JPH05266964A - Safety device for electric heater device - Google Patents

Abstract

PURPOSE:To prevent operation in a condition of wire disconnection and break or abnormal overheat and improper insulation, of a heater, by stopping its electrification by detecting the case that a current in a main circuit containing the heater is abnormally high and low CONSTITUTION:A current detected by a CT5 is converted into voltage Vo, to compare an upper limit value V1 of the voltage with its lower limit value V2 by comparators 16, 17. In a normal condition where a relation is V2<V0<V1, a transistor Q1 is conducted to actuate a relay 9, and a relay contact 4 is closed to electrify a heater 1. In an abnormal condition where a relation is V0<V2 or V1<V0, the transistor Q1 becomes nonconduction, and the relay contact 4 is opened to stop electrification. By pressing a reset switch 24, the heater can be reset to an electrified condition. In the abnormal condition, since an LED29 is put out, it can be known by a user.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety device for electric heating appliances used for household purposes and the like.

[0002]

2. Description of the Related Art FIG. 3 is an electric circuit diagram of an electric hot air heater commonly used in ordinary households. In this heater, a semiconductor heater 61 and a blower fan motor 62, which are connected in parallel, are connected to an AC 100V power source via an operation switch 63, and when heating, the operation switch 63 is turned on to turn on the semiconductor heater 61 and the blower fan. When the motor 62 is energized and heating is stopped, the operation switch 63 is turned off to stop energizing them.

Recently, ceramic heaters are often used as the semiconductor heaters. The reason for this is that even if an electric current flows, it does not glow red, there is no danger of fire, and there is a sense of security, or a positive temperature coefficient (PTC-Positive Temperature Coefficien) increases with increasing temperature.
t) and has a self-control function of controlling the temperature of the heater to a constant temperature by the element itself. The drawback of this ceramic heater is that it is fragile in strength, and it breaks during use or during transportation of the instrument and comes into contact with the non-charged part of the instrument, which causes electrical troubles during use. Therefore, for example, as shown in FIG. 4, a plurality of thin plate-shaped ceramic heaters 65 (four in the figure) are arranged, and the two ceramic heaters 65 function as mechanical protection and fins for heat exchange. The structure in which the ceramic heater is sandwiched between the conductive plates 66 and 67 is used to compensate for the strength defect of the ceramic heater.

[0004]

However, the size and weight of the ceramic heater having the above structure are large, and it is not suitable for home electric appliances which are required to be small and lightweight. Therefore, the size and weight of the ceramic heater can be reduced by molding it into a single plate as shown in FIG. 5, and the weakness in strength is that the electric circuit is used to detect the breakage of the heater at an early stage. It is possible to make up for it by preventing it.

However, the conventional circuit shown in FIG. 3 has a problem that the operation of the ceramic heater in a broken state cannot be prevented in advance, as described below. Both ends 71 and 72 of the ceramic heater 70 shown in FIG. 5 are made into electrodes by coating with a conductive material, and the resistance value between the electrodes is stable. If the resistance between the electrodes is 10Ω,
As shown in the figure, when the XY line is used to divide the device into halves, the resistance of each divided device should be about 5Ω. However, since the fracture surface is not coated with a conductive material, the original 1
It is a large value far exceeding 0Ω. For example, when the ceramic heater 70 is attached as shown in FIG. 6A and is broken as shown in FIG. 6B, the resistance value becomes much larger than the original resistance value, and the flowing current value becomes Very small FIG. 7 is a graph showing the relationship between the length of a heater element having a constant cross-sectional area and the electric resistance value. The resistance value normally increases in proportion to the length regardless of the type of heater as shown in the characteristic A. This is true not only for metal heaters but also for ceramic heaters. But,
When the heater element is broken, the resistance value decreases in the case of the metal heater according to the length, but in the case of the ceramic heater, the resistance value shows the characteristic shown by the broken line B and increases from the original resistance value. To do. FIG. 8 is a comparative graph of the electric resistance values when fracture occurs at point J in FIG. The normal resistance value is 10
When it is set to Ω, it decreases to several 10 Ω in the case of a metal heater, but increases to several KΩ in the case of a ceramic heater.
As described above, when the ceramic heater is on the verge of breaking or breaks, the resistance value becomes very large and the current becomes extremely small. Therefore, it is impossible to prevent the operation of the ceramic heater on the verge of breaking or in a broken state.

Further, when a normal metal heater is used instead of the semiconductor heater, if the metal heater is disconnected due to oxidation or the like and comes into contact with the non-charged portion of the device, the resistance value becomes small and an overcurrent is generated on the device side. However, since the position of disconnection is not constant, the magnitude of the leakage current is not constant, and it is difficult to protect with a current fuse or the like. Therefore, the conventional circuit causes abnormal overheating and insulation failure, which is dangerous. Also, in the case of both semiconductor heaters and metal heaters, the blower motor fails and does not rotate, the amount of blown air is extremely reduced due to the accumulation of dust and dust, and the heater is dusty or dusty When the temperature of the heater rises due to a decrease in the amount of air passing therethrough, the resistance of the heater increases and the current decreases, but the above conventional circuit is not designed to detect such a decrease in current. Therefore, it is dangerous because the heater overheats or the insulation fails. Therefore, an object of the present invention is to detect when the current of the main circuit including the heater becomes abnormally high or abnormally low and to stop the energization of the heater to thereby prevent the heater from breaking or breaking. It is an object of the present invention to provide an electric heating device capable of preventing operation in a broken state, abnormal overheating, and insulation failure.

[0007]

In order to achieve the above object, a safety device for an electric heating appliance according to the present invention is a current detecting means for detecting a current in a main circuit including a heater of the electric heating appliance, and a detection for the current detecting means. Based on the result of the judgment means for judging whether the current value of the main circuit is out of the predetermined range or not, the main circuit is shut off when the current value of the main circuit is out of the predetermined range. Switch means for resetting, reset means for returning the switch means to the state before shutting off, and display means for displaying whether or not the main circuit is in the shutoff state.

[0008]

The current detecting means detects the current of the main circuit including the heater of the electric heating device, and the judging means judges from the detection result of the current detecting means whether or not the current value of the main circuit is out of the predetermined range. .. Then, the switch means receives the determination result of the determination means and shuts off the main circuit when the current value of the main circuit is out of the predetermined range. Further, the display means displays whether or not the main circuit is in the cutoff state. In this way, the main circuit is shut off when the current value of the main circuit becomes abnormally high or abnormally low and falls outside the specified range. Alternatively, abnormal overheating and insulation failure can be prevented. Further, since the resetting means restores the switch means to the state before the interruption, the switch means does not automatically return to cause chattering. The user of this electric heating device can confirm the abnormality by the display means.

[0009]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. First Embodiment FIG. 1 is a circuit diagram of a safety device for an electric warm air heater according to a first embodiment of the present invention. In FIG. 1, 1 is a semiconductor heater, 2 is a fan motor, 3 is a power switch,
Reference numeral 4 is a normally-off relay contact for shutting off the circuit at the time of abnormality, and 5 is a CT (current transformer) for detecting the circuit current. A control circuit transformer 6 is connected to the secondary side of the power switch 3, and a relay 9 for driving the relay contact 4 is connected from the transformer 6 via a rectifier 7 and a three-terminal regulator 8 which is a voltage stabilizer. Power is being supplied. The output terminal of the rectifier 7 and the output terminal of the three-terminal regulator 8 are respectively capacitors 10,
It is grounded via 11. Further, a resistor 12 and rectifying diodes 13, 13, ... Are connected to the secondary side of the CT5, and these elements, resistor 14 and capacitor 1 are connected.
5, the circuit current is detected as a voltage value (V ₀ ).

This voltage V ₀ is input to the inverting input terminal of the first comparator 16 and the non-inverting input terminal of the second comparator 17. The first comparator 16 includes resistors 18 and 1
The voltage V _{1 at} the connection point with 9 is compared with the above V _0, and V ₁ > V ₀
If so, the output becomes "High", and if V ₁ <V _{0, the} output becomes "Lo".
The second comparator 17 compares the voltage V _{2 at} the connection point between the resistors 19 and 20 with the above V _0, and V ₀ >.
If it is V _{2, the} output becomes "High", and if V ₀ <V ₂ , the output is "High".
It is in a "Low" state. The resistances ₁ and ₂ are set so that the voltages V ₁ and V ₂ are respectively the upper limit value and the lower limit value of the voltage V ₀ during normal operation.
The values of 8, 19, 20 are set. The output terminals of the two comparators 16 and 17 are connected to the connection point between the collector of the transistor Q ₂ and the resistor 21, and the resistor 2
2 to the base of the transistor Q ₁ . The base of the transistor Q1 is grounded via the resistor 23. Both the "High" state of the output of the two comparators 16 and 17, i.e., if _{V 2 <V 0 <V 1} , the base voltage of Q ₁ is high, Q ₁ is turned on. On the other hand, one of the two comparators 16 and 17 is in the conductive state, that is, V ₂ <V ₁ <V ₀ or V ₀ <V ₂ <
If the V _1, the base voltage of Q ₁ is decreased to near 0V,
Q ₁ becomes non-conductive.

A reset switch 24 is connected between the collector of the transistor Q ₁ and the ground, and
It is connected to the base of the transistor Q ₂ via the resistor 25. The base of transistor Q ₂ is also grounded through resistor 26. When the transistor Q ₁ becomes conductive or the reset switch 24 is pressed, the relay 9 operates and the relay contact 4 is closed. In this state the base voltage of the transistor Q ₂ is located near 0V, the transistor Q ₂ is in a non-conductive state. Further, there is the transistor Q ₁ is non-conductive, and high base voltage of the transistor Q ₂ is reset switch 24 is OFF state, the transistor Q ₂ is located in a conductive state, the base voltage of the transistor Q ₁ is near 0V Then, the transistor Q ₁ keeps non-conducting state. Also, a surge absorbing diode 27 is provided in parallel with the relay 9,
The LED 29 connected in series with the resistor 28 is connected. Since the LED 29 lights up when the relay 9 operates, the LED 29 lights up when the circuit is in the energized state and turns off when the energization is stopped.

The circuit configured as described above operates as follows. Relay contact 4 when power switch 3 is not turned on
Is in the OFF state. When the power switch 3 is turned on, the voltages V ₁ and V ₂ respectively become set voltages, but the voltage V ₀
Has not yet occurred. Therefore, the output of the second comparator 17 is in the "Low" state, the transistor Q ₁ remains non-conductive, the relay 9 does not operate, and the relay contact 4 becomes O.
It remains FF. When the reset switch 24 is pressed in this state, the relay 9 operates, the relay contact 4 closes, current flows through the semiconductor heater 1, and the semiconductor heater 1 enters the heating state. The hold down the reset switch 24 the base voltage of the transistor Q ₂ is the transistor Q ₂ close to the 0V is off.

If the device is normal, the circuit current is within a predetermined range, so the detected voltage V ₀ is in the range of V ₂ <V ₀ <V ₁ , and the outputs of both the comparators 16 and 17 are "High". in a state, increases the base voltage of the transistor Q ₁ is, the transistor Q ₁ is turned on. At this time, even if the reset switch 24 is released, the transistor Q ₁ is in a conductive state, the relay 9 is still operating, and the heater 1 is continuously energized. Also, the collector voltage of the transistor Q ₁ is 0
It has dropped to near V and transistor Q ₂ remains non-conductive. Then, the LED 29 is lit, and the user knows that the device is operating normally.

For some reason, an overcurrent flows in the circuit and V ₂
When <V ₁ <V ₀ , the output of the comparator 16 is “Low”
Then, the transistor Q ₁ is turned off, the relay 9 does not operate, the relay contact 4 is turned off, and the power supply to the heater 9 is stopped. At the same time, the LED 29 is turned off, and the user can know the abnormality of the device. At this time, the base voltage of the transistor Q ₂ is increased, the transistor Q ₂ becomes conductive, the transistor Q ₁ is continues to hold the non-conductive state. Further, the semiconductor heater 1 is overheated due to the stop of the blower fan motor 2, or is on the verge of breakage or is in a breakage state, and the resistance value of the semiconductor heater 1 is much larger than a normal value. , When the heater current becomes very small and V ₀ <V ₂ <V ₁ , the output of the second comparator 17 becomes "Low" state,
The transistor Q ₁ becomes non-conductive, and as in the case of the overcurrent, the heater 9 is de-energized and the LED 29 is turned on. When the energization is stopped, the value of V ₀ returns to the initial state, but since transistor Q ₂ remains conducting, transistor Q ₁ remains non-conducting, thus
The relay 9 also remains OFF, and the heater 1 is not energized. However, in this state, if the reset switch 24 is pressed, it returns to the energized state, but if the abnormal state of the device continues, the energization is stopped immediately, which is safe.

Second Embodiment FIG. 2 is a circuit diagram of a safety device for a heating appliance according to a second embodiment of the present invention. In FIG. 2, 41 is a heater such as a metal heater or ceramic heater, 42 is a display lamp, 43 and 44 are relay contacts, 45 is a CT, 46 is a power switch, and 47 is a safety device such as a fuse. C above
A detection circuit 48 is provided on the secondary side of T45. The detection circuit 48 detects whether the circuit current is within a predetermined range, closes the power supply circuit of the relay 49 if it is within the predetermined range, and opens the power supply circuit of the relay 49 if it is outside the predetermined range. There is. The power source of the relay 49 may be alternating current or direct current. The excitation of the relay 49 turns on the relay contacts 43 and 44. Further, a reset switch 50 is provided in parallel with the detection circuit 48. When the reset switch 50 is pressed, the relay 49 is excited and the relay contacts 43 and 44 are turned on.

The circuit configured as described above operates as follows. Relay contact 4 when power switch 46 is on
Since 3, 44 are in the OFF state, no current flows in the circuit, and the detection circuit 48 keeps the power circuit of the relay 49 in the OFF state. In this state, reset switch 50
When is pressed, the power circuit of the relay 49 is closed, the relay 49 is excited, and the contacts 43 and 44 are turned on. If the device is normal, a current in a predetermined range flows in the circuit, and the detection circuit 48 detects this and closes the power supply circuit of the relay 49. Therefore, even if the reset switch 50 is released, the relay 49 remains excited, the relay contacts 43 and 44 remain ON, and the heater 41 continues to be energized. At this time, the display lamp 42 is lit, and the user knows that the device is in a normal operating state.

When the circuit current goes out of the predetermined range due to the increase or decrease in the resistance value due to the oxidation, disconnection or breakage of the heater 41, the detection circuit 48 detects that and the power supply circuit of the relay 49 is turned on. open. Then, the relay 49 is de-energized, the relay contacts 43 and 44 are turned off, and the power supply to the heater 41 is stopped. At the same time, the display lamp 42 is also turned off. The user can know that the apparatus is abnormal by turning off the display lamp 42. When the power supply is stopped, no current flows in the circuit, so the detection circuit 4
Reference numeral 8 keeps the power circuit of the relay 49 open, so that the relay 49 also remains in the non-excited state and the heater 1 is not energized. However, in this state, if the reset switch 24 is pressed, it returns to the energized state, but if the abnormal state of the device continues, the energization is stopped immediately, which is safe.

[0018]

As is apparent from the above, the safety device for an electric heating device according to the present invention detects the electric current of the main circuit including the heater of the electric heating device, and the main detection unit from the detection result of the electric current detecting device. With the determination means for determining whether the current value of the circuit is out of the predetermined range, and the determination result of the determination means,
Switch means for shutting off the main circuit when the current value of the main circuit is out of a predetermined range, reset means for returning the switch means to the state before shutting off, and whether or not the main circuit is in the shut-off state. Since the display means for displaying is provided, the following effects can be obtained. By shutting off the main circuit when the current value of the main circuit becomes abnormally high or abnormally low and becomes a value outside the specified range, it is possible to prevent the heater from operating in a broken or broken state, abnormal overheating, or insulation failure. It can be prevented. Since the resetting means restores the switch means to the state before the interruption, the switch means does not automatically return to cause chattering. The user of the electric heating device can confirm the abnormality by the display means.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional example.

FIG. 4 is an external view of a ceramic heater protected by a metal plate.

FIG. 5 is an external view of a ceramic heater that is not protected by a metal plate.

FIG. 6 is a view showing a mounted state (a) and a broken state (b) of the ceramic heater of FIG.

FIG. 7: Relationship between general heater length and resistance value (A)
Relationship between the length and resistance of the broken ceramic heater (B)
FIG.

8 is a diagram showing a comparison of electric resistance values when fractured at point J in FIG.

[Explanation of symbols]

1, 41 ... Heater, 2 ... Blower fan motor, 3, 46 ...
Power switch, 4,43,44 ... Relay contact, 5,45 ...
CT, 9,49 ... Relay, 16,17 ... Comparator, 2
4, 50 ... Reset switch, 29 ... LED, 42 ... Indicator lamp, 48 ... Detection circuit.

Claims (1)

[Claims] 1. A current detecting means for detecting a current of a main circuit including a heater of an electric heating device, and a judging means for judging whether or not a current value of the main circuit is out of a predetermined range based on a detection result of the current detecting means. A switch means for shutting off the main circuit when the current value of the main circuit is out of a predetermined range, and a reset means for returning the switch means to a state before shutting off, based on the determination result of the determining means; A safety device for an electric heating device, comprising: a display means for displaying whether or not a main circuit is in a cutoff state.