JP3752340B2 - Ultrasonic Doppler flow velocity / flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flow velocity / flow meter that measures the flow velocity and flow rate of a fluid using an ultrasonic Doppler effect, and more particularly to an ultrasonic flow velocity / flow meter suitable for an open channel.
[0002]
[Prior art]
The prior art of Japanese Patent Publication No. 7-3350 is known as an ultrasonic Doppler type fluid velocity measuring method and apparatus. Hereinafter, this is referred to as the first prior art.
[0003]
This device transmits an electrical signal of a specific frequency generated in a signal generator to a fluid flowing in a flow path via a transmitting transducer (transmitter), and receives a reflected wave emitted from an object in the fluid. A Doppler shift that measures the fluid velocity based on the difference signal (shift signal) received by the transducer (receiver) and the frequency of the transmission signal from the transmission transducer and the frequency of the reception signal received by the reception transducer. In the fluid velocity measurement method used, the transmitting transducer and the receiving transducer are provided close to each other at the bottom of the flow path, and the difference signal is scanned in a predetermined frequency band having a certain frequency width. After obtaining the intensity of each frequency band, when calculating the average flow velocity of the fluid by applying a weighted average method Further, the flow direction of the fluid is detected by comparing the difference signal between the frequency of the 90 ° phase-shifted signal obtained by shifting the electrical signal of the specific frequency by 90 ° and the frequency of the received signal with the difference signal. Like to do.
[0004]
The first prior art suggests that the fluid flow rate can be measured by combining the fluid velocity measuring device with a water level sensor.
In this first prior art, a water level sensor is required to obtain the flow rate, and the structure becomes complicated. Therefore, the present applicant has proposed an ultrasonic Doppler flowmeter that does not require a water level sensor in Japanese Patent Application No. 8-39243. This is hereinafter referred to as the second prior art.
[0005]
The ultrasonic Doppler flowmeter according to the second prior art includes a transmitting element that transmits an ultrasonic signal at a constant elevation angle θ with respect to the fluid flow direction at the center of the bottom surface of the open channel, and adjacent to the transmitting element. A receiving element that is arranged in almost the same direction and receives an ultrasonic reflection signal from solid particles or bubbles in the fluid and converts it into an electrical signal, and a transmission that continuously supplies a high-frequency signal to the transmitting element A circuit unit, a heterodyne detection unit that takes a frequency difference between a transmission signal frequency of the transmission element and a reception signal frequency of the reception element, an AD converter that converts the difference signal obtained by the heterodyne detection unit into a digital signal, A fast Fourier transform unit (FFT unit) that converts the signal into a frequency spectrum, a peak peak detection unit that obtains a peak peak frequency of the frequency spectrum obtained by the fast Fourier transform unit, and the peak peak detection It is obtained by a reception operation unit and a flow rate calculation unit for calculating a flow rate based on the frequency of the peak mountain calculated in parts.
[0006]
In the second prior art, when the received signal is heterodyne-detected, the signal to be mixed is subjected to heterodyne detection at a certain frequency higher or lower than the transmission signal, and the peak of the frequency spectrum obtained by the fast Fourier transform unit is obtained. By detecting this, the direction of fluid flow is discriminated based on whether the frequency of the received signal is larger or smaller than the frequency of the transmitted signal.
[0007]
When the frequency of the transmission signal is f ₀ , the elevation angle is θ, the fluid flow velocity is V, and the sound velocity in the fluid is C, the Doppler shift Δf is
| Δf | = (V / C) · 2f ₀ cos θ (1)
And is proportional to the flow velocity V.
[0008]
The frequency of the peak peak of the frequency spectrum is obtained by the peak peak detecting unit, and the flow velocity V is obtained by substituting the peak peak frequency into Δf of the following formula (2) obtained by modifying the formula (1).
[0009]
V = C · Δf / (2f ₀ cos θ) (2)
Since the flow velocity V thus obtained corresponds well to the average flow velocity V of the flow path obtained by the so-called Manning's equation, if the cross-sectional shape dimensions, water surface gradient, wall roughness coefficient, etc. of the open channel are known. The water level is determined from the Manning's formula for the average flow velocity, and the flow rate is obtained. The calculation for determining the flow rate is performed by the flow rate calculation unit.
[0010]
The Manning formula is well known as the following formula (3), which is often used as a formula for obtaining an average flow velocity for an open channel, and is well matched for small and medium rivers and channels (Nikkan Kogyo Shimbun) Company, published in 1979, flow measurement handbook, page 407).
[0011]
V = (1 / n) R ^2/3 / I ^1/2 (3)
V: Average flow velocity (m / s).
R: It is defined by the diameter depth (m), the water flow cross sectional area A / the wet side length P. However, Junbei length refers to the length of the channel wall in contact with the water flow.
[0012]
I: Water surface gradient.
n: Manning roughness coefficient.
In the second prior art, the peak of the frequency spectrum is detected by comparing the power values at the respective points from the low frequency region to the maximum frequency of the frequency spectrum one by one, and simply detecting the point having the maximum power value. The frequency was obtained as the peak mountain frequency.
[0013]
[Problems to be solved by the invention]
As a result of further research after the applicant proposed the second prior art, the following problems were found.
[0014]
Doppler polarized shift frequency Δf by flow Toka disturbance of the distribution of flow by the flow path, than from such that reflections from bubbles and dust are discrete, simply adding and averaging the results obtained by FFT, sudden As shown in FIG. 4, the frequency spectrum distribution is not a smooth curve. Therefore, it is difficult to determine the peak peak of the Doppler transition frequency, and there is a problem that malfunction occurs in measuring the flow velocity and flow rate.
[0015]
Also, if a large amount of dirt or mud is contained in the sewage drainage channel, dirt or mud accumulates on the front surface of ultrasonic transducers such as transmitters and receivers, and ultrasonic waves are highly concentrated. Since it moves slowly near the transducer, the reflected wave from near is strong, and the received wave from far is received with a considerably reduced intensity. Therefore, as shown by the dotted line in FIG. 5, the peak peak f _D due to the reflected wave from the original whole fluid is a value f _D smaller than the signal P (f ₀ ) having a low flow velocity as shown by the solid line in FIG. The peak peak detection becomes lower, the original peak peak f _D cannot be detected correctly, and malfunctions may occur in the flow velocity and flow rate measurement.
[0016]
This is also clear from the fact that when the dust deposited on the front surface of the ultrasonic transducer is removed, the malfunction immediately disappears and the normal operation is restored.
[0017]
Further, in the second prior art, the open channel or HiMitsurukan path, Doppler polarization shift (frequency peak mountain) peak frequency of the power spectrum of the (Doppler shift) is 20 than the frequency of the maximum flow rate was measured data The value is 25% lower, that is, a value corresponding to the average flow velocity, but when the water level becomes very low, a Doppler shift due to the surface wave caused by the flow occurs, occurs speed side than the peak mountain f _D shown, the frequency fw is undetermined between peak mountain f _D of the average flow velocity from zero, the peak value of the power the peak value of the peak mountain f _D of the average flow velocity (peak (Power value) may be exceeded.
[0018]
For this reason, there is a problem in that a malfunction may occur in which the peak peak fw of the power spectrum of the surface wave is detected as the peak peak f _D of the average flow velocity (see FIG. 6).
[0019]
Conventionally, simply search the spectrum obtained polarization shift (the shift) with FFT conversion of the frequency of the received signal from the low frequency range toward the high frequency range, intended to convert the flow rate with a frequency having a maximum power value Therefore, there has been a problem that the accurate flow velocity cannot be measured as described above.
[0020]
Therefore, an object of the present invention is to provide an ultrasonic Doppler flow velocity / flow meter capable of solving such problems.
[0021]
[Means for Solving the Problems]
In order to achieve the object, the invention of claim 1
From the water channel (1) through which the liquid flows and the transmitter and receiver of the ultrasonic wave installed at the bottom of the water channel (1), the center, or the bottom of the channel to avoid dust and mud A sensor (2), a drive circuit (3) for supplying a high frequency to the transmitter, an amplifier (4) for the received signal, a detection circuit (5) for detecting the received signal and the transmitted signal, and the received signal and the transmitted signal A filter unit (6) that extracts a shift frequency signal as a signal difference signal, an FFT unit (7) as a spectrum conversion unit that performs spectrum conversion of the shift frequency signal, and a flow velocity from a spectrum obtained by the FFT unit (7) A conversion unit (8) for conversion, and a display unit (9) for measurement results provided as necessary;
The power of the frequency between N−Mn and N + Mn has a width Mn before and after a point N having a frequency fn, where fft (N) is the spectrum power value obtained by simply averaging the Fourier transform results obtained by the FFT unit (7). taking the average value mean · fft (N), conversion example placed in the original power value fft (N) of the point N,
[0022]
Together with a similar manner between zero and the maximum value Nmax N to the moving average replaced with the average value, thus in the ultrasonic velocity, flow meter you flow rate converted based on the moving average spectral peak mountain
The comparison for detecting the peak peak is started from the maximum value Nmax of the frequency, and after detecting the first peak peak Np ₁ , the power value Mean · fft (N) becomes the power value Mean · fft (Np of the peak peak Np _{1. The} ultrasonic Doppler flow velocity / flow meter is characterized in that the comparison is stopped when the ratio to ₁ ) becomes a certain value or less and the frequency of the _first peak peak Np ₁ is converted into a flow velocity.
[0023]
In the present invention, by replacing the power value from zero of N to the maximum value Nmax with the average value Mean · fft (N) (moving average), the frequency having a sudden power value can be obtained by smoothing the distribution of the transition frequency. This is removed so that the peak of the spectrum can be easily detected (see FIG. 1B).
[0025]
In the second prior art, the detection of the power peak value of the spectrum starts from the low frequency range of N = 0 and compares the power value of each point one by one up to Nmax, and simply searches for the point Np having the maximum power value. However, the spectrum due to dust, mud, and surface waves was erroneously detected.
[0026]
Since there is nothing moving faster than running water in the water channel, in the invention of claim 1 , the peak detection operation is started from Nmax in the direction of decreasing frequency, and after detecting the first peak Np ₁ , the power value Mean The comparison is stopped when the ratio of fft (N) and Mean · fft (Np ₁ ) is below a certain value, and the peak peak Np ₁ at this time is determined as the peak peak of the spectrum due to the flow velocity, and the frequency at that time f _NP1 is converted into a flow velocity (see FIG. 1 (c)).
[0027]
By doing so, the peak Np ₂ of the surface wave spectrum, the peak Np ₃ of the spectrum due to dust and mud, and the like are not erroneously detected.
Note that the ratio Mean · fft (N) / Mean · fft (Np ₁ ) for determining whether or not to stop the comparison as the peak detection operation may vary depending on the conditions of the measurement location.
[0028]
The invention of claim 2 is the ultrasonic Doppler flow velocity / flow meter according to claim 1 ,
The fixed value is defined between 1/4 and 3/4.
The invention of claim 3
From the water channel (1) through which the liquid flows and the transmitter and receiver of the ultrasonic wave installed at the bottom of the water channel (1), the center, or the bottom of the channel to avoid dust and mud A sensor (2), a drive circuit (3) for supplying a high frequency to the transmitter, an amplifier (4) for the received signal, a detection circuit (5) for detecting the received signal and the transmitted signal, and the received signal and the transmitted signal velocity filter section for taking out a polarization shift frequency signal as a difference signal of the signal (6), an FFT section of the orthogonal transform unit for spectral transformation of polarization shifted frequency signal (7), from the spectrum obtained by the FFT unit (7) A conversion unit (8) for conversion, and a display unit (9) for measurement results provided as necessary;
The power of the frequency between N−Mn and N + Mn has a width Mn before and after a point N having a frequency fn, where fft (N) is the spectrum power value obtained by simply averaging the Fourier transform results obtained by the FFT unit (7). The average value Mean · fft (N) is taken and replaced with the original power value fft (N) at that point N.
[0029]
In the same way, N is replaced with an average value between zero and the maximum value Nmax, the moving average is performed, and the distribution curve of the spectrum thus moving averaged is differentiated or subtracted, and among the inflection points where the curve is convex upward, The ultrasonic Doppler flow velocity / flowmeter is characterized in that Np ₁ having the maximum N is determined as a peak peak of a flow velocity spectrum, and the frequency of the peak peak is converted into a flow velocity .
[0030]
When the difference starts from Nmax and Nmax−1 and is successively performed until N = 1 and N = 0, the differential curve shown in FIG. 2 is obtained from the solid curve in FIG. That is, the difference is calculated from Nmax, and the point Np ₁ where the crossing from zero to zero is first determined as the peak peak of the spectrum due to the flow velocity, and the transition frequency Δf _NP1 at this time is converted into the flow velocity.
[0031]
By doing so, the peak mountain Np ₂ caused by surface waves, or the Np ₃ caused by dust and mud was mistakenly recognized as the peak mountain caused by the flow velocity.
In the present invention according to claim 1 to 3, by substituting the frequency of the peak mountain detected from the frequency spectrum of the polarization shift frequency of the received signal (Doppler signal) to Δf of formula (2), in the second prior art and Similarly, the flow velocity V is obtained. That is, it is converted into the flow velocity V.
[0032]
Since the flow velocity V thus obtained corresponds to the average flow velocity, the water level is determined from this and the average flow velocity formula such as Manning's formula, and the flow rate is obtained.
In addition, the above description is a case where heterodyne detection is performed at the same or lower frequency as the transmission frequency. When performed at a higher frequency, the deviation frequency becomes lower as the flow velocity increases, and the peak frequency detection is performed on the lower frequency side. It will be reversed from the high frequency side.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Next, preferred embodiments of the present invention will be described based on examples of the drawings.
[Example 1]
In the first embodiment shown in FIGS. 1A, 1 </ b> B, and 1 </ b> C and FIG. 3, an ultrasonic signal is transmitted at an elevation angle θ from the ultrasonic transmitter of the sensor 2 into the liquid flowing in the water channel 1. The sensor 2 is provided with a receiver directed in substantially the same direction adjacent to the transmitter, and receives an ultrasonic return signal from dust or bubbles in the liquid and converts it into an electrical signal. The drive circuit 3 supplies a high frequency to the transmitter.
[0034]
The electric signal (reception signal) of the receiver is amplified by the amplifying unit 4, supplied to the mixing unit 11, mixed with the transmission signal from the driving circuit 3, detected by the detection circuit 5, and further filtered by the filter unit 6. in taking out a polarization shift frequency (Doppler shift frequency) signal as a difference signal of the received and transmitted signals.
[0035]
FFT section (fast Fourier transform section) 7 is spectrum transform the polarization shift frequency signal by fast Fourier transform. In this embodiment, the number of points of data output as a result of the Fourier transform is 1024, and when the frequency range is 5 kHz, the frequency resolution is 4.88 Hz.
[0036]
1). The spectrum data obtained by the moving average FFT unit 7 of the spectrum is converted into a flow velocity by the calculation unit 8 including a CPU made of MPU, and the measurement result is displayed on the display unit 9.
[0037]
The spectrum value of one FFT is 1/25 and is stored from 0 to Nmax in order from 0 to the first register of the arithmetic unit 9 (refer to FIG. 3, hereinafter refer to FIG. 3 for the second and third registers). When the FFT result of 1/25 is added to the first register and this is performed up to 25 times, a simple addition average of 25 times is obtained.
[0038]
Further, an average is taken between the widths Mn of 20 points before and after the Nx point of the first register, and stored in the Nx point of the second register. The average (moving average) is performed in the same manner in order from N = 0 to N = Nmax. However, an average (moving average) is performed between 0 and N + Mn when N−Mn <0, and between N−Mn and Nmax when N + Mn> Nmax (see FIG. 1B).
[0039]
The combination of the above-described values, the number of FFT data, the number of addition averages, and the number of moving averages is determined according to the conditions of the actual measurement location.
[0040]
2). Peak detection Next, the peak detection of the spectrum (detection of peak peaks) performed by the calculation unit 9 occurs in a lower frequency region than the flow velocity spectrum peak based on the flow velocity because the spectrum peak due to dust, mud, and surface waves is generated from the high frequency region. Do.
[0041]
The peak detection method starts from the comparison between Nmax and Nmax-1 of the second register in FIG. 3, and the larger N ₀ and Mean · fft (N ₀ ) are stored in the third register, and N = 0 in order. Then, Mean · fft (N ₀ ) and Mean · fft (Nx) of the third register are compared, and the one with the larger power value is rewritten to the third register.
[0042]
Even when the first large power value Mean · fft (Np ₁ ) thus obtained is compared with Nx after that, Mean · fft (Np ₁₎ ), That is,
Mean · fft (Nx) <(1/2) Mean · fft (Np ₁ )
When he became, regarded as a maximum value in Mean · fft the (Np ₁₎ to the highest frequency side of the spectrum, a polarization shift frequency Delta] f _NP1 at point Np ₁ and peak frequency of the velocity spectrum (FIG. 1 (c) reference).
[0043]
Then, Δf _NP1 is converted into a flow velocity, and the flow rate is calculated.
It should be noted that the ratio Mean · fft (Nx) / Mean · fft (Np ₁ ) when the peak detection is stopped.
The value of is changed between 1/4 and 3/4 according to the conditions of the actual measurement location.
[0044]
[Example 2]
When the difference is started from Nmax and Nmax−1 and is successively performed until N = 1 and N = 0, the differential curve shown in FIG. 2 is obtained from the solid curve in FIG.
[0045]
Therefore, the difference is performed from Nmax, and the point Np ₁ that _first crosses zero from plus is regarded as the peak of the flow velocity spectrum, and the deviation shift frequency Δf _NP1 at this time is set as the peak frequency of the flow velocity spectrum.
[0046]
Then, Δf _NP1 is converted into a flow velocity, and the flow rate is calculated.
By doing so, it is avoided that the peak mountain Np ₂ due to the surface wave, or the Np ₃ due to dust and mud is mistakenly recognized as the peak mountain due to the flow velocity.
[0047]
【The invention's effect】
Since the present invention is configured as described above, the sudden power value caused by disturbance in the flow velocity distribution of the water channel or bubbles can be obtained by moving and averaging the spectrum obtained by FFT into a smooth frequency distribution curve. It is possible to obtain an accurate average flow velocity by removing the data of the frequency possessed.
[0048]
Further, compared to the case where the FFT results are simply added and averaged, the frequency distribution curve can be smoothed in a short time by performing the moving average, and the measurement time can be reduced.
Further, the not to detect spectral peaks due to surface waves of water passage, and prevent malfunction due to surface waves accurately prompted average flow velocity, measurement accuracy is improved. In addition, even if dirt or mud that cannot be avoided in the sewer channel accumulates on the front of the sensor, there is no risk of interruption of measurement within a short period of time, and measurement can be performed stably for a long time. The reliability of the flow velocity / flow meter is improved.
[Brief description of the drawings]
1A is a block diagram, FIG. 1B is a diagram showing power values of FFT data, and FIG. 1C is a frequency distribution for explaining a method for detecting a peak of a flow velocity spectrum. It is a curve.
FIG. 2 is a differential curve obtained by subtracting the frequency distribution curve of FIG.
FIG. 3 is a diagram illustrating a register included in the calculation unit 8 of FIG. 1;
FIG. 4 is a diagram showing power values of FFT results of the prior art.
FIG. 5 is a diagram for explaining changes in a frequency distribution curve due to dust and mud adhering to the front surface of an ultrasonic transducer.
FIG. 6 is a diagram for explaining a peak peak of a power spectrum due to a surface wave generated by a flow.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Waterway 2 Sensor 3 Drive circuit 4 Amplification part 5 Detection circuit 6 Filter part 7 FFT part 8 Calculation part 9 Display part

Claims (3)

From the water channel (1) through which the liquid flows and the transmitter and receiver of the ultrasonic wave installed at the bottom of the water channel (1), the center, or the bottom of the channel to avoid dust and mud A sensor (2), a drive circuit (3) for supplying a high frequency to the transmitter, an amplifier (4) for the received signal, a detection circuit (5) for detecting the received signal and the transmitted signal, and the received signal and the transmitted signal A filter unit (6) that extracts a shift frequency signal as a signal difference signal, an FFT unit (7) as a spectrum conversion unit that performs spectrum conversion of the shift frequency signal, and a flow velocity from a spectrum obtained by the FFT unit (7) A conversion unit (8) for conversion, and a display unit (9) for measurement results provided as necessary;
The power of the frequency between N−Mn and N + Mn has a width Mn before and after a point N having a frequency fn, where fft (N) is the spectrum power value obtained by simply averaging the Fourier transform results obtained by the FFT unit (7). taking the average value mean · fft (N), conversion example placed in the original power value fft (N) of the point N,
Together with similarly between zero and the maximum value Nmax N to the moving average replaced with the average value, thus in the ultrasonic velocity, flow meter you flow rate converted based on the moving average spectral peak mountain
The comparison for detecting the peak peak is started from the maximum value Nmax of the frequency, and after detecting the first peak peak Np ₁ , the power value Mean · fft (N) becomes the power value Mean · fft (Np of the peak peak Np _{1. 1} ) The ultrasonic Doppler velocimeter / flowmeter is characterized in that the comparison is stopped when the ratio with respect to ₁ ) falls below a certain value, and the frequency of the _first peak peak Np1 is converted into a flow velocity. 2. The ultrasonic Doppler flow velocity / flow meter according to claim 1, wherein the constant value is set between 1/4 and 3/4. From the water channel (1) through which the liquid flows and the transmitter and receiver of the ultrasonic wave installed at the bottom of the water channel (1), the center or the bottom surface in order to avoid dust and mud Sensor (2), a drive circuit (3) for supplying a high frequency to the transmitter, an amplifying unit (4) for the received signal, a detection circuit (5) for detecting the received signal and the transmitted signal, and the received signal and the transmitted signal A filter unit (6) that extracts a shift frequency signal as a signal difference signal, an FFT unit (7) as a spectrum conversion unit that performs spectrum conversion of the shift frequency signal, and a flow velocity from a spectrum obtained by the FFT unit (7) A calculation unit (8) for conversion, and a display unit (9) for measurement results provided as necessary;
The power of the frequency between N−Mn and N + Mn has a width Mn before and after a point N having a frequency fn, where fft (N) is the spectrum power value obtained by simply averaging the Fourier transform results obtained by the FFT unit (7). The average value Mean · fft (N) is taken and replaced with the original power value fft (N) at that point N.
In the same way, N is replaced with an average value between zero and the maximum value Nmax, the moving average is performed, and the distribution curve of the spectrum thus moving averaged is differentiated or subtracted, and among the inflection points where the curve is convex upward, Np is the largest Np ₁ Is an ultrasonic Doppler flow velocity / flow meter, wherein the peak peak of the flow velocity spectrum is determined and the frequency of the peak peak is converted into a flow velocity.

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