Model 6485 and 6487 User’s Manual Measurements and Sourcing Voltage 3-3
Performance considerations
Warm-up period
The Model 6485/6487 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.
Install the shielding cap on the INPUT jack, then use the CAL:VOFFSET selection in the
main MENU. To perform correction via remote, send CAL:UNPR:VOFF.
Autozero
To help maintain stability and accuracy over time and changes in temperature, the Model
6485/6487 periodically measures internal voltages corresponding to offsets (zero) and
amplifier gains; a process known as autozeroing. With autozero disabled, measurement
speed increases up to three times, but measurement accuracy will be reduced. It is recom-
mended that autozero only be disabled for short periods of time.
To toggle autozero on or off, press the AZERO button. When autozero is enabled, a colon
w
ill be displayed after the reading. Via remote, send SYST:AZER ON or SYST:AZER
OFF.
Zero check and zero correct
Zero check
When zero check is enabled (on), the input amplifier is reconfigured to shunt the input signal
to low. From the front panel, enable/disable zero check by pressing the ZCHK key. Refer to
Table 3-3 for bus commands. Leave zero check enab
led when connecting or disconnecting
input signals.
Zero correct
NOTE The Model 6485/6487 saves a single zero correct value (not one for each
range).
For best results, acquire a new zero correct value after changing to the desired
range.
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