The Difference Between PLCs and Computers
What makes a PLC different from a typical computer? After all, computers are used to control things, they can even run a software PLC.
This short video is part of the introduction to a new training course I am producing on the Thinkific LMS. It also follows the text on page 6 of my new training manual, PLC Hardware and Programming: Multi Platform. Text is reproduced after the video.
So exactly what is a PLC?
A PLC is a digital computer used to control electromechanical processes, usually in an industrial environment. It performs both discrete and continuous control functions and differs from a typical computer in several important ways:
- It has Physical I/O; electrical inputs and outputs bring real world information into the system and control real world devices based on that information. If you were a PLC, your inputs can be thought of as “senses” like vision and touch, while your outputs could be thought of as your arms and legs.
- It is Deterministic; it processes information and reacts to it within defined time limits. PLCs operate on a timescale of milliseconds or even microseconds
- It is often Modular; it can have I/O modules, communication modules or other special purpose modules added to it for expansion. PLCs may also take the form of a computer or a small single module.
- It is programmed using several defined Languages. Some languages allow the program to be changed while the machine or system being controlled is still running.
- Software and Hardware are Platform Specific; components and programming software usually can’t be used between different manufacturers. But there are exceptions…
- It is Rugged and designed for use in industrial environments.
Unlike computers, PLCs are made to run 24 hours a day, 7 days a week and are able to resist harsh physical and electrical environments.
Where are PLCs used? PLCs are used for many different kinds of applications and industries. In a 2012 Control Engineering magazine poll, 87% of machine control applications used a PLC as the control platform. This includes assembly, packaging and other manufacturing operations. 58% of process control applications used PLCs, in such industries as chemical processing and the oil and gas industry. Power plants and wastewater treatment also fall into this category. 40% of motion control and robotics, 26% of batch control and 18% of diagnostic or testing applications used PLCs. Many applications are a combination of these.
PLCs are used anywhere, and everywhere!
Did I leave anything out? Can you think of other differences between typical computers and PLCs? How about other places where PLCs are used? Leave your comments below!