Power cycling issue

Looking for some advice about the best way to handle frequent power cycling to a SLC 5/05 based system. The power cycling is due primarily to the not so uncommon electrical storms we have here in the south. Without getting into all the specifics of the system, what I need to do is delay the restart of part of a process any time power is lost to the system for less than 5 minutes. I am primarily concerned about momentarily outages caused by electrical storms or other power grid issues. One of our techs addressed this issue on another system by installing a small UPS to power the PLC and then monitor an input to the PLC that is always enabled as long as there is power to the panel. If power is lost, thus the input turns off, then the restart of the process is delayed for 5 minutes.

I was wondering if you could just monitor a bit in the program that is set when the processor first powers up (which would indicate power had been lost) and use that to delay the restarting of the process. It would have to work any time power is lost to the process, no matter how short the duration. If power is lost to the PLC for milliseconds is there some time lag before the PLC program actually stops executing? Is this something you guys have had to deal with? What's the best solution?

S:1/15 is a first pass bit that is true when the processor powers up and stays true for the first scan.

Using the first-scan bit, in addition to monitoring the real-time clock in the PLC, would allow you to determine how long the power had been off for (also, how long the CPU was not in 'Run' mode).

You can't get millisecond resolution, but you can get accuracies in the minutes/seconds range you are looking for.

That being said, I'd still consider the UPS approach, especially using a full-time ONLINE UPS; if only for protection of the processor from electrical damage. Good power conditioning is very important. Many UPS's would fit the bill, my preference being Eaton's Ferrups series. If you want to know a particular brand NOT to use, PM me.