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PLC – Programmable Logic Controller: Manufacturing Explained

The Programmable Logic Controller, commonly referred to as a PLC, is a specialized computer designed to control industrial processes and machinery. It is a fundamental component in the world of manufacturing, playing a crucial role in automation and process control. This article will delve into the intricate details of PLCs, their function, their history, and their importance in modern manufacturing.

PLCs are designed to be robust and reliable, capable of withstanding harsh industrial environments. They are used in a wide range of industries, from automotive and aerospace to food processing and pharmaceuticals. By the end of this comprehensive glossary article, you will have a deep understanding of PLCs and their role in manufacturing.

History of Programmable Logic Controllers

The history of PLCs dates back to the 1960s, when the need for a more flexible and reliable method of controlling industrial processes became apparent. Traditional relay-based control systems were inflexible, difficult to modify, and prone to failure. The invention of the PLC provided a solution to these problems, revolutionizing the way industrial processes were controlled.

The first PLC was developed by Richard Morley and his team at Bedford Associates in 1968. The Modicon 084, as it was known, was designed for General Motors to replace the complex and cumbersome relay-based systems they were using at the time. The Modicon 084 was a success, and PLCs quickly became a standard component in industrial control systems.

Evolution of PLCs

Since their inception, PLCs have evolved significantly. Early PLCs were large, expensive, and limited in their capabilities. However, advances in technology have led to the development of smaller, more powerful, and more affordable PLCs. These modern PLCs are capable of controlling complex processes, integrating with other systems, and even communicating over networks.

Today, PLCs are a key component in the Industrial Internet of Things (IIoT), a network of devices, machines, and systems that communicate and interact with each other to improve efficiency and productivity in industrial settings. PLCs are now more than just controllers; they are intelligent devices that can make decisions, analyze data, and communicate with other systems.

Function of Programmable Logic Controllers

At its core, a PLC is a device that controls machinery and processes based on a set of programmed instructions. These instructions, known as a program or logic, are stored in the PLC’s memory and executed in a cyclic manner. The PLC continuously reads inputs from connected devices, processes these inputs based on the programmed logic, and then outputs commands to control devices.

The inputs to a PLC can come from a variety of sources, such as sensors, switches, or other devices. The outputs from a PLC can control a wide range of devices, including motors, valves, lights, and more. This flexibility allows PLCs to control a wide range of processes, from simple tasks such as turning on a light, to complex processes such as controlling an entire production line.

Programming PLCs

PLCs are programmed using a specialized programming language known as ladder logic. Ladder logic is a graphical programming language that represents a program by a series of “rungs” on a “ladder”. Each rung represents a logic operation, such as an AND or OR operation. This makes it easy to visualize and understand the logic of a program.

While ladder logic is the most common programming language for PLCs, there are other languages available as well. These include structured text, function block diagram, and sequential function chart. The choice of programming language depends on the complexity of the process being controlled and the preference of the programmer.

Types of Programmable Logic Controllers

There are several types of PLCs available, each with its own advantages and disadvantages. The three main types of PLCs are compact PLCs, modular PLCs, and rack-mounted PLCs.

Compact PLCs are small, all-in-one devices that are suitable for controlling simple processes. They have a fixed number of inputs and outputs, and are not expandable. Modular PLCs, on the other hand, are expandable and can be customized to fit the needs of a particular process. They consist of a base unit and various modules that can be added to increase the number of inputs and outputs. Rack-mounted PLCs are the largest and most powerful type of PLC. They consist of a rack that holds various modules, including a power supply, a processor, and multiple input and output modules.

Choosing the Right PLC

The choice of PLC depends on several factors, including the complexity of the process being controlled, the number of inputs and outputs required, the environmental conditions, and the budget. Compact PLCs are typically cheaper and easier to install, but they are less flexible and have fewer capabilities than modular or rack-mounted PLCs.

When choosing a PLC, it’s also important to consider the programming software. Some PLCs come with free programming software, while others require the purchase of a separate software package. The ease of use and capabilities of the programming software can have a big impact on the success of a PLC implementation.

PLCs in Manufacturing

PLCs play a crucial role in modern manufacturing. They are used to control a wide range of processes, from simple tasks such as controlling a conveyor belt, to complex tasks such as coordinating the movements of a robotic arm. PLCs are also used to monitor and control safety systems, ensuring the safe operation of machinery and processes.

One of the main advantages of PLCs in manufacturing is their flexibility. A PLC can be reprogrammed to control a different process, making it easy to adapt to changes in production requirements. This flexibility, combined with their reliability and robustness, makes PLCs an essential component in any modern manufacturing facility.

Integration with Other Systems

In addition to controlling processes, PLCs can also integrate with other systems in a manufacturing facility. This includes systems for data collection, quality control, maintenance, and more. By integrating with these systems, PLCs can provide valuable data and insights that can be used to improve efficiency, reduce downtime, and increase productivity.

For example, a PLC can collect data on the performance of a machine, such as its speed, temperature, and energy consumption. This data can then be analyzed to identify potential issues, predict failures, and optimize performance. This is a key aspect of predictive maintenance, a strategy that aims to prevent failures before they occur.

Future of Programmable Logic Controllers

The future of PLCs looks promising, with advances in technology leading to more powerful, flexible, and intelligent controllers. The integration of PLCs with the Industrial Internet of Things (IIoT) is a major trend, allowing PLCs to communicate and interact with other devices and systems in real-time.

Artificial intelligence (AI) and machine learning are also being integrated into PLCs, enabling them to make decisions, predict failures, and optimize processes autonomously. This will lead to even greater efficiency and productivity in manufacturing, and open up new possibilities for automation and control.

Challenges and Opportunities

While the future of PLCs is exciting, there are also challenges to overcome. One of the main challenges is the need for skilled programmers and operators. As PLCs become more complex and capable, the skills required to program and operate them are also increasing. This highlights the need for ongoing training and education in the field of PLCs.

Despite these challenges, the opportunities for PLCs in the future are vast. As more industries embrace automation and digitalization, the demand for PLCs is expected to grow. This, combined with the ongoing advancements in technology, makes it an exciting time to be involved in the world of PLCs.


In conclusion, Programmable Logic Controllers are a fundamental component in the world of manufacturing. They have revolutionized the way industrial processes are controlled, providing a flexible, reliable, and robust solution. With advances in technology, PLCs are becoming more powerful and intelligent, opening up new possibilities for automation and control.

Whether you’re a student, a professional, or simply interested in the world of manufacturing, understanding PLCs is essential. They are a key piece of the puzzle in the quest for efficiency, productivity, and innovation in manufacturing.

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Bryan Sapot
Bryan Sapot
Bryan Sapot is a lifelong entrepreneur, speaker, CEO, and founder of Mingo. With more than 24 years of experience in manufacturing technology, Bryan is known for his deep manufacturing industry insights. Throughout his career, he’s built products and started companies that leveraged technology to solve problems to make the lives of manufacturers easier. Follow Bryan on LinkedIn here.