Synchronization across data streams for remote vs embedded controllers

[tstay]

Hello, I am interested in starting to use National Instruments products.  I apologize if this post is not in the optimal discussion board, and am fine if it gets moved by a moderator or something similar.

I have previously used data acquisition boards from other companies and am hoping to switch to NI.  My question is about synchronizing different data streams.  If I have two different devices that connect to a PXI module, my understanding is that they are recorded on the same time step basis by being connected to the same backplane.  If I have a device that has a USB output, I also understand that I'll need to either plug it in to an external PC and use a remote controller, or buy an embedded controller where it can plug in directly.  I assume that if I use the embedded controller it will capture the data on the same time basis as the PXI modules (by sharing the same backplane).  If I use an external PC and remote controller, will I lose that ability to synchronize the USB-output device and my other analog output (e.g. BNC) devices connected to the PXI modules?  I would prefer to use an external PC if possible, but would definitely spend more for the embedded controller if it removes the hassle of trying to manually synchronize different data streams.  I hope that question makes sense.  If the answer depends on the software used I'd also be appreciative to know about that, as I only have a basic familiarity with LabView.

Thank you!

[ZYOng · Accepted solution]

There are two basic requirements to synchronize most instruments, regardless of signal acquisition or generation: a shared timebase and a shared start trigger.

Timebase

In PXI, all modules in the same chassis use the backplane PXI_Clk10 reference clock automatically. You can export and import the PXI_Clk10 to external chassis easily via the PXI_CLK10 OUT and PXI_CLK10 IN ports.

For USB devices, depending on the model, you might be able to import the 10 MHz external clock via the PFI ports. Some low cost USB devices only allow you to route the sample clock. That being said, USB devices have limited synchronization features.

Trigger

For PXI, there are 8 trigger lines on the PXI backplane in which you can route without external wiring.

For USB, you need to wire the trigger externally via the PFI ports. Note that external wiring contributes to some propagation delay. 

Reference: Synchronization Explained

If synchronization between devices is an important consideration, I would recommend you to get PXI(e) devices. If you don't want to spend extra money on the embedded controllers, you can opt for PXI Remote Control Module with a cheaper desktop. Some PXI chassis have built-in remote controller like PXIe-1073, PXIe-1083, PXIe-1090 etc. However, if you use the remote controller with third party host PC instead of NI embedded controllers, there is a possibility that you will encounter with some MXI compatibility issues and have to go thru the lengthy MXI-Express Compatibility and Connectivity Troubleshooting Guide. Moreover, using remote controller introduces latency in the communication between the CPU and device. So it is a trade-off between the costing and the performance.

[tstay]

Thank you very much for the clear explanation!  I will look into exporting the PXI_Clk10 and using a trigger, as well as the PXI(e) devices.  I appreciate the help!