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Industrial Ethernet Book 99

TAepcphlincoaltoiognys Comparison of the OPC UA client/server and OPC UA publisher/subscriber communication models. sites on the premises to ensure operators have access to the information wherever they are currently working. To extend support to specialist HMIs, it must be possible to exchange a range of predefined data records. A typical data exchange session can involve up to 30,000 data items sent between 50 to 100 clients, with a target refresh rate of 200 ms. Data exchange is cyclic. In addition, asynchronous events need to be communicated simultaneously to multiple HMIs to ensure they are visible throughout the premises. Every time an operator acknowledges an alarm or uses an HMI to intervene in some way, these HMIs control the state of the associated event. Control-to-Control Communication: There are two types of control-to-control communication. One type uses function blocks in a PLC program (“programmed control-to-control communication”) while the other type uses a centralized configuration tool (“configured control-to-control communication”). The setup and modification of programmed control-tocontrol communication requires modifications to be made to the PLC program, while the setup and modification of configured control-tocontrol communication requires a standardized configuration interface, but no actual changes to the PLC program. Data Flow: A server supplies a data flow of readings as fast as possible, whereby the reliability of this data transfer is not paramount. The data flow is either continuous or is transferred at high speed within a specified period of time. Accordingly, the exchange of data is either on-demand or permanent. Management of Video/Audio Streaming: A server provides access to a system that is equipped with video and/or audio sources. This type of server uses OPC UA standard services and protocols to support control tasks such as zooming a camera or making changes to video and audio streaming settings. The video/audio stream itself is transferred on a separate channel using standard protocols for video/audio streaming. OPC UA Pub/Sub use cases The following use cases require deterministic OPC UA publisher/subscriber data exchange. Cyclic Control-to-Control Communication: During normal operation, laser cutting equipment relies on cyclic communication between control systems (PLCs, NC and laser control systems) with a cycle time of 1 ms. Since this communication is used to handle control tasks, latencies and deviations must be minimal. Alongside time-sensitive cyclic communication, non-critical cyclic and eventdriven communication also takes place – for visualization data or data exchange with an MES or an ERP system, for example. E v e n t - D r i v e n C o n t r o l - t o - C o n t r o l Communication: During normal operation, a package identification system needs to exchange data not only with cameras and RFID systems but also with PLCs – e.g. for sorting work. Data exchange is event-driven (up to 18 events a second) and is triggered each time a package arrives. Since this communication is used to handle control tasks, latency needs to be very low (100 ms). Non-critical cyclic and event-driven communication also takes place. Cyclic Communication between Smart Sensors and Control Systems: In laser distance measurement work, sensors exchange data cyclically with a master controller or actuator. Cycle times of 10 ms are required here, which leads to a data volume of 15 MB per second. Time synchronization is required to coordinate measurements taken by the various sensors. Cyclic Communication between Robots and Tool Control Systems: The coordination of robot tools requires cyclic data exchange with a cycle SOURCE: SOFTING 30 industrial ethernet book 4.2017 SOURCE: OPC FOUNDATION OPC UA publisher and subscriber applications


Industrial Ethernet Book 99
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