N-samples set to -1 gives uneven # samples

[gstanczak]

Hello,

I am having a problem with the DAQmx read vi set to read N-samples and that set to -1, with data acquiring continuously at about 100hz.  I have a state machine (attached) with a config daq in one state, read in another, where the read calls itself repeatedly until cancelled.  I have a wait function after the read, to slow it down.

My issue is that if the wait function is ~15ms or greater, the number of samples read each iteration goes something like this....1 (sample), 1, 1, 128 (samples), 1, 1, 128 and so on.  The chart then updates smoothly for each single sample but then jumps when a 128 sample block is added.  If I decrease the delay below about 15ms, then 1, 2 or 3 samples are read every iteration, as expected.  I wired and indicator to the iteration counter and it appears to increment steadily.

Please read this too...I bought the new 9174 cDAQ chasis which is not compatible with DAQmx 8.3, the latest version compatible with LV7.1.  Someone's idea here to get it to work was to copy the 7.1 repository to temp folder, install DAQmx 9.2, then copy back the 7.1 repository to program files.  It appeared to work, but I am suspecting that this may be a result of that.  This problem is NOT evident when simulating the identical devices, only when the actual hardware is being used.

I thought this was a chart problem for a while.  I only recently narrowed it down to an acquisition problem.

Thanks for reading,

Greg

[JÞB]

I think your hitting the Auto start bug.  But, I can't tell for sure.  With all the incompatability issues you have I'm supprised it works at all.  LabVIEW 7.1 is just not going to drive modern equipment on modern OS's with modern drivers.  You'll need to use "legacy" (read: "obsolete" if you intend to sell this solution) equipment or upgrade your LabVIEW version.

[aeastet]

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@Jeff Bohrer wrote:

I think your hitting the Auto start bug.  But, I can't tell for sure.  With all the incompatability issues you have I'm supprised it works at all.  LabVIEW 7.1 is just not going to drive modern equipment on modern OS's with modern drivers.  You'll need to use "legacy" (read: "obsolete" if you intend to sell this solution) equipment or upgrade your LabVIEW version.

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I was thiniking the same thing about being amazed that it even worked at all.

[gstanczak]

I do manually call the Start Task VI at the end of the config state, if I understand the bug correctly.  But, if you are surprised its even working at all, I will just assume its some compatibility issue.

Its my fault that I checked compatibility of the cDAQ modules with 7.1 but not the chasis itself before ordering.

Thanks for the replies,

Greg