HP 421A Service manual

Table of contents

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,

НР

427A

SM:

94)—

opp

YP

OPERATING

AND

SERVICE

MANUAL

PROPERTY

OF

ELECTRICAL

ENGINEERING

VANDERBILT

UNNER

SITY

VOLTMETER

421A

HEWLETT

Åp;

PACKARD

Vilt

dH

K4XL's

8.

BAMA

This

manual

is

provided

FREE

OF

CHARGE

from

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“BoatAnchor

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Archive’

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a

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to

the

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who

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OPERATING

AND

SERVICE

MANUAL

-hp-

Part

No.

00427-90004

MODEL

427A

VOLTMETER

Serials

Prefixed:

947-

Appendix

C,

Manual

Backdating

Changes,

С

%

adapts

manual

to

serials

prefixed

550-,

621-,

731-

|

| |

|

4

3

|

|

1

ў

3

|

|

Copyright

Hewlett-Packard

Company

1969

P.O.

Box

301,

Loveland, Colorado,

80537

U.S.A.

Printed:

JAN

1970

a

a

e

e

Table

of

Contents

TABLE

OF

CONTENTS

Model

427A

Section

Page

I

GENERAL

INFORMATION

.

.

......

1-1

1-1.

Description.

.........

..

1-1

1-5.

Вайегу..............

1-1

1-7.

Instrument

and

Manual

Identification.

. .

.......

1-1

1-10.

Available

Accessories

......

1-1

1-12.

Cables

and

Adapters

.....

1-1

1-13.

Probes,

“22524

04

asa

a

Jal

Section

Page

п

INSTALLATION

.............

25-1

2-1.

Introduction.

...........

2-1

2-3

Initial

Inspection

. .

. .

.

557221

2-9.

Power

Requirements,

. . . . .

,

2-1

2-7.

Grounding

Requirements.

.

...

2-1

2-10.

Installation.

...........

2-1

2-12,

Bench

Mounting

........

2-1

2-14.

Rack

Mounting.

........

2-1

2-16.

Combination

Mounting

....

2-1

2-18.

Repackaging

for

Shipment

....

2-1

Section

Page

ІП

OPERATING

INSTRUCTIONS

......

3-1

3-1.

Introduction.

...........

3-1

3-3.

Front

and

Rear

Panel

Description

.........

Operating

Instructions

,....

Mechanical

Zero

Adjustment

Turn-On

Procedure.

.

.

.

.

1

DC

Measurements.

,....

2.

Resistance

Measurements

3.

AC

Measurements.

....

А

6

Section

IV

THEORY

OF

ОРЕБВАТІОМ,......

4-1.

General.

............

4-5.

DC

Орегаһоп..........

Ohms

Operation

........

.

AC

Operation.

.........

2.

Circuit

Descriptions,

.....

3.

DC

Amplifier

(A1).

. .

.,.

6.

DC

Offset

(А2)

...

.

9.

AC

Metering

Circuit

(A2)

ния

3.

Battery

Regulator

Al....

Section

У

MAINTENANCE

............

5-1,

Introduction

..........

9-3.

Required

Equipment

,......

5-5.

Performance

Checks

DB

Measurements.

,.....

.

У

ФА)

Q3 C2

Q3

023

2

C3

CO

и

|

09

se

(D

po

~

Eo

са

eR

ры

ы

PPP

PP

SP

hh

нь

н

!

1

3

|P

J

93

I

1

w

оо

tO

DD

to

ма

=

—

*

өл

өл

лс

р

ны

ка

ка

ка

(D

Section

У

MAINTENANCE

(Сопе'

4)

9-7.

АС

Accuracy

and

Frequency

Page

Response

Check.

....

5-1

5-14.

Resistance

2.

Check.

5-2

5-16,

DC

Accuracy.

4

4.50...»

5-2

5-18.

AC

Rejection

Check

.

sé

aaa

des

5-20.

Input

Impedance

Check

....

5-3

5-25.

Adjustment

and

Calibration

LIST

OF

TABLES

Number

Page

1-1.

Specifications

..,.............

1-0

3-1.

Effects

of

Harmonic

Distortion.

.

.

.

.

3-2

3-2.

DB

Range

Identification.

.

. .

.

..

..

3-2

5-1.

Required

Test

Equipment,

.......

5-0

5-2.

Resistance

Accuracy

Check.

. .

. .

.

.

5-2

01791-2

Procedures

.........

.

5-4

5-21.

Cover

Removal

........

5-4

5-30.

Amplifier

Balance

and

Zero

Offset

Adjustment.

.

. .

. .

5-5

5-31.

Regulator

Adjust

.......

5-5

5-32.

AC

Calibration.

........

5-5

5-36,

Resistance

Infinity

Adjustment

5-6

5-38.

DC

Calibration.

........

5-6

9-40.

Alternate

Performance

Checks

and

Calibration

Procedures.

.

5-6

5-42.

AC

Сїтсїв..........

5-6

5-45.

Resistance

Circuits.

. . .

..

5-6

5-47,

DC

Circuitfs

32,22

xxx

5-7

5-50.

АС

Rejection

.........

5-7

5-52.

Input

Impedance

Check

....

5-7

5-54.

Battery

Replacement.

.

.

....

5-7

5-56.

Troubleshooting.

.........

5-7

5-60.

Power

Supply

.........

5-8

5-63.

DC

Amplifier

.........

5-8

5-67.

AC

Metering

Circuit,

.....

5-8

5-71.

Adjustment

of

Factory

Selected

Components

......

....

5-8

5-13.

MRI

1.15114.

xw

ca

кез

5-8

5-75.

A2C2*

så xg

Xov

5-9

5-77.

A2R14*

T

.

5-9

5-80.

A2R16*

.....

4-8

ызык

va

10-9

5-82.

Etched

Circuit

Board

Repair.

5-9

Section

Page

VI

CIRCUIT

ПЛАСВАМ$.,,.......

2.

6-1

6-1,

Introduction

............

6-1

Section

Page

ҮП

REPLACEABLE

PARTS..........

7-1

1-1.

Introduction

............

7-1

7-4.

Ordering

Information.

.

.

. . .

. .

7-1

7-6.

Non-Listed

Parts.

.

.

...

века

41-1

Appendix

А

CODE

LIST

OF

MANUFACTURERS

B

SALES

AND

SERVICE

OFFICES

С

MANUAL

BACKDATING

CHANGES

Number

Page

5-3.

1%

Resistors............

Ux.

5-7

5-4.

Troubleshooting.

..........

..

5-7

5-5.

Power

Supply

Voltages

,........

5-8

5-6

AC

Metering

Circuit

Voltages

.....

5-8

7-1.

Replaceable

Parts.

..

.........

7-1

iii

Table

of

Contents

Model

427A

Voltmeter

, .

.

11096A

High

Frequency

Probe.

.

Location

of

Front

Panel

Controls

and

Indicators.

.

.

Impedance

Correction

Graph

Simplified

Block

Diagram

.

.

DC

ОрегаПоп.........

Ohms

Operation

.......

AC

Operation

DC

Offset

Circuit,

,.

» .

+

+=

AC

Accuracy

and

Frequency

Response

Check.

.

.

.

Моде!

427А

OF

ILLUSTRATIONS

Page

Number

Page

.

1-0

5-9,

Resistance

Accuracy

Сһеск.......

5-2

‚

1-1

5.3.

DC

Accuracy

and

Linearity

Check.

...

5-2

5-4,

AC

Rejection

Сһеск...........

5-3

.

3-0

5-5,

Input

Impedance

Check

.........

5-4

.

3-3

5-6.

Location

of

Internal

Adjustments

....

5-5

.

4-0

5-7,

Battery

Керісетепі...........

5-7

.

4-1

.

4-2

6-1.

Location

of

Switch

Components

....

-

6-2

.

4-2

6-2.

Component

Госапоп,..........

6-3

4-3

6-3.

Schematic

Diagram

...........

6-3

.

5-0

1-1.

Location

of

Mechanical

Рагів......

7-0

01791-2

а

~

а

da

Section

I

Model

427A

в

a

ын

| |

ҮМЕТЕН

HEWLETT

·

PACKARD

@

4274

VOLI

»

FUNCTION

3

EEE

Figure

1-1.

Model

427A

Voltmeter

Table

1-1.

Specifications

DC

VOLTMETER

Voltage

Ranges:

+100

mV

to

+1000

У

full

scale

па

1,

3,

10

sequence

(9

ranges).

AC

VOLTMETER

(Cont'd)

==

а

bl

си

ОПТ

а)

Input

Impedance;

10

megohms

shunted

by

40pF

on

10

mV

to

1

V

ranges;

20

pf

on

3

V

to

300

V

ranges.

Response:

Responds

to

the

average

value

of

the

in-

put;

calibrated

in

rms

voltsfor

а

sine

wave

input.

Overload:

300

V/rms

momentarily,

1

V

range

and

Accuracy:

+2%

of

full

scale

on

any

range

(09C

to

50°C),

Input

Resistance:

10

megohms

on

all

ranges.

Ре

у

below

AC

Rejection:

Superimposed

peak

ac

voltages

(60

M

:

Hz

and

above)

100

times

greater

than

full

scale

425

V/rms

maximum

above

1

V

range.

affects

reading

less

than

1%.

Maximum

450

OHMMETER

volts

peak.

Overload:

1200

Vdc

on

any

range.

AC

VOLTMETER

Voltage

Ranges:

10

mV

to

300

V

rms

full

scale

in

a

1,

3,

10

sequence

(10

ranges).

Frequency

Range:

10

Hz

to

1

MHz.

Accuracy:

(0°C

to

50°C),

RANGE

+2%

OF

FULL

SCALE

0.01

V

-

30

V

10

Hz

-

1

МН?

100

V

-

300

V

10

Hz

-

100

KHz

Frequency

Response:

Resistance

Ranges:

10

ohms

center

scale

to

10

meg-

ohms

center

scale

(7

ranges).

Accuracy:

+5%

of

reading

at

midscale

(00C

to

+50°C),

Polarity:

Common

terminal

negative,

source

Current:

OPEN

CIRCUIT

|

SHORT

CIRCUIT

RANGE

VOLTAGE

CURRENT

X10

3d8

edB

IdB

О

GENERAL

Floating

Input:

May

be

operated

up

to

500

Vdc

above

ground.

(Ohms

input

open

in

any

function

except

ohms--volts

input

open

when

instrument

is

in

off

position.)

Power:

22-1/2

volt

dry

cell

battery.

(Eveready

No.

763

ог

RCA

VS102.)

Option

01:

Battery

operation

and

ac

line

opera-

tion

(selectable

on

rear

panel).

115

or

230

V

+20%,

50

Hz

to

400Н2,

1/2

W.

IHz

SHz

lOHz

IMHz

eMHz 3MHz

4MHz

Frequency

response

10

mV

to 30

V

ranges,

1-0

01791-2

44

е

~

e

p

=

Model

427A

Section

I

SECTION

1

GENERAL

1-1.

DESCRIPTION.

1-2.

The

Hewlett-Packard

Model

427A

is

a

versatile,

compact,

self-contained

voltmeter.

It

is

capable

of

making

de

measurements

from

1

mV

to

1000

volts,

ac

measurements

from

0.

3

туѓо

300

volts

at

frequencies

from

10

Hz

to

1

MHz,

and

resistance

measurements

from

0.2

ohms

to

500

megohms.

With

the

01

option,

the

Model

427A

may

be

powered

either

by

a

115

or

230

volt

line

or

by

an

internal

22-1/2

volt

dry

cell

battery.

1-3,

The

use

of

solid

state

components

throughout

gives

the

Model

427A

both

ruggedness

and

reliability,

Battery

operation

makesthe

instrument

ideal

for

field

use

or

isolation

from

common

mode

ground

loops.

1-4,

Figure

1-1showsthe

Model427A,

and

Table

1-1

contains

а

list

of

the

Model

427A

Specifications,

1-5.

BATTERY.

1-6.

The

battery

used

in

the

Model

427A

is

a

22-1/2

volt

dry

cell,

Eveready

No.

763

or

an

RCA

VS102.

Typical

battery

life

is

morethan

300

hours

continuous

operation

or

700

hours

intermittent

operation.

1-7.

INSTRUMENT

AND

MANUAL

IDENTIFICATION.

1-8.

Hewlett-Packard

uses

a

two-section

eight-digit

serial

number

(000-00000).

If

the

first

three

digits

(prefix)

of

the

serial

number

on

your

instrument

do

not

agree

with

those

on

the

title

page

of

this

manual,

INFORMATION

change

sheets

supplied

with

the

manual

will

define

differences

between

your

instrument

and

the

Model

427A

described

in

this

manual.

1-9.

If

a

letter

prefixes

the

serial

number,

the

instrument

was

manufactured

outside

the

United

States.

1-10.

AVAILABLE

ACCESSORIES.

1-11.

The

following

accessories

are

available

to

in-

crease

the

test

capabilities

of

the

Model

427A.

1-12.

CABLES

AND

ADAPTERS.

-hp-

110014

45"

test

lead,

dual

banana

to

BNC

male

-hp-

11002А

5'

test

lead-dual

banana

to

alligator

clips

-hp-

110034

5"

test

lead-dual

banana

to

pencil

probe

and

alligator

clip

-hp-

10111A

shielded

BNC

female

to

banana

plug

adapter

1-13.

PROBES.

-hp-

Model

11074A

10:1

Voltage

Divider

Probe

extends

the

voltage

range

of

Model

427А

by

a

factor

of

10.

-hp-

Model

11039A

1000:1

Capacitive

Voltage

Divider

for

measuring

voltages

up

to

24

KV.

-hp-

Model

11096A

High

Frequency

Probe

ex-

tends

the

frequency

range

ofthe

427A

to

500

MHz.

The

voltage

range

is

0.25V

to

30V.

Figure

1-2.

11096А

High

Frequency

Probe

01791-2

1-1

e^

e

Mode1

427А

Section

П

SECTION

II

INSTALLATION

2-1.

INTRODUCTION.

2-2.

This

section

contains

information

and

instruc-

tions

necessary

for

installation

and

shipping

of

Model

427A

Voltmeter.

Included

are

initial

inspection

pro-

cedures,

power

and

grounding

requirements,

install-

ation,

and

instructions

for

repackaging

for

shipment,

2-3.

INITIAL

INSPECTION.

2-4.

This

instrument

was

carefully

inspected

both

mechanically

and

electrically

before

shipment.

It

should

be

physically

free

of

mars

or

scratches

and

in

perfect

electrical

order

upon

receipt.

To

confirm

this,

the

instrument

should

be

inspected

for

physical

damage

in

transit.

Also,

test

the

electrical

perform-

ance

of

the

instrument

using

the

procedure

outlined

in

Paragraph

5-5.

If

there

is

damage

or

deficiency,

see

the

warranty

on

the

inside

front

cover

of

this

manual,

2-5.

POWER

REQUIREMENTS.

2-6.

The

Model

427A

uses

а

22.

5

volt

dry

cell

battery

for

its

primary

power

source.

However,

if

Option01

is

included,

the

Model

427A

can

be

operated

from

any

source

of

115

or

230

volts

(420%)

at

50

to

400

Hz.

With

the

instrument

disconnected

from

the

ac

power

source,

move

the

slide

switch

(located

on

the

rear

panel)

until

the

desired

line

voltage

appears.

Power

dissipation

is

less

than

1/2

watt

maximum.

2-7.

GROUNDING

REQUIREMENTS.

2-8.

To

protect

operating

personnel,

the

National

Electrical

Manufacturers'

Association

(NEMA)

recom-

mends

that

the

instrument

panel

and

cabinet

be

ground-

ed.

The

Option

01

427A

is

equipped

with

a

three-

conductor

power

cable

which,

when

plugged

into

an

appropriate

receptacle,

grounds

the

instrument.

The

offset

pin

on

the

power

cable

three-prong

connector

is

the

ground

wire.

2-9.

To

preserve

Ше

protectionfeature

when

operating

the

instrument

from

atwo-contact

outlet,

use

а

three-

prong

to

two-prong

adapter

and

connect

the

pigtail

on

the

adapter

to

ground.

2-10.

INSTALLATION.

2-11.

The

Model

427A

is

fully

transistorized;

there-

fore,

no

special

cooling

is

required.

However,

the

instrument

should

not

be

operated

where

the

ambient

temperature

exceeds

+559С

(1310F).

For

additional

information,

address

inquiries

to

your

local

-hp-

Sales

and

Service

Office.

(See

Appendix

B

for

office

locations.

)

2-12.

BENCH

MOUNTING,

2-13,

Model

427A

is

shipped

with

plastic

feet

and

tilt

stand

in

place,

ready

for

use

as

а

bench

instrument.

01791-3

2-14.

RACK

MOUNTING.

2-15.

Model

427A

may

be

rack

mounted

by

using

an

Adapter

Frame

(-hp-

Part

No.

5060-0797).

The

adapt-

er

frame

is

a

rack

frame

that

accepts

any

combination

of

submodular

units.

It

can

be

rack

mounted

only.

2-16.

COMBINATION

MOUNTING,

2-17.

The

Model

427A

may

be

mounted

incombination

with

other

submodular

units

by

using

a

Combining

Case

(-һр-

Model

1051A).

If

the

427A

is

equipped

witha

carrying

handle,

it

will

be

necessary

to

remove

the.

top

cover

on

427A

before

inserting

it

into

the

Com-

bining

Case,

The

Combining

Case

is

a

full-module

unit

which

accepts

various

combinations

of

submodular

units.

Being

a

full-module

unit

itself,

itcan

be

bench

or

rack

mounted

and

is

analogous

to

any

full-module

instrument.

2-18.

REPACKAGING

FOR

SHIPMENT.

2-19.

The

following

paragraphs

contain

а

general

guide

for

repackaging

ofthe

instrumentfor

shipment,

Refer

to

Paragraph

2-20

if

the

original

container

is

to

be

used;

2-21

if

it

is

not,

NOTE

If

the

instrument

is

to

be

shipped

to

Hewlett-Packard

for

service

or

repair,

attach

a

tag

to

the

instrument

identifying

the

owner

and

indicating

the

service

or

repair

to

be

accomplished;

include

the

model

number

and

full

serial

number

of

the

instrument.

In

any

correspondence,

identify

the

instrument

by

model

number,

serial

number,

and

serial

number

prefix.

2-20.

If

original

container

is

to

be

used,

proceed

as

follows:

a.

Place

instrument

in

original

container.

If

original

container

is

not

available,

a

suitable

container

can

be

purchased

from

your

near-

est

-hp-

Sales

and

Service

Office.

b,

Ensure

that

container

is

well

sealed

with

strong

tape

or

metal

bands.

2-21,

И

original

container

is

notto

ре

used,

proceed

as

follows:

a.

Wrap

instrument

in

heavy

paper

or

plastic

before

placing

in

an

inner

container.

b.

Place

packing

material

around

all

sides

of

in-

strument

and

protect

panel

face

with

cardboard

strips.

c.

Place

instrument

and

inner

container

inaheavy

cartonor

wooden

box

and

seal

with

strong

tape

or

metal

bands.

d.

Mark

shipping

container

with

"DELICATE

INSTRUMENT,"

"FRAGILE"

etc,

2-1

Қ

шек

TET

сесия

таче

tn

oe

wama

=

Section

Ш

Model

427A

a

í

MODEL

427A

FRONT

PANEL

MODEL

427А

REAR

PANEL

(OPTION

Ol)

HEWLE1)

-

PACKARD

//7

427А

VOLTMETER

4)

FUNCTION

RANGE

АСУ

хок

IO

XIOOK

5

ре

30

хм

(

IOO

хюм

N

300

>

1000

—

ону

ос

ZERO/I

00

427А-8-0529

BATT/LINE

(option

01

only)

slide

switch:

Se-

COM

terminal:

Connects

to

instrument

com-

lects

either

battery

or

line

operation.

mon.

(Common

input

for

ACV,

OHMS

and

DCV.)

115/230

slide

switch

(option

01

only):

Selects

either

115

Vac

or

230

Vac

for

line

operation.

VOLTS

terminal:

Applies

unknown

ac

or

dc

voltage

to

instrument.

Line

input

(option

01

only):

Connects

ac

erati

er

to

instrument.

op

ing

pow

жігі:

2

FUNCTION

switch:

Selects

mode

of

operation.

Selections

are

OFF,

BATT,

+DC,

-DC,

OHMS

and

AC.

RANGE

switch:

Selects

appropriate

range

of

unknown

input.

e

©

DC

ZERO/2

«thumbwheel:

Usedto

electrical-

Mechanical

zero:

Mechanically

zeroes

the

ly

zerothe

instrument

in

DC

mode

and

to

infinity-

meter,

set

the

instrument

in

OHMS

mode.

©

Meter

face:

Displays

the

magnitude

of

unknown

OHMS

terminal:

Connects

unknown

resistance

resistance

or

voltage

in

ohms

or

volts

respec-

to

instrument.

tively.

о

00000

е

ғ

Figure

3-1.

Location

of

Front

Panel

Controls

and

Indicators

3-0

01791-2

жө

Model

427A

SECTION

INSTRUCTIONS

OPERATING

3-1.

INTRODUCTION.

3-2.

The

Model

427А

may

be

operated

ав

а

дс

volt-

meter,

ac

voltmeter,

ohmmeter

or

dB

meter.

This

section

contains

operating

instructions

for

each

mode

of

operation.

3-3.

FRONT

AND

REAR

PANEL

DESCRIPTION.

3-4.

Figure

3-1

shows

the

location

of

all

the

Model

427A

controls

and

indicators

and

explainsthe

function

of

each.

Тһе

Option

01

rear

panel

is

shown,

Тһе

standard

rear

panel

is

blank.

3-5.

OPERATING

INSTRUCTIONS.

NOTE

To

obtain

maximum

battery

life,

set

the

FUNCTION

switch

of

OFF

when

the

instrument

is

not

in

use.

3-6.

MECHANICAL

ZERO

ADJUSTMENT.

3-7.

Before

any

measurements

are

made,

complete

the

Mechanical

Zero

Adjustment

inthe

following

steps.

а.

Be

sure

instrument

has

been

off

for

at

least

one

minute.

b.

Rotate

Mechanical

Zero

Adjustment

screw

CLOCKWISE

until

meter

pointer

istothe

left

of

zero

and

moving

upscale

toward

zero.

c.

Continue

to

rotate

adjustment

screw

clockwise,

STOP

when

needle

is

exactly

on

zero,

If

needle

overshoots,

repeat

step

b.

а.

When

pointer

is

exactly

over

zero,

rotate

adjustment

screw

slightly

COUNTERCLOCK-

WISE

to

relieve

tension

on

suspension.

И

the

pointer

іпоуев

to

the

left,

repeat

whole

procedure,

but

make

the

counterclockwise

rotation

less.

3-8.

TURN-ON

PROCEDURE.

3-9,

STANDARD

INSTRUMENT,

a,

Rotate

the

FUNCTION

Switch

to

BATT/1.

5

MIN

position,

b.

Тһе

meter

should

read

1.

5

or

higher

on

the

0-3

scale

on

any

range,

indicating

that

the

battery

voltage

is

15

volts

or

higher.

И

the

reading

is

below

1.5,

replace

the

battery

according

to

the

steps

in

Paragraph

5-54.

01791-2

Section

ІП

3-10.

OPTION

01

INSTRUMENT.

а.

3-11.

а.

b.

с.

е,

3-12.

а.

Select

either

battery

ог

line

operation

withthe

rear

panel

BATT/LINE

slide

switch.

H

bat-

tery

operation

is

selected,

check

the

battery

according

to

Paragraph

3-9.

If

line

operation

is

selected,

set

the

115/230

slide

switch

to

indicate

the

proper

line

volt-

age,

Rotate

the

FUNCTION

switch

to

the

desired

function.

During

line

operation,

the

BATT/

1.5

MIN

check

position

displays

the

output

of

the

Option

01

power

supply.

The

reading

should

be

1,5

or

higher

on

the

0-3

scale

оп

any

range,

indicating

а

power

supply

output

of

15

volts

or

more.

This

serves

as

а

соп-

venient

check

of

the

Option

01

power

supply.

DC

MEASUREMENTS.

Rotate

the

FUNCTION

switch

to

+DCV

or

-DCV

depending

on

the

polarity

of

the

input.

Short

the

VOLTS

input

tothe

COM

input,

го-

tate

RANGE

to

0.

1,

and

adjustthe

DC

ZERO/

Өс

thumbwheel

for

zero

meter

deflection.

Remove

shorting

connection.

Н

there

is

a

zero

offset

with

COM

and

VOLTS

open,

refer

to

Paragraph

4-16

and

Paragraph

5-30.

Select

approximate

range

of

input

with

RANGE

switch,

DO

NOT

APPLY

MORE

THAN

1200

VDC

TO

ANY

DC

RANGE.

Connect

input

across

VOLTS

and

COM

ter-

minals

and

read

magnitude

of

input

on

meter.

RESISTANCE

MEASUREMENTS.

DAMAGE

ТО

427A

INPUT

CIR-

CUIT

МАҮ

RESULT

IF

DC

OR

AC

VOLTAGE

IS

APPLIED

TO

OHMS

TERMINAL.

Rotate

the

FUNCTION

switch

to

OHMS.

Selectthe

approximate

range

withthe

RANGE

switch;

and

withthe

input

terminals

open,

ай-

just

the

DC

ZERO/Qe

thumbwheel

for

an

=

indication

onthe

ohms

scale.

(Pointer

should

rest

on

the

mark

just

to

the

left

of

х).

3-1