Multi-channel AI (Voltage) with hardware triggering and pretrigger scans

[Jim Lynch]

Here is the system I have: Pentium 4, Windows XP, LabVIEW 8.2.1, 6250M Card

I need to perform nondestructive testing in which I use a hammer to generate an impulse and a set of sensors (up to 10 of them) to record the response.  The measured response contains noise (random and high frequency).  I remove the random noise by performing several tests and averaging the results.  Because I average the results, I want the results to line up in time.

I line up the results in time by the following algorithm

 - Start the VI and record to a buffer

 - Start recording based on a trigger voltage and channel

 - Record a defined number of pretrigger scans from the buffer (for each channel)

 - Record a defined number of posttrigger scans (for all channels).

My old data acquisition VI was written in LabVIEW 6, but that doesn't work with M-series cards.  I've been working on VI's with DAQmx, and have several that kind of work.

I can record one channel of data with triggering, the proper number of pretrigger scans, and the proper number of posttrigger scans or

I can record multiple channels of data with triggering but no pretrigger scans.

I looked at the example VI "Cont Acq&Graph Voltage-Analog SW Trigger.vi" but it doesn't quite work.

I have attached the VI that kind of works for me.

[Steve_B]

Hi Jim,

I am assuming that you are running into the issue that you can only select the analog trigger when it is the only channel in the task. I would recommend that you connect the signal you want to trigger on to the APFI line for your device and select the APFI line as your trigger source. You can still have the signal connected to your channel to make your measurement. The APFI 0 line for the 6250 is pin 20. When you are able to trigger your task for multiple channels you should be able to get the functionality you are looking for. Let me know if I have misunderstood your issue.