What is PLC

What Is A PLC :- A PROGRAMMABLE LOGIC CONTROLLER (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program to control the state of output devices.Almost any production line, machine function, or process can be greatly enhanced using this type of control system. However, the biggest benefit in using a PLC is the ability to change and replicate the operation or process while collecting and communicating vital information.

HISTORY OF PLCs :-

The first Programmable Logic Controllers were designed and developed by Modicon as a relay re-placer for GM and Landis.

• The first PLC invented was come out in 1960s AMERICAN COMPANY BEDFORD Associates
• The first PLC, model 084, was invented by Dick Morley in 1969
• The first commercial successful PLC, the 184, was introduced in 1973 and was designed by Michael Greenberg. 

             

HOW TO PLC WORK:-

The PLC is a specialist type of computer so the why and how PLC's work is needed to utilize them correctly and to your best advantage. They are used extensively but not solely in industry, to control machines and processes.

PLCs come in so many makes and different shapes and sizes. They can be so small as to fit in your pocket but also the more involved controls systems can be as large as a wardrobe with several interconnected large PLC racks.

Being a computer, it shares common terms with the typical PC (Personal Computer).

The Inputs.

A PLC input device means anything that can give an input to the PLC, that can influence the programs operation. These can consist of digital, analogue, switches, sensors, intelligent devices. This is because the full scale of their signal range, (called Full Scale Deflection or FSD for short), can be represented by one bit. There are eight bits in a byte, computers talk in bytes or multiples of bytes.

The Outputs.

Now, furthering how PLCs work it may not surprise you to know output devices can consist of digital (bit devices) and/or also, Typical outputs signals can range from 0-10V DC, -10V to +10V DC or 4-20mA and are used to control servo drives and positioning controls as well as pressure regulators and level control systems . Analogue devices (value devices)  digital output card is the compliment to the digital input card and turns a (bit) device on or off such as lights, LEDs, small motors, solenoids (electromagnets), and relays. Digital output cards are available with 8 up to 128 output per card, but again like the input cards any more than 16 would need a connector breakout card.

Advantages:-

This type of controller has made a significant contribution to factory automation. Earlier automation systems had to use thousands of individual relays, timers and sequencers, which had to be replaced or rewired whenever the automated process needed to change. In many cases, a programmable logic controller allows all of the relays and timers within a factory system to be replaced by a single controller. Modern PLCs deliver a wide range of functionality, including basic relay control, motion control, process control and complex networking. They also can be used in a distributed control system (DCS).

Industrial  Application:-

A programmable logic controller (PLC) is an electronic device used in many industries to monitor and control building systems and production processes. Unlike PCs and smartphones, which are designed to perform any number of roles, a PLC is designed to perform a single set of tasks, except under real-time constraints and with superior reliability and performance.  PLCs are designed to be extremely robust, often capable of withstanding extreme temperatures, humidity, vibration, and electrical noise,To meet the demands of harsh industrial environments  Logic controllers are commonly tasked with monitoring and controlling a very large number of sensors and actuators, and are therefore distinct from other computer systems in their extensive input/output (I/O) arrangements.