User`s guide

76 34450A User’s Guide
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
multimeter’s input terminals are a copper alloy. The table
below shows common thermoelectric voltages for connections
between dissimilar metals.
Tab le 3-1 Common thermoelectric voltages for connections between
dissimilar metals
Copper -to- Approx. mV / °C
Cadmium-Tin Solder 0.2
Copper <0.3
Gold 0.5
Silver 0.5
Brass 3
Beryllium Copper 5
Aluminum 5
Tin-Lead Solder 5
Kovar or Alloy 42 40
Silicon 500
Copper-Oxide 1000