Hydrogen detection in-situ sensing chip and preparation method thereof, sensor and self-calibration method

Abstract

The invention discloses an in-situ sensing chip for detecting hydrogen in transformer oil, a preparation method of the in-situ sensing chip, a sensor and a self-calibration method, in a sensing chip element, a heating resistor is laminated on a third insulating layer in a broken-line-shaped structure to form a heating area of a uniform thermophysical field; the second insulating layer is laminated on the heating resistor; the multiple gas sensitive resistors are arranged on the second insulating layer and located in the heating area, each gas sensitive resistor comprises a broken-line-shaped structure made of a palladium metal alloy material and a gas sensitive lead electrode connected with the broken-line-shaped structure, and the broken-line-shaped structures form a Wheatstone bridge structure; the temperature measuring resistor is arranged on the second insulating layer and is surrounded by the plurality of gas sensitive resistors in the heating area; the temperature measuring resistor comprises a single-wire structure made of a platinum material and temperature measuring lead electrodes arranged at the two ends of the single-wire structure; the Si3N4 isolation layer covers two opposite bridge arms of the Wheatstone bridge structure, the other two opposite bridge arms are exposed in the air, and the gas sensitive resistor outputs a responsive voltage signal based on hydrogen.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen detection in transformer oil, in particular to an in-situ sensing chip for hydrogen detection in transformer oil and a preparation method, a sensor and a self-calibration method. Background Art

[0002] During the operation of the transformer, transformer oil will be cracked into hydrogen, carbon dioxide, methane and other gases under the high temperature generated by the internal arc. Relevant researchers have found that the type and severity of transformer faults are closely related to the type and concentration of these gases in the transformer oil. Among them, hydrogen in transformer oil has a low temperature, a wide source, and a linear change in concentration. Therefore, hydrogen is the preferred gas in the single gas detection of transformer oil gas. At the same time, if multi-gas detection of transformer oil gas is to be performed, hydrogen is also an important gas in multi-gas detection.

[0003] Therefore, detecting hydrogen in transformer oil and maintaining the transformer according to the detection results is one of the effective means to ensure the normal operation of the power system. At present, the detection means of hydrogen in oil are often oil chromatography analysis and gas separation detection through a matching oil-gas separation device. There are problems such as the inability to perform in-situ measurement, the complexity of the matching oil-gas separation device, and the inability to achieve in-situ self-calibration. It is difficult to quickly, real-time and accurately measure the concentration of hydrogen in oil without destroying the original transformer oil environment, and it is impossible to meet the detection requirements of real-time fault analysis of transformers. In the prior art, other hydrogen in oil sensor measurement means do not have the in-situ self-calibration function, and the calibration means are only a simple combination of the back-end calibration algorithm and the sensor. There are still many shortcomings as follows: there are problems such as the complexity of sensor devices and the incompatibility of MEMS (Micro-electro-mechanical system) processes, which are difficult to meet the requirements of low-cost and large-scale manufacturing; complex back-end processing circuits are required to obtain the measured hydrogen concentration, which is costly and cannot be applied in large quantities; the combination mode of the back-end calibration algorithm and the sensor has poor reliability in practical applications, and it is difficult to achieve accurate self-calibration in long-term work.

[0004] The information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Summary of the invention

[0005] In view of the deficiencies or defects of the above-mentioned prior art, an in-situ sensor chip and preparation method, a sensor and a self-calibration method for detecting hydrogen in transformer oil are provided. The characteristics of hydrogen can be directly measured in oil by using a palladium alloy hydrogen sensor. Combined with the self-calibration structure and method, the problem of detecting hydrogen concentration in transformer oil to achieve real-time analysis of transformer operating status is fundamentally solved, thereby improving the accuracy of hydrogen concentration detection. Without disassembling the sensor, the sensor self-calibration mode can be used in real time during long-term use to perform baseline correction and response coefficient correction on the sensor itself, so as to achieve long-term continuous hydrogen concentration monitoring, and achieve real-time and reliable detection, analysis and early warning of transformer faults. The existing solutions overcome the problems of complex sensor devices, incompatibility of MEMS processes and large-scale manufacturing, complex back-end processing circuits, and difficulty in achieving accurate self-calibration in long-term work. The purpose of the present invention is achieved through the following technical solutions.

[0006] An in-situ sensing chip for detecting hydrogen in transformer oil comprises: a silicon substrate having an upper surface and a lower surface; A first insulating layer stacked on the lower surface; a third insulating layer stacked on the upper surface; A heating resistor, which is stacked on the third insulating layer in a zigzag structure to form a heating area with a uniform thermal physical field; a second insulating layer stacked on the heating resistor; A plurality of gas-sensitive resistors are arranged on the second insulating layer and located in the heating region, wherein the gas-sensitive resistors include a zigzag structure made of a palladium metal alloy material and a gas-sensitive lead electrode connected to the zigzag structure, wherein the zigzag structure is configured as a Wheatstone bridge structure. A temperature measuring resistor, which is arranged on the second insulating layer and surrounded by a plurality of gas-sensitive resistors in the heating area, the temperature measuring resistor comprising a single-wire structure made of platinum material and temperature measuring lead electrodes arranged at both ends of the single-wire structure; The Si3N4 isolation layer covers two opposite bridge arms of the Wheatstone bridge structure, and the other two opposite bridge arms are exposed to the air. The gas-sensitive resistor outputs a voltage signal in response to hydrogen.

[0007] In the in-situ sensing chip for detecting hydrogen in transformer oil, a plurality of gas-sensitive resistors are symmetrically distributed with the temperature-measuring resistor as the center, and the gas-sensitive lead electrode and the temperature-measuring lead electrode are both made of gold material.

[0008] In the in-situ sensing chip for detecting hydrogen in transformer oil, a connecting layer made of Ti material is deposited between the second insulating layer and the gas sensitive resistor and the temperature measuring resistor.

[0009] In the in-situ sensing chip for detecting hydrogen in transformer oil, the thickness of the gas sensitive resistor is 40nm, the thickness of the temperature measuring resistor is 100nm; the thickness of the gas sensitive lead electrode and the temperature measuring lead electrode are both 250nm, the thickness of the Si3N4 isolation layer is 250nm, and the thickness of the connecting layer is 20nm-30nm.

[0010] In the in-situ sensor chip for detecting hydrogen in transformer oil, the first insulating layer and the third insulating layer are both composed of four thin films of SiO2 / Si3N4 / SiO2 / Si3N4 in sequence.

[0011] In the in-situ sensor chip for detecting hydrogen in transformer oil, the heating resistor and the gas sensitive resistor are arranged in two layers, upper and lower, through a zigzag structure.

[0012] The preparation method of the in-situ sensing chip for detecting hydrogen in transformer oil comprises: Step S1, select a 4-inch double-sided polished silicon wafer as a silicon substrate, Step S2, using plasma enhanced chemical vapor deposition to sequentially prepare a first insulating layer and a third insulating layer of SiO2 / Si3N4 / SiO2 / Si3N4 located on both sides of the silicon substrate, Step S3, depositing gold material on one side of the third insulating layer by magnetron sputtering or electron beam evaporation to form a heating resistor with a zigzag structure, Step S4, using plasma enhanced chemical vapor deposition to sequentially prepare a second insulating layer of SiO2 / Si3N4 / SiO2 / Si3N4, Step S5, depositing a plurality of gas-sensitive resistors and temperature-measuring resistors on the upper side of the second insulating layer by magnetron sputtering or electron beam evaporation, connecting lead electrodes to the gas-sensitive resistors and the temperature-measuring resistors, the gas-sensitive resistors and the temperature-measuring resistors are distributed in the heating area, and the temperature-measuring resistors are located in the center of the gas-sensitive resistors, Step S6, using magnetron sputtering to prepare a Si3N4 isolation layer on two bridge arms opposite to the gas sensor resistor, Step S7, using a dry etching process to sequentially etch Si3N4 / SiO2 / Si3N4 / SiO2 / Si to release the silicon base material under the deposited metal material.

[0013] An in-situ self-calibration sensor for detecting hydrogen in transformer oil includes a hydrogen measuring probe, the hydrogen measuring probe includes: The preamplifier circuit board integrates the in-situ sensing chip for detecting hydrogen in transformer oil, the humidity (micro-water) sensor and the pressure sensor to obtain the hydrogen concentration value and the temperature, pressure and humidity analog signals. A post-signal processing circuit board is connected to the pre-amplifier circuit board to convert the temperature, pressure and humidity analog signals into digital signals through AD analog-to-digital conversion. The post-signal processing circuit board performs real-time and long-term self-calibration control of the temperature, pressure and humidity on the hydrogen concentration value.

[0014] The in-situ self-calibration sensor for detecting hydrogen in transformer oil further comprises: Front probe housing, The oil inlet is located at the front end of the front probe housing and can be installed on the transformer oil inlet through the transformer connection thread. The middle-end circuit housing is connected to the front-end probe housing via a sensor connecting thread, the front-end amplifier circuit board is arranged in the middle-end circuit housing, and the rear-end signal processing circuit board is connected to the front-end amplifier circuit board via a sealed connector. A signal output circuit board is disposed in the middle circuit housing and connected to the rear signal processing circuit board via a sealed connector. The rear end sealed shell is threadedly connected to the middle end circuit shell, and the rear end sealed shell is provided with a signal line transmission hole for leading out the signal line.

[0015] The self-calibration method of the in-situ self-calibration sensor for detecting hydrogen in transformer oil comprises the following steps: In the hydrogen detection range below 200ppm (the hydrogen concentration in transformer oil is generally lower than 80ppm), the response of the hydrogen detection in-situ self-calibration sensor to the hydrogen concentration is linear, and its expression is: Rs(x)=A+Kx, where A is called the sensor baseline, and K is called the sensor response coefficient. The hydrogen concentration is affected by the real-time temperature, humidity, and pressure, causing the sensor baseline A and the response coefficient K to drift, which are called the real-time baseline drift a1 and the response coefficient drift k1 respectively. After long-term continuous operation, the gas-sensitive resistor causes the sensor baseline A and the response coefficient K to drift due to the change of its own properties, which are called the long-term baseline drift a2 and the response coefficient drift k2 respectively. The real-time temperature, humidity (micro-water) and pressure are measured by the temperature measuring resistor of the hydrogen detection in-situ self-calibration sensor and the integrated humidity (micro-water) sensor and pressure sensor. In the real-time working process, based on temperature, humidity (micro-water), and pressure, the hydrogen concentration value is self-calibrated for real-time baseline drift a1 and response coefficient drift k1 through the compensation model; After long-term continuous operation, you can choose to enter the self-calibration mode. Through the temperature closed-loop control formed by the temperature measurement and heating resistor integrated on the hydrogen detection in-situ self-calibration sensor, the hydrogen detection in-situ self-calibration sensor is heated to the temperature required for self-calibration (150°C, the normal operating temperature is 60°C). At this temperature, the sensor will not react with the hydrogen in the transformer oil. At this time, the output value is the baseline value of the sensor at the self-calibration temperature. Therefore, according to the resistance temperature coefficient of the gas-sensitive resistor and the difference between the self-calibration temperature and the normal operating temperature, the baseline value after long-term operation at the normal operating temperature can be obtained. The difference between the baseline value and the initial working baseline value is the long-term working baseline drift. According to the difference, the self-calibration of the long-term baseline drift a2 can be completed; Further, four temperature points of 60°C, 90°C, 120°C and 150°C are selected. The baseline values ​​at these four temperature points can be obtained from the obtained baseline values ​​after self-calibration in combination with the temperature coefficient of the gas sensitive resistor. At the same time, the response value of the hydrogen concentration measured at this time can be directly read out by the sensor. The difference between the two is the response output at different operating temperatures caused by the hydrogen concentration in the oil at this time. The relationship between the response output and the operating temperature is established, and the established database of the relationship between the response output of different concentrations and the operating temperature is queried to obtain the actual hydrogen concentration in the transformer oil in the current environment. Using the relationship between the actual hydrogen concentration and the response output, self-calibration of the long-term working response coefficient drift k2 can be performed.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. By integrating the heating resistor, the temperature measuring resistor and the gas sensor together, the volume of the sensor is greatly reduced. At the same time, the layered design of the heating resistor makes the heating field more uniform, which is more conducive to the response of the gas sensor and the accurate measurement of the temperature by the temperature measuring resistor. The Wheatstone bridge structure design of the gas sensor makes the measured signal in the form of a voltage signal, which is easier to measure than the resistance signal and has a high sensitivity. The release of the silicon substrate under the deposited metal material film enables the sensor to reach the optimal operating temperature at a lower operating voltage, greatly reducing the power consumption of the sensor. The insulating layer selects a four-layer film structure of SiO2 / Si3N4 / SiO2 / Si3N4, which makes the film stress matching more reasonable and avoids stress concentration and film rupture. The two relative bridge arms of the gas sensor select a dense Si3N4 film as the covering material to block the entry of hydrogen, so that the gas sensor of the bridge structure outputs a voltage response signal.

[0017] 2. The hydrogen measurement probe composed of a micro-integrated palladium alloy thin film hydrogen sensor, a micro-water sensor and a pressure sensor has a very small volume, no more than 300mm3. By being directly installed on the transformer and in contact with the transformer oil, it can directly and in real time detect changes in the hydrogen concentration inside the transformer, so as to monitor the operating conditions inside the transformer in real time.

[0018] 3. The performance of palladium-gold alloy gas-sensitive materials is relatively stable, and they can directly contact transformer oil to measure hydrogen concentration. No oil-gas separation device is required. The test is simple, and in-situ and real-time measurements can be performed directly, greatly reducing the cost of monitoring the working status of the transformer.

[0019] 4. By combining long-term working self-calibration with real-time self-calibration of temperature, humidity (micro-water) and pressure, the excellent stability of the sensor in long-term working is achieved. Self-calibration is performed in real time during continuous working to maintain the hydrogen measurement accuracy under long-term continuous working and ensure the accuracy of measurement.

[0020] The above description is only an overview of the technical solution of the present invention. In order to make the technical means of the present invention clearer and to achieve the extent that those skilled in the art can implement it according to the contents of the specification, and in order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are exemplified below. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] By reading the detailed description of the preferred specific embodiments below, various other advantages and benefits of the present invention will become clear to those of ordinary skill in the art. The drawings in the specification are only for the purpose of illustrating the preferred embodiments and are not considered to be limitations of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative work. Moreover, the same reference numerals are used to represent the same components throughout the drawings.

[0022] In the attached picture: Figure 1 is a schematic diagram of a heating resistor layer of the present invention; Figure 2 It is a schematic diagram of the gas-sensitive resistor and the temperature-measuring resistor layer of the present invention; Figure 3 is a schematic cross-sectional view of a sensor chip of the present invention; Figure 4 is a flow chart of chip preparation of the present invention; Figure 5 It is a schematic flow chart of the self-calibration method of the present invention; Figure 6 It is a schematic diagram of the flow chart of the circuit implementation of the present invention; Figure 7 is a schematic diagram of the overall device of the sensor of the present invention; Figure 8 It is a schematic diagram of the installation of the sensor of the present invention on an oil-immersed transformer; In the figure: 1. AD analog-to-digital converter; 2. MCU; 3. gas-sensitive resistor; 4. gas-sensitive lead electrode; 5. temperature-measuring resistor; 6. temperature-measuring lead electrode; 7. gas-sensitive resistor and temperature-measuring resistor layer; 8. heating resistor; 9. Si3N4 isolation layer; 10. second insulating layer; 11. third insulating layer; 12. silicon substrate; 13. first insulating layer; 14. substrate release groove; 15. oil inlet; 16. transformer connection thread; 17. front-end probe housing; 18. sensor connection thread; 19. preamplifier circuit board; 20. sealed connector; 21. mid-end circuit housing; 22. post-signal processing circuit board; 23. signal output circuit board; 24. rear-end sealed housing; 25. signal line transmission hole; 26. hydrogen detection in-situ self-calibration sensor; 27. oil-immersed transformer.

[0023] The present invention is further explained below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the specific embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0025] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present invention, but the description is based on the general principles of the specification and is not intended to limit the scope of the present invention. The scope of protection of the present invention shall be determined by the attached claims.

[0026] To facilitate understanding of the embodiments of the present invention, several specific embodiments will be further explained below with reference to the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present invention.

[0027] For a better understanding, Figures 1 to 8 As shown, an in-situ sensing chip for detecting hydrogen in transformer oil includes: A silicon substrate 12 having an upper surface and a lower surface; A first insulating layer 13, which is stacked on the lower surface; A third insulating layer 11, stacked on the upper surface; A heating resistor 8, which is stacked on the third insulating layer 11 in a zigzag structure to form a heating area with a uniform thermal physical field; A second insulating layer 10, which is stacked on the heating resistor 8; A plurality of gas-sensitive resistors 3 are arranged on the second insulating layer 10 and located in the heating area. The gas-sensitive resistors 3 include a zigzag structure made of a palladium metal alloy material and a gas-sensitive lead electrode 4 connected to the zigzag structure. The zigzag structure is configured as a Wheatstone bridge structure. A temperature measuring resistor 5, which is arranged on the second insulating layer 10 and surrounded by a plurality of gas-sensitive resistors 3 in the heating area, wherein the temperature measuring resistor 5 comprises a single-wire structure made of platinum material and temperature measuring lead electrodes 6 arranged at both ends of the single-wire structure; further, the plurality of gas-sensitive resistors 3 and the temperature measuring resistor 5 located in the center thereof constitute a gas-sensitive resistor and temperature measuring resistor layer 7; The Si3N4 isolation layer 9 covers two opposite bridge arms of the Wheatstone bridge structure, and the other two opposite bridge arms are exposed to the air. The gas-sensitive resistor 3 outputs a voltage signal in response to hydrogen.

[0028] In the preferred embodiment of the in-situ sensing chip for detecting hydrogen in transformer oil, a plurality of gas sensitive resistors 3 are symmetrically distributed with the temperature measuring resistor 5 as the center, and the gas sensitive lead electrode 4 and the temperature measuring lead electrode 6 are both made of gold material.

[0029] In the preferred embodiment of the in-situ sensing chip for detecting hydrogen in transformer oil, a connecting layer made of Ti material is deposited between the second insulating layer 10 and the gas sensitive resistor 3 and the temperature measuring resistor 5 .

[0030] In the preferred embodiment of the in-situ sensing chip for detecting hydrogen in transformer oil, the thickness of the gas sensitive resistor 3 is 40nm, the thickness of the temperature measuring resistor 5 is 100nm; the thickness of the gas sensitive lead electrode 4 and the temperature measuring lead electrode 6 are both 250nm, the thickness of the Si3N4 isolation layer 9 is 250nm, and the thickness of the connecting layer is 20nm-30nm.

[0031] In a preferred embodiment of the in-situ sensor chip for detecting hydrogen in transformer oil, the first insulating layer 13 and the third insulating layer 11 are both composed of four thin films of SiO2 / Si3N4 / SiO2 / Si3N4 in sequence.

[0032] In the preferred embodiment of the in-situ sensing chip for detecting hydrogen in transformer oil, the heating resistor 8 and the gas sensitive resistor 3 are arranged in two layers in an upper and lower layer through a zigzag structure.

[0033] The preparation method of the in-situ sensing chip for detecting hydrogen in transformer oil comprises: Step S1, selecting a 4-inch double-sided polished silicon wafer as the silicon substrate 12, Step S2, using plasma enhanced chemical vapor deposition, sequentially preparing a first insulating layer 13 and a third insulating layer 11 of SiO2 / Si3N4 / SiO2 / Si3N4 on both sides of a silicon substrate 12, Step S3, depositing gold material on one side of the third insulating layer 11 by magnetron sputtering or electron beam evaporation to form a heating resistor 8 with a zigzag structure, Step S4, using plasma enhanced chemical vapor deposition to sequentially prepare a second insulating layer 10 of SiO2 / Si3N4 / SiO2 / Si3N4, Step S5, depositing a plurality of gas resistors 3 and temperature measuring resistors 5 on the upper side of the second insulating layer 10 by magnetron sputtering or electron beam evaporation, connecting the lead electrodes to the gas resistors 3 and the temperature measuring resistors 5, the gas resistors 3 and the temperature measuring resistors 5 are distributed in the heating area, and the temperature measuring resistors 5 are located in the center of the gas resistors 3, Step S6, using magnetron sputtering to prepare a Si3N4 isolation layer 9 on two opposite bridge arms of the gas sensor 3, Step S7, using a dry etching process to sequentially etch Si3N4 / SiO2 / Si3N4 / SiO2 / Si to release the silicon substrate 12 material below the deposited metal material.

[0034] An in-situ self-calibration sensor for detecting hydrogen in transformer oil includes a hydrogen measuring probe, the hydrogen measuring probe includes: The preamplifier circuit board 19 integrates the in-situ sensing chip, micro-water sensor and pressure sensor for detecting hydrogen in transformer oil to obtain the hydrogen concentration value and the temperature, pressure and humidity analog signals. The post-signal processing circuit board 22 is connected to the pre-amplifier circuit board 19 to convert the temperature, pressure and humidity analog signals into digital signals through AD analog-to-digital conversion. The post-signal processing circuit board 22 performs temperature, pressure and humidity compensation self-calibration on the hydrogen concentration value.

[0035] The in-situ self-calibrating sensor for hydrogen detection in transformer oil also includes: Front end probe housing 17, The oil inlet 15 is provided at the front end of the front probe housing 17 so as to be installed on the transformer oil inlet through the transformer connecting thread 16. The middle circuit housing 21 is connected to the front probe housing 17 via the sensor connection thread 18. The preamplifier circuit board 19 is arranged in the middle circuit housing 21. The rear signal processing circuit board 22 is connected to the preamplifier circuit board 19 via the sealed connector 20. The signal output circuit board 23 is disposed in the middle circuit housing 21 and connected to the rear signal processing circuit board 22 via the sealed connector 20. The rear end sealed housing 24 is threadedly connected to the middle end circuit housing 21 , and the rear end sealed housing 24 is provided with a signal line transmission hole 25 for leading out the signal line.

[0036] The self-calibration method of the in-situ self-calibration sensor for detecting hydrogen in transformer oil comprises the following steps: In the hydrogen detection range below 200ppm (the hydrogen concentration in transformer oil is generally lower than 80ppm), the response of the hydrogen detection in-situ self-calibration sensor to the hydrogen concentration is linear, and its expression is: Rs(x)=A+Kx, where A is called the sensor baseline, and K is called the sensor response coefficient. The hydrogen concentration is affected by the real-time temperature, humidity, and pressure, causing the sensor baseline A and the response coefficient K to drift, which are called the real-time baseline drift a1 and the response coefficient drift k1 respectively. After long-term continuous operation, the gas-sensitive resistor causes the sensor baseline A and the response coefficient K to drift due to the change of its own properties, which are called the long-term baseline drift a2 and the response coefficient drift k2 respectively. The real-time temperature, humidity, and pressure are measured by the temperature measuring resistor of the hydrogen detection in-situ self-calibration sensor and the integrated humidity (micro-water) sensor and pressure sensor. In the real-time working process, based on temperature, humidity (micro-water), and pressure, the hydrogen concentration value is self-calibrated for real-time baseline drift a1 and response coefficient drift k1 through the compensation model; Real-time temperature, humidity, and pressure calibration model: Real-time baseline drift a1=K p K t A+K h . Real-time response coefficient drift k1= K p K t K. K p , K t , K h They are the pressure, temperature, and humidity (micro water) calibration coefficients respectively.

[0037] After long-term continuous operation, you can choose to enter the self-calibration mode. Through the temperature closed-loop control formed by the temperature measurement and heating resistor integrated on the hydrogen detection in-situ self-calibration sensor, the hydrogen detection in-situ self-calibration sensor is heated to the temperature required for self-calibration (150°C, the normal operating temperature is 60°C). At this temperature, the sensor will not react with the hydrogen in the transformer oil. At this time, the output value is the baseline value of the sensor at the self-calibration temperature. Therefore, according to the resistance temperature coefficient of the gas-sensitive resistor and the difference between the self-calibration temperature and the normal operating temperature, the baseline value after long-term operation at the normal operating temperature can be obtained. The difference between the baseline value and the initial working baseline value is the long-term working baseline drift. According to the difference, the self-calibration of the long-term baseline drift a2 can be completed; Further, four temperature points of 60°C, 90°C, 120°C and 150°C are selected. The baseline values ​​at these four temperature points can be obtained from the obtained baseline values ​​after self-calibration in combination with the temperature coefficient of the gas sensitive resistor. At the same time, the response value of the hydrogen concentration measured at this time can be directly read out by the sensor. The difference between the two is the response output at different operating temperatures caused by the hydrogen concentration in the oil at this time. The relationship between the response output and the operating temperature is established, and the established database of the relationship between the response output of different concentrations and the operating temperature is queried to obtain the actual hydrogen concentration in the transformer oil in the current environment. Using the relationship between the actual hydrogen concentration and the response output, self-calibration of the long-term working response coefficient drift k2 can be performed.

[0038] In one embodiment, Figure 1 The schematic diagram of the heating resistor provided by the example of the present invention is shown, the heating resistor 8 is made of gold material and is designed as a zigzag structure so that it can form a uniform thermal physical field on the entire heating plane; a second insulating layer 10 is prepared on it to separate the heating layer from the gas sensitive resistor to prevent the chip from failing; specifically, the thickness of the gold film is selected to be 250nm, and the connecting layer is 50nmCr.

[0039] like Figure 2The schematic diagram of the gas-sensitive resistor and the temperature-measuring resistor layer provided by the example of the present invention shown in the figure, the gas-sensitive resistor 3 is a palladium metal alloy material, the temperature-measuring resistor 5 is a platinum material, the gas-sensitive lead electrode 4 and the temperature-measuring lead electrode 6 are both made of gold material, the gas-sensitive material is composed of a zigzag structure in the form of a Wheatstone bridge, in which two relative bridge arms are covered by a dense Si3N4 isolation layer 9, so that a responsive voltage signal can be output when hydrogen is detected, and the design of the bridge structure improves the detection sensitivity, so that the sensor has a better response to the hydrogen concentration at low concentrations; the temperature-measuring resistor adopts a single-line structure and is arranged in the middle of the gas-sensitive material, so that it can measure the temperature more accurately; specifically, the gas-sensitive resistor 3 is a thin film with a thickness of 40nm and a connecting layer of 20nmTi; the temperature-measuring resistor 5 is a thin film with a thickness of 100nm and a connecting layer of 30nmTi; the thickness of the gas-sensitive lead electrode film is 250nm and the connecting layer is 50nmCr; the thickness of the dense Si3N4 isolation layer is 250nm.

[0040] like Figure 3 The schematic cross-sectional view of the sensor chip provided by the example of the present invention shown in the figure shows, from bottom to top, a first insulating layer 13, a silicon substrate 12, a third insulating layer 11, a heating resistor 8, a second insulating layer 10, a gas-sensitive resistor and a temperature-measuring resistor layer 7, and a Si3N4 isolation layer 9, which have good thin film stress matching characteristics and improve the stability of the thin film; the substrate material is released through the ICP etching process, so that the sensor can reach a higher temperature under a lower heating voltage, thereby realizing the preparation of an ultra-low power consumption sensor; specifically, the ICP etching process is repeatedly implemented through 11 cycles of etching, wherein the SiO2 / Si3N4 / SiO2 / Si3N4 thin films are etched respectively in the first four cycles, 80nm of silicon is etched each time in the 5th to 10th cycles, and the 11th cycle selects reasonable parameters according to the previous etching conditions to complete the release of the entire silicon substrate.

[0041] like Figure 4The chip preparation flow chart provided by the example of the present invention shown in the figure selects a 4-inch double-sided polished silicon wafer as a substrate, and uses plasma enhanced chemical vapor deposition to sequentially prepare a first insulating layer 13 and a third insulating layer 11 of double-sided SiO2 / Si3N4 / SiO2 / Si3N4 thin film, and deposits a heating resistor material on one side of the third insulating layer 11 by magnetron sputtering or electron beam evaporation, and sequentially prepares a second insulating layer 10 of SiO2 / Si3N4 / SiO2 / Si3N4 thin film by plasma enhanced chemical vapor deposition, and sequentially prepares a second insulating layer 10 of SiO2 / Si3N4 / SiO2 / Si3N4 thin film by magnetron sputtering or electron beam evaporation on the upper side of the second insulating layer 10. Electron beam evaporation is used to deposit gas-sensitive resistors, temperature-measuring resistor materials and lead electrode materials. The lead electrodes are connected to the gas-sensitive resistors and temperature-measuring resistors. The gas-sensitive resistors and temperature-measuring resistors are distributed in the heating area. The temperature-measuring resistor is located in the center of the gas-sensitive resistor. Magnetron sputtering is used to prepare a thin film of dense Si3N4 isolation layer on the two opposite bridge arms of the gas-sensitive material. Finally, a dry etching process is used to etch Si3N4 / SiO2 / Si3N4 / SiO2 / Si in sequence to release the silicon substrate material under the deposited metal material. Furthermore, a substrate release groove 14 is provided under the silicon substrate 12.

[0042] like Figure 5 The flowchart of the self-calibration method provided by the example of the present invention is shown in FIG. The temperature, humidity (micro-water) and pressure can be directly used to complete the baseline and response coefficient self-calibration through the preset compensation model, and the long-term self-calibration working mode is mainly described here.

[0043] In the low concentration hydrogen detection range (below 200ppm), the sensor's response to hydrogen concentration can be approximately regarded as linear, and its expression is: Rs(x)=A+Kx Where A is called the sensor baseline, K is called the sensor response coefficient. The hydrogen concentration is affected by the real-time temperature, humidity and pressure, causing the sensor baseline A and the response coefficient K to drift, which are called the real-time baseline drift a1 and the response coefficient drift k1 respectively. After long-term continuous operation, the gas-sensitive resistor changes its own properties, causing the sensor baseline A and the response coefficient K to drift, which are called the long-term baseline drift a2 and the response coefficient drift k2 respectively. The real-time temperature, humidity and pressure are measured by the temperature measuring resistor of the hydrogen detection in-situ self-calibration sensor and the integrated humidity (micro-water) sensor and pressure sensor. In the real-time working process, based on temperature, humidity and pressure, the hydrogen concentration value is self-calibrated for real-time baseline drift a1 and response coefficient drift k1 through the compensation model; After long-term continuous operation, you can choose to enter the self-calibration mode. Through the temperature closed-loop control formed by the temperature measurement and heating resistor integrated on the hydrogen detection in-situ self-calibration sensor, the hydrogen detection in-situ self-calibration sensor is heated to the temperature required for self-calibration (150°C, the normal operating temperature is 60°C). At this temperature, the sensor will not react with the hydrogen in the transformer oil. At this time, the output value is the baseline value of the sensor at the self-calibration temperature. Therefore, according to the resistance temperature coefficient of the gas sensor and the difference between the self-calibration temperature and the normal operating temperature, the baseline value after long-term operation at the normal operating temperature can be obtained. The difference between the baseline value and the initial working baseline value is the long-term working baseline drift. The long-term baseline drift can be completed based on the difference. Self-calibration of line drift a2; further, four temperature points of 60°C, 90°C, 120°C and 150°C are selected, and the baseline values ​​at these four temperature points can be obtained by combining the obtained baseline values ​​after self-calibration with the temperature coefficient of the gas sensitive resistor. At the same time, the response value of the hydrogen concentration measured at this time can be directly read out by the sensor, and the difference between the two is the response output at different operating temperatures caused by the hydrogen concentration in the oil at this time, and the relationship between the response output and the operating temperature is established. The established database of the relationship between the response output of different concentrations and the operating temperature is queried to obtain the actual hydrogen concentration in the transformer oil in the current environment, thereby completing the self-calibration of the long-term working response coefficient drift k2 of the sensor according to the response value of the actual hydrogen concentration at the operating temperature.

[0044] Specifically, the normal operating temperature of the transformer is set at 60°C, the high temperature heating temperature of the self-calibration mode is 150°C, the short time of self-calibration heating is 10s, and the self-calibration interval is 30 days, so as to minimize the impact on the transformer oil; the specific changes can be made according to the actual measurement situation.

[0045] like Figure 6 The hardware flow diagram of the implementation of the self-calibration method provided by the example of the present invention is shown. Specifically, the ARM microcontroller STM32F407VET6 is used to form a signal acquisition, processing, storage and communication system, which can realize the driving and signal pre-amplification and acquisition of hydrogen sensors, humidity (micro-water) sensors, and pressure sensors, and the sensor data is flash-saved for no less than 30 days, and transmitted to the monitoring base station (host computer) through the combination of RS-485 wired communication + Bluetooth wireless communication. The signal acquisition and processing circuit board is divided into two parts: a preamplifier board and a conversion communication circuit board due to the actual need of installing the sensor in the transformer bushing. The preamplifier circuit board is directly immersed in the transformer oil, while the conversion communication circuit board is on the outside.

[0046] like Figure 7The schematic diagram of the overall sensor device provided by the example of the present invention shown in the figure; the oil inlet 15 is directly installed on the transformer oil extraction port through the transformer connection thread 16, the front probe housing is connected to the middle circuit housing 21 through the sensor connection thread 18, the preamplifier circuit board 19 integrates the hydrogen sensor, humidity (micro-water) sensor and pressure sensor, and is connected to the rear signal processing circuit board 22 and the signal output circuit board 23 through the sealing connector 20 to achieve ultra-high sealing performance to avoid transformer oil leakage, and the middle circuit housing 21 is connected to the rear sealing housing 24 through a thread. The signal line is led out through the signal line transmission hole 25. Specifically, all connecting threads are pipe threads with sealing properties, the sealing connector is selected as a 12-channel connection, and the circuit boards are all designed with electromagnetic protection.

[0047] like Figure 8 The schematic diagram of the sensor provided by the embodiment of the present invention is shown as being installed on an oil-immersed transformer; the hydrogen detection in-situ self-calibration sensor 26 is directly installed on the oil-immersed transformer 27. Specifically, the hydrogen detection in-situ self-calibration sensor is installed at the oil inlet of the transformer.

[0048] In one embodiment, the sensor substrate is preferably a silicon substrate, and the silicon substrate is covered with a silicon oxide insulating layer. Preferably, the third insulating layer and the first insulating layer are respectively distributed on the upper and lower surfaces of the substrate, and are composed of four layers of SiO2 / Si3N4 / SiO2 / Si3N4 thin films in sequence. The integrated palladium alloy bridge thin film hydrogen sensor integrates a heating resistor, a temperature measuring resistor and a gas sensitive resistor. The heating resistor and the gas sensitive resistor are arranged in two layers in an upper and lower layer through a zigzag structure, and the temperature measuring resistor is arranged in the center of the upper gas sensitive material structure.

[0049] Preferably, a second insulating layer is prepared between the heating resistor, the temperature measuring resistor and the gas sensitive resistor, which is composed of four layers of SiO2 / Si3N4 / SiO2 / Si3N4 thin films in sequence. Preferably, the thermistor is made of Pt material; the thermal resistor is made of Au material; and the sensitive resistor is made of palladium metal alloy material.

[0050] Preferably, a connecting layer of Ti material for increasing adhesion between the electrode and the insulating layer is deposited between the thermistor Pt material, the heating resistor Au material, the sensitive resistor palladium metal alloy material and the insulating layer.

[0051] Preferably, the gas sensitive resistor is designed as a Wheatstone bridge structure, with two opposite bridge arms deposited with a dense Si3N4 film by magnetron sputtering, and the other two opposite bridge arms exposed to the air. The silicon substrate material under the deposited metal material is released by a dry etching process to form a suspended film structure. The volume of the hydrogen measurement probe composed of an integrated palladium alloy thin film hydrogen sensor, a humidity (micro-water) sensor and a pressure sensor connected to a printed circuit board is not more than 300mm3 .

[0052] In one embodiment, the in-situ self-calibration detection method for hydrogen detection comprises: A closed-loop control of the gradient working temperature is performed using a heating resistor and a temperature measuring resistor. At the self-calibration temperature, low concentrations of hydrogen (below 200 ppm) will not react with the sensor, so that the sensor baseline after long-term operation at high temperature can be obtained. According to the resistance temperature coefficient of the gas sensor and the difference between the self-calibration temperature and the normal operating temperature, the baseline value after long-term operation at the normal operating temperature can be obtained. The difference between the baseline value and the baseline value at the initial operation is the long-term working baseline drift. The self-calibration of the long-term baseline drift a2 can be completed based on the difference. Further, 60°C, 90°C, 120°C, 1 At four temperature points of 50℃, the baseline values ​​after self-calibration can be obtained by combining the temperature coefficient of the gas sensitive resistor to obtain the baseline values ​​at these four temperature points. At the same time, the response value of the hydrogen concentration measured at this time can be directly read by the sensor. The difference between the two is the response output at different working temperatures caused by the hydrogen concentration in the oil at this time. The relationship between the response output and the working temperature is established, and the database of the relationship between the response output of different concentrations and the working temperature is queried to obtain the actual hydrogen concentration in the transformer oil in the current environment. The relationship between the actual hydrogen concentration and the response output can be used to perform self-calibration of the long-term working response coefficient drift k2. The zero-concentration baseline value after the long-term working baseline drift correction at the working temperature and the response value at the standard hydrogen concentration are used to complete the self-calibration of the long-term working response coefficient of the sensor.

[0053] The integrated palladium alloy bridge thin film hydrogen sensor, humidity (micro-water) sensor and pressure sensor are connected to the post-signal processing and output circuit through the front signal amplification circuit board connection line, and the temperature, pressure and humidity compensation self-calibration is directly performed according to the preset model to eliminate the hydrogen sensor baseline drift and response coefficient change caused by the temperature, pressure and humidity changes inside the transformer, and complete the self-calibration of the humidity, pressure and humidity baseline and response coefficient. As a preferred solution, the following scheme: the micro palladium alloy thin film hydrogen sensor, humidity (micro-water) sensor and pressure sensor are connected to the voltage divider circuit to read the resistance value; the voltage divider circuit outputs the voltage signal of the hydrogen concentration, humidity (micro-water) change and pressure change of the transformer oil inside the transformer; the voltage signal is amplified by the amplification and filtering circuit signal; the conditioned temperature, hydrogen concentration, humidity (micro-water) content and pressure analog signal are converted into digital signals through the AD analog-to-digital converter 1; MCU2 uses the preset compensation model to self-calibrate the hydrogen concentration signal for temperature, humidity, pressure and long-term working drift to obtain the accurate concentration value of hydrogen inside the transformer.

[0054] In one embodiment, the preamplifier circuit board 19 and the post-signal processing circuit board 22 are electromagnetically shielded. The post-signal processing circuit board 22 is provided with an AD analog-to-digital converter 1 and an MCU2. The AD analog-to-digital converter 1 converts the conditioned temperature, hydrogen concentration, humidity (micro-water) content and pressure analog signals into digital signals; the MCU2 uses a preset compensation model to self-calibrate the hydrogen concentration signal for temperature, humidity, pressure and long-term working drift, and obtains the accurate concentration value of hydrogen inside the transformer.

[0055] The basic principles of the present application are described above in conjunction with specific embodiments. However, it should be noted that the advantages, strengths, effects, etc. mentioned in the present application are only examples and not limitations, and it cannot be considered that these advantages, strengths, effects, etc. are required by each embodiment of the present application. In addition, the specific details disclosed above are only for the purpose of illustration and ease of understanding, not for limitation, and the above details do not limit the present application to being implemented by adopting the above specific details.

[0056] The above description has been given for the purpose of illustration and description. In addition, this description is not intended to limit the embodiments of the present application to the forms disclosed herein. Although multiple example aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, changes, additions and sub-combinations thereof.

Claims

1. An in-situ sensor chip for detecting hydrogen in transformer oil, characterized in that: These include, a silicon substrate having an upper surface and a lower surface; A first insulating layer stacked on the lower surface; a third insulating layer stacked on the upper surface; A heating resistor, which is stacked on the third insulating layer in a zigzag structure to form a heating area with a uniform thermal physical field; a second insulating layer stacked on the heating resistor; A plurality of gas-sensitive resistors are arranged on the second insulating layer and located in the heating region, wherein the gas-sensitive resistors include a zigzag structure made of a palladium metal alloy material and a gas-sensitive lead electrode connected to the zigzag structure, wherein the zigzag structure is configured as a Wheatstone bridge structure. A temperature measuring resistor, which is arranged on the second insulating layer and surrounded by a plurality of gas-sensitive resistors in the heating area, the temperature measuring resistor comprising a single-wire structure made of platinum material and temperature measuring lead electrodes arranged at both ends of the single-wire structure; The Si3N4 isolation layer covers two opposite bridge arms of the Wheatstone bridge structure, and the other two opposite bridge arms are exposed to the air. The gas-sensitive resistor outputs a voltage signal in response to hydrogen.

2. The in-situ sensing chip for detecting hydrogen in transformer oil as claimed in claim 1, characterized in that: Preferably, the plurality of gas-sensitive resistors are symmetrically distributed with the temperature-measuring resistor as the center, and the gas-sensitive lead electrodes and the temperature-measuring lead electrodes are both made of gold material.

3. The in-situ sensing chip for detecting hydrogen in transformer oil as claimed in claim 1, characterized in that: A connection layer made of Ti material is deposited between the second insulating layer and the gas-sensitive resistor and the temperature-measuring resistor.

4. The in-situ sensing chip for detecting hydrogen in transformer oil as claimed in claim 1, characterized in that: The thickness of the gas-sensitive resistor is 40nm, and the thickness of the temperature-measuring resistor is 100nm; the thickness of the gas-sensitive lead electrode and the temperature-measuring lead electrode are both 250nm, the thickness of the Si3N4 isolation layer is 250nm, and the thickness of the connection layer is 20nm-30nm.

5. The in-situ sensing chip for detecting hydrogen in transformer oil as claimed in claim 1, characterized in that: The first insulating layer and the third insulating layer are composed of four thin films of SiO2 / Si3N4 / SiO2 / Si3N4 in sequence.

6. The in-situ sensing chip for detecting hydrogen in transformer oil as claimed in claim 1, characterized in that: The heating resistor and the gas-sensitive resistor are arranged in two layers, upper and lower, through a zigzag structure.

7. An in-situ self-calibration sensor for detecting hydrogen in transformer oil, characterized in that: It includes a hydrogen measuring probe, which includes, A preamplifier circuit board, which integrates an in-situ sensing chip for detecting hydrogen in transformer oil, a humidity sensor and a pressure sensor as described in any one of claims 1 to 6 to obtain a hydrogen concentration value and temperature, pressure and humidity analog signals, A post-signal processing circuit board is connected to the pre-amplifier circuit board to convert the temperature, pressure and humidity analog signals into digital signals through AD analog-to-digital conversion. The post-signal processing circuit board performs temperature, pressure and humidity compensation self-calibration on the hydrogen concentration value.

8. The in-situ self-calibration sensor for detecting hydrogen in transformer oil according to claim 7, characterized in that: Also includes, Front probe housing, The oil inlet is located at the front end of the front probe housing and can be installed on the transformer oil inlet through the transformer connection thread. The middle-end circuit housing is connected to the front-end probe housing via a sensor connecting thread, the front-end amplifier circuit board is arranged in the middle-end circuit housing, and the rear-end signal processing circuit board is connected to the front-end amplifier circuit board via a sealed connector. A signal output circuit board is disposed in the middle circuit housing and connected to the rear signal processing circuit board via a sealed connector. The rear end sealed shell is threadedly connected to the middle end circuit shell, and the rear end sealed shell is provided with a signal line transmission hole for leading out the signal line.

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