WO1998017994A1

WO1998017994A1 - Heating-type sensor

Info

Publication number: WO1998017994A1
Application number: PCT/JP1997/003813
Authority: WO
Inventors: Osamu Yaguchi
Original assignee: Kabushiki Kaisha Riken
Priority date: 1996-10-22
Filing date: 1997-10-22
Publication date: 1998-04-30
Also published as: JP3705875B2; JPH10123085A

Abstract

The sensing unit (3) of a heating-type sensor is kept at a constant high temperature by a main heater (30) and an auxiliary heater (32). A leakage current caused by the deterioration of an insulating board (2) is absorbed by a guard heater. The sensing unit which can be kept at a high temperature, for instance 400 °C, and a heat conducting insulating board or film (2) on which the main heater and an auxiliary heater are provided closely to each other are included. Or, a leakage current preventive guard heater is provided adjacent to the auxiliary heater side between the main heater and the auxiliary heater. A bridge circuit (18) has the auxiliary heater on its one side and has a 1st resistor (12), a 2nd resistor (14) and a 3rd resistor (16) on the other three sides. A heating control circuit has an amplifier or a voltage follower (20) and an amplifier (24) whose reverse input terminal is connected to a series connection point between the 1st resistor and the auxiliary heater, whose nonreverse input terminal is connected to a series connection point between the 2nd resistor and the 3rd resistor and whose output terminal is connected to the control input terminal of the voltage follower. The amplifier controls a voltage applied to the bridge circuit and the main heater in accordance with the output of the bridge circuit. A 2nd amplifier (52) controls the voltage at a connection point (50) to the guard heater (40) so as to be equal to the voltage of a connection point (13) to the auxiliary heater in accordance with the output or a 2nd bridge circuit (44) including the auxiliary heater and the guard heater (40).

Description

Description Heating sensor technology

The present invention relates to a heating type sensor such as an oxygen gas sensor and a NOx gas sensor.

Background technology

Oxygen sensor 加熱 In the heating type sensor that heats the sensing part such as N 0 X sensor with a heater, the characteristic of the sensing part is also affected by the temperature fluctuation of the heating heater itself or the temperature change of the heater due to the temperature change of the environment. Will change. A conventional heater temperature control method for maintaining the heater temperature at a predetermined value of, for example, 300 to 400 degrees C is described in JP-A-610114785.

In this temperature control method, a temperature measuring element is arranged near the space of the heating type sensor to measure the environmental temperature, and the power supply to the heater is controlled based on the measurement result to keep the temperature of the sensing unit constant. Holding. This method requires a temperature sensor to measure the ambient temperature, and also complicates the structure of the heating type sensor itself and the mechanism of the heating control circuit, leading to an increase in cost.

Furthermore, in the indirect temperature measurement of the sensing unit, the temperature of the sensing unit cannot be accurately transmitted in the state of gas flowing through the space, and high accuracy cannot be expected.Therefore, a phase delay occurs in the control system due to the temperature propagation speed. The temperature may converge to a value different from the target value or may diverge, causing loss of control.

As a conventional example without an auxiliary heater, page 11 of Nikkei Electronics, published January 20, 1992, shows that a silicon dioxide chip projecting inward from the corner of a hollow silicon substrate chip. A tin oxide thin film gas sensor is disclosed in which four silicon thin film projection substrates are formed, and a tin oxide thin film gas sensor and a platinum electrode for heating are deposited on one surface of each projection substrate. The present inventor has proposed an improved measure of the above-mentioned method in Japanese Patent Application No. 7-322839.

Figure 1 shows an example of a previously known bridge-type heating control circuit. This time The circuit includes a bridge circuit 18 having, for example, a platinum thin film heater 10 on one side and resistors 12, 14, and 16 on the remaining three sides, respectively, and an emitter follower for supplying a voltage to the bridge circuit 18. Inverting input terminal is connected to series connection point 13 of resistor 12 and heater 10 and non-inverting input terminal is connected to series connection point 17 of resistors 14 and 16. And an amplifier 24 connected to the base of the emitter follower 20 via the resistor 22.

The resistance value of the platinum thin film heater 10 changes with temperature as shown in the temperature T-resistance R characteristic diagram of FIG. Further, assuming that the potential of the series connection point 13 is e 1 and the potential of the series connection point 17 is e 2, the potential el is equal to the potential e 2, that is, the resistance of the resistor 12 to the resistance The amplifier 24 and the transistor 20 connected in an emitter follower are operated so that the temperature of the heater 10 is maintained at a predetermined value so that the resistance value ratio becomes equal to that of the resistor 14 to the resistor 16.

Therefore, when the temperature of the heater 10 is lower than the predetermined temperature, the output voltage of the amplifier 24 and the emitter follower 20 increases due to el <e2, and the heater 10 is further heated. When the temperature of the heater 10 is higher than the predetermined temperature, the output voltages of the amplifier 24 and the emitter follower 20 decrease due to el> e2, and the power supply to the heater 10 is reduced.

From the above, it is clear that the bridge-type heating control circuit in Fig. 1 has the following problems. In order to easily detect the change in the resistance value of the heater 10 so as to prompt the temperature change accurately, the value of the resistor 12 may be made sufficiently larger than the value of the heater 10. However, the calorific value of the resistor 12 is larger than that of the heater 10, which increases energy loss and increases the temperature of the resistor 12 excessively, which is dangerous. When the value of the resistor 12 with the highest rate of change is equal to the value of the heater 10, the heat value of the resistor 12 is equal to the heat value of the heater 10. Therefore, there is a limit in increasing the variation of el, and the amount of heat generated by the resistor 12 must be allowed to some extent. On the other hand, the resistances 14 and 16 are comparative resistances, and can generate extremely small amounts of heat.

When the resistor 12 generates heat, its resistance value fluctuates in accordance with its temperature coefficient of resistance, that is, the reference resistance value fluctuates, so that it is difficult to obtain an appropriate heater temperature. Also, When the temperature coefficient of the resistor is positive, the heater 10 is heated and the resistor 12 also rises in temperature, and the resistance of the resistor 12 increases. Therefore, the time required to converge to el = e 2 is extended.

Disclosure of the invention

Therefore, a first object of the present invention is to provide a highly reliable heating type sensor that uses a main heater and an auxiliary heater to maintain a constant heater temperature even when the ambient temperature changes, and to minimize heat generation. It is to provide. Needless to say, an insulating substrate provided between the sensing unit and the main heater and the auxiliary heater has good thermal conductivity and does not fluctuate in value.

A second object of the present invention is to provide a highly reliable heating system in which the leakage current of the main heater does not affect the auxiliary heater even if the electrical insulation of the insulating substrate deteriorates, and the main heater can maintain the set temperature. An object of the present invention is to provide a heating and heating control circuit for a mold sensor.

According to the present invention, in the heating type sensor, the main heater and the auxiliary heater are arranged near the sensing unit to heat the sensing unit to a predetermined temperature. The resistance to the current to the main heater is set so that the current to the auxiliary heater is, for example, 10 times as large as the current to the auxiliary heater. Further, between the main heater and the auxiliary heater disposed on the insulating substrate, a guard heater is disposed adjacent to the auxiliary heater side. Therefore, a main heater and an auxiliary heater arranged on the same surface of the insulating substrate, and a guard heater arranged particularly adjacent to the auxiliary heater side are provided therebetween.

The resistance of these auxiliary heaters or guard heaters is set higher than that of main heaters, but the material is exactly the same as that of main heaters. Therefore, these masks are usually formed by depositing a predetermined metal for the same deposition time with a different mask pattern. Alternatively, the deposition time in the area where the main heater and the heater is formed is longer than that in the area where the auxiliary or guard heater is formed, and the thickness of the main heater and the heater is larger than that in the auxiliary or guard heater. Good.

The heating control circuit includes the auxiliary circuit as one side of a bridge circuit, connects the bridge circuit and the main circuit in parallel, and, based on an output of the bridge circuit, the bridge circuit and the main circuit. Power. According to the present invention, the sensing unit includes an insulating substrate in which the main heater and the auxiliary heater are arranged close to each other, and the bridge circuit has the auxiliary heater on one side and the first resistance, the second resistance and the second resistance on the remaining three sides. Including 3 resistors. The heating control circuit includes a voltage follower that supplies a voltage to the main heater, an inverting input terminal connected to a series connection point of the first resistor and the auxiliary heater, and a series connection of the second resistor and the third resistor. A point connected to a non-inverting input terminal and an output terminal connected to a control input terminal of the voltage follower.

The insulating substrate has thermal conductivity, and a main surface aligned with the sensing portion and an area of the sensing portion is fixed on one surface and the other surface of the insulating substrate around the main heater on the other surface. Is provided with the auxiliary heater.

This insulating substrate may be a substantially rectangular or elliptical printed wiring on a ceramic substrate such as aluminum nitride or silicon carbide used as a support plate for the sensing part, which has a thermal conductivity close to that of metal, a silicon dioxide layer, or a heat insulating support. It is a deposition film or a coating film formed on a linear or meandering heater having a sectional shape.

Therefore, the auxiliary heater becomes one side of the bridge circuit, and is mainly responsible for temperature sensing. The main heater is connected in parallel with the bridge circuit and heats the sensor so that the bridge circuit is balanced. The amount of heat generated by the auxiliary heater is much smaller than that of the main heater, so the heat generated by the resistor corresponding to the first resistor in Fig. 1 can be reduced, allowing accurate and quick temperature control. .

The heating control circuit according to the present invention includes: a main heater connected in parallel to a bridge circuit including an auxiliary heater; an amplifier for controlling a supply voltage to the bridge circuit and the main heater based on an output of the bridge circuit; A second amplifier for controlling the voltage of the guard heater to be equal to the voltage applied to the auxiliary heater based on the outputs of the second bridge circuit including the first heater and the guard heater.

The amplifier has an inverting input terminal connected to a first connection point between the first resistor and the auxiliary heater, a non-inverting input terminal connected to a second connection point between the second resistor and the third resistor, and an output terminal. For example, it is connected to the main heater and the bridge circuit via a voltage follower, and the bridge circuit is initially supplied with power by a starting resistor. Instead, the second amplifier has a non-inverting input terminal connected to the second connection point, an inverting input terminal connected to the guard heater, and an output terminal connected to supply current to the guard heater. Have been. A transistor is connected between the guard heater and a feeding point of the bridge circuit, and an output terminal of the second amplifier is connected to a base or a gate of the transistor. Therefore, the second bridge circuit includes a transistor connected between the guard heater and the feeding point of the bridge circuit, and the transistor is controlled by the second amplifier to which the guard heater voltage is also applied. The base or gate is controlled.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram of a conventional bridge-type heating control circuit.

Figure 2 shows the temperature (T) -resistance (R) characteristics of a platinum thin film heater.

FIG. 3 is a schematic plan view showing an embodiment of the gas sensor according to the present invention, in which a sensing unit is arranged on an invisible front side, and a main heater and an auxiliary heater are arranged on a visible back side.

FIG. 4 is a circuit diagram showing an embodiment of a heating control circuit according to the present invention.

FIG. 5 is a plan view of a heater for a heating-type sensor according to the present invention.

FIG. 6 is a circuit diagram showing a first embodiment of the heating control circuit according to the present invention.

FIG. 7 is a circuit diagram showing a second embodiment of the heating control circuit according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, the heating-type sensor of the present invention is obtained by adding an auxiliary heater to the sensor shown in FIG. 2 of Japanese Patent Application No. 7-322839. For example, a gas sensor is sandwiched between two porous electrode substrates, with one electrode substrate in contact with the gas to be tested and the other electrode substrate in contact with the atmosphere. On each porous electrode substrate, a main layer of platinum thin film or wire is laid, and an auxiliary heater of platinum thin film or wire is also laid at regular intervals in the main layer.

A heat-resistant, preferably heat-conductive insulating film is applied thereon, and an electrode is further formed thereon. The two porous substrates thus formed are paired with the electrodes inside. A porous sintered body of a substance that senses gas concentration, for example, tin oxide or lead oxide, is filled inside.

Therefore, the main heater and the auxiliary heater are heated to, for example, 410 ° C., and maintain the entire gas sensor at 400 ° C. The thinner the insulating film, the lower the thermal resistance and the better the thermal conductivity are used, and the measurement error can be minimized.

In the heating type sensor of the first embodiment, as shown in FIG. 3, a gas sensing part (not shown) heated to a high temperature is formed on the front side of the heat conductive insulating substrate 2 and two electrodes are provided at both ends. (Not shown) are formed. On the back surface of the insulating substrate 2, a platinum thin film main heater 30 is fixed in alignment with the sensing area so that the heating area is slightly wider than the sensing area of the gas sensing section. For example, a platinum thin film auxiliary heater 32 having a target resistance value of 410 ° C. is disposed around the heater.

Therefore, the inclined area in FIG. 3 indicates the heating area. The main heater 30 and the auxiliary heater 32 are preferably made of the same material or a metal having the same temperature coefficient, that is, a nichrome alloy, platinum, or a platinum alloy. In this case, the temperature change of the main heater 30 is the same as that of the auxiliary heater 32, and the resistance change is also the same as that of the auxiliary heater 32. Further, the main heater and the auxiliary heater may be arranged in a meandering or concentric platinum thin film or platinum wire.

The resistance value of this auxiliary heater is set higher than that of the main heater, but the material is exactly the same as that of the main heater. For example, these heaters are usually formed by depositing a predetermined metal or alloy for the same deposition time, even if the mask pattern is different. Alternatively, the deposition time in the area where the main heater is formed is longer than that in the area where the auxiliary or guard heater is formed, and the thickness of the main heater is made larger than that of the auxiliary or guard heater. Is also good.

FIG. 4 is a circuit diagram showing one embodiment of the heating control circuit of the heating type sensor according to the present invention. In FIG. 4, components similar to those shown in FIG. 1 are denoted by the same reference numerals. The difference between the heating control circuit of the present invention and the conventional heating control circuit shown in FIG. 1 is that the main heater 30 is connected in parallel to the bridge circuit 18 and the conventional heating circuit in the bridge circuit 18 is connected. This is the point that the auxiliary heater 32 of the present invention is connected to the continuation position, and the voltage that is not divided is directly supplied to the main heater 30.

That is, in the transistor 20 connected to the emitter follower, the collector is connected to the positive power supply voltage + Vc line, and the emitter is connected to the bridge circuit 18 and the main heater 30. This main heater 30 is grounded. On the other hand, in the bridge circuit 18, the first resistor 12 is connected between the emitter of the transistor 20 and the series connection point 13, and the auxiliary heater 32 is connected between the series connection point 13 and the ground.

A second resistor 14 is connected between the emitter of the transistor 20 and the series connection point 17, and a third resistor 16 is connected between the series connection point 17 and the ground via a variable resistor 34. You. These series connection points 13 and 17 are respectively connected to the inverting and non-inverting input terminals of an operational amplifier 24 having a FET or bipolar transistor input with negligible input current. The output of the amplifier 24 is connected to the base of the transistor 20 via the protection resistor 22. Further, a pull-up resistor 36 that supplies an initial voltage to the bridge circuit 18 when the emitter follower 20 is turned off is connected between the collector and the emitter of the transistor 20.

In the basic operation of this circuit, when the power is turned on, an unbalanced output voltage is not generated in the bridge circuit 18, so that a resistor 36 for supplying a starting voltage of, for example, 1 volt to the bridge circuit is required. Since the current to the main heater 30 is mainly supplied from the emitter follower 20, the starting resistor 36 has a considerably high resistance value, and its power consumption can be almost ignored. The resistance values of the main heater 30 and the auxiliary heater 32 are each low when the power is not supplied, and gradually increase when the power is supplied, and reach the target resistance value, for example, at 400 ° C. Therefore, the bridge circuit 18, the amplifier 24 and the emitter follower 20 increase the power supply voltage by the unbalanced output voltage of the bridge circuit 18 caused by the increase in the resistance value of the auxiliary heater 32, and the balanced power supply is performed. Allow the voltage to reach.

When the temperature of the auxiliary heater or the temperature of the main heater is lower than a predetermined value, the output of the amplifier 24, that is, the emitter voltage of the transistor 20 increases due to el <e2. This increases the power supply to the main heater. It is also slightly heated by the auxiliary heater. When the temperature of the auxiliary heater or the main heater is higher than the specified value, the amplifier 24 The power of the main heater and the auxiliary heater is reduced.

The variable resistor 34 is a potentiometer or a variable resistor for adjusting the heater temperature to a desired value. In the circuit of Fig. 4, the target temperature of the main and auxiliary heaters is the resistance ratio of the first resistor 12 to the auxiliary heater resistance ratio of the second resistance 14 to (the third resistance 16 + the variable resistance 34). Is set to be equal to

Therefore, when the auxiliary heater 32 reaches 400 ° C., the target power supply voltage is also supplied to the main heater 30, and at the same time, the main heater 30 also reaches 400 ° C. The temperature change of the main heater 30 is also transmitted to the auxiliary heater 32, and the supply voltage is increased or decreased so that the temperature change is returned to the target temperature. The target temperature may be controlled to be heated to 410 ° C. in consideration of, for example, a loss due to thermal resistance of a substrate or a film interposed between the gas sensing unit.

In the heating type sensor shown in Fig. 3, if the insulation characteristics of the insulating substrate on which the main heater and the auxiliary heater are arranged deteriorate, for example, due to aging, leakage current may flow between the main heater and the auxiliary heater. is there. There is a problem that the potential of e1 rises due to this leakage current, and the temperature of the auxiliary heater 32 falls below a predetermined value.

FIG. 5 is a plan view showing a second embodiment of the heating type sensor according to the present invention in which the above-mentioned problem is solved. In FIG. 5, components similar to those shown in FIG. 3 are given the same reference numerals. A gas sensing portion (not shown) that is heated to a high temperature is formed on the front side of the thermally conductive zirconia substrate 2, and two electrodes (not shown) are formed at both ends.

A platinum thin film main heater 30 is disposed around the back surface of the substrate 2 so as to be aligned with the sensing area, and a platinum thin film guard heater 40 is disposed inside the main heater 30. An auxiliary heater 32 made of a platinum thin film is arranged in the housing. Therefore, between the main heater 30 and the auxiliary heater 32 on the zirconium substrate 2, the guard heater 40 is arranged adjacent to the auxiliary heater 32 side. If the potential of each part of the auxiliary heater 32 is made equal to the potential of a part adjacent to the guard heater 40, the influence of the leakage current does not reach the auxiliary heater 32.

Of course, the resistance of these auxiliary heaters or guard heaters is set higher than that of the main heater, but the material is exactly the same as that of the main heater. So this These masks usually have different mask patterns and are formed by depositing a predetermined metal for the same deposition time. Alternatively, the deposition time of the area where the main heater is formed is longer than that of the area where the auxiliary or guard heater is formed, and the thickness of the main heater is made larger than that of the auxiliary or guard heater. Good.

FIG. 6 shows a second embodiment of the heating control circuit used in the heating type sensor according to the present invention. In FIG. 6, components similar to those shown in FIG. 4 are denoted by the same reference numerals, and the first transistor 20 having an emitter follower connection has a collector connected to the positive power supply voltage + Vc line and an emitter. The evening is grounded via the bridge circuit 18 and the main heater 30 connected in parallel.

Since the internal resistance of the bridge circuit 18 is considerably higher than the resistance of the main heater 30, most of the current is supplied to the main heater 30. In this bridge circuit 18, the first resistor 12 is connected in series with the auxiliary resistor 32 at the connection point 13, and the second resistor 14 is connected to the third resistor 16 and the variable resistor 3 via the connection point 17. Connected in series with 4.

These connection points 13 and 17 are connected to the inverting and non-inverting input terminals of the first operational amplifier 24, respectively. The output terminal of the amplifier 24 is connected to the base of the first transistor 20 via the protection resistor 22. Also, a pull-up resistor 36 that supplies an initial voltage to the bridge circuit 18 at the time of startup is connected between the collector and the emitter of the first transistor 20.

The first resistor 12 and the auxiliary heater 32 form a second bridge circuit 44 in cooperation with the guard heater 40 and the second transistor 42. The collector of the second transistor 42 is connected to the power supply point 46 of the main transistor 30, and the emitter is connected to the auxiliary heater 40 through the resistor 48.

A connection point 50 between the resistor 48 and the auxiliary heater 40 is connected to an inverting input terminal of the second operational amplifier 52. The second operational amplifier 52 has a non-inverting input terminal connected to the connection point 13 and an output terminal connected to the base of the second transistor 42 through the resistor 54.

FIG. 7 shows a third embodiment of the heating control circuit of the heating type sensor according to the present invention. In FIG. 7, components similar to those shown in FIG. 6 are denoted by the same reference numerals. Immediately Since the current supplied to the guard heater 40 is considerably smaller than the current supplied to the main heater 30, the second transistor 42 connected to the emitter follower can be omitted. Therefore, the output terminal of the second amplifier 52 is connected to the inverting input terminal to form the second bridge circuit 44.

The basic operation of the second embodiment of the heating control circuit according to the present invention is as follows. When the power is turned on, an unbalanced output voltage is not generated in the bridge circuit 18. For example, a 1-volt starting voltage is supplied to the bridge circuit 18 via the resistor 36. Since the current to the main heater 30 is supplied mainly from the emitter follower 20 in a steady state, a considerably high resistance value is used for the starting resistor 36, and the power consumption thereof can be almost ignored.

In addition, the resistance values of the main heater 30 and the auxiliary heater 32 are each low when the power is not supplied, and gradually increase when the power is supplied, and reach the target resistance value, for example, at 400 ° C. Therefore, the amplifier 24 and the emitter follower 20 increase the supply voltage by the unbalanced output voltage of the bridge circuit 18 caused by the increase in the resistance value of the auxiliary heater 32, and reach the balanced supply voltage. Let it. That is, the amplifier 24 controls the first transistor 20 so that the potentials e 1 and e 2 of the connection points 13 and 17 are equal, and maintains the temperature of the auxiliary heater 32 at a predetermined value. I do.

Therefore, when the temperature of the auxiliary heater 32 is lower than the predetermined temperature, the output of the amplifier 24 increases due to el <e2. Therefore, the supply voltage to the main heater 30, the auxiliary heater 32, and the guard heater 40 via the first transistor 20 is increased. When the temperature of the auxiliary heater 32 is higher than the predetermined temperature, the output of the amplifier 24 decreases at el> e2. Therefore, the supply voltage to the main heater 30, the auxiliary heater 32 and the guard heater 40 decreases. Of course, most of the current flows through the main heater 30, and the main heater 30 mainly generates heat.

The variable resistor 34 is a potentiometer or a variable resistor for adjusting the temperature of the auxiliary heater 32 to a desired value. In the circuit example of FIG. 6 or FIG. 7, the auxiliary heater 32 converges to a temperature satisfying R1: rH = R3: (R4 + VR1).

Next, the operation of the guard heater will be described. Connect the potential at the connection point 13 with the auxiliary e1, the potential at the connection point 50 with the guard heater 40 is e3, and when e3 and e1, the output voltage of the second amplifier 52 and the emitter voltage of the second transistor 42 are equal. As a result, the potential e 3 of the guard heater 40 rises.

When e3> e1, the output voltage of the second amplifier 52 and the emitter voltage of the second transistor 42 decrease, and e3 also decreases. Therefore, the second amplifier 52 controls the second transistor 42 so that the relationship of e 3 = e 1 is always maintained, and the influence of the leakage current on the auxiliary heater 32 is avoided.

Even if the insulation of the zirconia substrate deteriorates, a leakage current flows from the main heater 30 to the guard heater 40, and the potential of e3 rises, the second amplifier 52 immediately e3 = e Since it becomes 1, the auxiliary heater 3 does not affect 2. That is, the heater temperature does not change. Further, the resistor 36 is a pull-up resistor for preventing all of e1, e2, and e3 from reaching zero potential when the first transistor 20 is turned off. In the circuit of Fig. 6 or Fig. 7, the target temperature of the main and auxiliary heaters is the ratio of the first resistor 12 to the auxiliary heater resistance value of the second resistor 14 to 14 (third resistor 16 + variable resistor 34). It is set to be equal to the resistance value ratio. Also, the guard heater 40 functions so as not to act on the auxiliary heater 32 even if a leakage current is generated due to deterioration of the insulation of the heater substrate.

Therefore, when the auxiliary heater 32 reaches, for example, 400 ° C., the target supply voltage is also supplied to the main heater 30 and at the same time, the main heater 30 also reaches 400 ° C. The temperature change of the main heater 30 is also transmitted to the auxiliary heater 32 and the guard heater 40, and the supply voltage is increased or decreased so as to restore the temperature change to the target temperature. Further, the target temperature may be controlled to be heated to 410 ° C. in consideration of, for example, a loss due to thermal resistance of a substrate or a film inserted between the gas sensing unit.

This insulating substrate may be a substantially rectangular or elliptical printed wiring on a ceramic substrate such as aluminum nitride or silicon carbide used as a support plate for the sensing part, which has a thermal conductivity close to that of metal, a silicon dioxide layer, or a heat insulating support. It is a deposition film or a coating film formed on a linear or meandering surface having a cross-sectional shape. Of course, the transistor may be an M〇SFET in addition to the bipolar type. As described above, the heating control circuit of the heating type sensor according to the present invention can set the resistance values of the first resistor and the auxiliary heater higher than those of the conventional bridge type heating control circuit, and set the ratio to a predetermined value. The maximum sensitivity can be obtained at the set temperature, which can be set almost to 1: 1, and the amount of heat generated can be extremely reduced. Therefore, the change in the output voltage (change in el) due to the change in the temperature of the auxiliary heater, that is, the change in the resistance value as a result of the main heater can be increased, and more accurate temperature control can be performed.

In addition, the heating control circuit is safe because energy loss is reduced and internal temperature rise is suppressed. Further, since the fluctuation of the resistance value of the first resistance serving as the reference resistance is extremely small, an accurate temperature control function is obtained, and the convergence time to a predetermined temperature is reduced. Therefore, it is possible to maintain the temperature of the sensor under the heat generation of the heat source or the fluctuation of the ambient temperature constant at a high temperature of, for example, 400 ° C., thereby improving the reliability, and simplifying the structure at a low cost. In addition, unlike a convective heat transfer of gas, a substrate or a film provided between the sensing unit and the heater has a constant thermal conductivity that propagates through a solid, close to a metal. Therefore, a change in the temperature of the gas sensing unit or the heater due to a change in heat generation of the gas sensing unit or the heater itself or a change in the ambient temperature is compensated, and the sensitivity characteristics of the gas sensing unit are stabilized.

In the heating type sensor according to the second embodiment of the present invention, a part of the auxiliary heater side of the bridge circuit and the guard heater constitute a _second bridge circuit, and the guard heater voltage (e 3) is applied to the auxiliary heater 32. Since the second amplifier is provided so as to be equal to the applied voltage (el), even if the electrical insulation of the heater substrate such as zirconia is degraded, the first amplifier as in the first embodiment of the heating type sensor is used. The temperature does not fluctuate.

Further, since the value of the guard heater can be set high, the change in the output voltage due to the temperature change of the main heater can be increased. Also, the temperature rise in the heating control circuit can be suppressed. The auxiliary heater is mainly responsible for temperature sensing. The main heater is connected in parallel with the bridge circuit and heats the sensor so that the bridge circuit is balanced. Since the guard heater absorbs the leakage current caused by the main heater, accurate and quick temperature control is possible.

Claims

The scope of the claims

1. A heating-type sensor that places the main heater and auxiliary heater near the sensing unit and heats the sensing unit to a predetermined temperature.

2. The auxiliary heater is one side of a bridge circuit, the bridge circuit and the main heater are connected in parallel, and a heating control circuit for supplying power to the bridge circuit and the main heater based on an output of the bridge circuit is provided. The sensor according to claim 1, wherein the sensor is provided.

3. The sensing unit includes an insulating substrate in which a main heater and an auxiliary heater are disposed in close proximity to each other, and the bridge circuit has the auxiliary heater on one side and a first resistor, a second resistor and a third resistor on the remaining three sides. Respectively,

The heating control circuit includes a voltage follower that supplies a voltage to the main heater, an inverting input terminal connected to a series connection point of the first resistor and the auxiliary heater, and a second resistor and a third resistor. 3. The sensor according to claim 2, further comprising an amplifier having a non-inverting input terminal connected to the series connection point and an output terminal connected to a control input terminal of the voltage follower.

4. The insulating substrate has a thermal conductivity, and has a main heater fixed on one surface and aligned with the sensing unit and the sensing unit area on the other surface, respectively. 4. The sensor according to claim 3, wherein the auxiliary heater is disposed around the periphery.

5. The sensor according to claim 1, wherein a guard heater is arranged adjacent to the auxiliary heater between the main heater and the auxiliary heater.

6. A main heater connected in parallel to a bridge circuit including an auxiliary heater;

An amplifier for controlling a supply voltage to the bridge circuit and the main heater based on an output of the bridge circuit;

A second amplifier for controlling a voltage of the guard heater to be equal to a voltage applied to the auxiliary heater based on an output of a second bridge circuit including the auxiliary heater and a guard heater. Sensor according to clause 5,

7. The bridge circuit includes a first resistor, a second resistor, and a third resistor on the remaining three sides, and the amplifier has an inverting input terminal at a first connection point between the first resistor and the auxiliary heater. The non-inverting input terminal is connected to a second connection point between the second resistor and the third resistor, and the output terminal is connected to the main heater and the bridge circuit. The sensor according to item 6.

8. In the second amplifier, a non-inverting input terminal is connected to the second connection point, an inverting input terminal is connected to the Gardner terminal, and an output terminal is connected to supply current to the Gardner terminal. 7. The sensor according to claim 6, wherein:

9. A transistor is connected between the guard circuit and the feeding point of the bridge circuit, and the second amplifier has an output terminal connected to a base or a gate of the transistor. The sensor according to clause 6, wherein:

10. The sensor according to claim 6, wherein the bridge circuit is initially supplied with power by a starting resistor.