National Instruments NI PCI-6110 - Manual (Page 69)

© National Instruments Corporation 5-1 NI PCI-6110/6111 User Manual
5
Calibration
This chapter discusses the calibration procedures for the
NI PCI-6110/6111. NI-DAQ includes calibration functions for performing
all of the steps in the calibration process.
Calibration refers to the process of minimizing measurement and
output voltage errors by making small circuit adjustments. On the
NI PCI-6110/6111, these adjustments take the form of writing values
to onboard calibration DACs (CalDACs).
Most applications require some form of device calibration. If you do not
calibrate the device, the signals and measurements could have very large
offset, gain, and linearity errors.
Three levels of calibration are available to you and 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.
Loading Calibration Constants
The NI PCI-6110/6111 is factory calibrated before shipment at
approximately 25 °C to the levels indicated in Appendix A,
Specifications .
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 determines
when this is necessary and does it automatically. If you are not using
NI-DAQ, you must load these values yourself.
In the EEPROM there is 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.
This method of calibration is not very accurate because it does not take into
account the fact that the device measurement and output voltage errors can