Mid-infrared sensor for oil quality monitoring

Abstract

The application provides a mid-infrared sensor for oil quality monitoring, comprising a light source module, a detector module, an oil sample pool, a signal processing module, a multi-band spectral analysis module and a light intensity regulator. The multi-band spectral analysis module comprises a filter wheel, a driving motor and a plurality of narrow-band optical filters. The filter wheel is in the shape of a disc, and a plurality of mounting holes are arranged on the circumference of the disc. One narrow-band optical filter is arranged in each mounting hole. Each narrow-band optical filter corresponds to the characteristic absorption wavelength of a specific component in the oil. The driving motor drives the filter wheel to rotate, so that the plurality of narrow-band optical filters enter the light path in turn. The light intensity regulator comprises a variable diaphragm and a stepping motor. The light intensity of the detection signal is optimized by adjusting the position of the light transmission hole with different apertures. The application effectively solves the problems of spectral overlap and signal masking in the conventional technology by means of time-divided spectral separation detection, and improves the accuracy of the detection of the content of each component in the oil.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a mid-infrared sensor for oil quality monitoring. BACKGROUND

[0002] In the industrial fields of petrochemical industry, mechanical manufacturing, etc., various mechanical equipment needs to use oil such as lubricating oil and hydraulic oil to reduce friction, transmit power and dissipate heat during operation. The quality of oil directly affects the operating efficiency and service life of the equipment. As the operation time of the equipment increases, the oil will change due to oxidation, pollution, degradation, etc., and the oil quality needs to be monitored regularly to ensure normal operation of the equipment.

[0003] Oil is a complex mixture, usually containing alkanes, aromatic compounds, various additives, and various components such as oxidation products and external pollutants generated during use. These components have characteristic absorption peaks in the mid-infrared band, for example, the carbon-hydrogen bond of alkanes has a stretching vibration absorption peak near 2800 nanometers, the carbon-oxygen double bond of carbonyl compounds has a stretching vibration absorption peak near 3000 nanometers, and the oxygen-hydrogen bond of water molecules has a stretching vibration absorption peak near 3200 nanometers.

[0004] However, there is an overlapping wavelength region between the absorption peaks of different components. The carbon-hydrogen bond absorption peaks of alkanes and aromatic compounds are close, and the absorption peaks of carbonyl compounds and alcohol compounds also partially overlap. This spectral overlap phenomenon causes the absorption signals of each component to mask each other. The absorbance measured at a certain wavelength is the superposition of the absorption of multiple components at that wavelength, making it difficult to separate the individual contributions of each component, resulting in lower accuracy of quantitative analysis.

[0005] In addition, the composition of the oil changes dynamically over time. The base oil will gradually oxidize to form carbonyl compounds and alcohol compounds, the additives will be consumed or decomposed, and external water and impurities will mix into the oil. These changes interact with each other, making the spectral characteristics of the oil more complex. The existing detection method is difficult to accurately identify the content change of each component when faced with such complexity, affecting the positioning of the oil pollution source and the evaluation of the equipment operating state.

[0006] Therefore, it is necessary to propose a new technical solution to solve the above technical problems. SUMMARY

[0007] The purpose of the present application is to provide a mid-infrared sensor for oil quality monitoring to solve the technical problem that the existing mid-infrared sensor cannot accurately identify the content of each component in the oil.

[0008] The application provides a mid-infrared sensor for oil quality monitoring, which comprises a light source module, a detector module, an oil sample pool and a signal processing module, the light source module comprises a thermal radiation light source and a collimating mirror, the detector module comprises a thermoelectric detector and a focusing mirror, the oil sample pool is arranged in the light path between the collimating mirror and the focusing mirror, and the signal processing module is electrically connected with the thermoelectric detector, and the mid-infrared sensor further comprises a multi-band spectral analysis module, the multi-band spectral analysis module comprises a filter wheel, a driving motor and a plurality of narrow-band optical filters, the filter wheel is arranged in the light path between the oil sample pool and the focusing mirror, the filter wheel is disc-shaped, a plurality of mounting holes are arranged on the circumference of the filter wheel, one of the narrow-band optical filters is arranged in each of the mounting holes, each of the narrow-band optical filters corresponds to the characteristic absorption wavelength of a specific component in oil, the driving motor is connected with the filter wheel and is used for driving the filter wheel to rotate, so that the plurality of narrow-band optical filters enter the light path in sequence, and the mid-infrared sensor further comprises a light intensity regulator, the light intensity regulator is arranged in the light path between the multi-band spectral analysis module and the thermoelectric detector, the light intensity regulator comprises a variable diaphragm and a step motor, the variable diaphragm comprises a disc-shaped diaphragm base and a plurality of light transmission holes arranged on the diaphragm base, and the step motor is connected with the variable diaphragm and is used for driving the variable diaphragm to rotate, so that the light transmission holes with different apertures rotate to the optical axis position in sequence.

[0009] In the above-mentioned mid-infrared sensor, the plurality of light transmission holes are uniformly distributed along the circumferential direction of the diaphragm base, the light transmission holes are circular openings, the light transmission holes penetrate the thickness direction of the diaphragm base, and the apertures of the light transmission holes are arranged in an increasing order.

[0010] In the above-mentioned mid-infrared sensor, the mid-infrared sensor further comprises a control circuit, the control circuit is electrically connected with the driving motor, and the control circuit is used for sending pulse signals to the driving motor, and the driving motor is used for driving the filter wheel to rotate according to the pulse signals.

[0011] In the above-mentioned mid-infrared sensor, the step motor is electrically connected with the control circuit, the step motor is used for receiving pulse signals from the control circuit, the control circuit is used for sending pulse signals of a corresponding number to the step motor according to the transmittance data of the narrow-band optical filter currently located in the light path, and the variable diaphragm is driven to rotate to the position of the corresponding light transmission hole.

[0012] In the above mid-infrared sensor, when the filter wheel switches to the narrow-band optical filter with higher transmittance, the control circuit drives the variable diaphragm to rotate to a position with a smaller aperture; when the filter wheel switches to the narrow-band optical filter with lower transmittance, the control circuit drives the variable diaphragm to rotate to a position with a larger aperture.

[0013] In the above mid-infrared sensor, the multi-band spectral analysis module further comprises a position encoder, the position encoder comprises a code disc, a light-emitting diode and a photodetector, the code disc is coaxially installed with the filter wheel, the position encoder is electrically connected with the control circuit, the position encoder outputs a first phase signal, a second phase signal and a zero signal to the control circuit, the control circuit is used for judging the rotation direction of the filter wheel by detecting the phase relationship between the first phase signal and the second phase signal, calculating the rotation angle by counting the number of pulses, and performing position calibration by the zero signal.

[0014] In the above mid-infrared sensor, the mid-infrared sensor further comprises a photoelectric sensor, the photoelectric sensor is a light-receiving type photoelectric sensor, the filter wheel is provided with a notch, each narrow-band optical filter corresponds to a notch, and the photoelectric sensor is electrically connected with the control circuit.

[0015] In the above mid-infrared sensor, the narrow-band optical filter is a multi-layer film interference filter, comprising a transparent substrate layer and a plurality of layers of dielectric films deposited on the surface of the transparent substrate layer, and the plurality of layers of dielectric films are formed by alternately stacking high refractive index layers and low refractive index layers.

[0016] In the above mid-infrared sensor, the collimating mirror is an off-axis parabolic mirror, the reflecting surface of the off-axis parabolic mirror is coated with a metal reflecting film, the thermal radiation light source is a silicon carbide rod light source, the thermal radiation light source is arranged at an off-axis focal point position of the off-axis parabolic mirror, and the divergent light forms a parallel light beam after being reflected by the off-axis parabolic mirror.

[0017] In the above mid-infrared sensor, the oil sample cell is further provided with a heating element, a refrigeration element and a temperature controller, the heating element is a ceramic heating sheet, the refrigeration element is a semiconductor refrigeration sheet, and the temperature controller is electrically connected with the heating element and the refrigeration element.

[0018] The application provides a mid-infrared sensor for oil quality monitoring, which comprises a multi-band spectral analysis module, the multi-band spectral analysis module comprising a filter wheel, a driving motor and a plurality of narrow-band optical filters, the filter wheel being disc-shaped, a plurality of mounting holes being arranged on the circumference of the filter wheel, and one narrow-band optical filter being arranged in each mounting hole. Each narrow-band optical filter corresponds to the characteristic absorption wavelength of a specific component in the oil, and the driving motor drives the filter wheel to rotate, so that the plurality of narrow-band optical filters enter the light path one by one. When the mid-infrared light emitted by the thermal radiation light source forms a parallel light beam after passing through the collimating mirror, the light beam passes through the oil sample cell and the multi-band spectral analysis module in turn. At any moment, only one specific narrow-band optical filter is located in the light path, and the filter only allows light in a specific wavelength range to pass through, and light of other wavelengths is blocked. In this way, the composite spectrum originally containing absorption information of multiple components is decomposed into a plurality of independent narrow-band spectral signals. Each narrow-band spectral signal mainly reflects the absorption characteristics of the corresponding component at a specific wavelength, avoiding spectral interference and signal masking phenomenon between different components. The driving motor drives the filter wheel to rotate at a preset angle according to the instruction of the control circuit, so that different narrow-band optical filters enter the light path one by one, and the detection of multiple components such as alkanes, carbonyl compounds and water molecules in the oil is realized one by one. This time-division detection method ensures that the light signal received by the thermoelectric detector in each detection period has a clear spectral attribution, eliminating the analysis error caused by the superposition of multiple component signals in the traditional method.

[0019] The mid-infrared sensor for oil quality monitoring provided by the application further comprises a light intensity regulator, which comprises a variable diaphragm and a stepping motor. The variable diaphragm comprises a disc-shaped diaphragm base and a plurality of light transmission holes with different apertures arranged on the diaphragm base, and the stepping motor drives the variable diaphragm to rotate, so that the light transmission holes with different apertures are rotated to the position of the optical axis one by one. When the filter wheel switches to a narrow-band optical filter with high transmittance, the control circuit drives the variable diaphragm to rotate to the position of the light transmission hole with a small aperture, and when the filter wheel switches to a narrow-band optical filter with low transmittance, the control circuit drives the variable diaphragm to rotate to the position of the light transmission hole with a large aperture. This technical solution can keep the light signal intensity at different wavelengths within the optimal detection range of the thermoelectric detector, improving the detection accuracy and dynamic range.

[0020] In summary, the application realizes spectral separation and detection of different components in the oil through the multi-band spectral analysis module, and realizes adaptive optimization of the detection signal through the light intensity regulator, which eliminates the problems of spectral overlap and signal masking from the technical principle, and significantly improves the accuracy and reliability of oil quality monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic diagram of the mid-infrared sensor for oil quality monitoring provided by the embodiment of the application.

[0022] Figure 2 is a schematic view of a filter wheel in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application.

[0023] Figure 3 is a schematic view of a variable aperture in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application.

[0024] Figure 4 is a schematic view of a narrowband optical filter in the filter wheel shown in Figure 2

[0025] Figure 5 is a top view of an oil sample cell in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application.

[0026] Figure 6 is a cross-sectional view of an oil sample cell in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application.

[0027] Figure 7 is a schematic view of a position encoder in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application.

[0028] Figure 8 is a schematic view of a photoelectric sensor in a mid-infrared sensor for oil quality monitoring provided by embodiments of the present application. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0030] The terms "first", "second", and similar terms do not denote any order, quantity, or importance, but are used to distinguish different technical features. The term "a plurality of" and similar terms denote two or more, unless otherwise expressly specified.

[0031] Embodiments of the present application can be combined with each other.

[0032] ​Embodiments of the present application provide a mid-infrared sensor for oil quality monitoring, which is applied to oil monitoring scenarios of mechanical equipment in petrochemical industry, mechanical manufacturing and other fields. In oil containing multiple components, spectral overlap and mutual masking phenomenon exist in the infrared absorption characteristics of different components. Traditional single spectrum analysis method is difficult to accurately identify and quantitatively analyze the content of each component, which affects the positioning of oil pollution source. Alkane compounds, aromatic compounds, carbonyl compounds, alcohol compounds and water molecules in oil all have specific absorption peaks in the mid-infrared band, but there are wavelength overlap regions between these absorption peaks, which makes it impossible to effectively distinguish different components by single wavelength detection. When the oil is oxidized, contaminated or deteriorated during use, the content of various components will change, so it is necessary to accurately monitor these changes to judge the oil quality and equipment operating state.

[0033] As shown in Figure 1 The mid-infrared sensor of the embodiments of the present application includes a light source module and a detector module. The light source module includes a thermal radiation light source 102 and a collimating mirror 101, and the detector module includes a thermoelectric detector 109 and a focusing mirror 108. The mid-infrared sensor further includes a multi-band spectral analysis module and a control circuit 111. The mid-infrared light emitted by the thermal radiation light source 102 passes through the collimating mirror 101 to form a parallel light beam. The parallel light beam carries the absorption information of the oil after passing through the oil sample cell 103. The parallel light beam that transmits through the oil sample cell 103 enters the multi-band spectral analysis module for spectral decomposition. The decomposed light beam is converged by the focusing mirror 108 and finally reaches the sensing surface of the thermoelectric detector 109. Such an arrangement can ensure that the parallel light beam that transmits through the oil sample cell 103 enters the multi-band spectral analysis module completely, and the processed light signal can be effectively collected and focused by the focusing mirror 108 to the receiving surface of the thermoelectric detector 109.

[0034] The thermal radiation light source 102 is a silicon carbide rod light source, which can emit continuous mid-infrared spectrum in the state of being electrified and heated. The thermal radiation light source 102 is provided with a heat shield outside. The inner wall of the heat shield is coated with a reflective coating, which reflects the infrared light diffused to the surrounding back to the light source emission direction, improving the utilization efficiency of the light source.

[0035] The collimating mirror 101 is an off-axis parabolic mirror, and the reflecting surface of the off-axis parabolic mirror is coated with a metal reflective film. The collimating mirror 101 is used to convert the divergent light emitted by the thermal radiation light source 102 into a parallel light beam. The thermal radiation light source 102 is arranged at the off-axis focal point position of the off-axis parabolic mirror. The divergent light forms a parallel light beam after being reflected by the off-axis parabolic mirror. The propagation direction of the parallel light beam is parallel to but not coincident with the optical axis of the mirror, avoiding the obstruction of the light source to the emitted light beam.

[0036] The thermoelectric detector 109 comprises a plurality of thermocouples connected in series to form a thermoelectric chip. The package window of the thermoelectric detector 109 is made of zinc selenide material.

[0037] The focusing mirror 108 is a parabolic mirror. The focusing mirror 108 converges the light beam passing through the filter of the multi-band spectral analysis module to the sensing surface of the thermoelectric detector 109. The reflecting surface of the focusing mirror 108 is coated with a metal reflective film to minimize the loss of light signals during reflection. The distance between the focusing mirror 108 and the thermoelectric detector 109 is equal to the focal length of the focusing mirror 108, so that the light beam is focused on the sensing surface of the thermoelectric detector 109.

[0038] The multi-band spectral analysis module is used to physically separate the composite mid-infrared light signal according to different wavelengths.

[0039] The multi-band spectral analysis module comprises a filter wheel 104, a driving motor 107 and a position encoder. The filter wheel 104 is arranged in the optical path between the oil sample cell 103 and the focusing mirror 108. The filter wheel 104 is in the shape of a disc and is made of aluminum alloy material. The surface of the filter wheel 104 is subjected to black anodizing treatment to reduce the influence of stray light. As shown in Figure 2 The circumferential surface of the filter wheel 104 is uniformly provided with a plurality of mounting holes in the radial direction, for example, eight mounting holes. Each mounting hole is provided with a narrow-band optical filter 112. The angular interval between adjacent mounting holes is 45 degrees. Such an arrangement allows the filter wheel 104 to switch a filter every 45 degrees of rotation. The filter wheel 104 is installed on a support frame through a rotating shaft 105. One end of the rotating shaft 105 is connected to the output end of the driving motor 107.

[0040] Each narrow-band optical filter 112 corresponds to a characteristic absorption wavelength of a specific component in the oil. The first narrow-band optical filter has a center wavelength of 2800 nm and a bandwidth of 2750 nm to 2850 nm, and is used to detect the carbon-hydrogen bond stretching vibration absorption peak of alkanes, which are the main base components of the oil and whose content variation reflects the basic quality condition of the oil. The second narrow-band optical filter has a center wavelength of 2900 nm and a bandwidth of 2850 nm to 2950 nm, and is used to detect the carbon-hydrogen bond stretching vibration absorption peak of aromatic compounds, the presence of which usually indicates that the oil contains antioxidant or dispersant additives. The third narrow-band optical filter has a center wavelength of 3000 nm and a bandwidth of 2950 nm to 3050 nm, and is used to detect the carbon-oxygen double bond stretching vibration absorption peak of carbonyl compounds, the presence of which is an indication of the oxidation of the oil. The fourth narrow-band optical filter has a center wavelength of 3100 nm and a bandwidth of 3050 nm to 3150 nm, and is used to detect the oxygen-hydrogen bond stretching vibration absorption peak of alcohol compounds, which are usually derived from the oxidation products or external contaminants of the oil. The fifth narrow-band optical filter has a center wavelength of 3200 nm and a bandwidth of 3150 nm to 3250 nm, and is used to detect the oxygen-hydrogen bond stretching vibration absorption peak of water molecules, the content of which is one of the indicators for evaluating the quality of the oil. The sixth narrow-band optical filter has a center wavelength of 3400 nm and a bandwidth of 3350 nm to 3450 nm, and is used to detect the nitrogen-hydrogen bond stretching vibration absorption peak of amine compounds, which are derived from antioxidant additives in the oil. The seventh narrow-band optical filter has a center wavelength of 3500 nm and a bandwidth of 3450 nm to 3550 nm, and is used to detect the sulfur-hydrogen bond stretching vibration absorption peak of sulfides. The eighth narrow-band optical filter has a center wavelength of 2700 nm and a bandwidth of 2650 nm to 2750 nm, and is used as a reference channel, as the absorption of the oil in this wavelength range is weak and is used for baseline correction.

[0041] A gear transmission member 106 is provided between the drive motor 107 and the filter wheel 104. The gear transmission member 106 includes a driving gear and a driven gear, the driving gear is fixed on the output shaft of the drive motor 107, and the driven gear is fixed on the rotating shaft 105 of the filter wheel 104. The transmission ratio of the gear transmission member 106 is 1:4, that is, the drive motor 107 rotates 4 degrees to correspond to the rotation of 1 degree of the filter wheel 104, which improves the positioning accuracy of the filter. The driving gear is fixed on the output shaft of the drive motor 107. The driven gear is fixed on the flange of the rotating shaft 105 of the filter wheel 104. The gear meshing part is coated with lubricating grease.

[0042] The driving motor 107 is a step motor, and each step angle of the step motor corresponds to an angular displacement of the filter wheel 104 of 0.45 degrees.

[0043] The control circuit 111 includes a microcontroller, a driver circuit, a signal conditioning circuit, and an interface circuit. The microcontroller may, for example, be a 32-bit ARM processor. The driver circuit is used to drive the step motor. The signal conditioning circuit is used to process signals from the thermopile detector 109. The interface circuit is used to communicate with external devices.

[0044] The control circuit 111 is electrically connected to the driving motor 107 and is used to send driving pulse signals to the driving motor 107. When it is necessary to switch the narrowband optical filter 112, the control circuit 111 sends a corresponding number of pulse signals to the step motor to drive the filter wheel 104 to rotate to a specified position. For example, the control circuit 111 sends 1600 pulses, which corresponds to a rotation of the step motor by 180 degrees, a rotation of the filter wheel 104 by 45 degrees, and a switching from the first narrowband optical filter to the second narrowband optical filter.

[0045] During the rotation of the filter wheel 104, the transmittances of different narrowband optical filters 112 differ, resulting in a jump in the light intensity reaching the thermopile detector 109, and the thermopile detector 109 needs to reestablish thermal equilibrium, thereby prolonging the measurement response time.

[0046] To solve the above technical problems, the present application provides an optical intensity regulator in front of the thermopile detector 109. The optical intensity regulator includes a variable diaphragm 125, a step driver (not shown in the figure), and a second collimating lens 124. The focusing mirror 108 converges the light beam that has passed through the filter of the multi-band spectral analysis module to a preset focal position. The second collimating lens 124 is arranged at the focal position of the focusing mirror 108. The second collimating lens 124 converts the light beam converging to the focal position into a parallel light beam. The second collimating lens 124 is made of zinc selenide material. The second collimating lens 124 is a biconvex lens. Both surfaces of the second collimating lens 124 are coated with an antireflection film. The reflectivity of the antireflection film in the wavelength range of 2.5 microns to 4 microns is less than 1%. The focal length of the second collimating lens 124 matches the focal length of the focusing mirror 108. The front focal point of the second collimating lens 124 coincides with the focal point of the focusing mirror 108. The converging light rays form a parallel light beam after passing through the second collimating lens 124.

[0047] The variable diaphragm 125 is arranged on the side of the second collimating lens 124 away from the focusing mirror 108, as shown in Figure 3As shown, the variable diaphragm 125 includes a disc-shaped diaphragm base 1251 and a plurality of light transmission holes 1252 arranged on the diaphragm base 1251. The diaphragm base 1251 is provided with a central through hole 1253 at the center position, and the central through hole 1253 penetrates the thickness direction of the diaphragm base 1251. The plurality of light transmission holes 1252 (for example, 8) are uniformly distributed along the circumferential direction of the diaphragm base 1251, the light transmission hole 1252 is a circular opening, the light transmission hole 1252 penetrates the thickness direction of the diaphragm base 1251, the aperture of each light transmission hole 1252 is arranged in ascending order, for example, the aperture of the first light transmission hole is 1mm, the aperture of the second light transmission hole is 1.5mm, the aperture of the third light transmission hole is 2mm, the aperture of the fourth light transmission hole is 2.5mm, the aperture of the fifth light transmission hole is 3mm, the aperture of the sixth light transmission hole is 3.5mm, the aperture of the seventh light transmission hole is 4mm, and the aperture of the eighth light transmission hole is 4.5mm. A central shaft penetrates the central through hole 1253 and is fixedly connected with the diaphragm base 1251, one end of the central shaft is connected with the output shaft of the stepping motor, and the central shaft and the output shaft of the stepping motor are connected by a key groove connection mode to realize torque transmission. The other end of the central shaft is provided with an axial positioning ring, the axial positioning ring is coaxially installed with the central shaft, and the axial positioning ring is used to limit the axial displacement of the diaphragm base 1251 along the central shaft.

[0048] The thermoelectric detector 109 is arranged on the side of the variable diaphragm 125 away from the focusing mirror 108, and the sensing surface of the thermoelectric detector 109 is perpendicular to the optical axis. The parallel light beam converted by the second collimating lens 124 is irradiated onto the sensing surface of the thermoelectric detector 109 in the form of parallel light after passing through the light transmission hole 1252 of the variable diaphragm 125, and the cross-sectional diameter of the parallel light beam matches the aperture of the light transmission hole 1252.

[0049] The stepping motor includes a motor body and an output shaft, and the motor body is fixedly connected with the optical platform. The output shaft of the stepping motor extends from the upper surface of the motor body, and the output shaft is rigidly connected with the rotor of the motor body. The end of the output shaft is provided with a key groove, and the key groove is in matching connection with the key at the end of the central shaft.

[0050] The stepping motor is electrically connected with the control circuit 111. The stepping motor receives the pulse signal from the control circuit 111, and the rotor of the stepping motor produces stepping rotation under the driving of the pulse signal. The rotation of the rotor is transmitted to the central shaft through the output shaft, and the central shaft drives the variable diaphragm 125 to rotate synchronously. The rotation of the variable diaphragm 125 makes the light transmission holes 1252 with different apertures rotate to the optical axis position in turn, realizing the switching of the aperture of the light transmission hole 1252.

[0051] The signal processing module 110 pre-stores the transmittance data of each narrowband optical filter 112, which is stored in the memory of the signal processing module 110 in digital form. When the filter wheel 104 switches the narrowband optical filter 112, the control circuit 111 sends a corresponding number of pulse signals to the stepper driver according to the transmittance data of the narrowband optical filter 112 currently located in the light path, and drives the variable aperture 125 to rotate to the corresponding light transmission hole 1252 position. When the filter wheel 104 switches to a narrowband optical filter 112 with higher transmittance, the control circuit 111 drives the variable aperture 125 to rotate to the light transmission hole 1252 position with a smaller aperture, reducing the light flux passing through; when the filter wheel 104 switches to a narrowband optical filter 112 with lower transmittance, the control circuit 111 drives the variable aperture 125 to rotate to the light transmission hole 1252 position with a larger aperture, increasing the light flux passing through. Through this aperture compensation method, the light intensity reaching the thermoelectric detector 109 is kept within the preset target range, avoiding the re-establishment process of the thermoelectric detector 109 thermal balance, and shortening the measurement response time.

[0052] A beam shaper is arranged between the second collimating lens 124 and the variable aperture 125, which includes a cylindrical lens group and a beam homogenizer. The cylindrical lens group is used to adjust the cross-sectional shape of the parallel light beam, and the beam homogenizer is used to improve the uniformity of the light intensity distribution in the cross section of the light beam. The beam homogenizer is a hexagonal light pipe, and the inner wall of the light pipe is coated with a high-reflectivity film. After multiple reflections in the light pipe, the cross-sectional light intensity distribution tends to be uniform.

[0053] The control circuit 111 includes a light intensity monitoring module connected to the signal output end of the thermoelectric detector 109. The light intensity monitoring module monitors the light intensity value reaching the thermoelectric detector 109 in real time. When the light intensity monitoring module detects that the light intensity deviates from the preset target value, the light intensity monitoring module sends an adjustment instruction to the stepper driver to drive the variable aperture 125 to switch to the light transmission hole 1252 with an appropriate aperture, realizing closed-loop light intensity control. The preset target value is determined according to the linear response range of the thermoelectric detector 109, and the target light intensity value is set to 70% of the full-scale output of the detector, ensuring that the detector works in the linear response region and has sufficient signal-to-noise ratio.

[0054] The position encoder is an incremental photoelectric encoder with a resolution of 1000 lines / revolution, such as Figure 7As shown, the position encoder comprises a code disc 119, a light emitting diode 120 and a photoelectric detector 121. The code disc 119 is a disc with 1000 radial light transmission slits etched on the surface, and non-transmission areas between the slits, with an angular interval of 0.36 degrees between adjacent slits. The code disc 119 is coaxially installed with the filter wheel 104, and is connected to the rotating shaft 105 of the filter wheel 104 through a coupling. The light emitting diode 120 emits light that changes in brightness when passing through the light transmission slits of the code disc 119, and the photoelectric detector 121 receives the transmitted light signal and converts it into an electrical pulse signal.

[0055] The position encoder is electrically connected to the control circuit 111, and outputs a first phase signal, a second phase signal and a zero signal to the control circuit 111. The first phase signal and the second phase signal are two square wave signals with a phase difference of 90 degrees, each outputting 1000 pulses per revolution. The control circuit 111 determines the direction of rotation by detecting the phase relationship between the first phase signal and the second phase signal: when the phase of the first phase signal leads the phase of the second phase signal by 90 degrees, the filter wheel 104 rotates forward; when the phase of the second phase signal leads the phase of the first phase signal by 90 degrees, the filter wheel 104 rotates in reverse. The control circuit 111 calculates the rotation angle by counting the number of pulses of the first phase signal or the second phase signal, with each pulse corresponding to a rotation angle of 0.36 degrees. The code disc 119 outputs one pulse per revolution, and the pulse width is equal to the width of one light transmission slit. The zero signal is used for position calibration to eliminate cumulative errors.

[0056] The control circuit 111 comprises a pulse counter, a direction discrimination circuit and a position comparator. The pulse counter counts the pulses of the first phase signal, and the count value represents the current position. The direction discrimination circuit determines the direction of rotation according to the phase relationship between the first phase signal and the second phase signal, and controls the counting of the counter. The position comparator compares the current position with the target position, and calculates the position deviation. When the position deviation is zero, the control circuit 111 stops sending driving pulses to the stepper motor, achieving precise positioning. When a pulse of the zero signal is detected, the control circuit 111 clears the pulse counter and starts counting again, eliminating cumulative errors and achieving closed-loop position control.

[0057] In the filter switching process, the stepper motor needs to overcome the rotational inertia of the filter wheel 104 and the bearing friction. The control circuit 111 is used to adjust the size and duration of the driving current output to the driving motor 107 according to the load condition of the filter wheel 104. In the starting stage, the control circuit 111 gradually increases the driving current from 0 ampere in the static state to 2 ampere, with a duration of 10 milliseconds, to overcome the static friction. In the uniform speed running stage, the driving current is reduced to 1.5 ampere and remains constant. In the deceleration and stop stage, the control circuit 111 controls the pulse frequency according to the trapezoidal speed curve, and the pulse frequency gradually decreases from the highest frequency to zero according to the linear law, with a deceleration time of 15 milliseconds, to avoid overshoot caused by inertia.

[0058] When the driving motor 107 drives the filter wheel 104 to rotate, the plurality of narrowband optical filters 112 enter the light path in turn. An optical sensor is arranged in the light path. As shown in Figure 8 The optical sensor is a reflection type optical sensor, including a transmitting end 122 and a receiving end 123. The transmitting end 122 emits infrared light, and the receiving end 123 detects the transmitted light intensity. The edge of the filter wheel 104 is provided with a notch 1041 as a positioning mark, and each narrowband optical filter 112 corresponds to a positioning mark. When a specific narrowband optical filter 112 enters the predetermined position, the positioning mark is just located in the detection area of the optical sensor, and the optical sensor detects the change of light intensity and sends a position confirmation signal to the control circuit 111.

[0059] The optical sensor is electrically connected with the control circuit 111. After receiving the position confirmation signal, the control circuit 111 stops sending driving pulses to the stepper motor, thereby ensuring that the narrowband optical filter 112 is positioned on the optical axis. The control circuit 111 is also used to automatically send fine adjustment pulses for position correction when a filter position deviation is detected. The judgment basis of the position deviation is that the difference between the feedback position of the position encoder and the detection position of the optical sensor exceeds 0.2 degrees. When the position deviation is detected, the control circuit 111 calculates the deviation value and converts it into the corresponding pulse number, sends the correction pulse to the stepper motor, and makes the filter return to the correct position.

[0060] Mid-infrared light passing through the oil under test is sequentially passed through narrow-band optical filters 112 of different wavelengths. Each filter allows light within a specific wavelength range to pass through, while light of other wavelengths is reflected or absorbed. The transmittance curve of the narrow-band optical filter 112 exhibits a Gaussian distribution, with a transmittance greater than 90% at the center wavelength and a transmittance decreasing to 45% at the bandwidth edge, resulting in an out-of-band suppression ratio greater than 10^4. The light intensity passing through the filter directly reflects the absorption characteristics of the oil at a specific wavelength. According to the Lambert-Beer law, the relationship between the transmitted light intensity I and the incident light intensity I0 is I = I0 × exp(-α × c × l), where α is the absorption coefficient, c is the component concentration, and l is the optical path length. Different components produce different degrees of light intensity attenuation at their corresponding characteristic wavelengths, and the concentration of each component can be calculated by measuring the degree of attenuation.

[0061] The multi-band spectral analysis module employs time-division to achieve sequential detection of multiple wavelengths. Only one specific wavelength of light signal arrives at the thermopile detector 109 within each time period, thus avoiding mutual interference between signals of different wavelengths. The control circuit 111 controls the complete scan cycle to be 800 milliseconds, the dwell time of each filter to be 80 milliseconds, and the filter switching time to be 20 milliseconds. During the 80-millisecond dwell time, the control circuit 111 controls the thermopile detector 109 to perform 16 samples at a sampling frequency of 200 Hz. The control circuit 111 averages the 16 sampled values ​​to reduce the influence of random noise.

[0062] like Figure 4 As shown, the narrowband optical filter 112 is a multilayer interference filter. The interference filter includes a transparent substrate layer 1121 and a multilayer dielectric film deposited on the surface of the transparent substrate layer 1121. The transparent substrate layer 1121 is made of zinc selenide (ZnSe) material, which has a transmittance greater than 70% in the mid-infrared band from 2 micrometers to 15 micrometers. The transparent substrate layer 1121 has a thickness of 2 millimeters, a surface flatness better than λ / 10 (λ is the operating wavelength), and a surface roughness Ra less than 10 nanometers. Both surfaces of the transparent substrate layer 1121 are optically polished.

[0063] The multilayer dielectric film is composed of alternating layers of high-refractive-index layer 1122 and low-refractive-index layer 1123. The high-refractive-index layer 1122 is made of zinc sulfide (ZnS) with a refractive index of 2.25 at a wavelength of 3 micrometers. The low-refractive-index layer 1123 is made of magnesium fluoride (MgF2) with a refractive index of 1.35 at a wavelength of 3 micrometers. The refractive index difference between the high and low refractive index layers is 0.9, and this larger difference is beneficial for improving the spectral selectivity of the filter. The optical thickness of each layer is one-quarter of the working wavelength, i.e., the physical thickness d = λ / (4n), where λ is the center wavelength and n is the refractive index of the layer material.

[0064] The total number of layers of the multilayer dielectric film is greater than 30, for example, the total number of layers of the multilayer dielectric film is 31, and the film system adopts a mode of alternately arranging the high refractive index layer 1122 and the low refractive index layer 1123, that is, the first layer is the high refractive index layer 1122, the second layer is the low refractive index layer 1123, the third layer is the high refractive index layer 1122, and so on, and the thirty-first layer is the high refractive index layer 1122. The outermost layer is the high refractive index layer 1122, which is in contact with air and can reduce surface reflection loss. Each layer of film is prepared by an electron beam evaporation method, and the evaporation process is carried out in a high vacuum environment.

[0065] A plurality of interfaces are formed between the high refractive index layer 1122 and the low refractive index layer 1123 in the multilayer dielectric film, and the incident light is partially reflected and partially transmitted at these interfaces. When the reflected light of each interface meets the constructive interference condition, light of a specific wavelength is strongly reflected; when the condition of destructive interference is met, light of a specific wavelength can be transmitted. By controlling the thickness, refractive index and number of layers of each layer of film, high transmittance for a specific wavelength range and high reflectivity for other wavelengths can be achieved. Specifically, when the optical path difference of the reflected light of the interfaces of the two adjacent layers is an integer multiple of the wavelength, constructive interference occurs, and the reflection is enhanced; when the optical path difference is an odd multiple of half the wavelength, destructive interference occurs, and the reflection is weakened and the transmission is enhanced.

[0066] In order to improve the environmental stability of the optical filter, a protective film is further coated on the outermost layer of the multilayer dielectric film. The protective film is made of aluminum oxide (Al2O3) material, and the aluminum oxide protective film is used to protect the underlying dielectric film from moisture, dust and mechanical wear. The refractive index of the protective film is 1.65, which is between the high refractive index layer 1122 and the low refractive index layer 1123, so as to reduce the influence on the spectral characteristics of the optical filter.

[0067] The edges of the narrowband optical filter 112 are sealed with epoxy resin to prevent water vapor from penetrating into the film layers from the edges. The sealing glue is cured to form a firm bond with the substrate and the film layers. The optical filter is mounted in a metal frame, and a rubber sealing ring is provided between the metal frame and the optical filter, which can provide cushioning protection and prevent stress concentration.

[0068] The mid-infrared sensor further comprises a signal processing module 110, the signal processing module 110 being electrically connected with the thermoelectric detector 109, and the signal processing module 110 being electrically connected with the control circuit 111. The signal processing module 110 comprises an analog-to-digital converter, a digital signal processor and a memory. The analog-to-digital converter is a 16-bit precision successive approximation ADC, and the analog-to-digital converter is used to convert the analog voltage signal output by the thermoelectric detector 109 into a digital signal.

[0069] The digital signal processor adopts a 32-bit floating-point DSP chip, and has a parallel multiply-add operation unit for executing digital filtering and spectral analysis algorithms. The digital signal processor pre-processes the collected raw data, including removing direct current bias, digital filtering and normalization processing.

[0070] A mathematical model between absorbance of each wavelength and concentration of each component is pre-stored in the memory. The mathematical model is established by calibration experiment of standard samples, and the model adopts a form of multiple linear regression equation. Let absorbance measured at the i-th wavelength be Ai, and concentration of the j-th component be C j , then there is a linear equation group: A1=k 11 ×C1+k 12 ×C2+...+k 1n ×C n , A2=k 21 ×C1+k 22 ×C2+...+k 2n ×C n ,..., A m =k m1 ×C1+k m2 ×C2+...+k mn ×C n , where k ij is an absorption coefficient of the j-th component at the i-th wavelength, m is the number of wavelengths, and n is the number of components. The digital signal processor reads the mathematical model and the absorption coefficient matrix from the memory, substitutes the real-time measured absorbance values of each wavelength into the equation group, solves the equation group by the least square method, and calculates the concentration values of each component.

[0071] The signal processing module 110 further includes a temperature compensation circuit. The temperature compensation circuit includes a temperature sensor and a compensation algorithm module. The temperature sensor is a platinum resistance temperature sensor, and the temperature sensor is installed near the thermoelectric pile detector 109 to monitor the working temperature of the detector in real time. The temperature sensor is electrically connected with the control circuit 111 to send a temperature signal to the control circuit 111. The compensation algorithm module is implemented in the digital signal processor, and according to a pre-calibrated temperature-response curve, the detector output signal is temperature-compensated to eliminate the influence of temperature drift.

[0072] The mathematical model of temperature compensation is: V comp =V meas ×[1+α(T-T0)], where V comp is the compensated voltage value, V measThe measured voltage value is given, α is the temperature coefficient, T is the current temperature, and T0 is the reference temperature (25℃). The temperature coefficient α is obtained through experimental calibration; for the thermopile detector 109 in this embodiment, α = -0.002 / ℃. The compensation algorithm module is implemented in the digital signal processor using a lookup table and interpolation. The lookup table stores the compensation coefficients for every 1℃ interval within the range of -50℃ to 150℃, and the intermediate temperature values ​​are calculated through linear interpolation.

[0073] The control circuit 111 is used to send the processed oil component concentration data, equipment status information, and fault diagnosis results to the host computer monitoring system. The control circuit 111 is electrically connected to the communication interface.

[0074] The mid-infrared sensor also includes an oil sample cell 103, which is positioned in the optical path between the collimating mirror 101 and the multi-band spectral analysis module. Figure 5 and Figure 6 As shown, the oil sample cell 103 includes a cell body and an optical window 113. The cell body is made of stainless steel and has an inlet 114 and an outlet 115. The inlet 114 and the outlet 115 are equipped with connectors to facilitate the entry and exit of oil.

[0075] The optical window 113 is made of calcium fluoride (CaF2) material. Both surfaces of the optical window 113 are coated with antireflective films, and the reflectivity is less than 0.5% in the wavelength range of 2.5 micrometers to 4 micrometers. The optical window 113 is sealed to the pool body by an O-ring.

[0076] like Figure 6 As shown, the oil sample cell 103 is also equipped with a heating element 116, a cooling element 117, and a temperature controller 118. The heating element 116 is a ceramic heating element, which is attached to the outer wall of the cell. The cooling element 117 is a semiconductor cooling element, which is attached to the outer wall of the cell. The temperature controller 118 is electrically connected to the heating element 116 and the cooling element 117, and is also electrically connected to the control circuit 111. The control circuit 111 is used to set the target temperature of the temperature controller 118. The temperature controller 118 is used to control the heating element 116 and the cooling element 117 to maintain the temperature of the oil sample cell 103 within the set value ±0.5℃ range. The heating element 116, the cooling element 117, and the temperature controller 118 are used to control the oil temperature within the range of 20℃ to 80℃, simulating the oil state under actual working conditions.

[0077] The mid-infrared sensor further comprises a light beam collimation component disposed between the light source module and the oil sample cell 103 or between the oil sample cell 103 and the filter wheel 104. The light beam collimation component comprises a diaphragm and a first collimation lens. The diaphragm is adjustable in aperture for controlling the diameter of the light beam entering the oil sample cell 103. The first collimation lens is made of zinc selenide material for further improving the parallelism of the light beam. After passing through the light beam collimation component, the divergence angle of the light beam is reduced to less than 1 milliradian, thereby improving the spatial resolution of the measurement.

[0078] The optical elements of the mid-infrared sensor are mounted on an optical platform, and each optical element is fixed to the optical platform by an adjustable support.

[0079] In order to reduce the influence of environmental vibration, the optical platform is placed on a vibration isolation table. The vibration isolation table is of an air floating structure and is used for isolating vibrations with a frequency greater than 10 Hz. The vibration isolation table is further provided with an automatic leveling component for compensating for tilting caused by load changes.

[0080] The mid-infrared sensor further comprises a reference light path for monitoring the change of the light source intensity in real time. The reference light path comprises a beam splitter and a reference detector. The beam splitter is disposed behind the collimation mirror 101 for reflecting 5% of the light to the reference detector and transmitting 95% of the light to the oil sample cell 103. The beam splitter is made of a zinc selenide substrate with a partial reflection film coated on the surface, and the partial reflection film is composed of multiple layers of dielectric films. The splitting ratio of 5:95 is achieved by adjusting the thickness of the film layers. The reference detector has the same performance parameters as the thermocouple detector 109. The reference detector outputs a reference signal reflecting the real-time intensity of the light source. The reference detector is electrically connected to the control circuit 111.

[0081] The control circuit 111 simultaneously acquires the measurement signal and the reference signal, and eliminates the influence of the light source intensity fluctuation by calculating the ratio of the two. The specific compensation process is as follows: the control circuit 111 first records the reference light intensity I ref0 in the initial state, and in the subsequent measurement process, the current reference light intensity I ref and the measurement light intensity I meas are acquired in real time, and the data is sent to a digital signal processor. The digital signal processor calculates the measurement absorbance A meas =-log(I meas / I 0meas ), where I 0meas is the initial measurement light intensity. Then a compensation algorithm is applied: A corr =A meas ×(I ref0 / I ref ), where A corrThe corrected absorbance. This double-beam compensation method can eliminate the light intensity fluctuations caused by light source aging, temperature changes and other factors, and improve the stability and reproducibility of the measurement.

[0082] In the actual measurement process, the oil liquid conveying device extracts the oil liquid to be measured from the equipment oil tank and sends it into the oil liquid sample pool 103. The oil liquid conveying device includes a peristaltic pump, a filter and a pipeline. The peristaltic pump is electrically connected with the control circuit 111, and the control circuit 111 controls the flow of the peristaltic pump. The filter is used to remove large particle impurities in the oil liquid. After the measurement is completed, the oil liquid returns to the oil tank through the backflow pipeline, realizing online circulation measurement.

[0083] The control circuit 111 coordinates the entire measurement process, including filter switching, signal acquisition, data processing and result output. The control circuit 111 controls the work of each component according to the preset time sequence: first, rotate the first filter into the light path, wait for the signal to be stable, then control the analog-to-digital converter to collect data, then switch to the next filter, repeat the collection process, until all filters are measured. After the collected data is processed by the signal processing module 110, the concentration values of each component are obtained, and the control circuit 111 sends the concentration values to the upper computer monitoring system through the communication interface.

[0084] In order to verify the technical effect of the mid-infrared sensor provided by the embodiment of the present application in oil quality monitoring, a comparative test was carried out. The comparative example adopts a traditional single-wavelength (for example, 2900 nanometers) mid-infrared sensor. The embodiment adopts the multi-band spectral analysis module of the present application, which is configured with eight narrow-band optical filters 112 of different wavelengths. The test uses a standard oil sample, and the concentration of alkane compounds in the standard sample is 850 milligrams per liter, the concentration of carbonyl compounds is 45 milligrams per liter, the concentration of water is 120 milligrams per liter, the concentration of aromatic compounds is 78 milligrams per liter, and the concentration of alcohol compounds is 32 milligrams per liter. Each method is repeated 10 times, and the average value and relative standard deviation are calculated.

[0085] Table 1 Comparison of component detection results of different detection methods

[0086]

[0087] The test data show that the detection error of each component is large due to the influence of spectral overlap and mutual interference in the traditional single-wavelength detection method, and the detection error of carbonyl compounds reaches 37.8%, and the detection error of alcohol compounds reaches 28.1%. This is because at a wavelength of 2900 nanometers, multiple components are absorbed, resulting in mutual masking of signals, and the individual contribution of each component cannot be accurately identified. The multi-band spectral analysis module of the present application configures a special narrow-band optical filter 112 for each component, realizes effective separation in the spectrum, and the detection error of each component is controlled within 5%, and the detection accuracy is significantly improved. The relative standard deviation is less than 5%, indicating that the repeatability of the measurement is good. The test method uses a Fourier transform infrared spectrometer as a reference standard, and the standard sample is scanned under the same conditions to obtain the accurate concentration value of each component as the standard concentration. The test environment temperature is controlled at 25℃±1℃, and the relative humidity is controlled at 50%±5%, and the baseline calibration is performed before each measurement.

[0088] The embodiment of the present application realizes the simultaneous detection of multiple components in oil by the multi-band spectral analysis module, and solves the limitations of the traditional single-wavelength detection method. The multi-layer film interference structure of the narrow-band optical filter 112 provides excellent spectral selectivity, and each filter corresponds to the characteristic absorption wavelength of a specific component, avoiding the interference of spectral overlap. The time-division detection method simplifies the signal processing and improves the reliability of the measurement. The multi-element linear regression algorithm executed by the digital signal processor can accurately analyze the concentration of each component, and satisfactory results can be obtained even in a complex multi-component system. Temperature compensation and double-beam compensation further improve the accuracy and stability of the measurement.

[0089] In actual application scenarios, bubbles will be generated in the oil during transportation, and the bubbles will cause scattering and refraction in the mid-infrared light propagation path, interfere with the spectral absorption measurement, and cause random fluctuations and systematic errors in the measurement results.

[0090] To solve the above technical problems, the mid-infrared sensor for oil quality monitoring of the present application is provided with a cyclone separation chamber, a static settling chamber and an ultrasonic defoamer in front of the sample inlet 114 of the oil sample pool 103. The inner wall of the cyclone separation chamber is helically distributed, the helical inner wall of the cyclone separation chamber guides the oil to produce a helical flow trajectory, and the centrifugal force generated by the helical flow causes the bubbles with smaller density to gather towards the central axis of the cyclone separation chamber. The static settling chamber is connected with the outlet of the cyclone separation chamber, and the cross-sectional area of the static settling chamber is larger than that of the sample inlet pipe. After the oil flows from the cyclone separation chamber into the static settling chamber, the flow velocity is significantly reduced, and the bubbles move to the upper surface of the static settling chamber under the driving of the buoyancy and gather. The ultrasonic defoamer is installed at the side wall of the static settling chamber, and the transducer of the ultrasonic defoamer emits ultrasonic waves with a frequency of 40 kHz to the oil. The cavitation effect generated by the ultrasonic waves propagating in the oil can make the micro-bubbles break and dissipate. An exhaust valve is installed at the top of the static settling chamber, and the exhaust valve is connected with the control circuit 111 through electrical connection. The control circuit 111 controls the opening of the exhaust valve according to the preset time interval, and the gas gathered above the liquid surface is discharged from the static settling chamber. The mid-infrared sensor for oil quality monitoring of the present application further comprises a liquid level sensor, the probe of which extends into the interior of the static settling chamber. The liquid level sensor monitors the liquid level position of the oil in the static settling chamber in real time. When the liquid level position is lower than the preset value, the control circuit 111 adjusts the sample flow to ensure that the oil completely fills the subsequent optical measurement path.

[0091] In actual application scenarios, in the case of oil flow change or pipeline pressure fluctuation, the thickness of the oil in the oil sample pool 103 changes, causing the light absorption path length to be unstable, affecting the applicability of the Lambert-Beer law and the accuracy of the concentration calculation.

[0092] To solve the above technical problems, the mid-infrared sensor for oil quality monitoring comprises a liquid level sensor array, an overflow regulating valve and a pressure stabilizer. The liquid level sensor array is composed of three capacitive liquid level sensors, which are equally spaced along the vertical direction of the oil sample pool 103. The capacitive plates of each liquid level sensor are in contact with the oil, and when the oil level changes, the capacitance between the capacitive plate and the oil changes accordingly. The liquid level sensor converts the capacitance change into an electrical signal output. The overflow regulating valve is installed at the sample outlet 115 of the oil sample pool 103. The overflow regulating valve comprises an electric actuator and a variable orifice valve core. The drive shaft of the electric actuator is connected to the variable orifice valve core. The electric actuator is electrically connected to the control circuit 111 through a signal transmission line. The pressure stabilizer is installed at the middle section of the oil inlet pipeline. The pressure stabilizer comprises a buffer chamber and an elastic diaphragm. The internal space of the buffer chamber is used to contain part of the oil. The elastic diaphragm separates the buffer chamber into an oil chamber and a gas chamber. When pressure pulsation occurs in the pipeline, the elastic diaphragm deforms elastically, and the volume of the oil chamber changes accordingly, thereby absorbing and relieving the impact of pressure pulsation on the downstream. The control circuit 111 comprises a liquid level control module. The input end of the liquid level control module is connected to the signal output end of the liquid level sensor array. The liquid level control module receives the liquid level signal fed back by the liquid level sensor. When the liquid level control module detects that the liquid level deviates from the preset target value, the liquid level control module sends an adjustment instruction to the electric actuator. The electric actuator drives the variable orifice valve core to rotate, increases or reduces the flow area of the overflow regulating valve, and correspondingly increases or reduces the outflow of the oil, so that the liquid level in the oil sample pool 103 returns to the preset target range (the control error of the liquid level is within ±0.1 mm), and thus the corresponding optical path length change can be controlled within 0.5%.

[0093] In a multi-component complex oil, the concentration of some components is very low, but it has a significant impact on the quality of the oil. The existing narrowband filter 112 may not provide sufficient detection sensitivity, resulting in insufficient detection signal-to-noise ratio of trace key components.

[0094] To solve the above technical problems, a multi-pass reflection member and a signal accumulation processor are added in the multi-band spectral analysis module. The multi-pass reflection member is arranged in the light path inside the oil sample cell 103, and is located between the light inlet end and the light outlet end of the oil sample cell 103. The multi-pass reflection member includes two oppositely arranged concave mirrors, a first concave mirror is fixedly installed on the inner surface of the side wall of the oil sample cell 103, and a second concave mirror is fixedly installed on the inner surface of the opposite side wall of the oil sample cell 103. The reflection surfaces of the first concave mirror and the second concave mirror face each other. The central axis of the first concave mirror is parallel to but not coincident with the central axis of the second concave mirror, and there is a vertical offset distance between the two central axes. After the incident light beam enters the light inlet end of the oil sample cell 103, it first reaches the reflection surface of the first concave mirror, which reflects the incident light beam to the second concave mirror. The second concave mirror reflects the received light beam back to the first concave mirror, and the light beam forms a round-trip propagation light path between the first concave mirror and the second concave mirror. Each time the light beam is reflected from one concave mirror to the other, the light beam passes through the oil medium between the two mirrors, and the propagation path of the light beam in the oil presents a zigzag multi-segment polyline shape. Due to the vertical offset of the central axes of the two concave mirrors, the propagation path of the light beam changes slightly in space position after each reflection, so that the light beam can perform multiple round-trip propagation between the two mirrors without repeating the same light path. After multiple reflections, the light beam is finally reflected from the second concave mirror and exits the light outlet end of the oil sample cell 103, and enters the subsequent narrowband optical filter 112. The distance between the two concave mirrors in the multi-pass reflection member can be adjusted by a threaded drive rod and a moving guide rail. The threaded drive rod is connected to the support frame of one of the concave mirrors, and the moving guide rail guides the concave mirror support frame to move in a predetermined direction. When the threaded drive rod and the moving guide rail change the distance between the concave mirrors, the number of reflections of the light beam between the two mirrors and the total propagation distance of the light beam in the oil are also changed. The signal accumulation processor is integrated in the digital signal processor, and the signal accumulation processor performs numerical accumulation and average operation on the continuous multiple measurement results of the same filter position. Each accumulation operation includes 64 independent measurement data, and the signal-to-noise ratio of the final measurement result is improved by increasing the number of measurement data samples. The control circuit 111 also includes an adaptive gain control module, the input end of the adaptive gain control module is connected with the signal output end of the thermoelectric detector 109, and the adaptive gain control module monitors the intensity of the detector output signal in real time. When the signal intensity is weak, the adaptive gain control module automatically increases the amplification factor of the amplifier, and when the signal intensity is strong, the adaptive gain control module reduces the amplification factor of the amplifier, so as to avoid the saturation distortion phenomenon of the detector output signal.

[0095] The above detailed description of the embodiments of the application is not to be interpreted as including all combinations of the teachings of the various embodiments.

Claims

1. A mid-infrared sensor for oil quality monitoring, characterized by, The mid-infrared sensor comprises a light source module, a detector module, an oil sample pool and a signal processing module, the light source module comprises a thermal radiation light source and a collimating mirror, the detector module comprises a thermoelectric detector and a focusing mirror, the oil sample pool is arranged in the light path between the collimating mirror and the focusing mirror, the signal processing module is electrically connected with the thermoelectric detector, and the mid-infrared sensor further comprises: a multi-band spectral analysis module, the multi-band spectral analysis module comprises a filter wheel, a driving motor and a plurality of narrow-band optical filters, the filter wheel is arranged in the light path between the oil sample pool and the focusing mirror, the filter wheel is disc-shaped, a plurality of mounting holes are arranged on the circumference of the filter wheel, one of the narrow-band optical filters is arranged in each of the mounting holes, each of the narrow-band optical filters corresponds to the characteristic absorption wavelength of a specific component in the oil, the driving motor is connected with the filter wheel and is used to drive the filter wheel to rotate, so that the plurality of narrow-band optical filters enter the light path in turn; and an optical intensity regulator, the optical intensity regulator is arranged in the light path between the multi-band spectral analysis module and the thermoelectric detector, the optical intensity regulator comprises a variable diaphragm and a step motor, the variable diaphragm comprises a disc-shaped diaphragm base and a plurality of light transmission holes arranged on the diaphragm base, the step motor is connected with the variable diaphragm and is used to drive the variable diaphragm to rotate, so that the light transmission holes with different apertures rotate to the optical axis position in turn, the light transmission holes are uniformly distributed along the circumferential direction of the diaphragm base, the light transmission holes are circular openings, the light transmission holes penetrate the thickness direction of the diaphragm base, and the apertures of the light transmission holes are arranged in an increasing order; the mid-infrared sensor further comprises a control circuit, the control circuit is electrically connected with the driving motor, and the control circuit is used to send a pulse signal to the driving motor, and the driving motor is used to drive the filter wheel to rotate according to the pulse signal; the step motor is electrically connected with the control circuit, the step motor is used to receive the pulse signal from the control circuit, and the control circuit is used to send a corresponding number of pulse signals to the step motor according to the transmittance data of the narrow-band optical filter currently located in the light path, so as to drive the variable diaphragm to rotate to the corresponding light transmission hole position; when the filter wheel switches to the narrow-band optical filter with higher transmittance, the control circuit drives the variable diaphragm to rotate to the light transmission hole position with a smaller aperture, and when the filter wheel switches to the narrow-band optical filter with lower transmittance, the control circuit drives the variable diaphragm to rotate to the light transmission hole position with a larger aperture.

2. The mid-infrared sensor of claim 1, wherein, The multi-band spectrum analysis module further comprises a position encoder, the position encoder comprises a code disc, a light emitting diode and a photoelectric detector, the code disc is coaxially installed with the filter wheel, the position encoder is electrically connected with the control circuit, the position encoder outputs a first phase signal, a second phase signal and a zero signal to the control circuit, the control circuit is used for judging the rotation direction of the filter wheel by detecting the phase relationship of the first phase signal and the second phase signal, calculating the rotation angle by counting the number of pulses, and performing position calibration by the zero signal.

3. The mid-infrared sensor of claim 2, wherein, The mid-infrared sensor further comprises a photoelectric sensor, the photoelectric sensor is a light-receiving photoelectric sensor, the filter wheel edge is provided with a notch, each narrow-band optical filter corresponds to a notch, and the photoelectric sensor is electrically connected with the control circuit.

4. The mid-infrared sensor of claim 1, wherein, The narrow-band optical filter is a multilayer film interference filter, comprising a transparent substrate layer and a multilayer dielectric film deposited on the surface of the transparent substrate layer, and the multilayer dielectric film is formed by alternately stacking high refractive index layers and low refractive index layers.

5. The mid-infrared sensor of claim 1, wherein, The collimating mirror is an off-axis parabolic mirror, the reflecting surface of the off-axis parabolic mirror is coated with a metal reflecting film, the thermal radiation light source is a silicon carbide rod light source, the thermal radiation light source is arranged at the off-axis focal point of the off-axis parabolic mirror, and the divergent light forms a parallel light beam after being reflected by the off-axis parabolic mirror.

6. The mid-infrared sensor of claim 1, wherein, The oil sample cell is further provided with a heating element, a refrigeration element and a temperature controller, the heating element is a ceramic heating sheet, the refrigeration element is a semiconductor refrigeration sheet, and the temperature controller is electrically connected with the heating element and the refrigeration element.

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