What Is a PLC in Manufacturing and Why Do You Need It?

A PLC or programmable lоgic controller is an industrial computer that has been designed to remotely control manufacturing operations and equipment, such as machines, production lines, robotic devices, or any process that requires high reliability, programming and fault detection.

Instead of having multiple devices and employees managing various systems and tasks, PLCs can handle all of them at once.

Manufacturers need PLC controllers because they help automate industrial operations. Their implementation provides a competitive edge to all types of factory-based manufacturing. The rapid operation of internal timers, sequencers and relays in PLCs far surpasses that of traditional time delay relay systems. Consequently, an assembly machine using a PLC would achieve a significantly higher productivity rate.

Moreover, PLCs are extremely reliable real-time production control systems and are easy to program. They can seamlessly be adapted to emerging sensor technologies and sophisticated human-machine interface (HMI) devices, which means they progress in tandem with modern technological advancements.

When it comes to programmable logic controllers' advantages, there are several key points:

• Reliability: PLCs are known for their high reliability due to their rugged design, making them suitable for the harsh conditions of industrial environments.
• Flexibility: These systems are extremely flexible in terms of programming, as you can easily modify and update the control logic without extensive rewiring.
• Scalability: Modern manufacturing demands faster transfer of larger data volumes, which is what PLCs do through controlled processes.
• Speed: The high speed at which logic controllers compute and execute functions leads to faster and more efficient production processes.
• Cost-effectiveness: Using programmable logic controllers helps reduce costs by diminishing the need to invest in sophisticated hardware.
• Diagnostic capabilities: Such programmable systems provide advanced diagnostics that enable quicker issue identification, thus, reducing downtime and increasing productivity.
• Integration: PLCs can be seamlessly integrated with other automation systems, making them a versatile and valuable component in a wide range of industrial applications.
• Safety: Access to PLCs is restricted through both hardware features such as keylocks and software features like passwords.
• Problem-solving: Programmable logic controllers offer a significant advantage in problem-solving compared to other control systems, as many are equipped with diagnostic indicators monitoring various conditions.
• Communication capabilities: Programmable controllers are designed with communication capabilities to interact with local and remote computer systems.
• Fault protection: Such controllers offer effective responses to power interruptions and failures through alarm routines and special function instructions, enhancing fault protection and system monitoring.

Programmable logic controller inventors put a lot of effort into making sure that their control systems solved existing issues and were easy to use.

Back in the 60s, electromechanical relays were used to perform similar processes in the manufacturing industry. However, these were very big and heavy objects, difficult to maintain and to operate with. This pushed engineers to come up with new technologies of production and, eventually, to the development of the PLC prototype by Richard (Dick) Morley.

Modern PLCs are much more advanced than electromechanical relays in terms of speed, reliability, cost-effectiveness, data management and the ability to adjust them. This means PLCs could adapt to changes and different requirements and are also able to perform diagnostics and identify system flaws.

There are two types of PLCs you can use depending on your needs:

1. Unitary PLCs are more compact and simpler, with a given number of I/O (input/output) points, and usually could be directly connected to the devices or applications. 
2. Modular PLCs, on the other side, give you more flexibility in terms of customization and adding I/O modules.

Before choosing the right PLC type, you should know whether you are implementing it in a new or existing system, how many I/O points it requires, how complex are the processes you will be controlling, what programming language you will be using and in what type of environment your PLC will be run.

PLCs are essential elements in industrial process automation. They function based on instructions stored in a memory module that contains programmed commands and data. The system receives input from sensors and executes logical operations on the data to generate the desired output.

Let's investigate further.

PLC Programming and Setup

As with any other device, PLCs need instructions on how to perform. They are usually given via programming devices or software and are downloaded into the PLC RAM or memory. PLC runs on various programming languages (Instruction List, Structured Text, Function Block Diagram and others) but Ladder Logic is the most used one, being quite easy to read and program. 

Essential Elements of a PLC System

• Central processing unit (CPU) giving instructions to the PLC on how to function. It contains the memory of the computer and stores all the data needed for diagnostics and operation of different machines. The CPU can communicate with other devices and PLC systems.
• Input/Output modules that pipe the necessary information to the CPU and communicate tasks repeatedly. These could be digital or analog devices. Examples of input devices are sensors or switches, and for output devices – lights, valves or others.

PLC Functioning

After writing the program and setting the input/output modules, the PLC processes the information, performs the given instructions and brings the final output. Once inputs and outputs are defined, the PLC works in a repeating mode. The process includes steps during which input scanning is conducted, then the program created by the user is run, followed by output scanning communicating with other devices and performing diagnostics.

PLCs are very widely used and will remain in focus in the manufacturing industries for years to come. Although they need to adapt to the new technologies of production, they are easy to program and modify.

In the future, they will become more adaptive to climate changes and remote operations and more compatible with Industrial Internet of Things (IIoT) for better data management.