10-04-2021 01:08 PM
Hello,
I'm running on a Magtrol brand 4Q Dyno (it's a system designed and created entirely by the Magtrol company). They use an NI-9211 module for temperature readings. I've used this before, both on this system and on other self-designed systems. I was needing to collect more than just 4 temperatures, though, and changed over to a NI-9214, 16-Channel module. There was some Task changes to be made on their system and I got everything ready to go. The temps were recording as they should, however I had some fluctuation in the readings. I had 6 J-type TCs at various points on my motor/controller (running at 67V) and 1 ambient TC. I was using channels 0-6, and no common. No matter what combination of TC channel usage, Commons usage, TC wire shielding, nothing worked and I was getting a fluctuation of about 4C every few seconds. I'm recording at about 5Hz. I changed everything back to the NI-9211 and am only running 4 TCs and am getting no fluctuation in my temperature readings. I understand these modules aren't the same, but does anyone have an idea as to what I might be overlooking that is causing this fluctuation in the temperature readings? Thank you!
10-04-2021 01:48 PM
Did you ground the COM channel?
10-04-2021 02:04 PM
At first I didn't, then I tried with grounding the Com channel - no change with or without it being grounded.
10-04-2021 06:25 PM
I am inclined towards suspecting any potential on the thermocouples, for example, you mount a thermocouple onto a motor body, ideally, that motor body has to be grounded but it is not, in this case, any potential on the motor body is passed onto the thermocouple.
I might have overlooked - did you say that you see a consistent fluctuation on all the thermocouple channels? and can you share some waveform of the fluctuations?