GB2033581A - Pressure measuring apparatus - Google Patents

Abstract

A sub-assembly 8 for a pressure gauge comprises a Bourdon tube 18 on the free end 22 of which is mounted an amplifier movement 12. The actuator 44 for the movement 12 is secured to a fixed portion 20 of the tube 18 e.g. by a swaged clamp 50. Span adjustment is provided by an adjusting screw. The sub-assembly 8 includes all the operative parts of a gauge, and all that need be done to complete the gauge is to mount the sub-assembly 8 in a casing and secure a pointer to the output shaft 24 of the movement 12. In an alternative embodiment the amplifier is mounted on the fixed portion of the tube and the actuator is connected to the free end. <IMAGE>

Description

SPECIFICATION Pressure measuring apparatus This invention relates to pressure measuring apparatus, and more particularly to a pressure measuring sub-assembly suitable for use in a pressure gauge.

Pressure gauges as a commerciai commodity have largely enjoyed a more or less standard construction for many years. In a typical prior art construction, the Bourdon tube and amplifier forming the pressure measuring system are individually supported in the gauge structure. This has required not only the separate supports but the separate connections thereto and consequent post-assembly calibration of the instrument. While not affecting performance of the gauge, these factors have been recognised as requiring an excess of support structure while contributing to inefficiency of fabrication and calibration. despite recognition of this problem, a solution therefor has not heretofore been known.

According to the present invention there is provided a pressure measuring sub-assembly for a pressure gauge comprising: a) a pressure responsive element extending between a displacement portion thereof operatively displaceable in correlation to pressure changes to which the element is exposed and a relatively non-displaceable portion thereof; b) an amplifier for providing an output motion correlated to operative displacement of said displacement portion, the amplifier being secured to one of the said portions of the pressure responsive element; and c) an actuator connected to the pressure responsive element and extending to cooperate with the amplifier in effecting said output motion thereof.

In the preferred embodiment of the invention all components of the gauge amplifier or "movement", including the output pointer shaft, are operatively supported between the displacement end portion of the Bourdon tube and a relatively non-displacement portion thereof in a manner not requiring supplemental support for the amplifier in the ultimate assembly. With the Bourdon tube having an open inlet it can then be installed in any suitable gauge housing affording a self-supporting inlet connection therefor whereby the one joint provides both the fluid passage and the entire support for the pressure measuring system.

In a preferred embodiment affording an economy hereof, the amplifier is of a type disclosed in U.S.

patent 4,055,085 to R.H. Wetterhorn. As disclosed in the patent to Wetterhorn, the amplifier is supported on the free end of the Bourdon tube for floating conjoint movement with pressure displacement of the tube end. A remotely connected wire actuator extending into the motion path of the floating amplifier defines a pivot axis for a hinged gear sector arm. In pivotting about the actuator axis, the sector arm operably drives a rotatabie output shaft supporting the pointer. An actuator clamp is mounted directly into a gripping relation onto the fixed end of the Bourdon tube while slots in the clamp spaced from the tube amount can receive and anchor the actuator position.The clamp accepts both the Bourdon tube and the actuator wire in a loose relation but is of material composition and configuration that will respond to a bi-directional swaging force for effecting a crimped grip relation therewith. Because the actuator is not anchored until the Bourdon tube is pressurized for linearity calibration, each Bourdon tube is essentially able to select its own active wire length.

By means of the foregoing sub-assembly, its manufacturing costs as compared to otherwise comparable gauge internals of the prior art is dramaticaliy reduced. Moreover, by being a selfcontained sub-assembly, calibration can be effected in the sub-assembly state, thereby enabling precalibration in inventory prior to final assembly.

The invention will be better understood from the following description of preferred embodiments thereof, given by way of exampie only, reference being had to the accompanying drawings, wherein: Figure 1 is an elevation view schematically showing a pressure measuring system sub-assembly in accordance with a preferred embodiment; Figures 2 and 3 are elevation views of alternative embodiments to that of Figure 1 for the subassembly hereof; Figure 4 is a fragmentary front elevation of a pressure gauge utilizing the sub-assembly of Figure 1; Figure 5 is a side elevation of Figure 4; Figures 6 and 7 are plan views of the actuator clamp taken substantially along the lines 6,7-6,7 for the pre-swaging and post-swaging relations, respectively;; Figure 8 is a fragmentary front elevation of a pressure gauge utilizing the sub-assembly of Figure 1 with an alternative actuator clamp to that of Figure 4; Figure 9 is a side elevation of Figure 8; and Figures 10 and 11 are plan views of the alternative embodiment clamp taken substantially along the lines 10,11-10,11 for the pre-swaging and postswaging relations respectively.

Referring first to Figure 1, the pressure measuring sub-assembly construction 8 for a pressure gauge in accordance herewith is comprised of Bourdon tube 18 having a free end 22 adapted for displacement in correlation to the value of pressures 14 received at fixed inlet 20. Inlet 20 in turn is adapted for installation in a gauge housing providing an appropriate inlet connection by which the sub-assembly can be connected and rendered self-supporting, as will be understood. The composition of Bourdon tube 18 is preferably one having a wide range of service applications such as 316 stainless steel.

Supported from tube end 22 is a floating amplifier 12 of a type disclosed in the Wetterhorn patent supra for operating a pointer shaft 24. A wire actuator 44 has one end 46 extending into the motion path of amplifier 12 whereas its opposite end 66 is secured in either a clamp 50 or clamp 78 to be explained.

Either of the clamps 50 or 78 is in turn secured on a non-displacement portion of Bourdon tube 18 relatively near fixed end 20. It can be appreciated that the foregoing when assembled is completely self contained and self-supporting. When pre-calibrated, as will be explained, the sub-assembly is ready for end use in a pressure gauge by merely connecting tube end 20 in a rigid connection to an appropriate pressure source opening provided in a gauge housing with which it is to be used.

The sub-assembly embodiment of Figure 2 is similar in all respects to the previous embodiment except that lower end 66 of actuator 44 is secured directly to the Bourdon tube near its fixed end withoutthe benefit of a clamp as by welding orthe like.

For the sub-assembly embodiment of Figure 3, amplifier 12 and wire actuator 44 are inverted and interchanged as likewise disclosed in the cited patent to Wetterhorn. For these purposes, amplifier 12 is secured to the Bourdon tube near its fixed end 20 while actuator 44 is displaceable by tube end 22.

In a preferred arrangement, securing the amplifier is effected by means of a bracket 13 attached to the Bourdon tube as by welding or the like.

Referring now to Figures 4-7 of the drawings, the sub-assembly of Figure 1 is secured in a selfsupporting position in a pressure gauge 10 by a fixed end 20 of Bourdon tube 18 being welded or clamped at 17 to the outlet end of gauge socket 16. Amplifier 12 is mounted by weld 21 on tube end 22 as disclosed in co-pending application Serial No.

948,369 filed October 4, 1978. Being secured to the Bourdon tube in that manner enables the amplifier to float conjointly with displacement of tube end 22 to effectively drive shaft 24 supporting a pointer 26.

Arcuate displacement of the pointer by operation of shaft 24 reflects values of pressure as represented by graduations 30 on dial face 28.

As more fully described in the above Wetterhorn patent, amplifier 12 is comprised of a centrally upright inverted U-shaped carriage or frame 32 integrally formed to include symmetrically spaced apart side legs 34 and 36. The frame is secured by weld 21 at the free end 22 of Bourdon tube 18 for floating movement conjointly therewith and supports rotatable transverse shafts 24 and 38. The latter shaft provides a hinge support for a geared sector arm 40 while shaft 24 supports a pinion 42 meshing with sector arm 40 for displacing pointer 26 as described above. To effect operation of the amplifier there is provided an actuator 44 comprising elongated stainless steel wire of about 0.032 inches in diameter bent or offset at its upper end 46 for receipt in slot 48 of sector arm 40. At its other end, the actuator is secured in a clamp 50 in accordance herewith to be described.

Clamp 50, as seen in Figure 6, is of a laterally elongated structure having a vertically oriented thrubore 52 near one end. Bore 52 is of diameter slightly larger than the O.D. of Bourdon tube end 20 to enable a slip fit thereon before the latter is secured to socket 16. A pair of oppositely located relief areas 54 and 56 each communicate inwardly with bore 52 for reasons as will be explained. Laterally displaced from the axis of bore 52 is a transverse threaded bore 58 containing a set screw 60. Inwardly recessed slots 62 and 64 are each adapted to receive loosely the downwardly extending and upwardly extending portions, respectively, of reverse actuator bend 66 with the former slot being substantially located in vertical alignment with sector slot 48.

With the existing loose fitting arrangement of Figure 6, securing actuator wire 44 in clamp 50, as well as securing clamp 50 to Bourdon tube end 20, is effected in the manner of Figure 7. By first pressurizing the Bourdon tube to about fifty percent of rated capacity of the gauge to effect linearity adjustment as described in the Wetterhorn patent supra, actuator wire 44 is free to move upward along with sector arm 40. A pair of opposed crimping dies 68 and 70, shown in phantom, are then brought together in the direction of arrows 71. The imposed die force against the clamp is sufficient to crimp aperture 52 against the tube wall 20 while at the same time laterally crimping slot 64 about the wire rod of actuator 44 thereat.By comparing Figures 6 and 7, it can be seen that recess 56 has been substantially closed off to effect the appropriate grip with a uniform compression load against the Bourdon tube without clamp metal being extruded inwardly. Moreover, since swaging occurred with the Bourdon tube pressurized during calibration, the active wire length of actuator 44 is essentially selected by the Bourdon tube.

In effecting the above, it should be appreciated that Bourdon tubes typically vary in wall thickness from about 0.008 to 0.012 inches (0.2032 to 0.3048 mm) and are high stress members subject to internal working pressures of up to on the order of 30,000 psig (2.067 x 108 Pa gauge). It is important, therefore, in effecting the clamping grip therewith that additional cumulative stresses not be imposed which could either affect operation of the tube adversely or prompt its premature failure. In adhering to these limitations, it has been found that the clamp material can be any composition which when subject to crimping forces on the order of 1,000 pounds (4448 N), is able to deform without cracking.

Extruded aluminum is both suitable and most cost effective. Steel, brass, stainless steel, etc. are likewise suitable but somewhat less cost effective in current markets for those metals. With any of the named metals, overcrimping can be prevented by use of mechanical stops in the crimping dies. With crimping completed, span adjustment can be effected by needle nose 72 of set screw 60 being screwed toward or away from the actuator wire in slot 62 so as to displace the wire in the direction of arrow 74.

Referring now to Figures8-11,thegaugeconstruc- tion is identical in all respects to the previous embodiment with the exception of a clamp 78 hereof having a construction similar in principle but different in detail from that of clamp 50 above. Like clamp 50, clamp 78 includes a thrubore 80 for a slip fit mounting onto Bourdon tube end 20 and includes recesses 82 and 84 communicating therewith. Slots 86 and 88 are adapted to loosely receive the reverse bend lower portion of actuator 44and are symmetrically arranged with respect to the center line of bore 80. On bringing dies 90 and 92 toward each other while the Bourdon tube is pressurized for calibration as described above, the clamp is crimped as before with both leg portions of the actuator bend being secured as a result thereof.Span adjustment for this embodiment is effected by bending actuator wire 44 at offset 94 until an appropriate setting is achieved.

By the above description there is disclosed a novel sub-assembly construction for the pressure measuring system of a pressure gauge. With the amplifier components being operatively supported on the Bourdon tube, precalibration renders the subassembly readily usable in any suitable gauge housing providing a pressure opening to which the Bourdon tube can be connected in a self-supporting relation. Being independent of the housing construction except for a connection at the pressure opening, even to the extent of not requiring supplemental support, affords significant manufacturing advantages for the fabrication of pressure gauges in which it is utilized. At the same time, the simple and uncostly construction of the actuator clamp of the preferred embodiment affords a convenient means of enabling the Bourdon tube to essentially select its own active length of actuator wire.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense.

Claims (16)

1. A pressure measuring sub-assembly for a pressure gauge comprising: a) a pressure responsive element extending between a displacement portion thereof operatively displaceable in correlation to pressure changes to which the element is exposed and a relatively non-displaceable portion thereof; b) an amplifier for providing an output motion correlated to operative displacement of said displacement portion, the amplifier being secured to one of the said portions of the pressure responsive element; and c) an actuator connected to the pressure responsive element and extending to cooperate with the amplifier in effecting said output motion thereof.

2. A sub-assembly according to claim 1 in which the actuator is connected to the other of the said portions of the pressure responsive element.

3. A sub-assembly according to claim 2 in which the amplifier is operatively secured to the displacement portion of the pressure responsive element for floating conjoint movement therewith and the actuator is secured to the relatively non-displaceable portion of the pressure responsive element for extending into the motion path of said amplifier.

4. A sub-assembly according to claim 3 including a clamp operatively securing the actuator to the pressure responsive element.

5. A sub-assembly according to claim 4 in which the clamp comprises first gripping means for mounting onto a relatively non-dispiaceable portion of the pressure responsive element and second gripping means for securing the actuator.

6. A sub-assembly according to claim 5 in which said first and second gripping means are both swage imposed for effecting said mounting and securing, respectively.

7. A sub-assembly according to claim 6 in which said clamp is comprised of swageable metal composition, said first gripping means includes a first aperture through wk ich to receive a relatively nondisplaceable portion of the pressure responsive element and said second gripping means includes a second aperture displaced from the first aperture in which to receive the actuator.

8. A sub-assembly according to claim 7 in which the end of the actuator adjacent the clamp includes a reverse bend formation and said second gripping means includes a third aperture extending in a direction parallel to the direction of said second aperture.

9. A sub-assembly according to claim 8 in which each of said apertures are parallel to each other with said second and third apertures located displaced oppositely relative to the axis of said first aperture and substantially symmetrical with respect thereto.

10. Asub-assembly according to claim 7 in which the end of the actuator adjacent the clamp includes a reverse bend formation and said clamp means includes a third aperture through which said actuator can extend to said second aperture and a screw laterally engaging the actuator in said third aperture to enable span adjustment of the apparatus.

11. A sub-assembly according to any of claims 8 to 10 in which said second and third apertures comprise open slots extending inward from a face of said clamp.

12. A sub-assembly according to any of claims.7 to 11 in which said first aperture includes longitudinally extending radial recesses communicating outward from the wall surface thereof.

13. A sub-assembly according to any of claims 5 to 12 in which each of said first and second gripping means are effectively imposed while the pressure responsive element is subject to an application of pressure corresponding to about one-half of the rated capacity of the apparatus.

14. A sub-assembly according to any preceding claim including means to calibrate operation of the amplifier relative to the pressure responsive element.

15. A sub-assembly according to any preceding claim in which said pressure responsive element comprises a Bourdon tube.

16. A pressure measuring sub-assembly, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.