JP2014077653A - Ultrasonic flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly accurately detect an ultrasonic pulse signal which propagates fluid flowing in a pipe body by reducing an ultrasonic wave pulse signal propagating the pipe body in a pipe axial direction using FRP for the pipe body.SOLUTION: Ultrasonic wave transmitter/receivers 2a, 2b so provided as to be paired are fixed at a position along the outside of the upstream side and the downstream side of a tube body 1 in which a fluid to be measured flows. FRP (fiber-reinforced resin) is used for the tube body 1, and the arrangement direction of the fiber is a direction orthogonal to a tube axis of the tube body 1, that is, a circumferential direction. With the adoption of this tube body 1 made of FRP, the propagation from one of the ultrasonic wave transmitter/receivers 2a, 2b to the other one of the ultrasonic wave transmitters/receivers 2a, 2b shown by a dotted line via the tube body 1 is prevented to no small extent due to the arrangement direction of the fiber, and the ultrasonic pulse signal having propagated in the fluid shown by a solid line can be received with a high S/N ratio.

Description

  The present invention relates to an ultrasonic flowmeter that measures the flow rate of a fluid flowing through a tubular body using FRP for the tubular body.

  A pair of ultrasonic transmitters / receivers are arranged on the upstream side and downstream side of the outside of the tube through which the fluid flows, and an ultrasonic pulse signal is transmitted into the fluid flow through the tube wall from the outside of the tube. The flow velocity of the fluid is calculated from the difference between the time that the pulse signal propagates from the upstream side to the downstream side and the time that the pulse signal propagates from the downstream side to the upstream side, and this flow rate is multiplied by the cross-sectional area of the pipe to measure the flow rate in the pipe. Many time difference type ultrasonic flowmeters have been put to practical use.

  This method has been improved with the advancement of electronic circuit technology, but to achieve higher accuracy, it is necessary to more accurately determine the propagation time difference of the ultrasonic pulse signal. It is important to detect the pulse signal with a high S / N.

  However, a part of the ultrasonic pulse signal transmitted from one ultrasonic transmitter / receiver installed on the pipe of the ultrasonic flowmeter propagates through the pipe and is received by the other ultrasonic transmitter / receiver. It is received by superimposing it with the ultrasonic pulse signal that has passed through. However, since these signals have the same frequency, it is very difficult to separate them with a filter.

  On the other hand, an ultrasonic pulse signal is emitted into the pipe through which the fluid flows, and the Doppler frequency of the ultrasonic pulse signal reflected from foreign matter such as dust and bubbles contained in the fluid is detected to measure the flow rate in the pipe. For example, a Doppler type ultrasonic flow meter described in Patent Document 1 is known.

  In this Doppler type ultrasonic flowmeter, even if a tube made of a material that easily propagates an ultrasonic pulse signal is used, it is easy to separate the ultrasonic pulse signal that propagates through the tube from the Doppler detection signal used for measurement. It is. Further, even if the material of the tubular body propagates the ultrasonic pulse signal satisfactorily, in the case of the Doppler type, it does not become a great obstacle to the flow rate measurement.

  Cited Document 1 describes that FRP (fiber reinforced plastic) is used for the tube of the Doppler type ultrasonic flowmeter. As described above, the Doppler type ultrasonic flow rate is used. In the meter, the material of the tube is hardly a problem, and FRP is not used for the purpose as in the present invention.

  On the other hand, Patent Document 2 discloses that there is extremely strong anisotropy in the sound speed and propagation of the ultrasonic pulse signal depending on the arrangement direction of the fibers mixed in the FRP, and the sound speed and propagation of the ultrasonic pulse signal are disclosed. There is a large difference in the attenuation of the fiber depending on the direction and frequency of the fibers in the FRP. For example, the speed of sound along the direction in which the fibers are arranged is approximately five times greater than the direction perpendicular to the fibers, although depending on the frequency.

  FIG. 6 is a graph of attenuation characteristics with the horizontal axis representing the frequency due to the difference in FRP fiber arrangement direction. The magnitude of the ultrasonic pulse signal in the direction orthogonal to the fiber arrangement direction indicated by the solid line is sufficiently attenuated compared to the signal in the arrangement direction indicated by the dotted line. This is because the acoustic velocity of ultrasonic waves in the FRP is related to Young's modulus and material density in each fiber array direction, and attenuation is related to scattering due to the fiber array direction and absorption due to the viscosity of the material. .

  FRP is widely used as a material for aircraft and automobiles, and nondestructive inspection such as ultrasonic flaw detection technology is applied. In such examinations, it is empirically known that propagation is attenuated in proportion to the frequency of the ultrasonic wave, and an ultrasonic wave having a frequency of 100 kHz or higher where attenuation usually starts is rarely used. That is, how well ultrasonic waves can be propagated in the FRP for inspection is a major concern, and ultrasonic inspection has a frequency of 100 kHz or less where attenuation of propagation is hardly affected by the fiber arrangement direction. Is being used.

JP 2005-156401 A Japanese Patent Laid-Open No. 7-284198

  In a time-difference type ultrasonic flowmeter using a conventional metal tube or normal plastic tube, the ultrasonic pulse signal that propagates directly through the tube becomes a disturbance and propagates through the fluid for measurement. Since the S / N of the signal to be deteriorated is deteriorated, it is necessary to suppress the ultrasonic pulse signal propagating in the tubular body.

  In addition, when the measurement frequency is included in the vibration propagating from the inside of the tube to the tube, it is one factor that deteriorates the measurement accuracy for the same reason. However, these solutions have become issues. For this reason, circuit technology has been improved, but it is still not a sufficient solution.

  The object of the present invention is to eliminate the above-mentioned problems, attenuate the ultrasonic pulse signal propagating through the tube in the tube axis direction by using FRP for the tube, and accurately detect the ultrasonic pulse signal propagating through the fluid in the tube. It is to provide an ultrasonic flowmeter that can be detected well.

  In order to achieve the above object, an ultrasonic flowmeter according to the present invention has a pair of ultrasonic transmitters / receivers arranged on the upstream side and the downstream side of a fluid flowing through a pipe, and the one ultrasonic wave Time and flow in which an ultrasonic pulse signal is emitted from a transmitter / receiver into a fluid and received by the other ultrasonic transmitter / receiver alternately, and the ultrasonic pulse signal propagates forward to the fluid flow. In a time difference type ultrasonic flowmeter that determines the velocity of the fluid in the tube from the time difference propagating backward to the tube, and measures the flow rate flowing through the tube, all or part of the tube has acoustic propagation characteristics. The FRP fiber arrangement direction is selected so that the ultrasonic pulse signal hardly propagates in the tube axis direction in the tube axis direction, and is configured by an anisotropic FRP.

  Since the ultrasonic flowmeter according to the present invention uses FRP for the tube body and suppresses the ultrasonic pulse signal propagating in the tube axis direction through the tube body due to the anisotropy of its acoustic propagation characteristics, An ultrasonic pulse signal propagating therethrough can be obtained with high accuracy.

  That is, by utilizing the anisotropy of the acoustic propagation characteristics of FRP, the ultrasonic pulse signal propagating in the pipe body is increased by making the arrangement direction of the fibers constituting the pipe body substantially perpendicular to the pipe axis. It becomes possible to suppress.

1 is a configuration diagram of an ultrasonic flow meter of Example 1. FIG. It is explanatory drawing of the fiber arrangement direction of the pipe body which consists of FRP. It is a graph of the propagation characteristic of the ultrasonic pulse signal in the case of being along the fiber arrangement direction of FRP and the direction orthogonal to the arrangement direction. It is a graph figure of the propagation characteristic of the ultrasonic pulse signal received by propagating the water in the pipe body made of FRP and the stainless steel pipe body. 6 is a configuration diagram of an ultrasonic flow meter of Example 2. FIG. It is a graph of the attenuation characteristic for every frequency by the difference in the fiber arrangement | positioning direction of FRP.

  Details of the present invention will be described below based on the embodiment shown in FIGS.

  FIG. 1 is a configuration diagram of the ultrasonic flowmeter according to the first embodiment. This ultrasonic flowmeter employs a so-called V-shaped ultrasonic propagation method used when the diameter of the tube 1 is relatively small. A pair of ultrasonic transceivers 2a and 2b are fixed at positions along the upstream and downstream sides of the tube 1 through which the fluid to be measured flows.

  In particular, FRP (fiber reinforced resin) is used for the tube body 1, and the arrangement direction of the fibers F is a direction orthogonal to the tube axis C of the tube body 1, as shown in FIG. .

  In the time difference type ultrasonic flow meter of the first embodiment, ultrasonic pulse signals are alternately transmitted from the ultrasonic transmitters / receivers 2a and 2b in a state where the fluid flows in the tube 1, and the fluid in the tube 1 is transferred. It is reflected in a V shape on the tube wall on the opposite side of the transverse tube 1 and received by the other ultrasonic transceivers 2b and 2a. Then, the propagation time difference Δt of the ultrasonic pulse signal between the case where the flow is forward and the case where the flow is reversed is measured. Since this time difference Δt corresponds to the flow velocity V of the fluid, the flow rate Q is obtained as Q = S · Δt by multiplying by the cross-sectional area S of the tube 1.

  By adopting such an FRP tube 1, the propagation indicated by the dotted line through the tube 1 from one ultrasonic transceiver 2 a, 2 b to the other ultrasonic transceiver 2 b, 2 a The ultrasonic pulse signal that is blocked by the arrangement and propagated in the fluid indicated by the solid line can be received with high S / N.

  FIG. 3 is a graph showing an actual measurement of the relationship between the ultrasonic frequency and the S / N of the received signal when the tube body 1 made of FRP and the stainless steel tube body 1 are used. The solid line represents the case where the ultrasonic pulse signal tube 1 propagates in the direction orthogonal to the FRP fiber arrangement direction, and the dotted line represents the case where the stainless steel tube 1 propagates.

  Therefore, in the case of the FRP tube 1, the ultrasonic pulse signal propagates in the tube axis direction in the tube 1 less than in the case of the stainless tube 1, and the S / N of the received signal is large. I understand that. Further, as is apparent from this graph, it is preferable to use a frequency of 500 kHz to 3 MHz for the ultrasonic flowmeter using the FRP tube 1, and particularly, a good S / N at 1 to 1.5 MHz. A signal is obtained.

  FIG. 4A shows the ultrasonic wave obtained by attaching the ultrasonic transmitters / receivers 2a and 2b to the tube body 1 in which the fiber arrangement direction of the FRP is set to the direction orthogonal to the tube axis C. It is a graph of the propagation characteristic of a pulse signal. Moreover, (b) is the same graph in the case of the tubular body 1 made of stainless steel.

  In the tubular body 1 by FRP shown in (a), when an ultrasonic pulse signal is not received, the ultrasonic pulse propagated through the fluid in the tubular body 1 without detecting external disturbance noise. Since a signal is obtained and a waveform in which ultrasonic pulse signals are arranged in an orderly manner is obtained, signal processing becomes easy.

  On the other hand, in the stainless steel tubular body 1 shown in (b), the ultrasonic signal propagated through the tubular body 1 reaches earlier than the ultrasonic pulse signal propagated through the fluid of the originally necessary tubular body 1, The obtained ultrasonic pulse signal is a combination of a signal that has passed through the fluid in the tube 1, noise from the outside, and a signal that has propagated through the tube 1. It becomes difficult.

  The FRP tube 1 can receive an ultrasonic pulse signal that has propagated through the fluid at a maximum S / N of about 40 dB (100 times) better than the stainless tube 1. Also from this, it can be seen that the FRP tube 1 having the fiber arrangement direction orthogonal to the tube axis suppresses the propagation of the ultrasonic pulse signal propagating through the tube 1.

  In this way, by appropriately selecting the FRP fiber arrangement direction and using it as the material of the tube body 1, and preferably setting the frequency of the ultrasonic wave to be used to be 500 kHz or more, the calculation results in noise that is superfluous. The intensity at which the acoustic pulse signal propagates through the tube body 1 is reduced to 1/30 or less per 10 cm.

  FIG. 5 is a configuration diagram of the ultrasonic flowmeter according to the second embodiment, and is a configuration used in the case of the tube body 1 having a relatively large diameter. The path of the so-called I-type ultrasonic pulse signal is shown in FIG.

  Also in the second embodiment, the tube body 1 is made of FRP, and the arrangement direction of the fibers is orthogonal to the tube axis direction of the tube body 1. Even though there is an ultrasonic pulse signal that travels, there are few ultrasonic pulse signals that travel in the tube axis direction.

  In Examples 1 and 2, if the tube 1 is made of CFRP (carbon fiber reinforced resin) using carbon fiber, the tube 1 has conductivity, facilitating countermeasures against static electricity, If the ultrasonic transceivers 2a and 2b are covered with a metal body, an explosion-proof safety structure can be realized, and measurement using petroleum as a fluid becomes easy.

  In order to use FRP for a part of the pipe line, a flow meter unit including a circuit part capable of measuring the flow rate is inserted in the middle of the pipe line, or only the pipe body 1 in this flow meter unit is FRP. It is good.

Depending on the nature of the fluid, FRP may be eroded, so it is possible to coat the inside of the tube 1 made of FRP, or to provide a thin metal tube. Further, the ultrasonic transceivers 2a, 2b A short cylindrical tube made of FRP is inserted into only a part of the tube body 1 between them, or an FRP is arranged in the middle of the tube body 1 or outside the tube body 1 and the ultrasonic transceivers 2a and 2b are connected to the FRP The effect of preventing the propagation of the ultrasonic pulse signal is not negligible.

  In the above-described embodiment, it has been described that the arrangement direction of the FRP fibers is arranged in the circumferential direction of the tube body 1, but the tube body 1 propagates in the tube axis direction even if it is not necessarily in the circumferential direction. What is necessary is that the ultrasonic pulse signal can be effectively blocked. Further, even when the fiber arrangement direction is random or when a plurality of FRPs are stacked, it is effective if the arrangement direction averages and faces the circumferential direction.

1 Tubing 2a, 2b Ultrasonic transceiver

Claims (5)

  A pair of ultrasonic transmitters / receivers is arranged outside the upstream and downstream pipes of the fluid flowing through the pipe, and an ultrasonic pulse signal is emitted from the one ultrasonic transmitter / receiver into the fluid. Reception by the ultrasonic transceiver is repeated alternately, and the velocity of the fluid in the tube is determined from the time difference in which the ultrasonic pulse signal propagates forward to the fluid flow and the time to propagate backward to the flow. In the time difference type ultrasonic flowmeter for measuring the flow rate flowing through the tubular body, all or a part of the tubular body is constituted by FRP having anisotropy in acoustic propagation characteristics, and the ultrasonic pulse signal is An ultrasonic flowmeter, wherein an arrangement direction of the fibers of the FRP is selected so that it is difficult to propagate in the tube body in the tube axis direction.   The ultrasonic flowmeter according to claim 1, wherein the FRP fibers are arranged in a substantially circumferential direction of the tubular body.   The ultrasonic flowmeter according to claim 1, wherein the ultrasonic pulse signal uses a frequency of 500 kHz to 3 MHz.   The ultrasonic flowmeter according to claim 3, wherein the ultrasonic pulse signal has a frequency of 1 to 1.5 MHz.   The ultrasonic flowmeter according to any one of claims 1 to 4, wherein the tubular body and the ultrasonic transceiver are covered with a metal body to form an explosion-proof safety structure.

Images