Programmable Logic Controller (PLC)

What is a programmable logic controller (PLC)?

A programmable logic controller (PLC) is a ruggedized computer that is used for industrial automation to automate a range of electro-mechanical processes. These computers help regulate automation processes so that the unnecessary power consumption of manufacturing processes can be reduced effectively. 

A PLC consists of programmed microprocessors whose programs are written on a different computer and later downloaded into it through cables. These programs are stored in the non-volatile memory of the PLC. 

Even though they are industrial computers, they come in a variety of sizes and form factors. Some can even fit in your pocket, while some might require a huge heavy-duty rack. Some can be modular with only basic inputs and outputs, while some can be customized with additional functional modules. 

There are five standard PLC programming languages used that are- Ladder logic, Function Block Diagrams,

How does programmable logic controller (PLC) work?

A PLC performs three major tasks that are collecting inputs, executing programs, and giving outputs. It is a cyclic process in which the PLC first detects the state of all input devices that are connected to it. Then it executes the user-created program, and based on the inputs it gets on that execution, it determines the required changes and gives an output. 

So to break it down simply:

Step 1: Checking connections with the input devices

Step 2: Executing the user-uploaded program.

Step 3: Giving outputs based on how the inputs performed. 

Once these three steps are completed, the PLC performs a housekeeping step, which includes an internal diagnostic safety check that ensures everything is under normal conditions. After every cycle, the PLC restarts from step one, which is checking the inputs. 

The inputs data can come from a variety of sensors and devices that send information to the PLC, such as-

• On/ off switches on devices
• Analog readings of things like speed, pressure, and temperature
• Valves with open/ close states

Apart from these, there can also be human-facilitated inputs such as pushing buttons, switches, and sensors on devices like keyboards, touch screens, remotes, etc. 

The outputs given by PLC are not very different and include operations like,

• Opening and closing of valves
• Ringing alarms
• Adjusting the speed of a motor
• Adjusting temperature

 What are the types of PLC?

Based on the hardware setup, programmable logic controllers are of two types:

1. Fixed/ compact/ integrated PLCs
2. Modular PLCs

1. Compact PLC

A compact or integrated PLC is a small controller based around a microprocessor which can handle small automation tasks. It comprises a built-in programming language and an extensive yet user-friendly set of instructions that eliminates the need for heavy coding to execute certain applications. 

A compact PLC is primarily made of an input, output, power supply and processing unit and a terminal that connects the controller with other sensors and switches. 

Compact PLCs and much smaller than a central control unit, which makes them portable and usable with low-voltage cables. 

2. Modular PLC

A modular PLC is a control system that has programmable hardware components instead of the fixed-function components used in traditional central controllers. 

This allows the users to configure and reconfigure their controllers based on their needs, and it also saves manufacturers money. Plus, they are comparatively easier to install, which again saves on installation and re-installation charges.

Their easy upgradability eliminates the need of discarding the entire machine for more advanced technology. Hence they are best suited for high-growth companies that are planning to expand quickly.