Other Parts Discussed in Thread: PGA300, , PGA305
Tool/software:
I'm trying to understand the polynomial used for the linearization and temperature compensation. How do I calculate the coefficients and how are they used?
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PGA900 is programmable and the example firmware project uses a 2nd order polynomial. All PGA300, 302 and 305 devices use a 3rd order polynomial. See the appropriate device datasheets for the structure used.
The 3rd order polynomial will be used for this discussion which allows for 16 possible coefficients to be used.
If you have selected the proper coefficient values, then entering the calibration points as pressure and temperature data into the polynomial should also show the desired DAC outcome. If the result of the polynomial expression does not match the DAC result of the calibration data, make sure you have a non-zero value for ‘g0’ as this is the gain value for the most basic case. Also verify the values used for temperature digital offset and gain, and also the pressure digital offset and gain are appropriately applied prior to the polynomial computation.
Linear regression is best accomplished using matrix math either in Excel or Matlab.