Fluke 8842a instruction manual Reducing Thermal Voltages, Burden Voltage Error Calculation

Measurement Tutorial 4

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.).

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