Solartron 7151 Service Manual

7151

COMPUTING MULTIMETER

MAINTENANCE MANUAL

Issue 1: June 1984

SOLARTRON

Schlumberger

PartNo. 71510011

Solartron Instruments, Victoria Road, Farnborough

Hampshire, England GU14 7PW Telephone: Farnborough [phone]

Telex: 858245 Solfar G Cables: Solartron Famborough

A division of Schlumberger Electronics (UK) Ltd

Solartron pursues a policy of continuous development and product improvement	19©84
The specification in this document may therefore be changed without notice

n

7151 COMPUTING MULTIMETER

MAINTENANCE MANUAL

1642g/0072g

CONTENTS

Chapter	1	General
Chapter	2	Calibration Procedures
Chapter	3	Dismantling & Reassembly
Chapter	4	Circuit Descriptions & Diagrams
Chapter	5	Fault	Diagnosis Guide
Chapter	6	Parts	Lists & Component Layout

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Chapter 1 General

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CHAPTER 1

1.GENERAL

The Solartron 7151 Computing Multimeter performs all common measurement functions, and offers: a library of programs; clock controlled measurements; and a programmable power-on status.

The instrument is suitable for general purpose bench work, or for use within a system where 7151 would be operated via one of its remote 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 equipment which is capable of delivering high voltages (e.g. inductive circuitry giving high back emf's such as the secondary of a large mains transformer), it is most important that 7151's test leads are disconnected from the equipment before switched it off. This ensures that harmful back-emf's do not reach 7151. Care should always be exercised when handling the input leads, especially where high voltages are known to be present, or where high transients could occur.

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 the Operating Manual for further information.

3.SUMMARY OF OPERATION

A schematic block diagram of the 7151 is shown in Fig. 1.1. 7151 is essentially a voltage measuring instrument which uses the pulse width 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

0072g/1634g

1.1

analog to digital converter (ADC). With no input, the ADC produces two balanced pulse trains of mark space ratio 1:1. When an input is received, the mark-space ratios of the trains respond in an equal and opposite manner, proportional to the size of the input. These trains are then converted to a single end and gated into a reversible counter. The 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 consists essentially of a 8-bit microprocessor with 'Piggyback' ROM. The other circuits of 7151 are organised in a bus arrangement which is controlled by the 'earthy' logic and consists essentially of another 8-bit microprocessor. Isolated communication between the floating and earthy logic is acheived by opto coupled serial links. It is the earthy logic which is responsible for effective control of measurements, processing, remote control, the real time clock, the displays, and so on.

0072g/1634g

1.2

			A DRIVE	OHMS
			CONTROL		A DRIVE
					CONTROL
I/P	o-	INPUT SWITCHING	INPUT				+/-REF
TERMINALS »			AMP			CONVERTER	REFERENCE
				GAIN		COUNT
				CONTROL
				FLOATING	LOGIC	RESET	AUTO-CAL
							MEMORY

	A.C.	HOLD OFF
		WATCH-DOG
	CONDITIONING
		ATTEN. &
		GAIN CONTROL
		OPTO COUPLERS

		2 WIRE	SERIAL
		LINK
				KEYBOARD	8.	4	ROWS	KEYBOARD	&
				FRONT/REAR	SW.			FRONT/REAR	SW.
				DECODERS				DECODERS
	HOLD -OFF	4 COLUMNS
WATCH-DPG	RESET	EARTHY LOGIC
			1 COLUMN
				INTERFACE		8	ROWS	INTERFACE	SW.
	A8 TO A15	AO/DO TO	A7/D7	DECODERS				DECODERS

DATA BUS

ADDRESS BUS

ENABLE

	ADDRESS	CLOCK	SERIAL
	LATCHES

At) TO A7

7151 MULTIMETER FUNCTIONAL BLOCK DIAGRAM

	TO FLOATING	FLOATING
		POWER
	POWER RAILS
		SUPPLY

	TO EARTHY	EARTHY
		POWER
	POWER RAILS
		SUPPLY

DISPLAY

LATCHES DRIVER

DRIVER

INTERFACE BUS	LEVEL	CHANGING	TO
GPIA	TRANSCEIVERS		■ REAR	PANEL
			GPIB	SOCKET
	ANALOG OUTPUT
			TO
			REAR	PANEL
	LEVEL	CHANGING	AUXILIARY SOCKET

TRANSCEIVERS

7151 MULTIMETER FUNCTIONAL BLOCK DIAGRAM * FIG 1.1

Calibration Procedures

Chapter

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1

CHAPTER 2

Setting-Up And Calibration Procedures

General

These procedures enable the instrument to be set-up and calibrated to the factory despatch standards.

The procedures are categorised into the following sections:

1.Setting-up procedures

2.Initial calibration procedures

3.Final calibration procedures

Safety

The instrument must be disconnected from the mains supply when dismantling it to gain access to the preset controls and also when it is being reassembled (see Chapter 4 for dlssembly instructions).

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. Alternatively, a calibration program can be used which is a much faster method of calibrating 7151. Solartron can supply, on tape cassettes, a calibration program for the more common types of controllers.

The user is advised to re-calibrate 7151 annually.

If the instrument's existing state of calibration is judged to be satisfactory, the user can simply re-write the existing calibration constants by sending the REFRESH 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	0.002%
DC Current	0.02%
AC Volts	0.05%
AC Current	0.05%
Resistance	0.002%

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2.1

ENTERING CALIBRATION MODE

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

Using the controller, send the command CALIBRATE ON to 7151, putting It Into the calibration mode. The CAL Indicator should then be steady. Also displayed Is the word, 'CAL'. Once the calibration mode has been selected, the following conditions apply:

(a) Three commands cannot be used: TRIG	'OFF'		status	Is	adopted.
TRACK
NULL	'OFF'		status	Is	adopted,
	all		nulls being deleted.
(b) Four commands become available: HI
LO
WRITE	for	refreshing existing
REFRESH
	cal.	constants.

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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		It is
instrument displays			(and	outputs) its measured count, e.g.				214576.
of no consequence if			the	displayed count differs from the applied					input.

Repeat the above procedure for the Lo point. For example, reference = OV (short circuit), and send the LO command. For example LOO (leading zeroes need not be specified).

Having specified the Hi point and Lo point (in any order), send the command 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 controller.

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

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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 (2.5mm) in rear panel socket.

(b)Select the calibration mode by sending the CALIBRATE ON 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.

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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

Display Checks

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

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

K£2

V~

V===

AUTO 2 presses minimum

V

A

LOCAL

NULL 2 presses minimuim 6x92 presses minimum TRACK 2 presses minimum SAMPLE with "HOLD" asserted

COMPUTE

MENU

Display Response

"FILT" on/off

Finish with "FILT" off ma-

mA===

KQ

V~

V===

"AUTO" on/off

Check for downranging Check for upranging

"GPIB nm" where nm is address value.

"NULL" on/off "6x9" on/off "HOLD" on/off

“HOLD" goes out briefly and returns.

"NO PROG" “PROBES?"

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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 Amplifier e.g. Hewlett-Packard 746.

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

Switch on 7151 and allow to warm up for at least one hour before calibration.

The initial calibration procedures are detailed in the following tables:

Table No.	Initial	Procedure
2.1		calibration,	DC Volts
2.2	Initial	calibration,	Resistance
2.3	Initial	calibration.	Current
2.4	Initial	calibration,	AC 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

1Configure 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			Power on
4			Insert Calibration
			Key Jack
5	2VDC	s/c link	Adjust RV3.	±	100 yV
		VHI-VLO	DVM between link
		front	& ROME
6	2VDC	s/c	Check display ^	3	adjacent
		VHI-VLO	'for2scatter	values
		Front
7	0.2VDC	o/c	Check reading	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. Value may be exceeded at drift-correct.

8	2VDC	4V< plus	Measure C4 with
		overload	DMM referred	to
		< -100V	ROME
9	2VDC	-4V< minus	As above
		overload
		< -100V
10	2VDC	±1,99999V	Adjust RV1
		alternatively	CAL BAL
11	2VDC	+1.99999V &	Do calibration
		0.00000V	routine over	the
			interface
12	0.2VDC	0.199999V &	Do calibration
		0.00000V	routine over	the
			interface
13	20VDC	+19.9999V &	Do calibration
		0.00000V	routine over	the
			interface

+3.90	Positive		input-clamp
+3.05	test	(D6)
-3.05	Negative		input-clamp
-3.90	test	(D26)
+ and -	Cal. Bal		Adjustment
equal within Use continuous
1 bit	drift-correct (Yl).

+2V set-up

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

+20V set-up.

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2.7

Table 2.1 Cent.
TEST	RANGE &	INPUT	ACTION
	MODE
14	200VDC +199.999V &		Do calibration
		0.00000V	routine over	the
			interface
15	IkVDC	+10000.00V &	Do calibration
		0.00V	routine over	the
			interface

LIMITS COMMENTS

+200V set-up.

+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.

16			Exit Cal	Mode
17	2VDC	+1.00000V	Measure	+2 bits	Linearity. Change
		-1.00000V		pos-neg	polarity changing
				error	over inputs.

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2.8

Table

2.2

Initial Calibration,

Resistance

TEST

RANGE

5.

INPUT

ACTION

LIMITS

COMMENTS

1

MODE

DMM between

Measure

current

100±5yA

20kfl

I-

and LO

from -I.

to current.

DMM set

2

200kfl

As

above

As

above

10.0

±

0.5uA

3

2Mfi

As

above

As

above

1.0

±

0,5yA

4

2k£2

l.OOOOOkfl

Do

calibration

2KQ

range set

up

and

IQ

using

the interface

5

20kfi

lO.OOOOkQ

Do calibration

20KQ

range

set

and

IQ

using

the interface

up.

6

200kfi

lOO.OOOkQ

Do

calibration

200KQ

range set

and

IQ

using

the interface

up.

7

2Mft

1.00000MQ

Do

calibration

2MQ

range set

up

and

IQ

using

the interface

O.lyF

in

parallel will

reduce scatter

caused by series

mode

interference.

8

20MS2

10.0000MQ

Do

calibration

20MQ

range

set

and

IQ

using

the interface

up.

O.lyF

in

parallel will

reduce scatter.

9

2M$2

DMM

across

Measure

the o/c

+5.2V ±

IV

Q source

7150 HI & LO

volts

from Q

positive clamp.

source.

10

2M£2

240VAC

Apply VHI-VLO

Ohms

overload

test

/

50 Hz

10

seconds.

11

2Mfi

1.00000MQ

Check

after test 9

1.00000MQ

Survival check

for

±100

bits

damage after test

10.

12

DV

+1

kV

Check

display

± 10

bits

IkV step input

Auto

applied 5

test.

LO and

times

GUARD must

LO of

connect to

Cal. and also

to

mains ground.

7151

must uprange

withou power

restarts. It is

permissible

that

the spark-gap

operates.

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2.9

Table 2.3		Initial Calibration, Current
TEST	RANGE	&	INPUT	ACTION		LIMITS	COMMENTS
1	MODE		+1.00000A &	Calibrate over	the		1 Ampere Set-up
	DC A
			open circuit	bus
2	AC A		400 Hz	Calibrate over	the		2 Ampere Set-up
			1.99999A &	bus
			0.19999A
3				Exit Cal Mode
5	DC AC		+1.99999A	Measure voltage at		0.80 volt	Burden
				current front
				sockets with a
				DMM.

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2.10

Table	2.4	Initial Calibration, AC Volts
TEST	RANGE	&	INPUT	ACTION		LIMITS	COMMENTS
1	MODE		s/c	Adjust RV2 for		±150 bits	IC15	offset		null
	VAC
	various			minimum @ TP3		referred to	adjust.		Use DMM
	ranges					OV	to monitor			TP3
							Transformer			to be
							lamination
							mains-grounded.
							The lowest			figure
							possible		is
							required;		if
							necessary by
							error-sharing
							among	the	ranges.
2	20VAC		19.9999V	Note reading
			400Hz
3	20VAC		19.9999V	Adjust CV1 St R10		Value at test Attenuator HF
			50kHz	for flat response		12' ±0.010V	trim.	100 bit
							limit	applies
							when a dummy lid
							is fitted.
4	0.2VAC		0.199999V &	Calibrate over	the		0.2V LF Set-up
			0.019999V	bus.			Fluke	5101.
			400Hz
5	2VAC		1.99999V &	Calibrate over	the		2V LF Set-up
			0.19999V	bus.
			400Hz
6	20VAC		19.9999V S>	Calibrate over	the		20V Set-up
			1.9999V	bus.
			400Hz
7	200VAC		199.999V S.	Calibrate over	the		200V Set-up
			19.999V	bus.
			400Hz
8	IkVAC		750.00V &	Calibrate over	the		1 kV Set-up
			199.99V	bus.
			400Hz
9				Exit Cal Mode
10	0.2VAC		30KHz	Check		0.199999V ±
			0.199999V			.000120V
11	0.2VAC		lOKHz	Check		0.199999V ±
			0.199999V			,000096V

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2.11

Table 2.4 Cent.
TEST	RANGE &	INPUT	ACTION
12	MODE	10kHz	Check
	2VAC
		1.99999V
13	2VAC	30kHz	Check
		1.99999V
14	20VAC	30kHz	Check
		19.9999V
15	20VAC	10kHz	Check
		19.9999V
16	200VAC	10kHz	Check
		199.999V
17	200VAC	30kHz	Check
		199.999V
18	IkVAC	10kHz	Check
		750.00V
19	IkVAC	30kHz	Check
		750.00V
20	0.2VAC	s/c	Check

21	2VAC	10Hz	Check
		2.00000V
22	2VAC	20Hz	Check
		2.00000V
23	2VAC	40Hz	Check
		2.00000V
24	2VAC	100Hz	Check
		2.00000V
25	2VAC	100kHz	Check
		0.19999V
26	20VAC	100kHz	Check
		20.0000V
27	200VAC	100kHz	Check
		200.000V

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

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

COMMENTS

s/c zero. Trasnsformer laminations to be mains-grounded.

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2.12