PLC stands for Programmable Logic Controller

It looks at the inputs, and either turns its outputs on or off. To be able to work, the PLC first monitors different conditions. Basing on these conditions, an outcome is determined. The next step of PLC operation is the creation of logical rules by use of programmable software which allows for adaptability. The final is decision-making depending on logical rules. Decisions are determined by logical rules that the PLC is taught by way of its programming software.
The PLC functions by observing the interaction of four internal areas. The four internal areas of the PLC are the Central Processing Unit, CPU, the memory, the communication ports, and the Input/Output devices (AutomationDirect.com, 2010).
The CPU is the place where decision-making in the PLC takes place. It also has a memory, where the CPU stores the user’s control program, the Input/Output (I/O) status, and data. Communication ports make up the third internal area, and these allow for the user’s program to be loaded into the memory from a personal computer (PC). It also facilitates communication with other external memories including other PLCs in order to exchange data. The fourth internal area is made up of Input/Output devices
Why were PLC’s were invented/developed – PLCs were initially developed to meet specifications that were developed by General Motor’s Hydra-matic division to replace relay-based machine control due to their use of latter logic programming. PLCs would, therefore, help to allow for quick changes and reduction in wiring, and troubleshooting time. This was a huge development from the older relay-based control systems.
Non-industrial application of PLC’s includes – amusement parks, car-washes, and elevators.
The most widely used PLC programming language is latter logic, which is a carry-over from relay-based control systems.
What makes a PLC very versatile is the ability to program and re-program it. Re-programming makes it possible to change the outcome when, and if, the future conditions change, so as to meet the changing needs.