JP2011169665A - Flow velocity measuring method and ultrasonic flowmeter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To highly accurately measure a flow rate by deciding a transmission frequency at which flow rate measurement errors are minimal. <P>SOLUTION: A vibrator 31 is attached to a reflector 5, and the relation between the transmission frequency of the vibrator 31 and the signal strength of a reflection signal reflected and sent from the reflector 5 is acquired with respect to a predetermined transmission frequency range. Moreover the vibrator 31 is attached to a pipe for flow measurement, and the relation between the transmission frequency of the vibrator 31 and the signal strength of a reflection signal from the pipe itself or its transmission signal is acquired with respect to the predetermined frequency range. Next, this signal strength is divided by the strength of the reflection signal from the reflector 5, and based on the relation between the signal strength after the division and the transmission frequency of the vibrator 31 an optimum transmission frequency is decided. A flow velocity is measured by the transmission frequency. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flow rate measuring method and an ultrasonic flowmeter for measuring a flow velocity of a fluid to be measured by causing an ultrasonic wave having a predetermined transmission frequency to enter the fluid to be measured flowing in a pipe.

  An ultrasonic flowmeter is a device that measures the flow velocity of a fluid to be measured flowing in a pipe. The ultrasonic flowmeter assumes that bubbles and particles contained in the fluid under measurement in the pipe move at the same speed as the fluid under measurement, and measures the flow velocity distribution and flow rate of the fluid under measurement from the movement speed of these bubbles and particles. To do.

  A reflection correlation method is known as a method for obtaining a flow velocity distribution and a flow rate of a fluid to be measured. Ultrasonic waves are transmitted from the ultrasonic transducer outside the pipe to the fluid to be measured inside the pipe. The transmitted ultrasonic waves propagate in the order of the wedge, the pipe, and the fluid to be measured inside the pipe. When ultrasonic waves hit bubbles or particles in the fluid to be measured, they become reflectors and generate reflected waves. The reflected wave propagates through the fluid to be measured, the pipe, and the wedge inside the pipe and is acquired as a reflected signal. A predetermined time interval is given to the ultrasonic waves transmitted by the ultrasonic transducer. Based on the propagation time of the reflected wave obtained from the first transmitted ultrasonic wave and the propagation time of the reflected wave obtained from the next transmitted ultrasonic wave, the amount of movement of bubbles and particles that became the reflector is calculated. The flow rate of the fluid to be measured is obtained. Such a structure is provided upstream and downstream of the pipe, and the ultrasonic transducers are driven at the same transmission frequency.

  As another method for obtaining the flow velocity distribution and flow rate of the fluid to be measured, the Doppler method is known.

  By the way, in the ultrasonic flowmeter for obtaining the flow rate of the fluid to be measured from the reflected signal from bubbles or particles, the flow rate error changes depending on the transmission frequency of the ultrasonic wave transmitted by the ultrasonic transducer. This is because a wave reflected in the pipe in a multiple manner overlaps with a reflected signal that is a measurement target signal.

  As described above, it is known that the frequency of the wave affecting the measurement changes depending on the pipe wall thickness. Therefore, the optimum transmission frequency that reduces the influence of these waves on the reflected signal is obtained from the thickness of the pipe so that the flow rate error is reduced.

ｆ：送信周波数、Ｃ2：配管横波音速、ｔ：配管肉厚、θ2：屈折角度、ｍ：定数
ここで、
ｍ＝１，２，３，・・・
とした場合には、送信周波数ｆは配管の共鳴周波数となり、流量誤差が小さくなることが知られている。また、
ｍ＝１．５，２．５，３．５，・・・
とした場合には、送信周波数ｆは配管の非共鳴周波数となり、同様に流量誤差が小さくなることが知られている。したがって、上記の式（１）から配管の共鳴周波数あるいは非共鳴周波数となる周波数を算出し、その周波数を送信周波数として利用することで流量誤差の低減が図られる。 The transmission frequency with which the flow rate error is reduced can be obtained by the following equation.

f: transmission frequency, C2: pipe transverse wave sound velocity, t: pipe wall thickness, θ2: refraction angle, m: constant
m = 1, 2, 3,...
In this case, it is known that the transmission frequency f becomes the resonance frequency of the pipe and the flow rate error becomes small. Also,
m = 1.5, 2.5, 3.5,...
In this case, it is known that the transmission frequency f becomes a non-resonant frequency of the pipe, and the flow rate error is similarly reduced. Therefore, the flow rate error can be reduced by calculating the frequency that is the resonance frequency or non-resonance frequency of the pipe from the above equation (1) and using that frequency as the transmission frequency.

  The following Patent Document 1 describes a Doppler type ultrasonic flowmeter that obtains an optimum transmission frequency based on the thickness of a pipe.

JP 2006-30041 A

  However, the resonance frequency (or non-resonance frequency) calculated by the above formula (1) is not necessarily given correctly as the pipe wall thickness t and the pipe transverse wave sound velocity C2, and therefore, the actual resonance frequency (or non-resonance frequency) It will be different. For this reason, if the frequency at which the flow rate error obtained by calculation is reduced and the frequency at which the flow rate error is actually reduced are different, the flow rate error in actual flow rate measurement may be increased.

  The present invention eliminates the conventional problems and appropriately selects a transmission frequency that reduces the flow rate error regardless of parameters such as the thickness of the pipe or the sound velocity of the pipe shear wave, and can measure the flow rate of the fluid to be measured more accurately. It is an object to provide a method and an ultrasonic flow meter.

In order to achieve such a problem, the invention described in claim 1
In a flow measurement method for measuring the flow velocity of the fluid under measurement by causing ultrasonic waves of a predetermined transmission frequency to enter the fluid under measurement flowing in the pipe from the vibrator,
The vibrator is attached to a reflector, and a vibrator characteristic obtaining step for obtaining a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range;
The pipe is filled with a liquid having a constant flow velocity, and the vibrator is attached to the pipe, and the relationship between the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range. The required piping characteristics acquisition step;
A signal strength normalizing step of dividing the signal strength obtained in the piping property obtaining step by the signal strength obtained in the vibrator property obtaining step;
A transmission frequency determination step for determining an optimal transmission frequency based on the relationship between the signal strength after division obtained in this signal strength normalization step and the transmission frequency of the vibrator;
A flow velocity measuring step for measuring the flow velocity by causing the ultrasonic wave having the transmission frequency determined in the transmission frequency determining step to enter the fluid to be measured;
It is provided with.

The invention described in claim 2
The flow velocity measuring method according to claim 1,
In the transmission frequency determination step, the transmission frequency at which the signal strength after division obtained in the signal strength normalization step becomes a maximum value or a minimum value is determined as an optimal transmission frequency.

The invention according to claim 3
The flow velocity measuring method according to claim 1,
In the transmission frequency determination step, a frequency in the vicinity of the transmission frequency at which the signal intensity obtained in the piping characteristic acquisition step is maximum or minimum is determined as an optimal transmission frequency.

The invention according to claim 4
In the ultrasonic flowmeter that measures the flow velocity of the fluid under measurement by causing ultrasonic waves of a predetermined transmission frequency to enter the fluid under measurement flowing in the pipe from the vibrator,
In a state where the vibrator is attached to a reflector, vibrator characteristic data obtained for a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range; With the pipe filled with a liquid at a constant flow rate and the vibrator attached to the pipe, the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range Obtain the piping characteristic data for which the relationship was obtained, divide the piping characteristic data by the vibrator characteristic data, and determine the optimum transmission frequency based on the relationship between the signal strength after this division and the transmission frequency of the vibrator A transmission frequency determining unit to perform,
A transmission unit that generates ultrasonic waves of the transmission frequency determined by the transmission frequency determination unit from the vibrator;
It is provided with.

The invention described in claim 5
The ultrasonic flowmeter according to claim 4,
The transmission frequency determining unit determines a transmission frequency at which the signal strength after division becomes a maximum value or a minimum value as an optimal transmission frequency.

The invention described in claim 6
The ultrasonic flowmeter according to claim 4,
The transmission frequency determination unit determines, as an optimal transmission frequency, a frequency in the vicinity of the transmission frequency at which the signal intensity obtained in the pipe characteristic acquisition step is maximized or minimized.

According to the present invention,
The vibrator is attached to a reflector, and a vibrator characteristic obtaining step for obtaining a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range;
The pipe is filled with a liquid having a constant flow velocity, and the vibrator is attached to the pipe, and the relationship between the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range. The required piping characteristics acquisition step;
A signal strength normalizing step of dividing the signal strength obtained in the piping property obtaining step by the signal strength obtained in the vibrator property obtaining step;
A transmission frequency determination step for determining an optimal transmission frequency based on the relationship between the signal strength after division obtained in this signal strength normalization step and the transmission frequency of the vibrator;
A flow velocity measuring step for measuring the flow velocity by causing the ultrasonic wave having the transmission frequency determined in the transmission frequency determining step to enter the fluid to be measured;
With this, a flow rate measurement method can be provided in which the flow rate of the fluid to be measured can be measured more accurately by appropriately selecting a transmission frequency that reduces the flow rate error regardless of parameters such as pipe wall thickness or pipe transverse wave sound velocity. .

Moreover, according to the present invention,
In a state where the vibrator is attached to a reflector, vibrator characteristic data obtained for a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range; With the pipe filled with a liquid at a constant flow rate and the vibrator attached to the pipe, the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range Obtain the piping characteristic data for which the relationship was obtained, divide the piping characteristic data by the vibrator characteristic data, and determine the optimum transmission frequency based on the relationship between the signal strength after this division and the transmission frequency of the vibrator A transmission frequency determining unit to perform,
A transmission unit that generates ultrasonic waves of the transmission frequency determined by the transmission frequency determination unit from the vibrator;
Provides an ultrasonic flow meter that can measure the flow rate of the fluid under measurement more accurately by appropriately selecting the transmission frequency that reduces the flow error regardless of parameters such as pipe wall thickness and pipe transverse wave sound velocity. it can.

It is a figure which shows one Example of the ultrasonic flowmeter of this invention. It is an operation | movement flow of the flow volume measurement of the to-be-measured fluid Ls. It is a figure which shows the procedure 1 for determining the transmission frequency xs. It is a figure which shows the procedure 1 for determining the transmission frequency xs. It is a figure which shows the procedure 1 for determining the transmission frequency xs. It is a figure which shows the procedure 2 for determining the transmission frequency xs. It is a figure which shows the procedure 2 for determining the transmission frequency xs. It is a figure which shows the modification for implementing procedure 2. FIG.

FIG. 1 is a view showing an embodiment of the ultrasonic flowmeter of the present invention. In FIG. 1A, 1 is a pipe through which the fluid Ls to be measured flows, and 21 and 22 are wedges fixed obliquely at a predetermined angle so as to contact the outer peripheral surface of the pipe 1. The wedge 21 is fixed on the upstream side of the fluid Ls to be measured, and the wedge 22 is fixed on the opposite side of the wedge 21 on the downstream side of the fluid Ls to be measured. Reference numerals 31 and 32 denote ultrasonic vibrators attached to the ends of the wedges 21 and 22. Reference numerals 41 and 42 denote converters that calculate the overall control of the ultrasonic vibrators 31 and 32 and the flow rate of the fluid Ls to be measured.
The wedges 21 and 22, the ultrasonic transducers 31 and 32, and the transducers 41 and 42 have the same structure.

The ultrasonic transducer 31 transmits the ultrasonic wave S to the fluid Ls to be measured inside the pipe 1. The transmitted ultrasonic wave S propagates in the order of the wedge 21, the pipe 1, and the fluid Ls to be measured in the pipe 1. When the ultrasonic wave S hits bubbles or particles in the fluid Ls to be measured, they become reflectors, and a reflected wave (echo wave) Sb is generated. The reflected wave propagates through the fluid to be measured Ls, the pipe 1 and the wedge 21 inside the pipe 1 and is acquired as a reflected signal. The acquired reflected signal is transmitted to the converter 41. A predetermined time interval is given to the ultrasonic wave S transmitted by the ultrasonic transducer 31. Based on the propagation time of the reflected wave obtained from the ultrasonic wave S transmitted first and the propagation time of the reflected wave obtained from the ultrasonic wave S transmitted next, in the converter 41, bubbles and particles that have become reflectors And the flow rate of the fluid Ls to be measured is obtained.
A similar configuration (ultrasonic transducer 32, wedge 22, transducer 42) is also provided on the downstream side of the fluid Ls to be measured to obtain the flow velocity of the fluid Ls to be measured, and an average with the flow velocity obtained on the upstream side is obtained. The flow velocity of the fluid Ls to be measured is calculated.

  FIG. 1B is a diagram illustrating the configuration of the converter 41. The converter 41 includes a transmission / reception timing control unit 4a that controls transmission / reception timings of ultrasonic waves and reflected signals, a transmission unit 4b that controls the ultrasonic transducer 31 to generate ultrasonic waves, and a transmission frequency of ultrasonic waves to be transmitted. Based on the output of the A / D converter 4e, the A / D converter 4e for A / D converting the received reflected signal, the transmission frequency determining unit 4c for determining the reflected signal, the receiving unit 4d for receiving the reflected signal It is comprised from the calculating part 4f which calculates the flow volume of the measurement fluid Ls.

FIG. 2 is an operation flow for measuring the flow rate of the fluid Ls to be measured.
When the user selects a command for measuring the flow rate of the fluid Ls to be measured, this flow starts.
In step S1, the transmission frequency determination unit 4c sets the transmission frequency xs of the ultrasonic wave S determined in advance in the transmission unit 4b, and proceeds to step S2.
In step S2, the transmission unit 4b generates a transmission signal corresponding to the transmission frequency xs, and proceeds to step S3.
In step S3, the ultrasonic transducer converts the transmission signal into an ultrasonic wave S having a transmission frequency xs, enters the measured fluid Ls, and proceeds to step S4. A predetermined time interval is given to the ultrasonic wave S transmitted by the ultrasonic transducer 31.
In step S4, the receiving unit 4d receives the reflected signal Sb reflected from the fluid Ls to be measured. The reflected signal is A / D converted by the A / D converter 4e and input to the calculation unit 4f, and the process proceeds to step S5. The transmission timing of the ultrasonic wave S and the timing for receiving the reflected signal Sb are controlled by the transmission / reception timing control unit 4a.
In step S5, the calculation unit 4f causes the propagation time of the reflected wave obtained from the ultrasonic wave S transmitted first and the propagation time of the reflected wave obtained from the ultrasonic wave S transmitted next after a predetermined time interval. Is calculated. Then, the calculation unit 4f calculates the amount of movement of the bubbles and particles that have become the reflector based on the propagation time, and obtains the flow velocity of the fluid Ls to be measured.
Then, it progresses to step S6.
In step S6, the computing unit 4f calculates the flow rate of the fluid Ls to be measured based on the flow velocity calculated in step S5, and proceeds to step S7.
Finally, in step S7, the flow rate of the fluid Ls calculated in step S6 is displayed on some display means provided in the ultrasonic flowmeter, and the flow rate measurement is terminated.

  Next, a method for determining the transmission frequency xs will be described. The method of determining the transmission frequency xs includes a procedure for examining the characteristics of the ultrasonic transducer 3 itself (procedure 1), a procedure for examining the characteristics of the pipe 1 itself (procedure 2), and the characteristics obtained in procedure 2 according to the procedure 1. The procedure (normal procedure 3) for normalization using the characteristics obtained in step (3) and the procedure (procedure 4) for obtaining the optimum transmission frequency xs using the result obtained in the step 3 are divided.

  First, procedure 1 will be described. 3 and 4 are diagrams showing a procedure 1 for determining the transmission frequency xs. FIG. 3A shows a configuration diagram of the procedure 1, and FIG. 3B shows a result obtained by the procedure 1. FIG. 3A, the converter 41 shown in FIG. 1B is connected to the ultrasonic transducer 31 (not shown). FIG. 4 is a flowchart showing the procedure 1.

  In this procedure 1, the ultrasonic transducer 31 is attached to the reflective material 5 and the relationship between the transmission frequency of the ultrasonic transducer 31 and the signal intensity of the reflected signal reflected from the reflective material 5 is obtained.

  First, in step S <b> 100, the ultrasonic transducer 31 is installed on the reflector 5 via the wedge 21. The ultrasonic transducer 31 is fixed to the reflector 5 at the same angle as the attachment angle with respect to the pipe 1. The distance dr from the wedge 21 to the reflecting surface of the reflector 5 is the ultrasonic wave from the contact surface between the wedge 21 and the pipe 1 when the ultrasonic transducer 31 is attached to the pipe 1 to the outer wall surface on the opposite side of the pipe 1. Match the distance used as the propagation distance.

Next, in step S101, a range x0 to xn of the transmission frequency x is set, and the process proceeds to step S102.
The transmission frequency range x0 to xn is a range in which the resonance frequency and the non-resonance frequency of the pipe 1 are calculated using the formula (1) as a guide, and the calculated resonance frequency and non-resonance frequency are crossed at least one by one.

In step S102, the transmission unit 4b (not shown) generates a transmission signal corresponding to the transmission frequency x0 as an initial value of the transmission frequency x, and proceeds to step S103.
In step S103, the ultrasonic transducer 31 converts the transmission signal into an ultrasonic wave having a transmission frequency x0, enters the reflecting material 5, and proceeds to step S104.
In step S104, the receiving unit 4d (not shown) receives the reflected signal from the reflecting material 5. Note that the timing for transmitting the ultrasonic wave S and the timing for receiving the reflected signal Sb are controlled by a transmission / reception timing control unit 41 (not shown). The signal of the reflected signal is A / D converted by an A / D converter 4e (not shown) and input to the arithmetic unit 4f (not shown), and the process proceeds to step S105.
In step S105, the transmission frequency x0 and the maximum value y of the reflected signal are recorded, and the process proceeds to step S106.
In step S106, it is confirmed whether or not the transmission frequency x is equal to or higher than the frequency xn, and if it is equal to or higher than the frequency xn, the process proceeds to step S107. On the other hand, if the transmission frequency x is smaller than the frequency xn, the frequency is set to a frequency that is larger than the transmission frequency x by the minimum unit that can be set, and the process proceeds to step S102. That is, the transmission frequency x is sequentially changed in the range of frequencies x0 to xn, and the maximum value y of the reflected signal corresponding to each frequency is acquired.
Finally, in step S107, the relationship between the transmission frequency x and the maximum value y of the reflected signal is formulated (y = f (x)).

  That is, in the procedure 1, the ultrasonic wave S is incident on the reflecting material 5 from the ultrasonic transducer 31 at the transmission frequency x, and the signal intensity of the reflected signal reflected from the reflecting material 5 (maximum value y of the reflected signal) is calculated. Record the transmission frequency. This is repeated in the frequency range x0 to xn to obtain the relationship y = f (x) between the transmission frequency x and the reflected signal y.

  Next, procedure 2 will be described. 5 and 6 are diagrams showing a procedure 2 for determining the transmission frequency xs. FIG. 5A shows a configuration diagram of the procedure 2, and FIG. 5B shows a result obtained by the procedure 2. FIG. 5A, the transducer 4 shown in FIG. 1 is connected to the ultrasonic transducer 31 although not shown. FIG. 6 is a flowchart illustrating the procedure 2.

  In this procedure 2, the pipe 1 is filled with a liquid having a constant flow velocity, and the ultrasonic vibrator 31 is attached to the pipe 1. The transmission frequency of the ultrasonic vibrator 31 and the signal intensity of the reflected signal or transmitted signal from the pipe 1 itself are determined. Seeking a relationship.

  First, in step S110, the wedge 21, the ultrasonic transducer 31, and the AE (acoustic emission) sensor 6 are attached to the outer peripheral surface of the pipe 1. The ultrasonic transducer 31 is attached to the pipe 1 via the wedge 21. The attachment angle of the ultrasonic transducer 31 to the pipe 1 is the same as the attachment angle at the time of measuring the fluid Ls to be measured. The AE sensor 6 is attached to a position on the opposite side of the wedge 21 of the pipe 1 so that the transmission signal St in which the ultrasonic wave from the ultrasonic transducer 31 has passed through the fluid Ls to be measured can be received.

  The pipe 1 is filled with water at a constant flow rate (including zero flow rate) instead of the fluid Ls to be measured.

  Next, in step S111, the range of the transmission frequency x is set, and the process proceeds to step S112. The range of the transmission frequency x is the range of frequencies x0 to xn, as in Procedure 1.

In step S112, the transmission unit 4b (not shown) generates a transmission signal corresponding to the transmission frequency x0 as an initial value of the transmission frequency x, and proceeds to step S113.
In step S113, the ultrasonic transducer 31 converts the transmission signal into an ultrasonic wave having a transmission frequency x0, enters the pipe 1, and proceeds to step S114.
In step S114, the AE sensor 6 receives the transmission signal St that has been transmitted through the fluid Ls to be measured. The transmission signal St is A / D converted by an A / D converter (not shown), and the process proceeds to step S115.
In step S115, the transmission frequency x0 and the maximum value y ′ of the transmission signal St are recorded, and the process proceeds to step S116.
In step S116, it is confirmed whether or not the transmission frequency x is equal to or higher than the frequency xn, and if it is equal to or higher than the frequency xn, the process proceeds to step S117. On the other hand, if the transmission frequency x is smaller than the frequency xn, the frequency is set to a frequency that is larger than the transmission frequency x by the minimum unit that can be set, and the process proceeds to step S102. That is, the transmission frequency x is changed in the range of frequencies x0 to xn, and the maximum value y ′ of the transmission signal St corresponding to each frequency is repeatedly acquired.
Finally, in step S117, the relationship between the transmission frequency x and the maximum value y ′ of the transmission signal St is formulated (y ′ = f ′ (x)).

  That is, in the procedure 2, an ultrasonic wave is incident on the pipe 1 from the ultrasonic transducer 31 at the transmission frequency x, and the signal intensity (maximum value y ′ of the transmission signal) of the transmission signal St from the pipe 1 and the transmission frequency are determined. Record. This is repeated within the frequency range x0 to xn, and the relationship between the transmission frequency x and the transmitted signal y '(y' = f '(x)) is obtained.

  It is known that the maximum value y 'of the transmission signal St increases when the transmission frequency x corresponds to the resonance frequency of the pipe 1, and the maximum value y' decreases when it corresponds to the non-resonance frequency.

Next, procedure 3 will be described.
FIG. 7 is a diagram showing the results obtained in procedure 3. In the procedure 3, y ′ = f ′ (x) / y ′ = f ′ (x) obtained by multiplying the reciprocal 1 / f (x) of f (x) obtained in the procedure 1 by y ′ = f ′ (x) obtained in the procedure 2. Find f (x).
That is, the signal strength at each frequency is normalized by dividing the signal strength obtained at step 2 by the signal strength obtained at step 1.

  Next, in step 4, the normalized signal strength at each frequency is compared based on the strength y ″ obtained in step 3, and the transmission frequency used for actual measurement of the fluid Ls to be measured is determined. Determines the frequency xm at which the intensity y ″ of the normalized signal is the maximum value as the transmission frequency xs.

  The transmission frequency xs determined in this way is stored in the transmission frequency determination unit 4c in step S1 shown in FIG. In actual measurement of the fluid Ls to be measured, an ultrasonic wave having a transmission frequency xs is incident on the fluid Ls to be measured to measure the flow velocity (flow velocity measurement step).

This embodiment is configured as described above,
Procedure 1 for attaching the ultrasonic transducer 31 to the reflector 5 and determining the relationship between the transmission frequency of the ultrasonic transducer 31 and the signal intensity of the reflected signal reflected from the reflector 5 for a predetermined transmission frequency range x0 to xn. When,
The pipe 1 is filled with water at a constant flow rate, and an ultrasonic transducer 31 is attached to the pipe 1, and the transmission frequency of the ultrasonic transducer 31 and the signal intensity of the transmission signal St from the pipe 1 for a predetermined transmission frequency range x0 to xn. Procedure 2 for determining the relationship between
Procedure 3 for dividing the signal strength obtained in Procedure 2 by the signal strength obtained in Procedure 1;
Procedure 4 for determining the optimum transmission frequency xs based on the relationship between the signal intensity after division obtained in Procedure 3 and the transmission frequency of the ultrasonic transducer 31;
Since the transmission frequency with which the flow rate error is reduced is appropriately selected regardless of parameters such as the thickness of the pipe 1 and the pipe transverse wave sound velocity, the flow rate of the fluid Ls to be measured can be measured with higher accuracy.

Moreover, according to this embodiment,
With the ultrasonic transducer 31 attached to the reflective material 5, the relationship between the transmission frequency of the ultrasonic transducer 31 and the signal intensity of the reflected signal reflected from the reflective material 5 in a predetermined transmission frequency range x0 to xn. The ultrasonic transducer for a predetermined transmission frequency range x0 to xn in a state where the obtained transducer characteristic data y = f (x) and the pipe 1 are filled with water at a constant flow rate and the ultrasonic vibrator 31 is attached to the pipe 1 The pipe characteristic data y ′ = f ′ (x) obtained from the relationship between the transmission frequency of 31 and the signal intensity of the transmission signal St from the pipe 1 is obtained, and the pipe characteristic data y ′ = f ′ (x) is obtained as a transducer. Transmission that divides by the characteristic data y = f (x) and determines the optimum transmission frequency xs based on the relationship y ″ = f ″ (x) between the signal intensity after the division and the transmission frequency of the ultrasonic transducer 31 A frequency determining unit 4c;
A transmission unit 4b for generating ultrasonic waves of the transmission frequency determined by the transmission frequency determination unit from the ultrasonic transducer 31,
The ultrasonic flowmeter that can measure the flow rate of the fluid to be measured with higher accuracy by appropriately selecting the transmission frequency that reduces the flow rate error regardless of parameters such as the wall thickness of the pipe 1 and the sound velocity of the pipe transverse wave. Can be provided.

  In this embodiment, the ultrasonic transducer 31, the wedge 21, and the transducer 41 are provided on the upstream side of the fluid Ls to be measured, and the ultrasonic transducer 32, the wedge 22, and the transducer 42 are provided on the downstream side, and the measurement is performed. Although the average value of the flow velocity of the fluid Ls is taken, these configurations are not necessarily provided on the upstream side and the downstream side. What is necessary is just to obtain | require an average value by calculating | requiring the flow velocity not only upstream and downstream but using the same some structure.

  In this embodiment, in step 4, the frequency xm at which the normalized signal strength y ″ is the maximum value is determined as the transmission frequency xs. However, the frequency xm at which the strength y ″ is the minimum value is determined as the transmission frequency xs. May be. Alternatively, a frequency near the transmission frequency at which the piping characteristic data y ′ is maximum or minimum may be determined as the optimal transmission frequency xs. Note that the transmission frequency at which the pipe characteristic data y 'is maximum or minimum corresponds to the resonance frequency or non-resonance frequency of the pipe 1 itself.

  In the present embodiment, the AE sensor is used to measure the transmission signal St of the ultrasonic wave incident on the pipe 1 when performing the procedure 2. However, as shown in FIG. May be provided on the opposite side of the pipe 1, and the transmission signal St may be received by the ultrasonic transducer 31 '.

  Further, in this embodiment, when the procedure 2 is performed, the characteristics of the pipe 1 are examined by measuring the transmission signal St of the ultrasonic wave incident on the pipe 1, but the reflected signal from the wedge, flange, boss, etc. You may investigate the characteristic of the piping 1 by measuring. Or you may investigate the characteristic of the piping 1 by measuring the intensity | strength of piping multiwave.

  In this embodiment, the example in which the present invention is applied to the reflection correlation method ultrasonic flowmeter has been described. However, the present invention is not limited to the reflection correlation method, and can be applied to an Doppler method ultrasonic flowmeter.

In this embodiment, the procedure 1 of the method for determining the transmission frequency xs corresponds to the transducer characteristic acquisition step in the claims, the procedure 2 corresponds to the piping characteristic acquisition step, and the procedure 3 corresponds to the signal intensity normalization. Step 4 corresponds to a transmission frequency determination step.
The ultrasonic transducers 31 and 32 correspond to the transducers in the claims.

DESCRIPTION OF SYMBOLS 1 Piping 31, 32 Ultrasonic vibrator 4a Transmission / reception timing control part 4b Transmission part 4c Transmission frequency determination part 4d Reception part 4f Operation part Ls Fluid to be measured

Claims (6)

In a flow measurement method for measuring the flow velocity of the fluid under measurement by causing ultrasonic waves of a predetermined transmission frequency to enter the fluid under measurement flowing in the pipe from the vibrator,
The vibrator is attached to a reflector, and a vibrator characteristic obtaining step for obtaining a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range;
The pipe is filled with a liquid having a constant flow velocity, and the vibrator is attached to the pipe, and the relationship between the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range. The required piping characteristics acquisition step;
A signal strength normalizing step of dividing the signal strength obtained in the piping property obtaining step by the signal strength obtained in the vibrator property obtaining step;
A transmission frequency determination step for determining an optimal transmission frequency based on the relationship between the signal strength after division obtained in this signal strength normalization step and the transmission frequency of the vibrator;
A flow velocity measuring step for measuring the flow velocity by causing the ultrasonic wave having the transmission frequency determined in the transmission frequency determining step to enter the fluid to be measured;
A flow rate measuring method characterized by comprising:   The transmission frequency determination step determines a transmission frequency at which the signal strength after division obtained in the signal strength normalization step becomes a maximum value or a minimum value as an optimal transmission frequency. Flow rate measurement method.   2. The flow velocity according to claim 1, wherein in the transmission frequency determination step, a frequency in the vicinity of the transmission frequency at which the signal intensity obtained in the piping characteristic acquisition step is maximized or minimized is determined as an optimum transmission frequency. Measuring method. In the ultrasonic flowmeter that measures the flow velocity of the fluid under measurement by causing ultrasonic waves of a predetermined transmission frequency to enter the fluid under measurement flowing in the pipe from the vibrator,
In a state where the vibrator is attached to a reflector, vibrator characteristic data obtained for a relationship between a transmission frequency of the vibrator and a signal intensity of a reflected signal reflected from the reflector for a predetermined transmission frequency range; With the pipe filled with a liquid at a constant flow rate and the vibrator attached to the pipe, the transmission frequency of the vibrator and the signal intensity of the reflected signal or transmission signal from the pipe itself for the predetermined transmission frequency range Obtain the piping characteristic data for which the relationship was obtained, divide the piping characteristic data by the vibrator characteristic data, and determine the optimum transmission frequency based on the relationship between the signal strength after this division and the transmission frequency of the vibrator A transmission frequency determining unit to perform,
A transmission unit that generates ultrasonic waves of the transmission frequency determined by the transmission frequency determination unit from the vibrator;
An ultrasonic flowmeter comprising:   The ultrasonic flowmeter according to claim 4, wherein the transmission frequency determination unit determines a transmission frequency at which the signal intensity after division becomes a maximum value or a minimum value as an optimal transmission frequency.   5. The super frequency according to claim 4, wherein the transmission frequency determination unit determines a frequency in the vicinity of the transmission frequency at which the signal intensity obtained in the pipe characteristic acquisition step is maximum or minimum as an optimum transmission frequency. Sonic flow meter.

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