Boonton Electronics 71A, 71AR - Capacitance Test Signal; Capacitance Calibration Procedures

Instruments having serial numbers between 140 and 191
(inclusive), a 100 K ohm resistor is installed across
the fuse holder. Thus, if the fuse blows, bias voltage
will still appear at the "TEST" terminals but usually
at a somewhat lower level than is indicated by the bias
supply monitor. If such a voltage differential is ob-
served in these instruments, the condition of the fuse
should be checked. The resistor, which was intended
for current limiting with the fuse removed, may be
deleted from the circuit if desired. (NOTE: This
resistor is not installed in instruments having serial
numbers 192 and above.)
3.8.2 Connection for High Voltage DC Bias
In cases where a dc bias voltage of greater than 200 volts
i·s required, the circuit shown in Figure 3-2 may be used.
with this arrangement, the practical limit of the bias that
can be applied is the working voltage of the capacitor, C.
3.9 Capacitance Test Signal
For capacitance measurements, the crystal controlled 1 MHz
test signal is fixed at 15 millivolts RMS (±lmV). It is not
adjustable, and any attempts to alter the test level will
have a severe effect on measuring accuracy.
3.10 Capacitance Calibration Procedures
3.10.1 General
Calibration of the Models 71A and 7lAR* should be checked
and adjusted using both high Q and low Q (Q=3) tests. It
is not advisable to check and adjust calibration at either
the upper or lower limit of the measuring range; hence a
standard of 100 pF is particularly recommended. In any case,
the capacitance standard used must be a three-terminal device
capable of operation at 1 MHz.
The Boonton Electronics Model 7l-1A Capacitance Standard is
designed specifically for use with the Model 7lA and is
available as a separate accessory. It is a three-terminal
1 MHz standard which is adjusted to 100 pF (±.25%) against
NOTE: * The Model 71-lA Standard capacitor is built into the
Model 71AR. See paragraph 3.10~4.
3-12
71A