US2745721A

US2745721A - Combustible vapor detector

Info

Publication number: US2745721A
Application number: US293254A
Authority: US
Inventors: Tiffany Carter
Original assignee: Individual
Current assignee: Individual
Priority date: 1952-06-13
Filing date: 1952-06-13
Publication date: 1956-05-15
Anticipated expiration: 1973-05-15

Description

May 15, 1956 Filed June 13, 1952 c. TIFFANY COMBUSTIBLE VAPOR DETECTOR 2 Sheets-Sheet l CARTER TIFFANY. BY

UM lo-L ATTORNEYS.

y 5, 1956 c. TIFFANY COMBUSTIBLE VAPOR DETECTOR 2 Sheets-Sheet 2 Filed June 13, 1952 u mop X: 3F A N8 b g INVENTOR. CARTERTIFFANY. BY

UM, c641 (i h -L.

ATTOANEKS.

United States Patent 2,745,721 CQMBUSTIBLE VAPOR DETECTOR Carter Tiffany, Englewood, N. 3. Application June 13, 1952, Serial No. 293,254 Claims. (Cl. 23-255 This invention relates to gas detectors, and more particularly to improvements in such detectors which employ a catalytic agent for generating heat in response to the presence of a combustible vapor, such as hydrocarbon vapor and oxygen.

This application is a continuation-in-part of my co pending application Serial No. 158,313, filed April 26, 1950, now Patent No. 2,645,564, entitled Gas Detector App ratus.

Apparatus of this character suggested in the past has largely depended upon the measurement of a change in electrical resistance of an element sensitive to the presence of combustible vapor. The accuracy of such measurement of change in electrical resistance has been adversely affected by changes in ambient temperature and have required frequent and tedious adjustment in order to function satisfactorily. This has been particularly true with respect to apparatus employing a thermocouple. Prior apparatus of'this general character which have employed so -called balanced circuit means have also required frequent adjustment by skilled persons. Furthermore, the frequency of adjustment has been undesirably high thereby unnecessarily occupying the time of persons using the apparatus.

Fnrtherrnore, in devices of this general character heretofore suggested wherein operation depends upon an axial expansion differential between two small diameter wires, a serious elongation or axial'creep has occurred in the colder of the'two wires within a short time destroys the usefulness of the apparatus.

One of the objects of the present invention is to overcome the above difiiculties or to reduce them to insignifimes.

The invention in one aspect thereof is constituted by the combination including a pair of thermo-responsive or heat expansible Wire elements each having an outer extremity thereof secured to an outer extremity of an arm located therebetween which constitutes a signal arm. The opposite or inner extremity of each of the wire elements is' held in relatively clo'se relation to but spaced from the axis of such signal arm, for example, spaced from a base extremity of such arm, which extremity is opposite to the first-mentioned or outer extremity thereof. So-called base resilient means are employed for exerting upon the arm at or near such base extremity an axial thrust whereby the wire elements are maintained under equal tension when in a no gas condition. The wire elements thus a r e held in a V-forrnation with the signal arm therebetween, the reby forming a so-called V-tension mounting wherein the axis of the signal arm and a pair of lines extending perpendicularly from such axis to respective of said opposite (or inner) Wire extremities form two adjacent right triangles having common side portions along the axis of said signal arm and also having adjacent acute angle apices located near the outer extremity of the signal arm, The signal arm is provided with pivot means at its base extremity but is normally restrained from angular motion by such wire elements which hold same in place except when there occurs an expansion of one of the wire elements relative to the other at which time an angular shifting of the signal arm takes place. The wire elements are selected to have equal expansion characteristics for a given increase in temperature. However, in order to create an expansion diiferential in response to the occurrence of a combustible vapor (in the presence of oxygen), a catalytic agent is associated with one of the wire elements. The latter thus can be heated to a temperature higher than the other wire in response to such occurrence of combustible vapor and oxygen thereby creating the expansion differential between the two wire elements. The term expansion differential as employed herein refers to expansion axially rather than radially of the wire elements. The catalytic agent is sensitive to the combustible vapor and is capable of inducing an exothermic reaction in the presence of such combustible vapor and oxygen. Suitable means, such as a switch, are operatively associated with the signal arm for actuation in response to angular movement of the latter whereby a suitable signal device can in turn be actuated. Such switch includes a first contact secured to the signal arm and located at or near the outer extremity thereof and a second contact mounted upon a so-called resilient contact support. The latter resilient contact support is selected to have yielding characteristics which permit said base resilient means to expand sufiiciently to reduce the thrust thereof to a relatively low value at the point where said first and second contacts are in equilibrium, the resilient contact support nevertheless preventing excessive angular movement of the signal arm which might otherwise cause excessive pulling of and/ or a permanent set in the relatively hot wire element when the latter is in a heated condition and thus relatively reduced in tensile strength. At such last-mentioned equilibrium point the thrust upon the relatively cooler wire is at the aforementioned low value thereby avoiding the danger of causing a permanent set or an undesired stretching thereof which might otherwise occur if the force of the spring were not so diminished. In order to increase the sensitivity of the detector, the wire elements are subjected at all times to a basic heat when in operation which basic heat is distinct from the heat applied to one of them by catalytic action. For example, the wire elements may be basically heated by electric current flowing therethrough or in lieu thereof by external electrically heated coils surrounding same. Such wire elements are subjected to equal basic heat and thus raised to an equal basic temperature prior to the actuation of the device by a combustible vapor. After such actuation, the relatively cooler or non-catalyst bearing wire element may be subjected to a lower basic heat than the relatively hot wire element, for example, by shunting the relatively cooler Wire as will appear below. However, the invention is not limited to such reduction of basic heat.

-Various, further and more specific objects, features and advantages of the invention Will clearly appear from the detailed description given below taken in connection with the accompanying drawings which form a part of the specification and illustrate, by Way of example, preferred arrangements of apparatus for carrying out the invention. The latter consists of such novel combinations of features as may be shown and described in connection with the devices herein disclosed.

In the drawings:

Fig. 1 is a schematic illustration on an enlarged scale, partly in section and with parts broken away, of one embodiment of the present invention for detecting the presence of a combustible vapor;

Fig. 1a is a side elevation, partly in section and with parts broken away, and with certain other parts omitted for clarity, of the embodiment shown in Fig. 1, taken substantially along line 1a--1a of the latter figure;

Fig. 2 is a schematic diagram on an enlarged scale of a second embodiment of the invention which also is adapted for signalling the presence of a combustible vapor;

Fig. 3 is a schematic illustration of still another form of the invention showing one manner of electrically interconnecting the parts;

Fig. 4 is a fragmentary view on an enlarged scale, partly in section and with parts broken away, of pivot means for the signal arm which may be employed alternatively with those shown in the previous figures;

Fig. 5 is a schematic representation of the wire elements mounted in the so-called V-tension mounting and illustrating certain of the forces acting at the tip of the signal arm when in a no gas condition;

Fig. 6 is a vector diagram of the forces shown in Fig. 5;

Fig. 7 is a vector diagram of the forces acting at the tip of the aforementioned signal arm when the apparatus is in the presence of a combustible vapor and oxygen, such forces occurring at the tip of said signal arm and prior to the latter reaching equilibrium with the aforementioned resilient contact support; and

Fig. 8 is a vector diagram of the forces acting at the tip of the signal arm in the presence of said combustible vapor and oxygen and after said signal arm has achieved equilibrium with said resilient contact support.

Referring to the drawings in further detail, particularly to the embodiment of Fig. 1, heat expansible wires are shown, as at 10 and 11. They are associated with means for normally holding them under equal tension in a no gas condition and are incorporated in an electric circuit,

to appear hereinafter, in which they can be heated by a common source of electric energy; The

wires

10 and 11 are, in the form shown, so-called forty gauge in diameter, that is, they are .0031 inch in diameter. This size has been found to operate with a high degree of sensitivity for the purpose intended but, of course, the invention is not limited thereto. Each wire is of equal electrical resistance under normal conditions of no gas, that is, of no combustible vapor (such as hydrocarbon vapor). They are of equal expansion and contraction characteristics with respect to a common temperature change. Consequently both wires have the same coefiicient of expansion and both are of the same material, preferably so-called Nichrome steel.

Associated with the wire 10 is a catalytic substance, indicated schematically at 10, for example, a finely divided platinum, which may be held in such association by a suitable carrier, such as carbon, asbestos, or a ceramic material.

The means for magnifying or amplifying an axial expansion differential occurring between the

wires

10 and 11 will now be described, such means constituting the aforementioned V-tension mounting. This expression refers to means for maintaining the

wire elements

10 and 11 under tension in a ii-formation whereby a substantial magnification of any such axial expansion differential is efiected. Such V-tension mounting includes 'a foundation or base member 12 which mounts thereupon a signal arm indicated generally at 13, the latter being associated with the base member for angular movement relative thereto in response to the aforementioned axial expansion differential between the

wires

10 and 11.

The particular forty

gauge wires

10 and 11 in this embodiment have a tensile strength of about .4 lb. at room temperature and about .04 lb. when relatively hot, that is,

in the region of 1500 F.

In the embodiment shown, the signal arm 13 is supported by an L-shaped pivot arm 14, the foot portion 14a of which passes through and is firmly secured in a suitable perforation 12:: formed in the base member 12 and thus is held against angular change. Surrounding the upper portion of the pivot arm 14 is a tubular member 15 consisting, for example, of glass. A relatively small portion of the length of the tube 15 at the base thereof embraces such upper portion of the pivot arm and is axially shiftable thereupon, being urged upwardly as viewed in Figs. 1 and laby means of a coil spring 16 which surrounds said pivot arm 14. The tube 15 is slightly larger in inner diameter than the outer diameter of arm 14, thus enabling tube 15 to shift slightly angularly, as will appear below, while so embracing said arm 14. The coil spring 16 is restrained from urging the tubular member oif of the pivot arm 14 by means of the above-mentioned

wires

10 and 11 which, at one extremity of each thereof, is secured to the outer or free extremity of such signal arm 13. That is, extremities 10a and 11a of such wires are secured to a metallic signal arm tip portion 17. The

wires

10 and 11, at the opposite or

base extremities thereof

10b and 11b, are rigidly secured to terminal posts indicated respectively at 18 and 19 which in turn are secured to the base member 12. The latter preferably is of suitable electrically insulating material.

It is desirable for the

wires

10 and 11 to be of substantially identical lengths and for a base line drawn through the

terminal posts

18 and 19 normally to be substantially perpendicular to the longitudinal axis of the signal arm 13. .Thus the axes of the signal arm and of the

wires

10 and 11, together with lines drawn perpendiuclar to such signal arm axis from the

base extremities

10b, 11b, constitute adjacent acute triangles having common side portions along such signal arm axis, and having adjacent acute angle apices. q

I have found it advantageous for the distance between one of the terminal posts, as at 18, to the center of the foot portion 14a (Fig. la) to be about one-twelfth of the distance from such foot portion to extremities 10a, 11a. The foot portion 14a is, of course, preferably midway between the

terminals

18 and 19.

In the embodiment of Figs. 1 and la, the wire elements wand 11 are connected in series in an electrical circuit, including a source of electrical energy, such as a battery 20, having

terminals

21 and 22 which are respectively connected to the

terminals

18 and 19 by means of

leads

23 and 24. A master circuit switch, as at 25, is interposed in such circuit, for example, in the lead 23.

One of the'most serious problems which have been encountered in the past in the manufacture of gas detectors of this type, and a problem which has heretofore remained unsolved, has been the failure of the gas detector after a few actuations thereof because of a lengthening or gradual elongation of the cooler of the two wires,that is, of the wire element which has no active catalyst associated therewith. As will appear hereinafter, it will be clear that both of the wires are at substantially the same temperature during normal no gas operation, but in the presence of a combustible vapor the wire element having a catalyst associated therewith becomes relatively hotter than the other wire element. Consequently, such catalyst bearing wire element 10 is referred to sometimes herein for convenience as the hot wire and the other wire element 11 as the cold wire or cooler wire. The aforementioned gradual elongation or so-called creep of the cooler wire has heretofore been due to repeated applications thereto of excessive thrust from the signal arm spring, such as the aforementioned coil spring 16, the cooler wire in the past having been subjected to the thrust of such signal arm spring:

(a) At a time when denied the full aid of the wire in restraining such signal arm spring; 7

(b) Over periods of time which are sufficient to encourage creep or elongation of the cold wire; and

(c) When such signal armspring is relatively undistorted and thus is capable of exerting a thrust sufficient to cause such elongation or creep. l V

The coil spring 16 can be, in one form thereof, for

hot

example, /2 inch in length. (uncompressed) and when installed, as shown in Figs. 1 and. 1a, can be compressed by for example, /a inch or about 25% of its length. When the coil spring 16 is so compressed it may exert a thrust upon the signal arm 13. of, for example, about /2 oz., thereby placing the

wire elements

10 and 11 under tension of about /1 oz. each, under no gas condition. When the apparatus is in the presence of a combustible vapor, such as a hydrocarbon vapor and oxygen, the catalyst-bearing wire element 1 will elongate in the man er i l edn. t a or m nti ned r r d g a plication Serial No. 158,313 whereupon the'signal arm will shift to the left (Fig. 1) under the influence of coil spring 16. in the absence of some restraining means, such as a resiliently mounted contact 26 which is positioned for engaging and restraining the movement of the signal arm, as will appear below, the latter arm then may shift so far to the left (Fig. 1) that the wire element may be pulled apart (or a permanent set may be produced therein) when at a temperature of the order of 1500" F. Both

wires

10 and 11 are subjected to equal tension but the hotter wire 10 being of relatively reduced tensile strength, due to its higher temperature, would take a permanent set in the absence of some means for restraining angular movement of the signal arm 13. However, it is necessary to avoid damage not only to the hot wire 10 but also to the cooler wire 11. If contact 26 were rigidly fixed in its position shown in Fig. 1, instead of resiliently movable, spring 16 would exert substantially its maximum load upon wire 11 which load, due to the basic heated condition of wire 11, might stress it beyond its elastic limit. Consequently the characteristics of a resilient member, such as a leaf spring 27., for mounting the contact 26 is selected to restrain the angular movement of the signal arm 15 resiliently to prevent the aforementioned damage to both wires. The characteristics of such leaf spring 27 and coil spring 16 are jointly chosen to allow the.

latter to expand to such a point that its thrust is relatively very low at the point of equilibrium between the signal arm 13 and the spring 27 after engagement, thereby preventing damage to the cooler wire 11. The characteristics of said spring 16 are chosen whereby the angular motion to the left of signal. arm 13 is arrested and equilibrium with spring 27 is. reached after the coil spring 16 has expanded to such a point that its normal thrust is reduced substantially, for example, by 7580%. Thus even after many repeated actuatious of the device, the cooler wire will have been subjected only to re peated relatively minor thrusts from the coil spring 16 which will not have placed it under sufficient tension to stress it beyond its elastic limit thereby to cause any elongation or creep sufficient to reduce the accuracy or sensitivity of the apparatus.

Under normal circumstances of no gas, that is, no combustible vapor, the signal arm 13 will reflect no differential in axial expansion between the wire elements it) and 11 and such arm will thus normally be in a position substantially. perpendicular to the aforementioned base line drawn through the

terminals

18, 19. in such perpendicular position the signal arm tip portion 1'7 is spaced from the contact mounted upon the resilient arm or leaf spring 27. The latter is fixedly secured to the base member as at 23. The arm 27 is connected by means of a lead 29 to the aforementioned terminal 22. Suitable signal means, such as an incandescent lamp 3%), is interposed in the lead 29.

The gap between the contact 26 and the tip portion 17 normally can be, for example, .003 inch under no gas condition and this gap can be adjusted by any suitable vernier adjustment means.

Referring now to Figs. 58, the aforementioned change in the relationships of the forces acting in the apparatus due to the operation of the resilient members 1. V nd 2 i l no be discu e 1. isthe is tion only,

schematically illustrated the forces acting. at the tip region of ar l 13, such forces being in equilibrium in a normal no gas condition.

in Fig. 5 the arrow 16a represents the vertical thrust of the coil spring 16 upon the. signal arm 13. This force is in equilibrium with forces represented by arrows 10a and 11a (Fig. 5) attributable to the restraining action of the

Wires

10 and 11. Vectorially these forces are shown in Fig. 6. The forces 10a, 11a and 16a are vectorially represented in Fig. 6 at 10b, 11b and 16/), respectively. Inasmuch as the forces are in equilibrium, it is clear that the vectors 10b and may be easily calculated geometrically each as the hypotenuse of a right angle triangle and, in this instance, each is slightly in excess'of one-half of the value of 161 When the catalyst bearing wire element 10 reaches a higher temperature, as compared to wire element 11, due to the presence of a combustible vapor, the former wire element elongates slightly relative to' the other wire element and a state of unbalance occurs in the forces acting at the tip region of the signal arm. The coil spring 16 is permitted to expand and to urge the signal arm 13 to the left, as viewed in Figs. 1 and 5. A vector representation of such forces at this point is shown in Fig. 7 wherein it will be seen that the vector 16b is the same as before. The vector 11b remains substantially unchanged. However, due to the aforementioned slight elongation of the wire It), the vector 10]) diminishes to the value indicated at 10c thereby producing a resultant force represented by vector 10d having a component 10c which urges the signal arm to the left as aforementioned.

The tip 17 of the signal arm 13 thus shifts angularly to the left, in the form shown, about .003 inch until engagement is made with the resiliently supported con: tact 26, thus deforming the leaf spring 27, urging same also to the left until a condition of equilibrium is reached which is vectorially indicated in Fig. 8. Following the engagement between said tip 17 and the contact 26, the two may shift a further amount of, for example, .017 inch at which point said equilibrium occurs. The coil spring 16 at this time has expanded sufficiently to reduce the thrust therefrom to the value indicated at 16c. The counterthrust of the leaf spring 27 is indicated at 27a. Thus the extent of the force exerted upon the wire 11 is represented by the vector 11c, the latter being substantlally diminished as compared to 11b.

In operation of the embodiment of Fig. 1, the switch 25 is first closed thereby completing the electrical circuit comprising the battery 20, the lead 23, the wire 10, the wire '11, and lead 24. The

wire elements

10 and 11 consequently will have applied thereto equal basic heat and thus will be heated to a common temperature as the result of current flowing therethrough and due to this equal heating there will be no axial expansion differential therebetween. Consequently there will be no change in the angular position of the signal arm 13. However, a combustible vapor, such as hydrocarbon vapor, will create with the catalytic agent associated with wire element 10 an exothermic reaction in the presence of air whereby the temperature of the wire element 10 will be elevated over that of wire element 11 and thus will become relatively longer. It is believed that under conditions of no gas both wires by way of illustrareach an equal temperature of between about 600 to 900 F. in this form of the invention due to application of said basic heat. When the aforementioned axial expansion differential occurs due to the relative elongation of the wire element 10, the signal arm tip 17 shifts angularly to the left (Fig. 1) and engages the contact 26 as aforementioned after shifting, for example, about .003 inch. Thereupon the wire 11 is substantially entirely shunted out of the circuit causing the bulk of the electrical energy to pass through the relatively hot wire 10 raising its temperature to the order of 1500" F; The temperature of the relatively cooler wire 11 thus will be diminished, by way of illustration only, to the order of 350-400 F. One of the factors controlling the amount of current passing through the wire element 11 is the resistance of the signal means 30. When the signal arm tip portion 17 engages the contact 26 and thereby shunts the wire 11 the temperature of the latter, as aforementioned, will diminish from its normal operating temperature. Thus the wire element at this point will offer a relatively greater resistance to the flow of current through the circuit whereupon, also as aforementioned, its temperature will be increased. Such augmenting of the temperature differential between the wire elements causes the tip portion 17 to engage the contact 26 with greater intensity.

Referring now to the embodiment of Fig. 2, the novel device is constituted by a pair of heat

expansible wire elements

32 and 33 which also are mounted in a socalled V-tension mounting analogous to but somewhat different from that described in Fig. 1. This particular V-tension mounting is constituted by a base member 34 which is in bracket-like form and is secured to a main frame or foundation member 35. One extremity of each of the

wires

32 and 33 is secured to in electrical connection with the base member 34 as at 32a and 33a, respectively. The base member 34 is of suitable electrically conducting material, for example, brass or copper, and the

wires

32 and 33 being so secured thereto, are placed in electrical communication through a low resistance conductor. The opposite extremities of the

wires

32 and 33 are secured to the outer extremity of a signal arm 36 which is analogous to signal arm 13 above described.

Said wires may be so secured by means of a collar 37 attached to such outer extremity by means of a pin 38. The signal arm 36 preferably is of a non-conducting or insulating material, such as glass, and the base extremity thereof, as at 36a, is associated with a pivot means preferably at a point substantially midway between the lower extremities of the wires 32 and 33 (Fig. 2), although such pivot means can be well above or below such mid-point. Such pivot means comprises in the form shown a spherical bearing, as at 39, about which the signal arm may shift angularly when such motion is permitted by an axial expansion differential between said

wires

32 and 33. Said hearing or spherical member 3? is urged upwardly, as viewed in Fig. 2, by means of a helical spring, as at 40, which is contained within a cylindrical sleeve 41. The pressure exerted upon the signal arm 36 in an upward directiontFig. 2) may be adjusted by controlling an adjustment screw 42 which is in threaded engagement within the sleeve 41 and which engages one extremity of the coil spring 40.

The

wires

32 and 33 are both of copper or both of niehrorne steel and are covered with a coating of electrical insulation, for example, of ceramic material. agent, such as finely divided platinum, is applied to one of the wires, such as 32, by suspending same, for example, in the ceramic coating of such wire. The initial or basic heat for the

wires

32 and 33 is not applied by means of an electric current flowing therethrough but instead is applied by external heating coils, that is, coils which are separate from the

wires

32 and 33 and which surround'same. Such coils are shown as at 43 and 44 which respectively surround the

wires

32, 33 and are electrically insulated therefrom.

As above mentioned, the upper extremities of the wires 32and 33 are secured tothe outer or upper extremity A catalytic" of the signal arm 36 with the assistance of such collar 37. The outermost extremities of the

wires

32 and 33,

as at 32b and 3315, are in electrical connection with one another, for example by'direct contact or by virtue of contact with a common tip portion 45 of suitable conducting material. Tip portion 45 is positioned adjacent a contact 46 mounted upon a resilient leaf spring 47 analogous to spring 27 of Fig. l. The contact 46 is connectedto the base member 34 by means of a lead 49. Inter-.

trical energy, such as a battery 51, and a switch, as at 52. The above-described external heater coils 43 and 44 may be connected in parallel across the terminals of the battery 51, for example, as follows: The lower extremities of said coil, as at 43a and 44a, are directly connected to the electrically conducting base member 34. The upper extremities thereof, as at 43b and 44b are connected respectively by leads 53 and 54 to a terminal 55 which is interposed between the relay 50 and the battery 51. As a result of this interconnection of the elements, there will be, upon closing of the switch 52, a current always flowing through the

coils

43 and 44. Said currents are equal in amount and due to the identical characteristics of said coils, normally heat same to a common temperature thereby causing a common expansion of the wires but producing no expansion differential which will shift the signal arm 36 angularly from its centered position, as shown in Fig. 2.

In operation of the embodiment of Fig. 2, the master switch 52 is closed thereby energizing'the external heater coils 43 and 44 which heat the

wire elements

32 and 33 in equal amounts to the same temperature. The sensitivity of the device to the presence of a combustible vapor is substantially enhanced because of such heating. As aforementioned, the signal arm 36 will remain in its normal center position when the wires are so heated in a no gas condition, that is, when the device is not in the presence of a combustible vapor. However, when such vapor is present, the wire element 32 will elongate relative to the wire element 33, for reasons described above, thereby causing the tip portion 45 of the signal arm to engage the contact 46. Such engagement permits a flow of current through both of the

wires

32 and 33 thereby removing some of the electrical load upon the heater coils 43 and 44. Consequently the temperature of such heater heat to coil 44 thereby to augment the temperature differential between

Wires

32 and 33. It is desirable so to augment such temperature dilferential to insure a positive engagement of

contacts

45 and 46.

A third form of the invention is shown in Fig. 3 wherein a pair of

wires

57 and 58 are employed which also are, supported in a V-tension mounting identical to that shown and described in-connection with Fig. 2 with the exception that the base extremities 57a, 53a thereof are electrically insulated from a base member 59. The latter may be of electrically conducting material. Suitable insulating means are provided for such base extremities of the wires. Such extremities may be held by

glass beads

60 and 61, respectively, in a manner analogous to that described in my aforementioned copending application Serial No. 158,313 for Gas Detector Apparatus. The outer extremities of the

wires

57, 58 are secured to the end of a signal arm 62 by means of a collar 62a'ar1d a pin 62b. The base extremity of the signal arm 62, in the manner of that shown in Fig. 2, is urged in a direction to place the

wires

57, 58 under tension by means'of a coil spring 63 within a sleeve 64, said spring engaging a spherical member 65 upon which the base extremity of the signal arm rests. A threaded adjustment screw 66,

9 which engages the sleeve 64, controls the compression of the spring 63.

The base extremities 57a, 58a are connected to

suitable terminals

67 and 63 which are insulated from one another.

Both of the wires are preferably of nichrome, one having closely associated therewith a catalytic substance, such as finely divided platinum held by a neutral carrier substance, such as asbestos, carbon, a ceramic material or the like.

The device above described in Fig. 3 is employed in this embodiment in combination with a suitable signalling device, such as an incandescent lamp 69, and switching means generally indicated at 70, preferably in the form of a so-called microswitch.

The latter switching means includes a switch arm 71 which is pivotally mounted, as at 72, and provided with a suitable contact head 73 which is shiftable angularly between a pair of opposed fixed

contacts

74 and 75. Switch 7% is of the toggle variety. Thus if head 73 is shifted from contact 74 to 75, it must be manually reset into engagement with the former. A force acting upon the arm 71 will shift same so that the head 73 will shift from the position shown in Fig. 3, wherein it engages contact '74 into engagement with contact 75. Such force may be exerted through the intermediary of a switch actuating arm 76 which is secured to a housing 70a of the switch '70, as at 77. Arm 76 can be, for example, of a resilient material and can yield when engaged by signal arm 62. Arm is provided with a tip portion 76a having a tapered or pointed extremity for contacting the collar 63. A microswitch plunger 78 (of non-conducting material) is mounted for sliding axial movement between the actuating arm 76 and the switch arm 71. When the actuating arm "/6 is thrust to the right, as viewed in Fig. 3, the plunger 73 will shift the switch arm from contact 7d to contact 75. A resiliently actuated toggle linkage (not shown) of well known design can be employed for holding the switch arm 71in either of its extreme positions.

A wiring diagram for interconnecting said differential expansion sensitive device, the switch 70 and the signal means 69 will now be described. A suitable source of electrical energy, as at 79,, is employed having terminals 8t? and 81. i have found it desirable to interconnect said differential expansion device and the source of electrical energy 79 in such a way that the current normally will flow through the

wires

57 and 58 which are connected in series in such circuit. As above mentioned, the switch arm 71 normally is positioned to engage contact 74. Consequently, in order that such current may normally flow through such wires, the terminal 67 is connected to battery terminal 86) by means of a lead 82, switch arm '71 is connected to the battery terminal 81 by means of a lead 83, and the switch contact 74 is connected to the terminal 63 by means of a lead 84. A suitable master switch may be interposed in the lead 83, as at 85. Thus when the switch 35 is closed, an electrical circuit is formed as foliows: from terminal 80, lead 82,

wires

57 and 58, lead 84, contact 74, switch arm 71 and lead to battery terminal 81.

Thus under normal conditions the two

wires

57 and 58 are heated as a result of current flow therethrough and will expand, in the absence of a hydrocarbon vapor, in equal amounts, their physical and electrical characteristics having been selected such that they will expand equally under these circumstances. The switch arm 71 thus will remain in engagement with the contact 74. However, in the event that a hydrocarbon or combustible vapor occurs, the differential expansion means will reflect same. The wire element 57 will expand axially relative to the wire element 58 whereby the collar-member 63 will be caused to shift and engage the switch actuating arm 76.

I have found it desirable to interconnect contact 74 and the actuating arm 76 by a lead 87 (via lead. 84)

which. will efiect a shunting of the wire 58 when the above-mentioned engagement occurs between collar member 63 and the actuating arm 76 whereby the bulk of the electrical load in the circuit will be put upon the wire 57. The wire 58 thus will become relatively cool thereby accentuating the expansion differential theretween. Consequently the switch actuating arm 76 will be shifted to the right, as viewed in Fig. 3, an amount sufiicient to shift the switch arm 71 from contact 74 into engagement with contact 75 thereby energizing the signal means 69 which thereupon are immediately connected across the terminals of the batteries 79. In order to disconnect such signal means, the switch arm 71 must be manually disengaged from contact 75.

The microswitch 70 preferably is mounted in such a way that an extremely fine adjustment may be made of the gap between the collar 63 and the tip of the actuating arm 76. For example, the microswitch may be secured to an arm 88 pivotally mounted at one extremity at 89, the opposite extremity thereof being shiftable by means of an adjustment screw 90 in any suitable manner. For example, in the form shown, the screw 90 is secured against axial motion by means of fixed supports 90a and 9% which have unthreaded bores therethrough and which engage unthreaded annular grooves in said screw. A lug 91 secured to the extremity of the arm 88 is provided with a suitable threaded bore through which passes the screw 90.

The operation of the embodiment of Fig. 3 will be obvious from a consideration of the above description thereof.

in lieu of the pivotal mounting means shown in the previous embodiments for the signal arms therein, the pivotal mounting means of Fig. 4 may be employed. The latter pivotal mounting means are particularly well adapted for use with a solid signal arm, such as that shown at 92, which has a recess 92a formed in the lower extremity thereof for containing a resilient member, such as a coil 93, which performs a function analogous to

coil springs

16, 41 and 63, of Figs. 1, 2 and 3, respectively. The coil spring 93 is compressed as aforementioned initially to an extent, for example, of about 20 to 25% to provide a desired thrust upon the signal arm 92 thereby to hold the wire elements under tension also as described above. A disc member 94 engages the lower extremity of the spring 93 and as aforementioned centrally thereof a recess 94a into which extends the pointed extremity of a pin 95. The latter preferably is fixedly secured to a foundation member 96 through the intermediary of a plug 97 having a recess 97:: into which one extremity of the pin extends in tight frictional engagement. The pin 95 may be bent into L-shape as shown.

The embodiment of Fig. 3 is particularly adapted for relatively larger currents as compared to the currents which flow in the embodiments of Figs. 1 and 2. The wires 57 and 53 are selected of correspondingly larger diameter in order to accommodate such currents. The embodiment of Pig. 3 can be designed for currents, for example, of 10 amp res at volts or 5 amperes at 220 volts.

Instead of employing the signal means shown in each of the circuits described above, it is possible to substitute a suitable relay therefor which in turn is operatively connected to an externally or remotely located alarm system, for example, such relay may be connected to a local fire department alarm system. Furthermore, such relay can be energized by a supplementary power source which is not associated with a main power source.

While the invention has been described with respect to certain preferred examples which have given satisfactory results, it will be understood by those skilled in the art, after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is 11 a intended, therefore, in the appended claims to cover all such changes and modifications.

What is claimed is:

1. In a device for detecting the occurrence of a combustible vapor; a base member; a'signal arm; a pair of wire elements; one extremity of each of said wire elements being secured to said signal arm near one extremity of the latter, the opposite extremities of said wire elements being spaced apart and secured to said base member; such wire elements, the axis of said signal arm, and a pair of lines each extending perpendicularly from said axis to respective of said opposite Wire extremities forming two adjacent right angle triangles having a common side portion along said axis and also having adjacent acute angle apices; pivot means for the opposite extremity of said signal arm; signal arm resilient means for urging said signal arm resiliently and axially thereof in a direction normally to place said wire elements under tension thereby forming a V-tension mounting, said signal arm resilient means exerting a force upon said signal arm which is a function of the extent of deformation thereof, said wire elements having equal expansion characteristics responsive to a common temperature change; one of said wire elements including a catalyst for heating same relative to the other wire element in response to oxidation of combustible vapor under the influence of such catalyst; said signal arm under the influence of said resilient means being angulariy shiftable in response to an axial expansion differential between said wire elements whereby such resilient means can expand and the thrust thereof diminished as a function of such expansion; a contact for engaging said signal arm; limit-stop resilient means for such signal arm, such limit-stop resilient means having preselected structural strength characteristics for exerting a progressively increasing force against such signal arm, which force is a function of the extent of such signal arm angular movement from a norm position and thus of the extent of deformation of said limit-stop resilient means,

such limit-stop resilient means by virtue of such preselected structural strength characteristics creating a force adequate to arrest such angular movement of said signal arm in response to departure thereof in a critical amount upon said signal arm by said signal arm resilient means in turn to diminish the tension upon such other of said wire elements below the elastic limit of the latter element.

2. In a device for detecting the occurrence of a combustible vapor; a base member; a signal arm; a pair of wire elements; one extremity of each of said wire elements being secured to said signal arm near one extremity of the latter, the opposite extremities of said wire elements being spaced apart and secured to said base member; such wire elements, the axis of said signal arm, and a pair of lines each extending perpendicularly from said axis to respective of said opposite wire extremities forming two adjacent right triangles having a common side portion along said axis and also having adjacent acute angle spices; pivot means for the opposite extremity of said signal arm; base resilient means acting upon said signal arm near the base thereof for urging same resiliently and axially in a direction normally to place said wire elements under tension thereby forming a V-tension mounting, said wire elements having equal expansion characteristics responsive to a common temperature change; one of said wire elements including a catalyst for heating same relative to the other wire element in response to oxidation of combustible vapor under the influence of such catalyst; said wire elements normally being under equal tension in the absence of an axial expansion difierential therebetween, said base resilient means by a preselected amount to provide a preselected axial thrust upon said signal arm, the latter under the influence of such base resilient means being angularly shiftable in response to such an axial expansion differential between said wire elements whereby such resilient means can move toward an undistorted condition and the thrust thereof can diminish with such movement; said Wire element including the catalyst having a preselected elastic limit Within the temperature range of operation thereof when heated by said catalyst, said other wire element having also a preselected elastic limit within its temperature range of operation, such force exerted by said signal arm resilient means diminishing as a function of the angular movement of said signal arm from a norm position, resilient limit-stop means positioned for engagement by such signal arm and having strength characteristics for arresting the angular movement thereof in response to departure thereof in a critical angular amount from such norm position, said signal arm resilient means at such departure being substantially minimized in deformation as compared to its deformation when said signal arm is in such norm position, the tensioning forces exerted upon such other of said wire elements being less than the elastic limit thereof in response to said diminished deformation of said signal arm resilient means, the tensioning forces exerted upon said wire element including the catalyst being less than the elastic limit thereof responsive to said signal arm being displaced by said critical angular amount.

3. In a device for detecting the occurrence of a combustible vapor; a base member; a signal arm; a pair of wire elements; one extremity of each of said wire elements being secured to said signal arm near one extremity of the latter, the opposite extremities of said wire elements being spaced apart and secured to said base member; such wire elements, the axis of said signal arm, and a pair of lines each extending perpendicularly from said axis to respective of said opposite wire extremities forming two adjacent right triangles having a common side portion along said axis and also having adjacent acute angle apices; pivot means for the opposite extremity of said signal arm; resilient means for urging said signal arm resiliently and axially in a direction normally to place said wire elements under tension, said wire elements having equal expansion characteristics responsive to a common temperature change; one of said wire elements including a catalyst for heating same relative to the other wire element in response to oxidation of combustible vapor under the influence of such catalyst; said wire elements normally being under equal tension in the absence of an axial expansion differential therebetween, said resilient means in they absence of such combustible vapor being distorted by a preselected amount to provide a preselected axial thrust upon said signal arm, the latter under the influence of such resilient means being angularly shiftable in response to such an axial expansion differential between said 'Wire elements whereby such resilient means can move toward its normal undistorted conditionand the thrust thereof cantdiminish with such movement; said wire elements having preselected respective elastic limits, resilient limit-stop means operatively associated with such signal arm having strength characteristics for arresting the angular movement thereof in response to a selected departure thereof in a critical angular amount from a norm position, said firstmentioned resilient means in response to the occurrence of such selected departure being of substantially minimized deformation as compared to its deformation when said signal arm is in such norm position, the tensile forces acting upon said wire elements responsive to such departure being substantially less than the respective elastic limits thereof.

4. In a device for detecting the occurrence of a combustible vapor; a signal arm; a pair of wire elements; one

extremity of each of said-wire elements being secured to said signal arm near one extremity of the latter, the opposite extremities of said wire elements being spaced apart and fixedly secured; such wire elements, the axis of said signal arm, and a pair of lines each extending perpendicularly from said axis to respective of said opposite wire extremities forming two adjacent right triangles having a common side portion along said axis and also having acute angle apices; pivot means for the op posite extremity of said signal arm; resilient means for urging said signal arm resilientily and axially in a direction normally to place said wire elements under equal tension thereby forming a V-tension mounting, said wire elements having equal expansion characteristics responsive to a common temperature change; one of said wire elements including a catalyst for heating same relative to the other Wire element in response to oxidation of a combustible vapor under the influence of such catalyst; said resilient means normally being distorted by a preselected amount to provide a preselected axial thrust upon said signal arm in the absence of such combustible vapor, said arm under the influence of such resilient means being angularly shiftable in response to such an axial expansion differential between said wire elements whereby such resilient means can move toward its normal undistorted condition and the thrust thereof can diminish with such movement; and a second resilent means operatively associated with said signal arm for acting as a limitstop to the angular motion thereof, such second resilient means having strength characteristics for arresting such angular movement responsive to the preselected departure of such signal arm from a norm position, said Wire elements each having its respective preselected elastic limit, the strength of said first-mentioned resilient means being selected for exerting tensile forces upon said wire elements less than the combined elastic limits thereof, the elastic limit of said catalyst including wire element be ing substantially lower than the elastic limit of the other wire element in response to the former element being heated by such catalyst, the tensile forces acting upon said wire elements occurring in response to the aforementioned departure of said signal arm from its norm position to its position as arrested by said second resilient means being less than the elastic limit of said other wire element.

5. In apparatus for the detection of hydrocarbon vapors, a base member; a signal arm; a pair of wire elements having equal expansion and contraction characteristics responsive to a common. temperature change therein, one of said Wire elements constructed to include a catalyst for heating same in response to the occurrence in the surrounding atmosphere of hydrocarbon vapor and oxygen, said wire elements each having a base and an outer extremity, the base extremities of each of said wire elements being spaced apart and secured to said base member, the outer extremities of said wire elements being secured to said signal arm near one extremity thereof; means located substantially on the axis of said arm and in the region of said base member for mounting the opposite extremity of said arm for pivotal movement; said wire elements, the axis of said signal arm, and a pair of lines perpendicular to said axis and extending to the base extremities of respective of said wire elements, defining two adjacent acute substantially right triangles having common side portions along the axis of said signal arm and having adjacent acute angle apices; signal arm resilient means for exerting a thrust axially of said arm for placing said wire elements under tension, such resilient means normally being in an initial deformed condition and exerting a force upon said signal arm which is diminishable as a function of the expansion of such means from such initial deformed condition; said signal arm under the influence of such resilient means being angularly shiftable in response to an expansion differential between said Wire elements whereby such resilient means is expandable from said initial deformed condition; a contact positioned for engaging said signal arm in response to preselected angular movement of the latter; and counter-resilient means for mounting said contact for opposing resiliently a force acting thereupon exerted by said signal arm under the influence of said signal arm resilient means, said wire element which includes a catalyst having a preselected elastic limit Within the temperature range of operation thereof when heated by said catalyst, said other wire element also having a preselected elastic limit Within its temperature range of operation, such force exerted by said signal arm resilient means diminishing as a function of the angular movement of said signal arm from a norm position, resilient limit-stop means positioned for engagement by such signal arm and having strength characteristics selected for arresting the angular movement thereof in response to departure thereof in a critical angular amount from such norm position, said signal arm resilient means at such departure being substantially minimized in deformation by a selected amount as compared to its deformation when such signal arm is in such norm position, the strength characteristics of said signal arm resilient means being selected to produce a tensile force upon the other of said wire elements less than the elastic limit thereof in response to said diminished deformation of said signal arm resilient means, the aforementioned strength characteristics of said resilient limit-stop means being selected to limit the aforementioned departure of the signal arm from its norm position in said critical angular amount wherein the tensile force exerted upon said wire element including the catalyst is less than the elastic limit thereof responsive to said signal arm being displaced by said critical angular amount.

References Cited in the file of this patent UNITED STATES PATENTS 350,388 Perry Oct. 5, 1886 688,404 Freyman et al Dec. 10, 1901 692,007 Freyman et al Jan. 28, 1902 1,467,911 Arendt Sept. 11, 1923 2,057,246 Morgan et al Oct. 13, 1936 2,299,815 Gent Oct. 27, 1942 2,306,509 Talmey Dec. 29, 1942 2,535,950 Page Dec. 26, 1950 2,581,812 Page Jan. 8, 1952 2,645,564 Tiifany July 14, 1953 FOREIGN PATENTS 736,243 France Nov. 21, 1932 19,856 Great Britain Oct. 10, 1891 of 1890 146,829 Germany Dec. 17, 1903

Claims

1. IN A DEVICE FOR DETECTING THE OCCURRENCE OF A COMBUSTIBLE VAPOR; A BASE MEMBER; A SIGNAL ARM; A PAIR OF WIRE ELEMENTS; ONE EXTREMITY OF EACH OF SAID WIRE ELEMENTS BEING SECURED TO SAID SIGNAL ARM NEAR ONE EXTREMITY OF THE LATTER, THE OPPOSITE EXTREMITIES OF SAID WIRE ELEMENTS BEING SPACED APART AND SECURED TO SAID BASE MEMBER; SUCH WIRE ELEMETS, THE AXIS OF SAID SIGNAL ARM, AND A PAIR OF LINES EACH EXTENDING PERPENDICULARLY FROM SAID AXIS TO RESPECTIVE OF SAID OPPOSITE WIRE EXTREMITIES FORMING TWO ADJACENT RIGHT ANGLE TRIANGLES HAVING A COMMON SIDE PORTION ALONG SAID AXIS AND ALSO HAVING ADJACENT ACUTE ANGLE APICES; PIVOT MEANS FOR THE OPPOSITE EXTREMITY OF SAID SIGNAL ARM; SIGNAL ARM RESILIENT MEANS FOR URGING SAID SIGNAL ARM RESILIENTLY AND AXIALLY THEREOF IN A DIRECTION NORMALLY TO PLACE SAID WIRE ELEMENTS UNDER TENSION THEREBY FORMING A V-TENSION MOUNTING, SAID SIGNAL ARM RESILIENT MEANS EXERTING A FORCE UPON SAID SIGNAL ARM WHICH IS A FUNCTION OF THE EXTENT OF DEFORMATION THEREOF, SAID WIRE ELEMENTS HAVING EQUAL EXPANSION CHARACTERISTICS RESPONSIVE TO A COMMON TEMPERATURE CHANGE; ONE OF SAID WIRE ELEMENTS INCLUDING A CATALYST FOR HEATING SAME RELATIVE TO THE OTHER WIRE ELEMENT IN RESPONSE TO OXIDATION OF COMBUSTIBLE VAPOR UNDER THE INFLUENCE OF SUCH CATALYST; SAID SIGNAL ARM UNDER THE INFLUENCE OF SAID RESILIENT MEANS BEING ANGULARLY SHIFTABLE IN RESPONSE TO AN AXIAL EXPANSION DIFFERENTIAL BETWEEN SAID WIRE ELEMENTS WHEREBY SUCH RESILIENT MEANS CAN EXPAND AND THE THRUST THEREOF DIMINISHED AS A FUNCTION OF SUCH EXPANSION; A CONTACT FOR ENGAGING SAID SIGNAL ARM; LIMIT-STOP RESILIENT MEANS FOR SUCH SIGNAL ARM, SUCH LIMIT-STOP RESILIENT MEANS HAVING PRESELECTED STRUCTURAL STRENGTH CHARACTERISTICS FOR EXERTING A PRGRESSIVELY INCREASING FORCE AGAINST SUCH SIGNAL ARM, WHICH FORCE IS A FUNCTION OF THE EXTENT OF SUCH SIGNAL ARM ANGULAR MOVEMENT FROM A NORM POSITION AND THUS OF THE EXTENT OF DEFORMATION OF SAID LIMIT-STOP RESILIENT MEANS, SUCH LIMIT-STOP RESILIENT MEANS BY VIRTUE OF SUCH PRESELECTED STRUCTURAL STRENGTH CHARACTERISTICS CREATING A FORCE ADEQUATE TO ARREST SUCH ANGULAR MOVEMENT OF SAID SIGNAL ARM IN RESPONSE TO DEPARTURE THEREOF IN A CRITICAL AMOUNT FROM SUCH NORM POSITION, SUCH CRITICAL AMOUNT BEING LESS THAN AN AMOUNT CAUSING A PERMANENT SET IN SUCH WIRE ELEMENT INCLUDING THE CATALYST BUT BEING AT LEAST EQUAL TO AN AMOUNT CAUSING SUBSTANTIAL EXPANSION OF SAID SIGNAL ARM RESILIENT MEANS THEREBY TO REDUCE THE FORCE EXERTED UPON SAID SIGNAL ARM BY SAID SIGNAL ARM RESILIENT MEANS IN TURN TO DIMINISH THE TENSION UPON SUCH OTHER OF SAID WIRE ELEMENTS BELOW THE ELASTIC LIMIT OF THE LATTER ELEMENT.