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NI9214 vs NI9211

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!

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Did you ground the COM channel?


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At first I didn't, then I tried with grounding the Com channel - no change with or without it being grounded.

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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?

-Santhosh
Semiconductor Validation & Production Test
Soliton Technologies
NI CLD, CTD
LabVIEW + TestStand + TestStand Semiconductor Module (2013 - 2020)
NI STS for Mixed signal and RF
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