One External Trigger and then collect 10s of seconds of data

[VIGuy]

I need a synchronized capture of a long duration waveform.  The duration can be 10s of seconds (30, 50, etc).  This isn't my whole application just something that needs to happen once during the beginning.

Amongst other hardware we have a PCI 5922 High Speed Digitizer and PCI 6229 Multifunction DAQ.  Because of how the system is currently wired and because it is advantageous not to 'T' the signal the PCI 5922 is essentially the only device that can read the signal of interest.  However, I need the Analog Outs on the 6229 synchronized to the PCI 5922.  The 6229 will be clocked at 5 to 10 kHz. The 5922 needs at least a 1MHz clock.  However, at 1MHz, my 2 Megasample on board memory gets used up pretty fast (relative to the signal I need).  I will start the waveform generation and the scope capture with an external trigger.

For the most part my set up is working.   I have the external clock and I have a Counter dividing it down to a speed the 6229 AO can handle.  I have verified my trigger fires and that both devices respond to it.  What I am having trouble with is capturing all the data synchronously.  It seems I can do either: a) capture all the data unsynchronized (Fetch Forever Examples) or b) capture the first two 2 megasamples synchronously (1 filling of the onboard buffer).

I have been unable to adapt the The Multi-Fetch, Multi-Record and Capture More than On Board memory examples to my scenario.  I can only get them to work if I supply subsequent triggers to the scope. 

Is it possible to trigger once and then collect long duration waveforms from a PCI 5922?  If it helps I know the exact duration/number of samples I'll need.

Thanks for your help.

[Paul_C.]

Hi VI Guy,

 I would take a look at the niScope EX Multi Record Fetch More Than Available Memory.vi (Help » Find Examples » Hardware Input and Output » Modular Instruments » NI-Scope » Continuous Acquisition).  This should allow you to trigger and fetch for a long duration.  This will eventually run into a buffer overflow error, but not for quite a long amount of time because it is fetching records from the buffer individually as soon as they are ready.  From what I gathered, you’re talking in terms of just a few minutes.  Is this correct?  In addition, are you using the niScope Export signal vi for your triggering?  Have you tried exporting the "ready for start event" to a PFI line which would be used as the start trigger for the 6229 Analog output task?  I'm going to look into this a little more, but if you could give me the answers to these questions it would help a lot.  Also, it would be helpful to know the exact duration and number of samples.

Thanks,
Paul C

[Paul_C.]

Hi VI Guy,

I've been looking into it more and I think the best option for you is to use one of the continuous examples (such as the fetch forever) where the reference trigger is setup but never actually occurs.  Then I would use the export signal.vi to export a "ready for reference event" out of one of the PFI lines.  You can then connect this to the 6229 to be used as a start trigger to keep them synchronized.  It sounds like you already have the external sample clock that is synchronized for both.  Let me know if you have any questions about setting that up.  I went ahead and verified that the fetch forever example with the export ready for reference event trigger sends the trigger properly.  Let me know if you have any problems setting it up. 

Thanks,
Paul C.