Thermocouple Amplifier using AD595

[engcad]

Hi 

I'm trying to build a k-type thermocouple signal conditioning circuit using AD595 IC. I studied its data sheet and the related documents and read many advices on how I should connect the circuit. My connection is as shown in the attached image. 

My thermocouple tip type is exposed, however when I didn't ground it to the circuit common [as shown in the picture], the output is very high (about 13 volts) and illogical. I tried to wire the thermocouple leads to the circuit common, and I tried many suggested connections, the reading is fine but it has an offset which is not has a fixed value.

Finally, I tried to connect the negative terminal of the thermocouple with the circuit common using a 1 Mega Ohm resistor. The reading is fine at the room temperature but at about 100 deg. Celsius the reading has a negative offset value about -10 deg. Celsius. When I reduced the resistor value to only about 200 Ohms, the reading restores its logical reading at about 100 deg. Celsius However, the reading is not stable and the circuit accuracy is not acceptable.

Any suggestions about wiring the circuit and the thermocouple to enhance the performance and accuracy??

Thanks

[davidraj]

Hey, 

I dont know how much help we might be able to give you on here. 

Typically our signal conditioning solutions are like a TC01 to record one thermocouple. or some SCXI stuff that fit in PXI. 

We have front end signal conditioning hw where the circuit design portion is not from the user. Our stuff doesn't deal with building the circuit for an AD595. 

I suspect that there is a decent user base for the AD595 within the hobbyist market. 

These forums are pretty open, so you might be able to get some help here but I think you're more likely to get an answer in a hobbyist forum like https://forum.sparkfun.com/

David