Hi,

I have a DT85 set up that monitors four separate temperatures using 1/8" Diameter Type K thermocouples. The logger is set up a couple of meters away from the thermocouples and I usually leave my laptop connected to the data logger to display a real time graph of the temperatures during experimental runs.

I encountered a problem today involving interference of the thermocouple signals to the datalogger. I was finding that the temperatures were 10 - 20 degC lower than the expected temperature which was further verified using two other thermocouple readers (Fluke and Dick Smith) which displayed the correct value.

I found the problem to be the power cord of my laptop. When it was plugged into the AC the temperature dropped 20 degC instantaneously and returned to the correct value when I removed the cord.

Is there anyway I can shield the datalogger from this signal or is it simply the matter of not plugging my laptop into the power during experimental runs???

Good evening RFlan,

dataTaker uses switch mode power supplies internally and some times the switch mode power supply connected to the computer can cause interference. The only solution is to proved a ground from the dataTaker to the earth point at the power supply.

Cheers,
Roger

I have a very similar problem to RFlan. I have 12 1/8" Type K thermocouples connected to a steel tube that would normally be heated in a furnace. This steel tube has a couple of vibratory motors bolted to it. I also have 6 short Type K TC's just plugged into my DT85 to simulate others that are connected inside the furnace.

Before I turned on the motors, everything was reading OK (around 15 deg. C), but as soon as the motors where started, the first 12 TC's went crazy, reading somewhere around -50, while the separate 6 TC's remained unchanged.

After a few minutes trying to figure out what was going on, I switched off the motors and the reading came back up, but only to around -16 or so. Like RFIan, I checked these TC's with another instrument and found they were reading normal (~15 degC).

I have only just started using the DT85 and only then through the web interface software.

Can anyone suggest a reason and cure please?

Thanks,
Jim

Good morning Jim,

Your problem is most likely noise from the electric motors. You should be using shielded twisted pair thermocouple wires and the shielding needs to be connected to the digital ground on the dataTaker.

Cheers,
Roger