GB1564844A

GB1564844A - Device for measuring the flow rate of fluid in a duct

Info

Publication number: GB1564844A
Application number: GB198177A
Authority: GB
Original assignee: Crouzet SA
Current assignee: Thales Avionics SAS
Priority date: 1976-01-28
Filing date: 1977-01-18
Publication date: 1980-04-16
Also published as: IT1075066B; DE2702816B2; BE850488A; DE2702816C3; DE2702816A1; NL7700905A; FR2339841A1; FR2339841B1; CH611413A5

Description

(54) DEVICE FOR MEASURING THE FLOW RATE OF FLUID IN A DUCT (71) We, CROUZET, a French body corporate. of 128 avenue de la Republique, Paris 1 leme-France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a volumetric flow measuring device, and more particularly to a swirl flow type of flow meter.

The problem of measuring fluid has been previously solved by using very diversified techniques, mechanical as well as electromechanical or electronic.

Amongst the best known flow-meters, may be cited the turbine flow-meters, the pressure difference measuring flow-meters, the ultrasonic flow-meters, and the electro-magnetic flow-meters. All the proposed solutions display at least one ofthe following disadvantages: 1. Frictional force and wear due to the existence of movable mechanical parts resulting in a non-linearity of response of the device due to the absence of knowledge about and the nonstability of the frictional forces, the latter making the instrument also often unusable for measuring gas flows. A fall off in performance with time also occurs due to the wear of the movable mechanical parts; 2.The necessity of having a fluid stream flowing in well defined conditions, a modification of said conditions (turbulent of laminar flow) having an influence, for instance, in the case of a turbine flow-meter, on the linearity of the device, and the non-uniformity of the profile of the flow speeds in the duct of the measuring device leading to significant errors in devices relying on measurement of differential pressure.

3. Limitation in the range of use pressure difference devices being unusable for low flow rates; 4. Sensitivity of measurements to the presence of deposits and cavitation.

5. Relatively long response time (differential pressure or turbine flow-meters); 6. Output signal in analog form not very compatible with remote transmissions; 7. Operating difficulty, the ultra-sound and the electro-magnetic flow-meters requiring the use of a complicated and cumbersome equipment involving an increased risk of failures, higher costs, more difficult repairs and a higher energy consumption; 8. Difficulty in processing the initial measurements, the information relative to the flow measured with differential pressure flowmeters being obtained from the measurement of a pressure from which it is difficult to compute a flow rate.

9. Importance of the nature of the fluid, the use of an electro-magnetic flow-meter requiring a good knowledge and a good stability of the conducting properties of the liquid.

In order to eleminate these disadvantages, numerical devices have been previously proposed for measuring the volumetric flow of fluid flowing through a generally tubular body in which the fluid is given a swirling movement, the devices also having means producing a variable frequency periodic signal depending on the degree of swirl of the fluid and associ- ated logic means arranged for correcting said frequency.

These known devices, in the body of which the flux pressure and speed may vary periodically at all points of the wall of said body are usable for any homogeneous fluid in whatever flowing conditions; they comprise no movable mechanical parts and may guarantee a good testing stability in time; they may operate within a wide range of flow rates and they supply a numerical signal suitable for remote transmission.

However the construction of these known devices is often delicate and requires too high an accuracy for the practical manufacture of the shapes.

Furthermore, the means producing the variable frequency periodic signal does not always allow an optimal exploitation of the periodic signal.

An aim of the present invention is therefore to provide a device of simple construction with a linear response curve and a short response time.

With this aim in view the present invention provides a device for measuring the volu metric flow rate of a fluid flowing through a generally tubular body, comprising means for imparting a swirling or precessing motion to the fluid, and means operative to produce a periodic signal of frequency dependent on the precession motion of the fluid, characterized in that the precessing means comprises in succession, in the direction of fluid flow, a first cylindrical duct communicating with a converging cylindrical-conical axial chamber through a second duct the axis of which is displaced and inclined in relation to the axis of said chamber, the latter communicating coaxially with a cylindrical terminal duct through a third cylindrical duct of restricted diameter connected to said terminal duct by a diverging conical enlargement.

The invention will hereinafter be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a longitudinal cross-section through a mechanical part of one embodiment of a flow meter constructed in accordance with the present invention; Fig. 2 is a schematic view of the flow metering device of the embodiment; and Fig. 3 is a series of graphs in which various electric signals produced by the embodiment of Figs. 1 and 2 are plotted against time.

Fig. 1 shows the mechanical part 10 of the flow metering device, or flow-meter, the body of which is manufactured conventionally, for instance by casting or moulding.

Flow-meter 10 comprises a swirling means, in which the fluid entering via a duct 11 is deviated by a duct 13 and enters a cylindricalconical chamber 14 with a determined incidence in relation to the axis of the latter, thus causing at the outlet of chamber 14 the fluid to swirl. A staged duct generally diverging, made of two successive cylindrical ducts 15 and 17 of different diameters and connected by a conical enlargement 16 lie downstream of chamber 14. A fixed cross-piece 18 serves an anti-swirling means for stopping swirling movement of the fluid in chamber 17, whilst a filter 12, which may be a fixed bunch of small parallel ducts, is disposed in duct 11 and is mainly intended to stop the impurities carried by the fluid and accessorily to correct the eventual perturbations which may affect the flux upstream of the flow-meter.A sensor 19 is mounted on the side of the device 10 and comprises a piezo-electric or a kineticelectric transducer, for instance with hot wire, provided with peripheral members required for the processing of the signals supplied by sensor 19.

Fig. 2 shows the flow metering device according to the invention in a schematic form.

A sensor 19 mounted on the body of flowmeter 10 delivers a periodic electric signal 3.1 (Fig. 3) of frequency f related in linear mode to the flow according to the equation.

f=k0D -k1 k0 and kl being two positive constants.

A corrector 20 produces from frequency f a frequency F directly proportional to the flow, with a suitable scale factor.

Corrector 20 comprises a conformator 21 which, from signal 3.1 supplied by sensor 19, produces a rectangular wave signal 3.2, whereas a clock 22 supplies a periodic signal 3.3 (Fig. 3). An "exclusive or" device 23 is connected to receive signals 3.2 and 3.3 respectively supplied by conformator 21 and clock 22, signal 3.4 thus formed by device 23 being at logic level 1 when one and one onlv of signals 3.2 and 3.3 is at logic level 1. The function of counter 24 is to carry out the numerical evaluation of the average frequency F of the pseudo-periodic signal 3.4 delivered by circuit 23.

The speed or pressure variations of the swirling flux are most easily detectable when the geometrical and structural characteristics of the flow-meter 10 include or combine some or all of the following technological conditions: the inclination angle of duct axis 13 of the swirling means on the base of the cylindrical part of chamber 14 lies in the range between 40 and 50 ; the convergence angle of the conical part of chamber 14 connected to duct 15 lies in the range between 45" and 55 ; the diameter of the cylindrical part of chamber 14 is twice that of duct 15 which succeeds it; the shape of duct 15 is cylindrical with circular cross-section, the ratio of its length to its diameter Riving in the range between 1 and 2: sensor 19 is situated normally to duct axis 15, the projection of the axis of sensor 19 on the base of the cylindrical part of chamber 14 forming an angle lying in the range between 1200 and 1300 with the radius of the base crossing thentre of the opening through which duct 13 emerges into chamber 14; the sensitive extremitv of sensor 19 penetrates the inside of duct 15 by a distance lying between one tenth and one twentieth part of the diameter of duct 15.

WHAT WE CLAIM IS:- 1. A device for measuring the volumetric flow rate of a fluid flowing through a generally tubular body, comprising a means for imparting a swirling or precessing motion to the fluid, and means operative to produce a periodic signal of frequency dependent on the precession motion of the fluid, characterized in that the precessing means comprises in succession, in the direction of fluid flow, a first cylindrical duct communicating with a converging cylindrical-conical axial chamber through a second duct the axis of which is displaced and inclined in relation to the axis of said chamber, the latter communicating coaxially with a cylindrical terminal duct through a third cylindrical duct of restricted diameter

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. metric flow rate of a fluid flowing through a generally tubular body, comprising means for imparting a swirling or precessing motion to the fluid, and means operative to produce a periodic signal of frequency dependent on the precession motion of the fluid, characterized in that the precessing means comprises in succession, in the direction of fluid flow, a first cylindrical duct communicating with a converging cylindrical-conical axial chamber through a second duct the axis of which is displaced and inclined in relation to the axis of said chamber, the latter communicating coaxially with a cylindrical terminal duct through a third cylindrical duct of restricted diameter connected to said terminal duct by a diverging conical enlargement. The invention will hereinafter be further described by way of example with reference to the accompanying drawings in which: Fig. 1 is a longitudinal cross-section through a mechanical part of one embodiment of a flow meter constructed in accordance with the present invention; Fig. 2 is a schematic view of the flow metering device of the embodiment; and Fig. 3 is a series of graphs in which various electric signals produced by the embodiment of Figs. 1 and 2 are plotted against time. Fig. 1 shows the mechanical part 10 of the flow metering device, or flow-meter, the body of which is manufactured conventionally, for instance by casting or moulding. Flow-meter 10 comprises a swirling means, in which the fluid entering via a duct 11 is deviated by a duct 13 and enters a cylindricalconical chamber 14 with a determined incidence in relation to the axis of the latter, thus causing at the outlet of chamber 14 the fluid to swirl. A staged duct generally diverging, made of two successive cylindrical ducts 15 and 17 of different diameters and connected by a conical enlargement 16 lie downstream of chamber 14. A fixed cross-piece 18 serves an anti-swirling means for stopping swirling movement of the fluid in chamber 17, whilst a filter 12, which may be a fixed bunch of small parallel ducts, is disposed in duct 11 and is mainly intended to stop the impurities carried by the fluid and accessorily to correct the eventual perturbations which may affect the flux upstream of the flow-meter.A sensor 19 is mounted on the side of the device 10 and comprises a piezo-electric or a kineticelectric transducer, for instance with hot wire, provided with peripheral members required for the processing of the signals supplied by sensor 19. Fig. 2 shows the flow metering device according to the invention in a schematic form. A sensor 19 mounted on the body of flowmeter 10 delivers a periodic electric signal 3.1 (Fig. 3) of frequency f related in linear mode to the flow according to the equation. f=k0D -k1 k0 and kl being two positive constants. A corrector 20 produces from frequency f a frequency F directly proportional to the flow, with a suitable scale factor. Corrector 20 comprises a conformator 21 which, from signal 3.1 supplied by sensor 19, produces a rectangular wave signal 3.2, whereas a clock 22 supplies a periodic signal 3.3 (Fig. 3). An "exclusive or" device 23 is connected to receive signals 3.2 and 3.3 respectively supplied by conformator 21 and clock 22, signal 3.4 thus formed by device 23 being at logic level 1 when one and one onlv of signals 3.2 and 3.3 is at logic level 1. The function of counter 24 is to carry out the numerical evaluation of the average frequency F of the pseudo-periodic signal 3.4 delivered by circuit 23. The speed or pressure variations of the swirling flux are most easily detectable when the geometrical and structural characteristics of the flow-meter 10 include or combine some or all of the following technological conditions: the inclination angle of duct axis 13 of the swirling means on the base of the cylindrical part of chamber 14 lies in the range between 40 and 50 ; the convergence angle of the conical part of chamber 14 connected to duct 15 lies in the range between 45" and 55 ; the diameter of the cylindrical part of chamber 14 is twice that of duct 15 which succeeds it; the shape of duct 15 is cylindrical with circular cross-section, the ratio of its length to its diameter Riving in the range between 1 and 2: sensor 19 is situated normally to duct axis 15, the projection of the axis of sensor 19 on the base of the cylindrical part of chamber 14 forming an angle lying in the range between 1200 and 1300 with the radius of the base crossing thentre of the opening through which duct 13 emerges into chamber 14; the sensitive extremitv of sensor 19 penetrates the inside of duct 15 by a distance lying between one tenth and one twentieth part of the diameter of duct 15. WHAT WE CLAIM IS:-

1. A device for measuring the volumetric flow rate of a fluid flowing through a generally tubular body, comprising a means for imparting a swirling or precessing motion to the fluid, and means operative to produce a periodic signal of frequency dependent on the precession motion of the fluid, characterized in that the precessing means comprises in succession, in the direction of fluid flow, a first cylindrical duct communicating with a converging cylindrical-conical axial chamber through a second duct the axis of which is displaced and inclined in relation to the axis of said chamber, the latter communicating coaxially with a cylindrical terminal duct through a third cylindrical duct of restricted diameter

connected to said terminal duct by a diverging conical enlargement.

2. A device as claimed in claim 1 further comprising logic means operative to correct the frequency of the periodic signal to provide a corrected signal of frequency directly proportional to the rate of fluid flow.

3. A device as claimed in claim 1 or 2 wherein the angle of inclination of the axis of the second duct on the base of the cylindrical part of the chamber lies in the range 40 to 50 .

4. A device as claimed in any preceding claim wherein the diameter of the cylindrical part of the chamber is twice that of the third cylindrical duct.

5. A device as claimed in any preceding claim wherein the convergence angle of the conical part of the chamber connected to the third cylindrical duct lies in the range 45" and 55 .

6. A device as claimed in any preceding claim wherein the ratio of the length of the third cylindrical duct to its diameter lies in the range 1 to 2.

7. A device as claimed in any preceding claim in which the means for producing the periodic signal comprises a fluid pressure or speed sensor situated normally to the axis of the third cylindrical duct, wherein the projection of the axis or said sensor on the base of the cylindrical part of the chamber forms an angle lying in the range between 1200 and 1300 with the radius of said base crossing the centre of the opening through which the second duct emerges into said chamber.

8. A device as claimed in claim 6, wherein the sensitive extremity of the sensor penetrates inside of the third cylindrical duct by a distance lying in the range between one tenth and one twentieth of the diameter of said duct.

9. A device as claimed in claim 2 wherein the logic means comprises a logic generator supplying a constant frequency periodic signal, and a logic element of the exclusive or type calculating the sum of said signal with the variable frequency periodic signal through a shaping element, the pseudo-periodic logic signal resulting from said summation being applied to a final element operative to determine the average frequency of said resulting signal.

10. A numerical measuring device for measuring the volumetric flow rate of a fluid flowing through a generally tubular body, constructed and arranged substantially as herein described with reference to and as illustrated in the acompanying drawings.