Lightning strike effecting DCS


Thread Starter


Anybody could please assist on how to explain a situation when a Digital Output (which was not energized) from a Honeywell's Safety Manager PLC give an alarm message "Short circuit" and subsequently followed by alarm message "Actual output status invalid" for all other DO points, which caused the SM PLC to hang-up and tripped a petrochemical plant! when there were considerably big lightning strike?

Gerald Beaudoin

> there were considerably big
>lightning strike?

As far as I'm concerned, when it comes to lightning, all bets are off. I have seen cases where all the foil has been vaporized from a circuit board due to a lightning strike, while 50 volt rated diodes on the same board were unscathed.

So you can only image what a strike might do to a control system. Best take a good look at prevention techniques and TVSS (transient voltage suppression systems)to make sure the spikes don't get anywhere near your DCS.

Gerald Beaudoin