Dc Measurement Considerations; Thermal Emf Errors; Loading Errors (Dc Voltage) - Keysight Truevolt Series Operating And Service Manual

Measurement Tutorial

DC Measurement Considerations

Thermal EMF Errors

Thermoelectric voltages are the most common error source in low–level DC voltage measurements. Ther-
moelectric voltages are generated by circuit connections using dissimilar metals at different temperatures.
Each metal–to–metal junction forms a thermocouple that generates a voltage proportional to the junc-
tion temperature, as shown in the table below. You should minimize thermocouple voltages and tem-
perature variations in low–level voltage measurements. The best connections use copper–to–copper
crimped connections, as the DMM's input terminals are a copper alloy.
Copper to: Approx. µV / °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

Loading Errors (DC Voltage)

Measurement loading errors occur when the resistance of the DUT is an appreciable percentage of the mul-
timeter's input resistance, as shown below.
To reduce the effects of loading errors and to minimize noise pickup, set the multimeter's input resistance
to >10 GΩ (high-impedance) for the 100 mVDC, 1 VDC, and 10 VDC ranges. The input resistance is main-
tained at 10 MΩ for the 100 VDC and 1000 VDC ranges.
162 Keysight True volt Series Operating and Service Guide