In the paper, we share our research results and experiences with the redundant virtual sensors. The main focus is paid on the creation of the model for redundant virtual sensors, applying the concept of "digital twins" that are associated with physical sensors. Virtual sensor can be implemented as a software instance in Cloud (SaS) or physical device via Edge computing. The goal is to create a common model which would enable a generic approach independently on vendors' implementation. MQTT protocol was selected as the main integration platform that is supported by various IoT devices and mainly sensors. To enable feasible implementation of a redundant sensor, Edge computing is used as a platform to host digital twins for physical devices. The redundant sensors can be applied for variety fail-safe applications, such control systems of tunnels.
Applications of safety-related control systems demand reliable and credible inputs from physical sensors, therefore there is a need to extend their capabilities to provide a validated input with high availability. Our main idea is to insert virtual sensors between physical sensors and the control system’s logic. The created solution can validate the values of real sensors and with the use of multiple virtual sensors we can achieve high availability in addition, therefore our solution is entitled as a virtual redundant sensor. It works by the digital twin’s concept and uses fusion function to calculate validated results. The fusion function is used to transform the measured values from the physical sensors according to designed numerical models. The selection of a numerical model with assigned fusion functions can be performed via the WEB-based graphical user interface. Proposal of the numerical model is created and validated on the experimental workplace with emulation of physical sensors and MQTT integration (smart IoT sensors). The results of testing have shown that our solution can be applied to validate the values of physical sensors. Proposed fusion functions calculated results according to the selected model in all cases, while non-standard cases were handled according to our definition. In addition, the high availability concept with a group of two virtual sensors has proven fast recovery and availability of results for safety-related applications as well.
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