JPS63135821A - Karman vortex flowmeter - Google Patents

Abstract

PURPOSE:To improve the S/N ratio of the receiving signal of a receiver and to prevent the generation of malfunction, by providing the receiver at the position opposed to a super-directional oscillator generating an ultrasonic wave so as to locate the same slightly before or behind said oscillator. CONSTITUTION:When a main stream 5 flows through a conduit 1, a Karman vortex 6 is generated behind a vortex generating column 2 and the flow vertical to the main stream 5 and cyclically reversed in direction is generated. A super-directional oscillator 3 emits a primary ultrasonic wave 7 of which the sound flux is throttled only in the direction of a receiver 4. By this constitution, when the direction of the primary ultrasonic wave 7 coincides with the direction of the flow vertical to the main stream 5, the phase of the primary ultrasonic wave 7 received by the receiver 4 is allowed to advance and, when the flow direction is reverse, the phase is delayed. By measuring this phase difference, the Karman vortex 6 is detected and the flow rate of the main stream can be calculated. Herein, the reflected wave 8 generated by the wall of the conduit 1 in the periphery of the receiver 4 or by the receiver 4 also holds directionality to be reflected in a diagonally backward direction. Therefore, the reflected wave 8 in noise is not incident again on the receiver 4 and a S/N ratio is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a Karman vortex flow meter that is used, for example, to measure the intake air flow rate of an automobile engine.

[Conventional technology]

FIG. 3 is a cross-sectional view showing a conventional Karman vortex flow meter shown in, for example, Japanese Utility Model Publication No. 59-10576. The vortex generating column 3 is an oscillator attached to the wall of the conduit l behind the vortex generating column 2, and the receiver 4 is attached to the wall of the conduit 1 facing the oscillator 3. 5 is the main flow flowing through the conduit 1;
6 is a Karman vortex generated by the vortex generating column 2; 7 is an ultrasonic wave generated from the oscillator 3 toward the receiver 4; and 8 is a reflected wave reflected one or more times from the wall of the conduit 1 or the receiver 4.

Next, the operation will be explained. When the main stream 5 flows in the conduit 1, a Karman vortex 6 is generated behind the vortex generating column 2, thereby generating a flow in the conduit 1 that is perpendicular to the main stream 5 and whose direction is periodically reversed. - 10,000, oscillator 3) The generated ultrasonic waves 7 propagate in the receiver 4, but when this propagation direction and the direction of the flow perpendicular to the main flow match, the phase of the ultrasonic waves 7 received by the receiver 4 advances. and the phase is delayed when the direction of flow is reversed. By measuring this phase change, the solar karma/vortex 6 can be detected. Since the period of the Karman vortex 6 is proportional to the speed of the main stream 5, the flow rate can be determined by measuring this period.

[Problem that the invention seeks to solve]

The conventional Karman vortex flowmeter is configured as described above, but since the primary ultrasonic wave 7 generated by the oscillator 3 propagates while spreading, the sound wave energy of the primary ultrasonic wave 7 that directly reaches the receiver 4 is small. In addition, due to the spread of the wavefront 9, a part of the ultrasonic wave that reaches the wall surface of the conduit 1 around the receiver 4 is reflected by other walls and the receiver 4, resulting in a reflected wave 8, and then several more times. After being reflected, it reaches the receiver 4 as noise. This deteriorated the S/N ratio of the received signal and caused the Karman vortex flowmeter to malfunction.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to obtain a Karman vortex flowmeter that has a good signal-to-noise ratio of a signal received by a receiver and does not malfunction.

[Means for solving problems]

The Karman m#t meter according to the present invention uses a super-directional oscillator as an oscillator for generating ultrasonic waves, and is equipped with a receiver at a position facing the oscillator, slightly in front or behind the oscillator. .

[For production]

In this invention, the spread of the ultrasonic waves emitted from the oscillator with high directivity is small, and most of them reach the receiver directly. In addition, the sound waves reflected from the receiver and the wall of the conduit around the receiver maintain a high level of directivity, so if the receiver is in front of the oscillator, it will be reflected further forward, and if it is behind the oscillator, it will be reflected further back. , will not be received by the receiver as noise.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a cross-sectional plan view of a Karman vortex flowmeter, in which l is a conduit through which fluid flows, 2 is a vortex generating column installed in conduit 1, and 3 is scattered on the wall of conduit l immediately after vortex generating column 2. The attached superdirectional oscillator 4 is a receiver mounted slightly behind the oscillator 3 on the wall of the conduit 1 facing the oscillator 3.

Reference numeral 5 indicates the main stream flowing in the conduit 1, 6 indicates a Karman vortex generated by the interaction between the vortex generation column 2 and the main stream 5, 7 indicates a primary ultrasonic wave emitted from the oscillator 3 and reaches the receiver 4, and 8 indicates a reflected wave.

FIG. 2 shows the configuration of the superdirectional oscillator 3, and 9 is a sealed box l.
11 is an oscillator connected to this oscillator 9, 12 is five sound source holes arranged directly at equal intervals within a distance of wavelength λ/2 of the ultrasonic wave used, and 13 is each Sound source hole 12
This is a waveguide that communicates the airtight box 10 with the airtight box 10.

In the Karman vortex flowmeter described above, when the main stream 5 flows in the conduit 1, a Karman vortex 6 is generated behind the vortex generation column 2, and this K
A flow that is perpendicular to the main flow 5 and whose direction is periodically reversed is generated. - The superdirectional oscillator 3 uses the well-known phased array principle to adjust the phase and amplitude of the sound waves emitted from each sound source hole 12 according to the length and thickness of the waveguide 13. The primary ultrasonic wave 7 with a narrowed sound beam is emitted only in the direction of the transmitter 4. By this, −
When the vertical flow directions of the secondary ultrasonic wave 7 and the main flow 5 match, the phase of the primary ultrasonic wave 7 received by the receiver 4 is advanced, and when the directions are opposite, the phase of K is delayed. By measuring this phase change, the Karman vortex 6 can be detected, and since the period of the Karman vortex 60 is proportional to the flow velocity of the main stream 5, the flow velocity of the main stream 5, flow t, can be obtained by determining this period. .

Thus, most of the energy of the primary ultrasound 7 generated from the superdirectional oscillator 3 reaches the receiver 4;
A reflected wave 8 is generated by the peripheral wall of the conduit 1 or by the receiver. However, this reflected wave 8 also maintains its directivity, and since the -order ultrasonic wave 7 enters obliquely from the front, it is reflected obliquely backward. Therefore, the reflected wave 8 does not enter the receiver 4 again as noise, and the S/N ratio improves.

In addition, in the example, five point sound sources are arranged linearly as a superdirectional oscillator, but in order to improve directivity, it is better to have a large number of point sound sources, and to simplify the structure. The number of point sources can be reduced to three.

Further, a large number of point sound sources may be arranged two-dimensionally. In this way, directivity can be obtained not only in the front-rear direction but also in the up-down direction, improving performance. Furthermore, the mounting position of the receiver 4 should be shifted backward by the width of the receiver's pressure receiving surface from the oscillator, and as a superdirectional sound source, the phase should be shifted by πrad from the front and back of the diaphragm 11 of the oscillator 3. It is also possible to take out the ultrasonic waves and arrange them alternately. Further, the receiver 4 may also be directional, and the inner wall of the conduit 1 may be covered with a sound absorbing material.

〔Effect of the invention〕

As explained above, according to the present invention, a super-directional oscillator is used as the oscillator, and the receiver is installed slightly in front or behind the oscillator at a position facing the oscillator, so that the ultrasonic sound from the receiver is The switching energy can be concentrated in the receiver, the S/N ratio is improved, and the Karman vortex flow can be measured without malfunction.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional plan view of a Karman vortex flowmeter according to an embodiment of the present invention, FIG. 2 is a block diagram of a superdirectional oscillator, and FIG. 3 is a cross-sectional plan view of a conventional Karman vortex flow meter. DESCRIPTION OF SYMBOLS 1... Conduit, 2... Vortex generating column, 3 super-directional oscillator, 4... Receiver, 9... Oscillator, 11... Diaphragm, 12... Sound source hole, 13 ...Waveguide. Note that the same reference numerals in the drawings indicate the same or similar parts. Agent Masuo Oiwa Figure 1 Figure 2 I2; Long-ago marriage, many Figure 3 Procedural amendment (voluntary)

Claims (6)

[Claims] (1) A conduit through which the measurement fluid flows, a vortex generation column that generates Karman vortices in this conduit, and an ultrasonic wave that generates ultrasonic waves only in the direction of the receiver using the phased array principle on the conduit wall immediately after the vortex generation column. A Karman vortex flowmeter comprising a directional oscillator and a receiver on a conduit wall facing the oscillator, slightly behind or slightly in front of the oscillator. (2) The Karman vortex flowmeter according to claim 1, characterized in that the superdirectional oscillator is directly arranged with three or more point sound sources having opposite phases alternately. (3) The Karman vortex flowmeter according to claim 1, characterized in that the superdirectional oscillator has a large number of point sound sources arranged two-dimensionally. (4) The Karman vortex flowmeter according to claim 1, wherein the mounting position of the receiver is shifted backward by the width of the pressure receiving surface of the receiver from the mounting position of the superdirectional oscillator. (5) The Karman vortex flow rate according to claim 1, characterized in that the superdirectional sound source is constructed by extracting ultrasonic waves whose phase is shifted by π rad from the front and back of the diaphragm of the oscillator and arranging them alternately. Total. (6) The Karman vortex flowmeter according to claims 1 and 4, wherein the receiver is a directional receiver.