NOx concentration measurement ceramic chip and gas sensor

Abstract

The invention provides a NOx concentration measurement ceramic chip and a gas sensor. The instantaneity and the accuracy of NOx measurement under a dynamic atmosphere condition are improved. The chip comprises a ceramic body, and three cavities are arranged in the ceramic body and are sequentially communicated through slits. The first cavity is provided with a Pi oxygen detection electrode for detecting oxygen concentration; the second cavity is provided with a P1 main oxygen pump electrode, a Pm main oxygen pump electrode and a Pa oxygen monitoring electrode and is responsible for ionizing oxygen molecules and monitoring oxygen concentration to form pump current Ip1; the third cavity is provided with a P2 measuring electrode, oxygen in NOx is ionized, a current Ip2 is generated, and the concentration of NOx is represented. The control unit can detect the oxygen concentration in advance according to the voltage Vi between the Pi electrode and the Pr reference air electrode and foreseeably adjust the pump voltage Vp1 so as to keep V1 and V2 in a reasonable state, and the measurement accuracy is improved. Especially in the environment where the oxygen concentration and the air pressure of automobile exhaust and the like change rapidly, the chip can significantly improve the real-time performance and the accuracy of NOx measurement.

Description

Technical Field

[0001] The 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 air pollutants, mainly coming from diesel engine exhaust, boiler combustion exhaust, etc. In order to control the emission of nitrogen oxides, countries around the world have introduced strict emission policies and regulations. At present, the common treatment method for nitrogen oxides is to use selective reduction catalysis, that is, to use the reducing substance ammonia to neutralize nitrogen oxides to form pollution-free water and nitrogen. In order to use the catalytic reduction device more efficiently, save costs, and avoid secondary pollution, the device must be equipped with a nitrogen oxide sensor to detect the concentration of nitrogen oxides to determine the amount of reducing substances used. Therefore, the nitrogen oxide concentration sensor plays a very important role, and the ceramic chip in the sensor is the core component.

[0003] CN207516302U discloses a ceramic chip of a gas sensor, comprising a first oxygen ion conductor layer, an insulating layer and a second oxygen ion conductor layer stacked in sequence from top to bottom, the first oxygen ion conductor layer having a first cavity located above the insulating layer, the second oxygen ion conductor layer having a second cavity located below the insulating layer, the outer side and inner side of the oxygen ion conductor of the first cavity being coated with an outer main pump electrode and an inner main pump electrode respectively; the insulating layer being coated with a heater electrode; the inner side of the oxygen ion conductor of the second cavity being coated with a measuring electrode and an auxiliary pump electrode, and the outer side of the oxygen ion conductor of the second cavity being coated with a reference electrode; the first chamber in the first cavity is connected to the second chamber in the second cavity through a perforated slit on the insulating layer, a first diffusion barrier of a gas channel is arranged between the first cavity and the outer side of the chip, the perforated slit on the insulating layer serves as a second diffusion barrier of the gas channel, and a third diffusion barrier of the gas channel is arranged between the second cavity and the measuring electrode. The ceramic chip of the gas sensor achieves insulation separation of the ion conductive matrix through the design of the insulating layer and the airway cavity position structure, as well as the design of the heater electrode and other position structures, so that each pump unit is separated and has no mutual influence during the working process. The electrical signals of each working electrode are insulated, thereby reducing the interference between signals during the chip measurement process, improving the accuracy of telecommunication signal acquisition, and improving the accuracy of gas concentration testing. However, how to further improve the measurement accuracy of the chip under dynamic atmosphere conditions is still a challenge for the existing technology.

[0004] It should be noted that the information disclosed in the above background technology section is only used for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0005] The main purpose of the present invention is to overcome the defects existing in the above-mentioned background technology, and to provide a ceramic chip and a gas sensor for measuring NOx concentration, so as to improve the real-time performance and accuracy of the measurement under dynamic atmosphere conditions.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A NOx concentration measurement ceramic chip, comprising:

[0008] The ceramic body comprises 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;

[0009] The first chamber is provided with a Pi oxygen detection electrode for detecting the oxygen concentration of the incoming gas;

[0010] 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, 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 forms a Nernst voltage V1 with the Pr reference air electrode;

[0011] The third chamber is provided with a P2 measuring electrode, which is used to ionize oxygen in NOx into oxygen ions, and under the action of the voltage V2 between the Pr reference air electrode 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;

[0012] A control unit detects the oxygen concentration in advance according to the voltage Vi between the Pi oxygen detection electrode and the Pr reference air electrode. When it is detected that the voltage change speed of Vi is higher than a preset threshold, if Vi decreases, the pump voltage Vp1 is increased according to the pre-calibrated corresponding relationship between Vi and Vp1, and the amount of oxygen pumped from the second cavity to the Pm electrode is increased, so that the residual oxygen concentration in the second cavity is maintained at a predetermined low stable level. If Vi increases, the pump voltage Vp1 is reduced according to the pre-calibrated corresponding relationship between Vi and Vp1 to reduce oxygen pumping, so that the residual oxygen concentration in the second cavity is maintained at a predetermined low stable level.

[0013] Furthermore, 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.

[0014] Furthermore, a heating wire is included, which is used to heat up the chip by powering on and keep the chip at a constant operating temperature.

[0015] Furthermore, the ceramic body of the chip is mainly composed of zirconium oxide.

[0016] Further, 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 the area outside the first to third cavities.

[0017] Furthermore, the Pr reference air electrode is disposed on the other side of the zirconium oxide layer, in a cavity communicating with the outside air.

[0018] A gas sensor comprises the ceramic chip for measuring NOx concentration.

[0019] A NOx concentration measurement method uses the NOx concentration measurement ceramic chip to measure NOx concentration.

[0020] The present invention has the following beneficial effects:

[0021] 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 its unique design. The chip adopts a ceramic body made of zirconium oxide as the main material, and is provided with three cavities, which are connected in sequence through slits, so that the measured gas can be detected in order through each cavity. The first cavity is equipped with a Pi oxygen detection electrode, which is used to sense the oxygen concentration in the measured gas 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 measurement electrode, which is used to ionize oxygen in NOx and generate a current Ip2 to directly characterize 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 too large or too small Vp1. 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.

[0022] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the NOx concentration measurement ceramic chip according to an embodiment of the present invention.

[0024] Figure 2Schematic diagram of the voltages of the electrodes of the NOx concentration measurement ceramic chip according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] 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 and application of the present invention.

[0026] 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 fixing as well as for coupling or communication.

[0027] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0028] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0029] See also Figure 1 and Figure 2An embodiment of the present invention provides a NOx concentration measurement ceramic chip, including a ceramic body, which is preferably composed of zirconium oxide as a main component, and the ceramic body includes 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 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 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 fast and is higher than 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 increased by controlling to allow more oxygen to be pumped to the Pm electrode, thereby keeping the residual oxygen concentration in the second chamber at a predetermined very low stable level; if the Vi voltage increases, it indicates that the actual oxygen concentration of the measured gas is decreasing. The pump voltage Vp1 is reduced to reduce the pumping of oxygen, thereby keeping the residual oxygen concentration in the second chamber at a predetermined very low stable level.

[0030] 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 change rate 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.

[0031] When working, the oxygen concentration detected by the Pi electrode will be converted into a voltage Vi. The voltage Vi is calculated based on the Nernst cell principle and is a direct reflection of the oxygen concentration. The Pi electrode is the first to contact the measured gas. When the oxygen concentration in the measured gas changes, the voltage Vi will also change. Since the Vi voltage is directly related to the oxygen concentration, the change in oxygen concentration can be measured by monitoring the change in Vi through the Pi electrode without waiting for feedback from the Pa electrode. According to the correspondence between Vi and Vp1 at different oxygen concentrations determined in advance, when the Vi voltage is detected to decrease, it indicates that the oxygen concentration has increased. By increasing the pump voltage Vp1, more oxygen can be effectively pumped to the Pm electrode; when the Vi voltage is detected to increase, it indicates that the oxygen concentration of the measured gas has decreased. By reducing the pump voltage Vp1, too much oxygen is prevented from being pumped to the Pm electrode and interfering with the measurement of NOx. The Nernst voltage V1 of the Pa electrode can be used as a feedback signal to assist in fine-tuning Vp1 to achieve the effect of closed-loop control.

[0032] Through experimental multi-point calibration, the relationship between oxygen concentration and Vi voltage and Vp1 can be obtained in advance. In this way, when the Vi voltage changes rapidly, Vp1 can be directly adjusted according to the calibration result without waiting for feedback from the Pa electrode. In the present invention, the change of Vi voltage detected by the Pi electrode is used as the direct basis for adjusting Vp1, instead of waiting for the change of oxygen concentration at the P1 or Pa electrode, and Vp1 is predictably adjusted by the immediate change of Vi voltage, so that the change of oxygen concentration can be responded to more quickly, and Vp1 can be avoided from being too large or too small, thereby improving the accuracy of NOx measurement.

[0033] 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 a predetermined range, Vp1 is increased to form a closed-loop control. In a preferred embodiment, based on the results of experimental calibration, when the Nernst voltage V1 is greater than 430mV, the control unit reduces the pump voltage Vp1, and if the Nernst voltage V1 is less than 420mV, the control unit increases the pump voltage Vp1.

[0034] See also Figure 1 and Figure 2 In a preferred embodiment, 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 the area outside the first to third cavities.

[0035] See also 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 connected to the outside air.

[0036] The embodiment of the present invention further provides a gas sensor having the above-mentioned NOx concentration measuring ceramic chip.

[0037] The 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.

[0038] 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 an integrated multi-cavity design and an intelligent control mechanism. The chip adopts a ceramic body with zirconium oxide as the main component, and is provided with three cavities, which 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 to directly characterize 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 too large or too small Vp1. Especially in environments where 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. Through this integrated design and intelligent control, the present invention improves the measurement accuracy while also enhancing the sensor's adaptability to rapidly changing environments, meeting the need for accurate measurement of NOx concentration under dynamic atmosphere conditions.

[0039] The specific embodiments of the present invention are further described below.

[0040] like Figure 1 and Figure 2As shown, a NOx concentration measurement ceramic chip and a gas sensor having the ceramic chip are provided on a ceramic body mainly composed of zirconium oxide, and a Pi oxygen detection electrode, a Pm (and P1) main oxygen pump electrode, a Pa oxygen monitoring electrode, a P2 (NOx) measurement electrode, and a Pr reference air electrode are arranged. An aluminum oxide insulating layer is sandwiched between two layers of zirconium oxide to avoid the influence of the pump voltage VP1 adjustment on the measured value; the ceramic chip also includes a heating wire, which generates heat after being powered on during measurement, and can heat the chip and keep it at a constant working 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 can reflect the oxygen concentration of the gas; the measured gas enters the second cavity through the second slit, and the P1 electrode ionizes the oxygen molecules in the measured gas into oxygen ions. Under the action of the pump voltage VP1, the oxygen ions pass through the ceramic matrix and move to the Pm electrode and are reduced to oxygen molecules, forming a current Ip1; a Nernst voltage V1 is formed between the oxygen monitoring electrode Pa and the reference electrode Pr, and V1 can reflect 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 420-430 mV, indicating that the oxygen concentration at the Pa electrode is around 400 ppm, and the oxygen concentration that can enter the third chamber is close to 0), indicating that the oxygen concentration is too low, and the P1 electrode will decompose more NOx gas. At this time, Vp1 is reduced, and vice versa; 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.

[0041] The measured gas diffuses into the third cavity through the third slit, and the P2 electrode ionizes the oxygen in NOx into oxygen ions. Under the action of voltage V2, the oxygen ions move to the Pr electrode and are reduced to oxygen molecules, and generate current Ip2. Ip2 can characterize the NOx concentration in the measured gas. By obtaining the 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 is linearly related to the oxygen concentration, and the measurement accuracy is higher than Vi. Since Vi can detect the oxygen concentration of the measured gas in advance, the Vp1 voltage can be adjusted predictably to keep V1 and V2 in a reasonable state, which can improve the accuracy of the measured value, especially under conditions where the oxygen concentration and air pressure change suddenly, such as automobile exhaust, which can significantly improve the real-time and accuracy of NOx measurement.

[0042] According to the Nernst cell principle, Vi=(RT / 4F)*ln(Qr / Qi)

[0043] in:

[0044] R is the ideal gas constant, equal to 8.314570JK-1.mol-1.

[0045] T is temperature in K.

[0046] F is the Faraday constant, 1F is equal to 96485C.mol-1.

[0047] Qr is the oxygen concentration at the Pr electrode end. Due to the introduction of air, the oxygen concentration is 20.6%;

[0048] Qi is the oxygen concentration at the Pi electrode end.

[0049] When the chip temperature is constant, the oxygen concentration of the measured gas can be obtained by measuring the Vi voltage.

[0050] Since Pi will first contact the measured gas, the oxygen concentration of the measured gas can be determined according to the voltage Vi, and the gas diffuses to the P1 electrode after 50ms (specifically related to the slit size and cavity size, etc., 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 to the outside of the cavity, but it cannot be too large to cause the oxygen in NOx to be pumped out of the cavity. Since 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 Vp1 that relies on Pa will also have the problem of adjustment lag. In contrast, the present invention can start to adjust the pump voltage Vp1 when the gas diffuses to P1 based on the voltage Vi, which solves the problem of adjustment lag, and the Nernst voltage V1 is used as a feedback signal for fine-tuning, thereby achieving a more perfect closed-loop control.

[0051] Through experimental calibration, the specific correspondence between the voltage Vi between the Pi electrode and the Pr electrode and the pump voltage Vp1 under different oxygen concentrations can be determined, so that in actual measurement, Vp1 can be adjusted according to the Vi voltage value measured in real time to ensure the accuracy and response speed of the sensor. In this embodiment, the correspondence between the voltage Vi between the Pi electrode and the Pr electrode and the pump voltage Vp1 under different oxygen concentrations can be determined by multi-point calibration. 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 the cost factor, 4-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 that depends on the adjustment of the Nernst voltage V1.

[0052] The present invention is designed with an oxygen concentration detection electrode Pi, which can sense the oxygen concentration of the measured gas in advance. According to the change of Vi, the pump voltage Vp1 can be adjusted predictably to avoid the adverse effects caused by too large or too small Vp1, because too large Vp1 will cause P1 to decompose NOx, resulting in a low NOx measurement value, and vice versa, the oxygen will not be pumped completely and the oxygen will rush to the NOx measurement electrode P2, resulting in a large NOx measurement value. Under the atmosphere conditions of automobile exhaust where the oxygen concentration and pressure change rapidly, predictive adjustment can improve the influence of adjustment lag caused by feedback adjustment based solely on the back-end detection of residual oxygen concentration, and significantly improve the measurement accuracy and real-time performance under dynamic atmospheres.

[0053] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. 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 can be made herein without departing from the scope of protection of the patent application.

Claims

1. A ceramic chip for measuring NOx concentration, characterized in that include: A ceramic body, comprising 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 chamber 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, 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 forms a Nernst voltage V1 with the Pr reference air electrode; The third chamber is provided with a P2 measuring electrode, which is used to ionize oxygen in NOx into oxygen ions, and under the action of the voltage V2 between the Pr reference air electrode 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 according to the voltage Vi between the Pi oxygen detection electrode and the Pr reference air electrode. When it is detected that the voltage change speed of Vi is higher than a preset threshold, if Vi decreases, the pump voltage Vp1 is increased according to the pre-calibrated corresponding relationship between Vi and Vp1, and the amount of oxygen pumped from the second cavity to the Pm electrode is increased, so that the residual oxygen concentration in the second cavity is maintained at a predetermined low stable level. If Vi increases, the pump voltage Vp1 is reduced according to the pre-calibrated corresponding relationship between Vi and Vp1 to reduce oxygen pumping, so that the residual oxygen concentration in the second cavity is maintained at a predetermined low stable level.

2. The NOx concentration measuring ceramic chip according to claim 1, characterized in that: 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, forming a closed-loop control.

3. The NOx concentration measuring ceramic chip according to any one of claims 1 to 2, characterized in that: It also contains heating wires, which are used to heat up and keep the chip at a constant operating temperature.

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

5. The NOx concentration measuring ceramic chip according to any one of claims 1 to 4, 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.

6. The NOx concentration measuring ceramic chip according to any one of claims 1 to 5, characterized in that: The Pr reference air electrode is arranged on the other side of a zirconium oxide layer, in a cavity communicating with the outside air.

7. A gas sensor, characterized in that: A ceramic chip for measuring NOx concentration as claimed in any one of claims 1 to 6.

8. A method for measuring NOx concentration, characterized in that: The NOx concentration is measured using the NOx concentration measuring ceramic chip according to any one of claims 1 to 6.

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