A PLC (Programmable Logic Controllers) is an industrial computer used to monitor inputs, and depending upon their state make decisions based on its program or logic, to control (turn on/off) its outputs to automate a machine or a process.
NEMA defines a PROGRAMMABLE LOGIC CONTROLLER as: “A digitally operating electronic apparatus which uses a programmable memory for the internal storage of instructions by implementing specific functions such as logic sequencing, timing, counting, and arithmetic to control, through digital or analog input/output modules, various types of machines or processes”.
Traditional PLC Applications
*In automated system, PLC controller is usually the central part of a process control system.
*To run more complex processes it is possible to connect more PLC controllers to a central computer.
Disadvantages of PLC control
– Too much work required in connecting wires.
– Difficulty with changes or replacements.
– Difficulty in finding errors; requiring skillful work force.
– When a problem occurs, hold-up time is indefinite, usually long.
Advantages of PLC control
* Rugged and designed to withstand vibrations, temperature, humidity, and noise.
* Have interfacing for inputs and outputs already inside the controller.
* Easily programmed and have an easily understood programming language.
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