Thermal limiter

Claim 2

A circuit control device comprising a housing of thermoplastic material, a thermally responsive element in said housing adapted to change its state of conductivity when heated to a predetermined temperature, a heater element in the housing arranged to be electrically energized to raise the temperature of said thermally responsive element, a plurality of electrical terminals selectively connected to said heater element and said thermally responsive element whereby said heater element is arranged to be energized by an electrical source of energy external of said housing and said thermally responsive element is arranged to alter a circuit connected to said terminals, said housing defining a cavity, said heater element and said thermally responsive element being disposed in said cavity, substantially all of said cavity not occupied by said elements being occupied by a gas, a wall of said housing including an outer surface adapted to undergo a physical change perceptible externally of the housing when heated to a critical flow temperature, said heater being arranged in heat transfer relationship relative to said thermally responsive element and said wall such that said outer surface of said wall reaches said critical flow temperature and said physical change occurs at substantially the same time said thermally responsive element reaches said predetermined temperature and said change in conductivity state occurs whereby visual inspection of said housing wall reveals the condition of said thermally responsive element, said heater element being adapted to heat said wall by substantial radiation energy transfer.

Claim 3

A circuit control device comprising a housing of thermoplastic material, a thermally responsive element in said housing adapted to change its state of conductivity when heated to a predetermined temperature, a heater element in the housing arranged to be electrically energized to raise the temperature of said thermally responsive element, a plurality of electrical terminals selectively connected to said heater element and said thermally responsive element whereby said heater element is arranged to be energized by an electrical source of energy external of said housing and said thermally responsive element is arranged to alter a circuit connected to said terminals, a wall of said housing including an outer surface adapted to undergo a physical change perceptible externally of the housing when heated to a critical flow temperature, said heater being arranged in heat transfer relationship relative to said thermally responsive element and said wall such that said outer surface of said wall reaches said critical flow temperature and said physical change occurs at substantially the same time said thermally responsive element reaches said predetermined temperature and said change in conductivity state occurs whereby visual inspection of said housing wall reveals the condition of said thermally responsive element, said housing being a multisided, integrally molded structure, one face of said structure being closed by a separately formed wall element, said housing including an inner cavity in which said heater and thermally responsive elements are disposed, said cavity being occupied with a gas, said gas being confined within said cavity to cause a bubble to be formed on a sidewall of said integrally molded structure when the sidewall is elevated to said flow temperature.

Claim 4

A circuit control device comprising a housing of thermoplastic material, a thermally responsive element in said housing adapted to change its state of conductivity when heated to a predetermined temperature, a heater element in the housing arranged to be electrically energized to raise the temperature of said thermally responsive element, a plurality of electrical terminals selectively connected to said heater element and said thermally responsive element whereby said heater element is arranged to be energized by an electrical source of energy external of said housing and said thermally responsive element is arranged to alter a circuit connected to said terminals, a wall of said housing including an outer surface adapted to undergo a physical change perceptible externally of the housing when heated to a critical flow temperature, said heater being arranged in heat transfer relationship relative to said thermally responsive element and said wall such that said outer surface of said wall reaches said critical flow temperature and said physical change occurs at substantially the same time said thermally responsive element reaches said predetermined temperature and said change in conductivity state occurs whereby visual inspection of said housing wall reveals the condition of said thermally responsive element, said housing being a multisided, integrally molded structure, one face of said structure being closed by a separately formed wall element, said housing including an inner cavity in which said heater and thermally responsive elements are disposed, said cavity being occupied with a gas, said gas being confined within said cavity to cause a bubble to be formed on a sidewall of said integrally molded structure when the sidewall is elevated to said flow temperature.

Claim 5

A thermal limiter for controlling an electrical circuit comprising a multisided thin walled integrally molded body of thermal plastic material, a rigid separately formed wall carried on said body and closing off a cavity formed therein, said separately formed wall being formed of a material suitable for service in elevated temperatures, a thermally responsive element and a heater element supported in spaced relationship therebetween in said cavity by said wall, electrical connector means extending through said separately formed wall for connecting said elements in said electrical circuit, said heater element being adapted to be electrically energized through said connectors, said thermally responsive element being adapted to change its state of conductivity upon reaching a predetermined temperature to thereby alter the continuity of a circuit connected to at least one of said connectors, said cavity having a volume substantially larger than the combined volumes of said heater element and said thermally responsive element and being occupied by a gas, said heater element being adapted to transfer a substantial portion of its heat by radiation through the gas in said cavity to said thermally responsive element and at least one of the sidewalls of said body, said one sidewall having an area adjacent said heater element adapted to reach a flow temperature and exhibit a resulting physical change on its outer surface, the relative spacing of said heater element to said thermally responsive element and said one sidewall being selected such that the heat transfer relationship between said heater element and said thermally responsive element and between said heater element and said one sidewall are thermally analogous whereby said thermally responsive element is adapted to reach said predetermined temperature substantially simultaneously with the elevation of said one sidewall to its flow temperature such that the resulting physical change on the outer surface of the sidewall indicates the state of conductivity of said thermally responsive element, said cavity being hermetically sealed by a coating applied to an outer side of said separately formed wall, expansion of the gas in said cavity upon energization of said heater element being adapted to cause said adjacent area of said one sidewall to bubble outwardly of the plane of said sidewall.

Claim 6

A thermal limiter for controlling an electrical circuit comprising a multisided thin walled integrally molded body of thermal plastic material, a rigid separately formed wall carried on said body and closing off a cavity formed therein, said separately formed wall being formed of a material suitable for service in elevated temperatures, a thermally responsive element and a heater element supported in spaced relationship therebetween in said cavity by said wall, electrical connector means extending through said separately formed wall for connecting said elements in said electrical circuit, said heater element being adapted to be electrically energized through said connectors, said thermally responsive element being adapted to change its state of conductivity upon reaching a predetermined temperature to thereby alter the continuity of a circuit connected to at least one of said connectors, said cavity having a volume substantially larger than the combined volumes of said heater element and said thermally responsive element and being occupied by a gas, said heater element being adapted to transfer a substantial portion of its heat by radiation through the gas in said cavity to said thermally responsive element and at least one of the sidewalls of said body, said one sidewall having an area adjacent said heater element adapted to reach a flow temperature and exhibit a resulting physical change on its outer surface, the relative spacing of said heater element to said thermally responsive element and said one sidewall being selected such that the heat transfer relationship between said heater element and said thermally responsive element and between said heater element and said one sidewall are thermally analogous whereby said thermally responsive element is adapted to reach said predetermined temperature substantially simultaneously with the elevation of said one sidewall to its flow temperature such that the resulting physical change on the outer surface of the sidewall indicates the state of conductivity of said thermally responsive element, said cavity being hermetically sealed by a coating applied to an outer side of said separately formed wall, expansion of the gas in said cavity upon energization of said heater element being adapted to cause said adjacent area of said one sidewall to bubble outwardly of the plane of said sidewall.

Claim 7

A thermal limiter set forth in claim 3 wherein said coating on the outer side of said separately formed wall fixes the position of said connectors on said separately formed wall.