Trigger event, then wait for condition to start DAQ

[Azazel]

Goodday all,

I am using XP, LV 7.1, PCI-6115 DAQ card.  I would like to trigger my DAQ card, then once triggered wait for an event (voltage value) on one of the AI inputs before I actually start data aquisition.  Is this possible?

Thanks,

Azazel

[Travis G.]

Hello Azazel,

Although multiple triggers are not directly supported by your DAQ hardware, you can get around this by using a pulse train generated from one of the counters on your PCI-6115 as the sample clock for your analog input task.  This allows this pulse train task to have a digital start trigger, and the analog input task to have an analog start trigger, resulting in the functionality of having both an analog and digital start trigger for your task.  I've written an example program that shows how to program this in DAQmx.  I hope this helps,

Travis G.
Applications Engineering
National Instruments
www.ni.com/support

[Travis G.]

Here's the same program saved into LabVIEW 7.1...

[Azazel]

Both of my trigger signals are analog, so is it possible to connect the analog input into the digital counter?

Azazel

[Travis G.]

Hello Azazel,

Unfortunately, the counters on the DAQ device can only accept digital triggers, so the above program will not work with two analog triggers.  Have you considered using just a single analog trigger to start the acquisition of your data, and then monitoring the data post-acquisiiton for the second trigger level in LabVIEW?  You can implement an algorithm using the comparison functions and a case structure to monitor the data as its acquired, and when a certain condition is met, perform the operation you would like such as analysis or saving the data to file.

Another option would be to set up a retriggerable acquisition with an analog start trigger, and just throw out the data from the first acquisition.  The following example program shows how to implement this:

Example Program: NI-DAQmx: Acquire Analog Input Data Using an Analog Trigger - Multiple Times

I hope this helps.

Regards,
Travis G.
Applications Engineering
National Instruments
www.ni.com/support