Chapter 3 calibration, Loading calibration constants, Internal calibration – National Instruments NI PXI-7831R User Manual
Page 44: Calibration
© National Instruments Corporation
3-1
3
Calibration
Calibration refers to the process of minimizing measurement and output
voltage errors. On the NI PXI-7831R, these errors are corrected in the
analog circuitry by onboard calibration DACs (CalDACs). Because
calibration is handled by the analog circuitry, the data read from the AI
channels or written to the AO channels in the FPGA VI is already
calibrated.
Three levels of calibration are available for the NI PXI-7831R to ensure the
accuracy of its analog circuitry. The first level, loading calibration
constants, is the fastest, easiest, and least accurate. The intermediate level,
internal calibration, is the preferred method of assuring accuracy in your
application. The last level, external calibration, is the slowest, most
difficult, and most accurate.
Loading Calibration Constants
The NI PXI-7831R is factory calibrated before shipment at approximately
25 °C to the levels indicated in Appendix A,
. The associated
calibration constants (the values that were written to the CalDACs to
achieve calibration in the factory) are stored in the onboard nonvolatile
flash memory. These constants are automatically read from the flash
memory and loaded into the CalDACs by the NI PXI-7831R hardware on
power-up. This occurs before a VI is loaded into the FPGA.
Internal Calibration
The NI PXI-7831R can measure and correct for almost all of its
calibration-related errors without any external signal connections. This
calibration method is referred to as internal calibration. NI provides
software to perform an internal calibration. This internal calibration
process, which generally takes less than two minutes, is the preferred
method of assuring accuracy in your application. Initiate an internal
calibration to minimize the effects of any offset and gain drifts, particularly
those due to changes in temperature. During the internal calibration
process, the AI and AO channels are compared to the NI PXI-7831R