JP5641491B2 - Ultrasonic flow meter - Google Patents

Description

  The present invention relates to an ultrasonic flow meter, and more particularly to a technique for performing highly accurate flow measurement using a more accurate flow correction coefficient.

  An ultrasonic flow meter is known as a flow meter used for flow control in a chemical plant or the like. Some ultrasonic flowmeters combine measurement using a propagation time difference method and measurement using a reflection correlation method (see Patent Document 1). This ultrasonic flowmeter performs measurement by the propagation time difference method when there are few ultrasonic reflectors such as bubbles and fine particles in the fluid to be measured, and performs measurement by the reflection correlation method when there are many ultrasonic flowmeters. Hereinafter, this ultrasonic flowmeter will be described with reference to the block diagram of FIG.

  In FIG. 3, a fluid to be measured FLD (liquid, gas, gas, etc.) flows in the direction of the arrow through the measurement tube 2 having the measurement tube inner diameter (diameter) D. The ultrasonic flowmeter 1 includes an ultrasonic transducer A10 that emits and receives ultrasonic waves provided on the outer periphery of the measurement tube 2, and an ultrasonic transducer A10 provided on the outer periphery on the downstream side of the ultrasonic transducer A10. An ultrasonic transducer B11 having a function of receiving ultrasonic waves and emitting ultrasonic waves, a transmission circuit 30 for outputting a trigger signal for emitting ultrasonic waves from the ultrasonic transducers A10 and B11, and ultrasonic transducers A10 and B11. Includes a receiving circuit 40 for amplifying the received ultrasonic signal.

  Furthermore, the ultrasonic flowmeter 1 includes an A / B that converts ultrasonic signals received by the receiving circuit 40 into a digital signal, a switching circuit 20 that switches connection between the ultrasonic transducers A10 and B11, the transmitting circuit 30, and the receiving circuit 40. A D conversion circuit 50, a correlation calculation means 60 for calculating a discretized correlation value based on the digital signal generated by the A / D conversion circuit 50, and a flow velocity for obtaining a flow velocity from the correlation value calculated by the correlation calculation means 60 Measuring means 80 and switching determination means 70 for controlling the timing of ultrasonic transmission from the transmission circuit 30 and controlling switching of the switching circuit 20 are provided. Note that the ultrasonic transducer B11 may be provided at the same position as the ultrasonic transducer A10 (illustrated by a solid line) or at an opposing position as indicated by a dotted line.

  The connection of the switching circuit 20 in the measuring means (first flow rate measuring means) using the propagation time difference method is such that the ultrasonic transducer A10 and the transmitting circuit 30 are connected with the switching circuit 20 on the AS side so that the ultrasonic transducers A10 and B11 are used. And the ultrasonic transducer B11 and the receiving circuit 40 are connected to the BR side, and then the ultrasonic transducer B11 and the transmitting circuit 30 are connected to the BS side and the ultrasonic transducer A10 is connected to the AR side. And the receiving circuit 40 are connected.

  Thus, the ultrasonic signal CT emitted from the ultrasonic transducer A10 propagates through the fluid to be measured FLD, is reflected by the inner wall of the measuring tube 2, and is received by the ultrasonic transducer B11. Thereafter, on the contrary, the ultrasonic signal CT emitted from the ultrasonic transducer B11 propagates through the fluid to be measured FLD, is reflected by the inner wall of the measuring tube 2, and is received by the ultrasonic transducer A10.

  The connection of the switching circuit 20 in the measurement means (second flow rate measuring means) by the reflection correlation method is performed by connecting the ultrasonic transducer A10 and the transmission circuit 30 with the switching circuit 20 set to the AS side so that only the ultrasonic transducer A10 is used. The ultrasonic transducer A10 and the receiving circuit 40 are connected to the AR side.

  Thereby, the ultrasonic signal CH emitted from the ultrasonic transducer A10 is reflected by the ultrasonic reflector PT in the fluid to be measured FLD, and the reflected ultrasonic signal is received by the same ultrasonic transducer A10.

  In the case of measurement using the propagation time difference method, the correlation calculation means 60 converts the ultrasonic signal received by the ultrasonic transducer B11 and the ultrasonic transducer A10 (hereinafter, referred to as “propagation time difference type ultrasonic reception signal”) into a digital signal. On the other hand, a cross-correlation operation is performed to obtain a correlation value (hereinafter referred to as “first correlation value”). Then, the flow velocity measuring means 80 obtains a time difference at which the first correlation value is maximized, and uses the time difference, the sound velocity of the ultrasonic signal, and the angle in the traveling direction of the ultrasonic signal (hereinafter referred to as “flow velocity of the fluid under measurement”). 1st flow velocity "). The first flow velocity is the (first) average flow velocity of the fluid to be measured FLD in the measurement tube 2.

  Further, in the case of measurement by the reflection correlation method, the correlation calculation means 60 emits an ultrasonic signal from the ultrasonic transducer A10 at a fixed time interval twice or more, and for the digital signal of the ultrasonic reception signal received by itself, A cross-correlation calculation is performed to obtain a correlation value (hereinafter referred to as “second correlation value”). Then, the flow velocity measuring means 80 obtains the flow velocity of the fluid to be measured FLD (hereinafter referred to as “second flow velocity”) from the second correlation value. The second flow velocity is the (second) average flow velocity of the fluid to be measured FLD in the measurement tube 2.

  The switching determination means 70 sets the switching circuit 20 to the connection of the propagation time difference method if the intensity of the ultrasonic reception signal of the propagation time difference method or the first correlation value is larger than a predetermined value, and switches the switching circuit 20 if the intensity is less than the predetermined value. The flow rate is measured by either one of the measurement methods using the reflection correlation method.

  The predetermined value (hereinafter referred to as “measurement method switching value”) is a threshold value for switching to one of the measurement methods suitable for the ultrasonic flow rate measurement and the reflection correlation method. It is.

  That is, when the number of ultrasonic reflectors PT is small, measurement by the propagation time difference method is suitable. In this case, since the propagation of ultrasonic signals is small and the waveforms of ultrasonic reception signals are similar, the first correlation value is Intensity such as the amplitude of the ultrasonic reception signal increases.

  In addition, when the number of ultrasonic reflectors PT is large, measurement by the reflection correlation method is suitable. In this case, the first correlation value is decreased, and the intensity of the ultrasonic reception signal is also decreased.

JP 2005-181268 A

  When the flow rate is measured by the propagation time difference method, the flow rate is obtained by multiplying the first flow rate by the flow rate correction coefficient and the measurement pipe inner diameter D. This flow rate correction coefficient is a value calculated from a millet equation, a Birgel equation, or the like based on empirical values.

  There are individual differences (differences) in the surface roughness of the measurement tube 2 due to differences in manufacturing conditions of the measurement tube 2. Further, the surface roughness of the measuring tube 2 may change during the flow rate measurement due to corrosion of the measuring tube 2 or adhesion to the measuring tube 2. However, since the surface roughness is not reflected in the flow rate correction coefficient, there is a problem that an error occurs in the flow rate by the propagation time difference method obtained using the flow rate correction coefficient due to individual differences or changes in the surface roughness.

  In addition, due to this error, there is a problem that the flow rate output changes (shifts) when the propagation time difference method and the reflection correlation method are switched to each other.

  An object of the present invention is to provide an ultrasonic flowmeter that obtains a more accurate flow rate correction coefficient corresponding to the surface roughness and performs highly accurate flow rate measurement using the coefficient.

In order to achieve such an object, the invention of claim 1
Based on the first correlation value of the ultrasonic signal propagated through the fluid to be measured in the measurement tube from one ultrasonic transducer to the other ultrasonic transducer or the intensity of the propagated ultrasonic signal, the first correlation value is based on the first correlation value. In the ultrasonic flowmeter for calculating the flow rate based on either the measurement of the first flow velocity of the fluid to be measured or the measurement of the second flow velocity based on the second correlation value of the ultrasonic signal reflected by the ultrasonic reflector,
Flow rate correction coefficient determining means for obtaining a flow rate correction coefficient from the surface roughness coefficient of the measurement tube based on the ratio of the measured first and second flow rates;
A flow rate calculating means for determining a flow rate of the fluid under measurement using the flow rate correction coefficient of the flow rate correction coefficient determining means and the first flow velocity;
With
The flow rate correction coefficient determining means includes
A surface roughness coefficient calculating means for determining the surface roughness coefficient based on a first Reynolds number determined from the second flow velocity and a division result obtained by dividing the second flow velocity by the first flow velocity;
Flow rate correction coefficient calculating means for determining the flow rate correction coefficient based on the surface roughness coefficient determined by the surface roughness coefficient calculating means and the second Reynolds number determined from the first flow velocity;
It is characterized by comprising .
The invention of claim 2 is the invention of claim 1,
The surface roughness coefficient calculation means obtains the first pipe friction coefficient of the measuring tube from the division result, along with determining the surface roughness coefficient from said first Reynolds number and the first pipe friction coefficient,
The flow rate correction coefficient calculating means obtains a second pipe friction coefficient of the measuring tube from the second Reynolds number and the surface roughness coefficient, and obtains the flow rate correction coefficient from the second pipe friction coefficient.
It is characterized by that.
The invention of claim 3 is the invention of claim 2 ,
The surface roughness coefficient is a ratio between the surface roughness value of the measuring tube and the inner diameter of the measuring tube, and the surface roughness coefficient calculating means obtains the surface roughness coefficient using the Colebrook equation. Features.
The invention of claim 4 is the invention according to any one of claims 1 to 3 ,
Storage means for storing a flow rate correction coefficient obtained in advance by the flow rate correction coefficient determining means,
The flow rate calculation means uses a flow rate correction coefficient of the storage means.

  According to the present invention, the flow rate correction coefficient determining means obtains the surface roughness coefficient of the measuring tube based on the ratio between the first and second flow velocities, and obtains the flow rate correction coefficient from the surface roughness coefficient, thereby obtaining the surface roughness. A more accurate flow rate correction coefficient corresponding to the above can be obtained.

  Further, the flow rate calculation means obtains the flow rate by using the flow rate correction coefficient, thereby suppressing the occurrence of flow rate error due to the propagation time difference method and performing highly accurate flow rate measurement.

  Further, since the occurrence of errors can be suppressed, a change (shift) in the flow rate output can be suppressed when the propagation time difference method and the reflection correlation method are switched between each other.

  An embodiment according to the present invention will be described with reference to FIG. FIG. 1 is a configuration diagram of an ultrasonic flowmeter 100 according to the present invention, and the same components as those in FIG. 3 (background art) are denoted by the same reference numerals and description thereof is omitted.

  In FIG. 1, an ultrasonic flowmeter 100 includes an ultrasonic transducer A10, an ultrasonic transducer B11, a switching circuit 20, a transmission circuit 30, a reception circuit 40, an A / D conversion circuit 50, a correlation calculation means 60, a switching determination means 70, and The flow velocity measuring means 80 is provided, and the configuration and operation thereof are the same as those in the background art.

  In addition to these configurations, the ultrasonic flowmeter 100 according to the present embodiment includes a flow rate correction coefficient determination unit 110, a flow rate calculation unit 120, and a storage unit 130. The flow rate correction coefficient determining unit 110 includes a surface roughness coefficient calculating unit 111 having a first pipe friction coefficient calculating unit 112 and a flow rate correction coefficient calculating unit 115 having a second pipe friction coefficient calculating unit 116.

  The flow rate correction coefficient determination unit 110 receives the first flow rate and the second flow rate from the flow rate measurement unit 80 and outputs the obtained flow rate correction coefficient to the flow rate calculation unit 120 and the storage unit 130.

  The surface roughness coefficient calculation unit 111 receives the first flow velocity and the second flow velocity, and outputs the calculated surface roughness coefficient to the flow rate correction coefficient calculation unit 115. The first pipe friction coefficient calculating unit 112 calculates the first pipe friction coefficient of the measuring pipe 2 used by the surface roughness coefficient calculating unit 111.

  The flow rate correction coefficient calculation unit 115 receives the first flow velocity and the surface roughness coefficient, and outputs the obtained flow rate correction coefficient to the flow rate calculation unit 120 and the storage unit 130. The second pipe friction coefficient calculating means 116 calculates the second pipe friction coefficient of the measuring pipe 2 used by the flow rate correction coefficient calculating means 115.

  The flow rate calculation unit 120 receives the flow rate correction coefficient from the flow rate correction coefficient determination unit 110 or the storage unit 130 and the first flow rate from the flow rate measurement unit 80, outputs the obtained flow rate of the measured fluid FLD to the outside, and displays the display unit ( (Not shown). In addition, the storage unit 130 stores the received flow rate correction coefficient, and outputs the stored flow rate correction coefficient to the flow rate calculation unit 120.

  Next, the operation of the flow rate correction coefficient determination unit 110, which is a feature of the present embodiment, will be mainly described with reference to the operation flowchart of FIG. The first and second correlation values are Sk1, Sk2, the first and second flow velocities are V1, V2, the first and second pipe friction coefficients are fr1, fr2, the first and second Reynolds numbers are Re1, Re2, The surface roughness coefficient is represented by rp, and the flow rate correction coefficient is represented by Cor.

  In FIG. 2, the switching circuit 20 is connected in the propagation time difference method, the correlation calculating means 60 obtains the first correlation value Sk1, and the flow velocity measuring means 80 obtains the first flow velocity V1 (step S10). Thereafter, the switching circuit 20 is connected in the reflection correlation method, the correlation calculating means 60 obtains the second correlation value Sk2, and the flow velocity measuring means 80 obtains the second flow velocity V2 (step S20).

  Below, the outline | summary of the flow volume correction coefficient determination process P1 by the flow volume correction coefficient determination means 110 is demonstrated. The flow rate correction coefficient determination process P1 includes steps S30 and S40, a surface roughness coefficient calculation process P1a by the surface roughness coefficient calculation unit 111, and a flow rate correction coefficient calculation process P1b by the flow rate correction coefficient calculation unit 115. The surface roughness coefficient calculation process P1a includes steps S50 to S70, and the flow rate correction coefficient calculation process P1b includes steps S80 to S100.

  Step S40 and subsequent steps of the flow rate correction coefficient determination process P1 are preferably performed in a state where measurement by the propagation time difference method and the reflection correlation method is possible. Therefore, when the first correlation value Sk1 is greater than or equal to the first predetermined value or greater than the first predetermined value and the second correlation value Sk2 is greater than or equal to the second predetermined value or greater than the second predetermined value (“Yes” in step S30) ), The process proceeds to step S40. If not (“No” in step S30), the measurement is terminated.

  The first predetermined value is a threshold value for determining that measurement by the propagation time difference method is possible and that the device is operating properly. The second predetermined value is a threshold value for determining that measurement by the reflection correlation method is possible and that the device is operating properly.

  After shifting to step S40, the flow rate correction coefficient determination unit 110 obtains a ratio between the first flow velocity V1 and the second flow velocity V2 (hereinafter referred to as “flow velocity ratio”) (step S40).

  Thereafter, the surface roughness coefficient calculation process P1a is performed to determine the surface roughness coefficient rp based on the flow rate ratio, and the flow rate correction coefficient calculation process P1b is performed to determine the flow rate correction coefficient Cor from the surface roughness coefficient rp.

  Specifically, in the surface roughness coefficient calculation process P1a, the surface roughness coefficient calculation unit 111 calculates the first Reynolds number Re1 obtained from the first flow velocity V1 or the second flow velocity V2 (step S60), and the first Reynolds number Re1. The surface roughness coefficient rp is obtained based on the flow rate ratio (the division result obtained by dividing the second flow rate V2 by the first flow rate V1) (step S70).

  In the flow rate correction coefficient calculation process P1b, the flow rate correction coefficient calculation unit 115 obtains the second Reynolds number Re2 from the first flow velocity V1 (step S80), and based on the second Reynolds number Re and the surface roughness coefficient rp. A flow rate correction coefficient Cor is obtained (step S100).

  The outline of the flow rate correction coefficient determination process P1, the surface roughness coefficient calculation process P1a, and the flow rate correction coefficient calculation process P1b has been described above. Next, a more detailed description will be given using equations.

  The velocity distribution v (y) of the flow velocity of the fluid to be measured FLD obtained by the propagation time difference method and the reflection correlation method is obtained by the logarithmic velocity distribution equation of the following equation (1).

  In Expression (1), y is a coordinate in the radial direction from the center inside the measurement tube 2, vmax is a maximum flow velocity, vt is a friction velocity, kr is a Kalman constant, and a is a radius inside the measurement tube 2.

  In step S10, the first flow velocity V1 is obtained by substituting v (y) in the equation (1) into the following equation (2). The first flow velocity V1 is obtained by integrating the flow velocity distribution v (y) by y and dividing by a (corresponding to the average value of the flow velocity distribution).

  In step S20, the second flow velocity V2 is obtained by substituting v (y) in the equation (1) into the following equation (3). The second flow velocity V2 is obtained by integrating the flow velocity distribution v (y) by y (corresponding to the flow rate) and dividing it by the cross-sectional area inside the measurement tube 2.

  When the pipe friction coefficient is fr, vmax (maximum flow velocity) is obtained by the following equation (4).

  Moreover, vt (friction speed) is calculated | required by following formula (5).

  Note that equation (1) is a logarithmic velocity distribution equation, but other velocity distributions such as an exponential velocity distribution may be used.

  Since step S30 has been described above, a description thereof will be omitted. In step S40, the flow rate correction coefficient determination unit 110 calculates the flow rate ratio, that is, the division result K obtained by dividing the second flow rate V2 by the first flow rate V1 by the following equation (6) using equations (1) to (5). Can be sought.

  Here, when the Kalman constant kr is 0.4, the equation (6) becomes the following equation (7).

  In step S50, the first pipe friction coefficient calculation means 112 of the surface roughness coefficient calculation means 111 obtains the first pipe friction coefficient fr1 from the division result K. That is, the pipe friction coefficient fr is obtained by substituting the division result K into K in the equation (7), and this is set as the first pipe friction coefficient fr1.

  In step S60, the surface roughness coefficient calculation unit 111 obtains the first Reynolds number Re1 from the first flow velocity V1 or the second flow velocity V2.

  In step S70, the surface roughness coefficient calculation unit 111 obtains the surface roughness coefficient rp using, for example, the Colebrook equation of the following equation (8). That is, in Equation (8), the surface roughness coefficient rp is obtained by substituting the first pipe friction coefficient fr1 for fr and the first Reynolds number Re1 for Re.

  When the Colebrook equation is used, the surface roughness coefficient rp is a ratio between the surface roughness value e of the measurement tube 2 and the measurement tube inner diameter (diameter) D, that is, rp = e / D.

  In step S80, the flow rate correction coefficient calculating unit 115 obtains the second Reynolds number Re2 from the first flow velocity V1.

  In step S90, the second pipe friction coefficient calculation means 116 of the flow rate correction coefficient calculation means 115 obtains the second pipe friction coefficient fr2 from the second Reynolds number Re2 and the surface roughness coefficient rp. That is, the pipe friction coefficient fr is obtained by substituting the second Reynolds number Re2 into Re of the equation (8) and the surface roughness coefficient rp into rp, and this is set as the second pipe friction coefficient fr2.

  The flow rate correction coefficient Cor corresponds to the flow rate ratio (division result K) in equation (7). For this reason, in step S100, the flow rate correction coefficient calculating means 115 obtains the flow rate correction coefficient Cor (K) from the second pipe friction coefficient fr2 using the equation (7). That is, the flow rate correction coefficient Cor (K) is obtained by substituting the second pipe friction coefficient fr2 into fr of the expression (7). The above is the detailed description of the flow rate correction coefficient determination process P1.

  Next, in step S110, it is determined whether the intensity of the first correlation value Sk1 or the propagation time difference method ultrasonic wave reception signal is greater than the measurement method switching value.

  If it is larger (“Yes” in step S110), the measurement by the propagation time difference method is suitable, and therefore the process proceeds to step S120 in the flow rate calculation process P2, and the flow rate calculation means 120 determines the flow rate correction coefficient Cor and the first flow velocity V1. To determine the flow rate of the fluid to be measured FLD. That is, the flow rate can be obtained by multiplying the flow rate correction coefficient Cor, the first flow velocity V1, and the cross-sectional area inside the measurement tube 2.

  If it is small (“No” in step S110), the measurement by the reflection correlation method is suitable, and therefore the process proceeds to step S130 in the flow rate calculation process P2, and the flow rate calculation means 120 determines the second flow velocity V2 and the inside of the measurement tube 2 The flow rate can be obtained by multiplying by the cross-sectional area.

  According to the present embodiment, the flow rate correction coefficient determining means 110 obtains the surface roughness coefficient rp of the measuring tube 2 based on the ratio K between the first flow velocity V1 and the second flow velocity V2 (step S70 in FIG. 2). By obtaining the flow rate correction coefficient Cor from the surface roughness coefficient rp (step S100), a more accurate flow rate correction coefficient Cor corresponding to the surface roughness can be obtained.

  Furthermore, the flow rate calculation unit 120 obtains the flow rate using the flow rate correction coefficient Cor (step S120), thereby suppressing the occurrence of flow rate error due to the propagation time difference method, and performing highly accurate flow rate measurement. Can do.

  Further, since the occurrence of errors can be suppressed, a change (shift) in the flow rate output can be suppressed when the propagation time difference method and the reflection correlation method are switched between each other.

Also,
(1) The flow rate correction coefficient calculating means 115 obtains the second Reynolds number Re2 from the first flow velocity V1 (step S80), and obtains the flow rate correction coefficient Cor based on the second Reynolds number Re2 and the surface roughness coefficient rp ( Step S100), that is, since the flow rate correction coefficient Cor is obtained using the second Reynolds number Re2 reflected by the first flow rate V1 (flow rate by the propagation time difference method), even if the first flow rate V1 changes, it responds to this change. In addition, a more accurate flow rate correction coefficient Cor can be obtained.

  (2) The surface roughness coefficient calculation unit 111 can determine the surface roughness coefficient rp using the Colebrook equation of equation (8) (step S70). In this case, the surface roughness coefficient rp is a ratio (rp = e / D) between the surface roughness value e of the measurement tube 2 and the inner diameter (diameter) D of the measurement tube, and is a dimensionless quantity. The first pipe friction coefficient fr1 which is a dimensionless amount obtained by the calculation means 112 can be used in the equation (8).

  In addition to the above embodiment, as an example using the storage unit 130, the storage unit 130 receives and stores the flow rate correction coefficient Cor previously obtained by the flow rate correction coefficient determination unit 110. Then, the flow rate calculation unit 120 receives the stored flow rate correction coefficient Cor from the storage unit 130, and obtains the flow rate of the fluid to be measured FLD using the flow rate correction coefficient Cor and the first flow velocity V1 (step S120 in FIG. 2). .

  As described above, since the storage unit 130 stores the flow rate correction coefficient Cor in advance, it is not necessary to perform the flow rate correction coefficient determination process P1 of FIG. The processing burden can be reduced.

  Correlation calculation means 60, switching determination means 70, flow velocity measurement means 80, flow rate correction coefficient determination means 110, surface roughness coefficient calculation means 111, first pipe friction coefficient calculation means 112, flow rate correction coefficient calculation means 115, second The pipe friction coefficient calculating unit 116 and the flow rate calculating unit 120 may be realized by a processor such as a CPU that executes a program, or may be realized by a logic circuit or the like.

  In addition, this invention is not limited to the above-mentioned Example, In the range which does not deviate from the essence, many change and deformation | transformation are included. Moreover, combinations other than the combination of each means mentioned above can be included.

It is an example of the block diagram of the ultrasonic flowmeter to which this invention is applied. It is an example of the operation | movement flowchart figure of the ultrasonic flowmeter of FIG. It is an example of the block diagram of the ultrasonic flowmeter shown by background art.

Explanation of symbols

2 Measuring tube 10 Ultrasonic transducer A
11 Ultrasonic transducer B
DESCRIPTION OF SYMBOLS 20 Switching circuit 30 Transmitting circuit 40 Receiving circuit 50 A / D conversion circuit 60 Correlation calculating means 70 Switching determination means 80 Flow velocity measuring means 100 Ultrasonic flow meter 110 Flow rate correction coefficient determining means 111 Surface roughness coefficient calculating means 112 Coefficient calculation means 115 Flow rate correction coefficient calculation means 116 Second pipe friction coefficient calculation means 120 Flow rate calculation means 130 Storage means

Claims (4)

Based on the first correlation value of the ultrasonic signal propagated through the fluid to be measured in the measurement tube from one ultrasonic transducer to the other ultrasonic transducer or the intensity of the propagated ultrasonic signal, the first correlation value is used. In the ultrasonic flowmeter for calculating the flow rate based on either the measurement of the first flow velocity of the fluid to be measured or the measurement of the second flow velocity based on the second correlation value of the ultrasonic signal reflected by the ultrasonic reflector,
Flow rate correction coefficient determining means for obtaining a flow rate correction coefficient from the surface roughness coefficient of the measurement tube based on the ratio of the measured first and second flow rates;
A flow rate calculating means for determining a flow rate of the fluid under measurement using the flow rate correction coefficient of the flow rate correction coefficient determining means and the first flow velocity;
With
The flow rate correction coefficient determining means includes
A surface roughness coefficient calculating means for determining the surface roughness coefficient based on a first Reynolds number determined from the second flow velocity and a division result obtained by dividing the second flow velocity by the first flow velocity;
Flow rate correction coefficient calculating means for determining the flow rate correction coefficient based on the surface roughness coefficient determined by the surface roughness coefficient calculating means and the second Reynolds number determined from the first flow velocity;
An ultrasonic flowmeter comprising: The surface roughness coefficient calculation means obtains the first pipe friction coefficient of the measuring tube from the division result, along with determining the surface roughness coefficient from the the first Reynolds number and the first pipe friction coefficient,
The flow rate correction coefficient calculating means obtains a second pipe friction coefficient of the measuring tube from the second Reynolds number and the surface roughness coefficient, and obtains the flow rate correction coefficient from the second pipe friction coefficient.
The ultrasonic flowmeter according to claim 1 . The surface roughness coefficient is a ratio between the surface roughness value of the measuring tube and the inner diameter of the measuring tube,
The ultrasonic flowmeter according to claim 2 , wherein the surface roughness coefficient calculating means obtains the surface roughness coefficient using a Colebrook equation. Storage means for storing a flow rate correction coefficient obtained in advance by the flow rate correction coefficient determining means,
Ultrasonic flowmeter according to any one of claims 1 to 3, which comprises using a flow rate correction coefficient of the flow rate calculation means said memory means.

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