trigger each buffer vs trigger buffer list

[gistguy]

Hi. I have some questions.

I developed program to get triggered images and wondered for IMAQ Configure Trigger.

You know, IMAQ Configure Trigger has "trigger each buffer" and "trigger buffer list". I am not sure difference between both parameters definitely.

In case of trigger each buffer, when triggered(50Hz), frame rate only came 25Hz,an half of trigger frame rate.

But when triggered with having long integration time(1Hz), frame rate came 1Hz accurately.

In case of trigger buffer list, when triggered(50Hz), frame rate came 50Hz.

But when triggered with having long integration time(1Hz), frame rate was not 1Hz.

Image board(NI 1428) counted valid buffer number up to (0~49) with 50Hz and stopped a 1 second and then counted valid buffer number up to(50~99) and stopped a 1 second (buffer number is set 50)

Could you explain why this happened?

[Lorne H.]

gistguy,

I think the knowledgebase linked below will answer your question...

Why Is My Triggered Image Acquisition Not Getting the Expected Frame Rate?

Basically,  you are probably not asynchronously acquiring images from your camera and thus your camera is sending its images at a set frame rate.  When you trigger each buffer at 50 Hz you are seeing the problem discussed in the knowledgebase above, and thus your framerate seems to be about half of 50 Hz.  On the other hand when you trigger the buffered list you get a whole sequence of images (how ever large your ring buffer is) at the frame rate of your camera and this makes it seem like the buffered list is working when it is not.

To Clarify...

Trigger Each Buffer causes a single image to be transferred from the PCI-1428 to the computers memory.

Trigger Buffer List causes the entire ring buffer to be transferred from the PCI-1428 to the computers memory.

There are two solutions to your problem.

1.  Asynchronously trigger your camera.

2.  Change a setting on your camera so that it acquires images at a much faster rate (perhaps 100Hz ), yet, continue to trigger at 50 Hz.

Lorne Hengst

Application Engineer
National Instruments