Sensor and railway track system having sensor

Abstract

The invention relates in particular to a sensor (1). The sensor includes: a series resonance circuit (30) having a coil (31), a capacitor (32), and a series resistor (33) electrically connected in series; a DC power supply (10) which limits both current and voltage and outputs a predetermined maximum current (Imax) as an output current (I) if the output voltage (U) required to drive the predetermined maximum current (Imax) does not exceed a predetermined maximum voltage (Umax), otherwise outputs the maximum voltage (Umax); a converter (20) which is supplied on the input side by the DC source (10) and which applies an AC voltage (Uw) on the output side to the series resonant circuit (30), the frequency (f) of which is set in such a way that the DC source (10) feeds a maximum current (Imax) into the converter (20) at a maximum voltage (Umax) during sensor operation without detection; and a monitoring device (50), which generates a detection signal (RDS) if the output voltage (U) of the DC power supply (10) is lower than the maximum voltage (Umax) by more than a predetermined degree, and / or which generates a warning signal (WS) if the output current (I) of the DC power supply (10) is lower than the maximum current (Imax) by more than a predetermined degree.

Description

Technical Field

[0001] The invention relates to a sensor and a railway track equipment having the sensor. Background Art

[0002] Sensors for detecting wheels of rail vehicles are generally known in railway technology, for example in order to be able to detect the entry or exit of a rail vehicle into a predetermined section of a railway line and to report whether the corresponding section is free or occupied.

[0003] European patent document EP 1 479 587 B1 proposes a circuit arrangement for adjusting an inductive sensor. In this circuit arrangement, an oscillating circuit is set to a specific frequency with a specific amplitude by switching in an RC combination. The oscillating circuit is designed as a parallel oscillating circuit.

[0004] German laid-open patent application DE 199 15 597 A1 proposes a coil system consisting of at least two coil sections which, due to their oppositely directed partial windings, are intended to suppress common-mode interference from the outside.

[0005] A further coil system consisting of at least two partial coils is proposed in German patent document DE 10 221 577 B3. These coils are controlled with current pulses and are not designed as oscillating circuits and are therefore frequency-independent. Summary of the invention

[0006] The object of the present invention is to provide a sensor which is able to reliably detect the approach of, in particular, magnetizable objects, for example ferrous objects such as wheels of rail vehicles, but which nevertheless has a simple construction.

[0007] This object is achieved according to the invention by a sensor having the features of claim 1. Advantageous embodiments of the sensor according to the invention are specified in the dependent claims.

[0008] According to the invention, the sensor is characterized in that

[0009] a series resonant circuit having a coil, a capacitor and a series resistor electrically connected in series,

[0010] a DC power supply which is both current-limited and voltage-limited and which outputs the predetermined maximum current as the output current if the output voltage required to drive the predetermined maximum current does not exceed the predetermined maximum voltage, and which otherwise outputs the maximum voltage,

[0011] a converter which is supplied on the input side by a DC source and which applies an AC voltage to the series resonant circuit on the output side, the frequency of the AC voltage being set such that, in sensor operation without detection, the DC source feeds a maximum current into the converter at a maximum voltage, and

[0012] - A monitoring device, which generates a detection signal if the output voltage of the DC power supply is lower than the maximum voltage by more than a predetermined degree; and / or generates a warning signal if the output current of the DC power supply is lower than the maximum current by more than a predetermined degree.

[0013] A major advantage of the sensor according to the invention is that the detection signal is formed based on the measured values ​​acquired on the DC voltage side of the converter or on the output side of the DC power supply. The acquisition of the measured values ​​is thus decoupled from the AC voltage side and the series resonant circuit, so that the measurement has no influence or at least no significant influence on the series resonant circuit or its resonant frequency. The generation of the detection signal and / or warning signal always takes place at the same frequency and depends only on the DC current value or DC voltage value.

[0014] If the optimum frequency of the AC voltage is known for the respective application range of the sensor, the converter can form the AC voltage with this constant frequency known in advance.

[0015] However, in general, the optimum frequency is not always known precisely and may at least change over time. For this reason, it is considered advantageous if the sensor has a frequency generator which controls the converter, thereby predefining the frequency of the alternating voltage. The operating frequency of the frequency generator preferably corresponds to the frequency of the alternating voltage to be generated by the converter. The frequency generator preferably generates a sinusoidal or square-wave signal for controlling the converter, the frequency of which corresponds to the frequency of the alternating voltage to be generated for the series resonant circuit.

[0016] The monitoring device is preferably connected to the frequency generator and sets the operating frequency of the frequency generator and thus the frequency of the AC voltage. In the last-mentioned embodiment, the monitoring device can advantageously determine or at least readjust the optimal operating frequency itself if this seems reasonable.

[0017] It is considered particularly advantageous if the monitoring device is designed to check the operating frequency regularly or irregularly, independently or in response to external control commands.

[0018] With regard to the operating frequency check, it is advantageous if the monitoring device carries out the operating frequency check during sensor operation without testing.

[0019] With regard to the operating frequency check, it is advantageous if the monitoring device keeps the operating frequency of the frequency generator and thus the frequency of the AC voltage to be generated for the series resonant circuit unchanged if the DC source feeds a maximum current into the converter at a maximum voltage.

[0020] If the monitoring device determines that the DC power supply does not feed the maximum current or the maximum voltage into the converter, it is advantageous if, during the operating frequency check, the monitoring device changes the operating frequency of the frequency generator and thus the frequency of the AC voltage to be generated for the series resonant circuit until the monitoring device determines that the DC power supply feeds the maximum current into the converter at the maximum voltage.

[0021] Regarding the direction of the frequency variation of the operating frequency of the frequency generator, it is considered advantageous to increase the frequency if the output voltage of the DC source is below the maximum voltage and to decrease the frequency if the output current of the DC source is below the maximum current.

[0022] Alternatively or additionally, it can be advantageously arranged that, during the operating frequency check, the monitoring device increases and decreases the frequency relative to the corresponding previously set operating frequency and observes the influence of the frequency increase and frequency decrease on the output voltage of the DC power supply and the output current of the DC power supply.

[0023] Preferably, the monitoring device keeps the operating frequency unchanged if, relative to the respective current operating frequency, the output current of the DC source decreases when the frequency increases and the output voltage of the DC source decreases when the frequency decreases.

[0024] If the last described behavior cannot be determined, i.e., the output current decreases when the frequency increases and the output voltage decreases when the frequency decreases, it is advantageous if, during the operating frequency check, the monitoring device changes the operating frequency until the monitoring device determines that, relative to the respectively changed operating frequency, the output current of the DC power supply decreases when the frequency increases further and the output voltage of the DC power supply decreases when the frequency decreases further. Once the monitoring device determines this, the control device preferably further uses the changed operating frequency as the new operating frequency for the further operation of the sensor until the respective next operating frequency check.

[0025] The sensor is preferably a wheel rim detector which is designed to detect a wheel of a rail vehicle running on a railway track and passing the sensor, and to generate a wheel detection signal as a detection signal.

[0026] Furthermore, the invention relates to a railway track installation which is equipped with a sensor as described above; the sensor is arranged in the region of the railway track or mounted on the railway track and serves for wheel detection of wheels of rail vehicles travelling on the railway track and passing the sensor.

[0027] With regard to the advantages of the railway track device according to the invention and its advantageous embodiments, reference is made to the statements made above in conjunction with the sensor according to the invention and its advantageous embodiments.

[0028] Preferably, the monitoring device of the sensor generates a wheel detection signal if the output voltage of the DC power supply falls below the maximum voltage by more than a predetermined degree.

[0029] Preferably, the monitoring device of the sensor generates a warning signal if the output current of the DC power source falls below the maximum current by more than a predefined amount.

[0030] The components of the sensor are preferably arranged so that the series resonant circuit and the converter are close to the railway track. The DC power supply and the monitoring device are preferably arranged away from the railway track. The distance between the DC power supply and the railway track and the distance between the monitoring device and the railway track are preferably at least 10 times greater than the distance between the series resonant circuit and the railway track and the distance between the converter and the railway track.

[0031] The invention further relates to a method for setting a sensor as described above. According to the invention, a maximum current and a maximum voltage are predefined for the DC power supply, and the frequency of the AC voltage applied to the series resonant circuit is set so that the DC power supply feeds a maximum current into the series circuit at the maximum voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The present invention will be described in detail below with reference to embodiments;

[0033] Figure 1 shows components of an embodiment of a sensor according to the present invention,

[0034] Figure 2 Shown is equipped with Figure 1 sections of railway track equipment of sensors, and

[0035] Figure 3 The frequency diagram shows the Figure 1 and Figure 2 Discovery and setting of the optimal operating frequency of the sensor.

[0036] In the drawings, the same reference numbers are used for the same or similar components for the sake of clarity. DETAILED DESCRIPTION

[0037] Figure 1 1 shows components of an embodiment of a sensor 1 according to the invention, which can also be referred to as an inductive proximity sensor. The sensor 1 is a wheel rim detector which is designed to detect a wheel rim on a railway track 110 (see Figure 2 ) and passes the sensor 1 (see Figure 2 ) performs wheel detection and is able to generate a wheel detection signal RDS as a detection signal.

[0038] The sensor 1 includes a DC power supply 10 that is both current-limited and voltage-limited. Figure 1 In the exemplary embodiment of FIG. 1 , the DC power source 10 has a current source 11 which feeds a predetermined constant maximum current Imax into a downstream voltage limiter 12 of the DC power source 10 .

[0039] If the voltage Us applied to the input side of the voltage limiter 12, i.e. the voltage applied by the current source 11 to the voltage limiter 12, is less than a predetermined maximum voltage Umax or is at most as large as a predetermined maximum voltage Umax, the voltage limiter 12 outputs the maximum current Imax of the current source 11 as the output current I of the DC power supply 10.

[0040] If the voltage Us applied to the input side of the voltage limiter 12 reaches the maximum voltage Umax, the voltage limiter 12 only outputs the maximum voltage Umax as the output voltage U of the DC power supply 10, so in this case, the output current I of the voltage limiter 12 may be lower than the maximum current Imax of the current source 11.

[0041] In summary, that is to say, if the output voltage U required to drive the maximum current does not exceed the predetermined maximum voltage Umax, the DC power supply 10 outputs the predetermined maximum current Imax as the output current I, otherwise the DC power supply 10 outputs the maximum voltage Umax as the output voltage U.

[0042] The output current I or the output voltage U outputted by the DC power supply 10 or its voltage limiter 12 on the output side is fed into the downstream converter 20. A series resonant circuit 30 is arranged downstream of the converter 20 and is powered by the converter 20. The converter 20, which is fed with a DC current by the DC power supply 10 on the input side, applies an AC voltage Uw to the series resonant circuit 30 on the output side.

[0043] The series resonant circuit 30 includes a coil 31 , a capacitor 32 , and a series resistor 33 which are electrically connected in series.

[0044] In accordance with Figure 1In the embodiment of the present invention, the operating frequency of the converter 20, and therefore the frequency f of the AC voltage Uw applied by the converter 20 to the series resonant circuit 30, is set by a frequency generator 40 via a clock line 41 with the aid of a frequency generator signal Sf. The frequency generator signal Sf directly or indirectly controls the internal switching elements 21 of the converter 20, which are switched on and off at the same time. Figure 1 The converter 20 may include semiconductor switches such as transistors or similar elements as switch elements 21, which may be connected to form a half-bridge circuit or a full-bridge circuit. In other words, the converter 20 may be implemented as a controllable inverter of any structure type.

[0045] The frequency generator 40 can output a sinusoidal signal or a square wave signal as a frequency generator signal Sf on the output side to control the converter 20, and the frequency generator 40 is controlled by the monitoring device 50 of the sensor 1 via a control line 51. The monitoring device 50 predetermines the magnitude of the frequency of the frequency generator signal Sf to the frequency generator 40, and thus also determines the magnitude of the frequency f of the AC voltage Uw applied by the converter 20 to the series resonant circuit 30.

[0046] Preferably, monitoring device 50 sets the frequency f of AC voltage Uw applied by converter 20 to series resonant circuit 30 so that in non-detected sensor operation, DC power supply 10 feeds maximum current Imax into converter 20 at maximum voltage Umax; this will be described in more detail below.

[0047] The monitoring device 50 is connected to the output of the DC power source 10 via a measuring line 52 and a current and voltage sensor 60 , and measures an output voltage U and an output current I of the DC power source 10 using the current and voltage sensor 60 .

[0048] For the operation of the sensor 1, use is now made of the knowledge that the series resonant circuit 30, in particular its resonant frequency, can be influenced by external factors. For example, if iron material, such as the iron material of the rail vehicle wheel 120, approaches the coil 31, the resonant frequency of the series resonant circuit 30 changes and the electrical power that can be fed into the series resonant circuit 30 decreases, which is reflected as a decrease in the output voltage U applied by the DC power source 10 to the converter 20 (due to the current limitation by the current source 11).

[0049] Therefore, if the output voltage U of the DC power supply 10 is lower than a predetermined maximum voltage Umax by more than a predetermined degree, the monitoring device 50 generates a wheel detection signal RDS.

[0050] Figure 2 Shown is equipped with Figure 1 A section of a railway track device 100 of the sensor 1 . Figure 2 The installation situation on the railway track 110 is shown as a cross section through the railway track 110 . A rail vehicle wheel 120 is located with its wheel flange 121 above the railway track 110 .

[0051] Since the sensor 1 is arranged in the region of the railway track 110 or mounted on the railway track 110, it is suitable for wheel detection of a rail vehicle wheel 120. For this purpose, the coil 31 is preferably arranged in the sensor housing 1a of the sensor 1 so that the magnetic field of the coil 31 extends mostly vertically, so that the metal piece of the rail vehicle wheel 120 located above it can be well detected.

[0052] If the output voltage U of the DC power source 10 falls below the maximum voltage Umax by more than a predetermined degree, the monitoring device 50 of the sensor 1 generates a wheel detection signal RDS.

[0053] Since the sensor 1 is installed in the region of the railway track 110, the resonant frequency of the series resonant circuit 30 is also influenced by the iron material of the track. If now, in the event of a malfunction, the sensor 1 is removed from the railway track 110, for example because the sensor 1 falls off or is torn off the railway track 110 or is simply stolen, the influence of the iron of the railway track 110 disappears, so that the resonant frequency of the series resonant circuit 30 also changes; this causes the output current I of the DC power supply to drop.

[0054] Therefore, advantageously, when the output current I of the DC power supply 10 is lower than the maximum current Imax by more than a predetermined degree, the monitoring device 50 generates a warning signal WS, which indicates that the position of the sensor 1 has changed or other defects have occurred, and should be inspected or repaired.

[0055] according to Figure 1 and Figure 2 The sensor 1 preferably operates as follows:

[0056] start :

[0057] After the sensor 1 is installed, for example, Figure 2 After the sensor 1 is installed on the railway track 110, in the non-detection operation without affecting the railway wheel to be detected, the monitoring device 50 first searches for the optimal operating frequency of the frequency generator signal Sf of the frequency generator 40 (in the non-detection operation, not affected by the wheel to be detected), thereby searching for the optimal AC voltage Uw for the series resonant circuit 30.

[0058] During this search for the optimal operating frequency, the monitoring device 50 changes the operating frequency until the monitoring device 50 determines that, relative to the correspondingly applied operating frequency, the output current I of the DC power supply 10 decreases when the frequency is further increased, and the output voltage U of the DC power supply 10 decreases when the frequency is reduced.

[0059] Figure 3 This search is shown in more detail by way of example. It can be seen that the monitoring device 50 initially sets the first operating frequency f1 during the start-up. It can be seen that the output voltage U is less than the maximum voltage Umax. Therefore, the monitoring device 50 will change the operating frequency, i.e. Figure 3 As shown, the frequency is increased until the monitoring device 50 finds the optimal operating frequency fopt, at which the output current I of the DC power supply 10 decreases when the frequency is further increased, that is, relative to the optimal operating frequency fopt, and when the frequency is reduced, the output voltage U of the DC power supply 10 decreases.

[0060] Since the optimal operating frequency fopt determined in this way corresponds to the resonant frequency of the series resonant circuit 30, the magnitude of the impedance of the series resonant circuit 30 is minimal and the DC power supply 10 will feed the maximum current Imax into the converter 20 at the maximum voltage Umax.

[0061] Working frequency check :

[0062] The monitoring device 50 preferably performs an operating frequency check regularly or irregularly, independently or in response to an external control command SB. The operating frequency check is preferably performed in sensor operation without detection to avoid operating frequency check errors or delays due to the influence of interfering iron materials of passing rail vehicle wheels 120.

[0063] During the operating frequency check, if the DC power source 10 feeds the maximum current Imax into the converter 20 at the maximum voltage Umax, that is, the optimal operating point has been reached, the monitoring device 50 will keep the current operating frequency of the frequency generator 40 unchanged.

[0064] If the maximum voltage Umax or the maximum current Imax has not been reached, the monitoring device 50 changes the operating frequency until the monitoring device 50 determines that the DC source 10 feeds the maximum current Imax into the converter 20 at the maximum voltage Umax.

[0065] Alternatively or additionally, during the operating frequency check, the monitoring device 50 can increase and decrease the frequency relative to the corresponding previously set (i.e., current) operating frequency, and observe the impact of the frequency increase and frequency decrease on the output voltage U of the DC power supply 10 and the output current I of the DC power supply 10.

[0066] In the last-mentioned variant, if, relative to the corresponding current operating frequency, the output current I of the DC power supply 10 decreases when the frequency increases, and the output voltage U of the DC power supply 10 decreases when the frequency decreases, the monitoring device 50 will maintain the currently set operating frequency unchanged.

[0067] Otherwise, during the operating frequency check, the monitoring device 50 will change the operating frequency, specifically, until the monitoring device 50 determines that relative to the corresponding last set operating frequency, when the frequency is further increased, the output current I of the DC power supply 10 decreases, and when the frequency is further reduced, the output voltage U of the DC power supply 10 decreases; once the monitoring device 50 determines this, the monitoring device 50 will continue to use the last set operating frequency as the new optimal operating frequency fopt for further operation of the sensor until the next operating frequency check is performed.

[0068] The sensor 1 can be constructed as a multi-channel system, for example, a dual system with two sensors, which are installed one after another in the longitudinal direction of the track and are used for train direction recognition due to the overlap of the signals of the two sensors. Here, each sensor 1 preferably includes a series resonant circuit 30 with different resonant frequencies to avoid interference with the signal voltage due to the beat effect.

[0069] In combination Figures 1 to 3 In the illustrated embodiment, the operating frequency of the frequency generator 40 can be adjusted by the monitoring device 50 to find and set the optimal operating frequency fopt. If the optimal operating frequency fopt is known for a given use, for example because it has been measured or simulated, the converter 20 can also always be operated at the same constant operating frequency and control by the monitoring device 50 and the control line 51 between the monitoring device 50 and the frequency generator 40 can be omitted. In this case, a simple oscillating circuit with a fixedly predetermined operating frequency can also be used instead of the frequency generator 40.

[0070] The embodiment of the sensor 1 described above by way of example may (but not necessarily) have one or more of the following features, advantages or characteristics listed as key points:

[0071] The series resonant circuit 30 is preferably not operated as a free-running oscillator, but is preferably controlled at its resonant frequency by the converter 20 .

[0072] The converter 20 is preferably designed such that the power consumption of the converter 20 itself is negligible relative to the power consumption of the series resonant circuit 30 , so that the measured variables M of U and I substantially reproduce the power consumption of the series resonant circuit 30 .

[0073] - The frequency generator 40 may be a simple square wave generator.

[0074] - The converter 20 may include a simple bridge circuit consisting of transistors or the like, which is switched on / off digitally.

[0075] On the current / voltage lead to the converter 20 there is preferably a capacitor for smoothing the fed-in current I or voltage U.

[0076] The levels of the measured variables M of the output voltage U and the output current I which are present at the input of the converter 20 and which are generated during operation are preferably conducted via measuring lines 52 to a monitoring device 50 which can include a microprocessor, for example. The microprocessor evaluates the voltage and current levels and outputs a detection signal or a warning signal for further processing.

[0077] In the case of adjustment of the frequency to the optimum resonance frequency, the frequency of the frequency generator 40 is preferably detuned by means of a control signal, so that (as described) the values ​​Imax and Umax are produced at the input of the converter 20 .

[0078] The sensor 1 can advantageously be designed so that only a few components, such as the converter 20 and the series resonant circuit 30, are mounted directly on the track, since the mechanical load on these components is greatest on the track. The other components, namely the monitoring device 50, the frequency generator 40 and the DC power source 10, are preferably located at a greater distance, for example next to the track.

[0079] The series resonant circuit 30 can have a higher oscillation amplitude, i.e. absorb a higher energy. This in turn leads to a correspondingly higher interference immunity of the sensor 1, since the influence of the interference energy coupled in depends on the oscillating circuit amplitude, i.e. on the energy present in the series resonant circuit 30. A self-compensating arrangement with oppositely wound series sub-coils can be omitted.

[0080] The series resonant circuit 30 is preferably not operated as a self-excited oscillator with feedback, but its resonant frequency is controlled by means of a frequency generator 40 via the converter 20 .

[0081] - The optimum resonance frequency can be accurately set without directly measuring the oscillation amplitude. That is, the series resonance circuit 30 itself does not need to have signal decoupling for level measurement.

[0082] When a metal wheel passes by, the oscillating circuit amplitude decreases due to eddy current losses in the metal and field distortion of its alternating magnetic field. For a simple evaluation, only the power consumption of the series resonant circuit 30 can be observed: the series resonant circuit 30 is preferably supplied or controlled with a defined, upwardly limited amount of power.

[0083] -The series resonant circuit 30 has the lowest impedance at its resonant frequency. That is, at the resonant frequency, the series resonant circuit 30 absorbs the maximum possible power. If the fed frequency f rises above the resonant frequency, the fed current I decreases, while the applied voltage U remains constant. If the fed frequency f drops below the resonant frequency, the fed current I remains constant, while the applied voltage U decreases. Now, the frequency adjustment can be performed so that during frequency operation, the voltage U applied at the feed point of the converter 20 and the current I flowing in are measured: during frequency operation from low frequency to high frequency, the maximum possible current (Imax of the current source 11) only flows into the series resonant circuit 30 when the applied voltage is low. As the frequency f increases, the applied voltage U increases and, in the case of resonance, reaches a maximum value Umax at a constant current Imax. As the frequency f further increases, the current I decreases, and the applied voltage U remains constant at the maximum voltage Umax (due to the voltage limitation of the voltage limiter 21). That is, the resonant frequency is the frequency f at which the current I and the voltage U are maximum. Thus, the resonant frequency of the series resonant circuit 30 for the specific installation situation is found. This frequency f can be stored and used as the operating frequency during continuous operation. Since direct currents and direct voltages are involved, the measurement of these values ​​is very simple and does not require intervention in the actual series resonant circuit 30. As a result, the series resonant circuit 30 can be constructed very compactly, which minimizes possible interference decoupling. Signal distortions due to the power output of the measurement signal by directly measuring the amplitude voltage can also be avoided.

[0084] - At the operating point of the resonant frequency, the voltage U applied to the converter 20 decreases compared to the static value due to the attenuation effect of the iron block when the wheel passes. This voltage reduction can be used for detection and can be evaluated or further processed in subsequent units. The check of the resonant frequency in the static state, which may change due to mechanical or thermal influences, is preferably carried out by changing the instantaneous operating frequency by a defined degree for a short period of time, i.e. by changing the frequency change Δf. A frequency change Δf below the operating frequency reduces the feed voltage level by a specific value. A frequency change Δf above the operating frequency reduces the current level by a specific value. If the deviation values ​​on both sides are as expected, the set operating frequency is also the resonant frequency.

[0085] Finally, it should be mentioned that the features of all the exemplary embodiments described above can be combined with one another in any manner to form further embodiments of the present invention.

[0086] All features of the dependent claims can also be combined with each of the parallel claims, to be precise, can also be combined with one or more of the dependent claims individually or in any combination with one or more of the dependent claims to obtain further embodiments.

Claims

1. A sensor (1), It is characterized in that - a series resonant circuit (30) having a coil (31), a capacitor (32) and a series resistor (33) electrically connected in series, - a direct current power supply (10), which is both current-limited and voltage-limited, and outputs the predetermined maximum current (Imax) as the output current (I) if the output voltage (U) required to drive the predetermined maximum current (Imax) does not exceed the predetermined maximum voltage (Umax), and otherwise outputs the maximum voltage (Umax), a converter (20) which is supplied on the input side by the DC source (10) and which applies an AC voltage (Uw) to the series resonant circuit (30) on the output side, the frequency (f) of the AC voltage being set such that, in sensor operation without detection, the DC source (10) feeds the maximum current (Imax) into the converter (20) at a maximum voltage (Umax), and - a monitoring device (50), which generates a detection signal (RDS) if the output voltage (U) of the DC power supply (10) is lower than the maximum voltage (Umax) by more than a predetermined degree; and / or generates a warning signal (WS) if the output current (I) of the DC power supply (10) is lower than the maximum current (Imax) by more than a predetermined degree.

2. The sensor (1) according to claim 1, It is characterized in that the sensor (1) has a frequency generator (40) which controls the converter (20), thereby predefining a frequency (f) of the AC voltage (Uw), and The monitoring device (50) is connected to the frequency generator (40) and sets the operating frequency of the frequency generator and thereby the frequency (f) of the AC voltage (Uw).

3. The sensor (1) according to any one of the preceding claims, It is characterized in that The monitoring device (50) is designed to perform an operating frequency check regularly or irregularly, independently or in response to an external control command (SB).

4. The sensor (1) according to claim 3, It is characterized in that The monitoring device (50) is designed to check the operating frequency during operation of the sensor without testing.

5. The sensor (1) according to any one of claims 3 to 4, It is characterized in that During the operating frequency check, if the DC power source (10) feeds a maximum current (Imax) into the converter (20) at a maximum voltage (Umax), the monitoring device (50) keeps the operating frequency of the frequency generator (40) unchanged.

6. The sensor (1) according to any one of claims 3 to 5, It is characterized in that During the operating frequency check, the monitoring device (50) changes the operating frequency until the monitoring device determines that the DC power source (10) feeds a maximum current (Imax) into the converter (20) at a maximum voltage (Umax).

7. The sensor (1) according to any one of claims 3 to 6, It is characterized in that During the operating frequency check, the monitoring device (50) increases and decreases the frequency relative to the corresponding previously set operating frequency, and observes the effects of the frequency increase and frequency decrease on the output voltage (U) of the DC power supply (10) and the output current (I) of the DC power supply (10).

8. The sensor (1) according to claim 7, It is characterized in that If, relative to the corresponding current operating frequency, the output current (I) of the DC power supply (10) decreases when the frequency increases, and the output voltage (U) of the DC power supply (10) decreases when the frequency decreases, the monitoring device (50) keeps the operating frequency unchanged.

9. The sensor (1) according to any one of claims 7 to 8, It is characterized in that During the working frequency check, the monitoring device (50) changes the working frequency until the monitoring device determines that, relative to the corresponding changed working frequency, when the frequency is further increased, the output current (I) of the DC power supply (10) decreases, and when the frequency is further reduced, the output voltage (U) of the DC power supply (10) decreases, and once the monitoring device determines this, the changed working frequency is further used as the new working frequency for further operation of the sensor until the corresponding next working frequency check.

10. The sensor (1) according to any one of the preceding claims, It is characterized in that The sensor (1) is a wheel rim detector, which is designed to detect the wheels (120) of a railway vehicle running on a railway track (110) and passing the sensor (1), and to generate a wheel detection signal as a detection signal (RDS).

11. A railway track equipment (100), It is characterized in that - the railway track equipment is equipped with a sensor (1) according to any one of the preceding claims, wherein the sensor (1) is arranged in the region of a railway track (110) or is mounted on the railway track and is used for wheel detection of a rail vehicle wheel (120) travelling on the railway track (110) and passing the sensor (1).

12. The railway track equipment (100) according to claim 11, It is characterized in that If the output voltage (U) of the DC power supply (10) is lower than the maximum voltage (Umax) by more than a predetermined degree, the monitoring device (50) of the sensor (1) generates a wheel detection signal.

13. Railway track equipment (100) according to claim 11 or 12, It is characterized in that If the output current (I) of the DC power source (10) falls below the maximum current (Imax) by more than a predetermined amount, the monitoring device (50) of the sensor (1) generates a warning signal (WS).

14. A method for setting up a sensor (1) according to any one of the preceding claims, It is characterized in that - for the DC power supply (10), a maximum current (Imax) and a maximum voltage (Umax) are predefined, and The frequency (f) of the AC voltage (Uw) applied to the series resonant circuit (30) is set so that the DC power source (10) feeds a maximum current (Imax) into the series circuit at a maximum voltage (Umax).

15. The method according to claim 14, It is characterized in that - during the operating frequency check, adjusting the operating frequency of the frequency generator (40), thereby adjusting the frequency (f) of the AC voltage (Uw) applied to the series resonant circuit (30), until it is determined that when the frequency increases, the output current (I) of the DC power supply (10) decreases, and when the frequency decreases, the output voltage (U) of the DC power supply (10) decreases, and - Using the adjusted operating frequency as the new operating frequency for further operation of the sensor (1).

Images