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Chapter 1
DAQ System Overview
Calibration Circuitry
Calibration is the process of making adjustments to a measurement device to reduce errors
associated with measurements. Without calibration, the measurement results of your device will
drift over time and temperature. Calibration adjusts for these changes to improve measurement
accuracy and ensure that your product meets its required specifications.
DAQ devices have high precision analog circuits that must be adjusted to obtain optimum
accuracy in your measurements. Calibration determines what adjustments these analog circuits
should make to the device measurements. During calibration, the value of a known, high
precision measurement source is compared to the value your device acquires or generates. The
adjustment values needed to minimize the difference between the known and measured values
are stored in the EEPROM of the device as calibration constants. Before performing a
measurement, these constants are read out of the EEPROM and are used to adjust the calibration
hardware on the device. NI-DAQ determines when this is necessary and does it automatically.
If you are not using NI-DAQ, you must load these values yourself.
You can calibrate AO Series devices in the following two ways.
Internal or Self-Calibration
Self-calibration is a process to adjust the device relative to a highly accurate and stable internal
reference on the device. Self-calibration is similar to the autocalibration or autozero found on
some instruments. You should perform a self-calibration whenever environmental conditions,
such as ambient temperature, change significantly. To perform self-calibration, use the
self-calibrate function or VI that is included with your driver software. Self-calibration requires
no external connections.
External Calibration
External calibration is a process to adjust the device relative to a traceable, high precision
calibration standard. The accuracy specifications of your device change depending on how long
it has been since your last external calibration. National Instruments recommends that you
calibrate your device at least as often as the intervals listed in the accuracy specifications.
For a detailed calibration procedure for AO Series devices, refer to the AO Waveform
Calibration Procedure for NI-DAQmx document by selecting Manual Calibration Procedures
at
ni.com/calibration
Cables and Accessories
NI offers a variety of products to use with Analog Output Series devices, including:
•
BNC accessories
•
Connector blocks with screw terminals
•
I/O connector cables
1-4 | ni.com
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