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©National Instruments Corporation5-1PCI-6023E/6024E/6025E User Manual5CalibrationThis chapter discusses the calibration procedures for your board. If you areusing the NI-DAQ device driver, that software includes calibrationfunctions for performing all of the steps in the calibration process.Calibration refers to the process of minimizing measurement and outputvoltage errors by making small circuit adjustments. For these boards, theseadjustments take the form of writing values to onboard calibration DACs(CalDACs).Some form of board calibration is required for all but the most forgivingapplications. If you do not calibrate your board, your signals andmeasurements could have very large offset, gain, and linearity errors.Three levels of calibration are available to you and described in this chapter.The first level is the fastest, easiest, and least accurate, whereas the lastlevel is the slowest, most difficult, and most accurate.Loading Calibration ConstantsYour board is factory calibrated before shipment at approximately 25° C tothe levels indicated in Appendix A, Specifications. The associatedcalibration constants—the values that were written to the CalDACs toachieve calibration in the factory—are stored in the onboard nonvolatilememory (EEPROM). Because the CalDACs have no memory capability,they do not retain calibration information when the board is unpowered.Loading calibration constants refers to the process of loading the CalDACswith the values stored in the EEPROM. NI-DAQ software determineswhen this is necessary and does it automatically. If you are not usingNI-DAQ, you must load these values yourself.In the EEPROM there is a user-modifiable calibration area in addition tothe permanent factory calibration area. This means that you can load theCalDACs with values either from the original factory calibration or from acalibration that you subsequently performed.This method of calibration is not very accurate because it does not take intoaccount the fact that the board measurement and output voltage errors can