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How to Use *CAL?
What *CAL? Does
Re-Execute
*CAL? When:
76 Programming the HP E1415 for PID Control
positions they are currently in. The calibration becomes invalid if you move
these SCPs to different SCP locations.
When you turn power on to the HP E1415 after you have first installed your
SCPs (or after you have moved SCPs), the module will use approximate
values for calibration constants. This means that input and output channels
will function although the values will not be very accurate relative to the
HP E1415's specified capability. At this point, make sure the module is
firmly anchored to the mainframe (front panel screws are tight), and let it
warm up for a full hour. After it has warmed up, execute *CAL?.
The *CAL? command causes the module to calibrate A/D offset and gain,
and all channel offsets. This may take many minutes to complete. The actual
time it will take your HP E1415 to complete *CAL? depends on the mix of
SCPs installed. *CAL? performs literally hundreds of measurements of the
internal calibration sources for each channel and must allow 17 time
constants of settling wait each time a filtered channel's calibration source
changes value. The *CAL? procedure is internally very sophisticated and
results in an extremely well calibrated module.
When *CAL? finishes, it returns a +0 value to indicate success. The
generated calibration constants are now in volatile memory as they always
are when ready to use. If the configuration just calibrated is to be fairly
long-term, you should now execute the CAL:STORE ADC command to
store these constants in non-volatile memory. That way the module can
restore calibration constants for this configuration in case of a power failure.
After power returns, and after the module warms up, these constants will be
relatively accurate.
•
When you change the channel gain and/or filter cut-off frequency on
programmable SCPs (using INPut:GAIN, or INPut:FILTer ... )
•
When you re-configure SCPs to different locations. This is true even if
you replace an SCP with an identical model SCP because the
calibration constants are specific to each SCP channel's individual
performance.
•
When the ambient temperature within the mainframe changes
significantly. Temperature changes affect accuracy much more than
long-term component drift. See temperature coefficients in Appendix
A page 305 "Specifications".
NOTE
To save time when performing channel calibration on multiple HP E1415s
in the same mainframe, use the CAL:SETup and CAL:SETup? commands
(See "CALibration:SETup" on page 188. for details).
Chapter 3
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