National Instruments NI 7831R - Manual (Page 44)

Chapter 3 Calibration
NI 7831R User Manual 3-2 ni.com
If you have NI-RIO installed, you can find the internal calibration utility at
Start»All Programs»National Instruments»NI-RIO»device»Calibrate
7831R Device. Device is the NI PXI-7831R or NI PCI-7831R device.
Immediately after internal calibration, the only significant residual
calibration error is gain error due to time and temperature drift of the
onboard voltage reference. You can minimize gain errors by performing an
external calibration. If you are primarily taking relative measurements, then
you can ignore a small amount of gain error and self-calibration is
sufficient.
The flash memory on the NI 7831R stores the results of an internal
calibration so the CalDACs automatically load with the newly calculated
calibration constants the next time the NI 7831R is powered on.
External Calibration
An external calibration refers to calibrating your device with a known
external reference rather than relying on the onboard reference. The
NI 7831R has an onboard calibration reference to ensure the accuracy of
self-calibration. The reference voltage is measured at the factory and stored
in the flash memory for subsequent internal calibrations. Externally
calibrate the device annually or more often if you use it at extreme
temperatures.
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 that might have occurred since the last
calibration. You can save the results of the external calibration process to
flash memory so that the NI 7831R loads the new calibration constants the
next time it is powered on. The device uses the newly measured onboard
reference level for subsequent internal calibrations.
To externally calibrate your device, use an external reference several times
more accurate than the device itself.
Refer to the NI 7831R Calibration Procedure for a detailed calibration
procedure for the NI 7831R, available by clicking Manual Calibration
Procedures at
ni.com/calibration .