National Instruments NI 7831R User Manual

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National Instruments NI 7831R User Manual Manual pdf 44 page image

Chapter 3 CalibrationNI 7831R User Manual 3-2 ni.comIf you have NI-RIO installed, you can find the internal calibration utility atStart»All Programs»National Instruments»NI-RIO»device»Calibrate7831R Device. Device is the NI PXI-7831R or NI PCI-7831R device.Immediately after internal calibration, the only significant residualcalibration error is gain error due to time and temperature drift of theonboard voltage reference. You can minimize gain errors by performing anexternal calibration. If you are primarily taking relative measurements, thenyou can ignore a small amount of gain error and self-calibration issufficient.The flash memory on the NI 7831R stores the results of an internalcalibration so the CalDACs automatically load with the newly calculatedcalibration constants the next time the NI 7831R is powered on.External CalibrationAn external calibration refers to calibrating your device with a knownexternal reference rather than relying on the onboard reference. TheNI 7831R has an onboard calibration reference to ensure the accuracy ofself-calibration. The reference voltage is measured at the factory and storedin the flash memory for subsequent internal calibrations. Externallycalibrate the device annually or more often if you use it at extremetemperatures.During the external calibration process, the onboard reference value isre-calculated. This compensates for any time or temperature drift-relatederrors in the onboard reference that might have occurred since the lastcalibration. You can save the results of the external calibration process toflash memory so that the NI 7831R loads the new calibration constants thenext time it is powered on. The device uses the newly measured onboardreference level for subsequent internal calibrations.To externally calibrate your device, use an external reference several timesmore accurate than the device itself.Refer to the NI 7831R Calibration Procedure for a detailed calibrationprocedure for the NI 7831R, available by clicking Manual CalibrationProcedures at ni.com/calibration.