©NationalInstruments Corporation 5-1 ATE Series User Manual
5
Calibrating the Device
This chapter discusses the calibration procedures for the AT E Series
device. NI-DAQ includes calibration functions for performing all of the
steps in thecalibration process.
Calibration refers to theprocess of minimizing m easurementand output
voltageerrors by making small cir cuit adjustments. On the ATE Series
devices,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 devicecalib ration were performed, the signals and
measurements could havevery large offset, gain, and linearity errors.
Three levelsof calibration are available to you, and these are described in
thischapter. The first levelis the fastest, easiest, and least accurate, whereas
the last levelis the slowest, most difficult, and most accurate.

Loading Calibration Constants

The ATE Series device is factory calibrated before shipment at
approximately25 °Cto 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
nonvolatilememory (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
theCalDACs with the values stored in the EEPROM. NI-DAQ d etermines
when this isnecessary and does it automatically. If you are not using
NI-DAQ, youmust load these values yourself.
In theEEPROM there is a user-modifiable calibration area in addition to
the permanentfactory calibration area. This means that you can load the
CalDACswith values either from the original factory calibration or from
acal ibration that you performed subsequently.
Thismethod of calibration is not very accurate because it does not take into
accountthe fact that the device measurement and output voltage errors can