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International 2020 Elektronik 35 Sensors Predictive maintenance is a bonus if it receives data and there is a high degree of automation in how data is measured and captured What it amounts to is permanently supervising the condition of machines or plant and optimizing maintenance based on the findings For that purpose measured data must be identifiable and collected automatically RFID sensors combine identification with the capture of measured data Furthermore they set up on an existing tried and tested infrastructure Components of an RFID system RFID radiofrequency identification is a wireless technology enabling automatic identification of objects For that reason it is often called an auto ID technology The components of such a system consist of RFID tags readers and middleware to drive and read out the results An RFID tag is frequently also called a transponder a combination of transmitter and responder Upon entry into the field of the reader the tag reacts responds by automatically sending i e transmitting identification data Data held in or stored by an RFID tag is read out by means of magnetic or electromagnetic waves This transponder consists of an integrated circuit and an antenna The antenna is what primarily determines the size of a tag and is usually designed for different ambient conditions underground surrounding medium installed situation The aim is to optimize the reading distance or transmission Basically the reading range is greater the larger the antenna Range is maximized by an integrated battery Such systems are called active RFID Passive systems draw the operating energy of the transponder solely from the field of the reader The performance of a system will depend extra to the antenna of the tag and battery support on the selected frequency band Reading distance the influence of disturbing factors and transmission are the major parameters affected by this Table 1 Three frequency bands come into question ➔ LF low frequency 125 kHz ➔ HF high frequency 13 56 MHz ➔ UHF ultra high frequency 868 or 915 MHz Acomplete system extra to hardware components also consists of software or the socalled middleware This provides a connection between the hardware and higherlevel software systems like MES manufacturing execution system and ERP enterprise resource planning determines which data comes from which transponder and reads this out by matching mechanisms Hardware differs depending on the producer by frequency band the protocols used and interfaces In practice there are a large number of different RFID components which often makes system integration complex and can lead to dependence on a single producer source Measuring condition data by RFID sensors Information won by RFID can form a foundation for IoT and Industry 4 0 applications in many ways the major aspect is the unique identification of objects like machines components equipment or tools Enabling such objects to fulfill tasks as part of Industry 4 0 they must be able to communicate automatically Acombination with sensor technology shows the way to further areas of Industry 4 0 application especially a predictive maintenance scenario Information can thus be expanded to data indicating a condition like temperature humidity shock and vibration and so on The operator thus obtains insight deeper knowledge into the state of their equipment Special RFID circuits can be connected to sensors In this way it is possible in addition to identification data to determine and transfer the condition data of an object at the same time RFID circuits for sensors But conventional RFID transponder circuits do not allow the connection of sensors without more ado Special circuits have to be created that support the standard RFID protocol on the one hand and that also provide interfaces for sensor elements or modules Analog interfaces are suitable for connecting resistive inductive and capacitive sensors Digital interfaces such as I²Cor SPI very much simplify integration for the user and expand functionality For example in addition to generating measured values other settings like different operating modes of a sensor can be varied Batteryless sensors For passive systems the choice of sensors to be integrated should consider in particular the energy demand of a sensor because the energy for measurement and transmission is drawn solely from the field of the reader The bigger the Figure 1 Passive RFID temperature sensor on a screwed join in switchgear photo Fraunhofer IPMS 125 kHz LF 13 56 MHz HF 860960 MHz UHF Typical reading range up to 1 m up to 1 5 m up to 10 m Coupling inductive inductive electromagnetic Metal effect mean high high Water effect none low high Typical application animal identification access control logistics and transportation Table 1 Features of RFID technology by frequency band source Fraunhofer IPMS