Power flickers

Is it possible, practical, safe to incorporate a piece of code into a program to auto start a pump in the case of a power flicker, they are a real nuisence (bogged bin means a whole plant shutdown, clean out bin, do restart, downtime 1-2 hours), usually its only 1 or 2 pumps that drop out and not always the same ones! my thinking is everything running,pump drops out, do an auto start on that pump alone but allow only 1 auto start. Thoughts?

How about a UPS on your controller so the control system doesn't notice the "flicker" Pumps drop out for a frac of a second and then restart.

Without knowing more about your system it is impossible to determine if this is a safe or practical solution to your problem.

No I don't think its the controller that drops them out more the contactors that receive the flicker, used to happen on a milling plant we had without PLC control!

If power is lost your contactors are going to drop out, no question.

If your contactor outputs are sealed with the PLC program then it is possible they will just pick up again when power is restored (provided the PLC doesn't loose power). It depends mostly on how they are wired (aux contacts etc...) and what conditions the program has to maintain to keep them sealed in.

I don't like the idea of starting pump X when the PLC regains power just because pump X was running the last time the PLC lost power (it is possible though). What if the last time pump X was running was 2 weeks ago and you shut the power off for a maintenance outage? Do you want it to automatically start again?

I prefer to give the PLC a chance to remain in control during a bump. Therefore I tend to supply it with a UPS so that during a bump it doesn't have to "reboot". I also supply the ESR circuit with the same supply.

When doing this I also wire a "input control power present" input to the PLC so that an orderly shutdown can be initiated if the "bump" lasts more than a couple of seconds. Again if the UPS to the PLC can hold out for several hours I don't want the line to start up by itself when the power comes back on.

Is this proper? is this right?, I don't know for sure. I do know that our power utility is not very reliable. With a couple of our processess, without this type of scheme we are down for a couple of days and many hours labor getting a line to start up again just because we lost power for a few seconds.

Any thoughts about this would be welcomed.

Thamks for those ideas, I was thinking more of a conditional auto restart, only allowed if the rest of the plant is running,only allow 1 restart, not allowed if overrides are enabled etc.

I use the UPS format to keep all the PLC program active but not the I/O supplies so it will auto start if unattended. If a critical system it is usually backed up with an Emergency Generator also. I do not think I would do this with a system that clogs as if clogged it could cause more damage on a restart.

I do believe per OSHA and the NEC plus just for Safety in general a sign should be posted "THIS EQUIPMENT COULD AUTO START" and place this sign in several locations.

Leon