JP2000314742A - Flow velocity measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably measure flow velocity even in the case of the distance between opposed transducers being large by measuring flow velocity from the difference between upstream and downstream propagation times of amplitude- modulated ultrasonic wave, and the like. SOLUTION: In a propagation time difference method, flow velocity is measured from the difference between upstream and downstream propagation times of amplitude-modulated ultrasonic wave. In a phase difference method, phase difference between transmitted wave and a signal received after propagated obliquely upstream, and phase difference between transmitted wave and a signal received after propagated obliquely downstream, are measured to compute flow velocity by the difference between the reciprocals of these phase differences regardless of the sound velocity. For instance, transducers 1, 2 are opposedly arranged on both sides of a river, with a distance L at an angle α to a flow velocity direction V. The transducers 1, 2 are alternately switched to the transmit side and receive side by a switching circuit 3. An amplitude modulator 17 and a carrier wave oscillator 13 are connected to an output amplifier 18, and a modulation signal oscillator 14 and the carrier wave oscillator 13 generate sine waves.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for measuring the flow rate of a fluid in a river or a large artificial open channel, and the flow rate of a gas or a liquid in a pipe having a relatively large diameter. The present invention relates to a technique for measuring ultrasonic waves with ultrasonic waves.

[0002]

2. Description of the Related Art As is well known, the main part of an ultrasonic flow rate measuring apparatus for open channels and pipe pipes is a section for measuring the flow velocity using ultrasonic waves. The flow velocity measuring method used in most ultrasonic flow measuring devices is the ultrasonic propagation time difference method or the ultrasonic phase difference method.

FIG. 5 shows a block diagram of a typical flow velocity measuring apparatus using the ultrasonic propagation time difference method. In FIG. 1, a pair of transducers 1 and 2 for oscillating and receiving ultrasonic waves are disposed on one side and the other side of the flow path so as to face each other at an angle α and a distance L with respect to the flow direction. A switch circuit 3 connected to each of the transducer sections 1 and 2 alternately connects the transducer sections 1 and 2 to the ultrasonic pulse oscillation circuit 4.
And an input terminal of a reception amplification circuit 5 for amplifying a reception signal obtained by receiving an ultrasonic wave.

The receiving amplifier circuit 5 checks a received signal and forms a short pulse signal. The receiving amplifier circuit 5 performs a process from the moment when the ultrasonic pulse is emitted to the moment when the ultrasonic pulse propagates through the distance L and is received. A time interval measuring circuit 7 for measuring the propagation time and a flow rate calculating circuit 8 for calculating the flow rate V according to the ultrasonic transit time difference flow rate measuring formula are sequentially connected, respectively. Directly connected.

Referring to FIG. 5, a time t ₁ at which an ultrasonic pulse propagates obliquely downstream from the transducer section 1 to the transducer section 2, and conversely, the ultrasonic pulse propagates from the transducer section 2 to the transducer section 2. The time t ₂ at which the ultrasonic pulse propagates to the sub-unit 1 is as shown in equation (a), and the difference Δt = t ₂ −t ₁ between these propagation times is generally expressed by equation (b). Become. Here, c is the sound velocity in this fluid, and V is the average flow velocity in the L section.

[0006]

(Equation 5)

As represented by equation (b), the propagation time difference Δt =
Since t ₂ −t ₁ is proportional to the flow velocity V, it is called a propagation time difference flow velocity measurement method, and the flow velocity V is represented by the equation (c) from the equation (b). Equation (c) shows that the square of the sound velocity is c
^{Since the two} terms are included, the propagation time difference method is related to the sound velocity c. Since c ² can be expressed as in equation (d), substituting this into equation (c) gives the sound velocity as in equation (e). The final flow rate measurement formula does not include c. Here, d = Lcosα.

[0008] The method of measuring the propagation time difference flow velocity using such a flow velocity measurement formula is most frequently used. Patents for this flow velocity measurement method include, for example, US Patent No. 5,515,7.
No. 21, No. 5,780,747, Japanese Patent No. 2,6
No. 76,321.

The greatest advantage of the transit time difference flow velocity measurement method is that, as is apparent from equation (e), since the sound speed c in the fluid is not related to the flow velocity measurement, only the propagation times t ₁ and t ₂ are variables. The point is that the flow velocity can be obtained by directly measuring the flow velocity every time. Therefore, even if the sound velocity in the fluid changes drastically, the flow velocity can be easily measured.

As an ultrasonic phase difference velocity measurement method,
For example, it is disclosed in JP-A-10-104039 and German Patent Publication DE19722140A.

FIG. 6 (a) is a typical and FIG. 6 (b)
FIG. 2 (B) of the above-mentioned Japanese Patent Application Laid-Open No. 10-104039.
In the block diagram of the phase difference flow velocity measuring device disclosed in the above, 1 and 1 'is an ultrasonic receiving transducer unit, 2 and 2' are a transducer unit for transmitting an ultrasonic continuous sine wave,
A sine wave oscillator 9 having a frequency f is connected to the transmitting transducer units 2 and 2 'or 2, while a phase shifter (Phase shifter) is connected to the receiving transducer units 1 and 1'.
10, receiving amplifiers 11 and 11 ', phase difference detector (Phase
difference discriminator) 12 are sequentially connected.

When the output of the sine wave oscillator 9 having the frequency f is applied to the transmitting transducer units 2 and 2 ', the ultrasonic waves propagate obliquely upstream and obliquely downstream, and the ultrasonic wave propagates obliquely upstream and obliquely downstream. 1 ′, the phase of these received signals relative to the outgoing signal is φ ₁ = 2πft, respectively.
₁ , φ ₂ = 2πft ₂ . Here, t ₁ and t ₂ are given by equation (f).
The phase difference Δφ between the received signal of (1) and the received signal of 1 ′ is as shown in equation (g), and the flow velocity V is obtained from equation (h). Where c is the sound velocity in this fluid, L is the distance between the opposing transducer sections, V is the average flow velocity in the L section, α
Is the angle between the L direction and the flow direction.

[0013]

(Equation 6)

The phase difference velocity measurement method uses a continuous ultrasonic sine wave instead of transmitting and receiving pulsed ultrasonic waves, and the phase difference Δφ is proportional to the ultrasonic frequency f and the flow velocity. It is a feature. Therefore, even when the distance L and the flow velocity V are small, the phase difference Δ
By increasing φ, the measurement accuracy of the phase difference directly measured every time can be increased.

Further, since the ultrasonic continuous sine wave is transmitted and received, the attenuation is much smaller than that of the ultrasonic pulse. Furthermore, even if the amplitude of the received signal pulsates violently, it does not check the arrival time of the pulse, so it can be sufficiently amplified or an amplifier with an automatic amplification adjustment circuit can be used. Has such advantages that no problem occurs and the phase difference measurement can be performed reliably.

[0016]

However, each of the above-mentioned conventional methods of measuring the transit time velocities and the method of measuring the phase velocities has disadvantages, and their use is limited. First, the following problems can be pointed out regarding the disadvantages of the propagation time difference method (for further details, see, for example, Japanese Patent Application No. 10-291327).
No. "Ultrasonic flow measuring method and apparatus", Japanese Patent Application No. 11-6163.
(Refer to the conventional description of No. 0, "Open Channel Flow Measurement Method and Apparatus and Calibration Inspection Method").

That is, the ultrasonic pulse not only has a low transmission efficiency, but also has a large number of harmonic components, especially in the first several periods, so that when the propagation distance L increases, the attenuation of the sound pressure becomes remarkable. The form of the ultrasonic pulse at the receiving point becomes a bell shape in which the amplitude gradually increases in the first few cycles and then gradually converges. For this reason, the amplitude becomes an important factor, it is difficult to determine which amplitude of the signal to reach the signal, and the first 1 to 3 periods of the received signal sometimes attenuate to the same level as the noise level. An error occurs in the check at the instant of the arrival of the received signal, and the propagation time measurement error increases.

[0018] Also, overflows of various scales are constantly generated in rivers and open channels, and the propagation trajectory is refracted by these. Therefore, the intensity and sound pressure of the ultrasonic wave at the receiving point significantly pulsate. Therefore, not only does the signal arrive with a wave different from the original wave, but also reception failure often occurs.

In this case, if the pulse frequency is lowered or the intensity of the ultrasonic wave is increased in order to suppress or compensate for the attenuation, cavitation occurs in the water at the transmitting portion,
There is a risk of being unable to make calls.

Further, in a gas, since the attenuation of ultrasonic waves is much larger than that of a liquid, it is extremely difficult to measure the flow velocity.

Conversely, even when the ultrasonic wave propagation distance L is small or the flow velocity V is small, it is difficult to measure the flow velocity V with high accuracy. For example, L = 0.05 m, V = 0.1 m / s, c ≒ 1500
If m / s, the propagation time difference is only Δt = 3.14 · 10 ⁻⁹ s. If this Δt is measured with an error of 1%, the absolute measurement error must be less than _ΔΔt ≒ 3.10 ⁻¹¹ s. With such a small error, it is almost impossible to easily measure time.

As described above, even when the propagation distance L is large or small, or when the flow velocity V is small, it is not easy to measure the flow velocity by the propagation time difference method.

On the other hand, in the phase difference method, contrary to the propagation time difference method, the sensitivity and resolution can be increased by increasing the frequency f of the ultrasonic sine wave even when the propagation distance L and the flow velocity V are small. However, if the frequency f is too high or the propagation distance L or the flow velocity V increases, the phase difference Δφ exceeds the measurement range π of the phase difference detector, so that it is impossible to measure the flow velocity by the phase difference method. Become.

In the phase difference method, since continuous sine wave ultrasonic waves are used, the attenuation is much smaller than that of pulsed ultrasonic waves. Therefore, the phase difference method is suitable for measuring the gas flow velocity. Since the phase difference is much larger than π as the propagation velocity in the liquid is smaller than that of the liquid, it is often impossible to measure the gas flow velocity by the phase difference method.

For example, when the average flow velocity is V = 10 to 30 m / s in a pipe having a diameter of 300 mm, the sound velocity in the gas is c ≒ 4
If 00 m / s, α = 45 °, and f = 40 kHz (f is selected higher than the noise frequency band in the pipe pipe), the change range of the phase difference Δφ is as follows: Δφ = 9.42 to 28.26 rad = (2π + 0.998π) ~ (8π +
0.995π) rad, and Δφ> π rad.
φ cannot be measured.

Even for liquids, L = 10 m, V = 3 m / s, f = 200 kHz, c ≒ 1500 m in a relatively narrow open channel.
/ S, Δφ is Δφ ≒ 16.746 rad = 5π + 0.33
πrad> π rad.
φ cannot be measured.

In addition to this problem, there is another problem that the sound speed c must be measured separately, as is apparent from the equation (h). If the sound velocity of the fluid is c = const (constant) and the value of c is known, there is no need to separately measure the sound velocity c. However, the sound velocity in a gas or liquid is determined by the temperature, pressure, component, etc. Since it changes according to the change, in most cases, the sound speed c must be measured with sufficient accuracy and separately.

As described above, the phase difference Δφ is Δ
If φ> π rad or the speed of sound in the fluid changes, the well-known phase difference flow velocity measurement method cannot be easily realized.

Therefore, the present invention has been developed to solve the above-mentioned dissatisfaction point of the prior art, and can measure the flow velocity stably even when the distance L between the opposed transducer parts is large. The main purpose of the present invention is to provide a propagation time difference flow velocity measurement method and a phase difference flow velocity measurement method that utilizes a general phase difference detector and does not depend on the sound speed c even when the distance L and the flow velocity V are large as described above. I have.

[0030]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a transit time difference method, in which an ultrasonic wave is transmitted instead of an ultrasonic pulse, and this sine wave is amplitude-modulated at a predetermined frequency. The amplitude-modulated ultrasonic wave is used as a propagation time measurement mark to measure the flow velocity.

Also, in the phase difference method, the phase difference between the transmitted wave and the signal propagated and received in the obliquely upstream direction is compared with the phase difference between the transmitted wave and the signal propagated in the diagonally downstream direction and received. Phase difference, and by measuring the reciprocal of these phase differences,
It is characterized in that the flow velocity is calculated irrespective of the speed of sound.

In this case, when the ultrasonic wave is amplitude-modulated with a modulation signal having a lower predetermined frequency f _M and the above-mentioned phase difference is measured, the phase difference of the amplitude-modulated signal is measured to determine the phase difference of the ultrasonic wave. In addition to calculating mπ (m is an integer), the remaining phase differences βπ and γπ (β and γ are less than 1.0) are measured by a general phase difference detector, and mπ is added thereto, so that the ultrasonic wave is obliquely upstream. The phase difference when the signal is propagated and received in the direction and the phase difference when the signal is propagated and received in the obliquely downstream direction are precisely obtained.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION First, the method for measuring the flow velocity of a transit time difference of the present invention will be described in detail. FIG. 1 shows, as an example, a block diagram of an apparatus for implementing the flow velocity measuring method employing the propagation time difference method.

In FIG. 1, transducer units 1 and 2
Are arranged on both sides of a river, for example, at a distance L and at an angle α between the L direction and the flow velocity direction.

The transducer sections 1 and 2 are connected to a switch circuit 3 and are alternately switched between a transmitting side and a receiving side. The switch circuit 3 excites one of the transducer sections at each time. (Excite), and the other transducer section is connected to an automatic gain control (AGC) amplifier 19 of the received signal, which always receives the received signal. Maintain the optimum level while amplifying the frequency band of the modulation signal.

The output amplifier 18 has an amplitude modulator (amplitude modulator).
A ude modulator 17 and an oscillator 13 having a frequency f _C for an ultrasonic carrier wave are sequentially connected, and a reference numeral 14 connected to the amplitude modulator 17 via a switch circuit 24 which is in an open state during standby is a modulation signal. an oscillator of frequency f _M, the modulated signal generator 14 and the ultrasonic carrier oscillator 13
Is a sine wave oscillator.

The output of the modulation signal oscillator 14 is input to the zero-point crossing circuit 15 at a time and an interval designated by the switch circuit 23, and the zero-point crossing circuit 15
Oscillates a rectangular pulse when the input modulated signal first passes the zero point in the increasing process from negative to positive.

A monostable pulse oscillator (univib-rator) 16 operated by a pulse of the zero-point crossing circuit 15 oscillates a pulse having a designated length (τ ₂ ). Then, the switch circuit 24 closed by the pulse of the monostable pulse oscillator 16 inputs the output of the modulation signal oscillator 14 to the amplitude modulator 17 only while the pulse τ ₂ is being output.

On the other hand, the code 20 connected via the switch circuit 25 is a demodulator (amplitude demodulator) for detecting a modulation signal and sequentially amplifying the detected modulation signal from the demodulator 20 by a narrow band amplifier ( narrow-band amp
lifier) 21, a zero-point crossing circuit 22 that oscillates a rectangular pulse at the moment when the first cycle of the output signal of the amplifier 21 ends and then exceeds zero potential, and a time for measuring the time between two rectangular pulses. An interval measuring device 7 and a flow velocity calculating device 8 for calculating a flow velocity in accordance with an ultrasonic propagation time difference flow velocity measuring equation (the above-described equation (e)) are connected.

The switching circuit 25 serves to connect the output terminal of the receiving amplifier 19 to the input terminal of the demodulator 20 immediately after passing a part of the output signal of the output amplifier 18 to the demodulator 20. Here, reference numeral 27 denotes the output amplifier 1 described above.
Reference numeral 26 designates a signal attenuator for attenuating the output signal of 8, and a switch control device for individually controlling the respective switch circuits 3, 23 and 25.

FIG. 2 is a time chart for explaining the method for measuring the propagation time difference flow velocity in the above apparatus. It is well known that the ultrasonic wave acts as a carrier wave, and this frequency f _C is selected in consideration of the noise frequency band in the fluid, the directivity of the ultrasonic wave, the attenuation of the ultrasonic wave in the fluid, and the like. It is on the street.

The ultrasonic wave selected in this way (FIG. 2VI) is transmitted in the obliquely downstream direction or in the obliquely upstream direction, and when measuring the flow velocity, only a certain time τ ₂ (FIG. 2V)
Amplitude modulation (FIG. 2VI) is performed with a modulation signal (FIG. 2I) having a frequency f _M lower than f _C.

Then, starting from a certain moment of the amplitude-modulated wave, the amplitude-modulated ultrasonic wave propagates through the distance L and demodulates a signal received. By measuring the time up to, this time is set to the time t ₁ or t ₂ propagated in the flow velocity direction or the counter flow velocity direction.

The ultrasonic wave whose amplitude has been modulated in this way serves as a mark for measuring the propagation time. That is, since the amplitude is modulated for a certain time when measuring the flow velocity while continuously transmitting ultrasonic waves as, for example, a sine wave,
Not only is the transmission efficiency significantly improved compared to pulse transmission, but the frequency band of this ultrasonic wave is f _C ± f _M ,
Since the frequency band is extremely narrow as compared with the frequency band of a pulsed ultrasonic wave containing many harmonics, the attenuation is small.

Further, since the signal arrival instant is determined based on the presence or absence of the modulation signal regardless of the magnitude of the amplitude,
Even if the attenuation level changes instantaneously and the received sound pressure pulsates violently, there is no problem at all, and the received signal for a continuous wave is converted to a constant amplitude (level) using, for example, an AGC amplifier.
Can be reliably and easily achieved. This is the first aspect of the present invention.

Even if the amplitude-modulated electric signal is applied to the transducer section, an ultrasonic wave corresponding to this signal is not immediately transmitted, but the beginning of the amplitude-modulated ultrasonic wave. Since the half cycle is distorted by the transient, the half cycle of the received modulated signal is also distorted. In addition, this distortion changes its shape depending on the rate of change of the modulation signal (the degree of sudden relaxation due to the phase), resulting in a phase shift.

It is important that the amplitude of the ultrasonic wave is always modulated when the modulation signal has a certain phase. For example, as shown in FIG. 2V, the modulation always starts near the zero phase of the modulation signal, or near the peak or bottom where the rate of change is small. By doing so, since the distortion of the ultrasonic wave generated near the modulation start point is always constant or further reduced, it is possible to eliminate the propagation time measurement error caused by the minute displacement of the phase due to the distortion (claim 3).

Further, the electric signal subjected to amplitude modulation (FIG. 2 VI)
Is applied to the transducer section, and at the same time, the demodulator 20
And a modulation signal is detected (FIG. 2VII).
As shown in (2), the moment when, for example, the first cycle of this signal ends and then passes the zero potential is checked by using, for example, the zero-point crossing circuit 22 (FIG. 2VIII). Set the propagation time measurement start point.

Then, as described in claim 2, an amplitude-modulated signal received after propagating in a fluid (FIG. 2IX)
Also, the modulation signal is detected by the same demodulator 20 as described above (FIG. 2X), and similarly, for example, the moment when the first one cycle ends and the moment when the zero potential is passed is checked, the signal is used as the propagation time measurement end signal. (Fig. 2 XI).

As described above, for example, the same instant when the first one cycle ends and then passes the zero potential is used as the time interval measurement start signal (start) and the end signal (stop), respectively. In the case of, the propagation time measurement start / end signal can be obtained with a portion having little distortion and a small phase displacement, and even if a portion where a phase displacement occurs is the same displacement, and both the start and end times are the same. Similarly, since the phase displacement acts, the time interval is invariable,
Ultrasonic propagation time measurement accuracy is improved.

Further, a signal transmitted by the same demodulator 20 (FIG. 2)
VI) and demodulate the received signal to obtain a frequency f _M Modulation signal detection
Therefore, demodulator 20, amplifier 21, zero-point crossing
The delay time generated in the circuit 22 and the like is different between the start time and the end time.
Do not compensate for the delay time separately.
In addition, accurate transit time measurements are achieved.

The frequency f _{M of the} modulation signal must satisfy the following conditions. The first condition is that the sound pressure of the ultrasonic wave after propagation pulsates at the frequency f _P due to the instantaneous change in the attenuation at the time of propagation, so that f _M is significantly higher than this frequency f _P. . That is, f _M ≫f _P.

When the ultrasonic wave propagates through the fluid, the degree of attenuation changes due to various factors, which is the same as the amplitude modulation of the ultrasonic wave at the frequency f _P of the attenuation pulsation. Therefore, as described above, by making f _M much higher than f _P, it becomes easy to discriminate only the f _M frequency band,
It is possible to avoid the influence of the damping pulsation. Note that the damping pulsation frequency f _P is not so high, and is usually about 100 Hz or less in an open channel. Also, of course, f _P is not the frequency of the noise.

The second condition is that if a signal that has been amplitude-modulated for two or three cycles with an amplitude-modulated signal having a frequency f _M is demodulated, the demodulated signal will be distorted. At least 5 /
f _M or more is good. As a result, phase displacement caused by distortion can be prevented, and a propagation time measurement error can be suppressed. The first and second conditions are conditions based on the results of an experiment. However, depending on the characteristics of the demodulator, of course, it may be 5 / f _M or less.

The third condition is that when ultrasonic waves are transmitted and received alternately in the obliquely upstream direction and the obliquely downstream direction, the continuous time τ ₂ of the amplitude-modulated ultrasonic wave is the ultrasonic wave propagation time t ₁ or t ₁
It is better to make it about half of ₂ . If the length is too long, the original signal may be distorted due to the reverberation phenomenon.
That is, by satisfying the condition of Expression (1), the occurrence of reverberation is prevented, and only the original propagation signal is reliably received.
Then, the frequency of the amplitude modulation signal that satisfies the above three conditions is obtained by equation (2).

[0056]

(Equation 7)

Here, c _max is the maximum sound velocity assumed in the fluid, v _max = V _max cos α, and V _max is the maximum flow velocity. Although the frequency f _M is selected according to the equation (2), it is preferable to select f _M as low as possible within the range. This is because if a suddenly changing voltage is applied to the transducer section, a transient phenomenon occurs.

Therefore, ideally, f _M ≦ 0.1 f _C. When modulating the carrier, the modulation always starts when the modulating signal has zero phase as shown in FIG. 2V, for example, but since the carrier starts modulating at an arbitrary phase, the first one of the amplitude-modulated signal starts. The transient phenomenon occurs in the / 2 cycle part,
The waveform is distorted.

In order to prevent the waveform from being distorted for more than a half cycle, it is preferable that the carrier wave is included in a minimum of five cycles within a half cycle of the modulation signal. That is, in one cycle of the modulation signal,
The carrier wave is set to have 2 × 5 = 10 periods or more. Further, in order to efficiently filter the pulsation of the carrier wave when detecting the modulation signal, f _M ≪f _C is preferable.

For example, the distance between the transducer units 1 and 2 is L = 3 m, α = 45 °, V _max = 10 m / s, c _max
= 1500 m / s and f _C = 500 kHz, f _P ≪1005 <f _M ≦ 50 kHz from the equation (2) and the above. Therefore, it can be selected in the range of f _M ≒ 10 to 40 kHz. In consideration of the transient phenomenon of the transducer section, it is better not to select the maximum frequency f _M = 50 kHz in the inequality range or 1005 Hz from the viewpoint of preventing reverberation and suppressing distortion.

Note that the modulation percentage (modulation percentage)
) M should not exceed 50%. According to experiments, it is reasonable to set m = 25 to 30%. The attenuation of the ultrasonic wave pulsates at a low frequency fp, but its depth is 5
This is because, if the amplitude modulation degree is set to m> 50%, the amplitude-modulated ultrasonic wave may disappear because it is about 0%.

Now, the operation of the above-described apparatus shown in FIG. 1 will be described with reference to FIG.
The oscillator 14 for the modulation signal oscillates a substantially continuous sine wave signal (VI and I in FIG. 2).

At the moment when the flow velocity is measured, the switch
From the road controller 26₁ Rectangular pulse of time length (Fig. 2
II) is applied to the switch circuit 23, and the switch circuit 23
Is τ ₁ Frequency f output from oscillator 14 for time_M Modulation of
The signal is passed to the zero-point crossing circuit 15.

The operating voltage level of the zero-point crossing circuit 15 is "negative", and when the output signal of the oscillator 14 becomes 0 potential (u = 0) for the first time in the increasing process from negative to positive, the crossing circuit 15 inputs a rectangular pulse to the pulse oscillator 16 as indicated by III in FIG. 2, and the pulse oscillator 16 oscillates a pulse having a length of τ ₂ (IV in FIG. 2).

The switch circuit 24 is closed by the pulse of τ ₂ , the modulation signal of the frequency f _M is input to the amplitude modulator 17, and the ultrasonic carrier is amplitude-modulated for τ ₂ time as shown in FIG. 2VI. Thus, the modulation is always started in the same phase of the amplitude modulation signal.

Now, under the control of the switch circuit control device 26, the switch circuit 3 causes the transducer section 1 to become the output amplifier 18 (transmitting side), the transducer section 2 to become the receiving amplifier 19 (receiving side), and If they are connected, the output of the modulator 17 whose amplitude has been modulated is amplified by the output amplifier 18 and applied to the transducer unit 1 through the switch circuit 3, so that the transducer unit 1 Transmits (transmits) the modulated ultrasonic waves to the fluid. At the same time,
The output of the output amplifier 18 is input to the demodulator 20 through the attenuator 27 and the switch 25, and the output of the demodulator 20 demodulates and detects a modulation signal having a frequency f _M (VII in FIG. 2).

The demodulated and detected modulated signal is amplified by a narrow band amplifier 21 which mainly amplifies only the f _M frequency band, and
The signal is input to the point crossing circuit 22. The crossing circuit 22 oscillates a short pulse as shown in VIII of FIG. 2 at the moment when the first cycle of the input modulation signal is completed and the potential crosses the next zero potential.

This short pulse is input to the time interval measuring device 7 and serves as a time measurement start signal. Immediately thereafter, switch 25 disconnects attenuator 27 and instead connects the output of receive amplifier 19 to demodulator 20.

When the amplitude-modulated ultrasonic wave transmitted from the transducer section 1 propagates to the transducer section 2, it is received by the transducer section 2, and the received signal is automatically required by the receiving amplifier 19. (IX in FIG. 2).

The output signal of the amplifier 19 is input to a zero-point crossing circuit 22 through a demodulator 20 and a narrow-band amplifier 21. As described above, the short pulse of the zero-point crossing circuit 22 oscillated at the moment of passing the zero potential is input to the time interval measuring device 7 and serves as a stop signal for ending the time measurement. Therefore, the time measured by the time interval measuring device 7 is the time t ₁ between the first and second pulses of the zero-point crossing circuit 22.

Time interval t₁ When the measurement of
Switch 26 turns off the transducer units 1 and 2.
Switch 3 operates and the transducer unit 2 outputs
The transducer unit 1 receives and amplifies the output of the amplifier 18.
Respectively connected to the inputs of the
Repeatedly, the transducer unit 2
Ultrasonic propagation time t to part 1_Two Is measured. in this way
Time t measured ₁ And t_Two Enters the flow velocity calculator 8
Forced, flow velocity is required. For a flow meter,
The output of the arithmetic unit 8 is further input to the flow rate arithmetic unit.

Here, the most important and characteristic feature is that the propagation times t ₁ and t ₂ are set as described above.
In order to measure the time, the time measurement start (start) pulse signal and the same end (stop) pulse signal input to the time interval measuring device 7 are transmitted by the transducer unit 1 or 2 at the time of transmission. The amplitude-modulated signal and the amplitude-modulated signal at the time of reception in the transducer unit 2 or 1 are
It is processed and shaped by the same demodulator 20 and zero-point crossing circuit 22. In this way, the characteristics of the demodulator 20 and the zero-point crossing circuit 22 act equally, so that errors caused by these can be ignored, and the measurement accuracy of t ₁ and t ₂ is increased.

Unlike the prior art, even when the distance L between the transducer sections 1 and 2 is large, continuous ultrasonic waves are transmitted and received, so that the attenuation of the ultrasonic waves in the propagation process is reduced. Extremely small, and the modulated signal
Since it is used for the noise, even if the pulsation of the received sound pressure due to the contamination of noise or the change of the attenuation of the ultrasonic wave is not related to the magnitude of the amplitude, it does not hinder the discrimination and detection of this mark. Can also be used, and the propagation time can be reliably measured.

Although the above embodiment has mainly described an example in which an electric signal applied to the transmission transducer section is demodulated and detected and used as a start signal, the present invention is not limited to this. Instead, for example, a third transducer section is arranged near the transmitting transducer section at a distance L from the receiving transducer section, and the transmitting transducer section transmits the fluid in the fluid. There is no problem in receiving the sound wave immediately after transmission, demodulating and detecting the received signal, and using it as a start signal. Rather, the accuracy is further improved.

Next, with respect to the phase difference flow velocity measuring method, a detailed description will be given of an excellent phase difference flow velocity measuring method which has not been known so far, which is a premise of the constitution of the present invention.

The well-known phase difference flow velocity measurement method derives a phase difference flow velocity measurement equation which depends on the square c ² of the sound velocity c as shown in the above equation (h) but does not depend on the sound velocity c as follows. Is also possible. That is, the phase difference Δψ ₁ between the ultrasonic wave transmitted and the received wave that is propagated obliquely downstream and received,
In addition, the phase difference Δψ ₂ between the transmitted wave and the received wave that propagates obliquely in the upstream direction is represented by Expression (3). In this case v = Vcosα, the phase difference [Delta] [phi] ₁ and the phase difference Δ
difference [psi ₂ of the reciprocal is as shown in equation (4), the formula (4)
Therefore, the flow velocity V is given by the equation (5).

[0077]

(Equation 8)

Since there is no term of the sound velocity c in this flow velocity measurement formula, even if the fluid has a variable sound velocity c, the flow velocity measurement can be performed without performing the sound velocity measurement which had to be separately performed by the prior art. This is an excellent flow velocity measuring method which enables the apparatus to be simplified and does not naturally cause an error due to the measurement of the sound velocity.

However, in this flow velocity measurement formula, if the measurement error of the phase difference Δψ ₁ and the phase difference Δψ ₂ cannot be made so small as to be ignored, there is a disadvantage that the flow velocity measurement error becomes considerably large.

For example, if the phase difference Δψ ₁ = 2.0 rad and the phase difference Δψ ₂ = 2.2 rad,
Phase difference Δψ ₁ 'when measured at 0.5% and -0.5%
And Δψ ₂ ′ are as shown in Expression (6), and as a result, Expression (7).

If the error is 0, equation (8) is obtained. Therefore, the error of the reciprocal of the phase difference becomes equation (9), and the phase difference is measured with an error of ± 0.5%. It can also be understood that the error of the difference between these reciprocals is 10%.

[0082]

(Equation 9)

As described above, in order to realize the phase difference flow velocity measuring method (Equation 5) that is independent of the sound speed c, the phase difference Δψ
₁ and the phase difference Δψ ₂ must be precisely measured.

The phase difference Δψ ₁ and the phase difference Δψ ₂ which must be measured are expressed by the following equation (3).
The larger the L, the lower the sound velocity c, the more the frequency f of the ultrasonic wave
Is higher than π rad, the measurement using a general phase difference detector is difficult in any case.

Of course, given L, c, and v, it is possible to calculate an ultrasonic frequency f that does not exceed the measurement range π rad of a general phase difference detector. For example, in a natural gas pipe having an inner diameter D = 0.3 m, c ≒ 420 m
In the case of /s,V=30m/s,α=45°,L=0.424 m, f the phase difference [Delta] [phi] ₁ and the phase difference [Delta] [phi] ₂ not exceed [pi rad is as Equation (10).

However, in practical use, this frequency coincides with the noise frequency band in the pipe pipe, and a low-frequency sound wave oscillation transducer is used.
It is not easy to manufacture a small-sized device. Conversely, if f = 40 kHz is selected as a frequency that is significantly higher than the noise band, the above example becomes as shown in equation (11), and this time, 76π cannot be measured by the phase difference detector.

[0087]

(Equation 10)

In order to solve these problems, in the present invention, a carrier wave having a frequency f _C is transmitted in an obliquely downstream direction and an obliquely upstream direction while transmitting an ultrasonic wave whose amplitude is modulated by a modulation signal having a lower frequency f _M. The phase difference between the carrier and the modulated signal between the transmitted and received waves is measured.

First, the general expressions of the phase difference Δψ _M1 and the phase difference Δψ _M2 between the modulated signal of the transmitted wave and the modulated signal propagated and received and demodulated in the obliquely downstream direction and the obliquely upstream direction are expressed by the following equation (3). Is placed as in equation (3 ') based on Where n ₁ , n
₂ , a, and b are all variables, and in some cases, n ₁ = n _2. However, the phase difference that can be detected by a general phase difference detector is:
n ₁ and n ₂ are the remaining parts excluding the integral multiple of π.
Is an integer, and a and b are 1 or less.

The maximum and minimum sound speeds assumed in the fluid are c _max and c _min , the upper and lower limits of the maximum flow velocity measurement range are V _max and V _min, and V _max cos α =
_{v ma x, V min cosα =} v min, and if the maximum and minimum values of each of the phase difference [Delta] [phi] _M1 and [Delta] [phi] _M2 envisioned, represented by the formula (3 ') according to Equation (12).

Here, a general phase difference detector detects Δψ _M1 and Δψ _M1.
In order to effectively measure _M2 , the maximum and minimum values of the effective detection range of the detector should be b _max π, a _max π and b _min π,
when the a _{mi n} [pi (hereinafter course which like is greater than 0 [pi), the condition of equation (13) every [Delta] [phi] _M1 and [Delta] [phi] _M2 may be Naritate.

Then, the equation (1) corresponding to Δψ _M1 and Δψ _M2
4), the modulation frequency f
Select _M arbitrarily.

[0093]

[Equation 11]

When the modulation frequency f _M is determined in this manner, the specific change range (which does not exceed π) of the phase differences Δψ _M1 and Δψ _M2 can be obtained from equation (12). The integers n ₁ and n ₂ in (3 ′) can be calculated.

As described above, if n ₁ π and n ₂ π are obtained and known, even if the absolute values of the phase differences Δψ _M1 and Δψ _M2 greatly exceed π, bπ and aπ Is actually measured, and based on the result, n ₁ π and n
Adding ₂ [pi, it is possible to determine the phase difference [Delta] [phi] _M1 and the phase difference [Delta] [phi] _M2.

Note that, depending on the current flow velocity v and sound velocity c, n ₁ and n ₂ may be +1 or −1, but if f _M in the numerical range shown by the equation (14) is used, n ₁ or n ₁ can be obtained. And n ₂
Is always one-to-one with the measured values of bπ and aπ, so that, for example, the computer software can determine n ₁ and n ₂ from the measured values of bπ and aπ to reliably obtain Δψ _M1 and Δψ _M2 .

[0097] Also, in the numerical range given, [Delta] [phi] _M1 is better to select the utmost large f _M, for example, deviation of the noise frequency band of the pipe tube is increased, stable, [Delta] [phi] _M2
Measurement becomes easier.

At this point, as described above, f_M Select large
And bπ and aπ are not ranges but absolute
Beyond the value π (= 0), that is,
May change. On the other hand, general phase difference detection
Since the accuracy of the transmitter is often poor near 0 rad,
In such a case, bπ and aπ should not exceed π (= 0).
To f_M Is selected lower, and if necessary, a_max = B
_max = 0.98, b_min = A _min = 0.2
good.

In order for bπ and aπ not to exceed π (= 0), in the equation (12 ′) showing the measurable condition, n ₁ = const (constant) and n ₂ = cons
Since t is sufficient, integers n ₁ and n ₂ that satisfy Expression (15) are specifically used. Then, f _M at this time is expressed by equation (1)
Determined from the numerical range of 6).

As described above, for example, a _max = 0.98, b
_When designing with a margin for a _max and b _min , such as _min = 0.2, it is not necessary to strictly observe the inequality sign of Expressions (15, 16). In short, the change range of Δψ _M1 and Δψ _M2 is less than π. It is better to have n ₁ ,
It is also possible to determine the n ₂ and f _M.

[0101]

(Equation 12)

Further, in order to reduce the types of various constants and simplify the software, n _{1 is obtained} through Δψ _M1 and Δψ _M2.
= N ₂ = n = const. In this case, the measurable equation is substantially the equation (12 ″). Therefore, an integer n is selected by the equations (17) and (18), and f _{M is set} to decide. Also in this case, it is possible to select n or f _M beyond the range of the mathematical expression according to the selection of a _max and b _min .

[0103]

(Equation 13)

On the other hand, the phase difference Δψ between the carrier waves of the frequency f _C
C1 and [Delta] [phi] _C2 and placed by the equation equation based on (3) (3 '') is (wherein m _1, m ₂ is an integer, beta and γ is less than 1), the carrier frequency f _C in the present invention Since the amplitude is modulated by the modulation signal of the frequency f _M to propagate the ultrasonic wave, the equation (3 ′)
From equation (3 ″), the phase differences Δψ _C1 and Δψ _C2 and the phase difference Δψ
_M1, the relationship of [Delta] [phi] _M2 may be a formula (19), as a result, each of the obtained phase difference [Delta] [phi] _M1, wherein a value of [Delta] [phi] _M2 (1
Substituting into 9), m ₁ and m ₂ can be calculated.

[0105]

[Equation 14]

Then, of the phase difference between the carrier at the transmission point and the carrier propagating in the obliquely downstream direction and the obliquely upstream direction, only βπ and γπ which can be detected by a general phase difference detector are measured. And this directly measured result contains m ₁
By adding π and m ₂ π, the phase differences Δ 求 め る_C1 and Δψ _C2 between the carrier phase at the time of transmission and the carrier phases propagated and received in the obliquely downstream and upstream directions can be obtained. Thus, the flow velocity V is calculated by substituting these into the equation (5 ′) based on the above-described phase difference flow velocity measurement equation.

Here, the phase difference Δψ_C1And Δ
ψ_C2And their error δ _ΔψIs the phase difference detection
Vessel error δ_C Tens to hundreds of times smaller than
It will be cheap. That is, select from the numerical range shown in equation (14).
Frequency f_M Acts as a carrier using the modulated signal of
The ultrasonic wave is amplitude-modulated and transmitted.
To detect the demodulated signal that has been received and demodulated
Outgoing signal and the modulated signal
The general phase difference detector can detect the phase difference from the key signal.
Part Δψ_MM1 And Δψ_MM2 Is a constant error δ_M Measure with
Then, equation (20) is obtained.

Then, the measured value is added to the previously obtained n ₁ π
And n ₂ π, the phase difference including the error of the modulated signal between the transmitting and receiving points becomes as shown in equation (21). The phase difference Δψ _M1 ′ thus obtained is Phase difference Δψ _M2 '
Is multiplied by f _C / (πf _M ), a value obtained by dividing the phase difference Δψ _C1 and Δψ _C2 between the carrier waves of the frequency f _C from Equation (19) by π is given by m ₁ and m ₂ as described above. (Expression (1)
9 ')).

[0109]

(Equation 15)

Next, the portions Δ 位相_CM1 and Δψ _CM2 of the phase difference of the carrier wave which can be detected by using a general phase difference detector.
Is measured with a constant error δ _C , as shown in equation (22). Therefore, the phase difference Δψ _C1 'and Δψ
_C2 'is given by equation (23), and the flow rate V' obtained by measuring the true flow rate V with a certain error is given by equation (24).

The reason is that these phase differences Δψ _C1 'and Δψ _C2 '
The error δ _Δψ that occurs in equation (25) is as shown in equation (25), m ₁ and m ₂ are ≫1, and β and γ are conversely <1.0.
_ΔψC1 and [delta] _{Derutapusaishi2} much smaller compared to the [delta] _C.
That is, the above-mentioned error δ _Δψ is the error δ _{C of the} phase difference detector.
It is significantly smaller than.

[0112]

(Equation 16)

According to the present invention described above, when L and V are large and the sound velocity c is low, even if the phase difference greatly exceeds π rad, the flow velocity can be easily measured by a general phase difference detector. In addition to this, the phase difference between the transmitted wave and the received wave of the ultrasonic wave (carrier wave) can be precisely measured, so that the phase difference flow velocity measurement method that does not need the sound velocity measurement can be realized.

The following are specific examples of the present invention and examples of error calculation. When measuring the flow rate of natural gas with a pipe pipe having a diameter of 300 mm, c _max = 450 m / s and c _min = 420
m / s, L = 0.424 m, V _max cos α = 30 m / s, V
_min cos α = 0 m / s, and the frequency of the carrier ultrasonic wave is f _C =
Let's say 40kHz.

Here, b _min = a _min = 0, b _max = a
_{If max} = 1 is set, the modulation signal frequencies of Δψ _M1 and Δψ _M2 are selected from the numerical range of Expression (26) from Expression (14), and if f is selected to be 3962 Hz and 3449 Hz, these values can be obtained. The frequency of the modulated signal is significantly higher than the noise frequency f _M in the pipe described above.

[0116]

[Equation 17]

[0117] The range of variation of the phase difference [Delta] [phi] _M1 from equation (12) is 6.9995 ...... π~7.9994 ...... π, also the phase difference [Delta] [phi] _M2
Is 6.4994 ... π to 7.4993 ... π, so n ₁
Is an integer 6 or 7, n ₂ is also limited to 6 or 7, and both ranges are less than π. Therefore, when bπ and aπ are measured by a general phase difference detector, n ₁ and n corresponding to these are measured.
₂ can be specified. As a result, the phase difference Δψ _M1 and the phase difference Δψ _M2 are obtained based on the equation (3 ′). Therefore, the phase differences Δψ _C1 and Δψ _C2 are obtained as described above, and the flow velocity V is calculated.

As described above, f in the numerical range of the equation (14) is obtained.
The method of the present invention can be achieved by arbitrarily selecting _M. However, if two values f _M having different values are selected, the measurement sequence is somewhat complicated, the equipment cost is high, and a general phase difference detector is used. Is dissatisfied with the measurement accuracy near 0π.

[0119] Therefore, in consideration dissatisfaction point versatility and emphasizing the spread of and generally of the phase difference detector of the present invention, the following n ₁
= N ₂ = n = const, and other constants including the frequency f _{M of the} modulation signal are also equal in Δψ ₁ and Δψ ₂ , and the error is calculated based on a simpler and lower-cost method. An example of the device configuration will be described.

First, the measurement range of the phase difference detector is 0 to π r
It is a ad, adequately ample _{b mi n π = 0.2 π,} a
_By setting _max π = 0.98π, n is calculated from Expression (17) and Expression (18).
When the selection range of the modulation signal frequency f _M is obtained, equations (27) and (28) are obtained, respectively. Therefore, n = 3 is recorded and f _M = 1830 Hz is selected. Of course, this f _M
Is within the numerical range indicated by the equation (14), and is sufficiently higher than the noise frequency band.

[0121] Next Indeed, demodulates the received signal by propagating an ultrasonic wave amplitude-modulated diagonally downstream direction and the oblique upstream direction f _M = 1830Hz, the phase difference [Delta] [phi] _M1 and the phase difference by detecting the modulated signal Δψ _M2 is measured, and at this time, the flow velocity is v = Vc
Assuming that osα = 20 m / s and the sound velocity is c = 450 m / s, the true phase difference Δψ _M1 and the phase difference Δψ _M2 can be calculated from the equation (3 ′) using the equation (2).
It becomes like 9). Here, n = 3 is calculated and recorded n
Matches.

[0122]

(Equation 18)

On the other hand, the phase difference detector sets the phase difference to 0.30.
1787π = bπ and thus measured as 0.60893 π = aπ but measured at constant error [delta] _M at this time, δ _M = ± 1% Tosureba measurement result is shown in Equation (30), the following processes From equation (19 ′), m ₁ and m ₂ of the carrier are calculated by equation (3).
Calculate in 1) and record m ₁ = 72 and m ₂ = 78.

[0124]

[Equation 19]

The true phase differences Δψ _C1 and Δψ _C2 of the carrier are as shown in Equations (3) to (32), where m ₁ = 72 and m ₂ =
78 corresponded to m ₁ and m ₂ in the above formula (31). Then, Δψ _CM1 = 0.170213π and Δψ _CM2 = 0.883721π. However, if the phase difference detector actually measures with an error of δ _C = ± 1%, the equation (33) is obtained. By adding m ₁ π = 72π and m ₂ π = 78π to these, the phase difference Δ including the error of the phase difference detector measured by this method is obtained.
ψ _C1 'and Δψ _C2 ' are as shown in Expression (34).

[0126]

(Equation 20)

By substituting these into the flow velocity measurement equation (24), the result is as shown in equation (35). Although the true flow velocity is Vcosα = 20 m / s, the actual measurement result is V′cosα = 19.97 m / s, and the flow velocity measurement error is −
0.15%. Although the phase differences Δψ _MM1 and Δψ _MM2 , Δψ _CM1 and Δψ _CM2 that can be detected by a general phase difference detector were measured twice with an error of ± 1%, the flow velocity measurement error was −0.15.
%. The reason for this is that, as shown in equation (36), the measurement error of Δ よ う_C1 and Δψ _C2 has become very small.

Δψ_CM1 (Βπ) to δ_C = ± 1% error
Measured, β / m₁ = 0.1702 / 72 ≒ 1/423,
As can be understood from Expression (25), as in Expression (36),
Δψ _C1The measurement error has decreased. Of course, Δψ_CM2 
Δψ obtained by measuring (γπ) _C2The same applies to.

In the above example, the phase difference Δψ
_{MM1, 2 (bπ, aπ)} was assumed [Delta] [phi] _{CM1, 2} and a were measured with ± 1% of error, but an error of the phase difference detector is generally about ± 0.5%.

As described above, the phase difference flow velocity measuring method of the present invention
Without measuring the sound speed, even in a pipe with a large diameter and a gas having a high flow velocity or a lower sound velocity, the flow velocity is determined by the noise frequency f n ≪modulation signal frequency f
_M ≪ It is possible to measure stably at the carrier frequency f _C and accurately with an accuracy exceeding the performance of the phase difference detector.

FIG. 3 shows a block diagram of a phase difference flow rate measuring device as one example of implementing the phase difference flow rate measuring method of the present invention. In the figure, for example, a transmission-only transducer having a wide directional angle is opposed to a reception-only transducer section 1 and 1 'arranged on one side of a river, for example. The unit 2 is arranged. The transmitting-only transducer unit 2 is connected to the receiving-only transducer unit 1.
Is given by a distance L and the angle between the L direction and the flow velocity direction is α
On the other side of the diagonal upstream direction, and the receiving-only transducer unit 1 ′ is separated by a distance L and on the other side of the diagonal downstream direction where the angle between the L direction and the flow velocity direction is α. They face each other.

Reference numeral 13 denotes a carrier oscillator having a frequency f _C , reference numeral 14 denotes a modulation signal oscillator having a frequency f _M ,
Is an amplitude modulator, 18 is an output amplifier, 19 and 1
9 'is the receiving amplifier of the receiving transducer units 1 and 1',
Reference numerals 20 and 20 'denote demodulators for amplitude-modulated signals, and narrow-band amplifiers 21 and 21' amplify the modulated signals demodulated by the demodulators.

A phase difference detector (phase difference detector)
Scriminator) 28 and 28 'are directly detected detectable [Delta] [phi] _MM1 of the phase difference caused modulated signal, ₂ (bπ, aπ), saturated amplifier (amplifiier-limiter) 30 and 30' are amplitude modulated signal ( Outputs of receiving amplifiers 19 and 19 ')
The saturation amplifier, detector 31 and 31 'are effective detection portion [Delta] [phi] _CM1 of phase difference caused in a carrier wave, ₂ (βπ, γπ) detected.

Reference numerals 29 and 29 'denote phase difference adjusters (phase difference adjusters).
shifter), and when V = 0, the phase difference detectors 28 and 28 '
And adjusts the outputs of the detectors 31 and 31 'to zero. Reference numeral 32 denotes an arithmetic unit for calculating the flow velocity by calculating the phase differences Δψ _C1 and Δψ _C2 by the method of the present invention.

Each block in FIG. 3 operates as follows.
The amplitude modulator 17 has a frequency at which the carrier oscillator 13 oscillates.
f_C Of the carrier signal of the modulation signal oscillator 14
Number f _M Amplitude modulation with the modulation signal of Amplitude modulated
The signal is amplified by output amplifier 18 and transmitted
-Is applied to the power supply unit 2.

In this example, since the transmitting transducer unit 2 is a single transmitting transducer unit, the transmitting transducer unit 2 transmits an ultrasonic wave whose amplitude is modulated at a wide angle from an oblique downstream direction to an oblique upstream direction. The receiving transducer units 1 and 1 'generate a reception signal while receiving the amplitude-modulated ultrasonic waves propagating in the obliquely upstream direction and the obliquely downstream direction.

The received signal is amplified by amplifiers 19 and 19 'for amplifying the frequency band of f _C ± f _M and input to demodulators (detectors) 20 and 20'.
0 20 'in demodulating and detecting the modulated signal of a frequency f _M.
One of the modulation signals is input to the narrow-band amplifier 21 after passing through the phase adjuster 29, and the other modulation signal is directly input to the narrow-band amplifier 21 '. Input to detectors 28 and 28 '. Since the oscillation signal of the modulation signal oscillator 14 is input to the other input terminals of the low-frequency phase difference detectors 28 and 28 ', the low-frequency phase difference detectors 28 and 28' Δψ _MM2 and the phase difference Δψ _MM1 are measured and input to the arithmetic unit 32.

At the same time, one of the output signals of the receiving amplifiers 19 and 19 'passes through the phase difference adjuster 29', and the other is directly input to the saturation amplifiers 30 and 30 'and amplified to a saturated state, that is, discriminated. Are input to the carrier phase difference detectors 31 and 31 ', respectively.

Since the oscillation signal of the carrier oscillator 13 is input to the other input terminals of the phase difference detectors 31 and 31 ',
These outputs have a detectable phase difference Δψ _CM1 and a phase difference Δ
ψ _{CM 2} phase difference signals are output, and these phase difference signals are input to the arithmetic unit 32.

The arithmetic unit 32 includes n, f _M , f _C , L,
Since constants such as cos α are recorded, m ₁ and m ₂ are calculated in accordance with the above-described equation (3 ′, 19), and the phase difference Δψ _C1 and Δψ _C2 of the carrier are calculated by equation (3 ″). The flow velocity V is calculated by the equation (5 ').

When a volume flow meter is used for measuring the mass flow rate of a gas, the pressure and the temperature of the gas are separately measured. In such a case, if a flow meter that measures the flow velocity by the ultrasonic phase difference method is used, the sound velocity c can be calculated by using the measured values of the pressure and the temperature of the gas. The flow rate and the flow rate can also be measured by the equation (h).

However, when the diameter of the pipe is large or when the flow velocity is high, as described above, the phase difference Δφ ₁ and Δφ ₂ between the transmitted and received signals and the phase difference Δφ between both received signals exceed π. However, the phase difference cannot be measured with a general phase difference detector. Therefore, in the present invention, the carrier wave of the frequency f _C is amplitude-modulated with the modulation signal of the frequency f _M to transmit, receive, and demodulate the ultrasonic wave. The phase difference of the modulation signal does not exceed π. That is, f _M is determined from the numerical range of Expression (37).

Therefore, if the ultrasonic wave amplitude-modulated by the modulated signal is propagated in the obliquely downstream direction and the obliquely upstream direction, and the received signal is demodulated and the modulated signal is detected, the phase difference can be detected by a general phase difference detector. Δφ _M can be measured. Since the equation (38) holds in the means of the present invention, the value m of the integer part of the phase difference Δφ _C between the carrier reception signals is calculated.

[0144]

(Equation 21)

Here, a is less than 1, and an integer m is recorded. Since aπ (<π) is a part measured by the phase difference detector as the phase difference between the carrier reception signals, the phase difference aπ is actually measured, the phase difference Δφ _C is calculated by the equation (38), and this is calculated as the flow rate The flow velocity is calculated by substituting into the measurement equation (h ′).

[0146] error [delta] _DerutafaiC of the thus obtained phase difference [Delta] [phi _C is as shown in equation (39). That is, δ
_{This is because if aπ} is the relative error of the phase difference detector, the absolute error of aπ measured by the phase difference detector is _Δaπ = _δaπ · aπ. Since m> 1, a <1.0, δ _ΔφC
≪δ _aπ . For this reason, the accuracy of the flow velocity measurement is increased.

FIG. 4 shows an example of an apparatus for measuring the flow velocity by this method.
It was shown to. The symbols and operations in FIG. 4 are the same as those in the embodiment shown in FIG. However, the numerical values of the distance L, cos α, f _C and f _M are recorded in the flow velocity calculating device 32,
The flow velocity is calculated according to equations (38) and (h '). According to such a method, unlike the related art, Δφ _M <π can be satisfied, and Δφ _C ≫
Even if it is π, a general phase difference detector can be used, and the accuracy can be improved beyond the possessed accuracy of the phase difference detector itself.

In the embodiment of the phase difference method according to the present invention, the transducer section is arranged as shown in FIG. 4 and the phase difference Δφ between the receiving transducer sections 1 and 1 ′ is measured. Although the trans du - service unit 2 and trans du - measuring the phase difference between the sub unit 1 'as the [Delta] [phi ₂ - [Delta] [phi ₁ the phase difference between the sub unit 1, trans du - service unit 2 and the transformer du , Δφ
= Δφ ₁ −Δφ ₂ may be used to derive a phase difference between the transducer sections 1 and 1 ′. In this case, the operation and effect of the present invention are similarly exhibited.

Further, in the method of the phase difference Δψ and the method of the phase difference Δφ, the arrangement of the transducer section is not limited to that shown in FIGS.
(A) A method using two sets of opposing combinations of a transmitting transducer part and a receiving transducer part, or the same combination as a pair as shown in FIGS. It is also possible. In the propagation time difference method according to claims 1 to 4, conversely, the arrangement of the transducer section as shown in FIGS. 6A and 6B may be possible.

Further, here, the reference point for the phase difference measurement is set using the electric signal applied to the transmitting transducer unit. However, similar to the case of the above-described embodiment of the propagation time difference method,
The phase difference method is not limited to this. For example, a third transducer section is arranged near the transmitting transducer section at a distance L from the receiving transducer section. Ultrasonic waves transmitted by the transmitting transducer unit in the fluid are received immediately afterward, and the received signals may be used as a reference point for phase difference measurement, further improving the accuracy.

[0151]

According to the method of the present invention, the ultrasonic wave propagation time in a river, a large artificial open channel, or a large-diameter pipe pipe is determined by the ultrasonic wave propagation time difference method, and the flow velocity is reliably and accurately determined. The velocity can be measured by the ultrasonic phase difference method regardless of the speed of sound even if the speed of sound changes drastically and the phase difference greatly exceeds π. -Many excellent functions and effects can be achieved, such as being able to accurately measure the flow velocity of a high flow velocity fluid even in a small diameter pipe pipe.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a method for measuring a propagation time difference flow velocity according to the present invention.

FIG. 2 is a timing chart of the method of measuring the flow velocity of a transit time difference according to the present invention.

FIG. 3 is a block diagram showing an embodiment of an ultrasonic phase difference flow velocity measuring method according to the present invention.

FIG. 4 is a block diagram of another embodiment of the phase difference method of the present invention.

FIG. 5 is an explanatory diagram of a well-known principle of measuring the ultrasonic propagation time difference flow velocity.

FIG. 6 is an explanatory diagram of a well-known principle of ultrasonic phase difference flow velocity measurement.

[Explanation of symbols]

1, 2; transducer section, 3; switch circuit, 4;
Ultrasonic pulse oscillation circuit, 5; reception amplification circuit, 6; short pulse signal shaping circuit, 7; time interval measurement device, 8;
Flow velocity calculating device, 9; sine wave oscillator, 10; phase adjuster, 11; receiving amplifier, 12; phase difference detector, 13; ultrasonic carrier wave oscillator, 14; modulation signal oscillator, 15; 0 point crossing circuit, 16; Monostable pulse oscillator, 17;
Amplitude modulator, 18; output amplifier, 19; amplifier, 20;
Demodulator, 21; narrow-band amplifier, 22; zero-point crossing circuit, 23; switch circuit, 24; switch circuit, 2
5; switch circuit; 26; switch control device; 27; signal attenuator; 28; phase difference detector; 29; phase difference adjuster;
30; Saturation amplifier, 31; Phase difference detector, 32;

Continuing on the front page (72) Inventor Haksaw, Chang 102-1301, Pung-Dang-Gu-Tap-Dong-Chan-Mima-Uul, Song-nan, Republic of Korea (72) Inventor Yasuo Ito 1-4-7 Miyamae, Suginami-ku, Tokyo F-term ( Reference) 2F035 DA14 DA15 DA19 DA23 DA24

Claims (7)

[Claims] 1. A plurality of transducer sections are arranged opposite to each other at a predetermined interval on a transverse line obliquely crossing a fluid flow path, and transmit and receive ultrasonic waves in oblique upstream and oblique downstream directions. A method of measuring the difference between the propagation times of the ultrasonic waves to measure the flow velocity of the fluid, wherein the maximum frequency at which the attenuation pulsates when the ultrasonic waves propagate in the fluid is f _P , The maximum sound velocity assumed in c
_max , the ultrasonic wave propagation distance is L, the component of the maximum average flow velocity assumed in the section of the distance L in the distance L direction is v _max , and the frequency of the ultrasonic carrier is f _C, and the frequency f _{M of the} modulation signal is The frequency f is selected by equation (2).
Transmits and receives an ultrasonic wave amplitude-modulated for a predetermined time with the modulation signal of _M , and from a certain moment when the carrier wave is amplitude-modulated on the transmitting side, receives the ultrasonic wave propagated in the fluid and is included in the received signal. A flow velocity measuring method, comprising measuring a time until a certain moment corresponding to the above of the modulated signal and calculating a flow velocity V. (Equation 1) 2. The method according to claim 1, wherein at the time of transmission, an amplitude-modulated signal is input to a demodulator to detect a modulated signal, and a start time of ultrasonic wave propagation time measurement (start signal) is set. Amplitude-modulated ultrasonic waves are demodulated by the demodulator to receive a received signal received after propagating in a fluid to detect a modulated signal,
As the end point of ultrasonic propagation time measurement (stop signal),
A flow velocity measuring method characterized by measuring an ultrasonic propagation time. 3. The flow velocity measuring method according to claim 1, wherein the modulation start time point is always a certain phase of the modulation signal. 4. A modulated signal obtained by detecting an amplitude-modulated signal at the time of transmission and a modulated signal obtained by detecting from a received signal received after an amplitude-modulated ultrasonic wave has propagated through a fluid, respectively. 4. The flow velocity measuring method according to claim 1, wherein the same phase is used as a start signal and a stop signal. 5. A plurality of transducer sections are arranged opposite to each other at a predetermined interval on a transverse line obliquely crossing the inside of the fluid flow path, and transmit and receive ultrasonic waves in oblique upstream and oblique downstream directions. A method of measuring a change in phase that occurs when the ultrasonic wave propagates through a fluid to measure the flow velocity of the fluid, wherein an obliquely downstream direction and an obliquely upstream direction include an ultrasonic carrier having a frequency f _C , and amplitude-modulated with a modulation signal f _M, when the transmission and reception, the frequency f generated at between transmission and reception points
The phase difference Δψ _C1 and Δψ _C2 of the ultrasonic carrier wave of _C are measured, respectively, and the flow velocity of the fluid is calculated from the ultrasonic propagation distance L and the angle α formed by the flow velocity direction and the L-line direction by the equation (5 ′). A method for measuring flow velocity, comprising measuring V. (Equation 2) 6. The method according to claim 5, wherein the ultrasonic waves are directed obliquely downstream.
Transmission and reception when transmitted in the forward and oblique upstream directions, respectively.
Between the points, the frequency f_C Ultrasonic carrier and frequency f
_M , The phase difference generated in the modulated signal of Δψ_C1= M₁ π
+ Βπ and Δψ _C2= M_Two π + γπ and Δψ_M1= N₁ π
+ Bπ and Δψ_M2= N_Two π + aπ (where m₁ , M_Two , N
₁ , N_Two Are integers, and β, γ, a, and b are 1 or less).
The maximum and minimum sound speeds assumed in the fluid are c
_max And c_min , The upper and lower limits of the flow velocity measurement range
The directional component is v_max And v_min , Frequency f_M Modulation signal phase
Set the upper and lower limits of the measurement range of the difference detector to b_max , A_max And b
_min , A_min When the ultrasonic wave propagation distance is L, the modulation frequency f in the numerical range of Expression (14)_M Select this
N corresponding to₁ And n_TwoWith reference to the equations (3 ', 12).
The frequency f_M The ultrasonic signal modulated by the modulation signal of
Receive and receive, and from the received signal the frequency f_M Modulation signal
Measure out bπ and aπ_M1And Δψ_M2And then
Referring to equation (19), m₁ And m_Two And decide before
Measure βπ and γπ from the received signal and calculate Δψ_C1And Δψ_C2Seeking
A method for measuring flow velocity, comprising: (Equation 3) 7. On a transverse line obliquely crossing the inside of the fluid flow path
And a plurality of transducers facing each other with a predetermined interval
Arrange and emit ultrasonic waves in diagonally upstream direction and diagonally downstream direction
A phase that is received and occurs when the ultrasonic wave propagates through the fluid
A method for measuring the flow velocity of a fluid from the change in_C The ultrasonic carrier of frequency f_M With a modulated signal
Amplitude modulates ultrasonic waves in oblique upstream and oblique downstream directions
Each phase change of the ultrasonic carrier when propagated
Difference Δφ_C Is Δφ_C = Mπ + aπ (where m is an integer,
a is 1 or less) and the frequency f_M Phase of each modulated signal
Δφ_M And the ultrasonic propagation distance is L,
The angle between the flow velocity direction and the transverse line direction is α, and the minimum sound speed is c
_min , The transverse component of the maximum measured flow velocity_max Made
Time, the frequency f of the modulation signal_M In the numerical range of equation (37)
And the frequency f_M Ultrasonic signal amplitude-modulated with the modulation signal of
Is transmitted and received, and the frequency f_M Modulation signal
Signal and the phase difference Δφ_M (<Π) and determine the phase difference
Δφ_M And frequency f _C And frequency f_M (Equation 38)
With reference to m, aπ is calculated from the received signal.
Measure and phase difference Δφ_C Is calculated, and the flow velocity V is calculated as in equation (h ').
A flow velocity measuring method characterized by calculating (Equation 4)