FR2807514A1 - Pressure sensor, has Hall sensor with two point calibration avoids adjustment is simple and cheap - Google Patents

Abstract

The pressure sensor has a magnet (22) on the diaphragm (13) in contact with the liquid and acting on a Hall sensor (23) on a circuit board (24) with electrical connections which is calibrated at two points on the linear response.

Description

DESCRIPTION OF THE INVENTION The present invention relates to a sensor for measuring a physical quantity.

FR-A-2 772 913 discloses a measuring sensor comprising an influencing member mounted to move under the effect of variations of the physical quantity to be measured, for example a pressure. A component responsive to the movements of the influencing member is mounted on a wafer, for example a printed circuit board, which is supported in the body in a manner that is adjustable for calibration purposes.

For calibration, the sensor is subjected to a predetermined level of the physical quantity to be measured and the wafer is positioned so that the component provides the desired output signal for that level of the physical quantity.

This measurement sensor has the advantage of having a very simple structure and particularly inexpensive. It requires on the other hand, for its calibration, to adjust precisely the position of the plate carrying the component. In addition, calibration is performed for only one point.

The object of the invention is to provide a sensor of the kind indicated at the beginning whose calibration is easier to produce industrially and whose output signal is more accurate.

According to the invention, the sensor for measuring a physical quantity, comprising a body, an influencing member mounted to move in the body under the effect of the variations of the quantity to be measured, and a component undergoing a variable influence. according to the movements of the influencing member, the component being mounted on a wafer fixed in the body and supporting connections of the component, is characterized in that the component is of a type susceptible to a prior calibration of the response curve defining the output signal of the sensor as a function of the physical quantity to be measured.

Thus, it is possible to retain the very simple structure known from FR-A-2 772 913, the assembly of which can also be very simple, but there is no longer the obligation to perform mechanical manipulations to adjust the position. of the wafer for calibration. Calibration is done by modifying the response curve of the component. By using certain commercially available components, the calibration may concern for example two different points of the response curve and thus define for example a perfectly determined linear curve.

The invention has the advantage of proposing a calibration which takes into account both the tolerances on the mechanical part of the sensor which converts the physical quantity to be measured into a displacement of the influencing member, the tolerances on the positioning of the component sensitive to the influence member, and even the tolerances on the response curve of the component since this response curve is fixed at will by the person or the automaton operating the calibration.

In general, the invention thus provides a sensor which, thanks to its calibration capacity, has excellent precision, and which is very cheap to manufacture thanks to its simple structure and its calibration method. integrating easily into an industrial process. Because of its accuracy and cost, such a sensor is particularly suitable for "general public" applications, for example as a safety or control element in a central heating or domestic hot water production circuit.

Other features and advantages of the invention will emerge from the description below, relating to non-limiting examples.

In the accompanying drawings - Figure 1 is an axial sectional view of a pressure sensor according to the invention; - Figures 2 and 3 are sectional views along II-II and III-III respectively of Figure 1; FIG. 4 is a view in axial section of a flow sensor according to the invention, at rest, along IV-IV of FIG. 5; FIG. 5 is a view from above of the sensor of FIG. 4; - Figure 6 is a view similar to Figure 4 but showing the sensor activated by a fluid flow; and - Figure 7 is an axial sectional view of a third embodiment of the sensor.

In the example shown in FIGS. 1 to 3, the sensor comprises a generally cylindrical body 1 comprising a base 2 and a main body 3. The base 2 has a tubular configuration terminating, on the opposite side to the main body 3, by an externally threaded end-piece 4, screwed in a leaktight manner into a connection 6 of an enclosure 7 which is shown only in broken lines. In the present example relating to a pressure sensor, the chamber 7 contains the fluid whose pressure is to be measured. The enclosure 7 may for example be constituted by a piping of a hot water circuit in a central heating installation.

At its end adjacent to the main body 3, the base 2 is terminated by a crimping lip 8 having an end 9 folded against a rear face 11 of a crimping flange 12 of the main body 3. A sealing membrane 13 is pinch sealingly, all around its periphery, between the front face 14 of the flange 12 and an inner shoulder 16 of the base 2.

The crimping lip 8 is connected to the radially outer edge of the shoulder 16. The liquid present in the chamber 7 can thus penetrate the base 2 without exceeding the limit formed by the sealing membrane 13.

The main body 3 has an axial cavity of generally cylindrical shape 17. On the side of the base 2, the axial cavity 17 is closed by the membrane 13. A movable member 18, similar to a piston, is movably mounted in the cavity 17 The movable member 18 is fixed in a manner not shown, for example by gluing, to the face of the membrane 13 facing the main body 3 and therefore opposite to the face in contact with the fluid. A compression spring 19 is inserted axially between the movable member 18 and a bottom 21 of the cavity 17, opposite the membrane 13.

Thus, the pressure exerted by the fluid on the membrane 13 tends to move the movable member 18 towards the bottom 21 of the cavity 17 against the return action of the compression spring 19.

On its side facing the bottom 21 of the cavity 17, the movable member 18 rigidly carries an influencing member 22 constituted by a permanent magnet.

Furthermore, the sensor comprises a component 23 which is mounted in the cavity 17 facing the permanent magnet 22. The magnet 22 is in a central position on the face of the movable member 18 turned towards the bottom 21 of the cavity . In the example described where the influence member 22 is a permanent magnet, the component 23 is typically a Hall effect detector.

The component 23 is mounted on a wafer 24 fixed in the main body 3. As an electrical component 23 in the example described, the wafer is a printed circuit board.

The printed circuit board 24 is mounted in a plane substantially parallel to the axis 26 of the cavity 17, which corresponds to the direction of movement of the moving element comprising the influencing member 22, the movable member 18 and the portion of the membrane 13 to which the movable member 18 is fixed.

The printed circuit board 24 has an elongate shape parallel to the axis 26 and has an end 27 directed towards the movable member 18 and more particularly towards the influence member 22. The component 23 is fixed on the circuit board printed in the vicinity of the end 27 and on the face 28 of the wafer which is turned towards the axis 26. Thus, the axis 26 passes through the component 23, as shown more particularly in Figure 2.

For its mounting in the body 1, the printed circuit board 24 is engaged in a slot 29 (see also Figure 3) having a generally flattened rectangular shape corresponding to the profile of the wafer 24. The slot 29 is formed in a closure wall 31 of the main body 3. The wall 31 closes the cavity 17 on the opposite side to the movable member 18 and in particular carries the bottom face 21 mentioned above. The wafer 24 thus comprises a region 241 engaged in the slot 29, a region 242 projecting into the cavity 17 and carrying the component 23, and a region 243 protruding from the wall 31 on the side opposite the cavity 17 in a recess 32 formed in the end of the main body 3 on the opposite side to the base 2. The main body 3 further comprises in the wall 31 a threaded bore 33 which extends perpendicularly to the plane of the plate 24 from outside the main body 3 to a face of the slot 29. A clamping screw 34 screwed into the bore 33 has a head 36 accessible from the outside of the main body 3, and a clamping end 37 which bears against the face 28 of the wafer 24. The screw 34 thus immobilizes the wafer 24 in the slot 29 in a freely chosen position along a direction of sliding parallel to the axis 26 and to the direction of movement of the movable member the 18 and the organ of influence 22.

The component comprises, in association with a magnetic field sensitive member, an electronic circuit for programming the response curve determining the electrical output signal of the component as a function of the influence that it undergoes on the part of the device. 'influence. The component 23 is for example a HAL 800 UT integrated circuit available from MICRONAS INTERMETALL and which offers a linear response curve. Calibration consists of carrying out two different situations of influence on the component 23 and recording in a memory of the electronic circuit of the component the two respective voltages that one wishes to obtain for these two situations. In the application to the example of FIGS. 1 to 3 of implementation of the present invention, the calibration consists in establishing successively two different pressures against the membrane 13, and in programming the respectively desired voltage output for each of these two pressures. The calibration thus made alone compensates for the tolerances on the useful surface of the membrane 13, the apparent weight of the member 18 because the calibration can be performed with the sensor placed in the service orientation, the stiffness of the spring 19, the magnetization of the magnet 22, the positioning of the wafer 24, and the sensitivity of the component 23.

The component 23 has pins 38 which pass through corresponding holes formed in the wafer 24. The pins 38 are connected by welds 39 to conductive pads 41 formed on the face 42 of the wafer 24 opposite the face 28 carrying the component 23 In the example shown where the component 23 is a Hall effect detector, it comprises for example three pins 38, namely two for its power supply and one for the signal supplied. There are thus three ranges 41 (Figure 3) which consist of three conductive lines insulated from each other and each extending from the corresponding pin located in the area 242 of the wafer 24 to the zone 243 located in the area. recess 32 by traversing the entire length of the zone 241 located in the slot 29. One of the pins 38 can also be used to introduce the programming signals of the two aforementioned voltage levels during calibration. The recess 32 is intended to receive an electrical connector (not shown) having three individual contacts each connected to one of the pads 41. Therefore, in the preferred example shown, the printed circuit board 24 is not used. to support the component 23 in the body 1 and electrically connect the component 23 with the outside.

The bottom 21 of the cavity 17 carries an axial skirt 44 which surrounds the region 242 of the wafer 24. The free end 27 of the wafer 24 is axially recessed with respect to the free end 46 of the skirt 44. free end 46 abutment form for an annular region 47 of the movable member 18 which surrounds the magnet 22. When the pressure in the fluid reaches or exceeds the maximum for which the sensor is operational, the annular region 47 of the organ mobile 18 comes to bear against the free end 46 of the skirt 44. This prevents the movable member 18 or any element that it carries, such as the influence member 22, to come even indirectly in contact with the printed circuit board 24 or any element that it carries and in particular with the component 23.

In addition, the skirt 44 is surrounded by a portion of the coil spring 19 and contributes to the centering of the spring 19. The skirt 44 prevents any mechanical interference between the turns of the spring 19 and the region 242 of the printed circuit board 24 and with component 23.

The annular region 47 of the movable member 18 constitutes the top of a boss 48 for centering the adjacent end of the spring 19.

Preferably, the main body 3 is made of insulating material such as a hard plastic to avoid any risk that the pads 41 of the wafer 24 are short-circuited by the adjacent face of the slot 29. As shown in FIG. 3, this face may, however, have grooves 49 each receiving a respective one of the lands 41. The grooves 49 protect the beaches 41 from the mechanical pressure exerted indirectly by the immobilizing screw 34, and friction during the operations of mounting.

The base 2 can be made of metal suitable for the deformation of the lip 8 for crimping on the flange 12 of the main body 3. It is preferable that the base 2, the main body 3 and the movable member 18 are made in non-magnetic materials to avoid unwanted interaction with the magnet 22.

In operation, the movable member 18 takes along the axis 26 a position which is a function of the pressure in the fluid occupying the chamber 7. The sealing membrane 13 is deformed correspondingly. The Hall effect detector 23 provides, on one of the tracks 41, a signal which depends on the distance between the influencing member 22 and the detector 23. Thanks to the calibration, this signal is in a relationship of known proportionality with the pressure prevailing in the fluid.

The example shown in Figures 4 to 6 will be described only for its differences from the previous. The sensor 51 is a flow sensor mounted in a tubular body 53 intended to be traversed by the fluid whose flow rate is to be measured. The body 53 is intended to be inserted along a vertical axis in a path of the fluid so that the flow ascends through the body 53, as illustrated by an arrow 52 in FIG. 6. At each of its ends, the body 53 is provided with sealing connection means, not further shown, with the corresponding end of the remainder of the fluid path (not shown). An insert fixed in the duct 55 defined by the body 53 comprises an axial tubular guide 56 extending between two bushes 57, 60 crimped into the duct 55 and integral with the guide 56. The upper bushing 60 has a frustoconical bore 62 flared to the above. The movable member 58 comprises a rod 54 guided in axial sliding in the guide 56, and a shoe 63 engaged in the frustoconical bore. The flow passes inside the sleeve 57, around the tube 56 and then in the annular gap between the expansion 63 and the bore 62. The movable member 58 is biased downwards by its own weight and by a compression spring 59 inserted between the base of the tube 56 and a lock washer 61 carried by the rod 54 in the vicinity of its lower end.

According to a conventional principle for the measurement of a flow rate, the greater the flow rate to be measured and the greater the moving member 58 is displaced axially upwards, that is to say <I> to </ I> the most wide of the bore 62, corresponding to a larger passage section for the fluid around the expansion 63, under the action of the hydrodynamic forces created by the flow, and against the downward urging by the weight of the moving equipment and the force of the return spring 59.

The upper face of the shoe 63 carries an influence member 72 constituted by a permanent magnet, axially facing the sensitive component 23 mounted on the wafer 24 inside a finger 73 which protects the component 23 and the wafer 24 any contact with the fluid. The finger 73 is mounted through a lateral connection 74 of the tubular body 53. An O-ring 76 inserted between the finger 73 and the inner periphery of the connector 74 seals this assembly by preventing the fluid passing through the body 53 from fleeing towards outside the body 53 through the connector 74. The finger 73 is fully closed beyond the seal 76 on the inside of the tubular body 53. The finger 73 is made of non-magnetic material, for example plastic, in order not to prevent the permanent magnet 72 from influencing the component 23. The finger 73 points radially in the path of flow adjacent to the upper end of the sleeve 60 defining the bore 62. The magnet 72 is covered with a cap 77 of non-magnetic material which abuts against the finger 73 (situation shown in FIG. 6) when the movable member 58 is in the maximum displacement position, corresponding at least to the flow rate ma maximum for which the sensor is operational.

In the rest or minimum flow position shown in FIG. 4, the base of the expansion 63 rests against an abutment surface 78 formed at the junction between the bushing 60 and an arm 79 connected to the tube 56.

The component 23 and the wafer 24 may be similar to those described with reference to FIGS. 1 to 3. However, the component 23 has been rotated 90 relative to the wafer 23 to take on it a recumbent configuration, so that its sensitive face is again facing the influence member 72. The calibration is performed by performing two different predetermined rates through the tubular body 53 and programming the output voltages respectively desired for these two rates.

The example of Figure 7 will be described only for its differences from that of Figures 1 to 3. The sensor is intended to measure a differential pressure. The membrane 13 separates two chambers 87 and 97 formed in a housing 81 provided with a tubular connection 82, 83 for each of the chambers, respectively. The upper chamber 97 bathes the return spring 19 and the skirt 44, the component 23 and the region 242 of the wafer 24. The movable member 88, carrying the influencing member 22, is no longer a piston but a cup whose flat bottom is secured to the membrane 13 of the upper side thereof. The body 93 of the sensor, instead of defining a sliding bore 17, blooms to form the upper portion 81 of the housing. The slot 28 receiving the plate 24 is equipped with a seal 94 surrounding the plate 24.

Such a sensor can operate as a pressure difference sensor, for measuring the pressure difference between two spaces respectively connected to the connectors 82 and 83 of the sensor, as a flow sensor by connecting the fittings 82 and 83 respectively to the inlet and the neck. a venturi, or in a pressure switch.

The calibration of the sensor is performed in a manner similar to that described above, by performing two predetermined levels of the quantity to be measured and programming the expected level of voltage output for each of them.

Of course, the invention is not limited to the examples described and shown.

The wafer could carry connections other than electrical, for example optical. The component could be of a different type provided that it comprises or is associated with a calibration function such as software or electronics.

The invention is applicable to many devices comprising a function of converting a physical quantity into a displacement and of this displacement into a static signal.

The invention does not exclude a function or an operation of adjusting the position of the wafer in the body, for example for rough pre-calibration.

Claims (1)

<U> CLAIMS </ U> 1- Sensor for measuring a physical quantity, comprising a body (1, 51, 81), an influencing member (22, 72) mounted to move in the body under the effect of the variations of the magnitude to be measured, and a component (23) under varying influence as a function of the displacements of the influencing member (22, 72), the component (23) being mounted on a fixed plate (24) in the body and supporting connections of the component, characterized in that the component (23) is of a type capable of a prior calibration of its response curve defining its output signal as a function of the physical quantity to be measured. 2- sensor according to claim 1, characterized in that the component (23) is of a linear response curve type, definable by calibration for two values of the physical quantity. 3- sensor according to claim 1 or 2, characterized in that the component (23) is mounted adjacent an end (27) of the wafer (24) directed towards the influencing member (22, 72). 4- sensor according to one of claims 1 to 3, characterized in that the plate (24) is immobilized by braking in a slot (29) of the body (1). 5- sensor according to claim 4, characterized in that one (28) of the faces (28, 42) of the wafer (24) receives the support of an end (37) of an immobilizing screw ( 34) through one of the faces of the slot (29). 6. Sensor according to one of claims 1 to 5, characterized in that the plate (24) is mounted in a plane substantially parallel to the direction (26) of movement of the influencing member (22). 7- Sensor according to claim 6, characterized in that the body comprises a skirt (44) directed towards the influencing member (22) and whose end (39) preferably forms a stop limiting the stroke of the organ of influence (22), the skirt (44) separating the plate (24) and the component (23), located radially inward, and a return spring (19) of the influencing member, the spring being radially outside the skirt (44). 8- Sensor according to one of claims 1 to 7, characterized in that the influencing member (22) is attached at least indirectly to a membrane separating two chambers to move according to the pressure difference between the two rooms (87, 97). 9- sensor according to one of claims 1 to 5, characterized in that the wafer is mounted in a plane substantially perpendicular to the direction of movement of the influencing member (72). 10- Sensor according to one of claims 1 to 5 or 9, characterized in that the wafer is mounted away from contact with the fluid in a finger (73) projecting radially towards the axis (26) of movement of the influencing organ (72). 11- Sensor according to one of claims 1 to 10, characterized in that the wafer (24) is a printed circuit board. 12- sensor according to one of claims 1 to 11, characterized in that the influencing member (22, 72) is magnetic and the component (23) is a Hall effect detector. 13- Sensor according to one of claims 1 to 12, characterized in that the influencing member (22, 72) is part of a mobile assembly (18, 58) loaded by a return spring (19-, 59), which urges the moving element (18, 58) in a direction opposite to the component (23). 14- Sensor according to one of claims 1 to 13, characterized in that the influencing member (22) moves under the action of a pressure of a fluid. 15- sensor according to one of claims 1 to 14, characterized in that the sensor is a flow sensor. 16- Sensor according to one of claims 1 to 14, characterized in that the sensor is a pressure sensor. 17- Sensor according to one of claims 1 to 14, characterized in that the sensor is a pressure sensor.