Signal Conditioning

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Incorrect readings with PXIe-4353 module




I'm using a PXIe-4353 module along with the TB-4353 to measure temperature .The CJC source is set to "Built In". But the readings are 25 deg C higher than what is expected. But if the CJC source is set to "Constant" with the constant set to 0, it shows the correct readings. I have tried testing the card using a calibrated source as well as a K type thermocouple but both show the same results. But when I try to read the voltage using the 4353 with the calibrated source set to 30 deg C, it reads 1.2mV ( which corresponds to 30 deg C for K type). 


Please help out..



Shweta JP



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Message 1 of 5

Hello Shweta JP,


Have you checked the polarity of your thermocouple?  They have +/- wires that should be connected accordingly.  There are several common wire color schemes so you should be able to tell which wire is which from the color.  Here are a few common color schemes:


Standard       Positive (+) Color      Negative (-) Color

IEC                         Green                       White

BS                           Red                         Blue

ANSI                      Yellow                        Red


If your wires are different colors then I would recommend that you consult your sensor vendors documentation to confirm the proper wiring.


Also, when you use the "calibrated source" are you using copper wire or thermocouple wire?  If it is copper wire then I think there's a good chance you may have the thermocouple leads reversed.


Post back with what you find out about the wiring and if there is still a problem.



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Message 2 of 5

Hello Brooks,


Thanks a lot for the reply. I checked the polarity of the wires and connected it correctly. The readings I get with the 4353 using a K type thermocouple are accurate. But when I use a calibrated source, the readings show a 1 to 2 degree offset. I have enabled the cold junction compensation in the calibrated source as well. Also I'm using the same thermocouple wires to connect from the source to the module..



Shweta JP

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Message 3 of 5

Hello Shweta JP,


Your first post indicated an issue when using the built in CJC, but you seem to be talking about a different issue now.  Does this mean that when using the built in CJC on the PXIe-4353 you are getting accurate readings with the K Type thermocouple and now the issue is a 1-2 degree offset when using the calibrator?


What calibrator are you using and what temperature are you simulating?  If you could link to a data sheet that would be great.


Best Regards,

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Message 4 of 5

Hello Brooks


I'm sorry for the confusion. Let me be more clear. What I find now is that when I use the CJC built in for the PXIe-4353, the module seems to be showing accurate readings with the K type thermocouple. But when I use a calibrated source(with its compensation enabled), the module shows readings that are offset by a certain value (1 to 2 degrees). So is it that when a calibrated source is used, the CJC option for the module should be set to a constant rather than the built in?


The calibrated source is an Omega CA100 Compact Cal. The link to the manual is below


Thanks again!


Shweta JP

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Message 5 of 5