Offset Compensation; Fixed Input Resistance; Configuring For Ac Measurements; Ac Or Ac+Dc Voltage - Agilent Technologies 3458A User Manual

Offset Compensation

Fixed Input
Resistance

Configuring for AC Measurements

AC or AC+DC Voltage

62 Chapter 3 Configuring for Measurements
inaccurate 4-wire ohms measurements.
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 10W through 100kW 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 Appendix A for specifications concerning the maximum series
offset voltage for offset compensated ohms measurements.
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 12 shows the input resistances with FIXEDZ OFF.
With FIXEDZ ON, the input resistance is a constant 10 MW for all DC
voltage ranges. In the poweron/PRESET NORM state, fixed resistance is
disabled (OFF). To enable fixed resistance, send:
OUTPUT 722; "FIXEDZ ON"
To disable fixed resistance, send:
OUTPUT 722;"FIXEDZ OFF"
This section describes how to configure the multimeter for making AC or
AC+DC voltage, AC or AC+DC current, frequency, or period measurements.
The multimeter can make true RMS AC voltage or AC+DC voltage
measurements using one of three methods: analog RMS conversion, random
sampling conversion, or synchronous sampling conversion. Each
measurement method has six ranges: 10mV, l00mV, lV, l0V, 100V and
1000V, and a maximum resolution of 6½ digits on any range.
Table 15 shows the measurement characteristics and signal requirements for
each measurement method. Figure 11 shows the front terminal connections
for all types of voltage measurements.
For AC voltage measurements, the multimeter measures only the AC
component of the input signal. For AC+DC voltage measurements, the
multimeter measures the DC component and the AC component within the