Hopefully everyone using ANY I/O that’s not local to their control strategy has some kind of enabler chart like this one to re-enable units if they go off-line.
One of my coworkers, with an Opto-controlled home, has a wireless I/O unit that controls a number of devices including the water to fill his pool/hot tub. Since his wireless network can get knocked out by weather, he wants to be extra sure he doesn’t have a situation like this occur:
[INDENT]Centrally located controller sends a command to the (wireless) remote I/O unit to turn on a valve to add more water. Five minutes later the controller sends a command to turn off the water. If during those five minutes the connection to that wireless remote has gone down, the water will continue to flow…
[/INDENT]Instead of programming that logic in the central controller, he takes advantage of one of the many “intelligent I/O” features we have at the brain level. The strategy issues just one “Start On-Pulse” command, with a 5-minute pulse duration. Since the pulse is a brain function, the brain will still shut off the pump even if the brain gets cut off from the network during those five minutes. Now that’s distributed control!
Especially for remote I/O units like these, you may also want to use the built-in I/O Unit “Watchdog” feature to have the brain set outputs a certain way when communication is lost.
Any other tricks you use for especially remote or wireless I/O?