PLC Mini-Tutorial

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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

  1. PLCs are good at turning outputs on or off based on the state of inputs. (control)
  2. PLCs are good at bringing together and concentrating a lot of data and status that is uploaded into a computer in a compact form
  3. PLCs are more rugged than computers and typically last five, seven, ten years without needing replacement

Cons

  1. PLCs are not the best at handling large amounts of data or complex data.
  2. PLCs are not the best at reading and writing databases.
  3. PLCs are not the best at outputting resultant data to printers.
  4. 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. Donít 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, couldnít 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 donít forget where to come back to).

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