Accuracy in degrees C for X20AT4222 input card

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Hello Robert,

I’m going to give this my best try to explain, and I’m pretty sure this is accurate. [Corrected for accuracy]

If the X20AT module is operating at 25 C, then the equation for the accuracy of the module only is as follows:

+/- Accuracy = (MeasuredValue * Gain) + (FullMeasurementRange * Offset)

For the X20AT4222, operating at 25 C, and reading a PT100 with a value of 80 C, I get the following:
Accuracy = (80 * 0.00037) + (1050 * 0.000015)
Accuracy = +/- 0.04535 C

The Measured Value and Full Measurement Range are in the units provided by the module, and changes with the configuration of the module:

  • Resistance measurement, 4500 Ohms. Full Measurement Range = 4500 Ohms.
  • Resistance measurement, 2250 Ohms. Full Measurement Range = 2250 Ohms.
  • RTD measurement, -200 to 850 C. Full Measurement Range = 1050 C.

If the module is not operating at 25 C, then the equation expands slightly.

+/- Accuracy = MeasuredValue * (Gain + GainDrift * (ModuleTemp-25)) + FullMeasurementRange * (Offset + OffsetDrift * (ModuleTemp-25))

Note that this only takes into account the module accuracy, and not the sensor, or cable resistance to the RTD.

Best regards,
Austin

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