Signal Conditioning

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Unable to read channels with DAQ Assistant or DAQmx


I am using two SCXI 1112 modules (Slots 3&4) in an SCXI 1000 chasis.  The digitizer is a SCXI 1600 (Slot 1).  There is a SCXI 1531 (Slot 2) not being used.   I am able to see the thermocouple signals when using the test panels in measurement & Automation explorer for the SCXI 1112s (for example on SC1Mod3/aio).  In test panel, the response is as expected for all channels on the SCXI 1112.   When I read the channels with DAQ Assistant, the data is bad -  all channels show the about the same values (approximately the Constant CJC value) and noisy, even disconneted thermocouples give the same result.     Thinking that i had a software issue with DAQ assistant, I manually set up the channels using  DAQmx Create channel-DAQmx Timing-DAQmx Start Task-DAQmx Read chain, only to get the same results.   So, in summary, I can see the signals fine in the Automation Explorer test panels, but can't get the signals with Labview DAQMx or DAQ Assistant.  Below shows how the DAQ assistant is configured.

 DAQ Assistant Set up.JPG

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Because the test panels in the Measurement and Automation Explorer use DAQmx to interface with your thermocouple module I don't think you'll be having trouble with your drivers, especially since they're returning the correct result; and because of this I don't think there is much cause for concern. There will probably be some small configuration setting that we could be missing. By pressing run in the DAQ Assistant window with the correct thermocouple settings you should also see exactly the same results as you would see in MAX (They're the same panels). If they're different, that could be a sign that there are some problems with the thermocouple configuration information. Have you matched the thermocouple type exactly, with the correct value for CJC?


I'm wondering, as you seem to have used the Measurement and Automation Explorer (Seeing as all of your channels in the DAQ task are already named); have you already set up Scales for your data considering your channels are already made through MAX? If your data has scales enabled (Hence reading sensible measurements for temperature) if you import this data as thermocouple measurements again, this could be a cause some of the strangeness of the read data because the DAQ Assistant will be configured to perform unnecessary operations on it.


Could you please send your VI if you're still having difficulty with this problem? It'd be good to know what version of LabVIEW you're using too if I send you code to try out. I'd like to see the configuration you've selected and see if I can try to replicate your issue too, if possible.

Alex Thomas, University of Manchester School of EEE LabVIEW Ambassador (CLAD)

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