TM 9-4935-282-34
803D
b. The AC - DC polarity switch may be set to either of
ground the upper post and effectively place C1 (a 0.47 uf
two positions, positive or negative, for the DC mode of
capacitor) across the input terminals. Even if C1 was
operation. As seen in figure 3-2, the AC - DC polarity switch
disconnected, there would still be considerable capacitance
does not reverse the input posts when going from the positive
across the input due to transformer wiring capacitance and
to negative DC position. It reverses the meter and the internal
stray wiring capacitance. With this capacitance across the
reference supply. If the instrument did not contain positive and
circuit being measured several problems could arise. The
negative DC positions, the grounded side of any unknown
polarity switch provides equal convenience in measuring
voltage that is negative with respect to ground would have to
positive or negative voltages without the occurrence of these
be connected to the upper input binding post. This would
problems.
Figure 3-2. FUNCTION OF POLARITY SWITCH
3-5
