What are PLC's?

PLC is an acronym for Programmable Logic Controller (PLC). A PLC is a digital micro controller-based unit which is utilized in industry for the automation and control of various processes and applications. Common uses of a PLC can include control of an automated assembly line, machine, amusement park attraction, industrial robots - even home automation. The applications for a PLC are virtually limitless. PLC's provide a convenient, central point for sensory input and decision making. With innovations in microcomputer technologies, PLC's are becoming faster and just as powerful as the PC-Based automated systems which preceded them.

The first PLC was made by Modicon. In fact, MODICON is an acronym for Modular Digital Controller (MOdular-DIgitial-CONtroller). Prior to the arrival of PLC's, control of automated equipment was performed by utilizing large banks of relays. Changing the relay logic (programming) required extensive research and took hours to implement. Electricians had to physically install the wiring changes required to execute the new logic. When the fist Modicon PLC hit the market, large cabinets of inter-connected relays were replaced by a single unit about the size of a small suitcase. Changes to the logic could be made offline and then downloaded to the existing hardware without having to change a single wire. Manufacturers soon saw the tremendous capabilities of the PLC and began to implement it across the board.

With the inception of the PLC, a format needed to be designed which would be easily adaptable to the engineers and electricians who had to make the configuration changes to automated processes. Developers designed an interface which was similar in nature to electrical rung ladder diagrams. The resulting programming environment was called Rung Ladder Logic (RLL) and was/is the predominant manner in which logic programs for PLC's are designed. With advances in PLC and PC technologies, PLC programming software has began to emulate machine code programs. Even though many PLC programming packages contain machine language functionality (C++, Virtual C, etc.), virtually every PLC programming platform contains a RLL option.

To select the right PLC for your applications, you must carefully consider the abilities of the PLC against the requirements of the application. For instance, if you are selecting a PLC for a motion application, then you'll want to select a PLC which has a very fast scan-time and has specific hardware and software designed specifically for motion control. The operating system which a PLC employs will be just as important as the hardware. Usually, well developed operating systems will be more expensive than less developed systems, but will pay dividends down the road with time-saving features which will make the programmer more efficient.