What is ladder Diagram or Ladder Programming?

Ladder program is the programming language that represents in graphical form based on circuit diagram of relay hardware.

Ladder diagram represent the diagram of electrical components used for industrial logic systems. They are called "ladder" diagrams because they resemble a ladder, with two vertical rails (supply power) and as many "rungs" (horizontal lines) as there are control circuits to represent. If we wanted to draw a simple ladder diagram showing a lamp that is controlled by a hand switch, you can show below logic diagram:-

In the years of 1960, USA Company name Bedford associates first time released the device called as MODICON, this is the name of company for design and manufacturing and sale of computer products, The different firms developed their own versions of this device, and it eventually came to be known in non-proprietary terms as a PLC, or Programmable Logic Controller. The purpose of a PLC was to directly replace electromechanical relays as logic elements, substituting instead a solid-state digital computer with a stored program.

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