Solartron 7151 Service Manual

7151

COMPUTING MULTIMETER

MAINTENANCE MANUAL

Issue 1: June 1984

SOLARTRON

Schlumberger

Solartron pursues a policy of continuous development and product improvement
The specification in this document may therefore be changed without notice

Solartron Instruments, Victoria Road, Farn bo rough
Hampshire, England GU14 7PW Telephone: Farnborough [phone]
Telex: 858245 Solfar G Cables: Solartron Famborough
A division of Schlumberger Electronics (UK) Ltd

PartNo. 71510011

19©84

n

7151 COMPUTING MULTIMETER

MAINTENANCE MANUAL

1642g/0072g

CONTENTS

Chapter 1

Chapter 2

Chapter 3

Chapter 4

Chapter 5

Chapter 6

General

Calibration Procedures

Dismantling & Reassembly

Circuit Descriptions & Diagrams

Fault Diagnosis Guide

Parts Lists &

Component Layout

1642g/0072g

r

Chapter 1 General

1642g/0072g

f

CHAPTER 1

1. GENERAL

The Solartron 7151 Computing Multimeter performs all common

functions, and offers: a library of

measurements;

The instrument is suitable for general purpose bench work, or for use
within a system where 7151 would
control interfaces. The interfaces provided are the IEEE 488 (1978) STD
system and the RS232C V24 serial system.

2. SAFETY

The 7151 multimeter has been designed in accordance with the

recommendations of IEC 348. To ensure the user's safety, and the
continued safe operation of the instrument, it is advisable to fully
observe the procedures and specifications given in the Operating Manual

(Part No. 71510010).

An Earth wire is provided to ensure the user's safety. Therefore, if an
extension mains cable is used, check that the Earth connection is
maintained throughout the length of the extension.

When using 7151 on

(e.g. inductive circuitry giving high back emf's such as

a large mains transformer), it is most important that 7151's test leads
are disconnected from the equipment before

that harmful back-emf's do not reach 7151. Care should

exercised when handling the input leads, especially where
are known to be present, or where

and a programmable power-on status.

equipment which is capable

programs;

be operated via

high transients could

clock controlled

one of

of delivering

switched it off. This ensures

measurement

its remote

high voltages

the secondary

always be

high

occur.

voltages

of

Whenever it is likely that the safety of the instrument has been impaired

- e.g. if it shows visible signs of damage, if it fails to perform
correctly, or if the specifications have been exceeded in any way - it
should be made inoperative and referred to a suitable repair depot. Any
maintenance, adjustment or repair of the multimeter must be carried out
by

skilled personnel only, in accordance with the procedures and

precautions detailed in this Maintenance Manual (part no. 71510011).

A

Wherever this symbol appears on the front or rear panel it is
advisable to consult the appropriate section of
further information.

3. SUMMARY OF OPERATION

A schematic block diagram of the 7151 is shown in Fig. 1.1. 7151 is

essentially a
technique of analog to digital conversion.

All inputs to the instrument are first converted to dc voltages before
being passed to the input amplifier. This is simple enough for current

(dc) and resistance, but ac inputs also undergo rms conversion to dc.

All inputs are suitably scaled by the input amplifier and passed to the

voltage measuring instrument which uses the pulse width

the Operating Manual for

0072g/1634g

1.1

analog to digital converter (ADC). With no input,
balanced pulse trains of

received, the

opposite

then

manner, proportional to the size of the input. These trains are

converted to a single end and gated into a reversible counter. The

mark-space ratios of the trains respond in an

mark space ratio 1:1. When an input is

the

ADC produces two

equal and

nett result is a pulse count proportional to the measure of the input.

The measuring circuits are controlled by what is termed the 'floating'

logic and

'Piggyback' ROM. The other circuits of 7151 are organised in a
arrangement which is controlled by the 'earthy' logic and consists
essentially

between the floating and earthy logic is acheived by

links. It is the

of

measurements, processing, remote

displays, and so

consists essentially of a 8-bit microprocessor

with

of another 8-bit microprocessor. Isolated communication

opto coupled serial

earthy logic

which is responsible for effective control

control, the real time clock, the

on.

bus

0072g/1634g

1.2

A DRIVE

OHMS

I/P

TERMINALS »

CONTROL

A DRIVE

CONTROL

7151 MULTIMETER FUNCTIONAL BLOCK DIAGRAM

o-

INPUT SWITCHING

A.C.

CONDITIONING

INPUT

AMP

ATTEN. &
GAIN CONTROL

GAIN
CONTROL

FLOATING LOGIC

OPTO COUPLERS

CONVERTER

HOLD OFF

2 WIRE SERIAL

LINK

COUNT

RESET

+/-REF

WATCH-DOG

REFERENCE

AUTO-CAL

MEMORY

TO FLOATING

POWER

RAILS

TO EARTHY

POWER RAILS

FLOATING

POWER

SUPPLY

EARTHY

POWER

SUPPLY

ADDRESS BUS
ENABLE

WATCH-DPG

ADDRESS
LATCHES

At) TO A7

HOLD -OFF

RESET

A8 TO A15

EARTHY LOGIC

AO/DO TO A7/D7

4 COLUMNS

1 COLUMN

CLOCK

KEYBOARD 8.

FRONT/REAR SW.

DECODERS

INTERFACE
DECODERS

4 ROWS

8 ROWS

DATA BUS

SERIAL

KEYBOARD &

FRONT/REAR SW.

DECODERS

INTERFACE SW.

DECODERS

LATCHES

GPIA

DISPLAY

DRIVER

INTERFACE BUS

DRIVER

LEVEL CHANGING

TRANSCEIVERS

TO

■ REAR PANEL
GPIB SOCKET

ANALOG OUTPUT

TO

LEVEL CHANGING

TRANSCEIVERS

REAR PANEL

AUXILIARY SOCKET

7151 MULTIMETER FUNCTIONAL BLOCK

*

DIAGRAM

FIG 1.1

Chapter

Calibration

Procedures

1642g/00'72g

{

I

(

{

1

CHAPTER 2

Setting-Up And Calibration Procedures

General

These procedures enable the instrument to be set-up
factory

despatch

standards

.

and

calibrated to the

The procedures are categorised into the following sections:

1. Setting-up procedures

2. Initial calibration

3. Final calibration

procedures

procedures

Safety

The instrument must be disconnected from the mains supply when
dismantling it to gain access to the preset controls and also
being reassembled (see

Chapter 4 for dlssembly instructions)

when it is

.

When adjusting preset controls beware of high test voltages, the guard
potential on the guard plate and also the mains input supply.

Calibration Method

Owing to the automatic calibration circuits incorporated in 7151, it can
only be calibrated by connecting it to a remote controller and then using

the appropriate calibration commands.

program can be used which is a
Solartron

can

supply, on tape cassettes, a calibration program for the

much faster method of calibrating 7151.

Alternatively, a calibration

more common types of controllers.

The user is advised to re-calibrate 7151 annually.

If the instrument's existing
satisfactory, the user can
constants by sending the REFRESH

state of calibration is judged to be

simply re-write the existing calibration

command to 7151 once it is in the

calibration mode.

Calibration Source

It is recommended that the calibration source has an accuracy of at least
two times better than the accuracy specified for the various 7151
functions. The 7151 specification is given in the Operating

Manual and

the important percentage accuracies are as follows:-

DC Volts

DC Current
AC Volts
AC Current
Resistance

0.002%

0.02%

0.05%

0.05%

0.002%

0072g/1624g

2.1

ENTERING CALIBRATION MODE

Insert a shorted 2.5mm jack plug Into the rear panel
the front panel CAL Indicator to repeatedly flash. The short may be

CAL socket, causing

within the plug Itself, or externally via a switch. The plug must remain

fitted throughout the calibration, and can be removed after calibration
is complete.

Note: Do not switch mains power on or off when the shorting plug Is
fitted, otherwise the Internal calibration

Using the controller, send the command CALIBRATE
Into the

calibration

mode. The

CAL Indicator should then be steady.

Also displayed Is the word, 'CAL'. Once the calibration mode

constants may be

ON to 7151, putting It

altered.

has been

selected, the following conditions apply:

(a) Three commands cannot be used: TRIG

TRACK

NULL

'OFF' status Is adopted.
'OFF' status Is adopted,

all nulls being deleted.

(b) Four commands become available: HI

LO
WRITE
REFRESH

for refreshing

existing

cal. constants.

0072g/1624g

2.2

CALIBRATING MEASUREMENT RANGE

Using the controller, select the function and range to be calibrated by
sending the appropriate MODE and RANGE commands.

7151 must then be supplied with two precisely known reference inputs

(non-negative) one at approximately nominal full scale (referred to as

the Hi point), and

one at approximately zero (referred to as the Lo
point), in the case of ac ranges the Lo point should not be less than
approximately 5% of nominal full scale rather than zero. This ensures

that all inputs are within the optimum part of 7151's

linear range.

After a reference input is applied, 7151 must be informed of the precise
value of the input. This is achieved by using the HI command for a Hi
point, and the LO command for a Lo point. These commands must be

accompanied by an integer argument number, of up to six digits in length,

which expresses the applied input in terms of 5 x 9's count.

An integer value of 200000 corresponds to nominal full scale for any

range

For example, applying 2V on the 2V range, enter 200000

.

applying 20V on the 20V range, enter 200000
applying 5V on the 200V range, enter 005000

Apply the Hi point input to 7151 for the requisite function/range.

For example, 2.00843V on 2V dc range.

Using the controller, send the HI command to 7151.

For example, HI200843.

7151 responds by displaying 'Hi Pt' for about 1.5 seconds, during which
time it measures the applied reference input. When finished, the
instrument displays (and outputs) its measured count, e.g. 214576. It is

of no consequence if the displayed count differs from the applied input.

Repeat the above

(short circuit), and send the LO command. For example LOO (leading

zeroes need

Having
command

specified the Hi point and Lo point (in any order), send the

WRITE to 7151 (no argument required). This causes the
calibration constants for the selected range/function to be calculated
and

stored in memory. If successful, the message 'Good' is displayed.

If unsuccessful, an error message will be displayed and output to the

procedure for the Lo point. For example, reference = OV

not be specified).

controller.

Repeat the above instructions for each function/range to be calibrated.

0072g/1624g

2.3

RESTORING THE MEASUREMENT FUNCTIONS

Using the controller, send 7151 the command CALIBRATE OFF. The CAL

indicator will then flash indicating that the CAL shorting plug is still

fitted.

Withdraw the CAL

shorting plug. The

CAL indicator should then be

invisible, the instrument being ready for normal use.

SUMMARY

(a) Insert CAL shorting plug (2.
(b) Select the calibration mode by sending the CALIBRATE ON

5mm) in rear panel socket

.

command.

(c) Select the requisite function and range to be calibrated and perform

the calibration sequence. Repeat for each range/function to be

calibrated.

(d) De-select the calibration mode by sending the

CALIBRATE OFF

command.

(e) Remove CAL plug.

0072g/1624g

2.4

Setting-Up

Procedures

DC Power Supply Checks

Measure the dc supplies on PCB1 and PCB2 at the output pins of the
appropriate regulator IC's. Tolerances of the most important supplies,
mains voltage 240V, follow:

floating 15V unregulated
floating 15V regulated
floating 5V unregulated

floating 5V regulated
earthy 5V unregulated
earthy 5v regulated

between 20.7V and 21.6V

15 ± 0.75V

between 8.8V and 9.1V

5 + 0.25V

between 9.5V and 9.8V

5 ± 0.25V

Display Checks

The contrast of the display can be adjusted

by means of RV301. Make the

digits appear as black as possible but without introducing slurring when

a reading changes.

Keyboard Checks

The following sequence exercises all 16 keys.

Key Press

FILT 2 press minimum

Display Response

"FILT" on/off

Finish with "FILT" off
ma-
mA===

K£2

V~
V===
AUTO 2
V
A
LOCAL

presses

minimum

KQ

V~
V===

"AUTO" on/off
Check for downranging
Check for upranging

"GPIB nm" where nm is address
value.

NULL 2 presses minimuim
6x92

TRACK 2

presses
presses

minimum
minimum

SAMPLE with "HOLD" asserted

COMPUTE
MENU

"NULL" on/off

"6x9" on/off

"HOLD" on/off

“

HOLD" goes out briefly and

returns

.
"NO PROG"
“

PROBES?"

0072g/1624g

2.5

Initial

Calibration

Procedures

Test Equipment

1. General purpose DMM.

2. General purpose oscilloscope

3. Controller, e.g. Commodore PET fitted with BASIC III or BASIC IV
firmware.

4. Calibrator, e.g. Fluke 5101 fitted with GPIB interface.

5. ACV Calibrator, e.g. Hewlett-Packard 745.

6. ACV High Voltage

7. Capacitor O.lyF polypropylene attached to a twin 4mm banana
(3/4" centres)

Switch on 7151 and

Amplifier e.g. Hewlett-Packard 746.

.

allow to warm up for at least one hour before

plugs

calibration.

The initial calibration

Table

2.1

No.

2.2

2.3

2.4

procedures are detailed in the following tables:

Procedure
Initial
Initial
Initial
Initial

calibration, DC
calibration, Resistance
calibration. Current
calibration, AC Volts

Volts

Please

Note: The limits of error expressed in the following tables are

those adhered to by the factory for a new instrument. As an instrument

'ages', "components become more noisy or their tolerances increase.

Therefore, when calibrating a used instrument, it may

be

necessary to
accept limits of error that are marginally higher than those listed in
these pages. However, the instrument should always conform to the

commercial specification (see Operating Manual) after calibration.

0072g/1624g

2.6

Table 2.1 Initial Calibration, DC Volts

TEST RANGE & INPUT

ACTION

LIMITS

COMMENTS

MODE

1 Configure the rear panel interface switches and connect the controller to

7151.
Do

not insert the calibration Key Jack yet. FRONT/REAR switch to 'FRONT'.

2

3

4

5

6

7

2VDC

2VDC

0.2VDC

s/c link

VHI-VLO

front

s/c
VHI-VLO
Front

o/c

Power on

Insert Calibration
Key Jack

Adjust RV3.
DVM between link

& ROME

Check display ^

'for2scatter

Check reading

± 100 yV

3 adjacent
values

0 ± lOOyV

I/P amp gross
offset null.

2V range noise test.
The reading may jump
every 10 secs at

drift-correct

Input current
measurement.
may be exceeded at
drift-correct

.

Value

.

10

11

12

13

8

9

2VDC

2VDC

2VDC

2VDC

0.2VDC

20VDC

4V< plus
overload
< -100V

-4V< minus
overload
< -100V

±1,99999V

alternatively

+

1.99999V &

0.00000V

0.

199999V &

0.00000V

+19.

9999V &

0.00000V

Measure C4 with

DMM referred to

ROME

As above

Adjust RV1
CAL BAL

Do calibration

routine over the
interface

Do calibration

routine over the
interface

Do calibration

routine over the

interface

+3.90
+3.05

-3.05

-3.90

+ and -
equal within

1 bit

Positive input-clamp
test (D6)

Negative input-clamp

test (D26)

Cal. Bal Adjustment
Use continuous
drift-correct (Yl)

.

+2V set-up

+2V set-up. Use the
calibrator to deliver
0 volt

.

+20V set-up.

0072g/1624g

2.7

Table 2.1 Cent.

TEST RANGE & INPUT

MODE

14 200VDC +199.999V &

0.00000V

15 IkVDC +10000.

00V &

0.00V

16

17 2VDC +1.00000V

-1.00000V

ACTION

Do calibration

routine over the

LIMITS

COMMENTS

+200V set-up.

interface

Do calibration
routine over the
interface

+lkV Set-up. The

Calibrator LO and the

7151 LO input should

be mains grounded.

Check that the

spark-gap does not
operate. Apply for

1 minute and check

that the reading

does not drift more

than 2 bits.

Exit Cal Mode

Measure

+2 bits
pos-neg
error

Linearity. Change
polarity changing
over inputs.

0072g/1624g

2.8

Table 2.2 Initial Calibration, Resistance

TEST

1

2

3

4

5

6

7

RANGE
MODE

20kfl

200kfl

2Mfi

2k£2

20kfi

200kfi

2Mft

5. INPUT

DMM between

I- and LO

As above

As above

l.OOOOOkfl

and IQ

lO.OOOOkQ

and IQ

lOO.OOOkQ
and IQ

1.00000MQ

and IQ

ACTION

Measure current

LIMITS

100±5yA

COMMENTS

from -I.

DMM set to current.

As above

As above

Do calibration

10.0 ± 0.5uA

1.0 ± 0,5yA

2KQ range set up

using the interface

Do calibration

using the interface

Do calibration
using the interface

Do calibration
using the interface

20KQ range set
up.

200KQ range set
up.

2MQ range set up
O.lyF in
parallel will
reduce scatter
caused by series

mode interference.

10

11

12

8

20MS2

10.0000MQ
and IQ

Do calibration
using the interface

20MQ range set
up. O.lyF in
parallel will

reduce scatter.

9

2M$2

DMM across
7150 HI & LO

2M£2

240VAC
/ 50 Hz

2Mfi

1.00000MQ

Measure the o/c
volts from Q
source

.

Apply VHI-VLO

10 seconds.

Check after test 9

+5.2V ± IV

1.00000MQ
±100 bits

Q source

positive clamp.

Ohms overload test

Survival check for
damage after test

10.

DV

Auto

+1 kV
applied 5

times

Check display

± 10 bits

IkV step input

test. LO

GUARD must

connect to LO of

Cal. and also to

and

mains ground.

7151 must uprange

withou power

restarts. It is

permissible that

the spark-gap

operates.

0072g/1624g

2.9

Table 2.3 Initial Calibration, Current

TEST

1

2

3

5

RANGE
MODE
DC A

AC A

DC AC

& INPUT

+1.00000A &
open circuit

400 Hz

1.99999A &

0.19999A

+1.99999A

ACTION

Calibrate over the

LIMITS

COMMENTS

1 Ampere Set-up

bus

Calibrate over the

2 Ampere Set-up

bus

Exit Cal Mode

Measure voltage at
current front
sockets with

a

0.80 volt

Burden

DMM.

0072g/1624g

2.10

Table 2.4 Initial Calibration, AC Volts

TEST

1

2

3

RANGE &
MODE

VAC

various
ranges

20VAC

20VAC

INPUT

s/c

19.9999V

400Hz

19.9999V

50kHz

ACTION

Adjust RV2 for
minimum @

TP3

Note reading

Adjust CV1 St R10

for flat response

LIMITS

±150 bits

referred to
OV

Value at test

12'

±0.0

10V

COMMENTS

IC15 offset null
adjust.
to monitor TP3
Transformer

Use

DMM

lamination to be

mains-grounded.

The lowest figure
possible is
required; if
necessary by
error-sharing
among the ranges

Attenuator HF

trim. 100 bit
limit applies

when a dummy lid

is fitted.

.

10

4

5

6

7

8

9

0.2VAC

2VAC

20VAC

200VAC

IkVAC

0.2VAC

0.199999V &

0.019999V
400Hz

1.99999V &

0.19999V
400Hz

19.9999V S>

1.9999V
400Hz

199.999V S.

19.999V

400Hz

750.00V &

199.99V
400Hz

30KHz

0.199999V

Calibrate over the
bus.

Calibrate over the
bus.

Calibrate

bus.

Calibrate over the
bus.

Calibrate over the
bus.

Exit Cal Mode

Check

over the

0.
.000120V

199999V ±

0.2V LF
Fluke 5101.

2V LF Set-up

20V Set-up

200V Set-up

1 kV

Set-up

Set-up

11

0072g/1624g

0.2VAC

lOKHz

0.199999V

Check

2.11

0.

199999V ±

,000096V

Table 2.4 Cent.

TEST

12

13

14

15

16

17

18

19

RANGE &
MODE
2VAC

2VAC

20VAC

20VAC

200VAC

200VAC

IkVAC

Ik VAC

INPUT

10kHz

1.99999V

30kHz

1.99999V

30kHz

19.9999V

10kHz

19.9999V

10kHz

199.999V

30kHz

199.999V

10kHz

750.00V

30kHz

750.00V

ACTION

Check

Check

Check

Check

Check

Check

Check

Check

LIMITS

1.99999V ±
.00096V

1.99999V ±
.00120V

19.9999V ±

0.0120V

19.9999V ±
.0096V

199.999V +

.096V

199.999V ±

0.120V

750.00V +

0.46V

750.00V +

0.70V

COMMENTS

20

21

22

23

24

25

26

27

0.2VAC

2VAC

2VAC

2VAC

2VAC

2VAC

20VAC

200VAC

s/c

10Hz

2.00000V

20Hz

2.00000V

40Hz

2.00000V

100Hz

2.00000V

100kHz

0.19999V

100kHz

20.0000V

100kHz

200.000V

Check

Check

Check

Check

Check

Check

Check

Check

150yV

2.00000V ±

0.01456V

2.00000V ±

0.00416V

2.00000V ±

0.00096V

2.00000V ±

0.00880V

0.199999V ±

0.000880V

20.0000V ±

0.0880V

200.000V ±

0.880V

s/c zero.

Trasnsformer

laminations to be

mains-grounded.

0072g/1624g

2.12