Thermal Effects - Amprobe MO-100 User Manual

Thermal Effects

• Temperature can have a significant effect on the performance of a
milliohm meter due to the temperature coefficient of the resistance
under test and thermal EMF's across the dissimilar conductors.
• Most conductors have a large temperature coefficient of resistance. For
example: 0.4%/°C for copper. A copper conductor that has a resistance
of 10.00m ohm at 20°C will increase to 10.40m ohm at 30°C. This change
should be taken into account when making measurements.
• A current going through a resistance will also elevate its temperature. So
duration of the test can change the resistance.
• When measuring the resistance of item, such as current shunts, which
have joints of dissimilar conductors, thermal EMF can affect the accuracy
of the measurement. This condition can be detected if the reading alters
when the leads are reversed. To compensate for this effect, the average
of the two readings should be taken as the true measurement.
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