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do 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 adjust the CONDUCTANCE control
to the required position.
g. Adjust the PHASE control until the meter needle is exactly at midscale.
h. Return the CONDUCTANCE control to zero on the G-scale.
i. If the C/L switch is at C, proceed to Step I .
If the C/L switch is at L, set
it to the C position.
j. Set the meter switch to ZERO LEFT and zero-balance the bridge as described
in paragraph 3.5.
k. Set the meter switch to ZERO CENTER.
If necessary, adjust the C ZERO
FINE control for a midscale meter indication.
l. Advance the CAPACITANCE control to the required limit value.
(For, the
105 pF upper limit in the Step c example, the MULTIPLY C switch would be
in the 1 position and the CAPACITANCE control would be advanced to 100
on the upper dial and to 5 on the lower dial.
If the lower limit were required,
the CAPACITANCE control would be advanced to 95 on the lower dial.)
m. The Model 75D now is programmed to perform single-limit, go/no-go tests^
Sequentially connect the capacitive specimens to the test jig, coaxial test
leads, or the TEST binding posts, as applicable, and observe the NULL
INDICATOR meter.
(1)
Upper-Limit Test.
For a go result, the meter must indicate
in the LO sector of the meter scale. Midscale is the absolute
upper limit.
If the meter indicates in the HI sector of the
scale, the specimen is higher in capacitance than the upper
limit, and the test result is no-go.
(2)
Lower-Limit Test.
For a _go result, the meter must indicate
in the Hi sector of the meter scale. Midscale is the absolute
lower limit.
If the meter indicates in the LO sector of the
scale, the specimen is lower in capacitance than the lower
limit, and tne test result is no-go.
3.8.2
SINGLE-LIMIT INDUCTANCE TEST.
The Model 75D is used in the following
procedure to perform go/no-go tests of inductive specimens that are to be sorted.
In
this test. Model 75D compares the inductance (i.e., equivalent capacitance) of
each specimen with either an upper-limit value or a lower-limit value that has been
programmed into the instrument, and a go or no-go readout indicates the test result.
Although the instrument can be programmed for only one limit, dual-limit tests may be
performed by repeating the procedure for the other limit.
a. Check that the initial settings on the front panel of the Model 75D are in
accordance with Table 4.
75D
b-370
33
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