Chapter5 Calibratingthe Device
ATE Series User Manual 5-2 ni.com
varywith time and temperature. It is better to self-calibrate when the device
is installed in theenvironment in which it is used.
Self-Calibration
The ATE Seriesdevice can measureand correct for almost all of its
calibration-related errors without any external signal connections.
The NI software provides a self-calibration method you can use. This
self-calibration process, which generally takes less than a minute, is the
preferred methodof assuring accuracy in your application. You should
initiateself-calibration t o ensure that the effectso fa ny offset, gain, and
linearity drifts, particularly those due to warmup, are minimized.
Immediatelyafter self-calibration, the only significant residual calibration
error could be gain error due to time or temperature drift of the onboard
voltagereference. This error is addressed by external calibration, which
is discussed in the External Calibration section. If you are interested
primarilyin relative measurements, you can ignore a small amount of gain
error,and self-calibration should be sufficient.
External Calibration
TheAT E Seriesdevice has an onboard calibration reference to ensure the
accuracyof self-calibration. Its s pecificationsare listed in Appendix A,
Specifications.The reference voltage is measured at the factory and stored
in the EEPROM for subsequent self-calibrations. This voltage is stable
enoughfor most applications, but if you are using t hed evice at an extreme
temperatureor if the onboard reference has not been measured for a year or
more, you may wish to externally calibrate the device.
An externalcal ibration refers to calibrating the device with a known
externalreference rather than relying on the onboard reference.
Redeterminingthe value of the onboard reference is part of this process and
theresults can be saved in the EEPROM, so you should not have to perform
an externalcalibration very often. You can externally calibrate the device
bycalling the N I-DAQcalibration function.
Toexternally calibrate the device, be sure to use a very accurate external
reference. The reference should be severaltimes more accurate than the
deviceitself. For example, to calibrate a 12-bit device, the external
reference should be at least ±0.005% (±50ppm) accurate. To calibrate