Advanced AI reading w/ retriggered pulse train sample clock

[SomeGuy]

I'd like to set up a DAQ scheme with a retriggered pulse train sample clock that does not continuously read samples, but instead synchronously reads the next N bursts of samples at arbitrary times.  More specifically, my setup is as follows.  My analog input is an integrated photodiode signal.  The end of the integration is signaled by a falling TTL edge.  The repetition rate is 500 Hz.  A few times a second I command and then wait for a translation stage to move.  Following each move I'd like to tell the DAQ to read M (~ 10) fast samples after the next N (~ 3) falling TTL edges.

I know how to set things up to do the reading continuously, and I think that I can implement the arbitrary reading by allowing the AI task to overwrite unread samples.  However, when I perform the read I want to know for sure that it does not begin in the middle of a sample clock pulse train.  I've considered using the falling TTL edge as an AI start trigger in addition to it's use as the CO start trigger, but I'm concerned that various delays might cause the AI to start late and miss samples.

[wildcat_600]

Hello,

I was just wondering if you have looked at the LabVIEW example "Multi-Function-Ctr Retrigg Pulse Train Generation for AI Sample Clock.vi"?  This example can be found in the Example Finder.  It seems like it is very similar to what you want to do.  Even though the AI task is set up for Continuous operation it is basically acting as a Finite operation because the Sample Clock being generated is Finite.  This works great because the AI is always running and it will take a measurement every time a sample clock pulse is generated.  Therefore you should not miss any samples when taking a measurement. 

If you want to ignore the first few samples you can just remove those data points in software without too much effort.  For example, lets say your trigger occurs and you wait 3 sample clock pulses before you acquire the next 10 samples (10 sample clock pulses).   To program this just acquire 13 samples and delete the first 3 in your software. 

Please let me know if you have any more questions.  If you do post back please include what DAQ device you are using. 

Have a great day,

Brian P.
Applications Engineer