National Instruments NI PXI-7831R - Manual (Page 45)

Chapter 3 Calibration
NI PXI-7831R User Manual 3-2 ni.com
onboard voltage reference. The offset and gain errors in the analog circuitry
are calibrated out by adjusting the CalDACs to minimize these errors.
Immediately after internal calibration, the only significant residual
calibration error should be gain error due to time and 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.
The results of an internal calibration can be stored in the flash memory on
the NI PXI-7831R so that the CalDACs are automatically loaded with the
newly calculated calibration constants the next time the NI PXI-7831R is
powered on.
External Calibration
The NI PXI-7831R 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 and stored
in the flash memory for subsequent internal calibrations. This 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
a year or more, you may want to externally calibrate your device.
An external calibration refers to calibrating your device with a known
external reference rather than relying on the onboard reference. During the
external calibration process, the onboard reference value is re-calculated.
This compensates for any time or temperature drift related errors in the
onboard reference, which may have resulted since the last calibration. You
can save the results of the external calibration process to flash memory so
that the new calibration constants are automatically loaded the next time the
NI PXI-7831R is powered on and so that the newly measured onboard
reference level is used for subsequent internal calibrations.
To externally calibrate your device, be sure to use a very accurate external
reference. The reference should be several times more accurate than the
device itself.
For a detailed calibration procedure for the NI PXI-7831R, refer to the
NI PXI-7831R Calibration Procedure by clicking Manual Calibration
Procedures at
ni.com/calibration .