TC-08 Reading incorrect temperatures

Simon Denley · Post by **Simon Denley** » Mon Dec 08, 2003 4:02 pm

Hi

We are experiencing real problems trying to measure & log temperatures produced on an ultrasonic Generator PCB. We have taken the precautions detailed in other posts regarding good earthing but without success. We are using standard type K thermoucouples.

I am assuming that the problem is due to pick up from various parts of the circuit - (there are inductors & transformers & MOSFETSon the PCB)

If i connect channel 1 only, all is well. As soon as another thermocouple is connected to any of the other channels the temperature readings become unstable & incorrect.

Is there a way round the problem - can you get screened thermocouples?

Hope someone can help

Thanks

Simon

ricardo · Post by **ricardo** » Mon Dec 15, 2003 11:24 am

Hi,

I'm sorry you are having problems with the TC-08. Something else you could check is that you don't get overload on one channel, or between channels. The TC08 has an input range of approx 60mV. If more than 5V difference occurs between any of the inputs to the TC08 then incorrect readings will result. Additionally if more than 5V difference occurs between the TC08s ground (also computer ground and usually mains earth) then errors will occur. A typical example where this may occur would be if a thermocouple is used to measure the temperature of the motor on a machine tool. The casing of the motor, although earthed may be at a potential several volts different to that of the earth of the computer.

With regards to the screened thermocouples, we don't sell any but you may find something suitable from Kalestead.
http://www.kalestead.co.uk/

Best regards,

Ric