While traditional PLC-based systems were optimised predominantly for short cycle times as a replacement for complex relay technology in machine controls, Distributed Control Systems (DCS) for classic Proportional Integral Derivative (PID) closed-loop control focused mostly on scalability and system integration.
Driven by customer requirements and technological progress, both DCS and PLC have advanced and increasingly converged over the years. As a result, PLC systems have acquired more extensive visualisation systems. These are very similar to those that process engineers have used from the start and are being implemented to manage many wide-ranging, complex processing workflows. DCS, on the other hand, were optimised with regards to their performance and cycle times. Improvements like these help accommodate even highly time-critical processes and equip process plants for safety-related requirements, such as emergency stops and fire protection.
Growing requirements bring separate worlds together
The systems also converge in terms of scalability. DCS, which were designed from the start for large installations with tens of thousands of I/Os, were successful with simple engineering and retrofit capabilities. However, for today’s PLC-based systems, even I/O points in the high five digits don’t pose a challenge anymore. In addition, modern engineering environments, like TwinCAT 3 software, feature a broad range of libraries and plenty of function blocks, so that even highly complex closed-loop control structures can be designed quickly and reliably.
Developments regarding system architectures also deserve special attention. For example, distributed control systems focused almost from the start on distributed I/O chassis. These systems can collect data from the areas exposed to explosion hazards with little wiring complexity and accommodate installations that are spread over large areas. PLC-based systems, on the other hand, initially concentrated on self-contained machines in small areas.
This has changed as simple machines have evolved into highly complex production lines within tightly networked plants, and operators have become more interested in using distributed peripherals that can be linked to fast fieldbus systems and deliver the bandwidth needed to accommodate the resulting flood of data. As a result, systems that can offer distributed intelligence, like the DIN rail-mountable embedded PCs in the CX series from Beckhoff, are now a prevailing option, enabling direct connection of the EtherCAT based I/O system. In addition, deploying EtherCAT communication throughout allows operators to implement extremely time-critical and highly synchronised control processes across distributed production steps. This includes the ability to integrate with central production control systems, and to perform data analysis and optimise processes.
PLC system with maximum innovation potential
In terms of system architecture, the developments mentioned above have already made PLC systems very similar to the remote I/O systems that users are familiar with from the process control field. Especially in the context of Industry 4.0 concepts, the PLC approach has proven to be an innovation driver and has taken on a highly advanced structure that is clearly superior, particularly in terms of performance.
It is above all the vision of the Internet of Things (IoT), which has led PLC-based systems to take on some characteristics of distributed control systems in the past few years, especially in terms of integration capabilities. This, in turn, has increased support for mature protocols that offer cross-system data exchange, for example, based on OPC UA, but also for communication between the supervisory control level and the cloud through protocols, such as MQTT and AMQP.
While machine builders use these capabilities to implement the Industry 4.0 concept in its totality, process engineers require fully integrated solutions for a variety of reasons. They must cover all hierarchy levels ranging from data acquisition in hazardous areas to remote diagnostics of globally distributed systems via centralised process control systems. The goal is to reduce the required number of operators and maintenance staff. While this reduces costs, it also opens up new opportunities to make systems more efficient and reliable through the use of extensive diagnostics and analytics tools.
Open & modular automation technology a complete solution
With PC-based control, Beckhoff offers the ideal automation toolbox to implement all these requirements in a complete and integrated solution. Through the addition of specific innovations for process technology applications, process engineers now have access to the same automation system that has long been proven in machine design and factory automation.
The openness of the PC-based control concept deserves a special mention, as support for all major bus systems allows the easy integration of Beckhoff controllers into existing architectures. In addition, long-term product availability and backward compatibility provide the best possible investment protection and ensure outstanding spare parts supply. As an example, even first-generation EtherCAT components can still communicate with the latest product introductions. Benefits like these also make it easy and affordable to upgrade existing systems, for example, by adding cloud connectivity and IoT functions.
The benefits of integrated and open automation systems become especially apparent when designing new plants. On the field level, the use of ELX-series EtherCAT Terminals for the direct connection of intrinsically safe field devices enables significant reductions in space requirements and thus, cost requirements. In addition, the elimination of the need for separate safety barriers delivers clear advantages with regards to installation and diagnostics. DIN rail-mountable embedded PCs from the CX series, equipped with up to 12 CPU cores, makes it possible to distribute the execution of even the most complex control tasks with their high processing performance. Comprehensive product certifications ensure compliance with explosion protection requirements and enable installation in close proximity to the actual process.
PC-based control simplifies engineering & operation
On the control level, the finely scalable portfolio of Industrial PCs from Beckhoff enables custom-tailored solutions that can not only perform a wide range of control tasks but also provide easy integration into process control systems. Support for many standards and protocols ensures cross-system data communication on both, the higher-level control and the field system level.
The advanced TwinCAT HMI software solution enables the implementation of visualisation tasks according to the highest standards for efficient and reliable plant operation. In addition, the responsive TwinCAT HMI runs just as well on mobile devices as on industrial control panels and panel PCs. For process visualisation and control in hazardous areas (Zone 2/22), specific devices are available in the form of the highly attractive CPX panel series with state-of-the-art, multi-touch technology and robust aluminium enclosures.
With the wide range of TwinCAT functions available, engineering for the entire plant operation and data transmission to a higher-level control system or cloud services become a highly intuitive processes. Many diagnostic options and interfaces, such as the TwinCAT FDT container for integrating field device drivers (DTM), ensure quick and productive commissioning and easy access to the world of Beckhoff control technology.
Courtesy: Bechkhoff Automation