Hello All,

I am working with Pt1000 in 4 wire configuration and so far I have designed a current source providing current less than 1mA and now I am working on the difference amplifier. For the op amp I am using LM358 Dual Opamp in Single Supply configuration. I am using the resistances of 47k and 470k to give me a gain of 10. Now at the output I read voltages like 2.063V or 2.153V, how can I calculate temperature in degrees celcius from this information. e.g. is it like 2.063 /(10*3.85)!!!! Also when I replace Pt1000 with 1 kohm resistance i get some voltage like 1.921V, this voltage should correspond to 0 degrees, now how do I do normalization???

finally, should I stick with Difference Op Amp or switch over to Instrumentation Op Amp??? any advice!!!!!

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For an RTD circuit, the sensor will change its resistance with temperature. Normally, the output of the op amp is read by an a/d converter and then a microprocessor. There, the conversion is made to temperature. You didn't mention what was on the other end.

As far as how to do it, I've done it with a table lookup approach and linear interpolation. You can choose another algorithm if you wish.

The data on linearization is readily found on the internet. Omega has a good selection of RTDs and data.

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hey,

thanks for the reply. Yes, indeed, the output of the op amp will be read by the microcontroller(atmega16), eventually. But before doing that I just want to make sure that the difference opamp circuit is working. for that i am reading off the output voltages and trying to somehow calculate the temperature.

 

You could use a couple of buffer op-amps on the inputs to prevent the input impedance from interfering with the source impedance.

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