JP2007271374A - Device and method for detecting disconnection of wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for detecting disconnection of a wire that is applicable not only to a wire in non-use but also to a wire in use and can accurately detect the disconnection. <P>SOLUTION: This disconnection detecting device comprises a high-frequency pulse signal input section 100 for inputting a high-frequency pulse signal to a fixed cable 22a, among fixed cables 22a and 22b and a moving cable 24 with a predetermined length interconnected in series, a signal waveform measuring section 102 for measuring a reflected waveform of current flowing in the fixed cables 22a and 22b and moving cable 24 with the input signal from the high-frequency pulse signal input section 100, and a determining section 103 for determining the existence of the reflected waveform measured by the signal waveform measuring section 102 in a wire to be detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wire breakage detection apparatus and method suitable for use in detecting the breakage of wires such as bare wires (trolley wires) and windings (enameled wires), insulated wires and cables.

  Generally, an electric wire is formed by twisting a plurality of strands. If these wires are disconnected, the cross-sectional area of the wire decreases and the impedance rises, resulting in an accident such as the stoppage of equipment. For this reason, in order to prevent the occurrence of equipment accidents, wire breakage detection is usually performed.

  Conventionally, for example, a method of measuring the conductor resistance of an electric wire is used for detecting the disconnection of this kind of electric wire, and the following two methods (1) and (2) are known.

(1) A DC voltage is applied to both ends of the wire, the current flowing at this time is measured, the DC resistance of the wire is measured from the current and the applied voltage, and the change in resistance value (the resistance previously determined during soundness) The wire breakage is detected from the change to the value.

(2) In the method of (1) above, by applying an AC voltage instead of a DC voltage, the AC resistance of the electric wire is measured, and a broken wire is detected from the change in the resistance value (Patent Document 1).
Japanese Examined Patent Publication No. 7-69375

  However, the conventional wire breakage detection method cannot be applied to a wire in use. In other words, if the wires are wired as power transmission cables or power cables / signal cables in equipment, and power or signals are applied to these cables (equipment is in operation), the resistance of the wires cannot be measured. Therefore, disconnection detection cannot be performed.

  In addition, when the element wire is partially disconnected, it is difficult to detect the disconnection because the resistance change in the disconnected portion is smaller than the total resistance. That is, it is impossible to carry out detection of disconnection of the electric wire with high accuracy.

  Accordingly, an object of the present invention is to provide a wire breakage detection apparatus and method that can be applied not only to a non-use but also to a wire in use, and that can perform wire break detection with high accuracy. is there.

(1) In order to achieve the above object, the present invention provides a high-frequency pulse signal injection unit that injects a high-frequency pulse signal into an incident end of a group of wires composed of a plurality of wires connected in series with a predetermined length; A signal waveform measuring unit that measures a reflected waveform of a current flowing through the plurality of electric wires according to an injection signal by a high-frequency pulse signal injecting unit, and a determination unit that determines the presence or absence of the reflected waveform in the detection target electric wire by measurement of the signal waveform measuring unit An electrical wire breakage detecting device is provided.

(2) In order to achieve the above object, the present invention includes a step of injecting a high-frequency pulse signal into an incident end of an electric wire group composed of a plurality of electric wires connected in series with a predetermined length; There is provided a wire breakage detection method comprising a step of measuring a reflected waveform of a flowing current and a step of determining the presence or absence of the reflected waveform in a detection target wire.

  According to the present invention, it can be applied not only to a non-use but also to an electric wire in use, and disconnection detection with high accuracy can be performed.

[First embodiment]
FIG. 1 is a block diagram showing an electric wire breakage detection device used for carrying out the wire breakage detection method according to the first embodiment of the present invention.

[Overall configuration of disconnection detector]
In FIG. 1, a wire breakage detecting device denoted by reference numeral 90 includes a high-frequency pulse signal injection unit 100 that injects a high-frequency pulse signal from an incident end 21 into a fixed cable 22a, and a fixed cable based on an injection signal from the high-frequency pulse signal injection unit 100. The signal waveform measuring unit 102 that measures the reflected waveform of the current flowing through 22a and 22b and the moving cable 24, and the determining unit that determines the presence or absence of the reflected waveform detected by the measurement of the signal waveform measuring unit 102 (moving cable 24) 103.

  The fixed cables 22a and 22b are made of the same type of cable including the extra length portions 28a and 28b, respectively, and are connected to each other via the connection portion 23a. Among these, the fixed cable 22a is connected to the fixing power source 31 via the incident end 21, while the fixed cable 22b is connected to the moving cable 24 via the connecting portion 23b. The fixed cable 22a is detachably disposed between the incident end 21 and the connection portion 23a, and the fixed cable 22b is detachably disposed between the connection portions 23a and 23b. In order to adjust the lengths of the fixed cables 22a and 22b, a plurality of fixed cables having different lengths are prepared, and are exchanged according to the length of the moving cable 24.

  The moving cable 24 constitutes a group of cables (electric wires) together with the fixed cables 22 a and 22 b, spans the pulley 29, and is connected to the moving device 25. The pulley 29 and the moving device 25 are suspended from the slider 26 on the rail 27 via the wire 30.

(Configuration of the high-frequency pulse signal injection unit 100)
The high frequency pulse signal injection unit 100 includes a high frequency pulse generator 100A that generates a high frequency pulse signal, and a capacitor 100B that receives the high frequency pulse signal from the high frequency pulse generator 100A and applies it to the fixed cable 22a (incident end 21). And is connected to the incident end 21.

(Configuration of signal waveform measuring unit 102)
The signal waveform measuring unit 102 is connected to the high frequency pulse generator 100A. Then, the time from the generation of the high-frequency pulse signal until the reflected wave at the connection parts 23a and 23b and the mobile device 25 is detected by a current sensor (described later), and the injection signal by the high-frequency pulse signal injection unit 100 as described above. Thus, the reflection waveform of the current flowing through the fixed cables 22a and 22b and the moving cable 24 is measured and recorded. A non-contact type current sensor 101 that detects an induced current generated around the fixed cable 22a is connected to the signal waveform measuring unit 102.

(Configuration of determination unit 103)
The determination unit 103 is connected to the signal waveform measurement unit 102 and is configured to determine the presence or absence of a reflected waveform in the detection target cable (moving cable 24).

[Operation of Wire Breakage Detection Device 90]
The high frequency pulse signal generated by the high frequency pulse generator 100A is applied to the fixed cable 22a via the capacitor 100B and the incident end 21. This high-frequency pulse signal passes through the current sensor 101 (attachment location), propagates through the fixed cables 22a and 22b and the moving cable 24 to the moving device side, and is reflected by the connecting portions 23a and 23b and the moving device 25 where the impedance changes. To do. The high-frequency pulse signal is reflected by these connecting portions 23a and 23b and the moving device 25, propagates in the reverse direction (power supply side) through the moving cable 24 and the fixed cables 22a and 22b, and passes through the current sensor 101 again.

  Next, in the signal waveform measuring unit 102, the current signal detected by the current sensor 101 until the high-frequency pulse signal reflected from the moment when the pulse signal is generated by the high-frequency pulse generator 100A passes through the attachment location of the current sensor 101. The reflected waveform is measured based on the above and the measured reflected waveform is recorded.

  Then, the determination unit 103 determines the presence / absence of the reflected waveform of the current measured by the signal waveform measurement unit 102 in the detection target electric wire (moving cable 24).

  Next, an electric wire breakage detection method using the wire breakage detection device 90 shown in the present embodiment will be described with reference to FIG. FIG. 2 is a current waveform diagram shown for explaining the wire breakage detection method according to the first embodiment of the present invention.

  In carrying out this disconnection detection method, the signal propagation times of the fixed cables 22a and 22b and the moving cable 24 are equal (the signal propagation time ratio is the signal propagation time of the fixed cable 22a: the signal propagation time of the fixed cable 22b: the signal of the moving cable 24) The lengths of the fixed cables 22a and 22b were adjusted so that the signal propagation time was 1: 1: 1.

  When a high frequency pulse signal is injected from the high frequency pulse signal injection unit 100 to the fixed cable 22a (incidence end 21), multiple reflection pulses by the connection units 23a and 23b and the moving device 25 are measured by the signal waveform measurement unit 102 as shown in FIG. It was done. In this case, the multiple reflection pulses from the connection portion 23a appeared at times 2 × t1 (t1 = 200 ns) and 3 × t1, and the double reflection pulse from the connection portion 23b appeared at time 2 × t1. For this reason, the multiple reflection pulses from the connection portions 23a and 23b do not appear in the range from the time region t2 (time t2: integer multiple of time t1) to tN of the mobile cable 24 where it is desired to detect a half-break. As a result, the reflected pulse time tx (tx = 510 ns) when the cable half disconnection occurs in the moving cable 24 does not overlap with the multiple reflected pulse time from the connecting portions 23a and 23b, and the cable half disconnected line of the moving cable 24 is Easy to detect.

[Effect of the first embodiment]
According to the first embodiment described above, the following effects can be obtained.

(1) A high frequency pulse signal is applied to the fixed cable 22a, and the reflected waveform of the current flowing through the fixed cables 22a and 22b and the moving cable 24 is measured at that time. Even disconnection detection can be performed.

(2) Since the disconnection detection is performed using the reflected waveform of the current, the accuracy of the disconnection detection can be reliably increased as compared with the case where the disconnection detection is performed from the resistance change.

(3) The ability to detect disconnection even while the mobile device 25 is in use can be performed by periodically repeating the process from injection of a high-frequency pulse signal to determination of the presence or absence of a reflected waveform. For this reason, even when a disconnection location contacts or separates, a disconnection can be detected reliably and the reliability in disconnection detection can be improved.

(4) Since the detection time of the multiple reflected waveform signal by the connecting portions 23a and 23b does not overlap with the detection time of the reflected waveform signal due to disconnection, the determination of disconnection detection can be performed easily.

  In addition, in this Embodiment, although the case where it was the disconnection detection apparatus and method of an electric wire which can acquire the effect shown to said (1)-(4) was demonstrated, this invention is not limited to this, At least The intended object can be achieved by the wire breakage detection device and method capable of obtaining the effects shown in the above (1) and (2).

  The wire breakage detection device (method) for obtaining the effects shown in the above (1) and (2) includes the following (I) and (II). These (I) and (II) will be described.

(I) This is a method of injecting a high-frequency pulse into an operating cable conductor via an injection capacitor, detecting the high-frequency pulse current with a CT (current sensor) for detecting a high-frequency signal, and recording the magnitude thereof. This is an electric wire breakage detection method for detecting a partial breakage of a strand of an operating cable by examining a change with time.

  In such wire breakage detection method, in order to detect a wire breakage of a cable operating with a commercial frequency power supply, the signal injected from the outside must be a signal that is not affected by the commercial frequency power supply, The signal connected to the cable must not cause damage or malfunction.

  For this reason, the injection signal is a single pulse having a high frequency equivalent to the noise that can be cut by the noise cut function of the device input unit, and the signal injection unit has a structure in which a high frequency pulse can be easily injected using a capacitor having a low high frequency impedance. A high-frequency CT is used as the detection unit so that the commercial frequency current is cut and only the high-frequency pulse signal can be detected without contact.

  When a high-frequency pulse propagates through the cable conductor, the influence of the LC impedance of the propagation path becomes large, so that the detection sensitivity of the LC change at the time of disconnection is improved as compared with the measurement of the resistance R by a direct current or commercial frequency signal. . That is, the high frequency pulse detects the change in impedance of the LCR at the time of disconnection, and the detection sensitivity is improved as compared with the detection of only the change in R due to the direct current or the commercial frequency signal.

  Also, the disconnection due to the bending of the cable occurs from the outermost peripheral portion of the cable conductor, and the high frequency signal flows on the outer surface of the cable conductor due to the skin effect, so the detection sensitivity of the disconnection is improved over the direct current or commercial frequency signal. Therefore, it is possible to detect disconnection of the cable during operation by injecting a high-frequency pulse into the cable, measuring the high-frequency pulse current, and examining the change over time.

  As an electric wire breakage detection apparatus capable of carrying out such a breakage detection method, there is, for example, the one shown in FIG. In FIG. 3, when current is supplied to the device 1 from the power supply 7 by the moving cable 3, the moving cable 3 is bent by the movement of the device 1, and the partial breakage of the element wire may occur. is there. A high frequency pulse for detecting a partial disconnection of the strand of the moving cable 3 is injected from the high frequency pulse generator 9 into the cable 10 via a signal injection capacitor 6 connected to the power supply side cable. Detection of the injected high frequency pulse current is detected by a high frequency CT (current sensor) 4 installed on the power supply side cable, and is measured and recorded by the waveform recording measuring instrument 8. In the power source 7, the high frequency blocking inductor 5 is inserted so that the injection pulse does not flow into the power source side. Note that the high-frequency blocking inductor 2 is inserted into the device power supply input section in case the noise cut function of the device 1 connected to the power cable is weak.

  The high-frequency pulse current injected from the high-frequency pulse generator 9 into the cable 10 passes through the high-frequency CT 4 and propagates through the conductors of the cable 10 and the moving cable 3, and is reflected by the impedance changing portion of the high-frequency blocking inductor 2 to be reflected in the high-frequency CT 4. Propagate until. The signal detected by the high frequency CT4 is recorded for the time from the injection of the high frequency pulse until the reflected wave from the high frequency blocking inductor 2 is detected by the high frequency CT4.

  Such measurement is performed at regular time intervals, and the initial waveform recorded first and the waveform after the lapse are compared to determine the partial disconnection of the strand. Further, the disconnection position is estimated from the time until the position where the waveform difference occurs. In addition, when the above detection method is applied to a cable that has already been used and is suspected of being partially broken, it is possible to determine the partial breakage of the strand by measuring the waveform difference between two wires of the same structure. It is also possible to do this.

  A signal waveform measured by such a wire breakage detection device will be described with reference to FIG. In FIG. 4, when the measurement waveform 13 of the healthy product and the partially disconnected product is compared, a waveform difference 11 appears in the measurement waveform within the cable round-trip propagation time 10. The waveform difference 11 is caused by a change in impedance of a partially broken portion of the strand, and the injected high frequency pulse is partially reflected by the partially broken portion of the strand and measured as the waveform difference 11. If this part is the partial disconnection position of the strand, and the signal propagation speed is obtained from the moving cable length and the cable round trip propagation time 10, the partial disconnection position of the cable strand from the round trip propagation time 12 of the strand break (Propagation speed × time / 2) can be specified.

(II) This is a method of injecting a high-frequency pulse into an operating cable conductor via an injection capacitor, and detecting the high-frequency pulse current (reflected waveform by the connecting portion) with a CT (current sensor) for detecting a high-frequency signal. This is an electric wire breakage detection method for measuring the size of the wire to be detected and determining the presence / absence of the measurement target wire in the wire to be detected, thereby detecting a partial breakage of the strand of the cable being operated.

As an electric wire breakage detection apparatus capable of implementing such a breakage detection method, there is, for example, the one shown in FIG. 5, the same or equivalent members as in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.
As shown in FIG. 5, the disconnection detecting device is configured such that the lengths of the fixed cables 22a and 22b cannot be adjusted.

  A signal waveform measured by such a wire breakage detection device will be described with reference to FIG. 6 in the case where the moving cable 24 has no half breakage. In FIG. 6, the incident end pulse is at time “0”, the reflected pulse from the connecting portion 23a is at time t1, the reflected pulse from the connecting portion 23b is at time t2, and the reflected pulse from the mobile device 25 is at time tN. Observed. In addition, the multiple reflection pulses from the connection portion 23a are observed at times 2 × t1 and 3 × t1, and the double reflection pulse from the connection point 23b is observed at time 2 × t2.

  Next, the signal waveform measured by the wire breakage detection device in FIG. 5 will be described with reference to FIG. 7 in the case where the moving cable 24 has a half breakage. In FIG. 7, a cable half-break occurred in the moving cable 24, and the reflected pulse appeared at time tx (tx = 320 ns). However, in this case, the reflected pulse from the disconnection location overlaps with the double reflected pulse from the connection portion 23b at time 2 × t2 (t2 = 120 ns> t1 = 100 ns), and the reflected pulse of the cable half disconnection at time tx. Is difficult to detect.

  In contrast, in the present embodiment, the signal propagation times of the fixed cables 22a and 22b and the moving cable 24 are equal (the signal propagation time ratio is the signal propagation time of the fixed cable 22a: the signal propagation time of the fixed cable 22b: the movement Since the disconnection detection was performed by adjusting the length of the fixed cables 22a and 22b so that the signal propagation time of the cable 24 was 1: 1: 1), even if the connection portions 23a and 23b exist in the middle of the cable, the cable half It is easy to determine the reflected pulse of the disconnection.

[Second Embodiment]
FIG. 8 is a current waveform diagram shown for explaining the wire breakage detection method according to the second embodiment of the present invention.

  As shown in FIG. 8, the wire breakage detection method shown in the second embodiment is such that the signal propagation time ratio between the fixed cables 22a and 22b and the moving cable 24 is the signal propagation time of the fixed cable 22a: the signal of the fixed cable 22b. Propagation time: The characteristic is that the lengths of the fixed cables 22a and 22b are adjusted so that the signal propagation time of the mobile cable 24 is 1: 2: 1.

  Therefore, the time 3 × t1 of the multiple reflection pulse from the connection unit 23a overlaps with the time t2 of the reflection pulse from the connection unit 23b, and the multiple reflection pulse from the connection unit 23a at the time tN of the reflection pulse from the mobile device 25. The times 4 × t1 are overlapped. As a result, multiple reflection pulses from the connecting portions 23a and 23b do not appear in the range from the time region t2 to tN of the mobile cable 24 where it is desired to detect a half-break. Therefore, the reflected pulse when the cable half-break occurs in the moving cable 24 does not overlap with the multiple reflected pulses from the connecting portions 23a and 23b at the time tx, and the cable half-break of the moving cable 24 can be easily detected.

  In this case, a multiple reflection pulse from the connection portion 23a appears at an intermediate point (time 2 × t1) in the middle of the fixed cable 22b. However, when this range is also a half-break detection range, the detection accuracy is inferior in the vicinity of the time 2 × t1 at which the multiple reflection pulse from the connection portion 23a appears, so care must be taken in application. In general, if the propagation time of multiple cables connected in series is set to an integer ratio, the reflected pulses from the connection will overlap and be effective in improving the half-break detection accuracy, but there will be no parts with poor detection accuracy. It is desirable that the propagation times be equal. In addition, in FIG. 8, when the detection target electric wire for detecting the half-break is not in the final part but in the middle, assuming that the propagation time of the moving cable 24 is “1”, the propagation time of the other fixed cables 22a and 22b. It is desirable to make it an integral multiple thereof, that is, to minimize the propagation time of the moving cable 24.

[Effect of the second embodiment]
According to the second embodiment described above, the same effects as those of the first embodiment can be obtained.

[Third embodiment]
FIG. 9 is a current waveform diagram shown for explaining the wire breakage detecting method according to the third embodiment of the present invention.

  As shown in FIG. 9, the wire breakage detection method shown in the third embodiment is such that the fixed cables 22a, 22b have the same signal propagation time (the signal propagation time ratio is an integer ratio). It is characterized in that the length of 22b is adjusted. In this case, the signal propagation time A of the mobile cable 24 may be A ≦ B, assuming that the signal propagation time B of the fixed cables 22a and 22b.

  For this reason, the reflected pulse when the cable half breakage occurs in the moving cable 24 does not overlap with the multiple reflected pulses from the connecting portions 23a and 23b at the time tx, and the cable half breakage of the moving cable 24 is easily detected.

[Effect of the third embodiment]
According to the third embodiment described above, the same effect as that of the first embodiment can be obtained.

  As mentioned above, although the disconnection detection apparatus (method) of the electric wire of this invention was demonstrated based on said embodiment, this invention is not limited to said embodiment, Various in the range which does not deviate from the summary. For example, the following modifications are possible.

(1) In each embodiment, although the case where two fixed cables were connected was demonstrated, this invention is not limited to this, Three or more may be connected. Moreover, even if there is one fixed cable, disconnection detection is possible. When there is one fixed cable, the signal propagation time of the moving cable is set to be equal to or less than the signal propagation time of the fixed cable.

(2) In each embodiment, the case where the types of the fixed cables are the same has been described. However, the types may be different and the transmission speed of the pulse signal may be different. In this case, the reflected pulse detection (arrival) time (t1-0, t2-t1,...) May be set to the same time.

(3) In each embodiment, although the case where it applied to the disconnection detection which made the cable group connected to the mobile device 25 object was described, this invention is not limited to this, The cable group which leaves | separates from the mobile device 25 The present invention can also be applied in the same manner as in each embodiment when disconnection detection is performed on the target.

The block diagram which shows the disconnection detection apparatus of the electric wire used in order to implement the disconnection detection method of the electric wire which concerns on the 1st Embodiment of this invention. The current waveform figure shown in order to demonstrate the disconnection detection method of the electric wire which concerns on the 1st Embodiment of this invention. The block diagram which shows the disconnection detection apparatus (1) of the electric wire for comparing with the disconnection detection apparatus of the electric wire which concerns on the 1st Embodiment of this invention. The electric current waveform diagram shown in order to demonstrate the disconnection detection method of the electric wire implemented using the disconnection detection apparatus of the electric wire in FIG. The block diagram which shows the disconnection detection apparatus (2) of the electric wire for comparing with the disconnection detection apparatus of the electric wire which concerns on the 1st Embodiment of this invention. The electric current waveform figure shown in order to demonstrate the disconnection detection method (when there is no half-break) of the electric wire implemented using the electric wire disconnection detection apparatus in FIG. The electric current waveform figure shown in order to demonstrate the disconnection detection method (when there is a half-break) of the electric wire implemented using the electric wire disconnection detection apparatus in FIG. The current waveform figure shown in order to demonstrate the disconnection detection method of the electric wire which concerns on the 2nd Embodiment of this invention. The current waveform diagram shown in order to demonstrate the disconnection detection method of the electric wire which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Apparatus, 2, 5 ... Inductor, 3 ... Moving cable, 4 ... Current sensor, 6 ... Capacitor, 7 ... Power supply, 8 ... Waveform recording measuring device, 9 ... High frequency pulse generator, 22a, 22b ... Fixed cable, 23a, 23b ... connecting part, 24 ... moving cable, 25 ... moving device, 26 ... slider, 27 ... rail, 29 ... pulley, 30 ... wire, 31 ... power supply, 90 ... wire breakage detection device, 100 ... high frequency pulse signal Injection unit, 100A ... high frequency pulse generator, 100B ... capacitor, 101 ... current sensor, 102 ... signal waveform measurement unit, 103 ... determination unit

Claims (11)

A high-frequency pulse signal injection unit that injects a high-frequency pulse signal into an incident end of a group of wires composed of a plurality of wires connected in series with a predetermined length;
A signal waveform measuring unit for measuring a reflected waveform of a current flowing through the plurality of electric wires by an injection signal by the high-frequency pulse signal injection unit;
An electric wire breakage detection apparatus comprising: a determination unit that determines presence / absence of the reflected waveform in the detection target electric wire by measurement of the signal waveform measurement unit. The plurality of wires includes at least one fixing wire connected in series to the high-frequency pulse signal injection unit, and a moving wire connected in series to the at least one fixing wire. Become
The wire breakage detection device according to claim 1, wherein the at least one fixing wire is configured to be adjustable in length.   The high-frequency pulse signal injection unit includes a high-frequency pulse signal generator that generates a high-frequency pulse signal, and a capacitor that receives the high-frequency pulse signal from the high-frequency pulse signal generator and applies the high-frequency pulse signal to the electric wire. Wire breakage detection device as described.   The electric wire breakage detection device according to any one of claims 1 to 3, wherein the signal waveform measurement unit is connected to a current detection unit that detects an induced current generated around a predetermined electric wire among the plurality of electric wires. . Injecting a high-frequency pulse signal into the incident end of a group of wires composed of a plurality of wires connected in series with a predetermined length;
Measuring a reflected waveform of a current flowing through the plurality of electric wires;
And a step of determining the presence / absence of the reflected waveform in the detection target electric wire. The plurality of wires includes at least one fixing wire connected in series to the high-frequency pulse signal injection unit, and a moving wire connected in series to the at least one fixing wire. Become
The wire breakage detection method according to claim 5, comprising a step of adjusting a length of the at least one fixing wire. When the fixing wire is at least two fixing wires, the signal propagation time ratio in the at least two fixing wires is set to an integer ratio,
The wire breakage detection method according to claim 6, wherein the signal propagation time of the moving wire is set to be shorter than the signal propagation time of the at least two fixing wires.   The wire breakage detection according to claim 6, wherein when the fixing wires are at least two fixing wires, the signal propagation times of the at least two fixing wires and the moving wire are set to be equal. Method.   The signal propagation time of the at least two fixing wires is set to an integral multiple of the signal propagation time of the moving wire when the fixing wires are at least two fixing wires. Wire breakage detection method.   The wire breakage according to claim 6, wherein when the fixing wire is a single fixing wire, the signal propagation time of the moving wire is set to be equal to or shorter than the signal propagation time of the one fixing wire. Detection method.   The wire breakage detection method according to any one of claims 5 to 10, wherein a process from injection of the high-frequency pulse signal to determination of presence / absence of the reflected waveform is repeated.