Programming instructions

Chapter 22 SCXI Calibration—Increasing Signal Measurement Precision
LabVIEW Data Acquisition Basics Manual 22-8
© National Instruments Corporation
Calibrating SCXI Modules for Signal Generation
When you output a voltage or current value to your SCXI analog output
module, LabVIEW uses the calibration constants loaded for the given
module, channel, and output range to scale the voltage or current value to
the appropriate binary value to write to the output channel. By default,
calibration constants for the SCXI-1124 are loaded into the memory from
the EEPROM default load area.
Recalibrate your SCXI analog output module by following these steps.
1. Use the AO Single Update VI to output a binary value. If you are
calibrating a voltage output range, enter
0
in the
binary array
input
of the VI. If you are calibrating current range, enter
255
into the
binary array
input of the VI.
2. Measure the output voltage or current at the output channel with a
voltmeter or ammeter. This is your first volt/binary measurement:
Binary 1
= 0, and
Volt/Amp 1
is the voltage or current you measured
at the output.
3. Use the AO Single Update VI to output a binary value of 4,095.
4. Measure the output voltage or current at the output channel. This is
your second volt/binary measurement:
Binary 2
should be
4,095
and
Volt/Amp 2
is the voltage or current you measured at the output.
5. Use SCXI Cal Constants VI with the first voltage/binary measurement
from step 2 as the
Volt/Amp 1
and
Binary 1
inputs and the second
measurement from step 4 as the
Volt/Amp 2
and
Binary 2
inputs of
the VI.
You can save the constants on the module in the user area in EEPROM. Use
the user area as you are calibrating, and then use SCXI Cal Constants VI
again at the end of your calibration sequence to copy the calibration table
in the user area to the default load area in EEPROM. Remember that
constants that are stored in the default load area can be overwritten. If you
want to use the constants later, you should store a backup copy of the
constants in the user area in EEPROM.
Repeat the procedure above for each channel and range you want to
calibrate. Subsequent analog outputs will use your new constants to scale
voltage or current to the correct binary value.
For more information on the SCXI Cal Constants VI, refer to Chapter 29,
Calibration and Configuration VIs
, in the
LabVIEW Function and VI
Reference Manual
, or refer to the LabVIEW
Online Reference
, by selecting
Help»Online Reference…
.