Acquiring data continuously with a start and stop trigger

Question

I am currently acquiring data continuously (1000 samples at 5k/s) using a start trigger to start the acquisition and stopping the acquisition with a digital line. The problem with this is that I want the acquisition to stop immediately on a trigger, in otherwords I don't want it to finish with 500 or 200 samples of useless data. I am using a PCI 6024 E. Any suggestions would be appreciated.

Answer 1

The trick will be to minimize the number of post-trigger scans that will occur after your stop trigger. The stop (reference) trigger requires a minimum of 2 post-triggered scans. Therefore, the way to stop your acquisition as soon as possible is to configure your stop trigger to have only 2 post-triggered scans.
I've included a little bit of code to illustrate this in LabVIEW 7.0. The number of post-trigger scans will equal the buffer size less the number of pre-trigger scans. Since the minimum number of post-triggered scans is 2, we'd have to set the number of pre-trigger scans to the buffer size less 2. This is wired as the minimum number of pre-trigger scans acquired input to the AI Control.vi in the example.
This should do what you're
after. Best of luck to you as you get this all put together.
Jim Laudie
Applications Engineer, National Instruments
Attachments:
example.vi ‏85 KB