•
OPERATION
On three ranges which utilise the internal source
of
voltage,
a positive potential appears at the negative terminal
of
the instrument when set for
res
istance tests. The resistance
of
some components
var
i
es
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 s
ho
uld be con-
nected to the positive terminal
of
the capacitor and the ohms
x 1
Ok
range employed.
Before making resistance tests the pointer should
be
adjusted to zero in the following sequence :
1.
Set the left hand switch at
n.
2.
Join the leads together.
3.
On
the n x 1 range adjust zero by means
of
the knob
marked
n x 1.
4.
On the n x
100
range adjust zero by means
of
the knob
marked
n x 1 00.
5.
On
the n x 1
Ok
range adjust zero by means
of
the knob
marked
n X 1
Ok.
To test a resistance, set the ri
ght
-hand
sw
itch at the range
required, the leads
be
i
ng
connected across the unknown
component.
Resistance is
re
ad directly on the n x 1 range but readings
should be multiplied by 1 00
and
10,000 on
then
x 100 and
n x 1
Ok
ranges respectively .
If on joining the leads together it is impossible to ob
ta
in
zero
ohms setting, or
if
the pointer position
will
not re-
ma
in constant,
but
falls steadily, t
he
internal battery
or
cell concerned should be replaced. It is important that a
discharged unit
should not
be
left in the instrument, since
it
might cause damage
to
the meter. If
it
is impossible to
obtain readings on the
n x 1 and n x 1 00 ranges, the 1 A
fuse
located in
the
battery box should be checked.
NOTE: A 15V battery
may
age
in such a manner that al-
though
it
indicates a potenti
al
of 15V, its internal resistance
has
increased so much that some loss
of
accuracy can
occur on the high resistance range
(!l
.x
1
Ok).
If
erro
rs
are
suspected on the high resistancs range, remove the
battery and check its short circuit current on the 1
OOmA
de range.
If
the reading is below than 25mA
it
should be
discarded.
5
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