Virtual PLC in Industrial Edge Platform: Performance Evaluation of Supervision and Control Communication

Edge computing allows for data processing at reduced latency since the computational power is moved close to the data sources. Traditionally, edge computing has been often used in industrial scenarios for implementing gateways between the operational technology (OT) world and the IT (cloud) world. Recently, big manufacturers of industrial programmable logic controller (PLC) started promoting the use of containerized virtual PLC (vPLC) hosted inside edge computing platforms. They foresee an innovative integration of container based applications, including automation control, with all the data-centric services and applications already available for edge ecosystems. Even if a clear advantage from the scalability and maintainability could be expected, would vPLCs meet the stringent requirements of industrial automation? This article is part of a multistage research work, and as a first step, it is focused on the evaluation of the performance of vPLC when exchanging data with other machines, controllers, supervisors, and data acquisition systems in a machine-to-machine (M2M) scenario. After a brief overview of the involved technology, the design of a methodology for comparing real PLC and vPLC is described. Then, performance metrics, and an experimental setup for the evaluation of existing devices are defined taking care of the sources of uncertainty. The effectiveness of the proposed methodology is demonstrated by considering a real use case. Through the use of the suggested methodology, important insights into the use case are revealed: for instance, the considered vPLC could work as fast as a real PLC with minimum communication latency in the order of 3 ms but, currently, there is a random delay with an average of 50 ms whose source has been identified to be the IP stack implementation of the vPLC. Finally, the proposed methodology allows for the creation and validation of analytical models of the use case.