JPH09145654A - Temperature controller for sensor used in high-temperature environment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify structure and reduce a cost by fitting a gas detecting part on one face of a thermal conductive insulation substrate and controlling the temperature of the gas detecting part constantly according to the resistance value of a heater fixing on the other face thereof. SOLUTION: A porous gas detecting part 3 is between electrodes 6, and one face thereof is in contact with a gas to be detected, while the other face thereof is in contact with the air. A wire heater 4 is formed on a porous substrate 7, and a thermal conductive insulation film 2 is applied thereto, further an electrode 6 is formed thereon. The substrate 7 includes the electrode 6 therein, facing the other substrate, and its inside is filled with a substance, e.g. porous sintered body of tin oxide or lead oxide, to sense the gas concentration. A control circuit supplies a constant current to a heater 4 to keep the gas detecting part entirely at a constant temperature. The thinner the insulation film 2 is, the smaller the thermal resistance is, so that one with a higher thermal conductivity can reduce measuring errors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an O2 gas sensor and a NO
The present invention relates to a temperature control device for a sensor used in a high temperature environment such as an x gas sensor.

[0002]

2. Description of the Related Art For example, a heating type sensor used in a high temperature environment of 300 to 400 ° C. is disclosed in Japanese Patent Application Laid-Open No. 60-114758.
No. 5,986,086, entitled "Method of controlling temperature of heating sensor". This temperature control method measures the ambient temperature by arranging a temperature measuring element near the space of a heating type sensor that measures the concentration of gas, and controls the power supply of a heater that heats the sensor based on the measurement result. By doing so, the temperature of the sensor is kept constant.

[0003]

In this method, the structure of the heating type sensor is complicated because a temperature measuring element for measuring the ambient temperature is required, and the heater control circuit for heating the heating type sensor is also complicated. . In addition, the temperature of the sensor is measured indirectly across the space to prevent the temperature measuring element from deteriorating due to high temperature, so the temperature of the sensor changes depending on the state of the gas flowing in the space, and high accuracy cannot be expected. . Furthermore, a phase delay occurs in the control system due to the temperature propagation speed, and the temperature of the sensor may converge to a value different from the target, or in the worst case, the temperature may diverge and become extremely high or low. is there.

On page 111 of Nikkei Electronics on January 20, 1992, there is disclosed a tin oxide thin film gas sensor formed in four sets on a silicon substrate chip 1 of 1.5 mm square. As shown in FIG. 1, the gas sensor comprises a gas detector 3 of a thin film of tin oxide and a platinum electrode 4 for heating.
Are formed or vapor-deposited on the silicon dioxide thin film 2, and the vapor-deposited portion is dug out from the silicon substrate by the Si micromachining technique to make the gas detection unit 3 protrude into the air. Therefore, it is difficult to provide a thermometer capable of measuring a high temperature of 400 ° C. in the vicinity of the detector.

[0005] In view of the above circumstances, an object of the present invention is to provide a temperature control device for a sensor used in a high-temperature environment in which a heater for heating a gas detector substantially directly also serves as a temperature measuring element. As a matter of course, a substrate provided between the gas detection unit and the heater has good thermal conductivity, and a substrate whose value does not change is used.

Further, the present invention has a structure using a main heater for mainly heating a gas detector used in a high-temperature environment, and an auxiliary heater for compensating for a heating fluctuation of the main heater, that is, a temperature fluctuation of the gas detector. It is an object of the present invention to provide a temperature control device for a heating-type sensor that can be configured simply and at low cost.

[0007]

According to the temperature control device for a sensor used in a high-temperature environment of the present invention, a gas detecting portion is fixed to one surface of a heat conductive insulating substrate. A heater is fixed on the other surface of the insulating substrate so as to be aligned with the region of the gas detection unit, and a control circuit controls the temperature of the gas detection unit to be constant based on the resistance value of the heater.

In a modification of the temperature control device, a main heater is fixed to the other surface of the heat conductive insulating substrate so as to be aligned with a region of the gas detecting section, and an auxiliary heater is provided around the main heater. The control circuit is configured to control the temperature of the gas detection unit to be constant based on the resistance value of the auxiliary heater. This insulating substrate may be a ceramic substrate such as aluminum nitride or silicon carbide used as a support plate of the gas detection unit and having a thermal conductivity close to that of a metal, or a vapor-deposited film or a coating film formed on a heater disposed on a support. It is.

A temperature control device according to still another aspect of the present invention includes:
The gas detector is fixed on one surface of the insulating substrate. On one surface of the insulating substrate, a heater is fixed in parallel with the gas detector, or in a modification, a main heater and an auxiliary heater disposed around the main heater are fixed, and the resistance of the heater or the auxiliary heater is fixed. A control circuit controls the temperature of the gas detection unit to be constant based on the value. This insulating substrate is, for example, a silicon dioxide film.

The control circuit includes a reference resistor connected in series to the heater, an output terminal grounded through the reference resistor and the heater, and an inverting input terminal connected to a connection point between the reference resistor and the heater. An amplifier having a non-inverting input terminal connected to a first reference voltage;
A comparator for comparing the first reference voltage supplied to the amplifier based on a result of the comparison with a reference voltage.

The control circuit includes a reference resistor connected in series to the main heater, an output terminal grounded via the reference resistor and the main heater, and an inverting input terminal connected to a connection point between the reference resistor and the heater. Connected and non-inverting input terminal is first
A first amplifier that can be connected to a reference voltage; a second amplifier having a non-inverting input terminal connected to the output terminal of the first amplifier, an inverting input terminal connected to a second reference voltage, and an output terminal grounded via the auxiliary heater. And an amplifier.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, as shown in FIG. 1, the conventional tin oxide thin film gas sensor forms four silicon dioxide thin film projection substrates 2 projecting inward from the corners of a 1.5 mm square silicon substrate chip 1. On one surface of each protruding substrate 2, a gas detecting portion 3 of a thin film of tin oxide and a platinum electrode 4 for heating are deposited. Each of the platinum electrodes 4 consumes 20 mW of power for heating each of the detection units 3, and the resistance value when heated to 400 ° C. is determined in advance.

Next, in a sensor used in a high-temperature environment, for example, as shown in FIG. 2, a porous gas detector 3 is sandwiched between two electrodes 6, and one surface of the gas detector 3 is inspected. Contact with the gas to be made and the other side in contact with the atmosphere. In this case, a platinum thin film or a wire heater 4 is formed on the porous substrate 7, a heat-resistant, preferably heat-conductive insulating film 2 is applied thereon, and an electrode 6 is further formed thereon. The two porous substrates 7 formed as described above are assembled facing each other with the electrode 6 inside, and the inside thereof is filled with a substance for sensing a gas concentration, for example, a porous sintered body 3 of tin oxide or lead oxide. .

Therefore, a platinum thin film or wire heater 4
Is heated to, for example, 410 ° C., and the entire gas detector is maintained at 400 ° C. The thinner the insulating film 2, the lower the thermal resistance and the better the thermal conductivity are used, and the measurement error can be minimized.

Next, in a sensor used in a high-temperature environment, as shown in FIG. 3, a gas detecting portion (not shown) is formed in a plane on a thermally conductive insulating substrate 2 and two electrodes (not shown) are provided at both ends. (Not shown) is formed. In this case, a platinum thin-film heater 4 is fixed on the other surface, that is, the back surface, of the insulating substrate 2 so as to be aligned with the sensing region of the gas detection unit. The platinum thin film heater 4 functions as the main heater 4 when the platinum auxiliary heater 13 is disposed around.

FIG. 4 shows a control circuit according to a first embodiment of the present invention, in which a microcomputer controls a heater 4 for heating a gas detector to, for example, 400 ° C. This control circuit
A constant current is supplied to a heater 4 for heating a gas detection unit used in a high-temperature environment, and a voltage between both ends of the heater 4 is detected to obtain a resistance value of the heater 4, and the resistance value corresponds to a predetermined temperature. The constant current is increased or decreased so that the resistance value becomes constant.

Accordingly, the one-chip microcomputer system 14 has a multi-channel A / D converter 16 whose inputs are connected to both ends of the heater 4 and the emitter of the constant current drive transistor 15, and an output which is connected to the same base. And a D / A converter 17.

FIG. 5 shows a control circuit diagram of a second embodiment of the present invention. In this figure, a reference resistor 21 connected in series with a heater 4 for heating the gas detector to a high temperature is connected between the output terminal of an amplifier 22 and ground. In the amplifier 22, the output terminal of the operational amplifier 23 is connected to the voltage for current amplification, that is, the base of the transistor 25 of the emitter follower via the protection resistor 24. Therefore, this emitter is hereinafter referred to as an output terminal. When the gas detector 3 of FIG. 1 is used, the emitter follower can be omitted.

The amplifier 22 includes a heater 4 and a reference resistor 2.
1 is connected to the inverting input terminal,
The potential of the connection point 26 is equal to the voltage Vr1 of the first reference power supply 27.
The current is supplied to the reference resistor 21 and the heater 4 so as to be equal to. The first reference power supply 27 has a negative electrode grounded and a positive electrode connected to a non-inverting input terminal of the amplifier 22 via a resistor 29 (resistance value R1) of a voltage dividing circuit 28. The amplifier 22 has negligible current to the inverting input. The resistance value RH of the heater 4 is low when power is not supplied, gradually increases when power is supplied, and reaches the target resistance value, for example, at 400 ° C.

Therefore, the voltage at the output end of the reference resistor 21 is the same when the heater 4 is not energized.
When the temperature reaches the degree C, the target voltage value VT is reached. In order to detect and maintain when the temperature of the heater 4 reaches 400 degrees C,
A comparator 31 and a second reference power supply 32 having a voltage Vr2 equal to the target voltage value are used.

The comparator 31 has a non-inverting input terminal connected to the output terminal of the amplifier 22 and an inverting input terminal connected to the second reference power source 3.
2 and the negative electrode of the second reference power source 32 is connected to the first positive electrode.
Connected to the positive electrode of reference power supply 27. Therefore, the detected voltage is compared with the second reference voltage Vr2, and the first reference voltage is changed based on the comparison result. Or the comparator 31
The comparison output may sample and hold the voltage of the first reference power supply 27 swept in a sawtooth waveform to a target value.

In this embodiment, an analog switch which is turned on / off by a clock from an oscillation circuit (not shown) is provided between the output terminal of the comparator 31 and the remaining resistor 30 (resistance value R2) of the voltage dividing circuit 28. 33 are connected. The analog switch 33 is, for example, a dual monolithic SPST-CMOS analog switch 3 manufactured by Siliconix.
3 is used, and the switch element is turned on / off by a logic level applied to the control input terminal.

This switch element has, for example, an off-resistance of 1
0 M ohms or more and the on-resistance is 100 ohms or less.
Is included in the value R2. As long as the frequency of this clock is at least about 100 Hz, there is no practical problem. Therefore, the heating period and the comparison period are executed alternately.

First, in the energization, during the heating period, the first reference voltage is applied to the non-inverting input terminal to heat the heater 4 and increase the resistance value of the heater 4, and at the same time, the heater temperature, that is, the temperature of the gas detection unit. Gradually rise. Next, during the comparison period, when the detection voltage at the output terminal of the amplifier 22 is higher than the second reference voltage, the comparator 31 outputs a logic level H as shown on the left side of FIG.

Accordingly, a voltage higher than the first reference voltage is applied to the non-inverting input terminal to heat the heater 4 further than during the heating period, thereby increasing the resistance value of the heater 4. By alternately repeating the heating period and the comparison period, the resistance value of the heater 4 increases from a lower value to a target value.

In the comparison period a short time after the energization, the comparator 31 detects when the detected voltage matches the second reference voltage.
, The same voltage as the first reference voltage is output. Therefore, the resistance value of the heater 4 becomes the target value, and the gas detection unit is heated to the set temperature and equilibrated.

In the comparison period, if the resistance value of the heater 4 is higher than the target value, the comparator 31 determines that the temperature of the gas detector is higher than the target temperature, as shown on the right side of FIG. , The detection voltage becomes lower than the second reference voltage,
The logic level L is output. In this case, the comparator has a saturation voltage of, for example, 0.5 volt or less when the general-purpose operational amplifier is used, but ignores it. Therefore, the divided voltage of the first reference voltage is applied from the voltage dividing point 35 of the voltage dividing circuit 28 to the non-inverting input terminal, and the heater 4 is heated.

FIG. 6 is a waveform diagram of the applied voltage when the heater 4 is at or below the target temperature, when it reaches the target temperature, and when it exceeds the target temperature. The reference resistor 21 is disposed at room temperature, but uses a temperature-compensated resistor to prevent a change in the resistance value due to a change in current, or a resistor having a large allowable wattage or a resistor having a radiation fin attached. Used.

Therefore, the heater 4 has a target resistance value and considers the target temperature, for example, the loss due to the thermal resistance of the substrate or the film 2 inserted between the gas detector and the target temperature 410.
The heating is controlled to the degree C. For this reason, the temperature change of the gas detection unit due to the heat generation fluctuation of the heater itself or the change of the ambient temperature is compensated, and the sensitivity characteristic of the gas detection unit is stabilized.

Referring again to FIG. 3, the main heater 4 and the auxiliary heater 13 according to the present invention, which are arranged on the back side of the support substrate 2 of the gas detecting section having the gas detecting section 3 heated to a high temperature.
It is shown. In this figure, the heating region is positioned on the back surface of the support substrate 2 so that the heating region is slightly wider than the region of the gas detection unit.
, And an auxiliary heater 13 are linearly arranged. The main heater 4 and the auxiliary heater 13 may be arranged by a platinum thin film or a meandering platinum wire.

FIG. 7 is a control circuit diagram for the main and auxiliary heaters shown in FIG. In the figure, components similar to those shown in FIG. 5 are denoted by the same reference numerals, and description thereof is omitted. First,
The auxiliary heater 13 is connected between the output terminal of the comparator, that is, the second amplifier 31 and the ground. This second amplifier 31
The amplification factor is appropriately set by the two resistors 32 and 33.

In operation, the first amplifier 22 supplies power to the main heater 4 so that the same voltage as the first reference voltage is applied to the main heater 4. Therefore, the resistance value of the main heater 4 during heating rises to the target value as the temperature approaches 410 ° C., for example. In this case, the second amplifier 31 outputs the second detected voltage.
Since the voltage is higher than the reference voltage, the H level is output to fully heat the auxiliary heater.

When the resistance value of the main heater 4 approaches the target value, the temperature of the gas detecting section also approaches the target temperature, so that the heating degree of the auxiliary heater 13 is gradually reduced. Therefore, when the resistance value of the main heater 4 matches the target value, the auxiliary heater 1
The gain and offset amount of the second amplifier 31 are adjusted so that the heating degree of No. 3 becomes half.

When the resistance value of the main heater 4 exceeds the target value, the temperature of the gas detector also exceeds the target temperature, and the auxiliary heater 1
The heating degree of No. 3 is reduced to less than half. Therefore, the heating amount of the auxiliary heater 13 is determined by the allowable temperature compensation range of the gas detection unit.

For this reason, a change in the temperature of the gas detector or the heater due to a change in heat generation of the gas detector itself or a change in the ambient temperature is compensated. Therefore, the sensing characteristics of the gas detector are stabilized.

In the control circuit according to the present invention shown in FIGS. 5 and 7, the heater 4 is arranged on the ground side, and the reference resistor 21 is arranged on the output side of the amplifier 22. Therefore, the heater 4 and the reference resistor 21 can be exchanged. In this case, the operation is the same as that of the above circuit, except that the connection on the input side of the comparator 31 is switched. Further, the main heater and the auxiliary heater can be arranged concentrically.

[0037]

As described above, the temperature control apparatus for a sensor used in a high-temperature environment according to the present invention is capable of keeping the temperature of a gas detecting section under the heat generation of the heater or the fluctuation of the ambient temperature constant at, for example, 400 ° C. It is possible to maintain and improve the reliability, and to make the structure simple and inexpensive.

In particular, the auxiliary heater can be made of the same material as the main heater, and operates so as to keep the temperature of the gas detector at a predetermined value by compensating for the temperature change of the main heater. Further, unlike a convective heat transfer of a gas, a substrate or a film provided between a gas detection unit and a heater has a constant thermal conductivity propagating in a solid, which is close to a metal. For this reason, the sensing characteristics of the gas detection unit become stable without disposing a temperature measuring element such as a thermocouple or a thermistor.

[Brief description of the drawings]

FIG. 1 is a partially sectional perspective view showing one embodiment of a conventional gas sensor.

FIG. 2 is a partial sectional perspective view showing another embodiment of the gas sensor.

FIG. 3 is a plan view seen from the back side showing one embodiment of the gas sensor according to the present invention.

FIG. 4 is a schematic circuit diagram showing an embodiment of a control circuit using the microcomputer system according to the present invention.

FIG. 5 is a circuit diagram showing an embodiment of a control circuit using an inexpensive IC according to the present invention.

6 is a waveform diagram of a voltage applied to a heater in the control circuit shown in FIG.

FIG. 7 is a circuit diagram showing a second embodiment of the temperature control circuit of the present invention.

[Explanation of symbols]

 2 Substrate or film 3 Gas detector 4 Main heater 13 Auxiliary heater 21 Reference resistor 22 Amplifier 27 First reference power supply 28 Voltage dividing circuit 29 Resistance 30 Resistance 31 Comparator 32 Second reference power supply 33 Switch

Claims (6)

[Claims] 1. A heat conductive insulating substrate on which a gas detecting portion is fixed on one surface, a heater fixed on the other surface of the insulating substrate in alignment with a region of the gas detecting portion, and a resistance value of the heater And a control circuit for controlling the temperature of the gas detection section to be constant based on the temperature control device. 2. A heat conductive insulating substrate having a gas detecting portion fixed on one surface, a main heater fixed to another surface of the insulating substrate in alignment with a region of the gas detecting portion, and A temperature of a sensor used in a high-temperature environment, comprising: an auxiliary heater arranged around a main heater on the other surface; and a control circuit for controlling the temperature of the gas detection unit to be constant based on a resistance value of the auxiliary heater. Control device. 3. An insulating substrate having a gas detector fixed on one surface thereof, a heater fixed on the one surface of the insulating substrate, and controlling the temperature of the gas detector constant based on a resistance value of the heater. A temperature control device for a sensor used in a high-temperature environment, comprising a control circuit. 4. An insulating substrate having a gas detector fixed on one surface thereof; a main heater fixed on the one surface of the insulating substrate; an auxiliary heater arranged around the main heater on one surface of the insulating substrate; A temperature control device for a sensor used in a high-temperature environment, comprising: a control circuit for controlling the temperature of the gas detection unit to be constant based on the resistance value of the auxiliary heater. 5. A control circuit comprising: a reference resistor connected in series to the heater; an output terminal grounded through the reference resistor and the heater; and an inverting input terminal connected to the reference resistor and the heater. And an amplifier whose non-inverting input terminal can be connected to a first reference voltage; and comparing the voltage of the output terminal with a second reference voltage and supplying the second voltage to the amplifier based on the comparison result. 4. The temperature control device according to claim 1, further comprising: a comparator that changes the reference voltage. 6. A control circuit comprising: a reference resistor connected in series to the main heater; an output terminal grounded via the reference resistor and the main heater; and an inverting input terminal connected to the reference resistor and the heater. A first amplifier connected to a connection point and having a non-inverting input terminal connected to a first reference voltage, a non-inverting input terminal connected to an output terminal of the first amplifier, and an inverting input terminal connected to a second reference voltage; And a second amplifier having an output terminal grounded through the auxiliary heater.
Or the temperature control device according to 4.