A method for measuring NOx concentration

Abstract

The present invention provides a ceramic chip and gas sensor for measuring NOx concentration, which improve the real-time performance and accuracy of NOx measurement under dynamic atmosphere conditions. The chip includes a ceramic body with three cavities arranged therein, which are connected in sequence through slits. The first cavity is equipped with a Pi oxygen detection electrode for detecting oxygen concentration; the second cavity is equipped with a P1 main oxygen pump electrode, a Pm main oxygen pump electrode, and a Pa oxygen monitoring electrode, which are responsible for ionizing oxygen molecules and monitoring oxygen concentration, generating a pump current Ip1; the third cavity is equipped with a P2 measuring electrode, which ionizes oxygen in NOx and generates a current Ip2, which represents the NOx concentration. The control unit can detect the oxygen concentration in advance based on the voltage Vi between the Pi electrode and the Pr reference air electrode, and predictively adjust the pump voltage Vp1 to keep V1 and V2 in a reasonable state, thereby improving measurement accuracy. Especially in environments where the oxygen concentration and air pressure change rapidly, such as automobile exhaust, the chip can significantly improve the real-time performance and accuracy of NOx measurement.

Description

Technical Field

[0001] The present invention relates to a gas concentration measurement technology, in particular to a NOx concentration measurement ceramic chip and a gas sensor. Background Art

[0002] Nitrogen oxides (NOx) are common atmospheric pollutants, primarily originating from diesel engine exhaust and boiler combustion exhaust. To control NOx emissions, countries around the world have implemented strict emission policies and regulations. Currently, the most common treatment for NOx is selective catalytic reduction, which uses the reducing agent ammonia to neutralize NOx, resulting in pollution-free water and nitrogen. To achieve more efficient catalytic reduction, save costs, and avoid secondary pollution, the device must be equipped with a NOx sensor to detect NOx concentration and determine the amount of reducing agent used. Therefore, NOx concentration sensors play a crucial role, and the ceramic chip within the sensor is a core component.

[0003] CN207516302U discloses a ceramic chip for a gas sensor, comprising a first oxygen ion conductor layer, an insulating layer, and a second oxygen ion conductor layer stacked sequentially from top to bottom. The first oxygen ion conductor layer has a first cavity located above the insulating layer, and the second oxygen ion conductor layer has a second cavity located below the insulating layer. The outer and inner sides of the oxygen ion conductor of the first cavity are coated with an outer main pump electrode and an inner main pump electrode, respectively; the insulating layer is coated with a heater electrode; the inner side of the oxygen ion conductor of the second cavity is coated with a measuring electrode and an auxiliary pump electrode, and the outer side of the oxygen ion conductor of the second cavity is coated with a reference electrode; a first chamber within the first cavity and a second chamber within the second cavity are connected through a perforated slit in the insulating layer; a first diffusion barrier for a gas channel is provided between the first cavity and the outer side of the chip; the perforated slit in the insulating layer serves as a second diffusion barrier for the gas channel; and a third diffusion barrier for the gas channel is provided between the second cavity and the measuring electrode. The ceramic chip of this gas sensor achieves insulation separation of the ion-conducting matrix through the design of the insulating layer and the position structure of the airway cavity, as well as the design of the position structure of the heater electrode, so that each pump unit is separated and has no mutual influence during operation. The electrical signals of each working electrode are insulated, thereby reducing interference between signals during the chip measurement process, improving the accuracy of telecommunication signal acquisition, and improving the accuracy of gas concentration testing.

[0004] However, existing technologies still face challenges in further improving the measurement accuracy of chips under dynamic atmosphere conditions.

[0005] It should be noted that the information disclosed in the above background technology section is only used to understand the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0006] The main purpose of the present invention is to overcome the defects existing in the above-mentioned background technology and provide a NOx concentration measurement ceramic chip and gas sensor to improve the real-time performance and accuracy of measurement under dynamic atmosphere conditions.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A ceramic chip for measuring NOx concentration, comprising:

[0009] The ceramic body includes a first cavity, a second cavity, and a third cavity; the gas to be measured enters the first cavity through the slit, and the first cavity, the second cavity, and the third cavity are connected in sequence through the slit;

[0010] The first cavity is provided with a Pi oxygen detection electrode for detecting the oxygen concentration of the incoming gas;

[0011] The second cavity is provided with a P1 main oxygen pump electrode, a Pm main oxygen pump electrode and a Pa oxygen monitoring electrode. The P1 main oxygen pump electrode is used to ionize oxygen molecules in the measured gas into oxygen ions, and the Pm main oxygen pump electrode is used to receive the oxygen ions and reduce them into oxygen molecules to form a pump current Ip1; the Pa oxygen monitoring electrode is used to monitor the residual oxygen concentration in the cavity and form a Nernst voltage V1 between it and the Pr reference air electrode;

[0012] The third chamber is provided with a P2 measuring electrode, which is used to ionize the oxygen in NOx into oxygen ions, and under the action of the voltage V2 between it and the Pr reference air electrode, the oxygen ions move to the Pr reference air electrode and are reduced to oxygen molecules, generating a current Ip2, which represents the NOx concentration in the measured gas;

[0013] A control unit detects the oxygen concentration in advance based on the voltage Vi between the Pi oxygen detection electrode and the Pr reference air electrode. When it is detected that the voltage change rate of Vi is higher than a preset threshold, if Vi decreases, the pump voltage Vp1 is increased according to the pre-calibrated correspondence between Vi and Vp1, thereby increasing the amount of oxygen pumped from the second chamber to the Pm electrode, thereby maintaining the residual oxygen concentration in the second chamber at a predetermined low stable level. If Vi increases, the pump voltage Vp1 is reduced according to the pre-calibrated correspondence between Vi and Vp1 to reduce oxygen pumping, thereby maintaining the residual oxygen concentration in the second chamber at a predetermined low stable level.

[0014] Furthermore, the Nernst voltage V1 of the Pa electrode is detected and used as a feedback signal to fine-tune Vp1. When V1 is greater than a predetermined range, Vp1 is reduced, and when V1 is less than the predetermined range, Vp1 is increased, thereby forming a closed-loop control.

[0015] Furthermore, a heating wire is included for heating the chip by powering on and keeping the chip at a constant operating temperature.

[0016] Furthermore, the ceramic body of the chip is mainly composed of zirconium oxide.

[0017] Furthermore, the first to third cavities are arranged between two zirconium oxide layers, and an aluminum oxide layer is sandwiched between the two zirconium oxide layers in areas outside the first to third cavities.

[0018] Furthermore, the Pr reference air electrode is provided on the other side of the zirconium oxide layer, in a cavity communicating with the outside air.

[0019] A gas sensor is provided with the NOx concentration measuring ceramic chip.

[0020] A NOx concentration measurement method uses the NOx concentration measurement ceramic chip to measure NOx concentration.

[0021] The present invention has the following beneficial effects:

[0022] The NOx concentration measurement ceramic chip of the present invention significantly improves the real-time performance and accuracy of NOx measurement under dynamic atmosphere conditions through its unique design. The chip uses a ceramic body with zirconium oxide as the main material, and is provided with three cavities inside, which are connected in sequence through slits, so that the gas to be measured can pass through each cavity in an orderly manner for detection. The first cavity is equipped with a Pi oxygen detection electrode, which is used to sense the oxygen concentration in the gas to be measured in advance and generate a voltage Vi. The second cavity is equipped with P1 and Pm main oxygen pump electrodes and Pa oxygen monitoring electrodes. The P1 electrode is responsible for ionizing oxygen molecules, and the Pm electrode is responsible for reducing oxygen ions and forming a pump current Ip1. The Nernst voltage V1 formed between the Pa electrode and the Pr reference air electrode reflects the residual oxygen concentration in the cavity. The third cavity is equipped with a P2 measuring electrode, which is used to ionize oxygen in NOx and generate a current Ip2, which directly represents the NOx concentration. The control unit can dynamically adjust the pump voltage Vp1 according to the changes in Vi and V1, optimize the stability and accuracy of V1 and V2, and avoid the deviation of the NOx measurement value caused by Vp1 being too large or too small. Especially in an environment where the oxygen concentration and pressure change rapidly, such as automobile exhaust, the present invention can predictably adjust Vp1, improve the problem of adjustment lag, and ensure the accuracy and response speed of NOx measurement results.

[0023] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of the NOx concentration measurement ceramic chip according to an embodiment of the present invention.

[0025] Figure 2 Schematic diagram of the voltages of the electrodes of the NOx concentration measurement ceramic chip according to an embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0027] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and coupling or communication.

[0028] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0030] See Figure 1 and Figure 2An embodiment of the present invention provides a ceramic chip for measuring NOx concentration, comprising a ceramic body, which is preferably composed mainly of zirconium oxide, and the ceramic body comprises a first cavity, a second cavity, and a third cavity; the gas to be measured enters the first cavity through a slit, and the first cavity, the second cavity, and the third cavity are sequentially connected through the slit; the first cavity is provided with a Pi oxygen detection electrode for detecting the oxygen concentration of the incoming gas; the second cavity is provided with a P1 main oxygen pump electrode, a Pm main oxygen pump electrode, and a Pa oxygen monitoring electrode, the P1 main oxygen pump electrode is used to ionize oxygen molecules in the gas to be measured into oxygen ions, and the Pm main oxygen pump electrode is used to receive the oxygen ions and reduce them to oxygen molecules , forming a pump current Ip1; the Pa oxygen monitoring electrode is used to monitor the residual oxygen concentration in the cavity, and forms a Nernst voltage V1 between it and the Pr reference air electrode; the third cavity is provided with a P2 measuring electrode, which is used to ionize the oxygen in NOx into oxygen ions, and under the action of the voltage V2 between it and the Pr reference air electrode, the oxygen ions move to the Pr reference air electrode and are reduced to oxygen molecules, generating a current Ip2, Ip2 represents the NOx concentration in the measured gas; a control unit, which detects the oxygen concentration in advance according to the voltage Vi between the Pi oxygen detection electrode and the Pr reference air electrode, and determines the corresponding relationship between Vi and Vp1 under different oxygen concentrations according to pre-calibration. When it is detected that the Vi voltage changes too quickly and exceeds the preset threshold, it indicates that the oxygen concentration of the measured gas has changed rapidly. Then, after a certain delay (the time it takes for the gas to diffuse from the first chamber to the second chamber), Vp1 is adjusted accordingly: if Vi decreases, it indicates that the actual oxygen concentration of the measured gas is increasing. According to the calibrated correspondence between Vi and Vp1, the pump voltage Vp1 is controlled to increase so that more oxygen is pumped to the Pm electrode, thereby maintaining the residual oxygen concentration in the second chamber at a predetermined low and stable level; if the Vi voltage increases, it indicates that the actual oxygen concentration of the measured gas is decreasing. By reducing the pump voltage Vp1 to reduce the pumping of oxygen, the residual oxygen concentration in the second chamber is maintained at a predetermined low and stable level.

[0031] The controller can set the voltage change rate threshold according to the difference between the interval Vi sampling values. If the difference between the current sampling value and the previous sampling value exceeds the set value, it can be considered as a rapid change, and the difference in the Vi sampling values ​​is converted into the rate of change of the oxygen concentration. For example, the oxygen concentration change rate threshold can be set to 5% / second. When the oxygen concentration change rate converted from the difference in the Vi sampling values ​​is detected to be greater than 5% / second, it can be determined that the oxygen concentration is changing too fast. At this time, Vi is started as the main criterion for adjusting Vp1 to quickly respond to changes in oxygen concentration. Otherwise, it can be adjusted based on the feedback of the Nernst voltage V1 alone.

[0032] During operation, the oxygen concentration detected by the Pi electrode is converted into a voltage, Vi. This voltage, calculated based on the Nernst cell principle, directly reflects the oxygen concentration. The Pi electrode is the first to come into contact with the measured gas. As the oxygen concentration in the measured gas changes, the voltage Vi also changes accordingly. Because the Vi voltage is directly related to oxygen concentration, changes in Vi can be monitored by the Pi electrode to measure oxygen concentration changes without waiting for feedback from the Pa electrode. Based on the pre-calibrated relationship between Vi and Vp1 at different oxygen concentrations, a decrease in the Vi voltage indicates an increase in oxygen concentration. The pump voltage Vp1 is increased to efficiently pump more oxygen to the Pm electrode. An increase in the Vi voltage indicates a decrease in oxygen concentration. The pump voltage Vp1 is reduced to prevent excessive oxygen from being pumped to the Pm electrode and interfering with NOx measurement. The Nernst voltage V1 of the Pa electrode serves as a feedback signal to fine-tune Vp1, achieving closed-loop control.

[0033] Through experimental multi-point calibration, the relationship between oxygen concentration, Vi voltage, and Vp1 can be determined in advance. This allows Vp1 to be adjusted directly based on the calibration results when the Vi voltage changes rapidly, without waiting for feedback from the Pa electrode. In the present invention, changes in the Vi voltage detected by the Pi electrode serve as a direct basis for adjusting Vp1, rather than waiting for changes in oxygen concentration at the P1 or Pa electrodes. Predictive adjustment of Vp1 based on immediate changes in the Vi voltage allows for a faster response to changes in oxygen concentration, preventing Vp1 from being excessively large or small, thereby improving the accuracy of NOx measurements.

[0034] The Nernst voltage V1 detected at the Pa electrode is used as a feedback signal to fine-tune Vp1. When V1 is greater than a predetermined range, Vp1 is reduced; when V1 is less than a predetermined range, Vp1 is increased, forming a closed-loop control. In a preferred embodiment, based on experimental calibration results, the control unit reduces the pump voltage Vp1 when the Nernst voltage V1 is greater than 430mV, and increases it when the Nernst voltage V1 is less than 420mV.

[0035] See Figure 1 and Figure 2 In a preferred embodiment, the first to third cavities are disposed between two zirconium oxide layers, and an aluminum oxide layer is sandwiched between the two zirconium oxide layers in areas outside the first to third cavities.

[0036] See Figure 1 and Figure 2 In a preferred embodiment, the Pr reference air electrode is disposed on the other side of the zirconium oxide layer, in a cavity communicating with the outside air.

[0037] An embodiment of the present invention further provides a gas sensor having the above-mentioned NOx concentration measuring ceramic chip.

[0038] An embodiment of the present invention further provides a method for measuring NOx concentration, which uses the NOx concentration measuring ceramic chip to measure NOx concentration.

[0039] The NOx concentration measurement ceramic chip of the present invention significantly improves the real-time and accuracy of NOx measurement under dynamic atmosphere conditions through an integrated multi-cavity design and intelligent control mechanism. The chip uses a ceramic body with zirconium oxide as the main component, and is equipped with three cavities. They are connected in sequence through slits, so that the measured gas passes through each cavity in an orderly manner for detection. The first cavity is equipped with a Pi oxygen detection electrode to sense the oxygen concentration in advance and generate a voltage Vi; the second cavity is equipped with P1 and Pm main oxygen pump electrodes and Pa oxygen monitoring electrodes. The P1 electrode ionizes oxygen molecules, the Pm electrode reduces oxygen ions to form a pump current Ip1, and the Pa electrode monitors the oxygen concentration to form a Nernst voltage V1; the third cavity is equipped with a P2 measurement electrode, which ionizes oxygen in NOx and generates a current Ip2, which directly represents the NOx concentration. The control unit can dynamically adjust the pump voltage Vp1 according to the changes in Vi and V1, optimize the stability and accuracy of V1 and V2, and avoid the deviation of the NOx measurement value caused by Vp1 being too large or too small. Especially in environments with rapidly fluctuating oxygen concentrations and pressures, such as those in automobile exhaust, the present invention can predictively adjust Vp1, reducing regulation lag and ensuring the accuracy and responsiveness of NOx measurements. Through this integrated design and intelligent control, the present invention not only improves measurement accuracy but also enhances the sensor's adaptability to rapidly changing environments, meeting the demand for accurate NOx concentration measurement in dynamic atmospheres.

[0040] Specific embodiments of the present invention are further described below.

[0041] like Figure 1 and Figure 2A ceramic chip for measuring NOx concentration and a gas sensor using the same are shown. A ceramic body primarily composed of zirconium oxide is equipped with a Pi oxygen detection electrode, a Pm (and P1) main oxygen pump electrode, a Pa oxygen monitoring electrode, a P2 (NOx) measuring electrode, and a Pr reference air electrode. An alumina insulating layer is sandwiched between the two layers of zirconium oxide to prevent the influence of pump voltage VP1 on the measured value. The ceramic chip also contains a heating wire, which generates heat when powered during measurement, heating the chip and maintaining a constant operating temperature. The measured gas diffuses into the chip cavity through the first slit and is first detected by the Pi electrode. The voltage Vi between the Pi electrode and the Pr electrode reflects the oxygen concentration of the gas. The measured gas enters the second cavity through the second slit. The P1 electrode ionizes oxygen molecules in the measured gas into oxygen ions. Under the action of the pump voltage VP1, the oxygen ions travel through the ceramic substrate to the Pm electrode and are reduced to oxygen molecules, generating a current Ip1. A Nernst voltage V1 is generated between the oxygen monitoring electrode Pa and the reference electrode Pr, reflecting the residual oxygen concentration in the cavity. The Nernst voltage V1 formed between the oxygen monitoring electrode Pa and the reference electrode Pr is greater than the preset value (preferably 420~430mV, indicating that the oxygen concentration at the Pa electrode is around 400ppm and the oxygen concentration that can enter the third chamber is close to 0), indicating that the oxygen concentration is too low. The P1 electrode will decompose more NOx gas. At this time, Vp1 is reduced, and vice versa. Vp1 is increased; Vi or current Ip1 can represent the oxygen concentration of the measured gas, but IP1 is linearly related to the oxygen concentration, and the measurement accuracy is higher than Vi.

[0042] The measured gas diffuses through the third slit into the third chamber. The P2 electrode ionizes the oxygen in the NOx into oxygen ions. Under the action of voltage V2, the oxygen ions migrate to the Pr electrode and are reduced to oxygen molecules, generating a current Ip2. Ip2 represents the NOx concentration in the measured gas. By obtaining current Ip2, the NOx concentration in the measured gas can be accurately measured. By obtaining Vi or current Ip1, the oxygen concentration of the measured gas can also be monitored. Ip1 has a linear relationship with oxygen concentration, and the measurement accuracy is higher than Vi. Because Vi can detect the oxygen concentration of the measured gas in advance, the Vp1 voltage can be predictively adjusted to maintain V1 and V2 at appropriate levels, thereby improving the accuracy of the measured value. This is particularly important in conditions such as automobile exhaust where oxygen concentration and air pressure can change suddenly, significantly improving the real-time and accuracy of NOx measurement.

[0043] According to the Nernst cell principle, Vi = (RT / 4F)*ln(Qr / Qi)

[0044] in:

[0045] R is the ideal gas constant, which is equal to 8.314570JK-1.mol-1.

[0046] T is the temperature in K.

[0047] F is the Faraday constant, 1F is equal to 96485C.mol-1.

[0048] Qr is the oxygen concentration at the Pr electrode end. Due to the introduction of air, the oxygen concentration is 20.6%;

[0049] Qi is the oxygen concentration at the Pi electrode end.

[0050] When the chip temperature is constant, the oxygen concentration of the measured gas can be obtained by measuring the Vi voltage.

[0051] Since Pi is the first to come into contact with the gas being measured, the oxygen concentration of the gas being measured can be determined based on the voltage Vi. The gas diffuses to the P1 electrode after 50ms (the specific time depends on the slit size and cavity size, and the diffusion time is basically fixed after the chip is fixed). When the oxygen concentration at the P1 end changes, the corresponding pump voltage Vp1 is adjusted to ensure that oxygen can be fully pumped out of the cavity, but it cannot be too large, causing the oxygen in the NOx to be pumped out of the cavity. Because the monitoring electrode Pa is at the rear end of the cavity, there will be a lag in the diffusion of the gas, and the feedback adjustment of Vp1 based on Pa will also have the problem of adjustment lag. In contrast, the present invention can adjust the pump voltage Vp1 based on the voltage Vi when the gas diffuses to P1, solving the problem of adjustment lag, and the Nernst voltage V1 is used as a feedback signal for fine-tuning, thereby achieving more perfect closed-loop control.

[0052] Through experimental calibration, the specific correspondence between the voltage Vi between the Pi electrode and the Pr electrode and the pump voltage Vp1 at different oxygen concentrations can be determined. This allows Vp1 to be adjusted in actual measurements based on the real-time measured Vi voltage value, ensuring the accuracy and response speed of the sensor. In this embodiment, multi-point calibration can be used to determine the correspondence between the voltage Vi between the Pi electrode and the Pr electrode and the pump voltage Vp1 at different oxygen concentrations. Specifically, four gases with different oxygen concentrations, such as 20.6% (air), 16%, 1%, and 0% (nitrogen), can be selected for calibration to establish a quantitative relationship between the Vi voltage and Vp1. The more calibration points, the more accurate the data. Considering cost factors, a four-point calibration is more reasonable. The dynamic accuracy of this embodiment can be controlled within 3%, which is significantly improved compared to the 10% dynamic accuracy of the Nernst voltage V1 adjustment.

[0053] The present invention incorporates an oxygen concentration detection electrode Pi, which can proactively sense the oxygen concentration of the gas being measured. This predictive adjustment of the pump voltage Vp1 based on changes in Vi avoids the adverse effects of excessively high or low Vp1. Excessive Vp1 can cause P1 to decompose NOx, resulting in low NOx measurements. Conversely, insufficient Vp1 can lead to incomplete oxygen pumping, allowing oxygen to reach the NOx measurement electrode P2, resulting in high NOx measurements. In environments with rapidly changing oxygen concentrations and pressures, such as those associated with automobile exhaust, this predictive adjustment mitigates the lag associated with feedback control based solely on back-end detection of residual oxygen concentration, significantly improving measurement accuracy and real-time performance in dynamic atmospheres.

[0054] The above description further details the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be construed as being limited to these descriptions. Persons skilled in the art will appreciate that, without departing from the spirit of the present invention, they may make various substitutions or modifications to the described embodiments, and these substitutions or modifications should be considered to fall within the scope of protection of the present invention. Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "preferred embodiments," "examples," "specific examples," or "some examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with such embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Persons skilled in the art may combine and assemble the different embodiments or examples described in this specification, as well as features of different embodiments or examples, without conflicting opinions. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications may be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for measuring NOx concentration using a NOx concentration measuring ceramic chip, characterized in that: The NOx concentration measurement ceramic chip includes: The ceramic body includes a first cavity, a second cavity, and a third cavity; the gas to be measured enters the first cavity through the slit, and the first cavity, the second cavity, and the third cavity are connected in sequence through the slit; The first cavity is provided with a Pi oxygen detection electrode for detecting the oxygen concentration of the incoming gas; The second cavity is provided with a P1 main oxygen pump electrode, a Pm main oxygen pump electrode and a Pa oxygen monitoring electrode. The P1 main oxygen pump electrode is used to ionize oxygen molecules in the measured gas into oxygen ions, and the Pm main oxygen pump electrode is used to receive the oxygen ions and reduce them into oxygen molecules to form a pump current Ip1; the Pa oxygen monitoring electrode is used to monitor the residual oxygen concentration in the cavity and form a Nernst voltage V1 between it and the Pr reference air electrode; The third chamber is provided with a P2 measuring electrode, which is used to ionize the oxygen in NOx into oxygen ions, and under the action of the voltage V2 between it and the Pr reference air electrode, the oxygen ions move to the Pr reference air electrode and are reduced to oxygen molecules, generating a current Ip2, which represents the NOx concentration in the measured gas; A control unit detects the oxygen concentration in advance based on the voltage Vi between the Pi oxygen detection electrode and the Pr reference air electrode. When it is detected that the speed of change of the Vi voltage is higher than a preset threshold, if Vi decreases, the pump voltage Vp1 is increased according to the pre-calibrated correspondence between Vi and Vp1, thereby increasing the amount of oxygen pumped from the second chamber to the Pm electrode, thereby maintaining the residual oxygen concentration in the second chamber at a predetermined low stable level. If Vi increases, the pump voltage Vp1 is reduced according to the pre-calibrated correspondence between Vi and Vp1 to reduce oxygen pumping, thereby maintaining the residual oxygen concentration in the second chamber at a predetermined low stable level; the Nernst voltage V1 of the Pa electrode is detected as a feedback signal to fine-tune Vp1. When V1 is greater than a predetermined range, Vp1 is reduced, and when V1 is less than the predetermined range, Vp1 is increased, thereby forming a closed-loop control.

2. The NOx concentration measurement method according to claim 1, wherein: It also contains a heating wire, which is used to heat up and keep the chip at a constant operating temperature.

3. The NOx concentration measurement method according to any one of claims 1 to 2, characterized in that: The ceramic body of the chip contains zirconium oxide as a main component.

4. The NOx concentration measurement method according to any one of claims 1 to 2, characterized in that: The first to third cavities are disposed between two zirconium oxide layers, and an aluminum oxide layer is sandwiched between the two zirconium oxide layers in regions outside the first to third cavities.

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