TC-2095 + SCXI-1102 not reading Thermocouple

[byrd]

Hi,

I am hoping someone can help me troubleshoot my DAQ setup.   I have a SCXI-1000 with the SCXI-1600 USB controller, and the only SCXI module I have is the SCXI-1102.  That is connected to a TC-2095, which then connects to our thermocouples.  The problem is that in LabVIEW (and MAX), I am not getting a correct reading.  There is no change when I heat the TC up or cool it off.  I have tried more than one TC and there is no difference.  I have tried switching channels in the 2095, but that doesn't do anything either.  There is also no difference in the signal when the TC is unplugged.  The dip switches in the back of the 2095 are set to off for my channel, but on for all the other channels (which aren't being used yet), if that is any help.  It seems like this should be fairly straightforward to do, so I'm hoping the solution is one of those forehead-slappers.  Thanks!

Alex

[kikiduu]

Are you using a ordinary floating thermocouple? In that case you have to turn on the GND-REF  switch for the channel. If you are not sure, then just turn ON all the switches and measure.

Which VI are you using for acquisition? Is there any error generated by the VI? have you selected the correct thremocouple type?

[byrd]

Thanks for the reply.  The TC I'm using is classified as "Ungrounded Junction" on their website, so I'm assuming that means it's floating.  Turning the GND-REF switch on doesn't seem to change anything.  In looking at the manual for the 1102 (http://www.ni.com/pdf/manuals/371975d.pdf page 22), it looks like they say to wire the negative wire of the TC to the ground channel, which I cant seem to find on the TC-2095 or the 1102.

I'm not yet running a VI to get the signal, I'm just using the "Test Panels..." window in MAX.

Thanks again!

[Jordan F]

Hi,

Try creating a Thermocouple Task in MAX and see if your measurement is what you are expecting.  This can be done by right clicking on Data Neighborhood>>Create New in the configuration tree and selecting NI-DAQmx Task.  Also, I would recommend trying different channels on the TC-2095 to see if you get a different result. 

The TC-2095 is pretty straight forward on how to connect the thermocouple but you are correct in saying there could be some sort of grounding issue.  If possible, you could take the TC-2095 (and possibly the SCXI chassis) out and directly measure the thermocouple with your DAQ card.  I linked the TC-2095 specifications and it discusses how to arrange the switches on the back of the terminal block on pages 5 and 6. 

BNC/TC-2095 Rack-Mount Adapter Installation Guide and Specifications (pages 5 and 6)

http://www.ni.com/pdf/manuals/321731b.pdf

[byrd]

Hi Jordan,

Your suggestion helped me narrow down the problem.  I created the DAQmx Task in MAX and it worked...but here's the catch: channels 0...11 show bad readings like I described earlier, but 12...31 work perfectly.  I tried the TC in a higher channel than I was using before, but I don't remember if I've ever tried getting a reading from any channels outside of 0...11.  I also noticed that on the back, the first three sets of switches are for channels 0...11.  Could that be related?  Might it be bad hardware?

Thanks,

Alex 

[Jordan F]

What is your switch configuration for those channels.  Read the comments on pages 5 and 6 of the TC-2095 manual I posted.  It looks like if you might want the switch configuration to be  GND-REF "ON" and PULL-UP "OFF".  However, I would try some different configurations to see if any works.

[byrd]

Jordan,

All the switches are set to the on position currently.  I have tried all the combinations of switch settings for the channels that don't work.  Right now, the channels that don't work are set the same as the ones that do work, and I can't think of a reason some channels would work and some not work with the same switches set.

Thanks again for the help!

Alex

[Jordan F]

I think that you may have a problem with the hardware.  Do you have any other modules, SCXI chassis or terminal blocks that you can try?  Also, have you placed the working thermocouples in the channels that dont work to see there function?  If so, I think we can conclude that you may need to replace the TC-2095 or module.