AU2009211471A1 - Method for increasing the interference resistance of a wheel sensor and wheel sensor for carrying out the method - Google Patents

Abstract

The invention relates to a method for increasing the interference resistance of a wheel sensor, in particular for a track clear detection system, wherein a transmission signal (13) is produced in at least one sensor channel, said signal being inductively coupled (4) to a reception signal (5) that is fed to an evaluation device (10) for detection of a magnetic field change as a result of a railway vehicle having traveled over the track (3), and a corresponding wheel sensor. In order to counteract the interference effect using eddy current braking, it is provided that a level separation between a utility signal to be evaluated and an interference signal is maximized in relation to a phase difference (16) between the transmission signal (13) and the reception signal (5), said difference being specific to the interference signal.

Description

PCT/EP2009/050166 - 1 2008P00146WOAU Description Method for increasing the interference resistance of a wheel sensor, and wheel sensor for carrying out the method The invention relates to a method for increasing the interference resistance of a wheel sensor, in particular for a track-free signaling installation, wherein a transmission signal is produced in at least one sensor channel and is inductively coupled to a received signal which is supplied to an evaluation device in order to detect a magnetic field change as a consequence of a rail vehicle traveling over the track, and to a wheel sensor for carrying out the method. Wheel sensors are used in railroad systems for track-free signaling as well as for other switching and signaling tasks. This is done predominantly by using the effect that the iron wheels of the rail vehicles influence a magnetic field. Two channel sensors are required in order to identify the direction of travel. When a vehicle wheel moves over them, the two sensor channels produce signals successively with a time offset, and these are used to identify the direction of travel. The wheel sensors, which operate on the inductive principle of operation, can be subdivided not only on the basis of single channel or two-channel design but also interproximity switches, which detect the reaction of the iron wheels on a sensor which produces a magnetic field, and the systems which surround railroad rails, with a separate transmitter and receiver. When a wheel travels over it, this creates a received voltage in the receiving system of the sensor, in the form of a rolling-over curve, which is also referred to as a bell curve. The wheel is considered to have been identified when a fixed switching threshold is overshot or undershot - depending on the polarity and the coil arrangement. The invention relates to an inductively PCT/EP2009/050166 - 2 2008P00146WOAU operating single-channel or two-channel wheel sensor with a separate transmitter and receiver. All inductively operating sensors have the common feature that they are sensitive to interference and to inductively input interference voltages in the region of the operating frequency. One source of this is the eddy-current brakes which have been used for some years, for example in the ICE3, and which, by virtue of their design and their position close to the rail, can cause a similarly high influence on the received voltage as the wheels themselves, and can therefore lead to incorrect counts. The invention will be described in more detail in the following text using the example of eddy-current brakes, without any intention of restricting the invention to this specific interference signal source. In fact, the subject matter of the invention relates to any adverse effect in terms of interference resistance, which is caused by eddy-current brakes or other sources with a similar effect. In order to improve the interference resistance of the sensors to these interference variables, various solution approaches are known, which are specific to the type of sensor. In the case of wheel sensors of this generic type with separate transmitter and receiver resonant circuits, DE 10 122 980 Al proposes that the resonant frequency of the receiver resonant circuit be changed with respect to the transmitted frequency, in order in particular to suppress the interference influence of the eddy-current brake. A further possibility is to adjust the switching threshold such that the influence of the eddy-current brake does not in its own right actually overshoot the switching threshold and is therefore not interpreted as wheel identification, while the wheel itself causes an even stronger influence, which is above the switching threshold, and can therefore be correctly PCT/EP2009/050166 - 3 2008P00146WOAU detected. This solution is dependent on accurate measurement of the disturbance influence by the eddy-current brakes and is, in consequence, highly complex and also unreliable. One alternative to switching threshold adjustment is adjustment of the eddy-current brake in order not to overshoot a maximum permissible influence. This solution is equally complex and unreliable, and, furthermore, is not very practicable. The invention is based on the object of specifying a method for increasing the interference resistance of a wheel sensor, and of specifying a wheel sensor which is suitable for this purpose, which allow increased interference resistance to interference voltages from various causes, in a simple manner. According to the method, the object is achieved in that a level separation between a useful signal to be evaluated and an interference signal is maximized as a function of an interference-signal-specific phase difference between the transmission signal and the received signal. Use is in this case made of the fact that the eddy-current brake, in contrast to the wheel, changes the phase angle between the transmission signal and the received signal, because of its inductively acting design. This change in the phase angle is used to reduce the interference influence. The switching thresholds for wheel identification in consequence do not require complex and precise adjustment. There is likewise no need to adjust each individual eddy-current brake on the rail vehicle. A wheel sensor for carrying out the method is characterized, according to the invention, in that a device is provided in order to maximize a level separation between a useful signal PCT/EP2009/050166 - 4 2008POO146WOAU to be evaluated and an interference signal as a function of an interference-signal-specific phase difference between the transmission signal and the received signal. Normally, a rectifier, which is synchronized to the transmission signal and produces the received signal, is provided at the receiver end. When a wheel travels over, the useful signal is produced in the form of a rolling-over curve or bell curve to be evaluated. The level of the useful signal is dependent on the phase angle between the transmission signal and the received signal. This relationship is determined as the interference-signal-specific phase difference, and is used for interference-signal suppression. To this end, claim 2 provides that the phase angle of the received signal is regulated at a maximum level value of the received signal, and, according to claim 5, an adjustable phase shift is used for this purpose. In this case, either the synchronization signal of the rectifier or the received signal itself can be regulated or shifted. The selected phase angle therefore produces the best possible level value of the received signal. A further phase shift of the received signal caused by an eddy-current brake automatically leads to a reduction in the influence, because the maximum influence is no longer reached. Another preferred embodiment for maximizing the level separation between the useful signal and the interference signal consists, according to claim 3 and according to claim 6, in that the phase difference is determined and is used to attenuate the interference signal causing it. The phase-angle signal is in this case linked to the actual received signal such that a phase change has an attenuating effect on the received signal, thus reducing or eliminating this interference-signal-dependent influence.

PCT/EP2009/050166 - 5 2008P00146WOAU The invention will be explained in more detail in the following text with reference to illustrations in the figures, in which: Figure 1 shows a block diagram of a first embodiment of a wheel sensor, and Figure 2 shows a second embodiment of a wheel sensor, illustrated in the same way as in Figure 1. Each of the two figures illustrates a sensor channel with a transmitter 1 and a receiver 2, which are arranged on both sides of a railroad rail 3 and are inductively coupled 4. The transmitter 1 and receiver 2 are in the form of resonant circuits. When the wheel of a rail vehicle travels over them, the coupling 4 is changed, and therefore the received AC voltage is changed such that a rolling-over curve is produced, in the form of a bell curve. This signal increase is used for wheel identification. The received AC voltage 5 is rectified 6, synchronized in phase to the transmitter 1, is smoothed in the downstream low-pass filter 7, and is then amplified 8. The resultant analog signal 9 is assessed in an evaluation device 10, preferably a microprocessor. In order to minimize the interference caused by an eddy-current brake in the signal processing, provision is made, as is shown in Figure 1, for the evaluation device 10 to carry out sensor matching by means of a variable phase shift 11. For this purpose, the evaluation device 10 produces a control signal 12, which controls the phase shift 11 such that, starting from the original synchronization signal 13 of the transmitter 1, the received signal 5 is shifted 14 until the analog signal 9 reaches a maximum. This effectively regulates out PCT/EP2009/050166 - 6 2008P00146WOAU phase shifts caused by an interference signal, that is to say phase differences between the transmission signal and the received signal, such that the signal 9 to be evaluated is in the optimum phase range for wheel identification and in the sub-optimum phase range of interference influence. In the embodiment illustrated in Figure 2, the phase difference 16 between the transmission signal 13 and the received signal 5 is determined in a processing unit 15, and is supplied to the evaluation device 10. The evaluation device 10 assesses the level of the analog signal 9 as a function of the determined phase difference 16, with an interference level which corresponds to the phase difference 16 being subtracted. In this variant, sensor matching, that is to say phase adjustment by means of a phase shift 11 as shown in Figure 1, is superfluous. In principle, the process of determining the phase difference 16 as carried out by the processing unit 15 can also be carried out by the evaluation device 10, which means that there is no need for a specific processing unit 15.

Claims (6)

1. A method for increasing the interference resistance of a wheel sensor, in particular for a track-free signaling installation, wherein a transmission signal (13) is produced in at least one sensor channel and is inductively coupled (4) to a received signal (5) which is supplied to an evaluation device (10) in order to detect a magnetic field change as a consequence of a rail vehicle traveling over the track (3), characterized in that a level separation between a useful signal to be evaluated and an interference signal is maximized as a function of an interference-signal-specific phase difference (16) between the transmission signal (13) and the received signal (5).

2. The method as claimed in claim 1, characterized in that the level separation is maximized by regulating the phase angle of the received signal (5) at a maximum level value of the received signal (5).

3. The method as claimed in claim 1, characterized in that the level separation is maximized by determining the phase difference (16) and by using it to attenuate the interference signal causing it.

4. A wheel sensor for carrying out the method as claimed in one of the preceding claims, characterized in that a device is provided in order to maximize a level separation between a useful signal to be evaluated and an interference signal as a function of an interference-signal-specific phase difference PCT/EP2009/050166 - 8 2008POO146WOAU (16) between the transmission signal (13) and the received signal (5).

5. The wheel sensor as claimed in claim 4, characterized in that the device has a phase shift (11) which can be regulated at the maximum level value of the received signal (5).

6. The wheel sensor as claimed in claim 4, characterized in that the device has a processing unit (15) for detection of the phase difference (16), which acts on an attenuation unit in order to attenuate the interference signal causing it.