Then, during the 1920s, industrial automation evolved rapidly as factories began making use of relay logic and underwent electrification – using electrical power to drive their machines .
Software-based automation became a reality in 1964, when Dick Morley invented the programmable logic controller (PLC) for use in the US automotive manufacturing industry . The PLC replaced relay logic, but process changes could be accommodated simply by reprogramming rather than having to rip out and replace wires and relays.
This event significantly facilitated the third industrial revolution, or Industry 3.0, which gathered pace from the Seventies, and, in many factories, is still in operation today. Industry 3.0 saw most production processes become automated, although human intervention was still needed. A typical Industry 3.0 control system would comprise one or more PLCs, plus individual three-term controllers for devices like proportional valves or variable speed drives.
However, the PLCs were limited in their functionality; they could not be programmed to do anything like a general-purpose computer could. Instead, they acted as a programmable, convenient version of the hardwired relay systems they replaced. They spent their time performing Boolean logic tasks like:
“If Tank Heater 1 is ON AND Tank Level 1 is HIGH THEN START Agitator 1”
In fact, even to this day, a true PLC only performs such tasks, although some machines referred to as PLCs are far more powerful and widely functional. A good definition for PLCs is provided by the International Technical Commission’s (IEC’s) Standard IEC 61131 for industrial controllers. The Standard has ten parts covering general information, equipment requirement, user guidelines, communication protocols, safety, fuzzy control programming, and many other aspects regarding programmable controllers.
The third part, IEC61131-3, defines the programming language used for programmable logic controllers. The current edition (Third Edition) was released in 2013 .
This set of standards defines the basic architecture of specific programming languages and allowed programming in five different programming language standards. Of the five languages, three are graphical, and two are textual programming standards. They are listed below:
- Ladder diagram (LD)
- Function block diagram (FBD)
- Structured text (ST)
- Instruction list (IL)
- Sequential function chart (SFC)
Meanwhile, a typical manufacturing process also has monitoring and control requirements beyond the capabilities of a PLC, such as automatic inspection, measurement, verification, and flaw detection. Other examples include industrial imaging, and applications involving high speed data, or machine vision applications to automate quality control systems. These would be handled by a fanless industrial PC with a powerful processor programmed for the specific application, packaged within a ruggedised enclosure suitable for demanding factory environments.
All of this equipment – PLCs, three-term controllers, and industrial PCs – is typically connected back to a central, large-scale supervisory control and data acquisition (SCADA) system located in an environmentally managed control room and tended by human operators.
The SCADA computer and PLCs could be point-to-point wired to the process sensors and actuators, or connected via industrial buses such as Modbus, which uses serial communication lines, Ethernet, or the Internet Protocol Suite as a transport layer. The SCADA computer and its lower-level devices are often collectively described as Operational Technology, or OT, as distinct from traditionally office-based Information Technology (IT) systems.
The SCADA system also communicates upwards, usually through Ethernet, or possibly via Internet, to an enterprise IT system, to report on its operational status, throughput, and other parameters. This helps the IT system users to understand and cater for maintenance requirements and manage production schedules.
These Industry 3.0 systems, although effective in what they do, do not support the benefits available from modern smart technology. They are also bulky, power-hungry and expensive. A SCADA computer usually requires a complete, environmentally-conditioned control room, as mentioned, while PLCs and industrial PCs typically occupy at least a 3U 19” rack, if not 6U or more.
The situation has radically changed with the rise of Industry 4.0, the fourth industrial revolution. Industry 4.0 originated in 2011 from a project in the high-tech strategy of the German government, which promotes the computerisation of manufacturing. Actually, the term “Industry 4.0” was publicly introduced in the same year at the Hannover Fair.
There are four design principles identified as integral to Industry 4.0 :
Interconnection — the ability of machines, devices, sensors, and people to connect and communicate with each other via the Internet of Things, or the Internet of People (IoP).
Information transparency — the transparency afforded by Industry 4.0 technology provides operators with comprehensive information to make decisions.
Technical assistance — the technological facility of systems to assist humans in decision-making and problem-solving, and the ability to help humans with difficult or unsafe tasks.
Decentralised decisions — the ability of cyber physical systems to make decisions on their own and to perform their tasks as autonomously as possible.
Automation and control system manufacturers today can achieve these goals using modern computer, communications and input/output (I/O) hardware because products now available – as we shall see – are incredibly small, power-efficient and economical compared to earlier hardware, while offering high performance and functionality. And because they are small and power-efficient, it becomes easier to package them within industrial-type enclosures such as DIN rail mounting modules.
All of this means that single board computer (SBC) products from manufacturers including Raspberry Pi and Arduino are available for purchase at two levels:
- Plant process control engineers can purchase pre-engineered DIN rail modules configured as a PLC with suitable CPU, communications, process I/O and PLC software. They can then programme, install and commission the PLC on the plant as a smaller, lower-cost alternative to traditional PLCs.
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Electronics engineers within a control systems OEM manufacturer can purchase board level products from Raspberry Pi, Arduino and other manufacturers to build either general-purpose industrial PCs, or special-purpose solutions for specific applications. One example could be an edge controller mounted directly on the machine being controlled or monitored, gathering data from machine-mounted sensors (or driving machine-mounted actuators) and exchanging data with a gateway via a wired or wireless industrial network.
Another example would be the gateway itself; a device capable of exchanging data with one or more edge controllers, and then communicating with a remote or cloud server accordingly.
Either the edge controller or the gateway could pre-process the plant data, reducing the volume of data to be sent onward. This mitigates network loading and improves security.
Note that an Industrial PC can be configured to operate as a PLC. It could, for example, run OpenPLC – an open-source platform for PLC programming; it is based on user-friendly software that follows the IEC 61131-3 Standard as described above. OpenPLC can transform popular microcontrollers into PLCs. It is the first open source PLC that is fully functional and standardised in both software and hardware. OpenPLC also allows the incorporation of higher-level languages programmed by other software .
We can better understand the possibilities available if we take a closer look at some of the industrial SBC boards available, as well as some DIN mount PLCs based on these.
Industrial SBCs
Raspberry Pi
The Raspberry Pi Compute Model 4 provides the power of a Raspberry Pi 4 in a compact form factor designed for embedded applications.
Raspberry Pi Compute Module 4 incorporates a quad-core ARM Cortex-A72 processor, dual video output, and a wide selection of other interfaces. It’s available in 32 variants, with a range of RAM and eMMC Flash options, and with or without wireless connectivity.
Key features include a high-performance 64-bit quad-core processor, dual-display support at resolutions up to 4K, hardware video decode at up to 4Kp60, up to 8GB of RAM, Gigabit Ethernet, USB 2.0, dual camera interfaces, and PCIe Gen 2 x1 interface. The optional dual-band 2.4/5.0GHz wireless LAN and Bluetooth 5.0 have modular compliance certification.
This allows the board to be designed into end products with significantly reduced compliance testing, improving both cost and time to market. Either the onboard antenna or an external antenna kit can be used.