Keysight U2741A Guide D'utilisation page 48

3 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 digital multimeter's input
terminals are copper alloy. The table below shows common thermoelectric
voltages for connections between dissimilar metals.
Table 3-1 Thermoelectric voltage for dissimilar metals connections
Copper to -
Cadmium-Tin Solder
Copper
Gold
Silver
Brass
Beryllium
48
Approx. mV / °C
0.2
<0.3
0.5
0.5
3
5
Copper to -
Aluminum
Tin-Lead Solder
Kovar or Alloy 42
Silicon
Copper-Oxide
Keysight U2741A User's Guide
Approx. mV / °C
5
5
40
500
1000