Capacitive oil level passive detection system and method based on optical fiber energy transmission and communication

Abstract

The application provides a capacitive oil level passive detection system and method based on optical fiber energy transmission and communication, and relates to the field of oil level passive detection. The system comprises a host terminal unit, a remote oil level sensing unit and an optical fiber transmission link module. The host terminal transmits energy light to the remote end through the optical fiber, and the remote end is powered by the capacitive oil level sensor after photoelectric conversion. The capacitive measurement module converts the oil level change into an analog voltage signal, forms pulse return communication light after voltage-frequency conversion, returns to the host terminal through the optical fiber, and recovers the oil level information after frequency-voltage conversion. The application realizes complete passive power supply of the remote end by using optical fiber energy transmission, eliminates the electrical safety hidden danger of the airborne fuel tank environment, and is suitable for various airborne fuel measurement systems.

Description

Technical Field

[0001] This application relates to the field of passive oil level detection, and in particular to a capacitive passive oil level detection system and method based on optical fiber power transmission and communication. Background Technology

[0002] Capacitive fuel level measurement is widely used for fuel quantity monitoring and management in airborne fuel systems. Capacitive fuel level sensors typically employ a coaxial structure. Because fuel and air have different dielectric constants, changes in fuel level cause changes in equivalent capacitance, thus establishing a stable correlation between fuel level and capacitance. In engineering, for ease of subsequent processing and output, the sensor's internal capacitance measurement chip generally performs high-precision measurement of capacitance changes and converts them into an electrical signal through internal modulation / demodulation / integration circuits. Temperature compensation is also added, ultimately outputting a standard analog voltage signal proportional to the fuel level.

[0003] However, using the traditional "cable power supply + cable signal return" method in airborne environments (especially near fuel tanks / fuel lines) typically faces the following problems: Fuel tanks / fuel systems are highly safety-sensitive areas, and cable power supply and electrical connections pose potential risks of leakage and sparks, while strong electrical isolation is required (airborne systems usually have more stringent safety requirements); the electromagnetic conditions in airborne environments are complex, and analog voltage signals are easily affected by electromagnetic interference, ground loops, and attenuation during long-distance cable transmission, leading to decreased measurement accuracy and deterioration of system stability; airborne cabling space is limited, wire harness weight is sensitive, and the number of interfaces is sensitive, and traditional cable solutions can easily increase cabling complexity and maintenance workload.

[0004] In airborne oil level measurement scenarios, to achieve electrical isolation and electromagnetic interference resistance, oil level information can be transmitted via optical fiber, isolating the signal link from the strong electromagnetic environment on board. However, using only optical fiber communication still requires providing local power or batteries at the remote end, leading to issues with endurance, maintenance, and reliability. To avoid the safety and maintenance risks associated with remote power supply, optical fiber power transmission technology transmits high-power lasers within optical fibers and performs photoelectric conversion for power supply at the remote end, providing a feasible path for "passive power supply in hazardous / sensitive areas." However, in this type of "optical fiber power supply + optical fiber backhaul" system, capacitive oil level measurement typically outputs low-amplitude analog voltage signals. If the light intensity is directly modulated by amplitude, it is susceptible to the nonlinearity and temperature drift of optical devices, making it difficult to guarantee end-to-end linear consistency. Therefore, a signal carrying method more suitable for optical links is still needed.

[0005] Therefore, there is an urgent need to propose a systematic solution for airborne capacitive oil level measurement that can achieve remote passive power supply by using fiber optic power transmission, provide oil level signal modulation / demodulation methods suitable for high-reliability transmission via optical links, and be compatible with both dual-fiber and single-fiber link configurations to meet the differentiated requirements of airborne platforms for reliability, weight, number of interfaces, and maintainability. Summary of the Invention

[0006] The purpose of this invention is to address the problems of existing capacitive oil level detection systems in airborne environments, such as high electrical safety risks, susceptibility to interference of analog signals, and difficulty in simultaneously achieving high reliability, high linearity, and lightweight system integration requirements for remote power supply and signal feedback links. This invention provides a passive capacitive oil level detection system and method based on fiber optic power transmission and communication.

[0007] The above-mentioned objective of this application is achieved through the following technical solution: The fiber optic transmission link module is connected between the host unit and the remote oil level sensing unit. The host unit includes a laser energy emission module and an optical receiving and demodulation module; the energy light output by the laser energy emission module is transmitted to the remote oil level sensing unit via the optical fiber transmission link module. The remote oil level sensing unit includes: a photoelectric transducer module, a power management module, a capacitive oil level sensor and a capacitance measurement module, and a light emission and signal modulation module. The photoelectric transducer module converts light energy into electrical energy, which is then used by the power management module to power the remote oil level sensing unit. The capacitance measurement module is configured to convert the capacitance change of the capacitive oil level sensor into an analog voltage signal that is related to the oil level height. The optical emission and signal modulation module is configured to generate backhaul communication light based on the analog voltage signal, and transmit it back to the host unit via the optical fiber transmission link module; The optical receiving and demodulation module recovers the oil level measurement information from the return communication optical signal.

[0008] Optionally, the host unit may further include a laser drive control module; The laser drive control module is sequentially connected to the laser energy emission module and is used to set and adjust the output power of the laser energy emission module, as well as to implement overcurrent protection and overtemperature protection.

[0009] Optionally, the laser drive control module includes a constant current drive unit, which adopts a hardware closed-loop constant current structure and is slow-loop calibrated by a processor to achieve stable and adjustable laser drive current and safe monitoring. The laser drive control module also includes a temperature control unit, which includes a temperature acquisition circuit, a temperature control circuit, and a semiconductor cooler drive circuit, for constant temperature control of the laser energy emission module.

[0010] Optionally, the photoelectric transducer module is a photovoltaic power converter, used to convert the energy light transmitted through the optical fiber transmission link module into DC power output.

[0011] Optionally, the power management module includes a DC-DC converter circuit for regulating or buck-boosting the electrical energy output by the photovoltaic power converter to form at least one stable DC power supply for use by the capacitance measurement module and the light emission and signal modulation module.

[0012] Optionally, the capacitance measurement module includes a temperature compensation processing unit, which is configured to correct the analog voltage signal based on the temperature signal acquired by the temperature sensor.

[0013] Optionally, the optical fiber transmission link module is a dual-fiber link, including a first fiber and a second fiber, wherein the first fiber is used to transmit the energy light and the second fiber is used to transmit the return communication light; Optionally, the optical fiber transmission link module can also adopt a single optical fiber link, and the host unit and the remote oil level sensing unit are respectively equipped with a wavelength division multiplexer and a wavelength demultiplexer; the wavelength division multiplexer is configured to couple energy light and backhaul communication light of different wavelengths into the same optical fiber for transmission; the wavelength demultiplexer separates the mixed light received from the same optical fiber into energy light and backhaul communication light.

[0014] Optionally, the optical emission and signal modulation module includes a voltage-to-frequency conversion module, which converts the analog voltage signal output by the capacitance measurement module into a frequency signal proportional to it, and drives the optical emission and signal modulation module to form a pulse return communication optical carrying the frequency signal.

[0015] Optionally, the optical receiving and demodulation module includes: a photoelectric conversion unit and a signal recovery unit; The photoelectric conversion unit is configured to convert the backhaul communication optical light into an electrical signal; The return communication optical signal is an optical pulse frequency signal; the electrical signal is an electrical pulse frequency signal. The signal recovery unit is configured to extract the frequency signal from the electrical signal and recover the oil level measurement information; The signal recovery unit includes a frequency-to-voltage conversion subunit, which recovers the frequency signal into an analog voltage output signal corresponding to the oil level.

[0016] A passive capacitive oil level detection method based on fiber optic power transmission and communication, comprising the following steps: The host generates energy light, which is coupled into the optical fiber transmission link and transmitted to the remote end via the optical fiber. The remote receiver receives light energy, converts the light energy into electrical energy through photoelectric conversion, and then supplies power to the remote oil level detection circuit after voltage regulation. Collect capacitance change data from a capacitive oil level sensor and convert the capacitance change data into an analog voltage signal corresponding to the oil level height; The analog voltage signal is converted into a frequency signal proportional to it, and the frequency signal is used to drive the optical transmitter to form a return communication optical signal carrying frequency information. The return communication optical coupler is inserted into the optical fiber transmission link and transmitted back to the host. The host receives the return communication optical signal, converts it into an electrical signal, extracts frequency information from the electrical signal, and then converts the frequency information into an analog voltage output signal corresponding to the oil level, thus obtaining the oil level measurement information.

[0017] The beneficial effects of the technical solution provided in this application are: Remote passive power supply: The main unit transmits energy light via optical fiber, and the remote photoelectric conversion and voltage regulation power supply enable the oil level probe to work without local power supply or battery, reducing maintenance and safety risks.

[0018] Electrical isolation and electromagnetic interference immunity: Energy and information are transmitted through optical fiber, and the host end and the remote end are completely electrically isolated, which is suitable for stable measurement in complex airborne electromagnetic environments.

[0019] Higher transmission linearity and robustness: The "voltage-frequency-optical pulse-frequency-voltage" transmission method avoids the nonlinearity and temperature drift problems of analog amplitude modulation; link attenuation mainly affects the amplitude without changing the frequency information, and can be reliably recovered as long as the pulse is identifiable.

[0020] Single and dual fiber compatibility facilitates selection: dual fibers achieve physical isolation of energy and signal, resulting in a clear structure; single fibers achieve energy transmission and communication within the same fiber through wavelength division multiplexing, reducing the number of fibers and interfaces and facilitating airborne integration. Attached Figure Description

[0021] The present application will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings: Figure 1 This is a block diagram of the capacitive passive oil level detection system in the embodiments of this application; Figure 2 This is a schematic diagram of the dual-fiber embodiment in this application. Figure 3This is a schematic diagram of the single-fiber WDM embodiment in this application. Figure 4 This is a schematic diagram of the capacitive oil level sensor and voltage output principle in the embodiments of this application; Figure 5 This is a schematic diagram of voltage frequency modulation and optical pulse transmission in the embodiments of this application. Detailed Implementation

[0022] To provide a clearer understanding of the technical features, objectives, and effects of this application, the specific embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0023] The embodiments of this application provide a capacitive passive oil level detection method based on optical fiber power transmission and communication.

[0024] Please refer to Figure 1 , Figure 1 This is a block diagram of a capacitive passive oil level detection system based on fiber optic power transmission and communication, as described in an embodiment of this application. The system includes: The host unit, the remote oil level sensing unit, and the fiber optic transmission link module; The fiber optic transmission link module is connected between the host unit and the remote oil level sensing unit. The host unit includes a laser energy emission module and an optical receiving and demodulation module; the energy light output by the laser energy emission module is transmitted to the remote oil level sensing unit via the optical fiber transmission link module. The remote oil level sensing unit includes: a photoelectric transducer module, a power management module, a capacitive oil level sensor and a capacitance measurement module, and a light emission and signal modulation module. The photoelectric transducer module converts light energy into electrical energy, which is then used by the power management module to power the remote oil level sensing unit. The capacitance measurement module is configured to convert the capacitance change of the capacitive oil level sensor into an analog voltage signal that is related to the oil level height. The optical emission and signal modulation module is configured to generate backhaul communication light based on the analog voltage signal, and transmit it back to the host unit via the optical fiber transmission link module; The optical receiving and demodulation module recovers the oil level measurement information from the return communication optical signal.

[0025] The host unit also includes a laser drive control module; The laser drive control module is sequentially connected to the laser energy emission module and is used to set and adjust the output power of the laser energy emission module, as well as to implement overcurrent protection and overtemperature protection.

[0026] The laser drive control module includes a constant current drive unit, which adopts a hardware closed-loop constant current structure and is slow-loop calibrated by a processor to achieve stable and adjustable laser drive current and safe monitoring. The laser drive control module also includes a temperature control unit, which includes a temperature acquisition circuit, a temperature control circuit, and a semiconductor cooler drive circuit, for constant temperature control of the laser energy emission module.

[0027] The photoelectric power conversion module is a photovoltaic power converter used to convert the energy light transmitted through the optical fiber transmission link module into DC power output.

[0028] The power management module includes a DC-DC converter circuit, which is used to regulate or buck-boost the electrical energy output by the photovoltaic power converter to form at least one stable DC power supply for use by the capacitance measurement module and the light emission and signal modulation module.

[0029] The capacitance measurement module includes a temperature compensation processing unit, which is configured to correct the analog voltage signal based on the temperature signal collected by the temperature sensor, so as to reduce the impact of ambient temperature changes on the oil level measurement results.

[0030] The optical fiber transmission link module is a dual-fiber link, including a first fiber and a second fiber. The first fiber is used to transmit the energy light, and the second fiber is used to transmit the return communication light. The optical fiber transmission link module can also use a single optical fiber link, and the host unit and the remote oil level sensing unit are respectively equipped with a wavelength division multiplexer and a wavelength division demultiplexer; the wavelength division multiplexer is configured to couple energy light and return communication light of different wavelengths into the same optical fiber for transmission; the wavelength division demultiplexer separates the mixed light received from the same optical fiber into energy light and return communication light; the center wavelength of the energy light is selected from 808nm, 850nm, 1064nm or 1550nm, and the center wavelength of the return communication light is selected from 808nm, 850nm, 1064nm or 1550nm; the wavelengths of the energy light and the return communication light are combined and configured according to the link design, device response characteristics and wavelength division multiplexing requirements.

[0031] The optical emission and signal modulation module includes a voltage-to-frequency conversion module, which converts the analog voltage signal output by the capacitance measurement module into a frequency signal proportional to it, and drives the optical emission and signal modulation module to form a pulse backhaul communication optical carrying the frequency signal.

[0032] The optical receiving and demodulation module includes: a photoelectric conversion unit and a signal recovery unit; The photoelectric conversion unit is configured to convert the backhaul communication optical light into an electrical signal; The return communication optical signal is an optical pulse frequency signal; the electrical signal is an electrical pulse frequency signal. The signal recovery unit is configured to extract the frequency signal from the electrical signal and recover the oil level measurement information; The signal recovery unit includes a frequency-to-voltage conversion subunit, which recovers the frequency signal into an analog voltage output signal corresponding to the oil level.

[0033] A passive capacitive oil level detection method based on fiber optic power transmission and communication, comprising the following steps: The host generates energy light, which is coupled into the optical fiber transmission link and transmitted to the remote end via the optical fiber. The remote receiver receives light energy, converts the light energy into electrical energy through photoelectric conversion, and then supplies power to the remote oil level detection circuit after voltage regulation. Collect capacitance change data from a capacitive oil level sensor and convert the capacitance change data into an analog voltage signal corresponding to the oil level height; The analog voltage signal is converted into a frequency signal proportional to it, and the frequency signal is used to drive the optical transmitter to form a return communication optical signal carrying frequency information. The return communication optical coupler is inserted into the optical fiber transmission link and transmitted back to the host. The host receives the return communication optical signal, converts it into an electrical signal, extracts frequency information from the electrical signal, and then converts the frequency information into an analog voltage output signal corresponding to the oil level, thus obtaining the oil level measurement information.

[0034] As one embodiment, the center wavelength of the energy light is different from the center wavelength of the return communication light; the center wavelength of the energy light is selected from one of 808nm, 850nm, 1064nm or 1550nm; the center wavelength of the return communication light is selected from another of 808nm, 850nm, 1064nm or 1550nm.

[0035] Example 1: Example of an airborne passive fuel level detection system with dual optical fiber physical isolation.

[0036] like Figure 2As shown, this embodiment provides a dual-fiber physically isolated airborne passive oil level detection system, including a host unit, a remote oil level probe unit, and two independent fiber optic links: an energy transmission fiber and a signal transmission fiber. The host unit drives a laser to generate energy light through a high-precision laser drive circuit, and efficiently couples the energy light into the energy transmission fiber. The drive circuit integrates overcurrent and overtemperature protection logic to ensure the long-term stability and safety of the power supply link. After the energy light reaches the remote end via the energy transmission fiber, it is absorbed by a photoelectric conversion device and converted into primary electrical energy. This energy is then converted into a stable DC voltage by a DC / DC converter, powering the remote oil level detection module, signal modulation module, and optical transmission module, thus enabling the remote end to operate continuously without any local power supply or battery.

[0037] Example 2: Example of an airborne passive oil level detection system using a single-fiber WDM.

[0038] like Figure 3 As shown, this embodiment provides an airborne passive fuel level detection system based on single-fiber wavelength division multiplexing (WDM). The difference between this system and Embodiment 1 is that the energy light and information light are transmitted together on the same fiber. Wavelength division multiplexing / demultiplexing devices are installed at both the host and remote ends to achieve beam combining and splitting. The host-end laser drive module generates energy light (e.g., 1064nm), which is then combined with the information light channel via WDM and input into a single fiber. The remote-end WDM separates the energy light from the mixed light and guides it to a photoelectric conversion device for photoelectric conversion. The resulting primary electrical energy is then regulated by DC / DC to power the remote-end sensing and optical communication circuits. This structure offers advantages in reducing the number of fibers and interfaces, facilitating airborne integration, and reducing weight.

[0039] Example 3: Example of capacitive oil level measurement and temperature compensation output.

[0040] This embodiment describes the implementation of capacitive oil level measurement and temperature compensation output. Capacitive oil level sensors typically employ a coaxial structure, with the housing and internal electrodes forming the capacitor plates. When the oil level changes, the different dielectric constants of oil and air cause a change in the equivalent medium ratio, resulting in a stable correlation between the sensor's equivalent capacitance and the oil level height.

[0041] Since capacitance changes are not easily processed and transmitted over long distances, this embodiment incorporates a dedicated capacitance measurement chip within the sensor to perform high-precision measurement of capacitance changes. The capacitance signal is then converted into an electrical signal via internal modulation, demodulation, or integration circuitry. Simultaneously, a temperature compensation algorithm is superimposed on the capacitance measurement chip or its peripheral processing circuitry to reduce the impact of ambient temperature changes on the measurement results, ultimately outputting a standard analog voltage signal proportional to the oil level.

[0042] Example 4: Laser driving and temperature control protection example.

[0043] This embodiment describes the implementation of driving and temperature control protection for the laser powered by the host, aiming to provide stable, adjustable, and protected energy output for the fiber optic power transmission link. A highly stable constant current and temperature control system is constructed on the host side: the constant current drive section enables adjustable current output, employing a control structure of "hardware closed loop + MCU slow loop correction." The hardware closed loop is responsible for rapid current stabilization under high current, while the MCU is responsible for setting, slow loop fine-tuning, status display, and protection logic. The system integrates overcurrent and overtemperature protection strategies to improve the safety and long-term reliability of the power supply link.

[0044] The temperature control section preferably adopts a TEC closed-loop temperature control scheme: the laser temperature is obtained through temperature acquisition (such as NTC), the MCU executes PID closed-loop control, and outputs control quantities to the TEC drive device to achieve bidirectional temperature control (heating / cooling), and has current limiting and over-temperature protection; through the heat conduction and heat dissipation structure design, high-precision constant temperature can be achieved for a long time at the set temperature (e.g., 25℃), thereby reducing laser output drift and improving energy transfer efficiency stability.

[0045] Example 5: Voltage-frequency conversion module example.

[0046] This embodiment employs a voltage-frequency modulation method: the analog voltage is converted to a frequency signal through a voltage-to-frequency converter to obtain a pulse frequency signal that is strictly proportional to the voltage. This frequency signal directly drives the digital fiber optic transmitting module, encoding the oil level information into optical pulses and coupling them into the signal transmission fiber for transmission back to the host. The host's optical receiving module converts the returned optical pulses into an electrical frequency signal, which is then converted back to an analog voltage output through a frequency-to-voltage converter for use by the airborne acquisition / display / control system. Since this scheme transmits frequency information, link attenuation mainly affects the amplitude without changing the frequency. As long as the pulse is identifiable, it can be stably recovered, thus ensuring end-to-end linearity and transmission reliability.

[0047] Example 6: Example of a photovoltaic power converter (PPC) and its power management module.

[0048] This embodiment provides a photovoltaic power converter (PPC) for an airborne passive oil level sensor and its power management implementation. The PPC is located on one side of the remote sensing unit and is used to receive the power supply optical signal transmitted via optical fiber and convert it into electrical energy output. The electrical energy is processed by voltage regulation and protection circuits to form a stable DC power supply, which powers the remote oil level detection module, voltage-to-frequency conversion module, and optical transmission module, thereby enabling the remote unit to work continuously without local power supply / battery.

[0049] In a preferred embodiment, the power supply light is generated by a laser at the host end and coupled into an optical fiber for long-distance transmission. The remote PPC performs photoelectric conversion on the incident light to output primary electrical energy, which is then boosted or bucked by a DC / DC power supply board to adapt to the power supply requirements of each remote module. The remote load may include sensor modules, optical transmission modules, and interface modules, etc. The system can be designed with power supply capacity and margin according to typical power consumption conditions and maximum power consumption conditions.

[0050] In one embodiment, addressing the electrical safety risks, susceptibility to electromagnetic interference, complex wiring, and high maintenance costs associated with traditional cable power supply and electrical signal transmission in airborne fuel system level measurement, this invention provides a capacitive passive fuel level detection system and method based on fiber optic power transmission and communication. The system comprises a host unit, a remote fuel level probe unit, and a fiber optic link connecting the two, offering two optional architectures: "dual-fiber physical isolation" and "single-fiber wavelength division multiplexing."

[0051] The host unit is powered remotely via laser through optical fiber, eliminating the need for local power or batteries at the remote oil level sensor. The remote unit converts the oil level information into a signal suitable for high-reliability fiber optic transmission and transmits it back. The system simultaneously supports both dual-fiber and single-fiber (WDM) links to adapt to the varying requirements of airborne platforms in terms of reliability, weight, number of interfaces, and complexity. In this implementation, the system further employs a signaling architecture of "voltage-frequency modulation + optical fiber transmission + frequency-voltage recovery" to map the simulated oil level voltage to the frequency domain, avoiding the nonlinearity and temperature drift issues associated with analog amplitude modulation, and achieving secure electrical-optical-electrical isolation and high-reliability transmission.

[0052] (1) Oil level detection module (remote) The oil level detection module includes a capacitive oil level sensor and a capacitance measurement chip. The capacitive oil level sensor measures the oil level by detecting changes in capacitance caused by variations in oil level. The equivalent capacitance of its coaxial structure changes with the ratio of the oil / air dielectric constant, and there is a stable correlation between the oil level and the capacitance. The capacitance measurement chip performs high-precision measurement of capacitance changes and converts the capacitance signal into an electrical signal through an internal modulation / demodulation / integration circuit. Simultaneously, a temperature compensation algorithm is applied, ultimately outputting a standard analog voltage signal proportional to the oil level.

[0053] (2) Signal modulation module (remote, voltage-to-frequency conversion) Since the oil level detection module outputs an analog voltage, which is susceptible to interference during cable transmission, and the optical transmitter / receiver module exhibits nonlinear characteristics, directly modulating the light intensity with the voltage amplitude would lead to difficulties in ensuring linearity, distortion during temperature drift, and challenges in recovery at the receiving end. Therefore, this invention preferably employs voltage-frequency modulation to convert the analog voltage into a proportional frequency pulse signal, which is then used to directly drive the optical transmitter module, enabling the oil level information to be transmitted via the optical fiber link in the form of optical pulses.

[0054] (3) Fiber optic communication transceiver module (remote end / host end) The fiber optic communication transceiver module is used to transmit oil level measurement information back up the fiber optic link. It modulates the communication light using a pulse / switching method, rather than linearly carrying the analog voltage with light intensity amplitude. Based on this, the remote end converts the oil level analog voltage into a pulse frequency signal via voltage-frequency conversion, and then uses this frequency signal to directly drive the optical transmitting module, achieving a reliable mapping of "voltage information → frequency information → optical pulse." The host end receives the optical pulse, only needs to recover its frequency information, and then convert it back to an analog voltage output proportional to the oil level height via frequency-voltage conversion.

[0055] The remote optical transmitter module (TX) receives the pulse frequency signal output from the voltage-to-frequency conversion module and uses it as the modulation source for optical transmission. It then converts the electrical pulse signal into modulated light and couples it into the optical fiber. For the 808 / 850nm architecture, a digital fiber optic transmitter module can be used, which internally uses light-emitting diodes to achieve electro-optical conversion. For the 1550nm information light architecture, the remote end can also use an optical transmitter module that meets the 1550nm band, transmitting the measurement information back in the form of 1550nm information light. In the dual-fiber scheme, the communication light is independently coupled into the "signal fiber"; in the single-fiber scheme, the communication light needs to be bundled with the energy light via WDM and then separated at the host end.

[0056] The host-side optical receiver module (RX) converts the received information light into a corresponding electrical signal and recovers the oil level measurement information. After the return information light enters the host-side optical receiver module, it undergoes photoelectric conversion and outputs an electrical frequency signal. This electrical frequency signal is then converted back into an analog voltage signal proportional to the oil level height by a frequency-to-voltage conversion circuit, thus enabling the acquisition of oil level parameters. For a single-fiber solution, the host side needs to first separate the return information light from the mixed light using a wavelength division multiplexer before sending it to the optical receiver module. For a dual-fiber solution, the information light directly enters the optical receiver module from the signal fiber, resulting in independent channels and a clear structure.

[0057] (4) Power supply module (main unit) The power supply module is located at the host end and is used to generate energy light for remote passive power supply and couple it into the fiber optic link to achieve long-distance energy transmission and stable supply. This module includes a laser energy emission unit and its drive and temperature control protection units: the drive unit adopts a constant current control structure to achieve stable and adjustable output of energy light power and has safety protections such as overcurrent and overtemperature protection; the temperature control protection unit uses TEC closed-loop temperature control to stabilize the laser's operating temperature, thereby reducing output drift and improving long-term reliability and safety.

[0058] In the dual-fiber scheme, the module outputs energy light (808nm) and directly couples it into the "energy transmission fiber," which is physically isolated from the return signal fiber, resulting in a clear link. In the single-fiber wavelength division multiplexing scheme, after the module outputs energy light (1064nm or 808nm), it needs to be bundled with the return information light (1550nm or 850nm) through a wavelength division multiplexer before entering the same fiber. At the host end, the return information light is separated and received through a wavelength division multiplexer, thereby realizing bidirectional multiplexing of simultaneous energy transmission and communication on a single fiber.

[0059] (5) Photoelectric transducer and power management module (remote) The photoelectric transducer and power management module (remote end) is located in the remote sensing unit. It converts the light energy transmitted from the host unit via optical fiber into electrical energy and outputs a stable DC power supply to power the remote capacitive oil level measurement and signal feedback circuit. This module includes a photoelectric transducer (photovoltaic power converter PPC) and a power management circuit: the photoelectric transducer converts the incident light energy into primary electrical energy; the power management circuit regulates, filters, and distributes the primary electrical energy to form a stable power supply adapted to the remote load, providing power to the capacitive oil level sensor, capacitance measurement chip, voltage-to-frequency conversion module, and optical transmission module.

[0060] (6) Wavelength multiplexing and fiber optic transmission module (dual fiber / single fiber) The wavelength multiplexing and fiber optic transmission module is used to realize long-distance transmission of energy light and oil level information light between the host and remote ends, serving as the physical channel connecting the power supply link and the communication link. This module can be configured as a dual-fiber physically isolated structure or a single-fiber wavelength division multiplexing structure, depending on the link configuration: In the dual-fiber structure, the energy transmission fiber and the signal transmission fiber are independent, used to transmit energy light and return information light respectively, thus achieving physical isolation of the channel, resulting in a clear structure that is easy to maintain and isolate faults; in the single-fiber structure, the energy light and information light are multiplexed and transmitted within the same fiber using a wavelength division multiplexer, reducing the number of fibers and interfaces and facilitating system integration and weight reduction.

[0061] In a single-fiber wavelength division multiplexing (WDM) architecture, WDM / demultiplexing devices are installed at both the host and remote ends to combine and split the energy and information light beams to achieve channel isolation. At the host end, the energy and information light are coupled and input into a single optical fiber. At the remote end, the energy light is separated and sent to a photoelectric transducer for power supply, while the information light channel is used to transmit oil level information. The host end then separates the transmitted information light to an optical receiving link.

[0062] The wavelength combination of the energy light and the information light can be selected as dual-fiber 808nm / 850nm. When the energy light is 1064nm, the information light is preferably 1550nm; when the energy light is 808nm, the information light is preferably 850nm (selected according to device and link design). In addition, the single-fiber structure needs to consider the impact of WDM insertion loss and channel isolation on power margin and communication quality.

[0063] (7) Demodulation and interface output module (host side) The demodulation and interface output module is located on the host side and is used to receive, demodulate, and recover the oil level information light transmitted from the remote end, and output a usable oil level signal to the airborne data acquisition / display / control system. This module includes a light receiving and photoelectric conversion unit, a signal recovery unit, and an interface output unit: after the transmitted information light enters the light receiving module, it completes photoelectric conversion and outputs an electrical frequency signal. Then, through the signal recovery link, the frequency information is restored to an analog voltage signal or equivalent digital quantity proportional to the oil level height, and the output is an analog voltage interface, or output to the airborne acquisition / control unit through the interface circuit, thereby realizing the acquisition and upper-level processing of oil level parameters.

[0064] To avoid the nonlinearity and temperature drift issues of analog amplitude modulation, the remote end uses a voltage-frequency method to carry oil level information, while the host end demodulates the returned pulse signal and restores it to an analog voltage output through a frequency-voltage conversion. This restoration method is insensitive to optical link attenuation; as long as the pulse is identifiable, the frequency information can be stably restored, thus ensuring end-to-end linearity and transmission reliability.

[0065] The above are merely exemplary embodiments of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure.

[0066] This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described in this disclosure. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

Claims

1. A capacitive passive oil level detection system based on fiber optic power transmission and communication, the system comprising: The host unit, the remote oil level sensing unit, and the fiber optic transmission link module; The fiber optic transmission link module is connected between the host unit and the remote oil level sensing unit. The host unit includes a laser energy emission module and an optical receiving and demodulation module; The laser energy emission module outputs energy light, which is transmitted to the remote oil level sensing unit via the optical fiber transmission link module. The remote oil level sensing unit includes: a photoelectric transducer module, a power management module, a capacitive oil level sensor and a capacitance measurement module, and a light emission and signal modulation module. The photoelectric transducer module converts light energy into electrical energy, which is then used by the power management module to power the remote oil level sensing unit. The capacitance measurement module is configured to convert the capacitance change of the capacitive oil level sensor into an analog voltage signal that is related to the oil level height. The optical emission and signal modulation module is configured to generate backhaul communication light based on the analog voltage signal, and transmit it back to the host unit via the optical fiber transmission link module; The optical receiving and demodulation module recovers the oil level measurement information from the return communication optical signal.

2. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The host unit also includes a laser drive control module; The laser drive control module is sequentially connected to the laser energy emission module and is used to set and adjust the output power of the laser energy emission module, as well as to implement overcurrent protection and overtemperature protection.

3. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 2, characterized in that, The laser drive control module includes a constant current drive unit, which adopts a hardware closed-loop constant current structure and is slow-loop calibrated by a processor to achieve stable and adjustable laser drive current and safe monitoring. The laser drive control module also includes a temperature control unit, which includes a temperature acquisition circuit, a temperature control circuit, and a semiconductor cooler drive circuit, for constant temperature control of the laser energy emission module.

4. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The photoelectric power conversion module is a photovoltaic power converter used to convert the energy light transmitted through the optical fiber transmission link module into DC power output; The power management module includes a DC-DC converter circuit, which is used to regulate or buck-boost the electrical energy output by the photovoltaic power converter to form at least one stable DC power supply for use by the capacitance measurement module and the light emission and signal modulation module.

5. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The capacitance measurement module includes a temperature compensation processing unit, which is configured to correct the analog voltage signal based on the temperature signal collected by the temperature sensor.

6. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The optical fiber transmission link module adopts a dual optical fiber link, including a first optical fiber and a second optical fiber. The first optical fiber is used to transmit the energy light, and the second optical fiber is used to transmit the return communication light.

7. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The optical fiber transmission link module can also use a single optical fiber link, and the host unit and the remote oil level sensing unit are respectively equipped with a wavelength division multiplexer and a wavelength demultiplexer; the wavelength division multiplexer is configured to couple energy light and backhaul communication light of different wavelengths into the same optical fiber for transmission; the wavelength demultiplexer separates the mixed light received from the same optical fiber into energy light and backhaul communication light.

8. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The optical emission and signal modulation module includes a voltage-to-frequency conversion module, which converts the analog voltage signal output by the capacitance measurement module into a frequency signal proportional to it, and drives the optical emission and signal modulation module to form a pulse backhaul communication optical carrying the frequency signal.

9. The capacitive passive oil level detection system based on fiber optic power transmission and communication as described in claim 1, characterized in that, The optical receiving and demodulation module includes: a photoelectric conversion unit and a signal recovery unit; The photoelectric conversion unit is configured to convert the backhaul communication optical light into an electrical signal; The return communication optical signal is an optical pulse frequency signal; the electrical signal is an electrical pulse frequency signal. The signal recovery unit is configured to extract the frequency signal from the electrical signal and recover the oil level measurement information; The signal recovery unit includes a frequency-to-voltage conversion subunit, which recovers the frequency signal into an analog voltage output signal corresponding to the oil level.

10. A capacitive passive oil level detection method based on fiber optic power transmission and communication, based on the capacitive passive oil level detection system based on fiber optic power transmission and communication as described in any one of claims 1-9, characterized in that, The method includes the following steps: The host generates energy light, which is coupled into the optical fiber transmission link and transmitted to the remote end via the optical fiber. The remote receiver receives light energy, converts the light energy into electrical energy through photoelectric conversion, and then supplies power to the remote oil level detection circuit after voltage regulation. Collect capacitance change data from a capacitive oil level sensor and convert the capacitance change data into an analog voltage signal corresponding to the oil level height; The analog voltage signal is converted into a frequency signal proportional to it, and the frequency signal is used to drive the optical transmitter to form a return communication optical signal carrying frequency information. The return communication optical coupler is inserted into the optical fiber transmission link and transmitted back to the host. The host receives the return communication optical signal, converts it into an electrical signal, extracts frequency information from the electrical signal, and then converts the frequency information into an analog voltage output signal corresponding to the oil level, thus obtaining the oil level measurement information.

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