Full abbreviation of PLC is “Programmable Logic Controller”. In order to operate under tough conditions of industries like dust, wet, dry and high temperature, a PLC is specially designed. It’s a special type of computer. PLCs are broadly used in various types of industries because they’re fast, easy to operate and are considered easy to program. Automatic industrial processes like mineral processing plant, wastewater treatment plant and manufacturing plant’s assembly line use PLC machine for better productivity. Like a personal computer, a PLC also has a power supply, a CPU (Central Processing Unit), inputs and outputs (I/O), memory, and operating software.
There are numerous ways to program a PLC. It is programmed in from electromechanical relay based ladder logic and specially developed programming languages like BASIC and C. Nowadays, PLCs use one of the following 5 programming languages: Ladder Diagram, Structured Text, Function Block Diagram, Instruction List, or Sequential Function Charts. Users can view required data from manufacturing floor by using SCADA and HMI systems. These systems provide an interface for users to provide control input. PLCs are an important hardware component element in these systems. For communicating, monitoring and control automated processing such as assembly lines, machine functions and robotic devices, PLCs are used.
Following steps are followed in a PLC Scan Process:
Ø In the first step, cycling and monitoring of time are started by the operating system.
Ø Reading the data from the input module and checking the status of all the inputs. These processes are proceeded by CPU in this step.
Ø In this step, executing the user or application program written in relay-ladder logic or any other PLC-programming language are initiated by CPU.
Ø All the internal diagnosis and communication tasks are performed by CPU in this step.
Ø It writes the data into the output module according to the program results. In this way, all outputs are updated.
Ø As long as the PLC is in run mode, the process continues to run.