GB2423371A

GB2423371A - Inductive pressure sensor

Info

Publication number: GB2423371A
Application number: GB0602221A
Authority: GB
Inventors: Claudio Negro; Michele Farano; Sabrina Bindocci
Original assignee: Elbi International SpA
Current assignee: Elbi International SpA
Priority date: 2005-02-18
Filing date: 2006-02-03
Publication date: 2006-08-23
Anticipated expiration: 2026-02-03
Also published as: GB2423371B; CN200968892Y; FR2882434A3; DE202006002561U1; FR2882434B3; ITTO20050027U1; GB0602221D0

Abstract

The sensor (1) comprises a rigid casing (2) which has at least one input (5) for a pressure to be detected, and which defines a chamber (12) in which a movable diaphragm (6) having a surface (6b) that is operatively exposed to the pressure coming from the input (5) is mounted in a leaktight manner. A ferromagnetic core (13) is connected to the diaphragm (6) and is movable under the effect of the pressure, relative to a stationary coil (9), against the action of a reaction spring (16), in a manner such that, in operation, the inductance of the coil (9) varies according to the value of the hydraulic pressure. The casing (2) comprises a first, substantially cup-shaped body (3) with a tubular shank (3a) in which the input (5) is defined, and with an opening (3e) located at the opposite end, and a second, tubular, reel-shaped body (4) fixed in the first body (3) and having: a first end portion (4a) which clamps a peripheral portion (6a) of the diaphragm (6) in a hydraulically leaktight manner, an axially intermediate portion (4b) around which the coil (9) is wound, and a second end portion (4c) which defines a reaction surface (4e) against which the spring (16) associated with the movable core (13) reacts.

Description

INDUCTIVE PRESSURE SENSOR

The present invention relates to an inductive pressure sensor.

More specifically, the subject of the invention is an inductive hydraulic pressure sensor particularly for electric household appliances, boilers and the like, of the type comprising: a rigid casing which has at least one (first) input for the hydraulic pressure to be detected and which defines a chamber in which a movable diaphragm having a surface that is operatively exposed to the hydraulic pressure coming from the input is mounted in a hydraulically leaktight manner, a ferromagnetic core being connected to the diaphragm and being movable under the effect of the pressure, relative to a stationary coil carried by the casing, against the action of (first) resilient biasing means in a manner such that, in operation, the inductance of the coil varies according to the value of the hydraulic pressure.

The object of the present invention is to provide an inductive pressure sensor of the type defined above which has improved characteristics both with regard to the isolation of the water from the electrical parts of the sensor and to the simplification of the structure and assembly of the sensor.

These and other objects are achieved according to the invention by an inductive pressure sensor of the type specified above, characterized in that the casing comprises: a first, substantially cup-shaped body with a tubular shank in which the input is defined, and with an opening located at the opposite end to the tubular shank, and a second, tubular, reelshaped body fixed in the first body and having: a first end portion which clamps a peripheral portion of the diaphragm in a hydraulically leaktight manner, an axially intermediate portion around which the coil is wound, and a second end portion which defines a reaction surface against which the resilient means associated with the movable core react, the arrangement being such that the core is mounted so as to be movable inside the second body, between the diaphragm and the resilient biasing means.

Further characteristics and advantages of the invention will become clear from the following detailed description which is given purely by way of non-limiting example with reference to the appended drawings, in which: Figure 1 is a front view of a first inductive pressure sensor according to the invention, Figure 2 is an exploded perspective view which shows the inductive pressure sensor of Figure 1, Figure 3 is a section taken on the line 111-Ill of Figure 1, Figure 4 is a section taken on the line IV- IV of Figure 3, Figure 5 is a side view of a reel-shaped body included in the sensor according to the preceding drawings, Figure 6 is a section taken on the line VI-VI of Figure 3, Figures 7 and 8 are sectioned views similar to that of Figure 4 and show two variants of the sensor according to the invention, and Figure 9 is a sectioned view which shows a further variant of the device according to the invention.

An inductive hydraulic pressure sensor according to the invention is generally indicated I in the drawings.

The sensor 1 comprises a rigid casing, generally indicated 2, formed by a first, substantially cup-shaped body 3 and by a second, substantially tubular, reel-shaped body 4.

The cup-shaped body 3 has a lower tubular shank 3a in which an input connector or duct 5 for a hydraulic pressure to be detected is defined (Figures 3 and 4).

In the embodiment shown by way of example, the cup-shaped body 3 has, adjacent the tubular shank 3a, a first portion 3b with an enlarged diameter, then an intermediate portion 3c having a further enlarged diameter and, finally, an upper end portion 3d with an even further enlarged diameter.

The tubular reel-shaped body 4 has a lower end portion 4a the end rim of which clamps the peripheral portion 6a of a diaphragm, generally indicated 6, in a hydraulically leak-tight maimer relative to the cup- shaped body 3. The diaphragm 6 has a surface 6b which is operatively exposed to the hydraulic pressure coming from the input connector or duct 5 (Figures 3 and 4).

The reel-shaped body 4 has an axially intermediate portion 4b which has an outer annular flange 7 which, (preferably) on the side facing towards the diaphragm 6, that is, towards the input connector 5, clamps an annular hydraulic sealing member 18 relative to the cup- shaped body 3.

The reel-shaped body 4 has a second end portion 4c with a terminal portion 4d which closes the upper opening 3e of the cup-shaped body 3 and which defines a second outer annular flange 8 substantially parallel to the flange 7.

A coil 9 is wound around the intermediate portion 4b of the reel-shaped body 4 between the flanges 7 and 8.

The reel-shaped body 4 is fastened to the cup-shaped body 3 by means of snap-coupling projections 10 (Figures 3 and 4) which are formed in the lower axial portion 4a of the body 4 and are engaged in corresponding openings or seats 11 provided in the portion 3b of the cup-shaped body 3.

A chamber, generally indicated 12, is defined in the rigid casing of the sensor between the upper end of the shank 3a of the cup-shaped body and inside the end portion and intermediate portions 4a and 4b of the reelshaped body 4. A movable ferromagnetic core 13 extends in the chamber and is connected to the diaphragm 6. In the embodiment shown by way of example, the core 13 comprises a ring 14 of ferromagnetic material totally encapsulated in a casing 15 of electrically insulating material, for example, moulded plastics material.

A helical spring 16 bears, at its lower end, against the upper end of the core 13 and, at its upper end, against a reaction surface 4e defined in the upper end portion 4c of the reel- shaped body 4.

In operation, the core 13 is movable relative to the stationary coil 9 under the effect of the pressure applied to the input connector or duct 5 so that the inductance of the coil 9 varies according to that pressure.

The coil is connected, in a manner not shown, to a processing circuit comprising, for example, a capacitor the capacitance of which, together with the inductance of the coil 9, forms an LC circuit which is resonant at a frequency that is variable according to the inductance of the coil 9 and hence according to the pressure at the input 5 of the sensor.

The processing circuit may advantageously be carried by a printed-circuit board 30 (Figures 2-6) which, in the embodiment shown, is substantially U-shaped (Figure 2) and is fitted between the upper portion 4d and the flange 8 of the body 4, around the portion 4c thereof. An end 30a of the board 30 carries conductive connection tracks and is connected to a connector 31 (Figures 2 and 3) which is "pinched" between the reel-shaped body 4 and the cup-shaped body 3.

The sensor according to the invention as described above has many advantages.

In the first place, its carrying structure or casing 2 is constituted by solely two bodies, that is, the cup-shaped body 3 and the reel-shaped body 4, which are easily fitted together.

A further advantageous characteristic is represented by the double electrical isolation of the coil 9 from the hydraulic fluid (water) supplied to the input connector 5. The double isolation is ensured in one way by the peripheral portion 6a of the diaphragm 6 which is clamped in a leaktight manner between the bodies 3 and 4, as well as being ensured by the annular sealing member 18 which is clamped between the body 3 and the flange 7 of the reel-shaped body 4.

A further protection is represented by the total encapsulation of the ferromagnetic core 4 in the electrically insulating casing 15.

Figure 7 shows a pressure sensor according to the invention which has some modifications in comparison with the embodiment described above with reference to Figures 1-6.

In Figure 7 parts and elements that have already been described have again been attributed the same references as were used above.

A first difference in the device according to Figure 7 is that, in the upper end portion 4c of the reel-shaped body 4, there is a second input connector 19 through which a second pressure can be admitted to the portion of the chamber 12 which is located on the side of the diaphragm 6 remote from the first input connector 5.

By virtue of this feature, the sensor device of Figure 7 is of the differential type and, in operation, the axial position of the core 13 relative to the coil 9 depends on the difference between the pressures applied to the input connectors 5 and 19. Accordingly, the inductance of the coil 9 also depends on that pressure difference.

A second difference of the device of Figure 7 is represented by the addition of a further helical spring 17 reacting, at its lower end, against a shoulder provided in the tubular shank 3a of the cup-shaped body 3 and, at its upper end, against the diaphragm 6.

The spring 17 acts on the diaphragm 6 and on the associated core 13 in the opposite direction to the force exerted thereon by the spring 16.

The addition of the spring 17 is not necessarily bound to the implementation of the pressure sensor device in differential form as in the drawing, since this spring may optionally also be added in a sensor formed with a single pressure input as in Figures 1-6.

Figure 8 shows a further variant of the pressure sensor according to the invention. Parts and elements that have already been described have again been attributed the same reference numerals in this drawing.

The sensor according to Figure 8 is intended in particular for use in a domestic heating boiler, for example, a wall boiler. When such a boiler is installed on a construction site for an apartment block or the like, the installer may need to know whether there is a fluid under pressure in the input connector 5 of the pressure sensor before the sensor has been supplied with electrical energy and can provide its signal. To enable the installer to know whether the input connector 5 of the pressure sensor is under pressure in these conditions, in the variant of Figure 8, the input connector 5 is in communication with a duct 20 which extends at least partially outside the casing 2 of the sensor and is preferably at least partially transparent. A body such as a small, for example, red ball 21, is mounted so as to be movable in the duct 20 and, when hydraulic pressure is applied to the input connector 5, can adopt a position (such as that shown in solid outline in Figure 8) in which it is visible from the exterior and indicates the presence of pressure in the input connector 5.

If there is a lack of pressure in the input connector 5, the body 21 falls by gravity and is arranged in a rest position such as that shown in broken outline in Figure 8, resting on stop elements provided in the duct 20.

The variant described above with reference to Figure 8 can optionally also be implemented in a differential sensor of the type shown in Figure 7, with or without the additional spring 17.

In the variant shown in Figure 9 parts and elements that have already been described have again been attributed the reference numerals used above.

This variant is distinguished from the previous ones substantially by the following aspects.

The cup-shaped body 3 again has a stepped profile but with a smaller number of axial portions; the portion indicated 3d in Figures 3 and 7 is missing, whereas the portion 3c, the top of which defines the opening 3e of the body 3, is longer. The opening 3e is not closed by an upper portion of the reel-shaped body 4 but by a separate cover 50 which is connected, for example snap-connected, to the top portion of the body 3.

In the variant according to Figure 9, the central portion of the diaphragm body 6 is greatly thickened. As in the variant shown in Figure 7, a spring 17 is advantageously disposed between the diaphragm body 6 and the lower portion 3a of the body 3.

The core 13 also has a simplified construction.

A pressure indicating device such as that indicated 20 and 21 in Figure 8 may also be added in the variant according to Figure 9.

Claims

1. An inductive hydraulic pressure sensor (1), particularly for electric household appliances, boilers and the like, comprising a rigid casing (2) which has at least one (first) input (5) for a hydraulic pressure to be detected, and which defines a chamber (12) in which a movable diaphragm (6) having a surface (6b) that is operatively exposed to the hydraulic pressure coming from the input (5) is mounted in a hydraulically leaktight manner, a ferromagnetic core (13) being connected to the diaphragm (6) and being movable under the effect of the pressure, relative to a stationary coil (9) carried by the casing (2), against the action of resilient biasing means (16) in a manner such that, in operation, the inductance of the coil (9) varies according to the value of the hydraulic pressure, the sensor (1) being characterized in that the casing (2) comprises a first, substantially cup-shaped body (3) with a tubular shank (3a) in which the input (5) is defined, and with an opening (3e) located at the opposite end to the tubular shank (3a), and a second, tubular, reel-shaped body (4) fixed in the first body (3) and having: a first end portion (4a) which clamps a peripheral portion (6a) of the diaphragm (6) in a hydraulically leaktight manner, an axially intermediate portion (4b) around which the coil (9) is wound, and a second end portion (4c) which defines a reaction surface (4e) against which the resilient means (16) associated with the movable core (13) react, the arrangement being such that the core (13) is mounted so as to be movable inside the second body (4), between the diaphragm (6) and the resilient biasing means (16).

2. A pressure sensor according to Claim I in which, at the end facing the diaphragm (6), the intermediate portion (4b) of the reel-shaped body (4) clamps a hydraulic sealing member (18) relative to the first body (3).

3. A pressure sensor according to Claim 1 or Claim 2 in which the first end portion (4a) of the reel-shaped body (4) has snap-fastening means (10) engaged in corresponding retaining seats (11) of the first body (3).

4. A pressure sensor according to Claim 3 in which the fastening means (10) are located between the diaphragm (6) and the annular sealing member (18).

5. A pressure sensor according to any one of the preceding claims in which the core (13) has a tubular element of ferromagnetic material (14) encapsulated in an electrically insulating casing (15).

6. A pressure sensor according to any one of the preceding claims in which there are associated with the diaphragm (6) further resilient means (17) which act on the side (6b) of the diaphragm (6) that is operatively exposed to the hydraulic pressure to be detected and urge it in the opposite direction to the force exerted by the first resilient means (16).

7. A pressure sensor according to any one of the preceding claims in which a second input (18) for a second pressure to be detected is provided in the second end portion (4c) of the reel-shaped body (4), the second input (18) communicating with a portion of the chamber (12) which is located on the side of the diaphragm (6) remote from the first input (5), the arrangement being such that, in operation, the position of the core (13) relative to the coil (9) depends on the difference between the pressures applied to the first and second inputs (5, 18).

8. A pressure sensor according to any one of the preceding claims, particularly for use in domestic heating boilers, in which the at least one first input (5) is in communication with a duct (20) in which there is mounted a movable body (21) which, when pressure is applied to the first input (5), can adopt a position in which it is visible from outside the casing (2) and in which it indicates the presence of pressure at the first input.

9. A pressure sensor according to any one of the preceding claims in which the coil (9) is connected to a processing circuit carried at least partially by a circuit board (30) connected to the reel-shaped body (4).

10. A pressure sensor according to Claim 9 in which the circuit board (30) is substantially U-shaped and is arranged around a portion (4c) of the reel-shaped body (4).

11. A hydraulic pressure sensor according to any one of the preceding claims in which the second end portion (4c) of the second body (4) closes the opening (3e) of the first body (3).

12. A pressure sensor according to any one of Claims 1-10 in which a closure cover (50) is associated with the opening (3e) of the first body (3).

13. A pressure sensor substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.