Programmable Logic Controller Basics

Programmable Logic Controllers (PLCs) are widely used in the industrial applications for control the process systems  They are planted at the field terminals of the process. Programmable Logic Controllers (PLCs) are micro-controller devices to control the process by performing certain desired functions such as closing or opening valves, starting and stopping motors. PLCs typically uses programmable memory to store the commands or instructions which will be fed by the programmer to carryout desired operation and implements logical, arithmetical and other  functions to control the process.

The term 'Logic' in PLC is used because the programming implemented in PLC is Logic based so as to carryout certain control functions like switching on or off, closing the valves.

Input devices connecting the PLCs are sensor devices such as switches, relays and corresponding output devices will be valves, motors. These inputs and output devices are connected to the PLCs. Programmer inputs sequence of commands and programs in to the memory of the PLC. PLCs controller monitor the inputs and accordingly takes output control functions as per the instructions and programs  provided in the PLC

Computers and Programmable Logic Controllers are almost similar but computers are meant for calculations and display functions on the other hand PLCs are dedicated to carryout logical operations and execute control functions in Industries.