Test Instruments & Measuring Devices
V = ImRs + ImRm
= V - ImRm
V = voltage range desired
Im = meter current
Rm = meter resistance
Rs = multiplier resistance or series resistance
A 2 mA meter movement with internal resistance of 25 ohms is to be constructed
as a voltmeter.
What value must the series resistance be to measure full scale voltage of 100
Since Rm is negligibly low, then:
When a voltmeter is connected in a circuit, the voltmeter will draw current from that circuit.
This current causes a voltage drop across the resistance of the meter, which is subtracted from
the voltage being measured by the meter. This reduction in voltage is known as the loading
effect and can have a serious effect on measurement accuracy, especially for low current circuits.