NI6341 common starting trigger for AO and IO

[utoct]

Hello,

I use NI PCIE 6341 DAQ to output a digital signal and an analog signal, but there is alway some delay between each other when initializing. I am wondering if it is possible to set up a common software starting trigger to have those two channels start output at the same moment? How to do that with the counter clock?

Thanks.

[Kevin_Price]

Sure.  There's lots of ways to sync the AO and DO task outputs, let's look at 2 ways that use a counter.

1. (To be used if AO and DO are at the same rate).  Configure both AO and DO tasks to use a counter pulse train as their sample clock.  Start AO and DO tasks first, then start the counter pulse train task.  By sharing a sample clock *and* starting the clock after starting the AO and DO tasks, samples will be sync'ed without need for a trigger.

    In LabVIEW, you can query the counter task for its pulse output terminal using a DAQmx Channel property node.  You can then wire this to the 'source' input for the DAQmx Timing calls on your AO and DO tasks. 

2. If AO and DO are at different rates you can still sync their start times with a trigger.  Configure both AO and DO tasks to use a counter pulse as their start trigger signal.  Start AO and DO tasks first, then start the counter pulse task.

-Kevin P

[mikeporter]

Once you get the two tasks starting together, do they need to stay synchronized to each other?

Mike...

[DavidF_NI · Accepted solution]

Hi utoct,

Other members left good responses. The following articles offer good documentation on start triggers with NI-DAQmx.

Timing and Synchronization Features of NI-DAQmx

Synchronizing Analog Input C Series Modules with NI-DAQmx in LabVIEW

You can use a flat sequence structure to get the channels to start fairly close together depending on your project needs.

If you you need something more precise and you can use the same rate, then you can set the sample clock of the slave to be that of the master. By starting the master after the slave, the two channels will start on the same trigger. 

Regards,

David F.

Applications Engineering

National Instruments

www.ni.com/support

[utoct]

Yes, they need to be synchronized. The problem has been resolved. Thanks.

[utoct]

Yes. What you said in the last paragraph works.

I set DO's sample clock as AO's, then delay the start of AO. Note that if the delay is not sufficiently long, there would still be jittering between two channels at the beginning.

Thanks.

BY 

[DavidF_NI]

Glad to hear.

I would wire the error wire of the error output of the DO start task to the error input of the AO start task. This will force the AO task to start after the DO task. 

David F.

Applications Engineering

National Instruments

www.ni.com/support