RC polyphase filter, demodulation system using the same, contact-type anomaly detection device, remote monitoring system, and signal demodulation method using RC polyphase filter.

Abstract

The present invention provides an RC polyphase filter that does not require the generation of a phase-inverted signal for the input signal, a demodulation system, a contact-type anomaly detection device, a remote monitoring system, and a signal demodulation method using an RC polyphase filter. [Solution] The RC polyphase filter receives an external input signal to only one input terminal, and the output terminal connected only to the input terminal via a resistor is designated as the first output terminal. The output terminals are designated as the second, third, and fourth output terminals in order that their phases lag behind the phase of the output signal of the first output terminal. The differential signal between the output of the first output terminal and the output of the third output terminal is output as the first differential signal, and the differential signal between the output of the second output terminal and the output of the fourth output terminal is output as the second differential signal.

Description

[Technical Field]

[0001] The present invention relates to an RC polyphase filter, a demodulation system using the same, a contact-type anomaly detection device, a remote monitoring system, and a signal demodulation method using an RC polyphase filter. [Background technology]

[0002] In structures such as bridges, defects during manufacturing or deterioration over time can cause abnormalities such as poor joints, delamination of composite materials, fatigue cracks, and loosening of bolted connections, resulting in adhesion between materials. To ensure the safety of products and structures, it is necessary to detect these abnormalities. One method for detecting these abnormalities is nonlinear wave modulation, which utilizes the fact that the adhesion state of abnormal parts changes due to vibrations during use, and uses small-amplitude ultrasound to detect abnormalities. In nonlinear wave modulation, it is necessary to demodulate the modulation that occurs in the vibration and phase of the ultrasound. Conventionally, after digitally recording the modulated ultrasound signal with an A / D converter, a complex signal was generated using a Hilbert transform in a digital signal processor. Amplitude demodulation processing was performed using the sum of squares and root of squares calculation, and phase demodulation processing was performed using the phase difference calculation with the excitation ultrasound signal to obtain the amplitude demodulated signal and the phase demodulated signal.

[0003] Furthermore, in the diagnosis of abnormalities in rotating machinery, it is known that detecting the envelope of the vibration waveform is an effective way to evaluate abnormalities. In this signal processing, digital processing is generally used.

[0004] As mentioned above, in conventional anomaly diagnosis systems, demodulation of vibration signals and envelope detection require digital signal processing, which poses problems such as the need for high-sampling digital signal processors and the need for long-term data recording resulting in large data volumes.

[0005] In the field of wireless communication equipment, RC polyphase filters are used as quadrature waveform generators. An RC polyphase filter generates an I signal (In-phase signal) and a Q signal (Quadrature signal). By using two or four input signals with inverted phases, the RC polyphase filter performs differential operation within the circuit to obtain four signals with phases differing by 90 degrees. Patent Document 1 discloses an example of an RC polyphase filter.

[0006] In systems for diagnosing abnormalities in structures such as bridges, remote monitoring systems that simultaneously monitor numerous bridges are attracting attention. These systems utilize edge computing of sensor signals with demodulation systems, communicating only the demodulated low-frequency signals to a centralized control center. Edge computing systems installed on structures require compact and power-efficient configurations to accommodate installation in numerous locations. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 6749521 [Overview of the project] [Problems that the invention aims to solve]

[0008] In contact-type anomaly detection using nonlinear wave modulation in structural anomaly diagnosis systems for bridges and other structures, methods employing digital signal processing have problems such as requiring high-sampling digital signal processors and necessitating long-term data recording, resulting in large data volumes. On the other hand, analog processing using RC polyphase filters requires active circuits to generate a two-input differential signal as the input signal, making it unsuitable for structural anomaly diagnosis systems where securing sufficient power is difficult.

[0009] The object of the present invention is to provide an RC polyphase filter that does not require the generation of a two-input differential signal as an input signal, a demodulation system using the same, a contact-type anomaly detection device, a remote monitoring system, and a signal demodulation method using an RC polyphase filter. [Means for solving the problem]

[0010] The RC polyphase filter according to the present invention is characterized in that an external input signal is input to only one input terminal, and the output terminal connected only to the input terminal to which the input signal is input is designated as the first output terminal, and the second, third, and fourth output terminals are designated in order in which the phase of each output signal lags behind the phase of the output signal of the first output terminal, and the differential signal of the output of the first output terminal and the output of the third output terminal is output as the first differential signal, and the differential signal of the output of the second output terminal and the output of the fourth output terminal is output as the second differential signal.

[0011] Furthermore, the RC polyphase filter according to the present invention is an RC polyphase filter (N is an integer of 2 or more) in which a filter circuit is formed by connecting N stages of a filter circuit having four resistors, with one end of the Mth resistor connected to the Mth intermediate input terminal and the other end to the Mth intermediate output terminal (M is an integer from 1 to 4), and a capacitor connected between the Mth intermediate input terminal and the Kth intermediate output terminal (K is the remainder when the divisor of M+1 is 4), wherein the 1st to 4th intermediate input terminals of the first stage filter circuit are the 1st to 4th input terminals, and at the 1st to 4th intermediate output terminals of the Nth stage filter circuit, only a resistor is connected from the 1st input terminal. When a terminal with a path is designated as the first output terminal, a terminal with a path consisting only of a resistor from the second input terminal is designated as the second output terminal, a terminal with a path consisting only of a resistor from the third input terminal is designated as the third output terminal, and a terminal with a path consisting only of a resistor from the fourth input terminal is designated as the fourth output terminal, the device is characterized in that an external input signal is input only to the first input terminal, and the device has means for outputting a first differential signal which is the differential signal of the output of the first output terminal and the output of the third output terminal, and means for outputting a second differential signal which is the differential signal of the output of the second output terminal and the output of the fourth output terminal.

[0012] According to the above configuration, only one input signal is required, so an active circuit for generating a differential signal of the input signal is unnecessary. Therefore, the RC polyphase filter with the above configuration becomes a small-sized and power-saving circuit, which is suitable for constructing a system by edge computing.

[0013] The demodulation system according to the present invention is a demodulation system including a transmission element that inputs a first high-frequency signal to a structure, a reception element that receives a second high-frequency signal after the first high-frequency signal propagates through the structure, and a signal processing unit that processes a signal output from the reception element. The signal processing unit uses the second high-frequency signal as an input signal, and includes an analog processing unit that outputs an orthogonal waveform by the RC polyphase filter, and a digital processing unit that outputs an amplitude demodulation waveform and a phase demodulation waveform of the second high-frequency signal based on the orthogonal waveform output from the analog processing unit.

[0014] According to the above configuration, since an RC polyphase filter that does not need to generate a differential signal of the input signal is used, a demodulation system can be realized even in an environment where it is difficult to secure sufficient power.

[0015] The contact type abnormality detection device according to the present invention includes the demodulation system installed in a structure, a transmitter that inputs an ultrasonic signal to the transmission element, and a data processing device that receives the amplitude demodulation waveform and the phase demodulation waveform output from the demodulation system and performs an abnormality diagnosis of the structure.

[0016] According to the above configuration, the data communication capacity can be reduced, and a contact type abnormality detection device for performing an abnormality diagnosis of a structure can be configured at a low cost.

[0017] The remote monitoring system according to the present invention includes a plurality of the demodulation systems installed in a structure, and a centralized management center that receives the amplitude demodulation waveform and the phase demodulation waveform output from each of the plurality of demodulation systems and performs an abnormality diagnosis of the structure.

[0018] <000009According to the above configuration, data communication capacity can be reduced, and a remote monitoring system for diagnosing structural abnormalities can be constructed at a low cost.

[0019] The signal demodulation method using an RC polyphase filter according to the present invention is a signal demodulation method using an RC polyphase filter (N is an integer of 2 or more) in which a filter circuit is constructed by connecting N stages of a filter circuit having four resistors, with one end of the Mth resistor connected to the Mth intermediate input terminal and the other end to the Mth intermediate output terminal (M is an integer from 1 to 4), and a capacitor connected between the Mth intermediate input terminal and the Kth intermediate output terminal (K is the remainder when the divisor of M+1 is 4), wherein the first to fourth intermediate input terminals of the first stage filter circuit are designated as the first to fourth input terminals, and at the first to fourth intermediate output terminals of the Nth stage filter circuit, a path consisting only of a resistor exists from the first input terminal. When the input terminal is designated as the first output terminal, the terminal to which a path consisting only of resistors exists from the second input terminal is designated as the second output terminal, the terminal to which a path consisting only of resistors exists from the third input terminal is designated as the third output terminal, and the terminal to which a path consisting only of resistors exists from the fourth input terminal is designated as the fourth output terminal, an external input signal is input only to the first input terminal, a first differential signal which is the differential signal of the output of the first output terminal and the output of the third output terminal is output, a second differential signal which is the differential signal of the output of the second output terminal and the output of the fourth output terminal is output, and the amplitude demodulated waveform and phase demodulated waveform of the input signal are demodulated based on the first differential signal and the second differential signal.

[0020] According to the above configuration, an active circuit for generating differential signals from the input signals is unnecessary, allowing for the construction of a compact, low-power RC polyphase filter. Furthermore, by using this RC polyphase filter, a demodulation system, a contact-type anomaly detection device, and a remote monitoring system can be constructed at low cost. [Effects of the Invention]

[0021] The RC polyphase filter and signal demodulation method according to the present invention do not require an active circuit for generating a differential signal of the input signal. By using the RC polyphase filter according to the present invention, a demodulation system, a contact-type anomaly detection device, and a remote monitoring system can be configured. [Brief explanation of the drawing]

[0022] [Figure 1] This is a diagram showing the configuration of the demodulation system of the present invention. [Figure 2] This diagram illustrates the mechanism by which a contact-type anomaly causes modulation in a high-frequency signal. [Figure 3] Figure 3(a) shows the waveform received by the receiving element in the demodulation system of the present invention, with Figure 3(b) showing the waveform when there is no abnormality. [Figure 4] This is a block diagram showing the demodulation method for amplitude demodulated signals according to the present invention. [Figure 5] This is a block diagram showing the demodulation method for phase-demodulated signals according to the present invention. [Figure 6] This is a circuit diagram of a conventional RC polyphase filter. [Figure 7] This is a circuit diagram of an RC polyphase filter according to the first embodiment of the present invention. [Figure 8] Figure 8(a) shows the characteristics of the RC polyphase filter of the first embodiment, and Figure 8(b) shows the gain characteristics. [Figure 9] This waveform diagram compares the accuracy of the amplitude demodulated waveforms of analog processing using the RC polyphase filter of the first embodiment and conventional digital processing. [Figure 10] Figure 9 shows the degree of agreement between the amplitude demodulated waveforms of the analog and digital processing. [Figure 11] This is a diagram showing the configuration of a contact-type anomaly detection device using the demodulation system of the present invention. [Figure 12] This is a diagram illustrating the configuration of a bridge remote monitoring system using the demodulation system of the present invention. [Figure 13]This is a circuit diagram of an RC polyphase filter according to a second embodiment of the present invention. [Figure 14] This is a circuit diagram of an RC polyphase filter according to a third embodiment of the present invention. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, specific shapes, directions, numerical values, etc., are examples to facilitate understanding of the present invention and can be appropriately modified according to the application, purpose, specifications, etc. Furthermore, it is anticipated from the outset that the components of the embodiments and modifications described below can be selectively combined.

[0024] <First Embodiment> This document describes a demodulation system 10 used for detecting contact-type anomalies in structures such as bridges. Figure 1 is a diagram of the configuration of the demodulation system 10 of the present invention. In Figure 1, a contact-type anomaly is indicated by the anomaly section 11. A contact-type anomaly refers to anomalies where the medium is in close contact with each other, such as poor bonding, delamination of composite materials, fatigue cracks, and loosening of bolt fastenings. The demodulation system 10 is installed on a structure 1 such as a bridge and includes a transmitting element 12 that inputs a first high-frequency signal (frequency f1) to the structure 1, a receiving element 13 that receives a second high-frequency signal (frequency f2) after the first high-frequency signal has propagated through the structure 1, and a signal processing unit 14 that processes the signal output by the receiving element 13. In Figure 1, the structure 1 receives a low-frequency signal (frequency f2) as an environmental disturbance in addition to the first high-frequency signal for inspection. low The receiving element 13 of the demodulation system 10 receives the signals after the first high-frequency signal and low-frequency signal have propagated through the structure 1. Hereafter in this invention, when referring to values ​​such as resistor R1, the same symbol R1 will be used.

[0025] The transmitting element 12 vibrates in response to a first high-frequency signal, which is an ultrasonic vibration signal for inspection, and transmits the high-frequency vibration to the structure 1. The vibration of the first high-frequency signal propagates within the structure 1. The transmitting element 12 has the function of receiving an electrical signal and converting it into vibration. Specifically, a piezoelectric element is preferred, but it is not limited to this.

[0026] The receiving element 13 receives high-frequency vibrations propagating within the structure 1 and outputs a second high-frequency signal. When passing through the structure 1 having the abnormal part 11, the second high-frequency signal becomes a signal in which the amplitude and phase of the first high-frequency signal are modulated. The receiving element 13 has the function of receiving vibrations and converting them into electrical signals. Specifically, a piezoelectric element is preferred, but it is not limited to this.

[0027] The signal processing unit 14 includes an analog processing unit 15, an A / D conversion unit 16, and a digital processing unit 17. The analog processing unit 15 has an RC polyphase filter 20 (described later) and takes a second high-frequency signal as an input signal and outputs a quadrature waveform.

[0028] The A / D conversion unit 16 performs A / D conversion on the quadrature waveform output by the analog processing unit 15 and outputs it to the digital processing unit 17.

[0029] The digital processing unit 17 outputs the amplitude demodulated waveform and phase demodulated waveform of the second high-frequency signal based on the digital signal output by the A / D conversion unit.

[0030] The RC polyphase filter 20 receives the second high-frequency signal received by the receiving element 13. As will be described later, the RC polyphase filter 20 receives the first differential signal V out1 And the second differential signal V out2 It was configured to output [this].

[0031] The signal processing unit 14 is installed near the receiving element 13 along with the edge computer for signal processing. The edge computer can detect abnormal conditions in the structure 1 by inspecting the amplitude demodulated waveform and the phase demodulated waveform. Alternatively, as will be described later, the system may be configured to send the amplitude demodulated signal and the phase demodulated signal demodulated by the edge computer to a central control center. The central control center performs an abnormality diagnosis based on the received signals (Figure 11).

[0032] Figure 2 illustrates the mechanism by which modulation occurs in the high-frequency signal when the abnormal part 11, which is a contact-type anomaly, is subjected to ultrasonic waves. Structure 1 is constantly subjected to low-frequency environmental disturbances, and the contact state of the abnormal part 11 fluctuates in response to the low-frequency vibrations, causing the abnormal part to repeatedly open and close at low frequencies. When a high-frequency signal such as ultrasonic waves is input into structure 1 where the abnormal part 11 is located, modulation of the amplitude and phase of the high-frequency signal occurs. This phenomenon is called nonlinear wave modulation or vibroacoustic modulation, and contact-type anomaly detection detects the abnormal state of structure 1 by observing this modulation.

[0033] Figure 3 shows the vibration waveform received by the receiving element 13 in the demodulation system 10 of the present invention. Figure 3(a) is the waveform when there is no abnormal part 11, and Figure 3(b) is the waveform when there is an abnormal part 11. The receiving element 13 receives the frequency f of the environmental disturbance. low A low-frequency signal having and a high high-frequency f high A signal is received in which excitation signals having the following characteristics are superimposed.

[0034] If there is no abnormality 11, no modulation occurs in the high-frequency signal, and the receiving element 13 receives a signal in which the low-frequency signal shown in Figure 3(a) and the excitation signal are superimposed. If there is an abnormality 11, the receiving element 13 receives a signal in which the low-frequency signal shown in Figure 3(b) and the high-frequency signal modulated by the excitation signal are superimposed. The characteristics of the abnormality 11 appear in the amplitude demodulated waveform and phase demodulated waveform obtained by demodulating the modulated high-frequency signal. Here, the frequency f of the low-frequency signal excited by the environmental disturbance is... lowThe frequency is on the order of a few Hz. Therefore, ultrasonic vibrations of a few kHz or higher can be used as the excitation signal.

[0035] Next, the method for demodulating a modulated high-frequency signal according to the present invention will be described. Figure 4 is a block diagram showing the demodulation method for an amplitude-demodulated signal.

[0036] The amplitude demodulated signal is processed by an analog processing unit 15 that receives the modulated signal, an A / D conversion unit 16 (A / D converters 33a, 33b) that performs A / D conversion on the signal output by the analog processing unit 15, and a digital processing unit 17 that processes the digital signal output by the A / D conversion unit 16. The analog processing unit 15 has a complex analog circuit 31. In this invention, the complex analog circuit 31 corresponds to an RC polyphase filter 20. The complex analog circuit 31 converts the input modulated signal into a real part signal and an imaginary part signal. The real part signal and the imaginary part signal are then subjected to envelope detection by absolute value circuits 32a and 32b, respectively.

[0037] The A / D conversion unit 16 (A / D converters 33a and 33b) samples the output signals from the absolute value circuits 32a and 32b and sends them to the digital signal processor 34 of the subsequent digital processing unit 17. The digital signal processor 34 performs a sum-of-squares root calculation and outputs an amplitude demodulated signal.

[0038] Next, Figure 5 is a block diagram showing the demodulation method of the phase demodulated signal. The generation method of the phase demodulated signal is performed by the analog processing unit 15, the A / D conversion unit 16, and the digital processing unit 17. The complex analog circuit 41a, absolute value circuits 42a and 42b, and A / D converters 43a and 43b have the same configuration as the demodulation of the amplitude demodulated signal in Figure 4. Furthermore, the excitation signal is taken as input, the real part signal and imaginary part signal are obtained from the complex analog circuit 41b, and the signals output by the absolute value circuits 42c and 42d are A / D converted by the A / D converters 43c and 43d. Then, the phase difference calculation with the amplitude demodulated signal is performed by the digital signal processor 44 to output the phase demodulated signal.

[0039] Conventional digital demodulation methods involved digitally recording the modulated high-frequency signal with an A / D converter, generating a complex signal using a Hilbert transform in a digital signal processor, and then obtaining the amplitude demodulated signal and phase demodulated signal by performing amplitude demodulation using the sum of squares and root of squares calculation, and phase demodulation using the phase difference calculation with the excitation ultrasonic signal. In the demodulation system of the present invention, the low-frequency signal, which is the demodulated component, is extracted by analog processing using an analog circuit, and then digitally recorded with an A / D converter. This allows for recording with low sampling rates, reduces data capacity, and eliminates the need for high-speed processing of the digital calculations by the digital signal processor.

[0040] Next, we will explain the approximate characteristics of the conventional RC polyphase filter 200 as a Hilbert filter. Figure 6 is a circuit diagram of the conventional RC polyphase filter 200. The conventional RC polyphase filter 200 consists of a first stage composed of a resistor R1 and a capacitor C1, and a second stage composed of a resistor R2 and a capacitor C2. In Figure 6, it is configured as a two-stage filter circuit, but the number of stages is not particularly limited. The resistance value R of the resistors in each stage of the RC polyphase filter is all the same, and the capacitance value C of the capacitors is all the same. Here, the frequency f at which the gain of adjacent output signals is the same can be expressed as f = 1 / (2πRC). The frequency f is called the design frequency of the RC polyphase filter.

[0041] The configuration of the first stage of the RC polyphase filter 200 is described below. The first stage of the RC polyphase filter is formed by resistors R1 and capacitors C1. One end of each of the four resistors R1 is connected to the first to fourth input terminals, and the other end to the first to fourth output terminals. Capacitors C1 are connected between the first input terminal and the second output terminal, between the second input terminal and the third output terminal, between the third input terminal and the fourth output terminal, and between the fourth input terminal and the first output terminal. An external signal is input to the first input terminal, and its inverted signal is input to the third input terminal. The second and fourth input terminals are connected to the circuit ground.

[0042] The configuration of the RC polyphase filter after the second stage is the same as that of the RC polyphase filter in the first stage. In a multi-stage RC polyphase filter, the output terminals are as follows: the output terminal with a path consisting only of a resistor from the first input terminal is the first output terminal, the output terminal with a path consisting only of a resistor from the second input terminal is the second output terminal, the output terminal with a path consisting only of a resistor from the third input terminal is the third output terminal, and the output terminal with a path consisting only of a resistor from the fourth input terminal is the fourth output terminal.

[0043] In the RC polyphase filter 200 of FIG. 6, an input signal V in is input to the input terminal I1, and an inverted signal of the input signal V in is input to the input terminal I3. The input terminals I2 and I4 are connected to the ground. Output signals V o1 ~V o4 are output from the output terminals O1 to O4.

[0044] The transfer functions of the output signals of the RC polyphase filter 200 are given by equations (1) to (4), respectively.

Equation

[0045] The denominators of the transfer functions of equations (1) to (4) are all common. Therefore, the relationship (amplitude, phase relationship) between the output signals can be determined by the numerators of the transfer functions of each equation, and the following can be understood.

Table 1

[0046] When using a conventional RC polyphase filter 200 as a Hilbert filter, two inverted signals are required as input signals. If the inverted signals are generated without amplifying one of the signals, the amplitudes of the two signals will be half the amplitude of the original signal, raising concerns about a decrease in the signal-to-noise ratio. On the other hand, an active circuit is required to amplify the inverted signals. In anomaly diagnosis systems operating on limited power supplies, it is difficult to implement an active circuit.

[0047] Next, the RC polyphase filter 20 of the present invention will be described. Figure 7 is a circuit diagram of the RC polyphase filter 20 of the present invention. In the RC polyphase filter 20 of the present invention, an external input signal is input only to the first input terminal, and the output terminal connected only to the input terminal to which the input signal is input is designated as the first output terminal. The second output terminal, third output terminal, and fourth output terminal are designated in order in which the phase of each output signal lags behind the phase of the output signal of the first output terminal. The differential signal of the output of the first output terminal and the output of the third output terminal is output as the first differential signal, and the differential signal of the output of the second output terminal and the output of the fourth output terminal is output as the second differential signal. No signal is input to the second to fourth input terminals. The second and fourth input terminals are connected to the circuit ground. No external signal is input to the third input terminal, and it is not connected to any terminal.

[0048] The RC polyphase filter 20 receives the input signal V in The difference from the conventional RC polyphase filter 200 is that it has one signal. The configuration of resistors and capacitors is the same as the conventional RC polyphase filter 200 in Figure 6, so the same symbols are used for the circuit symbols R1, R2, C1, C2 and the input terminals I1~I4 and output terminals O1~O4. The output signal V is output to the output terminals O1~O4. o1 ~V o4 The same symbols as in Figure 6 are used.

[0049] The transfer function of the output signal of the RC polyphase filter 20 is given by equations (5) to (8).

number

[0050] Although the denominators of the transfer functions in equations (5) to (8) are all common, the form of the numerators of the transfer functions does not indicate that the conditions for a Hilbert filter are satisfied.

[0051] In the RC polyphase filter 20 of the present invention, the output signal V of the output terminal O1 o1 and the output signal V from output terminal O3 o3 Differential signal V out1 It outputs the output signal V from output terminal O2. o2 and the output signal V of output terminal O4 o4 Differential signal V out2 It has a configuration that outputs [this].

[0052] Differential signal V out1 and V out2 The transfer functions are given by equations (9) and (10).

number

[0053] The denominators of the transfer functions in equations (9) and (10) are of the same form, and from the numerators of the transfer functions, we can see that the phase difference is 90 degrees. Therefore, the differential signal V out1 and V out2 It can be seen that the conditions for a Hilbert filter are satisfied by using this method. In the RC polyphase filter 20 of the present invention, instead of using a single input signal, the characteristics of a Hilbert filter can be obtained by differential outputting the signals at the output terminals. Therefore, by using the RC polyphase filter 20, an active circuit that generates an inverted signal of the input signal becomes unnecessary, the overall circuit can be made smaller, and the effect of reducing power consumption can be expected.

[0054] Furthermore, the means for outputting differential signals in this invention are not limited. For example, a configuration in which the output signals from output terminals O1 and O3 are input to a signal measuring instrument and the respective differential signals are observed is conceivable. The same applies to output terminals O2 and O4.

[0055] Next, Figure 8 shows the accuracy evaluation results of the RC polyphase filter 20 of the present invention. Figure 8(a) shows the gain characteristics, and Figure 8(b) shows the phase characteristics. Differential signal V out1 The characteristics are shown by a dashed line, and the differential signal V out2 The characteristics are shown by the dashed line. Here, the constants for each stage of the RC polyphase filter 20 are R1=910Ω, C1=18nF, R2=470Ω, and C2=18nF. Therefore, the design frequencies for each stage are f1=9.71kHz and f2=18.7kHz.

[0056] The gain characteristics show that the gain crosses over between the design frequencies f1 and f2. The gain is almost flat between frequencies f1 and f2. The phase characteristics show that the phase difference is 90 degrees across the entire frequency band. From the above, it can be seen that the RC polyphase filter 20 functions as a good Hilbert filter between frequencies f1 and f2.

[0057] Figure 9 compares the accuracy of amplitude demodulated waveforms obtained by analog processing using the RC polyphase filter 20 of the present invention with those obtained by conventional digital processing. The waveform obtained by analog processing is shown as a solid line, and the waveform obtained by digital processing is shown as a dashed line. Although the waveform obtained by analog processing has amplitude attenuation, the frequencies of both are equal to 10 Hz. Note that the amplitude can be corrected in subsequent processing.

[0058] Figure 10 plots the cross-correlation between the amplitude demodulated waveform obtained by analog processing and the amplitude demodulated waveform obtained by digital processing in Figure 9. The maximum value of the cross-correlation is 99.997%, indicating that the two waveforms are identical. Shift τ is the delay in the RC polyphase filter 20, and this can be corrected.

[0059] As shown above, signal processing using the RC polyphase filter 20 can be performed with the same accuracy as conventional digital processing. Comparing analog and digital processing for a low-frequency signal of 10 Hz and a high-frequency signal of 10 kHz, in digital processing, the sampling frequency needs to be 1 MHz because the ultrasonic signal is sampled. On the other hand, in analog processing, the demodulated low-frequency signal is sampled, so a sampling frequency of about 1 kHz is sufficient. If five periods of the modulation component are sampled, the data will be 500 kHz in digital processing and 500 kHz in analog processing. Therefore, analog processing requires only 1 / 1000th of the data of digital processing, thus reducing the system size. From the above, it can be seen that by using an analog circuit RC polyphase filter instead of a conventional digital Hilbert filter, a high-speed digital signal processor is not required, and the data capacity can be reduced.

[0060] This invention relates to a contact-type anomaly detection method based on nonlinear wave modulation, where a modulated high-frequency signal is demodulated using analog signal processing to obtain a low-frequency signal, which is the demodulated component. This enables remote anomaly diagnosis using low-spec, inexpensive digital recording equipment, digital signal processing equipment, and communication equipment. Therefore, it can be implemented with an inexpensive system and requires small data capacity. By using the demodulation system of this invention to perform edge computing on sensor signals and communicating only the demodulated low-frequency signal to a centralized management center, a system for simultaneously monitoring multiple bridges can be realized.

[0061] Next, an example of the application of the demodulation system of the present invention will be described. Figure 11 is a diagram showing the configuration of a contact-type anomaly detection device 50 using the demodulation system of the present invention.

[0062] The contact-type anomaly detection device 50 comprises the demodulation system 10 installed on the structure 1, a transmitter 18 that inputs an ultrasonic signal to a transmitting element 12 of the demodulation system 10, and a data processing device 19 that receives amplitude demodulated waveforms and phase demodulated waveforms output from the signal processing unit 14 of the demodulation system 10 and performs an anomaly diagnosis of the structure 1.

[0063] The data processing device 19 is configured to receive the amplitude demodulated waveform and phase demodulated waveform output by the signal processing device 14. However, the configuration shown in Figure 11 is just one example, and the data processing device 19 may also be configured to incorporate the functions of the signal processing device 14 and directly input the output signal of the receiving element 13.

[0064] By using the demodulation system of the present invention, a contact-type anomaly detection device 50 can be realized that has a small data communication capacity and an inexpensive configuration, and can perform anomaly diagnosis of structures.

[0065] Next, Figure 12 shows a remote bridge monitoring system 100 using the demodulation system of the present invention. The remote monitoring system 100 includes a plurality of bridges 110, sensors 120 installed on the bridges 110, and a centralized control center 140 that receives amplitude demodulated waveforms and phase demodulated waveforms output from the sensors 120 and performs abnormality diagnosis of the bridges 110. The bridges 110 are equipped with the same demodulation system 10 as described above. The sensors 120 correspond to the demodulation system 10, and distributed processing is performed by edge computing 130. The sensors 120 perform signal demodulation processing in real time and wirelessly transmit the processed signals to the centralized control center 140. The centralized control center 140 performs abnormality analysis and can quickly perform the necessary processing.

[0066] The remote monitoring system 100 requires sensors 120 to be installed in various locations. By performing data processing using edge computing 130 near the sensors 120, communication delays and signal degradation are less likely to occur. Furthermore, it is advantageous in terms of energy efficiency and maintainability.

[0067] Furthermore, the sensor 120 installed on the bridge 110 is currently powered by vibrations of the bridge, as it is difficult to supply sufficient power to it. Therefore, the configuration of the sensor 120 needs to be simple. The demodulation system 10 of the present invention is an effective solution because it requires only one input signal for the RC polyphase filter 20, eliminating the need for an active circuit and allowing for a power-saving system configuration.

[0068] <Second Embodiment> Although the RC polyphase filter 20 of the first embodiment had a two-stage configuration, the RC polyphase filter applicable to the present invention is not limited to a two-stage configuration. The N-stage RC polyphase filter of the present invention is an RC polyphase filter (N is an integer of 2 or more) in which a filter circuit is connected in N stages, each having four resistors, with one end of the Mth resistor connected to the Mth intermediate input terminal and the other end to the Mth intermediate output terminal (M is an integer from 1 to 4), and a capacitor connected between the Mth intermediate input terminal and the Kth intermediate output terminal (K is the remainder when the divisor of M+1 is 4), wherein the first to fourth intermediate input terminals of the first stage filter circuit are the first to fourth input terminals, and at the first to fourth intermediate output terminals of the Nth stage filter circuit, a resistor is connected from the first input terminal. When a terminal with a path consisting only of resistors is designated as the first output terminal, a terminal with a path consisting only of resistors from the second input terminal is designated as the second output terminal, a terminal with a path consisting only of resistors from the third input terminal is designated as the third output terminal, and a terminal with a path consisting only of resistors from the fourth input terminal is designated as the fourth output terminal, the device has means for outputting a first differential signal which is the differential signal of the output of the first output terminal and the output of the third output terminal, and means for outputting a second differential signal which is the differential signal of the output of the second output terminal and the output of the fourth output terminal, when an external input signal is input only to the first input terminal. Furthermore, the one-stage RC polyphase filter of the present invention has four resistors, with one end of the M resistor connected to the input terminal of the M and the other end to the output terminal of the M (M is an integer from 1 to 4), and a capacitor connected between the input terminal of the M and the output terminal of the K (K is the remainder when the divisor of M+1 is 4). The RC polyphase filter has means for outputting a first differential signal, which is the differential signal of the output of the first output terminal and the output of the third output terminal, and means for outputting a second differential signal, which is the differential signal of the output of the second output terminal and the output of the fourth output terminal, to which an external input signal is input only to the first input terminal. Figure 13 shows a circuit diagram of the RC polyphase filter 21 of the second embodiment. In the second embodiment, components similar to those in the first embodiment are denoted by the same reference numerals as in the first embodiment and their descriptions are omitted.

[0069] The RC polyphase filter 21 of the second embodiment differs from the RC polyphase filter 20 of the first embodiment in that it has a single-stage configuration, but like the RC polyphase filter 20 of the first embodiment, it uses a single input signal and outputs a differential signal from the output terminals. The RC polyphase filter 21 has approximate characteristics of a Hilbert filter only at its design frequency f1 = 1 / (2πR1C1).

[0070] <Third Embodiment> Figure 14 shows the circuit diagram of the RC polyphase filter 22 of the third embodiment. In the third embodiment, the same reference numerals as in the first embodiment are used for components that are not described in the first embodiment. The RC polyphase filter 22 of the third embodiment differs from the RC polyphase filter 20 of the first embodiment in that it has an n-stage configuration. The design frequency of each stage is f i = 1 / (2πR i C i ) (where i = 1 to n). The RC polyphase filter 22 in Figure 14 can be made to operate as a Hilbert filter by increasing the number of filter stages, thereby widening the operating frequency bandwidth and improving the approximation accuracy of the Hilbert filter. On the other hand, increasing the number of filter stages reduces the gain, which is the ratio of the output voltage to the input voltage, so the S / N ratio becomes lower. Therefore, it is best to select the optimal number of filter stages considering the approximation accuracy of the Hilbert filter, the circuit size due to the multi-stage design, and the S / N ratio.

[0071] As described above, the demodulation system using the RC polyphase filter of the present invention can convert the input signal into a single signal, thus eliminating the need for an active circuit to generate an inverted signal.

[0072] The demodulation system of the present invention extracts the low-frequency signal, which is the demodulation component, through analog processing using an analog circuit, and then digitally records it using an A / D converter. Therefore, it is possible to record with low sampling rates, the data capacity is small, and the processing speed of the digital signal processor that performs the digital calculations does not need to be high.

[0073] This invention relates to a contact-type anomaly detection method based on nonlinear wave modulation, in which a modulated ultrasonic signal is demodulated, and obtains a low-frequency signal, which is the demodulated component, by analog signal processing. This enables the realization of a remote anomaly diagnosis system using low-spec, inexpensive digital recording equipment, digital signal processing equipment, and communication equipment.

[0074] It should be noted that the present invention is not limited to the embodiments and their modifications described above, and various changes and improvements are possible within the scope of the claims of this application. [Explanation of Symbols]

[0075] 1 Structure, 10 Demodulation system, 11 Anomaly section, 12 Transmitting element, 13 Receiving element, 14 Signal processing section, 15 Analog processing section, 16 A / D conversion section, 17 Digital processing section, 18 Transmitter, 19 Data processing section, 20, 21, 22 RC polyphase filter, 30 Amplitude demodulation processing block, 31 Complex analog circuit, 32a, 32b Absolute value circuit, 33a, 33b A / D converter, 34 Digital signal processor (sum of squares, root of squares calculation), 40 Phase demodulated signal, 41a, 41b Complex analog circuit, 42a, 42b, 42c, 44d Absolute value circuit, 43a, 43b, 43c, 43d A / D converter, 44 Digital signal processor (phase difference calculation), 50 Contact-type anomaly detection device, 100 Remote monitoring system, 110 Bridge, 120 Sensors, 130 edge computing systems, 140 centralized control centers, 200 RC polyphase filters

Claims

1. External input signals are input to only one input terminal. When the output terminal connected only to the input terminal to which the input signal is input is defined as the first output terminal, and the output terminals are defined as the second, third, and fourth output terminals in order that the phase of each output signal lags behind the phase of the output signal of the first output terminal, The differential signal of the output of the first output terminal and the output of the third output terminal is output as the first differential signal. The differential signal of the output of the second output terminal and the output of the fourth output terminal is output as a second differential signal. RC polyphase filter.

2. An RC polyphase filter (N is an integer of 2 or more) is formed by connecting N stages of a filter circuit, each having four resistors, with one end of the Mth resistor connected to the Mth intermediate input terminal and the other end to the Mth intermediate output terminal (M is an integer from 1 to 4), and a capacitor connected between the Mth intermediate input terminal and the Kth intermediate output terminal (K is the remainder when the divisor of M+1 is 4). The first to fourth intermediate input terminals of the first stage filter circuit are designated as the first to fourth input terminals, At the first to fourth intermediate output terminals of the Nth stage filter circuit, The terminal to which a path consisting only of a resistor exists from the first input terminal is the first output terminal. The terminal to which a path consisting only of a resistor exists from the second input terminal is the second output terminal. The terminal to which a path consisting only of a resistor exists from the third input terminal is the third output terminal. When the terminal to which only a resistor exists from the fourth input terminal is defined as the fourth output terminal, An external input signal is input only to the first input terminal. The third input terminal is not connected to any terminal that receives an external signal or potential. Means for outputting a first differential signal which is the differential signal of the output of the first output terminal and the output of the third output terminal, Means for outputting a second differential signal which is the differential signal of the output of the second output terminal and the output of the fourth output terminal, An RC polyphase filter having [a specific feature].

3. An RC polyphase filter is constructed having four resistors, with one end of resistor M connected to the input terminal of resistor M and the other end to the output terminal of resistor M (where M is an integer from 1 to 4), and a capacitor connected between the input terminal of M and the output terminal of resistor K (where K is the remainder when the divisor of M+1 is 4), An external input signal is input only to the first input terminal. The third input terminal is not connected to any terminal that receives an external signal or potential. Means for outputting a first differential signal which is the differential signal of the output of the first output terminal and the output of the third output terminal, Means for outputting a second differential signal which is the differential signal of the output of the second output terminal and the output of the fourth output terminal, An RC polyphase filter having [a specific feature].

4. A transmitting element that inputs a first high-frequency signal to a structure, A receiving element that receives a second high-frequency signal after the first high-frequency signal has propagated through the structure, A demodulation system having a signal processing unit that processes the signal output by the receiving element, The signal processing unit, An analog processing unit that uses the second high-frequency signal as the input signal and outputs an orthogonal waveform using an RC polyphase filter according to any one of claims 1 to 3, A digital processing unit outputs an amplitude demodulated waveform and a phase demodulated waveform of the second high-frequency signal based on the quadrature waveform output by the analog processing unit, A demodulation system having

5. A demodulation system according to claim 4, which is installed in a structure, A transmitter that inputs an ultrasonic signal to the aforementioned transmitting element, A data processing device that receives the amplitude demodulated waveform and the phase demodulated waveform output from the demodulation system and performs abnormality diagnosis of the structure, A contact-type anomaly detection device having the following features.

6. Multiple demodulation systems according to claim 4, installed in a structure, A centralized control center that receives the amplitude demodulated waveform and the phase demodulated waveform output from each of the multiple demodulation systems and performs abnormality diagnosis of the structure, Remote monitoring system.

7. A signal demodulation method using an RC polyphase filter (N is an integer of 2 or more) in which a filter circuit is constructed by connecting N stages of a filter circuit having four resistors, with one end of the Mth resistor connected to the Mth intermediate input terminal and the other end to the Mth intermediate output terminal (M is an integer from 1 to 4), and a capacitor connected between the Mth intermediate input terminal and the Kth intermediate output terminal (K is the remainder when the divisor of M+1 is 4), The first to fourth intermediate input terminals of the first stage filter circuit are designated as the first to fourth input terminals, At the first to fourth intermediate output terminals of the Nth stage filter circuit, The terminal to which a path consisting only of a resistor exists from the first input terminal is the first output terminal. The terminal to which a path consisting only of a resistor exists from the second input terminal is the second output terminal. The terminal to which a path consisting only of a resistor exists from the third input terminal is the third output terminal. When the terminal to which only a resistor exists from the fourth input terminal is defined as the fourth output terminal, An external input signal is input only to the first input terminal. A first differential signal, which is the differential signal of the output of the first output terminal and the output of the third output terminal, is output. A second differential signal, which is the differential signal of the output of the second output terminal and the output of the fourth output terminal, is output. Based on the first differential signal and the second differential signal, the amplitude demodulated waveform and the phase demodulated waveform of the input signal are demodulated. A signal demodulation method using an RC polyphase filter.

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