Keithley 191 User manual

Instruction Manual
Model 191
Digital Multimeter
01979, Keithley Instruments, Inc.
Cleveland, Ohio, U.S.A.

TABLE OF CONTENTS
6-1
6-l
6-1
h-l
6-l
6-l
6-2
6.2
ii

MODEL 191 DMM GENERAL INFORMATION
SECTION 1. GENERAL INFORMATION
l-l. INTRODUCTION.
1-2. The Keithley Model 191 is a 5-l/2 digit,
200,000-count, manual-ranging bench digital multi-
meter with dc volts and ohms ranges standard. It
provides highly accurate, stable, low noise and
fast-responding readings from 1uV to 1200 volts dc
on 5 voltage ranges, and 2 and 4 terminal measut-e-
ments from 1 milliohm to 20 lrlegohms on 6 resistance
ranges. The 191 is capable of 0.0005% resolution
and luVlln!G sensitivity. In addition, if you
purchased the Model 1910 AC Voltage Option, your "MM
will provide readings from 1OuV to lOO(1volts ac on
4 ra"gES. This option may alsn be purchased later.
1-3. Your OMM also has features and advantages that
might not be readily apparent. Soae of these aw:
. 5-l/2 digit LEO display with appropriate de-
cimal point - 0.5 inch digits permit monitorinq
nx?asurements fron1 across tllc r""!".
l Pushbutton NULL eliminates potenti"mrtPr
zeroing, corrects for lead resistance in ?-wire
ohms, bucks out thermal EMF's in 1ow IPYPI dc
nleasurements 3°C permits you t" medsuv? devi-
ations from a set value. The NULi~ light indi-
cates that the function is dctivc for "p~rat"r-
saietv and to lessen the? ChdrlCC Of I.IP‘3S,II'P,~IPnt
and field installed.
FIGURE l-l. Model 191 Digital Multimeter
I-1

GENERAL INFORMATIOP MODEL
191 DMM
l-3. Continued.
A Micro-processor based design that
provides:
A Combination of single slope and charge balance
AD conversion - for faster response and better
linearity.
Automatic non-linear digital filtering - for
faster response and reduced noise on the
display.
A reduction in the number of parts while main-
taining high accuracy and speed of measurement -
simplifies high accuracy measurements and cali-
bration of the instrument and provides higher
mean time between failures.
-1EEEEE error message indicates improper
uses of the instrument - prevents erroneous read-
ings and reduces possibility of injury to the
user or damage to the instrument.
Each range has:
Automatic polarity operation minus sign dis-
played, positive implied.
Effective input overload protection.
Overrange indication - polarity and overrange
digit displayed.
Decimal point positioned by range pushbutton.
Automatic Z/4 wire ohms operation - saves
time and simplifies Z-wire or 4-wire ohms
measurements.
A full line of optional accessories that
exterd the measurement capability of your llcdel
191.
Some of these accessory ncde1s are:
IGOO High voltage Probe allows your Dill1 to
measure fron 12OOV to 40kV dc.
1901 Plug-l" Current Adapter allows your D,,,, to
read dc current from lvA/digit to 2000mA. Hi th
the AC Voltage option, it reads from lOti/digit
to 2000nA ac.
1682 High Frequerxy (RF) Probe allows your Dills to
RedSUre fr0n 0.25v to 3ov t-lx ac wer a frequency
t-awe of 100kHr to 1OOMHr. It can be used
without the AC Voltage Option.
1685 Clamp-On AC Current Probe (when used with AC
Voltage Option) allws your Dllll to measure fron
zero to 200A rns ac.
1651 50.Ampere Current shunt allows your D!IM to
measure fron O-50A dc, ard with AC Voltaqe Option
fron IOA to 50A ms ac.
NOTE
Refer to Section 4 for more detailed information
on these accessories.
l-4. WARRANTY INFORMATION.
1-5. The Warranty is given on the inside front cover
of this Instruction Manual. If there is a need to
exercise the warranty, contact the Keithley
Representative in your area to determine the proper
action to be taken. Keithley maintains service
facilities in the United Kingdom and West Germany,
as well as in the United States. Check the inside
front cover of this Manual for addresses.
l-6. CHANGE NOTICES.
l-7. Improvements or changes to the instrument
which occur after printing of the Instruction Man-
ual will be explained on a Change Notice sheet
attached to the inside back cover.
1-8. SAFETY SYMBOLS.
1-9. Safety symbols used in this manual are as
follows:
The b IMPORTANT
symbol can be found in various places in
this Manual. Carefully read the associated
CAUTION statements with regard to proper use and
handling of the instrument. Oamage to the
instrument may occur if these precautions are
ignored.
This\ ~
svmbol can be found in various places in
this Manual. This symbol indicates those areas
on the instrument which are potential shock
hazards. Carefully read the associated WARNING
statements with regard to proper use and handling
of the instrument. Serious personal injury may
result if these precautions are ignored.
l-10. SPECIFICATIONS
I-11. Detailed specifications for the Model 191 are
given in Table 1-I.
l-2

MODEL 191 DMM GENERAL INFORMATION
TABLE l-l
SPECIFICATIONS

OPERATING INSTRUCTIONS YODEL
191 DMM
P1006
MODEL
AC OPl e
LINE/FUSE LINE'VOLTAGE
(F101) SELECT SWITCH
(S102)
FIGURE 2-1. Location of Line Fuse and Line Voltage Select Switch.
2-o

MODEL 191 DMM
SECTION 2. OPERATION.
~OPERATING INSTRUCTIONS
Z-l. INTRODUCTION.
2-2. This section provides information needed for
incoming inspection, preparation for use, and
operation of the Model 191 and its accessorieS.
2-3. UNPACKING AN0 INSPECTION,
2-4. The Model 191 was carefully inspected, both
mechanically and electrically before shipment. Upon
receiving the Model 191, unpack all items front the
shipping container and check for any obvious damage
which may have occured during transit. Report any
damages to the shipping agent. Retain and use the
original packaging materials if reshipment is
required. The following items are shipped with all
Model 191 orders:
a. Model 191 OMM.
b. A Copy of this Manual.
C. Installed or separate optional accessories, as
ordered.
2-5. PREPARATION FOR USE.
2-6. The Model 191 is shipped ready-for-use on the
line voltage marked on its rear panel. Instructions
on how to connect the Model 191 to your available ac
line power are contained in Paragraph Z-7 Line
Power.
2-7. LINE POWER
2-R. The Model 191 is provided with a 3-wire line
cord which mates with a 3rd wire earth grounded
receptacle. The instrument will operate on 3
voltage ranges of 60 or 50 Hertz ac power. Standard
voltage ranges are 105 to 125 volts and 210 to 250
volts. Either of these ranges may be selected by
positioning an internal slide switch and installing
the appropriate fuse for that range. An optional
line voltage range of 90 to 110 volts is available
by special order. Instruments with this range use a
different transformer. Connect the Model 191 to
your available ac power inaccordance with the
following procedures:
NOTE
The line voltage sct/tinq of the instrument
is marked on the &r panel. The following
procedure can be uqed to either confirm the
factory setting, or 40 set up the instrument for
operation on another ivoltage range. if the line
voltage range is chdnged, the box next to the
selected line voltaTe should be appropriately
marked as an externalI reminder of the setting.
Use a water soluable barking pen.
2-9. Line Voltage Selec~tion.
Z-10. Set up the Modejl 191 to operate on your
available ac line voltage as follows:
a. Turn the DMM botltom side up and loosen the
four screws in the boqtom cover. These sci-ews are
held captive hy rubber O-rings.
h. Hold the top an?
bottom cover together t"
prevent their separatjon and turn the DMb1 over to
normal position. Rem+, the top cover.
c. Set switch
8102 aind install the proper rated
line fuse, as indicated in Table 2-1. for your
available input line ~voltage. These items are
shown in Figure 2-l.
d. Reinstall the top cover.
TABLE 4-l.
Line Voltagq Selection
*Requires special~factory installed
transformer.
2-l

OPERATING INSTRUCTIONS MODEL 191 DMM
FIGURE 2-2. Rear View Showing Line Cord.
NULL POLARITY (NEGATIVE Is INDICATED, POSITIVE Is IMPLIED
FUNCTION* rblHEN MINUS (-) DISPLAY IS OFF.)
/
(I.3
1 SET POWER ON @j SELECT RANGE
0'
I", 3,.
4 CONNECT SOURCE
I
*SEE TEXT, PARAGRAPH 2-15.
FIGURE 2-3. Operating Controls.
2-2

OPERATING INSTRUCTIONS MODEL 191 DMM
Z-11. Connecting Line Power.
z-12. The Model 191 is provided with a 3-wire line
cord, shown in Figure 2-2, which mates with third-
wire grounded receptacles. Connect the instrument
to ac line power as follows:
\,
WARNING
Ground the instrument through a properly earth-
grounded receptacle before operation. Failure to
ground the instrument can result in sevet-e injury
or death in the event of short circuit or
malfunction. In addition, connect only t" the
line voltage selected. Application of incorrect
voltage can damage the instrument.
a. Plug the power c"rd into a properly grounded
outlet of a source having the selected line
voltage.
b. Operate the Model
191 as described in
Paragraph Z-13.
2-13. OPERATING INSTRUCTIONS
2-14. The basic operating instructions for the
Model 191 [IMM are outlined below, and Condensed
Operating instructions are provided on the bottom
cover of the instrument. These instructions should
only be used after becoming completely familiar with
the operation of the Model 191 through day-to-day
"SC?. Until this familiarity ha5 been achieved, best
performance and safest operation will be obtained by
using the individual instructions provided in this
section which describe how t" make specific function
mea*"reme"ts. Refer to Figure 2-3 and operate the
OMM a5 f0110w5:
/&CAUTION
no not exceed the Maximum Inputs limits given in
Table 2-2.
a. Turn on the power by depressing the ON/OFF
pushbutton. If the instrument is within 18-2R°C,
it is useable immediately, but a 1 hour warmup is
required to obtain rated accuracy. up to 1
additional hour may be required from temperature
extrelne5.
b. Select the function with the ACV, IDCV or n
pushbuttons.
c. Select the range by depressing the appropriate
pushbutton,
d. Connect the source to the INPUT terminals and
make the ,n,easurement. Accessories described in
Section 4 should he (used as required.
TAB
Summary of M
UNCTION RANGE
ZOOmV, 2
zov-1200
ALL
ALL
2-15. NULL FUNCTION.
Z-16. The NULL functi
and functions. It is
based function. The dr
function is selected.
depressed with an "n-5
that reading is subtrx
1ngs. The nulling pr"
of two numhers, and ha5
or function selected.
primarily designed to
compen*ation for te5t
emf's generated in circa
terminals,
the null f
measure variation5 db"'
example, +1.00000 VDC
the display, and variat
made by switching to t
This,is possible hecaur
is 100,000 (counts) in
sign is active for n (a
2-17. it is important
reduce5 the dynamic re
stance, if t1.00000 VL
voltages greater than
A,0 c"nverter (200,OOI
range would occur at *
readings less than -1
less than +lV) because
ing of -199,999 coun
dynamic range of the
Figure 2-4. In ocv
Dynamic Range and the
exceeded and thus, bot
of the meaS"i-erne"t.
dynamic range can be e
2-2
imum Inputs.
MAXIMUM INPUT
7OOV Continuous;
12OOV for 1 minute
Rh3Xllll"lll.
IZOOV Continuous
25OV rms; 360V peak
IOOOV rnis sine or dc
2 x 107 v .Hz
is operable "n all ranger
switch selectdblr software
nciator is lighted when the
?en the NULL pushbutton is
1~ reading on tlw display,
d from all subsequent read-
55 is merely d subtraction
"thing to do with the range
For this wds"n, althouyh
,vide convenient pushbutton
lad re5istance dnd thermal
s connected to the DMO INPill
:tion cd" also be used t"
or below a 5et valur. 101.
put coutd be used to null
ns ahovc 1O.OOOWO could be
2OMn range and n function.
the numher heing subtracted
th instances, and the minus
ACV) in the NULL mode.
o note that the use of NULL
e of meas"rerne"t. For in-
is the nullpd value. input
I would still overload the
counts), even though "ver-
10.000 counts displayed, and
would cause overrange (2V
f the maximum display read-
This reduction in the
~surement is illustrated in
unction, both the Display
nput dynamic range cd" he
:dn limit the dynamic range
ACV and n, only the input
!eded.
2-3

OPERATING INSTRUCTIONS MODEL
191 DMM
DISPLAY DYNAMIC RANGE
A
/ NULL \
199,999 VA&UE 199,999
MEASUREMENT
DYNAMIC RANGE
IN NULL MODE
(SHADED)
\ v /
INPUT DYNAMIC RANGE
FIGURE 2-4. Effect of NULL function on Dynamic
Range of DCV Measurement.
Z-18. The Use of NULL as pushbutton 'zero" is
described in DC Voltage and n Measurement
Procedures.
2-19. OVERRANGE INDICATION.
Z-20. Overrange is indicated by the minus sign
along with the over-range digit and the appropriate
decimal point. All of the remaining less signifi-
cant digits are blanked. Example: (-I--.---).
Overrange is indicated whenever the dynamic range of
DCV measurement is exceeded. With the NULL function
off, this occurs above
*199,999 CO”“tS. As
described in Paragraph Z-17, the dynamic range of
the measurement is reduced by an amount determined
by the size and polarity of the nulled signal when
the instrument is in the null mode.
2-21. ERROR INDICATION.
2-22. -1EEEEE is displayed when an improper range -
function is selected. These selections are:
ACV function - when AC option is not installed.
20Mn range - with ACV or DCV function selected.
ACV function with 2000, 200mV range selected.
2-23. DC VOLTAGE MEASUREMENT.
2-24. The Model 191 reads dc voltages from I
microvolt/digit to 1200 volts. The maximum
displayed reading is 139999. Overrange is indicated
by (-)I-----, except on 1200 volt range. On the
1200 volt range, the display can read beyond the
maximum allowable input voltage. Maximum allowable
input: 12OOV for I minute maximum, 700 volts
continuous on the 200mV and 2V ranges; 1200 volts
continuous on the ZOV-1200 volt ranges. Use the
Model 191 to measure dc voltage as follows:
A
CAUTION
Do not exceed the maximum allowable input voltage
limits. Instrument damage may occur.
a. Turn on power with the ON/OFF pushbutton and
depress the DCV pushbutton.
b. Select the desired range from the five ranges
available. The decimal point is positioned by the
range pushbutton. The 1200 VDC range is selected
by the 1000 pushbutton.
2-4

MODEL 191 DMM IOPERATING INSTRUCTIONS
c. Ensure that the NULL pushbutton is out (light
off) unless measurements are to be made as
deviations from a preset value.
d. Connect the signal to be measured between the
INPUT HI and LO binding posts. The binding posts
accept wires, spade lugs or banana plugs for ease
of connecting the circuit to be measured. LOW
thermal cabling and connections are recommended
for measurements on the 200mV range.
e. For the top four ranges, merely observe the
displayed digits, polarity sign and decimal point
locations. The top four ranges are direct-reading
in volts.
f. For the 200mV range, ZERO must set with the
NULL function to obtain rated accuracy. Zeroing
is necessary to compensate for thermal EMF's
generated by the connections to the circuit to be
measured. These voltages may be only a few
microvolts or several tens of microvolts. set
zero as follows:
1) Set Model 191 to 200mV range.
2) Disconnect the test leads at the circuit to
be measured and short them.
3) Depress the NULL pushbutton.
4) Reconnect the test lead and make the
measurement by applying the signal and reading
millivolts on the display.
RANGE
SETTING
200 n***
2k n
20k n
200k n
2000k "
20M n
g. The optional Mode
be used with the Modt
up to 40 Kilovolts, a
Paragraph Z-30.
2-25. RESISTANCE (n)
Z-26. The Model
191 I
millioha/diqit to 20
rarqes. The Model 191
4.wire oh,:6 operation.
sense leads are conmec
natically dew 4-termi
not connected, the me
For 46terminal meax
digit) can be obtaine
log as the maximum 1~
2-3 are mt exceeded.
measurements on the 20
the NULL furrtion to o
tlodcl 191 to measure 7
&CA"
MAXIMUM ALLOWABLE I
36OV peak, 25UV rms
voltage. Instrument
a. Turn on power and
h. Connect the circ
INPUT terminals and I
the six ranges avail
positioned by the ran
TABLE 2-3
Resistance Ranges
MAXIMUM OUTPUTS'
4-w,
I(Shorted) V(Openl MBX.
.,
-r
-4mA -4OOmV 7n
-4mA -4V 22"
-4OOuA -4v 700
-4OuA -4v 22on
-4uA -4v 7000
-4v 2200n
ALL RANGES
OVERRANGE: MAXIMUM
-l---_
ALLOWABLE
INPUT:
360Vpeak,
1g.ggggt-““-
MAXIM""
READING
199.999
1.99999
19.9999
199.999
1999.99
* HI binding post (red) is negative.
** Maximum resistance per lead for additional 1 digit en-or.
l ** Zero must be set by NULL to obtain rated accuracy.
1600 High voltage Probe can
191 to measure dc voltages
reduced accuracy. Refer to
JASUREMENT
IN ~nedsures resistdrre fron 1
eqohms. SEC Table 2-3 for
prwides d~tondt>c 2-wit-e or
This nedns that if the ohms
ed, the rneasurcment IS auto-
Ial if the sense leads are
iureiaent is done 2.terminal.
eme nts rated dCC"l'dCY (tl
on the top five rarqes as
ION
'UT VOLTAGE (all ranges):
Do not exceed maximum
amage may occur.
depress n pushbutton.
lit to be measured to the
,lect the desired range from
ble. The decimal point is
e pushhutton.
;*
250Vrms
2-5

OPERATING INSTRUCTIONS MODEL 191 DMM
c. For 4-terminal measurement c"nnect the sense
leads t" the circuit t" be measured and to the n
SENSE terminals on the 191. This arrangement
eliminates the err"r due to the voltage drop
across the current-carrying leads.
d. Ensure that the NULL pushbutton is out (light
off) unless measurements are to be made as
deviations from a preset value.
c. For the top five ranges of Z-wire or 4-wire
measurements, merely observe the displayed digits
and decimal point to make the measurement.
f. For d Z-wire or 4-wire ohms imeasurement on the
200n ra"qE, lCK0 rmust be set with the NULL
function to obtain rated accuracy. Zeroing is
necessary to colrlpfnsate for test Icad resistance
On Z-wire & Thermal Emfs on 2 & 4-wire. set LPr"
as follows:
1) IDisconnect the test leads at the circuit to
be rmeasured, and short them.
2) ocpress NU,.L p"shb"tt"n.
3) iReconnect the test leads and <make the
IIIEaSIItm!x!"t.
g. "iodf Test. Thr 2Kn range is rccomxnded for
diode testinq. On this range the forward oil
resistance Of J silicon diode will read
approximately 190n. (Hiqh Terminal is Negative)
Z-27. Ac VOLTAGE MEASUREMENT (WITH 1910 AC
OPTION).
2-28. With the Model 1910 option, the Model 191
reads ac voltages from 10 microvoltsldigit to 1000
volts. The instrument is avera9e responding and
displays the root !:ledo square value Of a 51~ W~VC
with a frequency of 50Hr t" 100kllr. Accuracy is
specified for 1000 counts and above. The maximum
reading is 199999. Overrange is indicated by (-)
i-----, except on 1000 volt range. On the 1000 volt
range, the display can read beyond the lmaximum
allowable input voltage. Maximum allowable input:
IOOOV r‘ms or dc; 2 x lO'V.tir. "se the Model 19,
to "leasure dC voltage as follows:
/!&CAUTION
Do not exceed maximunl allowable input voltage.
Instrument damage may occur.
a. Turn on power with ON/OFF pushbutton and
depress the ACV pushbutton.
h. Select the desired range from the 4 ranges
available. The decinlal point is positioned hy the
range pushbutton.
C. insure that the NULL pushbutton is out (light
off) ""less measurements are to he Imade as
deviations front a preset value.
NOTE
Do not use NULL to zero Lhe range. A Sllldll
residual zero reading is normal (approx. 20tiuV)
If NIJLI. is used to zero this offset. reailirlgs in
specified accuracy range wili be 1"~ by the
offset amount.
d. Connect the signal to be measured between the
INPUT Ill and LO binding posts. The hinding posts
accept wres, spade lugs or banana plugs for ease
of connecting the circuit to be measured. Observe
the displayed digits and decimal point.
e. The Model 1682 RF Probe can he used with the
Model 191 to measure 0.25V to 30V rms ac signals
with a frequency IOOkHr to IOOMHr (and above at
reduced accuracy). Refer to Paragraph 2-36.
2-6

MODEL 191 DMM
SECTION 3 PERFORMANCE VERIFICATION.
PERFORMANCE
VERIFICATION
3-1. GENERAL.
3-2. Performance verification may be performed upon
receipt of the instrument to ensure that no damaqc
or nisadjustment has occurred during transit. Veri-
fication may also be performed whenever there is
question of the instrument's accuracy, and following
calibration, if desired.
NOTE
For instruments that are still under warranty
(LESS than 12 month5 since date of shipment),
if the instrument's performance falls outside
specifications at any point, contact your
Keithley rcpresentativc or the factory iomedi-
ate1y.
3-3. RECOMMENDEDTEST EQUIPMENT.
3-4. Kecommended test equipment for performance
verification is listed in Table 3-1. Alternate test
equipment nay be used. However, if the dccuracy of
the alternate test equipment is not at least 3 tines
better than the instrument specifications, addition-
al allowance must be made in the readings obtained.
Some of the equipment listed in Table 3-l is not 3
times better than the 191 specifications because
such equipment is not readily available. In these
instances, the verification procedures indicate the
equipment manufacturer's specified uncertainty, and
include the uncertainty in determining the allowable
rcadiny for the Model 191.
ITEP
-
A
8
C
"
E
T
3-5. ENVIRONMENTAL COND1TIONS.
3-6. All neasurenents slhouid be made dt a" dnbirnt
tenpcraturc within the rpnge of 18' to 28°C (65" to
82Or). and a relative hu#idity of lcsr thdri 80%.
3-1. PERFORMANCE VERIFI$ATION PROCEDURE.
3-K. Use the f"llowin(i procedures to verify the
basic accuracy of the Moidfl Ill DI,!M for dc voltnge.
resistance and dc voitagc (rrlth l.lodei 1910 AC
Voltage Option installdd) 1mcd5urcnwnts. it thP
instrument is out Of s~pecificdtion at Jny po,nt,
perfor,, a complete ca)ibration a5 d,xc,.ibv! in
Section 6, ~nlcss the :instrwwnt 15 still iindrr
wavva"ty, as noted above.
NOTE
Performance verificbtion should bc pcrfonncd by
qualified pcrsonnel~ using accurdtc and rcliablr
test eq"lpncnt. ~
3-9. initial Conditions;
TABLE 3-l.
Recommended Test Equipment For Performance Vcrifica tilot
DESCRIPTION
DC Calibrator
AC Calibrator
High Voltage Amplifier
(Used with Model 745A)
IIccade Resistor
Kelvin-Varlcy Voltage
Uivider
(Used with Model 343A)
SPECIFICATION
190n, 1.9kn,19kil,
190k0,1.9Mn, lOMn,
t0.017,
.19v, 1.9v
with .2ppm Terminal
Linearity
1.
72OA
3-l

PERFORMANCE MODEL
191 DMM
VERIFICATION
b. Turn on the Model 191 and allow it to wdrrl up
for one hour.
t WARNING
Sonc procedures require the USC of hi9h volt-
age. Take cat-c to prevent contact with live
circuits which could cause electrical shock re-
sulting in injury or death.
3-11. DC Voltage Accuracy Check ('ZOV to 1ZOOV
Ranges).
4. Select dc voltaqe function.
h. Connect the DC calibrator (Item A, Table 3-l)
to the instrument.
c. Select the 2flV range, and apply positive 1OV
dc to the DMM. The readin &st be within the
limits specified in Table 3-2.
!i. Select each rcnaining range and apply r-c-
quircd voltage specified in Table 3-2. Verify
that the reading is rrithin specifications.
f. Repeat all checks with negative voltage.
TABLE 3-2.
DC Voltaqc Performance Check (2OV to 12OOV Ranoc).
I I
R‘?"%? Applied Allowable Readings at 18O to 28'C
Voltage
I 4
9.9986 to 10.0014
99.986 to 100.014
999.86 to 1000.14 I
I I I 1
3-12. DC Voltage Accuracy Check (200mV and 2V
Ranges).
2. Sclcct DCV and 200mV range.
b. Disconnect test leads at the DC calibrator
(A) and short them. Depress the Model 191 NULL
Ibutton. Verify a display indication of OO.OOOmV
+O.OOlnV flashin9.
c. Connect the DC calibrator (A), Kelvin-Varley
Voltage Divider (E) and Model 191 as shown in
Fi9urc 3-1. Set the voltage divider (E) for
.0190000 output.
i, Temporarily disconnect the test leads from
the DC calibrator (A) and short them. DepESS
Model 191 PlULL button for a display indication of
00.000 ~OO.OOLmV flashing.
c. Reconnect the DC calibrator (A) and set to an
output Of +10.00000V.
f. Verify that the Model 191 reading is between
t189.978 to t190.022nV. Note that the allowable
reading includes a 6 digit allowance for the
uncertainty of the DC calibrator (A) and Voltage
Divider (E).
~9~. Kopfat step d thru f with negative voltage.
h. Select the 2V range and rcleasc the NULL
button. Set the Kelvin-Varlcy Voltage Divider
(E) to .I90000 output.
1. Verify that the Model 191 reading is between
t1.89981 and t1.90019V. Note that the allowable
reading includes 24 digits for DC calibrator (A)
uncertainty.
i. llfpeat step i with negative voltage.
3-13. AC Voltage Accuracy Check (With Model 1910
AC Voltage Option Installed).
A. Select ac voltage function.
b. Connect the AC calibrator (Item R, Table 3-1)
to the DMM. Set the calibrator frequency to IkHr.
2. Set the DMM to the 2V range and apply IV ac
to the DMM. The reading must be within the
limits specified in Table 3-3.
d. Select the 20 and 200 volt ranges and apply
the required voltages as specified in Table 3-3.
Verify that the readings are within specifi-
+ 1.0 Kelvin - HIGH,
DC
Calibrator OUT Varley LOW
Voltage MODEL
(A) LOW Divider 191
(El
FIGURE 3-l. Test Circuit For 2OCmV And 2V Accuracy Check.
3-2

MODEL 191 DMM PERFORMANCE
VERIFICATION
2.
To check the 1000 volt range, connect the
High Voltage Amplifier (Item C, Table 3-l) to the
output of the AC calibrator per the manu-
facturer's instructions. Connect the amplifier
output to the Model 191 INPUT terminals. Set the
AC calibrator for amplifier output of 1000.00
volts at lktlz. Verify that the DMM reading is
within the specified limits in Table 3-3.
TABLE 3-3.
AC Voltage Accuracy Check
Range Applied Allowable Readings
Voltage
at 18’= to 28’C
at
2:; 101.ooov.ooov 9.9868.99868 toto 10.0132V1.00132V
2oov 1oo.oov
99.068 to 100.132V
1ooov 1ooo.ov 998.00 to 1002.00v
m
2ov 1o.ooov
9.9868 to 10.0132V
at 20ktlz
2ov 1o.ooov
9.9868 to 10.0132V
at 100kHr
2ov 1o.ooov 9.90 to 10.10
L
f. To check accuracy /at 5OHz. ZOktlz, and lOOkliz,
select the 20 volt ;ranqe, apply the voltage
specified in-Table 3-13 at 5011z, then repeat at
20kHz and 100kHz. Veinfy that the DMkl readings
are within the specifiied limits.
3-14. Resistance (n) Accjuracy Check.
5. Select resistancejfunction by depressing the
R pushbutton.
0. SeleCt 200n rc3ngfi
C. Connect the decape resistor (Itw 0. Table
3-I) to the DMM. ~
L!. Set the decade rjsistor to zero and comp~n-
sate for lead resist+xe by depressing the IiuLL
for a display indicition of 00.000 * 00.301
flashing.
J2. Set the decade rjsistar to 1900. Verify that
the reading for the! 200n range is within the
limits specified in Tbblc 3-4.
f. Select the Zkr! rpngc.
9. Set the decade rcpistor to LC~O and reset the
NULL.
h. Set the decade rbsistor to 1.900kn. vwify
that the reading is bithin the limits spc!clfiCd
in Table 3-4.
L. COntiNE by uSin the NULL to eliminate lead
resistance on each ra'ngc and measure the next rc-
sistance as specifiei in Table 3-4. Test each
item in the table andi verify that each wading is
within specificationsi.
TABLE 3-4.
Resistance Accuracy Check.
RANGE RESISTANCE ALLOUABLE READING AT 18' to 28'C ~ *
,
zoon 190n 189.955 to 190.045ri
?I9 digits
2kn 1.900 kn 1.89956 to 1.90044 kn 219 digits
20kn 19.00 kn
18.9956 to 19.0044 kn -p
+ 9 digits
200kn 190.00 kn
189.956 to 190.044 kn 219 diqits
2000kn 1900.0 kn
1899.22 to 1900.78 kn ?(19 digits
20Mn 10.000 nn 9.9908 to 10.0092 Mn 410
digits
* Manufacturer's specified uncertainty of the decade resistor (D)
This uncertainty has been added to the specified accuracy of the
obtain the allowable reading.
3-3

MODEL 191 DMM ACCESSORIES
SECTION 4.
4-1. GENERAL.
4-2. This section describes the various accessories
and options available for use with the Model 191
DMM.
4-3. LINE POWEROPTION.
4-4. The Model 191 can be powered by a line voltage
of 90 llOV, 50 - 60Hz with the special factory
installed transformer option. This option is
available by ordering a Model 191 DMM(90 IlOV, 50
- 60Hr).
4-5~ MODEL 1600 HIGH VOLTAGE PROBE.
4-6. The Model 1600 extends the DMM to 40kV. It
has a 1OOO:I division ratio which means that 1 volt
on the DMM corresponds to 1 kilovolt.
TO operate: Set the DMM to OCV and 200
Volt range. Connect the banana plug on the Model
1600 to the INPUT terminals. Connect the alli-
gator clip on the Model 1600 to source low. Connect
the probe tip to source high.
Specifications: Voltage Rang
40,000 volts DC.
Input Resistance:
1000 imegohms.
Division Ratio: 1OOO:l.
Ratio Accuracy
+1.5% at Z!ikV, decreasing to
fZ.fl% at 20kV and 30kV
f3.0% at 1OkV and 4OkV, and
+4.0% at 1kV.
Ratio Stability: tO.Ol% per "C; eO.l% per year.
Heating Effects: Self-heating due to application of
high voltage for period in excess of 1 minute will
cause a maximum of 0.2% additional error at 40kV
(error is less at lower voltage).
4-7 . MODEL 1651 50-AMPERE SHUNT
4-8. The Model 1651 allows current measurenlents to
be made from 0 to 50 amperes DC and from 10 t0
50 amperes AC with AC Voltage option. It is a
O.OOlohm kl% 4 terminal shunt. A fifty ampere
current will correspond to 50 millivolts.
To operate: Connect separate CUT-
rent leads (not furnished) between
the source and the Model 1651 hex-head bolts. Use
leads that are rated up to 50 ampere capacity.
Connect the voltage leads (furnished) between the
Model 1651 screw terminals and the DMM INPUT
ACCESSORIES !
terminals. Set the DMlj to ACV and 2V range or
DCV and 200 millivolt iange. "SC NULL to zero
on DC 200mV.
4-9. MODEL
1681 CLIP-04 TEST LEA0 SET
4-10. The Model
1681 COtdins two
leads 1.2~1 (48 inches) 1 ng, terminatedY p
probe.
with banana plug and spri,ng-action clip-on
4-11. MODEL 1682 RF PRO
4.12. The Model 1682 ex
voltage response of the
lOOkliz to lOOMHz,
To Operate: Set the DMM~to DCV
and 200 Volt range. Con ect the Model 1682
to the DMM INPUT termina 1 5.
Specifications:
Voltage Range: 0.25 to
Transfer Accuracy: to.5 B, 1OOkHz to 1OoMtlZ
sinewave. 1
0 volts rms.
peak responding calibr ted in rms of a
Input Impedance: 4 megop shunted by 3pF.
Maximum Allowable Input:1 30V pms AC. 2OOV UC.
Accessories Supplied: shraight tip. hook tip,
ground clip, hi adapt+, banana plug adapter.
4-13. NODEL 1683 UNIVERbAL TEST LEAD KIT.
4-14. Two test leads, 11.2m (48 inches)
long with 12 screw-in tips - 2 banana
/I"
f! J
plugs, 2 spade lugs. 2 alligator clips ,I\
with boots, 2 needle ti vs with chucks A
and 4 heavy duty tip plugs.
4-15. Model 1684 Carrying Case \
4-16. The Model 1684 is a hard
vinyl case with a fitte
1
foam /
i
insert with room for the Servic
Manual and small access+ies.
4-17. MODEL 1685 CLAMP-ON AC CURRENT PROBE.
4.18. The Model 1685 "edsure~ AC current by
clamping onto a single conductor. Interruption of
the current path is unngessary. The Model 1685
detects current by sensilng magnetic field produced
by current.
To Operate: Set the OM
4 to ACV and 20
volt range. Connect t/he Model 1685 to the DMM
4-l

ACCESSORIES MODEL
191 DMM
INPUT terminals. The DMM will display 0.1
volts per ampere.
Specifications:
Range: 2, 20
and 200
amperes r-m.
Accuracy: i-4% of range at
60Hz. ST% of range at 50Hz.
Temperature Coefficient: ?O.O5%/"C an the 20 and
200 ampere range. *0.3%/Y on the 2 ampere
range.
Maximum Allowable Current: 300 amperes rms.
Maximum Conductor Voltage: 600 volts rms.
Conversion Ratio: 0.1 volt rms per ampere.
4-19.
MODEL 1010 SINGLE RACK MOUNTING KIT.
4-20. The Model
1010 is a single rack mounting kit
with overall dimensions 5-I/4 inches (133mm) high
and 19 inches (4l33mm) wide.
4-21. MODEL 1017 DUAL RACK MOUNTING KIT.
4-22. The Model 1017 is a single/dual mounting kit
with overall dimensions 5-l/4 inches (133mm) high
and 19 inches (483mm) wide.
4-23. MODEL 1641 KELVIN TEST LEAD SET.
q-24. The Model
1641 test leads are for use in
making 4-terminal measurements. The test leads (1
pair) are 1.2m (48 inches) long twin-lead cables.
Each cable is terminated by a twin-banana plug and a
spring-clip Kelvin contact. Plug twin banana plug
into DMM horizontally (HI to HI and LO to LO).
4-25. MODEL
1901 CURRENT ADAPTER.
4-26. The Model 1901 allows your DMM to read dc
current from 1nAldigit to 2000mA. With the 1910 AC
Voltage Option it reads from lOnA/digit to 2000mA.
The Model 1901 plugs into the INPUT terminals of the
191. Maximum allowable continuous voltage drop
(full scale input voltage burden) is 200mV. Shunt
resistors are connected so as to eliminate contact
resistance errors. Use the Model 191 200mV dc range
and 2V ac range, for dc current and ac cut-rent
respectively. Input voltage burden can be reduced
by selecting the lowest shunt that provides the
necessary resolution.
4-27. MODEL
1910 AC VOLTAGE OPTION.
4.28. The Model 1910 (not shown) is a factory or
field installable option which allows your DMM to
read ac volts from IOuV/digit to 1OOOV. The Model
1910 is internally installed in the Model 191. It
is important to note that field installation or
removal/replacement of the Model
1910 requires
recalibration of ac voltage. Specifications for the
1910 are given in Table 1-l and ac voltage
measurements are described in Paragraph 2-27.
4-29. MODEL 1913 CALIBRATION COVER KIT.
4-30. The
1913 (not shown) contains a
calibration cover and an Instruction/Service
Manual for the Model 191 DMM. The calibration
cover is installed in place of the normal 191
top cover during calibration.
It allows the 191
to reach normal internal operating temperature
and has openings that are marked to facilitate
making the calibration adjustment.
4-2

MODEL 191 DMM THEORY OF OPERATION
SECTION 5. THEORY OF OPERATION
5-l.
GENERAL
5-2. This section contains circuit descriptions for
the Model 191 DMM and the Model 1910 AC Voltage
option. The information is arranged to provide d
description of overall instrument operation, fol-
lowed by descriptions of individual functional cir-
cuit blocks. To facilitate understanding, the des-
criptions arc keyed to accompanying simplified block
and schematic diagrams. Detailed schematics. of the
Model 191 and Model 1910 are provided in Section
1.
5-3. OVERALL FUNCTIONAL DESCRIPTION
0.00052 resolution. Whe
tion is installed, ac
1000 volts can be "leas"
of the Model 191 is
converter which uses b"
slope conversion techni
control of the microcc
high conversion speeds
some of the Imajor bcnef
Other benefits and func
to the use of the micr(
the number of componer
filtering; pushbutton n
signal; and automatic 2
will bc described 1n
sectlo".
5-4. The Model 191 is a 5.112 digit, ~200,000
count, bench DMM with 5 dc voltage and 6 resistance
ranges standard. It has luV and Inn sensitivity, and
,.“,“.-..J
MODEL 1910 ACV
AC VOLTAGE O--I- n
DCV ATTENUATOR/n
REF. RESISTORS ACV
& RAFIGE SWITCHING q
f2 ACV
A/D
COE'VERTEI
VZERO
VSIG
VREF
FIGURE 5-l. Simplified Signal Flow Block Diagram, Mod. 41
191 DMM.
57+
V/F
PULSES,
cnw.0111
PICRO-
COMPUTER
cl
DISPLAY
5-1

THEORY OF OPERATION MODEL
191 DMM
Charge-Balance
in
(b) Timing.
--I t-
loome‘
Inteqratian_Ph_asej Vsig 1 Vzero I Vsig I Vref I Vsig I vrero ----
Reading Updates 200msec
FIGURE 5-2. Block Diagram of DC Voltage Measurements.
5-5. Figure 5-1 provides a simplified signal flow
block diagram of the Model 191. As previusly men-
tioned, operation of the Model 191 is centered
around the A/D converter, operating under the con-
trol of the nicrocomputer. The A/D converter is
designed to handle input signals up to t2 Vdc, and
up to four separate signals (i.e., VLEKO, VSIG, Vn
and VREF). It can be seen from the diagram that
the function switches control which of the siqnals
that can be applied to the A/D convcrtcr, as well
as the signal conditioning path of the input signal
applied to the input terminals. The microcomputer,
through the A/D Control lines, controls the sf-
quence and timing of signals applied to the A/D
converter. Timin includes a precise 100 milli-
second integration period for the charge balance
phase of conucrsion, up to 1 millisecond for single
slope conversion and the necessary delays to allow
an input signal to Settle and to perform nathema-
tical calculations and housekeeping chores. The
microcomputer also provides the automatic zero and
automatic calibration corrections to eliminate zero
and gain errors frown the signal to be displayed.
This is done mathematically and requires that more
than just VSIG be converted. Three signals are re-
quired for dc voltage mesurements, and four signals
for ohms and JC volts. Lath signal required for
the wzas~~rement is applied to the A/D converter and
the resulting digitized value is stored in ~memory.
The microcomputer muses the stored values to calcu-
late the reading and sends it to the display. In
this way, the microcamputcr corrects for zero and
gain errors, arId the displayed reading is the digi-
tized value of the input signal within the speci-
fied accuracy of the instrument.
5-2