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p„ Adjust the variable capacitor for a midscale meter indication,
if necessary,
use the C ZERO FINE control to center the meter needle.
q. Energize the oven and time the test specimen for a thermal cycle in accordance
with the user's specification.
r. At each required temperature level, adjust the CAPACITANCE control for an
exact midscale indication on the meter and read the differential value on the
dial.
An upscale reading indicates the positive differential value of the
specimen with respect to the reference capacitance, and a downscale reading
indicates the negative differential value.
3.9.6
MEASURING DIFFERENTIAL INDUCTANCE IN PHASE MODE.
This method measures the differential inductance in terms of equivalent
capacitance, which is translated by simple computation.
a. Check that the initial settings on the front panel of the Model 75D are in
accordance with Table 4.
NOTE:
Allow one hour warm-up to ensure thermal stabilization
of the phase detector circuit.
b. If coaxial test leads or a test jig is to be used, connect either to the REMOTE
STD coaxial connectors.
c. Refer to the chart below and set the MULTIPLY C, DIVIDE G/MULTIPLY R,
and C/L switches to positions corresponding with the anticipated differential.
(Do not adjust the CONDUCTANCE control.)
ANTICIPATED
DIFFERENTIAL
VALUE
MULTIPLY C
SWITCH
DIVIDE G/
MULTIPLY R
SWITCH
CA
SWITCH
CONDUCTANCE
CONTROL
G-SCALE
25 pH to 250 pH
1
1
C
+1000
250 pH to 2.5 mH
0.1
1
L
-100*
2.5 mH to 25 mH
0.01
10
L
-100*
*
Tenth (red) subdivision on G-scale to the left of zero,
d. Zero-balance the bridge as described in paragraph 3.5.
e„ Set the meter switch to ZERO CENTER.
If necessary, adjust the C ZERO FINE
control for a midscale meter indication.
f. Refer to the chart in Step c, above, and set the CONDUCTANCE control to
the required position.
g. Adjust the PHASE control until the meter needle is at midscale.
75D
b-370
41
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