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Series 2600B

System SourceMeter® Instrument Reference Manual Section 2:

General operation

2600BS-901-01 Rev. B / May 2013 2-31

Autozero

The ADC of the Series 2600B uses a ratiometric A/D conversion technique. To ensure accuracy of

readings, the instrument must periodically obtain fresh measurements of its internal ground and

voltage reference. Separate reference and zero measurements are used for each aperture.

As summarized in the "Autozero settings" table, there are three different settings for autozero. By

default, the instrument automatically checks these reference measurements whenever a signal

measurement is made (AUTO). If the reference measurements are out of date when a signal

measurement is made, the instrument will automatically take two more A/D conversions, one for the

reference and one for the zero, before returning the result. Thus, occasionally, a measurement takes

longer than normal.

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 Series 2600B 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reference and zero values are out-of-date.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 previous display.

Keithley 2601B Reference Manual

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