Keithley 190 Service manual
INSTRUCTION MANUAL
Model
Digital Multimeter
IV0
@COPYRIGHT
FOURTH PRINTING, DECEMBER
1975,
KEITHLEY INSTRUMENTS, INC.
1977,
CLEVELAND, OHIO, U.S.A.
CONTENTS
ILLUSTRATIONS
-
1075
SPECIFICATIONS
MODEL 190
SPECIFICATIONS
AS A DC VOLTMETER
RANGE: -‘lo m~crovolts per d,git (1 volt full range) lo
IlOO volts full range in four decade ranges. 100%
““erranglng to 199999 on ai1 ranges except on the
1000.““II range,
ACCURACY’ (24 hours): 5(0.005% of reading +
0,005”0
i 0,00500 “I range,, * k?ss than 0~00001% Of
reading per ““I, from full range
TEMPERATURE COEFFICIENT: iO,OOZ% “1
readinglc
INPUT RESISTANCE: Greater than 1000 megohms on
the l-V”,, range, 10 megohms on the 10 to 1000.““If
ranges,
SETTLING TIME’: Less than 5 seconds to wfh,n
0 01% Of fInal reading.
NORMAL MODE REJECTION RATIO: Greater than 60
dB ““er one d,g,l on the 1 and IO-““,! ranges. decreasing I” 60 cl8 on the 1000~volt range. 50 Hz l”
180 HZ
COMMON MODE REJECTION RATIO: Greater than
100 dB over one dIgIt on the 1 and IO-““,, ranges,
decreasing to 80 dB “n the 1000-v”,, range. dc lo
180 HZ with 1 kll”hrr ““balance.
MAXIMUM ALLOWABLE INPUT: ,400 volts peak
mome”tary, 1000 ““It* c”ntl”“““S dc + rms ac.
AS AN AC VOLTMETER
RANGE: IO m~cr”v”,ts pei dig0 11 volt (~11 range) l”
1000 ““ifs r”,s ,“I, range in four decade ranges.
100% OverrangIng to 199999 on a,, ranges except
the 1000-“01t range.
ACCURACY 150 Hz to 10 klizl (90 davs,: &10~3% of
reading + 6.06%
of greater than 400 volts ac + dc begins t” cause
temporary additional err”r up 1” *0,3?& of reading
due lo paver heating effects. (Average reading “al!brated in rms of a sine wave).
TEMPERATURE COEFFICIENT: &(O.OI% of reading
+ 0.005% Of rangevc,
INPUT IMPEDANCE: 1 megohm shunted by less than
40 picotarads.
SETTLING TIME: Less iha” 5 sec”nds to with,” 0.1%
of final reading below 400 volts.
MAXIMUM ALLOWABLE INPUT: ,000 volts rms ac +
dc. but not m”re than 600 volts dc on any range.
01 range). (90 days); +(0.015% of reading
of range, tb ho0 wit,: A&xtion
AS AN OHMMETER
RANGE: 10 milliohms per digit (1 lcllohm full range) 1”
10 megohms full range in 11% decade ranges 1,OO”o
overranging lo 199999 on ail ranges~
ACCURACY (90 days): ?tO 02% of readlng + 0 O,“a
Of ranqe + O,2 ohm, exceDt _tio~08”o 0, lead,“” f
O.OlYo-“I range) on the lO:meg;hm range -
TEMPERATURE COEFFICIENT: ?10~002”~ “1 read,“”
1, 0,001% “1 range,/ c except i(0 01”” “‘i
“1 readlng’+ 0.001”~ “1 range) ‘“c “n the
10.megohm range,
SETTLING TIME: Less than 3 seconds plus 1 second
ppr megohm lo wIthin OOlOb of final readlng~
CONFIGURATION: Two-termina,. constant currents HI
VOLTAGE ACROSS UNKNOWN: 5 volts for fu,, ranqe~
MAXIMUM ALLOWASLE INPUT: 20 v”Its “n the-1~
kllohm range. 60 “011s “n the IO-k,iohm range, 250
volts on ail other ranges, c”nf~n~“us rms ac + dc
GENERAL
POLARITY: Automal~c
ZERO STABILITY: 0.7 digif,‘C
WARMUP: 30 minutes 1” within twice spec~hed act
curacy. two hours for complete stabilhzatlon,
DISPLAY: 5 d,g,ts plus 1 overrange d<g,f, decimal
location: polarsty and overload indication Less
than 1 Second per reading. ad,“stable to 10
seconds per reading in l-second steps,
ISOLATION: LO to CASE: greater than 100 megohms
shunted by 0.01 mlcrofarad LO may be floated up
to 2500 volts with respect 10 CASE,
OPERATING ENVIRONMENT: 15’,C to 35-C up to
70Da relative humidity.
POWER: 105-125 or 210-250 ““Its Isw!tch-selected,,
50-60 Hr. 20 watts,
CONNECTORS: HI. LO 8. CASE, B~nd,n” Posts
Digital Output, l&36 card edges
DIMENSIONS, WEIGHT: Overall bench size 4 in, Hugh
x 6-314 I”. wide x 13-l/2 I”. dee” ,100 x 220 Y 345
mm), Nel weight, 6 pounds (3.6 ig):
DIGITAL OUTPUT: BCD (8421: 0 = “0000”) TTL-tv”e
lines represent each of five digits. overrange df’rzit,
overload (“1 “1, polarity (+ = “I”), decimal pos$l!“n
and function (7 lines).
PRINT COMMAND: Logic “1” appears for 200 milli-
seconds after each display update.
HOLD CONTROL: Logic “0” retains iast data I”
display and digital “utput.
iv
1075
SECTION 1. GENERAL INFORMATION
0177
TABLE l-l.
Front Panel Controls
Control
Power Off
Reading Rare
Controls line power to instrument..
Sets reading rate and print rate at digital 3-3b
output.
Functional Description
Variable control from 1 seclreading
(max) ea 10 secslreading (ml”).
Input Terminals
HI:
LO:
Connection to input high for all measurements.
Connection to input law far all. measurements.
CASE: connection to chassis ground. [Shorting link
may be used between I.0 and CASE for grounded
0perati0n.l
Four pushbuttons selecr the desired input mode.
Voltage mode, dc
Voltage mode, ac rms
o,meter mode, ki1ohms
ohmmeter made, ten megohms full range.
Four pushburtons select full ranges for “DC, “AC,
and kn functions only. When IO,% function is
selected all range buttons are released.
1:
10: 19.9999 Decimal
100: 199.999 Position
1000:
1.99999
999.99
I
Zero
Range Multiplier:
Permits adjustment of zero offsee.
Paragraph
2-3d
3-b
~ 3-2
_-
Line Switch
Line Receptacle
TABLE 1-2.
Rear Panel Controls
Digital output
+lO” hf. Adjust
Card edge co”nector.
Calibration control.
-10” Ref. Adjust Calibration control.
3
MODEL 190
SECTION 2.
2-1.
GENERAL.
incoming inspectim and preparati** for use.
2-2. INSPECTION.
ted both mechanically and electrically before shipment.
Upon receiving the instrument, check for any obv*ous
damage which may have occurred during transit. &port
any damages to the shipping agent.
2-3. PREPARATION FOR "SE.
a. Line Voltage.
the posirion of the LINE switch (S301) on the rear
pa*&.
XI-60 Hz line voltages over the range 105 to 125" ms.
Select the 234V posirio" for operation from 50-60 Hz
line voltages over the range 210-250" rms.
is selected, check for the praper fuse type and rating
as follows:
Select the 117" positia" for operation from
b. Fuse Installation.
This section describes procedures for
me Model 190 was carefully inspec-
Before power is applied, check
After the line voltage range
111v: 1/4A (N-17)
234Y: ll8A
@lJ-20)
INITIAL PREPARATION
C.
Line Connection.
three-wire line card (Keithley part no. U-7) Which
provides connections to line power (high, c"mo", and
chassis).
pin should be connected to earth ground.
above chassis ground, make certain that the
"link" between LO and CASE on the front
pane1 is removed.
d.
racy requires a warm-up time (with pnwer on) af tw"
hours.
ternal circuitry has reached a temperature equilibrium. Ambient temperat"re variations afier sebiiizatio" mu~st be considered usFng the appropriate
temperature coefficients for each functLo*.
e.
vo1ra.w measurements, check the zero reading on the
l-volt range by connecting a low-thermal short across
the input terminals. Adlust the fmnt panel zera
control CO obtain a zero reading such that the "minus"
polarity sign flashes on and off.
For operator safety, the chassis ground
If the Fnstrwnent input LO is to be floated
Warm-up. Complete stabilization to raced accu-
This time is required to ensure that the in-
Zero Adjusment. To achieve rated accuracy on
This instrument requires a
1
4
MODEL 190
A
SECTION 3.
OPERAT’ING INSTRUCTIONS
overrange
Display
1.99999 "
19.9999 v
199.999 "
1000.00 v*
*Maximum allawable input: 1400 ” peak mOme”tarV
Connections. Make connections to the input HI
a.
and LO terminals.
terrain chat the shorting link is connected between
LO and CASE.
link must be removed.
b. Control Secfi”,Qs. To select the dc voleage
.ode, depress the “DC pushburton. To select the full
range sensitivity, depress the appropriate range pushbutton, 1, IO, 100, or 1000. Adjust the Reading Kate
to achieve the desired display rate.
For grounded applicationa, make
For floating applications, the shorting
1073
3-5. RESISTANCE MEAS”REMENTS. The Model 190 pravides
five ranges from I kilohm to 10 megohms full range.
tierrange capabiLity is 100% on all ranges.
d Maximum Overload. 20 “OltS dc or rills ac “1,
the I-kilohm range, 60 volts on Lhe IO-kilohm range
250 Volts on all other ranges.
TABLE 3 -'I.
Resistance Ranges
I
‘- Connections. ELake connections to the input HI
and LO terminals. When measuring semiconductors and
other polariiy sensitive devices it is important to
consider the polarity of the voltage developed across
the input terminals. ‘The HI terminal Fs negative with
respect co the 1.0 terminal. For grounded applications.
make certain chat the shorting link is connected between LO and CASE. For Elmring applications, rhe
shorting Link must be removed.
b. Voltage *cross the U”k”0w”. Full range “alrage
is 5 volts.
the unknow” is 10 volts. see Theory of operation for
a mmplete explanation of open-circuit voltage condition. Test current for each range is give* io
Table 3-4.
At 100% overrange, the voltage across
TABLE 3-4.
‘Test Current for Resistance Modes
The Model 190 should not be subjected to
a voltage input while in 102 or 10 MI1 ranges
even though protection is provided in case of
accidental overloads.
e.
Residual Resistance. since the ?kdel 190 uses
B two-wire configuration, an inherent offset of a few
digits may be noticed on the I kiloiun range. This
offset reading should be recorded and subtracted from
all readings on rile 1 k>C range.
also add to the resiscancr “ffset and should be co,,sidered as well.
a.
General. The M”del 190 provides BCD TX’,.-type
lines which represmt each of five digits, an overrange digit i”“), overload, polarity, decimal position, and function. The lines are 8421 configuration
where 0 = 0000; I” addition LO data outputs the 19”
provides a Prinr ~omand and ilold Control. Refer to
Table 3-6 for digital output pin identification.
b. Data outputs.
and 2 and Hold are Series 7400 TTL circuits (see
manufacturers literature for specilications). Polarit
bin 10) and overload (pin 1) outputs are “ot buf-
fered.
pull up resistors connected to the internal +5 V
S”PPlY,
Function 1 and 2 outputs consist of 4.7 kii
Refer to Table 3-5 for function ltie coding.
NOTI:
Lead resistance will
All outputs except runcti”” 1
Full Range ‘rest current Full Range Voltage
I
C.
Control settings. Five ranges are available on
the Model 190.
1” m.
1.
Kilohm Functian. For measurements over the
range from 0.01 ohms to 2000 kilohms, depress the
kD function pushbueco”. The” depress the appropriate range pushbucto”, 1, 10, 100, or 1000.
2. Ten mgohm Function. For meaSureme”tS from
100 ohms eo 20 megohms depress the 10 MS? function
pushbutton.
Both the kQ and 10 Mn pushbuttons should be
depressed to operate in the 10 Mn mode. The
Range pushbutton switches are released when
the 10 Mn pushbutfm is depressed to prevent
an ambiguous mode of operation. To select
either “DC, “AC, or kn modes while in 10 MQ
mode, simply depress any one of the Range
pushbuttons and then select the desired
F”“Cti0”.
‘TWO functions can be selected, kC# and
NOTE
C.
erinr: Command. Logic “1” appears for LOO milliseconds after each display update.
4 for a graphic description of the A/D converter
timing.
d.
Hold Control.
display and digital oufput.
tro1, an equiva1enr of 4 TTL gates current sinking
capabiliry is necessary.
e.
COMnO”. Pin 18 should be used for al.1 cmn,,~”
connections to the digital ““tput.
f. Connectians. Use of Model 1902 Digital outp,,t
connecfor (optional) is recommended for connections
to the M/36 card edge con”ectar.
F”“C?ZiO”
Selected 1 2 3
“DC 1 1
“AC 0 1 1
KG 1 1 1
lam 1 0 1
mere Logic 0 = 10” state
Logic “0” retains last data in
To enable the Hold co”-
TABLE 3 -5.
Function Coding
Functia” Line
Logic 1 = high state
Refer to Figure
0
6
INPUT +lV
I
1277
INTEGRATOR
ZERO
CROSSING
DETECTOR
PRINT
COMMAND
I
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I
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MAXIMUM CONVERSION RATE
2 READINGS PER SECOND
I
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I
p
OPERATING INSTR”CTlONS
3-7. MEAS”REMENT CONSI”EFATIONS
a.
connections.
recommended when source resistances are greater than
1 kihhm or when using the 10M.Z mode.
be exercised so as nof to degrade the insularian
characterisrics Of the binding posts.
tance modes, accuracy may be degraded if the eerminals
and/or leads become contaminated. care should also be
take” fO minimize effects of thermoelectric porcntia1.3
which may be generared as a result of temperature
differences between junctions of dissimilar metals.
1. DC Voltage. me dc voltage accuracy is
specified in terms of a percent of reading and a
percent of range. An additional factor of .OOOOl%
of reading, per volt from full range reflects an
uncertainty due CO voltage coefficients for measurements made at “ther than fuU range. Short term
accuracy is valid for a period of 24 hours afrer
complete calibration. Long term accuracy (90 days)
includes an additional .Ol% of reading uncertainty
due to aging of precision components.
the effects of power dissipated in the input resist”rs should be considered whenever more than 500
volts is continuously applied (for 1 minute or
longer). Heating may cause a* additional uncertain-
ty due to the temperature coefficients of individual
circuit elements.
“se of shielded input leads is
care should
In the resis-
In addition,
MODEL L90
3.
AC Voleage.
specified in terms of a percent of reading and a
percent Of range. In addition, the effects of
power dissipated in the input resistors stm~ld be
considered whenever more cllan 400 volts is applied.
4.
Resistance. hccuracy on IeSiStanCC ranges
is specified in terms of a percent of reading and
a percent of range. An addieional uncertainty due
to residual resistance should also be considered.
when making resistance measurenlents, ic is
important- co make certain that t’he 190 is
properly zeroed in “DC function. Fur example
an additional error of .OOOl% of reading can
occur per digit of voltage offset on the Ik:;
- loom ranges;
per digit offset on lOOOkG and 10MI: ranges
respectively.
The ac voltage accuracy is
NOTE
.OOl% and .Ol% of reading
2. DC Current. When tire Model 1901 Currenf
Adapter is used an additional iO.3% of reading
uncertainty must be considered. As in any current
measurement the input drop should also be consider-
ed.
For example, a full range drop of 200,“”
across the shunt results in an error of 1% if the
source is 20 volts.
017 7
I
MODEL 190
I
THEORY OF OPERATION
SECTION 4. THEORY OF OPERATION
4-L. GENERAL DESCRIPTION. The Model 190 Digital
nulrinieter utilizes a modified integrating technqiue
ior A/O CO""erSio".
integrated circuits are utilized for greater reliability and servicing. The circuitry is broken down
into two major areas and assemblies; fbe Analog
Assembly and Digital and Power Supply Assembly.
'me halog section provides input signal conditioni"g,atte"uatio", filtering, buffering comparixg, and
initiates the main control signal for the entire
system. The Digital section provides logic control,
counting, decading and display. Usa located on tke
Digital assembly are the power supplies far the entire
system.
Digital assembly thraugh 5301 and 5302.
TO follow through a block diagram description it will
be necessary to make several assumptions; assume the
display is reading 0.0000, the counters have bee" re-
set LO zero, the a"alag switch, Sl (Q117) has jut turned
on allowing ihe integrator to sample the voltage at
Lhe input terminals. A voltage of +lO MC is applied
.o the input terminals.
to the DC attenuator and divided t" 1 VDC which
gpasses through the filter section LO bypass any AC
compooenc t" common.
tion is applied co the input amplifier section whick
provides signal isolation and a fixed gain of 5. The
mplifier signal, now at 5 "DC, is applied CO the
hregrarar section via Sl (Q117), Analog Switch. The
analog Switch has been turned o" by a control level
provided by circuitry, (the primary control flip-flop),
in the Digirvl Hssembly.
signal causes the integrating capacitor, C141,,to
charge for a fixed period of time, (approximately
500 milliseconds), or 200,000 counta. The final
count pulse clears the COunrerS to 0.0000. AT the
end of this period of time, a combinaeia" of a lo&
level at the zero detector amplifier, and the resef-
ting of the primary control flip-flop, causes S1
(Q117) Analog Switch, to turn off and 53 CQ116),
minus Reference switch, to turn on. The counter
starts counting towards 200,000 again. With a minus
input from the reference now applied to the Integrat-
ing hplifier, C141, begins t" discharge towards zem.
Upon reaching zero ""its, the zero detect"= Amplifier
creates a logic pulse that stops the counter which
due t" the relationship of the Integrator and clock
has counted t" 100,000.
control far the lagic, it is gated to farm a strobe
far the storage section. Information prek?ent in
storage is now made available t" the decoder section
which furnishes levels that light the display with
the counted "umber 100,000. A delayed strobe pulse
fallows within 1.0 microsecond which resets the
counters to zero, and resets the primary central
flip-flop.
Swirch, to turn off, and S1 (Q117) Analog Switch, t"
turn 0".
The Analog assembly is connected t" the
This3 causes s3, (9116) minus Reference
The latest linear and digital
me 10 volt signal is routed
The output of the filter sec-
Application of the +5V
This pulse becomes a primary
4-2. ANALM: ASSEMBLY. The following paragraphs describe individual Analog circuits in detail. These
circuits are divided according t" their primary
function in rhe system. (Refer to Schematic 25864E).
a. DC Atfenuafor.
P.118, and parts of 5102 and 5101, pravides artenuario"
for input signals above 2 VDC (100% overrange on the
1 " range).
impedance for better input matching a" the lowest
dc range.
b. Input Filter.
tion of ac components and noise present on dc input
signals.
C. InpuL Amplifier.
ponents, this circuit provides input isolation and
signal conditioning. 4119 ii; a low leakage matched
Fl?r providing high input impedance and matched voltage and temperature tracking. A bipolar device, "UCputs from this FET are applied directly at Q*101, a"
operarional amplfier.
variable resistor, is used for initial balancing of
inpw PET pair while Q106 provides a canstant curre"~
source. 0119 and QAlOl, a" IC Operational Amplifier,
provide the gain required by the Input DC Amplifier
The maximum output swing at the Input timplifier, TP1,
is 210 MC. This output is fed directly to 9117, the
Analog Switch. P"te"tiometer R155, front panel zero,
is used for fine zer" adjustment.
d. Signal Switches (See Figure 5).
q110, Ql16, and Q117, these solid state switches
provide high speed, low leakage paths for signals
applied to the Integrating Amplifier. These switches
are drive" by logic levels fram the Digital Assembly
with Q109 and Qlll through Q115 supplying buffering.
e. Integrating Amplifier. Also a bipolar circuit
this Amplifier integrates dc levels fram signals applied through S1 (41171, 52 (QllO), and S3 (9116). A
unity dc Cain Amplifier, rhe precision ramps created
by the time c""stants of RI01 and Cl41 are directly
proportional co the clock speed in the Digital Section.
Using a modified dual slope principal, the charge
time of Cl41 is fixed at appmximately 500 ms, while
the discharge time is a function of the input voltage.
The maximum swing at the output of this amplifier,
TP4, is approximately t12 v peak. The output is fed
dir-ect1y to the comparator.
f. Zero Defecfor - Comparator. This circuit
creates the main control pulse and logic level necessary for proper digital and analog functions.
an IC Operational Amplifier, provides a dc gain ior
signals less than +I00 uV. The level at the output
of QA107, is determined by the polarity of the unknown
5102-30 is used to shart "ut the higb
A 10 megohm divider using RIII-
This section provides attenua-
Cmprised of rhree acti"e com-
R146, (Coarse Zero) a 100 :!
Comprised of
QA106,
1075
9
THEORY OF OPERaION
MODEL 190
10
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