US3020381A - Control device - Google Patents

Description

Hug-Jr- 4 Feb. 6, 1962 WITNESSES%QL V. L. CARISSIMI CONTROL DEVICE Filed Dec. 14, 1956 INVENTOR Vincent L. Corissimi.

ATTORNFY United States Patent 3,020,381 CONTROL DEVICE Vincent L. Carissimi, Fairfield, Conn, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Dec. 14, 1956, Ser. No. s2s,422

I 16 Claims. (Cl. 219-20) My invention relates to a device for controlling an electrical circuit and more particularly to a device forcontrolling the electrical energization of an electrical heating unit in an electric range.

In. the art of cooking, the particular temperature at which a food or mixture should be cooked varies due to the variations of the matter of the various foods and nrixlures. For a particular food or mixture, however, there is a particular optimum temperature range at which the cooking process should be performed. Obviously, therefore, the heat output of a heatingunit, such as an electrical heating unit, must be variable in order to obtain the various particularly desired temperatures. In addition, it is desirable that the desired temperatures be achieved as rapidly as possible, and thereafter only sutlicient heat be supplied to maintain the food or mixture at the desired temperature without the necessity of manual adjustment of the heat output of the heating unit.

Heretofore, various controls for such purposes have been developed which have not been entirely satisfactory due to their expensive components and the requisite calibration for proper operation. Other prior devices of simplified construction have not been satisfactory as they the heating element 2 is merely representative of the various types of standard heating elements commercially available, and that my invention may be utilized with any of such heating elements at any desired operating voltage. A three-line supply system is commonly em ployed, accordingly, the conductors L and L are shown with a third grounded neutral conductor N as an electrical supply.

As also shown, the heating element 2 is adapted to support a cooking vessel 8 on its upper surface and is pro vided with a central opening in which a control unit core structed in accordance with the principles of my invention is located. Although not shown, the heating element 2 is stationarily supported by suitable means, such as the frame of an electric range, in a Well-known manner. Further, it is who realized that water is a common cooking fluid employed and that at standard atmospheric conditions the boiling temperature of water is 212 F. The boiling point of Water varies with variations in atmospheric conditions so that it is necessary for a range manufacturer to supply a control unit which will function under all normally encountered atmospheric conditions As shown, the control device comprises an inverted cup-shaped sensor plate 12, the upper surface of which is have not given consistent operation due to various reasons such as contact wear, high current requirement or ambient temperature effects.

Accordingly, one object of my invention is to provide a new, improved and simplified control device for accurately varying the heat output of a heating element.

A more particular object of my invention is to provide a new and improved control device comprising a pair of tandem mounted bimetals which are connected to each other by means of an insulator.

Still another object of my invention is to provide a new and improved control device comprising a pair of tandem mounted bimetals which are connected to each other by means of an insulator with one end of one bimetal being rigidly secured to a heat source and the other bimeta being movable to make and break an electrical circuit.

A further object of my invention is to provide a new and improved control device comprising a pair of tandem mounted bimetals which are connected to each other by means or" an insulator and which bimetals move in opposite directions due to changes in their temperature.

These and other objects of my invention will become more apparent upon the consideration of the following detailed description of a preferred embodiment thereof, when taken in conjunction with the attached drawing, in which a cross-sectional view of a heating element is shown having a control. device constructed in accordance with the principles of my invention located therein, and the electrical control circuit thereof.

The use of electrical resistance heating elements, and particularly those for electrical ranges for which my control is ideally suited, are Well known in the art, and accordingly, their construction and operation need not be described in detail. In the drawing, an electrical heating element 2 is shown, which has as its opposite ends electrically connected by means of suitable electrical conductors 4 and 6 to suitable electrical supply conductors L and L respectively. As is customary, suitable terminals T and T are provided for securing conductors 4 and 6 to the conductors L and L and the heating element 2, respectively. It is to be realized that the particular showing of biased into engagement with the bottom of the vessel 8 as hereinafter described. The sensor plate 12 is preferably formed from a hi h heat conductivity and high creep strength material, such as stainless steel, which is resistant to the corrosive efiiects of food spillage which may occur during the cooking process. A generally L-shape d sensorbimetal 14 is located centrally of the underside of the sensor plate 12 with one of its legs being secured to the undersurt'ace thereof in any suitable manner such as by being resistance welded or brazed thereto. An elongated control bimetal 16 is located so as to be in alignment with the free leg of the sensor bimetal 14 and is supported from the free leg of the sensor bimetal 14 bya suitable support 18 so as to be both thermally and electricallyinsulated. from the sensor bimetal 14. The particular support 18 for thermally and electrically insulating the bimetals l4 and 16 does not constitute a part of this invention; however, one desirable method of accomplishing this purpose is to'secure transversely extendingrods to the adjacent ends of the bimetals 14 and 16, in any suitable manner such as by brazing or welding thereto, and thereafter securing the free ends of each of the rods together by means of a glass seal. Such rods may be made from any well-knownmaterial such as alloys identified by thetrademark Kovar of the Westing house Electric Corporation which has substantially the same coefficient of expansion as the sealing glass, whereby the seal between the rods and the glass Will not be ad-' versely affected by the thermal stresses induced therein due to the operation of the control device 10 at elevated temperatures. For a more particular description and showing of such a support reference is made herein to the copending application of George W. Nagel entitled Control Device, filed May 22, 1957, Serial No. 666,869, and which has been assigned to the same assignee as this invention. p I

The bimetals 14 and 16 may be made from any suitable pair of dissimilar materials having difierent cocfiicients is secured to the binietal 16 in any suitable manner such as by being welded, brazed or riveted thereto. The contact 2-9 is cooperable with a contact 22 of a material similar to that of contact 29 and which is adjustably secured to a generally L-shaped electrical conducting support 24 formed from a suitable electrical conducting material, such as an alloy of copper. it will be noted that the contact 22 is provided with an outwardly extending threaded shank 26 which threadedly engages an opening, not shown, in one leg of the support 24. The free end of shank 26 is provided with suitable engaging means such as a diametrically extending slot 27, whereby the position of the contact 22 with respect to the one leg of the support 24, and consequently the other contact 20, may be varied in small amounts. Accordingly the bimetal 16 which supports the contact 20 is formed from a resilient bimetallic material as is well known. Although this particular simplified adjustable contact 22 has been described, it is to be realized that other suitable adjustable means may be utilized between the support 24 and the contact 22. As will be more fully described hereinafter contact 2 is initially located to engage the contact 26 so that a pressure exists therebetween.

The other leg of the support 24 is rigidly secured in any suitable manner, such as by riveting, to a support 23 located below the free end of the control biinetal 16* and which is preferably formed of a high temperature insulating material. The support 28, in turn, is rigidly secured to the underside of the sensor plate 12 in any suitable manner, and, as shown, a plurality of upwardly extending tie rods 29 are secured to both the support 28 and the underside of the sensor plate 12 adjacent the fixed leg of the sensor bimetal 14. The particular manner of securing the ends of the tie rods 29 to the underside of the sensor plate 12 may be accomplished in various wellknown manners such as bending the ends of the tie rods 29 transversely and soldering, brazing or welding said transversely extending parts to the underside of the sensor plate 12. p

In order to obtain proper contact of the sensor plate 1.2 with the underside of the vessel 8 and to prevent the aforedescribed assembly from being fouled due to spillage, a cylindrical shield 34) is provided which is rigidly secured to the aforementioned frame, not shown, to which the heating element 2 is secured, and is also supported thereby. The shield 39 is formed preferably from a suitable corrosionesistant material such as stainless steel or aluminum, and is located so as to extend around the bimetals 14 and i6 and the support 24 with its upper edge being located closely adjacent the underside of the sensor plate 12, and with its lower edge being spaced below the support 24. The shield 30 is provided with inwardly extending supporting lugs 32 spaced around its periphery for receiving the bottom coil of a biasing spring 34 on their upper edge. Spring 34 is formed of any suitable spring material which does not lose its resiliency at elevated temperatures, such as stainless steel, so that it is capable of withstanding the induced thermal stresses produced by its alternate heating and cooling and is also resistant to corrosion. The upper coil of spring 34 engages the undersurface of the sensor plate 12 and extends around the tie rods 2? so as to bias the upper surface of the sensor plate 12, upwardly into engagement with the lower surface of the vessel 8. As can be appreciated, such positive engagement between the vessel 8 and the upper surface of the sensor plate 12 is desirable to insure good thermal transfer from the vessel to the sensor plate. In view of the fact that the bimetals 14 and 16, and supports 24 and 28 are rigidly secured to the sensor plate 12, it is obvious that they will be moved in the same manner by spring 34- 'as the sensor plate 12.

in order to obtain selective control of the operation of the control bimetal 16, a heater coil 36, of any suitable electrical resistance wire, is wound about the bhnetal 16 in the well-known manner and insulated therefrom. The heater coil 36 has one of its ends electrically connected by means of a suitable conductor 38 to another suitable electrical conductor 4% having one of its ends connected to the conductor 6. The other end of the heater coil 36 is electrically connected by a suitable electrical conductor 41 to the supply conductor N. Again a suitable terminal T may be employed for such purpose. As shown, the electrical conductor .1 is also electrically connected to the bimetal 16.

It will be noted that the heater coil 36 is connected between the supply conductors L and N so as to be operative regardless of energization of the heater coil 2. In order to vary the electrical input to the heater coil 36, a resistor 46 is connected to the conductor 6 and an adjustable tap 48 is electrically connected to the conductor 41 by means of a suitable electrical conductor 51. The tap 43 adjustably engages the resistor 46 so as to provide, in conjunction with the resistor 46, a variableresister in parallel with the heater coil. 36. It is also desirable that the conductor 6 be provided with an on-off switch so that the one side of the heater coil 2 may be disconnected from the line L Accordingly, a switch S having spaced contacts in the conductor 6 is provided which is located between the resistor 46 and the line L. Switch S may be of any conventional type; however, in order to eliminate duplication of switches, switch S is prefer-ably provided both with an on-off position and can be moved further to obtain adjustment of the tap 4% across the resistor 46. With such a construction, and by placing a suitably marked identification plate in juxtaposition with handle 43 of the switch S, the handle 43 may be moved to a given position so as to both electrically connect the heater 36 across the lines L and N and to also move the adjustable tap 48 to the desired operating position with respect to the resistor d6.

As also shown, conductor 4 is provided with a pair of normally open spaced contacts 50, similar to contacts 20 and 22, which are adapted to be electrically bridged by teams of a movable contact 52. The operation of the movable contact 52 is obtained by means of a bimetal 54 which is similar in construction to the bimetals 1e and 16 previously described, and around which a heater coil 56 is disposed, similar to the heater coil 56 and in the same manner. One end of the bimet-al 54 is secured by any suitable means to the aforementioned supporting frame, and its other end is movable into engagement with the movable contact 52 to cause the movable contact 52 to bridge the contacts 50 when the bimetal S4 is heated. Accordingly, the low expansion side of bimetal 54 is located so as to face the movable contact 52. One end of the heater coil 56 is electrically connected to the support 24 by means of a suitable electrical conductor 58, and the other end thereof is electrically connected to the conductor 40.

The system as shown is in the normal unheated position with switch S open and contacts 50 disconnected from each other. In this position it will be noted that the contact 29 engages the contact 22. By placing the vessel 8 upon the heating coil 2 the sensor plate 12 is depressed, but does not have any effect upon the engagement of the contacts 20 and 22. By moving the handle 43 of the switch S to the closed position the heater coil 36 is directly connected across supply lines N and L by means of the circuit comprising conductor 41, heater coil 36 and the conductors 3d, 4d and 6. Such current flow will immediately cause heating of the heater coil 36. The magnitude of such current how will be dependent, however, upon the position of the variable resistor 48- 46 connected across the heater coil 36.

At the same time switch S is closed, it will be noted that the heater coil 56 is directly connected across supply lines L and N by means of connected conductors 6, 4i!- and conductor 58, support 24, engaged contacts 2022, bimetal 16 and conductor 41. By means of the current flow through the heater coil 56 the bimetal 55 will expand to cause it free end to engage the cont-act 52 and move the contact 52 into bridging relationship with the spaced contacts 50 whereby the heater coil 2 will be connected across the supply lines L and L by means of the circuit comprising conductor 4, having electrically bridged contacts 50 therein, and conductor 6, having the closed switch S there-in. As soon as heating of the heating element 2 occurs heat will be transmitted to the vessel 8 and its contents, which in turn, will cause heat to be transmitted to the sensor plate 12 and the sensor bimetal 14 secured thereto.

Such heat flow through the vessel will tend to cause the sensor bimetal 14 to move counterclockwise as described. counterclockwise movement of the sensor bimetal 14 will, in turn, cause counterclockwise movement of the control bimetal 16'which is mechanically secured thereto. Such counterclockwise movement of the bimetal 16 will occur until the sensor bimetal 14 has received sufiicient heat so that it movescounterclockwise a sufiicient distance to overcome the contact pressure between the contacts 20 and '22 whereby the contact 20 will move away from the contact 22. Of note, however, is the fact that as the heater coil 36 has been heated during this period and as the deflection of the heated bimetal 16 is to close the contacts 20 and 22, it is necessary for the sensor bimetal 14 'toreceive sufficient heat to overcome this effect of the heated bimetal 16, in addition to the initial contact pressure between the contacts 20 and 22. Upon separation of contacts 20 and 22 the heater coil 56 will be disconnected from the supply lines L and N, so that bimetal 54 will no longer be heated and will start to lose its heat to the surrounding air. When bimetal 54 has cooled sufficiently it will move away from the contact 52 and cause the movable contact 52 to move out of engagement with the spaced contacts 50, whereby the heater element 2 will-be disconnected from the supply lines L and L and, in turn, will start to cool.

As has been indicated the contact 22 initially engages he contact 20 so that an initial pressure exists therebetween. The pressure of such initial engagement determines a portion of the force which must be overcome by the sensor bimetal 14 as described above. However, by varying the initial pressure between the contacts 29 and 22 as previously described, the total force which must be overcome by the sensor bimetal 14 may be varied and consequently the operating temperature of the sensor bimetal 14 may be varied.

Cooling of the heating element 2 will cause the vessel 8 and its contents to cool, and in turn, the sensor bimetal 14 will be cooled. Upon such cooling of the sensor bimetal 14. the sensor bimetal 14 will move clock-. wise so as to reestablish engagement of the contacts 20 and 22 by moving the contact 22 toward contact 2%). it will be noted however that the heater coil 36 is not disconnected from the supply lines L and N as long'as the switch S remains closed so that the bimetal 16 has a fixed clockwise elfect regardless of whether the contacts 20 and 22 are in or out of engagement with each other. Thus, the action of the bimetal 16 aids in the reengagement of the contacts 20 and 22.

The effect of the heater coil 36 can also be understood by considering the circuit without any heat being supplied by the heating coil 36. In such event when the sensor bimetal 14 receives sufiicient heat it will move counterclockwise so as to cause separation of the contacts 2t) and 22, and in turn as indicated, heating element 2 is deenergized. Upon deenergization of heater element 2 the vessel 8 is cooled and the sensor bimetal 14 is cooled and urges the contact 20 into engagement with force must be exerted by the sensor bimetal 14 before cycling of the device will occur.

By supplying the heating coil 36 with heat, contact 20 is urged toward contact 22 so that the sensor bimetal 14, in this case, must be additionally heated to obtain counterclockwise movement which is sufiicient to obtain separation of the contacts 20; and 22 than in the case where no heat is supplied to the bimetal 16. Accordingly, as more heating of the sensor bimetal 14 is required a higher cycling temperature maybe achieved. In view of the fact that the variable resistor 46-48 has an infinite number, within limits, of positions it can be seen that the cycling temperatures may readily be varied between a wide range of values as each setting of the variable resistor 46-48 will cause a change in the current flowing through the heating coil 36, and, consequently, a change in the heating rate of the bimetal 16.

.As is also well known in the art of thermostatic 'matee rial, a relationship exists between the thickness and length of two. thermostatic elements so that for the same temperature in both elements there is no movement of the bimetals with respect to each other. Such systems are usually referred to as being ambient compensated" and may be employed in the device as described in order to prevent changes in contact pressure under the various ambient temperature conditions in which the device functions. Thus, a thermal balance can be achieved between the sensor bimetal 14 andthe bimetal 16 so that the two bimetals 14 and 16 will be at substantially the same temperature at the control temperature at which thecontacts 2th and 22 separate. By obtaining such a thermal balance there is no transient heat transfer between the two bimetals 14 had 16. In terms of deflece tion, the deflection of the sensor bimetal 14 is balanced by the deflection of the bimetal 16 at the control temperature. It, of course, is to be realized that the contact pressure between the contacts 20 and 22 will affect the control temperature, that is, increasing the contact presbe obtained.

sure raises the control temperature. However, by initially setting contact 20 to just engage contact 22 at room temperature the above thermal balance can readily It will also be noted that although the control temperature is controlled by both the bimetals 14 and 16 functioning as described, the cycling action of the device is performed by the sensor bimetal 14 only, so that the bimetal 14 may properly be referred to as a cycler bimetal.

Having described a preferred embodiment of my invention in accordance with the patent statutes, it is desired that the invention be not limited to the specific construction shown, inasmuch as it is apparent that modifications thereof maybe made without departing from the broad spirit and scope of my invention, Thus, for example, the various methods of varying the current through the heater coil 36 as shown in my copending application entitled Control Device filed concurrently herewith Serial No. 628,383 and which application has been assigned to the same assignee as this invention, may be used. Accordingly, it is desired that the invention be interpreted as broadly as possible, and that it be limited only as required by the prior art.

I claim as my invention:

1. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance heating unit therefor comprising, a high thermal conductivity portion for engagement with a cooling vessel and having a first control portion which is movable with relation to said thermal portion in response to temperature changes in said thermal portion, a second control portion, supporting means supporting said second control'portion from said first control portion so as to be electrically and thermally insulated therefrom, means connected to said second control portion for controlling the energization of a resistance unit in response to movement of said first and second control portions, and an auxiliary electrical heater supported with respect to said second control portion to cause movement thereof.

2. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance heating unit therefor comprising, a high thermal conductivity portion for engagement with a cooling vessel and having a first control portion which is movable with relation to said thermal portion in response to temperature changes in said thermal portion, a second control portion, support means supporting said second control portion from said first control portion so as to be electrically and thermally insulated therefrom, means connected to said second control portion for controlling the energization of a resistance unit in response to movement of said first and second control portions, an auxiliary electrical heater supported with respect to said second control portion to cause movement thereof, and a variable electrical resistance connected with respect to said electrical heater to vary the magnitude of the current through said heater whereby the time required for movement of said second control portion is varied.

3. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance heating unit therefor comprising, a high thermal conductivity portion for engagement with a cooling vessel and having a first control portion which is movable with relation to said thermal portion in response to temperature changes in said thermal portion, a second control portion, support means supporting said second control portion from said first control portion so as to be electrically and thermally insulated therefrom, means connected to said second control portion for controlling the energization of a resistance unit in response to movement of said first and second control portions, an auxiliary electrical heater supported with respect to said second control portion to cause movement thereof,

said first control portion being movable when heated to prevent energization of a resistance unit, said second control portion being movable when heated in a direction opposite to that of said first control portion when heated, and a variable electrical resistance connected with respect to said electrical heater to vary the magnitude of the current through said heater whereby the time required for movement of said second control portion is varied. 4. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling the heat output of a heating unit therefor comprising, a high thermal conductivity portion for engagement with a cooling vessel and having a first control portion which is movable with relation to said thermal portion in response to temperature changes in said thermal portion, a second control portion, support means supporting said second control portion from said first control portion so as to be electrically and thermally insulated therefrom, means connected to said second control portion for controlling the heat output of a heating unit in response to movement of said first and second control portions, an auxiliary electrical heater supported with respect to said control portion to cause movement thereof, and a variable electrical resistance connected with respect to said electrical heater to vary the magnitude of the current through said heater whereby the time required for movement of said control portion is varied.

5. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance heating unit therefor comprising, a sensor plate of a heat conducting material, a first bimetallic member thermally secured to said sensor plate so as to have at least a portion thereof movable with respect to said sensor plate, a second bimetallic member, support means for supporting said second bimetallic member from said portion of said first bimetallic member so as to be electrically and thermally insulated therefrom, a pair of contacts one of which is mechanically connected to said second bimetallic member to be movable into and out of engagement with the other in response to movement of said first and second bimetallic members, an electrical resistance heater supported with respect to said second bimetallic member to cause movement thereof, and electrical circuit means electrically connected to each of said contacts for controlling the electrical energization of an electrical resistance unit.

6. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance unit comprising, a sensor plate of a heat conducting material, a first bimetallic member thermally secured to said sensor plate so as to have at least a portion thereof movable with respect to said sensor plate, a second bimetallic member, support means for supporting said second bimetallic member from said portion of said first bimetallic member so as to be electrically and thermally insulated therefrom, a pair of contacts one of which is mechanically connected to said second bimetallic member to be movable into and out of engagement with the other in response to movement of said first and second bi etallic members, an electrical resistance heater supported with respect to said second bimetallic member to cause movement thereof, a variable electrical resistance connected with respect to said heater to vary the magnitude of the current through said heater whereby the time required for said one contact to move into and out of engagement with said other contact is varied, and electrical circuit means electrically connected to each of said contacts for controlling the electrical energization of an electrical resistance unit.

7. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance unit comprising, a sensor plate, a sensor bimetal thermally secured to said sensor plate with a portion thereof being movable in response to temperature changes of said sensor plate, a control bimetal, electrical and thermal insulating means supporting said control bimetal from said movable portion of said sensor bimetal, a pair of normally engaged contacts one of which is mounted on said control bimetal so as to be movable in and out of engagement with the other, an electrical. heater mounted on said control bimetal to cause movement thereof toward the other of said contacts, and means for supporting said'other contact in fixed relationship with said sensor plate and electrically insulated therefrom.

8. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance unit comprising, a sensor plate, a sensor bimetal thermally secured to said sensor plate with at least a portion extending outwardly therefrom so as to be movable with respect to said sensor plate, an elongated control bimetal in alignment with and having one of its ends spaced from said movable portion of said sensor bimetal, electrical, thermal insulating means for supporting said control bimetal from said movable portion of said sensor bimetal, a pair of normally engaged contacts one of which is mounted on said control bimetal, and an electrical heater element mounted on said control bimetal for causing movement thereof toward the other of said contacts.

9. A control system operatively associated with and adapted to control an electrical resistance unit comprising, a control circuit having input and output terminals adapted to be connected to a suitable source of electrical energy and an electrical resistance unit, respectively, switch means in said circuit for connecting said input terminals to said output terminals, an electrical resistance heating element connected to said circuit independently of said switch means, a heat actuated member located to be heated by said heating element; operating means connected in parallel with said heating element, normally engaged separable contacts electrically connected in series in said parallel circuit one of which is mechanically connected to said heat actuated member, said actuated memberbeing movable when heatedto move said one contact toward the other of said contacts, another heat actuated member disposed to be heatedby an electrical resistance unit, said other heat actuated member being thermally insulated from and mechanically connected to said first-mentioned actuated member to move said one contact out of engagement with said other contact when said last-mentioned actuated member is heated whereby said operating means is deenergized. v

10. A control system operatively associated with and adapted to control an electrical resistance unit comprising, a control circuit having input and output terminals adapted to be connected to a suitable source of electrical energy and an electrical resistance unit, respectively, switch means in said circuit for connecting said input terminals to said output terminals, an electrical resistance heating element connected to said circuit independently of said switch means, a heat actuated member located to be heated by said heating element; operating means connected in parallel with said heating element, normally engaged separable contacts electrically connected in series in said parallel circuit one of which is mechanically connected to said heat actuated member, said actuated member being movable when heated to move said one contact toward the other of said contacts, another heat actuated member disposed to be heated by an electrical resistance unit, said other heat actuated member being thermally insulated from and mechanically connected to said firstrnentioned actuated member to move said one contact out of engagement with said other contact when said lastmentioned actuated member is heated whereby said operating means is deenergized, and means in said first-mentioned circuit for varying the current flow through said heating element. p

11. A control system operatively associated with and adapted to control an electrical resistance unit comprising, a control circuit having input and output terminals adapted to be connected to a suitable source of electrical energy and an electrical resistance unit, respectively,

switch means in said circuit for connecting said input terminals to said output terminals, an electrical resistance heating element connected to said circuit independently of said switch means, an elongated first heat-actuated member located to be heated by said heating element, a second heat-actuated member located to be heated by an electrical resistance unit having one of its ends spaced from one end of said first heat-actuated member, thermal insulating means for mechanically connecting adjacent ends of said members, operating means connected in parallel with sm'd heating element, and separable contacts electrically connected in series in said parallel circuit one of which is mechanically connected to the other end of said first heat-actuated member so as to be movable into and out of engagement with the other of said contacts to control the energization of said operating means.

I 12. A controlsystem operatively associated with and adapted to'control an electrical resistance unit comprising, a control circuit having input and output terminals adapted to be connected to a suitable source of electrical energy and an electrical resistance unit, respectively, a pair of electrical resistance heating elements connected in parallel to said circuit, heat-actuated members located adjacent said elements, respectively, so as to be heated thereby, a pair of separable contacts in said parallel circuit one of which is mechanically connected to one of said members to control the energization of the element for the other of said members, another heat-actuated member located to be heated by an electrical resistance unit having one of its ends spaced from said one member, thermal insulating means for mechanically connecting adjacent ends of said one and another member, said one and another member being movable when heated to move said one contact on said one memberinto and out of engagement with the other of said contacts, switch means for connecting and disconnecting said input terminals to said output terminals, and said other member comprising operating means for said switch means.

13. A control system operatively associated with and adapted to control an electrical resistance unit comprising, an energizing circuit adapted to be connected to an electrical resistance unit, said energizing circuit having 9. normally open switch means therein, a heater element and a variable resistance connected in parallel in said circuit so thatcurrent will normally flow therethrough, a heatact uated member arranged to ;;be heated by said heater element and which is electrically connected to said heater element, said heat-actuated member normally engaging Contact means to connect switch operating means in parallel with said heater element whereby said normally open switch means is closed, said heat-actuated member being movably supported so that upon heating said contact means is disengaged thereby and said switch operating means is deenergized, and said variable resistance being operable to vary the heat output of said heater whereby the time required for closing said switch means may be varied.

14. A control system operatively associated with and adapted to control an electrical resistance unit comprising, an energizing circuit adapted to be connected to an electrical resistance unit, said energizing circuit having a normally open switch means therein, a heater element and a variable resistance connected in parallel in said circuit so that current will normallyflow therethrou-gh, a heatactuated member arranged to be heated by said heater element and which is electrically connected to said'heater element, said heat-actuated member normally engaging contact means to connect switch operating means in parallel with said heater element whereby said normally open switch means is closed, said heat-actuated member being movably supported so that upon heating said contact means is disengaged thereby and said switch operating means is deenergized, said variable resistance being operable to vary the heat output of said heater whereby the time required for closing said switch means may be varied, and another heat-actuated member responsive to thermal energy externally of said circuit arranged to move said first-mentioned heat-actuated member in a direction opposite that in which said first-mentioned heat-actuated member moves when heated whereby said switch operat ing means is deenergized and said switch means is opened.

15. A control system operatively associated with and adapted to control an electrical resistance unit, a control circuit havinginput and output terminals adapted to be connected to a suitable source of electrical energy and an electrical resistance unit, respectively, a sensor bimetal having a fixed portion and a remote portion movable with respect to said fixed portion, an elongated control bimetal spaced from the remote portion of said sensor bi- 7 metal, thermal insulating means for mechanically securing one end of said control bimetal to said remote portion of said sensor bimetal, a pair of normally engaged separable contacts connected to said circuit one of which is mounted adjacent the other end of said control bimetal, switch means in said circuit for connecting said input terminals to said output terminals having an operating means connected in series with said contactsin said circuit, said sensor bimetal being movable when heated to cause separation of said contacts, and heating means in said circuit adjacent said control bimetal for causing movement of said control bimetal toward the other of said contacts.

16. A control device for controlling the temperature of a cooking vessel and its contents by means of controlling an electrical resistance heating unit therefor comprising, a high thermal conductivity portion for engagement with a cooking vessel and having a first control portion which is movable with relation to said thermal portion in response to temperature changes in said thermal portion, a second control portion, support means supporting said second control portion from said first control portion, means actuated by said second control portion for controlling the energization of a resistance unit in response to movement of said first and second control portions, an auxiliary electrical heater supported with respect to said second control portion to cause movement thereof, and a variable electrical resistance connected with respect to said electrical heater to vary the magnitude of the current through said heater whereby the time required for movement of said second control portion is varied.

References Cited in the file of this patent UNITED STATES PATENTS Bletz Apr 30, 1946 Clark Sept. 23, 1947 Akeley Oct. 3, 1950 Akeley Aug. 12, 1952 Fry May 11, 1954 Weeks Dec. 10, 1957

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