synchronizing operations of multiple crio

[Mitch_cottrell]

I have an application where i will have 2 cRIO controlers (about 10 feet apart) that each need to control a portion of an interrelated mechanical mechanism  In order to accomplish this I have 100ms to communicate between the two units that they are "ready" and everything is within parameters.  Then i will need to syncronize the operation that will take 5 ms total with multiple microsecond timed operations on each "side" of the process.

Because of the design of the system everything will be operating on battery power with no possibility of wired connections between the two cRIO boxes.   

I have thought about doing this with wireless eithernet communciations, but these are not generally dependable for time critical applications.  Any ideas on how this might be accomplished?

[WearWolf]

Hey Mitch_Cottrell,

You could wire your cRIOs into wireless routers and then utilize wireless communication but you may not be able to attain the speed that you are looking for. Is it not possible to use a gigabit eithernet switch between the two devices? What exactly is the phisical setup?

[Mitch_cottrell]

The two units are on rotating disks so wiring them with hardwire is not feasable.  no room for an appropriate set of slip rings etc.   so physically wiring them together is not an option.  If i could i could think of several solutions.

[Pie566942.0]

Hi Mitch,

One way synchronized measurements between distributed cRIOs can be accomplished is with the FPGA Timekeeper IP plus any shared PPS (pulse-per-second) reference.   The PPS can be tricky.

• (Best) Can you use a C-Series GPS module?  NI's provides a PPS and 3rd-party modules provide a PPS and more.
• (Better) Are there mechanical or electrical reference points that can be used on both ends?  For example, might there be an encoder or sync pulse on both sides that the cRIOs could use for PPS?
• (Good) Does the environment lend itself to an optical sync pulse?  For example, could you flash a strobe at photo-diodes on both ends and use that as a PPS?
• (Other) ???

Regards,

Steve K

[Nick@NI]

Hi Mitch,

You might want to check out software 1588 or NI-TimeSync, using that as a PPS source for the FPGA Timekeeper. See this post: http://forums.ni.com/t5/Real-Time-Measurement-and/1588-synchronization-of-distributed-cRIO-systems/t...

I don't believe we have any accuracy spec over wifi, but you could certaintly test it out and read the offset from time reference to give you a general idea of the synchronization performance.

Regards,