Keysight Technologies 3458A Guide D'utilisation page 96

3 Configuring for Measurements
OUTPUT 722;"AZERO OFF"
You should leave autozero on (AZERO ON command) for 4-wire ohms
NOTE
measurements. If you must disable autozero (AZERO OFF or ONCE), be sure to
make all measurement connections before disabling autozero and ensure that
the lead resistance will not change. If you disable autozero before making the
4-wire connections, or if you have a varying lead resistance with autozero
disabled (such as when scanning), you may get inaccurate 4-wire ohms
measurements.
Offset compensation
Because a resistance measurement involves measuring the voltage induced
across the resistance, any external voltage present (offset voltage) will affect the
measurement accuracy. With offset compensation enabled, the multimeter
corrects resistance measurements by canceling the effects of the offset voltage.
To do this, the multimeter first measures the input voltage with its current source
on. The current source is then disabled and the input voltage measured again, The
true induced voltage is the difference between the two measured voltages. You
can use offset compensation for both 2-wire and 4-wire ohms measurements. The
multimeter can only perform offset compensation on the 10 W through 100 kW
ranges; offset compensation does not function on the other ranges. In the
power-on/PRESET NORM state, offset compensation is disabled. To enable offset
compensation, send:
OUTPUT 722:"OCOMP ON"
Refer to the
voltage for offset compensated ohms measurements.
Fixed input resistance
When making DC voltage measurements, you can fix the multimeter's input
resistance using the FlXEDZ command. This is useful to prevent a change in input
resistance (caused by changing ranges) from affecting the measurements.
Table 3-4
input resistance is a constant 10 MW for all DC voltage ranges. In the power-on/
PRESET NORM state, fixed resistance is disabled (OFF). To enable fixed
resistance, send:
96
Appendix A for specifications concerning the maximum series offset
shows the input resistances with FIXEDZ OFF. With FIXEDZ ON, the
Keysight 3458A User's Guide