Model 6487 Reference Manual Measurements and Sourcing Voltage 3-3
Performance considerations
Warm-up period
Model 6487 can be used within one minute after it is turned on. However, the instrument
should be turned on and allowed to warm up for at least one hour before use to achieve
rated accuracy. If the instrument has been exposed to extreme temperatures, allow extra
time for the internal temperature to stabilize.
Voltage offset correction
Voltage offset correction should be performed periodically to null input amplifier offsets.
To perform correction:
1. Press the MENU key, select CAL, then press ENTER.
2. The unit will display the following:
CAL: VOFFSET
3. Press ENTER. The instrument will prompt as follows:
INPUT CAP
4. Connect the triax shielding cap to the INPUT jack.
5. Press ENTER to complete voltage offset correction.
6. Press EXIT to return to normal display.
To perform correction via remote, connect the triax shielding cap to the INPUT, then send
CALibration:UNPRotected:VOFFset.
Autozero
To help maintain stability and accuracy over time and changes in temperature, the
Model 6487 periodically measures internal voltages corresponding to offsets (zero) and
amplifier gains. These measurements are used in the algorithm to calculate the reading of
the input signal. This process is known as autozeroing.
When autozero is disabled, the offset and gain measurements are not performed. This
increases measurement speed up to three times. However, the zero and gain reference
points can eventually drift resulting in inaccurate readings of the input signal. It is recom-
mended that autozero only be disabled for short periods of time.
To disable autozero from the front panel, press the AZERO button. This button toggles
autozero on and off. It can also be enabled by restoring factory or GPIB default conditions.
When autozero is enabled, a colon will be displayed after the reading.
For example:
Autozero disabled: 0.00258 nA +00.0
Autozero enabled: 0.00258 nA: +00.0
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