DETECTION APPARATUS AND DETECTION METHOD

A detection apparatus according to the present disclosure includes a signal output unit configured to output a measurement signal that includes a component having a first frequency to a transmission line, a signal measurement unit configured to measure a response signal, from the transmission line, to the measurement signal output from the signal output unit and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that is based on the measurement signal, calculate an index value that indicates a strength of a correlation between the reference signal and the difference signal, and detect an abnormality in the transmission line on the basis of the calculated index value.

TECHNICAL FIELD

The present disclosure relates to a detection apparatus and a detection method. This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-092768, filed on Jun. 2, 2021, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

PTL 1 (Japanese Unexamined Patent Application Publication No. 2015-536456) discloses a method for monitoring a condition of an electrical cable. The method includes applying a broadband signal wave to an end of the electrical cable, wherein the broadband signal wave is phase and amplitude modulated, acquiring at the end of the cable the broadband signal wave transmitted and reflected by the electrical cable, and identifying impedance characteristics by using the acquired broadband signal wave.

For example, PTL 2 (Japanese Unexamined Patent Application Publication No. 2018-179531) discloses a transmission apparatus as follows. Specifically, in the transmission apparatus in which a first card and a second card are connected via a connector, the transmission apparatus includes a signal generation unit that outputs an AC signal having a frequency higher than the transmission rate of data input to the transmission apparatus, and a judgment unit that receives the AC signal via the connector and judges whether the first card and the second card are fitted with the connector on the basis of the power level of the received AC signal.

PRIOR ART DOCUMENT

Patent Literature

SUMMARY

A detection apparatus according to the present disclosure includes a signal output unit configured to output a measurement signal that includes a component having a first frequency to a transmission line; a signal measurement unit configured to measure a response signal, from the transmission line, to the measurement signal output from the signal output unit; and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that is based on the measurement signal, calculate an index value that indicates a strength of a correlation between the reference signal and the difference signal, and detect an abnormality in the transmission line on the basis of the calculated index value.

A detection method according to the present disclosure is a detection method performed in a detection apparatus. The method includes outputting a measurement signal that includes a component having a first frequency to a transmission line; measuring a response signal, from the transmission line, to the measurement signal; and calculating an index value that indicates a strength of a correlation between the measured response signal and a reference signal based on the measurement signal and detecting an abnormality in the transmission line on the basis of the calculated index value.

One aspect of the present disclosure can be achieved not only as a detection apparatus including such a characteristic processing unit but also as a semiconductor integrated circuit that achieves a part or all of the detection apparatus or as a system including the detection apparatus.

DETAILED DESCRIPTION

Conventionally, a technique for detecting an abnormality of a transmission line has been proposed.

Problems to be Solved by Present Disclosure

Beyond the techniques described in PTLs 1 and 2, a technique with which an abnormality in a transmission line can be detected with simple processing and configuration is desired.

The present disclosure has been made to solve the above-described problem, and an object thereof is to provide a detection apparatus and a detection method with which an abnormality in a transmission line can be detected with simple processing and configuration.

Advantageous Effects of Present Disclosure

According to the present disclosure, an abnormality in a transmission line can be detected with simple processing and configuration.

Description of Embodiments of Present Disclosure

First, the contents of embodiments of the present disclosure will be listed and explained.

(1) A detection apparatus according to the present disclosure includes a signal output unit configured to output a measurement signal that includes a component having a first frequency to a transmission line; a signal measurement unit configured to measure a response signal, from the transmission line, to the measurement signal output from the signal output unit; and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that is based on the measurement signal, calculate an index value that indicates a strength of a correlation between the reference signal and the difference signal, and detect an abnormality in the transmission line on the basis of the calculated index value.

As described above, by generating a difference signal that is a difference between the response signal from the transmission line when the measurement signal is output to the transmission line and the reference signal based on the measurement signal, and detecting the abnormality in the transmission line based on the index value indicating the strength of correlation between the reference signal and the difference signal, sine waves and rectangular waves of various frequencies from low frequency to high frequency, for example, can be used as the measurement signal, and the abnormality can be detected based on the phase difference between the reference signal and the difference signal by simple calculation processing without using a circuit such as a directional coupler for extracting a reflection signal generated in the transmission line. Thus, the abnormality in a transmission line can be detected with simple processing and configuration.

(2) In (1), the processing unit may be configured to calculate, as the index value, a phase difference between a component having the first frequency and included in the reference signal and a component having the first frequency and included in the difference signal.

With such a configuration, it is possible to detect the abnormality in the transmission line by focusing on a phase shift of a signal in the transmission line. In addition, since the effect of noise can be reduced as compared with a configuration in which, for example, a reflection coefficient is calculated as an index value other than the phase difference, it is possible to more accurately detect the abnormality in the transmission line.

(3) In (1) or (2), the processing unit may be configured to calculate, as the index value, a reflection coefficient between the reference signal and the difference signal. With such a configuration, it is possible to detect the abnormality in the transmission line by focusing on the attenuation amount of the signal in the transmission line.

(4) In any one of (1) to (3), the processing unit may be configured to calculate the index value by using an output signal output from a first filter in response to input, into the first filter, of a multiplication signal obtained from the difference signal and the reference signal, the first filter being configured to extract a direct-current component, and by using an output signal output from a second filter in response to input, into the second filter, of a multiplication signal obtained from the difference signal and a signal that is obtained by shifting a phase of a component having the first frequency and included in the reference signal by π/2, the second filter being configured to extract a direct-current component.

With such a configuration, noise resistance can be improved, and thus it is possible to more accurately detect the abnormality in the transmission line.

(5) In any one of (1) to (3), the processing unit may be configured to calculate the index value by using an output signal output from a third filter in response to input, into the third filter, of a multiplication signal obtained from the difference signal and a signal that includes a component having a second frequency different from the first frequency, the third filter being configured to extract a component having a difference frequency between the first frequency and the second frequency.

With such a configuration, since it is possible to calculate the index value by processing the low-frequency output signal output from the third filter using a circuit configuration having a lower operating frequency, it is possible to reduce the cost of hardware in the detection apparatus.

(6) In (2), the processing unit may be configured to calculate the phase difference by using an argument of a complex analysis signal of the reference signal and an argument of a complex analysis signal of the difference signal.

With such a configuration, it is possible to simplify arithmetic processing for calculating the phase difference between the reference signal and the difference signal.

(7) In any one of (1) to (6), the processing unit may be configured to generate the difference signal that is a difference between the response signal and the reference signal that is a signal obtained by making a delay adjustment to the measurement signal.

With such a configuration, by generating the difference signal using the response signal and the reference signal subjected to the delay processing according to the length of the transmission line, for example, it is possible to generate the difference signal in which the measurement signal superimposed on the response signal is more accurately canceled. Thus, it is possible to more accurately detect the abnormality in the transmission line using the generated different signal and to more accurately specify the position of occurrence of the abnormality.

(8) In (7), a delay amount of the reference signal relative to the measurement signal may be allowed to be changed and set.

With such a configuration, for example, since the delay amount can be set in accordance with the length of the transmission line, it is possible to more accurately detect the abnormality in the transmission lines having various lengths and to more accurately determine the position of occurrence of the abnormality.

(9) In any one of (1) to (6), the processing unit may be configured to generate the difference signal that is a difference between the response signal and the reference signal that is the response signal measured by the signal measurement unit upon a steady-state time.

With such a configuration, since it is possible to generate the difference signal in which noise is reduced using the response signal upon a steady-state time, it is possible to more accurately detect the abnormality in the transmission line using the generated difference signal.

(10) In any one of (1) to (9), the processing unit may be configured to detect a position of occurrence of the abnormality.

With such a configuration, when the abnormality occurs, it is possible to take appropriate measures such as repair or replacement of the position of occurrence of the abnormality.

(11) A detection method according to the present disclosure is a detection method performed in a detection apparatus. The method includes outputting a measurement signal that includes a component having a first frequency to a transmission line; measuring a response signal, from the transmission line, to the measurement signal; and calculating an index value that indicates a strength of a correlation between the measured response signal and a reference signal based on the measurement signal and detecting the abnormality in the transmission line on the basis of the calculated index value.

As described above, according to the method of generating the difference signal that is a difference between the response signal from the transmission line when the measurement signal is output to the transmission line and the reference signal based on the measurement signal and detecting the abnormality in the transmission line based on the index value indicating the strength of correlation between the reference signal and the difference signal, sine waves and rectangular waves of various frequencies from low frequency to high frequency, for example, can be used as the measurement signal, and the abnormality can be detected based on the phase difference between the reference signal and the difference signal by simple calculation processing without using a circuit such as a directional coupler for extracting a reflection signal generated in the transmission line. Thus, it is possible to detect the abnormality in the transmission line with simple processing and configuration.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated. Further, at least some of the embodiments described below may be arbitrarily combined.

First Embodiment

[Configuration and Basic Operation]

FIG.1is a diagram showing a configuration of a communication system according to a first embodiment of the present disclosure. Referring toFIG.1, a communication system301includes a relay apparatus101and a plurality of communication apparatuses111.

Relay apparatus101is connected to each communication apparatus111via a transmission line1. More specifically, transmission line1includes a cable portion and connector portions respectively provided at a first end and a second end of the cable portion. The connector portion provided at the first end of the cable portion is connected to a connector portion of relay apparatus101. The connector portion provided at the second end of the cable portion is connected to a connector portion of communication apparatus111. Transmission line1is, for example, an Ethernet (registered trademark) cable.

Communication system301is mounted on a vehicle, for example. In this case, communication apparatus111is, for example, an in-vehicle electronic control unit (ECU). Communication system301may be used for a home network or factory automation.

Relay apparatus101is capable of communicating with communication apparatus111. Relay apparatus101performs, for example, relay processing for relaying information exchanged among or between a plurality of communication apparatuses111connected to different transmission lines1. In addition, relay apparatus101functions as a detection apparatus and, for example, periodically performs detection processing of detecting an abnormality in transmission line1.

FIG.2is a diagram showing a configuration of a relay apparatus according to a first embodiment of the present disclosure. Referring toFIG.2, relay apparatus101includes a relay unit11, a plurality of detection processing units71, and a plurality of communication ports61. Detection processing unit71includes a signal output unit12, a signal measurement unit13, a processing unit14, and a storage unit15. Some or all of relay unit11, signal output unit12, signal measurement unit13, and processing unit14are achieved by a processor such as a central processing unit (CPU) and a digital signal processor (DSP). Storage unit15is, for example, a nonvolatile memory. Communication port61is, for example, a connector or a terminal. A connector portion of transmission line1is connected to each communication port61.

Relay unit11performs relay processing. For example, relay unit11performs relay processing of relaying a frame between communication apparatuses111. More specifically, relay unit11transmits a frame received from a certain communication apparatus111via the corresponding transmission line1and the corresponding communication port61to another communication apparatus111via the corresponding communication port61and the corresponding transmission line1in accordance with the destination IP address of the frame.

For example, relay apparatus101includes the same number of detection processing units71as the number of communication ports61. More specifically, detection processing unit71is provided corresponding to communication port61and performs detection processing of detecting the abnormality in transmission line1connected to the corresponding communication port61. Hereinafter, detection processing by one detection processing unit71in relay apparatus101will be described as a representative.

Signal output unit12outputs a measurement signal to transmission line1. As an example, signal output unit12outputs the measurement signal that is a sine wave of a frequency f to transmission line1. Frequency f is an example of a first frequency. More specifically, signal output unit12outputs a measurement signal ys (t) expressed as a function of time t in an outputting period T1to transmission line1to be detected. Signal output unit12may be configured to output a measurement signal not including an offset component to transmission line1, or may be configured to output a measurement signal including an offset component to transmission line1.

For example, outputting period T1is a period in which relay unit11does not perform the relay processing via transmission line1to be detected. More specifically, relay unit11outputs, to signal output unit12, period information indicating a period during which the relay processing via transmission line1is not performed. Signal output unit12receives the period information from relay unit11, and determines outputting period T1based on the received period information.

For example, storage unit15stores digital data Dt of measurement signal ys (t) to be output to transmission line1by signal output unit12and frequency information indicating the frequency of measurement signal ys (t). Digital data Dt is time-series data including a plurality of values indicating a waveform of a sine wave.

Signal output unit12outputs a sine wave having one or more cycles to transmission line1to be detected during outputting period T1using the data-group stored in storage unit15. More specifically, signal output unit12includes a digital to analog converter (DAC). Signal output unit12obtains digital data Dt from storage unit15at an outputting timing in accordance with a cycle C1corresponding to a cycle of an operation clock of the DAC, and outputs measurement signal ys (t) generated by converting the obtained digital data Dt into an analog signal by the DAC to transmission line1to be detected.

Signal output unit12outputs a synchronization signal indicating the detection timing to signal measurement unit13. When signal output unit12outputs the synchronization signal to signal measurement unit13, signal output unit12starts outputting period T1and outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1.

Signal output unit12obtains digital data Dt from storage unit15at the outputting timing according to cycle C1, and outputs the obtained digital data Dt to processing unit14as a digital measurement signal ysd (t) expressed as a function of time t. That is, signal output unit12outputs time-series data of the amplitude value of digital data Dt to processing unit14. Digital measurement signal ysd (t) is an example of a reference signal.

Signal measurement unit13measures a response signal from transmission line1to measurement signal ys (t) output by signal output unit12. For example, signal measurement unit13measures a response signal ym (t) expressed as a function of time t in a measurement period Tm.

More specifically, when receiving the synchronization signal from signal output unit12, signal measurement unit13starts measurement period Tm and measures response signal ym (t) in measurement period Tm. The length of measurement period Tm is equal to, for example, the length obtained by subtracting the round-trip propagation time of the measurement signal in transmission line1from the length of outputting period T1.

Signal measurement unit13includes an analog to digital converter (ADC). Signal measurement unit13generates a digital response signal ymd (t) by sampling the voltage level of transmission line1by the ADC at the sampling timing according to cycle C1in measurement period Tm, and outputs the generated digital response signal ymd (t) to processing unit14.

Processing unit14generates a difference signal ydiff (t) that is a difference between response signal ym (t) measured by signal measurement unit13and digital measurement signal ysd (t) based on measurement signal ys (t).

More specifically, processing unit14generates difference signal ydiff (t) by subtracting digital measurement signal ysd (t) received from signal output unit12from digital response signal ymd (t) received from signal measurement unit13.

FIG.3is a diagram showing a simulation result of a response signal measured by a signal measurement unit in the relay apparatus according to the first embodiment of the present disclosure. InFIG.3, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.3represents response signal ym (t), the dashed line inFIG.3represents measurement signal ys (t), and the dashed-and-dotted line inFIG.3represents a reflection signal yr (t) that is a signal obtained by reflecting measurement signal ys (t) in transmission line1.FIG.3shows a simulation result of each signal when a disconnection occurs at a position 10 m away from the end facing relay apparatus101in transmission line1having a length of 11 m.

Referring toFIG.3, response signal ym (t) measured by signal measurement unit13is a signal in which measurement signal ys (t) is superimposed on reflection signal yr (t). Processing unit14generates difference signal ydiff (t) indicating reflection signal yr (t) by subtracting digital measurement signal ysd (t) from digital response signal ymd (t).

Processing unit14calculates a phase difference Φ between the component of frequency f included in digital measurement signal ysd (t) and the component of frequency f included in difference signal ydiff (t), and detects an abnormality in transmission line1to be detected based on the calculated phase difference Φ. More specifically, in the detection process, processing unit14detects the disconnection in transmission line1as the abnormality in transmission line1to be detected. For example, processing unit14further detects the position of occurrence of the disconnection. Phase difference Φ is an example of an index value indicating a strength of correlation between digital measurement signal ysd (t) and difference signal ydiff (t).

For example, processing unit14calculates phase difference Φ using an argument θsd (t) of a complex analysis signal Csd (t) of digital measurement signal ysd (t) and an argument θdiff (t) of a complex analysis signal Cdiff (t) of difference signal ydiff (t).

More specifically, processing unit14calculates complex analysis signal Csd (t) by performing a Hilbert transform on digital measurement signal ysd (t) received from signal output unit12. Further, processing unit14calculates complex analysis signal Cdiff (t) by performing the Hilbert transform on the generated difference signal ydiff (t). Processing unit14may perform the calculation of complex analysis signal Csd (t) and the calculation of complex analysis signal Cdiff (t) in parallel or sequentially.

FIG.4is a diagram showing a simulation result of an argument of a complex analysis signal calculated by a processing unit in the relay apparatus according to the first embodiment of the present disclosure. InFIG.4, the horizontal axis represents time [second] and the vertical axis represents an argument [rad]. The solid line inFIG.4represents argument θdiff (t) of complex analysis signal Cdiff (t), and the dashed line inFIG.4represents argument θsd (t) of complex analysis signal Csd (t).FIG.4shows simulation results of argument θdiff (t) and argument θsd (t) calculated by processing unit14when the disconnection occurs at a position 10 m away from the end facing relay apparatus101in transmission line1having a length of 11 m, similarly toFIG.3.

Processing unit14calculates a difference between argument θsd (t) and argument θdiff (t) as phase difference Φ.

FIG.5is a diagram showing a method of specifying a position of occurrence of disconnection by a processing unit in the relay apparatus according to the first embodiment of the present disclosure.FIG.5shows a state where disconnection DC occurs in transmission line1. For example, transmission line1has a configuration in which a termination resistor is not provided at an end portion facing communication apparatus111.

Referring toFIG.5, measurement signal ys (t) output to transmission line1by signal output unit12is reflected at a reflection point in transmission line1to generate reflection signal yr (t). For example, when disconnection DC occurs in transmission line1, measurement signal ys (t) is reflected at the position of disconnection DC. On the other hand, when disconnection DC does not occur in transmission line1, measurement signal ys (t) is reflected at the end portion facing communication apparatus111in transmission line1.

Phase difference Φ between measurement signal ys (t) and reflection signal yr (t) is expressed by the following equation (1).

Here, L is the distance [m] from the end portion facing relay apparatus101in transmission line1to the reflection point of measurement signal ys (t), c is the speed of light [m/sec], and εr is the relative permittivity of transmission line1.

That is, a distance L from the end portion facing relay apparatus101in transmission line1to the reflection point of measurement signal ys (t) is represented by the following equation (2). After calculating phase difference Φ, processing unit14calculates distance L corresponding to the calculated phase difference Φ in accordance with equation (2).

FIG.6is a diagram showing a simulation result of a distance calculated by a processing unit in the relay apparatus according to the first embodiment of the present disclosure. InFIG.6, the horizontal axis represents time [second] and the vertical axis represents the distance [mm] from the end portion facing relay apparatus101in transmission line1to the reflection point.FIG.6shows a simulation result of distance L calculated by processing unit14when the disconnection occurs at a position 10 m away from the end facing relay apparatus101in transmission line1having a length of 11 m, similarly toFIGS.3and4.

Referring toFIG.6, processing unit14determines whether or not a disconnection occurs in transmission line1based on the calculated distance L. When the disconnection occurs in transmission line1, processing unit14further detects the position of occurrence of the disconnection in transmission line1.

More specifically, storage unit15stores transmission line information indicating a length Lc of transmission line1to be detected.

Processing unit14obtains the transmission line information in storage unit15, and calculates a difference length Ldiff by subtracting the calculated distance L from length Lc of transmission line1to be detected indicated by the obtained transmission line information.

Processing unit14compares the calculated difference length Ldiff with a predetermined threshold value Th1, and determines whether or not the disconnection has occurred in transmission line1based on the comparison result. More specifically, when difference length Ldiff is less than threshold value Th1, processing unit14determines that no disconnection has occurred in transmission line1. On the other hand, when difference length Ldiff is equal to or greater than threshold value Th1, processing unit14determines that the disconnection has occurred at the position of distance L from the end portion facing relay apparatus101in transmission line1.

For example, when processing unit14determines that the disconnection has occurred in transmission line1, processing unit14notifies the user of the determination result via a communication unit (not illustrated) and communication apparatus111.

Here, a maximum distance Lmax, which is the maximum value of distance L that can be correctly calculated in processing unit14, is ½ of a wavelength λ of measurement signal ys (t) and is represented by the following equation (3).

For example, frequencies f of measurement signal ys (t) output by signal output unit12and the above-described cycles C1are set in advance such that maximum distance Lmax is equal to or longer than length Lc of transmission line1to be detected.

Each device in the communication system according to the embodiment of the present disclosure includes a computer including a memory, and an arithmetic processing unit such as a CPU in the computer reads a program including a part or all of each step of the following flowchart from the memory and executes the program. The programs of the plurality of devices can be installed from the outside. The programs of the plurality of devices are distributed in a state of being stored in a recording medium or via a communication line.

FIG.7is a flowchart defining an example of an operation procedure when the relay apparatus according to the first embodiment of the present disclosure performs detection processing.

Referring toFIG.7, first, relay apparatus101waits for the timing at which the detection processing should be performed (NO in step S102), and starts outputting period T1and measurement period Tm (step S104) at the timing at which the detection processing should be performed (YES in step S102).

Next, relay apparatus101outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1, and measures response signal ym (t) from transmission line1to measurement signal ys (t) in measurement period Tm. More specifically, relay apparatus101outputs measurement signal ys (t) for one sample to transmission line1, and samples the voltage level of transmission line1to generate of digital response signal ymd (t) for one sample (step S106).

Relay apparatus101alternately repeats outputting measurement signal ys (t) for one sample and generating digital response signal ymd (t) for one sample until outputting period T1and measurement period Tm expire (NO in step S108), and generates difference signal ydiff (t) that is a difference between response signal ym (t) and digital measurement signal ysd (t) when outputting period T1and measurement period Tm expire (YES in step S108). More specifically, relay apparatus101generates difference signal ydiff (t) by subtracting digital measurement signal ysd (t) from digital response signal ymd (t) (step S110).

Next, relay apparatus101calculates phase difference Φ between the component of frequency f included in digital measurement signal ysd (t) and the component of frequency f included in difference signal ydiff (t). In more detail, relay apparatus101calculates phase difference Φ using argument θsd (t) of complex analysis signal Csd (t) of digital measurement signal ysd (t) and argument θdiff (t) of complex analysis signal Cdiff (t) of difference signal ydiff (t) (step S112).

Next, relay apparatus101calculates distance L corresponding to phase difference Φ in accordance with the above-described equation (2) (step S114).

Next, relay apparatus101calculates difference length Ldiff by subtracting the calculated distance L from length Lc of transmission line1to be detected (step S116).

Next, relay apparatus101compares the calculated difference length Ldiff with threshold value Th1(step S118).

Next, when difference length Ldiff is less than threshold value Th1(NO in step S120), relay apparatus101determines that no disconnection has occurred in transmission line1(step S122), and waits for a next timing at which the detection processing should be performed (NO in step S102).

On the other hand, when difference length Ldiff is equal to or greater than threshold value Th1(YES in step S120), relay apparatus101determines that the disconnection has occurred at a position at distance L from the end portion facing relay apparatus101in transmission line1(step S124).

Next, relay apparatus101notifies the user of the determination result via the communication unit (not shown) and communication apparatus111(step S126), and waits for a next timing at which the detection processing should be performed (NO in step S102).

In communication system301according to the first embodiment of the present disclosure, relay apparatus101is configured to perform the detection processing, but is not limited thereto. A device other than relay apparatus101in communication system301may be configured to perform the detection processing. Specifically, communication apparatus111may be configured to function as the detection apparatus and perform the detection processing.

Further, in communication system301according to the first embodiment of the present disclosure, transmission line1is configured to include the cable portion and the connector portion, but is not limited thereto. Transmission line1may be a wiring pattern formed on a circuit board. In this case, relay apparatus101detects an abnormality in transmission line1that is a wiring pattern.

In relay apparatus101according to the first embodiment of the present disclosure, processing unit14is configured to detect the disconnection in transmission line1as an abnormality in transmission line1to be detected in the detection processing, but is not limited thereto. Processing unit14may be configured to detect connection of an unauthorized device to transmission line1as an abnormality in transmission line1to be detected. Since the impedance at a connection point changes due to the connection of the unauthorized device to transmission line1when an unauthorized device is connected to transmission line1, measurement signal ys (t) output to transmission line1by signal output unit12is reflected at the connection point and a reflection signal is generated. Signal measurement unit13measures a response signal in which the reflection signal is superimposed on measurement signal ys (t) in the same manner as when a disconnection occurs in transmission line1. Processing unit14compares the absolute value of difference length Ldiff with threshold value Th1. When the absolute value of difference length Ldiff is less than threshold value Th1, processing unit14determines that an abnormality such as connection of an unauthorized device has not occurred in transmission line1. On the other hand, when the absolute value of difference length Ldiff is equal to or larger than threshold value Th1, processing unit14determines that an abnormality such as connection of an unauthorized device has occurred.

In relay apparatus101according to the first embodiment of the present disclosure, processing unit14is configured to calculate phase difference Φ using argument θsd (t) of complex analysis signal Csd (t) of digital measurement signal ysd (t) and argument θdiff (t) of complex analysis signal Cdiff (t) of difference signal ydiff (t), but is not limited thereto. Processing unit14may be configured to calculate phase difference Φ without using argument θsd (t) of complex analysis signal Csd (t) and argument θdiff (t) of complex analysis signal Cdiff (t) of difference signal ydiff (t). For example, processing unit14may be configured to calculate phase difference Φ by the following procedure.

That is, processing unit14normalizes the amplitude of difference signal ydiff (t) and the amplitude of digital measurement signal ysd (t) to a range of ±1. Processing unit14calculates a phase P1of difference signal ydiff (t) by passing the normalized difference signal ydiff (t) through an arcsine that is the inverse of a sine function. In addition, processing unit14calculates a phase P2of digital measurement signal ysd (t) by passing the normalized digital measurement signal ysd (t) through the arcsine that is the inverse of the sine function. Then, processing unit14unwraps, for example, phases P1and P2, and calculates the difference between phases P1and P2as phase difference Q.

In addition, in relay apparatus101according to the first embodiment of the present disclosure, processing unit14is configured to further detect the position of occurrence of the disconnection in transmission line1when the disconnection occurs in transmission line1, but is not limited thereto. Processing unit14may be configured to determine whether or not a disconnection occurs in transmission line1, but not to detect the position of occurrence of the disconnection.

In addition, in communication system301according to the first embodiment of the present disclosure, transmission line1is configured not to include the termination resistor at the end portion facing communication apparatus111, but is not limited thereto. Transmission line1may be configured to include a termination resistor for impedance matching at an end portion facing communication apparatus111.

In relay apparatus101according to the first embodiment of the present disclosure, processing unit14is configured to generate difference signal ydiff (t) by subtracting digital measurement signal ysd (t) from digital response signal ymd (t), but is not limited thereto. Processing unit14may be configured to generate difference signal ydiff (t) by analog signal processing using a differential amplifier or the like. In this case, processing unit14converts the generated difference signal ydiff (t) into a digital signal using the ADC, calculates phase difference Φ using the digital signal, and detects the disconnection based on the calculated phase difference Φ.

In relay apparatus101according to the first embodiment of the present disclosure, signal output unit12is configured to output the measurement signal that is a sine wave to transmission line1, is not limited thereto. Signal output unit12may be configured to output a measurement signal having a plurality of frequency components to transmission line1, or may be configured to output a measurement signal that is a rectangular wave to transmission line1.

For example, storage unit15stores digital data DtRW including a plurality of values indicating a waveform of a rectangular wave. Signal output unit12obtains digital data DtRW instead of digital data Dt from storage unit15and outputs a signal obtained by converting the obtained digital data DtRW into an analog signal as measurement signal ys (t) to transmission line1to be detected.

Here, the rectangular wave includes a frequency component of an odd multiple of the fundamental frequency. Signal measurement unit13extracts a part of the frequency components from the analog signal indicating the voltage level of transmission line1using, for example, a band pass filter (BPF), generates digital response signal ymd (t) by sampling the extracted analog signal using the ADC, and outputs digital response signal ymd (t) to processing unit14. Alternatively, a digital signal is generated by sampling the voltage level of transmission line1by the ADC, a part of the frequency components is extracted from the digital signal using the BPF, and the extracted digital signal is output to processing unit14as digital response signal ymd (t).

Meanwhile, there is a demand for a technique with which a disconnection in a transmission line can be detected with simple processing and configuration.

For example, a technique for detecting characteristics of transmission line1using time domain reflectometry (TDR) is conventionally known. When a change in the characteristics of transmission line1is detected using such a technique and an abnormality related to transmission line1is detected based on the detection result, it is necessary to output a rising pulse to transmission line1with high reproducibility in order to accurately detect the change in the characteristics of transmission line1, and as a result, a high-performance pulse signal generator is required.

In addition, when characteristics such as an S parameter of transmission line1are measured using a network analyzer and an abnormality related to transmission line1is detected based on the measurement result, in order to obtain sufficient detection accuracy, it is necessary to use an expensive and complicated measurement device and it is necessary to calibrate the measurement device every time measurement is performed.

On the other hand, in relay apparatus101according to the first embodiment of the present disclosure, signal output unit12outputs the measurement signal including the first frequency component to transmission line1. Signal measurement unit13measures a response signal from transmission line1in response to the measurement signal output by signal output unit12. Processing unit14generates a difference signal that is a difference between the response signal measured by signal measurement unit13and a reference signal based on the measurement signal, calculates a phase difference that is an index value indicating the strength of correlation between the reference signal and the difference signal, and detects an abnormality in transmission line1based on the calculated phase difference.

As described above, by generating a difference signal that is a difference between a response signal from transmission line1when a measurement signal is output to transmission line1and a reference signal based on the measurement signal, and detecting an abnormality in transmission line1based on a phase difference between the reference signal and the difference signal, for example, sine waves and rectangular waves of various frequencies from low frequency to high frequency, for example, can be used as measurement signal, and the abnormality can be detected based on the phase difference between the reference signal and the difference signal by simple calculation processing without using a circuit such as a directional coupler for extracting a reflection signal generated in transmission line1. Therefore, in relay apparatus101according to the first embodiment of the present disclosure, it is possible to detect an abnormality in the transmission line with simple processing and configuration.

Further, as described above, since the abnormality is detected based on the phase difference between the reference signal and the difference signal, it is possible to more accurately detect the abnormality because the resistance to the noise is high compared with a configuration, for example, using the TDR and the network analyzer for analyzing the amplitude of the response signal. In addition, the abnormality can be detected by simple processing without performing arithmetic processing such as fast Fourier transform (FFT). Further, as compared with a configuration using an optical signal or a radio wave, it is possible to detect the abnormality even in a state where a standing wave is generated in transmission line1.

Next, other embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

Second Embodiment

Compared with relay apparatus101according to the first embodiment, the present embodiment relates to a relay apparatus102that generates difference signal ydiff (t) using digital measurement signal ysd (t) in storage unit15. Relay apparatus102is the same as relay apparatus101according to the first embodiment except for the contents described below.

FIG.8is a diagram showing a configuration of a relay apparatus according to a second embodiment of the present disclosure. Referring toFIG.8, relay apparatus102includes a detection processing unit72instead of detection processing unit71, as compared with relay apparatus101according to the first embodiment. Detection processing unit72includes a signal measurement unit23instead of signal measurement unit13and a processing unit24instead of processing unit14, as compared with detection processing unit71. For example, transmission line1includes a termination resistor at the end portion facing communication apparatus111.

Detection processing unit72performs reference measurement processing for measuring a response signal in a steady state. More specifically, detection processing unit72performs the reference measurement processing in an initial state in which no disconnection occurs in transmission line1. After performing the reference measurement processing, detection processing unit72performs the detection processing, for example, periodically. Detection processing unit72may perform the reference measurement processing at regular or irregular intervals after performing the reference measurement processing in the initial state.

Signal output unit12outputs a synchronization signal to signal measurement unit23, and outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1.

When receiving the synchronization signal from signal output unit12, signal measurement unit23starts measurement period Tm and samples the voltage level of transmission line1by the ADC at the sampling timing according to cycle C1in measurement period Tm to generate a digital response signal ymdR (t) that is digital response signal ymd (t) in the steady state. Signal measurement unit23stores the generated digital response signal ymdR (t) in storage unit15. Digital response signal ymdR (t) is an example of a reference signal.

As in the reference measurement processing, signal output unit12outputs the synchronization signal to signal measurement unit13and outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1.

When receiving the synchronization signal from signal output unit12, signal measurement unit23starts measurement period Tm, and samples the voltage level of transmission line1by the ADC at the sampling timing according to cycle C1in measurement period Tm to generate a digital response signal ymdS (t) that is digital response signal ymd (t) at the time of operation. Signal measurement unit23outputs the generated digital response signal ymdS (t) to processing unit24.

Processing unit24generates difference signal ydiff (t) that is a difference between response signal ym (t) and digital response signal ymdR (t) that is response signal ym (t) measured by signal measurement unit23in the steady state.

More specifically, processing unit24receives digital response signal ymdS (t) from signal measurement unit23, obtains digital response signal ymdR (t) from storage unit15, and generates difference signal ydiff (t) by subtracting digital response signal ymdR (t) from digital response signal ymdS (t).

Processing unit24calculates a complex analysis signal CmdR (t) by performing the Hilbert transform on digital response signal ymdR (t) obtained from storage unit15. Further, processing unit24calculates complex analysis signal Cdiff (t) by performing the Hilbert transform on the generated difference signal ydiff (t). Then, processing unit24calculates the difference between an argument θmdR (t) of complex analysis signal CmdR (t) and argument θdiff (t) of complex analysis signal Cdiff (t) as phase difference Φ.

After calculating phase difference Φ, processing unit24calculates distance L corresponding to the calculated phase difference Φ in accordance with the above-described equation (2).

Processing unit24determines whether or not a disconnection has occurred in transmission line1based on the calculated distance L. When a disconnection occurs in transmission line1, processing unit24further detects the position of occurrence of the disconnection in transmission line1.

For example, processing unit24compares the calculated distance L with a predetermined threshold value Th2, and determines whether or not the disconnection has occurred in transmission line1based on the comparison result. More specifically, when the calculated distance L is less than threshold value Th2, processing unit24determines that no disconnection has occurred in transmission line1. On the other hand, when the calculated distance L is equal to or greater than threshold value Th2, processing unit24determines that the disconnection has occurred at the position of distance L from the end portion facing relay apparatus102in transmission line1.

FIG.9is a flowchart defining an example of an operation procedure when the relay apparatus according to the second embodiment of the present disclosure performs a detection processing.

Referring toFIG.9, first, relay apparatus102performs reference measurement processing. More specifically, relay apparatus102outputs measurement signal ys (t) to transmission line1to be detected, generates digital response signal ymdR (t) that is digital response signal ymd (t) in a steady-state time, and stores digital response signal ymdR (t) in storage unit15(step S202).

Next, relay apparatus102waits for the timing at which the detection processing should be performed (NO in step S204), and starts outputting period T1and measurement period Tm (step S206) at the timing at which the detection processing should be performed (YES in step S204).

Next, relay apparatus102outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1, and measures response signal ym (t) from transmission line1to measurement signal ys (t) in measurement period Tm. More specifically, relay apparatus101outputs measurement signal ys (t) for one sample to transmission line1, and samples the voltage level of transmission line1to generate digital response signal ymd (t) for one sample (step S208).

Next, relay apparatus102alternately repeats outputting measurement signal ys (t) for one sample and generating digital response signal ymd (t) for one sample until outputting period T1and measurement period Tm expire (NO in step S210), and generates difference signal ydiff (t) that is the difference between response signal ym (t) and digital response signal ymdR (t) when outputting period T1and measurement period Tm expire (YES in step S210). More specifically, relay apparatus102generates difference signal ydiff (t) by subtracting digital response signal ymdR (t) in storage unit15from digital response signal ymdS (t) (step S212).

Next, relay apparatus102calculates phase difference Φ between digital response signal ymdR (t) and difference signal ydiff (t). More specifically, relay apparatus102calculates phase difference Φ using argument θmdR (t) of complex analysis signal CmdR (t) of digital response signal ymdR (t) and argument θdiff (t) of complex analysis signal Cdiff (t) of difference signal ydiff (t) (step S214).

Next, relay apparatus102calculates distance L corresponding to phase difference Φ in accordance with the above-described equation (2) (step S216).

Next, relay apparatus101compares the calculated distance L with threshold value Th2(step S218).

Next, when distance L is less than threshold value Th2(NO in step S220), relay apparatus102determines that no disconnection has occurred in transmission line1(step S222), and waits for a next timing at which the detection processing should be performed (NO in step S204).

On the other hand, when distance L is equal to or greater than threshold value Th2(YES in step S220), relay apparatus102determines that the disconnection has occurred at a position at distance L from the end portion facing relay apparatus102in transmission line1(step S224).

Next, relay apparatus102notifies the user of the determination result via the communication unit (not shown) and communication apparatus111(step S226), and waits for a next timing at which the detection processing should be performed (NO in step S204).

As described above, in relay apparatus102according to the second embodiment of the present disclosure, processing unit24generates difference signal ydiff (t) that is the difference between response signal ym (t) and digital response signal ymdR (t) that is response signal ym (t) measured by signal measurement unit23in a steady-state time.

With such a configuration, compared with relay apparatus101according to the first embodiment of the present disclosure, it is possible to calculate difference signal ydiff (t) with reduced noise, and thus it is possible to more accurately detect the disconnection in transmission line1using the calculated difference signal ydiff (t). On the other hand, in relay apparatus101according to the first embodiment of the present disclosure, it is possible to detect the disconnection in transmission line1by a simpler configuration than that of relay apparatus102.

Next, other embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

Third Embodiment

Compared with relay apparatus101according to the first embodiment, the present embodiment relates to a relay apparatus103that performs detection processing using digital measurement signal ysd (t) obtained by performing delay adjustment on measurement signal ys (t) to be output to transmission line1. Relay apparatus103is the same as relay apparatus101according to the first embodiment except for the contents described below.

FIG.10is a diagram showing a configuration of a relay apparatus according to the third embodiment of the present disclosure. Referring toFIG.10, relay apparatus103includes a detection processing unit73instead of detection processing unit71, as compared with relay apparatus101according to the first embodiment. Detection processing unit73includes a processing unit34instead of processing unit14and further includes a delay adjustment unit16, as compared with detection processing unit71.

Signal output unit12outputs the synchronization signal to signal measurement unit13, and outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1. Signal output unit12obtains digital data Dt from storage unit15at the outputting timing according to cycle C1, and outputs the obtained digital data Dt to delay adjustment unit16as digital measurement signal ysd (t).

When receiving the synchronization signal from signal output unit12, signal measurement unit13starts measurement period Tm, generates digital response signal ymd (t) by sampling the voltage level of transmission line1by the ADC at the sampling timing according to cycle C1in measurement period Tm, and outputs the generated digital response signal ymd (t) to processing unit34.

Delay adjustment unit16receives digital measurement signal ysd (t) from signal output unit12, delays the received digital measurement signal ysd (t), and outputs the delayed digital measurement signal ysd (t) to processing unit34. More specifically, delay adjustment unit16outputs a digital measurement signal ysdD (t) whose phase is delayed with respect to measurement signal ys (t) to be output to transmission line1by signal output unit12to processing unit34.

For example, in relay apparatus103, the delay amount of digital measurement signal ysdD (t) to measurement signal ys (t) can be set and changed. More specifically, delay time dt of digital measurement signal ysdD (t) to be output by delay adjustment unit16to processing unit34can be set and changed. For example, the user sets delay time dt in delay adjustment unit16such that the amplitude of difference signal ydiff (t) generated by processing unit34in the initial state is less than a predetermined value.

Delay adjustment unit16receives the setting of delay time dt. In the detection processing, delay adjustment unit16delays digital measurement signal ysd (t) received from signal output unit12by delay time dt and outputs the delayed signal to processing unit34.

Processing unit34generates difference signal ydiff (t) that is a difference between response signal ym (t) and digital measurement signal ysdD (t) that is a signal obtained by performing delay adjustment on measurement signal ys (t). More specifically, processing unit34generates difference signal ydiff (t) by subtracting digital measurement signal ysdD (t) received from delay adjustment unit16from digital response signal ymd (t) received from signal measurement unit13.

Processing unit34calculates complex analysis signal Csd (t) by performing the Hilbert transform on digital measurement signal ysdD (t) received from delay adjustment unit16. Further, processing unit34calculates complex analysis signal Cdiff (t) by performing the Hilbert transform on the generated difference signal ydiff (t). Then, processing unit34calculates the difference between argument θsd (t) of complex analysis signal Csd (t) and argument θdiff (t) of complex analysis signal Cdiff (t) as phase difference Φ.

After calculating phase difference Φ, processing unit34calculates distance L corresponding to the calculated phase difference Φ in accordance with the above-described equation (2).

Processing unit34determines whether or not the disconnection has occurred in transmission line1based on the calculated distance L. When the disconnection occurs in transmission line1, processing unit34further detects the position of occurrence of the disconnection in transmission line1.

For example, processing unit34compares the calculated distance L with the predetermined threshold value Th2, and determines whether or not the disconnection has occurred in transmission line1based on the comparison result. More specifically, when the calculated distance L is less than threshold value Th2, processing unit34determines that no disconnection has occurred in transmission line1. On the other hand, when the calculated distance L is equal to or greater than threshold value Th2, processing unit34determines that the disconnection has occurred at the position of distance L from the end portion facing relay apparatus103in transmission line1.

FIG.11is a flowchart defining an example of an operation procedure when the relay apparatus according to the third embodiment of the present disclosure performs detection processing.

Next, relay apparatus103performs processing similar to that from step S102to step S114inFIG.7as processing from step S304to step S316, and performs processing similar to that from step S218to step S226inFIG.9as processing from step S318to step S326.

Relay apparatus103according to the third embodiment of the present disclosure has a configuration in which delay time dt of digital measurement signal ysd (t) can be set and changed in delay adjustment unit16, but is not limited thereto. Delay time dt of digital measurement signal ysd (t) in delay adjustment unit16may be a predetermined value, for example, according to the length of transmission line1such that the amplitude of difference signal ydiff (t) generated by processing unit34is less than the predetermined value.

Next, other embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

Fourth Embodiment

Compared with relay apparatus101according to the first embodiment, the present embodiment relates to a relay apparatus104that calculates phase difference Φ by correlation detection. Relay apparatus104is the same as relay apparatus101according to the first embodiment except for the contents described below.

FIG.12is a diagram showing a configuration of a relay apparatus according to a fourth embodiment of the present disclosure. Referring toFIG.12, relay apparatus104includes a detection processing unit74instead of detection processing unit71, as compared with relay apparatus101according to the first embodiment. Detection processing unit74includes a signal output unit22instead of signal output unit12and a processing unit44instead of processing unit14, as compared with detection processing unit71. Processing unit44includes LPFs4A and4B and mixers5A and5B.

Signal output unit22outputs the measurement signal that is a sine wave, to transmission line1. More specifically, signal output unit22outputs the synchronization signal to signal measurement unit13, and outputs measurement signal ys (t) to transmission line1to be detected in outputting period T1. More specifically, signal output unit22obtains digital data Dt from storage unit15at the outputting timing according to cycle C1, and outputs measurement signal ys (t) generated by converting the obtained digital data Dt into an analog signal by the DAC to transmission line1to be detected.

Further, signal output unit22outputs digital data Dt obtained from storage unit15to processing unit44as digital measurement signal ysd (t). Signal output unit22further outputs a digital measurement signal ysdP (t) that is a signal obtained by shifting the phase of the component of frequency f included in digital measurement signal ysd (t) by π/2 to processing unit44with reference to the frequency-information in storage unit15.

When receiving the synchronization signal from signal output unit22, signal measurement unit13starts measurement period Tm, generates digital response signal ymd (t) by sampling the voltage level of transmission line1at a sampling frequency fs by the ADC in measurement period Tm, and outputs the generated digital response signal ymd (t) to processing unit44. Here, sampling frequency fs is the reciprocal of cycle C1.

Processing unit44generates difference signal ydiff (t) by subtracting digital measurement signal ysd (t) received from signal output unit22from digital response signal ymd (t) received from signal measurement unit13.

Then, processing unit44calculates phase difference Φ using the output signal output from LPF4A by inputting a multiplication signal Ms1(t) of digital measurement signal ysd (t) and difference signal ydiff (t) to LPF (low pass filter)4A and the output signal output from LPF4A by inputting a multiplication signal Ms2(t) of digital measurement signal ysdP (t) and difference signal ydiff (t) to LPF4B. LPF4A is an example of a first filter. LPF4B is an example of a second filter.

More specifically, processing unit44generates multiplication signal Ms1(t) by multiplying digital measurement signal ysd (t) and difference signal ydiff (t) using mixer5A, and generates multiplication signal Ms2(t) by multiplying digital measurement signal ysdP (t) and difference signal ydiff (t) using mixer5B.

FIG.13is a diagram showing a simulation result of a multiplication signal generated by the processing unit in the relay apparatus according to the fourth embodiment of the present disclosure. InFIG.13, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.13represents multiplication signal Ms1(t), and the dashed line inFIG.13represents multiplication signal Ms2(t).FIG.13shows simulation results of multiplication signals Ms1(t) and Ms2(t) calculated by processing unit44in the case where the disconnection occurs at a position 10 m away from the end portion facing relay apparatus104in transmission line1having a length of 11 m.

When digital measurement signal ysd (t) is a cosine wave, multiplication signals Ms1(t) and Ms2(t) are expressed by the following equations (4) and (5).

Here, A1is the amplitude of measurement signal ys (t), A2is the amplitude of reflection signal yr (t), and ω is an angular frequency corresponding to frequency f. As shown in equations (4) and (5), multiplication signals Ms1(t) and Ms2(t) include a frequency-component Fc that is twice frequency f of measurement signal ys (t) and a direct-current component Dc that is a constant term.

Processing unit44attenuates frequency-component Fc of multiplication signals Ms1(t) and Ms2(t) using LPFs4A and4B described above to generate extraction signals MsD1(t) and MsD2(t) that are signals obtained by extracting direct-current component Dc of multiplication signals Ms1(t) and Ms2(t). The cut-off frequencies of LPFs4A and4B are, for example, equal to or lower than twice frequency f. LPFs4A and4B attenuate a frequency-component based on frequency f of measurement signal ys (t).

For example, processing unit44uses an average value filter as LPFs4A and4B. The first average value filter receives multiplication signal Ms1(t) and outputs extraction signal MsD1(t) that is an average value of multiplication signal Ms1(t) for each sample number N. The second average value filter receives multiplication signal Ms2(t) and outputs extraction signal MsD2(t) that is an average value of multiplication signal Ms2(t) for each sample number N. Here, N is a natural number. For example, sample number N, sampling frequency fs, and frequency f satisfy the following equation (6).

As a result, the positive and negative values of multiplication signal Ms1(t) cancel each other by the first average value filter, and extraction signal MsD1(t), in which frequency-component Fc of multiplication signal Ms1(t) is attenuated, is obtained. Further, the positive and negative values of multiplication signal Ms2(t) cancel each other by the second average value filter, and extraction signal MsD2(t), in which frequency-component Fc of multiplication signal Ms2(t) is attenuated, is obtained.

Sample number N, sampling frequency fs, and frequency f may be values that satisfy the following equation (7). Thus, the ADC that performs sampling at the lower sampling frequency fs can be used as the ADC for generating digital response signal ymd (t).

FIG.14is a diagram showing a simulation result of an extraction signal generated by the processing unit in the relay apparatus according to the fourth embodiment of the present disclosure. InFIG.14, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.14represents extraction signal MsD1(t), and the dashed line inFIG.14represents extraction signal MsD2(t).FIG.14shows simulation results of extraction signals MsD1(t) and MsD2(t) calculated by processing unit44in the case where the disconnection occurs at a position 10 m away from the end portion facing relay apparatus104in transmission line1having a length of 11 m, similarly toFIG.13.

Extraction signal MsD1(t) that is an output signal of the first average value filter and extraction signal MsD2(t) that is an output signal of the second average value filter are expressed by the following equations (8) and (9).

Processing unit44calculates phase difference Φ using extraction signals MsD1(t) and MsD2(t) in accordance with the following equation (10).

After calculating phase difference Φ, processing unit44calculates distance L corresponding to the calculated phase difference Φ in accordance with the above-described equation (2).

FIG.15is a diagram showing a simulation result of a distance calculated by the processing unit in the relay apparatus according to the fourth embodiment of the present disclosure. InFIG.15, the horizontal axis represents time [second], and the vertical axis represents the distance [m] from the end portion facing relay apparatus104in transmission line1to the reflection point.FIG.15shows a simulation result of distance L calculated by processing unit44when the disconnection occurs at a position 10 m away from the end portion facing relay apparatus104in transmission line1having a length of 11 m, similarly toFIGS.13and14.

Referring toFIG.15, distance L calculated by processing unit44substantially coincides with 10 m that is the distance between the end portion facing relay apparatus104and the disconnection position. As described above, by the detection method according to the present embodiment, it is possible to detect whether or not the disconnection has occurred in transmission line1and the position of occurrence of the disconnection.

After calculating distance L, processing unit44determines whether or not the disconnection has occurred in transmission line1based on the calculated distance L. When the disconnection occurs in transmission line1, processing unit44further detects the position of occurrence of the disconnection in transmission line1. The method of determining whether or not the disconnection has occurred in transmission line1and the method of detecting the position where the disconnection has occurred are as described in the first embodiment.

FIG.16is a flowchart defining an example of an operation procedure when the relay apparatus according to the fourth embodiment of the present disclosure performs detection processing.

Referring toFIG.16, first, relay apparatus104performs processing similar to that from step S102to step S110inFIG.7as processing from step S402to step S410.

Next, relay apparatus104generates multiplication signal Ms1(t) by multiplying digital measurement signal ysd (t) and difference signal ydiff (t) using mixer5A, and generates multiplication signal Ms2(t) by multiplying digital measurement signal ysdP (t) and difference signal ydiff (t) using mixer5B (step S412).

Next, relay apparatus104generates extraction signals MsD1(t) and MsD2(t) by attenuating frequency-component Fc of multiplication signals Ms1(t) and Ms2(t) using the average value filter (step S414).

Next, relay apparatus104calculates phase difference Φ using extraction signals MsD1(t) and MsD2(t) in accordance with the above-described equation (10) (step S416).

Next, relay apparatus104performs processing similar to that from step S114to step S126inFIG.7as processing from step S418to step S430.

In relay apparatus104according to the fourth embodiment of the present disclosure, processing unit44calculates phase difference Ø using the output signal output from LPF4A by inputting multiplication signal Ms1(t) to LPF4A and the output signal output from LPF4B by inputting multiplication signal Ms2(t) to LPF4B, but is not limited thereto. For example, processing unit44may be configured to use a BPF for extracting a direct-current component instead of LPFs4A and4B. Further, for example, signal measurement unit13generates digital response signal ymd (t) by sampling and holding the voltage level of transmission line1at frequency f of measurement signal ys (t), and outputs the generated digital response signal ymd (t) to processing unit44. In this case, processing unit44may be configured to calculate phase difference Φ using multiplication signals Ms1(t) and Ms2(t) without using LPFs4A and4B.

In relay apparatus104according to the fourth embodiment of the present disclosure, signal output unit22is configured to output the measurement signal that is a sine wave to transmission line1, but is not limited thereto. Signal output unit22may be configured to output a measurement signal having a plurality of frequency components to transmission line1, or may be configured to output a measurement signal that is a rectangular wave to transmission line1. More specifically, signal output unit22obtains digital data DtRW including a plurality of values indicating a waveform of a rectangular wave from storage unit15, and outputs a signal obtained by converting the obtained digital data DtRW into an analog signal as measurement signal ys (t) to transmission line1to be detected. Signal output unit22outputs digital data DtRW obtained from storage unit15to processing unit44as a digital measurement signal ysdRW (t). Signal output unit22further outputs a digital measurement signal ysdRWP (t) that is a signal obtained by shifting the phase of digital measurement signal ysdRW (t) by π/2 to processing unit44.

Signal measurement unit13generates a digital response signal ymdRW (t) by sampling the voltage level of transmission line1by the ADC at sampling frequency fs, and outputs generated digital response signal ymdRW (t) to processing unit44.

Processing unit44generates a difference signal ydiffR (t) by subtracting digital measurement signal ysdRW (t) received from signal output unit22from digital response signal ymdRW (t) received from signal measurement unit13. Processing unit44extracts a signal with a part of the frequency components from digital measurement signal ysdRW (t) using the BPF, and generate multiplication signal Ms1(t) by multiplying the extracted signal by difference signal ydiffR (t). In addition, processing unit44extracts a signal with a part of the frequency components from digital measurement signal ysdRWP (t) using the BPF, and generates multiplication signal Ms2(t) by multiplying the extracted signal by difference signal ydiffR (t). Processing unit44uses LPFs4A and4B to generate extraction signals MsD1(t) and MsD2(t) that are signals obtained by extracting direct-current component Dc of multiplication signals Ms1(t) and Ms2(t) and uses the generated extraction signals MsD1(t) and MsD2(t) to calculate phase difference Φ according to the above-described equation (10). In processing unit44, since the frequency component to be extracted using the BPF can be arbitrarily set, it is possible to perform the detection processing by focusing on an arbitrary frequency component included in the measurement signal that is a rectangular wave.

In relay apparatus104according to the fourth embodiment of the present disclosure, since phase difference Φ can be calculated by correlation detection, noise resistance can be improved as compared with relay apparatus101according to the first embodiment. Therefore, an abnormality in transmission line1can be detected more accurately. In addition, in relay apparatus104, since it is not necessary to calculate the complex analysis signal as compared with relay apparatus101, the implementation cost can be reduced. On the other hand, in relay apparatus101, since the time required for calculating phase difference Φ can be shortened compared to relay apparatus104, it is possible to determine the presence or absence of an abnormality at an earlier stage.

Processing unit44may be configured to calculate phase difference Φ by correlation detection using a rectangular wave digital signal.

Signal output unit22obtains digital data DtRW composed of a plurality of values indicating a waveform of a rectangular wave from storage unit15at an outputting timing according to cycle C1, and outputs measurement signal ys (t) that is a sine wave extracted from an analog signal obtained by converting the obtained digital data DtRW into an analog signal using the BPF to transmission line1to be detected.

Signal output unit22also outputs digital data DtRW obtained from storage unit15to processing unit44as digital measurement signal ysdRW (t). Digital measurement signal ysdRWP (t) that is a signal obtained by shifting the phase of digital measurement signal ysdRW (t) by π/2 is further output to processing unit44.

Processing unit44generates difference signal ydiffR (t) by subtracting digital measurement signal ysdRW (t) received from signal output unit22from digital response signal ymd (t) received from signal measurement unit13.

Processing unit44calculates phase difference Φ using the output signal output from LPF4A by inputting multiplication signal Ms1(t) of digital measurement signal ysdRW (t) and difference signal ydiffR (t) to LPF4A and the output signal output from LPF4B by inputting multiplication signal Ms2(t) of digital measurement signal ysdRWP (t) and difference signal ydiffR (t) to LPF4B.

More specifically, processing unit44generates multiplication signal Ms1(t) by multiplying digital measurement signal ysdRW (t) and difference signal ydiffR (t), and generates multiplication signal Ms2(t) by multiplying digital measurement signal ysdRWP (t) and difference signal ydiffR (t). In this case, since the multiplication of digital measurement signal ysdRW (t) and difference signal ydiffR (t), and the multiplication of digital measurement signal ysdRWP (t) and difference signal ydiffR (t) can be achieved by periodically repeating inversion and non-inversion of the original waveform, it is not necessary to use a complicated multiplier for generating multiplication signals Ms1(t) and Ms2(t), and the hardware can be simplified and the cost can be reduced.

FIG.17is a diagram showing a simulation result of the multiplication signal generated by a processing unit in a relay apparatus according to a modification of the fourth embodiment of the present disclosure. InFIG.17, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.17represents multiplication signal Ms1(t), and the dashed line inFIG.17represents multiplication signal Ms2(t).FIG.17shows simulation results of multiplication signals Ms1(t) and Ms2(t) calculated by processing unit44in the case where the disconnection occurs at a position 10 m away by from the end portion facing relay apparatus104in transmission line1having a length of 11 m.

Processing unit44attenuates frequency-component Fc of multiplication signals Ms1(t) and Ms2(t) using the average value filter to generate extraction signals MsDR1(t) and MsDR2(t) that are signals obtained by extracting direct-current component Dc of multiplication signals Ms1(t) and Ms2(t).

FIG.18is a diagram showing a simulation result of an extraction signal generated by the processing unit in the relay apparatus according to the modification of the fourth embodiment of the present disclosure. InFIG.18, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.18represents extraction signal MsDR1(t) and the dashed line inFIG.18represents extraction signal MsDR2(t).FIG.18shows simulation results of extraction signals MsDR1(t) and MsDR2(t) calculated by processing unit44in the case where the disconnection occurs at a position 10 m away from the end portion facing relay apparatus104in transmission line1having a length of 11 m, similarly toFIG.17.

Processing unit44calculates phase difference Φ by using extraction signals MsDR1(t) and MsDR2(t) instead of extraction signals MsD1(t) and MsD2(t) according to the above-described equation (10).

After calculating phase difference Φ, processing unit44calculates distance L corresponding to the calculated phase difference Φ in accordance with the above-described equation (2).

FIG.19is a diagram showing a simulation result of a distance calculated by the processing unit in the relay apparatus according to the modification of the fourth embodiment of the present disclosure. InFIG.19, the horizontal axis represents time [second], and the vertical axis represents the distance [m] from the end portion facing relay apparatus104in transmission line1to the reflection point.FIG.19shows a simulation result of distance L calculated by processing unit44when the disconnection occurs at a position 10 m away from the end portion facing relay apparatus104in transmission line1having a length of 11 m, similarly toFIGS.17and18.

Referring toFIG.19, distance L calculated by processing unit44substantially coincides with 10 m that is the distance between the end portion facing relay apparatus104and the position of the disconnection. As described above, by the detection method according to this modification, it is possible to detect whether or not the disconnection has occurred in transmission line1and the position of occurrence of the disconnection.

After calculating distance L, processing unit44determines whether or not the disconnection has occurred in transmission line1based on the calculated distance L. When the disconnection occurs in transmission line1, processing unit44further detects the position of occurrence of the disconnection in transmission line1. The method of determining whether or not the disconnection has occurred in transmission line1and the method of detecting the position where the disconnection has occurred are as described in the first embodiment.

Next, other embodiments of the present disclosure will be described with reference to the drawings. Note that the same or corresponding parts in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

Fifth Embodiment

Compared with relay apparatus104according to the fourth embodiment, the present embodiment relates to a relay apparatus105that calculates a reflection coefficient rc by correlation detection. Relay apparatus105is the same as relay apparatus104according to the fourth embodiment except for the contents described below.

FIG.20is a diagram showing a configuration of a relay apparatus according to a fifth embodiment of the present disclosure. Referring toFIG.20, relay apparatus105includes a detection processing unit75instead of detection processing unit74, as compared with relay apparatus104according to the fourth embodiment. Compared to detection processing unit74, detection processing unit75includes a processing unit54instead of processing unit44. Processing unit54includes LPFs4A and4B and mixers5A and5B.

Processing unit54calculates reflection coefficient rc between digital measurement signal ysd (t) and difference signal ydiff (t) using the output signal output from LPF4A by inputting multiplication signal Ms1(t) of digital measurement signal ysd (t) and difference signal ydiff (t) to LPF4A and the output signal output from LPF4B by inputting multiplication signal Ms2(t) of digital measurement signal ysdP (t) and difference signal ydiff (t) to LPF4B. Reflection coefficient rc is an example of an index value indicating a strength of correlation between digital measurement signal ysd (t) and difference signal ydiff (t).

More specifically, processing unit54generates multiplication signal Ms1(t) by multiplying digital measurement signal ysd (t) and difference signal ydiff (t) using mixer5A, and generates multiplication signal Ms2(t) by multiplying digital measurement signal ysdP (t) and difference signal ydiff (t) using mixer5B.

Processing unit54attenuates frequency-component Fc of multiplication signals Ms1(t) and Ms2(t) using LPFs4A and4B to generate extraction signals MsD1(t) and MsD2(t) that are signals obtained by extracting direct-current component Dc of multiplication signals Ms1(t) and Ms2(t).

Processing unit54calculates amplitude A2of reflection signal yr (t) in accordance with the following equation (11) using the known amplitude A1of measurement signal ys (t) and the generated extraction signals MsD1(t) and MsD2(t).

FIG.21is a diagram showing a simulation result of an amplitude generated by the processing unit in the relay apparatus according to the fifth embodiment of the present disclosure. InFIG.21, the horizontal axis represents time [second] and the vertical axis represents amplitude [V] of the signal. The solid line inFIG.21represents amplitude A2and the dashed line inFIG.21represents reflection signal yr (t).FIG.21shows a simulation result of amplitude A2calculated by processing unit54when the disconnection occurs at a position 10 m away from the end portion facing relay apparatus105in transmission line1having a length of 11 m.

After calculating amplitude A2, processing unit54calculates reflection coefficient rc according to the following equation (12).

FIG.22is a diagram showing a simulation result of a reflection coefficient generated by the processing unit in the relay apparatus according to the fifth embodiment of the present disclosure. InFIG.22, the horizontal axis represents time [second] and the vertical axis represents reflection coefficient. The solid line inFIG.22indicates reflection coefficient rc.FIG.22shows a simulation result of reflection coefficient rc calculated by processing unit54when the disconnection occurs at a position 10 m away from the end portion facing relay apparatus105in transmission line1having a length of 11 m, similarly toFIG.21.

Processing unit54can detect an abnormality in transmission line1based on time-course changes in amplitude A2and reflection coefficient rc. More specifically, after calculating reflection coefficient rc, processing unit54compares reflection coefficient rc with a predetermined threshold value Th3, and determines whether or not the disconnection has occurred in transmission line1based on the comparison result.

As shown in the equation (12), reflection coefficient rc changes according to the ratio of the absolute values of amplitudes A1and A2and phase difference Φ. When the specific impedance of transmission line1does not change, phase difference Φ is a constant value corresponding to distance L from the end portion facing relay apparatus105in transmission line1to the reflection point of measurement signal ys (t). For example, processing unit54can calculate distance L based on the calculated reflection coefficient rc and the attenuation amount per unit length of the signal in transmission line1.

In relay apparatus105according to the fifth embodiment of the present disclosure, processing unit54may be configured to calculate phase difference Φ in addition to reflection coefficient rc, and determine whether or not the disconnection has occurred in transmission line1based on reflection coefficient rc and phase difference Φ. More specifically, processing unit54comprehensively considers the determination results based on reflection coefficient rc and based on the phase difference Φ, and determines whether or not the disconnection has occurred in transmission line1.

Sixth Embodiment

Compared with relay apparatus104according to the fourth embodiment and relay apparatus105according to the fifth embodiment, the present embodiment relates to a relay apparatus106that calculates phase difference Φ and reflection coefficient rc using a signal including a component of a frequency (f+fb). Relay apparatus106is the same as relay apparatus104according to the fourth embodiment and relay apparatus105according to the fifth embodiment except for the contents described below.

FIG.23is a diagram showing a configuration of a relay apparatus according to a sixth embodiment of the present disclosure. Referring toFIG.23, relay apparatus106includes a detection processing unit76instead of detection processing unit74as compared with relay apparatus104according to the fourth embodiment. Compared to detection processing unit74, detection processing unit76includes a signal output unit32instead of signal output unit22and includes a processing unit64instead of processing unit44. Processing unit64includes a BPF6A, LPFs4C and4D, and mixers5C,5D, and5E.

Compared to signal output unit22, signal output unit32outputs a digital measurement signal ysdF (t) that includes a component of the frequency (f+fb) to processing unit64instead of outputting digital measurement signal ysdP (t) to processing unit44. Here, fb is a value smaller than f and close to 0. Digital measurement signal ysdF (t) is expressed by the following equation (13) where digital measurement signal ysd (t) is a cosine wave and the angular frequencies corresponding to frequencies fb are ωb.

Processing unit64calculates phase difference Φ and reflection coefficient rc by using the output signal output from BPF6A by inputting the multiplication signal of digital measurement signal ysdF (t) including the component of the frequency (f+fb) and difference signal ydiff (t) to BPF6A for extracting the component of the frequency (fb). BPF6A is an example of a third filter.

More specifically, processing unit64receives digital measurement signal ysd (t) from signal output unit32and generates difference signal ydiff (t) by subtracting digital measurement signal ysd (t) received from signal output unit32from digital response signal ymd (t) received from signal measurement unit13.

Processing unit64generates a multiplication signal Ms3(t) by multiplying digital measurement signal ysdF (t) and difference signal ydiff (t) using mixer5C. Multiplication signal Ms3(t) is expressed by the following equation (14).

As shown in Equation (14), multiplication signal Ms3(t) includes high-frequency components FH of angular frequencies 2ωt that are twice frequencies f of measurement signal ys (t) and low-frequency components FL of angular frequencies ωbt.

Processing unit64attenuates high-frequency components FH of multiplication signal Ms3using BPF6A to generate an extraction signal MsD3(t) that is a signal obtained by extracting low-frequency components FL of multiplication signal Ms3(t). BPF6A receives multiplication signal Ms3(t) and outputs extraction signal MsD3(t). Extraction signal MsD3(t) output from BPF6A is expressed by the following equation (15).

Processing unit64uses mixer5D to multiply extraction signal MsD3(t) and a digital signal Dfb (t) having amplitude A3and including the components of frequencies fb to generate a multiplication signal Ms4(t). In addition, processing unit64uses mixer5E to generate a multiplication signal Ms5(t) by multiplying extraction signal MsD3(t) and a digital signal DfbP (t) that is a signal obtained by shifting the phase of the component of frequency fb included in digital signal Dfb (t) by π/2. Here, amplitude A3may be the same as amplitude A1. Multiplication signals Ms4(t) and Ms5(t) are expressed by the following equations (16) and (17).

As shown in Equations (16) and (17), multiplication signals Ms4(t) and Ms5(t) include a frequency-component Fcb that is twice frequency-component fb and a direct-current component Dcb that is a constant term.

Processing unit64attenuates frequency-component Fcb of multiplication signals Ms4(t) and Ms5(t) using LPFs4C and4D to generate extraction signals MsD4(t) and MsD5(t) that are signals obtained by extracting direct-current component Dcb of multiplication signals Ms4(t) and Ms5(t). The cut-off frequencies of LPFs4C and4D are, for example, equal to or lower than twice frequency fb. LPFs4C and4D attenuate a frequency-component based on frequency fb.

LPF4C receives multiplication signal Ms4(t) and outputs extraction signal MsD4(t). LPF4D receives multiplication signal Ms5(t) and outputs extraction signal MsD5(t). Extraction signal MsD4(t) that is the output signal from LPF4C and extraction signal MsD5(t) that is the output signal from LPF4D are expressed by the following equations (18) and (19).

Processing unit64calculates phase difference Φ using extraction signals MsD4(t) and MsD5(t) in accordance with the following equation (20).

After calculating phase difference Φ, processing unit64calculates distance L corresponding to the calculated phase difference Φ in accordance with the above-described equation (2).

Further, processing unit64calculates amplitude A2of reflection signal yr (t) according to the following equation (21) using the known amplitude A1of measurement signal ys (t) and the generated extraction signals MsD4(t) and MsD5(t).

After calculating amplitude A2, processing unit64calculates reflection coefficient rc in accordance with the above-described equation (12). Processing unit64compares the calculated reflection coefficient rc with threshold value Th3, and determines whether or not the disconnection occurs in transmission line1based on the comparison result.

It should be understood that the above-described embodiments are illustrative in all respects and are not restrictive. The scope of the present invention is defined not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

The above description includes the following additional features.

A detection apparatus, comprising: a signal output unit configured to output a measurement signal that includes a component having a first frequency to a transmission line; a signal measurement unit configured to measure a response signal from the transmission line to the measurement signal output from the signal output unit; and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that based on the measurement signal, calculate an index value that indicate a strength of a correlation between the reference signal and the difference signal, and detect an abnormality in the transmission line on the basis of the calculated index value, wherein the processing unit calculates a distance from an end facing the detection apparatus in the transmission line to a reflection point at which the measurement signal is reflected in the transmission line based on the index value, and specifies a position of occurrence of the abnormality based on the calculated distance.

A detection apparatus, comprising: a signal output unit configured to output a measurement signal that includes a component having a first frequency to a transmission line; a signal measurement unit configured to measure a response signal from the transmission line the measurement signal output from the signal output unit; and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that is based on the measurement signal, calculate an index value that indicate a strength of a correlation between the reference signal and the difference signal, and detect an abnormality in the transmission line on the basis of the calculated index value, wherein the transmission line does not include a termination resistor.

A detection apparatus, comprising: a signal output unit configured to output a sine wave as a measurement signal to a transmission line; a signal measurement unit configured to measure a response signal from the transmission line to the measurement signal output from the signal output unit; and a processing unit configured to generate a difference signal that is a difference between the response signal measured by the signal measurement unit and a reference signal that is based on the measurement signal, and detect a disconnection in the transmission line based on a phase difference between the reference signal and the difference signal.

REFERENCE SIGNS LIST