synchronize counter output pulse trains on two S series DAQ cards

[Geena]

I need to set up re-triggerable synchronized AO/AI across two S series cards (PCI-6115). I was told to use counter output as the sample clock for AO/AI, for counter is retriggerable. The problem is that my AO and AI task has different sample rates and numbers. Using two counters on the first 6115 card, I can generate a finite pulse train, which can determine the sample rate and number for, e.g., AO task. I can use the two counters on the other 6115 card to generate another finite pulse train as the sampling clock of the AI task. A digital input will be used to trigger both pulse train generation. My question is how I can synchronize the two pulse trains, so that after being triggered by the digital input, they will have a fixed phase relationship with each other.

(The two 6115 cards are connected with RTSI cable, and MasterTimeBase from the master card is shared to the slave card to ensure synchronization.)

Thanks! 

[Chris_D]

Hey Geena,

To synchronize two pulse trains with your PCI-6115's you would do exactly as you have done by sharing the master timebase and a start trigger. Are you actually seeing a phase offset? How far out of phase is it? Does this vary between tests?

Message Edited by Chris_D on 09-08-2008 02:25 PM

[Geena]

I am seeing phase offset that varies between trials. I use an external trigger to trigger both devices. (I set P0.1 as output and physically wired P0.1 to PFI 4 on both cards.) I attached the vi here. Is the delay caused by the fact that I shared the external trigger? Is there a way to share the same trigger through RTSI?

Thanks.  

[Chris_D]

Hey Geena,

The delay very well could be caused by the external trigger. The properties of the wire such as length could introduce different propagation delays.

I have been trying to brainstorm some ways to share the start trigger through RTSI. Unfortunately, there is no counter start trigger terminal. One way you could do it is setup a dummy Analog Input task and set the ai/StartTrigger as the source for both counter start triggers. This would share the trigger through RTSI. The example linked below demonstrates the sharing of the start trigger between 2 Analog Output tasks. You can use this to see how to share the trigger to your counter tasks.

Synchronize Scans on Multiple E Series Boards
http://zone.ni.com/devzone/cda/epd/p/id/3127

I hope this helps and let me know if you have additional questions.

[Geena]

Thanks Chris. The example file you referred to is of too early a version for me to open. Would you please provide a version that Labview 8.6 can open?

[Chris_D]

Geena,

Whoops. I totally linked the wrong example. There is actually a LabVIEW shipping example that shows how to route the triggers over RTSI. It is actually automatically routed, you just have to reference to other devices correct device name and terminal. You can see the example by going to the NI Example Finder in LabVIEW at Help » Find Examples » Hardware Input and Output » DAQmx » Synchronization » Multi-Device » Multi-Device Synch-Analog Input-Cont Acquisition.vi.