I am trying to acquire data using a PCIe-6361 with LabWindows/CVI 8.1.0 (using DAQmx) on a Windows XP machine.
It's analog data synchronized to a digital trigger signal, and I have the data going into ai0, with the trigger going into PFI0. Right now, the trigger is set up as the start trigger, with the reference trigger unused.
First question is: what exactly is pretriggering? I've tried to read the various posts, and the help section is less than helpful.It seems to be data acquired prior to the start trigger.
I need to set the system up to act like an oscilloscope, with a post-trigger delay. That is, the trigger pulse comes along and then the system waits x milliseconds and then acquires data.
Solved! Go to Solution.
Pre-trigger samples are unique to reference triggers. Essentially a reference trigger is a "stop" trigger, where you have X samples to acquire before the trigger occurs and Y samples to acquire after.
If you want a delay from when the trigger occurs to when you start acquiring data, I would recommend to use a Start Trigger. There is a Start Trigger Delay property that will allow you to wait until X amount of time has passed from the trigger to when you start acquiring data. The delay is derived by counting ticks of the AI Sample Clock Timebase (100 MHz timebase by default, giving a resolution of 10 ns).
The relevant functions in the C API to delay the start of the acquisition are:
-DAQmxSetStartTrigDelay(taskHandle, float64 data);