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Measurement Tutorial
REDUCING THERMAL VOLTAGES
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Figure 4-5. Burden Voltage Error Calculation
4-14. REDUCING THERMAL VOLTAGES
When making very low-level dc measurements, thermal voltages can present an
additional source of error. Thermal voltages are the thermovoltaic potentials generated at
the junction between dissimilar metals. Thermal voltages typically occur at binding posts
and can be greater than 10 µV.
Thermal voltages can also cause problems in the low dc and ohms ranges, particularly in
the 20 mV and 20Ω ranges. Some low-value resistors are constructed with dissimilar
metals. Just handling such resistors can cause thermal voltages large enough to introduce
measurement errors.
The effect of thermal voltages can be reduced by using the following techniques:
1. Use tight connections.
2. Use clean connections (especially free of grease and dirt).
3. Use similar metals for connections wherever possible (e.g., copper-to-copper, gold-
to-gold, etc.).