3-4 Basic Operation Models 2500 and 2502 User’s Manual
Operation considerations
The following paragraphs discuss warm-up period, auto zero, and source delay.
Warm-up
The Model 2500 must be turned on and allowed to warm up for at least one hour to
achieve rated accuracies. See Appendix A for specifications.
Auto zero
Every A/D conversion (current reading) is calculated from a series of zero, reference, and
signal measurements. With auto zero enabled, all three of these measurements are per-
formed for each reading to achieve rated accuracy. With auto zero disabled, zero and refer-
ence are not measured. Disabling auto zero increases measurement speed, but zero drift
will eventually degrade accuracy. With auto zero disabled, periodically change measure-
ment speed.
Temperature changes across components within the instrument can cause the reference
and zero values for the A/D converter to drift due to thermo-electric effects. Auto zero acts
to negate the effects of drift in order to maintain measurement accuracy over time. Without
auto zero enabled, current measurements can drift and become erroneous.
NOTE Auto zero control affects both channels simultaneously.
Front panel auto zero
Set the auto zero state from the front panel as follows:
1. Press the MENU key.
2. Select A/D-CTRL from the main menu, then press ENTER.
3. Select AUTO-ZERO, then press ENTER.
4. Select ENABLE or DISABLE as appropriate, then press ENTER.
5. Press EXIT as necessary to return to normal display.
Remote command auto zero
Use the :SYSTem:AZERo command to enable or disable auto zero via remote. For exam-
ple, send the following command to disable auto zero:
:SYST:AZER ON
Conversely, send this command to disable auto-zero:
:SYST:AZER OFF
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