AVO AVOMETER 8 Gebruiksaanwijzing - Pagina 7

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•

OPERATION

three

ranges which utilise the internal source of voltage,

a positive

potential

appears at the

negative

terminal of

the instrument when set for resistance

tests.

The

resistance

of some components varies according to the direction of

the current through them and readings therefore, depend

upon

the

direction in which the

test

voltage is applied

quite apart from its magnitude. Such cases

include

elec-

trolytic capacitors and rectifiers.

When

measuring the

leakage resistance

of an electrolytic

capacitor, the

negative

lead from the meter should

be con-

nected

to the

positive

terminal

of the capacitor and

the ohms

1 Ok range

employed.

Before

making resistance

tests the

pointer

should

adjusted

zero in

the

following

sequence

Set

the left

hand

switch at n.

Join the leads

together.

the

n x 1

range

adjust zero by means of

the

knob

marked n x

the

n x

100 range

adjust zero by means of the knob

marked n x 1 00.

On the n x 1 Ok range adjust zero by means of the knob

marked n

1 Ok.

To test a resistance, set

the

right-

hand switch at the range

required, the leads being connected across the unknown

component.

Resistance is read directly on the n x

1 range

but readings

should

be multiplied by

00 and 10,000 on

then

x 100 and

x 1

Ok ranges respectively .

If on

joining

the

leads

together

it is impossible to obtain

zero

ohms setting, or if the pointer position

will not re-

main

constant, but falls steadily, the internal

battery or

cell concerned

should be

replaced.

is important

that a

discharged

unit should not be left

the instrument,

since

it might

cause

damage to the

meter.

If it

impossible

obtain readings

the

1 and

n x 1

00 ranges,

the 1

fuse

located

the battery

box

should

be checked.

NOTE: A 15V battery

may age

such a

manner

that

al-

though

it indicates a poten tial

15V,

its internal resistance

has

increased

much

hat some loss of

accuracy

can

occur on the

high resistance

range

(!l .x

1 Ok). If

errors

are

suspected on the

high resistancs range, remove

the

battery

and check

its

short circuit

current

the 1 OOmA

range.

the reading

is below

than

25mA it

should

discarded.