US2700084A - Electrical control device - Google Patents

Description

Jan. 18, 1955 w. c. BRQEKHUYSEN 2,709,084

ELECTRICAL CONTROL DEVICE Filed NOV. 2, 1951 2 Sheets-Sheet l v 1 N V EN TOR. M72281??? C firoefficysea A rrmtas Jan. 18, 1955 Filed NOV. 2, 1951 W. C. BROEKHUYSEN ELECTRICAL CONTROL DEVICE Z-Sheets-Sheet 2 INVENTOR. zz/zlfi'am, C Brae/f5 u ysen Arromvzy United States Patent Ofifice 2,700,084 Patented Jan. 18, 1955 ELECTRICAL CONTROL DEVICE William C. Broekhuysen, Brooklyn, N. Y. Application November 2, 1951, Serial No. 254,544 24 Claims. (Cl. 200-122) This invention relates to electrical control devices, and more particularly to electro-thermally actuated relays.

In the past considerable difficulty has been experienced in designing thermal relays, especially small thermal time delay relays, for the relatively long periods of delay required in many applications, and in particular those in which smallness in size is an important factor. This difficulty is more or less inherent in the use of bimetallic strips having external heating elements. In order to obtain the desired delay periods, it is necessary to increase the ratio between mass and surface areas of the heated member, or to reduce energy input and add insulation around it. The first requirement means that the thick ness of the bimetal must be increased, which results in a proportional loss of motion at the contacts. If it is compensated for ambient temperature by the use of a second (unheated) bimetallic strip, the latter must be increased in thickness similarly. The second requirement of the provision of additional insulation also reduces the contact motion, since it increases the stiffness by an uncertain amount, depending upon how tightly the insulation is clamped to the bimetal.

The above disadvantages are overcome by my inven tion. In accordance with my invention, I use only the difference in longitudinal expansion, i. e. elongation of two members as the means of effecting opening or closing of the relay contacts. in this manner the effects of greater or lesser rigidity of these two members are largely eliminated. This arrangement also makes it substantially unnecessary that the two members be identical in thickness in order to obtain full ambient temperature compensation. Furthermore, it permits increasing the thermal capacity of the heated member as much as the available space allows, without loss of contact motion.

In accordance with my invention, I heat one of the members, which can be effected by locating suitable heating means therewithin. In this manner substantially no heat is transmitted directly to the ambient or to the unheated member; instead, a substantially greater portion of the heat is employed effectively to elongate theheated member. It will be evident, therefore, that the energy input is reduced; the temperature differential betweenthe heated and the unheated member is increased, and the time-constant is lengthened. A further problem in the art, has been that of manufacturing hermetically sealed thermal time-delay relays to close tolerances of time setting. Heretofore such relays either were not capable of being adjusted after sealing or could only be adjusted at the factory by the use of special externally applied equipment, not forming a part of the relay, and which could not afford satisfactory close control or adjustment. This problem does not arise in connection with a thermal time delay relay constructed in accordance with my invention, because the relay provides means for. adjusting to close tolerances by the simple manipulation of a device which is located entirely without the hermetically sealed portion of the relay.

It is an object of the invention to provide an hermetically sealed thermal time delay relay which can be adjusted simply and repeatedly over a wide range, not only where it is made, but also, wherever it is in use, without destroying the hermetic seal, and wherein the adjustment remains unchanged at all times, even under adverse operating conditions.

A further object of the invention is to provide a device of the type describedv which is fully compensated for changes, in ambient temperatureover a wide range, or

;. additional modification to provide a device in which the timing or regulation varies with ambient temperature in a predetermined manner.

The invention is further characterized by the provision of a thermal control device which is extremely rugged and capable of withstanding severe shock and heavy vibration without faulty operation or damage.

The invention also consists of the provision of a device which lends itself to quantity production and does not require highly precise parts in order for the final product to operate within narrow tolerances.

Another object of this invention is to provide a thermally actuated control mechanism in which the direction of motion of the moving member is substantially instantaneously reversed when, during a heating cycle, the energizing current is interrupted, or when, during a cooling cycle, the energizing current is suddenly reapplied, and one in which, under continuous constant energization, the moving member reaches its ultimate position without first moving substantially beyond this position.

An additional important object of the invention is to provide a highly efiicient thermal time-delay relay which is smaller and more compact in size than any other device of this type, and yet, one which, despite its small size, affords a wide range of delay periods and fulfills all requirements to which it is subject.

Other objects of my invention will be set forth in the following description and drawings which illustrate preferred embodiments thereof, it being understood that the above statement of the objects of the invention is intended generally to explain the same without limiting it in any manner.

Referring now to the following detailed specification taken in conjunction with the accompanying drawings, which form a part of this specification, and in which like characters of reference indicate the same or like parts:

Figure l is an elevation in cross-section of a preferred form of construction of my invention.

Figure 2 is a top view of the structure shown in Figure 1 with the cover removed.

Figure 3 is a bottom view of the structure shown in Figure 1.

Figure 4 is a sectional view taken along line 4-4 in Figure 1.

Figure 5 is a sectional view taken along line 5-5 in Figure 1.

Figure 6 is a detailed view of the pivot point P shown in Figure 1.

Figure 7 is a diagrammatic representation of the structure shown in Figure 1.

Figure 8 is a partial, cross-sectional elevation of a modified form of structure embodying the invention.

Figure 9 is an elevation in cross-section illustrating an of the invention.

Figure 10 is a diagrammatic representation of the structure shown in Figure 9.

The structure, made in accordance with the invention, has been referred to herein as a thermal time-delay relay. However, it may also find application in other functions, such, for example, as a discriminator or regulator for potential, current or frequency in electrical circuits. Therefore, whenever in the following specifications the device embodying the invention is referred to as a timedelay relay, such other functions are meant to be included, since the construction of the device is substantially the same for all purposes.

In a preferred embodiment of the invention selected for purposes of illustration and shown in Figures l-S, the entire internal structure is supported on seven pins, numbered l to 7. Unless otherwise specified, all mechanical and electrical connections may conveniently be made by spotwelding. Pins 17 are insulated from and hermetically sealed into a suitable base, such as a disc-shaped metal base 8 by glass beads 10. Base 8 is provided with a rim 12 which is rigidly crimped in the lower edge of casing 14, preferably cylindrical in form. The seam is hermetically sealed by solder as at 16.

Theheated timing member, designated generally 20, consists of an open-seam elongated tubular metal shell 22. preferably substantially rectangularin cross-section, in

the center of which is a heater, consisting of a thin strip of an insulating material such as mica 24, on which is wound a number of turns of fine resistance wire 25, sandwiched in between two layers of suitable insulating material, such as mica 26 and 28. The remaining space within tubular shell 22 is filled up by strips of metal 30 to increase the thermal capacity of member 20. The entire assembly is tightly compressed within tubular shell 22 to form a solid unit. Tubular shell 22 and strips 30' are preferably made of a metal with a relatively high coeflicient of thermal expansion. It is preferred to use a corrosion-resistant metal, such as stainless steel.

Due to the intimate thermal contact between all parts of the heater and surrounding metal parts, forming together member 20, no substantial temperature difl'erential can exist at any time between any of these parts. Therefore the energy storage is substantially evenly distributed throughout member 20 at all times while it is being heated by an electrical current passing through wire 25, and it will substantially instantly start to cool when this current is interrupted.

As shown in Figure l, mica strips 24, 26 and 28 extend somewhat below lower ends of member 20 and shell 22, and thereby provide insulation for heater leads 27 of wire 25 which are connected to pins 2 and 3. The lower end of the outer face of tubular shell 22 is connected by a short flexible leaf spring 34 to a strip 32 attached to pins 1 and 4.

Pins 6 and 7 support the lower end of the compensating member 36 which preferably is channel-shaped for rigidity. A flat leaf spring 38 forms a flexible connection between channel 36 and strip 40 rigidly fixed to pins 67. For complete ambient temperature compensation, member 36 is made of a metal having the same coefiicient of thermal expansion, and is substantially the same length as member 20.

The invention includes a moving arm 42 which in the illustrated embodiment consists of an open channel partly surrounding member 36. Arm 42 is pivotally connected to the top of member 36 at a point designated P by two crossed springs 44 and 46. Spring 46 which is positioned substantially horizontally, extends through a suitable opening in the center of spring 44. As shown in Figure 6, this opening may be circular, and of such size that there is no engagement between springs 44 and 46. One end of spring 46 is secured to a bent-over tip portion 47 of member 36, and the other end to a flange of bracket 48 which is rigidly secured to arm or channel 42. Spring 44, which is arranged substantially at right angles to spring 46, is likewise secured to member 36 and to bracket 48. The top end of heated timing member 20 is attached to arm 42 by a flat substantially vertical leaf spring 50 at a point designated Q substantially horizontally aligned with point P.

A leaf spring 52 carrying at its lower free end a contact point 54, is secured to the inside of channel 42 at a point L. Spring 52 is biased so that it normally rests with a positive pressure against the inner lower edge of channel 42. A U-shaped leaf spring 56, the two ends of which are secured to the lower outer face of channel or arm 42, and to strip 32, respectively, tends to push channel 42 away from member 20. A glass bead 58 is fused to the tip of a wire 66 which in turn is fastened to the inside and adjacent the upper edge of channel 36, and rests firmly against the edge of tip portion 47. Stationary contact 62 is mounted on bracket 64 attached to pin on base 8.

At a suitable distance below the upper rim of casing 14, as shown in Figure l, a diaphragm 66 is brazed to the inner wall thereof, forming an hermetic closure. An L-shaped lever 68 is brazed into an opening 69 in diaphragm 66 near its edge. Glass bead 58 rests against the downwardly extending arm of lever 68. The other arm of lever 68 extends substantially horizontally over diaphragm 66 and is drilled, tapped and slotted at its end in such manner that screw 70 is clamped sufliciently tightly to prevent it from turning due to vibation, but can still be easily adjusted with a suitable tool, such as a screw driver. A small hole 72 in diaphragm 66 provides access to the interior of casing 14 in order to evacuate it and fill it with a dry inert atmosphere, such as nitrogen or other inert gas, after which opening 72 is sealed off with a drop of solder. Cover 74 closes ofi the top of casing 14 and protects lever 68 and screw 70. The latter can be adjusted through an opening 76 in cover 74.

Referring now to Figure 7, it is apparent that the pressure exerted by spring 56 serves to maintain bead 58 in contact with lever 68 at all times. When member 20 expands due to current passing through the heater winding 25, arm 42 will pivot around P, and contact 54 will move towards the right, as viewed in Figure 1, until it engages fixed contacts 62, closing a circuit from pins 1--467 to pin 5. Further expansion of member 20 will cause spring 52 to be lifted off the lower edge of arm 42. This limits the stresses that can be set up in the structure to safe values.

Turning screw 70 so as to raise the horizontal arm of lever 68 will move contact 54 towards contact 62 thereby reducing the time required for these contacts to engage under the influence of heat in member 20. It will be clear that, since members 20 and 36 are nearly parallel, the horizontal movement of contact 54, as a result of adjustment of lever 68, will be substantially equal to the horizontal movement of P. On the other hand, the vertical movement of Q, due to thermal expansion of member 20, will cause a horizontal movement of contact 54 which is amplified in the ratio of the distance 19-54 to distance PQ. As the crossed spring pivot at P is free from backlash and friction, this ratio can be made very high.

So long as members 20 and 36 are substantially equal in length, and are made of materials having substantially the same coefiicients of thermal expansion, a change in ambient temperature will cause no appreciable change in the relative position of P & Q and in the position of contact 54. Therefore there will be no change in the time-delay between the application of heating current to member 2i) and the closing of contacts 54 and 62. If it is desired that the time-delay should vary in a certain manner with changes in ambient temperature, that can be accomplished by making members 20 and 36 of ditferent materials having suitable coeflicients of thermal expansion.

The two leaf springs 34 and 50 oflfer a substantial thermal resistance to the transfer of heat by conduction from member 20 to the remainder of the structure. Moreover, the large area of member 42 provides excellent dissipation for the small amount of heat transferred by conduction through these springs. In addition, it shields compensating member 36 from any heating by direct radiation from member 20. Consequently the temperature difference between members 20 and 36 and the motion of contact 54 is very great in proportion to the amount of energy supplied to member 20.

The absence of any mass of large thermal capacity and high thermal resistance, such as a block of ceramic, at the junction of members 20 and 36, or in between these members, combined with a small but definite thermal conduction between them and a proper balance of their thermal capacities, results in a simultaneous but unequal rise in temperature of the two members, each to its ultimate temperature, when member 20 is heated as the result of the application of a predetermined amount of electrical power to heater resistance wire 25. During the heating period, the difference in temperature between members 20 and 36 increases steadily and never exceeds the final temperature differential. This simultaneous rise therefore causes a gradual approach of member 42 to its ultimate position without first passing beyond this position.

In addition, since stationary contact 62 is thermally isolated from compensating member 36, the making or breaking of physical and electrical contact between contacts 54 and 62 does not alter the thermal coupling between members 20 and 36 and therefore does not affect the ultimate position of member 42.

The structure shown in Figures l-7 can be modified in many ways within the scope of my invention. For example, it is quite simple to reverse the position of the contacts so that the circuit between them is normally closed and is broken when member 20 is heated. Another possible modification is shown in Figure 8, in which the wire 60 supporting the bead 58, has been extended so that the bead rests against the inner wall of the shell 14. Adjustment is made by deforming the shell at this point. Though this is not as practical if the relay is to be adusted by the user, it is quite satisfactory for factory adjustment for a fixed-time relay.

Figures 9 and 10 illustrate a modified form of the invention which is generally the same in construction as the device shown in Figures 1-7 inclusive. For that reason, the operating parts thereof are designated by the same reference numerals, with a few exceptions. Referring to Figures 9 and 10, it will be noted that fixed contact 162 is mounted on bracket 164 attached to pin 5 on base 8. Movable contact 154 is mounted on spring 152 secured to the exterior of movable arm 42. In other words, the contacts shown in Figures 8 and 9 are reversed as compared with contacts 54 and 62 in the form shown in Figures l-7 inclusive. As a result, the circuit through contacts 154 and 162 is normally closed, and opens when member expands due to internal heating.

Attached to the upper end of compensating member 36 is a support, such as a stiff wire 160, to which is attached a bead 158 resting against the left face of extension 71 of adjusting lever 63, as viewed in Figures 9 and 10, within casing 14. A bias spring 156, positioned between the lower ends of member 32 and arm 42, tends to push arm 42 to the right, as viewed in Fig. 9. Referring to Figure 10, it will be evident that a force exerted towards the right on the lower end of arm 42, tends to move bead 153 towards the right also, and thus bead 158 is maintained pressing against lever extension 71.

In the construction shown in Figures 9 and 10, member 36 is under longitudinal compression, and member 20 is under tension. In the form of device shown in Figures l-7 inclusive, member 36 is under tension and member 20 is under compression. If desired, the normally closed contacts of the device in Figure 9 may be employed in combination with the normally open contacts of the form disclosed in Figures 17 inclusive, so that when member 20 is heated internally, the normally closed contacts open, and the normally open contacts close, respectively. Also if desired, the normally closed contacts of the device in Figure 9 may be substituted for the normally open contacts of the structure shown in Figures l-7, or the normally open contacts of the device in Figures l-7 may be substituted for the normally closed contacts shown in Figure 9.

In the form shown in Figures 1-7 inclusive, and Figures 9 and 10, since stationary contacts 62 and 162, respectively, are substantially thermally isolated from compensating member 36, the making and breaking, or breaking and making, respectively, of physical and electrical engagement between contacts 54 and 62, and contacts 154 and 164, does not alter the thermal coupling between members Ztl and 36, and therefore does not affect the ultimate position of movable arm 42.

The invention above described may be varied in construction with the scope of the claims, for the particular embodiments selected to illustrate the invention are but a few of the possible concrete forms which my invention may assume. The invention, therefore, is not to be restricted to the precise details of the structures shown and described.

What ll claim is:

1. An electrothermally actuated relay having a sealed casing, comprising movable and fixed contacts in said casing, an elongated hollow controlling member substantially free from bending when heated in said casing, a movable arm having one end attached to said member, and the other end actuating said movable contact, and an electrical heating element on said hollow controlling member to elongate said member and move said arm in response to the longitudinal elongation of said controlling member to cause relative motion between said fixed contact and said movable contact.

2. An electrothermally actuated relay having a sealed casing, comprising movable and fixed contacts in said casing, an elongated channel shaped controlling member adapted to elongate longitudinally and in substantially a straight line when heated in said casing, a movable arm having one end attached to said member, and the other end actuating said movable contact, means normally biasing said arm away from said member to maintain said movable contact out of engagement with said fixed contact, and an electrical heating element enclosed within said controlling member to elongate said member and move said arm. in response to the longitudinal substantially straight line elongation of said controlling member to cause relative motion between said fixed contact and said movable contact.

3. An electrothermally actuated relay having an hermetically sealed casing, comprising a fixed contact in said casing, an elongated controlling member adapted to elongate longitudinally and in substantially a straight line when heated located in said casing, an elongated compensating member mounted in said casing, spaced from and in generally parallel relationship with said heated controlling member, a movable arm resiliently pivoted to said compensating member and to said heated controlling member, a movable contact actuated by said arm, and an electrical heating element located within and substantially enclosed by said heated controlling member for elongating said heated controlling member longitudinally to displace said arm about its resilient pivot in response to the longitudinal substantially straight line elongation of said controlling member and cause relative motion between said movable contact actuated by said arm and said fixed contact.

4. A thermal time delay electrical control device having an hermetically sealed casing, a fixed contact in said casing, an elongated electrically heated timing member in said casing, an elongated compensating member in said casing coacting with said timing member, said compensatingmember being substantially equal in length to said timing member, a movable arm resiliently connected at one end to said timing member and said compensating member, and a heater for heating and elongating said timing member only in the plane of said timing member to swing said arm towards said timing member in response to the substantially straight-line elongation of said timing member, and a contact carried by the free end of said arm adapted to engage said fixed contact as the result of the movement of said arm towards said heated timing member.

5. The device defined in claim 4 including a positioning element carried by said compensating member, and means on said casing adapted to engage said element and control the position of said arm before said heater is energized.

6. The device defined in claim 4 including a positioning element carried by said compensating member, an adjusting arm engaging said element, and means mounted on the exterior of said hermetically sealed casing for moving said adjusting arm to control the extent of movement of said contact carried by said movable arm into engagement with said fixed contact.

7. In a thermal time delay device comprising a casing, a fixed contact, an elongated heated timing shell, a compensating member, said member being substantially equal in length to said timing shell and spaced therefrom, a movable arm located between said shell and said member, means resiliently coupling one end of said arm to said shell and said member, a contact actuated by said arm, and a heater located Within said shell for heating and elongating said shell to bias said arm relative to said shell and thereby move said contacts into operative relationship.

8. The device defined in claim 7 including an hermetically sealed casing enclosing said device, an element on said compensating member for controlling the extent of movement of said contact actuated by said arm into engagement with said fixed contact, and means on said casing engaging said element to limit said movement of said contact.

9. The device defined in claim 8 including a diaphragm formed in said casing spaced axially therein from said shell, member and arm, a lever having an arm Wholly exterior of said casing and an arm extending through said diaphragm into said casing, means on said member engaging said lever arm in said casing, and means on said first-named lever arm for adjusting the position of said second-named lever arm to control the amount of movement of said contact by said movable arm when said heater is energized and said shell elongated.

it). The device defined in claim 8 including a diaphragm mounted in one end of said hermetically sealed casing, a lever secured to said diaphragm having an arm wholly exterior of said casing and an arm extending through said diaphragm into said casing, a bead disposed between said last-named arm and said com ensating member, and means for adjusting the position of said first-named arm relative to said diaphragm to move said last-named arm to displace said bead and thereby adiust the extent of movement of said movable contact.

11. in a thermal time delay electrical control device a fixed contact, an elongated timing member, a movable arm having one end attached to said member, an elongated resilient element attached to said arm, a movable contact mounted on said element, resilient means normally biasing said arm away from said timing member to maintain said movable contact out of engagement with said fixed contact, and an electrical heating element located within said timing member and electrically insulated therefrom for heating said timing member to elongate said member and move said arm to engage said movable contact with said fixed contact, said elongated resilient member being adapted to maintain said movable contact in engagement with said fixed contact independent of movement of said arm past said fixed contact.

12. A thermal time delay electrical control device comprising, a fixed contact, an elongated hollow heated timing member, an elongated compensating member, spaced from and in generally parallel relationship with said heated timing member, a movable arm, mechanism resiliently pivoting said movable arm to said compensating member and to said heated timing member, a contact actuated by said arm, and an electrical heating element enclosed within said hollow heated tirning member for elongating said hollow heated timing member to swing said arm about its resilient pivot and move said last-named contact into engagement with said fixed contact.

13. A thermal time delay electrical control device comprising a fixed contact, an elongated heated timing member, an elongated compensating member spaced from and in general parallel relationship with said heated timing member, a movable arm, mechanism resiliently pivoting said movable arm to said compensating member and to said heated timing member, a contact actuated by said arm, an electrical heating element enclosed within said heated timing member for elongating said heated timing member when a current flows through said heating element to swing said arm about its resilient pivot and cause relative motion between said contacts, said mechanism for resiliently pivoting said movable arm to said compensating member and to said heated timing member including a fiat resilient element connecting the free end of said heated timing member to said arm, an abutment on said arm, a flat spring connecting said abutment to said compensating member, and a second fiat spring arranged substantially at right angles with said first-named flat spring having its ends attached to said abutment and to said compensating member.

14. A thermal time delay electrical control device comprising, a fixed contact, an elongated heated timing member having a cavity, an elongated compensating member, spaced from and in generally parallel relationship with said heated timing member, a movable arm, a contact carried by said arm, mechanism resiliently pivoting said movable arm to said compensating member and to said heated timing member, and an electrical heating element enclosed in said cavity of said heated timing member for elongating said heated timing member to swing said arm about its resilient pivot and move said contact on said arm and disengage said movable contact from said fixed contact.

15. A device of the type described comprising an elongated controlling member having a fixed end and a free end, an elongated compensating element substantially equal in length to said member, resilient pivot means connecting said free end of said member and one end of said compensating element, a movable arm having one end connected to said means, and one end free, electrical heating means for heating and elongating said controlling member, adjusting mechanism including means for moving said connected end of said movable arm in a direction substantially at right angles to the direction of elongation of said timing member, said adjusting mechanism being so constructed and arranged that the movement transmitted to the free end of said arm in adjusting the position of said connected end of said arm is substantially unamplified as compared with the movement of said free end due to the elongation of said timing member.

16. An electro-thermally actuated control device comprising an elongated expansible member, an electrical heating element located within said expansible member and electrically insulated from said member, an elongated compensating member substantially parallel to and substantially equal in length with said expansible member, a pair of coacting contacts, a contact actuating element for controlling the relative positions of said contacts responsive to a change in length of said expansible member relative to said compensating member, a connection having limited thermal conductivity between said expansible member and said compensating member, said connection having a low thermal capacity, the thermal capacities of said expansible member and said compensating member and the thermal conductivity of said connection being so proportioned that when said expansible member is heated by a predetermined amount of electrical power,

8 said contact actuating member is moved towards and reaches an ultimate position Without first passing substantially beyond said position.

17. An electro-thermally actuated control device comprising an electrically heated elongated controlling member, an elongated compensating member substantially parallel to and substantially of the same size as said controlling member, a pair of coacting contacts, a contact actuating element for controlling the relative positions of said contacts responsive to a change in temperature of said controlling member relative to said compensating member, a connection having limited thermal conductivity between said controlling member and said compensating member, said connection having a low thermal capacity, the thermal capacities of said controlling member and said compensating member and the thermal conductivity of said connection being so proportioned that when said controlling member is heated by a predetermined amount of electrical power, said contact actuating member is moved towards and reaches an ultimate position without first passing substantially beyond said position, and mechanism for controlling the relative positions of said contacts, said mechanism including a lever pivotally connected to adjacent ends of said controlling member and said compensating member.

18. In the device defined in claim 16, mechanism for controlling the relative positions of said contacts, said mechanism including a lever pivotally connected to adjacent ends of said expansible member and said compensating member, and means for moving said lever.

19. An electro-thermally actuated control device comprising an elongated hollow controlling member, an elongated compensating member substantially parallel to and of the same length as said controlling member, an electrical heating element located within said hollow controlling member for heating and longitudinally expanding said controlling member, a pair of co-acting contacts, and mechanism including a contact actuating member for changing the realative positions of said contacts in response to the elongation of said controlling member relative to said compensating member when said hollow controlling member is heated by a current flowing in said heating element.

20. An electro-thermally actuated control device as claimed in claim 19 in which said mechanism for controlling the relative positions of said contacts includes a lever and means pivotally connecting said lever to the adjacent ends of said elongated hollow controlling and said compensating members.

. 21. An electro-thermally actuated control device having a base, an internally heatable elongated expanding member said member including a rigid elongated member enclosing a heating element, said member being pivotally connected at one end to said base, an elongated compensating member substantially parallel to, and equal in length to said expanding member, said compensating member being also pivotally connected at one end to said base, a lever with a short arm and a long arm, said short arm pivotally linking the other ends of the expanding and compensating members, thus forming substantially a quadrilateral, a pair of coacting contacts, the relative position of said contacts being controlled by the free end of said long arm of said lever, a hermetically sealed shell enclosing said device, a deformable portion in the wall of said shell, the inner face of said deformable portion coacting with one end of the short arm of said lever for moving said short arm in a direction substantially parallel to itself and at right angles to the expanding and compensating members, thereby changing the relative position of the contacts by an amount substantially equal to the change in deformation of the shell.

22. An electro-thermally actuated control device including a base, an internally heatable elongated expanding member pivotally connected at one end to said base, an elongated compensating member substantially parallel to, and equal in length to said expanding member, said compensating member being also pivotally connected at one end to said base, a lever with a short arm and a long arm, said short arm pivotally linking the other ends of the expanding and compensating members, thus forming substantially a quadrilateral, a pair of coacting contacts, the relative position of said contacts being controlled by the free end of said long arm of said lever, a hermetically sealed shell enclosing said device, an adjusting lever.

pivotally sealed in the Wall of said shell, said adjusting lever having an inner and an outer arm, said inner arm of said adjusting lever coacting with one end of the short arm of said first-mentioned lever, to move said firstmentioned lever in a direction substantially parallel to said short arm and at right angles to the expanding and compensating members, thereby changing the position of the free end of the long arm of said first-mentioned lever an amount substantially equal to the movement of the inner arm of said adjusting lever.

23. The electro-thermally actuated control device defined in claim 19 wherein said heating element is electrically insulated from said hollow controlling member, and means also enclosed Within said controlling member for controlling its thermal capacity.

24. The electro-thermally actuated control device defined in claim 19, wherein said controlling member consists of a channel shaped shell having means enclosing 10 said electrical heating element, strips of electrical insulating material insulating said heating element from said shell, and said shell also enclosing flat elongated strips of metal, the number and thickness of said strips determining the thermal capacity of said controlling member.

References Cited in the file of this patent UNITED STATES PATENTS 1,880,743 Botts Oct. 4, 1932 1,902,793 Willing Mar. 21, 1933 2,333,125 Schmidinger Nov. 2, 1943 2,371,018 Ashworth et a1 Mar. 6, 1945 2,446,307 Shaw Aug. 3, 1948 2,499,208 Zimmer Feb. 28, 1950 2,635,156 Welter Apr. 14, 1953

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