PT1000 Conditioning Circuit Gain Calculations

[AlphaRugal79]

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!!!!!

 

[Analog]

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!!!!!

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.

 

[AlphaRugal79]

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.

 

[Hero999]

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