Programmable Logic Controllers (PLC) - The Brain behind Industrial Automation

The Start ....

With the advent of industrial age, machines were used to automate process, which were routine in nature. This greatly allowed the reduction in production cost, benefitting the consumers.

Earlier Relay Logic Devices based on electromagnetism, were used to control machinery.

Two circuits, one with an open switch and another with a coil of wire, were placed parallel to each other. When current passes through the coil, it produced a magnetic field. This created a force of attraction, and the switch closes. The circuit gets completed, allowing the flow of current. This in turn drives a motor or an actuator.

Being a cost-effective solution, there were still some downsides. The installation part was highly complex.

A breakthrough came in 1964, when Dick Morely, an American inventor, designed a general-purpose computer to control industrial applications.

Known as Programmable Logic Controllers, or PLC, it brought about a revolution in industrial automation.

What is PLC

A specialized computer which can perform logical operations, while withstanding harsh environmental conditions like dust, humidity and temperature.

Based on the relay logic technique, switching was done digitally with electronic circuits and coding. This reduced overall complexity and installation overhead.

Ladder Logic is the coding language used. Also C/C++ in certain cases.

Components

The internal layout of PLC consist of five main components

1. Processor: Dubbed the brain of the computer, the microprocessor performs logical and analytical computations, based on environmental variables.

2. Input: The module that receives signals from sensors, or other measuring devices. Can be either analog or digital. This is then passed to the processor.

3. Output: Gets the calculated data from the processor, and converts it to readable signal. This in turn drives a motor, or an actuator.

4. Memory: Split into two divisions, the RAM (Random Access Memory) is used to store temporary data. ROM (Read Only Memory) stores the Operating System and programs, installed by the user.

5. Power Supply: 220V Alternating Current is converted into Direct Current. It is further split into smaller voltages to be fed into different components

The PLC is by definition a Real Time Operating System. The inputs are continuously scanned for any changes, and processor is always on stand by mode.

More information:

https://circuitdigest.com/tutorial/introduction-to-relay-logic-control-symbols-working-and-examples

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