Keysight DAQ970A Guia Del Usuario página 243

4 Measurement Tutorials
Offset compensation
Most connections in a system use materials that produce small DC voltages due to dissimilar metal-to-metal
contact (thermocouple effect) or electrochemical batteries. These DC voltages also add errors to resistance
measurements. The offset-compensated measurement is designed to allow resistance measurements in the
presence of small DC voltages.
Offset compensation makes two measurements on the circuit connected to the input channel. The first
measurement is a conventional resistance measurement. The second is the same except the internal DMM's test
current source is turned off (essentially a normal DC voltage measurement). The second measurement is subtracted
from the first prior to scaling the result, thus giving a more accurate resistance measurement.
Offset compensation can be used for 2-wire or 4-wire ohms measurements (but not for RTD or thermistor
measurements). The DAQ970A/DAQ973A disables offset compensation when the measurement function is changed
or after a Factory Reset (*RST command). An Instrument Preset (SYSTem:PRESet command) or Card Reset
(SYSTem:CPON command) does not change the setting.
If the resistor being measured does not respond quickly to changes in current, offset compensation will not produce
an accurate measurement. Resistors with very large inductances or resistors with large parallel capacitance would
fall into this category. In these cases, the channel delay parameter can be increased to allow more settling time after
the current source is switched on or off, or offset compensation can be turned off.
Keysight DAQ970A/DAQ973A User's Guide 243