c. Electrostatic effects are usually minimized by the metal envelope
which forms the potentiometer case.
4.
Special-type cables are used when making potentiometric measurements.
They are made of solid, untinned, shielded, twisted pair copper wire which
is used to prevent electromagnetic pickup from external sources and also to
prevent the thermocouple effect from being introduced by dissimilar metal
contact. The possible introduction of thermal EMF is the reason for using
untinned leads as interconnecting cables. All connections should be tightly
made to reduce contact resistance and prevent intermittent operation.
In
making connections, always remember to observe polarity and never apply the
high side of the potential to the low or common binding post. If this error
is made, the potentiometer will be at the same potential above ground as the
applied voltage, thus presenting a definite shock hazard.
9
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