Model 2657A High Power System SourceMeter® Instrument Reference Manual Section 2: General operation
2657A-901-01 Rev. B/December 2012 2-23
This extra time can cause problems in sweeps and other test sequences in which measurement
timing is critical. To avoid the extra time for the reference measurements in these situations, the OFF
selection can be used to disable the automatic reference measurements. Note that with automatic
reference measurements disabled, the instrument may gradually drift out of specification.
To minimize the drift, a reference and zero measurement should be made immediately before the
critical test sequence. The ONCE setting can be used to force a refresh of the reference and zero
measurements used for the current aperture setting.
Autozero settings
Autozero setting Description
OFF Turns automatic reference measurements off.
ONCE After immediately taking one reference and one zero measurement, turns
automatic reference measurements off.
AUTO Automatically takes new acquisitions when the Model 2657A determines
reference and zero values are out-of-date.
Front-panel autozero
To change autozero from the front panel:
1. Press the CONFIG key.
2. Press the MEAS key.
3. Turn the navigation wheel to select AUTO-ZERO, and then press the ENTER key or the
navigation wheel .
4. Turn the navigation wheel to select the mode (OFF, ONCE, or AUTO), and then press the
ENTER key or the navigation wheel .
5. Press the EXIT (LOCAL) key to return to the main display.
Remote command autozero
To set autozero from a remote interface:
Use the autozero command with the appropriate option shown in the following table to set autozero
through a remote interface (see smuX.measure.autozero
(on page 7-195)). For example, send the
following command to activate automatic reference measurements:
smua.measure.autozero = smua.AUTOZERO_AUTO
Autozero command and options
Command Description
smua.measure.autozero = smua.AUTOZERO_OFF
Disable autozero*
smua.measure.autozero = smua.AUTOZERO_ONCE
After immediately taking one reference and one zero
measurement, turns automatic reference measurements
off.
smua.measure.autozero = smua.AUTOZERO_AUTO
Takes new acquisitions when a measurement is made
and reference and zero values are out-of-date.
* Old NPLC cache values will be used when autozero is disabled (see NPLC caching (on page 2-24)).
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