WO1997011337A1

WO1997011337A1 - Cell for ultrasonically measuring the rate of fluid flow

Info

Publication number: WO1997011337A1
Application number: PCT/SI1995/000023
Authority: WO
Inventors: Matjaz Babic; Damir Zajc
Original assignee: Iskraemeco, Merjenje In Upravljanje Energije, D.D.
Priority date: 1995-09-21
Filing date: 1995-09-21
Publication date: 1997-03-27
Also published as: AU3489695A

Abstract

Cell (1) for ultrasonically measuring the rate of fluid flow is provided with two transducers (t1, t2) for generating and sensing a beam of ultrasonic waves and with three ultrasonic reflectors (r1, r2, r3) so that the ultrasonic beam between the transducers (t1, t2) is deflected three times. On the place where each time the ultrasonic transducers (t1, t2) are placed, an inner surface of a first wall (3) is formed like inclined planes (31, 31') which with respect to the cell axis (A) are situated symmetrically to two inclined planes (41, 41') of a second cell wall (4), on which inclined planes (41, 41') ultrasonic reflectors (r1 and r3), respectively, are placed. Everywhere along the cell (1) the cross section is approximately symmetrical with respect to the cell axis (A), and hence also the velocity distribution in the cell is symmetrical, whereby a more exact measurement is made possible.

Description

CELL FOR ULTRASONICALLY MEASURING THE RATE OF FLUID FLOW

The invention concerns a cell for ultrasonically measuring the rate of fluid flow, and more specifically it concerns a cell of said kind which is provided with two transducers for generating and sensing a beam of ultrasonic waves, the direction of transmission and the direction of reception of the ultrasonic transducers being per¬ pendicular to their transmitting and receiving surfaces which are parallel to an inner surface of the cell, and which is further provided with three ultrasonic reflectors placed essentially between the ultrasonic transducers so that the ultrasonic beam between both ultrasonic transducers is deflected three times.

There have been known flowmeters for ultrasonically measuring the rate of fluid flow, in which flowmeters two transducers for generating and sensing a beam of ultrasonic waves are placed in a cell conducting a fluid so that the ultrasonic trans¬ ducers are displaced with respect to each other in the direction of the fluid flow. The difference between times of flight of an ultrasonic signal between the ultrasonic transducers in the direction of the fluid flow and in the reverse direction is propor¬ tional to the velocity of the fluid. The measurement quality depends on the manner how the ultrasonic transducers are placed with regard to the direction of the fluid flow and how a trajectory of ultrasonic waves through the cell of the flowmeter for ultrasonically measuring the rate of fluid flow is formed.

In the published patent application DE-A1-28 28 937 a cell of a flowmeter for ultrasonically measuring the rate of fluid flow is disclosed, in which cell two transducers for generating and sensing a beam of ultrasonic waves are directed to each other and are placed on opposite cell walls and shifted with respect to each other along the axis of the cell so that the ultrasonic beam intersects the cell axis under an acute angle. From the patent US-3 906 791 there has been known a cell of a flowmeter for ultrasonically measuring the rate of fluid flow, in which cell two transducers for generating and sensing a beam of ultrasonic waves are both placed on the same cell wall and are shifted with respect to each other along the axis of the cell. On an opposite cell wall there is placed an ultrasonic reflector so that the ultrasonic beam trajectory between the transducers forms a letter V. A dis¬ advantage of the described solutions consists in that in the cell, due to the supports of the ultrasonic transducers being situated obliquely with respect to the cell axis, dead zones appear causing fluid flow turbulences and thereby an additional resis¬ tance to the flow and accumulation of dirt.

Further, in the published patent application DE-A1-35 39 948 a cell of a flowmeter for ultrasonically measuring the rate of fluid flow is disclosed, which cell is provided with two interdigital transducers for generating and sensing a beam of ultrasonic waves, the direction of transmission and the direction of reception of the ultrasonic transducers being oblique to their transmitting and receiving surfaces. The ultrasonic transducers are placed on the same cell wall, their transmitting and receiving surfaces being parallel to the inner surface of the cell, and shifted along the cell axis. On both opposite cell walls there are mounted three ultrasonic reflec¬ tors providing for a triple reflection of the ultrasonic beam on its trajectory between both ultrasonic transducers and the trajectory of the ultrasonic beam forms a letter W. The interdigital transducers for generating and sensing a beam of ultrasonic waves are constructionally difficult and expensive and, additionally, their electroacustical efficiency is low.

In the published patent applications EP-A1-0 303 255 and EP-A1-0 392 294 essen¬ tially a cell of a flowmeter for ultrasonically measuring the rate of fluid flow is dis¬ closed, which cell is provided with two transducers for generating and sensing a beam of ultrasonic waves, the direction of transmission and the direction of recep¬ tion of the ultrasonic transducers being perpendicular to their transmitting and receiving surfaces. The ultrasonic transducers are all placed on the same cell wall, their transmitting and receiving surfaces being parallel to the inner surface of the cell, and shifted along the cell axis. In regions opposite to the ultrasonic transducers a surface of the opposite cell wall exibits two planes that are inclined at an angle of 22,5° with respect to the cell axis and oriented to each other, the cross-sectional area of the cell between said inclined planes exceeding the cross-sectional area anywhere else. On the inclined planes and on the cell wall between both ultrasonic transducers three ultrasonic reflectors are mounted so that the ultrasonic beam is deflected three times and forms a letter M. Disadvantageosly, in these cells the cross section between the inclined planes is not symmetrical with respect to the cell axis, whereby the velocity distribution of the flow in the cell is influenced. Addition¬ ally, two of four sections of the ultrasonic beam trajectory are almost peφendicular to the fluid flow direction.

Consequently, the technical problem to be solved by the present invention is how to construct such a cell of a flowmeter for ultrasonically measuring the rate of fluid flow that the cell cross section all along the longitudinal cell axis will be at least ap¬ proximately symmetrical with respect to this axis, which cell, however, will be provided with two transducers for generating and sensing a beam of ultrasonic waves, the direction of transmission and the direction of reception of the ultrasonic transducers being perpendicular to their transmitting and receiving surfaces, which surfaces each time will be parallel to the inner surface of the cell on the respective mounting location, and that anywhere the ultrasonic beam will propagate at an acute angle with respect to the cell axis.

At the embodiment of the cell according to the invention for ultrasonically measur¬ ing the rate of fluid flow this is accomplished in that on the place where each time a first and a second ultrasonic transducer are placed, an inner surface of a first cell wall is formed like a third and a fourth inclined plane, respectively, forming a third and fourth angle, respectively, with the cell axis so that the third and the fourth in¬ clined plane are turned to each other and that the third and a first angle are ap¬ proximately equal to the fourth and a second angle, respectively, the first and the second angle being formed with the cell axis by an inner surface of an opposite second wall of the cell in regions opposite to the first and the second ultrasonic transducer, respectively. The cell according to the invention for ultrasonically measuring the rate of fluid flow is distinguished from known cells of this kind in that the cell cross section is symmetrical with respect to the longitudinal cell axis and anywhere the ultrasonic beam propagates at an acute angle with respect to the cell axis.

The invention will now be described by way of example and with reference to the accompanying drawing representing a longitudinal cross section of a cell according to the invention for ultrasonically measuring the rate of fluid flow.

A cell 1 according to the invention for ultrasonically measuring the rate of fluid flow is provided, as represented in the Fig., with two transducers tl, t2 for generating and sensing a beam of ultrasonic waves and with three ultrasonic reflectors rl, r2, r3. The cell 1 has a rectangular cross section normally crossing its longitudinal axis A and on both ends it continues into connecting tube pieces 2, 2' which are provided with threads 21 and 21', respectively, on their free ends. The longitudinal axes of the connecting tube pieces 2, 2' are coincident with the axis A of the cell 1.

The direction of transmission and the direction of reception of the ultrasonic transducers tl, t2 are perpendicular to their transmitting and receiving surfaces. Both ultrasonic transducers tl, t2 are placed on a first wall 3 of the cell 1 so that they are shifted with respect to each other along the axis A of the cell 1. Their trans¬ mitting and receiving surfaces are parallel to an inner surface of the wall 3 on the places where each time the ultrasonic transducers tl, t2 are placed.

In regions opposite to the ultrasonic transducers tl, t2 an inner surface of a second cell wall 4, which is situated opposite to the first wall 3, is formed like a first and a second inclined plane 41, 41', respectively, forming a first and a second angle β, β respectively, with the cell axis A. Actually, in the direction y of the fluid flow as the direction of regard, the cross sectional area of the cell 1 increases at the first in¬ clined plane 41 and the cross sectional area of the cell 1 decreases at the second in¬ clined plane 41'; hence the said inclined planes 41, 41' are turned to each other. The ultrasonic reflectors rl, r3 are placed on the first and the second inclined planes 41 and 41', respectively. The ultrasonic reflector r2, however, is placed on the first cell wall 3 between both ultrasonic transducers tl, t2 so that the ultrasonic beam between the ultrasonic transducers tl, t2 is deflected three times.

On the place where each time the first and the second ultrasonic transducer tl, t2 are placed the inner surface of the first wall 3 is formed like a third and a fourth in¬ clined plane 31, 31', respectively, forming a third and a fourth angle , a', respec¬ tively, with the cell axis A Actually, in the direction y of the fluid flow as the direc¬ tion of regard, the cross sectional area of the cell 1 increases at the third inclined plane 31 and the cross sectional area of the cell 1 decreases at the fourth inclined plane 31'; hence the said inclined planes 31, 31' are turned to each other.

In order to get the cross section of the cell 1 as symmetrical as possible with respect to the longitudinal axis A of the cell 1 and of the connecting tube pieces 2, 2' the third and the first angles , β approximately equal to the fourth and the second angles β', respectively. For the same reason a mutual shift a of beginnings of the third and the first inclined plane 31, 41 in the direction v of the fluid flow as the direction of regard, hence in the direction from the ultrasonic transducer tl towards the ultrasonic transducer t2, is made as small as possible and preferably it equals zero. The same applies to a mutual shift of ends of the second and the fourth in¬ clined planes 41', 31'.

In the cell 1 according to the invention for ultrasonically measuring the rate of fluid flow all sections si, s2, s3, s4 of the ultrasonic beam trajectory form an acute angle with the axis A of the cell 1. Hence, every one of these sections contributes to a dif¬ ference between the times of flight of an ultrasonic signal between the ultrasonic transducers in the direction y of the fluid flow and in the reverse direction. Since in the sections si, s4 of its trajectory the ultrasonic beam forms an acute angle with respect to the axis A, shifts a, a' appear for constructional reasons; the shifts a, a', however, are smaller to the same degree as the linear dimensions of the ultrasonic transducers and reflectors are smaller with respect to the longitudinal dimensions of the inclined planes.

Claims

1. Cell for ultrasonically measuring the rate of fluid flow, which cell is provided with two transducers (tl, t2) for generating and sensing a beam of ultrasonic waves, the direction of transmission and the direction of reception of the ultrasonic transducers (tl, t2), which are both placed on a first wall (3) of the cell (1) so that they are shifted with respect to each other along the axis (A) of the cell (1), being perpendicular to their transmitting and receiving surfaces, which are parallel to an inner surface of the first wall (3) on the places where the ultrasonic transducers (tl, t2) are placed, an inner surface of a second wall (4) of the cell (1) opposite to the first wall (3) in regions opposite to the ultrasonic transducers (tl, t2) being formed like a first and second inclined plane (41, 41') forming a first and a second angle (β, β') with the cell axis (A) so that the said inclined planes (41, 41') are turned to each other, and which cell is further provided with three ultrasonic reflectors (rl, r2, r3), the first and the third ultrasonic reflectors (rl, r3) being placed on the first and the second inclined planes (41, 41'), respectively, and the second ultrasonic reflector (r2) being placed on the first wall (3) of the cell (1) between the first and the second ultrasonic reflectors (rl, r2) so that the ultrasonic beam between the ultrasonic transducers (tl, t2) is deflected three times, characterized in that on the place where each time the first and the second ultrasonic transducer (tl, t2) are placed, the inner surface of the first wall (3) of the cell (1) is formed like a third and a fourth inclined plane (31, 31'), respectively, forming a third and a fourth angle (a, a'), respectively, with the cell axis (A) so that the third and the fourth in¬ clined planes (31, 31') are turned to each other and that the third and the first angle ( , β) are approximately equal to the fourth and the second angles ( β'), respectively.

2. Cell as recited in claim 1, characterized in that mutual shifts (a, a') of the beginnings of the third and the first inclined planes (31, 41) and of the ends of the second and the fourth inclined planes (41', 31') are rmnimal, the direction of regard being from the first ultrasonic transducer (tl) to the second ultrasonic transducer (t2).