Loading Calibration Constants - National Instruments PCI-445 Series User Manual

Calibration

Loading Calibration Constants

© National Instruments Corporation
This chapter discusses the calibration procedures for your PCI-445X. Your
PCI-445X comes with a calibration certificate. The certificate contains a
unique tracking number linking your device to the National Instruments
corporate databases where the traceability information is stored.
Calibration refers to the process of minimizing measurement and output
voltage errors by making small circuit adjustments. On the PCI-445X
devices, these adjustments take the form of writing values to onboard
calibration DACs (CalDACs). If you are using the NI-DAQ device driver,
that software includes calibration functions for performing all of the steps
in the calibration process. Some form of device calibration is required for
all but the most forgiving applications. If you do not calibrate your device,
your signals and measurements could have very large offset and gain errors.
The four levels of calibration available are described in this chapter. The
first level is the fastest, easiest, and least accurate, whereas the last level is
the slowest, most difficult, and most accurate.
Your PCI-445X device is factory calibrated at approximately 25 °C to the
levels indicated in Appendix A, Specifications. Before shipment, the
associated calibration constants—the values that were written to the
CalDACs to achieve calibration in the factory—are stored in the onboard
nonvolatile memory (EEPROM). Because the CalDACs have no memory
capability, they do not retain calibration information when the device is
unpowered. Loading calibration constants refers to the process of loading
the CalDACs with the values stored in the EEPROM. NI-DAQ software
determines when this is necessary and does it automatically.
The EEPROM contains a user-modifiable calibration area in addition to
the permanent factory calibration area. This means that you can load the
CalDACs with values either from the original factory calibration or from a
calibration that you subsequently performed.
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