The programmable logic controller: all-rounder in automation technology

PLC structure and principle

The operating principle of programmable logic controllers has remained the same since they were first launched. They receive input signals (sensors, switches, etc.) from systems and machines, process them sequentially and cyclically using programmed logic – typically in milliseconds – in order to then use the results to activate corresponding output signals for actuators such as motors, valves and relays.

In other words, a processor, memory, power supply unit, and the input and output modules (I/O modules) were enough for half a century to automate sequential or repetitive production processes little fault tolerance in sometimes the harshest industrial environments via PLC.

Areas of application for PLC automation

1. Manufacturing automation:
On production lines, PLCs control the production processes, move materials, and perform quality checks.

2. Machine control:
From miniature controllers to CNC and robot controllers – controlled by PLC.

3. Building automation:
PLCs control the heating, ventilation, air conditioning, lighting, and security systems in buildings.

4. Traffic and transport systems:
PLCs monitor and control traffic lights, elevators, conveyor belts, automatic doors, and other aspects of traffic and transport systems.

5. Power generation:
PLCs monitor and regulate power generation plants such as hydroelectric power plants, wind turbines, or solar power plants.

6. Chemical and pharmaceutical industry:
PLCs control and monitor chemical processes to ensure safety and product quality.

7. Food and beverage industry:
PLCs control filling and packaging processes, temperature monitoring, and hygiene standards.

8. Water treatment:
PLCs ensure drinking water quality in water treatment plants.

Programmable logic controllers—the benefits

Unlike the originally hard-wired programmed logic controllers based on relay switches, PLC innovation means that modern, programmable, and connected control technology scores points with high flexibility and reliability, low installation effort, simple duplicability and expandability, better diagnostic options, fast function change, and low power consumption and space needs.

There are only a few drawbacks in comparison to the PLC advantages. For example, it’s not worth using PLC automation for simple control tasks that don’t often change. In addition, the programmable version requires a corresponding technical infrastructure with digital devices and trained personnel.

Control technology—modular, soft, or virtual

Programmable logic controllers are used as a modular system, a compact device, or an embedded chip solution. Software-based controllers (soft PLC) are becoming increasingly important for less safety-critical use. They usually run on universal PC hardware with an operating system enhanced with real time.

Virtual controllers (vPLC) represent the next step in control technology and, unlike the soft PLC, function completely independently of the hardware. The path to the cloud finally enables integration into Industry 4.0 solutions and IIoT platforms to implement smart and adaptive production environments.

Smart production solutions for the smart factory

Given the current variety of protocols, however, this kind of control technology is difficult to implement. OPC UA (Open Platform Communications Unified Architecture), as a platform-independent, uniform communications standard, should therefore ensure the seamless flow of information between devices from different vendors from the field level to the cloud, and enable modern applications such as big data, machine learning, industrial image processing, artificial intelligence, and deep learning, or predictive maintenance. Enhanced with TNS (time-sensitive networking) and what is referred to as the publish-subscribe mechanism, OPC UA meets both the interoperability and real time requirements of the PLC industry.

The non-profit organization Universalautomation.org (UAO) is also committed to vendor-independent control technology. Through the IEC 61499 standard, the association is declaring war on proprietary automation systems. As an extension of the IEC 61131 industrial standard, it defines a model for distributed control systems. The event orientation allows function blocks to respond to events without being closely tied to a central control logic. That improves the flexibility, reusability, and scalability of PLC automation.