4.1.8.3 Polynomial or Quintic function
After converting the analog input to digital, a five order polynomial function can be used to compensate the
non-linearity of the input.
There are two methods for compensating the errors:
Using the master controller and perform the calculation on the master side.
Using the integrated polynomial function
Note
The polynomial can only be used for one of the analog inputs.
Two methods are available:
Input voltage measurement
Input resistance measurement
Case 1: Input voltage measurement
The polynomial function can be used to compensate the non-linearity of the input voltage:
Case 2: Input resistance measurement
When an RTD is used, the temperature is a function of the measured resistance:
If the internal analog input is chosen with a pull-up resistor, the result of the calculation would be the
resistor’s amount in Ω connected to the input terminals. With the coefficients set as a = 0, a = 1, a = 0, a
= 0, a = 0, a = 0 the result equals the exact value of the sensor resistance.
The image below shows the PT1000 curve with and without input resistor.
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