This article will discuss:
- The OPC Publish – Subscribe (PubSub) specifications.
- What the specifications mean to factory owners and their importance.
- How OPC PubSub can be implemented and drive OPC UA integrations across shop floors.
According to Automation World, the future of production will be defined by interoperability and collaboration across shop floors. This also includes the exchange of data, to ensure data-driven plant performance optimization which maximizes the manufacturing process. With the appropriate technology solutions – industrial cloud, sensors, embedded devices and controllers etc. – in place, optimal automation in industrial settings is achievable. Also, it is important to remember that implementation is key. This is where experienced IT system integrators and implementation standards and specifications come into play.
The need for standardization and a defined road map to ensuring interoperability are some of the major reasons the OPC Foundation was formed. The standards and regulations OPC provides are centered around helping businesses integrate a unified architecture road map across single or multiple facilities. An example of an OPC Foundation solution to accomplish optimized interconnectivity and enhanced collaboration is the OPC Unified Architecture (UA).
OPC UA is a vendor-neutral service-oriented architecture that ensures platform independence, security, and comprehensive information modeling to receive business insight. When its series of specifications are implemented, OPC UA delivers a seamless flow of data across multiple devices, legacy equipment, operating systems, electronic hardware etc. without worrying about vendor compatibility. This is in line with the foundation’s goals to provide secure open platform communications across shop floors. Thus, in 2018, the OPC Foundation released a new set of standards that will accelerate the adoption of OPC UA in the deepest levels of manufacturing facilities.
Introducing OPC UA Pub-Sub
The Publish-Subscribe standard is the 14th part of the OPC UA specification. It was designed to extend the situations where OPC UA can be feasibly adopted to solve and deepen automation. According to the OPC Foundation, PubSub enables the integration of OPC UA in two important ways. The first is at the deepest levels of a shop floor where electronic hardware requires low power and low-latency communications on local networks. The second application is the integration of OPC UA in scalable cloud-based applications.
As for integrating OPC UA in the deepest levels of a shop floor, a minute 8bit controller using a 2KB SRAM can be integrated into embedded devices. This ensures high-performing data exchange and communication networks are preserved. It also creates a pathway to integrate OPC UA in one-to-many, one-to-one, and many-to-many configurations. This can be done in a highly scalable cloud-based architecture where sending and receiving data is required for enhanced performance.
Another important aspect of PubSub is that it enables the use of OPC UA directly over the internet or cloud. This is accomplished through the use of popular data transportation messaging middleware such as Message Queue Telemetry Transport (MQTT), and Advanced Message Queuing Protocol (AMQP). If OPC UA is successfully implemented, it will facilitate interoperability and data sharing between third-party devices and applications with ease.
Practical applications of OPC UA PubSub and its importance
The importance of the PubSub specifications can only be understood when it is applied and brings direct benefits to system integrators and industrial niches. Although PubSub is still in its early stages and case studies of its applications are limited, inferences about its importance can still be made. An example of the importance of PubSub is its ability to deliver real-time guarantees. This is particularly important when real-time data transfer determines how a unified automated framework functions.
Automated environments are driven by transmission queues for different traffic classes with each class controlled by a specified transmission gate which is triggered in cycles. The time slots for each transmission queue is also time-synchronized. This means anytime a packet does not complete its transmission within the allotted time frame then it will be pushed back till the next cycle thereby hampering real-time communications.
OPC UA PubSub is built to eliminate this challenge. It does this by ensuring servers send or publish data to the network or middleware, and every client can receive or subscribe to this data in every time cycle. The ability to publish and subscribe to data regardless of the configured synchronization cycles guarantees real-time automation. In practice, downtimes in time-critical applications in manufacturing facilities can be eliminated by implementing OPC UA PubSub. The implementation will ensure applications at deeper levels, such as synchronizing the movement of conveyor belts. The middleware integrated with conveyors will receive real-time information and continue to function even if configured schedules are missed.
PubSub also serves as a solution to many of the limitations OPC UA implementations face. An example is eliminating the one client to one server (one-to-one) feature associated with OPC UA. PubSub ensures one-to-many or many-to-many configurations are possible. This makes OPC UA compatible with IoT and IIoT applications. By implementing PubSub, the data published to the message-oriented middleware can be accessed by multiple clients or subscribers. Subscribers can then access specific types of data without having to know what type of publishers there are. Accomplishing this will also accelerate the integration of IIoT in manufacturing.
OPC UA PubSub also supports peer to peer communications between multiple controllers, as well as, between controllers and human machine interfaces (HMI). It also guarantees real-time communications and asynchronous workflows between OPC UA servers and the cloud. In terms of security, PubSub specifications integrate SHA-256 algorithms to guarantee privacy and security when data is exchanged locally or through the cloud.
Lastly, OPC UA PubSub accommodates time-sensitive networking (TSN) technologies to drive time-critical applications in industries. According to us at EXOR International, the integration of OPC UA PubSub while accommodating TSN, sped up cycle times which occurred under two milliseconds and jitter of 100 nanoseconds. This ensures equipment can handle time-critical applications without encountering bottlenecks.
Conclusion
PubSub is the next step in the evolution of OPC standards that ensure industrial automation procedures function seamlessly. Its implementation is guaranteed to increase the adoption of OPC UA across today’s shop floors. It also has an important role to play in the integration of IoT and IIoT applications and devices in manufacturing.
