How to detect a trigger signal arrival from PXI?

[afreet]

Hi, I am using a PXI-5105 for my DAQ with an external trigger. I wonder is that possible that every time when my trigger arrives, and my 'nIScope Fetch.vi' starts to fetch data, I can detect this trigger and get a 'true of false' boolean in Labview at the same time so that I can use it for other subvi?

Thanks for any help!

An

[Dan_K]

Hello An,

The problem is that there is no defined way to perform this type of information, but there is a way that could give you some information.

You can do this by using the Records Done Property in the niScope Property Node. You can navigate to the specific property as below:



By checking to see if more records were acquired than the last time through the loop the fact that a trigger was observed and a record was acquired will be displayed by the LED turning true. A block diagram representation of this can be seen below:



Note: This does not include all of the other code that would be contained within the loop, such as your fetch VI.

Message Edited by Dan_K on 02-20-2009 03:33 PM

[afreet]

Thanks Dan_K, I sort of solved my problem by using a Sequence Structure, first fetching data when detecting a trigger, then perform other subvi. Since my data fetch time length is much shorter than the trigger period, it is safe to do that this way. What I really want to do is to make sure the data fetch through niScope and my other subvi start at the same time, but I don't know if that is possible. Anyway, thanks a lot!

An

[Dan_K]

Hello An,

It may be possible, but I wouldn't recommend it. When dealing with Scope applications it is usually best to have all of the driver calls within the same VI. Accessing the same session in multiple subVIs can cause problems, including race conditions. If you did want to pass the record acquired information to a subVI I would use global variables and set the value in your main VI and read it back out of your subVI.