US2934729A - Pressure responsive electrical instruments - Google Patents

Description

April 26, 1960 M. E. BOURNS PRESSURE RESPONSIVE ELECTRICAL INSTRUMENT Filed March 30, 1955 INVENTOR. M E. M BY United States Patent PRESSURE RESPONSIVE ELECTRICAL INSTRUMENTS Marlan E. Bourns, Riverside, Calif.

Application March 30, 1955, Serial No. 497,878

1 Claim. (Cl. 338-40) The present invention relates to new and improved pressure responsive electrical instruments, and in particular to pressure responsive otentiometers.

In the past a wide variety of different types of pressure responsive electrical instruments have been developed for many specific applications. The advent of guided missiles and like devices has necessitated the design of new and improved electrical instruments capable of being used under widely varying temperature conditions without loss of accuracy. It has also necessitated the construction of electrical instruments which are relatively insensitive to the effects of acceleration and which are sutficiently rugged so as to withstand a great deal of rough treatment.

An objective of the present invention is to provide pres sure responsive electrical instruments meeting the requirements broadly indicated in the preceding discussion. Another object of this invention is to provide temperature compensated, pressure responsive electrical instruments having an exceedingly accurate response when employed at diverse temperatures, and which are relatively simple and inexpensive to manufacture. Further objectives of the present invention and many advantages of it will be apparent to those skilled in the art from the remainder of this description, the appended claim and the accompanying drawings in which:

Fig. 1 is a side view of an electrical instrument of this invention;

Fig. 2 is an enlarged cross-sectional view taken at line 22 of Fig. 1;

Fig. 3 is a cross-sectional view of a modified form of the invention taken at line 3-3 of Fig. 4;

Fig. 4 is a cross-sectional view taken at line 4--4 of Fig. 3 and Fig. 5 is a cross-sectional view taken at line 55 of Fig. 3.

Wherever convenient for purposes of illustration and explanation, like numerals have been used to designate like parts in all figures of the drawings. In certain cases the proportional sizes of many of the parts have been altered so as to make an explanation of the invention more clear.

This invention may be briefly summarized as being concerned with pressure responsive, temperature compensated electrical instruments including: means defining a mounting member; pressure responsive means having a fixed end and a movable end mounted on said means defining a mounting member with said fixed end secured to said mounting member; spring means secured to said mounting member so as to project therefrom; first electrical means secured to said spring means; and second electricalmeans secured to said movable end so as to move with respect to said first electrical means when fluid under pressure is introduced into or removed from said pressure responsive means.

In Figs. 1 and 2 of the drawings an electrical instrument of the invention is shown which comprises a generally cylindrical, can-like housing 12 having an open end sealed by a lid 14 which is attached to this housing 12 by conventional means such as, for example, an adhesive, screw-threads, or the like. Within the cylindrical side wall 16 of the housing 12 there is provided an opening 18 formed so that the portions of the wall 16 surrounding this opening 18 engage a notch 20 in a mounting member 22. This mounting member 22 is formed of a non-conductive material. such as, for example, a filled phenolic resin, so as to have an internal passage 24 located therein.

This passage 24 is connected to a threaded opening 26 which is used to connect the instrument 10 to an appropriate source of fluid under pressure. The passage 24 is employed to convey this fluid to the interior of a curved metal Bourdon tube 28, the fixed end of which is mounted in a cavity 30 formed within the mounting member 22 surrounding the passage 24. Appropriate means such as, for example, a very eflicient adhesive are used to secure the Bourdon tube 28 within this cavity. The end of the Bourdon tube 28 remote from the mounting member 22 is closed, and is attached as by welding, to a small contact member 32. If desired, this contact member may be termed an electrical means as the term is employed in this specification inasmuch as it is designed so as to move along a resistance element 34 during the operation of the instrument 10 as fluid under pressure is either intro duced into or removed from the Bourdon tube 28.

The resistance element 34 is preferably formed by appropriate printed circuit techniques in an arcuate shape upon a non-conductive supporting member 36. If desired, the resistance layer 34 may also be termed an electrical means as this term is employed in this specification. The supporting member is secured, also through the use of an appropriate adhesive, to a straight, radially projecting end 38 of a bimetallic spring arm 40 having a curved center section 42 and another end 44 which is secured within another cavity 46 formed within the mounting member 22. The spring arm 40 is concentric with the Bourdon tube 28 and lies in a plane generally parallel to and closely adjacent the plane of the Bourdon tube. Further, it will be noted in Figure 2 that both the curved center section 42 of the spring arm 40 and the Bourdon tube 28 are bent through substantially the same included angle. Thus, this end 44 is secured so as to be incapable of movement with respect to this mounting member.

The advantages of the construction of the instrument 10 are best explained by describing the operation of this instrument. When fluid under pressure is introduced into or removed from the Bourdon tube 28 the contact member 32 is moved along the resistance layer 34 by virtue of the movement of the movable end of this tube so as to be placed in electrical communication with a dilferent portion of the resistance element 34. As a consequence of this, a change in an electrical value is transmitted externally of the instrument 10 through the contact member 32, the Bourdon tube 28, and a wire 48 which is attached to this Bourdon tube 28, as by soldering, immediately adjacent to the mounting member 22. An electric current is normally supplied to the ends of the resistance element 34 through wires 50 which are secured to the spring arm 40 by means of small threads 42. The ends of the wires 50 are secured to the ends of the resistance element 34 by conventional means, such as, for example, soldering. The wires 50 and the wire 48 are all passed externally of the instrument 10 through a non-conductive grommet 54 located within the wall 16 of the housing 12. By appropriate selection of the metals employed in manufacturing the spring arm 40 it is possible to construct this spring arm so that, as the instrument is subjected to either increasing or decreasing temperatures, this spring arm 40 will bend moving the resistance element 34 an amount equal to the amount the contact 3 member '32 is moved'because of expansion or contraction of the metallic Bourdon tube 28. Thus, with the'construction shown it is possible to create an instrument of the class described which may be termed temperature compensated inasmuch as the relative position of the two electrical means employed remains constant regardless of the expansion or contraction of the Bourdon tube 28 or the spring arm used to support the resistance element 34. It is also possible, using this principle of construction, to construct the spring arm 40 so that the resistance element 34 is moved with respect to the contact member 32 so as to compensate for any change in spring rate or rate of movement of the Bourdon tube 28 at different temperatures. It is frequently desirable to form the contact 32 so that this contact is comparatively wide so as to avoid the possibility of this contact moving of? of the resistance element 34 during the operation of the in strument 10.

The instrument 10 possesses another definite advantage which is important in obtaining accurate electrical measurements under dilferent acceleration conditions. With the construction illustrated both the Bourdon tube 28 and the spring arm 40 will bend in the identical manner as the instrument 10 is subjected to acceleration. Thus,

with this construction, errors resulting from acceleration are substantially eliminated.

In Figs. 3, 4, and 5 of'the drawings a modified instrument 56 of the invention is shown which includes a canlike housing 12, within the open end of which there is secured by screws 58 a non-conductive mounting member 60 formed of such a material as a filled phenolic resin. There is held within a central opening 62 within this mounting member 60 a thin-walled shaft 64 in such a manner that this shaft projects within the housing 12. Preferably the shaft 64 is mounted through the use of nuts 66 engaging appropriate threads 68 as shown. Attached as by welding or the like to the end of the shaft 54 remote from the mounting member 60 is a small collar 70 from which there project two bimetallic arins 72 and 74 in such a manner that these arms are aligned with one another. Both of these arms are provided with flattened ends which are secured by appropriate means such as, for example, an adhesive to two identical nonconductive, arcuate sheets 76 and 78 respectively. These sheets 76 and 78 may be formed of the same material as the mounting member 60 and are intended to provide a balanced construction so that the forces tending to bend the shaft 64 are substantially equally balanced on both sides of this shaft.

Within the mounting member 60 there is positioned, as by the use of an adhesive, a metallic ferrule 80 which is located within a circular depression 82 so that a spiral Bourdon tube 84 formed of metal may be welded to this ferrule in such a manner as to be coiled about the shaft 64. This Bourdon tube 28 has an end 86 located adjacent to the sheet 76. Within the end .86 there is secured, as by soldering or welding, a metal plug 88 serving to seal the Bourdon tube. From this plug there projects a rod 90 to the end of which there is secured, as by welding or the like, a contact member 32 which is designed to ride upon a printed circuit resistance layer 92 disposed upon the sheet 76 attached to the bimetallic arm 72.

A tapped opening 94 is provided within the mounting member 60 so that the instrument 56 may be connected to an appropriate source of fluid in order that the fluid may be introduced into or out of the Bourdon tube 84 through a short passage 96 connecting the opening 94 with the interior of this Bourdon tube 84. The Bourdon tube itself, with the construction shown in Fig. 3, is designed to carry an electrical current and is connected externally of the instrument 56 by means of a small wire 98 which is secured by welding or the like to the ferrule 80, and which is passed externally of the instrument 56 through a small passage 100 formed within this instrument. Terminal connections to the resistance element 92 are made through the use of wires 102 which pass through the shaft and which are secured 'to the' ends of the resistance element 92 as by solder or like means.

The operation of the instrument 56 is essentially similar to the operation of the instrument 10. When this instrument 56 is employed for the purpose intended fluid is either introduced into or removed from the Bourdon tube 84 so as to cause this tube to either tend to coil or uncoil about the shaft 64. Thus the contact member 32 is moved with respect to the resistance element 92 in the manner in which the contact member is moved with respect to a resistance member in any conventional potentiometer. The bimetallic arms 72 and 74 bend in the same direction about the shaft 64 as the instrument 56 is subjected to changing temperatures so as to achieve the same temperature compensating efiect previously described. Thus, this construction is also capable of being used so as to compensate for any changes in spring rate of th Bourdon tube as well as for any changes in the relative positions of the contact member 32 and the resistance layer 92 caused by temperature.

The instrument 56 is also of such a construction that the errors which might be caused by subjecting this instrument to the forces of acceleration may be compensated for by virtue of the'fac't that the relatively thin walls of the shaft 64 will bend when subjected to accelerating forces in the same manner as the Bourdon tube 84.

It is considered obvious that a number'of minor modifications 'may be made in both the instrument 10 and the instrument 56 as described herein without departing from the essential concept" of the present invention; The shaft 64 acts in the instrument 56 essentially as a spring when subjected to accelerating forces. Other equivalent spring means, such as; for example, a flexible rod or a coil spring can thus be substituted for this shaft so as to achieve the same results as herein indicated. While the use of himetallic arms is specified in this description, it is to be understood that other members not capable of bending because of the differential coefficients of expansion of two metals can be employed with a corresponding omission of the function of these bimetallic arms.

Those skilled in the art to which this invention pertains will also realize that in many cases instruments of the class herein described can be formed utilizing various Bourdon tubes and either temperature compensating means or spring means, or combined temperature compensating means and spring means, all of the broad category herein disclosed in which various mechanical linkages are employed so as to multiply mechanically the movement of any of these parts. Further, the block 78 previously described can be utilized to support a second resistance member if a dual type unit is desired. This block and the arm supporting it can, if desired, be omitted. The term helical" and spiral herein used is intended to define essentialy an elongated coil of the type shown in Fig.- 3; the term curved" is employed herein to designate a Bourdon tube in which all of the tube lies within a single plane, regardless of whether this tube is composed of a number of concentric turns or a single curved strip not projecting more than 360 around a point.

Those killed in the art will further realize that it is possible to make a number of other refinements in the instruments shown which are of substantially an engineering nature. For this reason the present invention is to be considered as being limited only by the appended claim.

I claim:

A temperature and vibration compensated, pressure sensitive instrument comprising a mounting member having a pressure port provided therein, a Bourdon tube connected at one end to said mounting member and communicating with said pressure port, said Bourdon tube extending in a generally circular are from said mounting member, a bimetallic supporting spring arm connected at one end to said mounting member adjacent said one end of said Bourdon tube, said supporting spring arm being bent into a generally circular arc concentric with said Bourdon tube and lying in a plane generally parallel to and closely adjacent the plane of said Bourdon tube, said spring arm and said Bourdon tube being curved in the same direction and through substantially equal included angles, a resistance element mounted on the free end of said spring arm, and a contact fixed to the free end of said Bourdon tube and wiping on said resistance element, 10

said bimetallic spring arm being operable to shift said resistance element with respect to said contact on said Bourdon tube so as to compensate for temperature changes, and the free end of said spring arm deflecting in 5 forces is substantially eliminated.

References Cited in the file of this patent UNITED STATES PATENTS 2,152,262 Klein et a1 Mar. 28, 1939 2,226,629 Mather Dec. 31, 1940 2,264,487 Smulski Dec. 2, 1941 2,622,177 Klose Dec. 16, 1952

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