Keithley 191 Service 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,
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,
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

will provide readings from 1OuV to
4 ra"gES. This option may alsn be purchased later.
and field installed.

manual-ranging bench digital multi-

and 2 and 4 terminal measut-e-

1910 AC

Voltage Option, your "MM

lOO(1 volts ac on

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? devi­ations from a set value. The NULi~ light indi­cates that the function is dctivc for "p~rat"r­saietv and to lessen the? ChdrlCC Of I.IP‘3S,II'P,~IPnt

FIGURE

l-l.

Model

191

Digital Multimeter

I-1

GENERAL INFORMATIOP

MODEL

191

DMM

Continued.

l-3.

A Micro-processor
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
display.

A reduction in the number of parts while main­taining high accuracy and speed of measurement ­simplifies high accuracy measurements and cali­bration of the instrument and provides higher

mean time between failures.

-1EEEEE error message indicates improper
uses of the instrument - prevents erroneous read­ings and reduces possibility of injury to the
user or damage to the instrument.

Each range has:
Automatic polarity operation minus sign dis­played, 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.

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.
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.

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.

Some of these accessory ncde1s are:

based design that

and reduced noise on

It can be used

the

Hi th

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
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.
l-7.

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.
1-9. Safety symbols used in this manual are as

follows:

The b
this Manual.
CAUTION statements with regard to proper use and

handling of the instrument.
instrument may occur if these precautions are
ignored.

This\ ~
this Manual.
on the instrument which are potential shock

hazards.
statements with regard to proper use and handling
of the instrument.
result if these precautions are ignored.

l-10.

I-11.
given in Table 1-I.

the warranty, contact the Keithley

CHANGE NOTICES.

Improvements or changes to the instrument

SAFETY SYMBOLS.

IMPORTANT

symbol can be found in various places in

Carefully read the associated

Oamage to the

svmbol can be found in various places in

This symbol indicates those areas

Carefully read the associated WARNING

Serious personal injury may

SPECIFICATIONS
Detailed specifications for the Model 191 are

l-2

MODEL

191

DMM

GENERAL INFORMATION

TABLE l-l

SPECIFICATIONS

OPERATING INSTRUCTIONS

P1006
MODEL
AC OPl

YODEL

191

DMM

e

LINE/FUSE

(F101)

LINE'VOLTAGE
SELECT SWITCH

(S102)

2-o

FIGURE 2-1.

Location of Line Fuse and Line Voltage Select Switch.

MODEL 191 DMM

~OPERATING INSTRUCTIONS

SECTION 2. OPERATION.

INTRODUCTION.

Z-l.
2-2.
incoming
operation of the Model

2-3.
2-4.
mechanically and electrically before shipment. Upon

receiving the Model 191,
shipping container and check for any obvious damage
which may have occured during transit.
damages to the shipping agent.

original

required.
Model 191 orders:

2-5.

2-6.

on how to connect the Model 191 to your available ac

This section provides information needed for

inspection, preparation for use, and

191 and

UNPACKING AN0 INSPECTION,

The Model 191 was carefully inspected, both

packaging materials if reshipment is

The following items are shipped with all

a. Model 191 OMM.
b. A Copy of this Manual.

Installed or separate optional accessories, as

C.
ordered.

PREPARATION FOR USE.

The Model 191 is shipped ready-for-use on the

line voltage marked on its rear panel. Instructions

line power are contained in Paragraph Z-7 Line
Power.

its accessorieS.

unpack all items front the

Report any

Retain and use the

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.

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.

Line Voltage Selec~tion.

2-9.

Z-10. Set up the Modejl 191 to operate on your

available ac line voltage as follows:

Turn the DMM botltom side up and loosen the

a.
four screws in the boqtom cover. These sci-ews are
held captive hy rubber O-rings.

Hold the top an?

h.

prevent their separatjon and turn the DMb1 over to
normal position. Rem+, the top cover.

Set switch

c.

line fuse, as indicated in Table 2-1. for your

available input line ~ voltage.

shown in Figure
d. Reinstall the top cover.

8102

2-l.

bottom cover

aind install the proper rated

if the line

together t"

These items are

2-7. LINE POWER
2-R.
cord which mates with a 3rd wire earth grounded
receptacle.
voltage ranges of 60 or 50 Hertz ac power.
voltage ranges are 105 to 125 volts and 210 to 250
volts.
positioning an internal slide switch and installing
the appropriate fuse for that range.

your available ac power inaccordance with the

The Model 191 is provided with a 3-wire line

The instrument will operate on 3

Standard

Either of these ranges may be selected by

An optional
line voltage range of 90 to 110 volts is available
by special order.
different transformer.

following procedures:

Instruments with this range use a

Connect the Model 191 to

TABLE 4-l.

Line Voltagq Selection

*Requires special~factory installed

transformer.

2-l

OPERATING INSTRUCTIONS MODEL

191

DMM

NULL

FUNCTION*

FIGURE 2-2.

POLARITY (NEGATIVE Is INDICATED, POSITIVE Is IMPLIED

rblHEN MINUS (-) DISPLAY IS OFF.)

Rear View Showing Line Cord.

/

2-2

1 SET POWER ON

(I.3

*SEE TEXT, PARAGRAPH 2-15.

I

@j SELECT RANGE

4 CONNECT SOURCE

0'

FIGURE 2-3. Operating Controls.

I", 3 ,.

OPERATING INSTRUCTIONS MODEL

2-2

Z-11.

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:

2-13. OPERATING INSTRUCTIONS
2-14.
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

"SC?.

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.
OMM a5 f0110w5:

Connecting Line Power.

WARNING

\,

Ground the instrument through a properly earth­grounded 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.

Plug the power c"rd into a properly grounded

a.
outlet of a source having the selected line
voltage.

Operate the Model

b.
Paragraph Z-13.

The basic operating instructions for the

Until this familiarity ha5 been achieved, best

Refer to Figure 2-3 and operate the

/&CAUTION
no not exceed the Maximum Inputs limits given in
Table 2-2.

Turn on the power by depressing the ON/OFF

a.
pushbutton.
it is useable immediately, but a 1 hour warmup is
required to obtain rated accuracy.
additional hour may be required from temperature

extrelne5.

Select the function with the ACV, IDCV or n

b.
pushbuttons.

Select the range by depressing the appropriate

c.
pushbutton,

Connect the source to the INPUT terminals and

d.
make the ,n,easurement.
Section 4 should he (used as required.

If the instrument is within 18-2R°C,

191

as described in

191

through day-to-day

up to 1

Accessories described in

Summary of M

UNCTION

2-15. NULL FUNCTION.
Z-16.
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,

measure variation5 db"'
example,
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
voltages greater than

A,0 c"nverter (200,OOI

range would occur at *
readings less than -1
less than +lV) because

ing of
dynamic range of the
Figure 2-4.
Dynamic Range and the
exceeded and thus, bot

of the meaS"i-erne"t.

dynamic range can be e

The NULL functi

the null f

+1.00000 VDC

t1.00000

-199,999 coun

TAB

RANGE

ZOOmV, 2

zov-1200

ALL

ALL

VL

In ocv

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 read­55 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.

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.

191

For in-

DMM

2-3

OPERATING INSTRUCTIONS

199,999

DISPLAY DYNAMIC RANGE

A

/ NULL \

VA&UE

199,999

MODEL

191

MEASUREMENT
DYNAMIC RANGE
IN NULL MODE

(SHADED)

DMM

\

v

INPUT DYNAMIC RANGE

FIGURE 2-4.

Effect of NULL function on Dynamic

Range of DCV Measurement.

Z-18.

described in DC Voltage and n Measurement
Procedures.

2-19.

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 signifi­cant digits are blanked. Example:
Overrange is indicated whenever the dynamic range of
DCV measurement is exceeded. With the NULL function
off,
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.

The Use of NULL as pushbutton 'zero" is

OVERRANGE INDICATION.

(-I--.---).

this occurs above

*199,999 CO”“tS. As

/

2-23. DC VOLTAGE MEASUREMENT.
2-24.

microvolt/digit to

displayed reading is 139999. Overrange is indicated
by (-)I-----, except on 1200 volt range. On the
1200 volt range,
maximum allowable input voltage. Maximum allowable
input: 12OOV for
continuous on the 200mV and 2V ranges; 1200 volts
continuous on the ZOV-1200 volt ranges. Use the
Model

The Model 191 reads dc voltages from I

1200 volts. The maximum

the display can read beyond the

I

minute maximum,

191

to measure dc voltage as follows:

CAUTION

A

Do not exceed the maximum allowable input voltage
limits. Instrument damage may occur.

700

volts

2-21.
2-22.
function is selected. These selections are:

2-4

ERROR INDICATION.

-1EEEEE is displayed when an improper range -

ACV function - when AC option is not installed.

20Mn range - with ACV or DCV function selected.

ACV function with 2000, 200mV range selected.

a.

Turn on power with the ON/OFF pushbutton and

depress the DCV pushbutton.

b. Select the desired range from the five ranges
available.
range pushbutton.
by the

The decimal point is positioned by the

The 1200 VDC range is selected

1000

pushbutton.

MODEL

c.
off) unless measurements are to be made as
deviations from a preset value.

d.

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.
displayed digits, polarity sign and decimal point

locations.

in volts.

f.

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.

microvolts or several tens of microvolts. set

zero as follows:

191

DMM

Ensure that the NULL pushbutton is out (light

Connect the signal to be measured between the

For the top four ranges, merely observe the

The top four ranges are direct-reading

For the 200mV range, ZERO must set with the

These voltages may be only a few

1) Set

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.

Model

191 to

200mV

range.

g. The optional Mode
be used with the Modt
up to 40 Kilovolts, a
Paragraph Z-30.

2-25.
Z-26.

millioha/diqit to 20
rarqes.

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

RESISTANCE (n)

The Model

The Model 191

191 I

tlodcl 191 to measure 7

&CA"

MAXIMUM ALLOWABLE I

36OV peak, 25UV rms
voltage.

a. Turn on power and
h. Connect the circ

INPUT terminals and I
the six ranges avail
positioned by the ran

Instrument

IOPERATING INSTRUCTIONS

1600

High voltage Probe can

191 to measure

reduced accuracy. Refer to

JASUREMENT
IN ~nedsures resistdrre fron 1

eqohms.

prwides d~tondt>c 2-wit-e or

This nedns that if the ohms

ed, the rneasurcment IS auto­Ial if the sense leads are
iureiaent is done 2.terminal.

eme nts

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.
e pushhutton.

SEC Table 2-3 for

rated

The decimal point is

dc voltages

dCC"l'dCY (tl

TABLE 2-3

Resistance Ranges

RANGE

SETTING

200 n***

2k n

20k n

200k n

2000k "

20M n

MAXIM""
READING

199.999

1.99999

19.9999

199.999

1999.99

MAXIMUM OUTPUTS'

I(Shorted) V(Openl

-4mA -4OOmV 7n

-4mA -4V 22"

-4OOuA

-4OuA

-4uA -4v 7000

1g.gggg t-““-

OVERRANGE: MAXIMUM

-l---_

* HI binding post (red) is negative.
** Maximum resistance per lead for additional

l

** Zero must be set by NULL to obtain rated accuracy.

1

digit en-or.

.,

-4v

-4v

-4v
ALL RANGES

-r

ALLOWABLE

360Vpeak,

MBX.

2200n

INPUT:

4-w,

700

22on

;*

250Vrms

2-5

OPERATING INSTRUCTIONS

MODEL 191 DMM

For 4-terminal measurement c"nnect the sense

c.
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,
function to obtain rated accuracy.
necessary to colrlpfnsate for test Icad resistance

On Z-wire & Thermal Emfs on 2 & 4-wire.

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.

diode testinq.

resistance Of J

approximately 190n. (Hiqh Terminal is Negative)

Z-27.
OPTION).

2-28.

reads ac voltages from 10 microvoltsldigit to 1000

lCK0 rmust be set with the NULL

Zeroing is

set LPr"

Thr 2Kn range is rccomxnded for

On this range the forward oil

silicon diode

Ac VOLTAGE MEASUREMENT (WITH 1910 AC

With the Model 1910 option, the Model 191

will read

volts. The instrument is avera9e responding and

displays the root !:ledo square

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,
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:

a. Turn on power with ON/OFF pushbutton and
depress the ACV pushbutton.

h.
available. The decinlal point is positioned hy the
range pushbutton.

C.
off) ""less measurements are to
deviations front a preset value.

the display can read beyond the lmaximum

/!&CAUTION

Do not exceed maximunl allowable input voltage.

Instrument damage may occur.

Select the desired range from the 4 ranges

insure that the NULL pushbutton is out (light

NOTE
Do not use NULL to zero Lhe range.
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.

accept wres,

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.

spade lugs or banana plugs for ease

value Of a 51~ W~VC

he Imade as

A Sllldll

The hinding posts

2-6

MODEL

191

DMM

SECTION 3 PERFORMANCE VERIFICATION.

3-1.

GENERAL.

Performance verification may be performed upon

3-2.
receipt of the instrument to ensure that no damaqc
or nisadjustment has occurred during transit. Veri­fication 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
Keithley rcpresentativc or the factory iomedi­ate1y.

3-3. RECOMMENDED TEST EQUIPMENT.
3-4. Kecommended test equipment for performance

verification is listed in Table 3-1. Alternate test
equipment nay be used.
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.

any point,

However, if the dccuracy of

contact your

PERFORMANCE

VERIFICATION

3-5. ENVIRONMENTAL COND1TIONS.

All neasurenents slhouid be made dt a" dnbirnt

3-6.

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.
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,
wavva"ty, as noted above.

3-9.

Use the f"llowin(i procedures to verify the

~nlcss the :instrwwnt 15 still iindrr

NOTE
Performance verificbtion should bc pcrfonncd by
qualified pcrsonnel~ using accurdtc and rcliablr
test eq"lpncnt. ~

initial Conditions;

Recommended Test Equipment For Performance Vcrifica

T

ITEP

DESCRIPTION

-

A

DC Calibrator

8

AC Calibrator

C

High Voltage Amplifier

(Used with Model 745A)

"

IIccade Resistor

E

Kelvin-Varlcy Voltage
Uivider

(Used with Model 343A)

TABLE 3-l.

SPECIFICATION

190n, 1.9kn,19kil,
190k0,1.9Mn, lOMn,
t0.017,

.19v, 1.9v

with .2ppm Terminal

Linearity

tilot

1.

72OA

3-l

PERFORMANCE

VERIFICATION

MODEL

191

DMM

b. Turn on the Model 191 and allow it to wdrrl up

for one hour.

WARNING
Sonc procedures require the USC of hi9h volt­age. Take cat-c to prevent contact with live
circuits which could cause electrical shock re­sulting in injury or death.

3-11. DC Voltage Accuracy Check ('ZOV to 1ZOOV

R‘?"%? Applied Allowable Readings at 18O to 28'C

I I

I 4

I

3-12. DC Voltage Accuracy Check (200mV and 2V

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.

Select each rcnaining range and apply r-c-

!i.

quircd voltage specified in Table 3-2.
that the reading is rrithin specifications.

f. Repeat all checks with negative voltage.

DC Voltaqc Performance Check (2OV to 12OOV Ranoc).

Voltage

I

Ranges).

2. Sclcct DCV and 200mV range.
b. Disconnect test leads at the DC calibrator

(A) and short them.

Ibutton. Verify a display indication of OO.OOOmV

+O.OOlnV flashin9.

t

I

TABLE 3-2.

99.986 to 100.014

999.86 to 1000.14

9.9986 to 10.0014

Depress the Model 191 NULL

Verify

c. Connect the DC calibrator (A), Kelvin-Varley

Voltage Divider (E) and Model 191 as shown in
Fi9urc 3-1.

.0190000 output.

Temporarily disconnect the test leads from

i,

the DC calibrator (A) and short them.
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

I

1

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.

Select the 20 and 200 volt ranges and apply

d.

the required voltages as specified in Table 3-3.

Verify that the readings are within specifi-

Set the voltage divider (E) for

DepESS

3-2

DC

Calibrator

(A)

+

OUT

FIGURE 3-l.

1.0

HIGH,

Kelvin -

Varley

LOW

Voltage

LOW

Divider

(El

Test Circuit For 2OCmV And 2V Accuracy Check.

MODEL

191

MODEL

191

DMM

PERFORMANCE

VERIFICATION

To check the 1000 volt range, connect the

2.

High Voltage Amplifier (Item C, Table 3-l) to the

output of the AC calibrator per the manu­facturer'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

Voltage

Allowable Readings

at 18’= to 28’C

at

2:;

2oov 1oo.oov

1ooov

10 1 .ooov .ooov

1ooo.ov

9.9868 .99868 to to 10.0132V 1.00132V

99.068 to 100.132V

998.00 to 1002.00v

m

2ov 1o.ooov

at 20ktlz

2ov 1o.ooov

at 100kHr

9.9868 to 10.0132V

9.9868 to 10.0132V

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.

are within the specifiied limits.

3-14.

Resistance (n) Accjuracy Check.

5. Select resistancejfunction by depressing the
R pushbutton.

0. SeleCt

C.

3-I) to the DMM.

L!.

sate for lead resist+xe by depressing the IiuLL
for a display indicition of 00.000

flashing.

Set the decade rjsistar to 1900. Verify that

J2.

the reading for the! 200n range is within the

limits specified in Tbblc 3-4.

f. Select the Zkr! rpngc.

Set the decade rcpistor to LC~O and reset the

9.
NULL.

h. Set the decade rbsistor to 1.900kn.

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 rc­sistance as specifiei in Table 3-4. Test each
item in the table andi verify that each wading is

within specificationsi.

200n rc3ngfi

Connect the decape resistor (Itw 0. Table

Set the decade rjsistor to zero and comp~n-

Veinfy that the DMkl readings

~

* 00.301

vwify

TABLE 3-4.

Resistance Accuracy Check.

RANGE RESISTANCE

zoon 190n

2kn

20kn 19.00 kn

200kn

2000kn

20Mn

* Manufacturer's specified uncertainty of the decade resistor (D)

This uncertainty has been added to the specified accuracy of the

obtain the allowable reading.

1.900 kn

190.00

1900.0

kn
kn

10.000 nn

ALLOUABLE READING AT 18' to 28'C

189.955 to 190.045ri

1.89956 to 1.90044 kn

18.9956 to 19.0044

189.956 to 190.044

1899.22 to 1900.78

kn -p
kn 219 diqits
kn

9.9908 to 10.0092 Mn

~ *

,

?I9 digits
219 digits

+ 9 digits

?(19

digits

410

digits

3-3

MODEL 191 DMM

ACCESSORIES

SECTION 4.

4-1. GENERAL.

This section describes the various accessories

4-2.
and options available for use with the Model 191
DMM.
4-3. LINE POWER OPTION.

The Model 191 can be powered by a line voltage

4-4.
of 90 llOV, 50 - 60Hz with the special factory

installed transformer option.
available by ordering a Model

- 60Hr).

4-5~ MODEL

4-6.
has a
on the DMM corresponds to 1 kilovolt.

TO operate:

Volt range.
1600 to the INPUT terminals.
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

Division Ratio:
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:
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
be made from 0 to 50 amperes DC and from
50 amperes AC with AC Voltage option.
O.OOlohm
current will correspond to 50 millivolts.

To operate: Connect separate CUT­rent leads (not furnished) between
the source and the Model 1651 hex-head bolts.
leads that are rated up to 50 ampere capacity.
Connect the voltage leads (furnished) between the
Model 1651 screw terminals and the DMM INPUT

1600

HIGH VOLTAGE PROBE.

The Model 1600 extends the DMM to 40kV. It

1OOO:I

division ratio which means that 1 volt

Set the DMM to OCV and 200

Connect the banana plug on the Model

imegohms.

1OOO:l.

tO.Ol%

1651

kl%

4 terminal shunt.

per "C;

allows current measurenlents to

This option is

191 DMM (90 IlOV, 50

Connect the alli-

eO.l%

per year.

10 t0

It is a

A fifty ampere

Use

ACCESSORIES

terminals.
DCV and 200 millivolt iange.
on DC 200mV.

4-9.
4-10.
leads 1.2~1 (48 inches) 1 ng, terminatedY p
with banana plug and spri,ng-action clip-on
probe.

4-11. MODEL 1682 RF

4.12. The Model 1682 ex
voltage response of the

lOOkliz to lOOMHz,

To Operate:

and 200 Volt range.

to the DMM INPUT termina
Specifications:

Voltage Range: 0.25 to
Transfer Accuracy:

peak responding calibr ted in rms of a
sinewave.

Input Impedance:

Maximum Allowable Input:1 30V pms AC. 2OOV UC.

Accessories Supplied: shraight tip. hook tip,

ground clip, hi adapt+, banana plug adapter.

4-13.
4-14.

long with 12 screw-in tips - 2 banana
plugs, 2 spade lugs. 2 alligator clips ,I\
with boots, 2 needle ti
and 4 heavy duty tip plugs.

4-15.

4-16.

vinyl case with a fitte

insert with room for the Servic
Manual and small access+ies.

4-17.

4.18.

clamping onto a single conductor.
the current path is unngessary.

detects current by sensilng magnetic field produced

by current.

To Operate: Set the OM

volt

Set the DMlj to ACV and 2V range or

MODEL

1681

CLIP-04 TEST LEA0 SET

The Model

NODEL 1683 UNIVERbAL TEST LEAD KIT.

Two test leads, 11.2m (48 inches)

Model 1684 Carrying Case

The Model 1684 is a hard

MODEL 1685 CLAMP-ON AC CURRENT PROBE.

The Model 1685 "edsure~ AC current by

range.

1681 CO tdins two

Set the DMM~to DCV

Connect t/he Model 1685 to the DMM

!

"SC NULL to zero

PRO

Con ect the Model 1682

5.

1

0 volts rms.

to.5 B, 1OOkHz to 1OoMtlZ

1

4 megop shunted by 3pF.

s with chucks

v

foam

1

Interruption of

The Model 1685

to ACV and 20

4

/I"

f! J

A

\

/

i

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:

200 ampere range.

range.
Maximum Allowable Current: 300 amperes rms.
Maximum Conductor Voltage: 600 volts rms.
Conversion Ratio: 0.1 volt rms per ampere.

4-19.

4-20.
with overall dimensions 5-I/4 inches (133mm) high

and

MODEL

1010

SINGLE RACK MOUNTING KIT.

The Model

19

inches (4l33mm) wide.

1010

?O.O5%/"C an the 20 and

*0.3%/Y on the 2 ampere

is a single rack mounting kit

4-25.
4-26. The Model 1901 allows your DMM to read dc

current from 1nAldigit to 2000mA. With the
Voltage Option it reads from lOnA/digit to 2000mA.

The Model 1901 plugs into the INPUT terminals of the

191.

(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.

MODEL

1901

CURRENT ADAPTER.

1910

Maximum allowable continuous voltage drop

AC

4-21. MODEL 1017 DUAL RACK MOUNTING KIT.

4-22.
with overall dimensions 5-l/4 inches (133mm) high

and

4-23. MODEL 1641 KELVIN TEST LEAD SET.

q-24.

making 4-terminal measurements. The test leads

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).

The Model 1017 is a single/dual mounting kit

19

inches (483mm) wide.

The Model

1641

test leads are for use in

(1

4-27.

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.
1910 is internally installed in the Model
is important to note that field installation or
removal/replacement of the Model
recalibration of ac voltage.
1910 are given in Table 1-l and ac voltage

measurements are described in Paragraph 2-27.

4-29. MODEL

4-30.
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.
to reach normal internal operating temperature
and has openings that are marked to facilitate
making the calibration adjustment.

MODEL

The

1913

1910

AC VOLTAGE OPTION.

1913

CALIBRATION COVER KIT.

(not shown) contains a

The Model

191. It

1910

requires

Specifications for the

It

allows the 191

4-2

MODEL 191 DMM

SECTION 5. THEORY OF OPERATION

GENERAL

5-l.

5-2. This section contains circuit descriptions for
the Model 191 DMM and the Model
option.
description of overall instrument operation, fol­lowed by descriptions of individual functional cir­cuit blocks. To facilitate understanding, the des­criptions 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.
5-4.

count, bench DMM with 5 dc voltage and 6 resistance

ranges standard. It has luV and Inn sensitivity, and

The information is arranged to provide d

OVERALL FUNCTIONAL DESCRIPTION

The Model 191 is a 5.112 digit, ~200,000

1910

AC Voltage

THEORY OF OPERATION

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".

,.“, “.-..J

MODEL 1910

AC VOLTAGE

DCV ATTENUATOR/n
REF. RESISTORS
& RAFIGE SWITCHING q

ACV

O--I- n

ACV

ACV

f2

COE'VERTEI

VZERO

VSIG

A/D

VREF

57+

V/F
PULSES,

cnw.0111

PICRO-

COMPUTER

DISPLAY

FIGURE 5-l.

Simplified Signal Flow Block Diagram, Mod.

41

191

cl

DMM.

5-1

THEORY OF OPERATION

MODEL

191

DMM

(b) Timing.

loome‘

--I t-

Inteqratian_Ph_asej Vsig 1 Vzero I Vsig

Reading Updates

FIGURE 5-2.

Block Diagram of DC Voltage Measurements.

200msec

Charge-Balance

I Vref I Vsig I

in

vrero ----

Figure 5-1 provides a simplified signal flow

5-5.
block diagram of the Model 191.
tioned,
around the A/D converter, operating under the con­trol of the nicrocomputer.
designed to handle input signals up to t2 Vdc, and
up to four separate signals (i.e., VLEKO, VSIG, Vn

and VREF).
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 sf­quence and timing of signals applied to the A/D
converter.

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-

5-2

operation of the Model 191 is centered

It can be seen from the diagram that

Timin includes a precise 100 milli-

As previusly men-

The A/D converter is

tical calculations and housekeeping chores.
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 re­quired 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 digi­tized value of the input signal within the speci­fied accuracy of the

instrument.

The

MODEL

191

DMM : THEORY OF OPERATION

5-6.

DC Voltage Measurement.

5-7.
5-2, the input signal either goes directly to the

A/D or is connected across a decade attenuator with
a total resistance of 10 megohms. The attenuation
of the dc input signal is determined by the range
selected.
signals to the A/D converter arc rcquircd for dc
volts operation (i.e.,
signal is presented to the AID input and (measured
for 100 milliseconds (See A/D Converter discuss­ion). Each digitized value is stored in memory and

then used to calculate a reading by the formula:

In dc volts operation, as shown in Figure

As previously mentioned, three input

"SIG, "ZERO and VREF). Each

(a) BLOCK DIAGRAM

-4oomv/-4V
Voltage

SO"rCe

r- --i

eference Resistor Decade

It can be seen that
tracted from both the
then the ratio is ti
needed because the r
milllivolts on the loti
5-R.
gram, VSIG is medsure
and VREF are alternati
This permits the disp
two integration (char!
ing that up to an addi
required (to complet
counting of the remail
tic.31 computations),

made approximately (
approximately 4 read'

As shown in th

the zero error is sub-

II and the reference, and

Multiplication by 2 is
nce is 2 volts (or 200
ic range).
ling portion of the dia­'ry other time dnd VZtRO

in the other tine slots.

3 be updated after every

am?) phases. Consider­11 70 milliseconds nay bc
Igle slope conversions.
in counters and mathcma­I display update cdn be

210 nilliseconds, or

;econd cd" be obtsined.

%

(b)

TIMING

9 IOOms /---

INTEGRATION PHASE 1 DELAY 1

READING UPDATE

FIGURE 5-3.

Block Diagram of Resistance Measureme:

VSIG 1 VLEKO DELAY

cl

'0 VKEt

_.

4

n%.

5-3

THEORY OF OPERATION

MODEL 191 DMM

5-9. Resistance Measurement.

5.10. In ohms operation, as shown in Figure 5-3,
the ohms voltage source is connected as an input to
the A,0 converter and to one end of the reference

resistor decade. The resistance reference resistors

are the same resistors that are use for dc volts

attenuation, but unlike dc volts, where only the
ratios affect accuracy, the absolute characteris-

tics of the resistors determine accuracy of the

ohms measurement. The value of the ohms reference
resistor (Itn) is determined by the range selected.
An ohms source voltage of -400 millivolts is used
on the 200~2 range, and -4V is used for all other n
ranges.
signals to the A/D converter are required. Each
signal is measured for 100 milliseconds and its
diyitirec value is stored in memory. The microcom­puter then calculates a reading using the formula:

It can be seen that "$2 - VKEF is the voltage across

Kn (Ifi X rtn) and that "SIG VZEKO is the volt-

age acrossRX ('n X i(X). therefore:

For resistance measurements, four input

nD,SP = vslc - VZEKO

vn VREF

includes
added to
,"easurt3"ents,
RX and the effect of lead resistance can be
calculated as shown.
this discussion why the stated accuracy for the 200

n range requires that the effect of lead resistance

be cancelled with the NULL pushbutton for both
Z-terminal and &terminal measurements.

the rESlSta"Cf of RI

the unkown (RX). For &terminal

the n SENSE leads are connected to

It can be readily seen from

and 'I4

Thus, the ohms reading depends only an the value of
the ohms rcfcrfncf resistor ("n).

5-11.
diagram, there are two 100 millisecond delays and
four 100 millisecond integration p?riods needed to
gather the information for calculating a reading
with the above formula.
times, as described for DC Measurements, are con­sidered it might appear that approxilnately 2
seconds would be necessary for three readings.
IloWeYfr, in actual operation, approximately three
valid readings per second can be obtained by calcu-

lating a new reading after each 300 milliseconds,

using the new data and the stored data from the

previous 300 milliseconds.
5-12. Up to this point in the discussion, the
Effect of lead
n~easurement has not been considered. As shown in
Figure
displayed ohms reading in both Z-terminal or 4­terminal meas"rements.

resistances of the test leads have been designated
3s '31 @4. If n
terminals are not connected to Rx, the sensing
occurs at the HI
rfsistors

AS shown on the tilning portion of the

When the additional delay

resistance an the resistance

5-4,

lead resistance can

For this explanation,

SENSE HI

KS

LO INPUT terminals through

and

the displayed

affect the

and LO

reading

FIGURE 5-4. Affect of Lead Resistance in

Ohms Measurements.

5-4

MODEL

191

DMM

THEORY OF OPERATION

FIGURE 5-5. Block Diagram of AC Voltage Measure+nts.

5-13. AC Voltage Measurement.
5-14.

5-5, the Model

between the input and the A/D converter. The
converts the ac input voltage to a dc voltage be­tween zero and -2 volts. On other than the 2V
range, the input signal is divided by 10,
1000 - depending on the range selected. For ac
voltage measurements, four input signals to the A/D
converter are required. Each signal is measured for

Where VSIG is the

line) is its dc offset, VREF is the 2V reference
and Vn is signal ground. The 2 is required because
of the 2V reference.

phase measurement, with the input signal measured
only once during the measurement, the maximum con-

version rate for ac volts is two valid readings/

second.

5-15.

5-16.
is given in Figure 5-6, and its waveform is shown
in Figure 5-7. In operation, the microcomputer
provides time division multiplexing of the input
signals by controlling switches S1 through 54.

The sequence and timing of the switches is depen­dent on the function selected (DC Volts, Ohms, or
AC volts).

input MUX switches to achieve the necessary high

off resistance, low leakage current and low thermal

In ac volts operation, as shown in Figure

1910

AC Voltage Option is placed

1910

100, or

100 milliseconds and its digitized value is stored
,n memory.
reading using the formula:

The microcolnputer then calculates a

V,, = L?VSIG - VZEKO).

(VKEF

1910

A/D Converter.

A simplified schematic of the A/D converter

Copper leaded JFETs are used for the

vn)

output, VZERO (AUTOZEKO

Since ac volts is d four

characteristics.
ing, high Z alnplificrlthat looks dt each input siq­nal with either a xi or. x10 gain. A gain of xi0 IS
used on the 200mVDC~ and 2000 ranges, all otner
ranges
applied to the Tra sconductance Ainpiifier. lhis
amplifier provides t o
input voltage to d cufrent, which goes to the ante­grater when requested, and provides a" offset CUT­rent so that its hi alar
verted to unipolar ou

5-17.

operates first in a
then in a single sl pc
second interval was selected to look dt each input
as the best compramis,e to achieve good line rcjcc­tion (50 and 60tlr) dbd relatively fast convex-soon
speed. A CB phase is ibegun when INPUT !II>AKLC goes
1OW.
period that allows thb signal to settle after tur-n­lng on the appropriate input MUX switch. The delay
is software generat d and is dcpendcnt on the
function selected,

INPUT DISABLE is released, Iin IS connected to
the integrator, and
flops then act as a!comparator, providing timing
and control. After V
U106A. 91 goes high at the next positive going
clock edge.

wing)
the ikt$raraPd)rqs "'bb ""fs gre~~~:cct:ha/C"21:~

maXlGl""\,

negative.

d$is also low at
(h low. At the next pegative clock edge

I ater) ,

by 42 going low agaio. What has happened to this
point is that lC8 wbs turned on for one clock

“SE xl.

The A/II conve ter, as shown in iigurc 5-I.

This occurs al the completion of d dcldy

and th"

1~0 is turted off and D] is enabled

TheI input Uuffcr is a non-~nveit-

The output of the input buffer IS

functions. It converts the

1

input

voltdqes

put cur-rents.

barge balance (CU) phase. and

(8s) phase. A 100 mills-

/

5 given is Table 5-1. llben

,"

o ramps positive. The D flip

d

exceeds the " threshold of

At theI next clock edge (negative

P

13 v.

s time which sets and holds

thil

imediately rmp5

are con-

(1 cycle

5-5

THEORY OF OPERATION

MODEL 191 DMM

El--

l/O LINES FROM UC.

*

+v

~RATDR -

U106A

D,

CK

’ CL

50OkHZ
CLOCK

INPUT

QI

U106B

-02 Q2 ­CK -

QZ--

r’-

cl

1

V-F
&iSE
OUTPUT

SINGLE-SLOPE

FIGURE 5-6.

cycle (2 microseconds) and then turned off. The
earliest it can be turned on again is one clock
cycle later.
counter is incremented by an inverted V-F PULSE
from 92. It cdn be seen that the flip flops
divide the clock frequency by two, limiting the

maximum number of charge balance integrations and

output co"nts to one half of the clock frequency.

And, since 50,000 clock cycles occur in the precise

100

millisecond charge balance period, the maximum
number of times that (12 can go high and be
counted is 25,000.

5-18. At the end of the charge balance phase, the

output of the integrator is resting at some posi-

tive voltage. The single-slope comparator output is
also positive and it will not switch until the in­tegrator output crosses zero. The comparator output

is ANDed with a one millisecond pulse in the digi­tal section to produce SINGLE SLOPE ENABLE.
allows ISS to flaw into the integrator. A 1MHz
clock is counted from the time SINGLE SLOPE ENABLE
went high until the single-slope comparator changes

state (vo crosses zero). When this occurs,

Each time 1,"~ is turned on, a

Simplified A/D Schematic.

This

ISS is shut off and the counting is stopped.
The amount of charge delivered by ISS in one
microsecond (IMHz period) is equal to I/256 of the
charge delivered by ICB in two microseconds.
The microcomputer multiplies the CL3 counts by 256

and adds the SS counts. to it to obtain the corn-

posite count ((6.4 million maximum).

TABLE 5-I

Settling Delays, SC") on to
Turn On Of Integrator.

JFET Delays (msecs)

SWITCH DC"

81

30
52 1
53 1
s4 x

AC" n

30 100

1 1
1 100
1 1

5-6

MODEL 191 DMM

-+1.5v

THEORY OF OPERATION

P

CHARGE BALANCE PHASE

IOOmsec

ELA:

*FOR

5-19.
5-20.

control and display circuitry is given in Figure
5-8. This diagram also shows location of the cir­cuits by printed circuit board.

5-21. Microcomputer.

5-22.

circuitry provide timing and control of both the
display and the A/O converter. Additional functions

provided by the microcomputer include the NULL
function and digital filtering. The Null function
is described in Paragraph 2-15 and digital
filtering is described later in this section. Count
prescaling, and recovery Crow d transient or‘ lost
program are additional functions provided by the
logic circuitry.

5-23.

system, that is comprised of d 6802 microprocessor

DIGITAL CONTROL and DISPLAY CIRCUITS.

A functional block diagram of the digital

The microcomputer and its associated logic

The microcomputer is d MicroBus 8 based

READOUT OF UP PRE-SCALE COUNTER

FIGURE 5-7. 191 A/D Waveform.

*

c

I

I

SINGLE SLOPE

PHASE __L

I msec

-B

ELA'

INTEGRATOR INPUT l

DISABLED -

N302) I

U303), and 1024 x R b&es of read only mm~ory which
provides the control ;program dnd is contnined on
either U305 (ROM) 0,. U304 and "305 (PROMs). The
microprocessor contdil/S a set of 72 variable length
instructions,

llWlll0ry (RAM) for tem+OTdTy storage. The FiA coo-

tdins four bytes 01 memory and provides the

Input/Output (I/O) c ntrol
the Imicrocomputer to
The microcomputer u+s partial memory decoding.

When Al5 is a logic I'O", either the 128 bytes of

RAM or bytes 129 thro gh
ted.
logic "0" RAM. logic !'I" PIA). When A15 is d logic

“1”

(ROM/PROMS),

512

A9 is high, the upper!512 bytes are selected.

d 6821 peripyerdl interfdce dddptw (Pin,

and 1281 x 8 bytes of rdndon, access

he other circuits in the ill.

1

A7 then determi es which is selected (A7 =

(high), read ~only rmemory is selected

and Ag Vetermines whether th? lower

bytes or the upper 512 bytes di-e selected. When

i:

*MEASUREMENT--­c

lines for intcrfaclng

132 in the PlA dw selec-

NEXT

PHASE

@Registered Trademark of Motorola, Inc

5-7

L --------- --__---__----

------ --1L ---------- 1

’ 3

g
F

FIGURE 5-8. Functional Block Diagram of Digital Control and Display Circuit.

5

MODEL

191

DMM

2.5kHz

CHARGE BALANCE

START/m

CLEAR

COUNTER

THEORY OF OPERATION

FIGURE 5-9.

5-24.
5-25.

5-0, a logic "0" on PA7 indicates that the NULL
function is selected and a logic "1" on PB7
indicates that the instrument is in DC volts. These
signals are from the front panel NULL and WV push­buttons, respectively. If not in DC volts mode, the
processor determines whether AC volts or Ohms has
been selected by looking at the value of the
reference voltage after it has been digitized.

5-26. Refer to Figure 5-8 and the timing diagram in
Figure 5-9 for
Charge-Balance phase begins with the MASTER RESET

line pulsing low, clearing U309A and 8 flip flops.
As described in the A/D converter discussion, the

appropriate signal to its input amplifiers is then
enabled by Sl,
After the completion of the appropriate delay
period given in Table 5-1, the "D" input to U309A

is made a "1". This same signal is ANDed at this
time to clear the H-F PRescaling counter U307. The
next rising edge of the 2.5kHz clock sets the Q

A/D Converter Control.

Looking at the A/D Controls Lines on Figure

the fallowing discussion. A

S2, S3 or S4 going to a logic "1".

Charge Balance Timing.

output of U309A low, ~enabling the input signal to

the integrator of thelAID. The processor now counts

250 interrupts from the 25kHz clock, and then sets
the "D" input to U309A to d "0". The next rising
edge of the clock sets INPUT DISABLE high again,
disabling the input 40 the integrator, and ending

the exact 100 millise ond integration period.

5-27.
PULSES are fed into lcounter U307. Each time the
counter overflows (a ter 256 counts) an interrupt

is generated which bhe processor counts in an

internal register.
the 8 most significant bits of the result.
5-28. At the end ofi the charge-balance phase, 8
bits of data are left on counter U307. This data is
obtained by pulsing t e MASTER RESET line into the
counter, and waiting
The number left on

minus the the
data becomes the ml die

result.
5-29. At the completi$n of remainder counting, the

Single-Slope phase ij begun by the SINGLE SLOPE

During the integration period above, V-F

1

1

Tfese interrupt counts become

1

for the counter to overflow.

he counter is equal to 256

1

number 'of MASTER RESET pulses. This

8 bits of the 24 bit

.j

5-9

THEORY OF OPERATION

MODEL

191

DMM

FIGURE 5-10.

START/STOP signal going high, setting the "D" input

of U3098 to a "1". On the next rising edge of the

IMHr clock, the SINGLE SLOPE BEGIN signal from Q of
U3095 goes high, and is ANDed with the COMPARATOR
OUTPUT signal to enable single-slope counting. The
IMtir clock is now fed to U307, and counted similar
to the charge balance phase.
phase ends when COMPARATOR OUTPUT goes low, and
gates off the IMHr clock to the counter. The
remainder left in the counter is again read, as in
the charge-balance phase. This result is added to
the charge-balance counts to generate the 24 bit

(22 bit maximum) result. Timing for the single-

slope phase is shown in Figure 5-10.

5-30.
5-31.

5-8, consist of the LEO digits, and the necex~ary
decoding and driver circuits. These operate under

the control of the microcomputer. The diagram shows

the possible location of the decimal points, but
they are controlled by the range switching which is
not shown.
5-32. Display information is fed out on lines PAg
through PA6 of the PIA I/O bus. It is updated at a

2.5ktlr rate. with each digit an for approximately

400 microseconds. Since the display is fully aulti-

plexed, 6 updates are required to turn each of the
six digits of the display on once. This means that
the entire display is updated 416 times a second.

An update begins by blanking the display and disab-

Display.

The display circuits, as shown in Figure

The single-slope

Single Slope Timing.

eLAwy

FIGURE 5-11.

k

I

?""ZC

I

IN Ill":

Display Timing.

5-10

MODEL 191 OMM

THEORY OF OPERATION

1

9.76 -102mscc pfriod U308

FIGURE 5-12.

ling the latch of "202.
PA6 pulsing to a logic "0" for 20 microseconds, and
the latch is disabled by pulsinq PA4 and PA5 to a
"1" for 10 imicroseconds. New segment data is now
presented on lines PA@ through PA3, and this data
is latched into U202 when PA4 and PA5 return low
after the

of the 20 microsecond period, the display is

unblanked, while new digit information is on the

PIA bus.

latched segment data being turned on until the
beginning of the next update.
shown in Figure S-11.

5-33.

5-34.

shown below the PIA on Figure 5-8. it consists of

two NAND gates, an AN0 gate, a 68OOpF capacitor and

counter U308 which divides by 256. Its function is

to restart the system by resetting the Microproces-

sor and PlA whenever either the prograiri is lost or

d long duration transient "CCII~S.

5-35. Timing of this circuit is shown in Figure

5-12.

10

microsecond period. At the completion

This results in the correct digit for the

Reset and Transient Recovery Circuit.

The reset and transient recovery circuit is

The circuit has two input signals, the 2.5kIlr

The display is blanked by

Reset and Transient Recovery Circuit Tilming.

Oisplay timinq is

i

1

I
k

l(i2nsec

clock and ILATCH ENARLi

by

U308 and LATCII ENA LE

normal operation, LAT$H iNARLt pulses low for 10
nicroseconds every 40
as described in the Di
Cb!ARLL is low, the vqltage on the cd~acitof (Vc)
rises exponentially. 1 When LATCI, LNARLC wt!irns
high, and while Vc is; dhovc the thwshold of thtz
ANn gate, a clear lpul e
normally U308 accuwul~tes one count and is then
cleared. A transient icdn mask the LATCH INAIII.C
pulses or a lost prag 'an, cd" prevent their appesr­dnce at all. If no

128

seconds,
accumulate in U3fl8 afld its output will go high.
This high is NANOed {vith +5 volts to clear the

nlicroprocessor and Pld. Coincidently, LATCH FNABLI:

is forced low and Vc

U308

continues to cou t

it overflows after Z$snts, its ""put returns
low. This removes the!RESET and allows the micro­pr"cess"i- to return t the proper location in the

control

pr"CeSS.

counts r,",, the 2.5kHz clock wi,,

pr"gra"l. completes the recovery

The 2.5kilz clock is counted

is used to clear 11308. In

16

microseconds (2.5kKz r&e),

play discussion. k!hilr i~ATCli

%

1s applied to "308. Thus.

{

ulses appear for 5, milli-

a

b 1 gins to rise to its naxiriw.

the 2.5kHr clock dnd when

5-11

THEORY OF OPERATION

MODEL 191 OMM

1 FIUXFET

INPUT BUFFER

FIGURE 5-13.

5-36. Digital Filtering.
5-37. When the 200mV or 200 Ohm range is selected,

a logic "0" is applied to PB7 of the PIA, which
tells the microprocessor to filter by averaging the

last 8 readings. For this condition, the last 8
readings are averaged together and displayed, as

lonq as the latest conversion is within digits of
the prfvious diplay. If the new conversion is more
than + digits away from the previous wading, the

new reading is displayed. Thus, speed is attained
for large signal changes, but random noise is re­duced by a factor of 8. For all other ranqes, the
microprocessor USES a threshold of +5 digits and
averaqes the last 4 readings. Thus, snallcr siqnal
changes arc responded to, while random noise is

reduced by a factor of 4.

5-38.

5-39.

fom in the lower riqht corner of Figure 5-8, and

the complete circuits are shown on page 2 Of

Schematic 301620. Basically, the 4MHz crystal

control oscillator is a Pierce type oscillator. Its

4MHr output is fed direct to the clock divider

before application to the microprocessor (U302).
11105 provides three outputs by dividing 4MHz by 4,
8 and 16.

inverters to provide zero to t4 volt square waves.
The 1MHz output is used for Single-Slope countinq,
5OOkllr is
Charge-Balance timing, and 25Oktlr is divided by 100

in U301 to produce the 2.5kHz clock.

Oscillator and Clock Divider.

These circuits are shown in block diaqranl

(U105),

and it is buffered by a CMOS inserter

Its outputs arc buffered by CMOS

used in

the A/D converter for

9k

Turning on JFET Switches.

5-40. A/D CONVERTER CIRCUITS

5-41. The A/D convfrtfr rust have a high input

impedance and be linear to within a few parts per

million over the + 2 volt operating range. To [meet

this critera, several innovative circuits had to bc
desiqned. These circuits are described in the
following paragraphs.

5-42. Input Buffer.
5-43. The input buffer is a non-inverting. hiqh

input impedance amplifier which looks at each input
with either x10 or xl lain. Its input signals are
multiplexed by switches Sl through 54 under the

control of the microcomputer. One of the first

problems encountered was the high transients that

appear as the multiplexing switches are turned on.

The effects of these transients were eliminated by
the use of software generated delays.

EYCP, necessary to drive the gate of the appropri-

ate JFET with the input siqnal voltage to turn 1t

on. This was accomplished with a bootstrap ampli-

fier (BSA) connected to the invertinq terminal of

the input buffer (SEE Figure 5-13). When switch 5

is opened, the gate of Q rises to the output of BSA

which

t"mS q on, which means that VI,, = V) = VG.

Note that this technique works regardless of input

buffer gain.

equals the

0

lk

It was, how-

input voltage (V[N). This

5-12

MODEL 191 DMM

THEORY OF OPERATION

FIGURE 5-14. Power Supply Comon Bootstrapped to Input Voltage.

5-44. As previously mentioned, the A/D convcrtfr

was designed for linearity. This means that the

input buffer must be linear over the full ~mfasure­ment range of t2V to no more than a few parts per
million. Since it also must be non-inverting, with

very hiqh input impedance, its gain linearity would

normally be determined by common mode non-linearity.
Most amplifiers specify 80 dB CMKK, and since CM

non-linearity would typically be a factor of 10 or
better, one could expect 10 ppn non-linearity frolv
CM Effects.
error, it was required that the common mode ~frors
be reduced.
either by improving CMRK through critical sclcction
of devices, br by eliminating the colirnon mode (CM)

voltage. The latter method was chosen, as shown in
Figure 5-14.

inverting operational amplifiers, the common mode

voltage

(power supply common). Thus, it can be seen that if
"IN -

common mode errors would be zero because VCM =

0. To achieve this,

Since this would be far to" much

Common mode errors can bf "v~rcomf

First consider that, for non-

(VCM) is equal to VIN VCOM

VC-M could

be made equal to Zero,

it was necessary to bootstrap

the power supply con~ion for the input a,n,i,if~cr- i)t
the input voltage. This wds accomplished !)y d:ld)":;
2 zmers, 2 transistbrs, and d few resistors. :hr

power supply common :is seen to be thr junctlori of
VKIOS and VI1106 (the ;"utPut of INSA), which is eqiial
to

"IN.

0, and the common mbde error is elininatcd. !i"te
that this techniques also raises input inpcdancc
because:

And, since there is in" bias change on the input
FETs of the input1 amplifier,
Z[NW". With the &mm"n mode error elimnatcd,
the only gain error is "pen loop gain nonlinearity
divided by loop gainj For closed loop unity ~jain,
non-linearity is 0.5 :ppm since "pen loop gain non-

linearity is 10% and "pen loop gain is 200,000.
For x10 gain, nonlinebrity is 5 PF~I.

Thus. VC,, =

VIII

I,!{= J and

"UX.!;F

5-13

THEORY OF OPERATION

IO = Ioff - Iin

MODEL

OUTPUT

191

DMM

Ioff

is made + Vin

Rin

Thus \,hen Vi" = Vin max, 10-0 (pcs. full scale)

Vin =O, IO 'Ioff (zero)

Vin = -Vjn max.

FIGURE 5-15.

5-45. Transconductance Amplifier.
5-46. This alnplifier performs two functions. It

converts the input voltage to an output current
that is sent to the integrator on request. It also
provides an offset current so that its bipolar
input voltages are converted to unipolar output
C"!-"?CTltS. BEcause of
operation, its linearity is cxccllent. Figure 5-15
shows how the circuit operates.

5-47. Integrator.
5-48. The integrator has been dfsigned to guard

against the !m"st common problems associated with
high speed integrator operation.
tors have two Imajor problems which limit their high
speed performance. One is the GAINBANDWIDTH of the
integrator amplifier, and the "th"r is the output
resistance of the same amplifier.

the current mode of

Io= Ioff + Vin max*z Ioff (minus f-s.)

Transconductance Amplifier Operation.

Active integra-

These effects

Flax.

Rin

can be seen by looking at the integrator rmodcl in
Figure 5-16. If a voltage step appears at Vi".
the amplifier will not respond immediately, and C

will initially be a short circuit. As shown in the

equation, the effect is that the wrong current will
be applied to the capacitor until the amplifier I‘"­covc~s. It can also be seen that if a bipolar input
amplifier was used for the integrator, charge could
be conducted away from the capacitor and cause
significant ~rr"rs. To guard against these prob­lems, the 191 uses an emitter follower on the inte­grator output to keep I?" small into the MHz reg­ion, and ail inputs to the integrator are current
sources. Also, FET input operational amplifier is
used, which would allow a few volts to appear on
the summing junction with no loss in charge.

5-14

MODEL 191 DMM

THEORY OF OPERATION

For step voltage inputs:

FIGURE 5-16.

REFERENCE

DIVIDER

+2v

+.2v

Integrator Problems at High Speed,

e-e0 = Vin

2.74k

+

6.1

13

k

k

FIGURE 5-17.

6

Simplified Schematic of Reference

UPPlY.

5-15

rHEORY OF OPERATION

MODEL

191

DMM

5-49.

5-50.

5-17.
was designed for linearity and low noise. This
means that stability and accuracy must be provided

by the reference.

cuit is a buried layer zener diode, with an "n-

board heater, which was selected because of its

stability, low noise,

and low dynamic resistance. It is driven by a con-

stant current (nominally ImA) developed by ampli­fier U102. Since the zener current is well regu­lated,

Far example: a 1 volt change In +V would only cause

a zener current change of about 150 nanoamperes.
And, since the dynamic resistance of the zfner is

0.5 ohms, the zen~r voltage would only change 7.5
nanovolts. Super stable tracking resistors are used

in the reference divider to provide very stable 2

volt and 0.2 volt reference voltages. The input

resistors of the divider are specially selected

nominal 100 microamperes of current to the divider.

For example: the values of resistance shown in the

diagram would be for a zener voltage of 6.95 volts.

5-51.

5-52.
tage regulators,
switching and full-wave rectifiers which make up
the power supply for the Model 191. There are three

component regulator used. The plus and minus 15

ment.

+ 5% dCC"raCy. Its input voltage is supplied from

REFERENCE SUPPLY.

The reference supply is shown in Figure

As previously mentioned, the A/D converter

The heart of the reference cir-

low temperature coefficient

it is imune to power supply variations.

(depending on the zener voltage) to provide a

POWER SUPPLY.

Page 4 of Schematic 301620 contains the vol-

line transformer, line voltage

integrated circuit

volts dc is provided by VRlOl and VR102, respect­ively. These are 3-terminal regulators with + 10%
accuracy.
volts dc from TlOl and
selected line voltage is supplied to the instru-

and input currents are limited by RI58 and R159.
Output voltages are filtered by
VR104 provides the t5 volts used in the analog

(ANLG) circuitry. It is a 3-terminal regulator with

TlOl and CRIOI,

(+0.5V) with minimum selected line voltage applied.

Input filtering is provided by
filtering by C116. 9126 and Q127 comprise a series
regulator which provides +5 volts for the Digital
and Display circuitry.
thus,
approximately 6.5 volts (+0.5V) from TlOl and CR103
when minmum selected line voltage is applied. Input
filtering is provided by C109, and CR106 prevents
thermal runaway in the event of a circuit fault.

They receive approximately +I8 and -18

lnput voltages are filtered by

has the same output accuracy.

regulators and one discrete

CR102

and is approximately 8 volts

It is slaved to VR104, and

when the minimum

Cl11

and Cl14

Cl10

and C113.

C115,

and output

It recei vcs

The allowable zener voltage is between 6.6 and 7.3
volts, with the resistors matched accordingly.

MODEL

1910

5-53.

5-54. The Model 1910 is basically a plug-in acldc
converter with variable gain that conditions the ac

input voltage for application to the A/D c""wrtfr.

The basic transfer function of the acldc converter

is shown on the simplified schematic (Figure 5-18).

The resistor values were selected so that

rn*~N = -I
ages above 2 volts, the feedback resistance

(Rf) is

range) to keep the output always less than -2Vdc.
The dc output is a half-wave rectified sine wave,
and the converter is average responding, calibrated
to the rms value of d sine wave.
blocks dc inputs, and the dc offset voltage of the
amplifier is autozeroed out. Output filtering is
provided by the combination of resistors K404-K406
and capacitors C401-C405.
5-55. In actual circuit operation (as shown in

schematic 299600, Section 7) the feedback rcsist­ante of U401 is controlled by K401, K402 and K403.

llith all three relays de-energized as shown, the

overall gain of the acldc convcrtcr is unity (i.e.,
1 Vat rmsIN = -1 VdcOUT). ilith both
K401 and K402 energized, gain is t
10 when K403 is energized with K401 and K402 de­energized. The relays are controlled by the front

panel range pushbuttons via the range select lines,
as shown on sheet I of schematic 301620. See Table

5.2 for gain chart of the ac voltage ranges.

*See Figure 5-18.

reduced (by selection of d higher

Attenuation

AC VOLTAGE OPTION.

‘%IuT.

Table 5-2

Gain Chart for AC Voltage

U401 FDBK
Resistance (Rf)*

For ac Input VOl t-

-__

499 kn

49.7 kn

4.7 kn

250.2 n

Capacitor C415

1000.

Energized
Relays

-

1

i

1

Gain is

NOW
K403
K402

K402.401

Vat

?

5-16

MODEL 191 DMM

THEORY OF OPERATION

'499kri

Basic Transfer Function:

*See Table 5-2 for feedback resistance CRf) vwsus range.

FIGURE 5-18.

Simplified Schematic of Model 1911

-L
c401

J i

OAUTO ZERO

-L
c405

5-17

MODEL 191 DMM

SECTION 6. MAINTENANCE

6,-l.

GENERAL

6-2. This section contains information necessary
to maintain the Model 191 DMM and the Model 1910
AC Volts Option. Adllstmentlcalibration, trou­bleshooting, and fuse replacement procedures are

provided. Calibration should be performed yearly

(every 12 months) 01‘ whenever performance verifi­cation (see Section 3) indicates that the Model
191 is out of specifications. If any step in the
calibration procedure cannot be performed prop­erly, refer to troubleshooting information in
this section OP contact your Keithley represent­ative or the factory.

NOTE
Calibration should be performed by quali­fied personnel using accurate and reliable
equipent

6-3. RECOMMENDED TEST EQUIPMENT.
6-4. Recommended test equipent for calibration

is listed in Table 6-l.

may be used. However, the accuracy of the alter-

nate test equipment must be at least 3 times
better than the Model 191 specifications, OP

equal to Table 6-1 specifications.
6-5.

ENVIRONMENTAL CONDITIONS.

6-6.

Calibration should be performed under

Alternate test equipment

MAINTENANCE

laboratory conditidns having en ambient tcmper­ature of 23 +l"C, abd d relative humidity of less
than 70X. If the ihstrument has been subjected to
temperatures outsidp of this range, or to hlgher­humidity, allow oneihour minimum for the instrunent
to stabilize et the specified environmental

conditions

procedure.

6-7.

6-8.

the adjustments indicated to calibr.ate the Mode!
191 DMM.

6-9.

6-10.

Model
access to the Model1

ing the instrument to reach normal internal oper­ating temperature.
follows:

before beginning

cALmffAT10~

Perform the ifollowing procedures dnd make

Installation bf the Model 1913 calibration

cover.

Calibration Ishould be performed using the

1913

calibratbon COVET. This cover permits

Disconnect!the line cord before rci!ioving
the cover.: To discharge voltage on
capacitors, depress the OFF/ON push­button after
cord.

PROCEDURE.

191

Install

t,

WARNING

adjustments, while allow-

disconnecting

the

calibration

the COYCI 3s

the

ii"?

Item Description

DC Calibrator

AC Calibrator

High Voltage Amplifier

(Used with Model 74511)

Decade Resistor

Kelvin-Varley Voltage
Divider(Used with Model

343A)

Recommended Test Lquipnent For Calibration.

TABLE 6-1.

Soecification

19v,19ov, 1ooov
?0.002% or 2ouv

O.lV, IV, IOV, IOOV
*o.o2z

1000 v
to.049,

1900, 1.9Kn 190Kn
Certified to 50 ppn

.19v, 1.9v

ilith 2 ppll
Terminal Linearity

Plfr. : Model

Fluki

K-P ~,

H-P

343A

745’“s

746A

ESI ~ RS725

Fluke

72OA

6-1

MAINTENANCE

MODEL

191

DMM

Turn off power and disconnect the line cord.

d.

Turn the instrument over so that the bottom

!L.

cover is facing up, loosen the four screws in the
bottom panel.

rubber O-rings.

Hold the top and bottom covers together to

C.

prevent their separation and turn the DMM "vcr to
normal position.

1. Carefully lift off the top cover.
e. Position the calibration cover in place on the

Model 191 and tighten the bottom panel screws.

6-11. warm up.
6-12.
pushbutton to ON position. Allow a one hour warm-up
time before beginning the calibration adjustments.

6-13.

6-14.

6.15. The troubleshooting instructions contained in
this section arc intended for qualified personnel
having a basic understanding of analog and digital
electronic principles and components used I" a ore­cision electronic test instrument.

have been written to assist in isolating the defect­iye circuit or subcircuit. Isolation of the specif­ic defective component has been left to the tech­nician.

Connect the line cord and depress

Calibration Adjustments.

Some procedures require the USC of high vnltaije.
Take care to prevent contact with live cir­cuits which could cause electrical shock re-

sulting in injury or death. Use an insulated
tool when making adjustments.

a. Refer to Table 6-2 and perform the listed ad-

justments in the sequence indicated.

the step sequence is also indicated on the Model
1913 Calibration cover by box numerals.
sequence must be followed exactly because the ad­justments are interrelated and dependent on the
preceeding steps.
calibrate the basic Model 191. If the Model 1910
AC Volts Option is installed, also perform steps 9
through 15.

Following calibration, to insure that all

5.
functions and ranges are operating properly, iuti-

lire the Performance Verification procedure in
Section 3.

If calibration cannot he accomplished or the

C.

Performance Verification procedure indicates a
problem, proceed to Troubleshooting information in
this section.

TROUBLESHOOTING.

These screws are held captive by

OFF/ON

\ WARNING

Note that

The

Perform steps 1 through 8 to

Instructions

NOTE

For instrunents that are still under warranty

(less than 12 months since date of shiomenti.

Tf the instrument's performance is outside of
specifications at any point,
Yeithley representative or the factory before
attempting troubleshooting or repair, other
than fuse replacement.

6-16.

6.17. This section contains tables listing step-by

step checks of the major DMM circuits descibed in

Section 5, Theory of Orteration. The following steps
outline the use of these tables and provide instrrrc­tion for preparing the DMM for toubleshooting. liead

all of these steps carefully before troubleshooting

the instrument.

6.18. it may be necessary to remove the shields on

the mother hoard and the Model 1910 AC voltage
Option (if installed) to gain access to test points
and circuit components for troubleshooting.

6-19.

G-20. Perform the following procedures to remove/

replace shields an molher Lboard and Model 1910 AC

Voltage Option.

TROUBLESHOOTING PROCEDURE.

NOTE

Recalibration of the Model 1910 AC Voltage

Option ~may be necessary if any of the follow-

ing occurs.

1) ilerr~oval/Re,~lacen~ent of Model 1910.

2) Disturbing position of Model 1910 in the

C"""eCt"r.

3) Iler~~"val/Keplace~~lent of shields on the Model
1'110.

Refer to Section 3-13
accuracy. If calibration is necessary perform
steps 9 through 15 in Table 6-2

Shield Removal/Replacement.

t

Disconnect the line cord before removing ttie

case COYPT.

2. Turn off power and disconnect the line cord.
Remove four SC,-ews fro," the botton, of the case and
separate the top cover fro", the botton cover.

b. Remove smother board shield by carefully lifting

shield from the retaining clips. To reinstall,
position shield on the four retaining clips so
that the small bent tah on side of shield is

positioned against the grounded retaining clip

(See Figure 6-Z).
from moving to" far towards the rear of the mother
board.
fully into retaining clips.

IPress firnlly on top of shield to engage

This tab prevents the shield

to

WARNING

contact your

check AC Voltaqe

6-2

MODEL 191 DMM

MAINTENANCE

t 1.0

DC

Calibrator

(A)

OUT

LOW

I

SET TO

1o.oooooov

FIGURE 6-1. Test Circuit For 200nVDC And 2VDC Calibrhtion.

c. To gain access to shields on the Model 1910 AC

Voltage Option disconnect the brown and blue wires
at the pushbutton switch and completely remove the
Model 1910 from connector P1006.
from PC board by removing the two retaining screws.
Refrain from any unnecessary touching of circuit
components.
verse the procedure to reinstall the Model 1910.
The wiring instructions for the Model 1910 are

located on the mother board shield.

6-21. Special Handling of Static Sensitive

b-22.

high impedance levels for low power consumption.
For this reason, a normal static charge build up on

your person or clothing can be sufficient to destroy

these devices.
sensitive devices in your Model 191 and provide

instruction on how to avoid damaging them when they

must be removed/replaced.

CMOS devices are designed to function at very

a. Static sensitive devices:

Keithley

Part Number Designation

LSI-8
LSI-18 u302

IC-168

The above integrated circuits should be

LT.

handled and transported only in protective con­tainers.
tubes or static protective foam. Keep the devices
in their original containers until ready for use.

Handle the board by its edges.

Devices.

The following steps list the static

Reference

u303

u202

Typically they will be received in metal

Detach shields

.0190000 FOR CAL

STEP 4b.

.1900000

b-

SET TO

FOR CAL

STEP 5.

MODEL

191

4-l

Remove the devicies frolv their protective con-

C.

tainers only at d pr/operly gounded war-k bench 01

table, and only afteb grounding yourself by using
d wrist strap. ~

Handle the devic~es only by the body. 00 not

d.

touch the pins.

e. Any printed circlit board into which d device

is to be inserted mvst also be grounded to th?

bench or table. ~

f. Use only anti-stt+tic type solder suckers.

9. Use only grounded tip soldering irons.
h. After soldering ,he device into the boat-cl,

or properly inserting it IntO the

receptacle, the deviqe is adequately protected and
normal handling can tje resumed.

6-23. Line Power. ~
6-24.

6-3, Line Power Checqs to verify that the pow?!
supplies are providing the correct voltages to the
electronic components.i

6-25.
G-26.

display should bc vctified bcforc troubleshooting
the signal conditionipg circuits.
convertor and displab per Tables 6-4
respcctivcly.

6-27.
G-28.

Model 1910 AC VoltdgCi Option.
per Table G-6.

In genera,, *tap tra"bleshooti"q with Table

A/D Converter a'jld Display.

proper operation of ttlc n/o convcrtcr dllil

Cheek tnc AllI

AC Converter.

Problcns +lith\ ac voltage !aay involve the

Check this c,rcuit

Inat i nq

and G-5

6-3

,

MAINTENANCE

MODEL 191 DMM

TABLE 6-2.

Calibration Adjustments.

step Function

ia n ZOOQ Dial "0" Ohms,

lb II 200n

2a n

2b n 2Kn
3

4a

4b
5

6

7 UC v
8 IN v
9

n 2OOKn

DC v 200 rn"

DC " 200 a"
IOC v 2 v Release NULI., 1.9OO"O ice !iqure h-i

UC "

AC v

Range

2Kn Dial "0" Ohms,

Applied* Adjustment Desired Test

Input

depress NULL 00.000 Decade IResistor (0
190

reset NULL .ooooo Decade Resistor

1.9Kn K123 1.90000 Decade Resistor
Release NULL.

19OKn I(124

Disconnect DC
Calibrator,

Short Input

depress NULL

.+190 I”” Ill25

t1.9 v 1126

2"" "

20 v
1000 Y +1000 v
1000 v

1190 v

+19v

IOOOV at Ik Hz i1401 1000.00 AC Calibrator (IS)

Point** Reading Equipment

Kl22 190.000

190.000

""."O" See Figure 6-I

190.000 See Figure 6-l

I1132 190.000 OC Calibrator (A)

11131

11130

19.0000

1000.00

Decade Resistor

Decade Resistor

IIC Calibrator

1)C Calibrator

and IHigh Voltage
Amplifier (C)

10

11 AC v
12

13
14
15
* Connect to INPUT ill and LO terminals.

l

* Refer To Figures 6-2 and 6.3 for location of Ad.iustment Points.

AC v 2v

20 v 1OV at lk Hz
AC V 200 v
AC V 200 v 1OOV at 5OkHz C412 100.000
AC V 2V
AC V 20 v

calibration.

IV at

Ik Hz 11410

11411

1OOV at lk Hz

1V at 50 ktlr
1OV at 5OkHr c4ox 10.0000 AC Calibrator

K409

c411 1 .ooooo

SENSE terminals should not be used during

1 .ooooo

10.0000

100.000 AC Calibrator

AC Calibrator
AC Calibrator

AC Calibrator
AC Calibrator

6-4

MODEL

191

DMM

MAINTENANCE

LINE FUSE F 101

\

+5

-15

DIGITAL BOARD

+15

x122
R123
R124
R125
R126

GROUNDED RETAINING CLIP

FIGURE 6-2.

Model 191 (Shield Removed)

6-5

MAINTENANCE

MODEL 191 DMM

- R401

R409

.R410

-R411
C408

6-6

FIGURE 6-3.

-c411

.c412

Model 1910 AC Voltage Option (Shields Removed)

MODEL 191 DMM

MAINTENANCE

6-29. DC Attenuator and Ohms Source and Resistors.

6-30. Problems with dc voltage or resistance ranges
may involve these signal conditioning circuits.

Check these circuits per Tables 6-7 and 6-8.

NOTE
Dust, flux or other contamination will degrade
performance on resistance and dc voltage ranges.

6-31. Digital Board.
b-32. Problems may exist with the microprocessor or

associated circuitry.

6.33.
common (INPUT LO terminal), unless otherwise noted
in the tables.

All measurements are referenced t" analog

Check out per Table 6-9.

STEP ITEM/COMPONENT

1 S102 line Switch

2

FlOl line fuse

REQUIRED CONDITION

Must be set to 115" or 230V

as appropriate.**

Continuity

6.34.

possible blown fuse (line power) refer t" Paragraph
6-35 for fuse rcolacetncnt instructions.

TABLE 6-3.

Line Power Checks.

If a gross f4ilure exists that indicates d

j UARNING

Some procedures in the foilowing tdbie~
require the $e "f high voltage.
to prcvcnt c+~tact with llvc cIrcult% wli:ch
could cause $lectr,cal shock r-rruit!",; ,n

injury or dcaith.
at INPUT LO ,P"tcntial.
floatinq high enough will create d thick
hazard betwccln the shield dntl i!ar-tll gr'oiind.

The ,m"thcr boar-d ~hifir! :I

A" input vo!ta9c

@MARKS

rake care

3

PI014 line cord

4

5

t5V pad*, Analog

6

"R104, IN.

7

t5V pad*, Digital

8

Emitter of 4126

tl5V pad*

9

"RIO1 IN.

10

-15

I1
12

* On main printed circuit board (see Figure 6-Z).
**On optional line voltage units set to 115V.

pad*

VR102 IN.

Plugged into live receptacle

Turn on power

15 volts, +54,
t7.4 volts

minilwn

+5 volts, 25%

i-6 volts minimum

t15 volts,

i-17.9 volts minimum

-15

volts, '10%

-17.9 volts minimum

210%

Output Of vi1104

Coll~ector "f 0126

OutpIut Of VRl02

lnp"!t to "Rio2

NOTEi: Not regulator

inay Iindicate shorted

I Odd.

G-7

MAINTENANCE

MODEL 191 DMM

TABLE 6-4.
A/D Converter.

CTFP I ITFM/C"MP"NFNT

,,_, .._..,_~...~.._~..

1

Display

2

UlD4,pin 10

3*

U104,pin 8

4*

Ul04,pi" 12

5*

U106,pin 3

6

7 U106,pin 11

K138

8

U113,pin 2

9

Ull4,pin 2

10

IKFIIIIIKED CONDITION

. . . . ~~~~

T",T 0" power. select 1000 VDC. NOTE: Some tests

000.00 12 Digits
0 to +4 volt square wave

at 4 MHz

0 to t4

at 1 MHZ.

volt square wave

I

0 to 14 Volt square WaYC
at 250

0 to 14

at

0 to t4

at 5OOkHr

0 volts for 400 milliseconds

-2.5 volts, ?7% ( 175mVolts)

ii volts, 17% ( 350mVolts)

ktiz

volt square WaYe

500

kHr.

volt square WaYe

t2 volts for IO0 milliseconds, Input Ruffer output

REMARKS

here could fail
because of Digital
Board problems and
YlCC Yersa.

4 MHz clock (P1005,

pin 2).

1 MHz Clock (P1005,
pi" 7).

250 kHz clock (P1005
pin 3).

500

kllz clock

500 kHr clock

Transconductance Pmp
bias.

Charge Dispenser

bias

Cl12

11
12 Cl12
13

External voltage

14

SO"t-Ce

Display

15

16

External Voltage

17

SO"I‘C!2

18

19

Display
External voltage

20

source

21

Display

LI

* Skip these‘steps, if steps 1 through 4 on Digital Board (Table 6-9) have been

performed.

0 volts +I5 millivolts
See waveform per Figure 5-7
Select 2 V DC Range
Apply +I.90000 volts

1.90000 *IO digits

Select 200mV OC range
Apply .OOOOOO volts

Depress NULL

00.000 *I digit
Apply

+190

millivolts Calibration point

190.000 210

digits

Integrator input
Integrator output

Calibrated point

If different, check

2 volt reference

(pin 7, 200mV

switch).

Calibrated point

Input offset nulled

If different, check

0.2

volt reference

(pi" 9, 200mV
switch) or X10 gain
Of Input Buffer.

6-8

MODEL

191

DMM

MAINTENANCE

TABLE 6-5.

Display.

TEP 1 ITEM/COMPONENT

1

2 +5V Digital Pad* +5 Volts eJ%

or P1002, pin 4

3

U201, pin 1,2,6, Digit drive. Low-enabled

7.9 and 13

4

U202, pin 9,10, HI-enabled
11,12,13,14 and
15

5

U202, pin 4 and 5 Negative - going pulse (t5V

6

J1002,

and 8 high (on).

-

* On main printed circuit board. See Figure (6-Z.)

pins 2,5,7 Appropriate DP line

IREQUIRED CONDITION

Turn on power. Select 1000

v DC range.

to OV) occurring every 400 rec.

(2.5kHz).

REMj,RKS

I

If low,icheck per

Table 6+3.

LED cathode

7 %gme$t OUtpUtS

Oepress~RANGE
pushbuttons to
checkall W's,

6-9

MAINTENANCE

TABLE 6-6.

AC Converter. (Model

MODEL 191 OMM

1910)

STEP

1

ITEM/COMPONENT

Display

Pin 1, DCV

Switch

Pin

12,

ACV

switch

External voltage
source

REQUIRED CONDITION

Short input

.OOOZO *lo digits

10 millivolts

Same as step 4, plus reading
at step 3.

Apply 1.00000 volts rms
at 1kHz

REMARKS

NOTE: Full scale
input on all ranges
should produce
approximately -2V

DC at output. (pin

I, DC VOLTS switch).

NOTE: Do not per­form unless AID
tests are completed.

Normal ZWII offset
range.

Impedance meter to

measure

(1090).

Output resistance is

300

kn

ACV Auto zero.

Calibration point.

Display

Pin I, DCV

switch step 4

Pin 12, ACV Same as step 5
switch

10
11

External voltage Apply
souI‘ce

12

Display

13

External voltage Select 200 VAC range
SO"lW2 and apply 100.000 volts rms.

14

Display

1.00000

-1

NOTE: If any of above checks
fail, proceed to bias checks,
step 18.

Select 20 VAC range

at 1kHz

10.0000 SO0

100.000

+lOO digits

volt, plus reading at

10.0000

volts rms

digits

?I00 digits

DC OutpUt

Auto zero

Calibration point

Calibration point

6-10

MODEL

191

DMM

TABLE 6-6. (Continued)
AC Converter. (Model

MAINTENANCE

1910)

STEPS

16

17

18 TURN OFF POWER.

19

20

21

ITEM/COMPONENT

15 Select 1000 VAC range

External voltage Apply 1000.00 volts rlns
SO"V2e

Display

Pin 2, U401

R405, CR401

R402, R406

REQU1KELl CONDITION REMARKS

1000.00

Remove Model
Voltage Option from Model

191.

install Model

191.

short INPUT. Turn on power.

0 volts +I0 millivolts. Sunning junction,

0 volts +lO millivolt5 DC output before

0 volts *IO millivolts Fcedhackicircuit

+lOO

digits

1910

Remove shields and TE-

1910

Select 2VAC range and play

Calibrat/on point

NOTE: w/th shields

AC removcd,~ display

will he noisy and

read man! millivolts

in Model

of AC pikkup. Ois-

wilh also

change wbth operator
inovelnenti

AC amplifier.

filter.

22

23

24

Q404, base

0403, emitter

Q401, base

-7.5 volts *IO%

t5.7 volts

-3.6 volts *lo%

NOTE: Model
calibrated if step

formed.

*10x

1910 must

be rf-

18 was

Base voltage

5 milliabp current
y3urce.

Rias foriC404

protectibn circuit.

per-

6-11

MAINTENANCE

TABLE 6-7.
DC Attenuator.

MODEL

191

DMM

.EP

ITEM/COMPONENT

1

External voltage

2

3 Display

4

5 External voltage

source

6 Display

7

8 External voltage Apply

source

REQUIRED CONDITION

Turn on power. Select
2oov DC range.

Apply t190.000 volts

190.00 i10 digits

Select 2OV DC range

Apply

19.0000 *IO digits

Select 1000 VDC range

t19.0000

tlOOO.OO

volts

volts

REMARKS

NOTE: These checks
should not be made
if a problem exists
on the 200mV DC or
zvoc ranges.

Calibration point

1OO:l Attenuator
(R129A,R,C,D, RI24

wiper).

Calibration point.

IO:1

Attenuator

(R129A,B,C,D, R131

wiper).

Calibration point.

9 Display 1000.00 f5 digits

1OOO:l Attenuator

(R129A,B,C,D, R130

wiper).

6-12

MODEL

191

DMM

MAINTENANCE

TABLE 6-8.

Ohms Source and Resistors.

;TEP ITEM/COMPONENT

1

2

Display

Pin 5, ACV

3

switch

4 Pin 3, U103

5

6 Display

1

Pin 5, ACV

8 Pin 3, U103

REQUIRED CONDITION

Select 200 range and short

INPUT with 18 gage (or lower

copper wire. (tin plated OK

Less than

-0.4 volts *9%

-0.4 volts

Select 2Kn range

.OOOOO +2 digits

-4 volts ?7%

-4 volts k7%

00.010

kl%

R[MARKS

NOTE: ~DO not per­form uhless AID con­vertcwand DC
attenupor tests are
completed.

Two wipe offset, in­cludinb thermals.

Ohms reference

WI taqp

Ohms rkference
divider.

Ohms rieference

vo1taqp.

Ohms r~fetcncc
divideir.

9

10

11

12

13

14

15
16

1.00000 k n

Display

Pin 5, ACV

INPUT ill

lO.OOOOk n

Display

lOO.OOOk"
resistor

Apply to input

(4-wire connection)

I.00000 ?I0 digits

-4 volt5 ?7%

-2 volts +7% (half of step 1

Apply to INPUT and select
20kn range

10.0000

IRepeat Steps

Apply to INPUT and
select 200kn range.

210

digits

11

and 12

Calibrated

reslstiance

Range iresistors :

R107,

iK109. I)105

QiO6 aire protection

trdnsilstor-5.

Ohms rjeference

Volta@.

Volta+? across un­known.;

Caliblated

rE515tpCe

Calibflatcd

resisqance

and

6-13

MAINTENANCE

MODEL 191 DMM

TABLE 6.8 (Continued)

Ohm5 Source and Resistors.

STEP

17

18

19

20

21

22

23

ITEM/COMPONENT

Display

1

.OOOOM

0

I‘e515tor

Display

10.000

re515toT

Display

Mn

REQUIRED CONDITION

100.000 210 digits

Repeat Steps 11 and 12

Apply to INPUT and select
2000kn range.

1.00000

Repeat Step 18

Apply to INPUT and

select 20Mn range

10.0000

+30 digits

+lOO

digits

REMARKS

Range resistors:
R107, 11109, R129D.

K130,

R129C, R124.

Use meter with high

input impedance
(bO%).

Calibrated

resistance

Range resistors:
R107, R109, R129D,

R130,,
Rl29B,

Use meter with high

input impedance

R129C, R124,

R131.

(ho%).

Calibrated
resistance.

Range resistors:
R107, R109, R129D,
R130, R129C, R124,
R129B, R131, P.132,
R129A,

R119.

6-14

24

Repeat Step 18

MODEL

191

DMM

STEP

ITE1l/COMPONENT

TABLE 6-9

Digital Board

REQUIRED CONOITiOEl

MAINTENANCE

I

REMARKS

1

u302,**

2

3 U302, pin 37 0 to +4 Yolt square waJe , liliz clr$ck.

4 U309, pin 11 0 to +4 Y 01 t square wzv e 1 MHz cldck.

U308, pin 4 0 to +4 volt square wale

5

6 U308, pin 13 0 to +4 volt square wale 2.5 kill diock.

7 U302, pin 40 +5 Y olts *5x Reset Ii*.

8 J1004, pin 4 Negative goim pulse idtch endble for

Turn on power. Select NOTE: Sine tests
1000 VAC rawje*

0 to +4 volt square wa/e 4 ,lHr cl+k.

at 4 EIHz

at 1 MHz

at 1

~1HZ

at 250 kliz

at 2.5 kliz

(1% to OV) occurriq Display B~Omd.

wet-y 400 usec.

here could fail be­cause of!A/O Con-

verter p oblens t 3rd

Y ice ver~a.

250 kllr dlock.

9 J1004, pin 9 Negative goim pulse

(+5V to OV) occurriq Display l$arc

every 400 usec.

10 J1004, pin 8 Rectaqular w.%e. +5V for S1 line fbr input

140 to 170 msec arc 0" signal rwltiplex.
for 370 to 400 msec.

11 51004, pin 7 nectarqu1ar wiue, t5v for

130 to 150 msec anj ov far

390 to 420 msec

12 J1004, pin 6 Rectangular wJ(e, t5V for

110 to 140

400 to 430 msec.

51004, pin 5 Rectamular wa/e, +5V for

13

110 to 140

420 to 450 msec.

* If Model 1910 AC Option is not installed, display should read-IEEF.E(1.

** Pin 38 for Revision A arrl 0 Digital Board,

Pin 39 for Revision C ard abwe Digital Board.

msec ald ov for signal cs~ tiplex.

Plsec ani ov for

Blankiq ~input for

S2 lim fbr input
signal mu) tiplex.

53 lim fbr input

54 line f/3r input
signal mu/tiplex.

6-15

MAINTENANCE

6-35.
6-36.

To replace fuse, proceed as follows:

a. Turn off power and disconnect the line cord.
Il.

four screws in the bottom cww.
held captive by rubber O-rings.

c. Hold the top and bottom covers together to pre-

vent their separation and turn the DMM over to nor­mal position.

4. Lift off the top cover.

LINE POWER FUSE (FlOl) REPLACEMENT.

Fuse is located internally in the Model

WARNING

t
Discomect the line cord before removing the
case COYBP.

Turn the DMM bottom side up and loosen the

These screws are

191.

MODEL 191 DMM

CAUTION

A

Do not install fuse with higher
specified.

FiOl is now accessible without removing any

e.

other components.

Remove FlOl, shown in Figure G-2, and replace

1.
per Table b-10.

LINE FUSE
VOLTAGE FlOl

* Optional line voltage range.

Replace the top COYCT.

9.

instrument damage may OCC"~.

TABLE 6-10.

Fuse Replacement.

KEITHLEY
PART NO.

rating

than

6-16

MODEL 191 DMM

REPLACEABLE PARTS

SECTION 7.

7-1.

GENERAL.

7-2.

This section contains information for ordering
replacement parts.
rately on Figure 7-l.
arranged in alphdbetical order of the Circuit Desig­nations of the components. A cross-reference list
Of manufacturers, containing their addresses, is
given in Table 7-1.

l-3.

ORDERING INFORMATION.

7-4. To place an order or to obtain information

concerning replacement parts contact your Keithley

representative or the factory. See the inside front

cover for addresses.
following information:

4. Instrument Model Number.
&. Instrument Serial Number.
c. Part Description
<. Circuit Designation (if applicable).
e. Keithley Part Number.

7-5. FACTORY SERVICE.

1.6.
factory for service,
Form which follows this section, dnd return it with
the instrument.

If the instrument is to be returned to the

Panel and covers are shown sepa-

The Replaceable Parts List is

When ordering, include the

please complete the Service

REPLACEABLE PARTS.

7-7.

SCHEMATICS.

7-a.

The Model

Of four pages:

Page 1 of 3016$ Signal Conditioning, Pg.

a.

7-19.

h. Page 2 of 301624 - A/D Converter, Pg. i-20.

Page 3 of 30162jD - Digital dnd Display. Pg.

c.

7-21.

5. Page 4 Of 30162:)\ Power supply, Pg. 1.22.

7-9. Model 1910 AC Vajltage Option (AC Converter):

Schematic No. 299600, Pp. 7-27.

7-10.
7-11.

Layout No. 296750, Pgs.; 7-23. 24.

7-12. Model 191 Display Board, i'C-486, Conpor~cnt

Layout No. 29667C, Pg. r-25,

7.13.
Layout fro. 29679C. pg. l-26.
7-14.
component Layout NO. 29$55c, Pg. 7-2a.

7-15.
7-16. A spare parts ki;t is dvdildble that contdln*
a complfment of spare pbrts that cd0 rmaintslo :i/, :,j
five Model
IiSt of the spare partsiis given in Table 1.2.

COMPONENT LAYOUTIS.

Model

Model 191 Digiyal Board. PC 490, Conponcnt

Model

1910

MODEL

1919

19111910’s

191

schelriatic (30162D) is comprised

191

Mothicr Board. PC-489. Conponent

AC Voltage Option, PC-496.

SPARE!PARTS KIT.

fdr aorrroximdtclv one war. :.

_ _

MFG.

CODE NAFlE AND ADDRESS
A-B Allen-Rradlcy Corp.

n-o

AC1 hcrican Conponents, Inc.

AMI American Microsystfns, Inc.

AMP Amphenol

BRG Berg Electronic, inc.

I

Milwaukee, ill 53204
Analog Devices, Inc.

Notwood, MA 02026

Conshohochen, PA 19428

Santa Clara, CA 95051

Broadview, IL 60153

NC

Cross Kcfercnce of Manufacturers

TABLE 7-l

FED
SUPPLY
CODE

01121

14298

31411

02660

IIFG.

CODE

Ii R Fi

C-D

c-w

CAD

CLR

COT

DTEl

flAtIS A:,,, A,1,,R,~S':

aourns , I nc.
lRivcrsidc,CA 92507

Cornell-Dubilicr I
Newark, NJ "7101: 14655

Continental-Wirt IFctronic Corp.

Warninster, PA 149i4

Caddock
ilivcrsidc, CA gZ'$li

Ccntralah IDivisio'

Milwaukee, lil 3 53,"1

Coto-Coil Co., Inc.

Providcncc, RI
Diclcttron (Consol~idatcd)

New York City, NY ~ 10013

i ,Li’

',l!'i

fO2'14

79711

,964i

7iigo

7,701

7-l

REPLACEABLE PARTS

MFG.
CODE

EC1

EFJ

ERI

F-I

G-I

HHS

INT

K-I

L-F

MEP

Electra Cube, Inc.
San Gabriel, CA 91776

E. F. Johnson Co.
Waseca, MN 56093

Erie Technological Products
Erie, PA 16512

Fairchild Instrument Corp.
Mountain View, CA 94043

General Instrument Corp.

Flewark, NJ 07104

H. H. Smith
Brooklyn, NY 11207

Intersil, Inc.
Cupertino, CA

Keithley Instruments, Inc.
Cleveland, Ohio 44139

Littlefuse, Inc.
Des Plaines, IL 60016

Mepco, Inc.
Morristown, NJ

NAME AND ADDESS

95014

TABLE 7-1 (CON'T)

Cross Reference of Manufacturers

LED
uPPLY
:ODE

14752

74970

72982

07263

72699

83330

32293

80164

75915

80031

‘IFG.
CODE

­MOT

NAT

NCG

NIC

PRP

SIE

SPG

ST0

T-I

ucc

MODEL

,lAME Arll! ADDESS

ilotorola Semi Products, Inc.
Phoenix, AZ 85008

National Semi. Corp.

Santa Clara, CA 95051
Nytronics Components Group, Inc.

Darlington, SC 29532

llichicon Corp
Chicago, IL 60645

[Precision Resistive Products
Mediapolis, IA 53237

Siemens Corp.

Iselin, NJ 08830

Sprague Electric Co.
Visalia, CA 93278

Standard Condenser
Chicago, IL

Texas Instruments, Inc.
Dallas, TX 75231

United Chcni-Con, Inc.
Rosenont, IL 60018

191 DMM

--

-ED
SUPPLY
ZO"C

04713

27014

83125

25088

14659

97419

01295

MOL

QTY.

2
1
2

1
1
1
1
1

1

1

2

Molex
OOwnerS Grove, IL 60515

KEITHLEY

PART NO.

LID-16

m-17

FU-17

IC-53
IC-93
IC-96
IC-152

IC-174
LSI-8*
LSI-18*
RF-28

SCHEMATIC DESIGNATION

OS202 thru OS206

DS201
FlOl
U108,U110
VU104
VRlOl
u401

VR102

u303

U302
CR401 thru CR408

27264

TABLE 7-2

MODEL

1919

SPARE PARTS KIl

r-

>TY.

* Anti-Static protection and handling required
** Better Replacelnent Part.
*** Cut off extra pin to use.

1
1
I

1

1

2

1
1
1

1
1

I

KEITHLEY

PAKT NO.

RL-57
TG-47
TG-61
TG-62

TG-84

TG-128

TG-136

TG-137

28234
30163

30167

SCHEMATIC DESIGNATION

(K4Dl***
Q107 thru
4117, 4123, 4402, (1403
4127, 4401

4118, Q405, 9128

Qlll

Q126
4103

4102,

), K402,K403

4110, Q119, Q404

thru 4116, q120 thru 4122,

Q105, 4106, Q124, 4125

(QlOl

u113, (U102, u103, u109, Ulll, u114)**

u112

7-2

MODEL

191

DMM

REPLACEABLE PARTS

REPLACEABLE PARTS LIST

Circuit
wsig. Description

Cl01

Cl02

Cl03 68pF

.luF,16VDC,

CCdl-D

.l,,F,l6VDC,

CerO

,lOOOV,

cem

Cl04

Cl05 .1UF,l6VDC,

Cl06 .luF,16VDC,

Cl07

.IuF,lhVDC,

Ce!9

CerD

CerD

.l”F ,16VDC,

Get-D

Cl08

Cl09

Cl10

Cl11 470,,F,50V,

Cl12

Cl13

Cl14

Cl15 lOOO,,F,iOV,

Cl16 lO,,F,ZOV,

.OluF,12DOV,

POlY

10,000,,F,10V,

ETT

lO,,F,ZOV,

ETT

ETT
36OOpF,5OOVDC,

POlY
lO,,F,ZOV,

ETT

470uF,50V,
ETT

ETT

ETT

“100”

Series (Sch. 301620 - Pgs. 7-19,

(PC-Board 489 -

Sch. Pg./ Item No./
Location

Z/D5 Z/D5 5/B2 5/B2

Z/E5 Z/E5

z/n5 z/n5

2lE5 2lE5

ZIG5 ZIG5

Z/H5 Z/H5

Z/H5 Z/H5

l/C2 llC2

4/m 4/m

4/E2 4/E2

4102 4102

Z/E3 Z/E3

4lE3 4lE3

4/03 4/03

4/05 4/05

4/E4 4/E4

CAPACITORS (C)

PC-Board
Locatibn

6182 6182

7152 7152

8lC2 8lC2

g/c2 g/c2

IO/C2 IO/C2

ll/C2 ll/C2

12/E2 12/E2

13/83 13/83

14103 14103

15184 15184

16/C4 16/C4

17104 17104

18154 18154

19/84 19/84

20104 20104

Pgs. 7-23, 24)

Mfg.

Code Desig. ~

CL0 CL0

CL5 CL5

CLB CLB

CLR CLR

CL0 CL0

CLR CLR

CL6 CL6

STD STD

NlC NlC

ITT ITT

ucc ucc

CLB CLB

ITT ITT

ucc ucc

NIC NIC

ITT ITT

20,

21, 22) ~

Mfg. ~ Keithley

UK16 ~

104

UK16

104 ~

DO-680 ~

UK16
104

UK16 ~
104

UK16 I
104

UK16

104 ~

IOULA i
10000 ~

TAPA ~

lOuFK20~
SOVRSI.

470 ~
CPK- ~

36005 ~

TAPA ~
lOpFK20~

SOVBSL ~

470

lOULA ~

1000 ~

TAPA 1

iouFK20i

Part NO.
C-238-.1

C-238-.1

C-64-68~

C-238-.1

C-238-.1

C-238-.1

C-238-.1

C-286-.01

c-179-10

C-276-470

C-138-3601

c-179-10

C-276-470

c-304.lOO(

c-179-*0

100

)I'

,

Cl17 .l,,F,16VDC,

CerD

Cl18 .luF,16VDC,

Qiil

Z/C5 Z/C5

Z/C5 Z/C5

21IC4 21IC4

22/C4 22/C4

CLB CLB

CLB CLB

UK-104 ~

UK-104 C-238-.1

C-238-.,

1

l-3

REPLACEABLE PARTS

MODEL

191

DMM

Circuit
Oesig.

Cl19

Cl20

Cl21

Cl22

Cl23

c201 4.7uF,35V,

Description

8.2pF,50V,
TubCer

.l"F ,16VDC,

CfZt-D
47pF,lOOOV,

&?I-"

.luF,16VDC,

CCZt-0

15OpF,lOOOV,
0Sl.D

EAL

“100”

Series (Sch. 301620 - Pgs.

Sch. Pg./
Location

2lA3

l/C2

2/E6

l/F3

l/G5

"200" Series (Sch. 301620 - Pgs. 7-19, 20,21, 22)

3/E2

"300" Series (Sch. 301620 - Pgs. 7-19, 20, 21, 22)

CAPACITORS (C) (COWT)

7-19, 20,

(PC-Board 489 Pgs. 7-23, 24)

PC-Board

Item No./

Location

23104

24/D2

25lC3

x/o3

27lG2

f

(PC-Board 486 - Pg. 7-23, 25)

3/c3 ITT

(PC-Board 490 Pg. 7-26)

Mfg.

Code
CLR

CLB

CLB

CLB

CLB

I

21, 22)

Mfg.

Desig.
C4OC8

R2K
"K-104

DO-470

UK-104

DO-151

f

TAPA c-179-4.7

4.7uFK20

Keithley

Part NO.
c-ztv+?+!p

C-238-.1

C-64-41?

C-238-.1

c-64.15op

i

Circuit

Desig.

c301

C302

c303

c304

Circuit
Desig. Description

c401

C402

c403

c404

4.7uF,35V,
EAL

68oopF,5oov,
ce rD

.luF,16VDC,

CFZI-II

.luF,lbVDC,

ce m

.56uF,50V,

MPF
lO~F,20V,

ETT

3.3uF.20V.
ETT

68OuF,3V,

Tant

Sch. Pgl
Lacatlon

3186 4lB2

3/C6 5lE2

3/F5 6/E2

3/F5 7IE3

I

"400" Series (Sch. 299600 Pg. 7-27)

Sch.
Location

F3

F4

F3

E4

PC-Board

Item No./

Location

Mfg.

Code
ITT

ERI

CL6

CLB

I

Model

1910

AC Voltage Option

(PC.-Board 496 Pg. 7-28)

PC-Board

Item No.

Location

5182

6183

?/R3

8lB3

Mfg.

Code

EC1

ITT

ITT

SPC

! !

Mfg. Keithley
Oesig. Part No. Description

TAPA

4.7FK20

851.z5vo
682M

UK16-104

UK16-104

Mfg.

txsiq.
625DlA

564J
TAPA

lOuFK20

TAPA c-179-3.3

3.3pFK20

C-179-4.7

C-238-.1

C-238-.1

Keithley

Part NO.
C-201-.56

c-179-10

7-4

MODEL

191

DMM

Circui
Desig.

CAPACITORS (C) (CAN'T)

Model 1910 AC Voltage Option

"400"

Series

(PC-Board 496 Pg. 7-28)

Sch.
Locatior

(Sch. 29960" - Pg. 7.27)

PC-Board

Item No.

Location

Mfg.

Code

Mfg.
Desim

REPLACEABLE PARTS

-

c

Keithlcy
Part 110.

-

c405

C406

c407

C408

c409

c410

c411

C412

c413

c414

c415

.56,,F,50V,

MPF

8820pF,63V,

Poly

418pF,5OOVDC,
Mica

Adjustable Capacitor

.O-ll3pF

3OpF,5OOV,
Mica

I.SpF,SOV"C,
Tub&r

.25-1.5pF,ZOOOV,

Trimmer

.25-1.5pF,ZOOOV,

Trimmer

.l!lF,16V"C,

CerD

lO,,F,20V,

ETT

.05uF ,1ooov,

Cer"

"100" Series (Sch. 301620

G3

"6

"5

05

"4

c4

"4

Bl

Cl

c2

82

(PC-Board 489 - Pgs. 7-23, 24)

9182

lo/B2

ll/C2

12/c2

13/C2

14102

15/"2

16/E2

17103

18/"3

19/E2

DIODES (CK)

- Pgs. 7.19, 20, 21, 2

EC1

DTN

G-l

ERI

C-D

ERI

EFJ

EFJ

CLR

ITT

SPT,

Mfg.
Code

G-i

6250:
564J

88201

63V,l

KDM

15FD
567-C

CD10,
OOJO:

301-c
HOl5i

273-C

002

273-C

002
"K-1(

TAPA
10 FK

41C1(
9AB

Mfg.

I)esir

W04M

$3

$3

co

V
‘F

lb.

-

-

-

l-

i-

C-201-.56

C-278.418p

c-225

C-236-30~

C-282-1.511

C-216

L-2lG

C-238-.,

c-179-10

C-29u-.05

Keithley
Part ,,o.

RF-46

Kectifier, Sillcon

G-I
G-l
MOT
F-I

MOT

\104M
KBPOZ

IN400
IN460
IN400

RF-46

RF-36

RF-38

RF-41

RF-3B

-

7-5

REPLACEABLE PARTS

DIODES (CR) (CON'T)

"200 Series (Sch. 301620 - Pgs. 7-19, 20, 21, 22)

(PC-Board 486 - Pg. 7-25)

MODEL

191

DMM

Circuit
Desig.

CR201

CR202

Circuit
Desig.

CR401

CR402

CR403

CR404

CR405

Description
Diodc,Diffused,

Silicon
Diode,Diffused,

Silicon

Description

Diode,Diffused,
Silicon

Diode,Diffused,
Silicon

Diode,Diffused,
Silicon

Diode,Diffused,
Silicon

Diode,Diffuscd,
Silicon

Sch. Pg.1 Item No./
Location

3lE2

WE2

Model 1910 AC Voltage Option

"400" Series (Sch. 299600 - Pg. 7-251

(PC-Board 496 - Pg. 7-28)

PC-Board
Location Code
5/E2 T-l

b/E2 T-l

Mfg. Mfg. Keithley

­PC-Board

Sch.
Location

F2

12

02

F5

E5

Item No./

Location

24183

25183

26183

27103

28/R3

Mfg.

Code
T-I

T-l

T-I

T-I

T- I

Desig.

IN915 RF-28

IN915 RF-28

Mfg.
Desig.

111915

IN915

IN915

IN915

lN915

Part No.

Keithley
Part NO.

IRF-28

RF-28

RF-28

R1-28

IRF-28

CR406

CR407

CR408

Circuit

Desig.
OS201

DS202

DS203

OS204

OS205

DS206

Diode,Diffused,
Silicon

Diode,Diffused,
Silicon

Diode,Diffused,
Silicon

Description
;;gital Display

Digital Display

Digital Display

Di9ital Display

Digital Display

Digital Display

E5

82

82

"200" Series (Sch 301620 - Pgs.

(PC-Board 486 - Pg. 7-25)

Sch. Pg/
Location

3102

3102

3102

3/D2

3/E2

3lE2

29103

3DID2

3UE2

DISPLAYS (DS)

PC-Board

Item No./

Location
8/52

g/c2

lo/c2

1 l/D2

12/02

13/E2

T-l

T-I

T-I

7-19,

Mfg.

Code
F-I

F-l

F-l

F-I

F-I

F-I

lN915

IN915

lN915

20, 21, 22)

Mfg.
Desiq.

FND

561

FND

560

FND

560

FND

560

FND
560

FNU
560

RF-28

RF-28

RF-28

Keithley
Part No.

DD-21

DD-20

DD-20

DD-20

DO-20

DO-20

7-G

MODEL 191 DMM

REPLACEABLE PARTS

Circuit

Desig.
OS207

Circuit
Dcsig. Description

FlOl

FlDl

Circuit

Desig.
JlODl

51002

51003

Description
Pilot Light,

LED

Fuse,SLO-BLO,

1/4A/25DV/3AC 250
Fuw,SLO-BLO,

1/8A/250V/3AG 125

Description
Connector,Femalc,

8 Contacts
Connector,Fcmale,

8 Contacts

Connector, 3 pins,
For line cord

"200" Series (Sch. 301620 Pgs. 7.19, 20, 21, 22)

“100”

Series (Sch. 301620

"1000" Series (sch. 301620 -

DISPLAYS (DS) (CON'T)

(PC-Board 486 Pq. 7-25)

Sch. Pg./ Item No./
Location

3102

(PC-Board 489

Sch. Pg./ Item
Location

4lA5

4lA5

(PC-Roard 489

Sch. Pg.,
Location

Several

Several

4lSeveral

PC-Board
Location
14/83

FUSES (F)

-

Pgs. 7-19, 20, 21, 22)

Pgs. 7-23, 24)
PC-Bc
Local

36/A3

37lA3

CONNECTORS (J)

PC-Board

Item No.,

Location

39/F5

4D/F2

Pgs. 7.19, 20, 21, 22)

Pgs. 7-23, 24)

Mfg.
Code Desig.

H-P 5082-

L-F 313.

L-F

Mfg.
Code

A-P

A-P

MOL

Mfg.

4494

Mfq.
nesiu.

313.

Mfg.
Dcsiq.

929853

04

929853.
04

2139-3

Ke~thlcy
Part No.

PL-63

i

Keithlcy
Part !iO.

CS-356-4

cs-356.4

CS-287-3

51004

J1005

J1006*

51007*
J1008*

JlOO9

JlOlO

JlOll

J1012

51013

*Located on Model

Cannector,Femalc.
12 Contacts

Connector,Femalc,

12 Contacts

Connector,Female,

12 contacts
Lug,Receptacle
Lug, Receptacle
Connector,Female,

Mini-PV
Binding Post,

Red
Binding Post,

Black
Binding Post,

Red
Binding Post,

Black

SeWr.31

Several

Several*

u2*
c2*

42105

43lL35

34/c3*

35/Fl*
36/A3*

l/F1

l/A2

l/A2 47lC5

l/Al 48IH4

l/Al

1910

AC Voltage Option (PC-496, Schematic 299600).

46lC4

49lH5 1,115

A-P

A-P

MOL 09.62-

AMP
AMP
BRG

HHS

HHS

HHS

929853.

06

929853.
06

3121
42428-s

42428-S

73691-f

1517

Red
1317

Black

,517

Red
1517

Black

CS-356-6

CS-356-6

CS-337-12

Lb90

LlJ-90

CS-236

BP-11-z

BP-l,-0

BP-11-Z

RP-II-0

7-7

REPLACEABLE PARTS

MODEL 191 DMM

I

Circuit
Desiq.

K401

I I

K402

1 K403 1 Relay, Reed

I

Circuit
ksiq.

LlOl

Circuit

Desig.

PI001 Connector, Male,

PI002

PI003

P1004 Connector, Male,

I

Description
Relay, Reed

Relay, Reed

I

TYP@

Description
Choke,2.5MHr

Description

8 Contacts
Connector, Male,

R contacts

Connector, Male,
3 Co"taCtS

8 contacts 12/83

Model 1910 AC Voltage Option

"400" Series (Sch. 299600 Pg.

(PC-Board 496 - Pg. 7-28)

I

Sch.
Location

C6

1 c4

I

"100" Series (Sch. 301620 Pgs. 7-19, 20, 21, 22)

(PC-Board 489 Pgs. 7-23, 24)

Sch. Pg.1 Item No./
Location

Z/E5

"1000" Series (Sch. 301620 - Pgs. 7-19, 20, 21, 22)

Sch. Pg.1 Item NO./
Location

3/c3,4

3/Several PC-486

illseverai PC-489

3/c3,4

RELAYS (K)

1 PC-Board

1 41/C2 1 COT

1 42lC2

item I
Locat

4OlC2

U0.l
IOn

Mfg.

Code
COT

COT

I I

I

CIIOKES CL1

PC-Board
Location
51/83

CONNECTORS (P)

PC-Board
Location

PC-486
17lA3

lBlF3

54lA4
PC-490 A-P

Mfg.

Code "erlg.
NCG

Mfg. Mfg.

7-27)

Mfg.
Deslg.

Mfg.

Sli"

100

Code Oesiq. Part No.
A-P 929830.

01-04

A-P 929638- cs-355-4

01-04

MOL A-2391. CS-288-3

3A

92983R- CS-355-6
01-06

Kfithley

Part NO.

I

Kfithley

Part No.

CH-14

Keithlcy

cs-355-4

7-8

P1005 Connector, Male,

PI006

PI007 Not Used
PI008
PI009 Pin, 1 Contact

8 Contacts 13/E3

Connector, Male,

Modified CS-338-12 55102

Not Used

3/severa1 PC-490

l/Several PC-489 K-I

l/F1

PC-489 K-l
56/E3

A-P 929838- CS-355-6

01-06

29995

24249

MODEL

191

DMM

REPLACEABLE PARTS

Circuit
t&rig.

q101

4102

q103
q104*

QlO5

()I06

0107
q108
4109

Q110

0111

Description
N-Chan,JFET

Transistor,NPN,
Case TO-106

NPN,Silicon
Transistor,PNP

Case TO-92
Transistor,NPN,

case TO-106
Transistor,NPN,

case TO-106

NPN,Switch
NPN,Switch
EIPN,Switch
NPN,Switch
II-Chan,JFET

Selected

"100" Series (Sch. 301620.Pgs. I-19, 20, 21, 22)~

(PC-Board 489-Pgs. 7-23, 24)

Sch. Pgl
Location

Z/E6

l/G5

I/H5

Z/G3

l/C4

l/C4

Z/A5

3/F3
Z/F3
Z/C3

l/G2

TRANSISTORS (9)

PC-Board

item No./

Location
6O/C2

61/D2

62102
63lC3

64104

65104

WD4
67/E3
6BlC4
69lD4
70/04

Mfg.

Code
INT

K-I

1-I
n-o

K-I

K-I

MOT
MOT
MOT
MOT
K-I

Mfg. ~

Desigi

,TE ~

4392 ~

TIP-4$ TG13,

nrmd

2113901/

2113904 iT.-4,

2N39O.J TG-47

m3904

Keithley

Part NO.

TG-77

X234

T&S4

28234

28234

TC-41

Tt-47
IG-I28

4112 FI-Chan,JFET

4113

q114

0115

qI16

4117

q11n
4119
4120

q121
9122

0123

q124

Selected
N-Chan,JFET

Sclccted
II-Chan,JFET

Selcct~d

El-Chan,JFET
Selected

El-Chan,JFET
Selected

PNP,Silicon,

Case TO-92
PNP,Silicon
NPN,Switch
N-Chan,JFET
II-Chan,JFET
N-Chan,JFET
PNP,Silicon,

Case TO-92
Transistor,NPN,

case TO-106

l/C2

Z/D3

Z/B3

Z/B4

l/E3

Z/El

Z/C6 77lC5
Z/C5
Z/B4
Z/B3

l/E4

Z/E2

l/H4

71104

72lC4

73104

74104

75104

76105

78iC5

19105
HO/D5
RI/D5
HZ/B5

B3/D5

K-i

K-I

K-I

K-I

K-I

MOT

MOT 2N39Otj
MOT ZN3904i
K-I
K-l
K-I

MOT

K-I

2N50B7

21,508,~

TC-12B

TGi2B

TG-121:

TGiZii

TC-128

TG-61

T&114

TG-47

TC-I28
l&1211

1

TC-128

TG6,

28234

REPLACEABLE PARTS

MODEL

191

OMM

“100”

Series (Sch. 30162D-Pgs. 7-19, 20, 21, 22)

Case TO-106

NPN,Case TO-92

Transistor,PNP

*In earlier units 4104 is a dual transistor (T&121) and q128 is not used.

"400" Series (Sch 299600 - Pg. 7-27)

Circuit
Desi9.

q401

4402

4403

Q404

4405

Transistor,NPN,

Silcon, Case TO-92
Transistor,PNP,

Silcon, Case TO-92
Transistor, PNP,

Silcon, Case TO-92

Silcon, Case TO-92
Transistor,PNP,

Silicon, Case TO-92

TRANSISTORS (9) (Can't)

(PC-Board 489 -Pgs. 7-23, 24)

:::;,:?;I

l/H3

4/03

4104
ZIG3

Model

(PC-Board 496 Pg. 7-28)

c2

84105 K-I 28234

85185
86lB5
87iC4

1910

AC Voltage Option

PC-Board

Item No./

Location.
45lA2

46lB2

47/B3

48/63

49lC2

Mfg.

Code

T-I TIP-32

MOT

MOT 2113906

Mfg.

Code

MOT

T-I

T-I

T-i

MOT

Mfg.

Desig.

2N5089

Mfg.
Oesiq.

2N5089

2N5087

2115087

2N3904

2113906

Keithley

Part No.

TG-136

TG-62

TG-84

Kfithley
Part No.

TG-62

TG-61

TG-61

TG-47

TC-84

i

7-10

Circuit

Desig.

RlOl

RI02

11103

R104

R105

RI06

Description

NOT USED

22n, 5%,
1/4U,CarbF

22n, 5%.

1/4W,CarbF

4.7ksl. a,
1/4W,CarbF

4.7Kfl, 5%,
1/4W,CarbF

lOMn, 10%.
1/4W,CarbF

"100" Series (Sch. 301620 - Pgs. 7-19, 20,~ 21, 22)

(PC-Board 489 - Pgs. 7-23.24)

Sch. Pg./
Location

Z/D5

Z/E5

2/E6

Z/E6

Z/D6

RESISTORS (R)

PC-Board

Itern NO./

Location

93103

94103

95183

WC3

9llC3

Code

ME,'

MEP

MEP

MEP

Desig.

CR25*

CR25*

CR25*

CR25*

CR25*

Keithley
Part No.

R-76-22

R-76-22

R-76.4.7K

R-76-4.7K

R-76.10M

MODEL 191 DMM

REPLACEABLE PARTS

Circuit
Desiqn. Description

RIO7 910n, .I%,

R108 73.2kn.

RI09

KllO

RI11

RI12

l/lOW,MtF

l%,

l/RII,MtF

101.15n. .I%,
1/1OW,MtF

8.06kn, I%,
1/8W,MtF

13.7kn, I%,
1/8W,MtF

6.04kn, I%,

l/Eu,Mt~

RI13

RI14 Selected-Part

RI15 Selected-Part

RIIG 162kn,

2.74kn,

1/8W,MtF

of matched set

of matched set

1,HW,MW

l%,

l%,

"100" Series (Sch. 301620 - Pgs. I-19, 20, 21, 22)

Sch. Pg./
Location

l/C5

l/C5

l/C6

l/C6

I/F3

l/F3

l/F2

I/E2

l/E2

l/E3

RESISTOR (R) (Can't)

IPC-Board 489 - PQS. 7-23. 24)

PC-Board Mfr.

item NO./

Location
98lC3 ACI

WC3

1oo/c3

101/c3

102IC3 PKP

103/c3

104lC3 PliP

105/03 K-l

106103 K-I

107/03

Code Desig.

PRP

AC1

PKP

PRP

PKP

Mfr.

VAR-.lfl

C6-910

*t

"AR­Ch-lOl.;l5

**

t*

+*

.lq

Keithly
Part No.

K-ZG3-91D

H-u-73.21:

K-263-101.15

I<-iii!-ti.06i:

,<-88-I?. ii,

2iI996

2'i'W>

ii-i!i!-,621,

RI17

RI18

RI19

R120

RI21

RI22

RI23

RI24

RI25

R126

RI27

ZZOkn, IO%,
1/21J,coolp

220kn, IO%,

l/ZW,Comp

200kn, 1X,
8W

9lOkn, 5%,

1/4W,CarbF

loon, 5%,

1/4U,CarbF
Zkn, IO%,

Cermet Trimmer
ZOkn, IO%,

Cermct Trimmer

zoon,

10%:

Cermft Trlnmer
IOOkn,

Cernet Trimmer
loon, 10%

Cernet Trimmer
Thick Film

lo%,

l/C5

l/G5

l/C2

I/(;1

l/E2

l/C6

l/C5

l/C4

l/E3

l/E2

l/E2,E3

108,03

109103

llOlE3

lll/E3

112/03

113/c3

114lC3

115IC3

116103

117103

118/03

n-R

n-n

IX"

ME P

E,EP CK25*

0Rfl

BRil

BKN

DKN

"Rll

K-l

3386I-;
l-202

3386F-:
l-203 ~

3386F-:

l-201

3299,1-

l-104

3299w

l-101

K-76-100

fnP-97-iK

KP-97-201:

KP-9-200

RP-104.100k

KP-,04-100

Ti -84

7-11

REPLACEABLE PARTS

MODEL

191

DMM

RI28

R129

11130

RI31

II132

RI33
RI34

RI35

R13h

Thick Film
Thick Film
zon, IO%,

2kn, IO%,
Ccrrwt Trimmer

Thick Film
Y.OYkn, I%,

llR11,MtF
lkn, I%,

1/DW,MtF
47k11, 5%,

ll411,Carbl

“100”

Series (Sch. 301620 Pgs. 7.19, 20, 21, 22)

RESISTORS (R) (CON'T)

(PC-Board 489 PYs. 7-23, 24)

PC-Board

item No/

Mfo. Mfo. Kfithlev

_..-

I/C3

z/Several
Z/C3

2/C4

Z/A4

119/03

120/03

121103

122/U3

123/03

124/04
125/04

126/[14

127/U4

K-I
K-I
RKR

Bill,

BKrl

K-I

PKP

PRP

MEP

338GF-

l-200

3386F-

I-202

3386F-

l-203

**

**

Cl?25*

TF-88
TF-83
KP-97-20

IRP-97.2k

RP-97.20k

TF-87

K-88.9.09k

K-RII-lk

il-76.47k

RI37
K13R

RI39

RI40

R141

K142

RI43

R144

11145

RI46
RI47

RI48

Thick Film

4.99kn, 18,
1/8W JYLF

47kn, 5%,

1/4W,CarbF

47kn, 5%.

1/4W,CarbF
330kn, 5%.

1/4W,CarbF
YlOkn, 5%,

11411,CarbF

910kn, 5%,

1/4W,CarbF

910kn, 5%.

llilW,Comp

Z/On, 5%,

1/4W,CarbF

Thick Film
390n, 5%.

1/411,CarbF

910kn, 5%,

lliiW,CarbF

2/scvera1
Z/C3

1104

Z/A5

Z/B3

I/E4

l/G4

l/C3

4104

2,Se"eral
3/C2

l/C4

128lC4

129/84

130lE4

131/05

132/05

133lE5

134105

135,E5

136/85

137/c5

138,F5

139iE3

K-I

PRP

MEP

MCP

MEP

MEP

MCP

n-R

MEP

K-I
MEP

MEP

**

CR25*

w25*

CR25*

CK25*

u-914.
5%

clQ5*

CR25*

CR25*

TF-85
K-88-4.99k

K-76-47k

K-76-47k

12-76-330

R-76.910k

K-76-YlOk

K-282-Y1Ok

11-76-270

TF-8h
11-76-390

K-76.910k

7-12

RI49

RI50

EZOkn, 5X,

ililW,CarbF

630kn, 5%.

1/4W,CarbF

l/C4

1103

140IE3

141lE4

I

MEP

MEP

ci(25*

CK25*

K-76.820k

1 K-76.630k

MODEL 191 DMM

REPLACEABLE PARTS

Circuit
Desiq.

RI51

R152

RI53

K154

R155

RI56

RI57

RI58

RI59

Description

IOOkn, IO%,

lW,

camp

IOOkn,
1W,Comp

1.5Mn, 10%.
1/411,CarbF

4.02ki7, IX,
l/aw,mF

lo%,

35.7kn, l%,

11811,MtF

24.3kn,
1/811,MtF

27kn, 5%,

1/4W, CarbF

l%,

1on, 5%,

1/4W,CarbF
Ion, 5%,

1/4Ll,CarbF

“100” Series

Sch. Pg./
Location

RESISTORS (R) (CON'T)

(Sch. 301620 - Pgs.

(PC-Board 489 - Pgs. 7-23, 24)

PC-Board

,tem NO./

Location

5

l/A2

l/A2

2/D3

l/F5

l/F5

l/F6

Z/A4

4102

4103

14uc4

143/G5

144lC5

145/E4

146iD4

147104

148104

149185

15O/B5

I

"200" Series (Sch 301620 Pgs.

(PC-Board 489 - PYs. 7-25)

7-19, 20, 21, 22)

Mfg.
Code

n-u

Mfg.
Ocsig.

r&104-

10%

A-R

G-104-

10%

MEP

PRP

PRP

PRP

MEP

1,E P

MEP

CR25'

**

l *

**

CK25'

CR25'

CR25*

7-19, 20, 21, 2

Keithley

Part NO.

R-2-,OOk

R-Z-look

IR-76-,.5tl

K-8%4.02k

R-88.35.7k

K-88-24.31:

K-76.2,k

R201
R202
R203

R301

R302

K303

Circuit

Desiq.
R401

R402

Thick Film
Thic/k Film

Thick Film

3.3kn, 5X, 3/A3
ll411,CarbF

3.3kn, 5X,
l/lill,CarbF

Description
Pot,SOn, IO%,

3/4w
24Yfl, .I%,

1/101l,WbI

3/F2
3102 24lC3
3lE2 25/E3

"300" Sfrics (Sch. 301620 PYs.

3105

3185 18/02

"400" Series (Sch. 299600 - Pg. 7-27)

Sch. Item No.1 Mfg. Mfg.
Location Location COdC

F3 52/02 BRN 3006P

E4

23/83 K-I

K-I

K-I

7-19, 20, 21, 2

(PC-Board 489 Pgs. 7-23, 24)

16/81

17102 MEP

MEP CK25*

Model

1910

AC Volts Option

(PC-Board 496 - Pg. 7-28)

PC-Board

53182 IKC

CR25*

Desig.

50

MAR6
249

,:,i”l:

R-76.3.3K

I(-16.3.3K

---.

Keithley
Part NO.

RP-89-50

K-241-24')

R403

2191n, .I%,

1/1OW,IIW

I

F3

54182 IKC

MAR6

2191

R-241-2191

7-13

REPLACEABLE PARTS

RESISTORS (R) (COrl'T)

Model

1910

"400" Series (Sch. 299600 - Pg. 7-271

(PC-Board 496 - Pg. 7-28)

AC Volts Option

MODEL 191 DMM.

Circuit
Desi9.

R404

R405

R406

R407

R408

R409

R410

R411

R412

R413

PC-Board

Sch.

Description

150kn, 5X,
1/4W,CarbF

150kn, 5%,
1/4W,CarbF

IOkn, 5%,
1/4W,CarbF

264.2n, 5%,Part 06

of Match Set

2400, 5%,
ll411,CarbF

Pot, loon, IO%,
3/4w

Pot, IOkn, IO%, 03
3/4w

Pot,lkn, lo%, 04
3/4w

4.75kn, .54.,part c5 63182
of Matched Set

54.7Kn, .5%, c4
Film

Location
G2

F2

F4

02 59/83

D5 60182

Item No./

Location

55lB2 EIE P

56182 MEP

57183 MEP

58182

61/W

62lC2

64182

Mfg.

Code

K-l

MEP

BRN

BRN

BRN

K-I

K-l

rlfg.

Desiq.
CR25*

CR25* R-76-150K

CK25* R-76.10K

CK25*

3006P

Kfithley
Part NO.

R-76.150K

R-266

R-76-240

RP-89-100

100

3006P

10K

3006P
IK

RP-89-IOK

RP-89-IK

11-266

R-275.54.7K

R414

R415

K416

R417

R418

* Manufacturers Designation includes Part Description; e.g.,
** Manufacturers Designation is GP 114, l%, TlOO, Resistance Value.

Circuit
Desig. Description

5101

s102 Switch DPDT

Thick Film,S%,
Special

495kn, .S%,Part c3 wc2
of Matched Set

33kn, 5%.
1/4W,CarbF

47kn ,5%,

1/4W,CarbF

ZMn, .S%,Part
of Matched Set

"100" Series (Sch. 301620

11 Station Several
Pushbutton

Several 65/C2

04

61 68/E2 CR25*

82 69/E2

PC-Board 489 - Pgs. 7-23, 24)

Sch. Pg. Iten No./ Mfg.
Location Location Code

4/A2 195/A4

67tQ2

SWITCHES (5)

PC-Board

194/E3-5 K-l

K-I TF-72

K-I R-266

MEP

MEP

K-I

CR 25, 22, 5%, 1/4W, Camp. for R102

- Pgs. 7-19, 20,

c-w GF326-0006

CR25*

21, 22)

Mfg. Keithley
Desig. Part NO.

R-76.33K

R-76.47K

R-266

3M SLC! - +\q

SW-397

7-14

MODEL

191

DMM

REPLACEABLE PARTS

“100” Series

(PC-Board 489 - Pgs. 7-23, 24)

Circuit Sch. Pg.1

Uesig. Description

TlOl

TlOl

Transformer, 4183

Standard V3rsion

Transformer, 4/53 179/82
Japanese Version

"100" Series (Sch. 301620 - Pgs. 7.19, 20,

Location Location

(PC-Board 489 - Pgs. 7-23, 24)

-_-

Circuit
Oesig.

UlOl

u102

u103

u104

Description

Selected-Part
of Matched Set

RI-FET,OP-Amp

(Selected IC-176)

BI-FET,Op-Amp

(Selected IC-176)

Hex inverter

Sch. Pg.1
Location

l/E3

l/F3

l/G5

2/sevcra1

TRANSFORMER (T)

(Sch. 301620 Pgs. 7-19, 20, 21, 22)

PC-Board

Item No./

178/82

INTERGRATEO CIRCUITS (U)

PC-Board

Item No./

Location
153/C2

154/02

155/D2

156/B3

Mfg. Mfg.
Code

K-l

K-l

Mfg.
Code

K-I

K-l 30154

K-l

NAT

Ocsig.

21, 22)

Mfg.

Oesig.

741504

KElthley
Part NO.

TR-173

TR-177

i

Kcithley
Part NO.

29996

30154

iI;-186

u105

U106

u107
UIOR

u109
UllO

Ulll
u112

u113

u114

u115

Up/oown
counter

Dual D-Type
Flip-Flop

Voltage comparator

Transistor array,

14.pin DIP
(Selected IC-53)

BI-FET,Op-Amp
Transistor array,

14-pin DIP
(Selected IC-53)

BI-FET,Op-Amp

Itegratcd Circuit
(Selected IC-218)

RI-FET,Op-Amp

(Selected IC-176)

BI-FET,Op-Amp

(Selected IC-176)

Voltage Quad
comparator

Z/F6

2/F3,G3 158/83

ZIG2
zlseveral

Z/E3
2/E3,E4

Z/C5

Z/C3

Z/D3

Z/El 166lC5

2/A5,A6 167105

157lC3

159lC4

160104

161/C4

162lC4

1631C4
164-04

165/C5

MOT

MOT

,lAT

K-I

llAT

K-l

NAT
K-I

K-I

K-I

bIC74LS

193P

flC74S

74P

L1131111

LF35111

LF35lll 16176

111339

IC-214

IC-2I6

IC-173
29198

IC-I76

29198

30167

30163

30154

iC-219

Ullh

Quad Z-Input

Nand Gate

z/Several 168/83

blAT

74L500

IC-163

7-15

REPLACEABLE PARTS

MODEL 191 DMM

INTEGRATED CIRCUITS 0~) (CON'T)

"ZOO" Series (Sch. 301620 - Pgs. 7-19, 20, 21, 22)

(PC-Board 486 - Pg. 7-25)

Circuit

Desig.
U201 MOS to LED segment 3/03

u202

Circuit
Desiq.

u301

1,302
u303

u304*

u305*

u305*

Description Location

and Digit Driver
BCD to 5eYen segment 3/E2

Latch/Decoder/Driver

"300" Series (Sch. 301620 - Pgs. 7-19, 20, 21, 22)

Dual 4 Bit Decade

and Binary Counter

Peripheral

Interface Adaptor

4096 Bit Cnos
UV E-PROM

4096 BIT CMOS

UV E-PROM
1024 X 8 BIT 3182

ROM

Sch. Pg./ Item No./

3lA2

3182

PC-Board
Location Code Desig. Part NO.
28/B2 F-I

29lE2 MOT

(PC-Board 489 Pgs. 7-23, 24)

PC-Board

Item NO.1

Location
21/Bl

22lC2

23/C3

02

25103

25103

Mfg. Mfg. Keithley

Mfg.

Code
T-I

MOT

AM1

K-I

K-I

K-I

Mfq.

Desiq.
SN74LS

390
MC6802
S682OL

Keithley

Part EiO.
IC-212

LSI-18

LSI-8

PKO-102-02

PKO-101-02

LSI-23

U306

u307

U308

u309

u310

u311

* Revision A,B and some C Digital Boards use two E-PROMS (IC-220 Programmed). All later

revisions use one ROM (LSI-23).

Circuit Sch.

Desig. Description Location

­u401 Monolithic JFET

Quad Z-Input

Nand Gate

Dual 4 BIT Decade
and Binary Counter,

Dual 4 BIT Decade
and Binary Counter

Integrated Circuit

Flip-Flop
Quadruple 2.Input

Positive-And Gate

3/severa1

Model

"400" (Sch. 299600 - Pg. 7-27)

(PC-Board 496 - Pg. 7-28)

C2 72lQ2

26lE2

27lC2

28lE2

29iE2

30/E2

31/E3

1910

AC Voltage Option

PC-Board

Item No./ Mfq.

Location Code

NAT

T-I

T-I

NSC

NAT

NAT

NAT LF3561~1

74L500

SN74LS

393

SN74LS

393

DM74LS

74N

DM74L
508N

74L500

Mfg. Kfithlfy
Ucsig. Part Ho.

IC-163

IC-213

IC-213

IC-144

IC-215

IC-163

i

IC-152

MODEL 191 DMM

REPLACEABLE PARTS

Circuit

Desiq.

"i?lOl

'JR102

VKlO3

VK104

VK105
VK106
VRlO7

Description
Three lcrminal

Positive Voltage
Rcqulator

Three Terminal
Ncqative Voltage
Regulator

Three Terminal
t5v Voltaq?
Kequlator

Lcncr Diode

‘100’

“100”

Series (Sch 301620

(PC-Board 489 Pgs. 7-23, 24)

ich. Pg./
Location

4102

4lE3

z/c5
Z/C6
Z/C4

Series

(PC-lioard 489 rqs. 1.23. 24)

VOLTAGE IKLGULATOKS (VI0

(Sch. 30162D

- Pgs. 7-19, 20,

CKYSTAL (Y)

Pgs. 7-19. 20, 21. 17)

M f q

Code

21, 22)

Mfq.

Ocsiq.

7-11

REPLACEABLE PARTS

TOP

COVER

25728E

OVERLAY

293845

MBBEL

191

DMM

\

BINDING POSTS

.RED BP-11-2

j-32 x l-1/4”

FIGURE 7-1.

Covers and Panels