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National Instruments Corporation 5-1 VXI-MIO Series User Manual
Calibration
Chapter
5
This chapter discusses the calibration procedures for your
VXI-MIO Series module. NI-DAQ and the VXI
plug&play
instrument
drivers include calibration functions for performing all of the steps in
the calibration process.
Calibration refers to the process of minimizing measurement and output
voltage errors by making small circuit adjustments. On the
VXI-MIO Series modules, these adjustments take the form of writing
values to onboard calibration DACs (CalDACs).
Some form of module calibration is required for all but the most
forgiving applications. If you do not perform module calibration, your
signals and measurements could have offset, gain, and linearity errors.
Three levels of calibration are available to you and described in this
chapter. The first level is the fastest, easiest, and least accurate, whereas
the last level is the slowest, most difficult, and most accurate.
Loading Calibration Constants
Your VXI-MIO Series module is factory calibrated before shipment at
approximately 25
°
C to the levels indicated in Appendix A,
Specifications
. The associated calibration constants—the values that
were written to the CalDACs to achieve calibration in the factory—are
stored in the onboard nonvolatile memory (EEPROM). Because the
CalDACs have no memory capability, they do not retain calibration
information when the module is unpowered. Loading calibration
constants refers to the process of loading the CalDACs with the values
stored in the EEPROM. NI-DAQ, the VXI
plug&play
instrument
drivers, or your application software determine when this is necessary
and do it automatically. If you are not using NI-DAQ, the
VXI
plug&play
instrument drivers, or your application software, you
must load these values yourself.
In the EEPROM there is a user-modifiable calibration area in addition
to the permanent factory calibration area. This means that you can load