JPH09229734A - Ultrasonic doppler flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform flow measurement even if a water level sensor does not exist. SOLUTION: An ultrasonic beam of a constant frequency is transmitted from a transmission element 4 provided at the center of the bottom part of a pipe passage with a wave angle in the direction of flow. An emission wave is received with a receiving element 5, and the frequency of Doppler shift is obtained in a heterodyne detection part 14. A signal except for noise is passed with a band pass filter 15. After AD conversion is performed with an AD converter, a frequency spectrum of the Doppler shift frequency is found with a high speed Fourier conversion part 17. The frequency of a peak is found in a peak detection part 18, and average flow velocity and flow are calculated in a flow operation part on the basis of the frequency. The flow of fluid naturally flowing down in the pipe passage is measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow meter utilizing the ultrasonic Doppler effect, and more particularly to an ultrasonic Doppler flow meter suitable for an open channel.

[0002]

2. Description of the Related Art As an ultrasonic Doppler type fluid velocity measuring method and its apparatus, there is one disclosed in Japanese Unexamined Patent Publication No. 5-87608.

This is a transducer for transmitting an electric signal of a specific frequency generated by a signal generator to a fluid flowing in a flow path through a transmitting transducer and receiving a reflected wave emitted from an object in the fluid. And a fluid velocity measuring method using Doppler shift for measuring the velocity of the fluid based on a difference signal between the frequency of the transmission signal transmitted from the transmission transducer and the frequency of the reception signal received by the reception transducer. In the above, the transmitting transducer and the receiving transducer are provided in the bottom portion of the flow path in a state of being close to each other, and the difference signal is scanned in a predetermined frequency band having a constant frequency width to determine the intensity of each frequency band. After obtaining the average velocity of the fluid by applying the weighted average method, A direction in which the fluid flows is detected by comparing a difference signal between the frequency of the 90 ° phase shift signal obtained by phase-shifting an electric signal of a constant frequency by 90 ° and the frequency of the reception signal with the difference signal. There is.

This publication also suggests that the fluid flow rate can be measured by combining the fluid velocity measuring device with a water level sensor. In addition, the following Manning (Manni), which agrees fairly well with small and medium rivers and canals, is used as an equation for calculating the average flow velocity with respect to the flow of open canals.
The formula of ng) is often used.

V = (1 / n) R ^2/3 · I ^1/2 (1) V: Average flow velocity (m / s). R: Diameter (m), defined by water flow cross-sectional area A / water-side length P. However, the wet side length refers to the length of the waterway wall in contact with the water flow.

I: Water surface gradient. n: Manning's roughness coefficient. In the average velocity formula method using this Manning's formula, the water surface gradient and the cross-sectional shape of the water flow are measured, the average velocity is calculated using the above formula, and the flow rate can be calculated (Nikkan Kogyo Shimbun, Showa). Issued in 1954, Flow Measurement Handbook, 40
7).

[0007]

Among the above-mentioned conventional techniques, the former has a problem that a transient response cannot be obtained because it uses a sweep tuning type frequency spectrum analysis.

Further, there is a problem that a water level sensor is required to obtain the flow rate and the structure becomes complicated. Of the above-mentioned conventional techniques, the latter also requires a sensor corresponding to the water level sensor when actually measuring the cross-sectional shape of the water flow, and there is a problem similar to the former in this respect.

Therefore, an object of the present invention is to provide an ultrasonic Doppler flowmeter capable of solving these problems.

[0010]

In order to achieve the above-mentioned object, the ultrasonic Doppler flowmeter according to claim 1 transmits an ultrasonic signal at a constant elevation angle to the fluid flow direction at the center of the bottom surface of the open channel. The transmitting element (4) for transmitting and the transmitting element (4) are arranged adjacent to the transmitting element (4) in substantially the same direction and receive the reflected signal of ultrasonic waves from solid particles or bubbles in the fluid and receive an electric signal. Of the receiving element (5) for converting into the transmitting element (4), the transmitting circuit section (9) for continuously supplying a high frequency signal to the transmitting element (4), the frequency of the transmitting signal of the transmitting element (4) and the receiving element (5). A heterodyne detection unit (14) that takes the frequency difference of the received signals, and an AD converter (1 that converts the difference signal obtained by the heterodyne detection unit (14) into a digital signal.
6), a fast Fourier transform unit (17) for converting the signal into a frequency spectrum, and the fast Fourier transform unit (1)
The peak crest detection unit (18) for obtaining the frequency of the peak crest of the frequency spectrum obtained in 7), and the peak crest detection unit (1)
And a reception calculation unit (12) having a flow rate calculation unit (19) for calculating the flow rate based on the peak mountain frequency obtained in 8).

According to the invention of claim 2, in the ultrasonic Doppler flowmeter according to claim 1, when heterodyne detection of a received signal is performed, heterodyne detection of a mixed signal is performed at a frequency higher or lower than a transmission signal by a certain amount. By detecting the peak crest of the frequency spectrum obtained by the fast Fourier transform unit, the direction of the fluid flow is determined by whether the frequency of the received signal is higher or lower than the frequency of the transmitted signal. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be described with reference to the drawings. 2 to 4, 1
Is a pipeline with an inner diameter of 1.8 m and a gradient of 1/1000, and the sewage naturally flows down from the right to the left as shown by the arrow in FIG.

Reference numeral 2 is a fluid, and 3 is an ultrasonic sensor portion which is attached to the central portion of the bottom surface of the pipe line 1, and the PZT which transmits an ultrasonic signal to the inclined portion at a constant elevation angle θ with respect to the flow direction of the fluid 2.
And a transmission element 4 formed of the same and arranged in the same direction adjacent to the transmission element 4 to receive an ultrasonic reflection signal from an object 6 formed of solid particles or bubbles in a fluid and receive an electric signal. It has a receiving element 5 for converting into.

As shown in FIG. 5, the ultrasonic sensor unit 3 is attached to the center of a metal plate 7 bent in a semicircular shape, and the metal plate 7 is placed along the inner wall surface of the conduit 2 of FIGS. , Both ends are fixed to the conduit 2 with bolts (not shown).

Each of the transmitting element 4 and the receiving element 5 has a diameter of 1
Transducer made of 5 mm PZT, 22 mm beside each other
Mounted separately, the elevation angle θ is 30 °, and the directivity of both elements has a half-value angle of 2 °. Reference numeral 8 in FIG. 2 denotes an axis of directivity of the transmitting element 4.

FIG. 1 is a block diagram of a signal processing circuit. Reference numeral 9 denotes a transmission circuit section, and a high frequency oscillator 10 of 2 MHz and an amplifier for amplifying a high frequency signal from the high frequency oscillator 10 to continuously excite a transmission element 4. It consists of 11.

Reference numeral 12 denotes a reception calculation section, which is an amplifier 13 for amplifying the reception signal of the reception element 5 by a factor of 1000, and the amplifier 13.
Frequency (Δf) of the difference between the frequency of the received signal and the frequency of the transmitted signal (2 MHz)
200 Hz to 3 kHz of a bandwidth that does not adversely affect the flow velocity measurement for removing the direct sneak of the transmission signal included in the output of the heterodyne detection unit 14 and the commercial power supply noise and the high frequency noise. A band-pass filter 15 that passes the signal, an A-D converter 16 that converts the output of the band-pass filter 15 into a digital signal, and a frequency spectrum of the difference signal that is converted into a digital signal by the A-D converter 16. A fast Fourier transform (hereinafter also referred to as FFT) unit 17 to obtain, a peak crest detection unit 18 that obtains a frequency of a peak crest of the frequency spectrum obtained by the FFT unit 17, and a frequency of the peak crest obtained by the peak crest detection unit 18. Flow rate calculation unit 19 for calculating the flow rate based on
Consists of

Reference numeral 20 denotes an integrated display unit for integrating the flow rates calculated by the flow rate calculation unit 19 and displaying the integrated flow rate (volume). The transmitting element 4 is excited by a high frequency power of 2 MHz-15 W and transmits an ultrasonic beam having a half value angle of 2 ° at an elevation angle of 30 °. The 2 MHz ultrasonic wave transmitted into the water hits the solid particles and bubbles 6 in the water, is reflected, is received by the receiving element 5, and is converted into an electric signal. Received signal is frequency 2 of transmitted signal
The frequency is Doppler-shifted by Δf from MHz.

Generally, assuming that the frequency of the transmission signal is f ₀ , the elevation angle is θ, the flow velocity of the fluid (water) is V, and the sound velocity in water is C, the Doppler shift Δf is | Δf | = (V / C) 2f ₀ cos θ (2), which is proportional to the flow velocity V.

In the case of FIG. 1 in which the ultrasonic wave emitting direction is opposite to the flow direction, the frequency of the received signal is shifted to a direction higher than the frequency of the transmitted signal, and the ultrasonic wave emitting direction is the flow direction. , The frequency of the received signal shifts in the direction lower than the frequency of the transmitted signal.

The transmission signal and the reception signal are mixed in the heterodyne detection section 14 to obtain beats of both signals and obtain a difference signal. That is, only the frequency-shifted signals are extracted. Since the ultrasonic beam from the transmitting element 4 is emitted at a constant elevation angle θ with respect to the flow, even if the water level changes, the solid particles and bubbles 6 floating from the bottom surface of the channel to the water surface are always irradiated. There is. Since the particles and bubbles are on the flow velocity at each water depth, the reflected waves from the particles and bubbles at each depth generate a Doppler shift corresponding to each flow velocity.

That is, a deep water depth is a reflected wave near the small Doppler shift with a slow flow velocity, and a shallow water depth is a reflected wave from a long distance with a fast flow velocity and a large Doppler shift.

Since the transmitted signal is continuously emitted,
The reception element 5 receives the combined reflected waves from the different water depths. Since the transmitting element 4 and the receiving element 5 are installed slightly apart from each other, the far reflected wave is a portion of the axis having a strong directivity, and the nearby reflected wave is a portion apart from the axis of the weak directivity. You will receive it.

Further, the transmitted beam is widened by the directional angle at a distance and the reflection area increases, but the ultrasonic wave is attenuated by that amount, so that the intensity of the reflected wave with respect to the distance becomes constant or gently decreases. . There is not much attenuation of ultrasonic waves due to absorption in water.

By the way, in the conduits of FIGS. 2 to 4, the water level of the fluid that naturally flows down is variously changed, and the relationship between the water depth on the Y axis in FIG. The distribution is shown in FIG. In Fig. 6, the horizontal axis is water depth
Indicated by

Further, in FIG. 6, the water levels of the broken lines a, b, c, d, e, and f are 22.5 to 23.5 cm and 23.8, respectively.
~ 24.0 cm, 25-26.3 cm, 33.5-3
6.5 cm, 40-42.5 cm, 45.5-47.5
The water level increases in order of cm, and the flow velocity also increases in accordance with the water level. The flow velocity did not change much depending on the water depth (%), and even if the water level changed, the profile (contour) was similar.

As shown in FIG. 6, the frequency spectrum obtained by the FFT section 17 of FIG. 1 in the case where the flow velocity at each water depth in the open channel has little change in the depth direction and has a similar shape to the change of the water level. Are shown in FIGS.

7-9, the water level is 26.3c, respectively.
m, 35.3 cm and 46.5 cm, and the broken line c in FIG.
In the frequency spectrum under the conditions corresponding to D and F,
The horizontal axis represents the frequency Δf (Hz) of the difference signal, and the vertical axis represents the amplitude of the difference signal.

Further, FIGS. 7 to 9 each store 20 times of data and average them. To obtain a smoother curve, it is sufficient to average more times of data. There is a disadvantage that the response speed of the meter decreases.

7 to 9, each frequency spectrum has a peak peak at a relatively high frequency. The frequency of this peak is 1.5 kHz in FIG. 7, 1.92 kHz in FIG. 8, and 2.3 kHz in FIG. As described with reference to FIG. 6, the peak of the frequency spectrum of the Doppler shift Δf near the maximum flow velocity does not change much in the depth direction of the flow velocity near the center (Y axis) of the conduit 2. , Because it is similar to changes in water level.

If the flow velocity distribution in the flow path does not satisfy these conditions, peak peaks do not occur in the frequency spectrum of the Doppler shift, so that the flow velocity / flow rate is measured based on the frequency of peak peaks as in the present invention. It is not possible.

The peak peak frequencies of the frequency spectra of FIGS. 7 to 9 are obtained by the peak peak detection section of FIG. 1, and the peak peak frequency is expressed by Δ in the following expression (3) obtained by modifying the expression (2).
The flow velocity V can be obtained by substituting for f.

V = C · Δf / (2f ₀ cos θ) (3) In this way, each flow velocity V calculated from the frequency of the peak peak of the frequency spectrum of FIGS. Are shown at points P ₁ , P ₂ and P ₃ in FIG. In FIG. 10, the broken line or points P ₁ , P ₂ and P ₃ are connected.

In FIG. 10, the curves G and C are shown in FIGS.
In the pipe having a circular cross section shown in Fig. 4, a curve showing the relationship between the water level of the open water channel and the average flow velocity V obtained from the Manning's equation of the mathematical formula (1), and the inner diameter of 1.8 m as the condition of the flow channel (pipe). The water surface gradient is 1/1000, which is the same as in FIGS. The curve G has a roughness coefficient n of 0.015, and the curve J has a roughness coefficient n of 0.013.

The roughness coefficient of the conduit 2 shown in FIGS.
Since it is considered, from FIG. ₁, P_Two, P_ThreeIs
It corresponds well to the average flow velocity V calculated by Manning's formula.
I understand. That is, the frequency spectrum of the Doppler shift
The frequency of the peak of Le corresponds to the average flow velocity in the channel
It can be said.

Therefore, if the average flow velocity is known on the basis of the frequency of the peak of the frequency spectrum, and if the cross-sectional shape dimension of the open channel, the slope, the roughness coefficient of the wall surface, etc. are known, the formula (expression) of the average flow velocity (mathematical formula) ( The water level can be determined from 1) and the flow rate can be calculated. In this way, the calculation to obtain the flow rate is
This is performed by the flow rate calculation unit 19 in FIG.

In the present invention, it is an important point that the ultrasonic beam from the transmitting element 4 has a structure that propagates from the bottom surface to the water surface at the center of the flow velocity distribution. Since the ultrasonic beam spreads during propagation after exiting from the transmitting element, it is not necessary to strictly install it in the center of the bottom of the pipeline, but if it is installed near or on the side wall, it is not possible to detect the average flow velocity. Therefore, it is not preferable.

Further, in the present invention, in order to detect the flow direction of the fluid, the reference frequency for performing the heterodyne detection is set higher or lower than the transmission frequency by a certain amount. Although it depends on the flow velocity of the liquid, about 3 to 5 kHz is preferable.

With respect to the transmission wave f ₀ by the heterodyne detection,
'When ₀ is ± Delta] f, the beat signal is low f' received wave f ₍₀₎
-F ₍₀₎ = Δf, the magnitude of the frequency cannot be determined, but if the reference signal is f ₁ only, the beat signal is f ′ ₍₀₎
− (F ₍₀₎ −f ₁ ) = ± Δf + f ₁ and the peak direction is detected to determine the flow direction (see FIG. 12).

Next, the average flow velocity detection and the flow direction detection are alternately performed.
The operation when the above is performed will be described. [Step 1] First, the controller 21 starts the heterodie
F to the detector 14₀Order to send. Peak peak detection
The output of the section 18 is output to the flow rate calculation section 19. [Step 2] The high frequency oscillator 10 is f₀Oscillates. [Step 3] The amplifier 11 f₀Power to f₀of
Electric power vibrates the transmitter to send ultrasonic waves into the liquid. [Step 4] The amplifier 13 causes the continuous reflected wave f '.₀Increase
Width. [Step 5] The heterodyne detection unit 14 uses f '.₀Receiving
Frequency f of signal and transmission ₀F'is mixed and amplified by the reference signal of₀−f₀Only the Doppler shift signal of = Δf is taken out.

[0041] (Note 1) Even if the Δf is larger f _'0 is higher than f _0, be less than f _0, characteristic on the distinction of the alternating current is not attached. (Note 2) The reason for converting from f ′ ₀ to Δf (several kHz) is that, when performing Doppler shift fast Fourier transform, in order to perform FFT of several 100 to several kHz from a signal of several MHz, a digital signal of that frequency is used. Data, ie 200Hz
At ~ 2MHz, more than 10,000 points of data are required, which is very difficult to calculate, and a high-speed AD converter is required, but it is very difficult to follow.

That is, since the FFT is performed, the frequency of the data is lowered to facilitate the signal processing. [Step 6] The bandpass filter 15 suppresses noise included in the Doppler shift signal Δf near 0 Hz. [Step 7] The AD converter 16 converts Δf which has been an analog signal up to now into a digital voltage signal at each point. [Step 8] The FFT unit 17 records a fixed number of digital data, for example, 2048 points at intervals of 0.1 msec, and fast Fourier transforms the digital data. In the fast Fourier transform, the maximum frequency at this time is twice 0.1 msec, that is, 5 k.
Analysis up to Hz is possible (see FIG. 11). Since the spectrum distribution will be uneven after one fast Fourier transform,
It is good to repeat several times and average. [Step 9] The peak crest detector 18 compares each point of the FFT signal (averaged) and sends out the signal of the frequency of the peak crest. [Step 10] When the frequency of the peak is found, the flow rate calculation unit 19 calculates the average flow rate from this data and the flow path element to calculate the flow rate.

The average flow velocity is calculated by the equation (3), V = C · Δf
/ (2f_O cos θ). Then in the flow direction
In case of judgment. [Step 11] Controller 21 is heterodyne
To the detection unit 14, for example, f ₀Sending a reference wave of -3 kHz
Then, the reference signal section 22 is driven. [Step 12] The high frequency oscillator 10 has the same frequency f as before.₀
Is oscillating. [Step 13] The transmission circuit 11 is also f₀Send
Put out. [Step 14] The reception amplifying unit 13 is also f ′ as before.₀
To amplify. [Step 15] In the heterodyne detector 14, f '₀
And (f₀-3 kHz) heterodyne detection
In the forward direction, a signal of 3 kHz + Δf is obtained, and in the reverse direction
Gives a signal of 3 kHz-Δf. [Step 16] The bandpass filter 15 is also the same as before.
Suppress noise. [Step 17] The A / D converter 16 is also converted as before.
I do. [Step 18] The FFT unit 17 raises 3 kHz + Δf.
Fast Fourier transform to display the frequency spectrum
The frequency spectrum is divided into 3 kHz as shown in Fig. 12.
When peak peak appears on the upstream side, and on the downstream side from 3 kHz
There may be peak mountains at. [Step 19] The peak crest detector 18 is the same as before. [Step 20] In the flow direction detection unit 23, the peak mountain inspection is performed.
Same as step 9 above, but exactly
It is not necessary to find the peak, 3kHz or more as shown in Figure 12.
To determine the flow direction by just saying whether there is a mountain in
You.

In this way, it is determined whether the frequency is higher than 3 kHz and the flow direction is displayed on the flow direction display section 24. [Step 21] When it is necessary to integrate the flow rate, the flow rate display unit 20 integrates or subtracts the instantaneous flow rate or stops the integration in the opposite direction depending on the flow direction.

Then, the process returns to step 1. Steps 1 to 1
0 is repeated several tens of times to obtain an averaged value, and the detection of the flow direction may be performed about once during that time.

As described above, the detection of the flow direction is a very simple method that can be performed in the heterodyne detection and FFT processing by only changing the reference frequency of the heterodyne by several kHz.

[0047]

Since the ultrasonic Doppler flow meter of the present invention is configured as described above, the flow rate can be measured based on the Doppler shift without using the water level sensor, and the flow direction can be determined. It is convenient for finding emergencies such as reverse drainage.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional front view of the conduit according to the embodiment of the present invention.

FIG. 3 is a vertical cross-sectional plan view of the pipeline according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conduit according to an embodiment of the present invention.

FIG. 5 is a perspective view around a speed sensor according to the embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the water depth and the flow velocity of the pipelines of FIGS.

FIG. 7 is a frequency spectrum of the difference signal according to the embodiment of the present invention.

FIG. 8 is a frequency spectrum of the difference signal according to the embodiment of the present invention.

FIG. 9 is a frequency spectrum of the difference signal according to the embodiment of the present invention.

FIG. 10 is a diagram showing the relationship between water level and average flow velocity.

FIG. 11 is an explanatory diagram showing a frequency spectrum.

FIG. 12 is an explanatory diagram showing a frequency spectrum.

[Explanation of symbols]

 1 Pipeline (Flow Path) 3 Speed Sensor 4 Transmitting Element 5 Receiving Element 9 Transmitting Circuit Section 12 Reception Computing Section 14 Heterodyne Detection Section 17 Fast Fourier Transform Section 18 Peak Mountain Detection Section 19 Flow Rate Calculation Section

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 11, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction contents]

This is a transducer for transmitting an electric signal of a specific frequency generated by a signal generator to a fluid flowing in a flow path through a transmitting transducer and receiving a reflected wave emitted from an object in the fluid. And a fluid velocity measuring method using Doppler shift for measuring the velocity of the fluid based on a difference signal between the frequency of the transmission signal transmitted from the transmission transducer and the frequency of the reception signal received by the reception transducer. In the above, the transmitting transducer and the receiving transducer are provided in the bottom portion of the flow path in a state of being close to each other, and the difference signal is scanned in a predetermined frequency band having a constant frequency width to determine the intensity of each frequency band. After obtaining the average velocity of the fluid by applying the weighted average method, The electric signal of a constant frequency so as to detect the direction of flow of the fluid by a difference signal between the frequency of the received signal and the frequency of the 90 ° phase signal obtained by 90 ° phase shift compared with said difference signal ing.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

Each of the transmitting element 4 and the receiving element 5 has a diameter of 1
Transducer made of 5 mm PZT, 22 mm beside each other
Mounted separately, the elevation angle θ is 30 °, and the directivity of both elements has a half-value angle of 2 °. In FIG. 2, reference numeral 8 indicates the central axis of the sound source of the transmitting element 4.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

Reference numeral 12 denotes a reception calculation section, which is an amplifier 13 for amplifying the reception signal of the reception element 5 by a factor of 1000, and the amplifier 13.
Low pass filter by mixing the output of
The frequency of the received signal and the frequency of the transmitted signal (2M
The heterodyne detection unit 14 that takes the frequency (Δf) of the difference of Hz) and the flow velocity measurement for eliminating the direct wraparound of the transmission signal included in the output of the heterodyne detection unit 14 and commercial power supply noise and high frequency noise are adversely affected. Bandpass filter 15 that allows passage of 200 Hz to 3 kHz having a bandwidth that does not appear, an AD converter 16 that converts the output of the bandpass filter 15 into a digital signal, and an AD converter 16 that converts the output to a digital signal. Fast Fourier transform (hereinafter also referred to as FFT) to obtain the frequency spectrum of the transformed difference signal
Section 17, a peak crest detection section 18 for obtaining the frequency of peak crests of the frequency spectrum obtained by the FFT section 17, and a flow rate calculation section for computing a flow rate based on the frequency of the peak crests obtained by the peak crest detection section 18. It consists of 19 and.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

The transmission signal and the reception signal are mixed in the heterodyne detection section 14 to obtain the beats of both signals, and the low pass
Obtain the difference signal through the filter . That is, only the frequency-shifted signals are extracted. In addition, this
-The pass filter is 200Hz ~ 3Kz immediately after
Since a bandpass filter is provided, omit it.
Can also. Since the ultrasonic beam from the transmitting element 4 is emitted at a constant elevation angle θ with respect to the flow, even if the water level changes, the solid particles and bubbles 6 floating from the bottom surface of the channel to the water surface are always irradiated. There is. Since the particles and bubbles are on the flow velocity at each water depth, the reflected waves from the particles and bubbles at each depth generate a Doppler shift corresponding to each flow velocity.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

Since the transmitted signal is continuously emitted,
The reception element 5 receives the combined reflected waves from the different water depths. Since the transmitting element 4 and the receiving element 5 are installed slightly apart, the reflected wave in the distance is a center with a strong directivity.
The signal in the direction of the axis, the reflected wave near is the central axis with weak directivity
Receives signals from directions away from. That is, the reception
Due to the directivity, reflected waves in the distance are strongly received, and
The waves will be received weakly.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0024

[Correction method] Change

[Correction contents]

Further, although the transmitted beam is widened by the directivity angle at a distance and the reflection area is increased, the ultrasonic wave is attenuated by that amount, so that the intensity of the received signal with respect to the distance of the reflecting object is constant or gently decreases. It will be about. There is not much attenuation of ultrasonic waves due to absorption in water.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0040

[Correction method] Change

[Correction contents]

Next, the average flow velocity detection and the flow direction detection are alternately performed.
The operation when the above is performed will be described. [Step 1] First, the controller 21 starts the heterodie
F to the detector 14₀Order to send. Peak peak detection
The output of the section 18 is output to the flow rate calculation section 19. [Step 2] The high frequency oscillator 10 is f₀Oscillates. [Step 3] The amplifier 11 f₀Power to f₀of
Electric power vibrates the transmitter to send ultrasonic waves into the liquid. [Step 4] The amplifier 13 causes the continuous reflected wave f '.₀Increase
Width. [Step 5] The heterodyne detection unit 14 uses f '.₀Receiving
Frequency f of signal and transmission ₀Mix reference signalsAnd roper
Through the filter f ′₀−f₀Only the Doppler shift signal of = Δf is taken out.

Claims (2)

[Claims] 1. A transmission element (4) for transmitting an ultrasonic signal to a central portion of a bottom surface of an open water channel at a constant elevation angle with respect to a fluid flow direction, and adjacent to the transmission element (4) in substantially the same direction. High frequency signals are continuously supplied to the receiving element (5), which is arranged toward the receiving element (5) for receiving the reflected signal of ultrasonic waves from solid particles or bubbles in the fluid and converting it into an electric signal, and the transmitting element (4). A transmission circuit section (9), a heterodyne detection section (14) for taking a frequency of a difference between a transmission signal frequency of the transmission element (4) and a reception signal frequency of the reception element (5), and the heterodyne detection section ( 14)
AD converter (16) for converting the difference signal obtained in 1. into a digital signal, a fast Fourier transform unit (17) for converting the signal into a frequency spectrum, and a peak of the frequency spectrum obtained by the fast Fourier transform unit (17) A reception calculation section (1) having a peak crest detection section (18) for calculating a crest frequency and a flow rate calculation section (19) for calculating a flow rate based on the peak crest frequency calculated by the peak crest detection section (18).
2) An ultrasonic Doppler flowmeter, comprising: 2. When heterodyne detection of a received signal is performed, heterodyne detection is performed on a mixed signal at a frequency higher or lower than the transmission signal by a certain amount, and peak peaks of a frequency spectrum obtained by the fast Fourier transform unit are detected. The ultrasonic Doppler flowmeter according to claim 1, wherein the direction of the fluid flow is determined by whether the frequency of the reception signal is higher or lower than the frequency of the transmission signal.