ESI 250-DA - AC Resistance Measurement Steps and Compensation

2. E. 3
MEASURING
AC
RESISTANCE
(cont.
)
SET
CIRCUIT
SELECTOR
SWITCH
TO
R X 1
OR R X
10
For resistors between 1.2 and 12
megohms, use
R x
10
position.
SET
MAIN
DIAL TO
3.
000
This makes
it
easier
to find the
cor-
rect
range.
SET
DETECTOR
SWITCH
TO
AC OR
EXT DET
This will connect from the bridge
to
the
ac
detector.
SET
THE
GENERATOR
SWITCH
TO
INTERNAL
AC
This will connect
the ac supply
to
the
bridge
.
TRY
TO
BALANCE
THE
BRIDGE AS
WITH DC
Usually the eye will not completely
open indicating uncompensated phase
shift.
CONNECT
A
VARIABLE
CAPACITOR
FROM
THE EXT
D-Q
TERMINAL
MARKED
G
TO
THE HIGH
C
TERMIN-
AL AND TRY
TO
OBTAIN
A NULL
WITH IT
AND
THE
MAIN
DIALS
Connecting
the
capacitor from
ground
to
either
of
the
generator
terminals
permits
compensation for some of the
possible equivalent
circuits of
the
unknown.
IF
A
NULL
CANNOT
BE
REACHED,
CONNECT
THE
VARIABLE
CAPACI-
TOR
BETWEEN
THE
EXTERNAL
D-Q
TERMINAL
MARKED G
AND
THE
HIGH
L-R
UNKNOWN
TERMINAL.
A
NULL
SHOULD
BE
OBTAINABLE
WITH
ONE CONNECTION
OR
THE
OTHER
This permits
balance over the remain-
ing possible circuit combinations.
If
a
non-linear element is
being measured
by
ac
,
a null balance may not
be
pos-
sible because
the
bridge
will not
be in
balance
at
all parts of the cycle.
THE
MEASURED
RESISTANCE
WILL
BE
CORRECT
FOR
EQUIVALENT
CIRCUITS
CONSISTING
OF
A
RESISTOR
AND
CAPACITOR
IN
PARA-
LLEL OR
A
RESISTOR
AND INDUCTOR
IN
SERIES
This
is
true even for fairly large values
of phase
shift. Resistance
accuracy
will be
0.3%
or better for resistors
between
1
ohm and 1 megohm
at a
frequency
of
1
kilocycle or less.
BEFORE
DISCONNECTING
THE
This disconnects the generator
RESISTOR
SET
THE
GENERATOR
while the resistor
is
being removed.
SWITCH
TO
EXT
GEN
BEFORE
LEAVING
THE
BRIDGE
This turns off the power supply.
SET
THE
AMP
SWITCH
TO
OFF
lelsl
i
I 250-DA
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