JPH05143178A - Temperature control circuit - Google Patents

Abstract

PURPOSE:To obtain a highly accurate and compact temperature control circuit by serially connecting a heat variable resistor having a positive resistor temperature coefficient to a heating conductor and connecting a controllable resistor in parallel with the conductor and the variable resistor. CONSTITUTION:The resistance of a variable resistor(VR) 10 is adjusted so as to be equal to synthetic resistance between the resistance of a heater 13 and that of a positive characteristic thermistor 14. The circuit 10 is arranged in a thermostat to be controlled at its temperature. When the atmospheric temperature in the thermostat is lower than control temperature, the resistor of the thermistor 14 is reduced correspondingly to the temperature difference, so that synthetic resistance is also reduced, much current is allowed to flow into the heater 13 and heat generation is increased. Thus the highly accurate and compact temperature control device can be attained by the simple constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control circuit applied to a constant temperature bath, a solder bath and the like.

[0002]

2. Description of the Related Art A temperature control circuit using a linear region having a large temperature coefficient of resistance of a positive temperature coefficient thermistor is known for highly accurate temperature control ("Latest Detection System Guide" issued by Technical Data Center Co., Ltd.). .. FIG. 4 shows the temperature control circuit 1.

The circuit 1 shown in FIG.
The adjustable resistors VR1 and VR2 and the positive temperature coefficient thermistor 4 are provided, and the triac 5, which is a switching element, is further provided.
6, a resistor R, a capacitor C, and a choke coil CH are provided, and the positive temperature coefficient thermistor 4 is used as a temperature detector to perform temperature control by a phase control method.

[0004]

In recent years, there has been a demand for miniaturization and simplification of the temperature control circuit as well, so that the structure of the temperature control circuit can be controlled with high accuracy, and moreover, it is necessary to minimize it. ..

Therefore, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a temperature control device which is highly accurate and which is downsized and simplified.

[0006]

According to a first aspect of the present invention, there is provided a temperature control circuit, wherein a heat variable resistor is connected in series to a heating conductor and has a steep positive linear temperature coefficient of resistance in a predetermined control temperature range; And an adjustable resistor connected in parallel with the conductor and the heat variable resistor.

According to another aspect of the temperature control circuit of the present invention, the adjustable resistor connected in series to the heating conductor, and the negative linear line steeply connected in parallel to the heating conductor and the adjustable resistor in a predetermined control temperature range. And a heat variable resistor having a dynamic temperature coefficient of resistance.

According to a third aspect of the present invention, there is provided a temperature control circuit according to the first aspect.
Alternatively, in the temperature control circuit described in item 2, the temperature coefficient of linear resistance is set to 10 ⁵ Ω / ° C. or more.

According to a fourth aspect of the present invention, there is provided a temperature control circuit according to the first aspect.
Alternatively, in the temperature control circuit according to the third aspect, the heat variable resistor is a positive temperature coefficient thermistor including at least a crystalline polymer.

[0010]

According to the temperature control circuit of the first aspect, first,
At the control temperature, the resistance of the adjustable resistor is adjusted so as to be equal to the combined resistance of the heat generating conductor and the heat variable resistor.
Next, this circuit is arranged in the fluid whose temperature is to be controlled. When the temperature of the controlled object is lower than the control temperature, the resistance of the heat variable resistor is reduced by that much, so the combined resistance is also reduced, and a large amount of current flows to the side of the heat variable resistor and the heating conductor, and the heating conductor Generates a lot of heat. On the contrary, when the temperature of the controlled object is higher than the control temperature, the resistance of the heat variable resistor increases correspondingly, so the combined resistance also increases and a large amount of current flows to the adjustable resistor side. The heat generation of the heat generating conductor is suppressed.

According to the temperature control circuit of the second aspect, first, at the control temperature, the resistance of the adjustable resistor is adjusted so that the combined resistance of the heat-generating conductor and the adjustable resistor becomes equal to the resistance of the heat variable resistor. Adjust. Next, this circuit is arranged in the fluid whose temperature is to be controlled. When the temperature of the controlled object is lower than the controlled temperature, the resistance of the heat variable resistor increases accordingly, so that a large amount of current flows to the heating conductor and the adjustable resistor side.
The heating conductor generates a lot of heat. On the contrary, when the temperature of the controlled object is higher than the control temperature, the resistance of the heat variable resistor decreases accordingly, so that a large amount of current flows to the heat variable resistor side, and the heat generation of the heat generating conductor is suppressed. To be done.

According to the temperature control circuit of the third aspect, by setting the linear resistance temperature coefficient of the heat variable resistor to 10 ⁵ Ω / ° C. or more, more precise control becomes possible.

According to the temperature control circuit of the fourth aspect, a high linear resistance temperature coefficient can be obtained.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic circuit diagram 10 showing a first embodiment of the temperature control circuit of the present invention. The circuit 10 includes a power source 1
2, a heater 13 as a heating conductor, and this heater 13
Positive temperature coefficient thermistor 14 as a variable heat resistor connected in series to the heater 13 and variable resistance VR10 as an adjustable resistor connected in parallel to the heater 13 and the positive temperature coefficient thermistor 14.
And have.

The positive temperature coefficient thermistor 14 comprises a crystalline polymer such as polyvinylidene fluoride and a predetermined amount of spiked Ni powder (spike-shaped Ni powder mixed with the crystalline polymer as a conductive substance). Inco Limited) and other conductive particles. Further, by appropriately selecting the type of crystalline polymer, the temperature range exhibiting a steep linear resistance temperature coefficient can be set to a desired value of 100 ° C. to 200 ° C. and the resistance temperature coefficient of 10 ⁵ Ω / ° C. or more. FIG. 2 is a graph showing an example of resistance temperature characteristics of the positive temperature coefficient thermistor 14. As shown in the figure, the temperature coefficient of resistance is 10 ⁴ Ω / ° C. from room temperature (0.6Ω) to 160 ° C., but 10 ° C. is exceeded when the temperature exceeds 160 ° C.
^It shows a steep rising characteristic of ⁷ Ω / ° C or more and a temperature of 17
The maximum resistance is 3 × 10 ⁷ at 6 ° C. Therefore, in the case of such characteristics, the control temperature range is 160 ° C to 1 ° C.
Suitable for 70 ° C. The positive temperature coefficient thermistor 14 is
Even if barium titanate (BaTiO3) is added with a rare earth element, the temperature range and resistance temperature coefficient exhibiting a steep linear resistance temperature coefficient can be set to desired values by changing the material composition in the same manner.

The variable resistor VR10 is selected such that the center of the variable resistance range is substantially equal to the combined resistance of the heater 13 and the positive temperature coefficient thermistor 14 at the control temperature.

Next, a case where the operation of the temperature control circuit 10 of the first embodiment having the above-mentioned structure is applied to a constant temperature bath will be described as an example.

First, the temperature inside the constant temperature bath is raised from room temperature to a control temperature (for example, 165 ° C.) by a heater other than the circuit 10. Then, at the control temperature, the resistance of the variable resistor VR10 is adjusted so as to be equal to the combined resistance of the heater 13 and the positive temperature coefficient thermistor 14. Next, the circuit 10 is placed in a temperature-controlled constant temperature bath. When the atmospheric temperature in the constant temperature bath is lower than the control temperature, the resistance of the positive temperature coefficient thermistor 14 decreases accordingly, and the combined resistance also decreases.
A large amount of current flows to the side of the positive temperature coefficient thermistor 14 and the heater 13, and the heater 13 generates a large amount of heat. On the contrary, when the ambient temperature is higher than the control temperature, the resistance of the positive temperature coefficient thermistor 14 is correspondingly increased, so that the combined resistance is also increased and a large amount of current flows to the side of the variable resistor VR10 and the heater 1
The heat generation of No. 3 is suppressed. In this way, the temperature inside the constant temperature bath is maintained at the control temperature.

According to the temperature control circuit 10 of the first embodiment described above, the temperature control is performed using the linear region where the temperature coefficient of resistance of the positive temperature coefficient thermistor 14 is 10 ⁷ Ω / ° C. Highly accurate temperature control is possible. The circuit 10 includes a power source 12, a heater 13, and a positive temperature coefficient thermistor 1.
4 and the variable resistor VR10, the positive temperature coefficient thermistor 14 is used not only as a temperature detector but also as a control element, so that a circuit element such as a switching element is not required, and miniaturization and simplification can be achieved.

FIG. 3 is a schematic circuit diagram 20 showing a second embodiment of the temperature control circuit of the present invention. This circuit 20 has a power source 1
2, a heater 13 as a heating conductor, and this heater 13
Variable resistor V as an adjustable resistor connected in series to
It has R20 and a negative characteristic thermistor 24 as a heat variable resistor connected in parallel to the heater 13 and the variable resistor VR20.

The temperature coefficient of resistance of the negative characteristic thermistor 24 is as low as about 0.5Ω / ° C. as compared with the temperature coefficient of the positive characteristic thermistor 14, but the temperature range showing the linearity of the temperature coefficient is lower than that of the positive characteristic thermistor 14. Since it is wide, it is suitable for a wide control temperature range. Further, instead of the negative characteristic thermistor 24, a critical temperature thermistor C such as a vanadium oxide semiconductor is used.
TR (Critical Temperature Resistor) may be used. This critical temperature thermistor CTR has a steep negative linear resistance temperature coefficient (about 10 ² Ω) in a temperature range of 65 to 70 ° C.
/ ° C), the control temperature range is 65 to 70.
Suitable for ℃.

Next, the operation of the temperature control circuit 20 of the second embodiment having the above construction will be described.

First, the temperature inside the constant temperature bath is raised from room temperature to a control temperature (for example, 100 ° C.) by a heater other than the main circuit 20. Then, at the control temperature, the combined resistance of the heater 13 and the variable resistor VR20 has a negative characteristic thermistor 24.
The resistance of the variable resistor VR20 is adjusted so as to be equal to the resistance of Next, the circuit 20 is placed in a temperature-controlled constant temperature bath. When the ambient temperature in the constant temperature bath is lower than the control temperature, the resistance of the negative characteristic thermistor 24 increases accordingly, so that a large amount of current flows to the heater 13 and the variable resistor VR20 side, and the heater 13 generates a large amount of heat. On the contrary, when the ambient temperature is higher than the control temperature, the resistance of the negative characteristic thermistor 24 decreases accordingly, so that a large amount of current flows to the negative characteristic thermistor 24 side, and the heat generation of the heater 13 is suppressed. .. In this way, the temperature inside the constant temperature bath is maintained at the control temperature.

According to the temperature control circuit 20 of the second embodiment, the temperature is controlled by using the linear region of the temperature coefficient of resistance of the negative characteristic thermistor 24. Similarly to the above, highly accurate temperature control can be performed. The circuit 20 includes a power source 12, a heater 13, a negative characteristic thermistor 24, and a variable resistor VR20.
Since the negative characteristic thermistor 24 is used not only as a temperature detector but also as a control element, a circuit element such as a switching element is not required as in the first embodiment, and the size and simplification can be achieved.

The present invention is not limited to the above embodiment,
Various modifications can be made without departing from the spirit of the invention.

[0027]

According to the present invention described in detail above, the following effects are exhibited.

According to the first aspect of the present invention, there is provided a thermal variable resistor having a steep positive linear temperature coefficient of resistance in a predetermined control temperature range, a heating conductor and an adjustable resistor, and the thermal variable resistor is provided. Since the temperature control device is used not only as a temperature detector but also as a control element, it is possible to provide a temperature control device which is highly accurate and is downsized and simplified.

According to the second aspect of the present invention, the thermal variable resistor is provided which has a steep negative linear resistance temperature coefficient within a predetermined control temperature range, a heating conductor and an adjustable resistor. Since the temperature control device is used not only as a temperature detector but also as a control element, it is possible to provide a temperature control device which is highly accurate and is downsized and simplified.

According to the third aspect of the present invention, since the linear resistance temperature coefficient of the heat variable resistor is set to 10 ⁵ Ω / ° C. or more, downsizing and simplification can be achieved and more precise control is possible. A temperature control device can be provided.

According to the invention described in claim 4, since a high linear resistance temperature coefficient can be obtained, it is possible to provide a temperature control device which can be downsized and simplified, and which can perform more precise control.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing a first embodiment of a temperature control circuit of the present invention.

FIG. 2 is a graph showing an example of resistance temperature characteristics of the positive temperature coefficient thermistor shown in FIG.

FIG. 3 is a schematic circuit diagram showing a second embodiment of the temperature control circuit of the present invention.

FIG. 4 is a circuit diagram showing a conventional temperature control circuit.

[Explanation of symbols]

 13 Heater (heating conductor) 14 Positive characteristic thermistor (thermal variable resistor) 24 Negative characteristic thermistor (thermal variable resistor) VR10, VR20 Variable resistor (adjustable resistor)

Claims (4)

[Claims] 1. A heat variable resistor connected in series to a heat generating conductor and having a steep positive linear temperature coefficient of resistance in a predetermined control temperature range, and an adjustable resistor connected in parallel to the heat generating conductor and the heat variable resistor. A temperature control circuit comprising a resistor. 2. An adjustable resistor connected in series with a heating conductor, and a heat variable resistor connected in parallel with the heating conductor and the adjustable resistor and having a steep negative linear resistance temperature coefficient in a predetermined control temperature range. A temperature control circuit comprising a resistor. 3. The linear resistance temperature coefficient is 10 ⁵ Ω /
The temperature control circuit according to claim 1, which has a temperature of not less than ° C. 4. The temperature control device according to claim 1, wherein the heat variable resistor is a positive temperature coefficient thermistor including at least a crystalline polymer.