JP2996109B2 - NOx sensor and NOx detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nitrogen oxide (hereinafter referred to as NO
The present invention relates to a NOx sensor for detecting the concentration of x) and a detection method thereof.

[0002]

2. Description of the Related Art In recent years, NOx emitted from internal combustion engines such as household combustion equipment and automobiles is not only harmful to the human body but also causes destruction of the global environment such as air pollution and acid rain. There is a strong demand for the establishment of an accurate and rapid detection technique, and the use of NOx sensors using electrolytes is increasing.

Conventionally, this type of NOx sensor has been disclosed in
The configuration as shown in Japanese Patent No. 18480 was common.
Hereinafter, the configuration will be described with reference to the drawings.

As shown in FIG. 8, a conventional NOx sensor is composed of a solid electrolyte 1 having oxygen ion conductivity, for example, stabilized zirconia, and a chamber 14 and 15 divided into two spaces by a wall 13 at the center. Forming and wall 1
A pair of electrodes 2 and 3 having a different area, such as a catalyst material having NOx decomposition characteristics, such as platinum, or a pair of the same areas formed of a material having different NOx decomposition rates, such as platinum and rhodium, sandwiching 3 therebetween. And a sensor element having a configuration for forming the electrodes. This NOx sensor is activated when NOx is introduced into the chambers 14 and 15.
The decomposition rate at each of the electrodes 2 and 3 due to the catalysis is asymmetric, and a potential difference is generated.
6 was used to determine the NOx concentration.

[0005]

However, in the above configuration, when the operating temperature changes, for example, when the location of the sensor changes in an atmosphere where there is a temperature distribution, the temperature differs from the specified operating temperature. When the battery is used in an air conditioner or when an abnormality such as deterioration occurs in the heater, the bulk resistance of the solid electrolyte and the NOx decomposition rate by the catalyst fluctuate. Therefore, the relationship between the potential difference and the NOx concentration is broken. Had the problem of not being able to.

Further, when oxygen is contained in the gas to be measured, the decomposition of NOx by the catalytic action on the electrode is inhibited by oxygen, so that there is a problem that an accurate NOx concentration cannot be obtained. .

Further, in the conventional configuration, when an abnormality occurs in the sensor element such as a lead wire being broken or an electrode being peeled off in the chamber during the measurement, the situation cannot be immediately confirmed, and the inspection cannot be performed. Therefore, there is a problem that it takes time and effort to lower the temperature and disassemble the sensor element.

The present invention solves such a conventional problem. Even when the operating temperature changes or when the gas to be measured contains oxygen, an accurate NOx concentration is obtained correspondingly. If an abnormality occurs in the sensor element,
It is an object of the present invention to provide a NOx sensor for judging and warning the situation and interrupting the measurement and a method for detecting the NOx sensor.

[0009]

In order to solve the above problems, a NOx sensor and a NOx detection method according to the present invention have the following configuration or method.

That is , the electrolyte, the first electrode, and the second
, An impedance measuring device, an oxygen concentration detecting means, and an arithmetic means for calculating the NOx concentration from the impedance and the oxygen concentration.

[0011] Further, the electrolyte and the electrolyte may be set in opposition.
Sensor comprising a first electrode and a second electrode
An impedance measuring device between the element and the electrode;
Computing means for calculating the NOx concentration from the dance,
The first electrode is made of a material containing at least one of a noble metal or a NOx adsorbing compound, is formed on one side of the electrolyte, and the second electrode is made of the same material as the first electrode, The electrolyte was formed on the other surface of the electrolyte so as to face the first electrode.

Further, an electrolyte, a first electrode, a second electrode, and the sensor element composed of a reference electrode, said sensor
AC between the first electrode and the second electrode of the semiconductor device
A voltage is applied to open the gap between the first electrode and the reference electrode.
An impedance measuring device for measuring impedance and a calculating means for calculating NOx concentration from impedance were used.

The first electrode is made of a material containing at least one of a noble metal and a NOx adsorbing compound, is formed on one side of the electrolyte, and the second electrode and the reference electrode are electrically conductive. The second material
Is formed on the other surface of the electrolyte so as to face the first electrode.

The NOx adsorbing compound is Ba ₂
It was configured to have a YCu ₃ O ₇ type structure.

[0015] Further, a sensor element composed of an electrolyte and a plurality of electrodes, a heater, a DC power supply, an impedance measuring instrument, an arithmetic means for obtaining NOx concentration from impedance, and a bulk resistance within a specified range. Comparing means for determining whether there is, signal means for warning an abnormality,
The DC power supply is turned off, and a stop means for interrupting the impedance measurement is provided.

Further, the electrolyte is a solid electrolyte substrate having oxygen ion conductivity.

Further, the impedance between the first electrode and the second electrode of the sensor element composed of the electrolyte, the first electrode, and the second electrode is measured by an impedance measuring device, and the calculation is performed. Means are to obtain a bulk resistance and an electrode resistance from the impedance, obtain a temperature corresponding to the bulk resistance, and obtain a NOx concentration corresponding to the electrode resistance and the temperature.

Further, the impedance between the first electrode and the second electrode of the sensor element composed of the electrolyte, the first electrode, and the second electrode is measured by an impedance measuring device, and oxygen is measured. Oxygen concentration is detected by concentration detection means, bulk resistance and electrode resistance are obtained from the impedance by calculation means, a temperature corresponding to the bulk resistance is obtained, and a method corresponding to the oxygen concentration and the electrode resistance and the temperature is employed. .

Further, the first element of the sensor element comprising an electrolyte, a first electrode, a second electrode, and a reference electrode .
By applying an AC voltage between the and the electrode second electrode in the impedance between the reference electrode and the first electrode
The impedance was measured by a impedance measuring instrument, the bulk resistance and the electrode resistance were determined from the impedance by the calculating means, the temperature corresponding to the bulk resistance was determined, and the method was adapted to the electrode resistance and the temperature.

Further, a sensor element composed of an electrolyte and a plurality of electrodes is heated and held at a predetermined temperature by a heater, an impedance between the electrodes is measured by an impedance measuring instrument, and a bulk resistance is calculated from the impedance by a calculating means. And the electrode resistance is determined, and whether or not the bulk resistance is within a specified range is determined by comparison means, and if it is within the range, the NOx concentration corresponding to the electrode resistance is determined by the calculation means, and If so, a method is used in which the abnormality of the heater or the sensor element is warned by signal means, the DC power supply for supplying voltage to the heater is turned off by stop means, and the measurement of impedance is interrupted.

[0021]

In general, a system composed of a solid electrolyte and electrodes can be approximated by an equivalent circuit as shown in FIG. 9, and its complex impedance Z is expressed by the following equation.

[0022]

(Equation 1)

Here, Z 'and Z "are a resistance component and a reactance component, respectively, of the complex impedance Z. Zb, Zgb, Ze are impedances of a bulk, a grain boundary, and an electrode, respectively, and are attached b, g.
b and e indicate a bulk, a grain boundary, and an electrode, respectively. R, C, ω and α are a resistance component, a capacitance component,
Represents angular frequency and depletion factor, ω
0 indicates the resonance angular frequency. In general, for Z '
When plotting Z ″, a curve composed of three arcs is obtained as shown in FIG. 10. Impedance based on bulk, grain boundaries, and electrodes is shown in order from the left arc in FIG.
As the angular frequency ω increases, the electrode, the grain boundary, and the bulk appear in this order, and the angular frequency at the apex of each arc corresponds to the respective resonance angular frequency ω0. The bulk, grain boundary, and electrode resistance can be determined from the real axis intercept of each arc. Further, when the thickness of the solid electrolyte and the electrode area are constant, N
The bulk and grain boundary resistance of the Ox sensor element is a function of temperature, and the electrode resistance is a function of temperature and NOx concentration.
Therefore, the impedance is measured by the present invention, the bulk resistance and the electrode resistance are obtained by the arithmetic means, and the temperature is obtained from the bulk resistance, and the NOx is obtained from the temperature and the electrode resistance.
Since the concentration can be obtained, an accurate NOx concentration can be obtained even when the operating temperature of the sensor fluctuates, and the reliability can be improved.

[0024] Further, by the configuration in which the oxygen concentration detecting means is added to the NOx sensor having the electrode containing the NOx adsorbing compound, even if the gas to be measured contains oxygen, the oxygen is not hindered on the electrode. , NOx concentration can be detected.

According to the structure in which the sensor element includes the electrolyte, the first electrode, the second electrode, and the reference electrode,
The first electrode is formed on one surface of the electrolyte using a material containing a NOx adsorbing compound, and the second electrode and the reference electrode are formed on the other surface using a conductive material. Since the second electrode and the reference electrode can be formed simultaneously, the workability can be improved.

The electrode resistance obtained by measuring the impedance between the electrodes of the sensor element represents the sum of the electrode resistances of the two electrodes. Therefore, when obtaining the electrode resistance, the configuration of the electrodes formed on both surfaces of the solid electrolyte substrate, for example, the material, the electrode area, and the like must be the same. But,
With the configuration using the reference electrode, the necessary electrode resistance can be obtained by measuring the impedance between the electrode on the desired side and the reference electrode.

Further, comparing means for judging whether or not the bulk resistance is within a specified range, signal means for warning an abnormality, and stopping means for turning off a DC power supply for supplying voltage to the heater and interrupting impedance measurement are provided. With the added configuration, when the bulk resistance calculated from the impedance between the electrodes by the comparison means is out of the specified range, it is determined that an abnormality has occurred in the heater or the sensor element, a warning is issued by the signal means, and the DC power supply is stopped by the stop means. It is economical and safe because the impedance measurement can be interrupted.

[0028]

EXAMPLE (Example 1) As shown in FIG. 1, the NOx sensor of Example 1 includes a solid electrolyte 1 having oxygen ion conductivity, a first electrode 2,
It comprises a sensor element comprising the second electrode 3, an impedance measuring device 4, and a calculating means 5.

First, a solid electrolyte 1 substrate of 10 mm square and 0.35 mm thickness made of stabilized zirconia to which 8 mol% of yttria was added was sufficiently washed, and platinum as a noble metal and NOx adsorption were formed on one surface as a first electrode 2. An electrode paste in which barium yttrium copper oxide (Ba ₂ YCu ₃ O ₇ ), which is an acidic compound, was mixed in an equimolar amount was screen-printed and dried. Next, on the other surface, the same electrode paste was printed in the same pattern as the second electrode 3 facing the first electrode 2 in the same pattern, dried, and baked in an electric furnace at about 820 ° C. for 10 minutes in the atmosphere. . The size of each electrode after firing was 8 mm square, and the thickness was about 40 μm. Next, a platinum lead wire having a diameter of 0.1 mm and a length of 20 mm was fixed to each electrode with a gold paste, and baked at 700 ° C. for 10 minutes in the atmosphere. About 450 minutes to preprocess the sensor element obtained as described above.
C., and a DC power supply was connected between the electrodes via a lead wire, and a current was passed in about 500 ppm NOx (helium balance) so that the current density became about 10 mA / cm ² for 10 minutes. This sensor element is connected to the impedance measuring device 4 and the calculating means 5 as shown in FIG.
Sensor.

The electrolyte 1 is composed of other stabilized zirconia, ceria, and yttrium-stabilized zirconia.
An oxygen ion conductive solid electrolyte such as bismuth oxide may be used, and the size and thickness are not limited as long as they are implemented. Also the first
The electrode 2 and the second electrode 3 are not limited to those described above.
Catalyst materials that decompose Ox into nitrogen and oxygen are considered, for example, porous noble metals such as platinum and rhodium, perovskite-type composite oxides such as lanthanum cobalt oxide, or oxides such as lanthanum copper oxide and manganese oxide and the like. Is considered to be suitable as an electrode material, and the size and thickness of the electrode are not limited as long as they are implemented. In the case of this embodiment, the first electrode 2 and the second electrode 3 need to have the same conditions such as the material and the area. The firing conditions depend on the materials used, but it is preferable to determine the most suitable conditions by experiments. The material, size, mounting method, etc. of the lead wire are not limited as long as they are implemented. In addition, although a current was passed through the sensor element as pre-processing, processing conditions such as temperature, atmosphere, current density, and time are not limited to those performed, and it is preferable to experimentally find optimum conditions.

The NOx sensor obtained in this manner is placed in a tubular electric furnace whose temperature can be controlled and has an inner diameter of 20 mm and a length of 50 mm.
It was fixed in a 0 mm quartz tube. Various concentrations of NOx gas were flowed into the quartz tube at a flow rate of about 200 cc / min. Then, the impedance between the electrodes was measured with an impedance measuring device at an applied voltage of 10 mV and a frequency range of 100 mHz to 1 MHz.

First, in order to check the bulk resistance of the solid electrolyte 1, the temperature of the electric furnace was changed from 400 to 550 ° C., and the impedance at each temperature was measured.
Bulk resistance was determined from the measured values. When the logarithm of the reciprocal of the bulk resistance Rb is plotted against the reciprocal of the absolute temperature T, FIG.
become that way. According to FIG. 2, the activation energy E is about 0.9.
3 eV, and the relationship between the absolute temperature T and the bulk resistance Rb can be expressed by the following equation.

[0033]

(Equation 2)

Here, R is a gas constant, and A can be obtained from the value of the intercept of the vertical axis in FIG. Therefore, if the bulk resistance is determined by impedance measurement, the temperature can be determined by the above equation. That is, according to the configuration of the NOx sensor of the present invention, it can be applied as a temperature sensor.

Next, the temperature was fixed at 450 ° C., the NOx concentration was changed from 500 ppm to 5000 ppm,
The x concentration characteristics were examined. The horizontal axis is the logarithm of the NOx concentration C _NOX ,
When the logarithm of the reciprocal of the electrode resistance Re is plotted on the vertical axis, the result is as shown in FIG. From FIG. 3, the NOx concentration C nox at this temperature is shown.
And the electrode resistance Re can be approximated by the following equation.

[0036]

(Equation 3)

Here, a and b are the slope and vertical axis intercept, respectively, obtained from the straight line in FIG. NOx concentration C
_Although the relationship between _NOX and electrode resistance Re can be considered other than the above equation,
It is preferable to derive the optimum relationship experimentally as necessary.

Further, similarly, at a temperature of 400 to 550 ° C., N
The impedance between the electrodes was measured at several points in the Ox concentration range of 500 ppm to 5000 ppm, and the characteristics of the electrode resistance were examined.

From the above results, when the reciprocal of the temperature T is plotted on the x-axis, the logarithm of the NOx concentration C _NOX is _{plotted on} the y-axis, and the logarithm of the reciprocal of the electrode resistance Re is plotted on the z-axis, the temperature T, the NOx concentration C _NOX and the electrode resistance Re Is considered to be able to be approximated by a plane such as the following equation.

[0040]

(Equation 4)

Where l, m and n are the intercepts of the x, y and z axes, respectively, and p is the perpendicular distance from the origin to the plane. The relationship between the temperature, the NOx concentration and the electrode resistance may be other than the above formula, but it is preferable to derive the optimum relationship experimentally as necessary.

As described above, with the configuration of the NOx sensor of the first embodiment, an accurate NOx concentration can be obtained only by measuring the impedance even when the operating temperature of the sensor fluctuates.

(Embodiment 2) The NOx sensor of Embodiment 2 is similar to that of Embodiment 1 as shown in FIG.
This is the same as the first embodiment except that the oxygen concentration detecting means 7 is added to the NOx sensor of FIG. The electrode according to the present invention has NO even when oxygen is contained in the atmosphere.
Since a material having a property of selectively adsorbing x is used, even if oxygen is contained in the gas to be measured,
Ox concentration can be detected.

Thereafter, in the same manner as in Example 1, the concentrations of NOx and oxygen in the atmosphere were changed variously to
The relationship between temperature and NOx and oxygen concentrations was examined. First, the oxygen concentration was fixed, the impedance between the electrodes was measured in the same manner as in Example 1, and the relationship among the electrode resistance, the temperature, and the NOx concentration was determined. It is considered that the relationship can be approximated by a plane equation as in the first embodiment. Next, reduce the oxygen concentration from several thousand ppm to
The same measurement was performed by changing to several tens%. At this stage, a relational expression between the electrode resistance, the temperature, the NOx concentration and the oxygen concentration has not been found, but the relationship between the oxygen concentration, the electrode resistance, the temperature and the NOx concentration is determined in advance according to the use environment of the NOx sensor. When the oxygen concentration in the gas to be measured is measured by the oxygen concentration detecting means 7 when actually detecting it,
Electrode resistance corresponding to or approximating the oxygen concentration,
The NOx concentration can be obtained by using the relational expression between the temperature and the NOx concentration.

Therefore, according to the configuration of the second embodiment, even when the gas to be measured contains oxygen, N
Ox concentration can be determined.

Embodiment 3 The NOx sensor of Embodiment 3 is the same as Embodiment 1 except for the configuration of the sensor element. Third Embodiment A NOx sensor according to a third embodiment will be described with reference to FIGS. 5 and 6, the sensor element is provided on one surface of the same solid electrolyte 1 substrate as in Example 1,
An electrode paste composed of the same mixture of platinum and barium-yttrium-copper oxide as in Example 1 was used.
A first electrode 2 having a size of 6 mm × 8 mm is formed, and an electrode paste made of a conductive material, platinum, is formed on the other surface so as to face the first electrode 2. The electrode 3 was formed, and a 1 mm × 8 mm reference electrode 6 was formed in the vicinity of the electrode 3 using the same electrode paste containing platinum. The electrode paste made of a conductive material may be another conductive material such as nickel, in addition to the implemented platinum. Although the size of each electrode is not limited, the resistance of the reference electrode 6 needs to be as small as possible. The location of the reference electrode 6 may be other than that shown in FIG. 6.
The second is that the printing process only needs to be performed once and the efficiency is high.
It is desirable to form it on the same surface as the electrode 3. In addition, the second electrode 3 and the reference electrode 6 may be formed by an electroless plating method, a sputtering method, or the like in addition to the screen printing method performed, but the screen printing method is preferable because the cost is low.

Next, lead wires were connected in the same manner as in Example 1, and a current was applied between the first electrode 2 and the second electrode 3 under the same conditions as in Example 1 as pretreatment.

The sensor element obtained as described above is connected between the first electrode 2 and the second electrode 3 so that an AC voltage is applied between the first electrode 2 and the second electrode 3 as shown in FIG. The impedance measuring device 4 is connected so that the impedance between the reference electrodes 6 can be measured.
A NOx sensor was used.

The same experiment as in Example 1 was conducted for this NOx sensor. The values of the bulk resistance and the electrode resistance were reduced by about half as compared with the measured values of Example 1. Since the impedance between the reference electrode 6 and the first electrode 2 having a small electrode resistance was measured, the bulk resistance was reduced to about half, and the electrode resistance was reduced to about half to indicate the electrode resistance of only the first electrode. Conceivable. Relationship between temperature and the bulk resistivity relationships and temperature and NOx concentration and the electrode resistance becomes the same result substantially Example 1, Example 2 NO
Also in the configuration of the x sensor, by measuring the impedance between the reference electrode 6 and the first electrode 2, if the bulk resistance and the electrode resistance are obtained, not only can the NOx concentration be detected, but also the second electrode 3 can be detected. Since it is sufficient that this material is a conductive material, the configuration is simpler and the cost is lower than in the first embodiment.

[0050] The NOx sensor (Example 4) Example 4 will be described with reference to FIG. The NOx sensor of the fourth embodiment is different from the first embodiment in that the heater 8, the DC power supply 9 for supplying a voltage to the heater 8, the comparing means 10 for determining whether or not the bulk resistance of the sensor is within a specified range, and the heater 8 Alternatively, the configuration is the same except that a signal unit 11 for warning when an abnormality occurs in the sensor element and a stop unit 12 for turning off the DC power supply 9 and interrupting the impedance measurement are added.

According to the configuration of the fourth embodiment, since the bulk resistance is expressed as a function of the temperature, if the heater 8 is abnormal, the bulk resistance changes when the temperature rises or falls suddenly. Therefore, it is determined whether or not the bulk resistance is within a predetermined range of the operating temperature by using the comparing means 10, and when the bulk resistance exceeds the range, a warning is issued by the signal means 11 such as a lamp or an alarm device as a heater abnormality. Can be.

If the gap between the electrodes is completely cut, for example, when the lead wire is broken, the substrate is cracked, or the electrode film is peeled off, the impedance does not draw an arc, and the impedance is partially removed. If so, the effective area of the electrode changes, so that the bulk resistance also changes. Therefore, if the range of the bulk resistance is specified in advance, the comparing means 10
If it is determined that the bulk resistance is out of the range and an abnormality has occurred in the sensor element, a warning can be issued by the signal means 11, and furthermore, what abnormality has occurred in the sensor element can be predicted to some extent from the impedance. Therefore, according to the configuration of the fifth embodiment, it is possible to save the trouble of taking out the sensor and disassembling and checking the situation as in the related art.

Further, it is safe and economical if the DC power supply 9 is turned off by the stopping means 12 and the impedance measurement is interrupted at the same time when the abnormality is warned.

[0054]

As described above, according to the NOx sensor and the method for detecting the same according to the present invention, the following effects can be obtained.

(1) The impedance between the electrodes formed on the electrolyte is measured, the temperature is determined from the bulk resistance, and the NOx degree is calculated from the temperature and the electrode resistance.
Even when the operating temperature is changed, the heater is deteriorated, or the location of the sensor is changed in an atmosphere having a temperature distribution, an accurate NOx degree can be obtained. Further, there is an effect that the configuration of the present invention can be applied as a temperature sensor.

(2) Since a material containing a NOx adsorbing compound is used for the electrode, the NO concentration can be calculated from the oxygen concentration, the bulk resistance (or temperature), and the electrode resistance when used in combination with the oxygen sensor. In addition, there is an effect that an accurate NO concentration can be obtained even if oxygen is contained in the gas to be measured.

(3) The electrode of the sensor element is a first electrode,
With the configuration including the second electrode and the reference electrode, the electrode containing the NOx adsorbing compound may be only the first electrode, and the second electrode and the reference electrode may be anything as long as they are an electronic conductor. There is an effect that the configuration is simplified and the cost is reduced. Further, since the second electrode and the reference electrode can be formed on the same surface, there is an effect that efficiency is improved in workability.

( 4 ) By measuring the impedance and determining the bulk resistance, it is possible to detect a change in the temperature or the effective electrode area of the sensor element. Therefore, it is determined whether or not the bulk resistance is within a specified range by comparing means. Beyond the range, signal means such as lamps and alarms can be used to warn of abnormalities in the heater or sensor element, etc.Furthermore, by turning off the heater and interrupting impedance measurement, it is safe and economical. It has the effect of becoming. In addition, abnormalities in the sensor element, such as disconnection or electrode peeling, may occur to some extent by measuring impedance without drawing an arc or reducing bulk resistance, even if the element is not taken out by lowering the temperature. There is an effect that the situation can be determined.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a NOx sensor according to one embodiment of the present invention.

FIG. 2 is a temperature characteristic diagram of a bulk resistance of the NOx sensor.

FIG. 3 is a NOx concentration characteristic diagram of a bulk resistance of the NOx sensor.

FIG. 4 is a schematic configuration diagram of a NOx sensor according to another embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a NOx sensor according to another embodiment of the present invention.

FIG. 6 is a top view and a cross-sectional view of the sensor element.

FIG. 7 is a schematic configuration diagram of a NOx sensor according to another embodiment of the present invention.

FIG. 8 is a sectional view of a conventional NOx sensor.

FIG. 9 is a diagram showing an equivalent circuit of a solid electrolyte / electrode system.

FIG. 10 is a diagram showing impedance of a solid electrolyte / electrode system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte 2 1st electrode 3 2nd electrode 4 Impedance measuring device 5 Computation means 6 Reference electrode 7 Oxygen concentration detection means 8 Heater 9 DC power supply 10 Comparison means 11 Signal means 12 Stop means

Claims (11)

(57) [Claims] 1. A sensor element comprising an electrolyte, a first electrode, and a second electrode, an impedance measuring device, an oxygen concentration detecting means, and NO based on impedance and oxygen concentration.
a NOx sensor comprising: an arithmetic unit for determining the x concentration. 2. An electrolyte, provided opposite to said electrolyte.
Sensor element composed of a first electrode and a second electrode
And an impedance measuring device between the electrodes, and an impedance
Calculating means for calculating the NOx concentration from the impedance, wherein the first electrode is made of a material containing at least one of a noble metal or a NOx adsorbing compound, is formed on one surface of the electrolyte, and the second electrode Is made of the same material as the first electrode, and the first surface is provided on the other surface of the electrolyte.
NOx sensor formed so as to face the electrodes of the NOx . 3. An electrolyte, a first electrode, a second electrode,
A sensor element composed of a reference electrode and the sensor element
Between the first electrode and the second electrode.
To apply an impedance between the first electrode and the reference electrode.
An impedance measuring device for measuring a-impedance, NOx sensor consisting of a calculating means for calculating the NOx concentration from the in-<br/> impedance. 4. The first electrode is made of a material containing at least one of a noble metal or a NOx adsorbing compound, is formed on one side of the electrolyte, and the second electrode and the reference electrode are
4. The NOx sensor according to claim 3 , wherein the NOx sensor is made of a conductive material, and the second electrode is formed on the other surface of the electrolyte so as to face the first electrode. 5. The NOx adsorbing compound is Ba ₂ YCu ₃ O ₇
5. The NOx sensor according to claim 2, which has a mold structure. 6. A sensor element comprising an electrolyte and a plurality of electrodes, a heater, a DC power supply, an impedance measuring device, an arithmetic unit for calculating NOx concentration from impedance, and a bulk resistance within a specified range. A NOx sensor comprising: comparing means for judging whether there is a signal; signal means for warning an abnormality; and stopping means for turning off the DC power supply and interrupting impedance measurement. 7. The electrolyte, NOx sensor according to claim 1, 2, 3, 4 or 6 wherein the solid electrolyte substrate having oxygen ion conductivity. 8. An impedance measuring device measures an impedance between the first electrode and the second electrode of a sensor element composed of an electrolyte, a first electrode, and a second electrode, and calculates the impedance. Means for obtaining a bulk resistance and an electrode resistance from the impedance, obtaining a temperature corresponding to the bulk resistance, and obtaining NOx corresponding to the electrode resistance and the temperature.
A NOx detection method for obtaining a concentration. 9. An oxygen measuring device for measuring the impedance between the first electrode and the second electrode of a sensor element composed of an electrolyte, a first electrode and a second electrode by an impedance measuring device. The oxygen concentration is detected by the concentration detecting means, the bulk resistance and the electrode resistance are obtained from the impedance by the calculating means, the temperature corresponding to the bulk resistance is obtained, and the oxygen concentration and the NOx concentration corresponding to the electrode resistance and the temperature are obtained. N O x detection method for finding. 10. A sensor element comprising an electrolyte, a first electrode, a second electrode, and a reference electrode.
An AC voltage is applied between the pole and the second electrode to impede the impedance between the first electrode and the reference electrode.
A NOx detection method for measuring a bulk resistance and an electrode resistance from the impedance by means of a measuring device , calculating a bulk resistance and an electrode resistance from the impedance, calculating a temperature corresponding to the bulk resistance, and obtaining a NOx concentration corresponding to the electrode resistance and the temperature; 11. A sensor element composed of an electrolyte and a plurality of electrodes is heated and held at a predetermined temperature by a heater, an impedance between the electrodes is measured by an impedance measuring instrument, and a bulk resistance is calculated from the impedance by arithmetic means. And the electrode resistance is determined, and whether or not the bulk resistance is within a specified range is determined by comparison means, and if it is within the range, the NOx concentration corresponding to the electrode resistance is determined by the calculation means, and If so, a NOx detection method in which an abnormality of the heater or the sensor element is warned by a signal means, a DC power supply for supplying a voltage to the heater is turned off by a stop means, and measurement of impedance is interrupted.