PLC (Programmable Logic Controller) is defined as a digital electronic device with a programmable memory to store instructions that perform specific functions such as logic, sequence, timing, counting, and arithmetic to control an industrial machine or process in accordance with the desired industry.
The concept of PLC (Programmable Logic Controller) as the name suggests is as follows:
Programmable: shows the ability that can easily be altered according to a program created and memory abilities in terms of programs that have been made.
Logic: to show its ability in processing the input by the arithmetic (ALU), namely comparing operation, add, multiply, divide, reduce and negation.
Controller: indicates the ability to control and regulate the process so as to produce the desired output

By Introductory-PLC.pen.io

I like the free
for learn plc, I recommend visit this link http://program-plc.blogspot.com