Agilent Technologies 34410A, Руководство пользователя

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34410A/11A User’s Guide 99
Measurement Tutorial 4
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.
Loading Errors (dc volts)
Measurement loading errors occur when the resistance of the
device–under–test (DUT) is an appreciable percentage of the multimeter's
own input resistance. The diagram below shows this error source.
To reduce the effects of loading errors, and to minimize noise pickup, you
can set the multimeter's input resistance to >10 G
W (the
HI
–
Z
setting) for
the 100 mVdc, 1 Vdc, and 10 Vdc ranges. The input resistance is
maintained at 10 M
W for the 100 Vdc and 1000 Vdc ranges.
Copper to
–
Approx. mV / °C Copper to
–
Approx. mV / °C
Cadmium-Tin Solder 0.2 Aluminum 5
Copper <0.3 Tin-Lead Solder 5
Gold 0.5 Kovar or Alloy 42 40
Silver 0.5 Silicon 500
Brass 3 Copper-Oxide 1000
Beryllium Copper 5