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Chapter 4 Calibration
NI 4472 User Manual 4-2 ni.com
Self-Calibration
Your NI 4472 can measure and correct almost all of its calibration-related
errors without any external signal connections. Your National Instruments
software provides a self-calibration method. Initiate self-calibration by
calling the DSA Calibrate.vi or the
Calibrate_DSA
function. This
self-calibration process, which generally takes less than a minute, is the
preferred method of assuring accuracy in your application. Initiate
self-calibration to minimize the effects of any offset and gain drifts,
particularly those due to temperature variations.
Your NI 4472 has an onboard calibration reference to ensure the
accuracy of self-calibration. Its specifications are listed in Appendix A,
Specifications . The reference voltage is measured at the factory or during
an external calibration operation and stored in the EEPROM for subsequent
self-calibrations.
Immediately after self-calibration, the only significant residual calibration
error could be gain error due to time or temperature drift of the onboard
voltage reference. This error is addressed by external calibration, which
is discussed in the
External Calibration section. If you are interested
primarily in relative measurements, you can ignore a small amount of
gain error, and self-calibration should be sufficient.
External Calibration
The onboard calibration reference voltage is stable enough for most
applications, but if you are using your device at an extreme temperature
or if the onboard reference has not been measured for two years or more,
you might want to externally calibrate your device.
External calibration refers to calibrating your device with a known external
reference rather than relying on the onboard reference. The new calibration
constants are stored in the onboard EEPROM, overwriting the factory
calibration constants.
Externally calibrate your device by calling the DSA Calibrate.vi or the
Calibrate_DSA
function. When you perform an external calibration, be
sure to use a very accurate external DC reference. The reference should be
several times more accurate than the device itself. For example, to calibrate
the NI 4472, the external reference should have a DC accuracy better than
±115 ppm (±0.001 dB).