Synchronization 2 usb-6009 devices - Please help

[tuanbui]

Hi,

I'm trying to capture data on 2 usb-6009 devices simultaneously.  I have set up the two DAQs as follow.

1. Using a function generator, generate a sine wave that is slower and not a multiple of the sampling rate (48KHz) and apply it to the odd numbered channels.

2. Connect the even numbered channels to ground.

3. Connect the PFI0 of each to a digital output of one of the DAQs.

4. Set up each DAQ to sample as fast (48KHz) as possible and trigger off of the PFI0 input.

5. Generate the digital output trigger - software write to "Dev1/port0"

6. Read the resulting samples and determine the difference between each of the odd channels between the DAQs in a given sample set.

My results are not as expected.  Using Excel to plot the data I see that the data of the 2 DAQs are shifted on every sampling set. 

I have verified on scope that the trigger works and that both got triggered.  I think the above setup is not complete and I think I need to

setup both DAQs to share the same source clock but I do not know how to setup 2 DAQs to share the same clock.  My questions are

1) Is my setup above ok?

2) if need to setup 2 DAQs to share the same clock, how to set it up?

3) Is it possible synchronize 2 usb-6009 devices?

Thanks,

Tuan

[Chris_K_ · Accepted solution]

Your above setup seems correct.  

The method you are using to synch the two devices is the best you can get.  The PFI line can only be used to read in a trigger or counter input.  You cannot use it to to import a sample clock.  Each 6009 must use it's own onboard clock.

Typically if you want to truly sinchronize two acquisitions you must share a sample clock and a start trigger.  Here we are only able to share a start trigger with the PFI line(as the hardware prevents you from sharing the clock) and let the individual clocks govern the actual acquisition so it is just not possible to truly synch two 6009s and you are currently doing the best that you can. 

ChrisK