©
National Instruments Corporation
4-1
DAQPad-MIO-16XE-50 User Manual
4
Calibration
This chapter discusses the calibration procedures for the analog I/O
circuitry on the DAQPad-MIO-16XE-50. NI-DAQ includes calibration
functions for performing all of the steps in the calibration process for the
analog I/O circuitry.
You cannot calibrate the constant current source used for cold-junction
sensing and external current excitation. The constant current source is
factory calibrated, and NI can recalibrate the unit if needed. To maintain the
cold-junction sensor accuracy, NI recommends recalibrating the current
source every year.
Calibration refers to the process of minimizing measurement and
output voltage errors by making small circuit adjustments. On the
DAQPad-MIO-16XE-50, these adjustments take the form of writing values
to onboard calibration DACs (CalDACs).
Some form of device calibration is required for all but the most forgiving
applications. If no device calibration were performed, the signals and
measurements could have very large offset, gain, and linearity errors.
This chapter describes three levels of calibration: loading calibration
constants, self-calibration and external calibration. 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
The DAQPad-MIO-16XE-50 is factory calibrated before shipment to the
levels indicated in Appendix A,
. 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 device is unpowered. Loading
calibration constants refers to the process of loading the CalDACs with the
values stored in the EEPROM. NI-DAQ determines when this is necessary
and does it automatically. If you are not using NI-DAQ, you must load
these values yourself.
