VXi VT1529A/B 사용자 설명서

The *CAL? (also performed using CAL:SETup then CAL:SETup?) is a 
very important step. *CAL? generates calibration correction constants for 
all analog input and output channels on-board the VT1422A. *CAL? must 
be performed in order for the VT1422A to deliver its specified accuracy.

*CAL? generates calibration correction constants for each analog input 
channel for offset and gain at all five A/D range settings. For programmable 
input SCPs, these calibration constants are only valid for the current 
configuration (gain and filter cut-off frequency). This means that *CAL? 
calibration is no longer valid if channel gain or filter settings (INP:FILT or 
INP:GAIN) are changed, but is still valid for changes of channel function or 
range (using SENS:FUNC...). Calibration becomes invalid if the SCPs are 
moved to different SCP locations.

For analog output channels (both measurement excitation SCPs as well as 
control output SCPs), *CAL? also generates calibration correction constants. 
These calibration constants are valid only for the specific SCPs in the 
positions they are currently in. Calibration becomes invalid if the SCPs are 
moved to different SCP locations.

When power is turned on to the VT1422A after the SCPs are first installed 
(and after they are moved), the module will use approximate values for 
calibration constants. This means that input and output channels will 
function although the values will not be as accurate as the VT1422A’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 one full 
hour. After it has warmed up, execute the *CAL? query.

The *CAL? query causes the module to calibrate A/D offset, gain, and all 
channel offsets. This may require several minutes to complete. The actual 
time it takes the VT1422A to complete *CAL? depends on the mix of SCPs 
installed. *CAL? literally performs hundreds of internal calibration source 
measurements for each channel and must allow seventeen 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 are always ready to 
use. If the configuration just calibrated is to be fairly long-term, the 
CAL:STORE ADC command should be executed 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 the module warms up, these constants will be relatively accurate.