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Sources of Error in DC Current Measurements
When you connect the internal DMM in series with a test circuit to
measure current, a measurement error is introduced. The error is
caused by the
DMM’s series burden voltage. A voltage is developed
across the wiring resistance and current shunt resistance of the internal
DMM as shown below.
V
s
= Source voltage
R
s
= Source resistance
V
b
= Burden voltage
R = Current shunt resistance
Error (%) =
−100 % x V
b
V
s
Sources of Error in AC Current Measurements
Burden voltage errors, which apply to dc current, also apply to
ac current measurements. However, the burden voltage for ac current
is larger due to the internal
DMM’s series inductance and the
measurement connections. The burden voltage increases as the input
frequency increases. Some circuits may oscillate when performing
current measurements due to the internal
DMM’s series inductance and
the measurement connections.
V
S
R
S
V
b
R
DMM
Chapter 8 Tutorial
Measurement Fundamentals
368