System and method for detecting furfural in transformer oil based on photo-thermal lens spectrum

Abstract

The invention discloses a system and a method for detecting furfural in transformer oil based on a photo-thermal lens spectrum. A quantum cascade laser is used as pumping laser, and a helium-neon laser is used as detection laser; a visible light-infrared light dichroscope, a chopper, a reflector, an attenuator, a plano-convex lens, a fixed optical path liquid pool, an iris diaphragm, a photoelectric detector, a lock-in amplifier, an upper computer and the like are arranged, so that in-situ rapid, accurate and high-sensitivity quantitative detection of trace furfural in the transformer oil is realized; through the pumping laser covering the infrared characteristic absorption spectral line in furfural, trace furfural molecules in the transformer oil absorb the pumping laser with the average power exceeding 100 mW to excite a strong thermal lens effect, and the detection performance is remarkably improved; in-situ and rapid detection of furfural in the transformer oil is realized by utilizing a thermal lens effect generated by absorption of furfural in the transformer oil on mid-infrared light.

Description

Technical Field

[0001] The invention relates to the technical field of transformer oil detection, and in particular to a system and method for detecting furfural in transformer oil based on photothermal lens spectroscopy. Background Art

[0002] Power transformers are one of the most important substation equipment in the power system. Their operational reliability is of great significance to the safety and stability of the power grid. Under the action of electricity and heat, the oil-paper insulation inside the operating transformer gradually ages and produces CO and CO 2 , and furfural, etc., which reflect the degree of insulation degradation. Among them, furfural molecules are only produced by the degradation of cellulose paper insulation materials. Therefore, detecting the content of dissolved furfural in transformer oil is one of the important technical means to evaluate the degree of aging of paper insulation inside the transformer. At present, the methods for determining the content of furfural in transformer oil mainly include high performance liquid chromatography, spectrophotometry, and colorimetry. These methods have high detection sensitivity, but they all require complex pretreatment of transformer oil samples such as extraction and distillation, which is difficult to meet the needs of live detection or in-situ detection.

[0003] Photothermal lens spectroscopy is mainly achieved by using the thermal lens effect of liquid. The thermal lens effect is a nonlinear effect. When a laser of a specific wavelength irradiates the target liquid, the target molecules absorb light energy, causing the local temperature to rise. The change in temperature further changes the local refractive index, thus forming a liquid thermal lens. At present, the liquid content analysis technology based on thermal lens mainly adopts a single beam configuration, and the light source used is mainly concentrated in the near-infrared band and the visible light band. It has limited application in liquid content analysis and has low detection sensitivity. Summary of the invention

[0004] The purpose of the present invention is to provide a detection system and method for furfural in transformer oil based on photothermal lens spectroscopy in view of the problems existing in the prior art, so as to realize in-situ rapid, accurate and highly sensitive quantitative detection of trace furfural in transformer oil.

[0005] To achieve the above object, the technical solution adopted by the present invention is: A furfural detection system in transformer oil based on photothermal lens spectroscopy, comprising: A first laser, the first laser being used to emit an infrared light beam; a second laser, the second laser being configured to emit a visible light beam; A visible light-infrared light dichroic mirror, wherein a chopper, an infrared light reflector and an infrared light plano-convex lens are sequentially arranged between the first laser and the visible light-infrared light dichroic mirror, and an adjustable attenuator, a visible light plano-convex lens and a first visible light reflector assembly are sequentially arranged between the second laser and the visible light-infrared light dichroic mirror; A fixed optical path liquid pool is arranged in the output direction of the visible light-infrared light dichroic mirror, and the fixed optical path liquid pool is used to contain transformer oil to be tested; A second visible light reflector assembly is arranged in the output direction of the fixed optical path liquid pool, a variable aperture is arranged in the output direction of the second visible light reflector assembly, a photoelectric detector is arranged in the output direction of the variable aperture, the photoelectric detector is connected to a phase-locked amplifier, and the phase-locked amplifier is connected to a host computer.

[0006] The furfural detection system in transformer oil is based on photothermal lens spectroscopy, with quantum cascade laser as pump laser and helium-neon laser as detection laser, to achieve in-situ rapid, accurate and highly sensitive quantitative detection of trace furfural in transformer oil; by emitting pump laser through the first laser covering the mid-infrared characteristic absorption line of furfural, trace furfural molecules in transformer oil absorb pump laser with an average power of more than 100mW and stimulate a strong thermal lens effect, which significantly improves the detection performance; utilizing the thermal lens effect produced by the absorption of mid-infrared light by furfural in transformer oil, in-situ and rapid detection of furfural in transformer oil is achieved; and the detection system can detect transformer oils of different aging degrees, which improves its detection applicability.

[0007] Furthermore, the first laser is a quantum cascade laser, which includes a laser emission head and a quantum cascade laser driver connected by a cable. The output infrared light wavelength of the quantum cascade laser is adjusted by adjusting the quantum cascade laser driver to realize the infrared light wavelength scanning function, and the emission spectrum range covers the infrared absorption spectrum line of furfural; the second laser is a helium-neon laser.

[0008] Furthermore, the chopper includes a chopper controller, a chopper base and a chopper blade. The modulation frequency of the chopper is 20Hz to 1kHz. The external reference output of the chopper controller is connected to the external reference input of the phase-locked amplifier to synchronize the demodulation frequency of the phase-locked amplifier with the chopper frequency and reduce noise.

[0009] Furthermore, the first visible light reflector assembly includes at least two visible light reflectors, and the visible light beam is reflected at least twice before reaching the visible light-infrared light dichroic mirror.

[0010] Furthermore, the second visible light reflector assembly includes 4 to 8 visible light reflectors, and the visible light beam reaches the variable aperture after being reflected 3 to 7 times.

[0011] Furthermore, the visible light-infrared dichroic mirror is arranged at an angle, the visible light beam is directed toward the visible light-infrared dichroic mirror to reach the fixed optical path liquid pool, and the infrared light beam is reflected behind the visible light-infrared dichroic mirror to reach the fixed optical path liquid pool.

[0012] Furthermore, the output port of the photodetector is connected to the input port of the lock-in amplifier via a BNC line, and the output port of the lock-in amplifier is connected to the host computer via a USB cable.

[0013] Furthermore, the fixed optical path liquid pool is clamped and fixed by two light-transmitting window sheets, and then clamped and fixed by two hollow metal sheets through four metal bolts, wherein a metal liquid injection port is provided on the outer side of one of the hollow metal sheets.

[0014] Furthermore, there are concentric holes between the light-transmitting window sheet and the hollow metal sheet that directly reach the fixed optical path liquid pool, and the fixed optical path liquid pool has a thickness of 100 to 1000 μm.

[0015] A detection method of furfural in transformer oil based on photothermal lens spectroscopy, the detection method comprising the following steps: Pumping standard transformer oil into the fixed optical path liquid pool; Turning on the first laser, the second laser, the lock-in amplifier, the photodetector, the chopper and the host computer; Turning on the laser output knob of the second laser, adjusting the pitch angles of the first visible light reflector assembly and the second visible light reflector assembly, and observing the time domain signal in the oscilloscope window of the lock-in amplifier at the same time, and stopping the adjustment when the amplitude of the time domain signal is the maximum; adjusting and setting the modulation frequency of the chopper; Turn on the laser output button of the first laser, and record the signal amplitude a1 demodulated by the lock-in amplifier; Pumping furfural transformer oil containing a known trace amount of furfural into the fixed optical path liquid pool, stopping the pumping after the demodulated signal of the lock-in amplifier is stable, and recording the amplitude a2 of the signal demodulated by the lock-in amplifier; The two sets of measured data a1, a2 and the corresponding furfural concentrations were linearly fitted to obtain a standard curve; Pumping the transformer oil sample to be tested into the fixed optical path liquid pool, stopping the pumping after the demodulated signal of the lock-in amplifier is stable, and recording the amplitude a3 of the signal demodulated by the lock-in amplifier; Substitute the signal amplitude a3 into the standard curve to obtain the furfural concentration value in the transformer oil sample to be tested.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The furfural detection system in transformer oil is based on photothermal lens spectroscopy, with quantum cascade laser as pump laser and helium-neon laser as detection laser, so as to realize the in-situ rapid, accurate and highly sensitive quantitative detection of trace furfural in transformer oil; 2. The pump laser is emitted by the first laser covering the mid-infrared characteristic absorption line of furfural, and the trace furfural molecules in the transformer oil absorb the pump laser with an average power exceeding 100mW to stimulate a strong thermal lens effect, which significantly improves the detection performance; 3. The thermal lens effect generated by the mid-infrared light absorption of furfural in transformer oil is utilized to realize the in-situ and rapid detection of furfural in transformer oil; 4. The detection system can detect transformer oils of different aging degrees, so as to improve its detection applicability; 5. Compared with high performance liquid chromatography, Raman spectroscopy and the like, the detection method of the present invention avoids the above problems. It avoids the need for complex pretreatment of transformer oil samples such as extraction and distillation; 6. By adjusting the optical path conditions, including the distance from the center of the fixed liquid pool to the silicon biased photodetector, the distance from the helium-neon laser beam to the center of the fixed liquid pool, etc., the performance of the detection system can be significantly improved; 7. The absorption of infrared light by the transformer oil sample to be tested in the fixed optical path liquid pool will change the local temperature distribution of the transformer oil sample to be tested, and then change the local refractive index, thereby causing a divergent effect on the visible light passing through the transformer oil sample to be tested; since the infrared light is modulated by the chopper to produce periodic infrared light pulses, the divergent effect caused by the visible light of the transformer oil sample to be tested will also change periodically, which is manifested as a periodic change in the intensity of the local visible light spot. The change in the intensity of the visible light spot is converted into a voltage signal by the photodetector, so that the host computer can obtain the output signal of the detection system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the overall layout of a furfural detection system in transformer oil based on photothermal lens spectroscopy according to the present invention; Figure 2 This is a time domain signal diagram when the present invention detects furfural in transformer oil; Figure 3 A schematic diagram of obtaining the furfural concentration value in the transformer oil sample to be tested by the standard curve of the present invention; In the figure: 1. first laser; 2. second laser; 3. chopper; 4. light-transmitting window piece 1; 5. light-transmitting window piece 2; 6. fixed optical path liquid pool; 7. visible light-infrared light dichroic mirror; 8-15. visible light reflector; 16. infrared light reflector; 17. adjustable attenuator; 18. visible light plano-convex lens; 19. infrared light plano-convex lens; 20. variable aperture; 21. photodetector; 22. phase-locked amplifier; 23. host computer; 24. BNC line; 25. visible light beam; 26. infrared light beam. DETAILED DESCRIPTION

[0018] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] In the description of the present invention, it should be noted that the directions or positional relationships indicated by the terms "middle", "upper", "lower", "left", "right", "inner", "outer", etc. are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. Example 1

[0020] like Figure 1 As shown, a furfural detection system in transformer oil based on photothermal lens spectroscopy comprises: A first laser 1, wherein the first laser 1 is used to emit an infrared light beam; A second laser 2, wherein the second laser 2 is used to emit visible light; A visible light-infrared light dichroic mirror 7, wherein a chopper 3, an infrared light reflector 16 and an infrared light plano-convex lens 19 are sequentially arranged between the first laser 1 and the visible light-infrared light dichroic mirror 7, and an adjustable attenuator 17, a visible light plano-convex lens 18 and a first visible light reflector assembly are sequentially arranged between the second laser 2 and the visible light-infrared light dichroic mirror 7; A fixed optical path liquid pool 6 is arranged in the output direction of the visible light-infrared light dichroic mirror 7, and the fixed optical path liquid pool 6 is used to contain the transformer oil to be tested; A second visible light reflector assembly is arranged in the output direction of the fixed optical path liquid pool 6, and a variable aperture 20 is provided in the output direction of the second visible light reflector assembly. A photodetector 21 is provided in the output direction of the variable aperture 20, and the photodetector 21 is connected to a phase-locked amplifier 22, and the phase-locked amplifier 22 is connected to a host computer 23.

[0021] The furfural detection system in transformer oil is based on photothermal lens spectroscopy, with quantum cascade laser as pump laser and helium-neon laser as detection laser, to achieve in-situ rapid, accurate and highly sensitive quantitative detection of trace furfural in transformer oil; by emitting pump laser through the first laser covering the mid-infrared characteristic absorption line of furfural, trace furfural molecules in transformer oil absorb pump laser with an average power of more than 100mW and stimulate a strong thermal lens effect, which significantly improves the detection performance; utilizing the thermal lens effect produced by the absorption of mid-infrared light by furfural in transformer oil, in-situ and rapid detection of furfural in transformer oil is achieved; and the detection system can detect transformer oils of different aging degrees, which improves its detection applicability.

[0022] The first laser 1 and the second laser 2 can respectively emit different types of laser beams, and the two do not interfere with each other when in use. The emitted light beams are processed accordingly and reach the visible light-infrared light dichroic mirror 7. The visible light-infrared light dichroic mirror 7 can not only separate and filter light of different wavelengths to allow light of a specific wavelength to pass through, but also reflect light beams so that the two light beams are emitted together to the fixed optical path liquid pool.

[0023] The chopper 3 is configured to modulate the signal, suppress the noise signal, and improve the stability and reliability of the output infrared light. The visible light plano-convex lens 18 and the infrared light plano-convex lens 19 can converge Gaussian light or point light source and convert it into Gaussian light. The infrared light reflector 16, the first visible light reflector assembly, and the second visible light reflector assembly can all change the propagation direction of the light beam and adjust the direction of the light beam. The configuration of the visible light reflector assembly can also change the optical path.

[0024] The infrared light beam 26 emitted by the first laser 1 passes through the chopper 3, the infrared light reflector 16 and the infrared light plano-convex lens 19 in sequence to reach the visible light-infrared light dichroic mirror 7, and then reaches the fixed optical path liquid pool 6 after being reflected by the visible light-infrared light dichroic mirror 7. Specifically, the infrared light of a specific frequency emitted by the first laser 1 is modulated by the chopper 3 to generate infrared light pulses, and the infrared light pulses change their propagation direction after passing through the infrared light reflector 16 and pass through the infrared light plano-convex lens 19. The infrared light pulses after being focused are reflected by the visible light-infrared light dichroic mirror 7 and directed toward the light-transmitting window and the fixed optical path liquid pool 6 to generate a thermal lens effect.

[0025] The visible light beam 25 emitted by the second laser 2 passes through the adjustable attenuator 17 (visible light adjustable attenuator), the visible light plano-convex lens 18 and the first visible light reflector assembly in sequence, and is emitted to the visible light-infrared light dichroic mirror 7. The visible light-infrared light dichroic mirror 7 will transmit the input visible light and reflect the input infrared light. Therefore, the visible light will pass through the visible light-infrared light dichroic mirror 7, the transparent window and the fixed optical path liquid pool 6 in sequence, and then pass through the second visible light reflector assembly to extend the light path, and finally reach the photodetector 21 after passing through the variable aperture 20.

[0026] Specifically, the 632.8nm visible light emitted by the second laser 2 is attenuated by the adjustable attenuator 17, then focused by the visible light plano-convex lens 18, and then amplified by a plurality of visible light reflectors in sequence, and then passes through the visible light-infrared light dichroic mirror and then through the light-transmitting window and the fixed optical path liquid pool.

[0027] Infrared light will be absorbed by furfural molecules in transformer oil and stimulate thermal lens effect, that is, a local negative lens will be generated in the infrared light irradiation area, and the negative lens will cause visible light to converge and diverge. In order to amplify the change of visible light, the visible light after passing through the fixed optical path liquid pool will be reflected by multiple visible light reflectors to extend the optical path. Then the visible light passes through the variable aperture to retain the area with the largest light intensity change and is emitted to the photodetector through the aperture.

[0028] The absorption of infrared light by the transformer oil sample to be tested in the fixed optical path liquid pool 6 will change the local temperature distribution of the transformer oil sample to be tested, and then change the local refractive index, thereby causing a divergent effect on the visible light passing through the transformer oil sample to be tested. Since the infrared light is modulated by the chopper 3 to produce periodic infrared light pulses, the divergent effect caused by the visible light of the transformer oil sample to be tested will also change periodically, which is manifested as a periodic change in the intensity of the local visible light spot. The change in the intensity of the visible light spot is converted into a voltage signal by the photodetector, and the time domain waveform of the voltage signal can be presented in the form of a curve. The voltage signal is transmitted to the phase-locked amplifier, which can extract the photothermal lens spectrum signal corresponding to the modulation frequency of the chopper, and finally transmit it to the host computer to obtain the output signal of the detection system.

[0029] Furthermore, the first laser 1 is a quantum cascade laser, which includes a laser emitter head and a quantum cascade laser driver connected by a cable. The output infrared light wavelength of the quantum cascade laser is adjusted by adjusting the quantum cascade laser driver to realize the infrared light wavelength scanning function, and the central wavelength is 1703.3cm -1 , the emission spectrum range covers the mid-infrared absorption spectrum of furfural; the second laser is a helium-neon laser, which can emit visible light.

[0030] Furthermore, the chopper 3 includes a chopper controller, a chopper base and a chopper blade. The modulation frequency of the chopper 3 is 20Hz to 1kHz. The external reference output of the chopper controller is connected to the external reference input of the phase-locked amplifier 22 to synchronize the demodulation frequency of the phase-locked amplifier with the chopper frequency, thereby reducing noise.

[0031] In this embodiment, the first visible light reflector assembly includes two visible light reflectors (8 and 9). After the visible light beam is reflected once, it reaches the visible light-infrared light dichroic mirror, and the visible light reflector there can amplify the light spot.

[0032] The second visible light reflector assembly includes 6 visible light reflectors (10-15). The visible light beam reaches the variable aperture after 5 reflections. The multiple visible light reflectors here can not only amplify the visible light, but also extend the optical path. Moreover, the path and direction of the visible light can be adjusted by adjusting the pitch angle of the visible light reflectors. The visible light reflectors are usually arranged on an adjustable optical bracket.

[0033] Furthermore, the visible light-infrared dichroic mirror 7 is arranged at an angle, the visible light beam passes through the visible light-infrared dichroic mirror 7 to reach the fixed optical path liquid pool 6, and the infrared light beam is reflected behind the visible light-infrared dichroic mirror 7 to reach the fixed optical path liquid pool.

[0034] Furthermore, the output port of the photodetector 21 is connected to the input port of the lock-in amplifier 22 via a BNC line, and the output port of the lock-in amplifier 22 is connected to the host computer 23 via a USB cable. The voltage signal is transmitted to the lock-in amplifier via a BNC line 24, and the lock-in amplifier 22 can extract the photothermal lens spectrum signal corresponding to the modulation frequency of the chopper 3, and finally transmit it to the host computer via a USB cable to obtain the detection system output signal.

[0035] Furthermore, the fixed optical path liquid pool 6 is clamped and fixed by two light-transmitting windows (light-transmitting window piece 1 4 and light-transmitting window piece 2 5), and then clamped and fixed by two hollow metal sheets through four metal bolts, wherein two fixed metal liquid injection ports with an inner diameter of 4 mm are arranged on the outer side of one of the hollow metal sheets.

[0036] Furthermore, there are two concentric holes between the light-transmitting window and the hollow metal sheet that directly reach the fixed optical path liquid pool, which are used to pass the transformer oil to be tested. The transformer oil can be evenly pumped into the fixed optical path liquid pool through a peristaltic pump and a fluororubber peristaltic pump tube with an outer diameter of 4 mm.

[0037] The fixed optical path liquid pool 6 has a thickness of 100-1000 μm. The thickness of the fixed optical path liquid pool can be 100 μm, 200 μm, 500 μm, 1000 μm or other lengths according to the detection performance requirements.

[0038] Furthermore, the material of the light-transmitting window sheet may be zinc selenide, calcium fluoride or potassium bromide. Example 2

[0039] A detection method for furfural in transformer oil based on photothermal lens spectroscopy, combined with Figure 1-Figure 3 As shown, the detection method comprises the following steps: S1: Pumping the standard transformer oil into the fixed optical path liquid pool 6; specifically, pouring the standard transformer oil into a 50 ml beaker, placing the fluororubber peristaltic pump tube into the beaker, turning on the peristaltic pump and adjusting it to a suitable speed, slowly pumping the standard transformer oil into the fixed optical path liquid pool 6, and turning off the peristaltic pump after the standard transformer oil flows out of the fluororubber peristaltic pump tube on the other side.

[0040] S2: Turn on the power of the first laser 1, the second laser 2, the phase-locked amplifier 22, the photodetector 21, the chopper 3, the host computer 23 and other devices.

[0041] S3: Turn on the laser output knob of the second laser 2 (helium-neon laser), adjust the pitch angles of the first visible light reflector assembly and the second visible light reflector assembly, and observe the time domain signal of the oscilloscope window of the phase-locked amplifier 22 at the same time, and stop adjusting when the amplitude of the time domain signal is the largest.

[0042] S4: Adjust and set the modulation frequency of the chopper 3; set a suitable chopper modulation frequency, generally 30 Hz, through the chopper controller.

[0043] S5: Turn on the laser output button of the first laser 1 (quantum cascade laser), record the signal amplitude a1 demodulated by the lock-in amplifier 22, and pump out the standard transformer oil in the fixed optical path liquid pool 6.

[0044] S6: pumping furfural transformer oil containing a known trace amount of furfural into the fixed optical path liquid pool 6, stopping the pumping after the demodulation signal of the lock-in amplifier 22 is stable, and recording the amplitude a2 of the signal demodulated by the lock-in amplifier 22; Specifically, furfural / transformer oil containing a known trace furfural concentration is poured into another 50 ml beaker, a fluororubber peristaltic pump tube is placed in the beaker, the peristaltic pump is turned on and adjusted to a suitable speed, and the furfural / transformer oil containing a known trace furfural concentration is slowly pumped into the fixed optical path liquid pool 6, and after the demodulation signal of the lock-in amplifier 22 is stabilized, the peristaltic pump is turned off and the demodulation signal amplitude a2 of the lock-in amplifier 22 is recorded at the same time, and the furfural transformer oil containing a known trace furfural concentration in the fixed optical path liquid pool 6 is pumped out.

[0045] S7: Perform linear fitting on the two sets of measured data a1 and a2 and the corresponding furfural concentrations to obtain a standard curve.

[0046] S8: Pump the transformer oil sample to be tested into the fixed optical path liquid pool 6. Specifically, pour the transformer oil sample to be tested into another 50 ml beaker, put the fluororubber peristaltic pump tube into the beaker, turn on the peristaltic pump and adjust it to a suitable speed, slowly pump the transformer oil sample to be tested into the fixed optical path liquid pool 6, stop pumping after the demodulation signal of the lock-in amplifier 22 is stable, and record the signal amplitude a3 demodulated by the lock-in amplifier 22.

[0047] S9: Substitute a3 into S7 to obtain the standard curve to obtain the furfural concentration value in the transformer oil sample to be tested.

[0048] This detection method uses a quantum cascade laser that covers the mid-infrared characteristic absorption line of furfural to emit pump lasers. After absorbing the pump laser with an average power of more than 100mW, trace furfural molecules in transformer oil stimulate a strong thermal lens effect, which significantly improves the detection performance; the thermal lens effect generated by the absorption of mid-infrared light by furfural in transformer oil is used to achieve in-situ and rapid detection of furfural in transformer oil. Compared with high-performance liquid chromatography, Raman spectroscopy, etc., this detection method avoids complex pretreatment such as extraction and distillation of transformer oil samples; by adjusting the optical path conditions, including the distance from the center of the fixed liquid pool to the silicon biased photodetector, the distance from the helium-neon laser beam to the center of the fixed liquid pool, etc., the performance of the detection system can be significantly improved. In order to reduce the differential influence of ambient environmental factors (including temperature, mechanical vibration, etc.) when the detection system detects furfural on site each time, a known oil sample is used to calibrate the standard curve before each measurement, so as to avoid the direct use of the known standard curve obtained by the experiment, which is difficult to ensure the consistency of the trace furfural concentration measurement results.

[0049] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A detection system for furfural in transformer oil based on photothermal lens spectroscopy, characterized in that: include: A first laser, the first laser being used to emit an infrared light beam; a second laser, the second laser being configured to emit a visible light beam; A visible light-infrared light dichroic mirror, wherein a chopper, an infrared light reflector and an infrared light plano-convex lens are sequentially arranged between the first laser and the visible light-infrared light dichroic mirror, and an adjustable attenuator, a visible light plano-convex lens and a first visible light reflector assembly are sequentially arranged between the second laser and the visible light-infrared light dichroic mirror; A fixed optical path liquid pool is arranged in the output direction of the visible light-infrared light dichroic mirror, and the fixed optical path liquid pool is used to contain transformer oil to be tested; A second visible light reflector assembly is arranged in the output direction of the fixed optical path liquid pool, a variable aperture is arranged in the output direction of the second visible light reflector assembly, a photoelectric detector is arranged in the output direction of the variable aperture, the photoelectric detector is connected to a phase-locked amplifier, and the phase-locked amplifier is connected to a host computer.

2. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1, characterized in that: The first laser is a quantum cascade laser, which includes a laser emission head and a quantum cascade laser driver connected by a cable, and the output infrared light wavelength of the quantum cascade laser is adjusted by adjusting the quantum cascade laser driver; the second laser is a helium-neon laser.

3. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1, characterized in that: The chopper comprises a chopper controller, a chopper base and a chopper blade. The modulation frequency of the chopper is 20 Hz to 1 kHz. The external reference output end of the chopper controller is connected to the external reference input end of the phase-locked amplifier.

4. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1, characterized in that: The first visible light reflector assembly includes at least two visible light reflectors, and the visible light beam reaches the visible light-infrared light dichroic mirror after at least two reflections.

5. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1 is characterized in that, The second visible light reflector assembly includes 4 to 8 visible light reflectors, and the visible light beam reaches the variable aperture after being reflected 3 to 7 times.

6. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1 is characterized in that: The visible light-infrared dichroic mirror is arranged obliquely, the visible light beam is directed toward the visible light-infrared dichroic mirror to reach the fixed optical path liquid pool, and the infrared light beam is reflected behind the visible light-infrared dichroic mirror to reach the fixed optical path liquid pool.

7. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1, characterized in that: The output port of the photodetector is connected to the input port of the lock-in amplifier via a BNC line, and the output port of the lock-in amplifier is connected to the host computer via a USB connection line.

8. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 1, characterized in that: The fixed optical path liquid pool is clamped and fixed by two light-transmitting window sheets, and then clamped and fixed by two hollow metal sheets through four metal bolts, wherein a metal liquid injection port is provided on the outer side of one of the hollow metal sheets.

9. The furfural detection system in transformer oil based on photothermal lens spectroscopy according to claim 8, characterized in that: The light-transmitting window sheet and the hollow metal sheet have concentric circular holes directly reaching the fixed optical path liquid pool, and the fixed optical path liquid pool has a thickness of 100 to 1000 μm.

10. The detection method of furfural detection system in transformer oil based on photothermal lens spectroscopy according to any one of claims 1 to 9, characterized in that: The detection method comprises the following steps: Pumping standard transformer oil into the fixed optical path liquid pool; Turning on the first laser, the second laser, the lock-in amplifier, the photodetector, the chopper and the host computer; Turning on the laser output knob of the second laser, adjusting the pitch angles of the first visible light reflector assembly and the second visible light reflector assembly, and observing the time domain signal in the oscilloscope window of the lock-in amplifier at the same time, and stopping the adjustment when the amplitude of the time domain signal is the maximum; adjusting and setting the modulation frequency of the chopper; Turn on the laser output button of the first laser, and record the signal amplitude a1 demodulated by the lock-in amplifier; Pumping furfural transformer oil containing a known trace amount of furfural into the fixed optical path liquid pool, stopping the pumping after the demodulated signal of the lock-in amplifier is stable, and recording the amplitude a2 of the signal demodulated by the lock-in amplifier; The two sets of measured data a1, a2 and the corresponding furfural concentrations were linearly fitted to obtain a standard curve; Pumping the transformer oil sample to be tested into the fixed optical path liquid pool, stopping the pumping after the demodulated signal of the lock-in amplifier is stable, and recording the amplitude a3 of the signal demodulated by the lock-in amplifier; Substitute the signal amplitude a3 into the standard curve to obtain the furfural concentration value in the transformer oil sample to be tested.

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