Instruction Manual
Models
8920A/8921A
True RMS ACXB Voltmeter
P/N 487157
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Fluke Corporation
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LIMITED WARRANTY
The JOHN FLUKE MFG. CO., INC., warrants each instrument it manufactures to be freefrom defects in material and workmanship under
normal use and service for the period of one year from date of purchase. This warranty extends only to the original purchaser. This
warranty shall not apply to fuses, disposable batteries (rechargeable type batteries are warranted for 90 days), or any product or parts
which have been subject to misuse, neglect, accident or abnormal conditions of operations.
In the event of failure of a product covered by this warranty, John Fluke Mfg. Co., Inc., will repair and calibrate an instrument returned to
an authorized Service Facility within one year of the original purchase; provided the warrantor’s examination discloses to itssatisfaction
that the product was defective. The warrantor may, at its option, replace the product in lieu of repair. With regard to any instrument
returned within one year of the original purchase, said repairs or replacement will be madewithout charge. If the fault has been caused by
misuse, neglect, accident or abnormal conditions of operations, repairs will be billed at a nominal cost. In such case, an estimate will be
submitted before work is started, if requested.
ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS SHALL BE LIMITED TO A PERIOD OF
TWELVE MONTHS FROM THE DATE OF PURCHASE. THE FOREGOING WARRANTY IS IN LIEU OF ALL
OTHER WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED
WARRANTY OF MERCHANTABILITY, FITNESS OR ADEQUACY FOR ANY PARTICULAR PURPOSE OR
USE. JOHN FLUKE MFG. CO., INC. SHALL NOT BE LIABLE FOR ANY SPECIAL. INCIDENTAL OR
CONSEQUENTIAL DAMAGES, WHETHER IN CONTRACT, TORT OR OTHERWISE.
NOTE: Somestates do not allow limitations on how long an implied warranty lasts, or the exclusion or limitation
of incidental or consequential damages, so the above limitations or exclusion may not apply to you. This
warranty gives you specific legal rights, and you may also have other rights which vary from state to state.
If any fault develops, the followlng steps should be taken:
1. Notify the John Fluke Mfg. Co., Inc. or nearest Service facility, giving full details of the difficulty, and include the Model number,
type number, and serial number. On receipt of this information, service data or shipping instructions will be forwarded to you.
2. On receipt of the shipping instructions, forward the instrument, transportation prepaid. Repairs will be made at the Service
Facility and the instrument returned, transportation prepaid.
SHIPPING TO MANUFACTURER FOR REPAIR OR ADJUSTMENT
All shipments of John Fluke Mfg. Co., Inc., instruments should be made via United Parcel Service or”BestWay”’ prepaid. The instrument
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CLAIM FOR DAMAGE IN SHIPMENT TO ORIGINAL PURCHASER
The instrument should be thoroughly inspected immediately upon original delivery to purchaser. All material in the container should be
checked against the enclosed packing list. The manufacturer will not be responsible for shortages against the packing sheet unless
notified immediately. If the instrument is damaged in any way, aclaim should befiledwith thecarrierimmediately. (Toobtain a quotation
to repair shipment damage, contact the nearest FlukeTechnical Center.) Final claim and negotiations with thecarrier must be completed
by the customer.
The John Fluke Mfg. Co., Inc. will be happy to answer all application or use questions, which will enhance your use of this instrument.
Please address your requests or correspondence to: JOHN FLUKE MFG. CO., INC., P.O. Box 43210, MOUNTLAKE TERRACE,
WASHINGTON 98043, Atten: Sales Dept. For European Customers: FLUKE (Nederland) B.V., Zevenheuvelenweg 53, Tilburg, The
Netherlands.
l
For European customers, Air Freight prepaid.
John Fluke Mfg. Co., Inc. 0 P.O. Box 43210
l
Mountlake Terrace, Washington 98043
Rev. 12177
TABLE OF CONTENTS
8920A/8921A
SECTION TITLE
1
c
2
INTRODUCTION AND SPECIFICATIONS......,,,,.,......
l-l
l-9
l-11
INTRODUCTION ..............................
SPECIFICATIONS ..; .........................
SPECIFICATIONS, OPTION
....................
OPERATING INSTRUCTIONS ..*.........*..,....,......
2-l
2-3
2-6
2-8
Z-10
2-12
2-14
2-16
2-21
2-37
2-43
2-50
2-52
2-58
2-65
2-67
INTRODUCTION ..............................
SHIPPING INFORMATION ...................... 2:
INSTALLATION
..............................
INPUT POWER ...............................
CONTROLS AND INDICATORS
...................
OPERATING NOTES ...........................
Fuse Replacement ........................
Display Indications .....................
Measurement Connections
.................
Input Signal Considerations .............
Range Selections
........................
Voltage Measurements ....................
dB Measurements
dBm Measurements
Linear Analog Output
........................ 2-11
....................... 2-11
..................
OPERATION .................................
PAGE
l-l
l-l
l-2
l-2
2-l
2-l
2-l
2-1
2-7
2-7
2-7
2-7
2-8
2-10
2-11
2-13
2-13
3
4
THEORY OF OPERATION . . ..*...,*..**...,............
3-l
3-3
3-5
3-10
3-13
3-15
3-17
3-20
3-24
3-37
3-40
INTRODUCTION ..............................
OVERALL FUNCTIONAL DESCRIPTION ............
Analog Circuitry ........................
Digital Circuitry .......................
DETAILED BLOCK DIAGRAM DESCRIPTION ........
Signal Conditioner
......................
RMS Converter ...........................
A/D Converter ...........................
Controller
..............................
Display and Annunciators ................ j-11
Power Supply
............................
MAINTENANCE . . . ..*.....*..........................
4-l
4-4
4-5
4-7
'1-9
4-11
4-13
4-15
4-17
4-19
INTRODUCTION ..............................
GENERAL MAINTENANCE .......................
Access Information
......................
Cleaning ................................
Fuse Replacement
PERFORMANCE CHECK
........................
.........................
Low and Midband Performance Check (Volts
Display
Mode)
.........................
dB Display Mode Check ...................
DC Low Level Check
AC Low Level Check
......................
......................
3-l
3-l
3-l
3-l
3-l
3-3
3-3
3-6
3-6
3-10
3-11
4-l
4-1
4-2
4-2
4-2
4-2
4-2
4-3
4-6
4-7
4-7
i
892OAf892lA
TABLE OF CONTENTS
SECTION
TITLE PAGE
4-21
4-23
4-26
4-29
4-31
4-33
4-35
4-37
4-39
4-43
4-45
4-47
High Frequency Response Check ...........
CALIBRATION ...............................
Power Supply Calibration ................
Low and Midband Accuracy Adjustment .....
Linear Analog Output (8920A only)
AC
Low
Level Calibration ................
High Frequency Calibration ..............
Rms Protection Circuit Calibration ......
TROUBLESHOOTING
...........................
RMS Sensor Replacement ..................
A/D Calibration Resistor Selection ......
DC Offset Resistor Selection ............
.......
4-7
4-11
4-11
4-13
4-15
4-15
4-17
4-19
4-20
4-25
4-26
4-26
LIST OF REPLACEABLE PARTS........................ 5-l
5-l
5-4
SCHEMATIC DIAGRAMS
INTRODUCTION ..............................
5-2
HOW TO OBTAIN PARTS ....................... 5-2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
8-1
ii
LlST OF TABLES
892QN0921 A
TABLE
l-l
l-2
l-3
1-4
2-l
2-2
2-3
3-l
3-2
3-3
3-4
3-5
4-l
4-2
TITLE PAGE
8920A/8921A Options
..............................
892OA/89216 Accessories (for C size instruments).
892OA/89216 Specifications .......................
l-2
l-2
l-3
8920A/8921A Options Specifications ............... l-7
Rack Mounting Kits ...............................
Input Power Selection ............................
Controls, Indicators, and Connect.~rs
............. 2-4
Signal Conditioner Gain Configuration
Controller Summary ...............................
Output Range Codes ...............................
............ 3-3
2-2
2-2
3-13
3-14
Over/Underload Conditions ........................ 3-15
Input Range Codes
................................
Recommended Test Equipment .......................
3-15
4-1
Low and Midband Performance Check (Volts Display
Mode) ..........................................
4-3
4-3
4-4
4-5
4-6
4-7
4-8
4-9
dB Display Mode Check ............................
DC Low Level Check
...............................
High Frequency Response Check ....................
Low and Midband Accuracy Adjustments
............. 4-13
4-6
4-7
4-11
High Frequency Calibration ....................... 4-17
8920A/8921A Troubleshooting Procedure ............
4-21
Attentuator Logic States ......................... 4-23
iii/iv
LIST OF ILLUSTRATIONS
892OA18921 A
FIGURE
2-l
2-2
2-3
2-4
2-5
3-l
3-2
3-3
3-4
3-5
3-6
3-7
3-8
4-l
TITLE
PTI Connection ...................................
Input Power Selection ............................
PAGE
2-2
2-3
Controls, Indicators, and Connectors ............. 2-6
Matched Impedance Measurement Techniques ......... 2-9
Typical dB Measurements
Overall Block Diagram
..........................
............................
Detailed Block Diagram ...........................
Signal Conditioner ...............................
RMS Converter ....................................
2-12
3-2
3-4
3-5
3-7
A/D Converter Simplified Schematic & Timing ...... 3-7
Controller Timing (A/D Converter) ................
Controller Functions
.............................
Display and Annunciators .........................
3-8
3-9
3-12
Low and Midband Performance Check Test Set-Up .... 4-5
4-2
4-3
4-4
4-5
4-6
4-7
4-8
5-l
5-2
5-3
5-4
5-5
DC Low Level Check Test Set-Up ...................
AC Low level CKeck Test Set-Up ...................
High Frequency Response Check Test Set-Up
Calibration and Test Point L.~cations
........ 4-10
.............
Linear Analog Output (8920A only) Test Set-Up ....
High Frequency Calibration Test Set-Up
...........
4-8
4-9
4-12
4-16
4-18
A/D Waveforms (General Conditions) ............... 4-24
Final Assembly, 892OA/8921A ...................... 5-4
Al 89206 Main PCB Assembly ....................... 5-8
Al 8921A Main PCB Assembly .......................
5-13
AlAl 892OA/89216 Display PCB Assembly ............ 5-16
A2 89208/8921A AC PCB Assembly ................... 5-22
v/vi
-
SECTION 1
INTRODUCTION AND SPECIFICATIONS
892OA/8921 A
l-l.
INTRODUCTION
inates whenever the REL switch is
depressed to indicate that any
NOTE
further dB measurements will be
referenced to the voltage present at
Unless otherwise specified, all
information, figures, tables
and general data presented in
this manual are applicable to
both the Model 892OA and 89218,
True RMS Voltmeters.
l-2.
The 89208 and 8921A are digital true rms voltmeters, capable of
accurately measuring the true rms
value of nonsinusoidal signals containing AC or AC + DC components.
The instruments have a frequency
range of
10
Hz to 20 MHz with a
full-scale crest factor of seven,
that time. When AUTO is selected on
the AUTO/HOLD switch (the out posi-
tion) the autorange mode selects the
applicable one of seven input ranges
to optimize the display. It appears
in this mode that the instrument has
one range spanning
1-5.
high
Complementing the instrument's
digital
resolution is an analog
panel meter for
132
dB.
use
in specialized
applications that require peaking or
nulling. This meter is not calibra-
ted since it is intended for peaking
and nulling indications only.
and are capable of displaying measurements in either volts or dB.
1-6.
It should be noted that both
standard models, the 89208 and
l-3.
on the dB/VOLTS switch enables the
volts display mode and three applicable front panel annunciators (V,
mV, and 2 MHz MAX). In this mode,
the instrument displays a
C
digit figure to indicate the true
rms value of any AC or AC + DC input
signal whose amplitude is between
180 UV and 7OOV rms (1OOOV peak).
Selecting the VOLTS position
3 l/2
89218, allow floating measurements.
The 89218 has been designed to
safely accept common mode inputs up
to 5oov rms,
or 7OOV peak. An isolation circuit allows the 8920A
input low to float up to approxi-
mately 0.6V peak with respect 'to
earth ground. Isolation of 0.6V peak
will accomodate the few hundred
millivolts of typical common mode
voltage. Full operator protection is
l-4.
The dB display mode (logarith-
mic) is enabled when dB is selected
on the front panel VOLTS/dB display
switch. In this mode, the instrument
displays the 4
l/2
digit dBm value
still maintained since under fault
conditions the diode isolation circuitry conducts and insures that the
common mode voltage is never greater
the 0.6~ peak.
of the input signal with reference
to l-of-12 manually selected impedances (50 to 1200 ohms). The dB
display mode also uses three annunciators, dB, RELATIVE REFERENCE, and
2 MHz MAX, to establish the instru-
ment's operating status. The RELA-
TIVE REFERENCE annunciator illum-
l-7.
Several options and access-
ories are available for use with the
89208 and 8921A. The options and
accessories are
in Table
l-l and
listed
and described
Table l-2 respectively. They are compatible with
both models and may be ordered for
1-1
8Q2W8021A
factory or field installation.
Detailed information concerning each
option and accessory is given in
Section 6.
1-8.
The PTI (Portable Test Instrument) case is a family of injection
molded plastic instrument packages
of various sizes which may be
stacked vertically and
latched
together to form portable test stat-
ions. When instruments are stacked
they should be limited to 40 pounds
total,
and the instrument drawing
the most power should be on the top.
Stacked instruments have a horizon-
Table 1-I. 892QAl8921A Options
tal air space between them to prevent heat conduction between instruments.
1-g.
l-10.
SPECIFICATIONS
Detailed specifications for
the Model 89208 and 8921A True RMS
Voltmeter are given in Table l-3.
l-11.
Specifications, Options
l-12. Detailed specifications for
the Model 89208 and 8921A's options
are given in Table
l-4.
-
OPTION DESCRIPTION'
89208/8921A-03
8920A-04
Counter Output
Logarithmic Analog
output
Table I-2.8920AB921A Accessories (for C size instruments)
ACCESSORY
MODEL NO.
Y2014
Rack Mounting Kit (single unit)
COMMENT I
Available in both
89208 and 89218
Available in 8920
only.
DESCRIPTION
I
1-2
Y2015
Y2020
Rack Mounting Kit (double unit)
I
Panel Adapter (DIN Size)
,-
Table 13.8929A/8921A Specifications
ELECTRICAL (Basic)
The electrical specifications given assume an operating temperature of
degrees C +/- 5 degrees C,
relative humidity up to
80%
and a minimum 90 day
calibration cycle.
23
Functions...............
Display,........,.,..,.. Digital
AC true RMS, AC + DC true RMS
Display, Panel
selectable for volts or dB:
analog peaking/nulling meter.
Ranging................. Autoranging, Hold to defeat
Autoranging,
step-up for manual
up-ranging.
Autoranging Points...... Ranging up at 2000 counts.
Ranging down at
180
counts.
Maximum Input........... 700V rms or 1000 V peak, not to
8
exceed 1 X 10
volts-Hz
product on any range.
Response Type...........
True RMS thermal converter,
will accept: sine, complex,
pulse or random waveforms.
Response Time...........
1.6 seconds typically to rated
accuracy within a range,
composed of 1 second settling
time and
0.6
seconds max
digitizing time.
Input Impedance......... 2 mV to 700V range =
Crest Factor............ 7 at full scale, increasing
Frequency Range
. . . . . . . .
ELECTRICAL (VOLTS Display Mode)
Ranges.................. 2 mV, 20 mV, 200 mV, 2V, 2OV,
Resolution
..**...*.**.* 0.05% of range.
10
M
ohm/shunted by <
30
pF.
down scale by: 7 X V range + V
input.
2 mV range - 2 MHz max.
20 mV- 20V range = 20 MHz max.
2oov
700V
-
range = 1 MHz max.
200V and 7OOV.
1-3
892OA/@21A
ELECTRICAL (dB Display Mode)
Table 13.802OA/SQ21A Specifications (cant)
dB Range................
dB Range References:
In
the
autorange mode the
instrument appears as though it
has a single range spanning
132
dB. Transients will appear in
the readout as the transition
through the analog voltage
range points occur.
dBm References.. . . . . . Twelve manually
selectable
impedances with which to
reference a 0 dBm, 1 mW signal
level. Impedances are 50, 75,
93, 110, 124, 135, 150, 300,
600,900,1000 and
1200 ohms.
Relative dB
Reference............
A voltage present when this
switch is depressed to its REL
position is held as 0 dB
reference
for all other
voltages .
dB Resolution...........
0.01
dB.
ACCURACY
The accuracy specification given below apply
vo ts a d dB display modes at 9% to
23&C
&5’C 90 days ? .
Table -1. AC: +-% of Voltage Reading or
AC Accuracy:
50 Hz
200 kHz 1 MHz 2 Mtiz 10 MHz
100%
of full scale,
+dB
to
the
20
MHz
2ov
2v
200mV
20
1.80-19.99
I
.
Temperature
(O’C-18’C, 28”C-50°C):
mV
.180-1.999 2 mV
mV
mV
-I
110
Coefficients:
3%
0.35
dB
Hz 20 Hz 50 Hz
0.5%
0.1 dB
1%
0.15 d8
0.25
dB
20
1
- 1 MHz
Hz
MHz - 20
200
0.35
kHz
MHz
1”“TSPECIFIED
dBI
-mm.. -.~
1 MHZ 2 MHz
.07%1
-c;
.Ol d8/ “C
Table 1-3. 892OA/8921A Specifications kont)
Table -2. AC + DC: +% of Voltage Reading or kdB
892OA/8921 A
I
180-700V 700V
18.0-l 99.9 200V
1.80-l 9.99 ?OV
.180-1.999 2~
18.0-l 99.9 200 mV
mV
1
1.80-l 9.99 20 mV
mV
I
1.180-1.999) 2 mV 1
Temperature Coefficients:
(O°C-180C, 28%SO’C)
I
I I
NOTE: DC only measurements can also be made using the 1000 Hz accuracy specification.
Hz 20,Hz
1
50 Hz 200 kHz 1 MHz 2 MHz 10 MHz 20 MHz
3%
0.35 d8
AC + DC Accuracy:
7 “‘7% 7
)T SPECIFIED
‘// /// ///
0.5 dB
V//f///
200kHz 1 MHz 2 MHz
2
mV range
20
mV range
and above
5%/ Oc;
.50/o/ Oc
.5dB/ ‘C
.05dB/ OC
ACCURACY
30% or 3 db
20% or 2dl.J
lO%ov ‘I db
0
Table -3. AC + DC Accuracy Below 2 mV and Above 1 MHz
1mV
lOt?lV
INPUf LEVEL
100 mV
l-5
_. .-
W2OA/8921A
GENERAL
Table 1-3. 992CWS921 A Specifications (cant)
Input...................
Displays................
AUTORANGING RATE:
Volts...................
dB . . . . . . . . . . . . . . . . . . . . . .
Reading Rate............
8920A isolated
BNC
input
floating up to O.6V peak)
8921A isolated dual banana plus
ground jack input.
5, 0.3" high, digit, 7-segment
LEDs with automatic decimal
point location and mV, V, dB,
RELATIVE REFERENCE, and "2 MHz
max annunciatorsl'. The display
also incorporates an uncalibrated analog meter for nulling
and peaking.
700 ms max/range change; 2.2
set max for 6 range changes.
950 ms max/range change; 2.9
set max for 6 range changes.
2.5 readings per second.
C
Overrange Indication....
Flashes maximum allowed reading
for that range.
Underrange Indication...
Flashes decimal point, but
continues to
display the
reading.
Maximum Comnon Mode
Voltage.................
8920A:
400 mV rms or 600 mV
peak.
89218: 500V rms or 700V peak.
Input Common Mode
Rejection............... >8O dB 8 50 or 60 Hz (with
100
ohms in either lead)
Linear Analog Output
Each range provides a linear
(8920A only) output with 2V dc equal to 2000
counts on the readout, ~1.0% of
reading relative to display;
essentially 0 ohm output resis-
tance into a >lO k load; nonisolated with output common the
same as input common; provided
only on the 8920A.
Table 1-3. 892OAB921A Specifications (cod
P-m
Storage Temperature..... -40' C to + 75' C
Operating Temperature... 0' C to 50' C.
‘-
Humidity Range.......... 80% RH
MTBF....................
Greater than
Power................... 1OOV ac
220V ac *lo%, or 240V ac
*lo%,
10,000
120V ac
hours.
*lo%,
r-105
to 25OV AC Max. selected by
internal switches, 45 to 440
Hz,
10
W max.
Dimensions.............. 40.3 cm
(12.9
in.) long x 20.3
cm (8.0 in.) wide x 10.8 cm
(4.3 in.) high.
Weight.................. 2.47 Kgm (5 lb. 7 02).
Table IQ. 892OA/8921A Option Specifications
Option -03, Counter Output Option
Output Voltage:
100
mV peak square wave.
Output Impedance: 50 ohms.
Maximum Isolated Level: 500 volts ac.
Compatibility:
89208 and 89218.
Option -04, Logarithmic Analog Output Option (8920A only)
Output Voltage dc
200 UV rms input = 0 dB, OV dc out.
700 V rms input =
i.e.,
100
mV =
1 dB
131
dB,
131V
dc out.
Linearity
Within each Range: kO.35 dB.
Over all seven Ranges: 22 dB.
--
Output Impedance:
1 ka
m....
-..
Compatibility: 89208 only.
l-711-8
A Message From
John Fluke Mfg. Co., Inc.
Some semiconductors and custom IC’s can be
damaged by electrostatic discharge during
handling. This notice explains how you can
minimize the chances of destroying such devices
by:
1. Knowing that there is a problem.
2.
Learning the guidelines for handling them.
3. Using the procedures, and packaging and
bench techniques that are recommended.
The Static Sensitive (S.S.) devices are identified in
The following practices should be followed to minimize damage to S.S. devices.
1. MINIMIZE HANDLING
the Fluke technical manual parts list with the symbol
1, g-J (1.
3. DISCHARGE PERSONAL STATIC
BEFORE HANDLING DEVICES
” ._
2. KEEP PARTS IN ORIGINAL CONTAINERS
UNTIL READY FOR USE.
4.
HANDLE S.S. DEVICES BY THE BODY
5. USE ANTI-STATIC CONTAINERS FOR
HANDLING AND TRANSPORT
6. DO NOT SLIDE S.S. DEVICES OVER
ANY SURFACE
8. HANDLE S.S. DEVICES ONLY AT A
STATIC-FREE WORK STATION
9. ONLY ANTI-STATIC TYPE SOLDERSUCKERS SHOULD BE USED.
10. ONLY GROUNDED TIP SOLDERING
IRONS SHOULD BE USED.
Anti-static bags, for storing S.S. devices or pcbs
with these devices on them, can be ordered from the
John Fluke Mfg. Co., Inc.. See section 5 in any Fluke
technical manual for ordering instructions. Use the
following part numbers when ordering these special
bags.
John Fluke
Part No.
453522
453530
453548
454025
Bag Size
6” x 8”
8” x 12”
16” x 24”
12” x 15”
SBCTION 2
OPBRATING IISTRUCTIGNS
8fmAm21A
2-1.
2-2.
Ilm0DtJcT1ON
The Information presented in
this section is intended to familiarize the operator with the capabilities and limitations of the
Model
8920A
and 8921A. Included are
instructions for the installation
and operation of both models as well
as a brief description and identi-
fication
of each control and indi-
cator located on the instrument.
2-3. SHIPPING INPORHATION
2-4.
The Models 8920A and
892111
are
packaged and shipped in a protective
container. Upon receipt of the
equipment,
a thorough inspection
should be made to reveal any possible shipping damage.
2-5. If reshipment of the instru-
ment is necessary,
container should be used.
the original
If the
original container is not available
a new container may be obtained from
the John Fluke Mfg. Co., Inc. Please
reference the instrument's model
number (8920A or 89218) when
requesting a new shipping container.
pushed firmly into the slots on the
case below. See Figure 2-l.
CAUTION
Before attempting to
lift a
i!
series of stacked lnstru-
merits, check each unit to
enaure that its case oonnectora are properly mated and
latched to the next lower
lnatrwnent.
2-8. INPUT POWER
2-9.
The 892OA and 89218 may be
operated from any one of the line
voltages shown in Table 2-2. Use the
following procedure to condition the
instrument for use with the local
line power.
1.
Disconnect the instrument from
line power and remove its top
cover (four screws on the
bottom of the unit hold the
top
2.
cover
Locate the power selection
in place).
switches S209 and S210 as
shown in Figure 2-2.
2-6. INSTALLATION
2-7.
The 89208 and 89218 are
designed for bench-top use, or for
installation in a standard 19-inch
equipment rack or panel mounted into
any DIN size opening. Available rack
mounting kits are listed in Table
2-l.
In bench-top environments the
8920A/8921A may be stacked with
other Fluke products that use the
PTI case. To connect two or more PTI
cases, pull the side connectors out,
place one case squarely on top of
another and press until the side
connectors on the top case can be
3.
Refer to Table 2-2 and set
switches S209 and S210 for
4.
desired
Install the top cover before
connecting the unit
line
voltage.
to
line
power.
2-10. CONTROLS AND INDICATORS
2-11. The 892OA/89216 controls,
indicators, and connectors are shown
in Figure 2-3 and
described in Table
2-3. Features peculiar to one
instrument are identified by model
number, i.e.,
89208 or 8921A.
2-l
092Qm921 A
Table 2-I. Rack Mounting Kits
MODEL NO. MODEL NO.
Y2014 Y2014
Y2015 Y2015
Y2020 Y2020
DESCRIPTION
Rack Mounting Kit
(single unit)
Rack Mounting Kit
(double unit)
Panel Adapter (DIN size)
I
SWITCH POSITION
(REAR PANEL)
s209
l
m
0
m
0
m
s210
l
m
0
m
l
m
Figure 2-1, PTI Connection
Table 2-2. Input Power Selection
SELECTED LINE SOURCE
ac 5105,
12OV, 50-400 Hz
lOOV, 50-400 Hz
22OV, 50-400 Hz
24OV, 50-400 Hz
(25OV, MAX)
10
WATTS MAX
892OAD921 A ’
Figure 2-2. Input Power Selection
2-3
8020#8921 A
Table 2;3. Controls, Indicators, and Connectors
REF
NO.
1
2
3
4
NAME FUNCTION
INPUT
892OA- A BNC input connector. The low side is
isolated from power ground through a pair
of parallel diodes.
89218
- Banana plugs provide high, low, and power
ground input connections. The HI and LO terminals
are isolated from power ground. Maximum common
mode voltage is 5OOV rms.
Analog Panel
Meter
Uncalibrated panel meter provides analog tracking
of input level; useful for peaking and nulling
indications.
Digital
LED display provides a direct readout of the input
Display signal level; includes decimal point and polarity.
Annunciators
LED's that light to indicate the selected meas-
urement function V (volts) , mV (millivolts), or
dB.
.2
5
MHz MAX.
6 RELATIVE
REFERENCE
POWER switch
dBm REFERENCE
An LED that lights to indicate that the instrument
has autoranged into the 2 mV range. This range has
a maximum frequency limit of 2 MHz.
An LED that lights to indicate that the voltmeter
is in the dB display mode and using a relative
voltage reference.
A push-push switch used to turn the instrument ON
(in) and OFF (out).
Rotary switch used to manually select one-of
twelve reference impedances when the dBm function
is selected.
2-4
Table 23. Controls, Indicators, and Connectors (cant)
9 dBm/REL A push-push switch used to select either the
relative dB or the dBm display mode. When REL is
depressed, the existing input level is used to
establish a 0 dB reference. Subsequent level
changes
at
the input are displayed in dB and
referenced to the operator established 0 dB level.
When d&n
is selected,
measurements are displayed
in terms of dBm and the dBm REFERENCE setting.
802W8021A
10
VOLTS/dB
A push-push switch used to select either the
voltage (out) or dB (in) display mode.
11
STEP UP A momentary pushbutton switch used to incre-
mentally step the voltmeter to its next higher
range.
This switch is enabled only when the
AUTO/HOLD switch is depressed.
12
AUTO/HOLD A push-push switch used to select the manual
(HOLD) or autorange (AUTO) function. Selecting
HOLD (in) enables manual upranging with the STEP
UP switch. Selecting AUTO (out) enables the unit
to autorange.
LO RANGE ENABLE A push-push switch which, when depressed adds the
13
2 mV range to the autorange loop. When the switch
is out the 2 mV range cannot be accessed.
14
AC/AC + DC A push-push switch used to include (in) or delete
(out)
dc components as part of the input signal
level.
15
F1 Line fuse, MDL 1/8A slow-blow.
DIGITAL OUTPUT An output port reserved for use with the Log-
16
arithmic Output Option -04 (89208 only). See
Section 6 for details.
COUNTER OUTPUT
17
18
Linear Analog A pair of banana jacks for Output accessing the dc
An output port reserved for use with the Counter
Output Option
-03.
See Section 6 for details.
linear analog output voltage (89208 only). This
voltage is proportional to the Vrma input and is
linearly scaled;
2V dc out equals a 2000 count
readout. The scale repeats for each range.
Input Power
19
A j-prong line power connector for connecting the
Connector unit to line power.
2-5
892OAm21 A
‘I
2-6
Figure 2-3.892OA/8921A Controls, Indicators, and Connectors
8920m921A
^.w.”
m-,
2-12. OPERATING NOTES
2-13.
cribe
The following paragraphs des-
various conditions which
should be considered before attempting to operate the 892OA/8921A.
2-14.
Fuse Replacement
2-15. The Model 8920A/8921A is fuse
protected from the power line. To
access the fuse press and turn (CCW)
the rear panel fuse cap, Fl. When
replacement is necessary use an MDL
type l/8 amp slo-blo fuse for all
voltage configurations.
2-16.
2-17.
Display Indications
In addition to the standard
digital readout, the front panel
display is equipped with a series of
unique visual indicators. These
include an overrange/overload indicator,
an underrange indicator, and
an analog meter. They function auto-
matically and help to insure error
free measurement results.
2-18.
When an input signal level
exceeds the display limit for the
selected range an overrange occurs.
The display digits flash while the
overrrange is present. Select a
higher range to eliminate the over
range condition.
2-19.
Measurement accuracy is
degraded when the higher voltage
ranges are used to measure low level
signals. A flashing decimal point is
provided to alert the operator to
this condition.
To eliminate the
underrange indication select a lower
range (or autorange).
2-20. An uncalibrated analog panel
meter complements the digital dis-
play,
signal
1005
aeleCt8d
and linearlly tracks the input
level. It provides a 0 to
full scale indication for the
range.
Thus, it is ideally
suited for nulllng and peaking
applications.
2-21. Measurement Connections
2-22. COAX OR OPEN LEADS
2-23. Shielded leads or coax should
be used at the input for low level
or high frequency measurements.
Unshielded leads may pick up interference from other instrumentation
causing errors at low levels. High
frequency errors are reduced by
minimizing inductance and capaci-
tance between the source and the
8920A/892lA input connector. Open
test leads are otherwise adequate.
2-24. SAFETY CONSIDERATIONS
2-25. Under normal operating con-
ditions the 8920A/8921A will not
present a potential electrical shock
hazard to the operator. However,
careless use of input-lead connectors and/or adaptors may create a
shock hazard.
WARNING
TO AVOID ELECTRICAL SHOCK
HAZARD DO NOT USE EXPOSED LO
INPUT LEAD CONNECTIONS ON THE
MODEL 8921A UNLESS CONNECTED
TO THE POWER GROUND. IF
COAXIAL OR OTHER EXPOSED
CONNECTIONS ARE USED FOR
FLOATING MEASUREMENTS, A SHOCK
HAZARD MAY EXIST.
2-26. The low input on the 89208 is
connected to power ground through a
pair of diodes (see front panel
connector). These diodes allow the
low input terminal to float up to
400 mV. Their function is two fold;
they provide isolation between input
low and power ground, and they protect the operator from the possibility of hazardous voltages existing
on the exposed low input connector.
2-27. At first glance, 400 mV of
isolation does not appear significant. However,
in most cases it
provides 8nOUgh isolation to prevent
ground loop currents and, therefore,
measurement errors due to ground
loops.
2-7
2-28.
89208
When the low input of the
is connected to a potential
greater than 400 mV above power
ground, the diode pair conducts and
effectively clamps the input common
mode voltage to w 600 mV maximum.
2-29. Under no circumstances should
the operator attempt to defeat the
function of the diodes. Specifically ;
removed,
the diodes should not be
the ground return on the
power cord should not be floated,
and an isolation transformer should
not be used to power the 89201. If
the diodes are defeated, a shock
hazard will exist at the low input
connector when the low input lead is
floated above 30 volts.
WARNING
TO AVOID ELECTRICAL
HAZARD DO NOT REMOVE OR
SHOCK
OTHERWISE DEFEAT THE INPUT
DIODE PAIR.
2-30. IMPEDANCE MATCHING
2-31. Two types of ac voltage meas-
urments are typically made; those
involving matched impedance systems
and those ‘where voltmeter loading is
minimized (high impedance measure-
ments) and no impedance matching
occurs.
2-32. High impedance measurements
are based on the assumption that the
voltmeter’s fixed
resistance and low input capacitance
will not appreciably load or otherwise affect the circuit being meas-
ured .
If open leads are used (to
hold down input capacity) and the
measurement frequency is low, this
assumption holds.
2-33. When matched impedance systems
are measured the impedance should be
determined as close as possible to
the 89208/8921A input, thereby mini-
mizing input inductance and enhanc-
10
MS2 input
ing accuracy at high frequencies.
This is accomplished by including
the meter as an integral part of the
circuit as shown in Figure 2-4A.
Notice that the integrity of the 50
system is maintained by using a 50
power divider. An alternate solution
is shown in Figure 2-4B. In this
case, the source is alternately
connected to the 8920A and the test
circuit. This allows the source to
be adjusted to a known level before
being connected to the test circuit.
Since both the meter and the test
circuit are 5051 loads the circuit
integrity is maintained.
2-34. COMMON MODE VOLTAGE MEAS-
UREMENTS
2-35. The Model 89218 is equipped
with isolated input connections and
can
accomodate common mode
(floating) voltages as high as 500V
rms. Higher common mode voltages may
cause instrument failure. The 89208
will accomodate common voltages as
high as 600 mV, usually enough to
open ground loops in the power connections.
2-36. Even though the 8921A is capable of making common mode measurements it is not a true balanced
input voltmeter.
It does not have
equal or balanced impedances between
the high and ground, and the low and
ground input terminals. On the 8921A
the LO-to-ground input capacitance
is
not matched with the high-to-
ground capacitance. Since the major-
ity of voltmeter applications do not
require balanced inputs, this slight
imbalance, however, will rarely
present a problem.
2-37. Input Signal Considerations
2-38. The 89208/8921A is basically a
true rms voltmeter and, as such, is
subject to input conditions not
encountered with the ordinary
average-reading ac voltmeter. Of
these,
the two most important are
W2oAm21A
i-
Figure 2-4. Matched Impedance Measurement Techniques
2-9
crest factor and input coupling.
Each is discussed separately.
2-39. CREST FACTOR
2-40. Crest factor is the ratio of
the peak voltage to the rms voltage
of a waveform. The 8920A/8921A will
accomodate signals having crest
factors of 7 at full-scale, increasing for down-scale readings. Use the
following formula to calculate below
full-scale crest factors:
Since range selection is essentially
automatic, the individual ranges are
not directly defined for the oper-
ator. Instead,
underrange and over-
range indicators are provided to
indicate when a range change is
necessary. These indicators appear
only when manual range selections
are being made or when the 700V
limit has been exceeded in the autorange mode.
2-46. AUTORANGE
7 x Ranne
Crest Factor: Input
2-41. INPUT COUPLING, AC/DC
2-42, The 892OA/8921A is equipped
with a FUNCTION switch which allows
the user to select either AC or AC +
DC coupling. When the switch is out,
AC coupling is selected. In this
function the dc component is removed
from the input signal and is not
measured
or displayed. Depressing
the FUNCTION switch selects AC + DC
coupling. This function allows the
89208/8921A to measure and display
the true rms value for the total
input signal; ac components and dc
components.
The dc component should
always be considered when power
dissipation is being determined.
2-43. Range Selection
2-44. The 89208/8921A is equipped
with seven voltage ranges and what
appears to be a single 'dB range
spanning
132
dB. Range selection is
accomplished automatically. However,
overside switches allow the operator
to interrupt the autorange function
and manually increment the ranges.
Thus, two methods of range selection
are possible, automatic or manual.
2-45. The autorange function is
designed to optimize the display
reading for a given input. Each
reading is displayed complete with
decimal point and units annunciator.
2-47. The proper measurement range
is automatically selected when the
AUTO/HOLD switch is in the AUTO
(out) position. if the LO RANGE
ENABLE switch is depressed, the
meter will autorange (up and down)
from the 2 mV range to the 700V
range. When LO RANGE ENABLE is not
depressed the 2 mV range is deleted
from the available ranges. The meter
is now capable of autoranging from
the 20 mV range to the 700V range.
NOTE
For the 2 mV range to be
selected, LO RANGE ENABLE must
be depressed and the input
signal level must be less than
2
mV. Downranging occurs at
180 digits and upranging
occurs at 2000 digits.
2-48. MANUAL
2-49. Manual range selection is
accomplished by automatically selecting a range using the autorange
mode and then depressing
the
AUTO/HOLD switch. The meter will
stay in that range regardless of
input level changes. If the range
becomes invalid for a given input
level,
an overrange or underrange
indicator will flash. If an under-
range is indicated (flashing decimal
point), select autorange (AUTO), and
after the proper range is selected
press HOLD. For overrange conditions
(flashing digits) momentarily press
2-10
892om921 A
the STEP UP switch once for each
desired range increment. Holding the
switch in will increment the meter
to the 700V range. Select autorange
(AUTO) to downrange.
2-50. Voltage Measurements
2-51.
The 8920A/8921A is a true rms
voltmeter. However, it has the abil-
ity to condition the display to
readout in terms of true rms ac
voltage, dB or dBm. If a voltage
measurement is desired, set the
VOLTS/dB switch to VOLTS (out). The
settings of the dBm/REL and dBm
REFERENCE switches do not influence
the voltage measurement.
2-52. dB Measurements
2-53. Decibel measurements, as made
by the 89208/89218 are voltage measurements referenced to a selected
level, and displayed as deviations
(in dB)
above
or below that level.
Therefore, before a meaningful dB
measurement can be made the dB dis-
play mode must be selected (VOLTS/dB
switch in) and a relative reference
level (0 dB) must be established.
2-54. ESTABLISHING A 0 dB REFERENCE
2-55. Use the following procedure to
establish a 0 dB reference level:
1.
Connect the reference source
to the 892OA/8921A input term-
inals. If desired measure and
adjust the reference supply
voltage level.
2.
Select the autorange mode
(AUTO).
3.
Release the dBm/REL switch
(out).
inals, depress the REL switch.
The display should now read 0
dB and the RELATIVE REFERENCE
annunciator should be lit.
NOTE
Subsequent voltage changes at
the input terminals will be
displayed in terms of + or dB units around the relative
reference (REL).
2-56. TYPICAL APPLICATION
2-57. A typical application for the
dB measurement mode is shown in
Figure 2-5. The relative reference
(0 dB) has been established at TP2.
Subsequent dB measurements at TPl,
TP3, TP4, and TP5 are displayed (in
dB) as shown.
2-58. dBm Measurements
2-59. Measurements made to a fixed
milliwatt reference are defined as
dBm. The 1 milliwatt reference is
generally assumed, as indicated by
m. However,
the system impedance
must be specified for a particular
measurement.
Once the impedance is
known and selected, the instrument
will display its measurements in
dBm.
2-60. The 8920A/8921A is equipped
with a rotary switch called dBm
REFERENCE (a). By setting the switch
to l-of-12 possible standard refer-
ence impedances (50R, 75a, 93s2,
llost, 124st, 135&
gOOn,
10009,
and
150n, 30052, 600i-&
12OOQ)
the operator
establishes that impedance as a
reference. When the system impedance
and the reference are the same, the
8920A/8921A manipulates subsequent
measurements within the system to
rea.dout in terms of dBm.
1
4.
5.
Depreaa the dB/VOLTS
switch
(in).
With the reference level still
connected
to the input term-
2-61. SELECTING A dBm REFERENCE
2-62. Use the following procedure to
select a reference impedance and
enable the dBm display mode:
2-11
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