초록 ▼

A heating cable for use with an electric underblanket the cable being of the type in which a sensor wire is employed coextensive with a heater wire and separated by a layer of meltable insulating material so that overheat conditions are sensed by contact between the sensor wire and the heater. A num

A heating cable for use with an electric underblanket the cable being of the type in which a sensor wire is employed coextensive with a heater wire and separated by a layer of meltable insulating material so that overheat conditions are sensed by contact between the sensor wire and the heater. A number of helically wound coextensive wires cooperate with switching means to provide overheat temperature sensing at various wattage levels of heating.

대표청구항 ▼

1. The combination comprising a cable having an elongated core of insulating material on which three coextensive and helically wound wires are disposed, said wires being separated by a meltable layer of insulating material which maintains said wires separated at normal operating temperatures and mel

1. The combination comprising a cable having an elongated core of insulating material on which three coextensive and helically wound wires are disposed, said wires being separated by a meltable layer of insulating material which maintains said wires separated at normal operating temperatures and melts under overheat conditions permitting the wires to contact each other, means connecting said wires to a source of electric power whereby when one of said wires functions as a heating element at least one of the other two of said wires may function as a sensor element, means responsive to a reduction in resistance between said sensor element and the other of said wires to disable the power to said cable. 2. The combination of claim 1 wherein said connecting means comprises a switching means which is setable to any one of a plurality of switch positions in which heating elements of different wattage are connected to said power source, at least two of said wires functioning as heating elements at various of said switch positions. 3. The combination of claim 1 wherein said connecting means comprises a switching means which is effective to connect selected ones of said wires across said power source to operate as heating elements, said wires having different resistances to provide various different wattage levels at various selected settings of said switching means, at each of said selected settings at least one of said wires operating as a sensor. 4. The combination of claim 3 wherein said responsive means includes a fuse in series with said switching means, a resistance in series with each sensor element, each said fuse being responsive to current through said resistors to interrupt power to said heaters when there is an overheat condition causing melting of said layer. 5. The combination of claim 1 wherein said sensor element is connected through a resistor to the junction of two oppositely polarized rectifiers which are connected in series across said power source, a fuse connected in series with said cable, said resistor and said fuse being in good heat exchange relationship whereby an overheat condition in said cable produces a reduced resistance or short circuit current in said sensor element which heats said resistor causing said fuse to blow opening the circuit to said cable. 6. The combination comprising a cable having an elongated core on which three coextensive and helically wound wires are disposed, one of said wires being helically wound oppositely from the other two, said wires being separated by a meltable layer of insulating material which maintains said wires separated and insulated from each other at normal operating temperatures and melts under overheat conditions permitting two or three wires to contact each other, manually controlled switching means connecting said wires to a source of electric power whereby two of said wires may function as heating elements while the third of said wires functions as a sensor element, means responsive to a low resistance path between said sensor element and the other of said wires to disable the powerr to said switching means. 7. The combination of claim 6 wherein said wires include a sensor wire wound directly on said core and first and second heater wires wound in the opposite direction from said sensor wire on top of said sensor wire. 8. The combination of claim 7 wherein said first and second heater wires are electrically insulated from each other and from said sensor wire by a meltable insulation coating which surrounds and joins said first and second heater wires as an insulated twin conductor cord which is wound directly on said sensor wire, an insulating jacket extruded over said coating, said wires and said core to enclose and electrically insulate said wires. 9. The combination of claim 6 wherein said switching means includes a manually adjustable switch having three operative positions, said switch having a low wattage position in which a first one of said wires is connected to said power source and a medium wattage position in which a second one of said wires is connected to said power source and a high wattage position in which said first and second wires are connected in parallel to said power source, a half-wave rectifier and a thermal fuse connected in series with said wires in any of said switch positions, a third one of said wires being a sensor wire having both ends connected together and to a resistor in good heat exchange relation to said fuse whereby a reduced resistance or short circuit between said sensor wire and said first and second wires cause said fuse to open the circuit to said cable. 10. The combination of claim 8 wherein said switching means includes a manually adjustable switch having three operative positions, said switch having a low wattage position in which a first one of said wires is connected to said power source and a medium wattage position in which a second one of said wires is connected to said power source and a high wattage position in which said first and second wires are connected in parallel to said power source, a half-wave rectifier and a thermal fuse connected in series with said wires in any of said switch positions, a third one of said wires being a sensor wire having both ends connected together and to a resistor in good heat exchange relation to said fuse whereby a reduced resistance or short circuit between said sensor wire and said first and second wires cause said fuse to open the circuit to said cable. 11. The combination of claim 10 wherein said sensor wire is connected through said resistor to the power source whereby said half-wave rectifier is between the connection and said heating wires. 12. The combination of claim 6 wherein said switch means provides a plurality of different selectable wattage levels when said cable is connected to said power source, only one of said wires functions as a heating element and the other two function as sensing elements at any selected wattage level for said switch means, said switch means at any selected wattage connectng one sensing wire to one side of the power source and one sensing wire to the other side of the power source. 13. The combination of claim 12 wherein said means responsive to a reduced resistance comprises a thermal fuse connected in series with said cable, a pair of resistances each connected in series with one of said sensing wires at any selected wattage, said resistances being in good heat exchange relation with said fuse to open said fuse whenever a short circuit occurs in the portion of the cable to which such sensor wire responds. 14. A heating cable for use in heating pads, underblankets and overblankets comprising an insulating stranded flexible core, a first wire helically wound on said core, second and third wires spaced from each other and helically disposed around said first wire, a first coating of meltable insulating material surrounding said second and third heater wires to maintain them is spaced relation to each other and with respect to said first wire, a jacket of insulating material enclosing said wires and said coating of insulating material, said first wire contacting either said second wire or third wire or both in the event of an overheat condition in which the temperature of said cable exceeds the melting temperature of said coating of insulating material. 15. The heating cable of claim 14 wherein said second and third wires are wound coaxially with said core, said coating of insulating material comprising a first layer and a second layer of insulating material, said first layer surrounding said core and first wire, said second wire being wound on said first layer, said second layer surrounding said second wire and said first layer, said third wire being wound on said second layer, and said jacket surrounding said third wire and said second layer. 16. The heating cable of claim 14 wherein said second and third wires comprise a twin lead conductor wherein said second and third wires are insulated and spaced apart by meltable insulating material, said twin lead connector being wound on said first wire with said second and third wire each being disposed in the configuration of a helix with both helices having the same diameter. 17. A heating pad cable and control adapted for operation at a plurality of different wattages comprising an elongated heating cable having a plurality of conductor wires which are coextensive with each other and are maintained in spaced relation by a meltable insulation, said insulation having a melting temperature such that it softens or melts in the event of a temperature rise which would present hazards to the user of said pad, such melting or softening permitting said wires to contact each other, switch means for operating said cable at a plurality of selected wattage levels, said switch means connecting various of said wires to a source of power to obtain said wattage levels, said switch means also connecting at each wattage level two of said wires to said power source one being connected to each of the two sides of the power source to function as sensor wires in the event of overheat conditions, means responsive to current flow in said sensor wires to disconnect said cable from said source in the event of an overheat condition, one of said sensor wires being operative to disconnect said cable if the overheat occurs at one-half of said cable and the other being operative to disconnect said cable if the overheat occurs at the other half of said cable. 18. The combination of claim 17 wherein said means responsive to current flow comprises a thermal fuse connected in series with said cable and a pair of resistors in good heat transfer relation with said fuse, each said resistor being connected to one of said sensor wires between said sensor wire and its connection to the power source. 19. The combination of claim 18 wherein said switch means has at least three operative manually selectable positions in which said wires are connected to said power source to provide three different wattage levels in said cable, said cable includes three wires a first of which is connected as a sensor in all three switch positions, a second of the three wires functions as a heater at two switch positions and having a half-wave rectifier in series with it at one of these switch positions, a third one of said wires functioning as a sensor wire in the two switch positions in which said second wire functions as a heater and functions as a heater in the switch position in which said second wire functions as a sensor. 20. The combination of claim 19 in which the means connecting said first wire to said power source includes a rectifier which limits current flow to the direction from said first wire to said power source.