timed acquisition

[Andrea]

Buongiorno,
I must do an acquisition with the box-car method: i.e. I have a
trigger signal and every time it happen I open a temporal windows to
read with the same time delay a little interval of the signal. To do
this I'm using the "ai start" and "ai clear" acquisition instrument.
The problem is: where do I must place my high precision (microsecond)
timer to know the absolute time of the windows acquisition? I have
placed the timer between the "ai start" and the "ai read". If, for
example, I must read the point between the 1500th and 1550th after the
trigger, and I know that the acquisition rate is 100K point per
second, I add at the timer value the delay 1500/100K. Here I suppose
that the "ai start" waits for the trigger and then pass to the "ai
read"
. Is it right? The other possibilities are: to place the timer
before the "ai start" or after the "ai read". Witch one give me the
right acquisition start time?
Thank you for the attention

Andrea

[Jason Stallard]

You can use frames and timers to measure how long it takes to complete a series of instructions. Get a millisecond tick count prior to start of frame, process the frame, then get a second millisecond tick count, subtract the old value from the new value, and this is your frame time in milliseconds. You can then subtract this time from whatevervalue and send this to a wait vi to pace the frame. Also I believe there's a way to get a timestamp from the AI vi's.