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Programmable logic controllers (PLC)

Industrial control system (ICS) is a collective term used to describe different types of control systems and associated instrumentation, which include the devices, systems, networks, and controls used to operate and/or automate industrial processes. ICS are typically used in industries such as electric, water and wastewater, oil and natural gas, transportation, chemical, pharmaceutical, pulp and paper, food and beverage, and discrete manufacturing (e.g., automotive, aerospace, and durable goods.)

Depending on the industry, each ICS functions differently and are built to electronically manage tasks efficiently. Today the devices and protocols used in an ICS are used in nearly every industrial sector and critical infrastructure such as the manufacturing, transportation, energy, and water treatment industries.

Programmable Logic Controllers (PLCs) are small industrial computers with modular components designed to automate customized control processes. PLCs are often used in factories and industrial plants to control motors, pumps, lights, fans, circuit breakers and other machinery.  The system also helps in detecting any errors or flaws and alerts the technician.


PLC Advantages

PLC systems are also preferred over traditional systems, like relays and switch boxes, due to their compact sizes. The number of relays, wires, and space needed to create even simple automation was problematic. Thousands of relays could be necessary to automate a simple factory process.

PLCs are available at a wide range of price points, including many extremely affordable basic models that small businesses and startups often use.
PLCs are extremely versatile, and most PLC models are suitable for controlling a wide variety of processes and systems.
PLCs are completely solid-state devices, which means they have no moving parts. That makes them exceptionally reliable and more able to survive the challenging conditions present in many industrial facilities.
PLCs have relatively few components, which makes them easier to troubleshoot and helps reduce maintenance downtime.

PLCs are efficient and don’t consume very much electrical power. This helps conserve energy and may simplify wiring considerations.

The deployment of PLC systems enables the identification and rectification of errors and can initiate rapid responses even without human intervention. Hence, these automated PLC systems are estimated to assist in reducing machine downtime from 20% to almost 4%.


PLC technologies

A programmable logic controller (PLC) or programmable controller is an industrial computer that has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, machines, robotic devices, or any activity that requires high reliability, ease of programming, and process fault diagnosis.


The main difference from most other computing devices is that PLCs are intended-for and therefore tolerant-of more severe conditions (such as dust, moisture, heat, cold), while offering extensive input/output (I/O) to connect the PLC to sensors and actuators.


PLC input can include simple digital elements such as limit switches, analog variables from process sensors (such as temperature and pressure), and more complex data such as that from positioning or machine vision systems.  PLC output can include elements such as indicator lamps, sirens, electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs.  The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a fieldbus or computer network that plugs into the PLC.


They can be designed for many arrangements of digital and analog I/O, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact. PLCs can range from small modular devices with tens of inputs and outputs (I/O), in a housing integral with the processor, to large rack-mounted modular devices with thousands of I/O, and which are often networked to other PLC and SCADA systems. Programs to control machine operation are typically stored in battery-backed-up or non-volatile memory.


How a Programmable Logic Controller Works

  • Input Monitoring: The PLC monitors relevant data inputs and sends the data to the CPU. Some PLCs only use data inputs with discrete (on/off) inputs, but PLCs with analog capabilities can accept analog inputs for continuous variables. Inputs may come from IoT devices, robots, safety sensors, human-machine interfaces, or almost any other type of data entry point.
  • Logic Programming: Every PLC is built with a microprocessor CPU, either 16-bit or 32-bit. Engineers and technicians program the PLC CPU to recognize certain conditions and values and to make changes in the outputs based on its programmed rules. The CPU is constantly checking the state of variables and making decisions based on programmed conditions. This simple premise allows a wide variety of designs and functions.
  • Output Control: Based on the programmed logic, the PLC controls various switches, motor starters, relays, and other devices connected to its outputs. This allows the PLCs to take control of mechanical processes such as the operation of a machine. Engineers can also link multiple system parts by programming PLCs to send their output signal to another PLC in a chain.

PLCs use built-in ports, such as USB, Ethernet, RS-232, RS-485, or RS-422 to communicate with external devices (sensors, actuators) and systems (programming software, SCADA, HMI). Communication is carried over various industrial network protocols, like Modbus, or EtherNet/IP. Many of these protocols are vendor specific.

A PLC is an example of a hard real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result. Modern PLCs generally contain a real-time operating system, such as OS-9 or VxWorks.


While Ladder Logic is the most commonly used PLC programming language, it is not the only one. The following table lists of some of languages that are used to program a PLC.

Ladder Diagram (LD) Traditional ladder logic is a graphical programming language. Initially programmed with simple contacts that simulated the opening and closing of relays, Ladder Logic programming has been expanded to include such functions as counters, timers, shift registers, and math operations.

Moreover, the increasing demand for improved control, secured connectivity, and enhanced performance has pushed PLC manufacturers to bank on IIoT technologies, such as machine-to-machine communication, smart sensors, industrial cloud, and cybersecurity. Also, to accommodate advanced features, cost-effectiveness, and interoperability, PLC manufacturers have begun to innovate and integrate conventional PLC systems with modern and contemporary technologies.



PLCs, like many other types of electronic equipment, are vulnerable to electromagnetic interference (EMI). They can also experience other kinds of common electronic malfunctions such as corrupted memory and communication failures.

PLCs from different manufacturers often use proprietary programming software. This makes PLC programming interfaces less interoperable than they might be, especially considering that their programming languages share common standards (see below).


Programmable Logic Controller (PLC) Market

The programmable logic controller (PLC) market was valued at USD 12.04 billion in 2021, and it is expected to reach USD 15.79 billion by 2027, registering a CAGR of 4.56% during the period 2022-2027.


The market is strongly impacted by the industrial output and the investment funneled into computers and software. These PLC systems have traditionally been the foundation of both process and discrete factory automation. The growing adoption of Industry 4.0 across the industrial verticals has augmented the market studied.


A major growth indicator for PLCs in the discrete-manufacturing sectors is the amplified deployment of robots across the automotive manufacturing, electrical, and electronics industries.


With a growing number of I/O points in the industry, there is a growing preference for DCS over PLCs due to the limited number of I/O points in a PLC system. For instance, in the process industries, such as chemicals, paper and pulp, and power generation, a PLC can operate only with a few hundred I/O points. The DCS can conveniently handle more than a thousand I/O points.


The programmable logic controller (PLC) market is segmented by type (hardware and software, services), end-user industry (food, tobacco, and beverage, automotive, chemical and petrochemical, energy and utilities, pulp and paper, oil and gas, water and wastewater treatment, and pharmaceutical), and geography.


Considering the production output trends across the discrete industries, such as automotive and electronics, and their investments in new establishments, the large PLCs are estimated to grow moderately over the forecast period.

Like large PLCs, small PLCs are well suited to handle complex sequencing functions. However, the trade-off between these two devices is cost and size. The expandability of the I/O module for these devices is limited to one or two modules, and it uses a logic instruction list or relay ladder language as a programming language.

In response to market demands, many features and functions are now provided by lower-end PLCs. Furthermore, it is expected that small PLCs will continue to evolve to include many of the features associated with higher-level PLCs, while at the same time, mid-level and high-end PLCs will start to offer smaller, more compact, and customized solutions to meet users’ needs.

Furthermore, the need for high-voltage operating devices led to nano PLCs becoming a popular choice among discreet industries and small industries. For instance, fixed nano PLCs are used in electronic applications, such as converters, inverters, and other basis controllers, due to the ease of control at high voltages. Furthermore, the ability to perform a single set of tasks with superior reliability and performance, except under real-time constraints, coupled with their capability to withstand extreme temperatures, humidity, vibration, and electrical noise, proliferating PLCs’ growth in several industrial applications.



Furthermore, increasing demand from North America, competing with the Chinese and European markets, is creating a considerable market for PLCs in the region.

The Asia-Pacific region holds the largest market share and is expected to register the highest growth. The manufacturing sector forms a significant part of China’s economy, which is undergoing a rapid transformation with the recent growth in IIoT due to the rise in Industry 4.0 across the manufacturing industries globally. This large-scale transformation has put the country in one of the leading positions in the PLC market globally.

The Government of India is aiming to increase the manufacturing sector’s share in the gross domestic product (GDP) to 25% by 2022. Thus, manufacturers are likely to incorporate Industry 4.0 and other digital technologies to achieve this target.

Japan also aims to achieve ‘Society 5.0″ by fully utilizing the action of technological innovation, including IoT, AI, and Big Data, derived from the fourth industrial revolution. To attain this, the government had announced ‘Connected Industries’ as a new framework in which industries are likely to create new solutions to various problems in society through the connectedness of various parts of modern life, including humans, machines, systems, and companies.


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