Intermediate infrared sensor for monitoring oil quality

Abstract

The invention provides an intermediate infrared sensor for oil quality monitoring. The intermediate infrared sensor comprises a light source module, a detector module, an oil sample pool, a signal processing module, a multiband spectrum analysis module and a light intensity regulator. The multi-band spectrum analysis module comprises an optical filter wheel, a driving motor and a plurality of narrow-band optical filters, the optical filter wheel is in a disc shape, a plurality of mounting holes are formed in the circumference of the optical filter wheel, one narrow-band optical filter is arranged in each mounting hole, each narrow-band optical filter corresponds to the characteristic absorption wavelength of one specific component in oil, and the characteristic absorption wavelength of the specific component in the oil corresponds to the characteristic absorption wavelength of the specific component in the oil. And the driving motor drives the optical filter wheel to rotate, so that the plurality of narrow-band optical filters enter an optical path in sequence. The light intensity adjuster comprises a variable diaphragm and a stepping driver, and the detection signal intensity is optimized by adjusting the positions of light through holes with different apertures. According to the method, through a time division spectrum separation detection mode, the problems of spectrum overlapping and signal masking in the traditional technology are effectively solved, and the accuracy of content detection of all components in the oil liquid is improved.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a mid-infrared sensor for oil quality monitoring. Background Art

[0002] In industries like petrochemicals and machinery manufacturing, various types of machinery and equipment require lubricating oil, hydraulic oil, and other fluids during operation to reduce friction, transmit power, and dissipate heat. The quality of these fluids directly impacts the equipment's operating efficiency and service life. As equipment ages, its composition changes due to oxidation, contamination, and degradation, necessitating regular monitoring of its quality to ensure proper operation.

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

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

[0005] Furthermore, oil composition changes dynamically over time. Base oils gradually oxidize to form carbonyl compounds and alcohols, additives are consumed or decomposed, and external moisture and impurities enter the oil. These interplays complicate the oil's spectral characteristics. Existing detection methods struggle to accurately identify changes in the content of individual components, hindering the identification of oil contamination sources and the assessment of equipment operating conditions.

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

[0007] The purpose of this application is to provide a mid-infrared sensor for oil quality monitoring to solve the technical problem that existing mid-infrared sensors are difficult to 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-mentioned mid-infrared sensor, when the filter wheel is switched to the narrow-band optical filter with higher transmittance, the control circuit drives the variable iris to rotate to a light-passing hole position with a smaller aperture; when the filter wheel is switched to the narrow-band optical filter with lower transmittance, the control circuit drives the variable iris to rotate to a light-passing hole position with a larger aperture.

[0013] In the above-mentioned mid-infrared sensor, the multi-band spectral analysis module also includes a position encoder, which includes a code disk, a light-emitting diode and a photodetector. The code disk is coaxially installed with the filter wheel, and the position encoder is electrically connected to the control circuit. The position encoder outputs a first phase signal, a second phase signal and a zero-position signal to the control circuit. The control circuit is used to determine the rotation direction of the filter wheel by detecting the phase relationship between the first phase signal and the second phase signal, calculate the rotation angle by counting the number of pulses, and perform position calibration through the zero-position signal.

[0014] In the above-mentioned mid-infrared sensor, the mid-infrared sensor also includes a photoelectric sensor, which is a through-beam photoelectric sensor. A notch is provided on the edge of the filter wheel, and each narrow-band optical filter corresponds to one notch. The photoelectric sensor is electrically connected to the control circuit.

[0015] In the above-mentioned mid-infrared sensor, the narrow-band optical filter is a multilayer interference filter, which includes a transparent substrate layer and a multilayer dielectric film deposited on the surface of the transparent substrate layer, and the multilayer dielectric film is composed of alternating high refractive index layers and low refractive index layers.

[0016] In the above-mentioned mid-infrared sensor, the collimating reflector is an off-axis parabolic reflector, the reflective surface of the off-axis parabolic reflector is coated with a metal reflective film, the thermal radiation light source is a silicon carbide rod light source, and the thermal radiation light source is arranged at the off-axis focal position of the off-axis parabolic reflector, and the divergent light is reflected by the off-axis parabolic reflector to form a parallel light beam.

[0017] In the above-mentioned mid-infrared sensor, the oil sample pool is also equipped with a heating element, a cooling element and a temperature controller. The heating element is a ceramic heating plate, the cooling element is a semiconductor cooling plate, and the temperature controller is electrically connected to the heating element and the cooling element.

[0018] The mid-infrared sensor for oil quality monitoring provided in this application includes a multi-band spectral analysis module, which includes a filter wheel, a drive motor, and multiple narrow-band optical filters. The filter wheel is disc-shaped and has multiple mounting holes on its circumference. Each mounting hole is equipped with a narrow-band optical filter. Each narrow-band optical filter corresponds to the characteristic absorption wavelength of a specific component in the oil. The drive motor drives the filter wheel to rotate, causing multiple narrow-band optical filters to enter the light path in sequence. When the mid-infrared light emitted by the thermal radiation light source passes through a collimating reflector to form a parallel beam, it passes through the oil sample cell and the multi-band spectral analysis module in sequence. At any given time, only one specific narrow-band optical filter is located in the light path. This filter only allows light within a specific wavelength range to pass through, blocking light of other wavelengths. In this way, the composite spectrum originally containing absorption information of multiple components is decomposed into multiple 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 between different components. The drive motor rotates the filter wheel at a preset angle according to the control circuit's instructions, allowing different narrowband optical filters to sequentially enter the light path, enabling the individual detection of multiple components in the oil, such as alkanes, carbonyl compounds, and water molecules. This time-segmented detection method ensures that the optical signal received by the thermopile detector within each detection cycle has a clear spectral identity, eliminating analytical errors caused by the superposition of multi-component signals in traditional methods.

[0019] The mid-infrared sensor for oil quality monitoring provided by the present application also includes a light intensity regulator, which includes a variable aperture and a stepper drive. The variable aperture includes a disc-shaped aperture base and a plurality of light holes of different apertures arranged on the aperture base. The stepper drive drives the variable aperture to rotate so that the light holes of different apertures rotate to the optical axis position in sequence. When the filter wheel is switched to a narrow-band optical filter with higher transmittance, the control circuit drives the variable aperture to rotate to the light hole position with smaller aperture. When the filter wheel is switched to a narrow-band optical filter with lower transmittance, the control circuit drives the variable aperture to rotate to the light hole position with larger aperture. This technical solution can keep the light signal intensity at different wavelengths within the optimal detection range of the thermopile detector, thereby improving the detection accuracy and dynamic range.

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

[0021] Figure 1 Schematic diagram of a mid-infrared sensor for oil quality monitoring provided in an embodiment of the present application.

[0022] Figure 2 This is a schematic diagram of a filter wheel in a mid-infrared sensor for oil quality monitoring provided in an embodiment of the present application.

[0023] Figure 3 This is a schematic diagram of a variable aperture in a mid-infrared sensor for oil quality monitoring provided in an embodiment of the present application.

[0024] Figure 4 yes Figure 2 Schematic diagram of narrowband optical filters in a filter wheel.

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

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

[0027] Figure 7 This is a schematic diagram of a position encoder in a mid-infrared sensor for oil quality monitoring provided in an embodiment of the present application.

[0028] Figure 8 This is a schematic diagram of a photoelectric sensor in a mid-infrared sensor for oil quality monitoring provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] The specific implementation methods of this application are described in detail below with reference to the accompanying drawings.

[0030] The terms "first", "second" and similar words do not indicate any order, quantity or importance, but are only used to distinguish different technical features. The term "plurality" and similar words mean two or more, unless otherwise expressly limited.

[0031] The embodiments of the present application may 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 thermopile detector 109 includes a thermopile chip formed by connecting a plurality of thermocouples in series. The packaging window of the thermopile detector 109 is made of zinc selenide material.

[0037] Focusing reflector 108 is a parabolic reflector that converges the light beam, which has passed through the filters of the multi-band spectral analysis module, onto the sensing surface of the thermopile detector 109. The reflective surface of focusing reflector 108 is coated with a metal reflective film, minimizing light signal loss during reflection. The distance between focusing reflector 108 and thermopile detector 109 is equal to its focal length, ensuring that the light beam is precisely focused on the sensing surface of the thermopile detector 109.

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

[0039] The multi-band spectrum analysis module includes a filter wheel 104, a drive motor 107, and a position encoder. The filter wheel 104 is set in the light path between the oil sample pool 103 and the focusing reflector 108. The filter wheel 104 is disc-shaped and made of aluminum alloy. The surface is black anodized to reduce the influence of stray light. Figure 2 As shown, filter wheel 104 has multiple mounting holes evenly distributed along its circumference in the radial direction. For example, eight mounting holes are provided. Each mounting hole is positioned within a narrowband optical filter 112. Adjacent mounting holes are spaced 45 degrees apart. This arrangement allows filter wheel 104 to switch between different filters with every 45-degree rotation. Filter wheel 104 is mounted on a support frame via a rotating shaft 105. One end of rotating shaft 105 is connected to the output of a drive motor 107.

[0040] Each narrowband optical filter 112 corresponds to the characteristic absorption wavelength of a specific component in the oil. The first narrowband optical filter has a central wavelength of 2800 nanometers and a bandwidth of 2750 to 2850 nanometers. This filter is used to detect the carbon-hydrogen stretching vibration absorption peak of alkanes in the oil. Alkanes are the main components of oil, and changes in their content reflect the basic quality of the oil. The second narrowband optical filter has a central wavelength of 2900 nanometers and a bandwidth of 2850 to 2950 nanometers. This filter is used to detect the carbon-hydrogen stretching vibration absorption peak of aromatic compounds. The presence of aromatic compounds generally indicates the addition of additives such as antioxidants or detergents and dispersants to the oil. The third narrowband optical filter has a central wavelength of 3000 nanometers and a bandwidth of 2950 to 3050 nanometers. This filter is used to detect the carbon-oxygen double bond stretching vibration absorption peak of carbonyl compounds. The presence of carbonyl compounds indicates oxidative deterioration of the oil. The fourth narrow-band optical filter has a central wavelength of 3100 nanometers and a bandwidth of 3050 to 3150 nanometers. It is used to detect the oxygen-hydrogen stretching vibration absorption peak of alcohol compounds, which are often derived from oil oxidation products or external contamination. The fifth narrow-band optical filter has a central wavelength of 3200 nanometers and a bandwidth of 3150 to 3250 nanometers. It is used to detect the oxygen-hydrogen stretching vibration absorption peak of water molecules. Water content is one of the indicators for evaluating oil quality. The sixth narrow-band optical filter has a central wavelength of 3400 nanometers and a bandwidth of 3350 to 3450 nanometers. It is used to detect the nitrogen-hydrogen stretching vibration absorption peak of amine compounds, which are derived from antioxidant additives in oil. The seventh narrow-band optical filter has a central wavelength of 3500 nanometers and a bandwidth of 3450 to 3550 nanometers. It is used to detect the sulfur-hydrogen stretching vibration absorption peak of sulfides. The center wavelength of the eighth narrow-band optical filter is set to 2700 nanometers, and the bandwidth is 2650 nanometers to 2750 nanometers. The eighth narrow-band optical filter serves as a reference channel. The absorption of oil in this wavelength range is weak, and it is used for baseline correction.

[0041] A gear transmission assembly 106 is provided between the drive motor 107 and the filter wheel 104. Gear transmission assembly 106 comprises a driving gear and a driven gear. The driving gear is fixed to the output shaft of the drive motor 107, while the driven gear is fixed to the rotating shaft 105 of the filter wheel 104. The transmission ratio of gear transmission assembly 106 is 1:4: a 4-degree rotation of the drive motor 107 corresponds to a 1-degree rotation of the filter wheel 104. This transmission ratio improves the accuracy of filter positioning. The driving gear is fixed to the output shaft of the drive motor 107, while the driven gear is fixed to the flange of the rotating shaft 105 of the filter wheel 104. Grease is applied to the meshing areas of the gears.

[0042] The driving motor 107 is a stepping motor, and each step angle of the stepping 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 can be, for example, a 32-bit ARM processor. The driver circuit is used to drive the stepper 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 drive motor 107 and is configured to send a drive pulse signal to the drive motor 107. When the narrowband optical filter 112 needs to be switched, the control circuit 111 sends a corresponding number of pulse signals to the stepper motor, driving the filter wheel 104 to rotate to a specified position. For example, if the control circuit 111 sends 1600 pulses, the stepper motor rotates 180 degrees, and the filter wheel 104 rotates 45 degrees, 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 vary, causing the light intensity reaching the thermopile detector 109 to change suddenly. The thermopile detector 109 needs to re-establish thermal equilibrium, which prolongs the measurement response time.

[0046] To address the aforementioned technical issues, the present application installs a light intensity regulator in front of the thermopile detector 109. The regulator includes a variable aperture 125, a stepper driver (not shown), and a second collimating lens 124. The focusing reflector 108 converges the light beam that has passed through the filter of the multi-band spectral analysis module to a predetermined focal position. The second collimating lens 124, positioned at the focal position of the focusing reflector 108, converts the converged light beam back into a parallel beam. The second collimating lens 124 is made of zinc selenide and is a biconvex lens. Both surfaces of the second collimating lens 124 are coated with an antireflection coating that has a reflectivity of less than 1% within the wavelength range of 2.5 to 4 microns. The focal length of the second collimating lens 124 matches that of the focusing reflector 108. The front focal point of the second collimating lens 124 coincides with the focal point of the focusing reflector 108, resulting in the converged light beam forming a parallel beam after passing through the second collimating lens 124.

[0047] The variable aperture 125 is arranged on the side of the second collimating lens 124 away from the focusing mirror 108, as shown in FIG. Figure 3As shown, the variable aperture 125 includes a disc-shaped aperture base 1251 and a plurality of light holes 1252 arranged on the aperture base 1251. A central through hole 1253 is opened at the center position of the aperture base 1251, and the central through hole 1253 runs through the thickness direction of the aperture base 1251. Multiple light holes 1252 (e.g., eight) are evenly distributed along the circumference of the aperture base 1251. The light holes 1252 are circular openings that extend through the thickness of the aperture base 1251. The apertures 1252 are arranged in ascending order. For example, the first light hole has a diameter of 1 mm, the second light hole has a diameter of 1.5 mm, the third light hole has a diameter of 2 mm, the fourth light hole has a diameter of 2.5 mm, the fifth light hole has a diameter of 3 mm, the sixth light hole has a diameter of 3.5 mm, the seventh light hole has a diameter of 4 mm, and the eighth light hole has a diameter of 4.5 mm. A central shaft passes through the central through hole 1253 and is fixedly connected to the aperture base 1251. One end of the central shaft is connected to the output shaft of the stepper drive. A keyway connection is used between the central shaft and the output shaft of the stepper drive to achieve torque transmission. An axial positioning ring is provided at the other end of the central axis. The axial positioning ring is installed coaxially with the central axis and is used to limit the axial displacement of the aperture base 1251 along the central axis.

[0048] The thermopile detector 109 is positioned on the side of the variable aperture 125 away from the focusing reflector 108, with its sensing surface perpendicular to the optical axis. The parallel light beam converted by the second collimating lens 124 passes through the aperture 1252 of the variable aperture 125 and then strikes the sensing surface of the thermopile detector 109 as parallel light. The cross-sectional diameter of the parallel light beam matches the aperture of the aperture 1252.

[0049] The stepper drive consists of a motor body and an output shaft, which is fixedly connected to the optical platform. The output shaft extends from the upper surface of the motor body and is rigidly connected to the motor's rotor. A keyway is provided at the end of the output shaft, which mates with a key at the end of the central shaft.

[0050] The stepper driver is electrically connected to the control circuit 111. The stepper driver receives pulse signals from the control circuit 111, driving its rotor to rotate in steps. This rotation is transmitted to the central shaft via the output shaft, which in turn drives the variable aperture 125 to rotate synchronously. The rotation of the variable aperture 125 causes the light apertures 1252 of different apertures to sequentially rotate to the optical axis, switching the diameter of the light aperture 1252.

[0051] The signal processing module 110 pre-stores transmittance data for each narrowband optical filter 112. This transmittance data is stored in digital form in the memory of the signal processing module 110. When the filter wheel 104 switches between narrowband optical filters 112, the control circuit 111 synchronously sends a corresponding number of pulse signals to the stepper driver based on the transmittance data of the narrowband optical filter 112 currently in the optical path, driving the variable iris 125 to rotate to the corresponding light passage 1252 position. When the filter wheel 104 switches to a narrowband optical filter 112 with higher transmittance, the control circuit 111 drives the variable iris 125 to rotate to a smaller aperture 1252 position, reducing the amount of light passing through. When the filter wheel 104 switches to a narrowband optical filter 112 with lower transmittance, the control circuit 111 drives the variable iris 125 to rotate to a larger aperture 1252 position, increasing the amount of light passing through. Through this aperture compensation method, the light intensity reaching the thermopile detector 109 is maintained within a preset target range, avoiding the re-establishment process of the thermal balance of the thermopile detector 109 and shortening the measurement response time.

[0052] A beam shaper is located between the second collimating lens 124 and the variable aperture 125. The beam shaper comprises a cylindrical lens assembly and a beam homogenizer. The cylindrical lens assembly adjusts the cross-sectional shape of the parallel beam, while the beam homogenizer improves the uniformity of the light intensity distribution within the beam's cross-section. The beam homogenizer is a hexagonal light pipe coated with a highly reflective coating. After multiple reflections within the pipe, the cross-sectional light intensity distribution becomes more uniform.

[0053] The control circuit 111 includes a light intensity monitoring module connected to the signal output of the thermopile detector 109. This module monitors the light intensity reaching the thermopile detector 109 in real time. When the light intensity monitoring module detects that the light intensity deviates from a preset target value, it sends an adjustment command to the stepper driver, driving the variable aperture 125 to switch to a light aperture 1252 of an appropriate aperture, thereby achieving closed-loop light intensity control. The preset target value is determined based on the linear response range of the thermopile detector 109. The target light intensity value is set at 70% of the detector's full-scale output to ensure that the detector operates within its linear response range and maintains a sufficient signal-to-noise ratio.

[0054] The position encoder is an incremental photoelectric encoder with a resolution of 1000 lines / revolution. Figure 7As shown, the position encoder includes a code disk 119, a light-emitting diode 120, and a photodetector 121. Code disk 119 is a circular disk with 1000 radial light-transmitting slits etched into its surface. The slits are separated by opaque areas, and the angular spacing between adjacent slits is 0.36 degrees. Code disk 119 is coaxially mounted with filter wheel 104 and connected to the rotating shaft 105 of filter wheel 104 via a coupling. Light emitted by LED 120 produces brightness variations when it passes through the light-transmitting slits of code disk 119. Photodetector 121 receives the transmitted light 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-position signal to the control circuit 111. The first and second phase signals are square wave signals with a 90-degree phase difference, each outputting 1000 pulses per revolution. The control circuit 111 determines the rotation direction by detecting the phase relationship between the first and second phase signals: when the first phase signal leads the second phase signal by 90 degrees, the filter wheel 104 rotates forward; when the second phase signal leads the first phase signal by 90 degrees, the filter wheel 104 rotates backward. The control circuit 111 calculates the rotation angle by counting the number of pulses in the first or second phase signal, with each pulse corresponding to a rotation angle of 0.36 degrees. The code disk 119 outputs one pulse per revolution, with a pulse width equal to the width of one light-transmitting slit. The zero-position signal is used for position calibration to eliminate cumulative errors.

[0056] The control circuit 111 includes a pulse counter, a direction determination 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 determination circuit determines the direction of rotation based on the phase relationship between the first and second phase signals and controls the counter's addition and subtraction. 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 drive pulses to the stepper motor, achieving precise positioning. When a pulse of the zero position signal is detected, the control circuit 111 clears the pulse counter and restarts counting, eliminating the accumulated error and achieving closed-loop position control.

[0057] During 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 magnitude and duration of the drive current output to the drive motor 107 according to the load of the filter wheel 104. During the startup phase, the control circuit 111 gradually increases the drive current from 0 amps in the static state to 2 amps for 10 milliseconds to overcome static friction. During the uniform speed operation phase, the drive current is reduced to 1.5 amps and maintained constant. During the deceleration and stop phase, the control circuit 111 controls the pulse frequency according to a trapezoidal speed curve, gradually reducing the pulse frequency from the highest frequency to zero according to a 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, multiple narrow-band optical filters 112 enter the light path in sequence. A photoelectric sensor is provided in the light path. Figure 8 As shown, the photoelectric sensor is a through-beam photoelectric sensor, comprising a transmitter 122 and a receiver 123. Transmitter 122 emits infrared light, while receiver 123 detects the intensity of the transmitted light. The edge of the filter wheel 104 is provided with notches 1041, which serve as positioning marks. Each narrowband optical filter 112 corresponds to a positioning mark. When a particular narrowband optical filter 112 enters a predetermined position, the positioning mark is located within the detection area of ​​the photoelectric sensor. The photoelectric sensor detects the change in light intensity and sends a position confirmation signal to the control circuit 111.

[0059] The photoelectric sensor is electrically connected to the control circuit 111. Upon receiving the position confirmation signal, the control circuit 111 stops sending drive 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 configured to automatically send fine-tuning pulses for position correction when a position deviation of the filter is detected. Position deviation is determined when the difference between the position encoder's feedback position and the photoelectric sensor's detected position exceeds 0.2 degrees. When a position deviation is detected, the control circuit 111 calculates the deviation value, converts it into a corresponding pulse number, and sends correction pulses to the stepper motor to return the filter to its correct position.

[0060] Mid-infrared light passing through the oil to be tested sequentially passes through narrowband optical filters 112 of different wavelengths. Each filter only allows light within a specific wavelength range to pass through, while light of other wavelengths is reflected or absorbed. The transmittance curve of narrowband optical filter 112 exhibits a Gaussian distribution, with a transmittance greater than 90% at the center wavelength and a transmittance reduced to 45% at the edge of the bandwidth. The out-of-band rejection ratio is 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. By measuring the attenuation degree, the concentration of each component can be calculated.

[0061] The multi-band spectral analysis module uses a time-slicing approach to achieve sequential multi-wavelength detection. Only one optical signal of a specific wavelength reaches the thermopile detector 109 during each time period, thus preventing interference between signals of different wavelengths. The control circuit 111 controls the complete scanning cycle to 800 milliseconds, the dwell time of each filter to 80 milliseconds, and the filter switching time to 20 milliseconds. During this 80-millisecond dwell time, the control circuit 111 controls the thermopile detector 109 to perform 16 sampling operations at a sampling frequency of 200 Hz. The control circuit 111 averages these 16 sampling values ​​to reduce the impact of random noise.

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

[0063] The multilayer dielectric film is composed of alternating high-refractive-index layers 1122 and low-refractive-index layers 1123. High-refractive-index layer 1122 is made of zinc sulfide (ZnS) with a refractive index of 2.25 at a wavelength of 3 microns. Low-refractive-index layer 1123 is made of magnesium fluoride (MgF2) with a refractive index of 1.35 at a wavelength of 3 microns. The refractive index difference between the high- and low-refractive-index layers is 0.9. This large refractive-index difference improves the filter's spectral selectivity. The optical thickness of each layer is one-quarter of the operating wavelength, or a physical thickness of d = λ / (4n), where λ is the center wavelength and n is the refractive index of the layer.

[0064] The total number of layers in the multilayer dielectric film is greater than 30. For example, the total number of layers in the multilayer dielectric film is 31. The film system employs an alternating arrangement of high-refractive-index layers 1122 and low-refractive-index layers 1123. That is, the first layer is a high-refractive-index layer 1122, the second layer is a low-refractive-index layer 1123, the third layer is a high-refractive-index layer 1122, and so on, up to the 31st layer, which is a high-refractive-index layer 1122. The outermost layer, high-refractive-index layer 1122, is in contact with air, thereby reducing surface reflection losses. Each thin film layer is produced by electron beam evaporation, and the evaporation process is performed in a high vacuum environment.

[0065] Multiple interfaces are formed between the high-refractive-index layer 1122 and the low-refractive-index layer 1123 in the multilayer dielectric film, and incident light is partially reflected and partially transmitted at these interfaces. When the reflected light at each interface meets the constructive interference condition, light of a specific wavelength is strongly reflected; when the destructive interference condition is met, light of a specific wavelength is allowed to pass through. By controlling the thickness, refractive index, and number of layers of each thin 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 at two adjacent interfaces is an integer multiple of the wavelength, constructive interference occurs, and reflection is enhanced; when the optical path difference is an odd multiple of half a wavelength, destructive interference occurs, reflection is weakened, and transmission is enhanced.

[0066] To enhance the filter's environmental stability, a protective film is applied to the outermost layer of the multilayer dielectric film. Made of aluminum oxide (Al2O3), this film protects the underlying dielectric film from moisture, dust, and mechanical abrasion. The protective film has a refractive index of 1.65, placing it between the high-refractive-index layer 1122 and the low-refractive-index layer 1123 to minimize its impact on the filter's spectral characteristics.

[0067] The edges of narrowband optical filter 112 are sealed with epoxy resin to prevent moisture from penetrating the film. Once cured, the sealant forms a strong bond with the substrate and film. The filter is mounted within a metal frame, with a rubber seal between the metal frame and the filter, providing both cushioning protection and preventing stress concentration.

[0068] The mid-infrared sensor also includes a signal processing module 110, which is electrically connected to the thermopile detector 109 and to a control circuit 111. Signal processing module 110 includes an analog-to-digital converter (ADC), a digital signal processor (DSP), and memory. The ADC is a 16-bit successive approximation ADC that converts the analog voltage signal output by the thermopile 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 measis the measured voltage value, α is the temperature coefficient, T is the current temperature, and T0 is the reference temperature (25°C). The temperature coefficient α is obtained through experimental calibration. For the thermopile detector 109 of this embodiment, α = -0.002 / °C. The compensation algorithm module is implemented in the digital signal processor using a table lookup and interpolation method. The lookup table stores the compensation coefficient at 1°C intervals from -50°C to 150°C. Intermediate temperatures are calculated using 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 further includes an oil sample pool 103, which is disposed in the optical path between the collimating reflector 101 and the multi-band spectrum analysis module. Figure 5 and Figure 6 As shown, the oil sample pool 103 includes a pool body and an optical window 113. The pool body is made of stainless steel and is provided with an inlet 114 and an outlet 115. The inlet 114 and the outlet 115 are equipped with connectors to facilitate the inflow and outflow of the oil.

[0075] The optical window 113 is made of calcium fluoride (CaF2) and has an antireflection coating on both surfaces. Its reflectivity is less than 0.5% within the wavelength range of 2.5 to 4 microns. The optical window 113 is sealed to the cell body via an O-ring.

[0076] like Figure 6 As shown, the oil sample pool 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 plate, which is tightly attached to the outer wall of the pool body. The cooling element 117 is a semiconductor cooling plate, which is tightly attached to the outer wall of the pool body. The temperature controller 118 is electrically connected to the heating element 116 and the cooling element 117. The temperature controller 118 is 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 control the temperature of the oil sample pool 103 within the set value ±0.5°C. 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°C to 80°C, simulating the oil state under actual working conditions.

[0077] The mid-infrared sensor also includes a beam collimating component, which is positioned between the light source module and the oil sample reservoir 103 or between the oil sample reservoir 103 and the filter wheel 104. The beam collimating component includes an aperture and a first collimating lens. The aperture is adjustable to control the diameter of the light beam entering the oil sample reservoir 103. The first collimating lens is made of zinc selenide and further improves the parallelism of the light beam. After passing through the beam collimating component, the divergence angle of the light beam is reduced to below 1 milliradian, improving the spatial resolution of the measurement.

[0078] Each optical element of the mid-infrared sensor is installed on an optical platform, and each optical element is fixed on the optical platform through an adjustable bracket.

[0079] To minimize the effects of ambient vibration, the optical platform is placed on a vibration isolation table. This air-floating table is designed to isolate vibrations with frequencies greater than 10 Hz. It also features an automatic leveling mechanism to compensate for tilt caused by load variations.

[0080] The mid-infrared sensor also includes a reference optical path, which is used to monitor changes in the intensity of the light source in real time. The reference optical path includes a beam splitter and a reference detector. The beam splitter is arranged behind the collimating reflector 101 and is used to reflect 5% of the light to the reference detector and transmit 95% of the light to the oil sample pool 103. The beam splitter uses a zinc selenide substrate with a partially reflective film coated on the surface. The partially reflective film is composed of a multilayer dielectric film, and a 5:95 splitting ratio is achieved by adjusting the film thickness. The reference detector has the same performance parameters as the thermopile detector 109. The reference detector outputs a reference signal, which reflects the real-time intensity of the light source. The reference detector is electrically connected to the control circuit 111.

[0081] The control circuit 111 collects the measurement signal and the reference signal at the same time, and eliminates the influence of the light source intensity fluctuation by calculating the ratio between the two. The specific compensation process is as follows: the control circuit 111 first records the reference light intensity I in the initial state. ref0 In the subsequent measurement process, the current reference light intensity I is collected in real time ref and measure the light intensity I meas , and sends the data to the digital signal processor. The digital signal processor calculates the measured absorbance A meas =-log(I meas / I 0meas ), where I 0meas is the initial measurement of light intensity. Then the compensation algorithm is applied: A corr =A meas ×(I ref0 / I ref ), where A corrThis dual-beam compensation method can eliminate light intensity fluctuations caused by factors such as light source aging and temperature changes, thereby improving measurement stability and reproducibility.

[0082] During the actual measurement process, the oil delivery device draws the oil to be measured from the equipment's oil tank and delivers it to the oil sample pool 103. The oil delivery device includes a peristaltic pump, a filter, and piping. The peristaltic pump is electrically connected to a control circuit 111, which controls the pump's flow rate. The filter removes large particles from the oil. After the measurement is complete, the oil returns to the tank through a return line, enabling online circulation measurement.

[0083] Control circuit 111 coordinates the entire measurement process, including filter switching, signal acquisition, data processing, and result output. Control circuit 111 controls the operation of each component according to a preset sequence: first, it rotates the first filter into the optical path, waits for the signal to stabilize, and then controls the analog-to-digital converter to acquire data. It then switches to the next filter, repeating the acquisition process until all filters have been measured. The collected data is processed by signal processing module 110 to obtain the concentration values ​​of each component. Control circuit 111 transmits these concentration values ​​to the host computer monitoring system via a communication interface.

[0084] To verify the technical effectiveness of the mid-infrared sensor provided in the embodiments of this application for oil quality monitoring, a comparative test was conducted. The comparative example employed a conventional single-wavelength (e.g., 2900 nm) mid-infrared sensor. The embodiment employed the multi-band spectral analysis module of this application, configured with eight narrow-band optical filters 112 of different wavelengths. The test utilized a standard oil sample containing 850 mg / L of alkanes, 45 mg / L of carbonyls, 120 mg / L of water, 78 mg / L of aromatics, and 32 mg / L of alcohols. Each method was repeated 10 times, and the average and relative standard deviation were calculated.

[0085] Table 1 Comparison of component detection results using different detection methods Test data show that the traditional single-wavelength detection method has large detection errors for each component due to spectral overlap and mutual interference. The detection error for carbonyl compounds reaches 37.8%, and the detection error for alcohol compounds reaches 28.1%. This is because at a wavelength of 2900 nanometers, multiple components absorb, resulting in mutual masking of signals and the inability to accurately identify the individual contributions of each component. The multi-band spectral analysis module of the present application achieves effective spectral separation by configuring a dedicated narrow-band optical filter 112 for each component. 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 good measurement reproducibility. The test method uses a Fourier transform infrared spectrometer as a reference standard, performs spectral scanning on the standard sample under the same conditions, and obtains the accurate concentration value of each component as the standard concentration. The experimental environment temperature is controlled at 25℃±1℃, the relative humidity is controlled at 50%±5%, and a baseline calibration is performed before each measurement.

[0086] The embodiments of the present application achieve simultaneous detection of multiple components in oil through a multi-band spectral analysis module, which solves the limitations of traditional single-wavelength detection methods. The multi-layer film interference structure of the narrow-band optical filter 112 provides excellent spectral selectivity. Each filter corresponds to the characteristic absorption wavelength of a specific component, avoiding the interference of spectral overlap. The time-division detection method simplifies signal processing and improves the reliability of measurement. The multivariate linear regression algorithm executed by the digital signal processor can accurately analyze the concentration of each component and obtain satisfactory results even in complex multi-component systems. Temperature compensation and dual-beam compensation further improve the accuracy and stability of the measurement.

[0087] In actual application scenarios, bubbles will be generated during the transportation of oil. The bubbles will cause scattering and refraction in the propagation path of mid-infrared light, interfering with spectral absorption measurement and causing random fluctuations and systematic errors in the measurement results.

[0088] To address the aforementioned technical issues, the mid-infrared sensor for oil quality monitoring disclosed herein is equipped with a cyclone separation chamber, a static settling chamber, and an ultrasonic defoamer in front of the sample inlet 114 of the oil sample reservoir 103. The inner wall of the cyclone separation chamber is spirally distributed, guiding the oil to produce a spiral flow trajectory. The centrifugal force generated by the spiral flow gathers bubbles of lower density toward the central axis of the cyclone separation chamber. The static settling chamber is connected to the outlet of the cyclone separation chamber. The cross-sectional area of ​​the static settling chamber is larger than that of the sample inlet tube. After the oil enters the static settling chamber from the cyclone separation chamber, the flow velocity decreases significantly. Driven by buoyancy, the bubbles move to the upper liquid surface of the static settling chamber and gather. The ultrasonic defoamer is mounted on the side wall of the static settling chamber. The transducer of the ultrasonic defoamer emits ultrasonic waves with a frequency of 40 kHz into the oil. The cavitation effect generated by the ultrasonic waves propagating in the oil can cause the tiny bubbles to rupture and dissipate. An exhaust valve is installed on the top of the static settling chamber. The exhaust valve is connected to the control circuit 111 through an electrical connection. The control circuit 111 controls the exhaust valve to open at a preset time interval to discharge the gas accumulated above the liquid surface from the static settling chamber. The mid-infrared sensor for oil quality monitoring in the present application also includes a liquid level sensor. The probe of the liquid level sensor 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 a preset value, the control circuit 111 adjusts the sample flow rate to ensure that the oil completely fills the subsequent spectral measurement optical path.

[0089] In actual application scenarios, when the oil flow rate changes or the pipeline pressure fluctuates, the oil thickness in the oil sample pool 103 changes, resulting in unstable light absorption path length, affecting the applicability of the Lambert-Beer law and the accuracy of concentration calculation.

[0090] In order to solve the above technical problems, the mid-infrared sensor for oil quality monitoring of the present application includes a liquid level sensor array, an overflow control valve and a pressure stabilizer. The liquid level sensor array is composed of three capacitive liquid level sensors, and the three liquid level sensors are evenly spaced along the vertical direction of the oil sample pool 103. The capacitor plate of each liquid level sensor is in contact with the oil. When the oil level changes, the capacitance value between the capacitor plate and the oil changes accordingly. The liquid level sensor converts the capacitance value change into an electrical signal output. The overflow control valve is installed at the sample outlet 115 of the oil sample pool 103. The overflow control valve includes an electric actuator and a variable aperture valve core. The drive shaft of the electric actuator is connected to the variable aperture valve core. The electric actuator establishes an electrical connection with the control circuit 111 through a signal transmission line. The pressure stabilizer is installed in the middle of the oil inlet pipeline. It includes a buffer chamber and an elastic diaphragm. The internal space of the buffer chamber is used to accommodate a portion of the oil. The elastic diaphragm divides the buffer chamber into an oil chamber and a gas chamber. When pressure pulsations occur in the pipeline, the elastic diaphragm elastically deforms, causing the volume of the oil chamber to change accordingly, thereby absorbing and alleviating the impact of the pressure pulsations on the downstream. The control circuit 111 includes 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 command to the electric actuator, which drives the variable aperture valve core to rotate, increasing or decreasing the flow aperture of the overflow control valve, and correspondingly increasing or decreasing the oil outflow rate, so that the liquid level in the oil sample reservoir 103 returns to the preset target range (the liquid level control error is within ±0.1 mm). Therefore, the corresponding optical path length change can be controlled within 0.5%.

[0091] In multi-component complex oil liquids, the concentrations of some components are very low but have a significant impact on the quality of the oil liquid. The existing narrow-band filter 112 may not provide sufficient detection sensitivity, resulting in insufficient signal-to-noise ratio for the detection of trace key components.

[0092] In order to solve the above technical problems, the present application adds a multi-pass reflection component and a signal accumulation processor to the multi-band spectral analysis module. The multi-pass reflection component is arranged in the optical path inside the oil sample pool 103, and the multi-pass reflection component is located between the light input end and the light output end of the oil sample pool 103. The multi-pass reflection component includes two oppositely arranged concave reflectors, the first concave reflector is fixedly mounted on the inner surface of the side wall of the oil sample pool 103, and the second concave reflector is fixedly mounted on the inner surface of the opposite side wall of the oil sample pool 103, and the reflective surfaces of the first concave reflector and the second concave reflector face each other. The central axis of the first concave reflector is parallel to but does not overlap with the central axis of the second concave reflector, and there is a vertical offset distance between the two central axes. After entering the light-input end of the oil sample cell 103, the incident light beam first reaches the reflective surface of the first concave reflector. The first concave reflector reflects the incident light beam to the second concave reflector, which then reflects the received light beam back to the first concave reflector. The light beam forms a round-trip light path between the first and second concave reflectors. Each time the light beam reflects from one concave reflector to the other, it passes through the oil medium between the two reflectors, and the light beam's propagation path in the oil takes on a zigzag, multi-segmented, broken-line shape. Due to the vertical offset between the central axes of the two concave reflectors, the light beam's propagation path undergoes slight spatial changes after each reflection. This allows the light beam to travel back and forth between the two reflectors multiple times without repeating the same light path. After multiple reflections, the light beam ultimately reflects from the second concave reflector and exits the light-output end of the oil sample cell 103, entering the subsequent narrow-band optical filter 112. The spacing between the two concave reflectors in the multi-pass reflection assembly can be adjusted via a threaded drive rod and a movable guide rail. The threaded drive rod is connected to the support frame of one of the concave reflectors, and the movable guide rail guides the concave reflector support frame to move in a predetermined direction. When the threaded drive rod and the movable guide rail change the spacing between the concave reflectors, the number of reflections of the light beam between the two reflectors and the total propagation distance of the light beam in the oil are correspondingly changed. A signal accumulation processor is integrated into the digital signal processor. The signal accumulation processor performs numerical accumulation and averaging operations on multiple consecutive measurement results of the same filter position. Each accumulation operation includes 64 independent measurement data. By increasing the number of measurement data samples, the signal-to-noise ratio of the final measurement result is improved. The control circuit 111 also includes an adaptive gain control module. The input end of the adaptive gain control module is connected to the signal output end of the thermopile detector 109. 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 amplifier amplification factor. When the signal intensity is strong, the adaptive gain control module reduces the amplifier amplification factor to avoid saturation distortion of the detector output signal.

[0093] The above is a detailed introduction to the embodiments of the present application. The contents of this specification should not be understood as limiting the scope of protection of the present application.

Claims

1. A mid-infrared sensor for oil quality monitoring, characterized in that: The mid-infrared sensor includes a light source module, a detector module, an oil sample pool, and a signal processing module. The light source module includes a thermal radiation light source and a collimating reflector. The detector module includes a thermopile detector and a focusing reflector. The oil sample pool is arranged in the optical path between the collimating reflector and the focusing reflector. The signal processing module is electrically connected to the thermopile detector. The mid-infrared sensor also includes: a multi-band spectral analysis module, comprising a filter wheel, a drive motor, and a plurality of narrow-band optical filters; the filter wheel is disposed in the optical path between the oil sample pool and the focusing reflector; the filter wheel is disc-shaped, and a plurality of mounting holes are provided on the circumference of the filter wheel; a narrow-band optical filter is disposed in each mounting hole; each narrow-band optical filter corresponds to a characteristic absorption wavelength of a specific component in the oil; the drive motor is connected to the filter wheel and is used to drive the filter wheel to rotate, so that the plurality of narrow-band optical filters sequentially enter the optical path; and A light intensity regulator is disposed in the optical path between the multi-band spectral analysis module and the thermopile detector. The light intensity regulator includes a variable aperture and a stepping driver. The variable aperture includes a disc-shaped aperture base and a plurality of light holes disposed on the aperture base. The stepping driver is connected to the variable aperture and is used to drive the variable aperture to rotate so that the light holes of different apertures rotate sequentially to the optical axis position.

2. The mid-infrared sensor according to claim 1, characterized in that The plurality of light-through holes are evenly distributed along the circumferential direction of the aperture base, the light-through holes are circular openings, the light-through holes pass through the thickness direction of the aperture base, and the apertures of the light-through holes are arranged in increasing order.

3. The mid-infrared sensor according to claim 1, characterized in that The mid-infrared sensor further includes a control circuit, which is electrically connected to the drive motor. The control circuit is used to send a pulse signal to the drive motor, and the drive motor is used to drive the filter wheel to rotate according to the pulse signal.

4. The mid-infrared sensor according to claim 3, characterized in that The stepper driver is electrically connected to the control circuit, and is used to receive a pulse signal from the control circuit. The control circuit is used to send a corresponding number of pulse signals to the stepper driver based on the transmittance data of the narrow-band optical filter currently located in the optical path, thereby driving the variable aperture to rotate to a corresponding light-clearing hole position.

5. The mid-infrared sensor according to claim 4, characterized in that: When the filter wheel is switched to the narrowband optical filter with higher transmittance, the control circuit drives the variable iris to rotate to a light-through hole position with a smaller aperture; and when the filter wheel is switched to the narrowband optical filter with lower transmittance, the control circuit drives the variable iris to rotate to a light-through hole position with a larger aperture.

6. The mid-infrared sensor according to claim 3, characterized in that: The multi-band spectral analysis module also includes a position encoder, which includes a code disk, a light-emitting diode and a photodetector. The code disk is coaxially mounted with the filter wheel. The position encoder is electrically connected to the control circuit. The position encoder outputs a first phase signal, a second phase signal and a zero position signal to the control circuit. The control circuit is used to determine the rotation direction of the filter wheel by detecting the phase relationship between the first phase signal and the second phase signal, calculate the rotation angle by counting the number of pulses, and perform position calibration through the zero position signal.

7. The mid-infrared sensor according to claim 3, characterized in that: The mid-infrared sensor also includes a photoelectric sensor, which is a through-beam photoelectric sensor. A notch is provided on the edge of the filter wheel, and each narrow-band optical filter corresponds to one notch. The photoelectric sensor is electrically connected to the control circuit.

8. The mid-infrared sensor according to claim 1, characterized in that The narrowband optical filter is a multilayer interference filter, comprising a transparent substrate layer and a multilayer dielectric film deposited on the surface of the transparent substrate layer, wherein the multilayer dielectric film is formed by alternating high refractive index layers and low refractive index layers.

9. The mid-infrared sensor according to claim 1, characterized in that: The collimating reflector is an off-axis parabolic reflector, the reflective surface of the off-axis parabolic reflector is coated with a metal reflective film, the thermal radiation light source is a silicon carbide rod light source, and the thermal radiation light source is arranged at the off-axis focal position of the off-axis parabolic reflector. The divergent light is reflected by the off-axis parabolic reflector to form a parallel light beam.

10. The mid-infrared sensor according to claim 1, characterized in that: The oil sample pool is further equipped with a heating element, a cooling element and a temperature controller. The heating element is a ceramic heating plate, the cooling element is a semiconductor cooling plate, and the temperature controller is electrically connected to the heating element and the cooling element.

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