National Instruments NI PXI-7831R User Manual

Also see for NI PXI-7831R: User manual User manual Note to Users User manual User manual

Contents

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

© National Instruments Corporation 3-1 NI PXI-7831R User Manual3CalibrationCalibration refers to the process of minimizing measurement and outputvoltage errors. On the NI PXI-7831R, these errors are corrected in theanalog circuitry by onboard calibration DACs (CalDACs). Becausecalibration is handled by the analog circuitry, the data read from the AIchannels or written to the AO channels in the FPGA VI is alreadycalibrated.Three levels of calibration are available for the NI PXI-7831R to ensure theaccuracy of its analog circuitry. The first level, loading calibrationconstants, is the fastest, easiest, and least accurate. The intermediate level,internal calibration, is the preferred method of assuring accuracy in yourapplication. The last level, external calibration, is the slowest, mostdifficult, and most accurate.Loading Calibration ConstantsThe NI PXI-7831R is factory calibrated before shipment at approximately25 °C to the 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 nonvolatileflash memory. These constants are automatically read from the flashmemory and loaded into the CalDACs by the NI PXI-7831R hardware onpower-up. This occurs before a VI is loaded into the FPGA.Internal CalibrationThe NI PXI-7831R can measure and correct for almost all of itscalibration-related errors without any external signal connections. Thiscalibration method is referred to as internal calibration. NI providessoftware to perform an internal calibration. This internal calibrationprocess, which generally takes less than two minutes, is the preferredmethod of assuring accuracy in your application. Initiate an internalcalibration to minimize the effects of any offset and gain drifts, particularlythose due to changes in temperature. During the internal calibrationprocess, the AI and AO channels are compared to the NI PXI-7831R