We have a DT85 reading temperatures from a Furnace, this has been working fine but a couple of days ago started to record negative readings when idle (i.e. not testing) and during tests.

The good old Hard Reset with a paperclip solved it for a few hours, but then it happened again. Has anyone any idea what could be happening?

Good morning ccowburn,

It's more likely to be a wiring or installation problem. Also try running the test command. If it fails with all sensors disconnected then there is some thing wrong with the logger and it will need to be returned for repair.

If it passes with all the sensors disconnected and fails when they are connected then there is a problem in the wiring.

Cheers,
Roger

Thanks for the reply,

Turns out it is an Electrical issue in the room the DataTaker is being used. If the large extractor fans are on the DT reads minus .. when you switch the fans off all is okay!!

Our Electrical bods are investigating

Good morning ccowburn,

Ok, Yes noise on the electrical lines can do that. When we are use thermocouples the Voltage levels being measured are in the Millionth of a Volt (For a K type thermocouple 1 degree C is about 40 Micro Volts) so it doesn't take much to affect the readings.

Look at a good quality power supply filter or powering DT80 from a different electrical circuit.

Cheers,
Roger