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ADN8834 PT100 calculations

Question asked by MrPTC on Mar 23, 2016
Latest reply on Mar 29, 2016 by MrPTC

Hello

 

Is it possible to use the chopper circuitry with a PT100 thermistor?

 

I'm trying to get those resistor values, namely Rx, with the equiation provided by the datasheet.

Problem is that the resistor result is negative. The divisor parcel is negative, so the resistor result is negative.

 

The document states that with Rlow(resistance at low endpoint), Rhigh(resistance at high endpoint), and Rmid you can calculate the Rx to get a linearization of the impedance/temperature ratio along the desired range.

 

So, let's say I want a range of 0ºC~20ºC. Rlow is 100 Ohm, Rhigh is 107.79 Ohm. And Rmid, I assume it's the resistance for 10ºC (in datasheet it states that Tmid "is the average") is 103.9 Ohm.

These are standard PT100 values.

 

So, I use this provided formula in "THERMISTOR SETUP" section, to get Rx, and it is negative. Always. No matter the values I  choose.

Clearly, I'm missing something.

 

So please, help me.

Thanks in advance.

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