JP6530789B2 - Axle detection device, axle detection system - Google Patents

Description

  The present invention relates to an axle detection device that detects an axle based on an AC magnetic field of a detector installed in a track.

  The axle detector realizes train detection with a simple configuration. In train detection, a sensor (transmission / reception detector) is installed at a block boundary to detect an axle. The sensor installation needs to properly set many adjustment elements such as angle, height, and level in order to realize reliable axle detection. As such adjustment technology, for example, even if there is a temperature fluctuation or a secular fluctuation, a technology for achieving stable axle detection by adjusting a reference value for detecting an axle based on the state of a transmission signal is proposed. (See Patent Document 1).

  The axle detection system 101 (axle detector) of a comparative example is shown with reference to FIG. The axle detection system 101 obtains a reception signal from the detection signal 150 (transmission detection element 151, reception detection element 152) installed on the track (rail) 99 and the AC signal supply to the transmission detection element 151 and the reception detection element 152. The transmission / reception device 120 and the transmission / reception control unit 121 are provided, and the axle (wheel) of the vehicle 90 is detected based on the change of the alternating magnetic field. The transmission / reception control unit 121 generally controls the components of the axle detection system 101.

  More specifically, as a function on the transmission side, the AC signal output from the frequency-fixed oscillation unit 131 is gain-adjusted by the gain adjustment unit 132 and amplified by the transmission amplifier 133. Thereafter, it is sent to the transmission detector (transmission coil) 151 of the detector 150 by the transmission transformer 134. A resonant capacitor 135 is disposed between the transmission transformer 134 and the transmission detector 151. The resonant capacitor 135 is adjustable in capacitance.

  As a function of the receiving side, the signal received by the receiving detector (receiving coil) 152 is transmitted to the receiving transformer 144 by the receiving cable 154. Resonant capacitors 145 are provided at both ends of the receiving transformer 144. The signal is sent from the reception transformer 144 to the phase detection unit 142 via the reception amplifier 143. The phase detection unit 142 acquires a reference phase which is an output of the oscillation unit 131, and outputs the received voltage to the determination circuit 141.

  As adjustment elements described above, the positions and angles of the detector 150 (transmission detector 151, reception detector 152), lengths of the transmission cable 153 and the reception cable 154, the resonance capacitors 135 and 145, and the gain adjustment unit 132 is there.

JP, 2000-6808, A

  By the way, in proper axle detection, what is important is to properly set the above-mentioned adjustment factor at the time of sensor installation. In general, the adjustment at the time of sensor installation tends to be very complicated, and a technique for reducing the number of adjustment steps and for automation has been required. That is, in the configuration shown in FIG. 6, the adjustment elements may influence each other, which may result in a large amount of adjustment effort. The technology disclosed in Patent Document 1 has a certain effect on temperature change and aging, but can not be applied as it is for adjustment at the time of sensor installation, and another technology has been required.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for solving the above-mentioned problems.

Axle detection apparatus of the present invention, depending on the transmission signal output a detection element which receives the coils and transmitting coils are arranged to sandwich the rail, from the transmission coil and the transmission unit for transmitting the transmission signal to the transmission coil and a reception device having a reception unit that determines whether the vehicle is present in the acquired the rail received signal from the receiving coil Te, and the transmission unit, the oscillator and the oscillation unit for oscillating said transmission signal And a gain adjustment unit configured to amplify the output transmission signal , wherein the reception unit compares the reception signal from the reception coil with the transmission signal output from the oscillation unit and outputs a reception voltage. And a plurality of frequencies set in a predetermined band in the oscillation unit, connected to the oscillation unit, the gain adjustment unit, and the phase detection unit, and the gain adjustment unit. The received voltage corresponding to the combination with a plurality of amplification factors set within a predetermined amplification range is measured by the phase detection unit with all the combinations of the plurality of frequencies and the plurality of amplification factors. After that, calibration is performed to extract the combination in which the received voltage is closest to a predetermined target value, and thereafter, the frequency and the amplification factor constituting the combination are the oscillating unit, and They are respectively set in the gain adjustment unit.
Further, the target value may be smaller than the maximum value of the reception voltage.
Further, in the calibration, the plurality of frequencies may be changed in the band from either the low side to the high side or from the high side to the low side only in one direction.
Further, in the calibration, even when the amplification factor changes, the plurality of frequencies are changed within the band only in one direction from the low side to the high side or from the high side to the low side. Good.
Further, the band may be determined according to the length of a transmission cable connecting the transmission coil and the transmission / reception device or the length of a reception cable connecting the reception coil and the transmission / reception device.
The axle inspection system according to the present invention comprises two of the axle detection devices using the transmission signals of different frequencies from each other, and in the calibration, the reception is performed in one of the axle detection devices using the transmission signals of low frequency. In the other axle detection device using the transmission signal of the high frequency, the received voltage is maximized by changing the plurality of frequencies in the band on the low frequency side bordering on the frequency of the oscillating portion where the voltage reaches the maximum value. The plurality of frequencies are changed in the band on the high frequency side bordering on the frequency of the oscillation unit which becomes a value.

  According to the present invention, it is possible to realize the reduction of the number of adjustment steps at the time of sensor installation of the axle detection device. That is, (1) reduction in total cost due to reduction in the number of adjustment steps, and (2) suppression of variation due to the skill level of the coordinator can be expected.

It is a block diagram showing an outline of an axle detection system concerning this embodiment. It is a block diagram which shows the specific structure of the detector and transmission-and-reception apparatus for 1 channel of an axle shaft detection system based on this embodiment. It is a graph which shows the example of a characteristic of a reception level (it shows with electric current value Ic [A] of a transmission detector) based on this embodiment. It is a graph which shows the example of a characteristic of the reception level at the time of calibration based on this embodiment. It is a flowchart of calibration based on this embodiment. 1 is a block diagram showing a schematic configuration of an axle detection system according to the background art.

  Next, modes for carrying out the present invention (hereinafter, simply referred to as “embodiments”) will be specifically described with reference to the drawings.

  FIG. 1 is a block diagram showing an outline of an axle detection system 1 according to the present embodiment. The feature of this embodiment lies in the adjustment function of the components of the axle detection system 1 (in particular, the adjustment function of the transmission level of the transmission path), and the axle detection method itself is a general technique. Focusing on such an adjustment function, and briefly explaining the detection method itself.

  The axle detection system 1 detects the wheels 92 of the vehicle 90 on the track 99 and notifies the signal control system 10. The signal control system 10 uses the notification from the axle detection system 1 for the operation control of the vehicle 90.

  The axle detection system 1 has a dualized axle detection system (CH1, CH2). That is, as a first channel (CH1), a detector (CH1) 50a and a transmission / reception device (CH1) 20a are provided. As a second channel (CH2), a detector (CH2) 50b and a transmission / reception device (CH2) 20b are provided. The components of the first channel (CH1) and the second channel (CH2) are basically configured by the same device. That is, when the detector (CH1) 50a and the detector (CH2) 50b are not distinguished from each other, they are referred to as "detector 50". When the transmitter / receiver (CH1) 20a and the transmitter / receiver (CH2) 20b are not distinguished from one another, they are referred to as "transmitter / receiver 20".

  FIG. 2 is a block diagram showing the configuration of the axle detection system 1, and here shows a block diagram of only one channel, that is, the detector 50 and the transmitting / receiving device 20. As shown in FIG.

  The detector 50 includes a transmission detector 51 that is a transmission coil and a reception detector 52 that is a reception coil, and is disposed at a position facing each other across one of the tracks 99 (rails). The transmission detector 51 and the reception detector 52 are integrated with the fixing stay, respectively, and in the case of fixing, adjustment of the installation mode such as height, position, angle (direction), etc. is unnecessary. That is, it is not necessary to practically consider the difference in the installation mode of the detector 50 at the time of calibration described later.

  The transmission detector 51 is connected to the transmission / reception device 20 via the connection terminal 39 by the transmission cable 53. Similarly, the reception detector 52 is connected to the transmission / reception device 20 via the connection terminal 49 by the reception side cable 54. The transmission side cable 53 and the reception side cable 54 are selected from a plurality of types (for example, three types of 5 m, 10 m, and 15 m) of fixed length cables. That is, since the lengths of the transmitting cable 53 and the receiving cable 54 are selected from a plurality of lengths, the conditions at the time of calibration can be greatly narrowed.

  The transmission / reception apparatus 20 includes a transmission unit 30 which is an output system to the transmission detector 51, a reception unit 40 which is an input system from the reception detector 52, a transmission / reception control unit 21, and a calibration unit 25.

  The transmission / reception control unit 21 centrally controls the components of the transmission / reception device 20. The calibration unit 25 performs adjustment when installing the axle detection system 1 with respect to the component having the adjustment function in order to optimize the detection function of the detector 50. Details of the adjustment procedure will be described later. When the detectors 50 are duplicated, only one calibration unit 25 is provided in common, and calibration is performed for each channel. After completion of the calibration, the axle detection system 1 is operated with the set values obtained by the calibration.

  The transmission unit 30 includes an oscillation unit 31, a gain adjustment unit 32, a transmission amplifier 33, and a transmission transformer 34 in order from the downstream side. On the path between the connection terminal 39 of the transmission cable 53 of the transmission detector 51 and the transmission transformer 34, a resonance capacitor 35 whose capacity is fixed is inserted in series.

  The oscillation unit 31 can change the oscillation frequency by the calibration unit 25 and outputs an alternating current signal to the gain adjustment unit 32 at the set frequency. Further, it is output to the phase detection unit 42 of the reception unit 40 as a reference phase. The gain adjustment unit 32 adjusts the output gain of the AC signal to a set value, and outputs the adjusted value to the transmission amplifier 33.

  The transmission amplifier 33 performs predetermined amplification processing on the signal acquired from the gain adjustment unit 32, and outputs the signal to a transmission transformer 34 which is a so-called matching transformer. With this configuration, oscillation occurs at a predetermined oscillation frequency by “L (coil component)” of the transmission detector 51 and “C (capacitance)” of the resonant capacitor 35.

  The reception unit 40 includes a reception transformer 44, a reception amplifier 43, a phase detection unit 42, and a determination circuit 41 in order from the upstream side. The reception transformer 44 is a so-called matching transformer, matches the impedance of the reception signal acquired from the reception detector 52 via the connection terminal 49, and outputs the impedance to the reception amplifier 43 as a reception input voltage. The reception amplifier 43 performs predetermined amplification processing on the signal, and outputs the signal to the phase detection unit 42.

  The phase detection unit 42 compares the reference phase acquired from the oscillation unit 31 with the signal acquired from the reception amplifier 43, and outputs the result as a reception voltage. The determination circuit 41 detects an axle based on the received voltage. A fixed resonant capacitor may be provided in parallel with the reception transformer 44 in the path of the reception transformer 44 and the connection terminal 49.

  Subsequently, calibration at the time of installation of the axle detection system 1 will be described with reference to FIGS. 3 to 5. FIG. 3 is a graph showing an example of reception level characteristics. In this graph, when the cable length is changed to three types (5 m, 10 m, and 15 m), the relationship between the oscillation frequency and the reception level (shown here by the current value Ic [A] of the transmission detector 51) is changed. It shows. FIG. 4 is a graph showing an example of the characteristic of the reception level at the time of calibration in a certain cable length.

  The characteristic of the reception level in FIG. 3 shows a substantially symmetrical waveform having a peak (peak shape) for each cable length. For the peak position (frequency), the cable length of 5 m is the largest, and the cable length of 15 m is the smallest.

  In the calibration process, the transmission level (transmission level, reception level) of the transmission path is optimized. Specifically, the oscillation frequency of the oscillation unit 31 and the gain value of the gain adjustment unit 32 are changed, and the current value of the transmission detection element 51 does not become an overcurrent, and the detection upper limit value as the maximum value in the non-magnetic saturation range. Set Th1max and Th2max. When applied to the axle detection system 1 of FIG. 1, that is, a dual system, it is necessary to separate the oscillation frequencies of the first channel (CH1) and the second channel (CH2) by a specified value or more (for example, 2 kHz or more) Considering the characteristics of the reception level exhibiting a mountain-shaped waveform, the reception level target value of the first channel (CH1) is Th1 in the frequency band fL lower than the peak position, and the second channel (CH2) in the frequency band fH higher than the peak position The calibration unit 25 adjusts the oscillation unit 31 and the gain adjustment unit 32 so as to set the reception level target value of the threshold value Th2 to be close to the target values Th1 and Th2.

  In the first channel (CH1) of the frequency band fL, the frequency is gradually changed from the low side to the high side, and calibration is performed so that the reception level approaches the target value Th1. On the other hand, in the second channel (CH2) of the frequency band fH, the frequency is gradually changed from the high side to the low side, and calibration is performed so that the reception level approaches the target value Th2. Further, as shown in FIG. 4, the gain value is changed from smaller to larger ones in order. By adopting such a procedure, the oscillation frequency at which the first channel (CH1) and the second channel (CH2) are separated by the specified value or more within a range where the signal current of the transmission unit does not become excessive and magnetic saturation does not occur. Can.

  FIG. 5 is a flowchart showing the procedure of calibration. FIG. 5 illustrates an example of application to the axle detection system 1 having the duplexed detector 50 of FIG. 1 and the characteristics of FIG. 4. When the calibration is started, the calibration unit 25 first calibrates the first channel (CH1) (S10), and then calibrates the second channel (CH2) (S20). Calibration of the first channel (CH1) and the second channel (CH2) is performed separately from the viewpoint of interference prevention. If no interference measures are taken and there is no concern about interference, calibration is performed at the same time. It may be

  Here, in the calibration of the first channel (CH1), when the gain setting value G1 reaches the maximum, the process shifts to the calibration of the second channel (CH2). Then, when the gain setting value G2 reaches the maximum in the calibration of the second channel (CH2), the calibration ends. The following more specifically describes.

  In the calibration (S10) of the first channel (CH1), the frequency setting value F1 (F1 (natural number): 1, 2,..., Fmax1) of the oscillation frequency of the oscillation unit 31 and the gain setting value of the gain adjustment unit 32 G1 (G1 (natural number): 1, 2, ..., Gmax 1) is sequentially set. Further, the detection upper limit value Th1max and the detection lower limit value Th1min are set to predetermined values.

  The calibration unit 25 turns on the transmission / reception device (CH1) 20a of the first channel (CH1) and turns off the transmission / reception device (CH2) 20b of the second channel (CH2) (S101). Subsequently, the calibration unit 25 initializes the gain setting value G1 = 0, the frequency setting value F1 = 0, and the reception level difference ΔRv = Th1max−Th1min (S102).

  Subsequently, in order to obtain specific gain setting value G1 and frequency setting value F1, calibration unit 25 increments gain setting value G1 (S103) and further increments frequency setting value F1 (S104). . As a result, the search (sweep) of the reception level Rv is sequentially performed under the condition of the gain setting value G1 = 1 (predetermined minimum gain) and the frequency setting value F1 = 1 (predetermined minimum frequency). That is, the search is sequentially performed from the smaller gain value and the smaller oscillating frequency.

  The calibration unit 25 acquires the reception signal from the phase detection unit 42 and calculates the reception level Rv (S105), and the reception level Rv is within a predetermined range, more specifically, between the detection upper limit Th1max and the detection lower limit Th1min. It is determined whether or not there is an interval (Th1min ≦ Rv ≦ Th1max) (S106).

  If the reception level Rv is within the predetermined range (Th1min ≦ Rv ≦ Th1max) (Y in S106), the calibration unit 25 determines the magnitude (| Th1-Rv |) of the difference between the target value Th1 and the reception level Rv. It is determined whether or not it is equal to or less than the recorded reception level difference ΔRv (initial value is set to Th1max−Th1min) (S107). If the reception level difference ΔRv or less (Y in S107), the calibration unit 25 rewrites the reception level difference ΔRv to the new | Th1-Rv | (S108), and further sets the gain setting value G1 and the frequency at that time. The value F1 is overwritten and stored in a predetermined memory of the calibration unit 25 (S109).

  When the reception level Rv is not within the predetermined range (Th1min ≦ Rv ≦ Th1max) (N in S106) or when | Th1-Rv | ≦ ΔRv (N in S107), and the gain setting value G1 and the frequency setting value F1 After overwriting (S109), the calibration unit 25 determines whether the frequency setting value F1 = Fmax1, that is, whether the search has advanced to the last frequency setting value in the gain setting value G1 at that time (S110). .

  If the frequency setting value F1 = Fmax1 (N in S110), the calibration unit 25 returns to the process of S104, increments the frequency setting value F1, and performs the subsequent processes again.

  If the frequency setting value F1 = Fmax1 (Y in S110), the calibration unit 25 initializes the frequency setting value F1 (F1 = 0) (S111), and the gain setting value G1 = Gmax1, ie, the last. It is determined whether the search is advanced to the gain setting value (largest gain value) (step S112).

  If the gain setting value G1 <Gmax1 (N of S112), the calibration unit 25 returns to the process of S103 and continues the subsequent processes. If the gain setting value G1 = Gmax1 (Y in S112), the calibration unit 25 ends the calibration of the transmission / reception device (CH1) 20a, and shifts to the calibration (S20) of the transmission / reception device (CH2) 20b.

  In the calibration (S20) of the second channel (CH2), the frequency setting value F2 (F2 (natural number): 1, 2,..., Fmax2) of the oscillation frequency of the oscillation unit 31 and the gain setting value of the gain adjustment unit 32 G2 (G2 (natural number): 1, 2, ..., Gmax 2) is sequentially set. Further, the detection upper limit value Th2max and the detection lower limit value Th2min are set to predetermined values. The detection upper limit Th2max and the detection lower limit Th2min for the second channel (CH2) may be the same as or different from the detection upper limit Th1max and the detection lower limit Th1min for the first channel (CH2).

  The calibration unit 25 turns off the transmission / reception device (CH1) 20a of the first channel (CH1) and turns on the transmission / reception device (CH2) 20b of the second channel (CH2) (S201). Subsequently, the calibration unit 25 initializes the gain setting value G2 = 0, the frequency setting value F2 = 0, and the reception level difference ΔRv = Th2max−Th2min (S202).

  Subsequently, in order to obtain the specific gain setting value G2 and the frequency setting value F2, the calibration unit 25 increments the gain setting value G2 (S203) and further increments the frequency setting value F2 (S204). . As a result, the reception level Rv is searched sequentially under the condition of the gain setting value G2 = 1 (predetermined minimum gain) and the frequency setting value F2 = 1 (predetermined maximum frequency). That is, the search is sequentially performed from the smaller gain value and the larger oscillating frequency.

  The calibration unit 25 obtains the reception signal from the phase detection unit 42 and calculates the reception level Rv (S205), and the reception level Rv is in a predetermined range, more specifically, between the detection upper limit Th2max and the detection lower limit Th2min. It is determined whether (Th2min ≦ Rv ≦ Th2max) (S206).

  If the reception level Rv is within the predetermined range (Th2min ≦ Rv ≦ Th2max) (Y in S206), the calibration unit 25 determines that the magnitude (| Th2-Rv |) of the difference between the target value Th2 and the reception level Rv is It is determined whether it is less than the recorded reception level difference ΔRv (initial value is set to Th2max−Th2min) (S207). If the reception level difference ΔRv or less (Y in S207), the calibration unit 25 rewrites the reception level difference ΔRv to a new | Th2-Rv | (S208), and further sets the gain setting value G2 and the frequency at that time. The value F2 is overwritten and stored in a predetermined memory of the calibration unit 25 (S209).

  When the reception level Rv is not within the predetermined range (Th2min ≦ Rv ≦ Th2max) (N in S206) or when | Th2-Rv | ≦ ΔRv (N in S207), and the gain setting value G2 and the frequency setting value F2 After overwriting (S209), the calibration unit 25 determines whether the frequency setting value F2 = Fmax2, that is, whether the search has advanced to the last frequency setting value in the gain setting value G2 at that time (S210). .

  If the frequency setting value F2 = Fmax2 (N in S210), the calibration unit 25 returns to the processing of S204, increments the frequency setting value F2, and performs the subsequent processing again.

  If the frequency setting value F2 = Fmax2 (Y in S210), the calibration unit 25 initializes the frequency setting value F2 (F2 = 0) (S211), and then the gain setting value G2 = Gmax2, that is, the last. It is determined whether the search is advanced to the gain setting value (largest gain value) of (S212).

  If the gain setting value G2 <Gmax2 (N in S212), the calibration unit 25 returns to the process of S203 and continues the subsequent processes. If the gain setting value G2 = Gmax2 (Y in S212), the calibration unit 25 ends the calibration of the transmission / reception device (CH2) 20a.

  As described above, according to the present embodiment, the oscillation frequency of the oscillation unit 31 of the axle detection system 1 can be adjusted, and calibration can be performed automatically at the time of installation. As a result, the number of adjustment steps at the time of laying of the sensing element 50 can be significantly reduced. That is, it is possible to realize (1) reduction of the total cost by reduction of the number of adjustment steps, and (2) suppression of variation due to the skill level of the coordinator.

  In the above-described calibration, the oscillation frequency of the oscillation unit 31 and the gain value of the gain adjustment unit 32 are obtained. However, the present invention is not limited to this. For example, with the gain value of the gain adjustment unit 32 fixed, calibration may be performed only for the oscillation frequency of the oscillation unit 31. Conversely, the orientation of the sensing element 50 and the capacitance of the resonant capacitor 35 may be adjusted in a plurality of steps, and may be included as calibration targets. When the types of lengths of the transmitting cable 53 and the receiving cable 54 are increased, naturally, the number to be grasped as the characteristics of the reception level shown in FIG. 3 increases. When the length can be freely changed, the number of man-hours for calculating such characteristics in advance and the required storage capacity increase. As such, when the required storage capacity is increased, it can be coped with by, for example, cooperating with a server on the network or the signal control system 10.

  The present invention has been described above based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of the respective constituent elements, and such modifications are also within the scope of the present invention. In the above embodiment, although the system of duplexing has been described, it is of course possible to apply even if only one CH is configured.

1 Axle Detection System 10 Signal Control System 20 Transmitter / Receiver 20a Transmitter / Receiver (CH 1)
20b Transmitter / receiver (CH2)
Reference Signs List 30 transmission unit 31 oscillation unit 32 gain adjustment unit 33 transmission amplifier 34 transmission transformer 35 resonance capacitor 40 reception unit 41 determination circuit 42 phase detection unit 43 reception amplifier 44 reception transformer 50 detector 50a detector (CH1)
50b Detector (CH2)
51 transmission detector 52 reception detector 53 transmission cable 54 reception cable

Claims (6)

A detector in which a transmitting coil and a receiving coil are disposed across a rail;
It has a transmission unit that transmits a transmission signal to the transmission coil, and a reception unit that acquires a reception signal from the reception coil according to the transmission signal output from the transmission coil and determines whether a vehicle exists on the rail. A transmitting / receiving device,
Equipped with
The transmission unit includes an oscillation unit that oscillates the transmission signal, and a gain adjustment unit that amplifies the transmission signal output from the oscillation unit .
The reception unit includes a phase detection unit that compares the reception signal from the reception coil with the transmission signal output from the oscillation unit and outputs a reception voltage.
The oscillation unit, the gain adjustment unit, and the phase detection unit are connected, and a plurality of frequencies set in a predetermined band in the oscillation unit and an amplification range predetermined in the gain adjustment unit After the reception voltage corresponding to the combination with a plurality of set amplification factors is measured by the phase detection unit for all the combinations of the plurality of frequencies and the plurality of amplification factors, the reception voltage is determined in advance. Calibration is performed to extract the combination that is closest to the target value, and thereafter, the frequency and the amplification factor that constitute the combination are set in the oscillation unit and the gain adjustment unit, respectively. An axle detection device characterized by   The axle detection device according to claim 1, wherein the target value is smaller than the maximum value of the received voltage.   3. The calibration according to claim 1, wherein the plurality of frequencies change in the band only in one direction from the low side to the high side or from the high side to the low side. Axle detection device.   In the calibration, each time the amplification factor changes, the plurality of frequencies change in the band only in one direction from the low side to the high side or from the high side to the low side. The axle detection device according to any one of claims 1 to 3.   The band may be determined according to a length of a transmission cable connecting the transmission coil and the transmission / reception device or a length of a reception cable connecting the reception coil and the transmission / reception device. The axle detection device according to any one of claims 1 to 4.   2. The axle detection device according to claim 1, wherein the transmission signals of different frequencies are used.
  In the calibration,
  In the one axle detection device using the low frequency transmission signal, the plurality of frequencies are changed in the low frequency side band bordering on the frequency of the oscillation unit at which the reception voltage becomes the maximum value;
  In the other axle detection device using the transmission signal of high frequency, the plurality of frequencies are changed in the band on the high frequency side bordering on the frequency of the oscillating portion where the reception voltage becomes the maximum value. Axle detection system.

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