Shutdown Keys

Hi Guys,

I'm new to this type of control systems.

What's a shutdown key & what is it used for?


Thanks!

You may have to provide some context for the term "shutdown key"

PLCs used in machine control are usually designed to be powered 24/7. The only time power is turned off may be to replace/modify add-on cards or other major system modification/maintenance.

There is the use of safety shutdown circuits which remove operational power to the output components of the circuit. But this usually does not shut down all logic power to the system.

I'm not sure if it's a North American thing or an Oil and Gas thing, I never came across one in the UK nor my first few jobs in Canada, but since I've moved to Alberta and Oil and Gas its one of the most common things I hear.

It's basically a matrix, the shutdown key is the safety circuits.

Imagine a spreadsheet, the left hand column would have all the safety inputs listed and the top row across would have all the safety outputs, following the columns down from each output there would be a code against any row where the input at the left had an effect, if the input has no effect on an output its blank.

Code could be SD = Shutdown, FC = Forced Closed, etc.

There's also a cause and Effect diagram which are non safety items doing the same thing.

Its a visual of the safety system. Apparently its good, I disagree, hate them.

Guys!

Big thank you!

A shutdown key is simply a cause and effect diagram.

All of the inputs are on the left handside column and the required outputs are along the top. It's very straight forward except you need to watch out for subsets of conditions.

For instance, if inputs A & B requires output C, D & E to respond, you have to make sure that input A alone or input B alone doesn't trigger this response unless they occur simultaneously.

And don't forget about issuing the correct alarms. But that's a different thread entirely.