JPS63302356A - Apparatus of measuring oxygen concentration - Google Patents

Abstract

PURPOSE:To enable the highly precise measurement of the concentration of oxygen by a method wherein a voltage supplied to a heater is controlled on the basis of an electric resistance value of the heater itself heating an oxygen concentration detecting member, for the purpose of keeping the temperature of the member stable. CONSTITUTION:In an oxygen detecting element 2, the part of a measuring electrode 12, a reference electrode 14 and a solid electrolyte body 4 constituting an oxygen concentration detecting member is heated to a prescribed temperature by heating members 18a and 20a. When an electric resistance value of heater elements 18 and 20 is denoted by gamma and resistance values of resistors 22, 24 and 26 by A, B and R in a resistance bridge circuit of a power supply circuit 21, a potential difference between a point (a) and a point (b) in the circuit 21 becomes zero when gamma.B=R.A. In this construction, a voltage difference between the points (a) and (b) is detected by a comparator 36 and a transistor 38 is controlled on the basis of the detection so that gamma=R.A/B, i.e. the voltage difference between the points (a) and (b) be zero. Thereby a voltage at a point (c) is controlled. Accordingly, the circuit 21 can be controlled so that the resistance value gamma, i.e. the resistance value of the elements 18 and 20 be fixed, and thus the implementation of highly precise measurement is enabled.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is an oxygen concentration measuring device suitable for use in an oxygen concentration measuring device, particularly a combustion control system of an automobile engine or a combustion control system of various industrial furnaces. Regarding the concentration measuring device, more specifically, it is an oxygen concentration device that maintains the temperature of the oxygen concentration measuring element (oxygen detection element) stably regardless of the temperature environment in which it is used, enables highly accurate measurement, and has excellent durability. This relates to a measuring device.

(Prior art) Oxygen sensors (oxygen concentration measuring devices) have been used as oxygen sensors (oxygen concentration measurement devices) to detect the oxygen concentration in the exhaust gas of automobile internal combustion engines and the oxygen concentration in the combustion exhaust gas discharged from industrial furnaces, boilers, etc. 2. Description of the Related Art Sensors that use zirconia porcelain, which is an ion-conducting solid electrolyte, to determine oxygen concentration using the principle of an oxygen concentration battery are known. In internal combustion engines, etc., in order to control the air-fuel ratio of the air-fuel mixture composed of air and fuel to a target value with high precision, the above-mentioned sensors are generally used to measure the correlation between the air-fuel ratio and the air-fuel ratio. By detecting the oxygen concentration in the exhaust gas, the air-fuel ratio of the air-fuel mixture is detected, and the amount of fuel supplied to the internal combustion engine or the like is feedback-controlled.

By the way, in order for such an oxygen sensor to operate effectively even when the temperature of the gas to be measured is relatively low, at least the oxygen concentration sensing portion of the oxygen sensing element in the oxygen sensor must be It is necessary to heat it to a predetermined high temperature with a heater (heating body), but in the past, for such heating, an indirect heating type heater was placed inside the inner hole of the oxygen sensing element, which has a bottomed cylindrical shape. (Refer to Japanese Unexamined Patent Publication No. 57-142555), and in the case of a laminated oxygen sensing element, a heater is integrally embedded in the laminated structure (Japanese Unexamined Patent Publication No. 55-1982). 14
0145) etc. have been clarified.

(Problem to be Solved by the Invention) However, in this type of oxygen sensor (oxygen concentration measuring device), the amount of heat generated by the heater (heating body) that heats the oxygen concentration detection part of the oxygen detection element, or the supply voltage to it is not particularly controlled, and therefore, due to changes in the environment in which such an oxygen concentration measuring device is used, for example due to changes in the temperature of the gas to be measured, the temperature of the oxygen concentration sensing part of such oxygen sensing element changes, and the following may occur. Therefore, there is a problem in that the electromotive force or pump current, which is the output depending on the oxygen concentration in the gas to be measured, changes, making accurate measurement impossible.

Additionally, as the temperature of the gas being measured rises, the temperature of the oxygen concentration detection section also rises, sometimes resulting in overheating, which poses the inherent problem of significantly shortening the life of the oxygen concentration detection section and heating element. It is.

(Means for Solving the Problems) Here, the present invention has been made to solve the above problems, and is characterized by an oxygen concentration detection section and an oxygen concentration detection section. and a heating element that heats the oxygen concentration sensor to a predetermined temperature, and further includes electric power or voltage supplied to the heating element to keep the temperature of the oxygen concentration detection section stable based on the electrical resistance value of the heating element. The oxygen concentration measuring device was configured to include a control means for controlling the oxygen concentration.

In the oxygen concentration measuring device according to the present invention having such a configuration, the electrical resistance of the heating element is measured using the temperature coefficient of resistance of the heating element. It is now possible to directly detect the temperature of the oxygen concentration detection section heated by the heating element, and the electrical resistance value of the heating element can be kept constant, or the electrical resistance value of the heating element at room temperature can be directly detected. By controlling the electric power or voltage supplied to the heating element using a predetermined control means so that the ratio between the electric resistance value and the electrical resistance value under the heating state of the oxygen concentration sensing part is constant, the oxygen concentration sensing part is heated. This makes it possible to stably maintain the temperature of the sample and keep it constant, thereby significantly improving measurement accuracy.

In addition, in such an oxygen concentration measuring device, the heating body is generally formed integrally with the oxygen concentration detection section, and under the oxygen concentration detection conditions, the heating body at least It is desirable that the sensor has a positive or negative temperature coefficient of resistance of 0.1%/℃, which allows for sensitive detection of temperature changes in the oxygen 4 degree detection section and more accurate temperature control. You get it.

Further, according to one embodiment of the present invention, a plurality of the heating bodies are provided, and the oxygen concentration detection section is configured to be heated to a uniform temperature by the plurality of heating bodies. The configuration is such that the electric power or voltage supplied to one heating element is controlled by the control means.In the case where a plurality of such heating elements are provided, Based on the electric resistance value of the heating element having a small calorific value among them, the electric power or voltage supplied to the heating element is controlled by the control means so as to keep the temperature of the oxygen concentration detection section stable. The Rukoto.

By the way, the heating body for detecting the electrical resistance value according to the present invention generally includes a heat generating part that directly heats the oxygen concentration detection part and a lead part for supplying power to the heat generating part. It is composed of
It is preferable that the resistance value at room temperature of the heating part is higher than the resistance value at room temperature of the lead part, so that the temperature of the oxygen concentration detection part can be detected more accurately. However, since the total resistance value of the heating element is the sum of the resistance value of the heating part and the resistance value of the lead part, if the resistance of the lead part becomes larger than the resistance of the heating part, the total resistance of the heating element This is because the resistance value cannot represent the temperature of the heat generating section, in other words, the temperature of the oxygen concentration detection section.

In addition, in the present invention, in order to adjust variations between individual devices (between oxygen concentration measuring devices), a predetermined first adjustment resistor is electrically connected to the power supply path of the heating element in each oxygen concentration measuring device. A structure in which the first adjustment resistor is provided in series or in parallel is preferably adopted, and by appropriately changing the resistance value of this first adjustment resistor, the electrical resistance value (output) of the heating element in the oxygen concentration measuring device can be adjusted to correspond to the temperature. It becomes possible to control to a predetermined value. The first adjustment resistor may be formed integrally with the heating body, but there is no problem even if it is formed separately. Furthermore, when adjusting the resistance value of the first adjustment resistor, the oxygen concentration detection section is heated to a predetermined temperature with a heating element or other indirect heater, and the electrical resistance value of the heating element and the first adjustment resistance are adjusted. This is carried out by adjusting the electric resistance value of the first adjusting resistor so that the sum of the electric resistance values of the adjusting resistors becomes a constant value.

Furthermore, according to an embodiment of the present invention, the control means causes the ratio between the electrical resistance value of the heating body at room temperature and the electrical resistance value of the oxygen concentration detection section under the heated state to be constant. In addition, the electric power or voltage supplied to the heating element is controlled, and this also makes it possible to absorb variations in electrical resistance values between individual elements. In this case, in a structure in which an oxygen sensing element formed by integrally forming the oxygen concentration sensing section and the heating body is connected to an external device via a connector,
The control means includes at least one of a second adjustment resistor whose electric resistance value is adjusted, which is provided in a power supply circuit to the heating body located on the connector or closer to the oxygen sensing element than the connector. It is constructed in such a way that it has one.

Note that this second adjustment resistor may be provided integrally with the power supply circuit portion to the heating body located on the oxygen sensing element, or may be provided in the power supply circuit portion on the connector, or between the connector and the oxygen sensing element. It is installed in the power supply circuit section between the

The present invention also provides a diffusion chamber for diffusing a gas to be measured introduced from an external space where the gas to be measured exists under a predetermined diffusion resistance, and an oxygen pump means for changing the oxygen concentration in the atmosphere in the diffusion chamber. The present invention is suitably applied to an oxygen concentration measuring device having an oxygen concentration detection section comprising an oxygen concentration battery means for detecting the oxygen concentration in the atmosphere in the diffusion chamber. The diffusion resistance of the gas to be measured in the diffusion chamber of such an oxygen concentration detection unit changes under the influence of temperature, causing changes in the pump current (output) of the oxygen pump means, etc., and the oxygen concentration in the gas to be measured changes. This is because it reduces the detection accuracy.

In addition, in the present invention, the heating body preferably includes:
It is formed using platinum as a conductor, and the oxygen concentration detection section is composed of an oxygen ion conductive solid electrolyte whose main component is ZrO□, and the heating section of the heating body is isolated from the gas to be measured. Therefore, it is desirable that the structure is such that it is not exposed to direct exposure.

(Examples) Hereinafter, some embodiments according to the present invention will be described in detail based on the drawings, and the structure of the present invention will be explained more specifically.

First, FIG. 1 is a developed structural diagram of an oxygen sensing element used in the oxygen concentration measuring device of the present invention, and FIG. 2 is a cross-sectional view of the oxygen concentration sensing portion at the tip of such an oxygen sensing element. It shows. This oxygen sensing element 2 has a narrow plate-like elongated shape, and an oxygen concentration sensing section utilizing the principle of an oxygen concentration battery is formed at the tip thereof.

As is clear from these figures, the oxygen sensing element 2 has a laminated structure. That is, a plate-shaped solid electrolyte body 4 made of stabilized zirconia that exhibits oxygen ion conductivity at high temperatures, a spacer member 6 made of the same solid electrolyte material, and a plate-shaped heater layer 8 are laminated, The solid electrolyte body 4 and the heater layer 8 are connected to each other by the notch part of the spacer member 6.
An air passage 10 that communicates with the atmosphere is formed between the two. Further, a measurement electrode 12 that is brought into contact with the gas to be measured is provided on the outer surface of the solid electrolyte body 4, and a measurement electrode 12 that faces the air passage lO of the solid electrolyte body 4 is provided so as to be opposed to the measurement electrode 12. On the inside surface,
A reference electrode 14 is provided so that air as a reference gas guided through the air passage 10 is brought into contact with the reference electrode 14 .

Further, the heater layer 8 is constructed by embedding a first heater element 18 as a heating body in an airtight electrically insulating ceramic plate 16. The first heater element 18 is composed of a heat generating part 18a for heating the oxygen concentration sensing part at the tip of the oxygen sensing element 2, and a lead part tab for connecting the heat generating part 18a to an external power source. has been done. In addition, the second heater element 2
0 is provided on the surface of the solid electrolyte body 4 on the side where the measurement electrode 12 is provided so as to surround the measurement electrode 12, and this second heater element 20 is also provided on the surface of the solid electrolyte body 4 on the side where the measurement electrode 12 is provided.
a and a lead portion 20b. in short,
The measurement electrode 12, the reference electrode I4, and the solid electrolyte body 4 in which these electrodes 12.14 are arranged constitute the oxygen concentration detection section by the respective heat generating parts 18a and 20a of the first and second heater elements 18.20. The parts can be heated to a predetermined temperature.

A power supply circuit 21 including control means for controlling power or voltage as shown in FIG. 3 is connected to at least one of the ports 18 and 20 (both in this case). In addition, in Fig. 3 of Kagaru, 22.24.
26.28.3o and 32.34 are predetermined resistors, 36 is a comparator, 38 is a power/voltage adjustment transistor, and 40 is a power source. A resistive bridge circuit is constituted by the resistors 22, 24 and 26 together with the heater element 18 (20).

Therefore, in the resistance bridge circuit of the power supply circuit 21, the load (electrical resistance value) of the heater element 18 (20): r, the resistance values of the resistors 22, 24 and 26: A,
Assuming that B and R, the potential difference between the point a and the point b in the power supply circuit 2I in FIG. 3 becomes O when rB=RA. Then, the comparator 36 connects a and b so that r=RA/B, that is, the voltage difference between a and b becomes O.
By detecting the voltage difference between them and controlling the transistor 38, the voltage at point C is controlled. Therefore, in the power supply circuit 21, r, in other words, the heater element 18 (20
) can be controlled so that the resistance value remains constant. In other words, heater element 1
This makes it possible to control the temperature of the oxygen concentration sensing portion at the tip of the oxygen sensing element 2 heated at B(20) to be constant.

As is well known, the oxygen sensing element 2 having such a structure includes the solid electrolyte body 4, the measurement electrode 12 exposed to the gas to be measured, and the reference electrode 1 exposed to the reference gas.
The electromotive force according to Nernst's equation based on the oxygen concentration difference is extracted as an output signal by the oxygen concentration detection section consisting of an electrochemical cell consisting of 4, and based on such an output signal, such Combustion control of an internal combustion engine or the like that generates a gas to be measured (exhaust gas) is performed.

At that time, according to the configuration of the present invention, the heater element 18 (20) is controlled so that the temperature of the oxygen concentration detection section is kept constant based on the electrical resistance value of the heater element 18 (20). Since the supplied power or voltage is controlled, the oxygen concentration detection section is always maintained at a predetermined temperature, and the temperature change is small, so for example, if the temperature of the gas to be measured changes. Also, stable output can be obtained from such an oxygen concentration detection section,
This allows highly accurate measurements. In addition, by controlling the temperature of such an oxygen concentration detection section, the temperature of such an oxygen concentration detection section and heater element 1B (
20) is not at risk of overheating, and its lifespan can be effectively extended.

By the way, in addition to having the basic structure as described above, the oxygen concentration measuring device also includes a diffusion chamber in which the gas to be measured is diffused under a predetermined diffusion resistance, and an atmosphere in the diffusion chamber. Some devices are composed of an oxygen pump means for changing the oxygen concentration and an oxygen concentration battery means for detecting the oxygen concentration in the atmosphere in the diffusion chamber. Since the diffusion resistance (diffusion constant) of the gas to be measured in the diffusion chamber is greatly affected by the temperature, the present invention can be advantageously applied to such a device, thereby effectively increasing the detection accuracy. Examples are shown in FIGS. 4 and 5.

That is, the oxygen sensing element 5 having the structure shown in those figures
0 is an oxygen sensing element 2 having a structure similar to the previous example, with an airtight electrically insulating ceramic layer 5 on the measurement electrode 12 side.
2. Furthermore, a plate-shaped solid electrolyte body 54 made of stabilized zirconia with oxygen ion conductivity is laminated to form an integral structure, and the solid electrolyte body 54 is connected to the outside through a ventilation hole 56 provided in the solid electrolyte body 54. A narrow flat space (diffusion chamber) 58 having a predetermined diffusion resistance and communicating with the space in which the gas to be measured is present is formed by a circular notch provided in the ceramic layer 52 between the two plate-shaped solid electrolytes. It is formed between the body 4.54. An annular inner pump electrode 60 and an annular outer pump electrode 62 are provided facing each other so as to be in contact with both sides of the solid electrolyte body 54, and these two pump electrodes 60, 62 and the solid electrolyte body 54 This constitutes an oxygen pump means which is an electrochemical cell.

Further, here, the first heater element 18 is equipped with an oxygen concentration detection section comprising such an oxygen pump means and an oxygen concentration battery means constituted by the measurement electrode 12, the reference electrode 14, and the solid electrolyte body 4. It is designed so that it can be heated to a certain temperature.

Therefore, in the oxygen sensing element 50 having such a structure, as is well known, in the flat space 58,
Measuring electrodes constituting an oxygen concentration cell means according to the oxygen concentration difference between the oxygen concentration in the gas to be measured diffused under a predetermined diffusion resistance and the oxygen concentration in the reference gas (air) in the air passage 10 12 and the reference electrode 14 is detected based on the principle of a concentration cell, and based on such an electromotive force, the inner pump electrode 6o and the outer pump electrode 62 constituting the oxygen pump means are detected. By passing a predetermined pump current between the two, a predetermined oxygen pumping action is performed, and the atmosphere in the vicinity of the inner pump electrode 60 of the flat space 58, in other words, the measurement of the oxygen concentration battery means. The atmosphere in the vicinity of the electrode 12 is controlled to be a predetermined atmosphere, and at that time,
By detecting the flow flowing between the two electrodes 60 and 62 of the oxygen pump means, the oxygen concentration of the target gas to be measured is measured.

Even in an oxygen concentration measuring device equipped with an oxygen sensing element having such a structure, by providing the first heater element 18 with a power supply circuit 21 as shown in FIG. The temperature of the target gas can be effectively maintained at a predetermined temperature, and thereby the target gas can be effectively maintained at a predetermined temperature without changing the diffusion resistance (diffusion constant) of the gas to be measured that is introduced into the flat space 58 and diffused. Since the oxygen concentration of the measurement gas can be measured, an output signal can be stably extracted from the oxygen concentration detection section.

In the above embodiments, the solid electrolyte body constituting the oxygen concentration detection section is made of stabilized zirconia, and in the present invention, the oxygen ion conductive solid electrolyte mainly composed of ZrO□ is Although it can be advantageously used as a material constituting the oxygen concentration detection section, other oxygen ion conductive solid electrolytes such as 5rCeO,
, Biz○3-Even if it is formed using a material such as a rare earth oxide solid solution, there is no problem with the river bank.

Furthermore, since the first heater element 18 and the second heater element 20 as heating bodies output the change in temperature in the oxygen concentration detection section as a change in their electrical resistance value, the first heater element 18 and the second heater element 20 are used for oxygen concentration detection. It is desirable to have a positive or negative temperature coefficient of resistance of at least 0.1%/°C under the conditions, so that the influence of reading errors in the electrical resistance of the heating element on the temperature of the heating element is reduced. Therefore, the temperature change of the oxygen concentration detection section can be detected with high accuracy, and the temperature control of the oxygen concentration detection section can be performed even more effectively. It should be noted that such a heating body is the electrode 12.14;
．． Similarly to No. 62, it is formed from a known conductive material such as a conductive metal such as platinum group metals such as platinum, palladium, rhodium, iridium, ruthenium, and osmium, or a conductive compound, but particularly preferably, It is desirable that the conductor be formed using platinum. In addition, in order to improve the close integration with the base, such a heating body is formed by mixing fine powder of ceramic nox into the above-mentioned conductive metal and firing the mixture. It is also possible to

Further, in the above-described specific example, the oxygen concentration detection section is heated by one or two heater elements, but it is also possible to provide even more heating elements. When a plurality of heating bodies (18, 20) are provided, the power or voltage supplied to at least one of them is controlled by the power supply circuit 21 (see FIG. 3) as described above. It will be controlled by

When a plurality of heating elements (18, 20) are provided, it is preferable to use a heating element with a smaller calorific value among them to keep the temperature of the oxygen concentration detection section stable based on its electrical resistance value. Therefore, it is desirable to control the power or voltage supplied to the heating elements. However, by using the electrical resistance value of the heating element that generates less heat, in other words, has a higher electrical resistance value, the larger the resistance value, the smaller the influence of errors caused by the circuit constants of the power supply circuit. It is.

Furthermore, in the heating element for detecting the electrical resistance value, a heat generating part (18a
, 20a) is preferably higher than that of the lead portions (18b, 20b) for supplying power to the heat generating portion. Resistance of lead part (R11
) and the resistance (RA) of the heat generating part: The larger the ratio: RIl/RA, the less the total resistance value of the heating element represents the temperature of the heat generating part, that is, the temperature of the oxygen concentration detection part.

By the way, there is some manufacturing variation in the electrical resistance value of the heating element (18, 20) provided in each oxygen concentration measuring device at a given temperature, but such variation between individual units is can be eliminated or suppressed by electrically providing a suitable first adjustment resistor in series or parallel to the power supply path of the heating element (18, 20), an example of which is shown in FIG. It is shown.

That is, in FIG. 6, heater element 18 (2
A first adjustment resistor 64 or 66 is provided in series with the lead portion 18a (20a) of 0), or a first adjustment resistor 68 or 70 is provided in parallel with the lead portion 18b (20b). -ing Moreover, the first adjustment resistors 64, 66, 68, 70 may be combined and arranged in plurality. especially,
Heater element 1 such as first adjustment resistor 64 and 68
8 (20), but it is also preferable that the oxygen sensing element 2 (20) be formed integrally with the oxygen sensing element 2 (20).
50) Even if it is provided outside, on a connection path with external equipment, on a connector, etc., there is no problem. Then, at least one of these first adjustment resistors 64, 66, 68, 70 is connected, and by adjusting the resistance value, d
The resistance between -=e is set to a predetermined resistance value when the temperature of the oxygen concentration detection section is a predetermined temperature.

The resistance value of the first adjusting resistor 64,66,68,70 can be adjusted, for example, by adjusting the resistance value of the first adjusting resistor 64,66,68,70.
) is heated to a predetermined temperature with a heating element (18, 20) or another indirect heater, and the sum of the electrical resistance value of the heating element and the electrical resistance value of the first adjustment resistor at that time is This can be easily carried out by adjusting the electrical resistance values of the first adjusting resistors by trimming or the like so that they become constant values.

Furthermore, in the present invention, instead of using the above-mentioned first adjustment resistor to absorb variations between individuals, the control means controls the electrical resistance value of the heating element at room temperature and the heating state of the oxygen concentration detection section. A configuration in which the electric power or voltage supplied to the heating element is controlled so that the ratio of the electric resistance values of the heating element below is constant may also be advantageously adopted.

That is, Ro: electrical resistance value of the heating element at room temperature, R
T: Electrical resistance value of the heating element under the target heating state of the oxygen concentration detection unit, α: Temperature coefficient of resistance of the heating element, To:
Room temperature, TT: Target heating temperature, ΔT (temperature difference):
If 'l'T-To, a (ratio): R7/R, then the following (1) 2 holds true.

Rr = Ro (1+αΔT) ・−−(1
) Then, this equation (1) is expanded as shown in the following equations (2) to (4).

a=Rt/Ro=1+αΔT'-・-(2),,
ΔT=(a-1)/α=T7-To... (3) TT=(a-
1)/α+To... (4) Therefore, if the mini constant is used, the heating temperature (T
A) becomes constant, thereby eliminating variations in heating temperature due to variations in the electrical resistance value (RO) of the heating element of each oxygen concentration measuring device, making it possible to heat to a constant temperature.

By the way, when controlling the heating temperature of the oxygen concentration detection section based on the ratio (a) of Rt/Ro,
First, measure the room temperature resistance (RO) of the heating element, and then
This is multiplied by a ratio (a) input in advance according to the target heating temperature, and the power or voltage supplied to the heating element is controlled by the value (RT = aRo). More specifically, (a) a voltage so low that the heat generation of the heating element can be ignored is applied to the heating element (therefore, the heating element is maintained at room temperature), and the voltage (V) at that time is and current (1), calculate Ro-V/I, and calculate R7 by multiplying by the ratio (a) input in advance. Then, calculate the actual electrical resistance value of the heating element (R ) from R,
(b) A software method using a computer that controls the voltage or power applied to the heating element so that R, or (b) a low voltage is applied to the heating element as described above to , and then the resistance 22 (A) of the circuit shown in FIG.
A hardware method will be adopted in which at least one of 24 (B) and 26 (R) is adjusted to satisfy the following equation (5).

γ=AR/B=Roa HHH (5) Furthermore, in the present invention, in the power supply circuit 21 shown in FIG. 2 (50) to an external device (the main part of the power supply circuit 21, in other words, the main body part of the control means), or located closer to the oxygen sensing element 2 than the connector. like(
It can be provided in the power supply circuit part on the oxygen sensing element 2 or in the power supply circuit part between the oxygen sensing element 2 and the connector, and in this way, it can be provided on the connector or on the side of the oxygen sensing element 2. The resistance value (A.

By adjusting B and R), the oxygen sensing element 2 can be replaced with another oxygen sensing element (the electrical resistance value of the heating body is different) without adjusting the main body of the control means (power supply circuit 21). It is possible. In addition, by adjusting the resistance value (A, B or R) of at least one of such resistors 22, 24, 26,
As shown in the formula below, it is possible to keep the heating temperature 2T constant, which makes it possible to absorb the initial variation in R8. This can be carried out on the element 2 side.

From the above equations (5) and (2), the following (6) 2 can be derived.

r = A R / B = Ro a = Ro (1+αΔT) ... (6) Then, by transforming this equation (6) and substituting equation (3) into it, we get the following equation (7). T, is A, R, B
(Ro, α, and To are constant values). Therefore, by determining the values of A and R1B, T7 can be made constant regardless of the value of γ.

1+αΔT=AR/RoB αΔT=AR/R,B-1 Δ'r= [(AR/ROB)-11/α,-,TT
= [(AR/ROB)-1]/α+T.

(7) Note that the power supply circuit 21 shown in FIG. 3 shows a specific embodiment of the present invention, and it goes without saying that other circuit configurations may be used. be.

As described above, regarding the configuration of the oxygen concentration measuring device according to the present invention,
Although the description has been made based on the structures of several oxygen sensing elements, it should be understood that the present invention is suitably applied to oxygen sensing elements with other structures, and even to oxygen concentration measuring devices. It is.

In short, the present invention is by no means to be construed as being limited to the specific examples illustrated above, and various modifications, modifications, improvements, etc. can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It goes without saying that the present invention also includes such embodiments.

(Effects of the Invention) As is clear from the above description, the oxygen concentration measuring device according to the present invention heats the oxygen concentration sensing portion based on the electrical resistance value of the heating body itself for heating the oxygen concentration sensing portion. The power or voltage supplied to the heating element is controlled to keep the temperature stable, and the temperature of the oxygen concentration sensor is directly detected and controlled. Depending on the usage conditions of the oxygen concentration measuring device, for example, the temperature of the oxygen concentration detection part will not change due to changes in the temperature of the gas to be measured, making it possible to measure oxygen concentration with high precision with stable output. In addition, since it controls the temperature of the oxygen concentration detection section, there is no risk of overheating of the oxygen concentration detection section and heating element, and its lifespan can be extended, allowing it to be used for a long period of time. This produces excellent effects, and this is where the present invention has great industrial significance.

[Brief explanation of drawings]

FIG. 1 is a developed structure diagram showing an example of the oxygen sensing element of the oxygen concentration measuring device according to the present invention, FIG. 2 is an explanatory cross-sectional view taken along the line nn in FIG. FIG. 4 is a circuit diagram showing an example of a power supply circuit for the heater element of such an oxygen sensing element, and FIG. FIG. 5 is an explanatory diagram of the V-V cross section in FIG. 4, and FIG. 6 is an explanatory diagram showing the arrangement position of the adjustment resistor with respect to the heater element. 2.50: Oxygen sensing element 4.54: Solid electrolyte body 6: Spacer member 8: Heater layer 10: Air passage 12: Measuring electrode 14: Reference electrode 16: Ceramic plate 18: First heater element 20: First Second heater element 18a, 20a: Heat generating part 18b, 20b: Lead part 21: Power supply circuit 22.24.26.28. 30.32.34: Resistor 36: Comparator

Claims (16)

[Claims] (1) It has an oxygen concentration detection section and a heating body that heats the oxygen concentration detection section to a predetermined temperature, and further maintains the temperature of the oxygen concentration detection section stably based on the electrical resistance value of the heating body. An oxygen concentration measuring device characterized in that it has a control means for controlling the electric power or voltage supplied to the heating element. (2) The oxygen concentration measuring device according to claim 1, wherein the oxygen concentration detection section and the heating body are integrally formed. (3) The oxygen concentration measuring device according to claim 1 or 2, wherein the heating body has a positive or negative temperature coefficient of resistance of at least 0.1%/°C under oxygen concentration detection conditions. (4) Claims 1 to 3 include a plurality of heating bodies, and the power or voltage supplied to at least one of the heating bodies is controlled by the control means.
The oxygen concentration measuring device according to any one of paragraphs. (5) Based on the electrical resistance value of the heating element with a small calorific value among the plurality of heating elements, the electric power or voltage supplied to the heating element is adjusted so as to keep the temperature of the oxygen concentration detection section stable. The oxygen concentration measuring device according to claim 4, wherein the oxygen concentration measuring device is controlled by the control means. (6) In a heating element for detecting electrical resistance, the room temperature resistance value of the heat generating part that directly heats the oxygen concentration sensing part is compared with the room temperature resistance value of the lead part for supplying power to the heat generating part. An oxygen concentration measuring device according to any one of claims 1 to 5. (7) The oxygen concentration measuring device according to any one of claims 1 to 6, wherein a first adjustment resistor is electrically provided in series or parallel to the power supply path of the heating body. (8) The oxygen concentration measuring device according to claim 7, wherein the first adjustment resistor is integrally formed with the heating body. (9) The oxygen concentration detection section is heated to a predetermined temperature with the heating element or another indirect heater, and the sum of the electrical resistance value of the heating element and the electrical resistance value of the first adjustment resistor is constant at that time. 9. The oxygen concentration measuring device according to claim 7 or 8, wherein the electrical resistance value of the first adjusting resistor is adjusted so that the electrical resistance value of the first adjusting resistor is adjusted to the oxygen concentration value. (10) The control means is supplied to the heating body such that the ratio between the electrical resistance value of the heating body at room temperature and the electrical resistance value of the oxygen concentration detection unit under the heating state is constant. The oxygen concentration measuring device according to any one of claims 1 to 6, which controls electric power or voltage. (11) In a structure in which an oxygen sensing element formed by integrally forming the oxygen concentration sensing section and the heating body is connected to an external device via a connector, the control means is located on the connector or provided in a power supply circuit to the heating body located closer to the oxygen sensing element than that;
11. The oxygen concentration measuring device according to claim 10, comprising at least one second adjusting resistor whose electrical resistance value is adjusted. (12) The oxygen concentration measuring device according to claim 11, wherein the second adjustment resistor is integrally provided in a power supply circuit portion to the heating body, which is located on the oxygen sensing element. . (13) The oxygen concentration detection unit includes a diffusion chamber for diffusing the gas to be measured under a predetermined diffusion resistance, an oxygen pump means for changing the oxygen concentration in the atmosphere in the diffusion chamber, and an oxygen pump means for changing the oxygen concentration in the atmosphere in the diffusion chamber. 13. The oxygen concentration measuring device according to any one of claims 1 to 12, comprising an oxygen concentration battery means for detecting the oxygen concentration of the oxygen concentration. (14) The oxygen concentration measuring device according to any one of claims 1 to 13, wherein the heating body is formed using platinum as a conductor. (15) The oxygen concentration measuring device according to any one of claims 1 to 14, wherein the oxygen concentration detection section is made of an oxygen ion conductive solid electrolyte containing ZrO_2 as a main component. (16) The oxygen concentration measuring device according to any one of claims 1 to 15, wherein the heat generating part of the heating body is shielded from the gas to be measured so as not to be directly exposed to the gas.