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b. Check that the oven is switched off and that ambient temperature requirements
are in accordance with the user's specifications,,
c. Connect a test specimen of known value to the oven-chamber terminals and
connect the oven coaxial cables to the REMOTE TEST coaxial connectors.
d. At the REMOTE STD terminals, connect a stable, variable capacitor whose
range covers the value of the test specimen plus the capacitance introduced
into the bridge circuit in Steps e and f below.
e. Establish a midscale reference by advancing the CAPACITANCE control to 500.
f. Set the MULTIPLY C switch to a position consistent with the anticipated
differential.
g. Adjust the variable capacitor for optimum meter null and then zero balance
the bridge as described in paragraph 3.5.
h. Energize the oven and time the test specimen for a thermal cycle in accordance
with the user's specification.
i. At each required temperature level, adjust the CAPACITANCE control for a
null 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 reference capacitance, and a downscale reading indicates the
negative differential value.
3.9.3 MEASURING DIFFERENTIAL INDUCTANCE IN AMPLI TUDE MODE.
In this method, inductance is measured in terms of equivalent capacitance,
which is translated to inductance 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 15 minutes for warm-up after energizing the
instrument.
b. If coaxial test leads or a test jig is to be used, connect either to the REMOTE
STD coaxial connectors.
c. Estimate the approximate differential value and set the MULTIPLY C switch
as indicated in the following chart:
ANTICIPATED DIFFERENTIAL
MULTIPLY C SWITCH
VALUE
SETTING
25 pH to 250 pH
1
250 pH to 2.5 mH
0.1
2.5 mH to 25 mH
0.01
75 D
b-370
37
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