JP3136002B2 - Ultrasonic flow meter - Google Patents

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, and more particularly, to a reflection type ultrasonic flow meter in which a pair of ultrasonic elements are mounted on a flow tube whose inner diameter is unknown or whose nominal value is unknown.

[0002]

2. Description of the Related Art An ultrasonic flowmeter uses an ultrasonic flowmeter which measures a flow velocity from a change in the propagation velocity of an ultrasonic wave which is superimposed on a fluid flow velocity when ultrasonic waves are emitted into a measurement fluid. When a constant frequency ultrasonic wave is emitted at a predetermined angle to the bubble particles contained in the measurement fluid and flowing at a speed substantially equal to the flow velocity of the measurement fluid, the emitted ultrasonic wave depends on the particle velocity. There is an ultrasonic Doppler system that utilizes the effect of receiving a Doppler shift, and ultrasonic flow meters of these systems are the mainstream. In the ultrasonic flow meter of the propagation time difference type, it is necessary that the measurement fluid does not contain particles.However, in the case of the Doppler type, the flow rate cannot be measured without particles, so that the measurement fluid without particles is used. In the flow rate measurement, an ultrasonic flow meter of a propagation time difference type is used.

[0003] The ultrasonic flow meter of the propagation time difference method is for obtaining the flow rate from the propagation time difference when the ultrasonic waves are emitted in the forward and reverse directions into the measurement fluid flowing at a predetermined flow rate as described above. The ultrasonic wave propagation speed and ultrasonic wave propagation distance in the measurement fluid of the sound wave must be known. Since the propagation speed of the ultrasonic wave, that is, the sound speed changes depending on the type and temperature of the fluid to be measured, in an ultrasonic flowmeter using the sound speed as a parameter, the change in the sound speed is a large fluctuation factor in flow measurement. For this reason, usually, a method of obtaining the reciprocal difference of the propagation time difference, that is, the propagation frequency difference, which does not involve the sound velocity in the measurement, is applied. On the other hand, the propagation distance of the ultrasonic wave cannot be determined unless the flow tube diameter is clear, and an error in the propagation distance causes a flow rate error. The exact dimensions of the flow tube are not clear in the normal flow tube, and it is extremely difficult to measure the exact size, especially when the flow meter is constructed by installing only the ultrasonic transmitter / receiver in the existing piping. Furthermore, the inside of a flow tube used for a long period of time may be corroded, and the inner diameter may be changed accordingly. This applies to the ultrasonic flow meter of the ultrasonic propagation time difference type, and the same applies to the reflection type ultrasonic flow meter.

[0004]

[Object] The present invention has been made in view of the above circumstances,
Conventionally, a method of determining the sound velocity using the inner diameter of a pipe is known, but by measuring the sound velocity of ultrasonic waves in the flow pipe, accurate measurement of the inner diameter of the flow pipe is possible even when the inner diameter of the flow pipe is unknown. Accordingly, it is an object of the present invention to provide a reflection type ultrasonic flowmeter having no flow error due to inaccuracy of the ultrasonic propagation distance.

FIG. 6 is a view for explaining the principle of a conventional reflection type ultrasonic flowmeter. Reference numeral 21 denotes a flow tube, reference numerals 22 and 23 denote a mounting cylinder of a transducer, reference numeral 24 denotes a transducer A,
25 is a transducer B, and 26 is an ultrasonic reflecting surface. The reflecting surface does not need to be specially mounted, and is added for explanation.

In the drawing, a flow tube 21 has an inner diameter D and a flow tube 21.
Mounting cylinders 22 and 23 are disposed at a predetermined distance from each other in the axial wall surface, and a transducer A for transmitting and receiving ultrasonic waves is provided in the mounting cylinder 22, and a transducer B is provided in the mounting cylinder 23.
Are arranged. A piezoelectric element is mounted in each of the transducers A and B. Ultrasonic waves are emitted from one of the transducers A and B at an emission angle of an angle φ with respect to the axis of the flow tube 21 and reflected by the ultrasonic reflecting surface 26. The signal is received by one of the other transducers B and A. Now, assuming that the measurement fluid is flowing at the flow velocity V in the direction of the arrow, the flow velocity V
Is obtained by the following equation (1).

[0007]

(Equation 1)

[0008] However, as is apparent from the equations (1) and (2), the flow velocity V cannot be obtained when the inner diameter D of the flow tube is unknown.

[0009]

To achieve the above object, the present invention provides (1)
An ultrasonic element is mounted, and has a pair of transducers arranged at a known interval in the axial direction of the flow tube wall, and a predetermined launch angle is applied to a tube wall facing from one of the ultrasonic elements. In a reflection type ultrasonic flowmeter that determines a flow rate based on a time difference until a reflected wave of an ultrasonic wave emitted in the forward and reverse directions of the flow is received by the other ultrasonic element, the ultrasonic wave propagating at the known interval Sound velocity measuring means for determining the sound velocity in the fluid from the propagation time of the fluid, and one ultrasonic wave from the measured sound velocity
Fired at a predetermined firing angle from the element to the opposing tube wall,
The greater the ultrasonic propagation distance calculating means for reflected waves to calculate the ultrasonic propagation distance to be received in the other of the ultrasonic element, and the ultrasonic propagation distance issued the calculated and the known distance
Ultrasound firing angle calculating means for calculating the acoustic firing angle, the
The flow tube inner diameter calculating means for calculating the flow tube inner diameter from the calculated ultrasonic launch angle and the ultrasonic propagation distance , and the measured sound velocity, ultrasonic propagation distance, ultrasonic launch angle and flow tube inner diameter Toransude determining the flow rate based, furthermore, (2) in the (1), equipped with the ultrasonic element
The Yusa, a flow rate measuring ultrasonic element disposed in the ultrasound firing angle for flow measurement, the sound velocity measuring ultrasonic element disposed at right angles to the flow tube axis in order to speed-of-sound measurement, the sound speed measuring greater (3) a transducer housing which integrally houses the ultrasonic element and the flow rate measuring ultrasonic element; and (3)
In the (1), Trang equipped with the ultrasonic element
A transducer that supports the ultrasonic element so that the ultrasonic element can be rotationally switched to an angle perpendicular to the flow tube axis for measuring the ultrasonic emission angle and the velocity of sound for measuring the flow rate and the ultrasonic element. (4) In (1), the propagation time of the ultrasonic wave propagating in the known interval and
Then , using the average value of the propagation time of the sub-polar wave of the ultrasonic wave directly propagated in the forward and reverse directions of the flow between the ultrasonic elements emitted from the pair of ultrasonic elements, respectively. Is what you do. Hereinafter, a description will be given based on an example of the present invention.

FIG. 1 is a view for explaining an ultrasonic flowmeter according to the present invention. In the figure, 1 is a flow tube, 2 and 3 are transducer mounting tubes, 4 is a transducer A, 5 is an ultrasonic element, 6 is a support rod, 7 is a transducer B, 8
Is an ultrasonic wave transmitting / receiving surface, and 9 is a support rod.

The flow tube 1 is a tube having an inner diameter D (unknown), and mounting tubes 2 and 3 are arranged on a surface of a tube wall 1a parallel to the tube axis with a center distance M accurately measured in advance. The transducer A is mounted in the mounting cylinder 2 via the support rod 6 in a posture in which the ultrasonic element 5 faces the ultrasonic reflecting surface 1b. Similarly, the transducer B is mounted in the mounting cylinder 3 via the support rod 9 with the ultrasonic wave transmitting / receiving surface facing the ultrasonic reflecting surface 10. Also,
The transducers A and B are mounted so as to be able to move by Y in the axial direction of the arrow, and the central position points P ₁ and P _{2 of the} ultrasonic elements 5 and 8 for transmitting and receiving ultrasonic waves are representative positions of ultrasonic emission. Stipulated. The points P ₁ and P ₂ are on the same line as the inner wall surface 1a of the flow tube 1 when measuring the flow rate, and the illustration shows the positions when measuring the speed of sound.

In the figure, the flow rate of the measured fluid is V in the direction of the arrow.
Let's say it is flowing. At the position where the illustrated transducers A and B are pulled down toward the flow tube axis, ultrasonic waves are transmitted from the transducer A to the transducer B in the forward direction of the flow. The time during this period is defined as t ₁ . Next, the time when the ultrasonic waves are emitted from the transducers B to A in the opposite direction of the flow is defined as t ₂ . Since the average propagation time at this time is (t ₁ + t ₂ ) / 2, the sound speed C = 2M / (t ₁ + t ₂ ) (3). When the flow velocity V = 0, if the ultrasonic wave propagation time t in any one direction is taken, the sound velocity C is determined by the sound velocity measuring means (not shown).
Is required.

The ultrasonic propagation time t _AB from the transducers A to B and the propagation time t _BA from the transducer B to the transducer A are

[0014]

(Equation 2)

The ultrasonic path length L is obtained by substituting the sound velocity C of the equation (3) into the equation (6). This operation is
It is obtained by an ultrasonic wave propagation distance calculating means (not shown).

Since the ultrasonic path length L and the distance M between the transducers A and B are known, the ultrasonic emission angle φ is determined by the ultrasonic emission angle calculation means (not shown) from the following equation (7). Can be

[0017]

(Equation 3)

Accordingly, since the ultrasonic path length L and the ultrasonic emission angle φ are obtained from (6) and (7), the fluid flow velocity V is obtained by substituting the equation (1). The flow velocity V has a predetermined flow velocity distribution in the flow tube 1, and the flow velocity distribution is based on the Reynolds number R of the fluid flowing in the flow tube 1.
Therefore, the flow velocity V needs to be corrected by the Reynolds number Re. K is the Reynolds number correction coefficient
Then, the flow rate Q is

[0019]

(Equation 4)

[0020] The inner diameter D of the flow tube 1
Is obtained by performing the operation of D = Lsinφ / 2 (9).

FIG. 2 is a view for explaining an example of the structure of the transducer according to the present invention. In FIG. 2, reference numeral 10 denotes a piezoelectric element for measuring the speed of sound. The same reference numerals as in FIG. The transducer 4 emits an ultrasonic element 5 composed of a piezoelectric element that emits an ultrasonic wave S ₁ at an angle φ with respect to an OO axis perpendicular to the axis of the flow tube 1 and an ultrasonic wave S ₂ for measuring sound velocity. The ultrasonic element 10 for measuring the speed of sound parallel to the OO axis is housed in the transducer outer casing 4a. The transducer 7 is also a transducer of the same shape in which the ultrasonic element 8 is disposed symmetrically with the ultrasonic element 5 of the transducer 4.

FIGS. 3A and 3B are diagrams for explaining another example of the structure of the transducer according to the present invention. FIG. 3A shows a state at the time of measuring a flow velocity, and FIG. In the figure, 11 is a holding part of the transducer, 12
Is an ultrasonic element part, 13 is a support part, 14 is an ultrasonic element, 1
5 is a transducer.

In the figure, a transducer 15 includes a holding unit 11, an ultrasonic element unit 12, and a support unit 13 for supporting the ultrasonic element 12 rotatably at a predetermined angle with respect to the support unit 11.
The ultrasonic element 12 includes an ultrasonic wave S ₃
The ultrasonic element 14 such as a piezoelectric element that emits light
It is fixed in parallel with.

The flow rate measurement is used in the state shown in FIG. 3A in which the holding unit 11 and the ultrasonic element unit are fixed, but before the flow rate measurement is performed, the ultrasonic element around the support unit 13 is shown in the state shown in FIG. Part 1
2, the ultrasonic element 12 is fixed in a direction perpendicular to one axis of the flow tube, and the speed of sound is measured by the above-described means. The measurement accuracy can be improved by setting the ultrasonic element driving frequency for flow rate measurement and the ultrasonic element driving frequency for sound velocity measurement to different values by selecting the element dimensions. In addition, this method is applicable not only to the reflection type ultrasonic flow meter, but also to another ultrasonic flow meter of the propagation time difference method.

FIG. 4 shows an ultrasonic flow meter according to the present invention.
FIG. 10 is a view for explaining still another embodiment, in which Ps ₁ is a main pole wave of ultrasonic waves, Ps ₂ is a second sub pole wave, and Ps ₃ is a third sub pole wave, and is the same as FIG. The working parts are given the same reference numbers as in FIG.

[0026] The pair of ultrasonic elements 4 and 7, although the most sound high pressure main Gokunami Ps ₁ is emitted perpendicularly from the element surface, different from the firing angle in addition to the main Gokunami Ps ₁ The second sub-polar wave Ps ₂ and the third sub-polar wave Ps ₃ are simultaneously emitted.
The second sub-polar wave Ps ₂ and the third sub-polar wave Ps ₃ are the type of the piezoelectric element,
Depending on the shape, for example, PZT with a diameter of 10 mm
To (lead zirconate titanate) in Shukyokuha Ps ₁ second
The sub-polar wave Ps ₂ is emitted at an angle of ± 25 °, and the third sub-polar wave Ps ₃ is emitted at an angle of ± 45 °. Therefore, the ultrasonic elements 4 and 7
Each third Fukukyokuha Ps ₃ is disposed at an angle phi _A and an ultrasonic element 4 and 7 so as to be opposite to the axis of the flow tube 1. In other words, the third sub-polar wave Ps ₃ emitted from the ultrasonic element 4 is directly received by the ultrasonic element 7 and
From the third sub-polar wave Ps ₃ is directly received by the ultrasonic element 4, and the propagation time t in the flow direction of each third sub-polar wave Ps ₃
Average time t of _AB 'and the propagation time _tBA ' in the opposite direction to the flow
_By finding 0 and dividing the distance M between the ultrasonic elements 4 and 7 by the average time t ₀ , the sound velocity of the measurement fluid is calculated.

FIG. 5 is a diagram for explaining the ultrasonic wave propagation time in FIG. 4. The horizontal axis represents time t, and the vertical axis represents voltage E.

When a driving voltage having a natural frequency is applied from an oscillator (not shown) to the ultrasonic element 4 or 7 at time t ₀ , the main pole wave Ps ₁ is reflected from the ultrasonic reflecting plate 1b and propagates a distance L
Is larger than the distance M and the attenuation rate is larger, but the main pole wave Ps
Received amplitude Ps ₁ Shukyokuha Ps ₁ since ₁ power is large increases compared to the third sub-electrode waves. Therefore, after driving the ultrasonic element 4 or 7, the propagation time t _AB or t _{BA of} the first main pole wave
After the measurement, the propagation time t _AB or t _BA is set to a reference time, for example, T _0, and the third sub-polar wave of small amplitude is received within the time t _AB ′ or t _BA ′ that is less than the reference time T _0. If so, this time t _AB ′ or t _BA ′ is the ultrasonic wave propagation time adopted as the propagation time of the third subpolar wave. According to this method, the speed of sound can be easily measured without using the special ultrasonic element or structure shown in FIGS.

[0029]

As is clear from the above description, according to the present invention, even when the inner diameter D of the flow tube 1 is unknown or only the nominal value is known, the distance M between the transducers A and B is correctly measured and arranged. If so, the sound velocity C of the measurement fluid is obtained, the ultrasonic path length L is obtained from the sound velocity C and the propagation time of the ultrasonic wave in the forward and reverse directions in the actual measurement, and then the distance M and the ultrasonic path length are obtained. The ultrasonic emission angle φ is determined from the height L and the flow tube inner diameter D, which is unknown from the ultrasonic emission angle φ and the ultrasonic path length L, is sequentially determined. Even when the inner diameter is unknown or only the nominal value is known, an accurate flow rate is required.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an ultrasonic flowmeter according to the present invention.

FIG. 2 is a diagram illustrating an example of a structure of a transducer according to the present invention.

FIG. 3 is a diagram for explaining another example of the structure of the transducer according to the present invention.

FIG. 4 is a view for explaining still another embodiment of the ultrasonic flow meter according to the present invention.

FIG. 5 is a diagram for explaining the ultrasonic wave propagation time in FIG. 4;

FIG. 6 is a view for explaining the principle of a conventional reflection type ultrasonic flowmeter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Flow tube, 2, 3 ... Transducer mounting cylinder, 4 ... Transducer A, 5 ... Ultrasonic element, 6 ... Support rod,
7 Transducer B, 8 Ultrasonic wave transmitting / receiving surface, 9 Support rod, 10 Piezoelectric element for measuring sound velocity, 12 Ultrasonic element section, 13 Support section, 14 Ultrasonic element, 15 Transducer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-233324 (JP, A) JP-A-61-120015 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/66-1/66 103

Claims (4)

(57) [Claims] 1. A tube wall having an ultrasonic element mounted thereon and having a pair of transducers arranged at a known interval in an axial direction of a flow tube wall, and a tube wall facing one of the ultrasonic elements. In the reflection type ultrasonic flowmeter for obtaining the flow rate based on the time difference until the reflected wave of the ultrasonic wave emitted in the forward and reverse directions of the flow at the predetermined emission angle is received by the other ultrasonic element, the known interval A sound velocity measuring means for determining the sound velocity in the fluid from the propagation time of the ultrasonic wave propagating through the ultrasonic wave, and a predetermined launch angle from one ultrasonic element to the opposite tube wall from the measured sound velocity.
And the reflected wave is received by the other ultrasonic element.
And ultrasonic propagation distance calculating means for calculating the ultrasonic propagation distance to that, the ultrasonic propagation distance is the calculated, the ultrasonic firing angle calculating means for calculating said ultrasonic firing angle from said known intervals The calculated ultrasonic launch angle and the ultrasonic
And characterized by having a said flow tube inner diameter calculating means for calculating the flow tube inner diameter than the wave propagation distance, determining the flow rate based on the measured sound velocity and ultrasonic wave propagation distance and the ultrasonic firing angle and flow tube inner diameter Ultrasonic flow meter. 2. A transducer equipped with said ultrasonic element.
The p o, the flow rate measuring ultrasonic element disposed in the ultrasound firing angle for flow measurement, the sound velocity measuring ultrasonic element disposed at right angles to the flow tube axis in order to speed-of-sound measurement, the sound speed measuring 2. The ultrasonic flowmeter according to claim 1, wherein said ultrasonic flowmeter comprises an ultrasonic element and a transducer housing for integrally storing said ultrasonic element. 3. A transducer equipped with said ultrasonic element.
And a support for rotatably supporting the ultrasonic element in an ultrasonic element part, a holding part, and an angle perpendicular to a flow tube axis for measuring an ultrasonic emission angle and a sound velocity for measuring the flow rate of the ultrasonic element. 2. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter comprises: 4. The propagation of an ultrasonic wave propagating in said known interval.
As the time, the average value of the propagation times of the sub-polar waves of the ultrasonic waves directly propagating in the forward and reverse directions of the flow between the ultrasonic elements emitted from the pair of ultrasonic elements is used. The ultrasonic flowmeter according to claim 1, wherein the ultrasonic flowmeter comprises: