Oil and gas lubrication monitoring system and monitoring method based on near-infrared spectroscopy

Abstract

The present invention discloses an oil and gas lubrication monitoring system based on near-infrared spectroscopy, comprising: a housing, an infrared emitting module, an infrared receiving module, a data acquisition card, and a computer. The housing is disposed at the end of the oil and gas lubrication pipeline, the infrared emitting module and the infrared receiving module are respectively mounted on the housing and disposed on opposite sides of the paint lubrication pipeline, the data acquisition card is respectively connected to the infrared receiving module and the computer, the infrared emitting module includes an infrared light source and a driving circuit, the infrared light source is connected to the driving circuit, and the infrared receiving module includes a photodetector, an amplifying circuit, and a filtering circuit, the amplifying circuit is respectively connected to the photodetector and the filtering circuit. The present invention reduces costs while making it easy to integrate the light source on a circuit board, resulting in a small size; adopts an infrared counter-radiation structure, has sensitive detection, and is very convenient to install; and monitors the operating status of the oil and gas lubrication system in real time online, promptly detecting faults and avoiding economic losses caused by insufficient lubrication of high-speed electric spindles.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas lubrication, and in particular to an oil and gas lubrication monitoring system and a monitoring method capable of real-time monitoring whether an oil and gas lubrication pipeline has a fault. Background Art

[0002] With the widespread adoption of high-speed electric spindles in industry, the requirements for bearing lubrication are becoming increasingly stringent. Oil-air lubrication, with its numerous advantages, such as energy conservation, environmental protection, and low oil consumption, is becoming the mainstream lubrication method. The basic principle of oil-air lubrication is to use high-speed, high-pressure air to drive the lubricating oil through the pipeline, forming a uniform annular flow to lubricate the spindle bearings. However, due to the extremely low oil consumption of oil-air lubrication, the pipeline diameter is small and the pipe wall is relatively thick. Typical lubrication pipelines have an inner diameter of 2.5mm and an outer diameter of 4mm. Even if the lubricating oil flow is interrupted, it is difficult to detect with the naked eye.

[0003] Currently, the main methods for detecting gas-liquid annular flow include conductivity probe testing, capacitance testing, and laser testing. Conductivity probe testing involves inserting a conductivity probe into the pipeline to measure the oil film thickness inside the pipe. Capacitance testing relies on the fact that the liquid and gas phases in two-phase flow have different dielectric constants. When the two phases mix, the equivalent dielectric constant between the capacitance sensor plates varies with the phase holdup and distribution, ultimately causing a change in capacitance. Laser testing primarily uses laser light to illuminate the pipeline and detect changes in the intensity of the transmitted light to indicate the flow of liquid within the pipe.

[0004] Conductivity probe testing, an invasive measurement method, interferes with fluid flow. Furthermore, conductivity probes are large, making them difficult to use in oil and gas lubrication pipes with a diameter of only 2.5 mm. Capacitance testing, because the dielectric constant varies significantly with the material, fluid, and environment, requires calibration under various operating conditions, making it less applicable. Laser testing requires a high-power laser transmitter probe, which increases its size and power consumption, making it difficult to integrate on small circuit boards. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a device which is small in size, easy to install, sensitive in response and can realize online monitoring of whether an oil and gas lubrication pipeline has a fault.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A near-infrared spectroscopy-based oil and gas lubrication monitoring system includes: a housing, an infrared transmitting module, an infrared receiving module, a data acquisition card, and a computer. The housing is disposed at the end of an oil and gas lubrication pipeline. The infrared transmitting module and the infrared receiving module are respectively mounted on the housing and disposed on opposite sides of the paint lubrication pipeline. The data acquisition card is connected to the infrared receiving module and the computer, respectively. The infrared transmitting module includes an infrared light source and a driving circuit, which are connected to the driving circuit. The infrared receiving module includes a photodetector, an amplifying circuit, and a filtering circuit, which are respectively connected to the photodetector and the filtering circuit.

[0008] The infrared light source is used to provide infrared light for detection, the driving circuit is used to drive the infrared light source so that the light emitted by the infrared light source is stable, the photodetector is used to receive the infrared light passing through the oil and gas lubrication pipeline and convert it into a current signal output, the amplifier circuit is used to convert the current signal output by the photodetector into a voltage signal, the filter circuit is used to filter the circuit noise amplified by the amplifier circuit during the amplification process, the data acquisition card is used to collect the analog voltage signal output by the infrared receiving module, and convert it into a digital signal and send it to the computer, and the computer is used to process the digital signal data and determine whether the oil and gas lubrication pipeline has a fault.

[0009] Preferably, filters are provided between the infrared emitting module and the oil and gas lubrication pipeline, and between the infrared receiving module and the oil and gas lubrication pipeline, respectively.

[0010] Preferably, the infrared emission module further includes a power supply filter circuit, and the power supply filter circuit is connected to the drive circuit.

[0011] Preferably, the infrared light source is formed by connecting a plurality of infrared light emitting diodes in parallel.

[0012] Preferably, the photodetector is a photodiode.

[0013] Preferably, the infrared receiving module further includes a dual-power supply filtering circuit, the amplifying circuit and the filtering circuit both include operational amplifiers, and the dual-power supply filtering circuit is respectively connected to the operational amplifier of the amplifying circuit and the operational amplifier of the filtering circuit.

[0014] A near-infrared spectroscopy-based oil-gas lubrication monitoring method, using the above-mentioned near-infrared spectroscopy-based oil-gas lubrication monitoring system, includes the following steps:

[0015] S1. Set the device parameters of the infrared transmitting module and the infrared receiving module according to the degree of infrared light absorption of the oil and gas lubrication pipeline and the oil. After assembling the oil and gas lubrication monitoring system, install it at the end of the oil and gas lubrication pipeline for monitoring.

[0016] S2. The infrared light source emits infrared light for detection. The photodetector receives the infrared light passing through the oil and gas lubrication pipeline and converts it into a current signal for output. The amplifier circuit converts the current signal output by the photodetector into a voltage signal. The filter circuit filters the circuit noise amplified by the amplifier circuit during the amplification process.

[0017] S3, the data acquisition card collects the analog voltage signal output by the infrared receiving module, converts it into a digital signal and sends it to the computer;

[0018] S4. The computer receives the digital signal data about the oil and gas lubrication pipeline transmitted by the data acquisition card, and processes it to generate a corresponding signal spectrum diagram;

[0019] S5. The computer determines whether the oil and gas lubrication system has a fault based on the corresponding signal spectrum diagram, and sets an indicator light to feedback the monitoring situation by lighting up.

[0020] Preferably, the processing flow of the digital signal data in S4 includes: removing baseline drift, wavelet transform signal decomposition, reconstructing each sub-band signal, calculating the mutual correlation coefficient between each sub-signal and the original signal, classifying and processing each sub-signal according to the mutual correlation coefficient, and performing wavelet reconstruction and power spectrum estimation on the processed sub-signals.

[0021] Preferably, the specific method of classifying and processing each sub-signal according to the mutual correlation coefficient is as follows: the frequency bands with mutual correlation values of 0.5≤r<1 are identified as obvious correlations and retained; the frequency bands with 0.1≤r<0.5 are identified as real correlations and subjected to wavelet threshold noise reduction processing, and the remaining frequency bands are directly discarded.

[0022] Preferably, a soft threshold denoising method is used to perform wavelet threshold denoising processing; a specific method of power spectrum estimation is to perform AR power spectrum estimation on the processed signal to find its peak frequency.

[0023] Compared with the existing technology, the present invention adopts an infrared light emitting diode instead of a laser emitter as the light source, which reduces the cost and makes the light source easy to integrate on the circuit board, greatly reducing the volume of the monitoring device; adopts an infrared counter-radiation structure to maintain a dark environment during the entire detection process, reducing the interference of ambient light, and it is very convenient to install by simply inserting the oil and gas lubrication pipeline into it; real-time online monitoring of the operating status of the oil and gas lubrication system can promptly detect faults in the operation of the oil and gas lubrication system, avoiding economic losses caused by insufficient lubrication of the high-speed electric spindle. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the structural block diagram of the oil and gas lubrication monitoring system.

[0025] Figure 2This is a structural diagram of the shell in the oil and gas lubrication monitoring system.

[0026] Figure 3 It is a near infrared spectrum diagram in the embodiment of the present invention.

[0027] Figure 4 Schematic diagram of an infrared emission module in an embodiment of the present invention.

[0028] Figure 5 Schematic diagram of an infrared receiving module in an embodiment of the present invention.

[0029] Figure 6 Schematic diagram of the processing flow of digital signal data in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The oil and gas lubrication monitoring system and monitoring method based on near infrared spectroscopy of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0031] See also Figure 1 and Figure 2 The present invention discloses an oil and gas lubrication monitoring system based on near-infrared spectroscopy. The oil and gas lubrication monitoring system based on near-infrared spectroscopy includes a shell, an infrared transmitting module, an infrared receiving module, a data acquisition card and a computer. The shell is arranged at the end of the oil and gas lubrication pipeline, the infrared transmitting module and the infrared receiving module are respectively installed in the shell and arranged on opposite sides of the paint lubrication pipeline, the data acquisition card is connected to the infrared receiving module and the computer respectively, the infrared transmitting module includes an infrared light source and a driving circuit, the infrared light source is connected to the driving circuit, the infrared receiving module includes a photodetector, an amplifying circuit and a filtering circuit, and the amplifying circuit is respectively connected to the photodetector and the filtering circuit.

[0032] See also Figure 1 and Figure 2 The oil and gas lubrication monitoring system based on near-infrared spectroscopy adopts a through-beam structure. The infrared emitting module is a circuit board integrating an infrared light source and a driver circuit. The infrared receiving module is a circuit board integrating a photodetector, an amplifier circuit, and a filter circuit. Filters are installed between the infrared emitting module and the oil and gas lubrication pipeline, and between the infrared receiving module and the oil and gas lubrication pipeline. The filters are installed in the housing. The data acquisition card is an NI acquisition card. The housing 1 has two symmetrical slots 11 at one end and a detection port 12 at the other end. The infrared emitting module and the infrared receiving module are installed in the slots 11 of the housing. The oil and gas lubrication pipeline is inserted into the detection port 12. The detection port 12 has slots at the upper and lower ends to facilitate the installation of the filters.

[0033] See also Figure 1The infrared light source is used to provide infrared light for detection, and the driver circuit is used to drive the infrared light source with a constant current to ensure the stability of the light emitted. The photodetector is used to receive infrared light passing through the oil and gas lubrication pipeline and convert it into a current signal output. However, since its output is very weak, in order to facilitate subsequent data acquisition, it is converted into a voltage signal of approximately 1-10V through an amplifier circuit. Since the amplifier circuit also amplifies circuit noise during the amplification process, a filter circuit is required to filter it. The NI acquisition card is used to collect the analog voltage signal output by the infrared receiving module, convert it into a digital signal, and send it to the computer. The computer is used to process the digital signal data and determine whether the oil and gas lubrication pipeline is faulty based on the processing results.

[0034] See also Figure 3 and Figure 4 The infrared transmitter module also includes a power supply filter circuit connected to the driver circuit. The infrared light source is composed of multiple infrared light-emitting diodes connected in parallel. The infrared receiver module's photodetector uses a photodiode. The module also includes a dual-power supply filter circuit. Both the amplifier and filter circuits include operational amplifiers, which are connected to the amplifier and filter circuits' operational amplifiers, respectively. Because oil-gas lubrication pipelines and oil have different absorption levels for infrared light, selecting an appropriate wavelength of infrared light can more fully reflect changes in the oil film within the pipeline.

[0035] See also Figure 1 The present invention also discloses a near-infrared spectroscopy-based oil and gas lubrication monitoring method, which uses the above-mentioned near-infrared spectroscopy-based oil and gas lubrication monitoring system, including the following steps:

[0036] S1. Set the device parameters of the infrared transmitting module and the infrared receiving module according to the degree of infrared light absorption of the oil and gas lubrication pipeline and the oil. After the oil and gas lubrication monitoring system is assembled, install it at the end of the oil and gas lubrication pipeline for monitoring.

[0037] S2. The infrared light source emits infrared light for detection. The photodetector receives the infrared light passing through the oil and gas lubrication pipeline and converts it into a current signal output. The amplifier circuit converts the current signal output by the photodetector into a voltage signal. The filter circuit filters the circuit noise amplified by the amplifier circuit during the amplification process.

[0038] S3. The data acquisition card collects the analog voltage signal output by the infrared receiving module, converts it into a digital signal and sends it to the computer.

[0039] S4. The computer receives the digital signal data about the oil and gas lubrication pipeline transmitted by the data acquisition card, and processes it to generate a corresponding signal spectrum diagram;

[0040] S5. The computer determines whether the oil and gas lubrication system has a fault based on the corresponding signal spectrum diagram, and sets an indicator light to feedback the monitoring situation by lighting up.

[0041] See also Figure 3 In this example, near-infrared spectroscopy was performed on a nylon tube made of PA11 and a Motorex brand 46# viscosity lubricating oil used in a high-speed electric spindle. The infrared wavelength was selected to ensure that the incident light intensity would not be excessively attenuated by the tube. Specifically, the tube had a low infrared light absorption rate at the target wavelength and a high transmittance. Furthermore, the oil had to have a high infrared light absorption rate, meaning a low transmittance. This ensures that changes in the oil thickness within the tube are fully reflected in the output light intensity. At an incident wavelength of 923 nm, the oil transmittance is lowest, and the tube transmission rate is above 70%. This wavelength of near-infrared light is suitable for use as the incident light.

[0042] See also Figure 4 The infrared wavelength was determined to be 923nm. Based on commercially available infrared diodes, a 940nm infrared LED was selected for the infrared transmitter module. The infrared light source consisted of three infrared diodes (LED1, LED2, and LED3) connected in parallel to ensure sufficient light coverage throughout the lubrication pipeline. 940nm filters were also installed between the two circuit boards that house the infrared transmitter and receiver modules and the pipeline to protect the circuit boards from oil contamination and reduce interference from ambient light. The filters only allow 940nm infrared light to pass through, while filtering out light of other wavelengths. The LM317 chip was selected as the voltage regulator chip U1 in the driver circuit. The voltage between its Vout and ADJ ports is maintained at a constant 1.25V. Resistor R1 generates the required constant current to ensure light source stability during illumination. The power supply filter circuit consists of capacitors C1 and C2 connected in parallel.

[0043] See also Figure 5 In the infrared receiver module, a PIN photodiode with the corresponding wavelength is selected to improve detection sensitivity. Based on the incident wavelength of 940nm determined previously, the VBP104FAS photodiode D1 is used as the photodetector, achieving a sensitivity of 0.79A / W at a peak wavelength of 980nm. The ADA4625-1 precision operational amplifier is used for the amplifier and filter circuits in the infrared receiver module, as is operational amplifier U2. This minimizes error and ensures detection sensitivity. The infrared receiver module also incorporates a filter circuit to filter out noise while meeting the target bandwidth.

[0044] See also Figure 6The computer processing flow of the collected digital signal data includes: removing baseline drift, wavelet transform signal decomposition, reconstruction of each sub-band signal, calculating the mutual correlation coefficient between each sub-signal and the original signal, classifying and processing each sub-signal according to the mutual correlation coefficient, and wavelet reconstruction and power spectrum estimation of the processed sub-signals.

[0045] For example, data collected at 0.40 MPa pressure is used to remove the DC component in the signal. This prevents errors in subsequent power spectrum peak estimation, which may occur when the peak frequency is 0 Hz. This is accomplished by fitting a fifth-order curve using the least squares method to determine the trend term. This term is then subtracted from the original signal to obtain the processed signal.

[0046] The processed signal is then decomposed into 32 sub-bands using a 5-layer wavelet packet decomposition. The principle of wavelet packet decomposition is as follows:

[0047] For a one-dimensional discrete packet, assume that the wavelet packet coefficient at position p in layer j is Then the wavelet packet coefficients of the low-frequency and high-frequency parts after decomposition corresponding to the j+1 layer are

[0048]

[0049]

[0050] On the contrary, for The reconstruction formula is:

[0051]

[0052] In order to find the specific frequency bands of noise and signal distribution, the cross-correlation coefficients between the 32 frequency bands and the original signal are decomposed and calculated.

[0053] According to the mutual correlation value, it can be seen that the signal is mainly concentrated in the low frequency band, and the 32 sub-frequency bands are classified and processed. Among them, the frequency bands with a mutual correlation value of 0.5≤r<1 are identified as obvious correlation and retained. The frequency bands with 0.1≤r<0.5 are identified as real correlation and wavelet threshold denoising is performed. The remaining frequency bands are directly discarded. The noise reduction effects of the four threshold rules are compared, and the respective noise reduction effects are obtained as shown in Table 1. In this embodiment, the Rigrsure soft threshold denoising method is used for wavelet threshold denoising.

[0054] Table 1 Comparison of noise reduction effects

[0055] Threshold rules Signal-to-noise ratio (dB) RMSE <![CDATA[E sn ]]> Rigrsure 11.1132 0.0513 99.52％ Heursure 2.3588 0.1405 59.18％ Sqtwolog 1.1309 0.1618 30.94％ Minimaxi 9.1586 0.0642 92.50％

[0056] Perform AR power spectrum estimation on the processed signal to find its peak frequency. Compared with traditional classical spectrum estimation, AR power spectrum estimation can maintain higher frequency domain resolution at lower sampling rates.

[0057] Let x(n) be the sequence to be converted and let u(n) be a white noise sequence. The AR model and the power spectrum of x(n) can be expressed as:

[0058]

[0059]

[0060] where σ 2 is the variance of the sequence u(n). k is the coefficient, which can be obtained by the Yule-Walker equation. p is the order of the AR model. The choice of p is mainly based on the Akaike Information Criterion (AIC), and its normalized expression is:

[0061] nAIC(p)=lnσ p 2 +2p / N

[0062] As the order p increases, the nAIC value decreases rapidly. When p is greater than 50, the nAIC value remains essentially unchanged. In this example, the AR model order is p = 50, and the corresponding nAIC value is -16.54620. The corresponding 50th-order AR regression curve is smooth and has a clear peak. Compared with the classical spectrum estimation, the power spectrum estimation based on the AR model clearly shows that its peak frequencies are f1 = 5.6875 Hz and f2 = 11.5 Hz.

[0063] Compare the signal spectrum diagrams of the oil-gas lubrication system after oil is cut off, the signal spectrum diagrams of the oil-gas lubrication system after gas is cut off, and the signal spectrum diagrams of the oil-gas lubrication system when it is operating normally. According to the differences in the signal spectrum diagrams when the oil-gas lubrication system is operating normally and in the fault state, determine whether there is a fault in the operation of the oil-gas lubrication system.

[0064] The method of judging whether the oil-gas lubrication system is in a fault state by comparing the signal spectrum is as follows:

[0065] A signal detection software program based on LabVIEW (a laboratory virtual instrument engineering platform) is written in the computer. The signal detection software program is equipped with a front panel with three color indicators: red, yellow, and blue. The red, blue, and yellow indicators light up according to the monitoring status of the oil and gas lubrication pipeline. The oil flow in the oil and gas lubrication pipeline is nothing more than the following three situations:

[0066] (1) There is no oil in the pipe or the oil does not flow. In these two cases, no oil can reach the lubrication point. At this time, the overall amplitude of the power spectrum is much smaller than the amplitude of the signal power spectrum when there is oil flowing, and the monitoring system lights up a red light to alarm.

[0067] (2) There is oil flow in the pipe but it is unstable. This mainly occurs when the air pressure is unstable. At this time, the oil distribution in the pipe is uneven in the axial direction and the oil flow rate is unstable. On the power diagram, it is reflected as a large difference in the peak frequency value of the signal before and after, and the monitoring system lights up yellow.

[0068] (3) The oil in the pipe flows evenly. At this time, the peak frequency of the power spectrum corresponding to the signal is obvious, and the frequency difference before and after is not large. The monitoring system lights up green.

[0069] To sum up, the present invention uses an infrared light emitting diode to replace the laser emitter as the light source, which reduces the cost and makes the light source easy to integrate on the circuit board, greatly reducing the volume of the monitoring device; adopts an infrared counter-radiation structure to maintain a dark environment during the entire detection process, reducing the interference of ambient light, and during installation, only the oil and gas lubrication pipeline needs to be inserted into it, which is very convenient to install; real-time online monitoring of the operating status of the oil and gas lubrication system can promptly detect faults in the operation of the oil and gas lubrication system, avoiding economic losses caused by insufficient lubrication of the high-speed electric spindle.

[0070] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications made under the technical spirit disclosed by the present invention should fall within the patent scope covered by the present invention.

Claims

1. An oil and gas lubrication monitoring system based on near infrared spectroscopy, characterized in that: include: A housing, an infrared transmitting module, an infrared receiving module, a data acquisition card, and a computer. The housing is located at the end of the oil and gas lubrication pipeline. The infrared transmitting module and the infrared receiving module are respectively installed in the housing and located on opposite sides of the paint lubrication pipeline. The data acquisition card is connected to the infrared receiving module and the computer, respectively. The infrared transmitting module includes an infrared light source and a drive circuit, which is connected to the drive circuit. The infrared receiving module includes a photodetector, an amplifying circuit, and a filtering circuit, which is connected to the photodetector and the filtering circuit, respectively. The infrared light source is used to provide infrared light for detection. The driving circuit is used to drive the infrared light source so that the light emitted by the infrared light source is stable. The photodetector is used to receive the infrared light passing through the oil and gas lubrication pipeline and convert it into a current signal for output. The amplifier circuit is used to convert the current signal output by the photodetector into a voltage signal. The filter circuit is used to filter the circuit noise amplified by the amplifier circuit during the amplification process. The data acquisition card is used to collect the analog voltage signal output by the infrared receiving module, convert it into a digital signal, and send it to the computer. The computer is used to process the digital signal data and determine whether the oil and gas lubrication pipeline has a fault. The oil and gas lubrication monitoring system based on near-infrared spectroscopy adopts a beam-type structure. The infrared transmitting module and the infrared receiving module are both integrated circuit boards. Filters are installed between the infrared transmitting module and the oil and gas lubrication pipeline, and between the infrared receiving module and the oil and gas lubrication pipeline. The filters are installed in the housing. The data acquisition card is an NI acquisition card. The infrared emission module also includes a power supply filter circuit, which is connected to the drive circuit. The infrared light source is formed by connecting multiple infrared light emitting diodes in parallel. The photoelectric detector adopts a photodiode, and the infrared receiving module also includes a dual-power filter circuit. The amplifying circuit and the filtering circuit both include operational amplifiers. The dual-power filter circuit is respectively connected to the operational amplifier of the amplifying circuit and the operational amplifier of the filtering circuit. Two symmetrical slots are provided at one end of the shell, and a detection port is opened at the other end. The infrared transmitting module and the infrared receiving module are respectively installed in the slots of the shell, and the oil and gas lubrication pipeline is inserted into the detection port. Card slots are provided at the upper and lower ends of the detection port to facilitate the installation of the filter.

2. A near-infrared spectroscopy-based oil-gas lubrication monitoring method, using the near-infrared spectroscopy-based oil-gas lubrication monitoring system according to claim 1, characterized in that: The following steps are involved: S1. Set the device parameters of the infrared transmitting module and the infrared receiving module according to the degree of infrared light absorption of the oil and gas lubrication pipeline and the oil. After assembling the oil and gas lubrication monitoring system, install it at the end of the oil and gas lubrication pipeline for monitoring. S2. The infrared light source emits infrared light for detection. The photodetector receives the infrared light passing through the oil and gas lubrication pipeline and converts it into a current signal for output. The amplifier circuit converts the current signal output by the photodetector into a voltage signal. The filter circuit filters the circuit noise amplified by the amplifier circuit during the amplification process. S3, the data acquisition card collects the analog voltage signal output by the infrared receiving module, converts it into a digital signal and sends it to the computer; S4. The computer receives the digital signal data about the oil and gas lubrication pipeline transmitted by the data acquisition card, and processes it to generate a corresponding signal spectrum diagram; S5. The computer determines whether the oil and gas lubrication system has a fault based on the corresponding signal spectrum diagram, and sets an indicator light to feedback the monitoring situation by lighting up.

3. The oil-gas lubrication monitoring method based on near infrared spectroscopy according to claim 2, characterized in that: The processing flow of digital signal data in S4 includes: removing baseline drift, wavelet transform signal decomposition, reconstructing each sub-band signal, calculating the cross-correlation coefficient between each sub-signal and the original signal, classifying and processing each sub-signal according to the cross-correlation coefficient, and performing wavelet reconstruction and power spectrum estimation on the processed sub-signals.

4. The oil-gas lubrication monitoring method based on near infrared spectroscopy according to claim 3, characterized in that: The specific method of classifying and processing each sub-signal according to the mutual correlation coefficient is as follows: the frequency bands with a mutual correlation value of 0.5≤r<1 are considered to be significantly correlated and retained; the frequency bands with a mutual correlation value of 0.1≤r<0.5 are considered to be truly correlated and subjected to wavelet threshold denoising, and the remaining frequency bands are directly discarded.

5. The oil-gas lubrication monitoring method based on near infrared spectroscopy according to claim 4, characterized in that: The soft threshold denoising method is used to perform wavelet threshold denoising. The specific method of power spectrum estimation is to perform AR power spectrum estimation on the processed signal and find its peak frequency.

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