9234 Pretrigger

[Kbaker4]

I am using a cDAQ 9174 Chassis with a couple 9234 Analog Modules... I'd like to record X seconds of data before a trigger, and Y seconds after the trigger into a TDMS file. I have no problem creating a trigger and storing the data after the trigger condition is met. I've looked into pretrigger and circular buffers, both of which I have no idea how to use or where the VIs for them would be... Please help!!!

Thanks!

[Kbaker4]

Found this... not sure how to use it but playing with it now... http://zone.ni.com/devzone/cda/epd/p/id/34

[thoult]

Also, http://zone.ni.com/devzone/cda/epd/p/id/3438

That's the one I used when I first started.

[Kbaker4]

The problem is I want a certain number of samples of pretrigger which the link I posted does accomplish. However I also need data post trigger as defined by the user... 

I want pre trigger and post trigger data samples to be set by the user... My original posting does the post data, the second link does pre data... No clue how to get them to work together to record all this data in a single TDMS file.

[thoult]

Pre trigger by M samples with a total sample length of N samples.

You'll have M samples before the trigger and N-M samples after the trigger.

[Kbaker4]

When this hits the threshold, why would it stop looping? I never see the triggered data on the output waveform graph, yet the trigger occured LED glows

[K_Joy]

Hi Kbaker4,

It looks like you might be getting an error that is not being reported. You loop is wired to stop on an error condition, but you do not wire the error out of the loop. If there is an error in your subVI, it would stop the loop and not show your data on the indicator. Drop a Simple Error Handler VI outside your loop and connect the error wire in to it. See if it gives you a specific error message. 

Regards,

Kelsey Johnson

Applications Engineer

National Instruments