Heathkit IM-18 User Manual

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(==3¢

Berea

{

)

Now

connect

the

negative

meter

lead

to

the

side

of

the

AC

line

with

the

lowest

reading,

Then

connect

the

test

probe

tothe

other

side

of

the

line,

{

)

Adjust

the

AC

Calibrate

control

until

the

meter

pointer

indicates

the

line

voltage,

{

)

Disconnect

the

test

lead

and

probe,

AC

CALIBRATE

WITHOUT

LINE

CORD

ADAPTER

CAUTION:

Do

NOT

use

the

common

(negative)

lead

of

the

VTVM

when

measuring

power

line

voltages,

This

lead

is

already

connected

to

the

circuit

ground

and

tothe

power

line

ground,

If

the

common

lead

should

contact

the

"hot"

side

of

the

power

outlet,

the

power

line

will

be

short-

circuited,

Connect

ONLY

the

meter

probe,

set

on

AC,

to

the

power

hne,

(

)

Temporariiy

remove

ihe

phone

plug

from

the

jack,

(

)

Set

the

Range

switch

to

1,5

V

andthe

Func-

tion

switch

to

AC,

(

)

Adjust

the

AC

Balance

control

so

no

move-

ment

is

detected

when

switching

from

AC

through

DC-

to

DC+,

(

)

Set

the

Range

switch

to

the

150

V

range

if

you

wired

your

VTVM

for

120

VAC

opera-

tion,

or

to

the

500

V

range

if

you

wired

the

VTVM

for

240

VAC

operation,

{

)

Set

the

Function

switch

to

AC,

(

)

Set

the

switch

on

the

test

probe

to

AC,

( )

Reinsert

the

phone

plug,

Page

25

{

)

Connect

the

test

probe

to

the

side

of

the

AC

line

with

the

highest

reading,

{

)

Adjust

the

AC

Calibrate

control

until

the

meter

pointer

indicates

the

line

voltage.

AGING

AND

FINAL

CALIBRATION

{

)

It

is

recommended

that

the

tubes

be

aged

before

final

calibration,

This

is

accom-

plished

by

keeping

the

instrument

turnedon

for

a

period

of

at

least

48

hours,

Final

calibration

should

be

done

in

the

same

way

as

the

initial

calibration,

Careful

calibration

will

result

in

a

more

accurate

instrument,

If

a

standard

AC

meter

is

available,

it

is

desirable

to

use

such

an

instrument

to

check

the

accuracy

of

the

VTVM,

Prefer-

ably,

use

a

voltage

near

full

scale

on

the

VTVM

as

for

instance,

140

volts

or

40

volts

on

the

150

V

or

50

V

range

respec-

tively,

The

DC

scales

may

also

be

cali-

brated

using

a

DC

meter

of

known

accuracy.

One

of

the

major

advantages

of

kit

form

instrument

assembly

is

that

the

kit

builder

becomes

thoroughly

familiar

with

the

cali-

bration

procedure

and

is

therefore

capable

of

periodically

checking

VTVM

operating

accuracy,

instead

of

assuming

that

usual

factory

instrument

calibration

is

still

valid,

After

final

calibration,

place

the

instrument

in

the

cabinet

and

secure

it

with

two

6-32

x

3/8"

sheet

metal

screws,

The

instrument

is

now

ready

for

use,

The

power

consumption

of

the

VTVM

is

very

low

and

there

is

no

objection

to

leaving

the

instrument

on

continuously

during

the

daily

work

period

rather

than

turning

it

off

each time

a

measurement

function

is

completed,

Daily

operation

for

a

period

of

several

hours

or

more

will

also

serve

the

purpose

of

minimizing

possi-

ble

moisture

accumulation,

Questions and Answers:

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Heathkit IM-18 Specifications

General

Brand	Heathkit
Model	IM-18
Category	Measuring Instruments
Language	English

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