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.

A couple of thoughts:

The equation for Rx is aimed at linearizing the response of a thermistor with a negative temperature coefficient, but a PT100 is an RTD (as opposed to a thermistor) which has a positive temperature coefficient. See an RTD resistance example here: http://www.micropik.com/PDF/pt100.pdf

The resistance change of a PT100 is VERY flat compared to that of a typical thermistor. You might want to consider whether or not you need to add a linearization scheme for your application.

Hopefully this helps somewhat.