JP3206709B2 - Water leak detection method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting water leakage from a water pipe buried underground, and more particularly to a method and apparatus for detecting water leakage using electromagnetic waves.

[0002]

2. Description of the Related Art Conventionally, when detecting water leakage from a water pipe buried underground, a microphone is pressed against the ground surface, and the sound of water leaking from the water pipe is enlarged and distinguished by the microphone. .

[0003]

However, the above-mentioned method of distinguishing the water leakage sound by the microphone has the following disadvantages. (1) Skill is required to determine whether or not water is leaking. (2) During use of water supply, it is difficult to detect water leakage due to the sound of water flowing through the water pipe or noise from the pump outlet. (3) Noise or vibration of the vehicle passing through the road may interfere with detection, and water leakage cannot be detected while the vehicle is passing. (4) The characteristics of the water leak sound are not clear, and the detection accuracy is not always high.

[0004] The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has as its object to easily and reliably detect water leakage from a water pipe buried underground. Another object of the present invention is to make it possible to detect water leakage without being affected by the sound of water flowing through a water pipe or the vibration of a vehicle.

[0005]

In order to achieve the above object, a water leakage inspection method according to the present invention radiates an electromagnetic wave into the ground, receives a reflected wave of the electromagnetic wave, and adjusts a frequency deviation due to a Doppler effect of the reflected wave. It is configured to check for the presence or absence of transfer and detect water leakage.

[0006] Also, a water leakage detection device according to the present invention includes a transmission signal generation unit for generating a transmission signal, a transmission antenna for radiating the transmission signal generated by the transmission signal generation unit into the ground,
A receiving antenna receiving the reflected wave of the transmission signal radiated from the transmission antenna; receiving a reference signal identical to the transmission signal generated by the transmission signal generation unit; removing a transmission signal component from the reception signal from the reception antenna; And a demodulator that outputs the demodulated signal output from the demodulator, and compares the phase of the transmission signal corresponding to the DC component of the demodulated signal with a reference value to obtain a deviation. And a signal control unit for outputting the transmission signal by shifting the phase of the deviation obtained by the control.
When the phase of the transmission signal is shifted by the deviation obtained by the signal control unit, it can be easily performed by shifting the frequency of the transmission signal. Alternatively, the transmission signal generator, the oscillator, and the phase shifter may be used, and the phase shifter may be controlled to shift the phase of the deviation. As the reference signal, a transmission signal generated by the transmission signal generation unit may be used, or a signal generation device different from the transmission signal generation unit may be provided, and the reference signal may be synchronized with the transmission signal generated by the transmission signal generation unit. A signal may be output.

[0007]

According to the present invention constructed as described above, water leakage can be easily and reliably detected by detecting the frequency shift of the reflected wave with respect to the transmission signal due to the Doppler effect. In other words, the reflected wave from a stationary object such as a buried object under the ground is received with a phase shift corresponding to the position where the stationary object exists with respect to the transmission signal radiated from the transmitting antenna into the ground. , Does not suffer from the Doppler effect, and does not cause a frequency shift. On the other hand, the reflected wave from the water leak is the reflection of the water leaking from the water pipe from an object moving relative to the transmitting antenna and the receiving antenna, causing a Doppler effect and causing a frequency shift. In the ground, generally, by detecting a frequency shift due to the Doppler effect, that is, a frequency shift from a place where no moving object is present, water leakage in the ground can be easily and reliably detected. In addition, since water leakage is detected using electromagnetic waves, it is possible to detect water leakage with high accuracy without being affected by the sound of water flowing through pipes or the noise and vibration of vehicles traveling on roads. it can.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method and apparatus for detecting water leakage according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
1 is a block diagram of a water leakage detection device according to an embodiment of the present invention.

In FIG. 1, there is provided a transmitting antenna 10 for radiating a transmission signal which is an electromagnetic wave in the ground, and a receiving antenna 12 for receiving a reflected wave of the transmission signal radiated from the transmitting antenna 10 from the ground. Then, the transmitting antenna 10
Is connected to an oscillator 14 that is a transmission signal generation unit that generates and outputs a high-frequency transmission signal. The receiving antenna 12 is connected to a demodulator 16 to which a reflected wave from the ground of the transmission signal emitted by the transmission antenna 10 is input as a reception signal. The demodulator 16 removes the component of the transmission signal output from the oscillator 14 from the reflected wave received by the reception antenna 12, and extracts a phase shift component corresponding to the frequency shift due to the Doppler effect from the received signal as described later in detail. A reference signal generator 18 for outputting a reference signal having the same frequency as the transmission signal output from the oscillator 14 in synchronization with the oscillator 14 is connected.

The output side of the demodulator 16 has a signal control unit 20.
And the amplifier 30 are connected. The signal control unit 20 includes a low-pass filter 22, a phase comparison unit 24, and a frequency control unit 2.
6. The low-pass filter 22 receives a demodulated signal output from the demodulator 16, extracts a DC component from the demodulated signal, and extracts a DC component from the demodulated signal.
To enter. As will be described in detail later, the phase comparison unit 24 calculates the phase shift of the reception signal reflected from a stationary object such as an underground object with respect to the transmission signal, and
Send to 6. Then, the frequency control unit 26 controls the transmission frequencies of the oscillator 14 and the reference signal generator 18 so that the phase shift obtained by the phase comparison unit 24 becomes zero. on the other hand,
The amplifier 30 amplifies the output signal of the demodulator 16 and inputs the amplified signal to the water leak detector.

In the embodiment constructed as described above,
The oscillator 14 generates a high-frequency transmission signal having a repetition frequency of 1 Ghz, for example, and radiates it from the transmitting antenna 10 into the ground. The transmission signal generated by the oscillator 14 has a frequency f ₀ , a time t, and an amplitude 1.

Equation 1 can be expressed as cos2πf ₀ t. Further, the reference signal generator 18 also generates the same signal as in Equation 1 in synchronization with the oscillator 14, and
Enter 6 The transmission wave radiated into the ground is reflected by an object under the ground and received by the receiving antenna 12. The transmission signal radiated from the transmission antenna 10 is a continuous wave (C
W) or a frequency-modulated continuous wave (FMCW).

By the way, from the point where the transmission signal is radiated, L
Assuming that the speed of light is c, the electromagnetic wave reflected from an object located at a distant point and returned is shifted in phase by 2 L / c from the transmission signal, as is well known. Therefore, underground L
_When there is a stationary object such as a pipe at the point ₁ , a reception signal reflected by the stationary object and entering the demodulator 16 via the reception antenna 12 has an attenuation rate a ₁ ,

## EQU2 ## a ₁ cos 2πf ₀ {t + (2L ₁ / c)}

On the other hand, if there is an object moving at a speed v _r at a point separated by L, the electromagnetic wave reflected by this object undergoes a frequency shift due to the Doppler effect. As is well known, the frequency shift amount f _d due to the Doppler effect is

## EQU3 ## f _d = 2 v _r / λ = 2 v _r f ₀ / c Here, λ is a wavelength.

For this reason, when an object that moves at the velocity v _r is present at the point at the depth L ₂ , the received signal reflected from the object and entering the demodulator 16 is f _d by the Doppler effect with respect to the transmitted signal. The frequency is shifted, and the phase is shifted by 2L ₂ / c. That is, the received signal reflected from a moving object has an attenuation rate a ₂ ,

Equation 4] _{a 2 cos2πf 0 {1+ (2v} r / c)} {t
+ (2L ₂ / c)｝. Then, since the principle of superposition holds for the electromagnetic field, the received signal entering the demodulator 16 is expressed by the following equation (2).
Expression 5 is obtained by adding Expression 4 and Expression 4.

## EQU5 ## a ₁ cos2πf ₀ {t + (2L ₁ / c)} + a _{2
cos2πf 0 {1+ (2v r /} c)} {t + (2L 2 /
c)｝

Since the demodulator 16 receives the same demodulation reference signal as the transmission signal shown in Equation 1, the output of the demodulator 16, that is, the demodulated signal is approximately

A ₁ cos 2πf ₀ (2L ₁ / c) + a ₂ cos ₂
the _{πf 0 {(2v r / c} ) t + (2L 2 / c)}.

By the way, in Equation 6, f ₀ , c,
Since L ₁ and L ₂ are constants not related to time,

Equation 7] can be expressed as _{C 1 + a 2 cos2πf 0 {} (2v r / c) t + C 2}. That is, the output (demodulated signal) of the demodulator 16 is composed of the DC component of the first term and the AC component of the second term in Expression 7. However, C ₁ and C ₂ are constants,

C ₁ = a ₁ cos 2πf ₀ (2L ₁ / c)

## EQU9 ## C ₂ = 2L ₂ / c

The output was demodulated signal of the demodulator 16 is input to the low-pass filter 22 of the signal control unit 20, only the extracted direct current component C ₁ is fed to the phase comparator 24. The phase comparison unit 24 has a reference phase

## EQU10 ## (1/2) π + nπ is set. Here, n is a natural number.

Then, the phase comparing section 24 calculates 2πf ₀ (2L ₁ / c) and (1/2) π + of the input DC component C _1.
nπ

The transmission frequency f ₀ that satisfies 2πf ₀ (2L ₁ / c) = (π / 2) + nπ is obtained and transmitted to the frequency control unit 26. The frequency control unit 26 controls the oscillator 14 and the reference signal generator 18 so that the output frequencies of the oscillator 14 and the reference signal generator 18 have a frequency f ₀ that satisfies Equation 11.

When the transmission frequency is controlled in this manner, the demodulated signal output from the demodulator 16 has a DC component C ₁ = 0,

## EQU12 ## Only the AC component represented by a ₂ cos 2πf ₀ {( ₂ v _r / c) t + C ₂ } is obtained. The output signal of the demodulator 16 represented by the equation (12) is amplified by the amplifier 30 and sent to a water leak detecting unit including, for example, an AC voltmeter. That is, when the received signal reflected from the ground is not affected by the Doppler effect, the demodulator 16
Is zero, and a demodulated signal is output only when the Doppler effect is being experienced. And since there is generally no moving object in the ground, if a demodulated signal is output, it may be determined that the leak is due to water leakage. Can be detected. Moreover, because it does not contain a DC component C ₁ Equation 8 contained in the demodulated signal of the conventional GPR, it is possible to increase the detection sensitivity.

In addition, since water leakage is detected by using electromagnetic waves, water leakage detection work can be performed at any place and at any time without being affected by the sound of water flowing through a water pipe, vibration or noise from a vehicle. be able to. In addition, by reducing the leakage of radio waves into the air and suppressing reflection from the ground,
Water leak detection can be performed without being affected by surrounding conditions. In addition, the water in the water pipe is considered uniform because the pipe is full, and even if the water is flowing,
The electromagnetic wave does not seem to move, and does not affect the detection of water leakage.

In the above embodiment, the heterodyne system in which the oscillator 14 and the reference signal generator 18 are provided independently has been described. However, a part of the output signal of the oscillator 14 is extracted and input to the modulator 16 as a reference signal. May be adopted. Further, in the above-described embodiment, the case where the transmission signal generation unit is configured by the oscillator 14 is described. However, the transmission signal generation unit is configured by the oscillator and the phase shifter, and the phase and the reference corresponding to the DC component of the demodulated signal are obtained. Is determined by the signal control unit 20 from the phase of
The phase of the transmission signal output from the oscillator may be shifted by the deviation obtained by the signal control unit by a phase shifter and output, thereby removing the DC component of the demodulated signal. In the above embodiment, the case where the DC component of the demodulated signal is removed by changing the frequency of the transmission signal has been described. However, the DC component may be removed by changing the circuit length in the device. When the transmission signal is represented by sin, the phase value of the comparison reference of the phase comparison unit 24 is nπ.

[0022]

As described above, according to the present invention, water leakage can be detected easily and reliably by receiving a reflected wave of electromagnetic waves radiated into the ground and detecting a frequency shift due to the Doppler effect. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram of a water leakage detection device according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Transmission antenna 12 Receiving antenna 14 Transmission signal generation part (oscillator) 16 Modulator 18 Reference signal generator 20 Signal control part 22 Low-pass filter 24 Phase comparison part 26 Frequency control part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 1-285843 (JP, A) JP-A 2-296184 (JP, A) JP-A 7-55625 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01M 3/16

Claims (5)

(57) [Claims] 1. An electromagnetic wave is radiated into the ground to receive a reflected wave, and a DC component is removed from a received signal to obtain an AC component.
Te, frequency shift due to the Doppler effect of the reflected wave from the water leakage
A method for detecting water leakage, comprising extracting only components and detecting water leakage. 2. A transmission signal generation unit for generating a transmission signal,
A transmission antenna that radiates a transmission signal generated by the transmission signal generation unit into the ground, a reception antenna that receives a reflected wave of the transmission signal radiated from the transmission antenna, and a transmission signal generated by the transmission signal generation unit. A demodulator that receives the same reference signal, removes and outputs a transmission signal component from a reception signal from the reception antenna, and captures a demodulation signal output from the demodulator and transmits the transmission signal corresponding to a DC component of the demodulation signal. Is compared with the reference value to obtain a deviation, and the transmission signal is output by shifting the phase of the deviation determined by controlling the transmission signal generation unit , and the reflected wave from the water leakage is output.
Only the AC component due to the Doppler effect
And a signal control unit for causing a force to be applied . 3. The signal control unit determines a transmission frequency at which a phase of the transmission signal corresponding to a DC component of the demodulated signal is equal to the reference value, and transmits a transmission signal having the determined frequency to a transmission signal generation unit. The water leakage detection device according to claim 2, wherein the water leakage is output from the water leakage detection device. 4. A generator for generating a transmission signal, and transmitting antenna for radiating the transmission signal the oscillator-generated in the ground, a receiving antenna for receiving a reflected wave of the transmission signal radiated from the transmitting antenna, the A reference signal generator that outputs the same reference signal as the transmission signal generated by the oscillator ,
A demodulator that receives the reference signal output by the reference signal generator and removes and outputs a transmission signal component from a reception signal from the reception antenna; and a demodulator that captures a demodulation signal output by the demodulator and outputs a DC component of the demodulation signal. A signal control unit that compares the phase of the transmission signal corresponding to the reference value with a reference value, determines a frequency that matches the phase with the reference value, and outputs a transmission signal of the determined frequency by controlling the oscillator. Characteristic water leak detection device. 5. An oscillator and a phase shifter for generating a transmission signal.
A transmission antenna for emitting a transmission signal generated by the transmission signal generation unit into the ground, a reception antenna for receiving a reflected wave of the transmission signal radiated from the transmission antenna, and the transmission signal A reference signal generator that outputs the same reference signal as the transmission signal generated by the generation unit, receives the reference signal output by the reference signal generator, and removes a transmission signal component from a reception signal from the reception antenna and outputs the signal. a demodulator that takes in the demodulated signal output of the demodulator, with a deviation as compared to the baseline phase of the transmitted signal corresponding to the DC component of the demodulated signal, the phase shifter
Controlling the transmission signal generated by the oscillator,
And a signal control unit for outputting the output with the phase shifted by the deviation .