usb 1808x : Synchronizing analog output and input using LabView

[Francois Ouellette]

Hello all,

I'm using the USB 1808x to generate a modulation signal to a laser (5 kHz square wave), and detecting a reflected signal from sensors, which are then analyzed. I need very good synchronization between the output and the input, because the measurement depends on the shape of the reflected signal. I'm now sampling both output and inputs at 200 kHz, but require synchronization to be better than, say, 100 ns between the two.

Right now, I use the LabView vi's to generate two tasks: one for output and one for input, as it seems I cannot generate a single task doing both. I've merged together the two examples VI's for continuous generation and continuous acquisition. The whole thing works well, except that there is always an arbitrary delay between the two that changes whenever I start the program, which is not just an integer number of samples, but can be a fraction too. It's really not clear (to me, anyway) what is the best way to synchronize the two. Should I use an external trigger or external clock? If so, how to use it within the available vi's? 

I will post details of my vi structure later if necessary.

Thanks for your help!

[Jeffrey]

Hello @Francois Ouellette,

I recommend you set one task to external clocking and the other task to internal clocking.  Since input follows the output, I would set/start the input task with external clocking so that it waits for the output task to start first.

you will need to install a physical wire (not a virtual one  ) from the USB-1808X's OCLKO to ICLKI prior to running your vi, starting the output task then the input task.

If that does not resolve it for you, then please save a copy of your vi, and then strip out anything not required for me to see to the issue you are referring.

Regards,

Jeffrey

[Francois Ouellette]

Hi @Jeffrey, I did just that, works like a charm! Thanks for your help!