OP07 thermocouple amplifier

Ranjeet,

I suggest a differential amplifier setup like this...(VG1 is thermcouple)

I did something like this only but the resister value is changed

But ideallly according to that gain needs to be 15 but now my gain is >100. Dont know what has just happened.

Here R1 = R2 = 18K

R3 = R4 = 270K

Ranjeet,

The gain should be 15. 

I hope my current circuit is OK. But the gain is sometimes 100 too sometimes. I have added 100uf capaitor at output too. but the gain is not fixed.

what could be the issue. 

Ranjeet,

I suggest measuring the voltage for every node while verifying that the output does not change during the nodal measurements. With every node's value available, the problem will be easier to find. 

Thanks will debug..But the circuit is OK I hope.Any other modification is needed. offset input I havent connected. I think I dont need to.