National Instruments NI 6013 User Manual

Also see for NI 6013: Note to Users

Contents

National Instruments NI 6013 User Manual Manual pdf 69 page image

Chapter 5 CalibrationNI 6013/6014 User Manual 5-2 ni.comaccount the fact that the device measurement and output voltage errors canvary with time and temperature. It is better to self-calibrate when the deviceis installed in the environment in which it is used.Self-CalibrationThe NI 6013/6014 can measure and correct for almost all of itscalibration-related errors without any external signal connections. NI-DAQprovides a self-calibration method. This self-calibration process, whichgenerally takes less than two minutes, is the preferred method of assuringaccuracy in your application. Initiate self-calibration to minimize theeffects of any offset and gain drifts, particularly those due to warmup.Immediately after self-calibration, the only significant residual calibrationerror could be gain error due to time or temperature drift of the onboardvoltage reference. This error is addressed by external calibration, which isdiscussed in the following section. If you are interested primarily in relativemeasurements, you can ignore a small amount of gain error, andself-calibration should be sufficient.External CalibrationThe NI 6013/6014 has an onboard calibration reference to ensure theaccuracy of self-calibration. Its specifications are listed in Appendix A,Specifications. The reference voltage is measured at the factory and storedin the EEPROM for subsequent self-calibrations. This voltage is stableenough for most applications, but if you are using the device at an extremetemperature or if the onboard reference has not been measured for a year ormore, you may wish to externally calibrate the device.An external calibration refers to calibrating the device with a knownexternal reference rather than relying on the onboard reference.Redetermining the value of the onboard reference is part of this process andthe results can be saved in the EEPROM, so you should not have to performan external calibration very often. You can externally calibrate the deviceby calling the NI-DAQ calibration function.To externally calibrate the device, be sure to use a very accurate externalreference. The reference should be several times more accurate than thedevice itself.