A method for monitoring oil particles based on electrostatic coupling edge field sensor

Abstract

The present application belongs to the technical field of oil liquid abrasive particle monitoring and charge signal monitoring, and relates to a lubricating oil abrasive particle monitoring method based on an electrostatic coupling edge electric field sensor. The method relies on a double-channel acquisition path constructed by the electrostatic coupling edge electric field sensor, and cooperates with an interface circuit to realize identification of abrasive particle signals in lubricating oil and suppression of temperature interference. The method comprises the following steps: inputting original charge signals (abrasive particle electrostatic signals and edge electric field signals) output by the electrostatic coupling edge electric field sensor into a low-frequency processing channel and a high-frequency processing channel respectively after IV conversion and isolation processing, so as to realize effective separation of low-frequency abrasive particle signals and high-frequency edge electric field signals; monitoring oil temperature by the edge electric field sensor and generating a temperature compensation parameter; and correcting the amplitude of the abrasive particle signals in combination with a temperature correction model. The present application can maintain the stability and accuracy of the output signals under the condition of strong oil temperature fluctuation and background noise interference, significantly improve the signal-to-noise ratio and reduce the false alarm rate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil wear particle monitoring and charge signal monitoring, and particularly relates to a lubricating oil wear particle monitoring method based on an electrostatic coupling edge electric field sensor. BACKGROUND

[0002] In the running process of mechanical equipment such as aero-engines, wind power gearboxes and marine power systems, a large number of metal or non-metal wear particles will be generated in lubricating oil due to friction and wear between relative motion pairs. By monitoring the number, size and change trend of wear particles in lubricating oil, the wear degree and potential failure state of key components can be judged, which is an important means to realize equipment health monitoring and predictive maintenance.

[0003] Existing lubricating oil wear particle monitoring methods mainly include optical monitoring method, magnetic resistance monitoring method and the like, but in complex working conditions such as high temperature and high speed, they often face problems such as low sensing sensitivity, poor anti-interference performance and difficult structure arrangement. In comparison, the electrostatic coupling edge electric field sensor can generate an electrostatic disturbance signal when the wear particle passes through the sensing area, realize non-contact monitoring, and has advantages such as simple structure and strong adaptability.

[0004] However, the electrostatic wear particle signal has characteristics such as weak amplitude, short time and strong randomness, and is often mixed with high-frequency coupling signals formed by the excitation electric field. If the sensor output is not processed by high and low frequency separation, the low-frequency charge signal generated by the wear particle is easy to be submerged by the high-frequency background component, resulting in false detection and missed detection.

[0005] In addition, in the running process of aero-engines and high-speed transmission equipment, the oil temperature shows large fluctuation with the change of working conditions. The change of oil temperature will affect the dielectric properties and electrostatic accumulation ability of oil, so that the electrostatic signal amplitudes generated by wear particles of the same size at different temperatures are significantly offset, resulting in unstable monitoring results and even misjudgment.

[0006] For example, patent US10648361B2 adopts a method for monitoring wear particles in lubricating oil, which uses a sequentially arranged coil induction structure to monitor the magnetic disturbance signal of metal wear particles, that is, first monitors through a coil, and then compares the voltage difference between the two coils to determine the existence of wear particles, but this method can only identify ferromagnetic particles and cannot monitor non-metal wear particles, and the change of oil magnetic conductivity and viscosity in high temperature running environment will cause signal amplitude fluctuation, thereby affecting the monitoring accuracy.

[0007] Therefore, it is of great significance to study a lubricating oil wear particle monitoring method based on an electrostatic coupling edge electric field sensor. SUMMARY

[0008] The present application aims to provide a lubricating oil abrasive particle monitoring method based on electrostatic coupling edge electric field sensors, which realizes synchronous collection of abrasive particle electrostatic signals and oil temperature signals through the combined structure of electrostatic sensors and edge electric field sensors, and corrects the abrasive particle signals in combination with a temperature compensation model, thereby improving the monitoring stability and identification accuracy under the condition of oil temperature fluctuation.

[0009] To achieve the above-mentioned purpose, the present application adopts the following scheme:

[0010] A lubricating oil abrasive particle monitoring method based on electrostatic coupling edge electric field sensors, the electrostatic coupling edge electric field sensor comprises an upstream annular sensing electrode, a semi-arc excitation electrode and a downstream annular sensing electrode, the upstream annular sensing electrode and the downstream annular sensing electrode are arranged on the two sides of the semi-arc excitation electrode, as shown in Figure 2 The method comprises the following steps:

[0011] (1) The electrostatic coupling edge electric field sensor is installed in the lubricating oil circuit and the lubricating oil is circulated, and the lubricating oil abrasive particles (such as 0.3mm bearing steel particles) are injected into the injection port upstream of the sensor in the lubricating oil circuit;

[0012] (2) An excitation signal is applied to the semi-arc excitation electrode, when the lubricating oil abrasive particles pass through the electrostatic coupling edge electric field sensor, the electrostatic sensor composed of the two annular sensing electrodes can simultaneously monitor the two electrostatic signals upstream and downstream of the lubricating oil abrasive particles, and the edge electric field sensor composed of the semi-arc excitation electrode and the two annular sensing electrodes can monitor the two edge electric field signals upstream and downstream;

[0013] (3) The electrostatic signals and edge electric field signals output by the two annular sensing electrodes are converted into voltage signals through an IV (current-voltage) conversion circuit;

[0014] (4) The voltage signals of step (3) are sent into a low-frequency processing channel and a high-frequency processing channel in parallel; in the low-frequency processing channel, after the high-frequency noise is filtered out by a low-pass filter circuit, the lubricating oil abrasive particle electrostatic signal is amplified by an inverting amplifier circuit; in the high-frequency processing channel, the high-frequency component of the edge electric field response is extracted by a band-pass filter circuit, and the amplitude feature is extracted through an absolute value circuit and a peak detection circuit; since the amplitude of the abrasive particle electrostatic signal in the lubricating oil circuit is weak, if it is not filtered and compensated, it is easy to be submerged in noise and excitation signal, therefore, the present application improves the monitoring resolution by double-channel collection and filter separation through the low-frequency processing channel and the high-frequency processing channel; the double-channel can realize signal decoupling at the hardware level, which effectively reduces the probability of the abrasive particle signal being submerged compared with the traditional full-frequency amplification processing;

[0015] (5) The signals processed in steps (3) and (4) are collected by a data acquisition module (i.e. a data acquisition card, such as NIUSB-9234) and displayed and recorded on an upper computer.

[0016] The electrostatic coupling edge electric field sensor organically couples the principles of both electrostatic sensors and edge electric field sensors into one unit. The electrostatic sensor captures random pulse-type electrostatic signals generated when abrasive particles pass through the sensing electrode area. These signals have low frequency and weak amplitude, making them susceptible to interference. This invention extracts and amplifies these signals using a low-pass filter channel to ensure stable identification of abrasive events. The edge electric field sensor acquires the electric field change signal caused by oil temperature. Since the dielectric constant of the oil changes with temperature, its influence on the electric field distribution near the sensor electrodes can be converted into a temperature reading through a charge signal, providing a reference for subsequent temperature compensation. The electrostatic sensor and edge electric field sensor are integrated into a single structure, and the electrostatic coupling edge electric field sensor can be installed in the return oil line, bypass branch pipe, or circulation loop.

[0017] As a preferred technical solution:

[0018] As described above, in the method for monitoring lubricating oil wear particles based on an electrostatic coupling edge electric field sensor, in step (1), the lubricating oil is driven by an oil pump to circulate in the lubricating oil circuit, and the oil flow rate is adjusted by a throttle valve to simulate different working conditions.

[0019] In the above-described method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor, in step (2), a high-frequency excitation signal of 1V and 1MHz is applied to the semi-arc excitation electrode through a direct digital synthesizer (DDS).

[0020] In the above-described method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor, step (3) involves an IV conversion circuit comprising an operational amplifier and a feedback branch, wherein the feedback branch is a feedback resistor R connected in parallel. f With feedback capacitor C f Composition: The IV conversion circuit converts the charge signal detected by the sensor into a voltage signal. Since this voltage signal is relatively weak, an amplification stage is set up in the low-frequency channel. The inverting input of the operational amplifier receives the current signal output by the electrostatic coupling edge electric field sensor, and the feedback resistor R... f With feedback capacitor C f Both ends are connected to the output terminal and the inverting input terminal of the operational amplifier, respectively, and the non-inverting input terminal of the operational amplifier is grounded.

[0021] Feedback resistor R f The feedback capacitor C is 1~100 MΩ. f The value is 0.1~10 pF.

[0022] As described above, in the method for monitoring lubricating oil wear particles based on an electrostatic coupling edge electric field sensor, the voltage signal in step (3) is first sent into the low-frequency processing channel and the high-frequency processing channel in parallel, and then enters the isolation stage circuit. Through electrical isolation, signal transmission and power supply isolation are achieved, thereby improving anti-interference capability and preventing common-mode interference transmission.

[0023] In the above-described method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor, the cutoff frequency f of the low-pass filter circuit in step (4) is... lp The center frequency of the bandpass filter circuit is 1.5 kHz, which preserves the low-frequency voltage fluctuations generated when the abrasive particles pass through, while suppressing the high-frequency excitation coupling components; bp The frequency of the excitation signal is 0.5 to 1.5 times that of the frequency of the high-frequency electric field, so that the high-frequency electric field response can be extracted, while filtering out electrostatic fluctuations below this frequency and broadband interference above this frequency.

[0024] As described above, in the method for monitoring lubricating oil abrasive particles based on an electrostatic coupling edge electric field sensor, step (5) involves correcting the signal using a temperature compensation formula before it is acquired by the data acquisition module. The abrasive electrostatic signal, after the above processing, is highly susceptible to temperature and background noise. Therefore, this invention introduces a temperature compensation formula in the data analysis stage of step (5) to correct the abrasive signal amplitude and improve the stability of the identification threshold. The temperature compensation formula is as follows:

[0025] ;

[0026] Among them, V corr V represents the amplitude of the lubricating oil abrasive signal after temperature compensation. meas The measured amplitude of the lubricating oil abrasive signal is given by k, which is the temperature compensation coefficient, and T is the real-time temperature of the oil. ref The reference temperature is equivalent to the room temperature of aviation lubricating oil. Before testing, the oil temperature of aviation lubricating oil at room temperature can be monitored as a reference temperature.

[0027] The lubricating oil wear particle monitoring method based on the electrostatic coupling edge electric field sensor described above uses a temperature compensation coefficient k obtained through calibration experiments on standard lubricating oil wear particle samples under different temperature conditions.

[0028] The lubricating oil wear particle monitoring method based on an electrostatically coupled edge electric field sensor, as described above, sets a signal judgment threshold. When the amplitude of the temperature-compensated signal exceeds the threshold, an alarm signal or early warning information is output, thereby achieving immediate response and risk warning for abnormal wear conditions. The threshold can be determined based on a fixed amplitude, historical noise statistics, or an adaptive algorithm. When the amplitude of the temperature-compensated monitoring signal exceeds the threshold, the system automatically outputs an alarm signal or a host computer early warning information; the alarm form may include audible and visual prompts, data marking, remote communication, or shutdown protection triggering.

[0029] Invention principle:

[0030] Existing lubricating oil abrasive monitoring technologies commonly employ inductive sensors. These sensors rely on the abrasive particles' disturbance of a magnetic field, thus only responding to ferromagnetic or magnetically conductive metallic abrasive particles and failing to monitor non-metallic particles (such as ceramics and non-magnetic coated particles), limiting their application. Current technologies typically use electrostatic sensors to monitor abrasive particles, utilizing triboelectric properties to identify non-metallic particles. However, this electrostatic monitoring method has a critical drawback: during the operation of aero-engines or high-speed gearboxes, the high-speed movement of bearings causes significant changes in lubricating oil temperature. These temperature variations directly affect the dielectric constant and charge accumulation capacity, resulting in different electrostatic response amplitudes for the same abrasive particles at different temperatures. This leads to significant fluctuations in monitoring results, making it difficult to guarantee accuracy. For example, one study (Experiments on enhancing the particle charging performance of an electrostatic precipitator. Aerosol Air Qual. Res. 19, 1411–1420. 2019.) suggests that the average charge of particles increases significantly with increasing temperature, causing deviations in the electrostatic response amplitude of abrasive particles at different temperatures.

[0031] This invention employs an electrostatically coupled edge electric field sensor, simultaneously outputting two signals:

[0032] 1. The low-frequency electrostatic signal channel is used to monitor transient pulses generated by the charging of abrasive particles;

[0033] 2. The high-frequency edge electric field signal channel is used to monitor the change in dielectric constant caused by oil temperature.

[0034] This invention utilizes edge electric field signals to estimate oil temperature and combines this with a temperature compensation model to correct the abrasive monitoring signal in real time, fundamentally eliminating the impact of temperature fluctuations on signal amplitude. Therefore, this invention not only solves the problem of existing technologies being unable to monitor non-metallic abrasive particles, but also addresses the instability of monitoring results caused by changes in oil temperature in existing electrostatic sensors, thus improving the accuracy and reliability of lubricating oil abrasive monitoring.

[0035] Beneficial effects:

[0036] (1) The present invention provides a method for monitoring lubricating oil abrasive particles based on an electrostatic coupling edge electric field sensor. The method uses an electrostatic sensor to monitor the charge disturbance formed when abrasive particles pass through, and uses an edge electric field sensor to extract the oil temperature change signal. Combined with the IV conversion, isolation circuit and parallel filtering channel in the interface circuit, the sensor output signal is separated into high and low frequencies before entering the analysis stage, so as to ensure that the abrasive particle signal and the excitation background signal are physically decoupled.

[0037] (2) The lubricating oil wear particle monitoring method based on electrostatic coupling edge electric field sensor of the present invention is different from the monitoring method that relies only on a single frequency band or directly amplifies the signal. It can perform high and low frequency signal separation and combine temperature compensation mechanism to enhance signal recognition ability, suppress environmental interference and improve monitoring reliability. It can be used to monitor the oil flow rate and sensor installation effect, and has self-diagnostic function to avoid identification errors caused by abnormal coupling interference.

[0038] (3) The present invention provides a lubricating oil abrasive monitoring method based on an electrostatic coupling edge electric field sensor. The method uses an electrostatic coupling edge electric field sensor to monitor metal and non-metal particles by utilizing the electrostatic signal generated when the abrasive particles pass through. A temperature compensation model is established by the coupling relationship between the oil dielectric constant and temperature, which effectively eliminates the influence of oil temperature changes on the monitoring results, thereby significantly improving the accuracy and stability of lubricating oil abrasive monitoring.

[0039] (4) The lubricating oil wear particle monitoring method based on electrostatic coupling edge electric field sensor of the present invention is applicable to the operating conditions of lubrication system in different temperature ranges, including the heating stage of aero-engine, steady-state operation of high-speed gearbox, steady-state operation of ship power system, etc. In engineering applications, it can significantly improve the signal-to-noise ratio and identification accuracy, and at the same time has good repeatability, real-time performance and environmental adaptability, and can be used for health monitoring of equipment with long cycle operation. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the lubricating oil circuit of the present invention;

[0041] Figure 2 This is a flowchart illustrating the usage procedure of the lubricating oil abrasive monitoring method of the present invention;

[0042] Figure 3 A schematic diagram of the electrostatic coupling edge electric field sensor structure of the present invention;

[0043] Figure 4 The excitation signal diagram generated by the direct digital synthesizer of this invention;

[0044] Figure 5 Waveform of electrostatic signal of lubricating oil abrasive particles sensed by the upstream annular induction electrode of the present invention;

[0045] Figure 6 Waveform of electrostatic signal of lubricating oil abrasive particles sensed by the downstream annular induction electrode of the present invention;

[0046] Figure 7 The consistency waveform diagram of the electrostatic signal of lubricating oil abrasive particles sensed by the upstream annular sensing electrode and the downstream annular sensing electrode of the present invention;

[0047] Figure 8 The output amplitude diagram of the edge electric field signal at different oil temperatures according to the present invention;

[0048] Figure 9 This invention relates to the relationship between lubricating oil temperature variation and interface circuit noise floor.

[0049] Figure 10 The circuit schematic of the IV conversion circuit of the present invention;

[0050] Figure 11 This is a circuit diagram of the low-pass filter circuit of the present invention;

[0051] Figure 12 This is a circuit schematic diagram of the bandpass filter circuit of the present invention;

[0052] Figure 13 This is a circuit diagram of the peak detection circuit of the present invention;

[0053] Among them, 1-Lubricating oil tank I, 2-Abrasive filter I, 3-Lubricating oil pump, 4-Relief valve, 5-Pressure gauge, 6-Throttle valve, 7-Flow meter, 8-Stop valve I, 9-Stop valve II, 10-Particle dispenser, 11-Stop valve III, 12-Electrostatic coupling edge electric field sensor, 13-Abrasive filter II, 14-Lubricating oil tank II, 15-Hydraulic pipe, 16-Lubricating oil abrasive particles, 17-Upstream annular sensing electrode, 18-Semi-arc excitation electrode, 19-Downstream annular sensing electrode. Detailed Implementation

[0054] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0055] A method for monitoring abrasive particles in lubricating oil based on an electrostatically coupled edge electric field sensor, such as... Figure 3 As shown, the electrostatic coupling edge electric field sensor includes an upstream annular sensing electrode 17, a semi-circular excitation electrode 18, and a downstream annular sensing electrode 19. The monitoring method includes the following steps:

[0056] (1) Install the electrostatic coupling edge electric field sensor in the lubricating oil circuit, drive the lubricating oil (such as 4050 aviation lubricating oil) to circulate in the lubricating oil circuit through the oil pump, and use the throttle valve to adjust the oil flow rate. At the same time, inject lubricating oil abrasive particles 16 into the injection port of the lubricating oil circuit.

[0057] like Figure 1 As shown, the lubricating oil circuit includes lubricating oil tank I1, abrasive filter I2, lubricating oil pump 3, overflow valve 4, pressure gauge 5, throttle valve 6, flow meter 7, shut-off valve I 8, shut-off valve II 9, particle dispenser 10, shut-off valve III 11, electrostatic coupling edge electric field sensor 12, abrasive filter II 13, lubricating oil tank II 14, and hydraulic pipe 15;

[0058] To ensure that particles enter from the designated inlet, before injecting the abrasive particles into the lubricating oil, shut-off valve I 8 is closed, while shut-off valves II 9 and III 11 are opened simultaneously, allowing the oil to flow through the particle dispenser. Then, the abrasive particles are injected into the lubricating oil at the injection port of the particle dispenser located upstream of the sensor. To avoid interference from non-target abrasive particles, abrasive filter I 2 is installed upstream of the lubricating oil tank, and abrasive filter II 13 is also installed downstream of the sensor, ensuring that the particles flowing through the sensor each time are abrasive particles injected from the injection port of the particle dispenser.

[0059] (2) For example Figure 4 As shown, a high-frequency excitation signal of 1V and 1MHz is applied to the semi-arc excitation electrode by a direct digital synthesizer. When the lubricating oil abrasive particles pass through the electrostatic coupling edge electric field sensor, the electrostatic sensor composed of two ring induction electrodes can simultaneously monitor the two electrostatic signals upstream and downstream of the lubricating oil abrasive particles. The edge electric field sensor composed of the semi-arc excitation electrode and the two ring induction electrodes can monitor the two edge electric field signals upstream and downstream.

[0060] The electrostatic signal waveforms of lubricating oil abrasive particles sensed by the upstream and downstream annular induction electrodes are shown below. Figure 5 As shown, Figure 6 As shown;

[0061] like Figure 7 The figure shows the consistency waveform of the electrostatic signals of lubricating oil abrasive particles sensed by the upstream and downstream annular sensing electrodes. This figure illustrates the response process of the upstream and downstream sensing electrodes in the same time domain when the same lubricating oil abrasive particle passes through the sensing area. It can be clearly observed that the two signals are highly consistent in waveform shape, but there is a certain delay on the time axis. This time difference reflects the transmission time required for the abrasive particle to pass through the spatial distance between the upstream and downstream sensing electrodes in the oil flow direction, verifying the continuity and identity of the signal source. Therefore, the signals monitored by the upstream and downstream electrodes both originate from the same abrasive particle event, indicating that the sensing structure of this invention has good signal consistency and repeatability, providing a reliable basis for the spatial positioning and motion trajectory analysis of the abrasive particle.

[0062] like Figure 8 The figure shows the output amplitude relationship of the edge electric field signal of the present invention at different oil temperatures. As can be seen from the figure, the output voltage decreases monotonically with increasing temperature, and the linear fitting equation is: Correlation coefficient The result indicates a linear relationship between the two. This is because after heating, the density and viscosity of 4050 aviation lubricating oil decrease, the intermolecular distance increases, and the polarization ability weakens, resulting in a decrease in dielectric constant and a corresponding decrease in the amplitude of the edge electric field induced signal. This result verifies the influence of oil temperature on the edge electric field signal and provides a basis for the establishment of a subsequent temperature compensation model.

[0063] like Figure 9 The figure shows the relationship between the noise floor of the interface circuit of the present invention and the temperature under different oil temperatures. It can be seen that as the temperature changes between 25°C and 65°C, the noise floor voltage of the interface circuit remains at about 0.2mV with a very small fluctuation range. This indicates that the interface circuit designed in this invention has excellent stability and anti-interference ability over a wide temperature range. The effect of temperature change on the noise floor of the circuit is negligible, thus ensuring the reliability and repeatability of lubricating oil abrasive signal monitoring.

[0064] (3) The electrostatic signal and edge electric field signal output from the two ring induction electrodes are converted into voltage signals through the IV conversion circuit;

[0065] like Figure 10 As shown, the IV conversion circuit consists of operational amplifier U1 (model OPA842) and feedback resistor R. f (10MΩ), feedback capacitor C f Composed of a 5pF capacitor and several power supply decoupling capacitors; the abrasive current signal I output by the electrostatic coupling edge electric field sensor. q Through capacitor C x After coupling, the input is given to the inverting input of operational amplifier U1, the non-inverting input is grounded, and the output is connected to R. f With C f The parallel feedback is sent to the inverting input, forming a transimpedance amplifier structure. R f Used to set the current-to-voltage conversion gain, C f This circuit is used to suppress high-frequency noise and stabilize the system phase. Capacitors C1 and C2 are connected in parallel to ground to filter out input noise. Capacitors C3 and C4 are connected to the -12V power supply, and capacitors C5 and C6 are connected to the +12V power supply, forming a dual-power supply filter network to suppress power supply ripple and transient interference. This circuit achieves high-impedance input, low-noise voltage conversion, and wideband response characteristics for the sensor output current signal, providing a stable input for subsequent signal processing.

[0066] Since the current flowing through the inductive electrode is equal to the sum of the currents flowing through the feedback resistor Rf and the feedback capacitor Cf, we can conclude that:

[0067] ;

[0068] in, The voltage signal output by the IV conversion circuit. This is the voltage signal for the abrasive particles. The voltage signal of the edge electric field. This represents the current signal of the abrasive particles. The imaginary unit, The angular frequency of the electrostatic signal. The angular frequency of the edge electric field signal. This represents the edge electric field signal.

[0069] (4) The voltage signal from step (3) is sent into the isolation stage circuit to achieve signal transmission and power supply isolation through electrical isolation;

[0070] The isolation stage circuit consists of an operational amplifier (model OPA842), resistors, and power supply filter capacitors. The input signal is connected to the non-inverting input of the operational amplifier via resistors, and the output is connected to the inverting input via feedback resistors, forming a gain-isolated amplification structure. A current-limiting resistor is provided at the input to protect the amplifier's input stage. Power supply filter capacitors are connected to the positive and negative power supply terminals respectively for power supply decoupling and noise filtering. This circuit effectively blocks common-mode interference and ground potential fluctuations, improving the system's anti-interference performance and signal transmission stability, providing a clean and stable input signal for subsequent filtering and amplification modules. The isolation stage circuit includes a first isolation stage circuit and a second isolation stage circuit; the output of the IV conversion circuit is connected to the inputs of both the first and second isolation stage circuits.

[0071] (5) Send the voltage signal from step (4) into the low-frequency processing channel and the high-frequency processing channel in parallel;

[0072] In the low-frequency processing channel, high-frequency noise is filtered out by a low-pass filter circuit, and then amplified by an inverting amplifier circuit to obtain the electrostatic signal of lubricating oil abrasive particles.

[0073] Low-pass filter circuit such as Figure 11 As shown, the low-pass filter circuit consists of operational amplifier U3 (model OPA842), resistor R9, and resistor R 10 and capacitor C 11 ~C 16 Composition. The input signal Uiv passes sequentially through resistor R9 and resistor R. 10 The series connection is then fed into the non-inverting input of operational amplifier U3. Specifically, R9 and R... 10 The capacitor C in parallel between 11 With grounding capacitor C 12Together they form a second-order low-pass filter network, used to suppress high-frequency components and retain low-frequency electrostatic signals generated by abrasive particles.

[0074] A feedback capacitor C is set in the feedback loop of operational amplifier U3. 11 It is used to suppress high-frequency components, allowing low-frequency signals to be amplified smoothly, while optimizing the frequency response and stability of the circuit. Capacitor C 13 C 14 Connect to the -12V power supply terminal, capacitor C 15 C 16 Connected to the +12V power supply, these capacitors serve as power supply decoupling and bypass capacitors, respectively, to suppress power supply ripple and transient noise, preventing power supply interference from entering the signal amplification path. A feedback loop is a closed signal path that connects the output and input (inverting or non-inverting) of an operational amplifier via feedback elements (such as capacitors and resistors), sending a portion of the output signal back to the input, allowing the output to influence the input.

[0075] The input signal is injected through port Uiv, and then passes through R9 and C. 11 The pre-stage network forms the initial filtering stage, which is then processed by R. 10 Grounding capacitor C 12 The composite filter further suppresses high-frequency components. The capacitive element C in the feedback loop... 11 Effective control of system bandwidth and phase characteristics enhances high-frequency interference suppression capability. Its cutoff frequency... The theoretical expression is:

[0076] ;

[0077] in, This is the cutoff frequency of the low-pass filter circuit; R9 and R 10 For the filter resistor, C 11 and C 12 For filtering capacitors; the electrostatic signal of oil is a low-frequency signal, with a frequency below 500Hz, so it is preferable to set the cutoff frequency of the low-pass filter to 1.5 kHz to extract the electrostatic signal of the abrasive particles;

[0078] By properly configuring R9 and R 10 C 11 With C 12 The parameters are set so that the cutoff frequency of the low-pass filter circuit is 1.5kHz, which can effectively extract the low-frequency electrostatic signal generated when lubricating oil abrasive particles pass through the sensing area, while attenuating the excitation signal and high-frequency interference from the environment, thereby achieving stable extraction and subsequent amplification of the abrasive particle signal.

[0079] The inverting amplifier circuit consists of an operational amplifier (model OPA842) and resistors (R). 11 R 12 It consists of a power supply filter capacitor and an input signal (U).l1 After being filtered by a low-pass filter circuit, it passes through a resistor (R). 11 A 1KΩ resistor is input to the inverting input of the operational amplifier, while the non-inverting input is grounded. An adjustable resistor R is set in the feedback loop. 12 (10kΩ) is used to provide negative feedback and adjust the voltage gain, thus forming a classic inverting amplifier circuit topology with theoretically adjustable voltage gain;

[0080] Its gain formula is:

[0081] .

[0082] In the high-frequency processing channel, a bandpass filter circuit is used to extract the high-frequency components of the edge electric field response, and the amplitude characteristics are extracted by an absolute value circuit and a peak detection circuit.

[0083] Bandpass filter circuit, such as Figure 12 As shown, the bandpass filter circuit includes an operational amplifier (model OPA603). The input signal (Uiv) first passes through resistor R. 13 (1.5kΩ) and capacitor C 21 A first-order high-pass filter network consisting of (100pF) capacitors is then applied, followed by capacitor C. 22 (100pF) and resistance R 14 A first-order low-pass filter network (3kΩ) is constructed to optimize the frequency response and suppress high-frequency interference. The cutoff frequency of the band-pass filter circuit is determined by the RC time constant, and its center frequency fbp is:

[0084] ;

[0085] The center frequency of the bandpass filter circuit is set to 1 MHz, and the passband range is 0.6 MHz to 1.6 MHz. The center frequency f of the bandpass filter circuit is... bp Equal to the excitation signal frequency;

[0086] The bandwidth BW of the bandpass filter circuit is determined by the feedback resistor R. 15 Feedback resistor R 17 and input resistance R 13 and grounding capacitor C 21 It is confirmed that its expression is:

[0087] ;

[0088] The upper and lower cutoff frequencies are respectively:

[0089] , ;

[0090] in, The lower cutoff frequency, Upper limit cutoff frequency;

[0091] By R 13 (1.5kΩ), R 17 (510Ω) and R 15 A feedback network consisting of 510Ω resistors is used to set the circuit gain, and its gain expression is as follows:

[0092] ;

[0093] The output of the bandpass filter circuit is connected to the input of the absolute value circuit, the output of the absolute value circuit is connected to the input of the peak detection circuit, and the output of the peak detection circuit is connected to the data acquisition module to acquire the edge electric field signal and upload it to the host computer system.

[0094] Absolute value circuits are typically composed of diodes and operational amplifiers (model OPA842), which flip the negative half-cycle of the input signal to the positive half-cycle and output a unidirectional pulsating DC signal to facilitate the subsequent peak detection circuit to capture the peak point.

[0095] Peak detection circuit such as Figure 13 As shown, the peak detection circuit includes a peak detection and peak hold module. The peak hold module consists of a rectifier unit (U9 + D4) and a peak hold unit (D3 + C). 48 + R 30 ) and voltage buffer unit (U 10 It consists of D3 positive electrode and C 48 The upper connection point is a peak hold node, whose voltage is used to store the peak value information of the input signal; it receives the signal output from the absolute value circuit. As a driving signal It is directly connected to the non-inverting input of operational amplifier U9 (model OPA842); U9 is powered by a dual ±12V power supply, with its positive and negative power supply terminals connected to decoupling capacitors C and C, respectively. 40 C 41 (+12V) and C 42 C 43 (-12V) is filtered and regulated to suppress the impact of power supply noise on detection accuracy. The output of U9 is connected to the negative terminal of diode D4, and the positive terminal of D4 is connected to the peak hold node. U9 and D4 form a precision rectifier unit to accurately capture the positive peak value of the input signal. The voltage from the rectifier unit enters the peak hold node through the unidirectional conducting element D3, and is then controlled by the energy storage capacitor C. 48 Storing peak charge completes peak hold; resistance R 30 Connected between two detection paths, used to limit C 48This improves the charging and discharging current and enhances dynamic stability during peak capture and decay. The node voltage is then maintained and fed into operational amplifier U. 10 The non-inverting input terminal of (model OPA842), U 10 Operating in voltage follower mode, its power supply terminals are connected by capacitors C and C respectively. 44 C 45 (+12V) and C 46 C 47 (-12V) decoupling filter to ensure output stability. (via U) 10 The stable peak DC voltage obtained after buffering, Uc is the output signal of the peak detection circuit, and the entire circuit is rectified by U9+D4 and D3+C. 48 Peak performance and U 10 The buffered output enables highly sensitive and stable monitoring of the peak value of the input signal.

[0096] The peak detection circuit captures and holds the instantaneous peak value of the input signal through the charging and discharging characteristics of diodes and capacitors. A diode is added between the input and output of this module; this not only provides effective input buffering but also prevents negative saturation, ensuring that the input processing can keep up with changes in the input signal voltage. Random noise (such as high-frequency glitches) in the signal is filtered out through the charging and discharging characteristics of the capacitor, retaining only the effective peak information and converting it into a stable DC level output. Its output voltage expression is:

[0097] ;

[0098] in, The output voltage signal of the absolute value circuit is the input signal of the peak detection circuit. After peak holding, this signal can reflect the instantaneous maximum amplitude of the input signal, which can be used for subsequent amplitude analysis and quantitative signal processing.

[0099] (6) The signals processed in steps (3) and (5) are corrected using a temperature compensation formula, and then collected by the data acquisition module (i.e., data acquisition card, such as NI USB-9234) and displayed and recorded on the host computer; the temperature compensation formula is as follows:

[0100] ;

[0101] Among them, V corr V represents the amplitude of the lubricating oil abrasive signal after temperature compensation. meas The measured amplitude of the lubricating oil abrasive signal is given by T, where T is the real-time temperature of the oil. ref The reference temperature is 0.037; k is the temperature compensation coefficient, which is obtained through calibration experiments on standard lubricating oil abrasive samples under different temperature conditions.

[0102] By setting a signal judgment threshold (threshold = 5mV), when the amplitude of the temperature-compensated signal exceeds the threshold, an alarm signal or warning information is output.

[0103] The NI USB-9234 data acquisition card (NI acquisition card) features four synchronous analog input channels, each supporting IEPE excitation output, with a maximum sampling rate of 51.2 kS / s, meeting the needs of high-frequency signal acquisition. Its 24-bit resolution analog-to-digital converter (ADC) ensures high-precision data acquisition. An integrated anti-aliasing filter automatically adapts to the sampling rate, effectively suppressing aliasing effects and improving data quality. It is suitable for dynamic signal acquisition and analysis in laboratory and industrial environments. Compatible with LabVIEW and NI DAQmx software, it enhances flexibility and ease of use, facilitating real-time data acquisition, processing, and visualization.

[0104] By setting the block diagram in LabVIEW, the acquisition module's program can effectively separate low-frequency and high-frequency signals. In this experiment, the NI acquisition card directly receives the output of the interface circuit of the electrostatic coupling edge electric field sensor, outputs the acquired signal to the PC, and displays the monitored signal waveform on the front panel window.

[0105] The electrostatic induction component of the electrostatic coupling edge electric field sensor effectively acquires the characteristics of metallic and non-metallic abrasive particles in the lubricating oil circuit. When the oil temperature in the lubricating oil circuit changes, the edge electric field effect can monitor the change in the dielectric constant of the lubricating oil circuit when the oil temperature changes. and The relationship between the change in temperature and the equation is:

[0106] ;

[0107] ;

[0108] In the formula, The dielectric constant of the oil at the initial temperature is . , Let be the dielectric constant of the upstream and downstream edge electric field effects when the oil temperature changes by Δt. is the temperature coefficient of the dielectric constant.

[0109] Edge electric field capacitance C c1 C c2 They are represented by the following formulas respectively:

[0110] ;

[0111] ;

[0112] In the formula, ε0 is the vacuum dielectric constant, ε1 and ε2 are the corresponding composite dielectric constants in the edge electric field, γ is the edge proportionality coefficient, L is the electrode length, and θ is the arc of the arc electrode.

[0113] The sensor's output terminal is connected to the interface circuit, therefore IV output voltage U i It can be represented by the following formula:

[0114] ;

[0115] In the formula U i Q is the sum of the abrasive particle signal voltage and the edge electric field signal voltage output by the IV conversion circuit, which are connected upstream and downstream of the sensor to interface circuit 1 and interface circuit 2 respectively. i To input the charge carried by the abrasive particles in the lubricating oil, C f This is the feedback capacitor.

[0116] The charge Q of lubricating oil abrasive particles i The formula is expressed as follows:

[0117] ;

[0118] In the formula C ci V represents the electric field capacitance at the upstream and downstream edges of the sensor. exc This represents the peak value of the excitation signal (excitation voltage).

[0119] because , Therefore, it can be inferred that: .

[0120] From all the above formulas, the output voltage U at terminal IV can be obtained. i With respect to the dielectric constant ε of the oil ti Edge electric field capacitance C ci The relationship between temperature change Δt and temperature change is expressed by the following formula:

[0121] .

[0122] Table 1

[0123] Dimensions (mm) Temperature (°C) Total number of particles Number of detections Detection rate (%) 0.3 25 30 27 90 0.5 25 30 29 96.7 0.7 25 30 30 100 1.0 25 30 30 100

[0124] This embodiment discloses the complete implementation details of a lubricating oil abrasive particle monitoring method based on an electrostatically coupled edge electric field sensor and a front-end interface circuit, including device parameters, filter cutoff frequency, judgment threshold, temperature compensation coefficient, and calibration procedure. Following the above procedure, 30 single-particle injection tests were conducted on lubricating oil abrasive particles (bearing steel particles) with four particle sizes of 0.3 mm, 0.5 mm, 0.7 mm, and 1.0 mm at 25°C and a flow rate of 1 L / min. The results are shown in Table 1 above, with detection rates of 90.0%, 96.7%, 100%, and 100%, respectively. The experimental results demonstrate that this invention can achieve higher detection rates under various particle size conditions, significantly improving the accuracy and reliability of lubricating oil abrasive particle monitoring.

Claims

1. A method for monitoring abrasive particles in lubricating oil based on an electrostatically coupled edge electric field sensor, wherein the electrostatically coupled edge electric field sensor comprises an upstream annular sensing electrode, a semi-arc excitation electrode, and a downstream annular sensing electrode, characterized in that... Includes the following steps: (1) Install the electrostatic coupling edge electric field sensor in the lubricating oil circuit and keep the lubricating oil circulating, and then inject the lubricating oil abrasive particles; (2) When an excitation signal is applied to the semi-circular excitation electrode, when the lubricating oil abrasive particles pass through the electrostatic coupling edge electric field sensor, the electrostatic sensor composed of two ring induction electrodes can simultaneously monitor the two electrostatic signals upstream and downstream of the lubricating oil abrasive particles, and the edge electric field sensor composed of the semi-circular excitation electrode and the two ring induction electrodes can monitor the two edge electric field signals upstream and downstream. (3) The electrostatic signal and edge electric field signal output from the two ring induction electrodes are converted into voltage signals through the IV conversion circuit; (4) Send the voltage signal from step (3) into the low-frequency processing channel and the high-frequency processing channel in parallel; In the low-frequency processing channel, a low-pass filter circuit is used to filter out high-frequency noise, and then an inverting amplifier circuit is used to amplify the electrostatic signal of the lubricating oil abrasive particles. In the high-frequency processing channel, a band-pass filter circuit is used to extract the high-frequency components of the edge electric field response, and then the amplitude characteristics are extracted by an absolute value circuit and a peak detection circuit. (5) The signals processed in steps (3) and (4) are corrected using a temperature compensation formula before being acquired by the data acquisition module and displayed and recorded on the host computer; the temperature compensation formula is as follows: ； Among them, V corr V represents the amplitude of the lubricating oil abrasive signal after temperature compensation. meas The measured amplitude of the lubricating oil abrasive signal is given by k, which is the temperature compensation coefficient, and T is the real-time temperature of the oil. ref For reference temperature; The temperature compensation coefficient k was obtained through calibration experiments on standard lubricating oil abrasive samples under different temperature conditions; By setting a signal judgment threshold, when the amplitude of the temperature-compensated signal exceeds the threshold, an alarm signal or warning information is output.

2. The method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor according to claim 1, characterized in that, In step (1), the lubricating oil is driven by the oil pump to circulate in the lubricating oil circuit, and the flow rate of the oil is adjusted by the throttle valve.

3. The method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor according to claim 1, characterized in that, In step (2), a high-frequency excitation signal of 1V and 1MHz is applied to the semi-arc excitation electrode through a direct digital synthesizer.

4. The method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor according to claim 1, characterized in that, In step (3), the IV conversion circuit includes an operational amplifier and a feedback branch, the feedback branch being a feedback resistor R connected in parallel. f With feedback capacitor C f Composition: The inverting input of the operational amplifier receives the current signal output from the electrostatic coupling edge electric field sensor, and the feedback resistor R... f With feedback capacitor C f Both ends are connected to the output terminal and the inverting input terminal of the operational amplifier, respectively, and the non-inverting input terminal of the operational amplifier is grounded. Feedback resistor R f The feedback capacitor C is 1~100 MΩ. f The range is 0.1~10 pF.

5. The method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor according to claim 1, characterized in that, Before the voltage signal in step (3) is sent into the low-frequency processing channel and the high-frequency processing channel in parallel, it first enters the isolation stage circuit, and the signal transmission and power supply are isolated through electrical isolation.

6. The method for monitoring lubricating oil wear particles based on an electrostatically coupled edge electric field sensor according to claim 1, characterized in that, The cutoff frequency f of the low-pass filter circuit in step (4) lp The center frequency f of the bandpass filter circuit is 1.5 kHz. bp It is 0.5 to 1.5 times the frequency of the excitation signal.

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