An instrument for providing a rapid, if approximate, value
for the resistance of part
of an electric circuit. It consists of an ammeter
(reverse calibrated in ohms) in series
with a fixed resistance, a battery, and a variable resistor. This last is
adjusted to zero the meter with the terminals of the instrument shorted.
The test resistance is then introduced between these terminals. The reduction
in the current so caused is a measure of the resistance.
|Simplified circuit diagram for an ohmmeter. A represents
the ammeter, Rf the fixed resistor, Rv
the variable resistor, and Rt the resistor under