It sounds like your scenario is not a network communication failure which would cause the FP's watchdog timer to trip.
I see 2 possibilities to guarantee a shutdown in the event the software stops functioning, whether it is user error, or program error.
1. If you are controlling something like a motor controller, they often have watchdogs built in to shutdown the motor in the event it loses communication. You basically want the watchdog on the device that is closest to always being in control of the system so that it is still in control and can shutdown the system in the event of faults from the other devices that should be communicating with it (in this case the FP and its software.) The FP's watchdog is on the wrong side of the critical communication link.
2. You say you already have some relays and hardware to shut things down in the event of a hardware fault. Wire a timer relay in line with that shutdown mechanism. A device that turns on for x amount of time after it receives a signal. Let's say 5 seconds. Have your software put out a digital signal to that timer relay periodically, let's say 2 seconds. Toggle on then toggle off. The relay would reset its timer on every signal. In the event the software stops for 5 seconds or more, the relay would timeout and opens the circuit that allows the equipment to run. I think a timer like in the attached link http://web6.automationdirect.com/static/specs/fuji116timers.pdf (page 3 of 4) set up for "signal-off delay" is what you are looking for. There are numerous brands of timers with different modes of operation, so you'll want to look at them closely to see if they function the way you want.
Message Edited by Ravens Fan on 08-06-2007 11:20 PM
