PLC- an Overview

Introduction

A Programmable Logic Controller, PLC, or Programmable Controller is a digital computer used for automation of industrial processes, such as control of machinery on factory assembly lines. Unlike general-purpose computers, the PLC is designed for multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. Programs to control machine operation are typically stored in battery backed or non-volatile memory. A PLC is an example of a real time system since output results must be produced in response to input conditions within a bounded time, otherwise unintended operation will result.

PLC are registered trademarks of the Allen-Bradley Company.

History

Why PLC

Starting of human kind, there is no information about automation so they have to do there all work manually. To reduce human effort the concept of automation introduced.

1. Manual control

Starting of human kind, all human did all their work manually.

Fig 1: Manual Control (hand pump)

2. Hydraulic Control

Later they invented a new way to do some work with help of hydraulic power. These day this mechanism is used in jcbs, and to open some buses doors.

Fig 2: Hydrolic Conntrol

3. Pneumatic Control

Many years later human invented a mechanism to do their work with pneumatic control. These days this mechanism use in air break in many vehicles.

Fig 3: Pneumatic control

4. Hard wire Control

Then human invented hard wire system for control hard type of systems. These days we can see this system use in movement of railway tracks.

Fig 4: Hard Wire Control

5. Electronic Control

Many times later human invented electronics system to help humans in their work.

Fig 5: Eletronic Control

6. Programmable Logic Control

Newly invented system is PLC. It helps human to perform many work from a single input system.

Fig 6: PLC