GB2145818A

GB2145818A - Flowmeters

Info

Publication number: GB2145818A
Application number: GB08322721A
Authority: GB
Inventors: Graham Francis Stacey; Martin John Collier
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1983-08-24
Filing date: 1983-08-24
Publication date: 1985-04-03
Also published as: GB2145818B; GB8322721D0

Abstract

A tube 1 carries a liquid in which, because of a bluff body 3, vortices are generated, the frequency of generation depending upon the speed of the liquid. The vortices act on a vane (not shown) which vibrates at a corresponding frequency and causes a shaft 4, to which it is attached, to move. In one embodiment, a plate 19, on which are carried four magnets, (two of which, 20 and 21 are shown) moves with the shaft 4. Pivoted above the plate 19 is a disc 24 which also carries magnets 25 and 26 having opposite polarity to those on plate 19. The disc 24 also has a reflector 9 on its surface which, when positioned directly under two optical fibres 11 and 12, causes light transmitted down one to be reflected back along the other to a detector (not shown). Movement of the plate 19 causes the disc 24 to move because of attraction between the magnets and hence light is transmitted to the detector in the form of pulses, the frequency of which is related to the speed of the liquid on the tube 1. Other embodiments are disclosed in Figs. 1-3.

Description

SPECIFICATION Flowmeters This invention relates to flowmeters and is particularly applicable to vortex shedding flowmeters.

For the purpose of this Specification, a flowmeter should be taken to include any instrument which: produces an output which varies with varying flow rate; which detects a particular flow rate; or which detects a change of flow rate through a critical value.

A vortex shedding flowmeter is one in which an obstruction, or bluff body, is placed in a fluid so that vortices are generated as the fluid flows past it. The frequency of production (i.e. shedding) of these vortices is related to the speed of the fluid flow. By observing the frequency of vortex shedding the flow speed can thus be deduced.

According to a first aspect of the invention there is provided a flowmeter comprising: a member mounted so that its position or movement is dependent on the velocity of fluid in a conduit; a source of electromagnetic radiation; means for transmitting the radiation from the source to the member, at least part of the member being located outside the conduit, said part being constructed and arranged so that it produces modifications of the radiation according to its position; and means for transmitting the modified radiation to a detector capable of detecting the said modification.

Since the said part of the member which produces modifications of the radiation is located outside the conduit it is easily accessible. It is thus possible to align it correctly or remove components for repair or replacement without difficulty. If flow of a harmful fluid is being monitored there is less risk of the said part becoming damaged or corroded than would be the case if it were located within the conduit. By employing optical or other electromagnetic radiation to carry information about fluid flow, problems of fire risk and/or interference from outside sources may be eliminated or reduced, compared with flowmeters in which electrical signals are used. The modifications could consist of, for example, a variation in amplitude or interruption in the radiation produced by movement of the said part.

Preferably, where the whole of the member is located outside the conduit, said member is coupled to a further member located within the conduit by means comprising a magnetic coupling. By employing a magnetic coupling the said member may be completely insulated from the fluid. It is preferred that the magnetic coupling comprises a first magnet of one polarity arranged to move with the said further member and a second magnet having opposite polarity arranged to move with the said member, so that the coupling is effected by the attractive forces between the magnets, although the first and second magnets could have the same polarity and movement be produced by repulsion between them. It is also preferred that the magnetic coupling comprises samarium cobalt magnets, which are highly resistant to demagnetisation.A plurality of magnets on each of the members could be employed to give an even force around them.

Preferably a flowmeter as previously described includes: means for generating vortices within the fluid; a vane located within the conduit and arranged to be vibrated at a frequency dependent upon the velocity of the fluid by the vortices; and means for using movement of the vane to control the position or movement of the said member. It is preferred that in such a flowmeter, where magnetic coupling is not employed, said member comprises a shaft attached to said part, and means for generating vortices comprises a bluff body located within the conduit, the shaft being contained within the bluff body and being attached to the vane by an elongate member extending through an aperture in the bluff body.It is also advantageous that two O-ring seals are located around the shaft on respective different sides of the elongate member or, alternatively, that a V-type lip seal is located around the shaft.

Preferably, said part has a reflective surface to reflect the radiation, and also preferably the reflective surface is part-spherical. Since the said part is located outside the conduit, the reflective surface tends to remain unobscured by the fluid.

According to a second aspect of the invention there is provided a flowmeter comprising: a first member located within a conduit, its position or movement being dependent on the rate of flow or change in flow of fluid within the conduit, and coupled magnetically to a second member outside the conduit to communicate its position or movement to the second member; and detecting means for monitoring the second member whereby the rate of flow or change in flow of the fluid can be monitored.

Some ways in which the invention may be performed are now described by way of example with reference to the accompanying drawings in which: Figure 1 is a part longitudinal section of apparatus in accordance with the invention; Figures 2 and 3 are part longitudinal sections of the apparatus of Fig. 1 with modifications thereto; and Figure 4 is a part longitudinal section of another apparatus in accordance with the invention. The same references are used for the same parts throughout.

With reference to Fig. 1, a conduit in the form of a tube 1 carries liquid flowing in the direction of arrow 2. A bluff body 3 having a rectangular cross-section is positioned across a diameter of the tube 1. As the liquid flows past the bluff body vortices are generated downstream of it, the frequency of their shedding depending on the speed of the liquid. The bluff body 3 is hollow, having a cylindrical cavity lying along its longitudinal axis X in which is located a shaft 4. An elongate member 5 is embedded in the shaft 4 and extends normally from it through an aperture 6 in the downstream face of the bluff body 3. A vane 7 is attached to the free end of the shaft 4 and is arranged to lie transversely across the flow of the liquid.

One end of the shaft 4 is located outside the wall of the pipe 1 where it is joined to a circular plate 8 having its plane normal to the axis X, to constitute a member, the movement of which depends on the flow of the liquid.

The plate 8 has a hemi-spherical reflector 9 on one surface. A cap 10 surrounds the plate 8 and is joined to the bluff body 3 at the wall of the tube 1. Two optical fibres 11 and 12 pass through the cap 10 and are held in position by a ferrule 1 3 so that their ends are located above the surface of the plate 8 on which the reflector 9 is carried and the same radius as the reflector 9.

The vortices generated by the bluff body 3 cause the vane 7 to vibrate. The movement of the vane 7 is transmitted via the elongate member 5 to the shaft 4 which rotates, causing the plate 8 to rotate also. Light is transmitted from an optical source (not shown) along the optical fibre 11 and, when the reflector 9 is directly under it, is reflected back to the optical fibre 1 2 which transmits it to a detector (not shown) capable of detecting the presence or absence of light. However, when the reflector 9 is not directly under the optical fibres 11 and 1 2 no light is passed to the detector. Hence by observing the interruption of light at the detector, the frequency of vibration of the vane 7 and therefore the speed of the liquid, may be determined.

Some fluid may enter the cavity containing the shaft 4 and the plate 8. This possibly is reduced by the introduction of two O-ring rubber seals 14 and 15, as shown in Fig. 2, around the shaft 4. One of the O-ring seals 14 is located on one side of the elongate member 5 and the other on the other side.

The inventors have found that this is a more satisfactory arrangement then the use of only one O-ring seal located around the shaft 4 between the elongate member 5 and the plate 8, which introduced a tendency for the shaft 4 to move, bringing the reflector 9 and the ends of the optical fibres 11 and 1 2 close together.

An alternative to the apparatus shown in Fig. 2 is illustrated in Fig. 3 in which, instead of two O-ring seals, a nitrile rubber V-type lip seal 1 6 is employed. This surrounds the shaft 4 and rotates with it, the seal being made between a thin edge of the lip seal 1 6 and a cage 1 7 which surrounds the seal 16. This type of seal introduces much less frictional resistance than an O-ring seal because of the area of contact between it and stationary parts of the apparatus is much less, and no appreciable compressive force is required to maintain the seal.

With reference to Fig. 4, a flowmeter includes a bluff body 3, shaft 4 and vane and elongate member (not shown) similar to those of the above-described apparatus. The bluff body 3 extends along the exterior of the wall of the pipe 1 and outwardly to form a base plate 18 which has a cylindrical depression in its upper surface. The shaft 4 protrudes from the pipe 1 and is joined to a circular planar plate 1 9 which lies within the depression.

Four sintered samarium cobalt magnets, two of which 20 and 21 are shown, are distributed equidistant around the circumference of the plate 1 9.

A sealing plate 22 is located on the base plate 1 8 and has a central raised portion on which is pivoted a disc 24 having similar dimensions to plate 1 9. The disc 24 also has four sintered samarium cobalt magnets spaced equidistant around its circumference (two of which 25 and 26 are shown) and each of these corresponds to a respective magnet having opposite polarity attached to the plate 1 9.

The magnets are positioned such that a small thickness only of the sealing plate 22 lies between those on the plate 1 9 and those of the disc 24. The surface of the disc 19 which does not carry the magnets has a hemispherical reflector 9.

A top plate 27 is located on the sealing plate 22 and two screws 28 and 29 pass through it, the sealing plate 22, the base plate 18 and into the wall of the pipe 1 to hold them firmly together. Two optical fibres 11 and 1 2 pass through the top plate 27 and are held in position by a ferrule 1 3. When the reflector 9 is positioned directly under them light (from a source not shown) sent down optical fibre 11 is reflected into optical fibre 1 2 and transmitted to a detector (not shown).

Two O-ring seals, 30 and 31 seal the tube 1 to prevent liquid flowing in it from escaping.

Vortices generated by liquid in the pipe 1 flowing past the bluff body 3 cause the vane to vibrate and hence the shaft 4 to move. The plate 1 9 also moves, and because of the attractive forces between the magnets of the plate 1 9 and disc 24, causes the latter to rotate. As the reflector 9 vibrates under the optical fibres 11 and 12, light is received by the detector only when the reflector 9 is directly under the optical fibres 11 and 12, and hence, by observing the frequency of light pulses received by the detector, the speed of the liquid may be determined.

Although the apparatus described above uses reflection to modify the light, other forms of modification could be employed, for example, interruption of a transmissive beam of light.

The light may be ultra-violet, visible or infra-red radiation.

Claims

1. A flowmeter comprising: a member mounted so that its position or movement is dependent on the velocity of fluid in a conduit; a source of electromagnetic radiation; means for transmitting the radiation from the source to the member, at least part of the member being located outside the conduit, said part being constructed and arranged so that it produces modifications of the radiation according to its position; and means for transmitting the modified radiation to a detector capable of detecting the said modification.

2. A flowmeter as claimed in claim 1 where the whole of the member is located outside the conduit, and wherein said member is coupled to a further member located within the conduit by means comprising a magnetic coupling.

3. A flowmeter as claimed in claim 2 and wherein the magnetic coupling comprises a first magnet of one polarity arranged to move with the said further member and a second magnet having opposite polarity arranged to move with the said member.

4. A flowmeter as claimed in claim 2 or 3 and wherein the magnetic coupling comprises samarium cobalt magnets.

5. A flowmeter as claimed in any preceding claim and including: means for generating vortices within the fluid; a vane located within the conduit and arranged to be vibrated at a frequency dependent on the velocity of the fluid by the vortices; and means for using movement of the vane to control the position or movement of the said member.

6. A flowmeter as claimed in claim 5 when dependent on claim 1 and wherein said member comprises a shaft attached to said part, and means for generating vortices comprises a bluff body located within the conduit, the shaft being contained within the bluff body and being attached to the vane by an elongate member extending through an aperture in the bluff body.

7. A flowmeter as claimed in claim 6 and including two O-ring seals located around the shaft on respective different sides of the elongate member.

8. A flowmeter as claimed in claim 6 and including a V-type lip seal located around the shaft.

9. A flowmeter as claimed in any preceding claim and wherein said part has a reflective surface to reflect the radiation.

10. A flowmeter as claimed in claim 9 and wherein the reflective surface is partspherical.

11. A flowmeter as claimed in any preceding claim and wherein the means for transmitting the radiation from the source to the said member includes a first optical fibre, and the means for transmitting the modified radiation to a detector includes a second optical fibre.

1 2. A flowmeter as claimed in any preceding claim and wherein the electromagnetic radiation is infra-red, visible or ultra-violet radiation.

1 3. A flowmeter substantially as illustrated in and described with reference to Fig. 1 of the accompanying drawings.

14. A flowmeter substantially as illustrated in and described with reference to Fig. 2 of the accompanying drawings.

1 5. A flowmeter substantially as illustrated in and described with reference to Fig. 3 of the accompanying drawings.

16. A flowmeter substantially as illustrated in and described with reference to Fig. 4 of the accompanying drawings.

17. A flowmeter comprising: a first member located within a conduit, its position or movement being dependent on the rate or flow or change in flow of fluid within the conduit, and coupled magnetically to a second member outside the conduit to communicate its position or movement to the second member; and detecting means for monitoring the second member whereby the rate of flow or change in flow of the fluid can be monitored.

1. A flowmeter comprising: a first member located within a conduit and mounted so that its position or movement is dependent on the velocity of fluid in the conduit; a second member linked for movement with the first member but located outside the conduit and being constructed and arranged so that it produces modifications to radiation transmitted from a source to a detector, the said modifications and therefore an output of the detector being dependent on the position of the second member.

2. A flowmeter as claimed in claim 1 and wherein the first and second members are mechanically linked.

3. A flowmeter as claimed in claim 1 and wherein the first and second members are linked by means comprising a magnetic coupling.

4. A flowmeter as claimed in claim 3 and wherein the magnetic coupling comprises a first magnet of one polarity arranged to move with the first member and a second magnet having opposite polarity arranged to move with the second member.

5. A flowmeter as claimed in claim 3 or 4 and wherein the magnetic coupling comprises samarium cobalt magnets.

6. A flowmeter as claimed in any preceding claim and including: means for generating vortices with the fluid; a vane located within the conduit and arranged to be vibrated at a frequency dependent on the velocity of the fluid by the vortices; and means for using movement of the vane to control the position or movement of the first member.

7. A flowmeter as claimed in claim 6 when dependent on claim 1 or 2 and wherein the first member comprises a shaft which is attached to the second member, and means for generating vortices comprising a bluff body located within the conduit, the shaft being contained within the bluff body and being attached to the vane by an elongate member extending through an aperture in the bluff body.

8. A flowmeter as claimed in claim 7 and including two O-ring seals located around the shaft on respective different sides of the elongate member.

9. A flowmeter as claimed in claim 7 and including a V-type lip seal located around the shaft.

10. A flowmeter as claimed in any preceding claim and wherein the second member has a reflective surface to reflect the radiation.

11. A flowmeter as claimed in claim 10 and wherein the reflective surface is partspherical.

1 2. A flowmeter as claimed in any preceding claim and wherein means for transmitting the radiation from the source to the second member includes a first optical fibre, and means for transmitting the modified radiation to a detector includes a second optical fibre.

1 3. A flowmeter as claimed in any preceding claim and wherein the electromagnetic radiation is infra-red, visible or ultra-violet radiation.

14. A flowmeter substantially illustrated in and described with reference to Fig. 1 of the accompanying drawings.

1 5. A flowmeter substantially as illustrated in and described with reference to Fig. 2 of the accompanying drawings.

1 6. A flowmeter substantially as illustrated in and described with reference to Fig. 3 of the accompanying drawings.

1 7. A flowmeter substantially as illustrated in and described with reference to Fig. 4 of the accompanying drawings.

18. A flowmeter comprising: a first member located within a conduit, its position or movement being dependent on the rate of flow or change in flow of fluid within the conduit, and coupled magnetically to a second member outside the conduit to communicate its position or movement to the second member; and detecting means for monitoring the second member whereby the rate of flow or change in flow of the fluid can be monitored.