Heater wire safety circuit

• US 9,320,084 B2
• Filed: 11/20/2012
• Issued: 04/19/2016
• Est. Priority Date: 11/29/2010
• Status: Active Grant

• Current Assignee: Multitech Medical Devices USA LLC
• Original Assignee: Weiss Controls, Inc.
• Inventors: Weiss, John W., Liao, Kuang-Pu
• Primary Examiner(s): Paschall, Mark
• Application Number:
  US13/682,101
• Publication Number:
  US 20130134149A1
• Time in Patent Office: 1,246 Days
• Field of Search: 219/212, 219/505, 219/501, 219/508, 219/481, 442/02
• US Class Current: 1/1
• CPC Class Codes: H05B 1/02 Automatic switching arrangements specially adapted to apparatus ; Control of heating devices thermally-actuated switches H01H37/00
• CPC Class Codes: H05B 2203/02 Heaters using heating elements having a positive temperature coefficient
• CPC Class Codes: H05B 3/146 Conductive polymers, e.g. polyethylene, thermoplastics
• CPC Class Codes: H05B 3/56 Heating cables

Abstract

A dual heater wire circuit for use with a heating pad or electric blanket includes two independent heater wire circuits. Each heater wire circuit includes a heater wire and a temperature sensor conductor. The temperature sensor conductor of each heater wire circuit is connected to a capacitor, or to a resistor, to define with the capacitor or resistor a voltage divider circuit. The juncture between the sensor conductors and either the capacitor or the resistor is provided to the input of a microprocessor. The electrical resistance of the temperature sensor conductors varies with temperature. The signal provided to the microprocessor from the voltage dividers formed between the sensor conductors of the heater wires and either the capacitor or resistor will vary in phase or voltage relative to the temperature of the heater wires. The microprocessor controls the duty cycle of the power signal provided to the heater wires.

Claims

1. A heater wire safety circuit for use with an electric blanket or heating pad, which comprises:

a first heater circuit and a second heater circuit, the first heater circuit including;

1) a first heater wire, the first heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with a source of alternating electrical power; and

d) a first diode, the first diode having an anode and a cathode, the cathode of the first diode being connected to the second end of the first conductor portion of the first heater wire, the anode of the first diode being connected to the first end of the second conductor portion of the first heater wire;

2) a first temperature sensor conductor, the first temperature sensor conductor being disposed in proximity to one of the first conductor portion and the second conductor portion of the first heater wire, the first temperature sensor conductor having a resistance which varies in response to the temperature of at least one of the first conductor portion and the second conductor portion of the first heater wire, the first temperature sensor conductor having a first end and a second end situated opposite the first end thereof; and

3) a second diode, the second diode having an anode and a cathode, the cathode of the second diode being in electrical communication with the source of electrical power and the first end of the first conductor portion of the first heater wire, the anode of the second diode being connected to the first end of the first temperature sensor conductor;

wherein the second heater circuit includes;

1) a second heater wire, the second heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with the source of alternating electrical power; and

d) a third diode, the third diode having an anode and a cathode, the anode of the third diode being connected to the second end of the first conductor portion of the second heater wire, the cathode of the third diode being connected to the first end of the second conductor portion of the second heater wire;

2) a second temperature sensor conductor, the second temperature sensor conductor being disposed in proximity to one of the first conductor portion and the second conductor portion of the second heater wire, the second temperature sensor conductor having a resistance which varies in response to the temperature of at least one of the first conductor portion and the second conductor portion of the second heater wire, the second temperature sensor conductor having a first end and a second end situated opposite the first end thereof; and

3) a fourth diode, the fourth diode having an anode and a cathode, the anode of the fourth diode being in electrical communication with the source of electrical power and the first end of the first conductor portion of the second heater wire, the cathode of the fourth diode being connected to the first end of the second temperature sensor conductor;

and wherein the heater wire safety circuit further comprises;

a capacitor, the capacitor having a first end and a second end, the first end of the capacitor being in electrical communication with the second end of the first temperature sensor conductor of the first heater circuit and being in electrical communication with the second end of the second temperature sensor conductor of the second heater circuit, the capacitor defining with the first temperature sensor conductor and the second temperature sensor conductor a voltage divider circuit, the voltage divider circuit generating a signal thereon which varies in phase angle in response to variations in the resistance of at least one of the first temperature sensor conductor and the second temperature sensor conductor;

a microprocessor, the microprocessor having a signal input, the signal input being in electrical communication with the voltage divider circuit and being provided with the phase-varying signal generated by the voltage divider circuit, the microprocessor generating a trigger signal in response to the phase-varying signal provided on the signal input of the microprocessor; and

a switching device, the switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the switching device being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the power signal input of the switching device being in electrical communication with the source of alternating electrical power, the trigger signal generated by the microprocessor being provided to the trigger signal input of the switching device, the switching device selectively switching between a substantially conductive state and a substantially non-conductive state in response to the trigger signal generated by the microprocessor and provided thereto to facilitate the control of the temperature of at least one of the first heater wire of the first heater circuit and the second heater wire of the second heater circuit.

2. A heater wire safety circuit as defined by claim 1, which further comprises:

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device; and

a crowbar circuit, the crowbar circuit being in electrical communication with the fuse, the crowbar circuit having a crowbar circuit switching device and a crowbar circuit resistor in electrical communication with the crowbar circuit switching device, the crowbar circuit resistor having a first end and a second end opposite the first end, the crowbar circuit switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the crowbar circuit switching device being in electrical communication with the first end of the crowbar circuit resistor, the second end of the crowbar circuit resistor being in electrical communication with the source of alternating electrical power, the power signal input of the crowbar circuit switching device being in electrical communication with the fuse, the microprocessor being in electrical communication with the crowbar circuit switching device and generating a crowbar circuit trigger signal, the crowbar circuit trigger signal being provided to the trigger signal input of the crowbar circuit switching device.

3. A heater wire safety circuit as defined by claim 1, which further comprises:

a polymetric positive temperature coefficient (PPTC) device, the PPTC device having a first end which is in electrical communication with the source of alternating electrical power, and a second end which is in electrical communication with the first end of the first conductor portion of the first heater wire of the first heater circuit and the first end of the first conductor portion of the second heater wire of the second heater circuit; and

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device.

4. A heater wire safety circuit for use with an electric blanket or heating pad, which comprises:

a first heater circuit and a second heater circuit, the first heater circuit including;

1) a first heater wire, the first heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with a source of alternating electrical power; and

d) a first diode, the first diode having an anode and a cathode, the cathode of the first diode being connected to the second end of the first conductor portion of the first heater wire, the anode of the first diode being connected to the first end of the second conductor portion of the first heater wire;

2) a first temperature sensor conductor, the first temperature sensor conductor being disposed in proximity to one of the first conductor portion and the second conductor portion of the first heater wire, the first temperature sensor conductor having a resistance which varies in response to the temperature of at least one of the first conductor portion and the second conductor portion of the first heater wire, the first temperature sensor conductor having a first end and a second end situated opposite the first end thereof; and

3) a second diode, the second diode having an anode and a cathode, the cathode of the second diode being in electrical communication with the source of electrical power and the first end of the first conductor portion of the first heater wire, the anode of the second diode being connected to the first end of the first temperature sensor conductor;

wherein the second heater circuit includes;

1) a second heater wire, the second heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with the source of alternating electrical power; and

d) a third diode, the third diode having an anode and a cathode, the anode of the third diode being connected to the second end of the first conductor portion of the second heater wire, the cathode of the third diode being connected to the first end of the second conductor portion of the second heater wire;

2) a second temperature sensor conductor, the second temperature sensor conductor being disposed in proximity to one of the first conductor portion and the second conductor portion of the second heater wire, the second temperature sensor conductor having a resistance which varies in response to the temperature of at least one of the first conductor portion and the second conductor portion of the second heater wire, the second temperature sensor conductor having a first end and a second end situated opposite the first end thereof; and

3) a fourth diode, the fourth diode having an anode and a cathode, the anode of the fourth diode being in electrical communication with the source of electrical power and the first end of the first conductor portion of the second heater wire, the cathode of the fourth diode being connected to the first end of the second temperature sensor conductor;

and wherein the heater wire safety circuit further comprises;

a resistor, the resistor having a first end and a second end, the first end of the resistor being in electrical communication with the second end of the first temperature sensor conductor of the first heater circuit and being in electrical communication with the second end of the second temperature sensor conductor of the second heater circuit, the resistor defining with the first temperature sensor conductor and the second temperature sensor conductor a voltage divider circuit, the voltage divider circuit generating a signal thereon which varies in magnitude in response to variations in the resistance of at least one of the first temperature sensor conductor and the second temperature sensor conductor;

a microprocessor, the microprocessor having a signal input, the signal input being in electrical communication with the voltage divider circuit and being provided with the magnitude-varying signal generated by the voltage divider circuit, the microprocessor generating a trigger signal in response to the magnitude-varying signal provided on the signal input of the microprocessor; and

a switching device, the switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the switching device being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the power signal input of the switching device being in electrical communication with the source of alternating electrical power, the trigger signal generated by the microprocessor being provided to the trigger signal input of the switching device, the switching device selectively switching between a substantially conductive state and a substantially non-conductive state in response to the trigger signal generated by the microprocessor and provided thereto to facilitate the control of the temperature of at least one of the first heater wire of the first heater circuit and the second heater wire of the second heater circuit.

5. A heater wire safety circuit as defined by claim 4, which further comprises:

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device; and

a crowbar circuit, the crowbar circuit being in electrical communication with the fuse, the crowbar circuit having a crowbar circuit switching device and a crowbar circuit resistor in electrical communication with the crowbar circuit switching device, the crowbar circuit resistor having a first end and a second end opposite the first end, the crowbar circuit switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the crowbar circuit switching device being in electrical communication with the first end of the crowbar circuit resistor, the second end of the crowbar circuit resistor being in electrical communication with the source of alternating electrical power, the power signal input of the crowbar circuit switching device being in electrical communication with the fuse, the microprocessor being in electrical communication with the crowbar circuit switching device and generating a crowbar circuit trigger signal, the crowbar circuit trigger signal being provided to the trigger signal input of the crowbar circuit switching device.

6. A heater wire safety circuit as defined by claim 4, which further comprises:

a polymetric positive temperature coefficient (PPTC) device, the PPTC device having a first end which is in electrical communication with the source of alternating electrical power, and a second end which is in electrical communication with the first end of the first conductor portion of the first heater wire of the first heater circuit and the first end of the first conductor portion of the second heater wire of the second heater circuit; and

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device.

7. A heater wire safety circuit for use with an electric blanket or heating pad, which comprises:

a first heater circuit and a second heater circuit, the first heater circuit including;

1) a first heater wire, the first heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof, at least one of the first conductor portion and the second conductor portion of the first heater wire having a resistance which varies with temperature;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with a source of alternating electrical power; and

d) a first diode, the first diode having an anode and a cathode, the cathode of the first diode being connected to the second end of the first conductor portion of the first heater wire, the anode of the first diode being connected to the first end of the second conductor portion of the first heater wire;

wherein the second heater circuit includes;

1) a second heater wire, the second heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof, at least one of the first conductor portion and the second conductor portion of the second heater wire having a resistance which varies with temperature;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with the source of alternating electrical power; and

d) a second diode, the second diode having an anode and a cathode, the anode of the second diode being connected to the second end of the first conductor portion of the second heater wire, the cathode of the second diode being connected to the first end of the second conductor portion of the second heater wire;

and wherein the heater wire safety circuit further comprises;

a capacitor, the capacitor having a first end and a second end, the first end of the capacitor being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the capacitor defining with the first heater wire and the second heater wire a voltage divider circuit, the voltage divider circuit generating a signal thereon which varies in phase angle in response to variations in the resistance of at least one of the first heater wire and the second heater wire;

a microprocessor, the microprocessor having a signal input, the signal input being in electrical communication with the voltage divider circuit and being provided with the phase-varying signal generated by the voltage divider circuit, the microprocessor generating a trigger signal in response to the phase-varying signal provided on the signal input of the microprocessor; and

a switching device, the switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the switching device being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the power signal input of the switching device being in electrical communication with the source of alternating electrical power, the trigger signal generated by the microprocessor being provided to the trigger signal input of the switching device, the switching device selectively switching between a substantially conductive state and a substantially non-conductive state in response to the trigger signal generated by the microprocessor and provided thereto to facilitate the control of the temperature of at least one of the first heater wire of the first heater circuit and the second heater wire of the second heater circuit.

8. A heater wire safety circuit as defined by claim 7, which further comprises:

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device; and

a crowbar circuit, the crowbar circuit being in electrical communication with the fuse, the crowbar circuit having a crowbar circuit switching device and a crowbar circuit resistor in electrical communication with the crowbar circuit switching device, the crowbar circuit resistor having a first end and a second end opposite the first end, the crowbar circuit switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the crowbar circuit switching device being in electrical communication with the first end of the crowbar circuit resistor, the second end of the crowbar circuit resistor being in electrical communication with the source of alternating electrical power, the power signal input of the crowbar circuit switching device being in electrical communication with the fuse, the microprocessor being in electrical communication with the crowbar circuit switching device and generating a crowbar circuit trigger signal, the crowbar circuit trigger signal being provided to the trigger signal input of the crowbar circuit switching device.

9. A heater wire safety circuit as defined by claim 7, which further comprises:

a polymetric positive temperature coefficient (PPTC) device, the PPTC device having a first end which is in electrical communication with the source of alternating electrical power, and a second end which is in electrical communication with the first end of the first conductor portion of the first heater wire of the first heater circuit and the first end of the first conductor portion of the second heater wire of the second heater circuit; and

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device.

10. A heater wire safety circuit for use with an electric blanket or heating pad, which comprises:

a first heater circuit and a second heater circuit, the first heater circuit including;

1) a first heater wire, the first heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof, at least one of the first conductor portion and the second conductor portion of the first heater wire having a resistance which varies with temperature;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with a source of alternating electrical power, the second end of the first conductor portion being in electrical communications with a source of alternating electrical power; and

d) a first diode, the first diode having an anode and a cathode, the cathode of the first diode being connected to the second end of the first conductor portion of the first heater wire, the anode of the first diode being connected to the first end of the second conductor portion of the first heater wire;

wherein the second heater circuit includes;

1) a second heater wire, the second heater wire having;

a) a first conductor portion;

b) a second conductor portion disposed in proximity to the first conductor portion over at least a portion of the length thereof, the first conductor portion having a first end and a second end situated opposite the first end thereof, the second conductor portion having a first end and a second end situated opposite the first end thereof, at least one of the first conductor portion and the second conductor portion of the second heater wire having a resistance which varies with temperature;

c) a low melt insulate layer situated between the first conductor portion and the second conductor portion along at least a portion of the length of the first conductor portion, the first end of the first conductor portion being in electrical communication with the source of alternating electrical power; and

d) a second diode, the second diode having an anode and a cathode, the anode of the second diode being connected to the second end of the first conductor portion of the second heater wire, the cathode of the second diode being connected to the first end of the second conductor portion of the second heater wire;

and wherein the heater wire safety circuit further comprises;

a resistor, the resistor having a first end and a second end, the first end of the resistor being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the resistor defining with the first heater wire and the second heater wire a voltage divider circuit, the voltage divider circuit generating a signal thereon which varies in magnitude in response to variations in the resistance of at least one of the first heater wire and the second heater wire;

a microprocessor, the microprocessor having a signal input, the signal input being in electrical communication with the voltage divider circuit and being provided with the magnitude-varying signal generated by the voltage divider circuit, the microprocessor generating a trigger signal in response to the magnitude-varying signal provided on the signal input of the microprocessor; and

a switching device, the switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the switching device being in electrical communication with the second end of the second conductor portion of the first heater wire of the first heater circuit and being in electrical communication with the second end of the second conductor portion of the second heater wire of the second heater circuit, the power signal input of the switching device being in electrical communication with the source of alternating electrical power, the trigger signal generated by the microprocessor being provided to the trigger signal input of the switching device, the switching device selectively switching between a substantially conductive state and a substantially non-conductive state in response to the trigger signal generated by the microprocessor and provided thereto to facilitate the control of the temperature of at least one of the first heater wire of the first heater circuit and the second heater wire of the second heater circuit.

11. A heater wire safety circuit as defined by claim 10, which further comprises:

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device; and

a crowbar circuit, the crowbar circuit being in electrical communication with the fuse, the crowbar circuit having a crowbar circuit switching device and a crowbar circuit resistor in electrical communication with the crowbar circuit switching device, the crowbar circuit resistor having a first end and a second end opposite the first end, the crowbar circuit switching device having a trigger signal input, a power signal input and a power signal output, the power signal output of the crowbar circuit switching device being in electrical communication with the first end of the crowbar circuit resistor, the second end of the crowbar circuit resistor being in electrical communication with the source of alternating electrical power, the power signal input of the crowbar circuit switching device being in electrical communication with the fuse, the microprocessor being in electrical communication with the crowbar circuit switching device and generating a crowbar circuit trigger signal, the crowbar circuit trigger signal being provided to the trigger signal input of the crowbar circuit switching device.

12. A heater wire safety circuit as defined by claim 10, which further comprises:

a polymetric positive temperature coefficient (PPTC) device, the PPTC device having a first end which is in electrical communication with the source of alternating electrical power, and a second end which is in electrical communication with the first end of the first conductor portion of the first heater wire of the first heater circuit and the first end of the first conductor portion of the second heater wire of the second heater circuit; and

a fuse, the fuse being in electrical communication with the source of alternating electrical power and being in electrical communication with the power signal input of the switching device.