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Measurement Tutorial
DC Measurement Considerations
Thermal EMF Errors
Thermoelectric voltages are the most common source of error in low–level DC
voltage measurements. Thermoelectric voltages are generated when you make
circuit connections using dissimilar metals at different temperatures. Each
metal-to-metal junction forms a thermocouple, which generates a voltage
proportional to the junction temperature. You should take the necessary
precautions to minimize thermocouple voltages and temperature variations in
low-level voltage measurements. The best connections are formed using
copper-to-copper crimped connections, as the multimeter's input terminals are a
copper alloy. The table below shows common thermoelectric voltages for
connections between dissimilar metals.
Table 3-1
Common thermoelectric voltages for connections between dissimilar metals
Cadmium-Tin Solder
Beryllium Copper
Tin-Lead Solder
Kovar or Alloy 42
Copper-Oxide
96
Copper -to-
Copper
Gold
Silver
Brass
Aluminum
Silicon
Approx. mV / °C
0.2
<0.3
0.5
0.5
3
5
5
5
40
500
1000
Keysight 34450A User's Guide
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