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When higher bias voltages than those provided are needed, an external bias source
may be used.
This voltage can be up to 400 volts, with a maximum current of 100 mA.,
and can be either positive or negative with respect to ground. Measurement of this voltage
and current must be made externally; a protective fuse or current-limiting resistor should
also be included in the external bias supply to protect the bridge components.
For three-term* nal biasing arrangements, two external supplies are needed.
This
would be useful for measurements on transistors with normal bias applied.
The link from
EXTERNAL HI to Ground is removed, and the two power supplies are connected to BIAS HI
and ground, and BIAS LO and ground.
PART II. AMPLITUDE-MODE MEASUREMENTS
3.6
GENERAL: Use the amplitude mode of operation to measure the C, G, Rp,
Q
or D of capacitive specimens or the L, G, Rp, Q or D of inductive specimens.
When readinq values on the CAPACITANCE or CONDUCTANCE dials during the
following procedures, apply the associated MULTIPLY C or DIVIDE G/MULTIPLY R
factor to the reading.
(If the ground-plane adapter is being used, Stepb of paragraph
3.6.1 is disregarded.)
3.6.1
C, G, Rp, Q and D Measurements.
a.
Check that the initial settings on the front panel of the Model 75D are in
accordance with the table in paragraph 3.4.
NOTE:
Allow 15 minutes for warm-up after energizing the instrument.
b.
If the test specimen is to be connected directly to the TEST binding posts,
remove the terminal shield.
If coaxial test leads or a test jig is to be used,
connect the leads or jig to the REMOTE TEST coaxial connectors.
(Disregard
this step if the ground-plane adapter is being used.)
c.
Determine the approximate capacitance value of the test specimen and set
the MULTIPLY C switch as indicated in the chart below.
APPROXIMATE VALUE
OF TEST SPECIMEN
(pF)
MULTIPLY C SWITCH
SETTING
100 to 1000
1
10 to 100
0.1
1 to 1©
0.01
0.1 to 1
0.Q01
0 to 0.1
0.0001
75D
b-370
24
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