How do I synchronize multiple rt targets?

[coreyGN]

I'm using a 6143 board and I need to synchronize 5 rt targets each with about 3 boards. Each board will wait for an analog input. When the first analog input hits one of the boards, I want to start recording data to disk on all 5 targets. Is this possible if i send out a signal on the digital out/in to trigger the recording? Also since the first board that receives the signal will be ahead of the rest, how do I synchronize them?

Another option that I might have is by just having the host start the 5 targets... but if the other way is doable (and not too difficult) that would be better.

[LYu]

Hi coreyGN,

In your synchronized acquisition, skew error seems to be the biggest concern. Skew is the error caused by the difference in start or trigger times between the devices.

To minimize the skew error, you can make use of trigger sharing to minimize the delay between the triggering of the first board and the other devices. This will introduce a smaller skew than using digital signals to trigger the other boards. The five targets will start simultaneously given that the skew is smaller than the clock period. The devices can be synchronized (sample data at the same time) through clock sharing or phase locking. Clock sharing will introduce some skew error due to the propagation delay of the clock signals. Phase locking will introduce a very small amount of drift (error caused by clocks running at slightly different rates). Depending on your sampling frequency and the length of the cable, this shouldn't be too significant.

I'm assuming that your RT targets are PXI systems, in which case you might want to check out the PXI-6553 module, which lets you accurately share PXI backplane sginals among multiple chassis. If you you don't want to use additional hardware, or if you're using PC systems, you can probably use PFI lines to route the triggers and clocks but this will be less accurate and slightly more difficult.