Industrial networking expands PLC functionality
Combining real-time Ethernet with visualization, control, and communication capabilities allows PLCs to open the door to a new level of visibility and control for manufacturers.
The days when workers served as the brain and brawn in manufacturing are long gone, while human-machine interaction has become commonplace on the factory floor. A prime example of this is the PLC, which has been the workhorse in automation and manufacturing industries across the board for many years. By interfacing with everything from sensors and machine guards to motion control and advanced identification devices, PLCs ensure operations run smoothly (see Figure 1). Through the flexibility offered with PLCs, manufacturers can manage multiple machines at once—achieving a higher level of integration and process automation machines and improving production quality and cost of operation.
The benefits of the PLC are well known. Their contributions toward efficiency enhancement and the behind-the-scenes support of industrial Ethernet make this heightened control possible. Together, these technologies make communication between humans and machine a seamless, profitable combination. Consisting of various protocols, industrial Ethernet was developed with deterministic capabilities to provide a cost-effective alternative to legacy automation systems.
With advanced capabilities, sophisticated functionality, and simplified installation, the PLC is a cornerstone of modern manufacturing. However, to effectively use these devices, users must understand the crucial role networking plays and the individual requirements that must be considered for an effective solution. Together, they form a unified infrastructure that can extend from the administrative to control- and floor-level networks, offering inherent scalability to continue to meet growing industry demands.
PLC technology breakdown
Since their inception, PLCs have become a keystone of industrial automation, often serving as a vital link between humans and machines. As control architecture continues shifting and network technology keeps advancing, these changes support integrated HMI-PLCs that leverage an established and portable programming environment. As a universal controller, PLCs can be programmed to perform a variety of tasks—from starting and stopping motors to mathematical computing operations. With the processing power, data storage, and communication capabilities of today’s modern computers, PLCs provide intelligent and rugged field-level application control (see Figure 2). PLCs are designed to act as miniature computers that can deliver reliable operation in various challenging environments, such as extreme temperatures, electrical noise, vibration, and shock.
A PLC interacts with the environment it controls through its I/O. PLC inputs accept signals from many types of sensors, switches, and other control devices. The PLC makes decisions based on the values of these input signals with regard to the program that’s written to leverage its power to make things happen in its environment. Historically, PLC programs have been created in ladder logic—a language that closely resembles a relay-based wiring schematic. However, modern PLC programming is not limited to ladder logic. The results of these decisions are sent to actuation devices through the PLC’s outputs. In many cases, the inputs provide feedback to the PLC to enable these decisions, while the outputs provide the results of these decisions in the form of something that can change the process or environment.
PLC advantages: Implementing PLCs offers numerous performance benefits, such as reduced hardware requirements, increased efficiencies, and less waste. Modern PLCs are highly customized solutions that can be tailored to individual control applications while consuming less real estate on the factory floor (see Figure 3).
As a built-in controller, PLCs simplify installation because they use less cabinet space. Also, visual displays of many PLCs improve machine/operator interaction and increase production efficiency. For example, local displays coupled with easy-to-use interfaces on PLCs can provide simple instructions for machine operators as well as a means for data entry to support alarm monitoring and/or recipe management.
Designed for easy maintenance and troubleshooting, repairs are reduced to simply replacing modular, plug-in components. The likelihood of faults and the time needed to fix these errors is significantly reduced, eliminating the need to rewire panels and devices. Now, errors can be corrected by retyping the logic. Additionally, fault detection circuits and diagnostic indicators incorporated in each major component can tell whether the component is working properly. With the programming tool, any programmed logic can be viewed to see if inputs or outputs are on or off.
Expanding PLC functionality with networking
Although PLCs opened the door for on-the-floor visual communication, it was their integration with networking devices that offered manufacturers a new level of visibility and control by combining real-time Ethernet with visualization, control, and communication capabilities.
To meet the growing operation needs of industrial automation, networks continue to expand, offering monitoring and control capabilities in areas not previously possible. Device networks are now using fieldbus-to-Ethernet integration to develop enterprise-wide control networks. Merging networking functionality with PLCs enables users to off-load main processor tasks for distributed control in the field, placing control-level devices closer to the action. Additionally, by combining control with distributed I/O, manufacturers can lower their total cost of operation by streamlining data acquisition, communication, and factory-wide connectivity.
Networking: For PLCs to become a networking tool, users must have the necessary bandwidth that allows real-time industrial Ethernet. Because connection and communication requirements are expanding, PLCs must increase support for multiple network technologies. While there is no one-size-fits-all industrial network for all of the advanced I/O solutions, PLCs can connect the enterprise layer to the plant as needed by accommodating multiple protocols. Because network protocols add functionality, PLCs are necessary components for driving and supporting these additional functions.
Maintaining these industrial automation networks continues to be a key component in ensuring these integrated system continue functioning. A reliable network is paramount. Therefore, maintaining network availability is crucial. This requires the system to support the necessary bandwidth and high data transmission rates to meet application specifications, as well as data protection during maintenance operations and fast recoveries if connection failures occur.
Along with speed and availability, redundancy is important for continued performance and reliability. Prolonged periods of unplanned system downtime can become a potential threat to plant productivity. However, redundancy technologies not only provide msec-level network recovery, but they can also substantially reduce deployment costs.
Distributed control: Using distributed control allows parts of the automated system to be decentralized and dispersed throughout the system. This means that certain portions of the system are controlled by separate controllers located close to the area of direct control. This allows multiple different form factors for a wide variety of application requirements. Further, by spreading the I/O data across the application as appropriate (either in-cabinet or on-machine), manufacturers are able to reduce their automation and control footprint by reducing the number of necessary components.
Distributed control enables users to implement a flexible modular design with the exact amount of I/O expansion to be added when necessary, providing an inherent scalability for fast, cost-effective updates for future expansion. Distributed intelligence reduces any additional load on the PLC, and also allows the system to accommodate future functional requirements by enabling expansion while using the same PLC to control automated applications. This means users can enrich their systems by expanding the size and functional capabilities, and still standardize on PLC systems.
During off-loading, some of the control functions from the main processor (either PLC or PC-control) to the distributed I/O—which are located either on-machine or in-cabinet—reduce network traffic. This occurs because through the distributed I/O, the main processor does not need to make requests of the remote I/O for status of inputs or to initiate an output. The distributed I/O system with control/programmable functionality can handle certain tasks, relegating communications to supervisory or status data to the main processor.
By enabling remote I/O configurations, manufacturers can achieve high-level connectivity with only a few I/O points required—even in widespread areas—providing a cost-effective control solution for diverse industries and applications. In large facilities where extensive monitoring and control is necessary, it is not practical or cost-effective to have a controller at each site. This would require a tedious and expensive installation process that would require each I/O point to be hardwired with cable running over long distances. For example, remote I/O systems can be used in acquiring data from remote plant or facility locations. Information such as cycle times, counts, duration, or events can be sent back to the PLC for maintenance and management reporting. Additionally, hardwiring increases the likelihood of errors, such as mis-wiring, which can require excessive downtime to correct.
Advanced I/O capabilities: Networking technology has expanded beyond standard digital input, digital output, analog input, and analog output functionality. For example, advanced I/O can include RFID technology, SSID for motion and serial inputs, data logging, barcode, and 2D matrix identification systems. Smarter, more advanced I/O produces greater amounts of data, which integrated PLCs must be able to manage.
Typical factory environments are looking for tighter control of their manufacturing process, which results in a need for more than discrete I/O. PLCs are configured with advanced I/O such as analog signal processing, temperature, and RFID—all of which consume considerably more bandwidth.
For example, PROFINET uses three different communication channels to exchange data with PLCs and other devices. The standard TCP/IP channel is used for parameterization, configuration, and acyclic read/write operations. The real-time (RT) channel is used for standard cyclic data transfer and alarms. RT communications bypass the standard TCP/IP interface to expedite the data exchange with PLCs. The third channel, isochronous real time, is the high-speed channel used for motion control applications.