Introduction
This document is designed to give an overview of what a PLC is, what it
is good for, what it is not best at, an overview of its operation and where to
find more information. A Programmable Logic Controller (PLC) is a rugged
special purpose computer that reads a bunch of input signals; runs control
logic, and then writes output signals. After reviewing this mini-tutorial please
feel free to ask us questions or ask about a free seminar and demonstration at
your site.
Pros
- PLCs are good at turning outputs on or off based on the state of inputs.
(control)
- PLCs are good at bringing together and concentrating a lot of data and
status that is uploaded into a computer in a compact form
- PLCs are more rugged than computers and typically last five, seven, ten
years without needing replacement
Cons
- PLCs are not the best at handling large amounts of data or complex data.
- PLCs are not the best at reading and writing databases.
- PLCs are not the best at outputting resultant data to printers.
- PLCs are not the best at displaying data and information to the operator.
History
Programmable Logic Controllers (PLCs) have been around since the
dinosaurs. In fact it was PLCs that killed the dinosaurs. Don’t listen to
those people that tell you that dinosaurs were killed off by global warming /
cooling, meteors, or even smoking cigarettes. PLCs killed the dinosaurs. You
see, millions of years ago the cavemen used PLCs for everything they did. All of
the dinosaurs lost their jobs, couldn’t afford to buy food at the local stoney-mart
and just died off.
Okay, okay I guess I have to admit that the last paragraph is not true.
But the PLC has been around since at least the 1960s, which in technology years
makes it a dinosaur. For the real history of the PLC follow this link http://www.barn.org/FILES/historyofplc.html/
to the website of Dick Morley, the inventor of the PLC (just don’t forget
where to come back to).
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