JP2014157129A - Ultrasonic flow meter, and ultrasonic wave absorbing material for ultrasonic flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an ultrasonic flow meter capable of accurately measuring a flow rate of gas; and an ultrasonic wave absorbing material for an ultrasonic flow meter.SOLUTION: An ultrasonic flow meter 100 includes: a first ultrasonic transmitter-receiver 20A which is provided in an outer periphery on the upstream side of a pipe A in which gas flows, and transmits and receives an ultrasonic wave; a second ultrasonic transmitter-receiver 20B which is provided in the outer periphery on the downstream side of the pipe A and transmits and receives an ultrasonic wave; a body part 50 which measures a flow rate of the gas on the basis of the time from transmission of an ultrasonic wave from the first ultrasonic transmitter-receiver 20A to reception in the second ultrasonic transmitter-receiver 20B and the time from transmission of an ultrasonic wave from the second ultrasonic transmitter-receiver 20B to reception in the first ultrasonic transmitter-receiver 20A; an ultrasonic wave absorbing material 10 which is provided in the outer periphery of the pipe A and absorbs ultrasonic waves propagating in the pipe A. The ultrasonic wave absorbing material 10 contains uncrosslinked butyl rubber.

Description

  Some embodiments according to the present invention relate to an ultrasonic flowmeter that measures a flow rate of a fluid flowing through a pipe using ultrasonic waves and an ultrasonic absorber for the ultrasonic flowmeter.

  Conventionally, as this type of ultrasonic flowmeter, one or more ultrasonic transducers constituted by an ultrasonic transducer and a bevel wedge are installed on the outer periphery of a pipe through which fluid flows, and the flow direction of the fluid and It is known that when an ultrasonic wave is propagated in the opposite direction, each propagation time is measured, and the measurement control unit calculates and outputs the flow rate of the fluid based on the propagation time (see, for example, Patent Document 1). .

Japanese Patent No. 3216769

  By the way, the ultrasonic wave emitted from the ultrasonic transducer is divided into a fluid propagation wave propagating through the fluid flowing through the pipe and a pipe propagation wave reflecting off the pipe wall of the pipe and propagating through the pipe. In the conventional ultrasonic flowmeter, the fluid propagation wave is a signal (signal component) to be detected, and the pipe propagation wave is noise (noise component) with respect to the signal.

  However, the conventional ultrasonic flowmeter cannot sufficiently reduce the energy (magnitude or strength) of the pipe propagation wave relative to the energy (magnitude or intensity) of the fluid propagation wave. It was difficult to distinguish from waves. Therefore, there is a possibility that the conventional ultrasonic flowmeter erroneously measures the flow rate of the fluid.

  Some aspects of the present embodiment have been made in view of the above-described problems, and provide an ultrasonic flowmeter capable of accurately measuring a gas flow rate and an ultrasonic absorber for the ultrasonic flowmeter. This is one of the purposes.

  An ultrasonic flowmeter according to the present invention is provided on the outer periphery on the upstream side in a pipe through which gas flows, and includes a first ultrasonic transmission / reception unit that transmits and receives ultrasonic waves, and an outer periphery on the downstream side in the above-described pipe A second ultrasonic transmission / reception unit that transmits and receives ultrasonic waves, and a time until the second ultrasonic transmission / reception unit receives ultrasonic waves transmitted from the first ultrasonic transmission / reception unit, A main body for measuring the flow rate of the gas based on the time until the ultrasonic wave transmitted from the second ultrasonic wave transmitting / receiving unit is received by the first ultrasonic wave transmitting / receiving unit; And an ultrasonic absorber that absorbs a pipe propagation wave through which the ultrasonic wave propagates through the pipe. The ultrasonic absorber includes uncrosslinked butyl rubber.

  According to this configuration, the ultrasonic absorber includes the ultrasonic absorber that is provided on the outer periphery of the pipe and absorbs the pipe propagation wave through which the ultrasonic wave propagates through the pipe, and the ultrasonic absorber includes uncrosslinked butyl rubber. Here, uncrosslinked butyl rubber has an acoustic impedance value close to that of the pipe material, and has a high ability to absorb vibrations in the ultrasonic frequency band (absorption performance). Thereby, the ultrasonic absorber can attenuate the pipe propagation wave in the process of propagating the pipe, and the energy (magnitude, size) of the pipe propagation wave reaching the first ultrasonic transmission / reception unit and the second ultrasonic transmission / reception unit. Or intensity) can be made sufficiently smaller than the energy (magnitude or intensity) of the gas propagation wave, that is, the SN ratio can be improved.

  Uncrosslinked butyl rubber is also a viscoelastic body having adhesiveness and elasticity. As a result, since the ultrasonic absorber is easy to adhere, it can be fixed in close contact with the outer periphery of the pipe, and the ultrasonic absorber is easily deformed by elasticity, so it can be applied to pipes of various materials, shapes, and surface conditions. It can be easily provided.

  Furthermore, it has been confirmed through experiments and the like that uncrosslinked butyl rubber has sufficient durability (environmental resistance) with respect to, for example, temperature and humidity in the usage environment of the ultrasonic flowmeter. Thereby, the ultrasonic absorber can utilize uncrosslinked butyl rubber without performing crosslinking (vulcanization) using sulfur or the like in order to enhance strength and environmental resistance.

  Preferably, the ultrasonic absorber further includes predetermined mixed particles mixed with uncrosslinked butyl rubber.

  According to this configuration, the ultrasonic absorber further includes predetermined mixed particles mixed with uncrosslinked butyl rubber. As a result, unmixed butyl rubber is used as the predetermined mixed particles, which have an acoustic impedance value close to that of the piping material and / or improve the ability to absorb vibrations in the ultrasonic frequency band (absorption performance). By mixing with the ultrasonic absorber, the SN ratio can be further improved.

  Preferably, the predetermined mixed particles are tungsten.

  According to this configuration, the predetermined mixed particles are tungsten. Thereby, an ultrasonic absorber that further improves the SN ratio can be easily realized (configured).

  Preferably, the predetermined mixed particles are ferrite.

  According to this configuration, the predetermined mixed particles are ferrite. Thereby, an ultrasonic absorber that further improves the SN ratio can be easily realized (configured).

  Preferably, the predetermined mixed particles are barium sulfate.

  According to this configuration, the predetermined mixed particles are barium sulfate. Thereby, an ultrasonic absorber that further improves the SN ratio can be easily realized (configured).

  The ultrasonic absorber for an ultrasonic flowmeter according to the present invention includes a time until the ultrasonic wave transmitted from the outer periphery on the upstream side in the pipe through which gas flows is received on the outer periphery on the downstream side in the pipe described above. The ultrasonic flowmeter for measuring the flow rate of the gas based on the time until the ultrasonic wave transmitted from the downstream outer periphery of the pipe is received by the upstream outer periphery of the pipe. A sound absorber, which is provided on the outer periphery of the pipe, absorbs the pipe propagation wave propagating through the pipe, and includes uncrosslinked butyl rubber.

  According to such a configuration, the ultrasonic wave is provided on the outer periphery of the above-described pipe, the above-described ultrasonic wave absorbs the pipe propagation wave propagating through the above-described pipe, and includes uncrosslinked butyl rubber. Here, uncrosslinked butyl rubber has an acoustic impedance value close to that of the pipe material, and has a high ability to absorb vibrations in the ultrasonic frequency band (absorption performance). As a result, the ultrasonic absorber can attenuate the pipe propagation wave in the process of propagating the pipe, and the received pipe propagation wave energy (magnitude or strength) is changed to the gas propagation wave energy (magnitude, Or the strength), that is, the SN ratio can be improved.

  Uncrosslinked butyl rubber is also a viscoelastic body having adhesiveness and elasticity. Thereby, since the ultrasonic absorber is easy to adhere, it can be closely attached and fixed to the outer periphery of the pipe, and the ultrasonic absorber is easily deformed by elasticity, so that the pipe A having various materials, shapes, and surface states. Can be easily provided.

  Furthermore, it has been confirmed through experiments and the like that uncrosslinked butyl rubber has sufficient durability (environmental resistance) with respect to, for example, temperature and humidity in the usage environment of the ultrasonic flowmeter. Thereby, the ultrasonic absorber can utilize uncrosslinked butyl rubber without performing crosslinking (vulcanization) using sulfur or the like in order to enhance strength and environmental resistance.

  According to the ultrasonic flowmeter of the present invention, the ultrasonic absorber can attenuate the pipe propagation wave in the process of propagating the pipe, and the pipe reaches the first ultrasonic transmission / reception unit and the second ultrasonic transmission / reception unit. The energy (magnitude or intensity) of the propagating wave can be made sufficiently smaller than the energy (magnitude or intensity) of the gas propagating wave, that is, the SN ratio can be improved. Therefore, the ultrasonic flowmeter can easily distinguish between the gas propagation wave and the pipe propagation wave, and can accurately measure the gas flow rate. In particular, when the pressure of the gas flowing inside the pipe is low, the energy (magnitude or strength) of the gas propagation wave is relatively small, but the ultrasonic absorber has an SN ratio even when the gas pressure is low. Therefore, the ultrasonic flowmeter can accurately measure the flow rate of a gas having a low pressure.

  According to the ultrasonic absorber for the ultrasonic flowmeter of the present invention, the ultrasonic absorber can attenuate the pipe propagation wave in the process of propagating the pipe, and the received pipe propagation wave energy (magnitude) , Or intensity) can be made sufficiently smaller than the energy (magnitude or intensity) of the gas propagating wave, that is, the SN ratio can be improved. Therefore, the ultrasonic flowmeter can easily distinguish between the gas propagation wave and the pipe propagation wave, and can accurately measure the gas flow rate. In particular, when the pressure of the gas flowing inside the pipe is low, the energy (magnitude or strength) of the gas propagation wave is relatively small, but the ultrasonic absorber has an SN ratio even when the gas pressure is low. Therefore, the ultrasonic flowmeter can accurately measure the flow rate of a gas having a low pressure.

It is a block diagram which shows an example of schematic structure of an ultrasonic flowmeter. It is an expanded sectional view explaining the structure of the 1st ultrasonic transmission / reception part shown in FIG. It is a sectional side view for demonstrating the calculation method of the flow volume of the gas which flows through the inside of piping. It is sectional drawing for demonstrating a mode that the ultrasonic wave transmitted from the 1st ultrasonic wave transmission / reception part is received by the 2nd ultrasonic wave transmission / reception part. 3 is a graph of a reception signal output from the reception circuit unit illustrated in FIG. 1. 3 is a graph of a reception signal output from the reception circuit unit illustrated in FIG. 1. It is a graph of the received signal of a virtual ultrasonic flowmeter provided with another ultrasonic absorber. It is a table | surface which shows the S / N ratio of the ultrasonic absorber of various materials. It is a table | surface which shows the S / N ratio of an ultrasonic absorber. It is a block diagram which shows the other example of schematic structure of an ultrasonic flowmeter.

  Embodiments of the present invention will be described below. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. Therefore, specific dimensions and the like should be determined in light of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings. In the following description, the upper side of the drawing is referred to as “upper”, the lower side as “lower”, the left side as “left”, and the right side as “right”.

  1 to 10 show an embodiment of an ultrasonic flowmeter and an ultrasonic absorber for an ultrasonic flowmeter according to the present invention. FIG. 1 is a configuration diagram illustrating an example of a schematic configuration of the ultrasonic flowmeter 100. As shown in FIG. 1, the ultrasonic flowmeter 100 is for measuring the flow rate of a gas (gas) flowing inside the pipe A. The gas that is the measurement target of the ultrasonic flowmeter 100 flows in the direction indicated by the white arrow in FIG. 1 (the direction from left to right in FIG. 1). The ultrasonic flowmeter 100 includes a first ultrasonic transmission / reception unit 20A, a second ultrasonic transmission / reception unit 20B, a main body unit 50, and an ultrasonic absorber 10.

  The first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B are provided on the outer periphery of the pipe A, respectively. In the example illustrated in FIG. 1, the first ultrasonic transmission / reception unit 20 </ b> A is disposed on the upstream side in the pipe A, and the second ultrasonic transmission / reception unit 20 </ b> B is disposed on the downstream side in the pipe A. The first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B transmit and receive ultrasonic waves, and transmit and receive ultrasonic waves to and from each other. That is, the ultrasonic wave transmitted by the first ultrasonic transmission / reception unit 20A is received by the second ultrasonic transmission / reception unit 20B, and the ultrasonic wave transmitted by the second ultrasonic transmission / reception unit 20B is received by the first ultrasonic transmission / reception unit 20A. Is done.

  FIG. 2 is an enlarged cross-sectional view for explaining the configuration of the first ultrasonic transmission / reception unit 20A shown in FIG. As shown in FIG. 2, the first ultrasonic transmission / reception unit 20 </ b> A includes a wedge 21 and a piezoelectric element 22.

  The wedge 21 is for making ultrasonic waves incident on the pipe A at a predetermined acute angle, and is a resin or metal member. The wedge 21 is installed such that the bottom surface 21 a contacts the outer peripheral surface of the pipe A. Further, the wedge 21 is formed with a slope 21b having a predetermined angle with respect to the bottom surface 21a. A piezoelectric element 22 is installed on the slope 21b.

  In the present embodiment, an example in which the bottom surface 21a is in contact with the outer peripheral surface of the pipe A is shown, but the present invention is not limited to this. A contact medium (coplant) may be interposed between the bottom surface 21a and the outer peripheral surface of the pipe A.

  The piezoelectric element 22 is for transmitting ultrasonic waves and receiving ultrasonic waves. A lead wire (not shown) is electrically connected to the piezoelectric element 22. When an electrical signal with a predetermined frequency is applied via the lead wire, the piezoelectric element 22 vibrates at the predetermined frequency and emits an ultrasonic wave. Thereby, an ultrasonic wave is transmitted. As indicated by the dashed arrows in FIG. 2, the ultrasonic wave transmitted from the piezoelectric element 22 propagates through the wedge 21 at an angle of the inclined surface 21b. The ultrasonic wave propagating through the wedge 21 is refracted at the interface between the wedge 21 and the outer wall of the pipe A to change the incident angle, and is further refracted and incident at the interface between the inner wall of the pipe A and the gas flowing in the pipe A. The angle changes and propagates through the gas. Since the refraction at the interface follows Snell's law, the angle of the inclined surface 21b is set in advance based on the speed of the ultrasonic wave when propagating through the pipe A and the speed of the ultrasonic wave when propagating through the gas. Can be incident on the gas at a desired incident angle and propagated.

  On the other hand, when the ultrasonic wave reaches the piezoelectric element 22, the piezoelectric element 22 vibrates at the frequency of the ultrasonic wave to generate an electric signal. Thereby, an ultrasonic wave is received. An electrical signal generated in the piezoelectric element 22 is detected by a main body 50 described later via a lead wire.

  The second ultrasonic transmission / reception unit 20B has the same configuration as the first ultrasonic transmission / reception unit 20A. That is, the second ultrasonic transmission / reception unit 20 </ b> B also includes a wedge 21 and a piezoelectric element 22. Therefore, the detailed description of the second ultrasonic transmission / reception unit 20B is omitted from the description of the first ultrasonic transmission / reception unit 20A.

  The main body 50 shown in FIG. 1 is for measuring the flow rate of the gas based on the time during which the ultrasonic wave propagates through the gas flowing inside the pipe A. The main body unit 50 includes a switching unit 51, a transmission circuit unit 52, a reception circuit unit 53, a timer unit 54, a calculation control unit 55, and an input / output unit 56.

  The switching unit 51 is for switching between transmission and reception of ultrasonic waves. The switching unit 51 is connected to the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B. The switching unit 51 can be configured to include, for example, a changeover switch. The calculation switching unit 51 switches the changeover switch based on a control signal input from the calculation control unit 55, and connects one of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B to the transmission circuit unit 52. In addition, the other of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is connected to the reception circuit unit 53. Thereby, one of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B transmits an ultrasonic wave, and the other of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B Ultrasound can be received.

  The transmission circuit unit 52 is for causing the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B to transmit ultrasonic waves. The transmission circuit unit 52 can be configured to include, for example, an oscillation circuit that generates a rectangular wave with a predetermined frequency, a drive circuit that drives the first ultrasonic transmission / reception unit 20A, and the second ultrasonic transmission / reception unit 20B. . In the transmission circuit unit 52, based on the control signal input from the arithmetic control unit 55, the first ultrasonic transmission / reception unit 20B and the second ultrasonic transmission / reception unit 20B using the rectangular wave generated by the oscillation circuit as a drive signal. Is output to one of the piezoelectric elements 22. Thereby, one piezoelectric element 22 of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is driven, and the piezoelectric element 22 transmits ultrasonic waves.

  The reception circuit unit 53 is for detecting the ultrasonic waves received by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B. The receiving circuit unit 53 can include, for example, an amplifier circuit that amplifies a signal with a predetermined gain (gain), a filter circuit that extracts an electric signal with a predetermined frequency, and the like. Based on the control signal input from the arithmetic control unit 55, the reception circuit unit 53 receives the electrical signal output from one piezoelectric element 22 of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B. Amplify, filter and convert to received signal. The reception circuit unit 53 outputs the converted reception signal to the calculation control unit 55.

  The timer 54 is for measuring time in a predetermined period. The timer unit 54 can be constituted by, for example, an oscillation circuit. Note that the oscillation circuit may be shared with the transmission circuit unit 52. The timer 54 measures the time by counting the number of reference waves of the oscillation circuit based on the start signal and stop signal input from the arithmetic control unit 55. The time measuring unit 54 outputs the measured time to the calculation control unit 55.

  The calculation control unit 55 is for calculating the flow rate of the gas flowing through the pipe A by calculation. The arithmetic control unit 55 can be configured by, for example, a CPU, a memory such as a ROM or a RAM, an input / output interface, or the like. The arithmetic control unit 55 controls each part of the main body unit 50 such as the switching unit 51, the transmission circuit unit 52, the reception circuit unit 53, the time measuring unit 54, and the input / output unit 56. Note that a method by which the arithmetic control unit 55 calculates the gas flow rate will be described later.

  The input / output unit 56 is for a user (user) to input information and to output information to the user. The input / output unit 56 can be configured by, for example, input means such as operation buttons, output means such as a display display, and the like. When the user operates an operation button or the like, various types of information such as settings are input to the arithmetic control unit 55 via the input / output unit 56. The input / output unit 56 displays and outputs information such as the gas flow rate, the gas velocity, and the integrated flow rate during a predetermined period calculated by the calculation control unit 55 on a display display or the like.

FIG. 3 is a side sectional view for explaining a method of calculating the flow rate of the gas flowing inside the pipe A. As shown in FIG. 3, the velocity (hereinafter referred to as the flow velocity) of the gas flowing in a predetermined direction (the direction from the left side to the right side in FIG. 3) inside the pipe A is V [m / s], and exceeds the inside of the gas. The velocity at which the sound wave propagates (hereinafter referred to as the sound velocity) is C [m / s], the propagation path length of the ultrasonic wave propagating through the gas is L [m], and the propagation axis of the pipe A and the ultrasonic wave of the pipe A Let θ be the angle formed with the path. Here, the first ultrasonic transmission / reception unit 20A installed on the upstream side (left side in FIG. 3) of the pipe A transmits the ultrasonic wave, and the second supersonic wave installed on the downstream side (right side in FIG. 3) of the pipe A. when the wave transmission and reception unit 20B receives the ultrasonic wave, the propagation time t ₁₂ to the ultrasonic wave propagates through the gas inside the pipe a is represented by the following formula (1).
t ₁₂ = L / (C + V cos θ) (1)

On the other hand, when the 2nd ultrasonic transmission / reception part 20B installed in the downstream of the piping A transmits an ultrasonic wave, the 1st ultrasonic transmission / reception part 20A installed in the upstream of the piping A receives the said ultrasonic wave. The propagation time t ₂₁ during which the ultrasonic wave propagates through the gas inside the pipe A is expressed by the following equation (2).
t ₂₁ = L / (C−V cos θ) (2)

From the equations (1) and (2), the gas flow velocity V is expressed by the following equation (3).
V = (L / 2 cos θ) · {(1 / t ₁₂ ) − (1 / t ₂₁ )} (3)

In the equation (3), the propagation path length L and the angle θ are known values before the flow rate is measured. Therefore, the flow velocity V is obtained by measuring the propagation time t ₁₂ and the propagation time t ₂₁ to obtain the equation (3). It can be calculated from

The flow rate Q [m ³ / s] of the gas flowing inside the pipe A is determined using the flow velocity V [m / s], the complement coefficient K and the cross-sectional area S [m ³ / s] of the pipe A. It is represented by the following formula (4).
Q = KVS (4)

Therefore, the arithmetic control unit 55 stores the propagation path length L, the angle θ, the complement coefficient K, and the cross-sectional area S of the pipe A in a memory or the like in advance. Then, the arithmetic control unit 55 measures the propagation time t ₁₂ and the propagation time t ₂₁ from the time measurement 54 based on the reception signal input from the reception circuit unit 53, thereby obtaining the expression (3) and the expression (4). The flow rate Q of the gas flowing inside the pipe A can be calculated.

  In this embodiment, the example in which the gas flow rate is calculated by the reciprocal propagation time method using FIG. 3 and equations (1) to (4) is shown, but the present invention is not limited to this. The arithmetic control unit 55 may calculate the gas flow rate by another method, for example, a known propagation time difference method.

  In the present embodiment, the ultrasonic wave transmitted by one of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20A propagates the gas inside the pipe A, and the first ultrasonic transmission / reception unit 20A and Although the example directly received by the other of the second ultrasonic transmission / reception unit 20A has been shown, the present invention is not limited to this. The ultrasonic wave propagating through the gas inside the pipe A can be reflected on the inner wall of the pipe A. Therefore, the other of the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20A may receive ultrasonic waves reflected 2n times (n is a positive integer) on the inner wall of the pipe A.

  The ultrasonic absorber 10 shown in FIG. 1 is provided on the outer peripheral surface of the pipe A. Specifically, the ultrasonic absorber 10 is disposed on the outer peripheral surface of the pipe A so as to cover at least a region between the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B. It is fixed in close contact with the outer peripheral surface. First ultrasonic transmission / reception unit 20A and second ultrasonic transmission / reception unit of ultrasonic absorber 10 such that first ultrasonic transmission / reception unit 20A and second ultrasonic transmission / reception unit 20B are in direct contact with the outer peripheral surface of pipe A. In the portion where 20B is arranged, a part of the ultrasonic absorber 10 is cut into a frame shape. The ultrasonic absorber 10 includes, as a main material, uncrosslinked, that is, uncrosslinked butyl rubber (IIR, a copolymer of isobutylene and isoprene).

FIG. 4 is a cross-sectional view for explaining how the ultrasonic wave transmitted from the first ultrasonic wave transmitting / receiving unit 20A is received by the second ultrasonic wave transmitting / receiving unit 20B. As shown in FIG. 4, for example, ultrasonic waves transmitted from the first ultrasonic transmitter-receiver 20A includes a gas propagating wave W ₁ which passes through the pipe A (transmitted) to propagating inside of the gas pipe A, pipe It is divided into a pipe propagation wave W ₂ that is reflected by the pipe wall of A and propagates through the pipe A. The gas propagation wave W ₁ again passes through the pipe A and reaches the second ultrasonic transmission / reception unit 20B. On the other hand, the pipe propagating wave W ₂ may also reach the second ultrasonic transmitter-receiver 20B while being reflected several times the inner and outer walls of the pipe A. Although illustration and detailed description thereof are omitted, the ultrasonic wave transmitted from the second ultrasonic wave transmitting / receiving unit 20A is also connected to the gas propagating wave W ₁ and the piping, similarly to the ultrasonic wave transmitted from the first ultrasonic wave transmitting / receiving unit 20A. The propagation wave W ₂ is divided into _two, and the gas propagation wave W ₁ passes through the pipe A and reaches the first ultrasonic transmission / reception unit 20A, and the pipe propagation wave W ₂ also reflects the inner wall and the outer wall of the pipe A multiple times. However, it can reach the first ultrasonic transmission / reception unit 20A.

  In general, whether a sound wave propagating through one medium is transmitted (passed) or reflected at an interface with the other medium is determined by a difference in acoustic impedance between the one medium and the other medium. In other words, the smaller the difference in acoustic impedance, the more the sound wave propagating in one configuration is transmitted to the other medium, and the greater the difference in acoustic impedance, the more acoustic wave propagating in one configuration is at the interface with the other medium. There is a tendency to reflect.

When the fluid flowing in the pipe A is, for example, a liquid, the difference between the acoustic impedance of the liquid and the acoustic impedance of the pipe material, for example, a metal such as stainless steel (SUS) or a polymer compound such as synthetic resin is Since the ultrasonic wave is relatively small, the ultrasonic wave transmits (passes) through the pipe A and propagates (flows) through the liquid flowing in the inside (transmission) is large (large), that is, the ratio of reflection on the pipe wall of the pipe A (reflection). rate) is small (small), the piping propagating wave W ₂ energy (size or strength) is small. On the other hand, the acoustic impedance of gas is small compared to the acoustic impedance of liquid. Therefore, when the fluid flowing inside the pipe A is a gas, the difference between the acoustic impedance of the gas and the acoustic impedance of the pipe A is relatively large, so that the ultrasonic wave transmits (passes) the pipe A. proportion of propagating liquid flowing inside (transmittance) less (small), i.e., ratio of reflected a tube wall of the pipe a (reflectance) many (large), the piping propagating wave W ₂ energy (size, (Or strength) is large.

Here, in the ultrasonic flowmeter that receives the ultrasonic gas propagation wave W ₁ , measures the propagation time, and measures the flow rate based on the propagation time, the gas propagation wave W ₁ is a signal to be detected (new synthesis) The pipe propagation wave W ₂ is noise (noise component) with respect to the signal. Therefore, the gas propagating wave W ₁ of the energy (size or strength) pipe propagating wave W ₂ of the energy (size or strength) with respect to the is not sufficiently small, the gas propagation wave W ₁ and the pipe propagating wave W Discrimination from ₂ becomes difficult. As a result, there is a possibility that the gas propagation wave W ₁ and the pipe propagation wave W ₂ will be mistaken and the measurement of the propagation time will be wrong, and the gas flow rate will be measured based on the incorrect propagation time.

The ultrasonic absorber 10 is provided on the outer periphery of the pipe A and absorbs the pipe propagation wave W ₂ propagating through the pipe A. Further, the ultrasonic absorption 10 includes uncrosslinked butyl rubber as described above. Here, uncrosslinked butyl rubber has an acoustic impedance value close to that of the material of the pipe A, and has a high ability to absorb vibrations in the ultrasonic frequency band (absorption performance). Thereby, the ultrasonic absorber 10 can attenuate the pipe propagating wave W ₂ in the process of propagating through the pipe A, reaches the first ultrasonic transmitter-receiver 20A and the second ultrasonic transmitter-receiver 20B, that is, The energy (magnitude or intensity) of the received pipe propagation wave W ₂ can be made sufficiently smaller than the energy (magnitude or intensity) of the gas propagation wave W ₁ , that is, the SN ratio can be improved. .

  Uncrosslinked butyl rubber is also a viscoelastic body having adhesiveness and elasticity. Thereby, since the ultrasonic absorber 10 is easy to adhere, it can be adhered and fixed to the outer periphery of the pipe A, and the ultrasonic absorber 10 is easily deformed by elasticity, so various materials, shapes, and surface states The pipe A can be easily provided.

  Furthermore, it has been confirmed through experiments and the like that uncrosslinked butyl rubber has sufficient durability (environmental resistance) with respect to, for example, temperature and humidity in the environment where the ultrasonic flowmeter 100 is used. Thereby, the ultrasonic absorber 10 can utilize uncrosslinked butyl rubber without performing crosslinking (vulcanization) using sulfur or the like in order to enhance strength and environmental resistance.

  In general, an ultrasonic wave means a sound wave having a frequency band of 20 [kHz] or higher. Therefore, the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B are sound waves in a frequency band of 20 [kHz] or higher. Preferably, the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B are ultrasonic waves in a frequency band of 100 [kHz] or more and 2.0 [MHz] or less. More preferably, the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B are ultrasonic waves in a frequency band of 0.5 [MHz] or more and 1.0 [MHz] or less. is there. In any case, the ultrasonic wave transmitted by the first ultrasonic transmission / reception unit 20A and the ultrasonic wave transmitted by the second ultrasonic transmission / reception unit 20B may be the same frequency or at different frequencies. There may be.

5 and 6 are graphs of received signals output from the receiving circuit unit 53 shown in FIG. 5 and 6, the horizontal axis represents time, and the vertical axis represents amplitude (voltage). 5 and 6, the upper graph is a graph in which the pressure of the gas flowing inside the pipe A is 0.5 [MPa], and the lower graph is the pressure of the gas flowing in the pipe A within 0.3 [MPa]. It is a graph of. Further, FIG. 5 is a graph in which the frequency of ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is 0.5 [MHz], and FIG. 6 shows the first ultrasonic transmission / reception unit 20A and It is a graph whose frequency of the ultrasonic wave which the 2nd ultrasonic transmission / reception part 20B transmits is 1.0 [MHz]. As shown in the upper graph of FIG. 5, the gas pressure is 0.5 [MPa], and the frequency of the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is 0. When the frequency is 5 [MHz], the ultrasonic absorber 10 can attenuate the pipe propagation wave W ₂ , and the arithmetic control unit 55 can generate the relatively large amplitude gas propagation wave W ₁ generated near the center of the graph. Can be identified and detected. Moreover, as shown in the upper graph of FIG. 6, the pressure of the gas is 0.5 [MPa], and the frequency of the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is 1. Similarly, in the case of 0.0 [MHz], the ultrasonic absorber 10 can attenuate the pipe propagation wave W ₂ , and the arithmetic control unit 55 propagates the gas having a relatively large amplitude generated near the center of the graph. The wave W ₁ can be identified and detected.

When the pressure of the gas flowing inside the pipe A is low, for example, when the pressure of the gas is lower than 0.5 [MPa], the acoustic impedance of the gas is proportional to the pressure. The energy (magnitude or intensity) of the gas propagation wave W ₁ is further reduced. However, when the pressure of the gas flowing through the pipe A is low, for example, even when the pressure of the gas is 0.3 [MPa], as shown in the lower graphs of FIGS. The absorber 10 can attenuate the pipe propagation wave W ₂ , and the arithmetic control unit 55 can identify and detect the gas propagation wave W ₁ having a relatively large amplitude generated near the center of the graph. Thus, the ultrasonic absorber 10 can sufficiently attenuate the pipe propagation wave W ₂ even when the energy (magnitude or intensity) of the gas propagation wave W ₁ is small, and the SN ratio can be reduced. Can be improved.

FIG. 7 is a graph of a reception signal of a virtual ultrasonic flowmeter including another ultrasonic absorber. The virtual ultrasonic flowmeter is the same as the ultrasonic flowmeter 100 except that the ultrasonic ultrasonic flowmeter includes an ultrasonic absorber different from the ultrasonic absorber 10. In FIG. 7, the horizontal axis represents time, and the vertical axis represents amplitude (voltage). Moreover, in FIG. 7, the frequency of the ultrasonic wave is 0.5 [MHz], the upper part is a graph in which the pressure of the gas flowing inside the pipe is 0.5 [MPa], and the lower part is the gas flowing inside the pipe. Is a graph with a pressure of 0.3 [MPa]. A virtual ultrasonic flowmeter provided with another ultrasonic absorber including asphalt as a main material is shown in FIG. 7 in comparison with the graph of the ultrasonic flowmeter 100 of the present embodiment shown in FIG. as such, it is not possible to ultrasound absorber sufficiently attenuate the pipe propagating wave W _2, to identify the pipe propagating wave W ₂ and the gas propagating wave W ₁ becomes difficult.

FIG. 8 is a table showing SN ratios of ultrasonic absorbers of various materials. In FIG. 8, the pressure of the gas flowing inside the pipe A is 0.3 [MPa], and the frequency of the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is 0.5. [MHz]. As shown in FIG. 8, when an ultrasonic absorber including asphalt is provided, the ratio between the maximum amplitude of the gas propagation wave W _{1 and} the maximum amplitude of the pipe propagation wave W ₂ (hereinafter referred to as SN ratio) is 3.8. Stop on. On the other hand, when the ultrasonic absorber 10 including uncrosslinked butyl rubber is provided, the SN ratio is 7.4, which is improved to about twice.

  In general, rubbers (rubber compositions) such as natural rubber and synthetic rubber have high vibration absorption performance. However, as shown in FIG. 8, even when rubbers (rubber compositions) other than uncrosslinked butyl rubber are used as the main material of the ultrasonic absorber, the gas flowing through the pipe A in the ultrasonic frequency band is used. In the case of propagation, it was found that the SN ratio was not improved.

  The ultrasonic absorber 10 is not limited to the case containing only uncrosslinked butyl rubber. The ultrasonic absorber 10 may include predetermined mixed particles mixed with uncrosslinked butyl rubber. Thereby, as a predetermined mixed particle, the value of the acoustic impedance is close to that of the material of the pipe A and / or the mixed particle that improves the ability to absorb vibrations in the frequency band of the ultrasonic wave (absorption performance) is uncrosslinked. By mixing with butyl rubber, the ultrasonic absorber 10 can further improve the SN ratio.

  Examples of the predetermined mixed particles include metal particles such as tungsten, organic compound particles such as ferrite, and inorganic compound particles such as barium sulfate.

  FIG. 9 is a table showing the SN ratio of the ultrasonic absorber 10. In FIG. 9, the pressure of the gas flowing inside the pipe A is 0.3 [MPa], and the frequency of the ultrasonic waves transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B is 0.5. [MHz]. As shown in FIG. 9, when the ultrasonic absorber 10 including only uncrosslinked butyl rubber is provided, as described above, the SN ratio is 7.4. On the other hand, when the ultrasonic absorber 10 further includes ferrite as the predetermined mixed particles 11, it is 8.9 when it further includes tungsten, 11.7 when it further includes tungsten, and 34. 2, the SN ratio is further improved as compared with the ultrasonic absorber 10 containing only uncrosslinked butyl rubber.

  In FIG. 1, the first ultrasonic transmission / reception unit 20 </ b> A is arranged above the pipe A in FIG. 1 so that the first ultrasonic transmission / reception unit 20 </ b> A and the second ultrasonic transmission / reception unit 20 </ b> B face each other. Although the example which arrange | positions the 2nd ultrasonic wave transmission / reception part 20B was shown in FIG., It is not limited to this. The first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B may be provided on the outer circumferences of the upstream side and the downstream side of the pipe A.

FIG. 10 is a configuration diagram illustrating another example of the schematic configuration of the ultrasonic flowmeter 100. The same components as those of the ultrasonic flow meter 100 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted as appropriate. As shown in FIG. 10, the first ultrasonic transmission / reception unit 20A is located on the outer circumference on the upstream side (left side in FIG. 10), and the second ultrasonic transmission / reception unit 20B is located on the downstream side (right side in FIG. 10). Provided on the outer circumference. The first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B are both arranged on the upper side of the pipe A in FIG. In the case of such an arrangement, for example, the ultrasonic gas propagation wave W ₁ transmitted from the first ultrasonic transmission / reception unit 20A is reflected by the inner wall of the pipe A to reach the second ultrasonic transmission / reception unit 20B ( V method).

As described above, according to the ultrasonic flowmeter 100 of the present embodiment, the ultrasonic waves provided on the outer periphery of the pipe A and transmitted by the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B pass through the pipe A. An ultrasonic absorber 10 that absorbs the propagating pipe propagation wave W ₂ is provided, and the ultrasonic absorber 10 includes uncrosslinked butyl rubber. Here, uncrosslinked butyl rubber has an acoustic impedance value close to that of the material of the pipe A, and has a high ability to absorb vibrations in the ultrasonic frequency band (absorption performance). Thereby, the ultrasonic absorber 10 can attenuate the pipe propagation wave W ₂ in the process of propagating the pipe A, and the pipe propagation wave reaching the first ultrasonic transmission / reception unit 20A and the second ultrasonic transmission / reception unit 20B. The energy (magnitude or intensity) of W ₂ can be made sufficiently smaller than the energy (magnitude or intensity) of the gas propagation wave W ₁ , that is, the SN ratio can be improved. Therefore, the ultrasonic flow meter 100 can easily identify the gas propagation wave W ₁ and the pipe propagation wave W _2, and can accurately measure the gas flow rate. In particular, when the pressure of the gas flowing in the pipe A is low, the energy (magnitude or strength) of the gas propagation wave W ₁ is relatively small, but the ultrasonic absorber 10 has a low gas pressure. Even in this case, since the SN ratio can be improved, the ultrasonic flowmeter 100 can accurately measure the flow rate of a gas having a low pressure.

  Uncrosslinked butyl rubber is also a viscoelastic body having adhesiveness and elasticity. Thereby, since the ultrasonic absorber 10 is easy to adhere, it can be adhered and fixed to the outer periphery of the pipe A, and the ultrasonic absorber 10 is easily deformed by elasticity, so various materials, shapes, and surface states The pipe A can be easily provided.

  Furthermore, it has been confirmed through experiments and the like that uncrosslinked butyl rubber has sufficient durability (environmental resistance) with respect to, for example, temperature and humidity in the environment where the ultrasonic flowmeter 100 is used. Thereby, the ultrasonic absorber 10 can utilize uncrosslinked butyl rubber without performing crosslinking (vulcanization) using sulfur or the like in order to enhance strength and environmental resistance.

  Moreover, according to the ultrasonic flowmeter 100 in the present embodiment, the ultrasonic absorber 10 further includes predetermined mixed particles mixed with uncrosslinked butyl rubber. Thereby, as a predetermined mixed particle, the value of the acoustic impedance is close to that of the material of the pipe A and / or the mixed particle that improves the ability to absorb vibrations in the frequency band of the ultrasonic wave (absorption performance) is uncrosslinked. By mixing with butyl rubber, the ultrasonic absorber 10 can further improve the SN ratio.

  Moreover, according to the ultrasonic flowmeter 100 in the present embodiment, the predetermined mixed particles are tungsten. Thereby, the ultrasonic absorber 10 that further improves the SN ratio can be easily realized (configured).

  Moreover, according to the ultrasonic flowmeter 100 in the present embodiment, the predetermined mixed particles are ferrite. Thereby, the ultrasonic absorber 10 that further improves the SN ratio can be easily realized (configured).

  Moreover, according to the ultrasonic flowmeter 100 in the present embodiment, the predetermined mixed particles are barium sulfate. Thereby, the ultrasonic absorber 10 that further improves the SN ratio can be easily realized (configured).

In addition, the ultrasonic absorber 10 for the ultrasonic flowmeter 100 in the present embodiment is provided on the outer periphery of the pipe A, and is transmitted from the upstream outer periphery of the pipe and the downstream outer periphery of the pipe. The ultrasonic wave absorbs the pipe propagation wave W ₂ propagating through the pipe A and includes uncrosslinked butyl rubber. Here, uncrosslinked butyl rubber has an acoustic impedance value close to that of the material of the pipe A, and has a high ability to absorb vibrations in the ultrasonic frequency band (absorption performance). Thereby, the ultrasonic absorber 10 can attenuate the pipe propagation wave W ₂ in the process of propagating through the pipe A, and the received pipe propagation wave W ₂ energy (magnitude or intensity) can be used as the gas propagation wave. It can be made sufficiently small with respect to the energy (magnitude or intensity) of W ₁ , that is, the SN ratio can be improved. Therefore, the ultrasonic flow meter 100 can easily identify the gas propagation wave W ₁ and the pipe propagation wave W _2, and can accurately measure the gas flow rate. In particular, when the pressure of the gas flowing in the pipe A is low, the energy (magnitude or strength) of the gas propagation wave W ₁ is relatively small, but the ultrasonic absorber 10 has a low gas pressure. Even in this case, since the SN ratio can be improved, the ultrasonic flowmeter 100 can accurately measure the flow rate of a gas having a low pressure.

  Uncrosslinked butyl rubber is also a viscoelastic body having adhesiveness and elasticity. Thereby, since the ultrasonic absorber 10 is easy to adhere, it can be fixed in close contact with the outer periphery of the pipe A, and the sound absorber 10 is easily deformed by elasticity, so that the pipes of various materials, shapes, and surface states A can be easily provided.

  Furthermore, it has been confirmed through experiments and the like that uncrosslinked butyl rubber has sufficient durability (environmental resistance) with respect to, for example, temperature and humidity in the environment where the ultrasonic flowmeter 100 is used. Thereby, the ultrasonic absorber 10 can utilize uncrosslinked butyl rubber without performing crosslinking (vulcanization) using sulfur or the like in order to enhance strength and environmental resistance.

  Note that the configurations of the above-described embodiments may be combined, or some components may be replaced. Further, the configuration of the present embodiment is not limited to the above-described embodiment, and various modifications may be made without departing from the scope of the present embodiment.

DESCRIPTION OF SYMBOLS 10 ... Ultrasonic absorber 20A ... 1st ultrasonic transmission / reception part 20B ... 2nd ultrasonic transmission / reception part 21 ... Wedge 21a ... Bottom 21b ... Slope 22 ... Piezoelectric element 50 ... Main-body part 51 ... Switching part 52 ... Transmission circuit part 53 ... Receiving circuit unit 54 ... Time measuring unit 55 ... Calculation control unit 56 ... Input / output unit 100 ... Ultrasonic flow meter A ... Piping W ₁ ... Gas propagation wave W ₂ ... Pipe propagation wave

Claims (6)

A first ultrasonic transmission / reception unit that is provided on the outer periphery on the upstream side in a pipe through which gas flows, and that transmits and receives ultrasonic waves;
A second ultrasonic transmission / reception unit that is provided on the outer periphery on the downstream side of the pipe and transmits and receives ultrasonic waves;
The time until the second ultrasonic transmission / reception unit receives the ultrasonic wave transmitted from the first ultrasonic transmission / reception unit, and the ultrasonic wave transmitted from the second ultrasonic transmission / reception unit A main body for measuring the flow rate of the gas based on the time until it is received by the first ultrasonic transmission / reception unit;
An ultrasonic absorber that is provided on an outer periphery of the pipe and absorbs a pipe propagation wave in which the ultrasonic wave propagates through the pipe;
The ultrasonic absorber includes uncrosslinked butyl rubber,
Ultrasonic flow meter. The ultrasonic absorber further includes predetermined mixed particles mixed with the uncrosslinked butyl rubber.
The ultrasonic flowmeter according to claim 1. The predetermined mixed particles are tungsten.
The ultrasonic flowmeter according to claim 2. The predetermined mixed particles are ferrite,
The ultrasonic flowmeter according to claim 2. The predetermined mixed particles are barium sulfate.
The ultrasonic flowmeter according to claim 2. The time until the ultrasonic wave transmitted from the outer periphery on the upstream side in the pipe through which gas flows is received at the outer periphery on the downstream side in the pipe, and the ultrasonic wave transmitted from the outer periphery on the downstream side in the pipe An ultrasonic absorber for an ultrasonic flowmeter that measures the flow rate of the gas based on the time until it is received at the outer periphery on the upstream side in
Provided on the outer periphery of the pipe, the ultrasonic wave absorbs a pipe propagation wave propagating through the pipe, and includes uncrosslinked butyl rubber.
Ultrasonic absorber for ultrasonic flowmeter.

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