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National Instruments Corporation 5-1 AT-MIO/AI E Series User Manual
Calibration
Chapter
5
This chapter discusses the calibration procedures for your AT E Series
board. If you are using the NI-DAQ device driver, that software
includes 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
AT E Series boards, these adjustments take the form of writing values
to onboard calibration DACs (CalDACs).
Some form of board calibration is required for all but the most forgiving
applications. If no board calibration were performed, your signals and
measurements could have very large offset, gain, and linearity errors.
Three levels of calibration are available to you, and these are 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 AT E Series board 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 board is unpowered. Loading calibration
constants refers to the process of loading the CalDACs with the values
stored in the EEPROM. NI-DAQ software determines when this is
necessary and does it automatically. If you are not using NI-DAQ, 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
the CalDACs with values either from the original factory calibration or
from a calibration that you subsequently performed.