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

 

This is the circuit i use, ground pin 1 to 4, use a single 12V supply no Negative supply needed, gain is set at 10mV per deg C, is accurate from zero C to 650C,, gain can be increased by an external resistor on pins 8,9.

I used a K-type thermocouple.

 

This is the circuit i use, ground pin 1 to 4, use a single 12V supply no Negative supply needed, gain is set at 10mV per deg C, is accurate from zero C to 650C,, gain can be increased by an external resistor on pins 8,9.

I used a K-type thermocouple.

View attachment 124725

Thanks for your reply
I need the negative supply to measure below zero temperatures (as described in the data sheet of AD595)

 

Ok, then use your psu but tie pin 1 to 4, it prevents drifting, it does for me, but I'm not measuring negative temperatures maybe pin 14 tied to ground will work for you.

 

Ok, then use your psu but tie pin 1 to 4, it prevents drifting, it does for me, but I'm not measuring negative temperatures maybe pin 14 tied to ground will work for you.

I tried this connection but instead I got a positive offset

 

Ok what if you use a +12/-12 psu or +/- 15, does it balance out?

All the circuits in the datasheet show pin 1 grounded to pin 4,