JPH08110254A - Ultrasonic flowmeter - Google Patents

Abstract

PURPOSE: To provide an ultrasonic flowmeter which can measure the flow rate highly accurately even when set in the vicinity of a bent part of a piping where the flow velocity distribution is disturbed. CONSTITUTION: A flow rate detection part of the ultrasonic flowmeter is constituted of a pair of stators 3a, 3b corresponding to ultrasonic wave transmitters/ receiver 10a, 10b, an arm 8 and a driving means. The pair of stators 3a, 3b coupled acoustically to a piping guide the wave transmitters/receivers 10a, 10b to rotate about an axis of the piping. The arm 8 couples the pair of ultrasonic wave transmitters/receivers 10a, 10b at a position to transmit/receive ultrasonic waves from each other, and the driving means moves the coupled transmitters/receivers 10a, 10b along the stators 3a, 3b. A measuring/controlling part measures the flow velocity at each of a plurality of positions preliminarily set around the axis of the piping by moving the coupled ultrasonic wave transmitters/receivers 10a, 10b via the driving means, operates an average value of tone flow velocities measured at the respective positions and outputs as an average value of the flow rate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flow meter for measuring the flow velocity or flow rate of a fluid based on the difference in the propagation time of ultrasonic waves due to the flow of fluid.

[0002]

2. Description of the Related Art When an ultrasonic wave propagates in a flowing fluid, the propagation speed differs depending on whether it travels from upstream to downstream or from downstream to upstream. The principle configuration of a transmission type ultrasonic flowmeter according to the prior art that measures the flow velocity by utilizing the fact that the velocity difference of the propagation velocity has a proportional relationship with the flow velocity of the fluid is shown in FIG.
The conventional technique will be described with reference to FIG.

In the ultrasonic flowmeter of FIG. 3, 1a and 1b
Is an ultrasonic transducer, 2a and 2b are oblique wedges that acoustically couple the fluid 9 in the pipe 5 and the ultrasonic transducer, and the ultrasonic transducer and the oblique wedge are acoustic. To form ultrasonic wave transmitters / receivers 10a and 10b. When an excitation pulse is applied to the ultrasonic transducer 10a upstream of the ultrasonic flowmeter of FIG. 3 to excite it, ultrasonic waves are emitted, and the emitted ultrasonic waves pass from the pipe 5 to the fluid inside the pipe via the bevel wedge 2a. Propagate to 9. Then, the sound wave propagating to the fluid 9 in the pipe arrives at the facing surface of the pipe, is guided by the bevel wedge 2b, is guided to the ultrasonic transducer 10b in the receiving mode, and is received. It From the upstream ultrasonic transducer 10a to the downstream ultrasonic transducer 10a
The propagation time of the sound wave until reaching b is T _12, and conversely, the propagation time when the downstream ultrasonic transducer 10b is excited and the sound wave is received by the upstream ultrasonic transducer 10a is T ₂₁ . Then, the respective propagation times T ₁₂ and T ₂₁ are expressed by the following equations (1) and (2).

[0004]

[Equation 1]

[0005]

[Equation 2]

Where D is the inner diameter of the pipe, τ is the propagation time in the pipe and the oblique wedge, C is the sound velocity in the fluid, V is the flow velocity of the fluid, and θ is the incident angle of the ultrasonic wave in the fluid. In addition, when there is a flow velocity, there is a time difference between T ₁₂ and T ₂₁ .

In the ultrasonic flow meter, an ultrasonic wave propagation time T _{12 in the} direction along the flow given by the equation (1) and an ultrasonic wave propagation time T ₂₁ in the opposite direction to the flow given by the equation (2) are provided. The flow velocity V is calculated by measuring and substituting in the simultaneous equations. In constructing the ultrasonic flowmeter, the ultrasonic transducer is arranged by sandwiching the fluid pipe 5 on both sides so that the ultrasonic propagation path is Z-shaped as shown in the principle explanatory diagram of FIG. In order to capture the reflected ultrasonic waves reflected by the pipe wall of the pipe and returned to the same side as the sound wave ejection side, the ultrasonic transducer is arranged on the same side of the pipe so that the propagation path of the ultrasonic wave is V-shaped. In some cases, they are arranged and configured as illustrated in FIG.

When the ultrasonic wave transmitter / receiver is arranged on the same side of the fluid pipe as illustrated in FIG. 4, the ultrasonic wave is reciprocally received in the diameter direction of the pipe, and therefore, in the formulas (1) and (2). By setting the inner diameter D of the pipe to 2D, the relationship between the propagation times T ₁₂ and T ₂₁ and the flow velocity V is given, which is completely the same in principle as the ultrasonic flowmeter configured as shown in FIG. When the ultrasonic wave transmitter / receiver is arranged on the same side of the pipe as shown in FIG. 4 to configure a V type ultrasonic flow meter, the mounting mechanism portion of the ultrasonic wave transmitter / receiver can be made compact and simple, and the ultrasonic wave transmitter / receiver can be transmitted and received. It becomes easy to attach the device to the piping and adjust its position.

By the way, since the actual fluid is somewhat viscous, when flowing through the pipe, the flow velocity decreases near the pipe wall and reaches the maximum flow velocity at the center of the pipe, as shown in FIG. 5 (a). Therefore, the flow velocity distribution U (X) is as follows. Therefore, the flow velocity detected by the ultrasonic flowmeter of the measurement principle of FIG.
The average flow velocity is represented by the equation (3) obtained by integrating and averaging the flow velocity distribution U (X) on the plane on which the straight line connecting the ultrasonic transducers 1a and 1b lies.

[0010]

(Equation 3)

When the straight pipe portion of the pipe is sufficiently long, the fluid flows in the pipe in axial symmetry with respect to the pipe axis, so the flow velocity distribution U (X) in the pipe is in axial symmetry with respect to the pipe axis.
As long as the line connecting the ultrasonic wave transmitters / receivers 1a and 1b is in a positional relationship across the pipe axis, the average flow velocity is detected independently of the mounting orientation of the ultrasonic wave transmitter / receiver with respect to the pipe axis. On the other hand, the flow is disturbed by bending at the part where the pipe is bent or where the diameter is suddenly increased, and the flow velocity distribution is no longer axially symmetric with respect to the pipe axis as illustrated in Fig. 5 (b). The mean flow velocity in the axial cross section of the pipe will differ depending on the rotational orientation about the axis of the cross section. Therefore, if an ultrasonic transducer is placed near the bent portion of the flow tube, the average velocity detected will depend on the mounting orientation of the ultrasonic transducer with respect to the tube axis, and the error in flow rate measurement will cause the ultrasonic transducer to be mounted. There will be a large azimuth.

The flow disturbed at the bent portion of the pipe so that the flow velocity distribution is not axisymmetric with respect to the pipe axis is averaged as a result of the interaction through the viscosity of the fluid while flowing in the straight pipe portion, which is sufficiently long. At the position, the velocity distribution U (X) is again axisymmetric with respect to the tube axis. Therefore, in the ultrasonic flowmeter according to the related art, it is required to arrange the ultrasonic wave transmitter / receiver with a sufficient straight pipe portion.

[0013]

A sufficient straight pipe length may not be ensured depending on the situation of the plant facility where the ultrasonic flowmeter is to be installed. In such a case, as illustrated in FIG. 6, an ultrasonic wave transmitter / receiver is arranged on a plurality of survey lines orthogonal to the pipe axis of the pipe, and a measuring device system for obtaining an average value of flow rate measurement values by a plurality of flow meters is provided. With this configuration, in principle, highly accurate measurement is possible even near the bent portion of the pipe.

However, it is difficult to actually arrange and attach a plurality of pairs of ultrasonic wave transmitters / receivers to the flow tube near the bent portion, the configuration of the apparatus system becomes complicated, and adjustment of installation connection and maintenance work are also performed. It becomes troublesome, and the cost becomes excessive. The present invention is an ultrasonic flowmeter capable of highly accurate flow rate measurement even if the flow velocity distribution in a pipe is disturbed and the influence thereof is avoided without increasing the number of measurement lines and the measurement is performed near a bent portion of the pipe. The purpose is to provide.

[0015]

A measurement control unit calculates and outputs a flow velocity flow rate of a fluid based on each propagation time when an ultrasonic wave is propagated in a fluid flow direction and an opposite direction. The time interval required for the ultrasonic flowmeter to measure the flow rate is
It is usually sufficiently fast compared to the time variation of the flow rate of the fluid in the pipe. Therefore, in the present invention, the flow rate detecting unit of the ultrasonic flowmeter is provided so as to be acoustically coupled to the pipe, and the ultrasonic wave transmitting / receiving unit that guides the circular movement of the pipe of the ultrasonic wave transmitter / receiver around the pipe axis. A pair of stays corresponding to each of the vessels, an arm that couples a pair of ultrasonic transducers at a position for transmitting and receiving ultrasonic waves, and an arm that integrally couples the ultrasonic transducers. And a drive means for moving along the stay, and the measurement control unit moves the ultrasonic transducers integrally coupled through the drive means to a plurality of predetermined positions around the pipe axis and at each position. The flow velocity is measured, and the average value of the flow velocity measured at each position is calculated and output as the average flow rate value.

[0016]

The pair of ultrasonic wave transmitters / receivers integrally connected by the arm moves along the stay acoustically connected around the pipe axis of the pipe by the driving means, and the pipe is placed at the moved position. The propagation time of the ultrasonic wave propagating through the medium fluid is measured, and the measurement control unit calculates the average value of the flow velocity measured at each position to obtain and output the average flow rate value.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of one embodiment of the ultrasonic wave transmitter / receiver mounting mechanism portion in the case of constructing a V type ultrasonic flowmeter according to the present invention will be described with reference to FIG. 1a in FIG.
And 1b are ultrasonic transducers, 2a and 2b are oblique wedges that acoustically couple the ultrasonic transducers with the fluid 9 flowing in the pipe 5, and the ultrasonic transducers and oblique wedges acoustically The ultrasonic wave transmitters / receivers 10a and 10b are formed by coupling. And 3a,
Reference numeral 3b is a stay that serves as a guide for moving the ultrasonic wave transmitters / receivers 10a and 10b along the outer circumference of the pipe 5 while maintaining acoustic coupling. The stay 3 is provided with a guide groove 31 around which a key 21 protruding from the beveled wedge 2 is fitted. It is firmly fixed.

Numeral 8 fixes and fixes a pair of ultrasonic wave transmitters / receivers 10a and 10b so as to simultaneously slide integrally along the stays 3a and 3b in parallel with the pipe axis, respectively. The ultrasonic waves emitted from the ultrasonic transducer 1a of one ultrasonic wave transmitter / receiver 10a propagate through the fluid 9 in the pipe 5 and the other end of the pipe is fixed. The ultrasonic transducer 1b of the other ultrasonic transmitter / receiver 10b is arranged at a position where the ultrasonic wave that is reflected by the other ultrasonic wave transmitter / receiver 10b is captured at a position where it returns to the incident side pipe wall and enters the pipe again and propagates. ing.

When the values of the speed of sound in these members are known from the materials of the pipe 5, the bevel wedge 2 and the fluid 9 flowing in the pipe, the refraction angle of ultrasonic waves at the interface between the members is the acoustic principle. Since it is obtained by a calculation formula based on the above, the detector mounting interval of the arm 8 can be determined by calculation if the dimensions of each member such as the bevel wedge 2, stay 3, and pipe 5 are given.

On the other hand, 7 is a thick disk-shaped loader composed of an elastic member rotatably attached to the arm 8 so as to press the outer wall surface of the pipe 5, or having an elastic member provided around the elastic member. The loader 7 constitutes driving means for moving the ultrasonic wave transmitters / receivers 10a, 10b integrally coupled with the step motor 6 mounted on the arm 8 along the stays 3a, 3b. That is, when the loader 7 is rotationally driven by the step motor 6, the two ultrasonic transducers 10a and 10b fixed to the arm 8 are guided by the stays 3a and 3b and acoustically coupled with this rotation. While keeping the above, the outer circumference of the pipe 5 is slidably rotated.

The ultrasonic flow velocity detecting section 10 having the ultrasonic wave transmitter / receiver mounting mechanism section having the structure shown in FIG. 1 described above is arranged in the pipe to be measured, and the pulse motor 6 is used to connect the ultrasonic flow velocity detecting section 10 around the pipe axis. When the ultrasonic wave transmitters / receivers 10a and 10b are oriented in different directions and the in-pipe flow velocity in each orientation is measured, the average flow velocity on the plane on which the straight line of the ultrasonic wave propagation direction in the pipe rides is measured in each orientation. By the way, in the V type ultrasonic flowmeter, the ultrasonic wave transmitters / receivers 10a and 10b are arranged on the same side of the pipes in parallel with the pipe axis and receive the reflected ultrasonic waves from the opposing pipe wall. If the ultrasonic wave transmitter / receiver is moved within the half circumference range of the pipe, it means that the entire circumference is equivalently moved. Therefore, the stays 3a and 3b for guiding the ultrasonic wave transmitters / receivers 10a and 10b along the outer circumference of the pipe 5 may be provided in the half circumference of the pipe, and the ultrasonic wave transmitter / receiver may be moved within this range.

The ultrasonic flow velocity detecting section 10 having the structure shown in FIG.
When the measurement is performed by arranging in a portion near the curved pipe portion of the pipe where the flow velocity distribution in the pipe is not axially symmetrical with respect to the pipe axis, the ultrasonic transducers 10a and 10b of the ultrasonic flow velocity detection unit 10 are connected to the pipe axis. The flow velocity value measured as the average flow velocity on the surface on which the straight line is placed varies depending on the orientation direction of the ultrasonic flow velocity detection unit 10 with respect to the tube axis, but the ultrasonic flow velocity detection unit has many directions.
If the average value of the flow velocity values obtained by setting 10 is obtained, the total average flow velocity in the pipe can be obtained.

FIG. 2 is provided with the ultrasonic flow velocity detecting section 10 having the configuration shown in FIG. 1, and the average value of the individual flow velocity measurement values obtained by orienting the ultrasonic flow velocity detecting section in different directions with respect to the pipe axis is obtained. FIG. 3 is a block diagram showing a configuration of an embodiment of a measurement control circuit according to the present invention for converting into a flow rate value and outputting. In FIG. 2, reference numeral 40 denotes an individual flow velocity calculation unit that drives the ultrasonic flow velocity detection unit 10 having the configuration of FIG. 1 to perform calculation processing for obtaining an average flow velocity corresponding to each configuration.

The individual flow velocity calculation unit 40 includes a forward / reverse switching unit 41 for alternately switching the ultrasonic transmission / reception states of the ultrasonic transmission / reception units 10a and 10b in the ultrasonic flow velocity detection unit 10 and a transmission / reception circuit 4.
2. Detect the difference between the propagation time T _{12 of the} ultrasonic wave transmitted from the ultrasonic wave transmitter / receiver 10a and received by 10b, and the propagation time T _{21 of the} ultrasonic wave transmitted / received in the opposite direction. And a flow velocity calculation program 44 for obtaining a flow velocity value by a calculation process based on the time difference detected by the time difference detection circuit 43.

On the other hand, reference numeral 60 designates the ultrasonic wave transmitters / receivers 10a, 10b by giving driving power to the step motor 6 of the ultrasonic flow velocity detecting section 10 through the drive circuit 61 when the calculation processing of the flow velocity in the individual flow velocity calculating section 40 is completed. Is a detection unit azimuth control unit for performing control for orienting the
In addition, 60, the individual flow velocity calculation unit 40, and the startup reset control of the average flow velocity calculation unit 50 described below are performed together.

The average flow rate calculation unit 50 is a calculation unit that calculates the average value of a plurality of flow velocity data obtained by the individual flow velocity calculation unit 40 and outputs the average flow rate value.
Flow rate value memory 51 for storing a plurality of flow rate calculation data output by the CPU and an average flow rate value calculation program for performing a process of obtaining an average value of the flow rate data stored in the flow rate value memory 51 and outputting it as an average flow rate value. It consists of 52 and
Each time the detection unit azimuth control unit 60 sets the azimuth of the ultrasonic wave transmitters / receivers 10a, 10b, the flow velocity value measured and calculated by the individual flow velocity calculation unit 40 is stored in the flow velocity value memory 51 and is set in advance. When the detection unit azimuth control 60 notifies that the setting of the ultrasonic wave transmitters / receivers 10a and 10b to each direction has completed one cycle,
The average flow rate value calculation program 52 obtains the average value of the data stored in the flow velocity value memory 51, multiplies the value by the cross-sectional area of the pipe, and outputs the average flow rate value.

By the way, the flow velocity distribution of the fluid flow in the portion of interest of the pipe is determined depending on the shape of the flow passage before and after the pipe of the interest, particularly in the front portion, and if the shape is fixed, the distribution of The form is also fixed. Therefore, when the ultrasonic flowmeter detection unit 10 according to the present invention is installed near the curved pipe section to measure the flow velocity, the fluctuation of the flow velocity value measured in each configuration of the ultrasonic transducers 10a and 10b is Since the same pattern is shown, it is possible to select an arrangement that gives a flow velocity value that is close to or close to the average value of the measured values in each coordination. Therefore, when the flowmeter detection unit 10 is installed, the flow velocity measurement value in each direction of the ultrasonic transducers 10a and 10b is checked, and the direction giving the measured value closest to the average value is selected. By fixing the settings of the transducers 10a and 10b, it is possible to obtain a measured value that can represent the average flow velocity without performing a circular scan around the pipe axis of the detection unit. The process of calculating the average value of the values obtained by moving the wave device and repeating the measurement a plurality of times is unnecessary, and the response speed of the flow velocity measurement can be greatly accelerated.

Further, the ultrasonic wave transmitters / receivers 10a and 10b are normally operated.
When it is clear that the orientation of the robot is fixed and used, the ultrasonic transducers 10a and 10b are connected to the stays 3a and 3b.
A means for fixing the ultrasonic transducers 10a, 10b to the stays 3a, 3b by setting the ultrasonic transducers 10a, 10b in a preselected orientation without operating the loader 7 and the step motor 6 which are driving means for moving along May be.

[0029]

According to the ultrasonic velocity measuring device of the present invention,
A pair of ultrasonic transducers, which are integrally coupled, move on a pair of stays that are acoustically closely attached to the periphery of the pipe, and the ultrasonic transducers are set in different directions with respect to the pipe axis. The flow velocity value is measured and the average value of the flow velocity detection measurement values in each direction is obtained and output, so even if the flow velocity distribution of the pipe hand fluid is not symmetrical with respect to the pipe axis, the average flow velocity value can be measured. Even if the flow rate distribution is not axisymmetric near the bent portion of the pipe, the ultrasonic flowmeter detection unit according to the present invention can be installed to obtain an effect of enabling accurate flowmeter measurement. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of an ultrasonic flow velocity detection unit of an ultrasonic flow meter according to the present invention.

FIG. 2 is a block diagram of an embodiment of a measurement control unit of an ultrasonic flow meter according to the present invention.

FIG. 3 is an explanatory view of the principle of the ultrasonic flowmeter.

FIG. 4 is an explanatory view of a detector arrangement of a V-type ultrasonic flowmeter.

[Fig. 5] Explanatory drawing of fluid flow velocity distribution in piping

FIG. 6 is a diagram showing an example of a relationship between an ultrasonic transducer arrangement direction and an error.

[Explanation of symbols]

 10 Ultrasonic Measuring Unit 10a, 10b Ultrasonic Transducer 1a, 1b Ultrasonic Transducer 2a, 2b Oblique Wedge 3a, 3b Stay 4 Compound 5 Piping 6 Step Motor 7 Drive Wheel 8 Arm 9 Fluid 40 Individual Velocity Calculation Unit 50 Average flow rate calculation unit 60 Detection unit Direction control unit

Claims (2)

[Claims] 1. An ultrasonic wave detection unit consisting of a pair of ultrasonic wave transmitters / receivers is installed on the outer circumference of a pipe through which a fluid flows, and the propagation time of each ultrasonic wave is measured when the ultrasonic wave is propagated in the direction opposite to the direction of the fluid flow. In the ultrasonic flow meter in which the measurement control unit calculates and outputs the flow rate of the fluid based on the propagation time, the ultrasonic detection unit is provided acoustically coupled to the pipe, and the ultrasonic transducer A pair of stays corresponding to each of the ultrasonic wave transmitters / receivers for guiding the circular movement of the pipe around the pipe axis, and the pair of ultrasonic wave transmitters / receivers are arranged at positions for transmitting and receiving ultrasonic waves. An ultrasonic wave transmitter / receiver integrally connected through the drive means, and an arm to be connected, and a drive means for moving the integrally connected ultrasonic wave transmitter / receiver along the stay. Detecting unit Direction control unit that controls the position with respect to the pipe axis And an individual flow velocity calculation unit that performs calculation processing for transmitting and receiving ultrasonic waves at each arrangement position of the ultrasonic wave transceiver to obtain an average flow velocity corresponding to each configuration, and an ultrasonic wave transceiver in the individual flow velocity calculation unit. An average flow rate calculation unit that temporarily stores a plurality of flow velocity data obtained corresponding to the respective arrangement positions, calculates the average value of the stored values, and outputs the average flow rate value. Sonic flow meter. 2. The ultrasonic flowmeter according to claim 1, wherein the flow rate detector comprises a fastening means for fixing the ultrasonic wave transmitter / receiver at an arbitrarily selected position along the stay.