US3771088A

US3771088A - Electrical switch construction and control system utilizing the same

Info

Publication number: US3771088A
Application number: US00267957A
Authority: US
Inventors: B Sliger
Original assignee: Robertshaw Controls Co
Current assignee: Robertshaw Controls Co
Priority date: 1972-06-30
Filing date: 1972-06-30
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

An electrical switch construction having a pair of electrical contacts carried by a support and being adapted to be disposed in spaced relation relative to each other. A condition responsive device is carried by the support and has a movable member that moves relative to the support in response to changes in conditions being sensed by the device. The member has at least one part thereof formed of electrical conductive material and has at least another part thereof formed of electrically nonconductive material. Such member is disposed between the contacts whereby the one part thereof is adapted to be in contact with the contacts to provide an electrical circuit therebetween when the device senses a certain condition and the other part is adapted to be in contact with at least one of the contact means to prevent an electrical circuit between the contacts when the device senses another condition.

Description

United States Patent 1 Sliger Nov. 6, 1973 337/393, 394, 315, 398, 399; ZOO/DIG. 25; 335/170 [56] References Cited UNITED STATES PATENTS 1,559,022 10/1925 Wensley 337/315 1,890,909 12/1932 Lincoln 337/393 Primary Examiner-Harold Broome Att0rney-Auzville Jackson, Jr. et al.

[57] ABSTRACT An electrical switch construction having a pair of electrical contacts carried by a support and being adapted to be disposed in spaced relation relative to each other. A condition responsive device is carried by the support and has a movable member that moves relative to the support in response to changes in conditions being sensed by the device. The member has at least one part thereof formed of electrical conductive material and has at least another part thereof formed of electrically non-conductive material. Such member is disposed between the contacts whereby the one part thereof is adapted to be in contact with the contacts to provide an electrical circuit therebetween when the device senses a certain condition and the other part is adapted to be in contact with at least one of the contact means to prevent an electrical circuit between the contacts when the device senses another condition.

20 Claims, 8 Drawing Figures ELECTRICAL SWITCH CONSTRUCTION AND CONTROL SYSTEM UTILIZING THE SAME This invention relates to an improved electrical switch construction as well as to an electrical control system utilizing such electrical switch construction or the like.

It is well known that separate electrical switches have been actuated by temperature responsive devices of the power element type with the operation of the switch being either the primary function of the device or the auxiliary function to the principal power producing function of the device. For example, such uses have been the actuation of warning lights, alarm devices or the like to indicate changes in temperature of the temperature responsive device or the actuation of secondary devices such as heaters, fans, etc. depending on the temperature of the temperature responsive device.

Another use is to interrupt the electrical current through a resistance type heater encircling the temperature responsive device to prevent damage to the device from excessive heating by the heater. Normally in systems of this type, a separate remote thermostatically operated device is incorporated to respond to the tem perature of a medium to be controlled, such as the temperature of the air space. The temperature responsive device of the electrical switch is used, in turn, to provide the mechanical driving force to position a valve or the like permitting a flow of a heating or cooling medium through a heat exchanger to effect the air space being controlled. Without the interruption of the heater current by the separate switch during periods of prolonged thermostatic demand for full power element movement, the resistance heater would continue to heat the power producing temperature responsive device without restraint. With the switch employed, however, the current to the heater can be discontinued at the maximum allowable power producing temperature responsive device stroke. With the current interrupted by the switch, the temperature responsive device will cool until the switch contacts reach a closed position and current is again communicated to the heater and the cycle is repeated.

It is a feature of this invention to provide an improved electrical switch construction to be utilized in the above manner as well as for other systems and purposes as desired.

In particular, it is a feature of this invention to provide an electrical switch construction wherein the movable element of a temperature responsive device has portions thereof that are conductive and nonconductive for respectively making and breaking-the electrical circuit between a pair of contacts disposed in engagement with the movable member.

For example, one embodiment of the electrical switch construction of this invention comprises a support means carrying a pair of electrical contact means adapted to. be disposed in spaced relation relative to each other. A condition responsivedevice is carried by tact with the contact means to provide a circuit therebetween when the device senses a certain condition and the other part is adapted to be in contact with at least one of the contact means to prevent a circuit between the contact means when the device senses another condition.

Accordingly, it is an object of this invention to provide an electrical switch construction having one or more of the novel features'set forth above or hereinafter shown or described.

Another object of this invention is to provide an electrical system utilizing such an electrical switch construction.

Other objects, uses and advantages of this invention are apparent from reading of this description which proceeds with reference to the accompanying drawing forming a part thereof and wherein FIG. 1 is a side view, partially in cross-section, illustrating one embodiment of the electrical switch construction of this invention as utilized in an electrical control system of this invention which is illustrated schematically in FIG. 1.

FIG. 2 is a view similar to FIG. 1 and illustrates the electrical switch construction in another operating condition thereof.

FIG. 3 is a top view of the electrical switch construction of FIG. 1.

FIG. 4 is a view similar to FIG. 1 and illustrates another embodiment of the electrical switch construction of the invention.

FIG. 5 is a view similar to FIG. 1 and illustrates another embodiment of the electrical switch construction of this invention.

FIG. 6 is a top view of electrical switch control of FIG. 5.

FIG. 7 is a view similar to FIG. 1 and illustrates another embodiment of the electrical switch construction of this invention.

FIG. 8 is a view similar to FIG. 1, except that the same is in full cross-section, and illustrates another electricalswitch construction of this invention.

While the various features of this invention are hereinafter described and illustrated as being particularly adapted for controlling a particular electrical control system, it is to be understood that the various features of this invention can be utilized singly or in any combination thereof to provide means for controlling other electrical control systems as desired.

Therefore, this invention is not to be limited to only the embodiments illustrated in the drawings, because the drawings are merely utilized to illustrate one of the the support means and has a movable member that moves relative to the support means in response to changes in conditions being sensed by the device. The member has at least one part thereof formed of electrically conductive material and has at least another part thereof formed of electrically non-conductive material. The member is disposed between the contact means whereby the one part thereof is adapted to be in conwide variety of uses of this invention.

Referring now to FIG. 1, one embodiment of the electrical switch construction of this invention is generally indicated by the reference numeral 10 and is illustrated as being utilized in an electrical control system of this invention that is generally indicated by the reference numeral 11 and comprises an electrical power source 12, a resistance heater l3 and a temperature responsive device 14. v

The electrical switch construction 10 0s this invention comprises a pair of contact means 15 and 16 respectively having

terminal ends

17 and 18 interconnected to

electrical leads

19 and 20.

The lead 20 is interconnected to one side 21 of the electrical power source 12 while the other side 22 of the electrical power source 12 is interconnected by a lead 23 to one side 24 of the electrical resistance heater 13. The other side 25 of the heater coil 13 is interconnected by a lead 26 to one side 27 of the temperature responsive device 14. The other side 28 of the temperature responsive device 14 is interconnected to the lead 19.

Thus, it can be seen that when a circuit is completed between the contact means 15 and 16 of the electrical switch construction of this invention in a manner hereinafter set forth and the temperature responsive device 14 senses that the temperature of the air surrounding the same is below the set temperature thereof and is thus interconnecting the lead 26 to the lead 19, electrical current from the power source 12 is adapted to flow through the resistance heater 13 and heat the electrical switch construction 10 of this invention to cause the same to extend a plunger or movable member 29 thereof in a manner hereinafter set forth and as illustrated in FIG. 2 to cause a suitable valve or other structure (not shown) of a heat exchanger means (not shown) to supply heated air or the like to tend to raise the temperature of the space being heated thereby. When the temperature responsive device 14 is satisfied, the same disconnects the lead 26 from the lead 19 so that no further current flows through the heater means 13 until the thermostat 14 again demands an increase in temperature.

When the circuit through the coil 13 is discontinued, the movable member 29 normally assumes the retracted position illustrated in FIG. 1 where the same is in its non-extended position and is not operating the heat exchanger valve.

The electrical switch construction 10 of this invention includes a temperature responsive device or power element 30 that operates on the well known principal of the piston and cylinder temperature responsive device wherein the piston thereof is extended from the cylinder upon an-increase in sensed temperature be- 7 cause of a thermally responsive wax charge material in the cylinder expanding upon the increase in temperature thereof and with the piston retracting into the cylinder upon a decrease in sensed temperature because the thermally responsive wax charge material in the cylinder contracts upon a decrease in temperature thereof.

Thus, it can be seen that the temperature responsive device 30 includes an outer cylinder housing 31 formed of a plurality of different sized

cylindrical sections

32, 33, 34 and 35 with the piston rod, stem or movable member 29 projecting out of a suitable opening formed in the upper end 36 of the upper cylindrical section 32 of the housing 31.

The movable member 29 has a lower end 37, FIG. 8, received within a stem seat 38 formed of rubber or other resilient material disposed within the housing 31 and having its lower end 39 engaging against a flexible diaphragm 40 separating the seat member 38 from a fusible, thermally expansive material 41 disposed in the lower end of the housing 31. For example, such fusible,

thermally expansive material 41 can comprise a wax containing powdered metal, heat conducting material which expands as the temperature thereof is increased. Such increase in temperature of the thermally expansive wax charge material 41 causes the same to expand and force the piston member 29 to move upwardly in the manner illustrated in FIG. 2 whereas when the thermally responsive wax charge material 41 senses a decrease in temperature, the same contracts and permits the piston member 29 to assume the retracted position illustrated in FIG. 1.

The electrical switch construction 10 includes an annular support member 42 formed of electrically nonconductive material and being press fitted over the upper cylindrical part 32 of the housing 31 in the manner illustrated in FIG. 1 or is otherwise secured thereto in any desired manner. The contact means 15 and 16 can each comprise a one piece electrically conductive member respectively having the

terminal portions

17 and 18 thereof passing through suitable openings in the support member 42 so as to be secured thereto and being suitably bent so that

elbow portions

43 and 44 thereof are respectively adapted to be disposed in sliding engagement with the movable member 29 of the temperature responsive element 30. The contact means 15 and 16 are so formed that the same have a natural bias to continuously urge the

elbow portions

43 and 44 thereof respectively into contact with the movable member 29.

In the embodiment of the electrical switch construction 10 illustrated in the drawings, the

elbow portions

43 and 44 of the contact means 15 and 16 are respectively disposed in different parallel planes passing transversely to the direction of movement of the member 29.

The piston member 29 of the thermally responsive element 30 is made of alternately spaced nonelectrically conductive material, such as nylon or other plastic material, and electrically conductive material such as copper, copp'er alloys or the like. For example, the piston member 29 has one conductive part 45 spacing a pair of

non-conductive parts

46 and 47 from each other while being disposed in stacked aligned relation.

The conductive part 45 of the piston element 29 is of such a length in relation to the

elbows

43 and 44 of the contact means 15 and 16 that when the temperature responsive device 30 is in a cool or retracted condition thereof wherein the piston member 29 is in its fully retracted position relative to the cylinder means 31, the conductive part 45 is engaged by both

elbows

43 and 44 of the contact means 15 and 16 so that an electrical circuit is provided or completed between the contact means 15 and 16. However, upon the heating of the temperature responsive device 30, the piston 29 is extended in the manner illustrated in FIG. 2 so that the non-conductive portion 47 now makes contact with at least the elbow 43 of the contact means 15 and thereby prevents the making of the electrical circuit between the contact means 15 and 16.

The operation of the electrical switch construction 10 as utilized in the control system 11 of FIGS. 1 and 2 will now be described.

As illustrated in FIG. 1, when the temperature responsive device 14 is satisfied, the same prevents electrical connection between

leads

26 and 19 so that no current flows through the resistance heater 13 and the power element 30 is in its non-heated condition whereby the piston member 29 thereof is in the fully retracted position illustrated in FIG. 1. Thus, the conductive part 45 of the member 29 is in contact with the contact means 15 and 16 so that an electrical circuit is completed therebetween. When the thermostat 14 senses a decrease in temperature below-the set temperature' thereof, the same interconnects the

leads

26 and 19 together so that the power source 12 is now adapted to send current through the heater coil 13 which heats the temperature responsive device 30 and causes the piston 29 thereof to extend in the manner illustrated in FIG. 2. Such extended piston 29 operates suitable valve means or the like (not shown) when in its extended condition to supply heat to the space being sensed by the temperature responsive device 14. However, since the piston 29 of the temperature responsive device 30 is now in its extended condition, it can be seen that the non-conductive part 47 thereof is now engaged by the elbow 43 of the contact means 15 so that the electrical circuit between the contact means 15 and 16 is broken. Thus, no current can flow through the heater means 13 even though the thermostat 14 may not be satisfied by the increase in heated air being directed thereto whereby the

leads

26 and 19 are still being electrically connected together by the thermostat 14. The opening if the thermostat 14 is still interconnecting the leads l9 and 26 together, current can again flow through the heater coil 13 to heat up the power element,30 and, thus, again extend the piston 29 in the previously described manner whereby the temperature responsive device is adapted to be cycled back and forth between its extended and non-extended condition of the piston member 29. Such cycling of the temperature responsive device 30 prevents damage thereto from excessive heating by the heater l3 sothat the device 30. will not be subjected to long periods where the piston 29 thereof is fully extended in its power stroke should the temperature responsive device 14 have prolonged temperature requiring periods.

Therefore, it can be seen that the improved electrical switch construction 10 of this invention can be formed of a relatively few parts to operate in a unique manner for opening and closing a circuit between a pair of-electrical contact means.

While the electrical switch constructionlo-has been previously described as opening the circuit between'the contact means upon the extending of the movable member of the temperature responsive device, it is to be understood that the movable member could be so constructed and arranged as the same will complete the circuit between the contact means only when extended and prevents a circuit therebetween when retracted;

For example, another electrical switch construction of this invention is generally indicated-by the reference numeral 10A in FIG. 4 and parts thereof similar to the switch construction 10 previously described are indicated by like reference numerals followed by the reference letter A.

As illustrated in FIG. 4, the conductive part 45A and

non-conductive parts

47A and 46A of the movable member 29A of the temperature responsive device 30A are so constructed and arranged that when the movable member 29A is in the fully retracted position illustrated in FIG. 4, the elbow 43A of the contact means A is in contact with the conductive part 45A but the elbow 44A of the contact means 16A isin engagement with the non-conductive part 46A so that a circuit cannot be completed between the contact means 15A and 16A when the movable member 29A is in its retracted condition. However, upon heating of the element 30A in the manner previously described, the piston 29A is extended in such a manner that the conductive part 45A can now be engaged by both

elbow portions

43A and 44A of the contact means 15A and 16A so that an electrical circuit is completed therebetween.

While the electrical switch constructions 10 and 10A of this invention have been previously described as having only two contact means, it is to be understood that the electrical switch constructions of this invention can have additional contact means carried by the support means and engaging against the movable member of the temperature responsive device.

For example, reference is now made to FIGS. 5 and 6 wherein another electrical switch construction of this invention is generally indicated by the reference numeral 10B and parts thereof similar to the switch constructions 10 and 10A previously described are indicated by like reference numerals followedby the reference letter B.

As illustrated in FIG. 5, a third contact means 48 is carried by the support means 428 and has its elbow 49 disposed in engagement with the movable part 298 of the temperature responsive device 308.

The conductive part 45B and non-conductive parts 468 and 47B of the piston member 298 are so constructed and arranged that when the thermostatic device 30Bis-not being heated and the piston member 29B is in its fully retracted condition as illustrated in FIG. 5, the conductive part 458 is being engaged by the elbow portions 438 and 44B of the contact means 158 and 168 so as to provide an electrical circuit therebetween while the elbow 49 of the third contact means 48 is in engagement with the non-conductive-part 468 so that no electrical circuit is completed between the contact means 48 and either one of the contact means 158 and 16B.

Upon heating of the temperature responsive device 30B to a certain temperature, the piston member 298 will be extended part way between its fully retracted and fully extended conditions so that the nonconductive part 478 is now engaged by the elbow 43B of the contact means 158 whereby an electrical circuit is prevented between the contact means 158 and 168 by the non-conductive part 478 and the elbow 49 of the third contact meand 48 remains in contact with the non-conductive portion 468 so that the contact means 48 is not electrically connected to either of the contact means 158 and 168.

However, upon further heating of the temperature responsive device 308 so that the piston member 493 is in its fully extended condition, the conductive part 458 of the member 298 is now so positioned that the

elbows

44B and 49 of thecontact means 168 and 48 are now engaging the conductive part 458 whereby an cylinder temperature responsive device of the power element type, the electrical switch construction of this invention can be moved by other condition responsive devices if desired.

For example, reference is made to FIG. 7 wherein another electrical switch construction of this invention is generally indicated by the reference numeral C and parts thereof similar to the switch constructions 10, 10A and 10B previously described are indicated by like reference numeral as followed by the reference letter ILCiQ As illustrated in FIG. 7, the movable member 29C has its lower end 50 secured to a movable wall 51 of a vapor filled bellows 52 carried within a housing means 53 having its neck portion 54 telescopically receiving the annular support means 42C previously described and that carries the contact means C and 16C.

The movable member 29C has the conductive parts 45C and

non-conductive parts

46C and 47C previously described but can also have an additional conductive part 55 and a non-conductive part 56 as illustrated so that the non-conductive parts will prevent an electrical circuit between the contact means 15C and 16C in the manner previously described in different positions of the movable member 29C as caused by the collapse or expansion of the bellows construction 52. Likewise, the

conductive parts

45C and 55 can provide an electrical circuit between the contact means 15C and 16C when the same are so positioned by the bellows 52 to be disposed in contact with the contact means 15C and 16C in the manner previously described.

While the contact means of the electrical constructions of this invention have been previously described as each being a one-piece member having an elbow contacting the movable member of the temperature responsive device, it is to be understood that other forms of contact means can be utilized if desired.

For example, reference is now made to FIG. 8 wherein another electrical switch construction of this invention is generally indicated by the reference numeral 10D and parts thereof similar to the electrical switch constructions 10, 10A, 10B and 10C previously described are indicated by like reference numerals followed by the reference letter D.

As illustrated in FIG. 8, the contact means 15D and 16D each comprises a one-piece bent member providing the

terminal portions

17D and 18D previously described but with the same carrying

conductive contact members

57 and 58 at the upper end thereof for engagement with the movable member 29D. For example,

such contacts

57 and 58 can each be formed of a highly electrically conductive material, such as silver, gold, copper, copper alloys, etc., and is attached to the

leaf contact member

15D and 16D so that the same will bear against the movable member 29D.

In all of the switch constructions previously described, it may be found that the. non-conductive portionsof the movable pistonmember of the temperature responsive device can be formulated with an abrasive type material such as fiberglass, etc. which will effectively clean the contacting portions of the contact means each time during the movement of the nonconductive portions past the engaging part of the contact means.

Thus, it can be seen that this invention not only provides an improved electrical switch construction that is adapted to readily make and break an electrical circuit between a pair of contact means thereof in response to a condition being sensed by a condition responsive device of the construction, but also this invention provides an electrical control system utilizing such an electrical switch construction. v

While the form of the invention now preferred has been described as required by the patent statute, it is to be understood that other forms can be utilized and all come within the scope of the appended claims.

What is claimed is:

1. An electrical switch construction comprising support means, a pair of electrical contact means carried by said support means and being adapted to be disposed in spaced relation relative to each other, and a condition responsive device carried by said support means and having a movable member that moves relative to said support means in response to changes in conditions being sensed by said device, said member having one part thereof formed of electrically conductive material and having another part thereof formed of electrically non-conductive material, said member being disposed between said contact means whereby said one part thereof is adapted to be in contact with said pair of contact means to provide a circuit therebetween when said device senses a certain condition and said other part is adapted to be in contact with only one of said pair of contact means to prevent a circuit between said pair of contact means when said device senses another condition, said contact means respectively engaging said member in different parallel planes that pass transversely to the direction of movement of v said parts whereby the other of said contact means is always in contact with said one part of said member when said device is sensing either of said two conditions.

2. An electrical switch construction as set forth in claim 1 wherein said member has said parts thereof disposed adjacent each other in aligned relation.

3. An electrical switch construction as set forth in claim 2 wherein said conductive part is disposed intermediate a pair of non-conductive parts of said member of which one comprises said other part of said member.

4. An electrical switch construction as set forth in claim 3 wherein a third contact means is carried by said support means and engages said member in a plane different from but parallel to said first-named planes.

5. An electrical switch construction as set forth in claim 1 wherein said condition responsive device is a temperature responsive device.

6. An electrical switch construction as set forth in claim 6 wherein said parts of said member are so constructed and arranged that said non-conductive part of said member is moved into said contact with said one contact means when said device senses a temperature above a certain temperature.

7. An electrical switch construction as set forth in claim 5 wherein said parts of said member are so constructed and arranged that said non-conductive part of said member is moved into said contact with said one contact means when said device senses a temperature below a certain temperature.

8. An electrical switch construction as set forth in claim 1 wherein said device comprises a piston and cylinder temperature responsive device wherein said piston is extended from said cylinder upon an increase in sensed temperature and is retracted into said cylinder upon a decrease in sensed temperature, said piston comprising said movable member.

9. An electrical switch construction as set forth in claim 8 wherein said support means comprises an annular member telescoped and secured on said cylinder of said temperature responsive device.

10. An electrical switch construction as set forth in claim 4 wherein said third contact means engages said one part of said member when said device is sensing said other condition whereby said one part is adapted to provide a circuit between said other contact means and said third contact means when said device is sensing said other condition, said third contact means engaging the other of said pair of non-conductive parts of said member when said device is sensing said certain conditions whereby said other non-conductive part is adapted to prevent a circuit between said other contact means and said third contact means when said device is sensing said certain conditions.

11. An electrical control system comprising an electrical power source, an electrical circuit interconnected to said source, and an electrical switch construction disposed in said electrical circuit and having support means, a pair of electrical contact means carried by said support means and being adapted to be disposed in spaced relation relative to each other, and a condition responsive device carried by said support means and having a movable member that moves relative to said support means in response to changes in conditions being sensed by said device, said member having one part thereof formed of electrically conductive material and having another part thereof formed of electrically nonconductive material, said member being disposed between said contact means whereby said one part thereof is adapted to be in contact with said pair of contact means to provide a circuit therebetween and thereby complete said electrical circuit when said device senses a certain condition and said other part is adapted to be in contact with only one of said pair of contact means to prevent a circuit between said pair of contact means and thereby open said electrical circuit when said device senses another condition, said contact means respectively engaging said member in different parallel planes that pass transversely to the direction of movement of said parts whereby the other of said contact means is always in contact with said one part of said member when said device is sensing either of said two conditions.

12. An electrical control system as set forth in claim 1 1 wherein said member has said parts thereof disposed adjacent each other in aligned relation.

13. An electrical control system as set forth in claim 12 wherein said conductive part is disposed intermediate a pair of non-conductive parts of said member of which one comprises said other part of said member.

14. An electrical control system as set forth in claim 13 wherein a third contact means is carried by said support means and engages said member in a plane different from but parallel to said first-named planes.

15. An electrical control system as set forth in claim 11 wherein said condition responsive device is a temperature responsive device.

16. An electrical control system as set forth in claim 15 wherein said parts of said member are so constructed and arranged that said non-conductive part of said member is moved into said contact with said one contact means when said device senses a temperature above a certain temperature.

17. An electrical control system as set forth in claim 15 wherein said parts of said member are so constructed and arranged that said non-conductive part of said member is moved into said contact with said one contact means when said device senses a temperature below a certain temperature.

18. An electrical control system as set forth in claim 1 1 wherein said device comprises a piston and cylinder temperature responsive device wherein said piston is extended from said cylinder upon an increase in sensed temperature and is retracted into said cylinder upon a decrease in sensed temperature, said piston comprising said movable member.

19. An electrical control system as set forth in claim 18 wherein said support means comprises an annular member telescoped and secured on said cylinder of said temperature responsive device.

20. An electrical control system as set forth in claim 14 wherein said third contact means engages said one part of said member when said device is sensing said other condition whereby said one part is adapted to provide a circuit between said other contact means and said third contact means when said device is sensing said other condition, said third contact means engaging the other of said pair of non-conductive parts of said member when said device is sensing said certain conditions whereby said other nonconductive part is adapted to prevent a circuit between said other contact means and said third contact means when said device is sensing said certain conditions.

Claims

1. An electrical switch construction comprising support means, a pair of electrical contact means carried by said support means and being adapted to be disposed in spaced relation relative to each other, and a condition responsive device carried by said support means and having a movable member that moves relative to said support means in response to changes in conditions being sensed by said device, said member having one part thereof formed of electrically conductive material and having another part thereof formed of electrically non-conductive material, said member being disposed between said contact means whereby said one part thereof is adapted to be in contact with said pair of contact means to provide a circuit therebetween when said device senses a certain condition and said other part is adapted to be in contact with only one of said pair of contact means to prevent a circuit between said pair of contact means when said device senses another condition, said contact means respectively engaging said member in different parallel planes that pass transversely to the direction of movement of said parts whereby the other of said contact means is always in contact with said one part of said member when said device is sensing either of said two conditions.

12. An electrical control system as set forth in claim 11 wherein said member has said parts thereof disposed adjacent each other in aligned relation.

18. An electrical control system as set forth in claim 11 wherein said device comprises a piston and cylinder temperature responsive device wherein said piston is extended from said cylinder upon an increase in sensed temperature and is retracted into said cylinder upon a decrease in sensed temperature, said piston comprising said movable member.