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2600AS-901-01 Rev. B / September 2008
Section 3: Basic Operation
Series 2600A System SourceMeter® Instruments Reference Manual
Auto zero
The Series 2600A 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. The time interval between needing to update these reference measurements is
determined by the integration aperture being used for measurements. Separate reference and
zero measurements are used for each aperture.
There are three different settings for auto zero as summarized in
. 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 If the reference measurements are out of date when a signal measurement is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. Keep in mind 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 just prior to 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.
Front panel auto zero
Set the auto zero from the front panel as follows:
1.
Press the
CONFIG
key, and select
MEAS
from the menu.
2.
Select
AUTO-ZERO
, then press
ENTER
or the
navigation wheel
.
3.
Select the desired mode (
OFF
,
ONCE
, or
AUTO
), and then press
ENTER
or the
navigation
wheel
.
4.
Press
EXIT
as necessary to return to the normal display.
Remote command auto zero
Use the auto zero command with the appropriate option shown in
to set auto zero via
remote (see
for more details). For example, send the following command to activate
Channel A automatic reference measurements:
Table 3-4
Auto zero settings
Auto zero
setting
Description
OFF
Turns automatic reference measurements off.
ONCE
Turns automatic reference measurements off, but immediately taking
one reference and one zero measurement.
AUTO
Automatically takes new acquisitions when processor determines
reference and zero values are out-of-date.
