Sensor, and railway track system comprising a sensor
Patent Information
- Application Number
- EP2023733871
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-21
- Filing Date
- 2023-06-06
- Publication Date
- 2025-01-15
- Estimated Expiration
- 2043-06-06
AI Technical Summary
Existing railway track sensors face challenges in reliably detecting magnetizable objects, such as rail vehicle wheels, while maintaining simplicity and avoiding interference from external sources.
A sensor system featuring a series resonant circuit with a coil, capacitance, and series resistance, powered by a current- and voltage-limited direct source, and equipped with a converter that applies alternating voltage at a frequency set by a frequency generator, along with a monitoring device that generates detection and warning signals based on DC voltage and current levels, decoupled from AC voltage measurements.
The system provides reliable detection and warning signals without influencing the series resonance circuit, allowing for optimal frequency adjustment and interference resistance, ensuring consistent performance in detecting rail vehicle wheels.
Smart Images
Figure 1.1
Abstract
Description
[0001] Description
[0002] Sensor and railway track system with sensor
[0003] The invention relates to sensors and railway track systems with sensors.
[0004] Sensors for detecting wheels of rail vehicles are well known in railway technology, for example to detect when a rail vehicle enters or leaves a given section of a railway line and to report the respective section as free or occupied.
[0005] European patent EP 1 479 587 B1 presents a circuit arrangement for calibrating inductive sensors. In this circuit arrangement, an oscillating circuit is adjusted to a specific frequency with a specific amplitude by connecting RC combinations. The oscillating circuit is designed as a parallel oscillating circuit.
[0006] The German laid open document DE 199 15 597 A1 presents a coil system consisting of at least two partial coils which are intended to suppress common mode interference coming from outside due to their opposing partial windings.
[0007] The German patent DE 10 221 577 B3 presents another coil system consisting of at least two partial coils. The coils are controlled by current pulses and are not designed as resonant circuits, thus being frequency-independent.
[0008] The invention is based on the object of providing a sensor that can reliably detect the approach of magnetizable objects, for example, iron-containing objects such as rail vehicle wheels, while still being simple in design. 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 subclaims.
[0009] According to the invention, the sensor is characterized by
[0010] - a series resonant circuit comprising a coil, a capacitance and a series resistance electrically connected in series,
[0011] - a DC source which is both current and voltage limited and outputs a predetermined maximum current as output current, provided that the output voltage required to drive this maximum current does not exceed a predetermined maximum voltage, and otherwise outputs the maximum voltage,
[0012] - a converter which is fed on the input side by the DC source and on the output side applies an AC voltage to the series resonant circuit, the frequency of which is set in such a way that the DC source - in detection-free sensor operation - feeds the maximum current at maximum voltage into the converter, and
[0013] - a monitoring device which generates a detection signal when the output voltage of the DC source falls below the maximum voltage by a predetermined amount and / or generates a warning signal when the output current of the DC source falls below the maximum current by a predetermined amount.
[0014] A key advantage of the sensor according to the invention is that the detection signal is generated based on measured values acquired on the DC voltage side of the converter or the output side of the DC source. The measured value acquisition is thus decoupled from the AC voltage side and the series resonant circuit, so that the measurement has no, or at least no significant, influence on the series resonant circuit or its resonant frequency. The detection signal and / or warning signal are always generated at the same frequency and solely as a function of DC current or DC voltage values.
[0015] If the optimal frequency of the alternating voltage for the respective application area of the sensor is known, the converter can generate the alternating voltage with this previously known constant frequency.
[0016] As a rule, however, the optimal frequency will not always be known exactly; at the very least, it can change over time. For this reason, it is considered advantageous if the sensor has a frequency generator that controls the converter and thus specifies the frequency of the alternating voltage. The operating frequency of the frequency generator preferably corresponds to the frequency of the alternating voltage that the converter is to generate. To control the converter, the frequency generator preferably generates a sine-wave signal or a square-wave signal whose frequency corresponds to the frequency of the alternating voltage to be generated for the series resonant circuit.
[0017] The monitoring device is preferably connected to the frequency generator and adjusts its operating frequency and thus the frequency of the alternating voltage. In the latter embodiment, the monitoring device can advantageously determine the optimal operating frequency itself or at least adjust it if this seems appropriate.
[0018] It is considered particularly advantageous if the monitoring device is designed to carry out an operating frequency test regularly or irregularly, independently or in response to an external control command.
[0019] With regard to the operating frequency test, it is advantageous if the monitoring device performs the operating frequency test in detection-free sensor mode. Regarding the performance of the operating frequency test, it is advantageous if the monitoring device leaves the operating frequency of the frequency generator, and thus the frequency of the alternating voltage to be generated for the series resonant circuit, unchanged when the DC source feeds the maximum current at maximum voltage into the converter.
[0020] If the monitoring device determines that the DC source is not feeding the maximum current or the maximum voltage into the converter, it is advantageous if it changes the working frequency of the frequency generator and thus the frequency of the alternating voltage to be generated for the series resonant circuit as part of the working frequency test, and does so until it determines that the DC source is feeding the maximum current at maximum voltage into the converter.
[0021] Regarding the direction of the frequency change of the working frequency of the frequency generator, it is considered advantageous if the frequency is increased when the output voltage of the DC source is less than the maximum voltage and reduced when the output current of the DC source is less than the maximum current.
[0022] Alternatively or additionally, it can be advantageously provided that the monitoring device initiates a frequency increase and a frequency reduction within the scope of the operating frequency test - based on the previously set operating frequency - and observes the effects of the frequency increase and the frequency reduction on the output voltage of the DC source and the output current of the DC source.
[0023] The monitoring device preferably leaves the working frequency unchanged if - related to the respective current working frequency - the output current of the DC source decreases when the frequency is increased and the output voltage of the DC source decreases when the frequency is reduced. If the last-described behavior, i.e. that the output current decreases when the frequency is increased and the output voltage decreases when the frequency is reduced, cannot be determined, it is advantageous if the monitoring device changes the working frequency as part of the working frequency test until it determines that - related to the respectively changed working frequency - the output current of the DC source decreases when the frequency is increased further and the output voltage of the DC source decreases when the frequency is reduced further.As soon as it detects this, it preferably uses the changed operating frequency as the new operating frequency for further sensor operation until the next operating frequency test.
[0024] The sensor is preferably a wheel flange detector which is designed to detect the wheels of rail vehicle wheels traveling on a railway track and passing the sensor and generates a wheel detection signal as a detection signal.
[0025] The invention also relates to a railway track system which is equipped with a sensor as described above; the sensor is arranged in the region of a railway track or attached to it and serves to detect the wheels of rail vehicle wheels traveling on the railway track and passing the sensor.
[0026] With regard to the advantages of the railway track system according to the invention and its advantageous embodiments, reference is made to the above statements in connection with the sensor according to the invention and its advantageous embodiments.
[0027] The sensor's monitoring device preferably generates a wheel detection signal when the output voltage of the DC source falls below the maximum voltage by a predetermined amount. The sensor's monitoring device preferably generates a warning signal when the output current of the DC source falls below the maximum current by a predetermined amount.
[0028] The sensor components are preferably arranged such that the series resonant circuit and the converter are located close to a railway track. The DC source and the monitoring device are preferably arranged away from the railway track. The distance between the DC source 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.
[0029] The invention also relates to a method for adjusting a sensor as described above. According to the invention, a maximum current and a maximum voltage are specified for the DC source, and the frequency of the AC voltage applied to the series resonant circuit is adjusted such that the DC source feeds the maximum current into the series circuit at the maximum voltage.
[0030] The invention is explained in more detail below using exemplary embodiments; by way of example,
[0031] Figure 1 Components of an embodiment of a sensor according to the invention,
[0032] Figure 2 shows a section of a railway track system equipped with the sensor according to Figure 1, and
[0033] Figure 3 shows how to find and adjust the optimal operating frequency of the sensor according to Figures 1 and 2 using a frequency diagram. For the sake of clarity, the same reference numerals are used in the figures for identical or comparable components.
[0034] Figure 1 shows components of an exemplary embodiment of a sensor 1 according to the invention, which can also be referred to as an inductively operating proximity sensor. The sensor 1 is a wheel flange detector designed to detect the wheels of rail vehicle wheels 120 (see Figure 2) traveling on a railway track 110 (see Figure 2) and passing the sensor 1, and can generate a wheel detection signal RDS as the detection signal.
[0035] The sensor 1 comprises a DC source 10 that is both current- and voltage-limited. In the exemplary embodiment shown in Figure 1, the DC source 10 comprises a current source 11 that feeds a predetermined constant maximum current Imax into a downstream voltage limiter 12 of the DC source 10.
[0036] The voltage limiter 12 outputs the maximum current Imax of the current source 11 as the output current I of the DC source 10, provided that 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 or at most as large as a predetermined maximum voltage Umax.
[0037] If the voltage Us applied to the input side of the voltage limiter 12 reaches the maximum voltage Umax, the voltage limiter 12 outputs only this maximum voltage Umax as the output voltage U of the DC source 10, so that in such a case the output current I of the voltage limiter 12 can fall below the maximum current Imax of the current source 11.
[0038] In summary, the DC source 10 outputs the specified maximum current Imax as output current I, provided that the output voltage U required to drive this maximum current does not exceed the specified maximum voltage Umax, and otherwise it outputs the maximum voltage Umax as output voltage U.
[0039] The output current I or the output voltage U output by the DC source 10 or its voltage limiter 12 is fed into a downstream converter 20. Downstream of the converter 20 is a series resonant circuit 30, which is fed by the converter 20. The converter 20, which is fed with DC current on the input side by the DC source 10, applies an AC voltage Uw to the series resonant circuit 30 on the output side.
[0040] The series resonant circuit 30 has a coil 31 , a capacitor 32 and a series resistor 33 which are electrically connected in series.
[0041] The operating frequency of the converter 20 and thus the frequency f of the alternating voltage Uw applied by the converter 20 to the series resonant circuit 30 is set in the embodiment according to Figure 1 by a frequency generator 40 using a frequency generator signal S f via a clock line 41. The frequency generator signal S f directly or indirectly controls internal switching elements 21 of the converter 20, which are only schematically sketched in Figure 1. The converter 20 can contain, as switching elements 21, for example, semiconductor switches such as transistors or the like, which can be connected, for example, in a half-bridge circuit or a full-bridge circuit. In other words, the converter 20 can be designed as a controllable inverter of any design.
[0042] The frequency generator 40, which can output, for example, a sine or square wave signal as a frequency generator signal S f for controlling the converter 20, is controlled by a monitoring device 50 of the sensor 1 via a control line 51. The monitoring device 50 specifies the level of the frequency of the frequency generator signal S f to the frequency generator 40 and thus also determines the level of the frequency f of the alternating voltage Uw applied by the converter 20 to the series resonant circuit 30.
[0043] The frequency f of the alternating voltage Uw applied by the converter 20 to the series resonant circuit 30 is preferably set by the monitoring device 50 such that the DC source 10 - in detection-free sensor operation - feeds the maximum current Imax at the maximum voltage Umax into the converter 20; this will be explained in more detail below.
[0044] The monitoring device 50 is connected to the output of the DC source 10 via a measuring line 52 and a current and voltage sensor 60 and uses these to measure the output voltage U and the output current I of the DC source 10.
[0045] The operation of sensor 1 utilizes the knowledge that series resonant circuit 30, and in particular its resonant frequency, can be influenced by external influences. If, for example, iron material, such as the iron material of a rail vehicle wheel 120, is brought close to coil 31, the resonant frequency of series resonant circuit 30 changes and the electrical power that can be fed into series resonant circuit 30 drops, which—due to the current limitation by current source 11—is reflected in a drop in the output voltage U applied by DC source 10 to converter 20.
[0046] The monitoring device 50 accordingly generates the wheel detection signal RDS when the output voltage U of the DC source 10 falls below the predetermined maximum voltage Umax by a predetermined amount.
[0047] Figure 2 shows a section of a railway track system 100 equipped with the sensor 1 according to Figure 1. Figure 2 shows the installation situation on the railway rail 110 as a cross-section through the railway rail 110. A rail vehicle wheel 120 with its wheel flange 121 is located above the railway rail 110.
[0048] Since the sensor 1 is arranged in the region of the railway track 110 or attached thereto, it is suitable for detecting the rail vehicle wheel 120. For this purpose, the coil 31 is preferably arranged in the sensor housing 1a of the sensor 1 such that the magnetic field of the coil 31 runs predominantly vertically, so that the metal mass of the rail vehicle wheel 120 lying above it can be easily detected.
[0049] The monitoring device 50 of the sensor 1 generates the wheel detection signal RDS when the output voltage U of the DC source 10 falls below the maximum voltage Umax by a predetermined amount.
[0050] Since sensor 1 is mounted near railroad track 110, the resonant frequency of series resonant circuit 30 is also influenced by the iron material of the rail. If, in the event of a malfunction, sensor 1 is removed from railroad track 110, for example, because it falls off, is torn off, or is simply stolen, the influence of the iron of railroad track 110 is eliminated, which also changes the resonant frequency of series resonant circuit 30. This leads to a drop in the output current I of the DC source.
[0051] Accordingly, it is advantageous if the monitoring device 50 generates a warning signal WS when the output current I of the DC source 10 falls below the maximum current Imax by a predetermined amount. This warning signal indicates that the position of the sensor 1 has been changed or another defect has occurred, requiring inspection or repair.
[0052] The sensor 1 according to Figures 1 and 2 is preferably operated as follows: Commissioning:
[0053] After the installation of the sensor 1, for example on the railway track 110 according to Figure 2, the monitoring device 50 first searches for the optimum operating frequency of the frequency generator signal S f of the frequency generator 40 and thus the optimum alternating voltage Uw for the series resonant circuit 30 - in detection-free operation without the influence of railway wheels to be detected.
[0054] In the course of this search for the optimum operating frequency, the monitoring device 50 changes the operating frequency until it determines that - based on the respectively applied operating frequency - with a further increase in frequency the output current I of the DC source 10 decreases and with a reduction in frequency the output voltage U of the DC source 10 decreases.
[0055] Figure 3 shows an example of the search in more detail. A first operating frequency fl can be seen, which is initially set by the monitoring device 50 during commissioning. It can be seen that the output voltage U is less than the maximum voltage Umax. Accordingly, the monitoring device 50 will change the operating frequency, namely increase it as shown in Figure 3, until it finds the optimum operating frequency fopt, at which - i.e. related to this optimum operating frequency fopt - the output current I of the DC source 10 decreases with a further increase in frequency and the output voltage U of the DC source 10 decreases with a reduction in frequency.
[0056] Since the optimum operating frequency fopt determined in this way corresponds to the resonance frequency of the series resonant circuit 30 , the magnitude of the impedance of the series resonant circuit 30 is minimal and the DC source 10 will feed the maximum current Imax at maximum voltage Umax into the converter 20 .
[0057] Working frequency test:
[0058] The monitoring device 50 will preferably perform an operating frequency test regularly or irregularly, independently or in response to an external control command SB. The operating frequency test is preferably performed in detection-free sensor mode to avoid errors or delays in the operating frequency test due to the influence of interfering ferrous material from passing rail vehicle wheels 120.
[0059] As part of the working frequency test, the monitoring device 50 will leave the current working frequency of the frequency generator 40 unchanged if the DC source 10 feeds the maximum current Imax at maximum voltage Umax into the converter 20, i.e. the optimal operating point has already been reached.
[0060] If the maximum voltage Umax or the maximum current Imax is not reached, the monitoring device 50 changes the operating frequency until it determines that the DC source 10 feeds the maximum current Imax into the converter 20 at the maximum voltage Umax.
[0061] Alternatively or additionally, the monitoring device 50 can initiate a frequency increase and a frequency reduction within the scope of the operating frequency test - based on the previously set (i.e. the current) operating frequency - and observe the effects of the frequency increase and the frequency reduction on the output voltage U of the DC source 10 and the output current I of the DC source 10.
[0062] In the latter variant, the monitoring device 50 will leave the currently set operating frequency unchanged if - based on this respective current operating frequency - the output current I of the DC source 10 decreases when the frequency is increased and the output voltage U of the DC source 10 decreases when the frequency is reduced.
[0063] Otherwise, the monitoring device 50 will be
[0064] Working frequency test, change the working frequency until it determines that - based on the last set working frequency - with further increase in frequency the output current I of the DC source 10 decreases and with further reduction in frequency the output voltage U of the DC source 10 decreases; as soon as it determines this, it will continue to use the last set working frequency as the new optimal working frequency fopt for further sensor operation until the next working frequency test.
[0065] Sensor 1 can be constructed as a multi-channel system, e.g., as a dual system with two sensors mounted one behind the other in the longitudinal direction of the rail and used to detect the direction of a train due to their signal overlap. In this case, the individual sensors 1 preferably have series resonant circuits 30 with different resonant frequencies to avoid interference caused by beat effects on the signal voltages.
[0066] In the exemplary embodiments explained in connection with Figures 1 to 3, the frequency generator 40 can be adjusted with regard to its operating frequency by the monitoring device 50 in order to find and set the optimum operating frequency fopt. If the optimum operating frequency fopt for a given application is already known, for example because it was measured or simulated, the converter 20 can also always be operated with the same constant operating frequency and there is no need for control by the monitoring device 50 and the control line 51 between the monitoring device 50 and the frequency generator 40. In such a case, a simple oscillator circuit which fixedly specifies the operating frequency can be used instead of the frequency generator 40.
[0067] The exemplary embodiments for the sensor 1 explained above can - but do not have to - have one or more of the features, advantages or properties listed below: - The series resonant circuit 30 is preferably not operated as a self-oscillating oscillator, but is preferably controlled with its resonant frequency via a converter 20.
[0068] - The converter 20 is preferably designed in such a way that its own power consumption is negligible compared to that of the series resonant circuit 30 , so that the measured variables M for U and I essentially reflect the power consumption of the series resonant circuit 30 .
[0069] - The frequency generator 40 can be a simple square wave generator.
[0070] - The converter 20 can comprise a simple bridge circuit of transistors or the like, which are switched on / off digitally.
[0071] - A capacitor for smoothing the supplied current I or voltage U is preferably located on the current / voltage supply to the converter 20.
[0072] - The levels of the measured variables M for the output voltage U and the output current I which arise during operation and are present at the input of the converter 20 are preferably fed via a measuring line 52 to the monitoring device 50 which may, for example, comprise a microprocessor. This evaluates the voltage and current levels and outputs the detection signal or the warning signal for further processing. In the case of a frequency adjustment to the optimum resonance frequency, the frequency of the frequency generator 40 is preferably detuned via a control signal such that the values Imax and Umax are set at the input of the converter 20, as described.
[0073] - The sensor 1 can advantageously be constructed so that only a few components such as the converter 20 and the series resonant circuit 30 are mounted directly on the rail because the mechanical load on the components is greatest on the rail. The other components, i.e. the monitoring device 50, the frequency generator 40 and the DC source 10, are preferably located at a greater distance, e.g. next to the track. - The series resonant circuit 30 can have a high oscillation amplitude, i.e. absorb a high amount of energy. This in turn leads to a correspondingly high immunity to interference of the sensor 1 because the effect of any coupled-in interference energy depends on the oscillation circuit amplitude, i.e. the energy in the series resonant circuit 30. A self-compensating arrangement with oppositely wound partial coils in series can be omitted.
[0074] - The series resonant circuit 30 is preferably not operated as a feedback, self-oscillating oscillator, but is controlled at its resonant frequency via the converter 20 with the aid of the frequency generator 40.
[0075] - Precise adjustment of the optimal resonance frequency is possible without having to directly measure the oscillation amplitude. The series resonant circuit 30 itself therefore does not need to have a signal output for level measurement.
[0076] - When a metal wheel passes over a wheel, the resonant circuit amplitude decreases due to the eddy current loss in the metal and its field distortion of the alternating magnetic field. For a simple evaluation, only the power consumption of the series resonant circuit 30 can be considered: The series resonant circuit 30 is preferably supplied or driven with a fixed, upper-limited power quantity.
[0077] - The series resonant circuit 30 has the lowest impedance at its resonant frequency. At the resonant frequency, the maximum possible power is absorbed by the series resonant circuit 30. If the fed-in frequency f increases above the resonant frequency, the feed-in current I decreases, while the applied voltage U remains constant. If the fed-in frequency f decreases below the resonant frequency, the feed-in current I remains constant, while the applied voltage U decreases. Frequency adjustment can now be carried out in such a way that, during a frequency sweep, the voltage U present at the feed-in point of the converter 20 and the incoming current I are measured: During a frequency sweep from low to high frequencies, only the maximum possible current (Imax of the current source 11) will flow into the series resonant circuit 30 when the applied voltage is low.As the frequency f increases, the applied voltage U increases and, with a constant current flow Imax, reaches the maximum value Umax in the resonance case. As the frequency f continues to increase, 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). The resonance frequency is therefore the frequency f at which the current I and the voltage U are at a maximum. The resonance frequency for the series resonance circuit 30 has thus been found in the specific installation situation. This frequency f can be saved and used as the operating frequency during operation. Since it is a direct current and a direct voltage, these values are easy to measure without having to intervene in the actual series resonance circuit 30. This can therefore be designed very compactly, which minimizes any potential interference.Signal distortion caused by the power extraction of a measuring signal which directly measures the amplitude voltage can also be avoided.
[0078] At the operating point of the resonance frequency, when the wheel passes over, the voltage U applied to the converter 20 drops compared to the rest value due to the damping effect of the iron mass. This voltage reduction can be used for detection and evaluated or further processed in a downstream unit. A check of the resonance frequency in the rest state, which may have changed due to mechanical or thermal influences, is preferably carried out by briefly changing the current operating frequency by a defined amount Frequency change Af. A frequency change Af below the operating frequency causes the supply voltage level to decrease by a specific value. A frequency change Af above the operating frequency causes the current level to decrease by a specific value. If the deviation values on both sides are as expected, then the set operating frequency is also the resonance frequency.
[0079] Finally, it should be mentioned that the features of all the embodiments described above can be combined with one another in any desired manner in order to form further other embodiments of the invention.
[0080] All features of subclaims can also be combined individually with each of the subordinate claims, either individually or in any combination with one or other subclaims, in order to obtain further embodiments.
Claims
Patent claims 1. Sensor ( 1 ) , characterized by - a series resonant circuit (30) comprising a coil (31), a capacitor (32) and a series resistor (33) connected electrically in series, - a DC source (10) which is both current and voltage limited and outputs a predetermined maximum current (Imax) as output current (I), provided that the output voltage (U) required to drive this maximum current (Imax) does not exceed a 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 applies an AC voltage (Uw) on the output side to the series resonant circuit (30), the frequency (f) of which is set such that the DC source (10) - in detection-free sensor operation - feeds the maximum current (Imax) at maximum voltage (Umax) into the converter (20), and - a monitoring device (50) that generates a detection signal (RDS) when the output voltage (U) of the DC source (10) falls below the maximum voltage (Umax) by a predetermined amount, and / or generates a warning signal (WS) when the output current (I) of the DC source (10) falls below the maximum current (Imax) by a predetermined amount.
2. Sensor (1) according to claim 1, characterized in that - the sensor (1) has a frequency generator (40) that controls the converter (20) and thus specifies the frequency (f) of the alternating voltage (Uw), and - the monitoring device (50) is connected to the frequency generator (40) and sets its operating frequency and thus the frequency (f) of the alternating voltage (Uw).
3. Sensor (1) according to one of the preceding claims, characterized by the fact that the monitoring device (50) is designed to perform an operating frequency test regularly or irregularly, independently or in response to an external control command (SC).
4. Sensor (1) according to claim 3, characterized in that the monitoring device (50) is designed to perform the operating frequency test in detection-free sensor operation.
5. Sensor (1) according to any one of the preceding claims 3 to 4, characterized in that the monitoring device (50) leaves the operating frequency of the frequency generator (40) unchanged during the operating frequency test when the DC source (10) feeds the maximum current (Imax) at maximum voltage (Umax) into the converter (20).
6. Sensor (1) according to any one of the preceding claims 3 to 5, characterized in that the monitoring device (50) changes the operating frequency during the operating frequency test until it determines that the DC source (10) feeds the maximum current (Imax) at maximum voltage (Umax) into the converter (20).
7. Sensor (1) according to any one of the preceding claims 3 to 6, characterized in that the monitoring device (50) initiates a frequency increase and a frequency reduction as part of the operating frequency test - with reference to the previously set operating frequency - and the effects of the frequency increase and the frequency reduction on the output voltage (U) of the DC source (10) and the output current (I) of the DC source (10) observed.
8. Sensor (1) according to claim 7, characterized in that the monitoring device (50) leaves the operating frequency unchanged when - with reference to the respective current operating frequency - the output current (I) of the DC source (10) decreases when the frequency increases and the output voltage (U) of the DC source (10) decreases when the frequency decreases.
9. Sensor (1) according to one of the preceding claims 7 to 8, characterized in that the monitoring device (50) changes the operating frequency during the operating frequency test until it determines that - with reference to the respective changed operating frequency - the output current (I) of the DC source (10) decreases with further frequency increase and the output voltage (U) of the DC source (10) decreases with further frequency reduction, and - as soon as it determines this - uses the changed operating frequency as the new operating frequency for further sensor operation until the next operating frequency test.
10. Sensor (1) according to one of the preceding claims, characterized in that the sensor (1) is a flange detector designed for wheel detection of railway vehicle wheels (120) traveling on a railway track (110) and passing the sensor (1) and generates a wheel detection signal (RDS) as a detection signal.
11. Railway track system (100) , characterized by the fact that - this is equipped with a sensor (1) according to one of the preceding claims, - wherein the sensor (1) is located in the area of a railway track (110) is arranged or attached to it and serves to detect railway vehicle wheels (120) traveling on the railway track (110) and passing the sensor (1).
12. Railway track system (100) according to claim 11, characterized in that the monitoring device (50) of the sensor (1) generates a wheel detection signal when the output voltage (U) of the DC source (10) falls below the maximum voltage (Umax) by a predetermined amount.
13. Railway track system (100) according to claim 11 or 12, characterized in that the monitoring device (50) of the sensor (1) generates a warning signal (WS) when the output current (I) of the DC source (10) falls below the maximum current (Imax) by a predetermined amount.
14. Method for adjusting a sensor (1) according to one of the preceding claims, characterized in that - for the DC source (10) the maximum current (Imax) and the maximum voltage (Umax) are specified and - the frequency (f) of the alternating voltage (Uw) applied to the series resonant circuit (30) is adjusted such that the DC source (10) feeds the maximum current (Imax) at maximum voltage (Umax) into the series circuit.
15. The method of claim 14, characterized in that - as part of an operating frequency test, the operating frequency of a frequency generator (40) and thus the frequency (f) of the alternating voltage (Uw) applied to the series resonant circuit (30) is adjusted until it is determined that, with an increase in frequency, the output current (I) of the DC source (10) decreases and, with frequency reduction, the output voltage (U) of the DC source (10) decreases, and - the adjusted operating frequency is used as the new operating frequency for the continued operation of the sensor (1).