Does DAQmx support multiple trigger events?

[Fedor]

I am using USB 6251 board to record a number of short AI traces of fixed length. Each trace is triggered by external digital edge trigger. Right now I'm using DAQmx "Stop Task" and "Start Task" after I read each trace to make the board ready for the next trigger, which creates a lot of overhead. I wonder if there's a better way to do this. For example, can NI-DAQmx be configured to acquire multiple records. It seems that NI-Scope can do that, but I don't think this board is supported by NI-Scope.

Fedor.

[Abhinav T]

Fedor,

If all your triggers are coming on the same digital line you should be able to setup a re-triggerable counter output task that acts as the sample clock for your analog input. There is an excellent example of this in the LabVIEW shipping examples. You can access this by going to Help >> Find Examples... >> Hardware Input and Output >> NI-DAQmx >> Synchronization >> Multi-Function >> Multi-Function-Ctr Retrigg Pulse Train Generation for AI Sample Clock.vi

This example shows you how you can use the re-triggerable function of the counter and apply that to analog input. If you need more help with understanding how this example works, please post back and I will be more than happy to explain it further.

[Fedor]

Abhinav,

Thank you for the clever example. There's an issue with my setup though. I didn't mention it in the 1st post, but the AI sample clock is driven by the external source as well (it's synchronous lock-in detection setup), so I don't see how I can use that particular example.

Fedor.

Message Edited by Fedor on 07-08-2007 12:59 PM

[David L.]

Fedor,

The way we perform a re-triggerable analog input with a DAQ card is to stop the clock somehow. We can do this like the example Abhi listed, or we can use an external clock and stop it ourselves. What I mean by this is that the card will not acquire any points unless the sample clock is running, and if we put a ‘-1’ for the DAQmx read timeout, this will allow you to only acquire samples when your clock is running without timing out when no clock is present. We can use the example Cont Acq&Graph Voltage-Ext Clk.vi as a starting point for using an external clock.

Regards,