JP2661376B2 - Safety circuit for electric heating equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a safety circuit for electric heating equipment, and more particularly, to detecting the temperature of a heating wire when controlling the supply of electricity to the heating wire based on a temperature set by a user. The present invention relates to a safety circuit having a double temperature detection circuit.

[0002]

2. Description of the Related Art As shown in FIG. 3, a temperature control device for an electric heating apparatus, for example, an electronic carpet, has a heat-sensitive wire 12 for measuring the temperature of a heating wire 11 and a temperature measured by the heat-sensitive wire 12 as a voltage. A main body temperature detection circuit 1a read by
A main body temperature setting circuit 3 for setting a temperature by a user; a temperature detected by the main body temperature detecting circuit 1a;
And a heater control circuit 4 for controlling the energization of the heating wire 11 by turning on and off the relay MR based on the comparison with the temperature set in the step (1).

With the above configuration, the heater control circuit 4
The temperature of the main body of the electronic carpet can be controlled so as to maintain the temperature set by the user. When the temperature of the main body rises abnormally, a current is supplied to a resistor R attached to the heater control circuit 4 so that a fuse TFU thermally coupled to the resistor R is connected to the resistor R.
Can also be cut.

[0004]

By the way, the above-mentioned electronic control device has a function of detecting a short circuit, an open circuit, a leak circuit, a short circuit of a diode, an open circuit, a reverse leak circuit, a short circuit of a resistor, an open circuit, etc. of the main body temperature detecting circuit 1a. If a failure occurs, the temperature control becomes impossible, and in the worst case, the heating wire is continuously energized, which may cause a burn or a danger of fire on the cushion or futon covering the electric heater.

In order to prevent the above situation as much as possible, it is conceivable to provide the main body temperature detecting circuit 1a twice. For that purpose, what is most commonly considered is to provide two heat-sensitive wires 12 and two main body temperature detection circuits 1a, respectively, to detect the main body temperature independently of each other, and to control the temperature by another circuit even if one of them fails. However, since two heat-sensitive wires are arranged on the heating wire, the structure of the heating wire and the like becomes complicated, and the cost increases.

[0006] If only one heat sensing wire is used and only the main body temperature detection circuit is provided in duplicate, the above-mentioned problems relating to the structure of the heating wire and the like do not occur, but the two main body temperature detection circuits are connected to the heat sensing wire. If one of the main body temperature detection circuits becomes defective, the change in the input impedance may adversely affect the detection function of the other main body temperature detection circuit. The present invention relates to an electric heating device that can reliably perform temperature control by preventing two main body temperature detection circuits from interfering with each other when one heat sensitive wire and two main body temperature detection circuits are used. It is intended to provide a safety circuit.

[0007]

To achieve the above object, a safety circuit for an electric heating apparatus according to the present invention comprises a heat sensing wire for measuring the temperature of a heating wire, and a heat sensing wire connected between a heat sensing wire and a power supply terminal. A current transformer connected in series, a first temperature detection circuit for detecting a temperature of the heating wire by detecting a terminal voltage of the heating wire, and a heating wire for detecting a current flowing through the heating wire through the current transformer. A second temperature detection circuit for reading the temperature of the temperature, a temperature setting circuit for the user to set the temperature,
A heater control circuit for controlling energization of a heating wire based on a comparison between the temperature read by the first temperature detection circuit or the temperature read by the second temperature detection circuit and the temperature set by the temperature setting circuit; When at least one of the temperature read by the temperature detection circuit and the temperature read by the second temperature detection circuit indicates an abnormality, the power supply cut-off means for cutting off the power supply to the heating wire.

[0008]

According to the safety circuit for an electric heating device having the above-described configuration, if both the first temperature detection circuit and the second temperature detection circuit are normal, the temperature read by the first temperature detection circuit is obtained.
Alternatively, the temperature can be controlled based on the temperature read by the second temperature detection circuit. However, even if the first temperature detection circuit becomes defective and its input impedance fluctuates, the first temperature detection circuit performs the voltage detection function. Since the input impedance of the temperature detection circuit is originally set to be higher than the impedance of the heating wire, it does not significantly affect the current flowing through the current transformer. Therefore, it is possible to cut off the power supply at the time of abnormality based on the output of the second temperature detection circuit.

Even if the second temperature detecting circuit becomes defective and its input impedance fluctuates, the heating wire is connected to the first temperature detecting circuit via the current transformer. The current fluctuation of the primary circuit is small.
Does not significantly affect the detection voltage of the temperature detection circuit.
Therefore, in this case, the power supply can be cut off at the time of abnormality based on the output of the first temperature detection circuit.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIG. 1 is a diagram showing a schematic configuration of a temperature control circuit of an electric carpet. Reference numeral 10 denotes a heating unit of the electric carpet, which includes a heating wire 11 and a heat sensing wire 12. Thermal line 12
Is composed of, for example, two conductive wires arranged via a vinyl chloride mixture. The impedance decreases when the temperature is high, and increases when the temperature is low. The heat-sensitive wire 12 is connected to one power supply terminal through the resistor R1 and the primary circuit of the current transformer CT. Heat sensing line 1
A first body temperature detecting circuit 1 is connected to an intermediate point between the resistor 2 and the resistor R1, and detects a voltage divided by the resistor R1 and the like and the heat-sensitive wire 12. On the other hand, the secondary circuit of the current transformer CT is connected to the second main body temperature detection circuit 2, and the main body temperature detection circuit 2 detects a current flowing through the secondary circuit. The temperature setting circuit 3 is a circuit that generates an electric signal corresponding to the temperature selected by the user with the slide resistance VR. As shown, the heater control circuit 4 generates an electric signal corresponding to the temperature detected by the first main body temperature detection circuit 1 (not shown;
And an electric signal corresponding to the temperature detected by the main body temperature detecting circuit 2) and an electric signal corresponding to the set temperature set by the temperature setting circuit 3 to control the temperature of the heater 11 to be constant. , For controlling the on / off of the relay MR via the power transistor Q1. MR1, MR
Reference numeral 2 denotes a relay switch driven by the relay MR.

The resistors R2 and R3 attached to the heater control circuit 4 and the second main body temperature detecting circuit 2, respectively, are thermally coupled to the fuse TFU. The fuse TFU is turned on when R3 is energized.
For fusing. In the above temperature control circuit, the input impedance of the first main body temperature detection circuit 1 is set to be larger (for example, about 100 times) than the resistance R1 or the impedance of the heat-sensitive wire 12 at a high temperature. Therefore, even if a failure occurs in the first main body temperature detecting circuit 1 and the input impedance increases, the current flowing through the current transformer CT slightly decreases, which affects the temperature detection of the second main body temperature detecting circuit 2. It is rare to give. Further, when a failure occurs in the first main body temperature detecting circuit 1 and the input impedance decreases, the current transformer C
Since the current flowing through T increases, the second main body temperature detecting circuit 2 operates on the safe side, and in this case, the detected temperature of the second main body temperature detecting circuit 2 is not affected.

Further, even if a failure occurs in the second main body temperature detecting circuit 2 and the input impedance fluctuates, the current hardly changes because the current transformer CT is interposed. 1 is hardly affected. Therefore, even if one of the first main body temperature detecting circuit 1 and the second main body temperature detecting circuit 2 becomes defective,
The other circuit can continue temperature detection without being affected, and can reliably cut the fuse TFU when detecting a temperature higher than a predetermined threshold.

FIG. 2 is a diagram showing a specific example of the temperature control circuit. The circuit constituting the first main body temperature detecting circuit 1 is shown in FIG.
The circuits constituting the main body temperature detection circuit 2 are surrounded by numbered frames. The fuse TF
The primary winding of the current transformer CT, the resistor R1, and the heat-sensitive wire 12 are connected in series via U. Resistance R1 and heat-sensitive wire 12
Is input to a rectifier circuit including a rectifier diode D1 and a smoothing capacitor C1 through an input resistor R4. The rectified voltage is divided by the resistors R5 and R6 and enters the comparators OP1 and OP3. Further, a variable resistor VR for temperature setting is arranged in parallel with the resistor R5, and the voltage of the intermediate tap enters the comparator OP2.

Here, the resistance value R4 and the resistance value (R5 + R
6) is set sufficiently higher than the impedance and resistance value R1 of the heat-sensitive wire 12. For example, R1 = 5-10
For kΩ, R4 = 100 kΩ, R5 = 10 kΩ, R
6 = 100 kΩ. Comparators OP1, OP2,
Each reference terminal of OP3 passes through a rectifier circuit including a rectifier diode D2 and a smoothing capacitor 21 to connect resistors R8 and R8.
Reference voltages E1, E2 and E3 set by R9 and R10 are input, respectively.

The comparator OP2 is for temperature control,
Its output is connected through resistors R14 and R17 to the base of transistor Q1 which drives relay MR. The normally closed relay contacts MR1 and MR2 are linked with the relay MR, and turn on and off the power supply to the heating wire 11 according to the presence or absence of power supply to the relay MR. The comparator OP1 is for preventing abnormal temperature rise, and its output terminal is connected to the trigger terminal of the SCR1 through a resistor R18. SCR1 is a fuse TF
This is for turning on and off the current supply to the resistor R2 thermally coupled to U.

The comparator OP3 is for detecting disconnection of the heat-sensitive wire 12. When detecting a voltage rise of the resistor R6 due to disconnection of the heat-sensitive wire 12, the comparator OP3 turns on the diode D4 to turn on the relay MR.
To turn off the power supply to the heating wire 11. On the other hand, the current flowing through the secondary winding of the current transformer CT is equal to the input resistance R20.
Is detected as a voltage between both ends. Then, the signal is amplified by the amplifier OP4 through the rectifier diode D7 and compared with the reference voltage E4 determined by the ratio of the resistors R23 and R24 in the comparator OP5. The output of the comparator OP5 is input to SCR2.
The SCR2 turns on and off the current supply to the resistor R3 thermally coupled to the fuse TFU.

In the above temperature control circuit, the comparator OP
2 measures a voltage obtained by multiplying the voltage of the heat-sensitive wire 12 rectified by the rectifier circuit by a predetermined multiplier determined by the set value of the variable resistor VR, and compares the voltage with the reference voltage E2. It turns on and opens the relay contacts MR1 and MR2. If the voltage is lower than the reference voltage E2, the transistor Q1 is turned off,
Relay contacts MR1, MR2 remain open. Thereby, the heating wire 1 is set at a temperature corresponding to the set value of the variable resistor VR.
1 can be controlled at a constant temperature.

The comparator OP2 compares the voltage itself of the heat-sensitive wire 12 rectified by the rectifier circuit with the reference voltage E1, and if it is lower, turns on the SCR1 to energize the resistor R2 and blow the fuse TFU. As a result, abnormal heating of the heat-sensitive wire 12 can be prevented. In addition, the current transformer CT
, The comparator OP5 detects this and turns on the SCR2 to flow a current through the resistor R3 to blow the fuse TFU. Thereby, abnormal temperature rise of the heat-sensitive wire 12 can be prevented.

Therefore, normally, when an abnormal temperature rise of the heat sensitive wire 12 is detected, the comparator O of the first main body temperature detecting circuit 1 is detected.
P2 or the comparator OP5 of the second main body temperature detection circuit 2
Are activated, and the one that is activated earlier blows the fuse TFU. Even if the capacitor C1 constituting the first main body temperature detecting circuit 1 is short-circuited or the comparators OP1 to OP3 fail and the input impedance decreases, the values of the resistors R4, R5 and R6 are sufficient. So high
The temperature detection of the second main body temperature detection circuit 2 is not affected. The reason why the values of the resistors R4, R5, and R6 can be set high is that the input impedances of the comparators OP1 to OP3 are high and the first main body temperature detection circuit 1 is made to function as a voltage detector.

Further, a resistor R20, capacitors C7 and C8, and an operational amplifier OP constituting the second main body temperature detecting circuit 2
Since the primary side of the current transformer CT has almost no effect even if the impedance of the current transformer CT fluctuates due to failure of the fourth or the like, the second
The normal temperature detection can be performed by the main body temperature detection circuit 2 described above. This is because the second main body temperature detection circuit 2 is made to function as a current detector using the current transformer CT.

The present invention is not limited to the above-described embodiment. For example, the specific circuit shown in FIG. 2 using an operational amplifier or the like is merely an example for implementing the present invention. Various design changes can be made without changing the gist of the present invention.

[0022]

As described above, according to the safety circuit of the electric heating apparatus of the present invention, the first temperature detection circuit and the second temperature detection circuit are provided, respectively, and have no influence on each other. Thus, reliable temperature control can be performed, and safety of the electric heating device can be achieved.

[Brief description of the drawings]

FIG. 1 is a temperature control circuit diagram of an electric carpet incorporating a safety circuit of the present invention.

FIG. 2 is a specific example of a temperature control circuit diagram.

FIG. 3 is a temperature control circuit diagram of a conventional electric carpet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st temperature detection circuit 2 2nd temperature detection circuit 3 Temperature setting circuit 4 Heater control circuit 11 Heating wire 12 Heat sensitive wire CT Current transformer

Claims (1)

(57) [Claims] 1. A heat-sensitive wire for measuring the temperature of a heating wire (11).
(12), a current transformer (CT) connected in series between the heating wire (12) and the power supply end, and the temperature of the heating wire (11) by detecting the terminal voltage of the heating wire (12). A first temperature detection circuit (1) to be detected and a current flowing through the heat sensing wire (12) are connected to a current transformer.
(CT), a second temperature detection circuit (2) for detecting the temperature of the heating wire (11), a temperature setting circuit (3) for the user to set the temperature, and a first temperature detection circuit A heater control circuit (which controls energization of the heating wire based on a comparison between the temperature read in (1) or the temperature read in the second temperature detection circuit (2) and the temperature set in the temperature setting circuit (3). Four)
When at least one of the temperature read by the first temperature detection circuit (1) and the temperature read by the second temperature detection circuit (2) indicates an abnormality, the power supply to cut off the power supply to the heating wire A safety circuit for an electric heating device, comprising: a shutoff unit.