PLC hardware speed, I/O, communications, redundancy, Part 2: Future of the PLC

Programmable logic controller (PLC) insights

• In a November 9 webcast, “PLC series: PLC hardware speed, I/O, communications, redundancy,” David Ubert, senior automation specialist at Black and Veatch, and Eelco van der Wal, managing director at PLCopen, discussed how PLC designs have changed to meet automation and control challenges in recent years.
• In Part 2, Ubert discusses the technical aspects and future direction of PLCs.

In the ever-evolving field of industrial automation, programmable logic controllers (PLCs) have been a mainstay, adapting to the changing needs of various automation applications. Known for their robustness and versatility, PLCs remain a preferred choice for machine control, motion control, and even certain process control applications. However, as the demands of modern automation grow increasingly complex, it’s essential to understand where PLCs fit best in today’s industrial landscape.

In a November 9 webcast, “PLC series: PLC hardware speed, I/O, communications, redundancy,” David Ubert, senior automation specialist at Black and Veatch, and Eelco van der Wal, managing director at PLCopen, discussed scenarios where PLCs are most effective, how their designs have changed to meet contemporary automation challenges, and what key criteria end-users should pay attention to when selecting PLCs for specific applications.

The transcript of their presentation has been provided with minor edits and adaptations.

Evolution of PLCs and their overlapping with DCS

David Ubert: Over time, PLCs have rapidly evolved, increasingly overlapping with distributed control systems (DCS) in functionality. Today’s PLCs boast advanced high-speed communication systems and complex input/output (I/O) systems. They are also suitable for corrosive environments, with some manufacturers providing conformal coating for electronics. This adaptability allows PLCs to be utilized in simple applications like sump pumps and more complex scenarios.

Features of PLC systems

I have outlined some key features of PLCs on this slide, which I will discuss in detail. These features include diverse communication options, varying types of PLC cards, I/O capacity, footprint size, processing power, and vendor compatibility. Let’s delve into the communication options available with modern PLCs.

Communication options in PLC systems

A fundamental aspect of PLC systems is the interconnectivity between them. For example, two PLC racks can communicate over an Ethernet platform through a switch. This setup is common among all PLC manufacturers, although some use proprietary networks for peer-to-peer communication. Additionally, PLCs can connect to remote I/O systems, where one rack acts as the controller and the other as an extension for I/O. Different protocols may be used for these connections.

Moreover, PLCs can communicate with vendor systems or peer-to-peer over fiber optics using various protocols, such as Ethernet, RS-232, RS-485, and Fieldbus technologies. While there are many proprietary protocols, standard ones are also widely used in PLC systems.

Advancements in PLC technology

One exciting development is the advancement of Ethernet protocol, now available in a two-wire format and suited for industrial applications. Historically associated with IT environments, Ethernet is now integrated into industrial settings for communication between control systems, vendor panels, and even instrumentation. This represents a significant progression in PLC technology.

Development of PLC I/O cards

PLC I/O cards have evolved significantly. When I first began programming PLCs, a typical digital I/O card had eight points. Now, the standard is a 16-point card. These cards are used for various functions, like monitoring the status of valves or pumps, indicating a closed valve with a limit switch or confirming a running pump, thus enhancing the versatility and efficiency of control systems.

The analog I/O card, a typical component in modern PLC systems, usually accommodates around eight I/O points. This limitation arises due to the increased hardware requirements of analog cards, such as space and isolation components. These requirements are essential for maintaining functionality and isolation within the system.

Specialty cards in PLC systems

In addition to standard I/O cards, PLCs also feature specialty cards designed for specific applications. For instance, high-speed counters are necessary for applications like flowmeters in water or solution systems, where a high volume of pulses indicates flow rate. These specialty cards can include RTD cards for reading temperature and even cards with artificial intelligence capabilities. Additionally, PLCs offer modules with basic programming functionalities. Each manufacturer has its unique range of IO and specialty cards, with some providing high-density modules accommodating up to 32 points, requiring smaller gauge wire.

Technological evolution of PLC processors

The PLC processor has undergone significant technological advancements. Comparing with the past, where a home computer had a processor with limited capacity and storage, PLC processors now are capable of handling high-speed applications efficiently. The programming languages and the processors work synergistically, enabling rapid program execution. These advanced processors facilitate the operation of various applications, broadening the scope of PLC usage.

Network connectivity and vendor compatibility in PLC systems

Network connectivity and vendor compatibility are crucial aspects of modern PLC systems. In scenarios such as a water plant or industrial setting, the integration of a vendor panel performing specific functions is common. The use of network protocols, particularly industrial Ethernet, has revolutionized communication between different control panels. This advancement eliminates the need for complex I/O-based communication, fostering interoperability among different systems. Nowadays, manufacturers aim to support common protocols, enabling seamless network integration.

Best practices in selecting PLC hardware

When selecting PLC hardware, it is vital to employ best practices and engage qualified personnel for system design. Each application demands a unique approach, even in similar plant designs in different locations. Factors to consider include cost, which is often overlooked. The cost implications of a PLC upgrade or a new control system can be substantial. Manufacturers typically offer PLCs in varying tiers – low-end, mid-range, and high-end – with costs and capabilities increasing at each level. Selection depends on the requirements of the specific application, such as IO capacity and processing speed.

Importance of local support for PLC systems

Another critical consideration is local support, which is frequently underestimated. The availability of local support, whether from a system integrator, the PLC manufacturer, or a distributor, is crucial for efficient operation and maintenance of the system. Ensuring access to reliable support resources can significantly impact the long-term success of a PLC installation.

Configuration and redundancy in PLC systems

I recall an experience from the past where lack of proper planning led to complications, a situation I vowed never to encounter again. This brings us to the topic of PLC configuration. We’ve discussed different sizes of PLC platforms – large, medium and small. The configuration of networks in these platforms is critical, whether it’s a star network, broadband, or fiber. These choices are essential to ensure the PLC supports the intended control system. Another crucial aspect is redundancy, a topic I am particularly passionate about. Redundancy is a significant design element, and it’s crucial to avoid errors in its implementation.

Types of redundancy

Implementing a redundant system undoubtedly adds complexity. The type of staff available to maintain this system plays a vital role in determining the appropriate form of redundancy. There are various options, including cold redundancy, warm redundancy, and hot backup. Cold redundancy might involve having a spare PLC processor on standby. In case of a failure, the replacement process may take several hours, but the backup is ready to be installed. Warm backup involves having two operational PLCs, where maintenance personnel can switch to the backup in case of a failure. Hot backup, ideally, involves separate control panels in different plant areas. This redundancy is essential for critical systems where downtime can result in significant financial loss, time wastage, or safety hazards.

Hardware upgrades in PLC systems

Hardware upgrades are a common and necessary practice. These upgrades can enhance manufacturing output, for instance, increasing the production of widgets. Newer PLCs can offer improved speeds, network capabilities, and I/O capabilities, which directly impact system performance. Upgrading to compatible PLC platforms across a plant can also address space requirements. For example, replacing large, outdated panels with more compact and efficient ones.

Cybersecurity and legacy systems

An interesting point in the realm of hardware upgrades is cybersecurity. While outdated PLC equipment might not be a primary target for hackers, its obsolescence poses risks due to lack of support and patches, making the system vulnerable. Upgrading hardware is not just about improving performance or space efficiency; it’s also crucial for enhancing cybersecurity and reducing system downtime.

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