A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.
It is used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many machines, in many industries.
- CPU – Keeps checking the PLC controller to avoid errors. They perform functions including logic operations, arithmetic operations, computer interface and many more.
- Memory – Fixed data is used by the CPU. System (ROM) stores the data permanently for the operating system. RAM stores the information of the status of input and output devices, and the values of timers, counters and other internal devices.
- I/O section – Input keeps a track on field devices which includes sensors, switches.
- O/P Section – Output has a control over the other devices which includes motors, pumps, lights and solenoids. The I/O ports are based on Reduced Instruction Set Computer (RISC).
- Power supply – Certain PLCs have an isolated power supply. But, most of the PLCs work at 220VAC or 24VDC.
- Programming device – This device is used to feed the program into the memory of the processor. The program is first fed to the programming device and later it is transmitted to the PLC’s memory.
System Buses – Buses are the paths through which the digital signal flows internally of the PLC. The four system buses are: