thermocouple circuit design

[pranav gokhale]

i want to design a type j thermocouple circuit by using lm35 as cold junction compensation,
plz help!!!

 

[mrcube_ns]

Is there any particular reason why you want to use LM35.

There are chips which are made to do cold junction compensation. Such LT1025, from linear technology, or analog devices AD594/AD595 (which do compensation and amplify signal).


Mr.Cube

 

[fejohn1231]

Is here the solution for you. Look example circuits.

regards

 

[FvM]

Is here the solution for you.

I agree that Figure-23 is an intelligent solution for the problem. Unfortunately ist's restricted to instrumentation amplifiers with differential feedback input. But there are many other ways to substract the temperature dependant cold junction reference voltage from the TC output, applying a suitable factor.

As a drawback of Figure-23, it doesn't work correctly below zero degree C. A negative supply or a more complex modification would be needed to overcome this issue.

 

[fejohn1231]

Obviusly is good if need a precision instrument above zero. From the question not seems out the goal of circuit.