JPH0352084B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control circuit for an electric heating device.

Conventionally, in an electric heating device installed on a carpet or the like, as shown in the cross-sectional view in FIG.
The temperature sensing electrode 3 which also functions as a heater is stretched on one side, and the temperature sensing electrode 3 which also functions as a heater is stretched on the other side of the heat sensitive element 5, which is formed by further covering both surfaces with insulating films 4, 4. Power supply relay 6
A power source 7 is connected through the normally open contact 6a, and the power source 7
is converted into a constant voltage DC power supply V _D by a power supply circuit 8, and the high frequency voltage outputted from an oscillation circuit 9 operating with the output voltage V _D is divided by a voltage dividing capacitor 10 to detect the temperature of the thermal element 5 throughout the period. A voltage signal is applied between the electrodes 2 and 3 and corresponds to the impedance of the heat-sensitive element 5 to the filter circuit 11 and the detection circuit 12.
The detected value is input to the comparison circuit 14 that constitutes the front stage of the next-stage switching circuit 13, and the reference voltage circuit composed of the resistor 15, variable resistor 16, and resistor 17 of this comparison circuit 14 is output. The comparison circuit 14 compares the detected value with a reference voltage given by the reference voltage, and when the detected value falls below this reference voltage, the switching circuit 13, which had been kept in the on state within the safe temperature range up to that point, is
The transistor 18 constituting the latter part is turned off, and the excitation coil of the power supply relay 6 connected in series to this transistor 18 stops driving, and a current is created between the power source 7 and the temperature detection electrode 3 which also serves as a heater. The normally open contact 6a connected thereto is reversed from the on state to the off state, thereby cutting off the power supply path of the heater circuit.

However, plastic materials such as polyamide materials used as the thermosensitive resin 1 are
As shown by A and B in the figure, the temperature-impedance characteristic changes depending on the difference in moisture absorption (in Figure 3, A indicates a case where the moisture absorption is small, and B indicates a case where the moisture absorption is large). have

That is, in FIG. 3, when the moisture absorption of the heat-sensitive element 5 is small A, the impedance becomes Z _A at temperature T _A , and when the moisture absorption is large B, the impedance becomes Z _A at temperature T _B. Therefore, when the moisture absorption is large, the same signal level is input to the comparison circuit 14 of the conventional example at a lower temperature than when the moisture absorption is small, and the power supply is stopped before the temperature rises to the predetermined set temperature. However, the disadvantage is that the user ends up using the system at a temperature lower than the intended set temperature.

The heat-sensitive element 5 having a patterned temperature detection electrode 3 which also serves as a heater as shown in FIG. 2 is stretched on one side of the heat-sensitive resin 1 is particularly susceptible to the above-mentioned moisture absorption.

Therefore, an object of the present invention is to provide a temperature control device for an electric heating device that can perform accurate temperature control operations without causing fluctuations in detected temperature even due to changes in moisture absorption of a thermosensitive element made of plastic material. The object of the present invention is to provide a control circuit.

This invention utilizes the correlation between the moisture absorption of the heat-sensitive element and the dielectric loss tangent tan δ (δ: dielectric loss angle) to prevent erroneous adjustment of the control set temperature due to changes in moisture absorption. It is designed to correct.

The relationship between the moisture absorption and the dielectric loss tangent tan δ will be explained below with reference to FIG. 4. That is, in the same figure, A, B, C, and D indicate the temperature-dissipation tangent characteristic curves of the heat-sensitive element with moisture absorption as a parameter (moisture absorption decreases in the direction of A → D), and at the same temperature T _A There is a tendency for the dielectric loss tangent tan δ to increase as the moisture absorption increases. On the other hand, the temperature-impedance characteristics corresponding to each moisture absorption A, B, C, and D exhibit the tendency shown in FIG. 5, as is clear from the explanation shown in FIG _.
The impedance increases as the moisture absorption decreases. From the above trends, it is known that a combination of a predetermined value of dielectric loss tangent and impedance corresponds to a predetermined temperature regardless of changes in moisture absorption. For example, in FIGS. 4 and 5,
When the moisture absorption of the heat-sensitive element is A, (tanδ _A , Z _A )
The detected value of (tan δ _D , Z _D ) corresponds to the temperature T _A when the moisture absorption is _D.

An embodiment of the present invention utilizing the above characteristics is shown in FIG. That is, the temperature control circuit of this electric heating apparatus has a correction circuit shown by K in FIG. 6 inserted between the filter circuit 11 and the switching circuit 13 of the temperature control circuit of the conventional electric heating apparatus.

This correction circuit K includes a current detection circuit 19 that detects the current flowing through the heat-sensitive element 5 from a voltage signal corresponding to the impedance of the heat-sensitive element 5 sent from the filter circuit 11, and detects the output of the oscillation circuit 9. A reference voltage detection circuit 20, an output signal of this reference voltage detection circuit 20, and the current detection circuit 1
From the signal of 9, the dielectric loss tangent tan δ of the heat-sensitive element 5 is obtained.
(or dielectric loss angle δ) Phase detection circuit 2
1, an impedance detection circuit 22 that detects the impedance of the heat-sensitive element 5 based on the output signal of the current detection circuit 19, and a combination value ( tan δ, Z), a calculation circuit 23 calculates and outputs the moisture absorption of the heat-sensitive element 5 at this time and the temperature corresponding to the impedance at the moisture absorption, and a voltage level corresponding to the temperature value outputted by the calculation circuit 23. The voltage level correction circuit 24 inputs the signal to the comparison circuit 14 of the switching circuit 13 at the next stage.

With this configuration, it is possible to avoid the inconvenience that temperature detection becomes inaccurate due to fluctuations in the impedance of the heat-sensitive element 5 based on changes in moisture absorption, and the voltage level is always adjusted to correspond to the correct temperature regardless of changes in moisture absorption. can be input to the switching circuit 13, and on/off control can be performed at the correct set temperature.

As described above, the temperature control circuit of the electric heating device of the present invention includes a heater circuit in which a heater is connected to a power source via a power supply relay, a heat-sensitive element disposed opposite to the heater, and a predetermined high frequency applied to the heat-sensitive element. an oscillation circuit that generates a voltage, an impedance detection circuit that detects an impedance change of the heat-sensitive element due to a temperature change of the heater, a phase detection circuit that detects a dielectric loss angle of the heat-sensitive element, and this phase detection circuit. an arithmetic circuit that receives each detection value of the dielectric loss angle detected by the impedance detection circuit and the impedance detected by the impedance detection circuit, and outputs the temperature of the heater corresponding to the detected value; and a voltage level corresponding to the detected temperature of the arithmetic circuit. Since the device is equipped with a voltage level correction circuit that outputs voltage level and a switching circuit that compares the output of the voltage level correction circuit with a predetermined threshold value and drives the power supply relay to open and close, the heat-sensitive element changes due to changes in moisture absorption. This has the effect that even if there is a fluctuation in the impedance of the sensor, accurate temperature control can be performed without being affected by the fluctuation.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a cross-sectional view showing a heat-sensitive element in the circuit, Fig. 3 is a diagram showing a temperature-impedance characteristic curve of the heat-sensitive element, and Fig. 4 shows moisture absorption as a parameter. FIG. 5 is a diagram showing a temperature-impedance characteristic curve of a heat-sensitive element with moisture absorption as a parameter. FIG. 6 is a circuit showing an embodiment of the present invention. It is a diagram. 1...Thermosensitive resin, 2...Temperature detection electrode, 3...
Temperature detection electrode that also serves as a heater, 5...Heat-sensitive element, 6...
...Power supply relay, 8...Power supply circuit, 9...Oscillation circuit, 10...Voltage division capacitor, 11...Filter circuit, 13...Switching circuit, 14...
Comparison circuit, 19... Current detection circuit, 20... Reference voltage detection circuit, 21... Phase detection circuit, 22...
Impedance detection circuit, 23... Arithmetic circuit, 2
4...Voltage level correction circuit.

Claims (1)

[Claims] 1. A heater circuit that connects a heater to a power supply via a power supply relay, a heat-sensitive element disposed opposite to the heater, an oscillation circuit that generates a predetermined high-frequency voltage to be applied to the heat-sensitive element, and a an impedance detection circuit for detecting an impedance change of the heat-sensitive element; a phase detection circuit for detecting a dielectric loss angle of the heat-sensitive element; a dielectric loss angle detected by the phase detection circuit; and an impedance detected by the impedance detection circuit. an arithmetic circuit that receives each detected value and outputs the temperature of the heater corresponding to the detected value; a voltage level correction circuit that outputs a voltage level corresponding to the detected temperature of this arithmetic circuit; and an output of this voltage level correction circuit. and a switching circuit that opens and closes the power supply relay by comparing the power supply relay with a predetermined threshold value.