Boonton Electronics 71A, 71AR - Page 11

mente with varying meter readings, this emf may show up
as slight irregularities in the dc output: switching the
meter off eliminates this. In addition, switching the
meter off eliminates needless wear of the meter movement
when the dc output is used for widely varying test values.
(In the Model 71A, this function is performed by the rear!
panel "METER ON/OFF" switch, control #22.) This control
is inoperative on the 71A-R.
2.5.2 Rear Panel, Models 71A and 71AR
±
BIAS: This terminal and BIAS GND (#23) provide for appli-
cation of the dc bias voltage up to ±200 volts at 250 rnA to
the capacitance test specimen. Bias voltage appears across
both "TEST" and "DIFF" terminals.
FUSE: 250 rnA fuse prevents internal damage in case the
bias voltage is short-circuited at the "TEST" or "DIFF"
terminals either by accidental contact or by a shorted
test specimen. See paragraph 3.8· for further details.
® DVM+: Connection to this terminal and the "GND" terminal
(#16) irrmediately below provides a dc analog of the measured
value suitable for use with a digital voltmeter. Output for
full-scale is 100 mV or 300 mV depending upon numerics of
the selected range, so that when ranges are switched the dvm
follows automatically.
~ 1.1 Mn RESISTOR: For dvm's having an input resistance of
10 megohms or greater, this resistor should be left in posi-
tion. For dvm's having an input resistance of 1 megohm,
it should be removed.
GND:
Ground connection for DVM or REC output.
REC:
connection to this terminal and to the "GOO" terminal
(#16)
provides a linear analog output of the measured value,
whose
level varies from 0 to approximately 1.7 volts (into
loads
greater than 10 megohms) for full-scale on all ranges.
DVM ADJ: This control adjusts the level of the de analog
output so that the dvm will be in agreement with a standard
capacitor. See paragraph 3.14.4.
CAL 1: Calibration adjustment for high Q measurements.
For calibration procedures, see paragraph 3.10.
2-6
71A
b