National Instruments Module SCXI-1125, Руководство пользователя

Страница: 67 / 101

Chapter 5 Using the SCXI-1125
SCXI-1125 User Manual 5-30 ni.com
Calibration
The SCXI-1125 is shipped with a calibration certificate and is calibrated by
the factory to the specifications described in Appendix A,
Specifications .
Calibration constants are stored inside the calibration EEPROM and
provide software correction values that are used by your application
development software to correct your measurements for both offset and
gain errors in the module.
Due to the nature of the analog circuitry in your SCXI-1125 module, gain
errors tend to be more stable over time, therefore requiring less frequent
calibration. Offset errors, however, are more susceptible to drift due to time,
temperature, and other environmental changes, and can affect the
measurement accuracy of your module. You may wish to periodically
calibrate the module for offset drift using the following procedure to ensure
that the measurements on the SCXI-1125 are as accurate as possible. Refer
to Appendix A,
Specifications , for more details about the analog stability
of your SCXI-1125 module.
Calibration Procedures
You can calibrate the offset on the SCXI-1125 using National Instruments
software. When calibrating the offset on the SCXI-1125, make sure the
DAQ device you are using has been calibrated recently or you will
invalidate the offset calibration on the SCXI-1125. The SCXI-1125
provides input switching that allows you to programmatically shunt the
differential input channels of the SCXI-1125. Once the channels are
shunted, the channel can be read by a calibrated DAQ device or calibrated
DMM. These offsets voltages, read by the calibrated device, can be saved
in the calibration EEPROM in the SCXI-1125 for software correction of
offset.
Caution Ensure that the calibration on the DAQ device or DMM you are using is up to date
and traceable. If you adjust the gain or offset values using an uncalibrated device, you will
invalidate the calibration on the SCXI-1125 and any measurements taken with the module
may not be accurate.
Remember that the calibration you perform on the SCXI-1125 is only as
accurate as the calibration device you are using. Refer to Appendix A,
Specifications , for accuracy specifications for the SCXI-1125.