Programmable Logic Controllers (PLC) is an electronic computer is easy to use (user friendly) which has control functions for various types and levels of various difficulties.
Definition Programmable Logic Controller according to Capiel (1982) are electronic systems that operate in the digital and designed to use in industrial environments, where the system uses a programmable memory for internal storage of instructions that implement with specific functions such as logic, sequence, timing, enumeration and arithmetic operations to control the engine or process through the modules I / O digital and analog.
The National Electrical Manufacturers Association (NEMA) defines a PLC 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 I / O modules various types of machines or processes."
PLC is designed to replace a circuit relay sequential in a control system. Beside it can be programmable; this tool can also be controlled, and operated by people who do not have knowledge in computer operation. This PLC has a programming language easily, understandable and can be operated when the program was created by using the software according to the type of PLC used is entered.