sync multiple x series USB devices

[ldclaar]

I am currently working with a system of 4 USB X series (NI USB-6356).  I am using all 32 analog input channels for data acquisition.  I need the data acquistion to be synchronized.  I have a start trigger for my master DAQ, unfortunately it cannot be physically wired to all 4 of my devices (due to low supply current).  Thus, I am looking for a software solution.  I am hpoing there is a way to write the LabView programsuch that when master device receives the trigger, all devices start their read task.  The attached picture is my program so far, I have about 300us delay.

Does anyone know if I can change the program to get the acquisition more synchronized?

Thank you,

Leslie

[Wan-L]

Here's a white paper with a good example on how to do Multi Device Sync:

http://www.ni.com/white-paper/6829/en/

To be synchronized, two devices must start at the same time and share a timebase. This is why you route the start trigger and the sample clock from the master to the slave. In your case, you can daisy chain the start triggers of each device. For example. Device 1 starts on its own. Device 2 reads device 1's start trigger, starts, then sends its own start trigger to device 3, and so on...

However, you will not be able to do the same with the sample clock. I'm curious, have you tried to export one sample clock to 3 other devices and experienced errors?

[ldclaar]

Thank you for you help.  I'm not sure how to have Device 2 read the signal from Device 1 without generating a new pulse for each (I feel like this would introduce delay).  So I am building a circuit that will amplify the initial start trigger.

I have been able to export the master sample clock to the three slaves.  We've had to use shielded cables to wire the sample clock to the other devices and have not experienced any errors thus far.

Leslie

[Wan-L]

What you do is export start trigger from device 1 to a PFI (like what you do with the sample clock) and connect that PFI to device 2. You then export device 2's own start trigger to its own PFI which is connected to device 3. This assumes you have enough PFI lines. And yes, there will be more delay, but it will be hard to say how significant the delay is. If you have strict synch requirements, multiple x series usb devices shouldn't be the solution to begin with. However, if the method you are currently using to share the clock is working, maybe you can use it to share the start trigger as well.