Surface heating appliances

Abstract

To detect the deterioration of a cord heater and stop the energization.SOLUTION: A plane warming device 100 according to the present invention includes a cord heater 30 wired to a heating unit 10 and having a heater wire 32, a temperature detection wire 34, and an intermediate layer 33, and a control unit 40 that controls the temperature of the heating unit 10 by alternately switching between energization and de-energization of the heater wire 32 on the basis of temperature information detected by the temperature detection wire 34. The control unit 40 continues de-energization of the heater wire 32 on the basis of information regarding at least one of energization and de-energization of the heater wire 32.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a planar heating device.

Background Art

[0002] Conventionally, a planar heating device using a one-wire type cord heater in which a heater wire and a temperature detection wire are integrally formed is known (see Patent Document 1). Such a planar heating device controls the heater wire to generate heat based on the temperature information detected by the temperature detection wire so as to reach the desired temperature of the user.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if an object is left on the planar heating device for a long time, the heat dissipation property at that position is impaired, and it is locally heat-retained and remains in a high-temperature state. If such a high-temperature state continues, the intermediate layer between the heater wire and the temperature detection wire gradually deteriorates, and there is a risk that the heater wire and the temperature detection wire will short-circuit. Planar heating devices generally have a temperature fuse as a safety device, and when the heater wire and the temperature detection wire short-circuit, the temperature fuse melts. However, depending on the degree of deterioration of the intermediate layer, the temperature fuse may not melt or may melt earlier than expected.

[0005] An object of the present invention is to detect deterioration of a cord heater and stop energization.

Means for Solving the Problems

[0006] The present invention relates to a planar heating device comprising: a cord heater wired to a heating section and having a heater wire, a temperature detection wire, and an intermediate layer located between the heater wire and the temperature detection wire; and a control means that controls the temperature of the heating section by alternately switching the energization of the heater wire and de-energizing it based on temperature information detected by the temperature detection wire, wherein the control means is Regardless of the temperature information detected by the temperature detection line, if the period of energizing and de-energizing the heater wire is below a threshold, if the information regarding the time the heater wire is energized is below a threshold, if the time the heater wire is de-energized is below a threshold, or if the number of times the heater wire is energized or de-energized is above a threshold, then the temperature information detected by the temperature detection line is not affected. The method is characterized by continuing to suspend power supply to the heater wire. [Effects of the Invention]

[0007] According to the present invention, it is possible to detect deterioration of the cord heater and stop the power supply. [Brief explanation of the drawing]

[0008] [Figure 1] This diagram schematically shows the configuration of a surface-type heating device. [Figure 2] This figure shows an example of a general configuration of a cord heater. [Figure 3] This figure shows an example of the internal structure of a surface-type heating device. [Figure 4] This figure shows an example of changes in the voltage of a temperature detection line. [Figure 5] This figure shows an example of temperature changes in a cord heater. [Figure 6] This is a diagram to explain leakage current. [Figure 7] This figure shows an example of how the voltage of the temperature detection line changes when the leakage current increases. [Figure 8] This figure shows an example of the voltage change of the temperature detection line when there is leakage current. [Figure 9] This flowchart shows an example of the process in the first embodiment. [Figure 10] This flowchart shows an example of the processing in the second embodiment. [Figure 11] This flowchart shows an example of the processing in the third embodiment. [Figure 12] This figure shows an example of the configuration of the power supply control unit in the fourth embodiment. [Figure 13]This is a diagram illustrating the process of the power supply control unit. [Figure 14] This flowchart shows an example of the processing in the fourth embodiment. [Figure 15] This figure shows an example of the configuration of the power supply control unit in the fifth embodiment. [Figure 16] This flowchart shows an example of the processing in the fifth embodiment. [Modes for carrying out the invention]

[0009] The surface-type heating device according to this embodiment will be described below with reference to the drawings. In this embodiment, the surface-type heating device is applied to an electric carpet. Figure 1 is a schematic diagram showing an example of the configuration of the surface-type heating device 100. The surface-type heating device 100 starts operating by receiving power, for example, AC 100V.

[0010] The surface-type heating device 100 comprises a heating section 10, a controller 20, and a cord heater 30. The heating section 10 is a surface-shaped area on which the user rests to receive warmth. When viewed from above, the heating section 10 is, for example, rectangular in shape and has a wide area along the horizontal direction. The heating section 10 is constructed by laminating a surface layer, a cushion layer, an insulation layer, etc., from top to bottom. The surface layer is the part that comes into contact with the user and can be made of, for example, felt or polyvinyl chloride (PVC). The cushion layer distributes the force applied to the heating section 10 when the user rests on it, providing elasticity to the user and retaining the heat generated by the cord heater 30. The cushion layer can be made of, for example, urethane. The insulation layer prevents the heat generated by the cord heater 30 from radiating to the floor surface. The insulation layer can be made of, for example, felt.

[0011] The controller 20 alternately switches between energizing and de-energizing the heater wire 32 of the cord heater 30 described below to control the temperature of the heating unit 10. The controller 20 is disposed at a site exposed to the heating unit 10. An electric connection is made between the controller 20 and a temperature setting unit 21 for a user to set the temperature of the heating unit 10 to a desired temperature, and a notification unit 22 for notifying the user of the driving state of the planar heater 100. The temperature setting unit 21 is, for example, a switch for setting a desired temperature level (e.g., Lv1 to Lv5) by a user sliding a knob, and a voltage corresponding to the slid position is input to the controller 20. Here, the temperature level Lv1 corresponds to "weak" where the temperature of the heating unit 10 is low, and the temperature level Lv5 corresponds to "strong" where the temperature of the heating unit 10 is high. The notification unit 22 is, for example, a light emitting unit such as an LED, and notifies the user of the driving state of the planar heater 100 at the current time by changing the lighting time and the extinguishing time.

[0012] The cord heater 30 converts electric power into heat and generates heat when energized. The cord heater 30 is wired to the heating unit 10. Specifically, the cord heater 30 is wired along the planar direction between the cushion layer and the heat insulating layer in the heating unit 10. The cord heater 30 heats the heating unit 10 evenly by wiring it to meander in the planar direction across the entire surface of the heating unit 10 or wiring it in a spiral shape. Note that the cord heater 30 may be wired to the heating unit 10 by previously generating a unit in which the cord heater 30 is sandwiched from above and below by a member such as a sheet-like non-woven fabric and laminating the generated unit between the cushion layer and the heat insulating layer.

[0013] FIG. 2 is a diagram showing an example of the schematic configuration of the cord heater 30. A so-called single-wire type cord heater is used for the cord heater 30. Specifically, the cord heater 30 includes a core 31, a heater wire 32, an intermediate layer 33, a temperature detection wire 34, and an outer skin layer 35. The core 31 is, for example, a polyester resin, and the heater wire 32 is disposed on the outer periphery thereof. The heater wire 32 is a conductor such as a copper alloy, for example, and is disposed so as to be spirally wound around the outer periphery of the core 31. The intermediate layer 33 is a polymer layer such as a nylon resin, for example, and the temperature detection wire 34 is disposed on the outer periphery thereof. The temperature detection wire 34 is a conductor such as nickel, for example, and is disposed so as to be spirally wound around the outer periphery of the intermediate layer 33. The temperature detection wire 34 has a characteristic that its resistance value increases as the temperature rises. The outer skin layer 35 is, for example, polyvinyl chloride and is disposed on the outermost periphery. Note that the cord heater 30 is not limited to the above-described configuration and materials. For example, the heater wire 32 and the temperature detection wire 34 can be arranged in the opposite manner, or other layers can be added and arranged, and the configuration and materials can be changed as appropriate.

[0014] FIG. 3 is a diagram showing an example of the internal configuration of the planar heater 100. As shown in FIG. 3, in addition to the above-described cord heater 30, the planar heater 100 includes a control unit 40 and various elements and circuits. The control unit 40 and various elements and circuits are disposed in the above-described controller 20.

[0015] Among the cord heaters 30 shown in FIG. 3, the resistance H1 is the heater wire 32. One end in the length direction of the heater wire 32 is connected to the contact h1, and the other end is connected to the contact h2. Also, the resistance S1 is the temperature detection wire 34. One end in the longitudinal direction of the temperature detection wire 34 is connected to the contact s1, and the other end is connected to the contact s2. Note that the heater wire 32 and the temperature detection wire 34 are insulated from each other by the intermediate layer 33.

[0016] Furthermore, AC100V power is supplied to contacts v1 and v2 to energize the heater wire 32. Between contact v1 and contact v2, the heater wire 32 (resistor H1), switch SW, and thermal fuse TF1 are connected in series. By energizing the heater wire 32, it generates heat and heats the heating section 10. When switch SW is ON, power is supplied to the heater wire 32, and when it is OFF, power to the heater wire 32 is stopped. Switching the switch SW ON and OFF is done by relay RL or the power supply control unit 50 described later. The thermal fuse TF1 is heated by resistor TF1-R which is integrated with the thermal fuse TF1, and melts when it exceeds a predetermined temperature. When the thermal fuse TF1 melts, power to the heater wire 32 is cut off even if switch SW is ON. Therefore, the heater wire 32 does not generate heat and cannot heat the heating section 10 until it is replaced with a new thermal fuse TF1.

[0017] Furthermore, a control power supply, for example, DC 5V, used for temperature control is supplied from contact u1 to contact u2. Here, the control power supply is supplied by converting AC 100V using a voltage conversion circuit (not shown). Between contact u1 and contact u2, a resistor R1, a variable resistor VR1, a temperature detection line 34 (resistor S1), and a resistor R2 are connected in series. The temperature detection line 34 changes the resistance S1 according to the temperature, and a DC voltage corresponding to the temperature is input to the control unit 40. Resistors R1 and R2 are resistors for voltage division so that the voltage input to the control unit 40 is an appropriate value, and the variable resistor VR1 is a resistor for adjustment according to the type (model) of the surface heating device. In addition, the smoothing circuit 38, which consists of resistor R3 and capacitor C1, is a circuit for smoothing the voltage input to the control unit 40.

[0018] Furthermore, the anodes of diodes D1 and D2 are connected to both ends of the temperature detection line 34, and the cathodes of diodes D1 and D2 are connected together to one end of resistor TF1-R. The anode of diode D3 is connected to the other end of resistor TF1-R, and the cathode of diode D3 is connected between the thermal fuse TF1 and the switch SW.

[0019] The control unit 40 includes an electrical supply control unit 50 and a temperature control unit 60. The power supply control unit 50 controls the power supply to the heater wire 32 of the cord heater 30 when it detects deterioration of the cord heater 30. The processing performed by the power supply control unit 50 will be described later.

[0020] The temperature control unit 60 controls the temperature of the heating unit 10 by alternately switching the power supply to the heater wire 32 on and off based on the temperature information detected by the temperature detection line 34. The temperature control unit 60 includes an AD converter 61, an AD converter 62, a table 63, a selector 64, an upper limit comparator 65a, a lower limit comparator 65b, and a relay switching unit 66.

[0021] The AD converter 61 converts the voltage corresponding to the temperature detected by the temperature detection line 34 into a digital signal and outputs it to the upper comparator 65a and the lower comparator 65b, respectively. The AD converter 62 converts the voltage corresponding to the temperature level set by the temperature setting unit 21 into a digital signal and outputs it to the selector 64. Table 63 holds information on the upper and lower threshold values ​​for each temperature level (Lv1 to Lv5) set by the temperature setting unit 21. For example, if the upper threshold value for temperature level Lv1 is Vrmax1, the lower threshold value for temperature level Lv1 is Vrmin1, the upper threshold value for temperature level Lv5 is Vrmax5, and the lower threshold value for temperature level Lv5 is Vrmin5, then the relationships are Vrmax1>Vrmin1, Vrmax5>Vrmin5, Vrmax5>Vrmax1, and Vrmin5>Vrmin1. The selector 64 extracts upper and lower threshold values ​​corresponding to the temperature level set by the temperature setting unit 21 and outputs them to the upper comparator 65a and the lower comparator 65b, respectively.

[0022] The upper limit comparator 65a compares the voltage value input from the detection line input terminal (hereinafter referred to as the detection line input) which is output based on the temperature detection line 34 with the upper limit threshold, and outputs the result of the comparison to the relay switching unit 66. The lower limit comparator 65b compares the voltage value input from the detection line input with the lower limit threshold, and outputs the result of the comparison to the relay switching unit 66. The relay switching unit 66 switches relay RL on and off based on the comparison results from the upper limit comparator 65a and the lower limit comparator 65b. Specifically, the relay switching unit 66 turns on relay RL when the voltage value of the detection line input is at or below the lower limit threshold. Also, the relay switching unit 66 turns on relay RL when the voltage value of the detection line input reaches the lower limit threshold and then moves into the range between the lower limit threshold and the upper limit threshold. On the other hand, the relay switching unit 66 turns off relay RL when the voltage value of the detection line input is at or above the upper limit threshold. Also, the relay switching unit 66 turns off relay RL when the voltage value of the detection line input reaches the upper limit threshold and then moves into the range between the lower limit threshold and the upper limit threshold. When relay RL is turned on, switch SW is turned on, and power is supplied to heater wire 32. Conversely, when relay RL is turned off, switch SW is turned off, and power is stopped from being supplied to heater wire 32.

[0023] Here, the changes in the voltage of the temperature detection line 34, the change in the energization state of the heater line 32, and the change in the temperature of the cord heater 30, corresponding to the operation of the temperature control unit 60 as described above, will be explained with reference to Figure 4. Note that Figure 4 shows the operation in a normal state where there is no leakage current, in which case the voltage of the temperature detection line 34 and the voltage of the detection line input are the same. Figure 4(a) shows the change in voltage across the temperature detection line 34, Figure 4(b) shows the change in the energized state of the heater line 32, and Figure 4(c) shows the change in temperature of the cord heater 30. Note that the voltage across the temperature detection line 34 shown here is the voltage value that has been smoothed by the smoothing circuit 38 and output to the control unit 40.

[0024] The voltage value Va1 shown in Figure 4(a) is the voltage value of the temperature detection line 34 when the temperature of the cord heater 30 is rising. Here, since the voltage value has reached the lower threshold and then moved into the range between the lower and upper thresholds, relay RL is on, and as shown in Figure 4(b), the heater wire 32 is energized (on state). Therefore, as shown in Figure 4(c), the temperature of the cord heater 30 continues to rise. Note that the on state shown in Figure 4(b) is indicated by time in HHs. Subsequently, when the voltage value reaches the upper threshold, relay RL turns off, and the power supply to the heater wire 32 is stopped (off state). Also, as the power supply to the heater wire 32 is stopped, the temperature of the cord heater 30 decreases from Toff.

[0025] The voltage value Vb1 shown in Figure 4(a) is the voltage value of the temperature detection line 34 when the temperature of the cord heater 30 is decreasing due to the de-energization of the heater wire 32. Here, since the voltage value has reached the upper threshold and then moved to the range between the lower and upper thresholds, relay RL is off, and as shown in Figure 4(b), the power supply to the heater wire 32 is stopped (off state). Therefore, as shown in Figure 4(c), the temperature of the cord heater 30 continues to decrease. The time of the off state shown in Figure 4(b) is indicated by HLs. Subsequently, when the voltage value reaches the lower threshold, relay RL turns on, and power is supplied to the heater wire 32 (on state). With the power supplied to the heater wire 32, the temperature of the cord heater 30 rises from Ton. As shown in Figure 4(a), the voltage value of the temperature detection line 34 repeatedly rises and falls between the lower threshold and the upper threshold, causing the energization of the heater line 32 to alternately switch on and off, as shown in Figure 4(b), and the temperature of the cord heater 30 repeatedly rises and falls, as shown in Figure 4(c). Furthermore, as the temperature level set in the temperature setting unit 21 increases, the lower and upper threshold values ​​compared in the upper comparator 65a and lower comparator 65b also increase. Therefore, the higher the temperature level set in the temperature setting unit 21, the more the cord heater 30 will repeatedly rise and fall at higher temperatures.

[0026] Figure 5 shows an example of the changes in the temperature of the cord heater 30 and the surface temperature of the heating section 10 after power is supplied to the surface heating device 100. The period of temperature rise and fall of the cord heater 30 shown in Figure 5 is the same as the period of temperature rise and fall of the cord heater 30 shown in Figure 4(c), and Figure 5 is a graph in which the time on the horizontal axis is set to be longer than the time on the horizontal axis in Figure 4(c). The unit of the horizontal axis in Figure 5 is time [h (hour)].

[0027] As shown in Figure 5, as the temperature of the cord heater 30 repeatedly rises and falls, the surface temperature of the heating section 10 also repeatedly rises and falls in approximately the same cycle. At this time, the surface temperature of the heating section 10 also rises and falls in the same way as the temperature of the cord heater 30, according to the temperature level set by the temperature setting unit 21. The temperature range between the upper and lower limits of the surface temperature of the heating section 10 is smaller than the temperature range between the upper and lower limits of the cord heater 30, and the temperature change is such that it does not bother the user. In this way, the temperature control unit 60 controls the temperature of the heating unit 10 by alternately switching the power supply to the heater wire 32 on and off based on the temperature information detected by the temperature detection line 34.

[0028] Next, we will explain how to detect the deterioration of the cord heater 30. Figure 6 shows the state in which leakage current is generated due to the deterioration of the cord heater 30. Specifically, Figure 6(a) shows the leakage current when the AC power supply is a positive half-wave, and Figure 6(b) shows the leakage current when the AC power supply is a negative half-wave. The intermediate layer 33 of the cord heater 30 deteriorates as the ambient temperature rises, and its insulation resistance decreases as it deteriorates. As the insulation resistance of the intermediate layer 33 decreases, the alternating current flowing through the heater wire 32 leaks through the intermediate layer 33 to the temperature detection wire 34.

[0029] As shown in Figure 6(a), when the AC power supply is a positive half-wave, contact v1 is positive and contact v2 is negative. The leakage current leaking from the heater wire 32 through the intermediate layer 33 to the temperature detection wire 34 flows to the smoothing circuit 38 via contact s1 and branch point A, and also flows to the control GND via contact s2. Note that when the AC power supply is a positive half-wave, the voltage on the diode D1 and D2 side is higher than that on contacts s1 and s2, so the leakage current does not flow from contacts s1 and s2 to diode D1 and D2. As the leakage current flows to the smoothing circuit 38 via contact s1 and branch point A, a voltage corresponding to the leakage current is added to the voltage detected by the temperature detection wire 34 and input to the control unit 40.

[0030] As shown in Figure 6(b), when the AC power supply is a negative half-wave, contact v1 is negative and contact v2 is positive. The leakage current that leaks from the heater wire 32 through the intermediate layer 33 to the temperature detection wire 34 flows through contacts s1 and s2 to diodes D1 and D2, then to resistor TF1-R and diode D3. Note that when the AC power supply is a negative half-wave, the voltage on the branch point A side is higher than the voltage on the diode D1 and D2 side, so the leakage current does not flow to branch point A side. Furthermore, if the deterioration of the intermediate layer 33 progresses further, the heater wire 32 and the temperature detection wire 34 will be short-circuited, causing the leakage current to flow further to resistor TF1-R, which will heat up and become hot, causing the thermal fuse TF1 to blow. When the thermal fuse TF1 blows, the power supply to the heater wire 32 is cut off even when the switch SW is on, and it functions as the final protection circuit.

[0031] Now, focusing on the voltage at branch point A shown in Figures 6(a) and 6(b), a voltage corresponding to the leakage current is generated at branch point A only when the AC power supply is in the positive half-wave. On the other hand, focusing on the voltage input to the control unit 40 of the circuit shown in Figures 6(a) and 6(b), the voltage corresponding to the leakage current, which was generated only when the AC power supply was in the positive half-wave, is smoothed by the smoothing circuit 38.

[0032] Figure 7 shows the change in voltage detected in response to leakage current. Here, the AC power supply is assumed to be 60Hz. As shown in Figure 7, when the leakage current is low, a voltage dv corresponding to the leakage current is generated at branch point A every 1 / 60th of a second, i.e., every half wave of AC. This voltage dv corresponding to the leakage current is smoothed by the smoothing circuit 38 to become voltage adv (see "Smoothed Value" shown in Figure 7). As a result, the voltage detected by the temperature detection line 34 plus the voltage adv corresponding to the leakage current is input to the control unit 40. Furthermore, as the leakage current increases, a voltage dv+ higher than voltage dv is generated at branch point A every 1 / 60th of a second, corresponding to the leakage current (see the dashed line in Figure 7). This voltage dv+ corresponding to the leakage current is smoothed by the smoothing circuit 38, resulting in a voltage adv+ higher than voltage adv. As a result, the voltage detected by the temperature detection line 34 plus the voltage adv+ corresponding to the leakage current is input to the control unit 40.

[0033] Thus, when the voltage added according to the leakage current is input to the control unit 40, the changes in the voltage of the temperature detection line 34 and other behaviors will differ compared to the case where no current is leaking and only the voltage detected by the temperature detection line 34 is input to the control unit 40. Specifically, the changes in the voltage of the temperature detection line 34, the changes in the energization state to the heater line 32, and the changes in the temperature of the cord heater 30 in accordance with the operation of the temperature control unit 60 when the voltage added according to the leakage current is input to the control unit 40 will be explained with reference to Figure 8.

[0034] Figure 8(a) shows the change in voltage of the temperature detection line 34. The change in voltage of the temperature detection line 34 when there is leakage current is shown by a solid line, and the change in voltage of the temperature detection line 34 when there is no leakage current is shown by a dashed line. Note that the change in voltage of the temperature detection line 34 when there is no leakage current is the same as the change of the solid line in Figure 4(a). Figure 8(b) shows the change in the energized state of the heater wire 32. The change in the energized state when there is leakage current is shown by a solid line, and the change in the energized state when there is no leakage current is shown by a dashed line. Note that the change in the energized state when there is no leakage current is the same as the change of the solid line in Figure 4(b). Figure 8(c) shows the change in temperature of the cord heater 30. The change in temperature of the cord heater 30 when there is leakage current is shown by a solid line, and the change in temperature of the cord heater 30 when there is no leakage current is shown by a dashed line. Note that the change in temperature of the cord heater 30 when there is no leakage current is the same as the change of the solid line in Figure 4(c).

[0035] The voltage value Va2 shown in Figure 8(a) is the voltage value of the temperature detection line 34 when the temperature of the cord heater 30 is rising. The voltage value Va2 is the same as the voltage value Va1 when there is no leakage current, with a voltage Δv (offset Δv) added to it. The voltage Δv corresponds to the voltage adv and voltage adv+ shown in Figure 7. Here, as shown in Figure 8(b), the heater line 32 is energized (on state), and as shown in Figure 8(c), the temperature of the cord heater 30 continues to rise. After this, the voltage value reaches the upper limit threshold faster due to the addition of voltage Δv, causing the relay RL to turn off and the power supply to the heater line 32 to stop (off state). Therefore, as shown in Figure 8(b), the on state time HH is shorter than the on state time HHs when there is no leakage current because the power supply to the heater line 32 is stopped earlier due to the voltage value reaching the upper limit threshold faster. Furthermore, as shown in Figure 8(c), the temperature of the cord heater 30 begins to decrease faster before reaching temperature Toff compared to when there is no leakage current, because the current to the heater wire 32 is stopped earlier. Also, as shown in Figure 8(a), when the voltage value reaches the upper limit threshold, the current to the heater wire 32 is stopped, eliminating the leakage current itself. As a result, the addition of voltage Δv immediately disappears, and the voltage value of the temperature detection line 34 returns to the voltage value of the dashed line shown in Figure 8(a) when there is no leakage current, and then gradually decreases.

[0036] The voltage value Vb2 shown in Figure 8(a) is the voltage value of the temperature detection line 34 when the temperature of the cord heater 30 is decreasing due to the cessation of power to the heater wire 32. Here, the relay RL is off, and the power supply to the heater wire 32 is stopped (off state) as shown in Figure 8(b). Therefore, as shown in Figure 8(c), the temperature of the cord heater 30 continues to decrease. Subsequently, the voltage value reaches the lower threshold earlier because the addition of voltage Δv has been eliminated, so the relay RL turns on and power is supplied to the heater wire 32 (on state). Therefore, as shown in Figure 8(b), the off state time HL is shorter than the off state time HLs when there is no leakage current because power is supplied to the heater wire 32 earlier because the voltage value reaches the lower threshold earlier. Also, as shown in Figure 8(c), the temperature of the cord heater 30 starts to rise earlier than when there is no leakage current because power is supplied to the heater wire 32 earlier.

[0037] Similarly, due to the effects of the voltage value of the temperature detection line 34 being increased by voltage Δv, and the immediate cancellation of this increase, the ON state time HH during which the heater line 32 is energized, and the OFF state time HL during which the energization is stopped, become shorter than when there is no leakage current. As a result, the cycle of energization and de-energization of the heater line 32 becomes shorter. In addition, the cycle of temperature rise and fall of the cord heater 30 also becomes shorter, and the temperature of the cord heater 30 (average temperature) decreases because it does not reach the temperature Toff that occurs when there is no leakage current. Furthermore, as the leakage current increases, the voltage Δv increases, and therefore the cycle of energizing and de-energizing the heater wire 32 becomes shorter as the leakage current increases. Similarly, as the leakage current increases, the cycle of temperature rise and fall of the cord heater 30 also becomes shorter, and the temperature (average temperature) of the cord heater 30 decreases.

[0038] In this embodiment, the power supply control unit 50 detects deterioration of the cord heater 30 before the thermal fuse TF1 blows, based on the various changes described above caused by the generation of leakage current, and stops the power supply to the heater wire 32, and continues to stop the power supply. The specific processing by the power supply control unit 50 will be described below with reference to a flowchart. (First embodiment) In the first embodiment, the power supply control unit 50 continues to de-energize the heater wire 32 based on information regarding the energization and de-energization of the heater wire 32, specifically, the cycle of energization and de-energization of the heater wire 32. Figure 9 is a flowchart showing an example of processing by the power supply control unit 50 in the first embodiment. In the flowcharts from Figure 9 onward, the power supply control unit 50 executes a program stored in its memory.

[0039] In S10, the power supply control unit 50 obtains the ON state time HH for which the heater wire 32 is energized (see Figure 8(b)). The power supply control unit 50 obtains the ON state time HH for which the heater wire 32 is energized by measuring the time for which the relay switching unit 66 outputs an ON signal to relay RL. However, the power supply control unit 50 may also obtain the ON state time HH by measuring the time for which relay RL is ON, or the time for which switch SW is ON.

[0040] In S11, the power supply control unit 50 obtains the time HL during which power is stopped from the heater wire 32 (see Figure 8(b)). The power supply control unit 50 obtains the time HL during which power is stopped from the heater wire 32 by measuring the time during which the relay switching unit 66 outputs an OFF signal to the relay RL. However, the power supply control unit 50 may also obtain the time HL during which the relay RL is OFF, or the time during which the switch SW is OFF.

[0041] In S12, the power supply control unit 50 acquires the power supply and de-energy supply cycles. The power supply control unit 50 acquires the power supply and de-energy supply cycles by adding the ON state time HH and the OFF state time HL. As described above, as the leakage current increases, the power supply and de-energy supply cycles for the heater wire 32 become shorter.

[0042] In S13, the power supply control unit 50 calculates the difference between the acquired power supply and power supply deactivation periods and the power supply and power supply deactivation periods when there is no leakage current. The power supply and power supply deactivation periods when there is no leakage current correspond to the sum of the ON state time HHs and the OFF state time HLs shown in Figure 4(b), and are stored in the memory of the power supply control unit 50 in advance. The power supply control unit 50 may also repeat steps S10 to S13 multiple times to calculate the average value of the difference.

[0043] In S14, the power supply control unit 50 determines whether the period difference is greater than or equal to a predetermined value (threshold Ta). If it is greater than or equal to the predetermined value, the process proceeds to S15; otherwise, it returns to S10. The predetermined value is stored in the memory of the power supply control unit 50 in advance and remains constant regardless of the temperature level set by the temperature setting unit 21. The predetermined value is set to be smaller than the difference between the period of power supply and de-energy supply when the thermal fuse TF1 is blown (immediately before) and the period of power supply and de-energy supply when there is no leakage current. The period difference may be an average value calculated by repeating S10 to S13 multiple times.

[0044] In S15, the power supply control unit 50 determines that the cord heater 30 is degraded and, regardless of the temperature information detected by the temperature detection line 34, cuts off the power supply to the heater wire 32 and continues to do so. Specifically, the power supply control unit 50 continues to cut off the power supply to the heater wire 32 by turning off the relay RL or the switch SW via a safety circuit (not shown). The power supply cut-off process by the power supply control unit 50 takes precedence over the temperature control process by the temperature control unit 60. The power supply control unit 50 also informs the user that the power supply is being cut off due to the degradation of the cord heater 30 by changing the time the notification unit 22 is lit and the time it is turned off.

[0045] As described above, according to this embodiment, by continuously stopping the power supply to the heater wire 32 based on the power supply and de-power supply cycle, deterioration of the cord heater 30 can be detected early before the thermal fuse TF1 blows. Furthermore, since the power supply and de-power supply cycle is longer than the period of the AC power supply waveform, it is not necessary to measure the cycle with high precision, thus enabling low-cost detection of deterioration of the cord heater 30.

[0046] In the first embodiment, the case in which a cycle of energization and de-energization is used was described, but if the difference between the ON state time HH, during which the heater wire 32 is energized, and the ON state time HHs, when there is no leakage current, is greater than or equal to a predetermined value (threshold Tb), the de-energization of the heater wire 32 may be continued. Also, if the difference between the OFF state time HL, during which the heater wire 32 is not energized, and the OFF state time HLs, when there is no leakage current, is greater than or equal to a predetermined value (threshold Tc), the de-energization of the heater wire 32 may be continued. Furthermore, the power supply to the heater wire 32 may be kept off if the ON state time HH (when the heater wire 32 is energized) is less than or equal to a predetermined time (threshold Td). Similarly, the power supply to the heater wire 32 may be kept off if the OFF state time HL (when the heater wire 32 is not energized) is less than or equal to a predetermined time (threshold Te). Additionally, the power supply to the heater wire 32 may be kept off if the measured energization and de-energy supply period is less than or equal to a predetermined period (threshold Tf).

[0047] (Second example) In the second embodiment, the power supply control unit 50 continues to deactivate the heater wire 32 based on information regarding the energization and deactivation of the heater wire 32, specifically the number of times the heater wire 32 has been energized and deactivated. Figure 10 is a flowchart showing an example of processing by the power supply control unit 50 in the second embodiment.

[0048] In S20, the power supply control unit 50 counts the number of times the heater wire 32 is energized and de-energized, and adds this to the first counter. The power supply control unit 50 adds "1" to the first counter when the power is energized, and then adds "1" to the first counter when the power is de-energized. The power supply control unit 50 counts the number of times the power is energized and de-energized by counting the number of times the relay RL is turned on and off, or by counting the number of times the switch SW is turned on and off. As described above, as the leakage current increases, the cycle of energizing and de-energizing the heater wire 32 becomes shorter, so as the leakage current increases, the number of times the power is energized and de-energized in a given time period becomes larger.

[0049] In S21, the power supply control unit 50 determines whether the number of times counted within a certain period of time (first counter) has exceeded a predetermined number (threshold N, for example, 10 times). If it has exceeded the predetermined number, "1" is added to the second counter and the process proceeds to S22. On the other hand, if it has not exceeded the predetermined number, the process returns to S20 and continues counting the number of times power is supplied and desupplied. The threshold N is stored in the memory of the power supply control unit 50 in advance and is constant regardless of the temperature level set by the temperature setting unit 21. Furthermore, the threshold N is set to be less than the number of times power is supplied and desupplied to the heater wire 32 when the thermal fuse blows.

[0050] In S22, the power supply control unit 50 determines whether the number of times the number of counts (first counter) has been equal to or greater than a predetermined number for a predetermined number of consecutive times (threshold M, for example, 3 times) during a certain period of time. That is, it determines whether the second counter has been continuously incremented and reached a predetermined number of times (threshold M, for example, 3 times). If it has been the predetermined number of consecutive times, the process proceeds to S23. On the other hand, if it has not been the predetermined number of consecutive times, the process returns to S20, resets the counted numbers (first counter and second counter), and continues counting the number of times the power has been supplied and the power has been cut off.

[0051] In S23, the power supply control unit 50 determines that the cord heater 30 is degraded and, regardless of the temperature information detected by the temperature detection line 34, stops the power supply to the heater line 32 and continues to stop the power supply. This process is the same as the process in S15 described above. Thus, according to this embodiment, by continuing to interrupt the power supply to the heater wire 32 based on the number of times power is supplied and then cut off, deterioration of the cord heater 30 can be detected early before the thermal fuse TF1 blows.

[0052] In the second embodiment, the case of counting the number of times the power was turned on and off was described, but it is also possible to count only the number of times the power was turned on and determine whether the number of times counted within a certain period of time reached a predetermined number (threshold N / 2, for example, 5 times) or more, or to count only the number of times the power was turned off and determine whether the number of times counted within a certain period of time reached a predetermined number (threshold N / 2, for example, 5 times) or more. Furthermore, if the number of times counted reaches a predetermined number before a certain period of time has elapsed, the count may be reset without waiting for the certain period of time to elapse, and the timing of the next certain period of time may be started and the number of times the power was turned on and off may be counted. In this way, by starting the timing of the next certain period of time without waiting for the certain period of time to elapse, deterioration of the cord heater 30 can be detected earlier.

[0053] (Third embodiment) In the third embodiment, the power supply control unit 50 continues to shut off the power supply to the heater wire 32 based on information regarding the temperature of the cord heater 30, specifically the average temperature of the cord heater 30. Figure 11 is a flowchart showing an example of processing by the power supply control unit 50 in the third embodiment. In the third embodiment, the surface heating device 100 has a temperature sensor that measures the temperature of the cord heater 30. Preferably, the temperature sensor can measure at multiple points on the cord heater 30, and for example, a film-type multi-point sensor that is attached to the cord heater 30 separately from the cord heater 30 can be used. The temperature information measured by the temperature sensor is input to the power supply control unit 50.

[0054] In S30, the power supply control unit 50 continuously acquires temperature information from temperature sensors at multiple points on the cord heater 30 over a certain period of time. The power supply control unit 50 stores the acquired temperature information of the cord heater 30. In S31, the power supply control unit 50 calculates the average temperature of the cord heater 30 from the temperature information obtained from multiple points. As described above, the average temperature of the cord heater 30 decreases as the leakage current increases.

[0055] In S32, the power supply control unit 50 calculates the difference between the calculated average temperature of the cord heater 30 and the average temperature of the cord heater 30 when there is no leakage current. The average temperature of the cord heater 30 when there is no leakage current is the temperature corresponding to the temperature level set by the temperature setting unit 21 and is stored in the memory of the power supply control unit 50 in advance. The power supply control unit 50 may also repeat steps S30 to S32 multiple times to calculate the average value of the difference.

[0056] In S33, the power supply control unit 50 determines whether the temperature difference is greater than or equal to a predetermined value (threshold Tg). If it is greater than or equal to the predetermined value, the process proceeds to S33; otherwise, it returns to S30. The predetermined value is stored in the memory of the power supply control unit 50 in advance and remains constant regardless of the temperature level set by the temperature setting unit 21. The predetermined value is set to be smaller than the difference between the average temperature of the cord heater 30 when the thermal fuse TF1 blows and the average temperature of the cord heater 30 when there is no leakage current. The temperature difference may be the average value calculated by repeating steps S30 to S32 multiple times.

[0057] In S34, the power supply control unit 50 determines that the cord heater 30 is degraded and, regardless of the temperature information detected by the temperature detection line 34, stops the power supply to the heater line 32 and continues to stop the power supply. This process is the same as the process in S15 described above. Thus, according to this embodiment, by continuously stopping the power supply to the heater wire 32 based on the temperature of the cord heater 30, deterioration of the cord heater 30 can be detected early before the thermal fuse TF1 blows.

[0058] In the third embodiment, we described a case where temperature information at multiple points on the cord heater 30 is continuously acquired over a certain period of time and the average temperature is calculated. However, the temperature at which the temperature switches from rising to falling (upper limit temperature) and the temperature at which the temperature switches from falling to rising (lower limit temperature) at multiple points on the cord heater 30 may also be stored, and the average temperature may be calculated from the upper and lower limit temperatures at multiple points. Alternatively, the upper limit average temperature may be calculated by averaging only the upper limit temperatures at multiple points over a certain period of time, and the difference between this average temperature and the upper limit average temperature of the cord heater 30 when there is no leakage current may be calculated to determine whether or not it is above a predetermined value (threshold Th).

[0059] Alternatively, the power supply to the heater wire 32 may be kept off if the average temperature at multiple points on the cord heater 30 is compared with a predetermined temperature (threshold Ti) and the temperature is above the predetermined temperature. Alternatively, the power supply to the heater wire 32 may be kept off if the upper limit average temperature at multiple points on the cord heater 30 is compared with a predetermined temperature (threshold Tj) and the temperature is above the predetermined temperature.

[0060] Furthermore, the deterioration of the cord heater 30 may be detected by replacing the energization and deenergization cycle of the first embodiment with the cycle when the temperature of the cord heater 30 switches from rising to falling, replacing the ON state time HH when the heater wire 32 is energized in the first embodiment with the time when the temperature of the cord heater 30 is rising, or replacing the OFF state time HL when the heater wire 32 is not energized in the first embodiment with the time when the temperature of the cord heater 30 is falling.

[0061] (Fourth embodiment) In the fourth embodiment, the power supply control unit 50 continues to shut off the power supply to the heater wire 32 based on the voltage information, which is added to the voltage detected by the temperature detection line 34 according to the leakage current. Figure 12 shows an example of the internal configuration of the surface-type heating device 100 according to the fourth embodiment. Here, a block diagram of the power supply control unit 50 for the surface-type heating device 100 has been added. The power supply control unit 50 includes a half-wave rectification and zero-crossing detection unit 121, a sampling pulse generation unit 122, a voltage detection unit 123, a subtractor 124, a comparator 125, and a smoothing circuit 38.

[0062] The half-wave rectification and zero-crossing detection unit 121 detects the timing of the negative half-wave of the AC power supply, which does not produce a voltage corresponding to the leakage current even when there is leakage current. The sampling pulse generation unit 122 generates sampling pulses based on the negative half-wave timing detected by the half-wave rectification and zero-crossing detection unit 121.

[0063] Figure 13 is a diagram illustrating the processing performed by the half-wave rectification and zero-crossing detection unit 121 and the sampling pulse generation unit 122. Figure 13(a) shows the waveform of the AC power input to the half-wave rectifier and zero-cross detection unit 121. The half-wave rectifier and zero-cross detection unit 121 rectifies the negative half-waves of the input AC power based on its waveform. Figure 13(b) shows the waveform after rectifying a negative half-wave. The half-wave rectification and zero-crossing detection unit 121 detects the timing when the voltage value crosses 0[V] (zero-crossing) based on the rectified waveform. Figure 13(c) shows the waveform after detecting the timing when the voltage value crosses 0[V] (zero crossing). The sampling pulse generation unit 122 generates sampling pulses at predetermined time intervals from the timing when the voltage is generated. Figure 13(d) shows the timing for generating sampling pulses. The sampling pulse generation unit 122 outputs the generated sampling pulses to the voltage detection unit 123.

[0064] The voltage detection unit 123 receives the voltage value of the temperature detection line 34 before smoothing at branch point A. The voltage detection unit 123 measures the voltage value of the temperature detection line 34 at the timing of the sampling pulse output from the sampling pulse generation unit 122. Therefore, the voltage detection unit 123 can measure the voltage value Vso of the temperature detection line 34 as if there were no leakage current, even when there is leakage current.

[0065] The smoothing circuit 38 smooths the voltage value of the temperature detection line 34 at branch point A. Therefore, if there is leakage current, the smoothing circuit 38 outputs a voltage value (Vso + ΔV) that is added according to the leakage current. If there is no leakage current, the smoothing circuit 38 outputs the voltage value Vso of the temperature detection line 34.

[0066] The subtractor 124 subtracts the voltage value measured by the voltage detection unit 123 from the voltage value output by the smoothing circuit 38, and outputs the subtracted value to the comparator 125. For example, if there is leakage current, the subtractor 124 subtracts the voltage value Vso measured by the voltage detection unit 123 from the voltage value (Vso + ΔV) added according to the leakage current output by the smoothing circuit 38, and outputs the voltage value ΔV to the comparator 125. The comparator 125 compares the voltage value output from the subtractor 124 with a predetermined threshold. If the voltage value is greater than or equal to the predetermined threshold, it cuts off the power supply to the heater wire 32 and continues to cut off the power supply.

[0067] Figure 14 is a flowchart showing an example of processing by the power supply control unit 50 of the fourth embodiment. In S40, the power supply control unit 50 acquires the voltage value of the temperature detection line 34 after it has been smoothed by the smoothing circuit 38 during the time that the heater line 32 is energized. Specifically, the power supply control unit 50 can acquire the voltage value of the temperature detection line 34 after it has been smoothed by measuring the voltage value input to the control unit 40. As described above, the voltage value of the temperature detection line 34 increases as the leakage current increases.

[0068] In S41, the power supply control unit 50 calculates the difference between the acquired voltage value of the temperature detection line 34 and the voltage value of the temperature detection line 34 when there is no leakage current. Here, the voltage value of the temperature detection line 34 when there is no leakage current can be obtained by the voltage detection unit 123 measuring the voltage value of the temperature detection line 34 at the timing of the sampling pulse generated by the sampling pulse generation unit 122, as described above. Note that the voltage value of the temperature detection line 34 when there is no leakage current may be stored in the memory of the power supply control unit 50 in advance with a value corresponding to the temperature level set by the temperature setting unit 21. The power supply control unit 50 may also repeat steps S40 to S41 multiple times to calculate the average value of the difference.

[0069] In S42, the power supply control unit 50 determines whether the voltage difference is greater than or equal to a predetermined value (threshold Vc). If it is greater than or equal to the predetermined value, the process proceeds to S43; otherwise, it returns to S40. The predetermined value is stored in the memory of the power supply control unit 50 in advance and remains constant regardless of the temperature level set by the temperature setting unit 21. The predetermined value is set to be smaller than the difference between the voltage value when the thermal fuse blows and the voltage value when there is no leakage current. Note that the voltage difference may be an average value calculated by repeating steps S40 to S41 multiple times.

[0070] In S43, the power supply control unit 50 determines that the cord heater 30 is degraded, and stops the power supply to the heater wire 32, and continues to stop the power supply. This process is the same as the process in S15 described above. Thus, according to this embodiment, by continuing to stop the power supply to the heater wire 32 based on the temperature information of the temperature detection line 34 after it has been smoothed by the smoothing circuit 38, deterioration of the cord heater 30 can be detected early before the thermal fuse TF1 blows.

[0071] In the fourth embodiment, the case of calculating the difference between the voltage value of the smoothed temperature detection line 34 and the voltage value of the temperature detection line 34 when there is no leakage current was described. However, during the time that the heater line 32 is energized, the voltage value of the smoothed temperature detection line 34 may be compared with a predetermined voltage value (threshold Vd), and if it is greater than or equal to the predetermined voltage value, the power supply to the heater line 32 may be kept off.

[0072] (Fifth example) In the fifth embodiment, the power supply control unit 50 continues to shut off the power supply to the heater wire 32 based on the voltage information, which is added to the voltage detected by the temperature detection line 34 according to the leakage current. Figure 15 shows an example of the internal structure of the surface-type heating device 100 according to the fifth embodiment. Here, a block diagram of the energizing control unit 50 for the surface heating device 100 has been added. Components similar to those in Figure 12 are denoted by the same reference numerals and their explanations are omitted. The energizing control unit 50 is located between branch point A and the smoothing circuit 38.

[0073] The power supply control unit 50 has a delay unit 126. The delay unit 126 receives the voltage value of the temperature detection line 34 before smoothing at branch point A. The delay unit 126 measures the peak voltage value output for each half-wave of the AC power supply from the input voltage value and outputs the measured peak voltage value to the subtractor 124 with a delay. This delay is to match the timing of the measurement of the voltage value of the temperature detection line 34 by the voltage detection unit 123. The delay unit 126 also sequentially outputs the measured voltage values, including the peak voltage value, to the smoothing circuit 38.

[0074] The subtractor 124 subtracts the voltage value measured by the voltage detection unit 123 from the voltage value output by the delay unit 126, and outputs the subtracted value to the comparator 125. The comparator 125 compares the voltage value output from the subtractor 124 with a predetermined threshold, and if the voltage value is greater than the predetermined threshold, it stops the power supply to the heater wire 32 and continues to stop the power supply.

[0075] Figure 16 is a flowchart showing an example of processing by the power supply control unit 50 of the fifth embodiment. In S50, the power supply control unit 50 acquires the peak voltage value of the temperature detection line 34 before it is smoothed by the smoothing circuit 38 during the time that the heater line 32 is energized. Specifically, the power supply control unit 50 can acquire the voltage value of the temperature detection line 34 before it is smoothed by measuring the voltage value at branching point A shown in Figure 3. As described above, if there is leakage current, a voltage is generated for each half-wave of the AC according to the leakage current.

[0076] In S51, the power supply control unit 50 calculates the difference between the acquired peak voltage value of the temperature detection line 34 and the voltage value of the temperature detection line 34 when there is no leakage current. Here, the voltage value of the temperature detection line 34 when there is no leakage current can be obtained by the voltage detection unit 123 measuring the voltage value of the temperature detection line 34 at the timing of the sampling pulse generated by the sampling pulse generation unit 122. Note that the voltage value of the temperature detection line 34 when there is no leakage current may be stored in the memory of the power supply control unit 50 in advance with a value corresponding to the temperature level set by the temperature setting unit 21.

[0077] In S52, the power supply control unit 50 determines whether the voltage difference is greater than or equal to a predetermined value (threshold Ve). If it is greater than or equal to the predetermined value, the process proceeds to S53; otherwise, it returns to S50. The predetermined value is stored in the memory of the power supply control unit 50 in advance and remains constant regardless of the temperature level set by the temperature setting unit 21. Furthermore, the predetermined value is set to be smaller than the difference between the voltage value when the thermal fuse blows and the voltage value when there is no leakage current.

[0078] In S53, the power supply control unit 50 determines that the cord heater 30 is degraded, and stops the power supply to the heater wire 32, and continues to stop the power supply. This process is the same as the process in S15 described above. Thus, according to this embodiment, by continuing to cut off the power supply to the heater wire 32 based on the temperature information of the temperature detection line 34 before it is smoothed by the smoothing circuit 38, deterioration of the cord heater 30 can be detected early before the thermal fuse TF1 blows.

[0079] In the fifth embodiment, the case of calculating the difference between the peak voltage value of the temperature detection line 34 before smoothing and the voltage value of the temperature detection line 34 when there is no leakage current was described. However, the peak voltage value of the temperature detection line 34 before smoothing may be compared with a predetermined voltage value (threshold Vf), and if it is greater than or equal to the predetermined voltage value, the power supply to the heater line 32 may be kept off.

[0080] Although the present invention has been described above using the embodiments and examples described above, the present invention is not limited to the embodiments and examples described above, and modifications can be made within the scope of the present invention, and each embodiment and modification may be combined as appropriate. In the embodiments described above, the case where the surface heating device is an electric carpet was explained, but it is not limited to this case and may also be applied to electric mats, electric blankets, etc. Furthermore, it is not limited to AC 100V products, but can also be applied to AC 200V products. [Explanation of symbols]

[0081] 100: Surface heating device 10: Heating section 20: Controller 21: Temperature setting section 22: Notification section 30: Cord heater 32: Heater wire 33: Intermediate layer 34: Temperature detection wire 38: Smoothing circuit 40: Control unit 50: Power supply control unit 60: Temperature control unit

Claims

1. A cord heater is wired to the heating section and has a heater wire, a temperature detection wire, and an intermediate layer located between the heater wire and the temperature detection wire. A planar warming device having a control means that controls the temperature of the warming section by alternately switching the energization and de-energization of the heater wire based on temperature information detected by the temperature detection line, The control means is If the period of energizing and de-energizing the heater wire is below a threshold, If the information regarding the time during which power is supplied to the heater wire is below a threshold, If the time during which power is not supplied to the heater wire is less than or equal to the threshold, Alternatively, if the number of times the heater wire is energized and then de-energized exceeds a threshold, A planar warming device characterized by continuing to shut off the power supply to the heater wire regardless of the temperature information detected by the temperature detection line.

2. A cord heater having a heater wire, a temperature detection wire, and an intermediate layer located between the heater wire and the temperature detection wire, A planar warming device having a control means that controls the temperature of the warming section by alternately switching the energization and de-energization of the heater wire based on temperature information detected by the temperature detection line, The control means is If the difference between the period of energizing and de-energizing the heater wire and the period of energizing and de-energizing the heater wire when there is no leakage current is greater than or equal to a threshold, If the difference between the time the heater wire is energized and the time the heater wire is energized when there is no leakage current is greater than or equal to a threshold, If the difference between the time during which the heater wire is not energized and the time during which the heater wire is not energized when there is no leakage current is greater than or equal to a threshold, A planar warming device characterized by continuing to shut off the power supply to the heater wire regardless of the temperature information detected by the temperature detection line.

3. It has a thermal fuse that cuts off the current to the heater wire, The aforementioned threshold is The surface heating device according to claim 2, characterized in that the thermal fuse is smaller than the difference between the period of energization and de-energization to the heater wire when the thermal fuse interrupts the energization to the heater wire and the period of energization and de-energization to the heater wire when there is no leakage current.

4. It has a thermal fuse that cuts off the current to the heater wire, The control means is The planar heating device according to claim 1 or 2, characterized in that the power supply to the heater wire is kept off before the thermal fuse cuts off the current.

5. The control means is The planar heating device according to any one of claims 1 to 4, characterized in that it notifies the user via a notification unit that the power supply to the heater wire remains cut off.

6. A cord heater is wired to the heating section and has a heater wire, a temperature detection wire, and an intermediate layer located between the heater wire and the temperature detection wire. A control means controls the temperature of the heating section by alternately switching the power supply to the heater wire and stopping the power supply based on the temperature information detected by the temperature detection line, A surface-type warming device having a temperature detection means for detecting the temperature of the cord heater, separate from the temperature detection line, The control means is A surface-type warming device characterized by continuing to suspend power supply to the heater wire based on temperature information detected by the temperature detection means.

7. A cord heater is wired to the heating section and has a heater wire, a temperature detection wire, and an intermediate layer located between the heater wire and the temperature detection wire. A planar warming device having a control means that controls the temperature of the warming section by alternately switching the energization and de-energization of the heater wire based on temperature information detected by the temperature detection line, The control means is A surface-type heating device characterized by continuing to shut off the power supply to the heater wire based on the temperature information detected by the temperature detection line and the temperature information detected by the temperature detection line when there is no leakage current.

8. It has a smoothing means for smoothing the temperature information detected by the temperature detection line, The control means is The planar warming device according to claim 7, characterized in that the power supply to the heater wire is continuously stopped based on the information obtained after the temperature information detected by the temperature detection line has been smoothed by the smoothing means.

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