PXI 5114 - Seperate Triggers for Each Channel

[mhvoth]

We are using a PXI-5114 High Speed Digitizer.  We were wondering if it was possible to set different triggers for each of the two channels.  We are analyzing a NTSC composite video signal and would like to observe two different lines of video in a LabVIEW VI.

[Matt_E.]

Hello,

It is not possible to configure each channel of the 5114 to run separately.  When you configure an acquisition you select a trigger source and when that trigger occurs all enabled channels will acquire the configured amount of data.  What you could do is have your two video sources running to channel 0 and channel 1 respectively, configure an acquisition with ch 0 as the video trigger source and only acquire data from channel 0.  Once you have your record from this channel you could configure a new acquisition with ch 1 as the video trigger source and only acquire data from channel 1.  This allows you to get data from both of your video sources, just not at the same time.  Would this approach work for your application?

Regards,
-Matt

[mhvoth]

Thanks for the reply.  I think this approach will work.  For our application, if viewing the video on a monitor, we are attempting to time how long a specific image takes to move from the top of the screen to the bottom.  So basically we could trigger the upper line on ch0.  Then configure a new aquisition for ch1 and trigger the lower line.  Correct?

[Matt_E.]

I would like to clarify a little bit about what you are trying to accomplish.  Do you have one or two separate video sources you wish to hook up to your digitizer?  When you refer to "lines" are you referring to the individual horizontal lines that make up a single video frame?

The amount of time it takes to reconfigure the digitizer for a new acquisition is not deterministic and will depend upon the speed of your machine as well as any other activity you have going on over the PXI bus.  As a result, reconfiguring in between an event may not be fast enough depending on how quickly you expect the image to be moving.  I am also not quite sure how setting up a trigger for the top horizontal line and then another one for the bottom horizontal line will get the measurement you are looking for because each line will be refreshed at a periodic rate by the video source.  Triggering on a specific line will give you a record with the digitized data for that line but it seems like you will need to do some kind of processing on that data to tell if the data contains this line of the digitized image contains is object you were looking for or not.

Please let me know if it does not sound like I am envisioning the application correctly.

-Matt