Specifications

Performing Channel Calibration (Important!)
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. *CAL? must be performed in order for the VT1419A to
deliver its specified accuracy. Wait for the module to thoroughly warm-up (1 hour)
before executing a *CAL? operation. See the guidelines and notes on the following
page.
The “Front Panel” example program shown in Chapter 5 provides a calibration
function that executes *CAL? and also performs the CAL:STORE ADC command
to store the results of the calibration to the VT1419A’s non-volatile flash memory.
“cal_1419.vee” can be merged into any VEE application to perform the calibration
function.
Operation and
Restrictions
*CAL? generates calibration correction constants for each analog input channel for
offset and gain at all 5 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 calibration is no longer valid if channel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 also
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.
How to Use *CAL? When power is turned on to the VT1419A after first installing the SCPs (or after
SCPs have been 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 very accurate relative to the VT1419A’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
the *CAL? operation.
What *CAL? Does 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 required
to complete *CAL? depends on the mix of SCPs installed. *CAL? performs
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 calibrated is to be fairly long-term, execute the
CAL:STORE ADC command to store these constants in non-volatile memory. This
way the module can restore calibration constants for this configuration should a
power failure occur. After power returns and after the module warms up, these
constants will be relatively accurate.
Programming the VT1419A Multifunction
Plus
Performing Channel Calibration (Important!)
Chapter 3 71
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