Intermittent application hang when using DAQ assistant

[Dan_N]

Hi mtmike,

The DAQmx code that you have generated from your DAQ assistant VI is still creating and clearing a task each time that the while loop iterates, which could still be causing the problem. I've attached a screenshot of a VI that creates a task once, then reads data as many times as necessary, and then finally closes out the task. This architecture is the real advantage of DAQmx VIs, as you have to create and clear a task each time a while loop iterates with a DAQ assistant. Try running the VI with the DAQmx architecutre pictured in the screenshot, and let me know how that goes. Also, the wait timer does not need to be in a case structure. Also, make sure you've got an error handler VI (located under Programming>>File I/O), as there may be some errors related to this hang that you aren't seeing.

If that does not work, try followin the steps under John P's post in this forum. If you've noticed that the problem is dependent on Windows 7, it could be the issue that the forum describes. Note that you'll need to use DAQmx 9.4 to implement the fix in said forum. Let me know how those two fixes work for you.

Best,

Dan N

Applications Engineer

National Instruments 

[pkieselbach]

Dan,

I updated to NI-DAQmx 9.4 and installed the patch for building installers with NI products 11.1, then re-built and installed the application.  Since then I have not seen any further application intermittancy in about four hours of operation.  Subjectively, it seems like the application is responding more "smoothly" now*.  CPU usage is about 15% idling and 36% max.  Since the problem was quite intermittant I cannot say for sure that it is solved, but so far, so good.  It should get a good workout starting in a week or so.

* This program is used for calibrating flow rates on several adjustable orifices and involves setting pressure and flow rate (which interact).  Prior to this update it seemed like the flow and pressure feedback had a slight lag (compared with another similar application) - perhaps a couple of 10ths of a second - just enough to make life interesting for the operator.  Now that lag seems to be gone.  Again, this is quite subjective.

Pete

[mtmike]

Turns out it was the WIndows 7 issue described in the linked post. Upgrading to NI-DAQmx v9.4 and setting the USB transfer request counts to 1 fixed all the problems. Thanks!

[Dan_N]

Mtmike - Glad we were able to figure it out!

Pete - Sounds like things are working. If the problem ever comes back, go ahead and post back.

Best,

Dan N

Applications Engineer

National Instruments 

[Phil_T.]

I had a similar problem using 2 USB-6008 with Labview 8.5 and DAQmx 8.6. My application was running 2 seperate loops, 1 to monitor a vibration sensor and the other to perform various tests on a UUT. I noticed during one of my test if I aborted then tried to exit Labview would lock up at the clear DAQmx Task. It turns out that I forgot to put a DAQmx Start Task in that particular test step. I was surprised the step was even allowed to start without a start task.