Programming instructions

Chapter 22 SCXI Calibration—Increasing Signal Measurement Precision
© National Instruments Corporation 22-7 LabVIEW Data Acquisition Basics Manual
7. Take another binary reading or average of readings. If your binary
reading is the maximum binary reading for your DAQ device, try a
smaller input voltage. This is your second volt/binary measurement.
8. Use the SCXI Cal Constants VI with the first volt/binary measurement
from step 4 as
Volt/Amp 1
and
Binary 1
inputs, and the second
measurement from step 7 as
Volt/Amp 2
and
Binary 2
inputs of the
VI. The following illustration shows how you should enter the values
into these inputs in LabVIEW if your volt/binary measurements are
0V/0 and 5V/2045. Keep in mind that your input names may vary
depending on your application setup.
9. If you are using SCXI-1102 or SCXI-1122 inputs, you can save the
constants in the module user area in EEPROM. Store constants in 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,
constants stored in the default load area can be overwritten. If you want
to use a set of constants later, keep a copy of the constants stored in the
user area in EEPROM.
Note
If you are storing calibration constants in the SCXI-1102 or SCXI-1122
EEPROM, your binary offset and gain adjust factors must not exceed the ranges
given in the respective module user manuals.
For other analog input modules, you must store the constants in the
memory. Unfortunately, calibration constants stored in the memory are lost
at the end of a program session. You can solve this problem by creating a
file and saving the calibration constants to this file. You can load them
again in subsequent application runs by passing them into the SCXI Cal
Constants or the Scale Constant Tuner VIs.
Repeat the above procedure for any additional channel or gain settings you
want to calibrate.