PLC automation is the key technology used in industries to control machinery and processes. PLC stands for Programmable Logic Controller. It is a special computer used in industrial automation to make decisions based on specific instructions programmed into it

A PLC helps industry units streamline processes, improve productivity and efficiency, reduce human error, and enable real-time monitoring. PLC automation is widely used in various industries, including manufacturing, automotive, oil and gas, mining, food and beverage, building automation, chemical processing, and more.

In this blog, we’ll discuss the basics of PLCs, how they work, different types, and key advantages. Let’s dive in!

What is Programmable Logic Controller?

A programmable logic controller or PLC is a specialized computer designed for controlling machines and processes in industrial automation. It acts like a brain of a machine which takes input form sensors like temperature or pressure, then process that information using a program—a set of instructions written by a programmer, and then sends output signals to actuators like motors or valves to perform specific tasks.

A PLC can control machines or processes to automate assembly lines (like robotic arms and conveyor belts), manufacturing, power plants, packaging applications, and more. It’s also utilized in building automation like HVAC, security systems and lighting.

History of PLC

Industrial automation began long before PLC. Till the mid 20th century, industrial automation relied on using electromechanical relay circuits, which required a lot of relays, wires and space. In the 1960s, the first Programmable Logic Controller was created. Unlike the complex relay circuits, PLC was more flexible, allowing programmers to easily update it to do specific tasks.

As technology advanced, PLCs became smaller, more powerful, and more user-friendly. And the growth of programming devices and communication made it easier for PCs to connect with PLCs, allowing not only programming but also simpler testing and troubleshooting. While the first PLC automation had limited memory and speed, today’s PLCs can connect with other PLCs, motor drives, HMIs, and Ethernet, making the automation process more versatile and flexible.

How Does a PLC work?

The key components of a PLC are input/output (I/O) modules, CPU, rack and power supply. Using these components, a PLC works through a series of steps, called “Scan Cycle”. Here’s what’s included in a scan cycle:

Input Reading: The PLC first gathers information from its input devices, like sensors, switches and buttons. The inputs tell the PLC what’s happening in the system, for example, whether a machine has stopped working or if the temperature or pressure has reached a certain level.

Processing: The processor, that is CPU, is the brain of the PLC. It processes the input data using a pre-written program or instructions. It evaluates the inputs to determine what actions need to be taken based on the conditions set in the program.

Output Control: Based on the processor's decisions, the PLC sends signals to output devices like motors, valves, and lights through the rack. For example, if an input device detects a machine is overheating, the PLC sends a signal to the output device to turn off the machine, helping to prevent damage and ensure safe operation.

Housekeeping Tasks: After updating the outputs, the PLC performs some housekeeping tasks, like checking for any errors or communicating with other devices. This ensures everything is running smoothly and that any issues are quickly detected.

The PLC repeats this entire scan cycle hundreds to a thousand of times per second. This allows PLC automation to work continuously in real-time, ensuring that machines or processes run smoothly for the required duration.

Types of PLCs

There are two major types of Programmable Logic Controllers:

Fixed or Compact PLC

Fixed PLCs or Fixed I/O PLCs are integrated with built-in input/output, which means their input and output are fixed and decided by the manufacturer. Fixed PLCs are suitable for smaller applications.

Modular PLC

These types of PLCs have separate modules of I/O, communication, power supply and processing. Modular PLCs allow for multiple expansions and configurations, providing scalability.

Other than these two major types, PLCs can also be classified on the basis of their size and output.

Types of PLCs Based on Output

Digital Output PLCs: These PLCs send on/off control signals, to control devices like relays, lights, and motors.

Analog Output PLCs: These PLCs send varying output signals to control devices that require a range of values, like speed and temperature.

Relay Output PLCs: These use electromechanical switches (relays) to control higher voltages and currents, providing safety and isolation.

Transistor Output PLCs: These use electronic transistors for output control, offering fast and durable switching compared to relays.

Triac Output PLCs: These are used to control AC devices, like motors and lamps, that require high voltage.

Types of PLCs Based on Size

Large PLC: Such PLCs have more than 5000 I/O points, ideal for complex and large-scale applications.

Mini PLC: This PLC has 128 to 512 I/O points, suitable for small to medium-sized applications.

Micro PLC: This PLC comprises of 15 to 128 I/O points, ideal for small machines and basic control tasks.

Nano PLC: This PLC has less than 15 I/O points and is used in PLC trainer systems.

Safety PLCs

These are special types of PLCs designed for safety-critical applications. These PLCs ensure compliance with safety standards and must conform to IEC 61508 – Functional Safety of Electrical/Electronic/Programmable Electronic Safety-related Systems. Although safety PLCs work similar to regular PLCs, the difference is that they provide fail-safe operation.

Advantages of PLC Automation

PLCs are much better than hard-wired relay circuits because of many reasons. Here are some reasons why:

Flexibility: PLCs are highly flexible. You can reprogram them for different tasks as your needs change, without needing to replace hardware.

Complex Applications: PLCs can manage more complicated tasks than relays. They can handle multiple inputs and outputs at once, making them suitable for advanced automation processes.

Compact Size: PLCs are smaller than traditional relay setups. This means they take up less space in control panels, which is especially useful in tight environments.

Faster Changes: When you need to make changes to a system, PLCs allow for quick reprogramming. Unlike relays, which require rewiring, you can adjust settings and logic in software, saving time.

Centralized Monitoring: With PLCs, you can monitor the entire system from one central location. This makes it easier to spot problems without having to check each section of the system individually.

Durability: PLCs are built to last longer than relays. They have no moving parts, which means they are less likely to wear out and can handle tough industrial environments better.

Easier Error Correction: If there’s an error, fixing it is simpler with a PLC. You can modify the program directly, rather than dealing with physical connections as you would with relays.

Simplified Documentation: Keeping records of how the system works is easier with PLCs. You can store all the information electronically, making it quick to update and access when needed.

Cost Efficiency: PLCs make it easy to duplicate applications. If you want to set up a similar system elsewhere, you can copy the program quickly, which helps reduce costs in both time and materials.

PLC Applications

PLCs, from brands like Allen-Bradley, Siemens, Omron, Schneider Electric and Mitsubishi Electric, offer reliable automation solutions that help several industries increase efficiency and productivity. Here's how PLCs are used across different sectors:

Manufacturing: PLCs are widely used in automated production units, controlling assembly lines, robotic arms, and conveyor systems. Allen-Bradley is popular in North American factories, while Siemens is widely used in global operations like automotive and electronics

Packaging: PLCs automate tasks that require high production speeds and accuracy in the packaging industry like filling, labeling, and sorting. Allen-Bradley is common in food and beverage packaging, while Siemens is used in pharmaceutical and consumer goods packaging.

Agriculture: PLCs can automate processes like irrigation, crop monitoring, and feeding systems, improving farming efficiency. Omron and Mitsubishi Electric PLCs are popular in agricultural automation, especially in Asia.

Material Handling: PLCs play a vital role in controlling conveyor systems, sorting machines, and automated vehicles in warehouses and distribution centers.

Heavy Machinery: PLCs control cranes, excavators, and mining equipment in industries like construction and mining. Siemens PLCs are commonly used in global heavy machinery applications, while Allen-Bradley is popular in North America.

What is PLC Programming?

PLC programming is the process of creating software or instructions for Programmable Logic Controllers to automate industrial processes.

Ladder Logic is the most commonly used PLC programming language. It closely resembles relay circuit diagrams, using horizontal and vertical lines to represent electrical circuits. Each step of the ladder represents the condition or switch that controls whether the machine turns off or on.

There are four more common programming languages used for PLC automation. These include:

Function Block Diagrams (FBD): A graphical approach where functions are depicted as blocks linked by lines to illustrate data flow.

Structured Text (ST): A high-level text-based language similar to traditional programming languages like Pascal, which allows for complex logic

Instruction List (IL): A low-level programming language that resembles assembly language, although it’s less commonly used today.

Sequential Function Charts (SFC): A visual method for outlining the sequence of operations in a process—-similar to a traditional flowchart.

PLC programming plays a crucial role in automation by enabling precise control of machinery and processes, simplifying complex tasks and reducing costs by replacing bulky relay circuits. This improves efficiency and reliability in industrial operations.

How Sedin Engineering Helps Industries with Smart PLC Automation Solutions?

Sedin offers exceptional industrial automation solutions tailored to your specific requirements. With years of experience in the industry, we are committed to boosting your operational efficiency and productivity.

Our team has extensive expertise in PLC programming and automation. We design high-quality HMIs for operator interaction and use simulation tools for safe and optimized machine operation and ensuring safety compliance. We also provide support for maintenance and troubleshooting complex automation processes to help our clients to efficiently speed up their industrial processes.

Ready to take your industrial operations to the next level? Contact us today to discover how our PLC automation expertise can transform your processes and drive your success!