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how to continuosly acquire data with analog pre triggering

I am trying to acquire analog data with pretriggering capability on a continuous basis (Cont. Acq&graph voltage-Int Clk-Analog Ref).   I am just now switching over to DAQMX so I am not that familiar with its capabilities.  I have a simple program I have written in DAQMX that is set up for Analog ref and the start read and stop task are written in a while loop to accomplish a continuos acq.    The program works for E series card (6032) but not  M series card (6251), I am skipping a lot of the pulses.  For example I am feeding in a 5 V TTL signal at 100 Hz to AI0.  With the E seires card  this program acquires all 100 pulses a seconds, while with the m series card the program acquires only 20 pulses or so.  The time delay betweens acq seems to be long?  I am attaching the labview code.
 
thanks for your help
V
 
 
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Duplicate Post, see here:

http://forums.ni.com/ni/board/message?board.id=170&message.id=159012

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Actually, it's a triplicate post so far 😉
 
(sorry we got a race condition... ;))
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Hi V,

Unfortunately, analog operations are not retriggerable and restarting a task slows it down significantly.  I have not heard of such a significant setup time between the series boards before, but I think your best option will be to create a reference in software.  You could create a continuous analog task with two channels, one being your signal and the other your analog reference.  During acquisition you could determine when your reference crosses the threshold and then keep a subset of the data starting at your current position minus your number of pretriggered samples and continuing for your total number of samples. 

There may be another way around this depending on your application.

Regards,

Micaela

Micaela N
National Instruments
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