METHOD AND SYSTEM FOR CONTROLLING A HEATING ELEMENT WITH TEMPERATURE SENSITIVE CONDUCTIVE LAYER

• US 20100237060A1
• Filed: 03/19/2010
• Published: 09/23/2010
• Est. Priority Date: 03/19/2009
• Status: Active Grant

• Current Assignee: Weiss Controls, Inc.
• Original Assignee: Weiss Controls, Inc.
• Inventors: Novikov, Lenny
• Granted Patent: US 8,772,679 B2
• Time in Patent Office: Days
• US Class Current: 219/488
• CPC Class Codes: H05B 1/0272 For heating of fabrics

Abstract

Methods and system for controlling a heater conductor in a heating element including a sensor conductor separated from the heater conductor by an NTC layer. The heating element is coupled to a control circuit and the flow of electricity from a direct current source through the circuit is controlled such that a change of the resistance of the NTC layer is indicative of the temperature of the heater conductor. This resistance is detected based on a time or amplitude analysis and based thereon, a heating mode of the heater conductor is controlled. In a variation, the circuit is operated in a two-period measurement mode wherein the energy transferred through the NTC layer in one period is equal and opposite to the energy transferred through the NTC layer in the other period.

Claims

1. A method for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor and separating them from one another, the method comprising:

heating the heater conductor in a heating mode by causing DC power current from a direct current (DC) source to flow through the heater conductor and increase its temperature;

periodically terminating the heating mode and entering into a measurement mode in which an alternating current (AC) source provides an excitation signal to enable measurement of resistance of the NTC layer; and

controlling initiation of the heating mode based on the measurement of the resistance of the NTC layer in the measurement mode.

2. The method of claim 1, wherein the step of heating the heater conductor comprises:

interposing a first switch between a first end of the heater conductor and the DC source;

interposing a second switch between a second end of the heater conductor and ground; and

closing both switches.

3. The method of claim 1, wherein the DC source is connected to a first end of the heater device, further comprising:

arranging a reactive element relative to the NTC layer and the AC source such that the reactive element is charged and discharged through the NTC layer;

coupling a first input of a phase shift detector to the AC source and a second input of the phase shift detector to said reactive element; and

comparing a phase shift between an output signal from the AC source and an AC signal on the reactive element relative to a preset value, initiation of the heating mode being controlled based on the comparison of the phase shift relative to the pre-set value.

4. The method of claim 3, wherein with rising temperature of the heater conductor, the resistance of the NTC layer and the resulting phase shift decrease such that when the detected phase shift is smaller than the preset value, a further heating of the heater conductor is temporarily suspended.

5. The method of claim 3, further comprising selecting the reactive element to be one of a capacitive element and an inductive element.

6. The method of claim 1, wherein the DC source is connected to a first end of the heater conductor, further comprising:

arranging a resistive element relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

comparing, using a voltage detector, an output voltage of the voltage divider with a preset value, initiation of the heating mode being controlled based on the comparison of the output voltage of the voltage divider relative to the pre-set value.

7. The method of claim 1, wherein the DC source is connected to a first end of the heater conductor, further comprising:

arranging a resistive element relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

comparing, using a voltage detector, a ratio of an output voltage of the voltage divider and the AC source voltage with a preset value, initiation of the heating mode being controlled based on the comparison of said ratio with the pre-set value.

8. The method of claim 5, wherein with an increase in temperature of the heater conductor, the resistance of the NTC layer decreases and the output voltage of the voltage divider increases, and when the voltage detector determines that the output voltage of the voltage divider is greater than the pre-set value, a further heating of the heater conductor is temporarily suspended.

9. The method of claim 1, further comprising:

interposing a first switch between a first end of the heater conductor and the DC source;

interposing a second switch between a second end of the heater conductor and ground; and

interposing a third switch between the sensor conductor and the AC source.

10. The method of claim 1, further comprising:

interposing a first switch between a first end of the sensor conductor and the DC source;

interposing a second switch between a second end of the sensor conductor and ground; and

interposing a third switch between the heater conductor and the AC source.

11. A system for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor and separating them from one another, the system comprising:

a direct current (DC) source;

a first switch operatively coupled between said DC source and a first end of said heater conductor;

a second switch operatively coupled between a second end of said heater conductor and ground;

an alternating current (AC) generator;

a third switch operatively coupled between said AC generator and said sensor conductor; and

a controller that controls heating of the heater conductor in a heating mode by closing said first and second switch while said third switch is open thereby causing DC power current from said DC source to flow through the heater conductor and increase its temperature,

said controller being further arranged to periodically terminate the heating mode and enter the system into a measurement mode in which said AC generator provides an excitation signal to enable measurement of resistance of said NTC layer by opening said first and second switches and closing said third switch,

said controller being further arranged to control initiation of the heating mode based on the measurement of the resistance of the NTC layer in the measurement mode.

12. The system of claim 11, further comprising:

a reactive element arranged relative to the NTC layer and the AC source such that the reactive element is charged and discharged through the NTC layer;

a phase shift detector having a first input operatively coupled to the AC source and a second input operatively coupled to said reactive element; and

a comparator which compares a phase shift between an output signal from the AC source and an AC signal on the reactive element relative to a preset value, wherein initiation of the heating mode being controlled based on the comparison of the phase shift relative to the pre-set value.

13. The system of claim 12, wherein with rising temperature of the heater conductor, the resistance of the NTC layer and the resulting phase shift decrease such that when the detected phase shift is smaller than the pre-set value, said controller is arranged to temporarily suspend a further heater of the heating conductor.

14. The system of claim 12, wherein said reactive element is operatively coupled between said second end of said heater conductor and ground.

15. The system of claim 12, wherein said reactive element is operatively coupled between a second end of said sensor conductor and ground.

16. The system of claim 11, further comprising:

a resistive element operatively arranged relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

a voltage detector operatively coupled to the heater conductor and a voltage divider, the voltage detector comparing an output voltage of the voltage divider with a preset value, wherein initiation of the heating mode being controlled based on the comparison of the output voltage of the voltage divider relative to the pre-set value.

17. The system of claim 11, further comprising:

a resistive element operatively arranged relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

a voltage detector operatively coupled to the voltage divider and the AC source, the voltage detector comparing a ratio of an output voltage of the voltage divider and the AC source voltage with a preset value, wherein initiation of the heating mode being controlled based on the comparison of said ratio with the pre-set value.

18. The system of claim 16, wherein with an increase in temperature of the heater device, the resistance of the NTC layer decreases and the output voltage of the voltage divider increases, and when said voltage detector determines that the output voltage of the voltage divider is greater than the pre-set value, said controller is arranged to temporarily suspend further heating of the heater conductor.

19. A system for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor and separating them from one another, the system comprising:

a direct current (DC) source;

a first switch operatively coupled between said DC source and a first end of said sensor conductor;

a second switch operatively coupled between a second end of said sensor conductor and ground;

an alternating current (AC) generator;

a third switch operatively coupled between said AC generator and said heater conductor; and

a controller that controls heating of the heater conductor in a heating mode by closing said first and second switch while said third switch is open thereby causing DC power current from said DC source to flow through the heater conductor and increase its temperature,

said controller being further arranged to periodically terminate the heating mode and enter the system into a measurement mode in which said AC generator provides an excitation signal to enable measurement of resistance of said NTC layer by opening said first and second switches and closing said third switch,

said controller being further arranged to control initiation of the heating mode based on the measurement of the resistance of the NTC layer in the measurement mode.

20. The system of claim 19, further comprising:

a reactive element arranged relative to the NTC layer and the AC source such that the reactive element is charged and discharged through the NTC layer;

a phase shift detector having a first input operatively coupled to the AC source and a second input operatively coupled to said reactive element; and

a comparator which compares a phase shift between an output signal from the AC source and an AC signal on the reactive element relative to a preset value, wherein initiation of the heating mode being controlled based on the comparison of the phase shift relative to the pre-set value.

21. The system of claim 20, wherein with rising temperature of the heater conductor, the resistance of the NTC layer and the resulting phase shift decrease such that when the detected phase shift is smaller than the pre-set value, said controller is arranged to temporarily suspend a further heating of the heating conductor.

22. The system of claim 20, wherein said reactive element is operatively coupled between said second end of said sensor conductor and ground.

23. The system of claim 20, wherein said reactive element is one of a capacitive element and an inductive element.

24. The system of claim 19, further comprising:

a resistive element operatively arranged relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

a voltage detector operatively coupled to the sensor conductor and a voltage divider, the voltage detector comparing an output voltage of the voltage divider with a preset value, wherein initiation of the heating mode being controlled based on the comparison of the output voltage of the voltage divider relative to the pre-set value.

25. The system of claim 19, further comprising:

a resistive element operatively arranged relative to the NTC layer and the AC source such that the resistive element forms a voltage divider with resistance of said NTC layer; and

a voltage detector operatively coupled to the voltage divider and the AC source, the voltage detector comparing a ratio of an output voltage of the voltage divider and the AC source voltage with a preset value, wherein initiation of the heating mode being controlled based on the comparison of said ratio with the pre-set value.

26. The system of claim 24, wherein with an increase in temperature of the heater device, the resistance of the NTC layer decreases and the output voltage of the voltage divider increases, and when said voltage detector determines that the output voltage of the voltage divider is greater than the pre-set value, said controller is arranged to temporarily suspend further heating of the heating conductor.

27. A method for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater device and the sensor conductor to separate them from one another, the method comprising:

heating the heater conductor in a heating mode by causing DC power current from a direct current (DC) source to flow through the heater conductor and increase its temperature;

periodically terminating the heating mode and entering into a measurement mode in which;

in a first period, closing a switch to cause DC current from the DC source to flow through the NTC layer and charge a capacitor, detecting when the voltage of the capacitor reaches a threshold via a threshold detector, and determining a time delay between closure of the switch and the capacitor reaching the threshold via a time delay detector, and

in a second period following the first period, causing the capacitor to discharge through the NTC layer such that an amount of energy transferred through the NTC layer during the first and second periods is equal; and

controlling initiation of the heating mode via a controller based on the time delay.

28. The method of claim 27, wherein the step of heating the heater conductor comprises:

interposing a first switch between a first end of the heater conductor and the DC source;

interposing a second switch between a second end of the heater conductor and ground; and

closing both switches.

29. The method of claim 27, further comprising heating the sensor conductor during the heating mode by causing DC current from the DC source to flow through the sensor conductor and increase its temperature such that the sensor device acts as a supplementary heater conductor.

30. The method of claim 29, wherein the step of heating the sensor conductor comprises:

interposing a first switch between a first end of the sensor conductor and the DC source;

interposing a second switch between a second end of the sensor conductor and ground; and

closing both switches.

31. The method of claim 27, wherein the time delay is proportional to a resistance of the NTC layer and as the heater conductor increases in temperature, the resistance of the NTC layer and the resulting time delay decrease such that the time delay detector compares the time delay with a preset value and when the detected time delay is smaller than the pre-set value, a further heating of the heater conductor is temporarily suspended.

32. A system for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor to separate them from one another, the system comprising:

a direct current (DC) source;

a first switch operatively coupled between said DC source and a first end of said heater conductor;

a second switch operatively coupled between a second end of said heater conductor and ground;

a third switch operatively coupled between said DC source and a first end of said sensor conductor;

a fourth switch operatively coupled between a second end of said sensor conductor and ground;

a capacitive element arranged relative to said NTC layer to be charged and discharged through said NTC layer;

a controller that controls heating of the heater conductor in a heating mode by closing said first and second switches thereby causing DC power current from said DC source to flow through said heater conductor and increase its temperature, said controller being arranged to periodically terminate the heating mode and enter the system into a measurement mode in which in a first period, said third switch is closed and said first, second and fourth switches are open causing DC power current from said DC source to flow through said NTC layer and charge said capacitive element;

a threshold detector that detects when the voltage of said capacitive element reaches a threshold; and

a time delay detector that determines a time delay between closure of said third switch and said capacitive element reaching the threshold, and

said controller being further arranged to enter the system into a second period of the measurement mode following the first period in which said fourth switch is closed and said first, second and third switches are open to cause said capacitive element to discharge through said NTC layer until said capacitive element is fully discharged, whereby an amount of energy transferred through said NTC layer during the first and second periods is equal,

said controller being further arranged to control initiation of the heating mode based on the time delay detected by said time delay detector.

33. The system of claim 32, wherein said capacitive element is operatively coupled between said second end of said heater conductor and ground.

34. The system of claim 32, wherein said capacitive element is operatively coupled between said second end of said sensor conductor and ground.

35. The system of claim 32, wherein said controller is further arranged to close said third and fourth switches in the heating mode to thereby cause DC power current from said DC source to flow through the sensor conductor and increase its temperature such that the sensor conductor acts as a supplementary heater conductor.

36. The system of claim 32, wherein the time delay is proportional to a resistance of said NTC layer and as said heater conductor increases in temperature, the resistance of said NTC layer and the resulting time delay decrease such that said time delay detector compares the time delay with a preset value and when the detected time delay is smaller than the pre-set value, said controller is arranged to temporarily suspend further heating of the heating conductor.

37. A method for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor to separate them from one another, the method comprising:

heating the heater conductor in a heating mode by causing DC power current from a direct current (DC) source to flow through the heater conductor and increase its temperature;

periodically terminating the heating mode and entering into a measurement mode in which;

in a first measurement period,

causing DC power current from the DC source to flow through the NTC layer in a first direction, and

in a second measurement period following the first measurement period,

causing DC power current from the DC source to flow through the NTC layer in a second direction opposite to the first direction, and

controlling time of the flow of DC power current through the NTC layer in the second direction to provide that energy transferred through the NTC layer in the second measurement period is substantially equal to energy transferred through the NTC layer in the first measurement period; and

controlling initiation of the heating mode via a controller based on the magnitude of the DC current passed through the NTC layer in at least one of the first and second measurement periods.

38. The method of claim 37, wherein the step of causing DC power current from the DC source to flow through the NTC layer in the first direction during the first measurement period comprises developing a voltage drop on a first load resistor, resistance of the NTC layer coupled with the first load resistor forming a voltage divider, the first measurement period further comprising:

comparing, using a voltage detector, an output voltage of the voltage divider with a preset value,

initiation of the heating mode being controlled via the controller based on the comparison of the output voltage of the voltage divider relative to the pre-set value.

39. The method of claim 37, wherein the step of causing DC power current from the DC source to flow through the NTC layer in the first direction during the first measurement period comprises developing a voltage drop on a first load resistor, resistance of the NTC layer coupled with the first load resistor forming a voltage divider, the first measurement period further comprising:

comparing, using a voltage detector, a ratio of an output voltage of the voltage divider and the AC source voltage with a preset value, wherein initiation of the heating mode being controlled via the controller based on the comparison of said ratio with the pre-set value.

40. The method of claim 37, wherein the step of causing DC power current from the DC source to flow through the NTC layer in the second direction during the second measurement period comprises developing a voltage drop on a second load resistor, the step of controlling time of the flow of DC power current through the NTC layer in the second direction comprising controlling the time of the flow of DC power current through the NTC layer based on the voltage drops on the first and second load resistors, resistance of the first and second load resistors and a time of the first measurement period.

41. The method of claim 38, wherein with an increase in temperature of the heater conductor, the resistance of the NTC layer decreases and the output voltage of the voltage divider increases, and when the voltage detector determines that the output voltage of the voltage divider is greater than the pre-set value, a further heating of the heater conductor is temporarily suspended.

42. The method of claim 37, wherein the step of heating the heater conductor comprises:

interposing a first switch between a first end of the heater conductor and the DC source;

interposing a second switch between a second end of the heater conductor and ground; and

closing both switches.

43. The method of claim 37, further comprising heating the sensor conductor during the heating mode by causing DC power current from the DC source to flow through the sensor conductor and increase its temperature such that the sensor conductor acts as a supplementary heater conductor.

44. The method of claim 37, wherein the step of heating the sensor conductor comprises:

interposing a first switch between a first end of the sensor conductor and the DC source;

interposing a second switch between a second end of the sensor conductor and ground; and

closing both switches.

45. The method of claim 37, wherein the step of controlling time of the flow of DC power current through the NTC layer in the second direction during the second measurement period comprises controlling the time based on a time in which DC current flowed through the NTC layer in the first measurement period, and amplitudes of the current through the NTC layer in the first and second measurement periods such that a product of the amplitude and time for the first measurement period equals the product of the amplitude and time for the second measurement period.

46. A system for controlling heating of a heater conductor of a heating element including a sensor conductor and a negative temperature coefficient (NTC) layer interposed between the heater conductor and the sensor conductor to separate them from one another, the system comprising:

a direct current (DC) source;

a first switch operatively coupled between said DC source and a first end of said heater conductor;

a second switch operatively coupled between a second end of said heater conductor and ground;

a third switch operatively coupled between said DC source and a first end of said sensor conductor;

a fourth switch operatively coupled between a second end of said sensor conductor and ground; and

a controller that controls heating of the heater conductor in a heating mode by controlling said switches to cause DC power current from said DC source to flow through said heater conductor and increase its temperature, said controller being arranged to periodically terminate the heating mode and enter the system into a measurement mode in which in a first period, said switches are controlled to cause DC power current from said DC source to flow through said NTC layer in a first direction,

said controller being further arranged to, in a second measurement period following the first measurement period, control said switches to cause DC power current from said DC source to flow through said NTC layer in a second direction,

said controller being further arranged to control a time of the flow of DC power current through said NTC layer in the second direction to provide that energy transferred through said NTC layer in the second measurement period is substantially equal to energy transferred through said NTC layer in the first measurement period and to control initiation of the heating mode based on the energy being transferred through said NTC layer in at least one of the first and second measurement periods.

47. The system of claim 46, further comprising:

a first load resistor;

a second load resistor, said controller being arranged to enter the system into the first period of the measurement mode wherein the DC power current from said DC source flowing through said NTC layer causes a voltage drop to develop on said first load resistor, resistance of the NTC layer coupled with said first load resistor forming a voltage divider, said controller being further arranged to enter the system into the second period of the measurement mode wherein the DC power current from said DC source flowing through said NTC layer develops a voltage drop on said second load resistor; and

a voltage detector arranged to compare an output voltage of said voltage divider with a preset value;

said controller being further arranged to control a time of the flow of DC power current through said NTC layer device based on the voltage drops on said first and second load resistors, resistance of the first and second load resistors and a time of the first measurement period, and to control initiation of the heating mode based on the comparison of the output voltage of the voltage divider relative to the pre-set value.

48. The system of claim 47, wherein said first load resistor is operatively coupled between said second end of said heater conductor and ground, said second load resistor is operatively coupled between said second end of said sensor conductor and ground, further comprising a fifth switch operatively coupled between said second end of said sensor conductor and said second load resistor and which is controlled by said controller.

49. The system of claim 47, wherein with an increase in temperature of said heater conductor, the resistance of said NTC layer decreases and the output voltage of the voltage divider increases, and when said voltage detector determines that the output voltage of the voltage divider is greater than a preset value, said controller is arranged to temporarily suspended further heating of the heater conductor.

50. The system of claim 46, wherein said controller is further arranged to close said first, second, third and fourth switches in the heating mode to thereby cause DC power current from said DC source to flow through the sensor conductor and the heater conductor and increase the temperature of the sensor conductor such that the sensor conductor acts as a supplementary heater device.

51. The system of claim 46, wherein said controller controls the time of the flow of DC power current through said NTC layer in the second direction during the second measurement period based on a time in which DC current flowed through said NTC layer in the first measurement period, and amplitudes of the current through said NTC layer in the first and second measurement periods such that a product of the amplitude and time for the first measurement period equals the product of the amplitude and time for the second measurement period.