Retrigger 9775 Using 9206

[downerdce]

I have the following cards:

(2) NI 9775 (Using for analog captures, Sample Rate (4 to 800,000), Samples to Read (400 - 800))

(1) NI 9401 (Used as digital square wave trigger for analog capture, rate is from 10hz - 40hz)

(1) NI 9361 (Counter, unused in this application, listed in case it has relevance)

(1) NI 9206 (Used to enable "retrigger" on the 9775)

The document "NI 9775 Considerations" states:

NI 9775 Considerations - NI-DAQmx Help - National Instruments

"The NI 9775 also does not support Analog Triggering or Retriggering, unless in a task with the NI 9205 or NI 9206."

I cannot get my loop to execute fast enough to capture 20 times per second. I am trying to use the 9206 to somehow accomplish this using hardware retriggering. I found some discussion of this here: Re: Analog Reference Trigger on 9205 with 9223, but with different Sample Rates on each Card. How to... but it does not seem they resolved the issue. I cannot find documentation or examples on accomplishing this. I've attached the VI I am working with.

Any help greatly appreciated. Thank you.

some more info here: NI 9775 Considerations - NI-DAQmx 19.1 Manual - National Instruments

[Kevin_Price]

Not really a cDAQ expert, but trying to help a bit.

1. Is the digital square wave at the 9401 an external signal or is it a pulse train you generate from the cDAQ chassis?

2. Since the triggering restriction calls out analog triggering specifically, I'm inclined to hold out hope that the 9775 might support *digital* retriggering.  I'm not sure though.  The "Considerations..." page you linked mentions Continuous streaming mode and "Record" mode, neither of which quite fits the periodic burst mode you'd want from retriggering.

3. Still, I'd look to try retriggering off the digital square wave at the 9401.  Seems worth a try.

4. The discussion you linked *does* seem to resolve eventually, but it takes multiple pages to get there.  Might you have stopped at the end of page 1 and not noticed that there were more pages?

   (Unfortunately, even though I was in that thread a fair bit, I can't really comment usefully on its details -- too long ago to stay fresh in mind.)

-Kevin P

[downerdce]

Hi Kevin,

1. It is an external signal coming in (currently at 10hz).

2. I've tried to setup a VI for retriggering but it has no discernable effect on the loop time. I'm not sure if it's actually working or not with retriggering, but it executes without errors.

3. I'm trying to do that, but it doesn't seem to be doing it fast enough.

4. I will dig through that post some more and see if I can find any answers.

[Kevin_Price]

The lack of errors when you set the "Retriggerable" property seems encouraging to me.

With hardware-based retriggering, you don't need to stop and restart the task and incur the associated overhead.  You just start once and keep reading each capture worth of samples before the next pulse comes in to retrigger another capture.

I made some minimal mods to the vi you posted because that's faster than explaining by keyboard.  Give it a try.

-Kevin P

[Edit:  Oops, forgot to attach the vi at first]

[downerdce]

Thanks Kevin, I don't see the VI though?