JP3144177B2 - Vortex 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 transducer mounted on a wall of a pipe downstream of a vortex generator and attached to a vortex generated by the vortex generator by a measurement fluid. Vortex flowmeter that emits ultrasonic waves from one side and receives vortices with the other ultrasonic transducer, and in particular, an vortex flowmeter improved to reduce the effect of noise due to ultrasonic waves leaking into the pipeline About.

[0002]

2. Description of the Related Art FIG. 4 is a configuration diagram showing the configuration of a conventional vortex flowmeter. Reference numeral 10 denotes a vortex generator for generating Karman vortices inserted in the flow, and here, a trapezoidal columnar object is exemplified. 11 is a vortex generated by the vortex generator 10,
Reference numeral 12 denotes a conduit through which the measurement fluid flows.

[0003] 13 is an ultrasonic transducer on the transmitting side, and 14 is an ultrasonic transducer on the receiving side. The ultrasonic transducer 13 and the ultrasonic transducer 14 are attached to the pipe 12 on the downstream side of the vortex generator 10 so as to face each other so as to be substantially perpendicular to the flow direction of the measurement fluid. The number of generated Karman vortices (the number of vortices flowing per unit time) is detected.

An oscillation circuit 15 generates an oscillation voltage for driving the ultrasonic transducer 13, an amplification circuit 16 amplifies a signal received by the ultrasonic transducer 14, and an amplifier circuit 17. A detection circuit 18 detects the amplified received signal, and an amplifier 18 amplifies the signal detected by the detection circuit.

In the above configuration, if no vortex exists in the propagation path of the ultrasonic signal shown by the dotted line in FIG. 4, the distance between the ultrasonic transducer 13 and the ultrasonic transducer 14 is set to D. If the speed of sound in the medium is V, the propagation time τ ₀ is given by τ ₀ = D / V.

Next, the propagation time τ ₁ when the Karman vortex exists at the position indicated by the dotted line and the direction of the ultrasonic wave is the same as the direction of the velocity component V ₁ of the vortex is shown in FIG. Let d be the diameter of, and τ ₁ = [d / (V−V ₁ )] + [(D−d) / V].

The propagation time τ ₂ when the Karman vortex exists at the position of the dotted line and the direction of the ultrasonic wave is opposite to the direction of the velocity component V ₂ of the vortex is τ ₂ = [d / (V + V) ₂ )] + [(D−d) / V].

As described above, the amplitude of the ultrasonic wave sent from the ultrasonic wave transducer 13 to the measurement fluid is amplitude-modulated by the vortex 11 and its envelope changes according to the change of the vortex 11. By measuring the number of times, the number of vortices 11 can be detected.

By the way, these ultrasonic transducers 13,
14 has a mounting structure as shown in FIGS. 6 (a) and 6 (b). The mounting structure in FIG. 6A is used when the measurement fluid is a liquid, and the mounting structure in FIG. 6B is used when the measurement fluid is a gas.

First, the configuration of FIG. 6A will be described. A through hole 19 is formed in the conduit 12, and a metallic holder 20 is inserted and fixed therein. This holder 20
Has a stepped portion 21 on its outer surface and is formed in a columnar shape.
A hole 23 having a bottom 22 is formed in the inside thereof, and a vibrator 24 is fixed to the bottom 22.

The holder 20 is provided with a groove 25 on its outer surface, in which an O-ring 26 is fixed and inserted into the through hole 19 of the conduit 12 to hold the liquid seal. I have.

When the measurement fluid is a liquid, the acoustic impedance Z (= ρc: ρ is density and c is sound velocity) is large.
Metal is used as the holder 20. However, when the holder 20 is fixed to the pipe 12, the holder 20 is made of an elastic body in order to reduce leaked ultrasonic waves that propagate from the ultrasonic transducer 13 to the ultrasonic transducer 14 via the pipe 12. O-ring 2
6 attached.

On the other hand, in the case of gas, it is attached by the structure of FIG. A through hole 19 is formed in the conduit 12, and a cylindrical sleeve 28 fixed to a support plate 27 is inserted and fixed therein. A net 29 is fixed to the tip of the sleeve 28.

A support rod 30 is provided at the center of the support plate 27.
A vibrator 31 is fixed at right angles to the support rod 30 via a cone, and the vibrator 31 is provided with a cone 32 in the axial direction of the pipe 12, that is, a net 29, in order to give directionality to the transmission of ultrasonic waves. The direction is fixed.

When the measurement fluid is a gas, the acoustic impedance Z is small. Therefore, the structure in which the vibrator 31 is brought into contact with the pipe is avoided, and the vibrator 31 is brought into contact with the measurement fluid as shown in FIG. The configuration is such that

[0016]

However, the above-described vortex flowmeter having the mounting structure shown in FIG. 6A can reduce the ultrasonic leakage from the pipeline, but has a problem in corrosion resistance due to the use of the O-ring 26. In addition, the vortex flowmeter having the mounting configuration shown in FIG. 6B has a configuration in which the vibrator is in direct contact with the measurement fluid, and thus has problems in corrosion resistance and dirt. The use is limited.

[0017]

According to the present invention, a pair of ultrasonic transducers are attached to a pipe wall of a pipe on the downstream side of a vortex generator by means of a fluid to be measured. In the vortex flowmeter that emits ultrasonic waves from one of the ultrasonic transducers to the vortex generated by the vortex generator and receives the vortex by the other ultrasonic transducer, An ultrasonic transmitter that is provided on the front tube wall on the side of the transducer and transmits ultrasonic waves to the previous conduit in a direction toward the other ultrasonic transducer; The vessel is provided with adjusting means for adjusting the applied voltage and phase applied from the oscillator, and the ultrasonic noise propagating through the previous pipeline is canceled by the preceding adjusting means.

[0018]

[Usage] An ultrasonic transmitter is provided on the pipe wall of a pipe downstream of the vortex generator on the side of one ultrasonic transmitter / receiver for transmitting ultrasonic waves, and the other ultrasonic transmitter receives ultrasonic waves. The ultrasonic wave is transmitted to the previous conduit in the direction toward the sound wave transducer.

The adjusting means adjusts the applied voltage and the phase applied from the oscillator to the ultrasonic transmitter to cancel the ultrasonic noise propagating through the previous pipe by the adjusting means.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing the configuration of one embodiment of the present invention. Parts having the same functions as those of the conventional vortex flow meter shown in FIGS. 4 and 6 are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

A drive voltage is applied to the ultrasonic transducer 33 as a continuous sine wave from the oscillation circuit 15, whereby the piezoelectric vibrator 34 housed in the ultrasonic transducer 33 is driven to be introduced into the measurement fluid. The ultrasonic transducer 35 is emitted as an ultrasonic signal S, and is amplitude-modulated and phase-frequency-modulated by the vortex 11 generated by the vortex generator 10 and faces the opposing ultrasonic transducer 35.
Received at.

Ultrasonic wave transmitter / receiver 33 functioning as a wave transmitter
Is composed of a holder 36, a vibrator 37, a gasket 38 and the like. The holder 36 is made of metal and has a recess at the center thereof, in which the vibrator 37 is housed.

Further, a flare portion extending outward is provided on the peripheral surface of the holder 36.
A gasket 38 made of metal is arranged between them to secure a liquid seal against the measurement fluid.

The line 12 of the ultrasonic transducer 33
An ultrasonic transducer 39 functioning as a receiver having the same structure as the ultrasonic transducer 33 is fixed to the pipe 12 on the side facing the center axis of the ultrasonic transducer. An ultrasonic transmitter 40 in which a transducer is housed is fixed to the outer wall of the pipe 12 at a position close to the ultrasonic transmitter / receiver 33.

FIG. 2 shows an equivalent circuit for transmitting ultrasonic waves. The ultrasonic transducer 33 and the ultrasonic transducer 40 shown in FIG. 1 are driven by the oscillation circuit 15,
The drive voltage of the oscillation circuit 15 is directly applied to the ultrasonic wave transmitter / receiver 33, but is applied to the ultrasonic wave transmitter 40 via the adjustment circuit 41.

Next, the operation of the embodiment configured as described above will be described with reference to the operation explanatory diagram shown in FIG. An ultrasonic signal S is transmitted to the measurement fluid via the ultrasonic transducer 33 by the driving voltage of the oscillation circuit 15, and the ultrasonic signal S is amplitude-modulated by the vortex 11 generated by the vortex generator 10, The number of times the envelope changes according to the number of vortices 11 is detected via the amplifier circuit 16.

In this case, the amplitude modulation signal V _S amplitude-modulated by the vortex 11 is given by V _S , where A ₁ and A ₂ are constants, f _V is the frequency of the vortex street, and f is the frequency of the ultrasonic signal _S. = [A ₁ + A ₂ sin (2πf _V t)] sin (2πft) (1)

However, in practice, the ultrasonic transducer 33 transmits the ultrasonic signal S propagating through the measurement fluid as shown in FIG.
In addition, the ultrasonic noise N ₁ propagating through the metal pipe 12
Is sent. This ultrasonic noise N ₁ is given by N ₁ = A ₃ sin (2πft + θ ₁ ) (2) where A ₃ is a constant and the phase difference is θ ₁ .

Therefore, the signal V received by the amplifier circuit 16 is as follows: V = V _S + N ₁ = [A ₁ + A ₂ sin (2πf _Vt )] sin (2πft) + A ₃ sin (2πft + θ ₁ ) (3)

Here, from the ultrasonic transmitter 40 to the pipe 12
Ultrasonic noise N indicating the ultrasonic wave by the following equation _TwoSend as
(A_Four: Constant, phase difference: θ_Two) And N_Two= A_Foursin (2πft + θ_Two(4) is obtained.

Therefore, in the pipe 12, N ₂ is superimposed on the ultrasonic noise N _{1. In} this case, A ₄ = A ₃ , θ ₂ =
The adjustment is performed by the adjustment circuit 41 so as to satisfy the relationship θ ₁ + π. By doing so, the noises are cancelled, and only the amplitude modulation signal V _S is received by the amplifier circuit 16.

In the above configuration, the ultrasonic noise N ₁ ,
Since N ₂ actually propagates in the pipe 12 and the distances to the ultrasonic wave transducer 33 are almost equal, the temperature change due to the fluid in the pipe 12, that is, the sound speed change is not affected.

Therefore, the adjustment circuit 41 only needs to initially set the amplitude value and the phase difference of the drive voltage. In the above description, the example in which the amplitude is modulated by the vortex has been described. However, the same effect can be expected even if the structure is subjected to the phase modulation or the frequency modulation.

[0034]

As described above, according to the present invention, an ultrasonic transmitter is provided on a pipe wall of a pipeline in addition to a pair of normal ultrasonic transmitters and receivers. Since the ultrasonic noise transmitted from the ultrasonic transducer to the pipeline is canceled, a highly reliable vortex flowmeter can be obtained.

Specifically, when the fluid is a liquid, a metal gasket or the like can be used without using a sealing mechanism using an elastic body such as an O-ring. It is possible to configure an ultrasonic transducer using a metal holder instead of a method of contacting with a fluid.

Further, according to the present invention, the reliability of the sealing mechanism is improved, the application to a corrosive fluid is facilitated, and the versatility as an industrial flow meter is remarkably enhanced.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of one embodiment of the present invention.

FIG. 2 is an equivalent circuit on the transmitter side of the embodiment shown in FIG. 1;

FIG. 3 is an operation explanatory diagram for explaining the operation of the embodiment shown in FIG. 1;

FIG. 4 is a configuration diagram showing a configuration of a conventional vortex flowmeter.

FIG. 5 is an explanatory diagram illustrating the operation of the vortex flowmeter shown in FIG.

6 is a configuration diagram illustrating a detailed configuration of a holder of the vortex flow meter shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vortex generator 11 Vortex 12 Pipeline 13, 14 Ultrasonic transducer 15 Oscillation circuit 33, 39 Ultrasonic transducer 40 Ultrasonic transducer 41 Adjustment circuit

Claims (1)

(57) [Claims] 1. A pair of ultrasonic transducers are mounted on a pipe wall of a pipe downstream of a vortex generator, and a vortex generated by the vortex generator by a measurement fluid is superposed from one of the ultrasonic transducers. In a vortex flowmeter that emits a sound wave and receives the vortex with the other ultrasonic transducer, a direction toward the other ultrasonic transducer that is provided on the tube wall on the side of one ultrasonic transducer. An ultrasonic transmitter that sends out ultrasonic waves to the pipeline, and an adjusting unit that adjusts an applied voltage and a phase applied from an oscillator to the ultrasonic transmitter are provided, and the pipeline is A vortex flowmeter, wherein the propagating ultrasonic noise is canceled by the adjusting means.