Sensor circuit

Abstract

The invention relates to a sensor circuit (1) for monitoring the electric line of a sensor conductor (S), comprising: - an RFID transponder (2) having a first antenna input (AP), a second antenna input (AN) and a measuring input (IN) for measuring a voltage or a current, and designed to output by radio the state measured at the measuring input (IN), - two sensor connections (S1, S2) which are designed to be connected to a sensor conductor (S), the first sensor connection (S1) being connected to the first antenna input (AP) and the second sensor connection (S2) being connected to the measuring input (IN), - a semiconductor module (D1) with a blocking direction and a passage direction, which is connected to the second antenna input (AN) and to the measuring input (IN) and blocks currents from the measuring input (IN) to the second antenna input (AN). The invention further relates to a device having such a sensor circuit and to a method for monitoring.

Description

[0001] Sensor circuit

[0002] The invention relates to a sensor circuit for monitoring the electrical conduction of a sensor wire, in particular for structural monitoring of an object, a device with a planar component and such a sensor circuit, and a method for operating such a sensor circuit.

[0003] Structural monitoring of objects is beneficial or necessary in many areas of daily life. Structural monitoring refers to monitoring the integrity of an extended component of a device. This essentially means monitoring the structural integrity of the device. For example, it is sometimes necessary to monitor a rope or thread so that a crack can be detected as quickly as possible. However, monitoring is not only desired for longitudinally extended components, but also for those with a large surface area.

[0004] An example of this is a fishing net. This includes both nets used to catch fish, such as fishing nets, and nets designed to keep fish in a specific area, such as those used in fish farms. These nets are typically made of many threads intertwined in a web-like pattern using warps and wefts. If one of these threads breaks, the net has a hole there. If several threads break in one area, the hole can become so large that fish can escape from the net.

[0005] Currently, net monitoring is done visually or manually. The net is removed from the water and viewed, or inspected underwater.

[0006] A quick automated check is not yet possible.

[0007] The object of the invention was to overcome the disadvantages of the prior art and to provide a sensor circuit and a method for the automated monitoring of a longitudinally or planarly extended object, which achieves optimal monitoring with a minimum of effort.

[0008] This object is achieved by a sensor circuit according to claim 1, a device according to claim 8 and a method according to claim 10. A sensor circuit according to the invention serves to monitor the electrical conduction of a sensor conductor and comprises the following components:

[0009] - an RFID transponder with a first antenna input, a second antenna input and a measuring input for measuring a voltage or a current, and designed to output the state measured at the measuring input by radio,

[0010] - two sensor terminals designed to be connected to a sensor conductor (e.g. a wire or a stranded wire), the first sensor terminal being connected to the first antenna input and the second sensor terminal being connected to the measuring input,

[0011] - a semiconductor device with a reverse direction and a forward direction, which is connected to the second antenna input (AN) and the measuring input (IN), and blocks currents from the measuring input to the second antenna input.

[0012] RFID transponders are widely known in the state of the art. RFID (radiofrequency identification) refers to a technology for transmitter-receiver systems for automatic and contactless data exchange in the near-field and far-field ranges, particularly with UHF RFID.

[0013] An RFID transponder typically consists of a microchip (often in the millimeter range) and an antenna system. Passive transponders do not require a power source, as the power can be supplied externally via the antenna system by an RFID reader.

[0014] The coupling of an RFID transponder with an RFID reader occurs via alternating magnetic fields generated by the RFID reader within a short range or via high-frequency radio waves, which not only transmit data but can also supply the transponder with energy. The RFID reader contains software that controls the actual reading process. Communication between transponders and RFID readers usually takes place within a defined frequency range, which is often subject to regional regulations. Particularly advantageous frequency ranges for the invention are "very high frequencies" (UHF, 300 MHz - 3 GHz), which can have a considerable range. When transmitting data, the RFID transponder usually first transmits its serial number (UID) and, if necessary, further data (UID) using load modulation, meaning it consumes part of the energy of the alternating field. The RFID reader can detect this.

[0015] An RFID transponder suitable for the invention has, in addition to the antenna inputs, a measurement input designed for measuring a voltage or current. Furthermore, the RFID transponder is designed to wirelessly output the state measured at the measurement input (to an RFID reader). The aforementioned "additional data" thus includes data on the state measured at the measurement input. This can be in the form of a data word (e.g., when using an analog-to-digital converter (ADC)) or simply a set bit (e.g., when using a comparator).

[0016] This RFID transponder is wired in a special way so that a signal that hits an antenna connected to the antenna terminals is used not only to read the RFID transponder but also to stimulate the measurement input.

[0017] It should be noted that the circuit described here merely represents the functional heart of a monitoring device. Monitoring is possible after supplementing the sensor circuit with an antenna and a sensor conductor (which could then be referred to as a "monitoring device"). However, these two components are variable or interchangeable and can certainly be part of another object. The antenna is connected to the antenna inputs, and the sensor conductor to the sensor terminals. The sensor terminals are therefore designed to be connected to the sensor conductor (e.g., a wire or stranded conductor).

[0018] The first sensor connection is connected to the first antenna input, and the second sensor connection to the measurement input. If a sensor wire is connected to the sensor connections, the first antenna input would be connected to the measurement input through the sensor wire (possibly via the electronic components connected to it).

[0019] In addition to this connection, the sensor circuit also includes a semiconductor component with a reverse direction and a forward direction, e.g., a diode or a transistor connected to the second antenna input and the measurement input, which blocks currents from the measurement input to the second antenna input. A diode, for example, would be connected with its anode to the second antenna input and with its cathode to the measurement input. This semiconductor component ensures that currents can flow from the second antenna input to the measurement input and blocks currents in the opposite direction. The semiconductor component preferably also serves to regulate the voltage and is particularly designed as a Zener diode.

[0020] It should be noted that "connected" in this application always means "conductively connected for alternating currents" or "connected." This can be a capacitive coupling, which is particularly practical for the RFID transponder. However, an electrically conductive connection, i.e., a directly conductive (possibly metallic) connection, is preferred (at least for the other components).

[0021] The basic principle of the invention is based on the fact that energy is constantly being transferred when an RFID reader reads the RFID transponder. A portion of this energy, which is "received" via the antenna and applied to the antenna inputs, is then diverted via the sensor cable and fed to the measuring input of the RFID transponder. This causes the measuring input to change its state, which can be queried wirelessly. If the sensor cable is damaged, no change in state is detected. It is preferable to read the RFID transponder multiple times, as it can sometimes take some time for a change in state to occur or be registered.

[0022] A device according to the invention has an object to be structurally monitored. This object is, in particular, longitudinally extended like a rope or flat like a plate or a net. For monitoring purposes, the device comprises a sensor circuit according to the invention with a sensor conductor, the ends of which are preferably already connected to the sensor terminals, and an antenna connected to the two antenna inputs, thus essentially preferably a monitoring device. The sensor conductor is arranged in or on the object to be monitored, preferably in such a way that in the event of structural damage to the object, the sensor conductor is severed in the area of ​​the damage.This means that it is not loosely attached to the object, where it could fall off if damaged, but rather that it is attached to the object in such a way that if a force acts in the area of ​​the sensor conductor that could damage the object, this force is sufficient to also damage the sensor conductor there. If the sensor conductor is severed, this can be detected by the sensor circuit during its readout.

[0023] The object to be monitored is preferably designed as a net, particularly preferably as a fishing net (a net for catching or keeping fish), with the sensor conductor being attached to the threads of the net and spanning a surface area of ​​the net. However, the sensor conductor can also be part of a thread of the net, in particular the warp and / or the weft. The device preferably comprises several sensor circuits (or monitoring devices). Alternatively or additionally, the sensor lines of several threads of the net can form a series circuit.

[0024] The object to be monitored is preferably designed as a fence, in particular as a wire fence, with the sensor conductor being attached to the fence or formed from a wire of a fence, and spanning a surface area of ​​the fence. The device preferably comprises several sensor circuits (or monitoring devices). Alternatively or additionally, the sensor lines of several wires of the fence can form a series circuit, but should be insulated on their outer surfaces.

[0025] A preferred object for monitoring can also be a building, a vehicle, a road, or an aircraft. Basically, the invention is advantageous for any object whose structure can (and should) be monitored in some way. The object comprises a number of sensor lines that are attached to or in the object, in particular in the region of a structural weakening line of the object. Particularly preferably, they span this weakening line, in particular transversely or meandering along the course of the weakening line. The object is in particular designed as a conveyor belt, and at least one of the devices is arranged in or on the object such that its sensor path runs essentially transversely to the length of the object (e.g., conveyor belt), wherein the device is preferably surrounded by material of the object (e.g., conveyor belt). However, an expansion joint of a bridge could also be monitored in this way.

[0026] Another preferred object is a wind turbine for energy generation. Here, an RFID reader can be attached to a static component near the rotor blades, e.g., on the mast or nacelle. A number of sensor circuits are mounted in a rotor blade to be monitored, with sensor wires running across the length and / or width of the rotor blade. The number of antennas for the number of sensor circuits should be located where the reader can supply them with power and read the RFID transponders.

[0027] A monitoring system according to the invention for structural monitoring of an object comprises a monitoring device, an RFID reader and an object to be monitored with a number of sensor wires (in or on the object).

[0028] A method according to the invention for operating a sensor circuit according to the invention with a sensor wire and an antenna (i.e. a monitoring device) comprises the following steps:

[0029] - generating an electromagnetic wave with a predetermined reading frequency of the RFID transponder with a predetermined minimum power, preferably by means of an RFID reader,

[0030] - Reading the RFID transponder of the sensor circuit using an RFID reader, whereby information about the state measured at the measuring input is read out.

[0031] The information about the state measured at the measurement input essentially directly indicates whether the sensor wire is intact or not (this would be interpreted as damage to an object being monitored). This information, which could essentially be a single bit (voltage yes / no), can then be output or used to control an alarm device or system. However, it should be noted that it can take several milliseconds for the measurement input to indicate a change in state. Therefore, it is preferable to perform multiple readouts and assume an intact sensor wire if a corresponding state has been indicated at least once.

[0032] For example, the information can simply be stored in a data set and used later for evaluation. An alarm can also be issued if a structural change (e.g., a crack) has occurred. In addition to or as an alternative to a warning, a process can be halted, e.g., a conveyor belt can be stopped or a wind turbine with devices in its rotor blades can be shut down in a controlled manner (in the form of an emergency stop) if one of the devices indicates a crack (due to its failure). The process can therefore include the following additional step:

[0033] - Control of a process and / or an alarm system based on the information and / or output of the information, in particular on a display device and / or to a storage device. Cracks in a road, for example, can be easily detected by driving along the road with a vehicle with an RFID reader attached to the bottom. A bridge can have a monitoring device at its expansion joint, with the sensor conductor extending across the expansion joint.

[0034] However, the integrity of a load can also be checked wirelessly. For example, elements could be equipped with contact surfaces that, when correctly positioned, connect to sensor terminals of a sensor circuit. If an element is missing or incorrectly positioned, this would be detected. For example, this could be used to monitor the placement of life jackets on seats in an airplane.

[0035] Preferably, an additional transmitter generates a further electromagnetic wave outside the readout frequency to operate the RFID transponder. This second wave should be radiated in addition to the above-mentioned electromagnetic wave (first wave) and, in particular, should strike the sensor wire. This provides the RFID transponder with additional energy that can be used for measurement. The frequency of the second wave should lie outside the readout frequency, which means that the frequencies of the first and second waves (including their widths) do not touch in the frequency domain. The (average) frequency of the second wave can certainly deviate by one or more orders of magnitude from the (average) frequency of the first wave, since the second wave is not used for readout. The (average) frequency of the second wave is preferably lower than that of the first wave, preferably lower than 10% of the first wave, in particular lower than 5% of the first wave.For example, with a readout frequency of 900 MHz, the frequency of the second wave can be around 10 MHz.

[0036] Further particularly advantageous embodiments and developments of the invention emerge from the dependent claims and the following description, wherein the patent claims of a certain category can also be developed according to the dependent claims of another category and features of different embodiments can be combined to form new embodiments.

[0037] A preferred sensor circuit comprises a first matching unit between the two antenna inputs and a second matching unit between the second antenna input and the measurement input. These matching units serve to match the signals picked up by the antenna in the sensor conductor and preferably comprise an inductance, in particular a parallel circuit comprising an inductance and a capacitor. The two matching units are tuned to one another in such a way that, for a predetermined signal at the antenna terminals with the readout frequency of the RFID transponder, in particular a carrier frequency or a sine wave, a maximum signal reaches the measurement input. This can be achieved, for example, by changing the values ​​of both matching units while simultaneously measuring the signal at the measurement input.If a suitable matching of the matching units has been achieved for a configuration consisting of sensor circuit, sensor conductor and antenna, this can be used for identical monitoring devices.

[0038] A preferred sensor circuit comprises a diode, which is connected by its anode, in particular via a second matching unit, to the first antenna input, and by its cathode to the first sensor terminal. This diode serves to select a positive half-wave for the measurement input. As an alternative to this diode, any semiconductor can be used, e.g., a transistor or a FET.

[0039] According to a preferred sensor circuit, the semiconductor component is a diode, preferably a Zener diode, which is connected with its anode to the second antenna input and with its cathode to the measuring input. As an alternative to this diode, any semiconductor can basically be used, e.g. a transistor or a FET. Preferably, an LED is used instead of or in addition to the Zener diode. This is connected with its anode to the measuring input and with its cathode to the second antenna input. Due to the generally low voltages and currents, it is preferable to operate the LED without a series resistor. The LED has the advantage that RFID transponders, which operate with low voltages, can be effectively protected from excessive power, since in this case part of the power is consumed by the LED lighting. For example, the operating voltage of an infrared LED is typically between 1.2 and 1.8 V (typ.1.3 V), a red LED between 1.6 and 2.2 V, a yellow or green LED between 1.9 and 2.5 V and a UV LED between 3.1 and 4.5 V. If the desired operating voltage for the RFID transponder is 1.8 volts, a red LED with an operating voltage of 1.8 V could be suitable, for example.

[0040] The semiconductor component is preferably connected in parallel with a capacitor, whereby the capacitor is preferably dimensioned such that its charging time is less than 10 ms. The charging time depends on the current flowing into the capacitor and thus on the induced current and the resistance in front of the capacitor. The capacitor serves to smooth the signal at the measuring input. It should not be too large so that a signal is available at the measuring input as quickly as possible at the low induced currents. Therefore, the capacitance of the capacitor should preferably be less than 100 nF, in particular less than 50 nF, even more preferably no more than 20 nF, or in special cases in particular no more than 1 nF. The capacitance is preferably greater than 10 pF, in particular greater than 100 pF. A good value in practice could be 10 nF.

[0041] The semiconductor component is preferably connected in series with a resistor, in particular an ohmic resistor, between the second sensor terminal and the second antenna input. The resistor is preferably connected to the second sensor terminal and the measurement input. In a series connection, the measurement input would therefore be a tap between the resistor and the semiconductor component. It should be noted that the resistor would be connected in series with a sensor conductor. It should therefore be selected taking into account the resistance of the sensor conductor.

[0042] The semiconductor component is preferably connected in parallel with a nonreactive resistor, preferably together with the aforementioned capacitor. This serves to compensate for currents that could flow parallel to the sensor conductor between the sensor terminals due to a conductive environment, e.g., salt water. However, the resistor should be relatively large so that the currents flowing through the resistor do not become excessive. The resistance value should preferably be greater than 1 kΩ, preferably greater than 10 kΩ, or even greater than 100 kΩ.

[0043] A preferred sensor circuit comprises an antenna connected to the two antenna inputs, preferably a dipole antenna.

[0044] The second antenna input is preferably connected to the internal GND (ground) of the RFID transponder.

[0045] According to a preferred sensor circuit, the measuring input comprises an ADC or a discriminator, thus being able to represent voltages or currents in numerical values ​​or at least in bit information. The measuring input is preferably designed to detect a (particularly positive) voltage or current. The RFID transponder is preferably designed to output the detected voltage or current in the form of a digital data set (e.g., data word or bit). It is preferred that the measuring input is designed to determine whether a voltage or current at the measuring input lies within a signal value range and, in this case, generates a data word from the RFID transponder or at least sets a bit that can be read wirelessly from the RFID transponder.

[0046] A preferred sensor circuit comprises a sensor conductor whose ends are connected to the sensor terminals. The sensor conductor is preferably longer than 5 cm, in particular longer than 50 cm, preferably longer than 1 m, in particular longer than 10 m.

[0047] In practice, however, it should be noted that every conductor has a resistance, and the surrounding medium can also exhibit resistance. For example, when monitoring a fishing net, a tear in the sensor conductor would not completely interrupt the current flow through the sensor conductor, as a (small) portion of the current can still flow through the seawater. Although the resistivity of seawater is significantly greater than that of the sensor conductor, a measurable current could still flow at the tear due to the small distances between the ends of the sensor conductor.It is therefore preferred that the sensor circuit, based on a predetermined "operating resistance" and a larger predetermined "defective resistance", is set or can be set so that a voltage at the measuring input lies within the signal value range when the sensor line has the operating resistance and lies outside the signal value range when the sensor line has at least the defective resistance. The special wiring of the sensor circuit, which results in part of the received energy being able to flow as current through the sensor wire, means that even with small resistances a decision can be made as to whether a voltage lies within the signal value range or not (since the voltage is sufficiently large). The defective resistance is preferably less than 1 kΩ, in particular less than 100 Ω or even less than 50 Ω, but always greater than the operating resistance, preferably more than 10 Ω greater, in particular more than 50 Ω greater.

[0048] The sensor conductor is preferably designed as a double line, the ends of which are connected to one another and are remote from the sensor connections. Such a sensor conductor can be easily arranged in an object without having to worry about reconnecting the end of the sensor conductor. The sensor circuit is preferably designed so that the measuring input also serves as an input for an external voltage source to improve the signal from the RFID transponder. RFID transponders exist with a voltage input that is designed for an external power supply (often connected to the second antenna input). It is particularly preferred that the state of this voltage input is measured simultaneously in the RFID transponder and can be queried wirelessly. If the measuring input and voltage input are separate in an RFID transponder, it is preferred that these two are connected to one another in the sensor circuit.In this way, the energy of the RFID reader captured by an antenna can be used to additionally amplify the signal of the RFID transponder.

[0049] Since objects can be subject to wear and tear in addition to destruction, it is advantageous to embed multiple sensor conductors at different distances from the object's surface. However, it is also possible to arrange the sensor conductors of different monitoring devices one above the other. If the surface is worn, the sensor conductors closest to that surface will be destroyed first, indicating wear.

[0050] The invention is explained in more detail below with reference to the accompanying figures using exemplary embodiments. In the various figures, identical components are provided with identical reference numerals. The figures are generally not to scale. They show:

[0051] Figure 1 shows an example of a sensor circuit according to the invention,

[0052] Figure 2 shows an example of a monitoring device according to the invention,

[0053] Figure 3 shows an example of a sensor conductor as a double line,

[0054] Figure 4 shows an example of a device according to the invention and an application example of a method according to the invention,

[0055] Figure 5 shows another example of a monitoring device according to the invention,

[0056] Figure 6 shows an example of a device according to the invention in a conveyor belt. Figure 1 shows an example of a sensor circuit 1 according to the invention for monitoring the electrical conduction of a sensor conductor S. This sensor conductor is shown here in dashed lines with a switch, which is intended to indicate that the sensor conductor is normally intact and that its severance indicates a defect in the monitored object.

[0057] The sensor circuit comprises an RFID transponder 2 with a first antenna input AP, a second antenna input AN, and a measurement input IN. In this example, the measurement input IN is an input to which an additional voltage (VDD) can be applied against the second antenna input AN (GND) to increase the transmission power of the RFID transponder 2. It is also designed to measure whether a voltage is present there. If a voltage is present, a bit is set in a register. This register can be output when the RFID transponder is read, allowing it to be wirelessly checked whether a voltage is present at the measurement input IN.

[0058] The sensor conductor S, e.g. a wire or a stranded wire, is connected to two sensor terminals S1, S2. These, in turn, are connected to the antenna inputs AP, AN and the measuring input IN by means of electronic components in such a way that the electromagnetic wave used for reading by an RFID reader F (see, for example, Figure 4), with the readout frequency of the RFID transponder, is present at the measuring input as a voltage. The energy of the wave can thus be used both to increase the transmission power of the RFID transponder and to determine the structural integrity of the sensor conductor. If the sensor conductor S is intact, then when interrogated by an RFID reader F, the RFID transponder 2 sends a strong signal indicating that the bit is set. If the sensor conductor S is defective (as indicated here by the open switch), then the RFID transponder 2 sends a signal indicating that the bit is not set.

[0059] The sensor circuit 1 comprises the following components: A Zener diode D1 as a semiconductor component D1 , which is connected with its anode to the second antenna input AN and with its cathode to the measuring input IN. Its blocking direction is therefore directed towards the measuring input IN and thus limits the maximum voltage at the measuring input. Its breakdown voltage should be dimensioned so that it is slightly below the maximum permissible voltage of the measuring input IN. The Zener diode D1 is connected in parallel with a capacitor C, which serves to smooth the received wave. This circuit is in turn connected in series with an ohmic resistor R, which is connected to the second sensor connection S2 and the measuring input IN. The measuring input IN is therefore located as a tap between resistor R and the cathode of the Zener diode D1.

[0060] The first sensor terminal S1 is connected to the first antenna input AP via a coil and a diode D2. The diode selects a positive half-wave of the alternating current induced at the antenna inputs AP, AN. The coil serves as inductor L2, together with another inductor L1 between the antenna inputs AP, AN, to maximize the signal at the measurement input IN. More complex matching units L1, L2 can also be used instead of the coils. It is difficult to specify specific values ​​or ratios for the coils, as this depends on the components in the circuit. In this case, it is advantageous to adjust the best values ​​on a test setup by changing the coil parameters.

[0061] Figure 2 shows an example of a monitoring device 3 according to the invention with a sensor circuit 2, an antenna A and a sensor conductor S. The sensor circuit 2 is located on a circuit board, to whose terminals the antenna A and the sensor conductor are soldered. In this example, insulators have been melted around the individual conductors, which can be seen as thickened portions in recesses of the circuit board. This advantageously serves as strain relief, although the structure can also be additionally cast in synthetic resin. The sensor conductor S is located in a flat object N and monitors its structural integrity. If the object N is damaged anywhere, the sensor conductor S will also be damaged at that point, and when the monitoring device 3 reads the data, corresponding information is output.

[0062] Figure 3 shows an example of a sensor conductor S as a double line. This is connected on one side to the sensor terminals S1, S2 of a sensor circuit 1, and on the other side, the two lines are interconnected, forming a closed loop. Such a double line can be installed very easily within an object N.

[0063] Figure 4 shows an example of a device 4 according to the invention and an example of a method according to the invention. The object N to be structurally monitored is designed here as a fishing net N, wherein the sensor conductor S is attached to the threads of the net and spans a surface area of ​​the net. Alternatively, it could also be part of the threads of the net, e.g., woven into the threads as an insulated wire, which are then linked to form the net. The antenna A of the monitoring device 3 (i.e., sensor circuit 1, antenna A, and sensor conductor S) is arranged here at the edge of the fishing net N and is currently being read by a ship. This ship has a radio mast F with an RFID reader F and is currently transmitting radio waves at the readout frequency of the RFID transponder 2 of the sensor circuit 1.These radio waves are picked up by antenna A and generate a current in the sensor circuit, which, through the closed sensor conductor S, results in a voltage at the measuring input IN of RFID transponder 2. The information regarding the presence of this voltage is read out as the ship passes by. This can be read out multiple times, as it may take some time for the voltage to be present at the measuring input IN.

[0064] The reading is carried out by generating an electromagnetic wave with a predetermined reading frequency of the RFID transponder 2 with a predetermined minimum power, preferably by means of an RFID reader F and reading the RFID transponder 2 of the sensor circuit 1 by means of an RFID reader F, wherein information about the state measured at the measuring input IN is read out.

[0065] Figure 5 shows a further example of a monitoring device 3 according to the invention comprising sensor circuit 1, antenna A and sensor conductor S, which is accommodated in a buoy B.

[0066] Figure 6 shows an example of a monitoring device (3) according to the invention in a conveyor belt (5). Here, the sensor conductor S runs in a meandering fashion through the conveyor belt (5) and is connected to a sensor circuit 1 with antenna A. Only a portion of the conveyor belt (5) is shown. It can comprise a plurality of such monitoring devices 3 and be several meters or even several hundred meters long.

[0067] Finally, it should be noted once again that the devices described in detail above are merely exemplary embodiments that can be modified in a variety of ways by a person skilled in the art without departing from the scope of the invention. Furthermore, the use of the indefinite articles "a" or "an" does not exclude the possibility that the features in question may be present multiple times. Likewise, terms such as "element" or "device" do not exclude the possibility that these may consist of multiple, possibly spatially separated, subunits. The expression "a number" is to be understood as meaning that the number is greater than zero (i.e., as "at least one").

[0068] List of reference symbols

[0069] 1 sensor circuit

[0070] 2 RFID transponders

[0071] 3 Monitoring device

[0072] 4 Device

[0073] 5 Conveyor belt

[0074] A antenna

[0075] ON antenna input

[0076] AP antenna input

[0077] B Buoy

[0078] D1 Zener diode / semiconductor component

[0079] D2 diode

[0080] C capacity

[0081] F Radio mast / RFID reader

[0082] IN measuring input

[0083] L1, L2 inductance / matching unit

[0084] N Object / Fishnet

[0085] R resistance

[0086] S sensor wire

[0087] S1, S2 sensor connection

Claims

Patent claims 1. Sensor circuit (1) for monitoring the electrical conduction of a sensor conductor (S), comprising: - an RFID transponder (2) with a first antenna input (AP), a second antenna input (AN) and a measuring input (IN) for measuring a voltage or a current, and designed to output the state measured at the measuring input (IN) by radio, - two sensor terminals (S1, S2) designed to be connected to a sensor conductor (S), wherein the first sensor terminal (S1) is connected to the first antenna input (AP) and the second sensor terminal (S2) is connected to the measuring input (IN), - a semiconductor component (D1) having a blocking direction and a forward direction, which is connected to the second antenna input (AN) and the measuring input (IN), and blocks currents from the measuring input (IN) to the second antenna input (AN).

2. Sensor circuit according to claim 1, comprising a first adaptation unit (L1) between the two antenna inputs (AP, AN) and a second adaptation unit (L2) between the second antenna input (AN) and the measuring input (IN), wherein the two adaptation units (L1, L2) have been coordinated with one another in such a way that, with a predetermined signal at the antenna connections (AP, AN) with the readout frequency of the RFID transponder (2), a maximum signal reaches the measuring input (IN), preferably wherein an adaptation unit (L1, L2) comprises an inductance (L1, L2), in particular a parallel circuit comprising an inductance (L1, L2) and a capacitor.

3. Sensor circuit according to one of the preceding claims, comprising a diode (D2) which is connected with its anode, in particular via a second matching unit (L2), to the first antenna input (AP) and with its cathode to the first sensor terminal (S1).

4. Sensor circuit according to one of the preceding claims, characterized in that the semiconductor component (D1) - a diode which is connected with its anode to the second antenna input (AN) and with its cathode to the measuring input (IN), preferably wherein the diode is a Z-diode (D1) and / or - a light-emitting diode which is connected with its cathode to the second antenna input (AN) and with its anode to the measuring input (IN) and / or - is connected in parallel with a capacitor (C) having a capacity of less than 100 nF, and / or - is connected in parallel with an ohmic resistor having a resistance value greater than 1 kΩ, and / or - is connected in series with a, in particular ohmic, resistor (R) between the second sensor terminal (S2) and the second antenna input (AN), wherein the resistor (R) is preferably connected to the second sensor terminal (S2) and the measuring input (IN).

5. Sensor circuit according to one of the preceding claims, comprising an antenna (A) connected to the two antenna inputs (AN, AP), preferably a dipole antenna.

6. Sensor circuit according to one of the preceding claims, characterized in that the measuring input (IN) comprises an ADC or a discriminator and is designed to detect a positive voltage or a current and the RFID transponder (2) is designed to output a detected voltage or a detected current in the form of a digital data set, preferably wherein the measuring input (IN) is designed to determine whether a voltage or a current at the measuring input (IN) lies in a signal value range and, in this case, generates a data word from the RFID transponder (2) or at least sets a bit which can be read out from the RFID transponder (2) by radio.

7. Sensor circuit according to one of the preceding claims, comprising a sensor conductor (S), the ends of which are connected to the sensor terminals (S1, S2), preferably wherein the sensor conductor (S) is longer than 5 cm, preferably longer than 1 m, in particular longer than 10 m, preferably wherein the sensor conductor (S) is designed as a double line, the ends of which are remote from the sensor terminals (S1, S2) are connected to one another.

8. Device with an object (N) to be structurally monitored, the device comprising a sensor circuit (1) according to one of claims 1 to 7 and an antenna (A) which is connected to the two antenna inputs (AP, AN), as well as a sensor conductor (S), wherein the sensor conductor (S) is in or on the object (N) to be monitored is arranged so that in the event of structural damage to the object (N), the sensor conductor (S) is severed in the area of the damage.

9. Device (3) according to claim 8, characterized in that the object to be monitored (N) is designed as a belt, in particular as a conveyor belt (5), into which at least the sensor conductor (S) is embedded and spans a surface area of the belt, or is designed as a net, preferably as a fishing net (N), wherein the sensor conductor (S) is attached to the threads of the net and spans a surface area of the net and / or wherein the sensor conductor (S) is part of a thread of the net, in particular the warp and / or the weft, preferably wherein the device (3) comprises a plurality of sensor circuits (1) according to claim 7 and / or the sensor lines (S) of a plurality of threads of the net form a series circuit.

10. A method for operating a sensor circuit (1) according to claim 7 with an antenna (A) connected to the two antenna inputs (AN, AP), comprising the steps: - generating an electromagnetic wave with a predetermined reading frequency of the RFID transponder (2) with a predetermined minimum power, preferably by means of an RFID reader (F), preferably wherein a further electromagnetic wave for operating the RFID transponder (2) is generated by means of an additional transmitter outside the reading frequency, - Reading the RFID transponder (2) of the sensor circuit (1) by means of an RFID reader (F), wherein information about the state measured at the measuring input (IN) is read out.

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