DAQmx Channel Calibration Wizard Requires Max/Min Values

Updated Dec 18, 2018

Reported In

Software

  • Measurement & Automation Explorer (MAX)

Issue Details

I have setup a Task in DAQmx and I would like to calibrate it for better accuracy. The known source that I am calibrating against cannot be set all the way to the max and min values I am expecting in my measurement. Why does the Channel Calibration Wizard in DAQmx require these endpoints to be specified?

Solution

DAQmx is designed to interpolate between calibration data points that are specified. This enables it to achieve the most accurate value at any given point in the measurement range. As the number of calibration points increases, so does the accuracy of the calibration curve.

The simplest interpolation between two points is a line, and given only calibration values for the max and min, DAQmx will assume a linear variation from the max to the min. This is a reasonable assumption based on the information provided to DAQmx. If DAQmx was given several points and asked to extrapolate to the max and/or min that lied outside of those points, there would be no way for it to do so accurately. For example, the behavior inside the reference points might be largely linear, but drop off steeply outside of this range. DAQmx would have no way of knowing this.

Because there is no way to accurately extrapolate, DAQmx forces the user to provide calibration values for the endpoints, or uses default values instead.

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