCI. commdnci <xer
the bus, while CLEAR 7OY sends the SIX i-<>rnrnand to
a device with a primary address of 9.
4.6.1 Controller Handler Software
Before a specific controller can be used over the IEEE-488
bus, it must have IEEE-488 handler software installed. With
some controllers like the HP-85 the software is located in
an optional I/O ROM, and no software installation is
necessary on the part of the user. In other cases, sottware
must be loaded from a diskette and initialized, as is the
case with the Model 8573 interface.
Other small computers that can be used as IEEE-488 con-
trollers may not support all IEEE-488 functions. With some,
The Model 8573 statements listed in Table 4-4 take on d
somewhat different form. These statements use the IBM
BASIC CALL statement, with the various variables passed
as shown in the table. Ilw command words such as IBCLR
(Interface Bus Clear) and IBSRE (Intcrfxc Bus Send
Remote Enable) are, in fact, BASIC variables themselves,
which must bc initialized at the start of exh BASIC PI’“gram. In addition, you must remember not to USC these
keywords for any other purpose in your BASIC program
4-7
IEEE-488 PROGRAMMING
Table 4-4. BASIC Statements Necessary to Send Bus Commands
I “P-R5 statmllent 1 Model AS73 Statement
4.6.3 Model 6573 Software Configuration
Before using the Model 8573 examples throughout this section, you must configure the software with the procedure
below. Note that the binary handler file GPIB.COM and
the system configuration file CONFIG.SYS must be present on the DOS boot disk, as described in the Model 8573
Instruction Manual.
1. Boot up your system in the usual manner and enter
BASICA.
2. Load the Model 8.573 software file called “DECL.BAS”
Modify the program by changing the XXXXX values in
lines 1 and 2 to 16000.
3. Add the following lines to the declaration file:
;i ,_~, (3 $ ::: Ii 6 ,; I:, 1 :I;: qj 3 7 ,I:: fi L,, L, 1 :[y: F 1: ,,.I 1, I:: ,./ A:$ ? i:; I:: 1, ii I.; ‘:I
13
,.., fi$:zi b I,E,,,!,S” 1 1 ,::&LL IE:FI ,.., D,::,.,(q:$, p,j.‘?q:.; ,:I
1.1
” l.,j;~; ::::,l) ,I:(>,. j,,, 1 fi pti 1, I: p, 1 ,? 4.:,:: ? I.,):,: ::/
4. Now save the modified declaration file for use with the
programming examples in this section. Remember that
you must load and run this short program before using the programming examples in this section. Also, do
not use the BASIC NEW or CLEAR commands after
running this program.
4.7.1 Front Panel Error Messages
The Model 194 has a number of front panel error messages
associated with IEEE-488 programming. These messages
are intended to inform you of certain conditions that may
occur when sending device-dependent commands to the
instrument. as summarized in Table 4-5.
Table 4-5. Front Panel IEEE-488 Messages
Message
NOT IN REMOTE Instrument programmed with
IDDC
IDDCO
NO A/D IN CH 2 F20 or F21 command sent with
NO SCANNER
*Future ‘194 option
Description
REN false.
Illegal Device-Dependent
Command
Illegal Device-Dependent Command Option
no channel 2.
Scanner command sent with no
scanner.*
4.7 FRONT PANEL ASPECTS OF IEEE-488
OPERATION
The following paragraphs discuss aspects of the front panel
that are part of IEEE-488 operation, including front panel
error messages, IEEE-488 status indicators, and the UKAL
key.
4-8
The following paragraphs discuss each of these messages
in detail. Note that the instrument may be programmed
to generate an SRQ (paragraph 4.9.16), and the Ul error
word can be checked for specific error conditions
(paragraph 4.9.15) if any of these errors occur.
Not In Remote Error
A not in remote error will occur if the instrument receives
a device-dependent command and the REN (Remote
Enable) line is false. In this instance, the following error
message will be displayed on the front panel:
NOT IN REMOTE
The error condition can be corrected by placing the REN
line true before attempting to program the instrument.
HP-85 Programming Example-To demonstrate the NO
REMOTE error message, type in the following lines:
Note that the NOT IN REMOTE error message is briefly
displayed when the second statement above is cxccuted.
IEEE-488 PROGRAMMING
Note that the IDDC error message is bristly displayed
when the second statement above is cxccutrd.
Note that the IDDC error message is briefly displayed
when the second statement above is executed
IDDCO (Illegal Device-Dependent Command Option
Error)
Model 8573 Programming Example-Enter the statements
below to demonstrate the NO REMOTE error message:
Note that the NOT IN REIMOTE error message is displayed
when the second statement above is executed
IDDC (Illegal Device-Dependent Command) Error
An IDDC error occurs when the unit receives an invalid
command over the bus. For example, the command string
ElX includes an illegal command because the letter E is
not part of the instrument’s programming language. When
an illegal command is received, the instrument will briefly display the following error message:
IDDC
To correct the error condition, send only valid commands.
Refer to paragraph 4.9 for device-dependent command
programming details.
Sending the instrument a legal command with ‘,n illegal
option that cannot be automatically scaled within bounds
will result in the following front panel cuor message:
IDDCO
For example, the command Y65X has .m illegal option (hi)
that is not part of the instrument’s programming language
Thus, although the command (K) itself is v.~lid, the option (9) is not, and the IDDCO error will result.
To corrwt this error condition, use only valid ~omm~md
options, as discussed in paragraph 4.9.
NOTE
Programming channel 2 (C2X) with no ch.mncl 2
module will result in an IDDCO c’rror.
HP-85 Programming Example-Dcmonstratc an IDDCO
error with the following statements:
REP,I(ITE 7M’i
,:,,m,TF’l.IT 7W-1 :
i . yt,:;;::,,: . 1
HP-85 Programming Example-To demonstrate an IDDC
Note that the IDDCO error message is briefly displayed
when the second statement above is executed.
4-9
IEEE-488 PROGRAMMING
Model 8573 Programming Example-Use the statements
below to demonstrate an IDDCO error:
Note that the IDDCO error message is displayed when the
second statement above is executed.
4.7.2 IEEE-488
The REMOTE, TALK, and LISTEN indicators show the
present IEEE-488 status of the instrument. Each of these
indicators is briefly described below.
Status Indicators
STATUS INDICATORS
TALK-This indicator will be on when the instrument is
in the talker active state. The unit is placed in this state
by addressing it to talk with the correct MTA (My Talk Ad-
dress) command. TALK will be off when the unit is in the
talker idle state. The instrument is placed in the talker idle
state by sending it an UNT (Untalk) command, addressing it to listen, or with the IFC (Interface Clear) command.
LOCAL key will be locked out. When REMOTE is turned
off, the instrument is in the local mode.
4.7.3 LOCAL Key
The local key cancels the remote mode and restores local
operation of the instrument.
LOCAL KEY
Since all front panel keys except LQCAL are locked out
when the instrument is in remote, this key provides a convenient method of restoring front panel operation. Pressing LOCAL will also turn off the REMOTE indicator and
return the display to the normal mode if user messages
were previously displayed with the D command.
Note that the LOCAL key will also be inoperative if the
LLO (Local Lockout) command is in effect.
LISTEN-This indicator will be on when the Model 194 is
in the listener active state, which is activated by addressing the instrument to listen with the correct MLA (My
Listen Address) command. LISTEN will be off when the
unit is in the listener idle state. The unit can be placed in
the listener idle state by sending UNL (u&ten), addressing it to talk, or by sending IFC (Interface Clear) over the
bus.
REMmE-As the name implies, this indicator shows when
the instrument is in the remote mode. Note that REMOTE
does not necessarily indicate the state of the REN line, as
the instrument must be addressed to listen with REN true
before the REMOTE indicator will turn on. When the instrument is in remote, all front panel keys except for the
4-10
4.8 GENERAL BUS COMMAND
PROGRAMMING
General bus commands are those commands such as DCL
that have the same general purpose regardless of the instrument. Commands supported by the Model 194 are
summarized in Table 4-6, which also lists HP-85 and Model
8573 statements necessary to send each command. Note
that commands requiring a primary address assume that
the Model 194 primary address is set to 9 (its factory default
address). If you are using Model 8573 programming examples, be sure to use the declaration file, as described
in paragraph 4.6.3.
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