Pressure sensor for counting passage of vehicles - contains flexible printed circuit membrane acting as electrical switch contact which joins two fixed elements when under pressure

the present invention provides a sensor threshold fluid pressure such as those used for counting the passage of vehicles on a road across which is arranged a rubber tube connected to the threshold detector pressure which provides a pulse every time that a vehicle wheel passes over the rubber tuhe.

Such sensors already exist from long but often have 1.' disadvantage of low reliability or robustness and a limited duration, or too expensive.

The present invention provides a novel threshold detector fluid pressure which is particularly reliable, robust, and a very simple design and inexpensive due to the large mechanical simplicification that it would eliminating many movable mechanical parts formerly required.

More specifically, the threshold detector fluid pressure according to the invention comprises a flexible membrane, one face of which is in fluid communication with tin which it is sought to detect overflow pressure threshold and whose displacement acts to close an electrical contact when the threshold is exceeded, this detector being characterized in that the membrane consists of a flexible printed circuit having a face that includes a copper-plated portion capable of coming into contact with two fixed contact elements for the short-circuiting when the movement of the membrane reaches a certain value.

The copper-plated portion of the membrane is located at center thereof and preferably has an annular shape to be able to short-circuit two • contact elements also forms generally annular and both disposed concentrically to the copper-plated portion of the membrane.

The contact elements with which the membrane engages preferably have shapes which are for the first those of a outer toothed gear wheel, and for the second those of a toothed pinion gear, the teeth of the first member being impbriquées with the teeth of the second with a narrow insulating gap between the tooth surfaces of the two elements. The contact members can be made of same on a copper plate chemically etched.

Furthermore, it is anticipated that the membrane is applied resting against a load distribution element of fluid comprising, on a side in contact with the membrane, a chemically etched copper plate on which the insulating channels etched portions are connected to each other and distributed over a wide surface facing the membrane, the channels communicating with the fluid whose pressure is to be detected to accommodate flow in the channels and and distribute the pressure over the whole surface of the membrane.

May be provided for example that the etched portions of the copper-plated insulating plate comprise a central circular surface and a circular circumferential surface, and a plurality of channels distributed circularly and each extending between the two surfaces, the fluid is introduced through a pipe opening out opposite the central circular surface by a channel drilled in the copper plate at the central circular surface.

Other features and advantages of the invention shall become apparent from the following detailed description and which is made with reference to the accompanying drawings in which:

-figure 1 represents a cross-section of the pressure sensor according to the invention;

-figure 2 represents a plan view of the pressure-distributing element;

-figure 3 represents the shape of the contact elements, co-operating with the membrane;

-figure 4 represents a plan view of the membrane itself.

In body of the sensor pressure threshold consists of two parts bolted one on lfautre to thereby form a closed chamber 10 in which can move a flexible membrane 12.

ha diaphragm is attached to the housing around the outer periphery of the chamber 10, for example ' simply by clamping the periphery of the membrane between the two parts bolted to one another and constituting the housing, one of the parts, 14, of the housing is provided with a central opening 16 open to a side of the membrane 12, the other side of the membrane 12 constituting the chamber 10 isolated completely from the opening 16 by said membrane.

a fitting 18 is welded around the opening 16, said pipe fitting being for connecting to the opening 16 a conduit 20 in which the gas or fluid in which it is sought to detecting a threshold pressure, the conduit 20 is, for example, itself connected to a rubber tube provided on a road to permit counting of vehicles travelling on the tube, each passage of a wheel on the tube in the same causing an overpressure detected by the detector.

The other part, 22, of the sensor housing, that is to say that which does not include the opening 16, is either closed and filled with gas or air at a pressure determined with respect to which it is desired to detect positive pressure in the conduit 20, or simply open in communication with the outside atmosphere, and that is relative to the atmospheric pressure is detected over-pressure.

Two, contact elements are arranged on top of the central portion of the diaphragm 12 and are connected to the outside by electrical wires 24, 26 respectively. The contact elements, normally insulated from each other are to be courtcircuités by the membrane 12 when an overpressure is detected, and the wires 24 and 26 are therefore connected to a electrical sensing element not shown, capable of establishing a signal any desired, electrical or other, each after the threads 24 and 26 are brought to the same potential by the membrane 12 which courtcircutte the contact elements.

The contact elements are carried by the underside, facing the membrane 12, of a wafer 28. The wafer 28 is fixed to a plug 30 which can be screwed into a central opening of the upper part 22 of the sensor housing, such that the more or less deep screwing of the cap 50 causes an approach more or less of the wafer and 28 of the membrane 12.

This reconciliation the contact elements of the wafer 28 and the membrane 12 permits adjustment of the pressure threshold to be detected.

Preferably, the " cap 30 is screwed onto the housing 22 with the interposition of a spring brake 32 which facilitates maintaining the wafer 28 in the selected position, avoiding loosening and accidental unscrewing, over time, of the screw cap 30.

A Figure 2 is represented in top view the constitution of the lower part 14 of the sensor housing.

It is a circular plate copper-plated, pierced at its periphery with holes 34 for bolting to the plate 14 of the upper part 22, and pierced at its center of the opening 16 for the fluidic-_# connection of the conduit 20 is copper-bonded plate. aql 14 preferably on both sides, being complete the copper plating on the rear side and enables easier welding on the face of the fitting 18 inserted into the opening 16.

On the front side, visible in Figure 2, the copper plating is not complete but is formed in a pattern by photo etching, in such a way that the plate 14 forms a distribution of fluid pressure for dispersing in a wide surface of the membrane 12 fluid from the opening 16 of relatively small cross section relative to the surface of the membrane.

The copper-plated surface of the plate 14 comprises a distribution insulating parts ^, i.e. on which the copper has been removed by chemical etching, the insulating portions form of channels communicating with each other and communicating with the opening 16 of the plate 14, such that when the membrane 12 is applied against the upper surface of the plate 14, fluid from the opening 16 may not flow where the membrane is in contact with the copper parts but can flow into the channels formed in the copper, the membrane passing above these channels.

the channels are therefore distributed over a wide surface of the membrane to distribute as much as possible the fluid pressure below.

For example, the etched portions insulating

the upper surface of the plate 14 comprise a central surface 36 surrounding the opening 16, a circular circumferential surface 38 located relatively close to the surface on which the parts 14 and 22 are bolted together, and a plurality of channels 40 each extending between the central surface 36 and the peripheral surface 38, the channels 40 cireulairement being distributed around the central surface 36 to ensure good fluid distribution, the channels 40 may be directed and the circular plate 14, or have a more complex form such that the spiral shape renrésentée in Figure 2.

If the membrane 12 was stuck, the force that should deform should be large because there is then an enlargement of the surface of the membrane, the membrane 12 is mounted floating its periphery between the upper and lower portions of the sensor housing bolted; it is thus readily arched air and the sealing contact is sufficient for the measurement, the membrane is simply put on the plate 14 which, by being made of copper plate double-sided etched on only one side by photo etching conventional chemical, consisting of a side a air distribution element, and the other a surface which allows easy attachment by welding a connecting element 18.

Of course, the plate 14 which is a part of the sensor housing is a plate rigid copper-plated.

the contact elements, which are carried by the wafer 28 are represented in Figure 3. They are formed by chemical etching on a wafer copper-plated single-sided or double-sided. Preferably, one of the contact elements is constituted by a central copper-plated surface of the wafer 28, and the other is constituted by a peripheral surface of the wafer 28. An example shape etched portions of the wafer 28 is represented in Figure 3. one of the contact elements is constituted by a copper-plated surface having a shape of outer toothed gear wheel 42, and the other contact element by a surface copper-plated 44 surrounding the first and having a shape of inner toothed gear wheel, the teeth of the first member being interleaved with the teeth of the second with a narrow insulating gap 46 between the copper faces gears of the two elements.

In order to make a contact between the inner surface 42 and the outer surface 44, it is possible to use a conductive ring having a diameter corresr during the diameter common means of the pinions constituted by the inner and outer surfaces 42 and 44.

Indeed, with such a ring, can be contacted either side of the contact elements, in the case where the application of the conductive ring on the contact elements is not uniform.

It should be noted that the wafer 28 is preferably copper-plated on both sides to facilitate attachment of the wires 24 and 26 which are welded on the backside of the wafer 28.

A Figure 4 is represented the membrane 12 capable of short-circuit of the contact elements 42 and 44 of the wafer 28: the membrane consists of a single-sided printed circuit (the side facing the contact elements), on which the bulk of the copper plating has been deleted and onn wherein ' complied with that a conductive ring 48 common means corresponding to the diameter of the pinions 42 and 44 as explain of the*

Unlike the plate 14 and to the wafer 28, the membrane 12 is a flexible printed circuit and not rigid * this flexibility mainly in that of the support of the copper-plated surface; but are thus a thin support, for example or mylar kapton (Marks).

In maintaining as part copper-plated that the central ring 48, of small dimension relative to the remainder of the membrane, and is the flexibility of the insulating sheet supporting the copper-plated surface.

The air distribution element 14 is employed to cause the annulus-clad 48 also applies evenly as possible across the contact elements of the wafer 28 ; however, if an imbalance occurred, the constitution ring the conductive surface of the membrane 12 and the-shaped constitiüon pinions on the contact elements of the wafer 28 would such that contact would occur in any case from the pressure threshold is exceeded.