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36 Elektronik International 2020 Sensors energy budget of a sensor the smaller the possible distance between a reader and RFID tags Extra to the existing infrastructure an advantage of using RFID is that wireless and passive i e batteryless sensors can be created and used in surroundings that are difficult of access or rough and tough An application where both are the case is switchgear Measuring temperature in switchgear The state of switchgear cannot be determined alone by the parameter current What says more is heating up of the conductor rails especially at the screwed joins Current flow may be the source of the heating up but the development of heat in switchgear depends on a whole number of other factors such as ambient temperature conditions of setting up and ventilation and circulation inside the switchgear The insurers of switchgear recommend annual thermographic examination for early tracing of potential dangers and avoidance of production outages This process can nevertheless present drawbacks switchgear is frequently located where it is very inaccessible And precisely the screwed connections of interest are difficult to reach for thermographic measurement Measurement is often made dangerously close to live parts because shutting down could falsify results What is more thermography is a single examination calling for a high degree of analytic experience to draw the right conclusions Passive sensor technology allows continuous monitoring which is an advantage for this application The Fraunhofer IPMS has developed a system that enables direct temperature measurement at different contact points of switchgear Figure 1 This is not possible by cabled sensors They could not be brought directly near the wanted point of measurement because of the high voltage on the conductor rails Direct measurement uses RFID sensors operating in the UHF band The condition monitoring system Figure 2 allows permanent supervision of the contact points showing temperature heatmap and temperature over time Operation in metallic surroundings Passive UHF sensor technology presents special demands as regards arrangement and orientation of the RFID tags and the antennas of the reader The electromagnetic field radiFigure 2 Several RFID temperature sensors interconnected to form a condition monitoring system producing a live thermal image of the switchgear photo Fraunhofer IPMS