A method and apparatus for in-situ monitoring of dissolved gases in oil using photoacoustic spectroscopy

Abstract

The application belongs to the technical field of gas detection, and particularly relates to a photoacoustic spectroscopy oil dissolved gas in-situ monitoring method and device. The device comprises a modulation module, an excitation light source, a collimator, a photoacoustic cell, an optical microphone and a signal demodulation and processing system. One end surface of the optical microphone shell is provided with a sound-sensitive film, and the second end surface opposite to the sound-sensitive film is provided with an outer micro-flow hole, a micro-flow hole channel and a back cavity through hole which are in communication with each other. The back cavity through hole is in communication with a cavity, and the outer micro-flow hole is in communication with the outside of the optical microphone shell, and is used for balancing the pressure inside and outside the cavity. The second end surface is further provided with a fiber limiting through hole penetrating through the second end surface, which is used for inserting a ceramic plug and a detection optical fiber. The end surface of the ceramic plug and the detection optical fiber in the cavity and the sound-sensitive film constitute an FP microcavity. The application can in-situ monitor the dissolved gas in the transformer oil without degassing, eliminates many uncertainties introduced by oil-gas separation, and greatly reduces the false positive rate and the false negative rate of the system.

Description

Technical Field

[0001] This invention belongs to the field of gas detection technology, specifically relating to a method and device for in-situ monitoring of dissolved gases in oil using photoacoustic spectroscopy. Background Technology

[0002] Transformers, converter transformers, high-voltage shunt reactors, and other oil-filled electrical equipment (hereinafter referred to as "equipment") are the heart of the power grid, and their safe operation is of great significance to ensuring power supply and grid security. With the construction of new power systems, the proportion of high-voltage, large-capacity oil-filled electrical equipment is increasing, making it a top priority for power supply security. However, equipment failures and even explosions caused by internal overheating and discharge pose a significant threat to the safe and stable operation of the power grid. Therefore, continuous monitoring and early warning of the internal operating status of the equipment are essential. Currently, the most effective method is to judge this by the absolute content and relative increase of characteristic gases dissolved in the insulating oil.

[0003] Photoacoustic spectroscopy, as a highly sensitive gas detection technology, offers advantages over traditional gas chromatography, including no need for carrier gas, no need for periodic calibration, long service life, and low maintenance workload, leading to its widespread application in online monitoring of dissolved gases in oil. However, current photoacoustic spectroscopy oil dissolved gas monitoring devices heavily rely on oil-gas separation units for degassing. This process is not only time-consuming and unable to provide timely warnings of equipment failures, but its performance is also limited by the gas content of the insulating oil. When the insulating oil has a low gas content, the characteristic gas content extracted by the oil-gas separation unit is low, resulting in insufficient response signals from some monitoring devices and low data reliability. Conversely, when the insulating oil has a high gas content, especially when equipment discharge causes a sudden increase in gas and oil-gas mixing, the degassing units of some monitoring devices may malfunction, failing to reflect the equipment status in a timely manner. Degassing units are generally classified into two types based on their working principle: vacuum degassing and dynamic headspace degassing. When using dynamic headspace degassing, external air is inevitably introduced into the insulating oil, leading to an increase in the gas content of the returned oil and affecting equipment safety. When using vacuum degassing, especially with piston pumps and diaphragm pumps, the pump's frequent reciprocating motion often causes poor sealing, resulting in malfunction of the device or even oil leakage, thus affecting equipment safety. Therefore, there is an urgent need for a method and device for in-situ monitoring of dissolved gases in oil using photoacoustic spectroscopy without degassing. Summary of the Invention

[0004] The purpose of this invention is to provide a method and device for in-situ monitoring of dissolved gases in oil using photoacoustic spectroscopy. By setting up an optical microphone microfluidic, it is possible to directly monitor dissolved gases in oil without degassing, eliminating many uncertainties introduced by oil-gas separation and greatly reducing the false alarm rate and false alarm rate of the system.

[0005] To achieve the above objectives, the present invention provides an optical microphone, comprising an optical microphone housing containing an internal cavity, wherein a sound-sensitive film is provided on one end face of the optical microphone housing, and an external microfluidic hole, a microfluidic hole channel, and a back cavity through hole are provided on a second end face opposite to the sound-sensitive film; the back cavity through hole communicates with the cavity, and the external microfluidic hole communicates with the outside of the optical microphone housing, for balancing the pressure inside and outside the cavity;

[0006] The second end face is also provided with an optical fiber limiting through hole that penetrates the second end face for inserting a ceramic ferrule and a probe optical fiber; the end faces of the ceramic ferrule and the probe optical fiber located in the cavity and the acoustic thin film constitute an FP microcavity.

[0007] Furthermore, the diameter of the outer micropores, micropore channels, and back cavity through-holes is 150-250 μm.

[0008] Furthermore, both the outer microfluidic hole and the back cavity through hole are perpendicular to the second end face, and the microfluidic hole channel is a spiral channel located in the second end face, used to connect the outer microfluidic hole and the back cavity through hole.

[0009] Furthermore, the optical fiber limiting through hole is located at the center of the second end face; the outer wall of the ceramic ferrule contacts the inner wall of the optical fiber limiting through hole, and the probe optical fiber is inserted into the ceramic ferrule.

[0010] The present invention also provides an in-situ monitoring device for dissolved gases in oil by photoacoustic spectroscopy, comprising a modulation module, an excitation light source, a collimator, a photoacoustic cell, an optical microphone, and a signal demodulation and processing system; the optical microphone is any of the optical microphones described above, and the optical microphone is placed inside the photoacoustic cell; the photoacoustic cell is used to hold transformer oil containing dissolved gases to be measured.

[0011] The modulation module is used to adjust the excitation light generated by the excitation light source; the collimator is used to collimate the excitation light emitted from the excitation light source and then incident it into the photoacoustic cell; the optical microphone is used to detect the photoacoustic signal generated by the gas to be measured; the signal demodulation and processing system is used to demodulate the signal of the optical microphone and extract the harmonic signal amplitude to obtain the concentration of the gas to be measured.

[0012] Furthermore, the modulation module performs modulation via a signal generator or a chopper;

[0013] The signal demodulation and processing system uses intensity demodulation or phase demodulation to demodulate the signal of the optical microphone, and extracts the amplitude of the harmonic signal through lock-in amplification technology.

[0014] Furthermore, the photoacoustic cell can be a resonant photoacoustic cell or a non-resonant photoacoustic cell, and when a resonant photoacoustic cell is used, the optical microphone is placed in the exact center of the photoacoustic cell.

[0015] Furthermore, the gas to be tested includes one or more of CO, CO2, CH4, C2H2, C2H4, and C2H6.

[0016] This invention also provides a method for in-situ monitoring of dissolved gases in oil using photoacoustic spectroscopy, comprising the following steps:

[0017] S1. After the excitation light is modulated, the beam is collimated and incident into the photoacoustic cell. The gas to be tested dissolved in the oil in the photoacoustic cell absorbs the modulated light energy and generates a photoacoustic signal in the photoacoustic cell.

[0018] S2. The photoacoustic signal generated by the gas is detected by an optical microphone based on the optical FP interferometry principle;

[0019] S3. By demodulating the signal of the optical microphone and extracting its harmonic signal amplitude, the gas concentration information is obtained based on the relationship between the harmonic signal amplitude and the gas concentration.

[0020] Furthermore, the input wavelength of the excitation light is the same as the peak absorption wavelength of the gas to be tested dissolved in the oil.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0022] 1. This invention provides an optical microphone with a back cavity through-hole on the cavity body and a microfluidic hole on the outer shell of the optical microphone. One end of the microfluidic hole is connected to an external oil medium, and the other end is connected to the back cavity through-hole to realize the connection between the external oil medium and the optical microphone cavity. This is used to balance the internal and external pressure of the acoustic diaphragm, ensuring that oil does not enter the FP cavity, so that the optical microphone can still maintain a high sensitivity response in oil. This solves the problems of low sensitivity and active charging of the probe in traditional electrical microphones in oil.

[0023] 2. The photoacoustic spectroscopy method for in-situ monitoring of dissolved gases in oil provided by this invention employs an optical microphone with micropores, enabling highly sensitive in-situ monitoring of dissolved gases in oil without degassing. It eliminates the need for an oil-gas separation device, reducing system complexity; significantly shortens response time, allowing for rapid and timely fault warnings; eliminates many uncertainties introduced by oil-gas separation, greatly reducing the system's false alarm and false alarm rates; and solves the problems of poor detection accuracy, long response time, untimely fault warnings, and high false alarm and false alarm rates currently caused by oil-gas separation.

[0024] 3. The optical microphone probe of this invention is completely passive and inherently safe. It is completely immune to electromagnetic interference and will not introduce any electrical signals into the oil, thus reducing the risk. Attached Figure Description

[0025] Figure 1 This is a flowchart of the photoacoustic spectroscopy method for in-situ monitoring of dissolved gases in oil according to the present invention.

[0026] Figure 2 This is a schematic diagram of the in-situ monitoring device for dissolved gases in oil using photoacoustic spectroscopy according to the present invention.

[0027] Figure 3 This is a schematic cross-sectional view of the optical microphone of the present invention.

[0028] Figure 4 This is a schematic diagram of the microfluidic aperture of the optical microphone of the present invention.

[0029] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0030] 1-Excitation light source; 2-Collider; 3-Photoacoustic cell; 4-Optical microphone; 5-Acoustic-sensitive film; 6-Optical microphone cavity; 7-Back cavity through-hole; 8-Optical microphone housing; 9-Outer microfluidic hole; 10-Modulation module; 11-Signal demodulation and processing system; 12-Fiber end face; 13-Ceramic ferrule; 14-Detection fiber; 15-Microfluidic hole channel; 16-Fiber limiting through-hole. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Example 1

[0033] like Figure 2 As shown, this embodiment provides an in-situ monitoring device for dissolved gases in oil using photoacoustic spectroscopy, including: a modulation module 10, an excitation light source 1, a collimator 2, a photoacoustic cell 3, an optical microphone 4, and a signal demodulation and processing system 11.

[0034] The modulation module 10 is used to modulate the excitation laser. The beam emitted from the excitation light source 1 is collimated by the collimator 2 and then incident into the photoacoustic cell 3. The photoacoustic cell 3 is filled with transformer oil containing the gas to be measured. The dissolved gas in the oil absorbs the modulated light energy and generates a photoacoustic signal. The photoacoustic signal is detected by an optical microphone 4 based on the optical FP interference principle. The optical microphone 4 is in direct contact with the oil. The optical microphone 4 is provided with microflow holes 9 to balance the internal and external pressures of the acoustic thin film 5, so that it can maintain a high sensitivity response in the oil. The signal demodulation and processing system 11 demodulates the signal of the optical microphone 4 and extracts its harmonic signal amplitude to retrieve the gas concentration information.

[0035] The photoacoustic cell 3 is also equipped with an oil inlet and an oil outlet, which are used for oil inlet and oil outlet respectively.

[0036] In this embodiment, the optical microphone 4 adopts the following... Figure 3 and 4 The open cavity structure shown includes an optical microphone housing 8 containing a cavity 6 inside. One end face of the optical microphone housing 8 is provided with an acoustic diaphragm 5, and the second end face opposite to the acoustic diaphragm 5 is provided with an external microfluidic hole 9, a microfluidic hole channel 15, and a back cavity through hole 7 that are interconnected. The back cavity through hole 7 is connected to the cavity 6, and the external microfluidic hole 9 is connected to the oil in the photoacoustic cell 3 of the optical microphone housing 8 to balance the pressure inside and outside the cavity 6.

[0037] The second end face is also provided with an optical fiber limiting through-hole 16 penetrating the second end face for inserting a ceramic ferrule 13 and a probe optical fiber 14; the end faces of the ceramic ferrule 13 and the probe optical fiber 14 located within the cavity 6 and the acoustic thin film 5 constitute an FP microcavity. The outer microfluidic hole 9 and the back cavity through-hole 7 are both perpendicular to the second end face. The microfluidic hole channel 15 is a spiral channel located within the second end face, used to connect the outer microfluidic hole 9 and the back cavity through-hole 7. The optical fiber limiting through-hole 16 is located at the center of the second end face; the outer wall of the ceramic ferrule 13 contacts the inner wall of the optical fiber limiting through-hole 16, and the probe optical fiber 14 is inserted into the ceramic ferrule 13.

[0038] The optical microphone 4 is based on the principle of optical Fabry-Perot interference. An FP microcavity (fiber Fabry-Perot interference cavity) is formed between the acoustic-sensitive film 5 and the fiber end face 12. The photoacoustic signal induces vibration in the acoustic-sensitive film 5, thereby changing the intensity and phase of the interference light. The cavity 6 of the optical microphone has a back cavity through-hole 7, and the outer shell 8 has a microfluidic hole 9. One end of the microfluidic hole 9 is connected to an external oil medium, and the other end is connected to the back cavity through-hole 7, enabling communication between the external oil medium and the optical microphone cavity 6. This balances the internal and external pressures of the acoustic-sensitive film 5, preventing oil from entering the FP cavity and allowing the optical microphone to maintain high sensitivity even in oil. This solves the problems of low sensitivity and active probe charging in traditional electrical microphones in oil.

[0039] The diameter of its micro-orifice 9 is 200μm, which is determined by the capillary radius of the oil molecules. It forms a capillary effect with the oil medium around the orifice. Due to the liquid pressure, the oil will enter the micro-orifice channel 15, thereby compressing the air in the cavity. Its pressure will increase accordingly until it reaches equilibrium with the external static oil pressure, so that the microphone cavity 6 is kept with air medium, thus achieving the microphone's ability to have low acoustic impedance and withstand static oil pressure.

[0040] The acoustic thin film 5 used in the optical microphone 4 can be made of metal or non-metal. In this example, the acoustic thin film is made of silicon nitride and is fabricated using MEMS technology. It has a diameter of 1.5 mm and a thickness of 400 nm.

[0041] The micro-orifice 9 of the optical microphone 4 can be fabricated by machining or by microelectromechanical systems (MEMS) technology. In this example, it is fabricated by machining, and its encapsulation shell material is brass.

[0042] In this embodiment, the signal demodulation and processing system 11 uses intensity demodulation or phase demodulation to demodulate the signal of the optical microphone 4 and extracts its harmonic signal amplitude through lock-in amplification technology to further deduce the gas concentration information.

[0043] Example 2

[0044] like Figure 1 and 2 As shown, this embodiment provides an in-situ monitoring method for dissolved gases in oil using photoacoustic spectroscopy, including: a modulation module 10, an excitation light source 1, a collimator 2, a photoacoustic cell 3, an optical microphone 4, and a signal demodulation and processing system 11. The photoacoustic cell 3 is filled with transformer oil containing dissolved gases to be measured; the excitation light source is used to excite the dissolved gases in the oil to generate sound waves, i.e., photoacoustic signals; the collimator 2 is used to collimate the beam emitted from the excitation light source and direct it into the photoacoustic cell; the optical microphone 4 is in direct contact with the oil and is used to detect the photoacoustic signals generated by the gases. The in-situ monitoring method includes:

[0045] S1. After the excitation light is modulated by the modulation module, the beam is collimated and incident into the photoacoustic cell 3. The gas dissolved in the oil absorbs the modulated light energy and generates a photoacoustic signal in the photoacoustic cell 3.

[0046] S2. The photoacoustic signal generated by the gas is detected by an optical microphone 4 based on the optical FP (Fabry-Perot) interference principle;

[0047] S3. By demodulating the signal of the optical microphone 4 and extracting its harmonic signal amplitude, the gas concentration information is obtained by inverting the relationship between the harmonic signal amplitude and the gas concentration.

[0048] Specifically, in S1, the excitation light source 1 is selected based on the absorption spectrum of the dissolved gas in the oil.

[0049] In this example, for the measurement of acetylene gas, the excitation source 2 is selected based on the absorption spectrum of dissolved acetylene in oil, while avoiding the absorption peaks of the background oil in the near-infrared band. Due to the principle of "like dissolves like," the electron cloud density of dissolved acetylene in oil decreases, and the intermolecular distance decreases, resulting in a weakening of stretching vibrations. This causes the absorption spectrum to redshift and broaden compared to the gas phase. In this example, the excitation source 1 is a DFB laser with a wavelength of 1532.8 nm, corresponding to the peak wavelength of the dissolved acetylene absorption spectrum. Simultaneously, at a 1 cm optical path length, the transmittance of the background oil in this band is higher than 90%.

[0050] In this example, the acetylene oil sample was prepared using No. 25 transformer oil and acetylene standard gas. The acetylene gas was introduced into the No. 25 transformer oil and stirred with a magnetic stirrer for more than two hours. After degassing and calibration by gas chromatography, its concentration was determined to be 5.5 ppm.

[0051] Specifically, in S1, the excitation light can be modulated by generating a modulation signal through a signal generator and then loading it onto the laser, or it can be modulated externally through a chopper or other means. In this embodiment, modulation is performed by generating a modulation signal through a signal generator and loading it onto the laser driver. Sine wave modulation is used, with a modulation frequency of 4kHz and a modulation amplitude of 600mVpp.

[0052] Specifically, in S1, the photoacoustic cell 3 can be a non-resonant photoacoustic cell or a resonant photoacoustic cell; if a resonant photoacoustic cell is used, the size and resonant frequency of the photoacoustic cell 3 are designed according to the physical parameters of the oil. Specifically, in S1, if the photoacoustic cell 3 is a resonant photoacoustic cell, the optical microphone 4 needs to be placed at the point of strongest sound pressure inside the photoacoustic cell.

[0053] In this embodiment, a resonant photoacoustic cell is used, and the optical microphone 4 is placed in the center of the photoacoustic cell 3, that is, at the point of maximum sound pressure.

[0054] Specifically, in S2, the optical microphone 4 is based on the principle of optical FP interference. An FP microcavity is formed between the acoustic-sensitive film 5 and the fiber end face 12. The photoacoustic signal induces the acoustic-sensitive film 5 to vibrate, thereby changing the intensity and phase of the interference light. The cavity 6 of the optical microphone has a back cavity through-hole 7, and the outer shell 8 of the optical microphone has a microfluidic hole 9. One end of the microfluidic hole 9 is connected to an external oil medium, and the other end is connected to the back cavity through-hole 7, thus enabling communication between the external oil medium and the optical microphone cavity 6. This balances the internal and external pressures of the acoustic-sensitive film 5, ensuring that oil does not enter the FP cavity, allowing the optical microphone to maintain high sensitivity even in oil. This solves the problems of low sensitivity and active charging of the probe in traditional electrical microphones in oil.

[0055] In summary, the direct application of photoacoustic spectroscopy in oil-soluble environments presents the following challenges. This invention provides solutions to these challenges, as detailed below:

[0056] 1. Changes in the absorption spectrum of gases in oil interfere with the absorption spectrum of background oil. This invention measures the absorption spectrum of transformer oil in the near-infrared band, and analyzes and tests the changes in the absorption spectrum of dissolved gases in oil and the absorption spectrum of background oil, providing a reference for finding a suitable excitation light source wavelength. Due to the principle of "like dissolves like," the electron cloud density of dissolved gases in oil decreases, and the intermolecular distance decreases, resulting in a weakening of stretching vibrations, causing the absorption spectral lines to redshift and broaden compared to the gas phase.

[0057] 2. Optical microphones are difficult to apply directly in oily environments. Fully open-cavity optical microphones allow oil to seep into the microcavity, disrupting the interference spectrum, while closed structures cause an imbalance in the pressure difference between the inside and outside of the acoustically sensitive film, leading to deterioration of the film's response. This invention proposes an oil-immersed optical microphone based on a back-cavity microfluidic encapsulation, preventing oil from entering the optical microcavity, ensuring the contrast and stability of the interference spectrum, and balancing the internal and external pressure difference, thus preventing the acoustic response of the film from deteriorating in oily environments.

[0058] Overall, this invention can achieve in-situ monitoring of dissolved gases in oil without degassing, solving the problems of poor detection accuracy, long response time, untimely fault warning, and high false alarm and missed alarm rates caused by oil-gas separation. It has the following four significant advantages: (1) No oil-gas separation device is required, reducing the complexity of the system; (2) The response time is greatly shortened, enabling rapid and timely fault warning; (3) Many uncertainties introduced by oil-gas separation are eliminated, greatly reducing the false alarm and missed alarm rates of the system; (4) The optical microphone probe is all-optical and passive, inherently safe, completely immune to electromagnetic interference, and does not introduce any electrical signals into the oil, reducing the risk.

[0059] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A photoacoustic spectroscopy in-situ monitoring apparatus for dissolved gases in oil, characterized by, The device comprises a modulation module, an excitation light source, a collimator, an optoacoustic cell, an optical microphone, and a signal demodulation and processing system; the optical microphone comprises an optical microphone shell with a cavity therein, one end face of the optical microphone shell is provided with a sound-sensitive film, and the second end face opposite to the sound-sensitive film is provided with an outer micro-flow hole, a micro-flow hole channel, and a back cavity through hole which are in communication with each other; the back cavity through hole is in communication with the cavity, and the outer micro-flow hole is in communication with the outside of the optical microphone shell for balancing the pressure inside and outside the cavity; the diameters of the outer micro-flow hole, the micro-flow hole channel, and the back cavity through hole are each independently 150-250 μm; The second end face is also provided with a fiber limiting through hole penetrating through the second end face, for inserting a ceramic ferrule and a detection optical fiber; the ceramic ferrule and the detection optical fiber are located at the end face in the cavity, and the sound-sensitive film and the end face constitute an FP microcavity; a resonant optoacoustic cell is adopted, and the optical microphone is placed in the middle of the optoacoustic cell; The optoacoustic cell is used for containing transformer oil in which a to-be-detected gas is dissolved; due to the liquid pressure, the oil enters the micro-flow hole channel, thereby compressing the air in the cavity, the pressure is correspondingly increased, until the static oil pressure with the outside reaches balance, so that the air medium is maintained in the microphone cavity; The modulation module is used for adjusting the excitation light generated by the excitation light source; the collimator is used for collimating the excitation light emitted by the excitation light source and then entering the optoacoustic cell; the optical microphone is used for detecting the photoacoustic signal generated by the to-be-detected gas; and the signal demodulation and processing system is used for demodulating the signal of the optical microphone and extracting the harmonic signal amplitude to obtain the concentration of the to-be-detected gas; The outer micro-flow hole and the back cavity through hole are both vertically provided on the second end face, and the micro-flow hole channel is a spiral channel located in the second end face, for connecting the outer micro-flow hole and the back cavity through hole.

2. The photoacoustic spectroscopy in-situ oil dissolved gas monitoring device according to claim 1, characterized in that, The fiber limiting through hole is located at the center position of the second end face; the outer wall of the ceramic ferrule is in contact with the inner wall of the fiber limiting through hole, and the detection optical fiber is inserted into the ceramic ferrule.

3. The photoacoustic spectroscopy in-situ oil dissolved gas monitoring device according to claim 1, characterized in that, The modulation module is modulated by a signal generator or a chopper; The signal demodulation and processing system demodulates the signal of the optical microphone by using an intensity demodulation method or a phase demodulation method, and extracts the harmonic signal amplitude by using a lock-in amplification technology.

4. The photoacoustic spectroscopy in-situ oil dissolved gas monitoring device according to claim 1, characterized in that, The to-be-detected gas comprises one or more of CO, CO2, CH4, C2H2, C2H4, and C2H6.

5. A method of photoacoustic spectroscopy in-situ monitoring of dissolved gases in oil, characterized by, The photoacoustic spectroscopy in-situ monitoring device for dissolved gas in oil according to any one of claims 1-4 comprises the following steps: S1, after the excitation light is modulated, the light beam is collimated and enters the optoacoustic cell, and the to-be-detected gas dissolved in the oil in the optoacoustic cell absorbs the modulated light energy to generate a photoacoustic signal in the optoacoustic cell; S2, the photoacoustic signal generated by the gas is detected by the optical microphone based on the optical FP interference principle; S3, the concentration information of the gas is obtained based on the relationship between the harmonic signal amplitude and the gas concentration by demodulating the signal of the optical microphone and extracting the harmonic signal amplitude.

6. The photoacoustic spectroscopy in-situ oil dissolved gas monitoring method of claim 5, wherein, The input wavelength of the excitation light is the same as the peak absorption wavelength of the to-be-detected gas dissolved in the oil.

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