Fluke 540B - Page 23

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540B

STEP

CONTROL POSITION OPERATION

a

RANGE SHUNT

Connect

ac

source

under

test

or,

if

using

the

A45

Transfer

Swi

tch,

set

POWER

ON

the

OUTPUT MODE

switch

to

AC.

Tap

the

GAL V s

witch

agai

n

st

the

SENSITMTY

LOW

sp

ring

tension

to

MOMENTARY

just

long enough to

see

if

th

e GALVA-

MODE

OFF

NOMETER

needle

will

sta

y on

scale.

Adjust

the

COARSE

and

MEDIUM

GALV

REFERENCE

ADJUST

controls

until

a

reading

is

obtained.

REFERENCE

COARSE

ADJUST MEDIUM

b

GALV

OPEN

Adjust

the

GALV

ZERO

control

for

zero

reading

on

the

GALVA-

SENSITTITITY

MED

NOMETER.

GALV

ZERO

c GALV

LOCK

Adj

ust

the

MEDIUM

and

FINE

controls

for

a

zero

reading

on

the

GAL-

REFERENCE

MEDIUM VANOMETER.

ADJUST

FINE

d

GALV

OPEN

Adjust

the

GALV

ZERO

control

for

zero

reading

on

the

GALVA-

SENSITIVITY HIGH NOMETER.

GALV

ZERO

e

GALV LOCK

Adjust

the

FINE

control

for

a

zero

reading

on

the

GALVANOMETER.

REFERENCE

ADJUST FINE

f

GALV

OPEN

Disco

nnect

the

ac

circuit

under

test

from

the

current

shunt

and

connect

SENSITIVITY LOW

the

de

current

source,

using

care

not

to

exceed

the

c

urrent

rating

of

the

s hunt.

If

using

the

A45

Transfer

Switch,

se

t

the

OUTPUT MODE

s

witch

to

DC.

g

GALV

Tap

the

GALV

switch

against

the

spring

tension

to

MOMENTARY

just

long

enough

to

see

if

the

GALVANO

METER

needle

will

sta

y on

scale

whil

e

slowl

y

increasing

the

de

source

cur

ren

t

until

zero

is

reached

on

the

GALVANOMETER. Do

not

adjust

the

REFERENCE

ADJUST

con

-

trols

in

this

mode.

h GALV

LOCK

Fur

ther

refine

the

adjustment

of

de

current

so

urc

e

to

maintain

a

zero

SENSITIVITY MED

reading

on

the

GALVANOMETER

in

the

ME

D

and

HIGH

sensiti

vity

HIGH

positions

.

i

GALV

OPEN

Disco

nnect

the

de

source

and

connect

the

ac

current

to

be

measured

to

the

shunt.

H

using

the

A45

Transfer

Switch,

set

the

OUTPUT MODE

switch

to

AC .

j

GALV LOCK

Readjust

the

REFERENCE

ADJUST FINE

control

for

ze

ro

on

the

GAL-

VANOMETER.

k

GALV

OPE

N

Disconnec

t

the

ac

current

under

test

and

reconn

ect

the

de

source

to

the

shunt.

If

using

the

A45

Transfer

Switch,

set

the

O

UTPUT

MODE

s wi

tch

to

DC.

1 GALV LOCK

Adjust

the

de

current

source

to

maintain

a

zero

r

eading

on

the

GAL-

VANOMETER.

Measure

and

record

the

de

current

.

m

Repeat

steps

i

thro

ugh 1

at

least

three

times

or

until

repeatibility

is

attained.

Measure

and

record

the

de

c

urrent.

n

Reverse

the

input

polarity

to

the

thermocouple

by

depressing

the

POLARITY

switch

.

Repeat

steps

i

through

1

at

least

three

times

or

until

repeatibilit

y

is

attained.

Measur-e

and

record

the

de

current.

0

The

rms

v

alue

of unknown

ac

curren

t

is

equal

to

the

average

of

the

two

de

currents

recorded

in

steps

m

and

n .

NOTE:

If

a

test

report

from

a

sta

ndards

laboratory

is

used

,

calculate

the

unknown

ac

current

from

the

following equation:

=

(1

ao

I

Iac

+ 100

1

dc

Wh

ere:

Idc

=

average

value

of

the

two

de

current

s

from

step

o.

Iac

-

Idc

ao

=

100 =

ac

to

de

percent

difference

from

Idc

the

test

report.

Figure 2-

9.

MEASURING

AN UNKNOWN

AC

CURRENT

2-11

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