Reference/Pretrigger with NI-IMAQ

[Michelle_N]

Introduction

Although there is no native way to configure a reference trigger within the IMAQ driver, you can set up a ring acquisition to create a refernce trigger.

Steps to Complete

Run the attached VI with an IMAQ framegrabber. Be sure to change the IMAQ Occurrence Config2 VI for the channel you are triggering. The VI will start acquiring images as soon as you run the VI. The code will execute until the Wait on Occurrence VI, at which point the VI will wait for a trigger. When a trigger occurs, an occurrence will be present and the code will finish executing. You will get the last valid buffer (the buffer in which the trigger occurred). Then, since this is a ring acquisition, you can go back through the array of images, starting at the "last valid buffer" to view your pre-trigger images.