Compressor oil level measuring method and system based on ultrasonic non-contact detection

Abstract

The invention relates to a compressor oil level measuring method and system based on ultrasonic non-contact detection, and the method comprises the steps: transmitting an ultrasonic pulse through an ultrasonic transducer, and receiving an echo signal reflected from an oil surface; environment temperature is collected; calculating the current sound velocity of the ultrasonic wave in the oil, and determining the flight time difference of the ultrasonic wave according to the echo signal; the real-time oil level height is calculated according to the current sound velocity and the flight time difference; when the intensity of the echo signal is lower than a preset threshold value, switching to a transmission detection mode, transmitting ultrasonic waves and receiving transmission waves through an ultrasonic transducer, and updating the height of the oil level according to the intensity attenuation of the transmission waves so as to realize non-contact real-time accurate monitoring of the oil level of the high-pressure oil cavity of the compressor. The hole opening leakage risk is eliminated; and the measurement reliability under the complex working condition is ensured.

Description

Technical Field

[0001] This invention relates to the field of industrial testing technology, and in particular to a method and system for measuring compressor oil level based on ultrasonic non-contact testing. Background Technology

[0002] Traditional compressor oil level detection primarily relies on contact sensors (such as float-type and capacitive sensors), which require installation through openings in the oil tank housing, posing a risk of high-pressure oil leakage and reducing structural strength. While non-destructive testing technologies exist (such as radio frequency admittance and external ultrasonic sensors), the acoustic impedance mismatch of the metal housing results in ultrasonic wave penetration rates of less than 1%, hindering accurate measurement. Furthermore, oil foam, impurities, and temperature drift further interfere with measurement accuracy. Existing solutions struggle to simultaneously meet the three major requirements of non-contact installation, high-pressure sealing, and adaptability to complex oil conditions, thus limiting the reliability of compressor condition monitoring. Summary of the Invention

[0003] The main objective of this invention is to provide a compressor oil level measurement method and system based on ultrasonic non-contact detection. By using ultrasonic transmissive film coupling, dynamic compensation of sound velocity and temperature, and adaptive switching of reflection-transmission dual modes, the invention aims to achieve non-contact real-time accurate monitoring of the oil level in the high-pressure oil chamber of the compressor, eliminate the risk of leakage through openings, and ensure measurement reliability under complex operating conditions.

[0004] To achieve the above objectives, the present invention provides a compressor oil level measurement method based on ultrasonic non-contact detection, comprising the following steps:

[0005] The ultrasonic transducer emits ultrasonic pulses and receives the echo signals reflected from the oil surface.

[0006] Collect ambient temperature;

[0007] Calculate the current speed of sound of the ultrasonic wave in the oil and determine the time difference of flight of the ultrasonic wave based on the echo signal;

[0008] Calculate the real-time fuel level altitude based on the current speed of sound and the time difference of flight;

[0009] When the echo signal strength is lower than a preset threshold, the system switches to transmission detection mode, emits ultrasonic waves through an ultrasonic transducer, receives transmitted waves, and updates the oil level based on the attenuation of the transmitted wave strength.

[0010] Furthermore, prior to the step of emitting ultrasonic pulses via the ultrasonic transducer, the following steps are included:

[0011] An ultrasonically permeable film is attached to the outer wall of the compressor housing at the location corresponding to the oil sump.

[0012] The ultrasonic transducer is fixed to the outside of the ultrasonic sound-permeable film.

[0013] Further, the step of emitting ultrasonic pulses via an ultrasonic transducer and receiving the echo signal reflected from the oil surface includes:

[0014] The ultrasonic pulses emitted by the ultrasonic transducer penetrate the ultrasonic sound-transmitting film attached to the outer wall of the compressor housing and the metal housing to enter the oil cavity.

[0015] The echo signal reflected from the oil surface and returned along the original path is received by the ultrasonic transducer.

[0016] Furthermore, the steps for collecting ambient temperature data include:

[0017] The real-time temperature of the outer surface of the ultrasonic sound-permeable film is detected by a temperature sensor;

[0018] The detected temperature value is taken as the ambient temperature.

[0019] Further, the step of calculating the current sound velocity of the ultrasound in the oil includes:

[0020] Call the pre-stored oil sound velocity-temperature correspondence curve;

[0021] Based on the collected ambient temperature, match the corresponding sound velocity value in the relationship curve;

[0022] The output matched sound velocity value is used as the current sound velocity of the ultrasonic wave in the oil.

[0023] Furthermore, the step of determining the ultrasonic time-of-flight difference based on the echo signal includes:

[0024] The received echo signal is converted from analog to digital.

[0025] Extract the time interval between the time of the ultrasonic wave emission pulse and the time of the received echo pulse;

[0026] Generate ultrasonic flight time difference.

[0027] Furthermore, the steps for calculating the real-time fuel level altitude based on the current speed of sound and the time difference between flight include:

[0028] The detection distance of the ultrasonic wave to the oil surface is calculated based on the current speed of sound and the time difference of flight.

[0029] The real-time oil level is determined based on the difference between the known total height of the oil tank and the detection distance.

[0030] Furthermore, the steps of emitting ultrasonic waves through an ultrasonic transducer and receiving transmitted waves include:

[0031] Determine whether the intensity of the echo signal is lower than a preset threshold;

[0032] If the value is below the preset threshold, the ultrasonic transducer will be switched to transmission detection mode.

[0033] The ultrasonic transducer is controlled to emit a continuous wave at a fixed frequency.

[0034] Receives transmitted waves that penetrate the oil layer on the opposite side of the oil cavity;

[0035] The intensity attenuation of the received transmitted wave relative to the emitted wave is measured.

[0036] Furthermore, the step of updating the oil level height based on the attenuation of transmitted wave intensity includes:

[0037] The measured intensity attenuation value is compared with the pre-stored ultrasonic attenuation coefficient of the oil.

[0038] Inversion calculation of the thickness penetrating the oil layer;

[0039] Update the oil level based on the oil layer thickness.

[0040] This invention also provides a compressor oil level measurement system based on ultrasonic non-contact detection, comprising: the compressor oil level measurement method and system based on ultrasonic non-contact detection provided by this invention, which has the following beneficial effects: This invention achieves non-contact, high-precision measurement of compressor oil level. It solves the problem of sound wave penetration through the metal casing by using ultrasonic transparent thin-film coupling technology, avoiding the risk of leakage caused by openings; it also eliminates measurement errors caused by oil temperature drift by real-time temperature compensation of sound velocity; and by adopting a reflection-transmission dual-mode adaptive switching mechanism, it automatically activates transmission detection when oil foam or impurities interfere with the reflection signal, ensuring continuous monitoring capability under complex operating conditions and improving the safety and maintenance efficiency of the compressor lubrication system. Attached Figure Description

[0041] Figure 1 This is a flowchart illustrating a compressor oil level measurement method based on ultrasonic non-contact detection in one embodiment of the present invention.

[0042] Figure 2 This is a structural block diagram of a compressor oil level measurement system based on ultrasonic non-contact detection in one embodiment of the present invention.

[0043] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] Reference Figure 1 This is a flowchart illustrating a compressor oil level measurement method based on ultrasonic non-contact detection proposed in this invention, comprising the following steps:

[0046] S1, which transmits ultrasonic pulses through an ultrasonic transducer and receives echo signals reflected from the oil surface;

[0047] S2, collect ambient temperature;

[0048] S3, calculate the current speed of sound of the ultrasonic wave in the oil, and determine the time difference of ultrasonic wave flight based on the echo signal;

[0049] S4 calculates the real-time fuel level altitude based on the current speed of sound and the flight time difference;

[0050] S5, when the echo signal intensity is lower than a preset threshold, switch to transmission detection mode, emit ultrasonic waves through ultrasonic transducer, receive transmitted waves, and update the oil level height according to the intensity attenuation of transmitted waves.

[0051] In one embodiment, prior to the step of emitting ultrasonic pulses via an ultrasonic transducer, the following steps are included:

[0052] An ultrasonically permeable film is attached to the outer wall of the compressor housing at the location corresponding to the oil sump.

[0053] The ultrasonic transducer is fixed to the outside of the ultrasonic sound-permeable film.

[0054] Specifically, an ultrasonically sound-permeable film (such as polytetrafluoroethylene or polyimide) is tightly bonded to the outer wall of the compressor housing corresponding to the oil groove location, and fixed along the edge of the film by a sealing ring (such as an oil-resistant fluororubber sealing ring) to ensure resistance to static working pressure >10MPa. The ultrasonically sound-permeable film is used to solve the problem of acoustic impedance mismatch in metal housings, because the acoustic impedance of steel housings is as high as 45×10⁻⁶. 6 Rayl impedance, while air impedance is only 430 Rayl, resulting in an ultrasonic wave reflectivity >99% at the shell-air interface. This embodiment utilizes a thin-film material with an acoustic impedance between that of metal and oil (such as 2.5 × 10⁻⁶ PTFE). 6 Rayl; Polyimide 3.2×10 6 Rayl) is used to achieve gradual acoustic impedance matching, improving penetration efficiency. After the ultrasonic transducer is fixed, an elastic support tightly presses the ultrasonic transducer to the outside of the film, and the radiating surface of the transducer is coated with silicone grease to eliminate air gaps. The elastic support can compensate for the difference in thermal expansion of materials and prevent coupling failure under high-temperature conditions; the fluororubber sealing ring blocks the permeation path of high-pressure oil vapor.

[0055] In one embodiment, step S1 includes:

[0056] The steps of emitting ultrasonic pulses via an ultrasonic transducer and receiving echo signals reflected from the oil surface include:

[0057] The ultrasonic pulses emitted by the ultrasonic transducer penetrate the ultrasonic sound-transmitting film attached to the outer wall of the compressor housing and the metal housing to enter the oil cavity.

[0058] The echo signal reflected from the oil surface and returned along the original path is received by the ultrasonic transducer.

[0059] In practical implementation, a short pulse signal with a center frequency of 100kHz and a pulse width ≤10μs is emitted by an ultrasonic transducer. This ultrasonic pulse first penetrates the 0.5mm thick polytetrafluoroethylene acoustic film attached to the outer wall of the compressor casing, and through acoustic impedance matching (film impedance 2.5×10⁻⁶), the ultrasonic pulse penetrates the 0.5mm thick polytetrafluoroethylene acoustic film attached to the outer wall of the compressor casing. 6 Rayl with steel casing 45×10 6 Rayl's gradual transition allows over 85% of the energy to penetrate the composite structure and enter the oil cavity. When the ultrasound propagates in the oil at a temperature-dependent sound velocity v0 to the oil-gas interface, it is affected by a sudden change in impedance (oil 1.3×10). 6 Rayl (430Rayl) generates a strong reflected wave with a reflection coefficient of 0.998 for air. This reflected wave passes through the oil cavity, metal shell, and acoustic membrane sequentially along its original incident path and returns to the ultrasonic transducer, forming a detectable echo signal. This original path return mechanism is quantitatively characterized by the propagation equation, which is:

[0060]

[0061] In the formula, I0 is the emission intensity, the oil attenuation coefficient α≈0.05dB / cm, d is the distance from the oil surface to the inner wall of the casing, and T is the emission intensity. out T in Transmittance and reflection coefficient terms of ultrasonic input / output housing-thin film composite structure The return of the original path avoids scattering interference from the internal structure of the housing (such as bearings and rotors). This embodiment maintains stable detection even under ±10mm oil level fluctuation conditions by optimizing the pulse frequency and path design, thus meeting the engineering requirements for non-contact measurement of high-pressure sealed oil chambers.

[0062] In one embodiment, step S2 includes:

[0063] The steps for collecting ambient temperature data include:

[0064] The real-time temperature of the outer surface of the ultrasonic sound-permeable film is detected by a temperature sensor;

[0065] The detected temperature value is taken as the ambient temperature.

[0066] In practical implementation, the temperature sensor is installed in conjunction with the ultrasonic transducer. The temperature sensor is integrated into the elastic bracket of the ultrasonic transducer, ensuring that the probe end is parallel to the transducer's radiating surface and tightly adheres to the outer surface of the thin film. The elastic bracket is made of beryllium copper alloy with a thermal conductivity of 1.5 W / m·K, providing sufficient elastic pressure (50±5 N) while achieving uniform thermal contact between the sensor and the thin film surface, with a thermal resistance of <0.05 K / W. A 0.2 mm thick alumina ceramic heat-conducting sheet (thermal conductivity 30 W / m·K) is embedded in the sensor probe end, ensuring efficient heat conduction with the thin film surface (contact thermal resistance <0.01 K / W) and electrical isolation from the metal bracket. Thermally conductive silicone grease (thermal conductivity 1.8 W / m·K) is filled in the sealed space formed between the transducer's radiating surface and the thin film to eliminate the influence of air gaps on temperature transmission. Compared to a separately installed temperature sensor, this integrated design not only saves installation space but also ensures the consistency of the thermal environment between the temperature detection point and the actual ultrasonic penetration path, resulting in more accurate sound velocity compensation. The ambient temperature is determined by detecting the temperature value using a temperature sensor.

[0067] In one embodiment, step S3 includes:

[0068] The steps for calculating the current sound velocity of an ultrasonic wave in oil include:

[0069] Call the pre-stored oil sound velocity-temperature correspondence curve;

[0070] Based on the collected ambient temperature, match the corresponding sound velocity value in the relationship curve;

[0071] The output matched sound velocity value is used as the current sound velocity of the ultrasonic wave in the oil.

[0072] In practical implementation, considering the nonlinear variation of the sound velocity of compressor lubricating oil with temperature (the typical temperature coefficient of sound velocity for lubricating oil is -3.5 m / s / ℃), a pre-stored high-precision sound velocity-temperature relationship curve is used to achieve real-time sound velocity compensation. This sound velocity-temperature relationship curve is established through laboratory calibration: within a temperature range of 20–120℃, sound velocity measurements are performed on samples of the same type of lubricating oil at 5℃ intervals (using the pulse-echo method, accuracy ±0.1%). After collecting 30 sets of discrete data points, a continuous relationship curve is established using cubic polynomial fitting.

[0073] v(T) = aT 3 +bT 2 +cT+d

[0074] In the formula, v(T) represents the propagation speed of ultrasound in oil at temperature T (unit: m / s), T represents the ambient temperature (unit: ℃), and a, b, c, and d are fitting coefficients for a specific oil product. Specifically, a = 1 / T, which characterizes the higher-order nonlinearity of sound speed with temperature; b reflects the second-order temperature effect; c represents the linear temperature coefficient; and d is the reference sound speed value. The microcontroller uses the real-time temperature T collected by the temperature sensor... env The current speed of sound is calculated using bilinear interpolation on a pre-stored curve, and the data is then used at the calibration data point [T]. k ,T k+1 [Positioning T in the middle] env For calculating the speed of sound within a given temperature range (e.g., 82.3℃ falls between 80℃ and 85℃), the interpolation formula is:

[0075]

[0076] In the formula, T k T k+1 For adjacent calibration temperature points (unit: °C), v(T) k ), v(T) k+1 ) represents the corresponding calibrated speed of sound (unit: m / s). Let v(T) be the speed of sound. env The current sound velocity value is used as the propagation velocity of ultrasonic waves in the oil. During the cold start phase of the compressor (the non-steady-state process of oil temperature from 30℃ to 90℃), this implementation improves the acquisition accuracy compared to the traditional formula method. The pre-stored oil sound velocity-temperature correspondence curve is solidified in the microcontroller FLASH, which supports updating the oil type on-site via RS485 interface to adapt to the sound velocity characteristics of different lubricating oils.

[0077] In one embodiment, the step of determining the ultrasonic time-of-flight difference based on the echo signal includes:

[0078] The received echo signal is converted from analog to digital.

[0079] Extract the time interval between the time of the ultrasonic wave emission pulse and the time of the received echo pulse;

[0080] Generate ultrasonic flight time difference.

[0081] In practical implementation, the received microvolt-level echo signal is preamplified with a gain of 60dB and then digitized by a 16-bit resolution, 20MSPS sampling rate analog-to-digital converter (ADC) (quantization noise < 1μV), converting the analog echo into a discrete-time sequence signal s[n] (n = 0, 1, 2, ..., N-1). The start time t0 of the transmitted pulse and the arrival time t1 of the echo pulse are captured, and a dual-threshold dynamic detection algorithm is used to extract the time difference: the transmitted pulse is marked, and a high-speed timer is started when the rising edge of the transmission trigger signal exceeds 0.5V; the arrival of the echo is determined by detecting the point n where the discrete-time sequence signal s[n] first exceeds the background noise mean + 3σ (σ is the noise standard deviation). pre , in [n pre -10,n pre Within the +50 interval, calculate the signal envelope. (H is the Hilbert transform), take the time corresponding to the maximum value of env[n] as t1; generate the time difference: Δt=t1-t0-τ offset , where τ offset =0.8μs is the inherent system delay (pre-calibrated value). To suppress compressor vibration interference (typical interference frequency 1-5kHz), adaptive filtering is introduced in the time difference calculation: a 128th order FIR band-stop filter is designed, and the final ultrasonic flight time difference is generated.

[0082] In one embodiment, step S4 includes:

[0083] The steps for calculating real-time fuel level altitude based on the current speed of sound and the time difference between flight and flight include:

[0084] The detection distance of the ultrasonic wave to the oil surface is calculated based on the current speed of sound and the time difference of flight.

[0085] The real-time oil level is determined based on the difference between the known total height of the oil tank and the detection distance.

[0086] In practical implementation, real-time oil level calculation is based on the propagation characteristics of ultrasonic pulses in the oil medium. Based on the temperature-compensated current speed of sound v(T) (unit: m / s) and the precisely measured flight time difference Δt (unit: s), the one-way vertical distance d (unit: m) from the ultrasonic transducer radiating surface to the oil surface is calculated. Its physical essence is the propagation path length of the ultrasonic wave within the time difference Δt, and the calculation formula is as follows:

[0087]

[0088] In the formula, v(T) is the speed of sound in the oil after temperature compensation, Δt is the time interval between ultrasonic wave transmission and echo reception (including system delay compensation), and the coefficient is... This is used to correct the round-trip path of the ultrasonic wave (transmitter → oil surface → receiver). The calculated one-way distance d is compared with the pre-calibrated total height H of the oil tank. 总 Perform geometric conversion: H 油 =H 总 -d, where H 总 d is the vertical distance from the ultrasonic transducer radiating surface to the bottom of the oil tank (mechanically calibrated during installation, accuracy ±0.1mm), d is the real-time distance from the transducer radiating surface to the dynamic oil level, and H is the vertical distance from the transducer radiating surface to the bottom of the oil tank. 油 This represents the actual oil level in the oil tank (target output value). This embodiment achieves non-contact, high-precision dynamic monitoring of the oil level in the high-pressure sealed oil chamber through sound-time conversion and geometric calculation.

[0089] In one embodiment, step S5 includes:

[0090] The steps of emitting ultrasonic waves and receiving transmitted waves via an ultrasonic transducer include:

[0091] Determine whether the intensity of the echo signal is lower than a preset threshold;

[0092] If the value is below the preset threshold, the ultrasonic transducer will be switched to transmission detection mode.

[0093] The ultrasonic transducer is controlled to emit a continuous wave at a fixed frequency.

[0094] Receives transmitted waves that penetrate the oil layer on the opposite side of the oil cavity;

[0095] The intensity attenuation of the received transmitted wave relative to the emitted wave is measured.

[0096] In practical implementation, when the echo signal intensity in the reflection mode falls below a preset threshold (typically set to -45dBm) due to oil foam or impurities, the system automatically switches to transmission detection mode to maintain measurement continuity. A true RMS detection circuit determines whether the echo signal voltage is below 0.56mV (corresponding to -45dBm power), a threshold determined based on reflection intensity attenuation experiments when oil foam coverage is >30%. Once the switching condition is met, the ultrasonic transducer switches from pulse mode to transmitting a 100kHz fixed-frequency continuous wave (peak-to-peak voltage 30V), while a receiving transducer installed on the opposite side of the oil cavity captures the transmitted wave penetrating the oil layer. The receiving end uses a logarithmic amplifier to directly measure the intensity attenuation ΔA (unit: dB) of the transmitted wave relative to the transmitted wave. This physical characteristic represents the energy loss of the ultrasonic wave as it passes through the oil layer, and the calculation formula is ΔA = 20log 10 (I tx / I rx ), where I tx Emitted wave intensity (unit: W / m) 2 ), I rxReceived wave intensity (unit: W / m) 2 The contralateral receiving design allows ultrasonic waves to penetrate vertically through an oil layer thickness of H. oil (Slope path 2d in non-reflection mode) The foam layer is located on the oil surface, and its impact on the direct path is much smaller than that on the reflection path, thus avoiding the strong scattering interference from the oil surface foam in the reflection mode. The receiver uses a logarithmic amplifier (such as AD8307) to directly output the attenuation value ΔA, and simultaneously acquires the transmitted wave voltage and the received wave voltage for cross-verification. This implementation expands the adaptability of non-contact detection to various operating conditions through intelligent mode switching and penetrating acoustic energy measurement.

[0097] In one embodiment, the step of updating the oil level height based on the attenuation of transmitted wave intensity includes:

[0098] The measured intensity attenuation value is compared with the pre-stored ultrasonic attenuation coefficient of the oil.

[0099] Inversion calculation of the thickness penetrating the oil layer;

[0100] Update the oil level based on the oil layer thickness.

[0101] In practical implementation, the conversion of the transmitted wave intensity attenuation value ΔA to the oil level height is based on the exponential attenuation law of ultrasound in oil media. A pre-stored oil ultrasound attenuation coefficient α (unit: dB / m) is used; this coefficient is obtained through laboratory calibration with the same type of lubricating oil. For typical mineral oil, α = 5 dB / m at a frequency of 100 kHz. Oil layer thickness H... oil (Unit: m) Solved using the inversion equation:

[0102]

[0103] In the formula, α is the inherent decay coefficient of the oil (related to oil type, temperature, and cleanliness). The inverted H... oil This is the current oil layer thickness. Since the transmission measurement path is a vertical penetration through the oil cavity (transmitter → oil layer → receiver), this thickness is directly equivalent to the oil level height H. 油 This implementation, through attenuation coefficient inversion and dynamic online calibration, ensures continuous oil level monitoring even when the reflection mode fails, thus solving the monitoring blind spot problem under high-pollution conditions in the compressor lubrication system.

[0104] Reference Figure 2 Here is a structural block diagram of a compressor oil level measurement system based on ultrasonic non-contact detection according to an embodiment of the present invention, comprising:

[0105] An ultrasonic transceiver unit is used to transmit ultrasonic pulses through an ultrasonic transducer and receive echo signals reflected from the oil surface.

[0106] Temperature acquisition unit, used to acquire ambient temperature;

[0107] The signal processing unit is used to calculate the current speed of sound of the ultrasonic wave in the oil and determine the time difference of flight of the ultrasonic wave based on the echo signal.

[0108] The fuel level calculation unit is used to calculate the real-time fuel level altitude based on the current speed of sound and the flight time difference.

[0109] The oil level update unit is used to switch to transmission detection mode when the echo signal intensity is lower than a preset threshold. It emits ultrasonic waves through an ultrasonic transducer, receives transmitted waves, and updates the oil level height according to the intensity attenuation of the transmitted waves.

[0110] For the specific implementation of each unit in the above device example, please refer to the method embodiments described above, and will not be repeated here.

[0111] In summary, this invention uses an ultrasonic transducer to emit ultrasonic pulses and receive echo signals reflected from the oil surface; it collects ambient temperature; calculates the current speed of sound in the oil and determines the time difference of flight of the ultrasonic wave based on the echo signal; it calculates the real-time oil level based on the current speed of sound and the time difference of flight; when the intensity of the echo signal is lower than a preset threshold, it switches to transmission detection mode, emits ultrasonic waves through the ultrasonic transducer, receives the transmitted waves, and updates the oil level based on the intensity attenuation of the transmitted waves, thereby achieving non-contact, real-time, and accurate monitoring of the oil level in the high-pressure oil chamber of the compressor, eliminating the risk of leakage from openings, and ensuring measurement reliability under complex operating conditions.

Claims

1. A method for measuring compressor oil level based on ultrasonic non-contact detection, characterized in that, Includes the following steps: The ultrasonic transducer emits ultrasonic pulses and receives the echo signals reflected from the oil surface. Collect ambient temperature; Calculate the current speed of sound of the ultrasonic wave in the oil and determine the time difference of flight of the ultrasonic wave based on the echo signal; Calculate the real-time fuel level altitude based on the current speed of sound and the time difference of flight; When the echo signal strength is lower than a preset threshold, the system switches to transmission detection mode, emits ultrasonic waves through an ultrasonic transducer, receives transmitted waves, and updates the oil level based on the attenuation of the transmitted wave strength.

2. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, Prior to the step of emitting ultrasonic pulses via the ultrasonic transducer, the following steps are included: An ultrasonically permeable film is attached to the outer wall of the compressor housing at the location corresponding to the oil sump. The ultrasonic transducer is fixed to the outside of the ultrasonic sound-permeable film.

3. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of emitting ultrasonic pulses via an ultrasonic transducer and receiving echo signals reflected from the oil surface includes: The ultrasonic pulses emitted by the ultrasonic transducer penetrate the ultrasonic sound-transmitting film attached to the outer wall of the compressor housing and the metal housing to enter the oil cavity. The echo signal reflected from the oil surface and returned along the original path is received by the ultrasonic transducer.

4. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of collecting ambient temperature includes: The real-time temperature of the outer surface of the ultrasonic sound-permeable film is detected by a temperature sensor; The detected temperature value is taken as the ambient temperature.

5. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of calculating the current sound velocity of the ultrasonic wave in the oil includes: Call the pre-stored oil sound velocity-temperature correspondence curve; Based on the collected ambient temperature, match the corresponding sound velocity value in the relationship curve; The output matched sound velocity value is used as the current sound velocity of the ultrasonic wave in the oil.

6. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of determining the ultrasonic time-of-flight difference based on the echo signal includes: The received echo signal is converted from analog to digital. Extract the time interval between the time of the ultrasonic wave emission pulse and the time of the received echo pulse; Generate ultrasonic flight time difference.

7. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of calculating the real-time fuel level altitude based on the current speed of sound and the flight time difference includes: The detection distance of the ultrasonic wave to the oil surface is calculated based on the current speed of sound and the time difference of flight. The real-time oil level is determined based on the difference between the known total height of the oil tank and the detection distance.

8. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 1, characterized in that, The step of emitting ultrasonic waves through an ultrasonic transducer and receiving transmitted waves includes: Determine whether the intensity of the echo signal is lower than a preset threshold; If the value is below the preset threshold, the ultrasonic transducer will be switched to transmission detection mode. The ultrasonic transducer is controlled to emit a continuous wave at a fixed frequency. Receives transmitted waves that penetrate the oil layer on the opposite side of the oil cavity; The intensity attenuation of the received transmitted wave relative to the emitted wave is measured.

9. The compressor oil level measurement method based on ultrasonic non-contact detection according to claim 8, characterized in that, The step of updating the oil level height based on the attenuation of transmitted wave intensity includes: The measured intensity attenuation value is compared with the pre-stored ultrasonic attenuation coefficient of the oil. Inversion calculation of the thickness penetrating the oil layer; Update the oil level based on the oil layer thickness.

10. A compressor oil level measurement system based on ultrasonic non-contact detection, characterized in that, include: An ultrasonic transceiver unit is used to transmit ultrasonic pulses through an ultrasonic transducer and receive echo signals reflected from the oil surface. Temperature acquisition unit, used to acquire ambient temperature; The signal processing unit is used to calculate the current speed of sound of the ultrasonic wave in the oil and determine the time difference of flight of the ultrasonic wave based on the echo signal. The fuel level calculation unit is used to calculate the real-time fuel level altitude based on the current speed of sound and the flight time difference. The oil level update unit is used to switch to transmission detection mode when the echo signal intensity is lower than a preset threshold. It emits ultrasonic waves through an ultrasonic transducer, receives transmitted waves, and updates the oil level height according to the intensity attenuation of the transmitted waves.

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