Thermocouples randomly stop working, then start again with SCXI 1102

[BBalmforth]

Hello,

I am creating a DAQ system for a thermal fluid flow loop experiment using a number of thermocouples, humidity sensors, and flow meters. I've been testing this system for a while now, and until recently, I haven't had any problems. Now, however, the thermocouples will randomly stop stop working when I run the VI. When I turn the system off and wait a while, then turn it back on for another test, they are working again. I'm not sure what is causing the problem, but I've tried changing which channeles the thermocouples are connected to, but the problem persists. I am using all type T thermocouples with SCXI 1102 cards and SCXI 1303 terminal blocks. The DAQ card is a NI PCI-6052E. The card is old, so it may need replacing, which I am open to if needed.

Thanks in advance!

[Travis-E]

Hello BBalmforth,

When the thermocouples stop working, are you experiencing a railed reading or is it going to zero? Does this occur at around the same time each run? Have you tried changing the slot the PCI card is in on your computer? We can also check your PCI card with the DAQ diagnostic Utility. You can find it at this link:

http://joule.ni.com/nidu/cds/view/p/id/2244/lang/en

This will give you a preliminary idea of the status of your DAQ card. 

Regards,

-Travis E

[BBalmforth]

Hi Travis,

Thanks for the diagnostic link, I installed it and it says my card is fine. I tested the system again today, and the thermocouples were working fine, then I turned it off and turned it back on again and the thermocouples are not working again. I didn't touch the thermocouples, the chassis, or the terminal block the thermocouples were attached to, so I'm not sure what could be happening.The thermocouples are reading -34 C and -4 C. The thermocouples that are on the same block read the same value, but the other block reads differently. It only seems to happen when I restart the system.

Thanks.

[Travis-E]

Hello BBlamforth,

I would like to try seeing if there could be a chassis related issue. Try taking out all of the modules in your SCXI Chassis except for one and only connect one thermocouple to it. Run your test and see if the thermocouple stops working. The next thing you can try is replacing the cable between the DAQ card and the SCXI chassis. Also do you have another SCXI chassis to test with, your current chassis may be running into power issues.

Regards,

-Travis E

[BBalmforth]

Hi Travis,

I've done some more testing, and I think it may be more of a DAQ card issue. When I turn the chassis off and turn it back on, the thermocouples stop working, but the start working again once I restart the computer. I'm not sure why turning the chassis off would effect the DAQ card in the computer, however. The card is older, so replacing it is an option.

Thanks

[Travis-E]

Hello BBalmforth,

The issue I am concerned with is the fact that the card checked out with the Diagnostic tool. What version of the DAQmx driver did you upgrade to? I also want to eliminate the SCXI side, lets try disconnecting the SCXI chassis and connect a 9V battery. You can then take a regular voltage measurement and cycle power on your computer and see if you can restart the voltage acquisition. This could be related to software and how things are recognized as resources.

Regards,

-Travis E

[BBalmforth]

Hi Travis,

Sorry about the long time between replies, things have been busy here. I tried the 9V battery, and the measurement works fine. There is 5V signal on the channel before I connect the battery, and a ~9.5V signal with the battery, even after power cycling. The thermocouples all start working again once the computer is reset, so if nothing else, I could just leave instructions to not turn off the SCXI chassis between experiments unless the computer is also restarted. 

Thanks

[NEWKlear]

Hey BBalmforth,

There should be no need to leave the SCXI chassis on between measurements, however there should be no harm in leaving the cards on at all times.  Does the problem persist if we move the PCI (or PXI) slot that the DAQ card is in?  And were all the thermocouples affected?  I saw that you posted two readings, was this for a group of TCs or for two individual TCs? 

Best Regards,

[BBalmforth]

Hi J Newk,

I haven't tried moving to a different PCI slot, but I will try that next. All of the thermocouples were affected, two one one block, one on a different block, accross four different terminal blocks/SCXI cards, all are 1303s and 1102s. The different readings corresponded to the different terminal blocks; both thermo couples on one block showed -34, while the single thermocouple on the other block showed -4. An HX85BA humidity sensor that also detects temperature changes also seemed to be affected, even though it is connected to a different chassis, card, and terminal block. Only the termperature measurement for the HX85 was affected as far as I could tell. I also have a mass flow meter connected to the same chassis as the HX85, and its flow reading was unaffected.

Thanks,

-BBalmforth