GB2195768A

GB2195768A - Hall flowmeter

Info

Publication number: GB2195768A
Application number: GB08623669A
Authority: GB
Inventors: Simon Christopher Honey; Dr Emanuel Cohen
Original assignee: HEME INT Ltd; Pilkington Brothers Ltd
Current assignee: HEME INT Ltd; Pilkington Group Ltd
Priority date: 1986-10-02
Filing date: 1986-10-02
Publication date: 1988-04-13
Also published as: GB8623669D0

Abstract

A flowmeter for determining the rate of flow in a fluid flow system comprises a stainless steel tube (1) which is adapted for connection between an inlet pipe (4) and an outlet pipe (5) of a fluid flow system. Mounted centrally within the tube (1) is a frusto-conical plug (6). A spring loaded (10) piston(9) is slidably mounted within the tube (1) and co- operates with the frusto-conical plug (6) to effectively prevent flow of fluid from the inlet pipe (4) to the outlet pipe (5) when the fluid flow pressure is lower than the bias provided by the spring (10). As the fluid flow increases the pressure against the piston (9) increases and the piston (9) moves proportionately within the tube. This movement is detectable by means of the magnetic field of the magnetic piston (9) (or of magnetic means movable with a non-magnetic piston) coupling with a Hall effect device (12) mounted outside the tube (1) and provides linearly varying electrical signals which are used to enable measurements of fluid flow to be made. If the travel of the piston 9 is sufficiently large, more than one Hall device may be provided. <IMAGE>

Description

SPECIFICATION Flowmeter This invention relates to a flowmeter for use particularly, but not exclusively, in high pressure fluid systems to detect the rate of flow of fluid therein.

One known way of ascertaining the rate of flow of fluid in a fluid system is to connect a glass tube to the system, within which tube is slidably received a suitable piston arranged to alter position therein in response to variation of flow in the fluid flow system. By noting the position of the piston at any given instant against a known scale it is relatively easy to determine the flow rate in the fluid system.

However, there are problems if this principle is to be utilised in e.g. a fluid flow system where particularly high pressures are involved.

Clearly, the use of a transparent tube, such as a glass tube, would be impractical and stronger materials such as metal tubes have to be considered in such circumstances. This in turn gives rise to the problem of how it is then possible to determine accurately the position of the piston at any given instant since it is then no longer visible. One known method of achieving this end is to utilise a magnetic piston within a tube of non-magnetic metal such as stainless steel, on the outside of which is slidably mounted a ring of magnetisable material such as iron.In such an arrangement, it will be apparent that as the magnetic piston inside the stainless steel tube moves in response to variations in flow, the ring of magnetisable material follows the path of the magnetic float and hence it is possible to compare such movement with a known scale to determine the flow rate within the fluid flow system.

Whilst the aforementioned flowmeter can be useful in determining the flow rate within a highly pressurised fluid flow system, it will be clear that if such flow rate varies rapidly then the ring of magnetisable material will tend to lag behind the movement of the magnetic piston and hence give a false reading at any given instant. Furthermore, such an arrangement tends not to be particularly accurate and is affected by e.g. inertia of the moving parts and friction between them.

It is an object of the present invention to provide apparatus in which the aforementioned disadvantages are obviated and which can accurately determine the flow rate within a fluid flow system, for example a high pressure system, at any given instant.

According to the invention there is provided a flowmeter comprising a conduit for connection to a fluid flow system in which the rate of flow of said fluid is required to be determined, magnetic means being slidably received in the conduit and being arranged to alter position in response to variation of flow in said fluid flow system, and a Hall effect device disposed at least in part within the magnetic field of the magnetic means to thereby indicate by variation in electrical output of the Hall effect device the position of the magnetic means at any given instant, and hence the flow rate of the fluid in the fluid flow system.

Conveniently, the Hall effect device is positioned on the outside of the conduit which may be a tube, in such a manner that at a zero or low rate of fluid flow in the system the magnetic flux derived from the magnetic means is at a minimum and rises to a maximum as the magnetic means is moved along the conduit by an increase in fluid flow within the fluid flow system.

There may be more than one Hall effect device, particularly if the length of travel of the magnetic means is too long for a singie Hall effect device to operate efficiently. This is particularly true in the case where a linear variation in electrical output of the or each Hall effect device is required, in which case two or more Hall effect devices may be spaced apart along the length of the conduit such that each is operable to monitor the position of the magnetic means at any given instant and in so doing produce a linearly varying electrical output signal. The magnetic means may comprise a magnetic piston or float. Alternatively, the magentic means may be separate to but movable with a non-magnetic piston or float.

The flowmeter may include purely electronic means, such as digital read-out means to indicate at any given instant the flow rate. Alternatively, a bar-graph may be used comprising a series of illuminable displays each indicative of a particular rate of fluid flow or range of rate of fluid flow.

Recording means may be associated with the flowmeter to provide an electronic or written record of e.g. variations in rate of flow over a given period or whenever the flowmeter is in use.

The invention also extends to a method of determining the rate of flow in a fluid flow system, which method comprises the steps of providing a conduit for connection to a fluid flow system, which conduit includes magnetic means being slidably received therein, the magnetic means being arranged to alter position in response to variation of flow in said fluid flow system, arranging a Hall effect device within the magnetic field of the magnetic means to thereby indicate by variations in electrical output of the Hall effect device the position of the magnetic means, comparing said position of the magnetic means at any given instant to a known scale and thereby determining the rate of flow of fluid within the fluid flow system.

Preferably, the electrical output from the Hall effect device is compared at any given instant to two predetermined values, such as one low and one high value, the arrangement being such that on reaching either value the electrical output triggers alarm contacts which may then become de-energised. Conveniently, by utilizing a pair of predetermined values with which to compare the output from the Hall effect device the method and apparatus of the invention may be used to operate remote safety or control equipment in response to e.g.

insufficient or too much fluid flowing in the fluid flow system.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic view of apparatus -according to the invention, and Figure 2 is a graph showing the curve characterising the magnetic field of the apparatus of Fig. 1.

Referring firstly to Fig. 1, a flow meter according to one embodiment of the invention comprises a conduit in the form of a stainless steel tube 1 on respective ends of which are threaded collars 2,3 for connecting the tube 1 between an inlet pipe 4 and outlet pipe 5 of a fluid flow system.

A frusto-conical plug 6 is mounted centrally within the tube 1 on a flange 7 and is received within the collar 2. The flange 7 has a series of circumferentially disposed apertures 8 which permit fluid to flow from the inlet pipe 4 to the outlet pipe 5 as indicated by the arrows.

Magnetic means in the form of an annular magnetic piston 9 is slidably received within the bore of the tube 1 and has an inner surface corresponding to that of the outer surface of the frusto-conical plug 6 such that, in the position shown, the piston 9 actively blocks fluid flow between the inlet pipe 4 and outlet pipe 5.

A coil spring 10 is also received within the tube 1 and is secured under compression between the piston 9 and a washer 11 such that the piston 8 is permanently biased to the position shown but is slidable upwardly within the tube 1 to the limit permitted by the coil spring 10.

It will be apparent from the drawing that fluid flowing from the inlet pipe 4 to the outlet pipe 5 will tend to move the magnetic piston 9 upwardly within the stainless steel tube 1 and the extent of such movement will be dependent upon the rate of fluid flow Thus, when little or no fluid is flowing, the piston 9 occupies the position shown and increasing fluid flow progressively moves the position of the piston 9 upwardly until the limit dictated by the maximum compression of the coil spring 10 is reached.

On the outer side of the stainlees steel tube 1 is mounted a Hall effect device 12 which includes a Hall chip of the Gallium Arsenide type. The Hall effect device is supplied with a constant bias current and is disposed at a location on the outer side of the stainless steel tube 1 such that, in the position shown, the magnetic field created by the magnetic piston 9 produces in the Hall effect device 12 an electrical Hall voltage indicative of zero flow or a required minimum flow. In accordance with the invention, it will be apparent that as the flow between the inlet pipe 4 and outlet pipe 5 increases the magnetic field of the piston 9 is progressively moved upwardly along the tube 1, thus creating an increase in electrical output from the Hall effect device 14. In this way, at any given instant the position of the piston 9 can be determined within the tube 1 and thus the rate of flow of fluid within the fluid system can be readily determined.

Claims

1. A flowmeter comprising a conduit for connection to a fluid flow system in which the rate of flow of said fluid is required to be determined, magnetic means being slidably received in the conduit and being arranged to alter position in response to variation of flow in said fluid flow system, and a Hall effect device disposed at least in part within the magnetic field of the magnetic means to thereby indicate by variation in electrical output of the Hall effect device the position of the magnetic means at any given instant, and hence the flow rate of the fluid in the fluid flow system.

2. A flowmeter as claimed in claim 1, in which the Hall effect device is positioned on the outside of the conduit in such a manner that at a zero or low rate of fluid flow in the system the magnetic flux derived from the magnetic means is at a minimum and rises to a maximum as the magnetic means is moved along the conduit by an increase in fluid flow within the fluid flow system.

3. A flowmeter as claimed in claim 2, in which there is provided more than one Hall effect device where the length of travel of the magnetic means is too long for a single Hall effect device to operate efficiently.

4. A flowmeter as claimed in claim 3, in which when the flowmeter incorporates two or more Hall effect devices they are positioned in spaced-apart relationship along the length of the conduit such that each is operable to monitor the position of the magnetic means at any given instant and in so doing produce a linearly varying electrical output signal.

5. A flowmeter as claimed in claim 4, in which the magnetic means comprises a magnetic piston or float.

6. A flowmeter as claimed in claim 4, in which the magnetic means is separate to, but movable with, a non-magnetic piston or float.

7. A flowmeter as claimed in any preceding claims, in which the conduit comprises a tube.

8. A method of determining the rate of flow in a fluid flow system, which method comprises the steps of providing a conduit for connection to a fluid flow system, which conduit includes magnetic means being slidably received therein, the magnetic means being arranged to alter position in response to variation of flow in said fluid flow system, arranging a Hall effect device within the magnetic field of the magnetic means to thereby indicate by variations in electrical output of the Hall effect device the position of the magnetic means, comparing said position of the magnetic means at any given instant to a known scale and thereby determining the rate of flow of fluid within the fluid flow system.

9. A method of determining the rate of flow in a fluid flow system in which the conduit is a tube.

10. A method of determining the rate of flow in a fluid flow system substantially as described herein, with reference to, and as shown, in the accompanying drawing.

11. A flowmeter substantially as described herein with reference to, and as shown, in the accompanying drawing.