signal conditioning using RTD

[annie017]

i want to know about how we will design the signal conditiong circuit for RTD... using 3op-amp instrumentation amplifier...if know any thing about it then please tell me... asap..

[Dennis_Knutson]

What NI hardware are you using?

[Henrik_Volkers]

About just.... both are in Texas.... replace the N with a T 😉

😄

[johnsold · Accepted solution]

I like to design circuits like that, although it is almost always cheaper to buy an instrumentation amplifier from TI or AD than to pay me to do it.

Can you ask specific questions so we do not need to guess what you want?

Lynn

[Henrik_Volkers · Accepted solution]

and to add something constructive...

If you want to learn something about RTD conditioning circuits:

Start with Art of electronics

Next are some NS and TI general appnotes on OP amps

And finally the best appnotes on analog circuitry (my personal choice) visit linear.com and read the appnotes from Jim Williams.

And no matter what you have read and are told: Heat the iron and bread board your circuit, hook up a scope and practise .....

To your circuit: DC supply is critical, RTD R_0 value? Four wire measurement? Offset compensation? ..... 

If you just want to measure a temperature: for 5 bucks you can buy a thermometer incl. display, no need to build it.

[annie017]

actually this my project... i have to use only RTD... pls tell me how much dc supply is required ?..
and i want to measure the temperature from 0 degree celcius to 70 degree celcius ...so how much gain is required to optained such a range...and tell me the exact procedure to do this... please...

[annie017]

i want to creat temperature indicator ...and range is 0 degree celcius to 70 degree celcius...
so tell me the gain of the system,..and i am using RTD PT100...bridge resistenace is of 100 ohms...and all other elements are of 1k ohm... POT we have to adjust according to the gain...
i have only one ques. which is the perfect value for gain of this range...????
and if you know anything then kindly tell me.

[johnsold]

We cannot answer that question because you have not told us enough about your system. What is the voltage range of the device you marked "Display" in the image in your first post? Which of several temperture coefficients does your RTD use? What resolution and accuracy do you need on the final temperature readings?

For alpha = 0.00385 the resistance at 70 degrees C is 127.08 ohms. If you use a 1 mA excitation current, the voltage across the RTD will go from 100.0 mV at 0 degrees to 127.1 mV at 70 degrees. 

If you excite the bridge with 200 mV (to provide 1 mA at 0 degrees), the differential output at 70 degrees will be about 112 mV and the current in the RTD will have dropped to 881 uA.

Lynn

[Benarji]

Since it has been a very long back you asked the question, I don't know whether you find the solution for your project or not. The below link will help for the designers who are working on this.

https://www.ti.com/lit/pdf/tidu433

If you find the exact solution, Please post that solution here, so that it will be helpful for some others...