DAQmx random errors with parallel loops

[UFO182]

I am encountering random DAQmx errors while running 2 or more parallel while loops....obviously all of them doing data fetching. I don't remember the exact error codes or if it is the same all the time. Just wanted to see if anyone else has experienced random DAQmx errors with multiple parallel loops. I am using the following:

8350 3Mhz controller with 2GB of RAM and built in MXI-4 bridge to a PXI-1036 Chassis

PXI chassis has the following cards installed: 4070 DMM, 2575 Mux; 4224 DAQ (X2), 6508 DIO

Windows Xp, LabVIEW 8.2, DAQmx 8.0

If the error was always at the same place it would make sense, however it just seems to occur randomly.....sometimes during a DIO function, sometimes a DAQ function and sometimes a DMM function. I even have times when the entire vi will execute without errors!!! Sometimes it bombs out after just a few seconds....other times maybe towards the end of the vi (minutes). The only connection between the loops are presetups, variables and a common stop variable.....other than that, they are on their own.

I have used the DAQmx express for most of my data acquisitions and this is the only common link I have found so far. Not looking for perfect answers here, but again just curious if anyone else has run into these types of random errors.

[UFO182]

I forgot to add that I am up to 70% processor usage as monitored via Task Manager. Is there a such thing as duty cycle overload on a computer? I would think that they are designed to run at 100% maximum speed. How about the MXI-4 throughput? Is it possible the 8350 controller (at 70%) is working the PXI communications too much? What kind of errors should I expect when the MXI-4 thoughput is exceeded?

[Neil_S.]

UFO182,

There are a number of issues that can occur with DAQ applications including buffer and FIFO overflows, trying to use reserved resources and so forth.  In general if programmed correctly and within the limitations of the hardware creating multiple parallel loops should not be a problem.  Parallel loops can however, add complexity to your code and introduce race conditions if not used properly, especially when variables are shared among loops.  The specific DAQmx errors that are returned are priceless in discovering the source of the problem.  I could speculate endlessly about potential issues and never include the actual one you are seeing.  If you can provide the actual error codes I will be happy to comment on how these conditions may arise and how to overcome them.

I will make mention of one potential problem that can occur when using multiple data acquisition products simultaneously.  If you are using a large portion of the PCI/PXI bandwidth data may not be able to transfer across the bus fast enough to keep up with the acquisitions.  This however, is only likely in scenarios where high sampling rates, a large number of simultaneous channels, and small on-board FIFOs meet.  This may be what you are experiencing but I think it is more likely the errors are caused by a different source.

Let me know which errors  you are getting and I will be happy to discuss some ways to avoid them.

Regards,

Neil S.
Applications Engineer
National Instruments

Message Edited by Neil S. on 03-27-2007 01:10 PM