Signal conditioning circuit applicable to all types of thermocouples.

[m.h.s]

Hi all,

If you have the signal conditioning circuit that is applicable to all types of thermocouples , then send me its link. I am making DAQ card which has a 10 bit ADC. The signal conditioning should be perfect enough that the output voltage from

the signal conditioning circuit is in the range of 0 - 5 volts that can be applied to ADC. The input of the signal conditioning

circuit for my application is -10mV to + 80mV. I  also read the NI tutorials for signal conditioning of thermocouples, that

also helped me but i want signal conditioning circuit with its explanation.

Waiting for your useful reply.

[Doug_L._Bear]

Hey,

I noticed on your other post you were pointed to Omega's website.  That is probably a great place to start.  I did some google searching and found a few other possibly useful links for you.

http://www.edaboard.com/ftopic67377.html

http://zone.ni.com/devzone/cda/tut/p/id/4802

http://forums.ni.com/ni/board/message?board.id=170&thread.id=432465

In the future, please don't double post, it makes it harder for everyone to find what they are looking for when issues are posted twice.

[Alain_S]

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Alain S wrote:

ALL TYPES of thermocouple will be hard to find unless you buy a converter from  Omega or Phoenix Contact

But you may start with AD594 or MAX 6675 

Is this also for your PIC 18F..... project?

If yes I think you better off with raw IC isn't it?

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If the links don't work here, go to the other thread 🙂

[Coq_Rouge]

May I suggest this forum also http://forum.allaboutcircuits.com/index.php This forum is better for solving problem regarding pure electronics problems. It is just a friendly tip

[m.h.s]

My problem is  still unsolved if i reduce my requirement from all types of thermocouples to just J,K,E,R,N,B,S and T ,

then is there any signal conditioning circuit ?  I dont want to use any cold junction IC . I will measure the temperature of hot junction from thermocouple and the temperature of cold junction from thermistor or RTD. The rest of the calculation , i will handle in labview.

My requirements are mentioned above. IS THERE ANY CIRCUIT ? simple signal conditioning circuit but efficient?

Thanks for all your replies .

[Coq_Rouge]

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muzammil_IIEE wrote:

My requirements are mentioned above. IS THERE ANY CIRCUIT ? simple signal conditioning circuit but efficient?

Thanks for all your replies .

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Dear Muzammil Saleem

Your Google is as good as mine. If some people in this forum have circuit they will give you some clues. But if not, I guess you have to come up your own idea for this project. It is perhaps why you did get this assignment 😉 Is this some kind of educational assignment?

Edit: And one more thing. This forum is much like girls. If you get to pushy, it will get suspicious about your intention and turn the back on you. Just a friendly tip

Message Edited by Coq Rouge on 08-14-2009 10:01 PM

[AnalogKid2DigitalMan]

Lets see:

I open my Omega catalog, turn to the transmitter section selection guide and in 1 minute I find the TX62 and TX64 that does J, K, T, E, R, S, B, and N. has a 4-20mA output that can be scaled to a 1-5V output via a precision 250 ohm resistor. Also does RTD.

-AK2DM

[AnalogKid2DigitalMan]

And I might add that there are scores of temperature controllers available from many manufacturers that can handle more than the 8 type of T/C's you listed with analog outputs for the process variable.

-AK2DM

[Alain_S]

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muzammil_IIEE wrote:

My problem is  still unsolved if i reduce my requirement from all types of thermocouples to just J,K,E,R,N,B,S and T ,then is there any signal conditioning circuit ?

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Wow! Wikipedia tell me about 10 types of TC, you asked for 8, that's still ALL for me! Should I   or should I  

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muzammil_IIEE wrote: 
I don't want to use any cold junction IC . I will measure the temperature of hot junction from thermocouple and the temperature of cold junction from thermistor or RTD. The rest of the calculation , i will handle in labview.

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You know where to measure the cold junction temperature? Ok then I won't elaborate 🙂

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muzammil_IIEE wrote: 
My requirements are mentioned above. IS THERE ANY CIRCUIT ? simple signal conditioning circuit but efficient?

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You can start with a TX62 like AK2DM suggested, but @315$ it's maybe too expensive 

The TXDIN70 I suggested from the same Omega brand starts @85$

Basically you don't need any circuit!

With the correct NI DAQ card, just read in the voltage and convert it yourself to a temperature using polynomial or lookup table.

But of course if it's for your PIC 18f4550 DAQ project, you can't use a NI DAQ card, right?

So just amplify the TC voltage with a precise amplifier IC, read that voltage in the PIC, send it through USB to the PC with the LV application and here again use a polynomial or lookup table to convert that amplified voltage to temperature.

If it's for your PIC based DAQ project I would go this way, but who am I ?

You see plenty of possibilities, but since we don't know the whole picture it's hard to point out the correct/perfect solution.

[Coq_Rouge]

I think this educational assignment is very doable. Since temperature measurement is a slow process I even think the PIC controller unit can do all the calculations. With a proper designed cold junction compensation circuit it should not be a problem. But be careful to use correct materials. Selecting wrong materials may give wrong temperature measurement.