a. The Model 845AR controls are placed as follows:
POWER
ON
OPR/ZERO
OPR
RANGE
as desired
b. The voltage divider is adjusted for zero or null deflection on the
Model 845AR meter while placing the RANGE switch to successively more
sensitive ranges.
c. The unknown voltage is calculated by dividing the standard cell
voltage by the final division ratio of the divider.
Figure 4-5.
Standard cell voltage measurements
7.
The Model 845AR may be used as a dc isolation amplifier having a
voltage gain of up to 120 db, depending on the settings of the RANGE switch
and the OUTPUT LEVEL control.
To compute the maximum voltage gain on any
range of the Model 845AR, use the following formula:
8.
Voltage measurements at the microvolt level involve the persistent
problems of thermoelectric effects. These effects may be compensated for by
temporarily disconnecting the voltage from the circuit under measurement and
noting the meter deflection of the Model 845AR on the desired range. This
reading must then be subtracted from all subsequent voltage measurements. A
thorough understanding of these effects can lead to reducing or eliminating
them completely.
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