DSA Calibration
Your device contains digital correction circuitry to compensate for gain and offset errors in the analog and ADC circuitry. The gain and offset calibration constants are stored in nonvolatile memory (EEPROM) on your device. NI-DAQmx writes these calibration constants to the digital correction circuitry.
To achieve the maximum accuracy, you should perform external calibration at least once per year (the recommended external calibration interval) and perform self-calibration prior to measurement sessions or otherwise, as desired. You should calibrate your device only after your computer and the device have been powered on and warmed up for at least 15 minutes.
Self-Calibration
Self-calibration is executed with the Self Calibrate VI/function. When you self-calibrate a DSA device, you do not need signal connections. However, for devices with analog output channels, values generated on those output channels can change during the calibration process. If you have external equipment connected to the AO channels and changing the AO voltage could damage the external equipment, you should disconnect the external equipment before performing the self-calibration.
External Calibration
External calibration is performed using a customized calibration program and external test equipment that has itself been calibrated to the required accuracy or standard. This operation is usually performed by a specialized metrology laboratory. The equipment and connections required to externally calibrate a device varies depending on the device category. For NI PXI-447X and PXI-446X devices, you need a stable and accurate DC voltage signal to calibrate the AI subsystem. NI PXI-446X devices also include an adjustable frequency timebase. You need a stable sinusoidal frequency source to calibrate this timebase. The NI PXI-4461 also supports analog output. You need a digital multimeter (DMM) to calibrate the AO subsystem. The DC voltage, frequency source, and DMM can be manually or automatically controlled and switched between channels, depending on the nature of the customized calibration program.