Test Instruments & Measuring Devices
VOLTMETERS
The accuracy of a voltmeter (Kv) is defined as the ratio of measured voltage when the meter is
in the circuit (Vw) to the voltage measured with the meter out of the circuit. Equation (14-2) is
a mathematical representation of the accuracy of a voltmeter, or true voltage (Vo).
(14-2)
Kv
Vw
Vo
Meter accuracy can also be determined by comparing the relationship between the input and
circuit resistances using Ohm’s Law as described below.
Kv
Vw
Vo
Vw
ImRin
ImRin
Vo
Im
Vo
Ro
Rin
Vo
Rin
Ro
Rin
Vo
Kv
Rin
Ro
Rin
where
Im
= meter current
Vo
= true voltage
Ro
= circuit resistance
Rin
= input resistance of the voltmeter
Kw
= indicated voltage
Kv
= meter accuracy
Rev. 0
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