Position sensor for a fluid flow control device

Abstract

A device for controlling the flow of a fluid through a conduit from an upstream side of the device to a downstream side of the device. The device includes a valve housing having defined therein a valve aperture, a valve member movably mounted relative to the valve aperture. The valve member is arranged to be displaced reciprocally in a direction to selectively open and close the valve aperture. The device also includes a magnet mounted on or relative to the valve member, with the magnet being displaced by displacement of the valve member. A plurality of magnetic field sensors are mounted on the valve housing.

Claims

1. A device for controlling the flow of fluid through a conduit from an upstream side of the device to a downstream side of the device, the device comprising: a valve housing having defined therein a valve inlet, a valve outlet and a valve aperture, wherein the valve inlet, the valve outlet and the valve aperture are coaxial with each other; a valve member movably mounted relative to the valve aperture and arranged to be displaced reciprocally in an axial direction coaxial with the valve aperture to selectively open and close the valve aperture; a magnet that is discrete from the valve member and is not rigidly connected to the valve member, wherein the displacement of the valve member exerts a force on the magnet to displace the magnet in a direction parallel to the direction of displacement of the valve member; a biasing member arranged to bias the magnet towards the valve member; and a magnetic field sensor mounted on the valve housing.

2. The device as claimed in claim 1, wherein the valve member is coaxial with the valve aperture.

3. The device as claimed in claim 1, wherein the valve housing comprises a valve core on which the valve member is mounted, and wherein the valve member comprises a cap that surrounds, and moves over the outer surface of, the valve core.

4. The device as claimed in claim 1, wherein the magnet is mounted such that the magnet retains the same circumferential and/or radial position when the magnet is displaced by the valve member.

5. The device as claimed in claim 1, wherein the magnetic field sensor comprises a multiple axis sensor.

6. The device as claimed in claim 1, wherein the device comprises a cavity in which the magnet is located and arranged to be displaced.

7. The device as claimed in claim 6, wherein the cavity comprises a pressure balancing aperture fluidly connected to a control space.

8. The device as claimed in claim 6, wherein the biasing member is located in the cavity.

9. The device as claimed in claim 1, wherein the magnet is movably mounted on the valve housing.

10. The device as claimed in claim 1, wherein the valve member comprises an annular groove for receiving the end of the magnet.

11. The device as claimed in claim 1, wherein the magnet is mounted at a position that is radially offset from a central axis of the device.

12. The device as claimed in claim 1, wherein the valve housing comprises a cavity in which the magnetic field sensor is located.

13. The device as claimed in claim 1, wherein the magnetic field sensor is arranged at atmospheric pressure.

14. The device as claimed in claim 1, wherein the magnetic field sensor is isolated from the working fluid of the fluid flow control device.

15. The device as claimed in claim 1, wherein the device comprises a control unit arranged to determine the position of the valve member from an output received from the magnetic field sensor.

16. The device as claimed in claim 15, wherein the control unit is arranged to perform error minimisation on the output from the magnetic field sensor to determine the position of the valve member.

17. The device as claimed in claim 1, wherein the magnet comprises a permanent magnet.

18. The device as claimed in claim 1, wherein the device comprises a sheath surrounding the magnet.

19. The device as claimed in claim 1, wherein the magnet has a length that is greater than a maximum displacement of the valve member.

20. The device as claimed in claim 1, wherein: the magnet comprises one or more grooves which extend axially along the magnet; and the valve housing comprises a stopping member protruding from the valve housing, wherein the stopping member is arranged to project into the one or more grooves and to restrict the displacement of the magnet in the direction towards the valve member when the stopping member engages with an end of the one or more grooves.

Description

(1) FIG. 1 shows a cross-sectional view of a device in accordance with an embodiment of the invention wherein both the magnet and the position sensors are axially mounted within the valve core;

(2) FIG. 2 shows exemplary position measurements for three position sensors for a nominal magnetisation of the magnet;

(3) FIG. 3 shows exemplary position measurements for three position sensors when magnetisation is reduced but original calibration curves are used;

(4) FIG. 4 shows a step in an exemplary error minimisation algorithm whereby an estimated magnetisation is determined;

(5) FIG. 5 shows a cross-sectional view of a device in accordance with an embodiment of the invention wherein the magnet is embedded within the movable valve member and the sensors are mounted within a radial hole in the valve core;

(6) FIG. 6 shows a cross-sectional view of a device in accordance with an embodiment of the invention wherein a ring magnet is positioned along a central axis within the actuator and the sensors are mounted within a radial hole in the valve core;

(7) FIG. 7 shows a cross-sectional view of a device in accordance with an embodiment of the invention wherein the magnet is embedded within the movable valve member and three position sensors are mounted within three separate radial holes in the valve core; and

(8) FIG. 8 shows a cross-sectional view of a device in accordance with an embodiment of the invention wherein the magnet is embedded within the movable valve member and a single position sensor is mounted within a radial hole in the valve core.

(9) There are many different industrial situations in which it is important for the exact displacement of a valve member within a valve to be determined. As will now be described, embodiments of the present invention provide apparatus that is able to determine such information.

(10) FIG. 1 shows a cross-sectional view of a fluid flow device 1 comprising an electronic position sensing apparatus in accordance with an embodiment of the present invention. The device 1 comprises a housing 2, a valve core 4 and a cylindrical valve cap 6, all of which are made from non-ferrous materials (e.g. plastic or 316 stainless steel). The housing 2 defines an inlet aperture 8. The valve core 4 is mounted on the downstream end of the housing 2, and comprises a cylindrical upstream portion 5 which extends within the housing 2 in the upstream direction. The valve core 4 further comprises a number of outlet apertures 34.

(11) The cylindrical valve cap 6 comprises a cylindrical central bore, the diameter of which is substantially equal to the diameter of the upstream portion 5 of the valve core 4. The valve cap 6 further comprises a cylindrical upstream portion 7 that extends centrally in the upstream direction. The diameter of the upstream portion 7 is substantially equal to the diameter of the inlet aperture 8. The valve cap 6 is arranged to move reciprocally along the outer surface of the upstream portion 5 of the valve core 4.

(12) The valve cap 6 is movable between two extreme positions: a fully-closed position, wherein the upstream end 7 of the valve cap 6 is located fully within the inlet aperture 8 so as to prevent the flow of fluid through the aperture 8, and a fully-open position, wherein the inner surface 10 of the valve cap 6 abuts the upstream surface of the upstream portion 5 of the valve core 4 so as to allow a maximum flow rate through the aperture 8.

(13) The valve core 4 comprises a central bore 3 that extends from the upstream surface of the valve core 4 to an inner surface 14. A spring 12 is positioned within the central bore 3 between the inner surface 10 of the valve cap 6 and the inner surface 14 of the valve core 4 such that the spring 12 acts to bias the valve cap 6 into the fully-closed position.

(14) The valve core 4 further comprises a first axial hole 16 and a second axial hole 18. The first axial hole 16 extends into the valve core 4 from the upstream surface of the upstream portion 5 of the valve core 4. The second axial hole 18 extends into the valve core 4 from the downstream surface of the valve core 4.

(15) A magnet subassembly 20 is located within the first axial hole 16. The magnet subassembly 20 comprises an extender portion 19 and a magnet 21, wherein the extender portion 19 is rigidly connected to the upstream end of the magnet 21 such that the extender portion 19 protrudes in the upstream direction towards the valve cap 6. The valve cap 6 comprises an annular groove 50 located to receive the upstream end of the extender portion 19 of the magnet subassembly 20. A non-ferrous spring 22 mounted around the magnet 21 within the first axial hole 16 acts to bias the magnet subassembly 20 towards the valve cap 6 such that the upstream surface of the extender portion 19 is continuously pushed against the annular groove 50 of the valve cap 6. In an alternative embodiment, the spring 22 may be positioned within the first axial hole 16 such that it acts between the downstream end of the magnet 21 and the downstream end of the first axial hole 16 to bias the magnet subassembly 20 towards the valve cap 6 in the same way. Therefore, any axial movement of the valve cap 6 results in an equal corresponding axial movement of the magnet subassembly 20 within the first axial hole 16.

(16) The spring 22 is chosen to provide a force that is sufficient to maintain the contact between the magnet subassembly 20 and the inner surface 10 of the valve cap 6, even during fast operation of the valve, i.e. the momentum of the magnet subassembly 20 must be small in comparison to the force of the spring 22. However, the force of the spring 22 must also be small enough not to affect the operation of the main spring 12 (e.g. the spring 22 may provide around 1% of the overall spring force).

(17) The magnet subassembly 20 is contained within a sheath to avoid direct contact with the fluid. The sheath acts as a protective layer and reduces friction as the magnet subassembly 20 moves axially. Furthermore, the sheath may be required in order to conform with requirements set by the Water Regulations Advisory Scheme (WRAS) and the ATEX directives (Directives 99/92/EC and 94/9/EC).

(18) The first axial hole 16 further comprises pressure balancing apertures 23 that extend between the first axial hole 16 and the central bore 3 of the valve core 4. The pressure balancing apertures 23 fluidly connect the first axial hole 16 and the valve core 4 such that any build-up of unwanted pressure within the first axial hole 16 may be vented to the central bore 3.

(19) The magnet subassembly 20 further comprises grooves 27 which extend axially from the tip of the magnet subassembly 20 in the downstream direction. The valve core 4 comprises a stopping member 25 that partially protrudes from the upstream portion 5 of the valve core 4 into the entrance of the first axial hole 16 such that the stopping member 25 is arranged to project into the grooves 27 when the magnet subassembly 20 is located within the first axial hole 16. The stopping member 25 is complementary to the grooves 27 such that the stopping member 25 runs in the grooves 27 during displacement of the magnet subassembly 20 and such that the stopping member 25 abuts the downstream end of the grooves 27 at the maximum displacement of the magnet subassembly 20 in the direction of the inlet aperture 8, thereby halting the displacement of the magnet subassembly 20 and retaining it in the first axial hole 16.

(20) The engagement of the stopping member 25 with the grooves 27 also prevents rotation of the magnet subassembly 20, such that circumferential asymmetry of the magnetic field does not affect the accuracy of the position measurement.

(21) A printed circuit board (PCB) 24 is located within the second axial hole 18 and comprises three magnetic field sensors (Hall effect sensors) 26 arranged such that the magnetic radial field lines of the magnet 21 cut through the top of the sensors 26. Electric cables fed through a radial hole 28 extending from the second axial hole 18 to the exterior of the device 1 provide power to the PCB 24 and allow measurements of the magnetic field strength to be sent from each of the sensors 26 to a processor 30. The downstream end of the second axial hole 18 is sealed by a plug 32 that prevents the flow of fluid in to the second axial hole 18, thereby protecting the PCB 24.

(22) The magnetic field strength measurements are processed by the processor 30 using an error minimisation algorithm in order to estimate the axial position of the valve cap 6. Such error minimisation would not be possible if only one magnetic sensor 26 were to be used.

(23) The distance between the first axial hole 16 and the second axial hole 18 is chosen to maximise the linearity and gradient of the measured magnetic field strength signal. In this case, the distance between the magnet 21 and the sensors 26 is 20 mm.

(24) In this embodiment, the magnet 21 is not rigidly connected to the moving element 6 of the valve 1. In axial flow valves, it is common for the moving element 6 to move circumferentially. If the magnet 21 were rigidly mounted on the valve cap 6, the circumferential movement of the valve cap 6 would result in a circumferential movement of the magnet 21 away from the sensors 26. As it is important to maintain an appropriate distance between the magnet 21 and the sensors 26 in order to ensure the accuracy of the field strength measurements, such an arrangement of the magnet 21 would be disadvantageous. On the other hand, the arrangement shown in this embodiment allows the valve cap 6 to move circumferentially without affecting the distance between the magnet 21 and the sensors 26.

(25) The length of the magnet 21 is chosen to be equal to the travel of the valve cap 6 plus the length of the PCB 24 that is occupied by the sensors 26. Therefore, at all positions of the valve cap 6 between fully-open and fully-closed, the sensors 26 will be positioned axially within the end limits of the magnet 21. This is beneficial as the field strength of the magnet 21 becomes non-monotonic past the limits of the magnet 21.

(26) Operation of the apparatus shown in FIG. 1 will now be described.

(27) During normal operation of the valve 1, fluid flows into the valve 1 through the inlet aperture 8 and leaves the valve 1 via outlet apertures 34. The pressure of the upstream fluid on the upstream portion 7 of the valve cap 6 forces the valve cap 6 in the downstream direction, against the force of the spring 12. If the force of the fluid pressure exceeds the opposing force of the spring 12, the valve cap 6 is moved downstream towards its fully-open position.

(28) As the magnet subassembly 20 is arranged to abut the inner surface 10 of the valve cap 6, the axial movement of the valve cap 6 causes the magnet subassembly 20 to be displaced, against the force of the spring 22, by a distance equal to the axial displacement of the valve cap 6. The movement of the magnet 21 relative to the sensors 26 means that a changing value of magnetic field strength is continuously measured by the sensors 26.

(29) The magnetic field sensors 26 provide measurements of magnetic field strength to a processor 30, which interprets the data according to the calibration functions of each sensor 26.

(30) Exemplary calibration curves for three sensors 26, S1, S2 and S3, for a nominal magnetisation M.sub.0 of the magnet 21 are shown in FIG. 2. As can be seen, the signal s.sub.i measured by each of the sensors 26 corresponds to an axial displacement x.sub.i. If the magnetisation M of the magnet 21 is equal to the nominal magnetisation M.sub.0, the instantaneous signal readings s.sub.i of each sensor 26 should correspond to the same value of displacement x.

(31) However, the magnetisation of magnets 21 naturally decreases over time and is further effected by other factors such as temperature. If the magnetisation M during operation is less than the nominal magnetisation M.sub.0 and the original calibration curves are used, the inferred displacement x.sub.i from the three sensors 26 will be different, as shown in FIG. 3. It will be appreciated that this variation is a clear source of error.

(32) The displacement x.sub.i of the magnet 21 at nominal magnetisation M.sub.0 is given by the equation:
x.sub.i=c.sub.i.sup.?1(s.sub.i)(1)

(33) If the magnetisation M of the magnet 21 has been reduced from the nominal magnetisation M.sub.0 by a factor of

(34) $\frac{M}{M_{0}},$
the displacement of the magnet is given by:

(35) $\begin{matrix} x_{i} = c_{i}^{- 1} (\frac{s_{i} M_{0}}{M}) & (2) \end{matrix}$

(36) It can be seen that the calibration function c.sub.i is linear in magnetic field strength. Therefore, a vertical compression of the above function illustrates a reduction in the magnetisation of the magnet 26. Consequently, a more accurate estimate of magnetisation may be obtained by vertically compressing the above function until the values of x.sub.i inferred from the signals s.sub.i measured by each sensor 26 are substantially equal i.e. finding the value of

(37) $\frac{M}{M_{0}}$
for which the Root Mean Square Error (RMSE) in x.sub.i is minimised. This is illustrated in FIG. 4.

(38) For three sensors 26, this may be expressed mathematically as:

(39) $\begin{matrix} \underset{\frac{_{M}}{M_{0}}}{\arg \min} {.Math.}_{i = 1}^{n = 3} {[c_{i}^{- 1} (\frac{s_{i} M_{0}}{M}) - \frac{1}{3} {.Math.}_{i = 1}^{n = 3} c_{i}^{- 1} (\frac{s_{i} M_{0}}{M})]}^{2} & (3) \end{matrix}$

(40) The value of

(41) $\frac{M}{M_{0}}$
obtained from Equation 3 may be used to calculate an accurate value of the displacement x of the magnet 21, which is equal to the displacement of the moving element 6 of the valve 1. For the obtained value of

(42) $\frac{M}{M_{0}},$
x.sub.1=x.sub.2=x.sub.3=x(4)

(43) The application of error minimisation algorithms such as this means that the accuracy of the position estimate is substantially less affected by the demagnetisation of the magnet 21. This algorithm can be performed in real-time to ensure the accuracy of valve displacement measurements.

(44) The sensors 26 may each be configured to provide a single signal (e.g. if the sensors 26 are single axis magnetic field sensors) or multiple signals (e.g. if the sensors 26 are multiple axis magnetic field sensors).

(45) Where one or more multiple axis sensors 26 are used, the sensor(s) 26 may be arranged to measure both a horizontal component M.sub.x and a vertical component M.sub.y of the magnetic field.

(46) A magnetic field angle ?.sub.XY may be determined according to the following equation:

(47) $\begin{matrix} ?_{X Y} = \tan^{- 1} \frac{M_{y}}{M_{x}} & (5) \end{matrix}$

(48) The change in the angle of the magnetic field line relative to the horizontal and vertical axes at increasing axial displacements of the valve cap 6 is substantially linear. Thus, an accurate axial position of the valve cap 6 may be determined by calculating the magnetic field angle ?.sub.XY and identifying the corresponding axial displacement from a calibration curve, as discussed above.

(49) Multiple single-axis sensors may be used rather than multiple-axis sensors. However, in this case, only steep monotonic parts of the correlation curve may be used. Determining the axial position of the valve cap 6 according to a magnetic field angle calculated in the manner described above increases the useful range of the position sensing apparatus and provides a determination that is independent of temperature fluctuations.

(50) FIG. 5 shows a cross-sectional view of a fluid flow device 101 comprising electronic position sensing apparatus in accordance with an embodiment of the present invention. The device 101 comprises a valve core 104, an upstream valve casing 136 and a downstream valve casing 138. The upstream valve casing 136 defines an inlet aperture 108 and the downstream valve casing 138 comprises a valve seat 140 surrounding and defining an outlet aperture 134. The flow of fluid in FIG. 5 is from left to right, following a conduit 142 defined within the valve casings 136, 138.

(51) The valve core 104 defines a central bore 146 that extends axially from the downstream end of the valve core 104 into the valve core 104. A piston 144 is located within the central bore 146 such that the piston 144 is capable of moving axially within the central bore 146 when actuated by an actuator (not shown). A valve cap 106 is attached to the downstream end of the piston 144 such that the valve cap 106 moves axially with the piston 144.

(52) The piston 144 and valve cap 106 are movable between two extreme positions: a fully-open position and a fully-closed position. In the fully-open position, the valve cap 106 is located within the central bore 146, leaving a flow path for the flow of fluid through the outlet aperture 134 from the upstream side of the device 101 to the downstream side. In the fully-closed position, the piston 144 and valve cap 106 are moved such that valve cap 106 is sealed against the valve seat 140. This prevents the fluid from flowing through the device 101 via the outlet aperture 134.

(53) The valve core 104 further comprises a radial hole 148 that extends into the valve core 104 from the exterior surface of the valve core 104. A PCB 124 is located within the radial hole 148 and comprises three magnetic field sensors (Hall effect sensors) 126. Electric cables fed through radial hole 148 provide power to the PCB 124 and allow measurements of the magnetic field strength to be sent from each of the sensors 126 to a processor 130.

(54) A magnet 121 extending in the axial direction is embedded centrally within the piston 144. As the magnet 121 is rigidly embedded within the piston 144, the axial displacement of the piston 144 corresponds exactly to the axial displacement of the magnet 121. As the magnet 121 is located centrally within the piston 144, any circumferential movement of the valve cap 106 does not cause a change in distance between the magnet 121 and the sensors 126.

(55) During normal operation of the device 101, the flow of fluid through the device 101 from the inlet aperture 108 to the outlet aperture 134 is controlled by the movement of the piston 144 and valve cap 106 by the actuator (not shown). As the valve cap 106 is moved towards the valve seat 140, the flow through the device 101 is restricted. Therefore, the fluid flow may be throttled by adjusting the axial displacement of the piston 144 and valve cap 106.

(56) The sensors 126 continuously measure the strength of the magnetic field of the magnet 121 as it moves with the piston 144 and valve cap 106. In the same way as the above embodiment, the measurements may be processed by the processor 130 using an error minimisation algorithm in order to determine the axial position of the piston 144 and valve cap 106.

(57) FIG. 6 shows a cross-sectional view of a fluid flow device 201 comprising an electronic position sensing apparatus in accordance with an embodiment of the present invention. The device 201 is essentially the same as the device 101 discussed above. However, the axial magnet 121 has been replaced by a ring magnet 221 that is embedded within the piston 244.

(58) A PCB 224 comprising three Hall effect sensors 226, electrically connected to a processor 230, is located within a radial hole 248. The magnet 221 is positioned within the piston 244 such that, at all axial positions of the piston 244, the sensors 226 are positioned within the end limits of the magnet 221.

(59) Furthermore, as the ring magnet 221 is embedded centrally within the piston 244, any circumferential movement of the valve cap 206 does not cause a change in distance between the magnet 221 and the sensors 226.

(60) During normal operation of the device 201, flow through the device 201 is throttled by the axial displacement of the piston 244 and valve cap 206. The sensors 226 continuously measure the strength of the magnetic field of the ring magnet 221 as it moves with the piston 244 and valve cap 206. In the same way as the above embodiments, the measurements may be processed by the processor 230 using an error minimisation algorithm in order to determine the axial position of the piston 244 and valve cap 206.

(61) FIG. 7 shows a cross-sectional view of a fluid flow device 301 comprising an electronic position sensing apparatus in accordance with an embodiment of the present invention. The device 301 is essentially the same as the device 101 discussed above. However, the valve core 304 comprises an additional two radial holes 348 which extend into the valve core 304 from the exterior surface of the valve core 304. The radial holes 348 are spaced axially within the valve core 304.

(62) A PCB 324 comprising a Hall effect sensor 326, electrically connected to a processor 330, is located within each radial hole 348. The magnet 321 is positioned within the piston 344 such that, at all axial positions of the piston 344, the sensors 326 are positioned within the end limits of the magnet 321.

(63) In the same way as the above embodiments, the sensors 326 continuously measure the strength of the magnetic field of the magnet 321 as it moves with the piston 344 and valve cap 306. The measurements may be processed by the processor 330 using an error minimisation algorithm in order to determine the axial position of the piston 344 and valve cap 306.

(64) FIG. 8 shows a cross-sectional view of a fluid flow device 401 comprising an electronic position sensing apparatus in accordance with an embodiment of the present invention. The device 401 is essentially the same as the device 101 shown in FIG. 5, except the PCB 424, located within a single radial hole 448, comprises only one sensor 426. The sensor 426 is a multiple-axis (e.g. dual axis) sensor. Using only a single sensor helps to reduce the power consumed by the sensor.

(65) In the same way as the above embodiments, the sensor 426 continuously measures the strength of the magnetic field of the magnet 421 as the magnet moves with the piston 444 and valve cap 406. The measurements may be processed by the processor 430 using an error minimisation algorithm in order to determine the axial position of the piston 444 and valve cap 406.

(66) It can be seen from the above that, in at least preferred embodiments, the invention provides a fluid flow control device in which a magnetic position sensing apparatus having multiple magnetic field sensors is provided, such that they experience different parts of the magnetic field of a magnet mounted on or relative to the valve member of the fluid flow control device. This helps to provide a more accurate determination of the position of the valve member and may allow the measurements to be automatically calibrated for changes (e.g. degradation) of the magnetic field of the magnet with time and/or temperature.

Position sensor for a fluid flow control device

Assignee

Inventors

Cpc classification

Classification Explorer

F16K1/12

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F16K37/0033

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

G01L9/0082

PHYSICS

Classification Explorer

F16K1/38

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

International classification

Classification Explorer

F16K1/38

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F16K1/12

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

F16K37/00

MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING

Classification Explorer

G01L9/00

PHYSICS

Abstract

Claims

Description