GB2188155A

GB2188155A - Pressure transducer assembly

Info

Publication number: GB2188155A
Application number: GB8607026A
Authority: GB
Inventors: Henri Rosenberg; Joseph Terrance Furness
Original assignee: Furness Controls Ltd
Current assignee: Furness Controls Ltd
Priority date: 1986-03-21
Filing date: 1986-03-21
Publication date: 1987-09-23
Anticipated expiration: 2006-03-21
Also published as: GB2188155B; GB8607026D0

Abstract

A pressure transducer assembly comprises two plate members 11, 11a mounted face to face with a diaphragm 10 therebetween, the plate members 11, 11a being shaped so as to form respective chambers 14, 14a to which in use differential pressure is applied, each plate member 11, 11a carrying respective electrode means 16, 16a and including around its outer edge an annular portion 13, 13a. The plate members 11, 11a are formed of stiff resilient material such as steel, the inner edges 26, 26a of the annular portions 13, 13a abuting one another with the diaphragm 10 therebetween and being spaced from one another about their outer radii, and the two plate members 11, 11a are held together by means of a clamp ring 24 which surrounds the annular portions 13, 13a and flexes them so as to urge them towards one another to thereby grip the diaphragm 10 between the plate members 11, 11a. <IMAGE>

Description

SPECIFICATION Pressure transducer The present invention relates to a pressure transducer assembly and a method of manufacture thereof.

Pressure transducers are widely used in industry.

In conventional pressure transducers there is normally provided a diaphragm of conductive material, usually metal, which separates two chambers, the two chambers being connected respectively to differential pressure sources.

Electrodes are provided adjacent each side of the diaphragm and changes of differential pressure are reflected in movement of the diaphragm which is in turn reflected in the change of capacitance between each ofthe electrodes and diaphragm. Measurement of the change of capacitance can be used to measure the differential pressure. Various methods of manufacture of such pressure transducers have been described and we would refer to our earlier Patent Application No.8414416 (published under No.

2,162,319).

The present invention provides a pressure transducer assembly and a method of manufacture therefore which may be more readily suitable for automatic assembly of pressure transducers and mass production methods.

The present invention provides according to one aspect, a pressure transducer comprising two plate members mounted face-to-face with a diaphragm therebetween, the two plate members being shaped so as to form respective chambers, differential pressure being applied, in use, to the two chambers, each plate member carrying respective electrode means and including around its outer edge an annular portion, the plate members being formed of stiff resilient material, the annular portions being formed so asto diverge from one another, and the two plate members being held together by means of a clamp ring which surrounds the annular portions and flexes the annular portions so asto urgethem towards one another to thereby grip the diaphragm between the plate members.

The present invention provides a method of manufacturing such a pressure transducer comprising mounting two plate members formed of stiff resilient material and including electrode means face-to-facetogetherwith a diaphragm therebetween, the plate members including annular outer portions formed so asto abut one another abouttheir inner radii and be spaced from one another about their outer radii, tensioning the diaphragm, and providing a clamp ring to surround the annular portions and to clamp the annular portions abouttheir outer radii so asto resiliently urge them towards each other so as to clamp the plate members together and to maintain the diaphragm under tension.

A pressure transducer in accordance with the invention and a method of manufacture thereof will now be described by way of example onlywith reference to the accompanying drawings in which: Figure lisa vertical axial section of a transducer assembly in accordance with the present invention, and Figures2to 8 are vertical axial sections of an apparatus for assembling the transducer assembly shown in Figure 1 at various stages of operation.

Referring to Figure 1 there is illustrated an axial section of a differential pressure transducer accordingtothe invention. The pressuretransducer comprises a circular diaphragm 10 of thin diaphragm material such as stainless steel (typically of a thickness of 0.025 mm), first plate member 11 pressed from resilient sheet material such as stainless steel sheet, and comprising a chamber forming portion 12 and a surrounding annular portion 13. There is also provided a second plate member 11 a identical to the first plate member 11.

Mounted within a first chamber 14 between the first plate member 11 and diaphragm 10 is an electrode 16, the electrode 16 being of conductive material and being generally circular, there being provided an insulated spacing washer 17 between the rear surface ofthe electrode 16 and the plate member 11.

The plate member 11 includes a central hole 18 through which passes a tube 19 attached to and forming partofelectrode 17. The tube 19 is threaded on its outer surface and mounts a nut 21 which clamps a terminal 22 between the nut21 and the outer surface of the first plate member 11 via an insulating washer 23.

The plate member 11, electrode 16, washers 17 and 21 andterminal22form a plate assembly 15.

The second plate member 11 a mounts identical components to that offirst plate member 11,these components carrying the same reference numerals as those attached to the first plate member but with the addition of "a".

The two annular portions 13, 13a, are formed soas to be coincident around their inner edges 26, 26a (with the diaphragm 10 extending therebetween) but with their outer edges 27, 27a spaced apart so that the annular portions 13, 13a are not in a plane but extend out of a plane. Adjacenttheir outer edges 27, 27a and facing the diaphragm 10 there are provided elastomeric ring seals 28, 28a, the seals 28, 28a being attached to the respective annular portions, 13, 13a by means of adhesive or otherwise.

The two plate assemblies 15, 1 5A of the transducer are clamped togetherwith the diaphragm 10 therebetween by means of a clamp ring 29 which extends around the outer edges 27, 27a ofthe annular portions 13, 13a,the clamp ring 29 incorporating turned over portions 31,31 a which bearon thetop and bottom surfaces oftheannular portions 13, 1 3a respectively to resiliently flex the annular portions 13, 13a, towards one another, whereby the annular portions 13,1 3a, and diaphragm 10 are sealingly connected together by means of the elastomeric seals 28.The distortion of the annular portions 13, 13a bytheclamp ring 29 provides sufficient pressure between the inner edges 26 ofthe annular portions 13, 13a so asto maintain anytension provided inthediaphragm 10 and also provides an air-tight seal atthatpoint.

A method of manufacturing a pressure transducer assembly illustrated in Figure 1 is described with reference to Figure 2 onwards.

The apparatusforforming the pressure transducer comprises a first lower plunger 32 in the shape of a piston, the upper wend of the plunger 32 incorporating a blind bore 33 thereby forming an annularwall 34.

Surroundingthefirst lower plunger32 is a second cylindrical lower plunger 36, the inner edge of the upper end of which is cut away to form a rebate 37.

The rebate37forms a transverse shoulder38 and an outerannularwall portion 39.

Athird cylindrical lower plunger 41 surrounds the second cylindrical lower plunger 36, the upper edge ofthe plunger41 incorporating a stepped portion 42.

Parts 32 to 42 form a lower assembly 35. Axially mounted above the lower assembly 35 is an upper assembly 35a which comprises parts corresponding to parts 32 to 42. It should be noted, however, that there is a slight difference in the sectional shape of the rebate 37a in thatthere is a curved surface 43 between the shoulder 38a and the inner face ofthe outerangularwall portion 39a.

Operation of the apparatus will now be described to assemble a pressure transducer. A clamp ring 29 is inserted into the rebate 37 as shown in Figure 2. At this point oftime the clamp ring 29 is manufactured so as to only include one turned over portion 31.

The lower assembly 35 and upper assembly 35a are moved apartfrom one another as shown in Figure 2. In this position a firsttransducer plate assembly 15 is mounted in the lower assembly 35 as shown in Figure 3. The lower face ofthetransducer annular portion 13 rests on the end wall ofthefirst lowerplunger32,thechamberforming portion 12 extending into the blind bore 33. It will be noted that the diameter of the blind bore 33 is slightly greater than the outerdiameterofthe chamberforming portion 12.

Theupperand lowerassemblies35,35aarethen moved so that a web 44 of diaphragm material extends therebetween and a second transducer plate assembly 1 5A is placed in position on the web 44 abovethe lowerhalfassembly 15 (see Figure 4) and the upper plunger4laand plunger32aarethen lowered to the position shown in Figure 5.

The plunger32a is then in engagement with the transducer plate assembly 1 5a as shown in Figure 5 so thatthe lower edge of the first upper plunger 32a engages with the upper surface ofthe annular portion 13a.Thetwo plungers41,41a are moved to cooperate with one anotherwherebytheirstepped portions clamp the web 44therebetween.

As shown in Figure 6 the plunger 32 is then moved upwardly against the resistance ofthe plunger 32a to tension the diaphragm between the two transducer plate assemblies 15,15a ofthe transducer. When the correct tension has been applied the plungers 32, 32a are urged together under a clamping force of approximately 20 to 50 tonnes (metric equivalent) to maintainthetension in the diaphragm.

Thentheplunger36 is moved upwardlyso asto engage the lowerturned over portion 31 with the underside ofthe annular portion 13 and so thatthe clamp ring 29 cuts the webs 44 (see Figure 7).

Movement downwards ofthe plunger 36a causes the clamp ring 29 to engage with the curved surface 43 to swage the clamp ring 29 so as to form the upper turned over portion 31 a (see Figure 8). In this operation (assisted by the clamping pressure between the plungers 32, 32a) the annular portion 13, 13a areflexed towards one another and are clamped in that position bytheturned over portions 31,31 a ofthe clamp ring 29.

The upper and lower assemblies 35,35a arethen moved apart and the completed transducer may be removed. The operation may then be repeated by moving the upper and lower assemblies 35, 35a awayfrom the web 44 and movementofthe plungers and web and feeding thetransducer plate assemblies and clamp ring may be carried out automatically.

Claims

1. A pressuretransducercomprising two chamber members mounted face to face with a diaphragm therebetween to form two chambers, differential pressure being applied, in use, to the two chambers, each chamber member including around its outer edge an annular portion, the annular portions each being formed of stiff resilient material and being formed so asto radially diverge from one another, andthetwo chamber members being held together by means of a clamp means which flexes the annular portions so asto urge them towards one another to thereby grip the diaphragm between the chamber members.

2. A pressure transducer as claimed in claim 1 in which the two chamber members each comprise a shaped plate member which provides both the annular portion and a chamberforming portion.

3. A pressure transducer as claimed in claim 1 or 2 in which each chamber member is identical.

4. A pressure transducer as claimed in any of claims 1 to 3 in which the clamp means comprises a clamp ring.

5. Apparatus as claimed in any of claims 1 to 4 in which the chamber members and the clamp means are formed of steel.

6. A pressure transducer as claimed in any of claims 1 to 5 in which the annular portions are arranged so thattheir inner most edges are adjacent to one another and clamp the diaphragm therebetween, the remainder of the annular portions diverging away from one another outwardly ofthe innermost edges.

7. A pressure transducer as claimed in any of claims 1 to 6 in which sealing means are provided between each annular portion and the diaphragm to thereby seal the pressure transducer.

8. A pressure transducer substantially as herein before described with reference to the accompanying drawings.

9. A method of manufacturing a pressure transducer comprising (a) mounting two chamber membersface-to-facetogetherwith a diaphragm therebetween,the chamber members including their outeredges annular portions partofwhichannular portions are shaped so as to abut one another with the diaphragm therebetween and other parts of which diverge from one another, (b) tensioning the diaphragm, (c} engaging a clamp means with the annular portions so asto resiliently urgetheir divergent parts towards one another so asto clamp the chamber members togetherand maintain the diaphragm undertension.

10. Amethodasclaimed inclaim Sinwhichthe chamber members each comprise a shaped plate member formed of stiff resilient material which provide both the annular portion and a chamber forming portion.

11. A method as claimed in claim 9 or 10 in which each chamber member is identical.

12. A method as claimed in anyofclaims 9to 11 in which the clamp means comprises a clamp ring.

13. A method of manufacturing a pressure transducerofthetype claimed in claim 1 comprising mounting one chamber members, stretching the diaphragm across said chamber members, mounting a second chamber member and engaging it with the diaphragm whereby the diaphragm extends between the two chamber members, urging the two chamber members towards one another to clamp the diaphragm therebetween, mounting a clamp means adjacent the annular portions, and engaging said clamp means with the annular portions so astoflexthe annular portions so asto urge their divergent parts towards one anotherto thereby grip the diaphragm between the chamber members.

14. A method as claimed in claim 13 in which the diaphragm is initially provided in the form of a strip of material and after clamping between the two chamber members and before engagement ofthe clamp means, the strip of material is cut around one ofthe chamber members.

15. A method as claimed in claim 13inwhich before the first chamber member is engaged with the diaphragm, a seaiing ring is provided in engagement with the annular portion so as to be mounted between the annular portion and the diaphragm, and thereafter a sealing ring means is provided between the annular portion of said second chamber member and said diaphragm.

16. Amethod asclaimed inanyofclaims 13to 15 in which the clamp means is in the form of a clamp ring and isfolded so asto engage said annular portions.

17. A method as claimed in claim 9 substantially as hereinbefore described with reference to the accompanying drawings.