Programmable logic controllers (PLCs) are integral to industrial automation and industrial process control. PLCs manage various actuators, analog, and digital sensors, and communicate complex interfaces in changing protocols.

Other than control functions, PLCs execute data conversion and signal processing. PLCs, driven by developments in the Industrial Internet of Things (IIoT), delivers secure and scalable solutions, high performance, low power, and small footprint.

Nowadays, PLCs finds wide use in digital world applications. The sequential and repeated operations in industries are normally carried out using PLC. They are ready for Industry 4.0. This article highlights PLC design and its challenges in industrial application.

What is a Programmable Logic Controller (PLC)?

A programmable logic controller, commonly known as PLC, is a solid-state, digital, and industrial computer that uses integrated circuits instead of electromechanical devices to implement control functions.

As per NEMA, PLC is defined as as digital electronic devices that utilize programmable memory to implement particular functions and store instructions. The list of particular functions include logic, arithmetic sequencing, timing and counting, and also control of processes and machines.

PLCs underwent noticeable form-factor changes over the years - from industrial PCs and Programmable Automation Controllers (PAC) in PC-like form-factors to compact enclosures and mini-PLCs. The PLC functionality has also evolved. Other than discrete control functions, PLCs now come with functionalities like Human Machine Interface (HMI), real-time industrial ethernet, motion-control, and data communication gateways. Several contemporary industries implement smart manufacturing, where connected systems are leveraged for enterprise and Machine-to-Machine (M2M) interaction. PPLCs are redesigned for reliable, flawless work and immunity against hostile, noisy, dusty environments and also for being water-resistant. Real-time availability and operational capability over a broad environmental temperature range are also required. Element14 has partnered with many different suppliers who offer a broad portfolio of PLC products. (For more information on PLC products, please click here)

Classification of PLC

PLCs are classified into three types based on output: Transistor output, triac output, and relay output PLC. The relay output type is ideal for both AC and DC output devices. Transistor output type PLC uses switching operations and is used in microprocessors.

PLCs are engineered to be robust, capable of withstanding extreme temperatures, electrical noise humidity, and vibration. Logic controllers control and monitor a huge population of actuators and sensors and are thus distinct from other computer systems in their considerable input/output (I/O) presentation.

PLC Anatomy

PLCs are compact modular devices with multiple inputs and outputs (I/O) in a housing incorporated with the processor. The range may peak at big rack-mounted modular devices where thousands of I/O are networked to SCADA systems. The Programmable Logic Controllers (PLCs), inside the Industrial Control System (ICS), serve as a useful bridge between the physical and cellular communication protocols like PROFIBUS, BACnet, DNP3, OPC, EtherCAT, and CIP.

Three modules make up each PLC system: CPU module, many input/output (I/O) modules, and power supply module.

Block Diagram of PLC Module
Figure1: Block Diagram of PLC Module
  • CPU module: This module contains a central processor along with its memory part. This processor executes all needed data processing and computations by receiving appropriate inputs and producing the corresponding outputs
  • Power supply module: A 5V DC output is needed to run PLC's computer circuitry, which is duly supplied by the power supply module. This is fundamentally the module in charge of system power-up. It accepts AC power and then converts it to DC power that the remaining two modules (Input/output and CPU modules) use.
  • I/O Modules: The input/output modules oversee the sensors and actuator's connection to the PLC system to sense different parameters like pressure, flow, and temperature. The I/O modules are either analog or digital

PLC Programming allows the user to configure the control system using an established syntax. Ladder, Boolean, and Grafcet are different types of the programming languages used. The Ladder and Boolean languages implement operations in the same way, but they differ in how their instructions get represented and how they get inputted into the PLC. The Grafcet language controls instructions differently, depending on the actions and steps in a graphically oriented program. Several different programming languages are in use today, each supplying PLC its programming specifications built on the IEC 61131-3 standard. For more information on PLC Programmer products click here.

PLCs in Industrial Applications

PLCs finds use in various application in power plants, smart grid system, manufacturing units, monitoring machine tool or equipment, building the system, and process control functions. We will discuss a few of the PLC use-cases employed in industrial automation.

a) Automatic Mixing and Bottle Filling System using PLC's in the beverages and juice industry

In an automatic mixing and bottle filling system, initially, two liquids, namely water and protein liquid, from two different containers are to be mixed in a mixing container as shown in the following figure2. The mixed solution is to be filled in the bottles one after another. The start button initiates the whole system operation. Here the sensor output is input to the PLC, and outputs of PLC control the valves, mixer, and conveyor belt. The first liquid (water) flows into the mixing container for 10 seconds. The second liquid then flows into the mixing container for 15 seconds. The mixing operation takes place for 20 seconds. The stop button controls the operation. Please click here for more information on Process Controller products.

b) To process flat glasses and control material ratio using PLC Controller in Glass industry

PLCs are employed in the glass industry to control the material ratio and process flat glasses. This continuously evolving technology has advanced over the years and thus created a consistently rising demand for PLC control mode in the glass industry. Glass production is a sophisticated process. Companies involved frequently use PLCs with bus technology as its control mode. The PLC records analog data in glass production and digital-quality, position control in the process.

c) Mixing of Raw materials using PLC in Cement Manufacturing Industry

Manufacturing cement involves the mixing of different raw materials inside a kiln. The final product quality is impacted by these raw materials and their respective proportions. Data must be accurate to ensure the use of correct quantity and quality of raw materials. A distributed control system consists of PLC in user mode and configuration software being used in management and production processes. The PLCs, to be specific, controls coal kiln, shaft kiln, and ball milling.

Automatic Mixing and Bottle filling system
Figure2: Automatic Mixing and Bottle filling system


Good automation and process control are vital in the competitive world. PLC based automation works make production activities profitable. PLCs can simplify complex operations and reduce setup time. The works in ceramic, cement, packaging industry, chemical, food processing, and so on strongly needs PLC systems for excellent performance and profit.

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