How to read actual value before reference trigger appeares?

[dragonos_de]

Hi guys,


I'm programming in C#, .Net.

I use a reference trigger to get pretrigger-data.
How can I get the actual value of an analog channel before the reference trigger appears?

At the moment I can only access the values after the reference trigger has appeared.


Best wishes,
Alex

[Brooks_C]

Hello Alex,
 
When you use a reference trigger the samples aren't available to read until the trigger is received.  They are put in a circular buffer and overwritten as more samples are taken, but only the samples chosen by the reference trigger are kept and made available to the DAQmx Read.  In order to see these values before the trigger occurs I would recommend using a continuous acquisition and implementing a software reference trigger using the Trigger and Gate Express VI.  The continuous acquisition will let you view all of the data as its taken and then the Trigger and Gate VI can implement the same reference trigger.  The only difference will be that if you're using a digital reference trigger you'll need to just wire it into one of the analog input and set the level in the Trigger and Gate Express VI appropriately.
 
I hope this helps and have a great day!
 
Cheers,