Abstract:

To propose the method of evaluating and improving the real-time performance of Ethernet for plant automation (EPA) industrial ethernet, the real-time performance of EPA nonperiodic data transmission was studied. By analyzing EPA communication scheduling mechanism and its time delay generating regularity, nonperiodic messages were categorized as some modes according to their entering-queue time. The scheduling characteristics, communication delay of each mode and their interacting relations were studied, and the models of real-time performance of EPA system were established. Analyses and an instance verification, 3 key factors limiting the real-time performance of EPA nonperiodic messages transmission were found: ① priority inversion during the messages transmission; ② communication overhead of deterministic scheduling mechanism; ③ the processing method of nonperiodic messages that enter queue after the device gives up its competition right of transferring nonperiodic messages.

Key words: industrial Ethernet, nonperiodic data, real-time performance, time delay