DE102023132477A1 - Sensor circuit - Google Patents

Abstract

The invention relates to a 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 device (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).
The invention further relates to a device with such a sensor circuit and a method for monitoring.

Description

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.

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 tear 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.

One 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 will have a hole there. If several threads break in one area, the hole can become so large that fish can escape from the net.

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

A quick automated check is not yet possible.

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 areally extended object, which achieves optimal monitoring with a minimum of effort.

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.

• - einen RFID-Transponder mit einem ersten Antenneneingang, einem zweiten Antenneneingang und einem Messeingang zum Messen einer Spannung oder eines Stroms, und dazu ausgelegt den am Messeingang gemessenen Zustand per Funk auszugeben,
• - zwei Sensoranschlüsse, die dazu ausgelegt sind, mit einem Sensorleiter (z.B. einem Draht oder einer Litze) verbunden zu werden, wobei der erste Sensoranschluss mit dem ersten Antenneneingang verbunden ist und der zweite Sensoranschluss mit dem Messeingang verbunden ist,
• - ein Halbleiterbaustein mit einer Sperrrichtung und einer Durchlassrichtung, der mit dem zweiten Antenneneingang (AN) und dem Messeingang (IN) verbunden ist, und Ströme vom Messeingang zum zweiten Antenneneingang sperrt.

A sensor circuit according to the invention is used to monitor the electrical conduction of a sensor conductor and comprises the following components:

• - 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,
• - 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,
• - 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.

RFID transponders are widely known in 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.

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.

The coupling of an RFID transponder with an RFID reader is achieved by alternating magnetic fields generated by the RFID reader within a short range or by high-frequency radio waves, which not only transmit data but 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. Frequency ranges particularly advantageous 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 sends its serial number (UID) and then, if necessary, further data (UID) by means of load modulation, i.e. consumes part of the energy of the alternating field. This can be detected by the RFID reader.

An RFID transponder suitable for the invention has, in addition to the antenna inputs, a measurement input designed to measure 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).

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 measuring input.

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 and 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).

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

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, which is connected to the second antenna input and the measurement input and 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 for voltage regulation and is particularly designed as a Zener diode.

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).

The basic principle of the invention is based on the fact that energy is always 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.

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, 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 if the object is structurally damaged, the sensor conductor is severed in the area of the damage. This means that it is not loosely attached to the object, so that it can fall off in the event of damage, 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.

The object to be monitored is preferably designed as a net, particularly preferably as a fishing net (a net for catching or keeping fish), wherein the sensor conductor is attached to the threads of the net and has 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 wrap. 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.

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 multiple sensor circuits (or monitoring devices). Alternatively or additionally, the sensor lines of multiple wires of the fence can form a series circuit, but should be insulated on their outer surfaces.

A preferred object for monitoring can also be a building, a vehicle, a road, or an aircraft. The invention is fundamentally 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, particularly in the region of a structural weakening line of the object. Particularly preferably, they span this weakening line, particularly transversely or meandering along the course of the weakening line. The object is particularly 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 substantially transversely to the length of the object (e.g., conveyor belt), with the device preferably being surrounded by material of the object (e.g., conveyor belt). However, an expansion joint of a bridge could also be monitored in this way.

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.

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).

• - erzeugen einer elektromagnetischen Welle mit einer vorgegebenen Auslesefrequenz des RFID-Transponders mit einer vorgegebenen Mindestleistung, bevorzugt mittels eines RFID-Lesegeräts,
• - Auslese des RFID-Transponders der Sensorschaltung mittels eines RFID-Lesegeräts, wobei eine Information über den am Messeingang gemessenen Zustand ausgelesen wird.

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:

• - 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,
• - 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.

The information about the state measured at the measurement input essentially indicates directly 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 one bit in size (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. It is therefore preferable to perform multiple readouts and assume an intact sensor wire if a corresponding state has been indicated at least once.

• - Steuerung eines Prozesses und/oder eine Alarmanlage basierend auf der Information und/oder Ausgabe der Information, insbesondere auf einer Anzeigevorrichtung und/oder in eine Speichereinrichtung.

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:

• - 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 in a storage device.

Cracks in a road, for example, can be easily detected by driving along the road with a vehicle equipped with an RFID reader on the bottom. A bridge may have a monitoring device at its expansion joint, with the sensor conductor extending across the expansion joint.

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.

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.

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. Once a suitable match of the matching units has been achieved for a configuration comprising sensor circuit, sensor conductor, and antenna, this can be used for identical monitoring devices.

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.

According to a preferred sensor circuit, the semiconductor component is a diode, preferably a Zener diode, which is connected by its anode to the second antenna input and by its cathode to the measurement input. As an alternative to this diode, any semiconductor can be used, e.g., a transistor or a FET.

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, particularly 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.

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 the series connection, the measurement input would therefore be a tap between the resistor and the semiconductor component. It should be noted here 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.

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

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

According to a preferred sensor circuit, the measurement input comprises an ADC or a discriminator, thus it can represent voltages or currents as numerical values or at least as bit information. The measurement 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 a current at the measuring input is 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.

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.

In practice, however, it should be noted that every conductor has a resistance and the surrounding medium can also have a resistance. For example, when monitoring a fishing net, a tear in the sensor conductor would not lead to a complete interruption of the current flow through the sensor conductor, since a (small) part of the current can still flow through the seawater. Although the specific resistance 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. Therefore, it is preferred that the sensor circuit is set or adjustable based on a predetermined "operating resistance" and a larger predetermined "defect resistance" such 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 defect resistance. The special wiring of the sensor circuit, which allows a portion of the received energy to flow as current through the sensor wire, means that even with small resistances, a decision can be made as to whether a voltage is within the signal value range or not (since the voltage is sufficiently large). The defect 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.

The sensor conductor is preferably designed as a double conductor, the ends of which are connected to each other, facing away from the sensor terminals. Such a sensor conductor can be easily arranged within an object without having to worry about reconnecting the end of the sensor conductor.

The sensor circuit is preferably designed so that the measurement input simultaneously serves as an input for an external voltage source to enhance the RFID transponder signal. RFID transponders exist with a voltage input 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 simultaneously measured in the RFID transponder and can be queried wirelessly. If the measurement input and voltage input are separate in an RFID transponder, it is preferred that these two are connected to each other in the sensor circuit. In this way, the energy of the RFID reader captured by an antenna can also be used to amplify the RFID transponder signal.

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.

• 1 ein Beispiel für eine erfindungsgemäße Sensorschaltung,
• 2 ein Beispiel für eine erfindungsgemäße Überwachungsvorrichtung,
• 3 ein Beispiel für einen Sensorleiter als Doppelleitung,
• 4 ein Beispiel für eine erfindungsgemäße Vorrichtung sowie ein Anwendungsbeispiel für ein erfindungsgemäßes Verfahren,
• 5 ein weiteres Beispiel für eine erfindungsgemäße Überwachungsvorrichtung,
• 6 ein Beispiel für eine erfindungsgemäße Vorrichtung in einem Förderband.

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:

• 1 an example of a sensor circuit according to the invention,
• 2 an example of a monitoring device according to the invention,
• 3 an example of a sensor conductor as a double line,
• 4 an example of a device according to the invention and an application example of a method according to the invention,
• 5 another example of a monitoring device according to the invention,
• 6 an example of a device according to the invention in a conveyor belt.

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.

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) is applied against the second antenna input. AN (GND) can be applied to increase the transmission power of RFID transponder 2 and is simultaneously designed to measure whether a voltage is present there. If a voltage is present there, a bit is set in a register. This register can be output when the RFID transponder is read, allowing it to be checked wirelessly whether a voltage is present at the measuring input IN.

The sensor conductor S, e.g., a wire or a stranded wire, is connected to two sensor terminals S1 and S2. These, in turn, are connected to the antenna inputs AP and AN and the measurement input IN via electronic components in such a way that the electromagnetic wave of an RFID reader F (see, for example, 4 ), with the readout frequency of the RFID transponder, is applied to 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 the RFID transponder 2 sends a strong signal when interrogated by an RFID reader F, 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.

Sensor circuit 1 comprises the following components: A semiconductor Zener diode D1, whose anode is connected to the second antenna input AN and its cathode to the measurement input IN. Its reverse bias is thus directed toward the measurement input IN, thus limiting the maximum voltage at the measurement input. Its breakdown voltage should be dimensioned so that it is slightly below the maximum permissible voltage of the measurement 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 a resistor R, which is connected to the second sensor terminal S2 and the measurement input IN. The measurement input IN is thus located as a tap between the resistor R and the cathode of the Zener diode D1.

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.

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 connections 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 in 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 there and, when the monitoring device 3 reads the data, corresponding information is output.

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 connected to each other, forming a closed loop. Such a double line can be installed very easily in an object N.

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 the antenna A and produce a current in the sensor circuit, which, through the closed sensor conductor S, results in a voltage at the measuring input IN of the RFID transponder 2. The information about the voltage is read out as the ship passes by. This can be read out multiple times. sen, as it may take some time until the voltage is applied to the measuring input IN.

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.

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.

6 shows an example of a monitoring device (3) according to the invention in a conveyor belt (5). The sensor conductor S here 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.

Finally, it should be noted once again that the devices described in detail above are merely exemplary embodiments which can be modified in a variety of ways by those 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 several, possibly spatially separate, subunits. The expression "a number" is to be understood as meaning that the number is greater than zero (i.e., as "at least one").

List of reference symbols

1

Sensor circuit

2

RFID transponder

3

monitoring device

4

device

5

conveyor belt

A

antenna

TO

Antenna input

AP

Antenna input

B

buoy

D1

Zener diode / semiconductor component

D2

diode

C

capacity

F

Radio mast / RFID reader

IN

Measuring input

L1, L2

Inductance / matching unit

N

Object / Fishnet

R

Resistance

S

Sensor wire

S1, S2

Sensor connection

Claims (10)

A 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 configured to wirelessly output the state measured at the measuring input (IN), - two sensor terminals (S1, S2) configured 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) with 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). 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. 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). Sensor circuit according to one of the preceding claims, characterized in that the semiconductor component (D1) - is 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 Zener diode (D1) and/or - is connected in parallel with a capacitor (C) which has a capacitance of less than 100 nF, and/or - is connected in series with a, in particular ohmic, resistor (R) between the second sensor connection (S2) and the second antenna input (AN), wherein the resistor (R) is preferably connected to the second sensor connection (S2) and the measuring input (IN). 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. 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 strength 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. 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) and are connected to one another. Device with an object (N) to be structurally monitored, the device comprising a sensor circuit (1) according to one of the Claims 1 until 7 and an antenna (A) connected to the two antenna inputs (AP, AN), and a sensor conductor (S), wherein the sensor conductor (S) is arranged in or on the object (N) to be monitored in such a way that in the event of structural damage to the object (N), the sensor conductor (S) is severed in the area of the damage. 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), in 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 wrap, preferably wherein the device (3) comprises several sensor circuits (1) according to Claim 7 and/or the sensor lines (S) of several threads of the network form a series circuit. Method for operating a sensor circuit (1) according to Claim 7 with an antenna (A) which is connected to the two antenna inputs (AN, AP), comprising the steps of: - generating an electromagnetic wave with a predetermined readout frequency of the RFID transponder (2) with a predetermined minimum power, preferably by means of an RFID reader (F), - 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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