HK1152562B - Pressure sensor with a diaphragm and depth gauge comprising the same - Google Patents

Description

Pressure sensor with diaphragm and depth gauge including the same

Technical Field

The invention relates to a pressure sensor comprising: a body having a cavity for receiving pressurized fluid and a bearing element surrounding the cavity; a cover fastened to the body with a stop strip having a closed profile corresponding to the support element of the body; a diaphragm disposed between the body and the cover so as to seal the pressure chamber and being bendable under the influence of a pressure difference between both sides thereof, wherein a peripheral region of the diaphragm is disposed between the support element and the stopper band; and a transmission mechanism coupled to the central region of the diaphragm for transmitting diaphragm deflection data to a measurement or indication mechanism. The invention also relates to a depth gauge comprising such a pressure sensor.

Background

In the pressure sensors used, in particular in pressure gauges or depth gauges, the diaphragm (also called "membrane") usually takes the form of a metal disc, with concentric corrugations in order to vary the elastic deflection amplitude. Such a diaphragm can be fixed into the sensor by welding (see, for example, german patent application No.10147124), but can also be fixed without welding, for example by clamping, as can be seen in WO patent application No. 01/01098. However, the precise manufacture of such a diaphragm is quite complicated and the level of reproduction is not high. Moreover, when the sensor is subjected to a pressure exceeding the operating pressure, it is not easy to prevent the diaphragm from undergoing plastic deformation.

Thus, the use of flat membranes is sought, but the method of fastening the membranes continues to result in quite significant drawbacks. This reduces the elastic deformation that the diaphragm can undergo before plastic deformation if the peripheral region of the diaphragm is welded to the sensor structure; therefore, the sensitivity of the sensor is reduced. In addition, welding introduces different stiffness properties for each weld. The resulting diaphragm deflection inaccuracies obviously reduce the accuracy of the sensor and further make it difficult to use stop members to prevent plastic deformation of the diaphragm. Securing the diaphragm by inserting it into the sensor structure also leads to some of the aforementioned drawbacks.

We will also illustrate the possibility of giving the non-welded diaphragm a wide U-shaped profile, in which the flat shape is surrounded by a vertical edge cooperating with a sealing gasket. In this case, the diaphragm is voluminous, the raised edge is used only for sealing, and most importantly, the bend in the U is the region of stress concentration caused by fluid pressure, thereby limiting the elastic deformation that the diaphragm can undergo before entering the plastic domain.

Disclosure of Invention

The object of the present invention is to create a pressure sensor of simple construction which allows the diaphragm to flex as freely as possible under fluid pressure, while maintaining a good level of sealing. An additional purpose is to prevent any risk of plastic deformation of the diaphragm over the entire pressure range that the sensor may have to withstand, even beyond the operating pressure. Another additional object is to allow the sensor to be simply manufactured and easily assembled.

The invention therefore provides a pressure sensor of the type indicated in the preamble above, which is characterized in that the diaphragm has a substantially flat shape and that the peripheral region of the diaphragm can pivot on the stop strip when the diaphragm bends under the influence of an increase in the fluid pressure in the pressure chamber. In particular, this means that the peripheral region of the diaphragm is not rigidly connected to the body or to the cover by welding or insertion therein, and is therefore substantially free to accompany any bending of the diaphragm.

Due to these features, the diaphragm may have a greater elastic deformation for a given pressure than when fixed by welding or inserting its peripheral region. Thus, the increased deflection of the central region thereof facilitates transmission to a measuring or indicating mechanism. The elimination of rigid fastening systems reduces the inaccuracies created by the variability of such fastening systems and thus improves the accuracy of the pressure sensor. Furthermore, the flat disc-shaped diaphragm can be manufactured simply and cheaply with high precision and reproducible levels, for example by cutting a metal sheet.

Preferably, the diaphragm and the stop strip are annular, so that the bearing force of the diaphragm is always uniform along the closed contour of the stop strip.

According to a particularly advantageous embodiment of the invention, the cover has, opposite the diaphragm, a stop surface located between the central hole of the cover and the stop band and designed to retain the diaphragm as long as it has reached a deflection corresponding to the limit pressure. This allows the sensor to withstand experimental pressures significantly higher than the maximum operating pressure when using a very compliant diaphragm, as will be described later, and thus provides a high level of sensitivity to the pressure sensor without the risk of plastic deformation of the diaphragm.

Further characteristics and advantages of the invention will be apparent from the following description of two embodiments of the invention, given by way of non-limiting example in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a schematic front view of a depth gauge having a pressure sensor according to the present invention.

Fig. 2 is a schematic partial sectional view taken along line ii-ii in fig. 1, and shows a first embodiment of the present invention.

Fig. 3 is an enlarged view of detail iii of fig. 2.

FIG. 4 is a view similar to FIG. 3 and showing another embodiment of the invention.

Detailed Description

Fig. 1-3 schematically show the use of a not shown depth gauge 1 worn on the diver's wrist for indicating the depth of water via a pointer 2, which pointer 2 is rotated relative to the scale 3 of the dial 4 using a pressure sensor 5 accommodated in a depth gauge housing 6. The pressure sensor is connected to the pointer 2 by mechanical transmission means, in particular a rotating shaft 7 with a transverse probe 8. It should be noted that the depth gauge 1 may be combined with a watch inside the same case, but this is not essential.

The pressure sensor 5 is mounted on a rear cover 11 of the housing, the rear cover 11 generally forming the body of the sensor. The sensor is disposed above a pressure chamber 10 formed in a rear cover 11 and communicates with the outside of the housing via a hole (not shown) so that the fluid contained in the chamber is subjected to pressure mainly around the depth gauge. The pressure sensor 5 has a flat annular diaphragm 12, the peripheral region 13 of which is held between the back cover 11 and a rigid cover 14, the rigid cover 14 being fastened into the housing 6 and having a central hole 15. The return spring holds the free end of the probe 8 pressed against the pad 16, the pad 16 being fixed in the central region of the diaphragm 12. The washer 16 is able to move vertically in the hole 15 and thus to pivot the shaft 7. Between the hole 15 and the peripheral region 13 of the diaphragm, the cover has a slightly concave bottom surface which delimits a cavity 18 communicating with the remaining internal volume of the casing 6 via the hole 15. This recessed surface forms a stop surface 20, which stop surface 20 limits deflection of diaphragm 12 whenever diaphragm 12 is subjected to a differential pressure that exceeds a threshold pressure, as will be described below. The interior volume of the housing contains air or other gas at a pressure close to atmospheric pressure at sea level. A sealing gasket 21 (preferably an O-ring joint) presses against the peripheral region 13 of the diaphragm 12 and isolates the internal volume from the pressure chamber 10. The sealing gasket 21 also acts as a support element for constantly pressing the peripheral region 13 of the diaphragm against the cover 14.

As shown more clearly in fig. 3, the O-ring joint 21 is housed in an annular groove in the back cover 11, slightly further in the radial direction, the back cover 11 having a vertical edge 24 which abuts the cover 14 and whose height is chosen so that the joint 21 is strongly prestressed against the diaphragm 12 to ensure sealing between them over the entire operating pressure range of the pressure sensor. The compression of the joint 21 presses the peripheral region 13 of the diaphragm against a portion of the cover 14, i.e. the support band 25, the support band 25 following the edge of the recessed stop surface 20 and practically opposite the position of the joint 21. The support strip 25 is planar in this example, but it may also have a convex or sharp transverse profile. In order to avoid any adverse effect on the deformation properties of the membrane, the position at which the joint 21 forms the support element must here not protrude further than the closed contour of the stop strip 25.

The deformation of the diaphragm 12 must be maintained in the elastic domain over the entire pressure range to which the sensor 5 will be subjected. The membrane is preferably metal. Due to its planar shape when parked, the diaphragm is easy to manufacture, for example by cutting a stainless steel sheet. The other elements of the sensor (other than the O-ring joint 21) may be made of metal or a rigid synthetic material, for example.

When the gauge 1 is immersed to a certain depth in water, the diaphragm 12 elastically bends under the increased differential pressure between the chambers 10 and 18. The pressure sensor 5 detects the deflection of the diaphragm via the vertical movement of the spacer 16. The mechanical transmission means between the probe 8 and the pointer 2 are arranged to produce a substantially linear movement of the pointer as a function of the pressure variations.

The shape given to stop surface 20 corresponds to the deformation profile of diaphragm 12 for the aforementioned limit pressure. An easily machined spherical cap approximates this profile, which is theoretically parabolic for a small deflection annular diaphragm. The limit pressure is preferably slightly higher than the maximum operating pressure of the depth gauge. Since the gauge must generally withstand a maximum test pressure that is significantly higher than the maximum operating pressure, the main function of the stop surface 20 is to prevent any plastic deformation of the diaphragm under such test conditions, since the diaphragm is then supported by the lid 14, the lid 14 being much stiffer than the diaphragm. Only the central portion of the diaphragm opposite the aperture 15 is subject to excessive bending, but the additional stress is reduced and can remain in the elastic domain at the appropriate size. Of course, these advantages also exist in situations where the pressure sensor is occasionally subjected to excessive pressure (e.g., a water hammer in a manometer).

Given that the peripheral region 13 of the diaphragm is neither welded nor inserted into the structure supporting the diaphragm, the diaphragm can pivot almost freely on the support band 25 to deflect and move closer to the stop surface 20. In the arrangement of fig. 3, this movement only changes the compression force of the O-ring joint 21 and therefore has no effect on the seal. A groove 26 is provided between the tab 21 and the edge 24 to allow the diaphragm edge to move downwardly without obstruction. With regard to the assembly of the sensor 5, it is clear that this is particularly simple, in particular because it only requires the insertion of the cover 14 into the housing 6, the insertion of the tabs 21 into the grooves 22, the placement of the membrane 12, positioned transversely by the edges 24, on the tabs and then the fixing of the rear cover 11 to the housing in a conventional manner. The height of the edge 24 automatically determines the prestress of the joint 21.

According to another embodiment of the invention, shown in fig. 4, the diaphragm 12 and the depth gauge arrangement are similar to those described in the example of fig. 1-3, but the sealing gasket 21 is placed against the top surface of the diaphragm 12, thus being located in an annular groove 30 on the side of the lid 14 between the outer edge 31 and the annular inner edge 32 of the lid. The bottom surface of rim 32 forms a stop strip 25, and peripheral region 13 of septum 12 permanently abuts stop strip 25. In the rest state of the pressure sensor, the diaphragm 12 is pressed against the stop band 25 by means of a support element 34, the support element 34 surrounding the pressure chamber 10 and forming part of the rear cover 11 or being formed integrally with the rear cover 11. The support element 34 has an annular outline with a diameter slightly smaller than that of the stop band 25, so as to elastically pre-stress the diaphragm 12 against said band. Furthermore, the thrust of the support element 34 on the diaphragm compresses the joint 21 (which may also have a toroidal shape in this example) with a high level of prestress, which is greater than that required for the maximum operating pressure. This prestress is created by fastening the back cover 11 to the housing 6.

As shown in the foregoing examples, the arrangement of fig. 4 allows unrestricted deformation of diaphragm 12 within the operating pressure range, and supports the diaphragm via stop surface 20 of the cover when the foregoing threshold pressure is exceeded. The pivoting of the peripheral region 13 of the diaphragm on the stop strip 25 is accompanied by a slight reduction in the compression of the joint 21, but no loss of sealing due to the high initial prestress of the joint. In one variant, the joint 21 may be placed along the inside of the edge 32 (thus the left side in fig. 4) so that the compression of the joint increases with the external pressure, but the bending of the diaphragm is then slightly reduced by the resistance due to the joint.

The above examples show that the invention allows the manufacture of pressure sensors, in particular depth gauges, which are capable of a high level of precision, due to a sufficiently large elastic deflection amplitude of the diaphragm while avoiding the risk of plastic deformation. This object is achieved by a membrane that is easy to manufacture with a high level of reproducibility and easier to assemble while ensuring a high quality seal.

Claims (8)

1. A pressure sensor, comprising: a body having a pressure chamber for receiving a fluid and a support element surrounding the chamber; a cover fastened to the body and provided with a stop strip having a closed profile corresponding to the support element of the body; a diaphragm disposed between the body and the cover to seal the pressure chamber, the diaphragm being bendable under the influence of a pressure difference between its two surfaces, wherein a peripheral region of the diaphragm is disposed between the support element and the stopper band; and a transmission means connected to a central region of the diaphragm for transmitting the diaphragm deflection data to the measuring or indicating means, wherein the diaphragm has a substantially flat shape, a peripheral region of the diaphragm being able to pivot on the stop strip when the diaphragm bends under the influence of an increase in the fluid pressure in the pressure chamber, the support element being a sealing gasket mounted on the body and compressed between the body and the peripheral region of the diaphragm to permanently press the peripheral region against the stop strip, the sealing gasket being arranged substantially opposite the stop strip and not projecting towards the outside of the closed contour of the stop strip.

2. The pressure sensor of claim 1, wherein the diaphragm and the stop band are annular.

3. The pressure sensor of claim 2, wherein the diaphragm is formed from a flat metal disk.

4. The pressure sensor of claim 1, wherein, opposite the diaphragm, the cap has a stop surface between the central aperture of the cap and the stop band, the stop surface being shaped to retain the diaphragm as long as the diaphragm reaches a deflection corresponding to the threshold pressure.

5. The pressure sensor of claim 4, wherein the stop surface has a substantially spherical cap shape.

6. The pressure sensor of claim 1, wherein the support element is rigid and the sealing gasket is disposed and compressed between the peripheral region of the diaphragm and the cover proximate the stop band.

7. A depth gauge having a housing containing a pressure sensor, the pressure sensor comprising: a body having a pressure chamber for receiving a fluid and a support element surrounding the chamber; a cover fastened to the body and provided with a stop strip having a closed profile corresponding to the support element of the body; a diaphragm disposed between the body and the cover to seal the pressure chamber, the diaphragm being bendable under the influence of a pressure difference between its two surfaces, wherein a peripheral region of the diaphragm is disposed between the support element and the stopper band; and a transmission means connected to a central region of the diaphragm for transmitting diaphragm deflection data to the measuring or indicating means, wherein the diaphragm has a substantially flat shape, a peripheral region of the diaphragm being able to pivot on the stop band when the diaphragm is bent under the influence of an increase in the pressure of the fluid in the pressure chamber, the support element being a sealing gasket mounted on the body and compressed between the body and the peripheral region of the diaphragm to permanently press said peripheral region against the stop band, the sealing gasket being arranged substantially opposite the stop band and not projecting towards the outside of the closure profile of the stop band.

8. The gauge of claim 7 wherein the pressure sensor body forms a providing pressure chamber through a back cover of the housing and the support element is integrally formed with or removably attached to the back cover.