2.2.2
THINGS
TO
WATCH
OUT
FOR
2.
2.
2.
1
HIGH
RESISTANCE
MEASUREMENTS
Care
must
be
taken
to
avoid
leakage
resistance across the unit being measured.
If
an
external
electronic
null
detector
is being
used it
may
be
affected
by ac
hum
and
by
the hum
output
of the
internal dc
generator. In this case a battery
supplying
the EXT
GEN
terminals
may
be
necessary. If a
battery supply is used
connect
a
protective
resistor
in
series with it.
Use a resistor of greater than
(I/4
)
(battery
voltage)^
ohms,
2. 2.
2.
2 LOW
RESISTANCE
MEASUREMENTS
On
the
low
resistance
ranges the lead
resistance in the unknown arm becomes
significant.
A
correction
for this
resistance
can be made
as
follows;
1.
Short
the test
leads
together at
the point where they are
to
be
connected
to
the unknown
resistor
and
measure
this "ZERO
RESISTANCE".
2.
Connect
the
test
leads to
the
unknown resistor and measure the
"RESIST-
ANCE
READING".
3.
The
"RESISTANCE
VALUE"
of
the unknown resistor is then the
"RESIST-
ANCE
READING"
minus
the
"ZERO RESISTANCE",
4.
If the
unknown
resistance
is to be
connected directly
to
the terminals,
the
"ZERO
RESISTANCE"
reading
can
be taken by
connecting
a
piece
of heavy
copper wire
between
the
unknown
resistance terminals.
(#14
AWG
copper
wire
has a
resistance of about 0.00025 ohm/inch.)
lelsin
250-DA
6/59
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