Datron 1081 Instruction Manual

USER'S

.

HANDBD

□

K

·

1081

datr1

1

1I

_.-------INSTRUMENTs---

(

digital

multimeter

)

USER'S HANDBOOK

for

THE

DATRON

AUTOCAL

1081

DIGITAL

MULTIMETER

{for

maintenance procedures

refer

to

the Calibration and Servicing Handbook)

850042 Issue 2(February

1984)

For any assistance contact your nearest Datron

Sales

and Service Center.

Addresses can be found

at

the back

of

this handbook.

Due

to

our

po

icy o con I u · . .

design

to

the 1nstrumen

c1c

u ·

I

. f t·n ally updating our products this handbook may contain minor differences in specification, components and circuit

. . t . t ally supplied Amendment sheets precisely matched to your instrument serial number are available on request.

1984

Darron

Instruments

r

I

l

J

CONTENTS

SECTION 1 THE

1081

AUTOCALSTANDARDSMULTIMETER

Standard

and

optionalmeasurement facilities

Accessories

Principles

of

operation

SECTION2 BASIC MEASUREMENT

PROCEDURES

Maximum

input

voltages

Safety

Controls

DC

voltagemeasurement procedure

AC

voltagemeasurementprocedure

Resistancemeasurementprocedure

Rear signal input

Display messages

SECTION3 ADVANCED

OPERATIONAL

PROCEDURES

Externaltriggers

and

'Hold'

Rearinputs

Ratiomeasurement procedure

Selftest

Specmode

Platinum

resistancethermometermeasurements

Resistancedisplay

'Hi

Res' modemeasurements

Computation

facility

Load/reset

store

(A-B)

..,.c

Max

andMin

Limits

Recall memory

SECTION

4

SYSTEMS

APPLICATION

VIA

THE

IEEE

INTERFACE

Connectingthe

1081

intoa system

Addressselection

Usingthe

1081

inasystem

Programminginstructions

Control

of

OMM

inputs

Control

of

OMM

outputs

Servicerequest

ParallelPoll

Control

of

computingfunctions

Calibrationviathebus

Specreadout, test and

in~ut_

zero

Programstring

character_1st1~s

Operationalsequence guidelines

l~

Page

1-1

1-2

1-3

2-1

2-2

2-4

2-5

2-6

2-8

2-9

3-1

3-2

3-3

3-4

3-5

3-6

3-7

3-8

3-10

3-11

3-13

3-14

3-15

4-1

4-3

4-4

4-5

4-6

4-7

4-8

4-9

4-10

SECTION5 INSTALLATION

Unpacking

and

inspection

Preparationfor operation

Connectors

and

pindesignations

SECTION6 SPECIFICATIONS

General

DC

Voltage

AC

Voltage

Resistance

Temperature

Ratio

and

"fransfer

Standard Internal delays

SECTION7 SPECIFICATIONVERIFICATION

Introduction

Equipmentrequirements

Verificationprocedures

Specificationverification report

S-J

S-

J

S-1

S-2

6-1

6-J

6-2

6-4

6-6

6-

8

6-9

6-10

7-1

7

-1

7-1

7

-3

7

-4

l

,J

l~

J

SECTION 1 THE

1081

AUTOCAL STANDARDS MULTIMETER

The

Datron

1081

6½/7½

digit AUTOCAL

STANDARDS microprocessor-controlled digital

~ultimeter

(DMM) is a high precision measuring

instrument.

It features exceptionally high stability

and

systems capability.

The

instrument provides

full measurement capability, computation facil-

ities,

self

check routines

and

calibration memory.

Standard

and

optional

measurement

facilities

The

instrument

is offered in two versions, either

complete

with all options

or

as

a basic

DC

voltage

instrument

to

which individual options can be

added

to

provide

further

measurements:

Resistance (including temperature)

True

RMS

AC

voltage

DC

coupled

true

RMS

AC

voltage

Ratio

o/o,

/J.,

/J._o/o

The

full

range

of

options

is

as follows:

Option

JO:

True

RMS

AC

Converter

Option

20:

4-Wire Resistance Converter

·

Option

40: Selectable Rear/Reference Input

Option

50:

IEEE

488-1978

Standard

Digital

Interface

Option

52:

Remote

Trigger

Option

70:

Analog

Output

Calibration

TheAUTOCAL instruments have been designed

to

make the removal

of

the covers for calibration

unnecessary, as full calibration_

of

all ranges

and

functions can be carried

out

from the front panel.

Theprocedure for calibrating

the

instrument

is

con-

tained

in

the Calibration

and

Servicing

Handbook.

Accidental

or

unauthorised use

of

the calibration

routine

is

prevented by a key operatedswitch

on

the

instrument rear panel.

Message read-out

The measurement display doubles as a message

display, providing a clear read-out

of

14

different

messages. Full details

of

the meanings

of

these

displays can be found in sections 2

and

3.

Self test

Pressing the '-+' then

'Test'

key starts a

self

test

procedure, during which a sequential routine:

-checks, in

turn,

all the display segments, char-

acters and legends

-verifies the correct functioning

of

individual

measuring circuits

-checks the

non

-volatile calibration

memory

Option

80: 115V 60Hz Line

Operation

Option

81: 115V

50Hz

Line

Operation

Option

82: 115V 400Hz Line

Operation

Option

90:

Rack

Mounting

Kit

On

completion

of

the test, theinstrument re

turn

s

to

thelast selected function

and

range to provide

rapid

return

to

measurement. In the event

of

the self test

failing, an

error

message

is

displayed.

1-1

Computing

The range and function selection

keys

double

as

a

keyboard for the input

of

data

so

that measure-

ments can

be

compared

with

previously recorded

data or manually input data

for

display of:

-measurement offset

-percentage deviation

-maximum and minimum value storage

-the exceeding

of

limits (upper and

lower)

Full details

of

these facilities are

given

in

section

3.

Systems

use

The AUTOCAL

1081

instrument

can

form

part

of

a system

by

means ofthe IEEE

488

standard digital

interface option. The details

for

the connections of

the instrument to the

system

and

programming

details for the controlling machine

can

be

found

in

section 4.

1-2

Accessories

The instrument

is

supplied

with

the

f

II

0

OWin

g

accessories:

Description

Power cable

Hexagon

key

2mm

A/F

Hexagon

key

2.5mm

A/F

Set

of

calibration

keys

User's Handbook

Calibration and Servicing Handbook

Power

fuse

(230V)

or Power

fuse

(1

I

5V)

Part

Nurnber

920012

630101

630109

7CXXJ68

850042

850048

920()24

920084

In

addition, the following accessories

are

available

for

use

with

the

1081

instrument:

Pan

Description

HVP

high

voltage probe

RMK

rack mounting kit (option

90)

1501

de

luxe

lead kit

PRT

100:

Platinum resistance

thermometer probe (I

OOfl)

Additional documentation

Number

400335

440063

440070

630161

The Calibration and Servicing Handbook

contains

information required to adjust and

service

the

DMM.

It

contains detailed description

of

the

circuits, trouble shooting diagrams,

calibration

procedures, parts lists and circuit

diagrams

.

I

l

i

1

i

Principles of operation

-------

-~-

-

--

---

.

~~

------------

-~~

-

--

-1 INTl•ACI

""""'

"'••

] l

~

'<>-

n

-+-+--___J

I

_ , - -'------0

'-o--

DC I

- I ISOLATOR I

- I I

-= I

"-NEL

- \

]

I ~

~-

.-c-

---+-~---~

'"""

~

I

-]

I

"""•

= I

,_

'

"""'

=~'<>-

- I

I

DCJA

C

7

AC

CONVlflTOfl

ANM.00

TO

..,.,.,.

COIMOTOO

i.-----+---j

To

heh

·-

-

1- -

-----

--

- - -

---

--

- - -

--

------

- -

-~~o_\

OUTGUAAO

Fig. 1.1

DMM

simplified block diagram

Figure

1.1

shows

how

the

DMM

achieves

its

basic

measurement functions,

its

advanced measurement

and computing functions and the interfacing

with

other equipment

in

systems applications.

Voltage

measurement

The instrument comprises a

fully

floating isolation

amplifier with electronically

switched

gain

ranges

providing a

full

range output

which

is

applied

to

the

analog to digital converter.

AC

voltage

measure-

ment

is

achieved

using

a True

RMS

AC

converter

which converts

AC

signals

to

DC

and

applies

the

DC

voltage to the analog-to-digital converter.

Resistance measurement

is

achieved

by

passing

the

current from

an

internal precision current

source

through the unknown resistance and

sensing

the

voltage developed across the resistance.

Temperature measurement

is

achieved

by

passing

current from

an

internal precision current

source

through a platinum resistance thermometer (PRT)

probe and

sensing

the voltage developed

across

the

probe. This

is

converted digitally

and

then

dis-

played

in

°C (PRT),

or

Q

(kQ

PRT)

.

Analog to digital conversion

The

signal

from

the

DC

isolator or

AC

converter

is

applied

to

the input of a

high

gain integration

amplifier.The integration capacitor starts charging

from

a

zero

state at a rate proportional

to

the

magnitude ofthe incoming signal. The integration

period

is

approximately

160mS

.

.....

,

INTIOIIA

TIOfllll

MflflllNCl

wnOIIAHON

Fig.

1.2 Simplified measurement cycle

At

the

end

of this period, a reference

signal

of

opposite polarity

to

the input

signal

is

applied

and

the

time

taken

for

the

capacitor

to

discharge

to

zero

volts

is

measured

(null

detection), providing

an

accurate computation of

the

input

signal

mag-

nitude.

1-3

J

1

I

1J

SECTION

2

BASIC

MEASUREMENT

PROCEDURES

Preliminaries

Before

using the instrument it is important that it

has

been correctly installed as detailed in section

5.

Maximum

input voltages

The

following tables give the maximum input

voltages

to

the DMM (front panel) for each

of

the

operating

ranges.

~or

rear

panel

and

ratio inputs, maximum inputs

indicated

at

1000

or

650V RMS must be reduced to

250V

RMS

.

The

&symbolis used

to

remind the user

of

special

precautions detailed in his Handbook

and

is

placed

adjacent

to

terminals

and

switches thataresensitive

to

overvoltage conditions.

NOTES:

a)

With the local

1,!Uard

, remote guard ,witch

,ct

to •f.,K

al

(iuard'.

this value reduces

to

0V

. i.e. the terminals arc intcrnJlly lin~cd.

b) Values specified a

,,

umc peak l'oltagc

~

RMS ,oltagc x

rT

Also. maximum rnpu1, ol

IO00

nr

(,50V

RMS rcdun· to

250V

RMS

for rear

and

ratio rnpu1,.

Maximum permissible voltage between Iron! and rear input, i,

equal to the maximum input at the front input fnot ,witched)

or

250V

RMS

(switched).

c) Logic Grounds for remote interfaces are internally connected to

Safety

Ground

.

d) When the 2-wirc

fl

/4-wire

.Q

switch

is

set to "2-wirc

.Q

'.

the

·1+· terminal is internally linked to the 'Hi' terminaland the 'I ·

terminal

is

internally linked to the

'Lo'

terminal.

el Maximum slew-rate

of

'Guard'

with respect to Safety Ground

or

Logic

Ground~50V

/uS

(5

x

10

1 volt Hz) for normal operation

(accuracy

is

degraded as volt Hz product increases).

f)

Maximum slew-rate

of

any terminal

10

Safety Ground should be

~

lkV/

uS

(10' volt Hz) or the instrument may revert to the

'power up' condition

(i

.e. select

DC

I000V range).

H,

.---

l ,

OOOV

lo

2sov

f

df

1

,llOOV

,·

l ,

OOOV

2sovldl

l ,

OOOV

1.000V 250V

,,

I l ,

OOOV

I.

OOOV

ov

l ,

OOOV

l ,

OOOV

6SOV

I.

OOOV

1.

000V

650V

I 000V

I

2SOV

250V

6SOV

650V

DC& A

CVI

o tage

GUARD

2sov

1

•1

ssov

l

•I

550vl•

I

!l',

GUARD

6SOV

SAFITY

GROUND

LOGIC

GROUND

·

650V 0V J

Table

2.1

Maximum

RMS

inputvoltages [bl

H,

....-

i~ov

'"

2sovldl 250V I

250V

2sov

l

ul

250V

250V 250V 250V

I.

OOO

V

6SO

V I.

OOOV

I.

OOO

V 650V l.()O()V

I

250V

GUARD

25

0V

2r,ovl•I

650V

ssovl•I

650V

sso

vl•I

Resistance

l!',

GUARD

6SOV

SAFET

Y

6

50V

ov

I

GROUND

LOGIC

GROUND

Table 2.2

Maximum

RMS

inputvoltages

[bl

2-1

-

Safety

The

1081

Multimeter

is

designed to

be

Class

I

equipment

as

defined

in

IEC

Publication

348

and

UL

1244

concerning safety requirements. Pro-

tection

is

assured

by

a

direct

connection v

ia

the

power cable from ground to exposed metal parts

and internal ground screens.

The

line

connection

must

only

be

inserted

in

a

socket outlet provided

with

a protective ground

contact and continuity

of

the ground conductor

must

be

assured

between

the socket and the

instrument.

WARNING:

ANY

INTERRUPTION OF THE

PROTECTIVE

GROUND CONDUCTOR

INSIDE

OR

OUTSIDE

Controls

Fig.

2.1

Front panel

·Line

on/

off

('Power') switch

When

set

to the

Off

position,

this

switch

isolates

the

instrument from the

line

supply.

When

switched

to

the

On

position, the instrument

powers

up

and

automatically selects

its

DC

IOOOV

range

.

After ½ hour, the instrument

is

near to

its

full

specification, but should

be

left

on

for

2 hours

before

use

if

full

accuracy

is

required.

Function keys

The four

keys

'PRT', 'kfl', 'AC' and 'DC' -

provide the means to

select

the

mode

of

operation

of

the instrument and contain

LED

indicators that

light to show the

selected

function.

'Zero'. This facility

is

available

on

all

DC

voltage

and Ohms ranges,

by

manual or

systems

operation.

2-2

THE INSTRUMENT OR DISCONNECTION

OF

THE PROTECTIVE GROUND

TERMINAL

MA

y

MAKE

THE APPARATUS DANGERous.

INTENTIONAL INTERRUPTION

IS

PRO-

HIBITED.

THE TERMINALS MARKED WITH

THE

t,

SYMBOL

CARRY

THE POTENTIAL

OF

THE

SOURCE

UNDER

TEST

. THESE

TERMINALS AND

ANY

OTHER

CONNECT-

IONS

TO

THE SOURCE COULD

CARRY

LETHAL

VOLTAGES.

AT

NO

TIME

SHOULD

THESE

CONDUCTORS

BE TOUCHED

DURING

A TEST OF HIGH

VOLTAGES.

IF

DIFFICULTY

IS

FOUND WITH THE

TEST

,

ENSURE

THAT THE SOURCE

IS

RENDERED

SAFE

BEFORE ATTEMPTING TO

IMPROVE

CONNECTIONS.

When

the 'Zero'

key

is

pressed, the

DMM

a)

accepts the measured input

as

a zero

offset

for

the range selected, providing

it

does

not

exceed

approx

l.50/o

of

full

range.

b)

stores the offset value

in

non-volatile

memory

.

c)

compensates ALL SUBSEQUENT

READINGS

taken on that

range

by

the stored off

set

value

,

until the user redefines the zero.

If the measured input offset exceeds

1.50/o

of

full

range from the calibrated

DMM

zero,

no

offset

is

stored and the Error 4 message

is

displayed

.

Aseparate zero

off

set correction

is

stored

for

each

range. When the

DMM

is

in

'Auto' during

the

Zero

routine, all ranges are zeroed automatically

in

ascending order.

,.

J

1

J

l

]

l

-=

]

CAUTION

The stored off

set

correction

is

applied

to

all

readings,

so

that the correct procedure

is

to

re-zero

the

DMM

whenever the input zero condition

is

changed. Failure to observe this procedure

will

cause an incorrect zero compensation to

be

applied.

'Filter'

key.

The 'Filter'

key

is

pressed to increase

the normal mode

AC

noise rejection

in

measure-

ment

of

DC

volts, PRT or resistance.

In

Filter

mode, a block average of 4

is

set.

AC

Filter

keys.

The

AC

Filter

keys

extend the

low

frequency response ofthe instrument

to

10Hz, 1

Hz

or 0.lHz.

Range select keys

The instrument range of inputs

in

each

function

is

as

follows:

lOnV

-1,000VDC

.lµV -

l,OOOV

true

RMS

AC

1µ!2

-

20M!2

Fig. 2.2 Rear panel

Calibration enable keyswitch

The calibration procedure

is

detailed

in

the

Calibration and Servicing Handbook. The

calibration

switch

is

of the locking

type

to

avoid

accidental or unauthorised initiation of

the

calibration procedure.

Autorange ('Auto')

key.

This

key

commands the

instrument

to

select

the optimum ranges

for

the

measurement, saving the operator this task and

introducing

very

little delay.

Mode

and compute keys

The function

of

these

keys

is

given

in

Section 3.

4 wire/2 wire switch

During resistance measurements, this switch should

be

set

to

match the connection arrangement.

Local/remote guard switch

Selection of'Local Guard' connects the front panel

'Guard' internally

to

the front panel

'Lo'

terminal

for

voltage measurements, and to the front panel

'!2

Guard' terminal for resistance measurement.

Selection

of 'Remote Guard' isolates the 'Guard'

terminal

from

all

others and enables a remote

connection

to

be

made from the internal guard

screens

to

the

source ofany common mode voltage.

©

Calibration interval switch

The

calibration interval switch should

be

set

to

correspond

with

the intervals that elapse between

re-calibrations of the

DMM.

The setting

of

the

switch

determines the selection of specification

values

displayed

when

the ,.,.., then 'Spec'

key

is

pressed

(see

Section 3 -

Spec

mode).

2-3

DC

voltage measurement procedure

6½

digits

4

Connect

guard

if

remote

guard

■

elected

2 Select RANGE

--

- -

AANGE-----..

FUN

CT

I

ON

5

Apply

signal

to

'Hi'

and

'Lo'

terminals

3 Select 'Filter'

if

required 1 Select 'DC'

Simple lead connection

For the majority

of

applications

the

simple

lead

connection shown

below

with

'Local Guard'

selected

will

be

adequate.

The

disadvantage of

this

simple arrangement

is

that the connecting

leads

form a loop. If a stray alternating

magnetic

field,

e.g. from the line transformer of a neighbouring

instrument, passes through the loop

it

will

behave

as

a single turn secondary

winding

inducing

unwanted

AC

voltages into the measuring circuit.

Use

of

a twisted pair

will

reduce

the

loop area

as

adjacent twists

will

automatically

cancel

any

induced voltages. If problems

with

stray pick-up

are encountered,

it

is

recommended that a

screened

twisted pair cable

be

used

with

the

screen

connected

to the

'Lo'

or 'Guard' terminal.

Hi

··

--i

(Local r

---

--I

Guanll~

Use of remote guard connection

The 'Guard' terminal should

be

used

with

'Remote

Guard' selected

when

the source to

be

measured

presents an unbalanced impedance

to

the

measur-

ing terminals and common

mode

voltages are

present. Regardless of

how

the 'Hi' and 'Lo'

terminals are connected, the 'Guard' terminal

should refer to the source of common

mode

voltage.

This

will

ensure that errors,

caused

by

2-4

common mode currents flowing

in

the

measuring

circuits, are minimised

by

providing a

separate

common mode current path

as

shown

in

the

examples

below.

Rl, Cl

R2,C2

CASE

~AO-

- - -,

Hi

I C,

R,1

I

Lo

'++--~;;

I

------

I

C2

R2

~t1

-

~---L__

----;Vcm,L--~

2

= Input impedance

R3,

C3

Vcml,

Vcm2

= Input to guard

leakage

impedance

= Guard to

case

leakage

impedance

= Common mode

voltages

AC

voltage measurement procedure

5½

digits

~

4 Connect guard,

if

remote guard

selected 2 Select RANGE

RANGE

l+

I

~

(j

l\

rd

4w~~n

2w11'1!n

1§11~~13~

LOC.ftl

Gulrd

I!

Re-

Guard

>

o , 2 3 4 5 6

7<

KEY(IIIO,\RD

------c"

Er:J=i

~

•-CINrMt•PV

~

u .....

Zuo

Fi

tl1r

,n

IOHI IHI.

•IHt

FUNCTION

5 Apply signal

to

'Hi' and 'Lo' Select 1 Select AC

10Hz/1Hz/.1Hz

terminals if required

Low

frequency measurements

To

measureanysignal

of

frequency below

IOOHz

to

full accuracy, DC coupling MUST be selected

as

shown

below. Selection

of

I

OHz,

IHz or

0.1

Hz

filter, increases the settling time as shown in Section

6 - Specifications.

DC

coupled AC voltage measurement procedure 5½ digits

I+

4 Connect guard,

if remote guard

selected 2 Select RANGE

4wuen

el

2w

1

ren

LCX"I

Gulrd

I!

Remote

Guard

RANGE

1111~1!i!i~

>

o 1 2 3 4 5 6

7<

a 9 •

KE

IRo

...

-_-c-,..-,-M,-<

..

~

□

l,a

........

--

Ztro

Fithr

,n

kn

fOHI

IM

z •I

Ht

FUNCTION--......+../

--+

Tnl

s,..c

.,

.....

~old ~i\

-•f

/;

RGbo

NIIII

~'MODE~

5 Apply signal

to

'

Hi'

and 'Lo'

terminals

3 Select

10Hz/1Hz/.1Hz

if required

1 Select

AC

and

DC

keys simultaneously

AC

voltage measurement

Whilst for DC voltage measurement the resistance

of

the connection lead

is

generally unimportant so

long as it

is

small compared with the input

impedance

of

the measuring device, with AC

voltage measurement the capacitance may give rise

to

an

appreciable shunting effect causing source

loading as well as voltage drop in the leads. The

approximate

'Hi'

to

'Lo

' capacitance

of

the leads

in

the

Datron lead kit are:

low thermal-emf lead with spade

terminals-65pf,

otherleads-160pf.

In extreme cases, use

of

separate leads

will

give

lower capacitance (dependent upon spacing but

typically

4pf)

but

will

be liable to corrupt the

measurement

by

adding induced signals. The table

below gives the approximate impedances at differ-

ent frequencies.

FREQUENCY

LEAD

CAPACITANCE

4pF

65pF

160pF

100Hz

400M.U

20M.U

10MO

1kHz

40MO

2Mf2

1Mf2

10kHz

4MO

200kf2

100kf2

100kHz

400kf2

20kf2

10kf2

1MHz

40kf2

2kf2

1k.U

Table 2.4

Connection

lead

capacitance

2-5

Resistance measurement procedure

1 Select '2-wire' or

'4-wire'

as

required

(see

below)

4 Select R~NGE

I+

I-

~

2 Connect resistance (see below)

RANGE

5 Select filter

if required

2-wire measurements

I•

(2-Woretl)

Ho

· .

nGuard

(Local

Guard)

Guard

3 Select kn

For the majority ofapplications,

the

simple

2-wire

arrangement

will

be

adequate.

However,

the

value

displayed

will

include

the

resistance

of

the

connect-

ing

leads.

Use

a

screened

twisted

pair

cable

to

reduce

induced

voltages, particularly

where

Rx

is

high.

2-6

t!l~]~~

(A-Sl

-'-

C Ma,c Mon

~t

\

ual

ci,u,..

rre

ac

"'.l,H'J

'--COMPUTE~

4-wire measurements

I+

Hi

'

------

-

--

-

----,-,.,

I-

'

~---

-

--

----

-

..

,

With

a

4-wire

connection

the

lead

resistances

have

negligible

effect

and

only

the

value

of

Rx

is

dis-

played.

The

4-wire

connection,

as

shown

above

using

two

screened

twisted

pair

cables,

is

also

suitable

for

measuring

high

resistances

with

long

cables

since

the

effects of

leakage

and

capacitance

between

leads

is

eliminated.

When

making

very

high

resistance

measurements

the

'il

Guard'

terminal

should

also

be

connected

to

a

guard

screen

wrapped

around

the

resistor,

or

the

case

it

is

mounted

in,

to

reduce

any

errors

due

to

noise

.

True 4-wire zero

For accurate measurements of

Ohms

it

is

ESSENTIAL that a correctly connected

zero

source

is

used

when

operating 'Input zero' before

making a

series

of resistance measurements.

Two

arrangements

are

shown

below,

depending

upon the resistance to

be

measured,

which

ensure

that thermal emf effects

are

eliminated.

(Local

Guard) -

Less than 10k.Q

I+

-----------,-

,

Hi

v---

,

:-,t-------___;.......,i..~

----

-----

--'-

"

Guard

.Q

Guard

- - - - - - - - - - - --

Lo

O-

........

-':----------....;.

'

__:

'

I-

Fig. 2.1 Zero resistance source connections

'In-circuit' measurements

•n

Guard' can

be

used

to

make

'in-circuit'

resist-

ance measurements

by

guarding out parallel

resist-

ance paths

so

that

only

the

value

of

Rx

will

be

displayed.

Similarly,

•n

Guard'

can

be

used

to

reduce

the

settling

time

if

Rx

is

shunted

by

any

capacitance

and

a suitable tapping point

is

available.

Providing that

Ra

and

Rb

are

no

less

than

250Q

(l

.5kQ

on

lOOOkQ

or

lOMQ

Ranges),

and

the

Q Guard resistance

(Rg)

is

less

than

5Q;

the

actual

value

Rx

can

be

calculated

from

the

displayed

value

Rd

by:

Rx=Rdx(I

+E).

Deviation fraction 'E'

can

be

found

within

I

11/o

by

the

simplified formula:

E

(Rd

.

Rg)

,

(Ra.Rb)

(Local _

Guard)

10k

!1

or

greater

It ,

--

- - - - - - - - - - -

-7,

Guard

.Q

Guard

Copper

Shorting

link

----------

, -

I-

.....,_

----------__

..,,,

(Where

Rg

is

the

QGuard lead-resistance from

the

junctio~ of

Ra

and

Rb,+0.25Q.)

Example:

If Rd=

lOOQ,

Rg

= IQ, Ra= Rb=

lOkQ,

then the

value

of E

is

given

by:

IOO

x I -

JO

-t.(l f d'

)·

E I

Ok

x I

Ok

-

ppm

o

rea

mg

'

The

value

of

Rx

is

thus

given

by:

Rx=

100.(1

+

10

-6) Ohms,

=

100.0001

Ohms

I•

h•Ia

--------

Ia

Hi

----

-

-~

'

Ix

Guard

lloc1I

Guard

I n

Gu1td

Ia

R1

Lo

I-

h -- -- -- --

~--

----,:

Ib

•O

Ra

Rb

2-7

Rear signal input

:he

measurement source

ma

y be

conn

ec

t

ed

to

th

e

REAR SIGNAL l/P'

plug

in

ste

ad

of

the

front

panel terminals

when

front

panel

'Rear

Sig'

is

selected.

For

all

rear panel inputs

the

ma

x

imum

limit

is

250V

RMS

. '

Wh ·

en

usmg

the rear

panel

input

plug

the

front

panel switches '4-wire n / 2

wire

Q'

and

'Local

Guard/Remote Guard'

are

inoperative. Therefore

a_connection

must

alwa

ys

be

made

to

the

'Guard'

pm

H and

for

2-wire

resi

s

tance

measurement

external connections

must

be

made

from

'Hi' to

'I+'

and

'Lo'

to 'I - '

Not used '--.... Hguard

l+-~~I

G""'

-------7•"

,L lep.ol

lo

Input Hi

Fig. 2.2 Rear

input

7 pin plug

2-8

Thermal EMF

Th

e

rmal

emf

s

are

significant

in

DC

voltage

and

current resistance

mea

surement

s,

es

pecially

when

mea

s

uring

tow

voltage

s

or

large

currents.

Th

es

e

unpredictable thermal emf

error~

arise

when

di

s

similar

metal

junctions

are

at

different

temp

.

cratures.

To

minimise

thermal emf errors use

the

s

ame

material throughout

the

measuring

circuit,

particularly

avoid

the

use

of s

teel

p~obes,

nickel

plated

terminals and tinned copper

wire.

The

table

below

shows

thermal emfs relative

to

hard

drawn

copper

at

23

°

C.

MATERIAL EMFµV!°C

SILVER

+0.03

GOLD

+0

.

01

TIN

-3

LEAD

-3

NICKEL

-22

If

dissimilar

metal

junctions are

used

ensure

that

they

are

offset

by

other junctions of

the

s

ame

material

at

the

same

temperature and

allow

for

thermal

emfs

by

making the measurement

twice

with

reversed

polarity.

A

lead

with

gold

plated copper

terminals

is

provided

in

the

Datron lead

kit

for

making

low

thermal

emf

connections.

_Display

messages

Alpha numeric messages

will

appear on the display

when

an

input, computational or memory error

occurs. A message

will

also appear

when

a limit

is

transgressed and during the self test routine.

Message

Error O L

Error I

Error 2

Error 3

Error 4

Error 5

Error 6

Error 7

Error 9

IP·O

FAIL

Hi Lt

Lo Lt

Err

Lt

PASS & Legend

Cont

Cause

Overload

199999(9)

Arithmetic Overflow

Invalid Data Entry/Recall

Spec>

100%

or unspecified

Zero or calibration input error

DC

Self Test failure

kn Self Test failure

AC Self Test failure

Arithmetic Underflow

Zero memory error

Calibration memory error

Hi

Limit transgressed

Lo

Limit transgressed

Hi

and

Lo

Limit transgressed

Self Test pass

message

}

Continuous Average mode selected

Correction

Reduce input signal or up range

Adjust C store, rear signal or

reference input

Adjust Data value/Recall

Adjust applied input and repress

key

Refer to Calibration & Servicing

Handbook

Adjust C store, rear signal or

reference input

Repeat input zero procedure

Ref

er

to Calibration &Servicing

Handbook

Amend

limit

values

2-9

i

J

SECTION

3

ADVANCED

OPERATIONAL

PROCEDURES

I

lJ

E

I

)

I

)

l

1

I

J

The

procedures for exercising the features that

~upplement the basic measurement functions

of

the

instrument

are detailed

in

this section.

External triggers and 'Hold'

In

RANGE

11~111~!a

>

o 1 2 3 4 5 6

7<

KE~RO----c.

I~~~

~

,~~~-

Zero

Fith,-

ll'lf

Jii..rt

~

DC

\.'""'

'"'

''"'

FUNCTION

1 )

When

the instrument

is

under local control,

readings are taken at a rate

in

accordance with its

internal read rate specification. When the

'Hold'

key

is

pressed the reading

in

progress

is

completed

and

displayed,

but

no

Datron 1081 Instruction Manual

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