Resonant low-temperature liquid level sensor detection system

Abstract

The invention discloses a resonant low-temperature liquid level sensor detection system, and belongs to the technical field of low-temperature liquid level detection. The system is mainly formed by sequentially connecting a frequency sweep power supply module, a power amplification detection module, a series resonance network and an output detection device. According to the working principle, broadband excitation is provided through the sweep frequency power supply module, and after signal amplification, isolation and impedance matching are conducted through the power amplification module, a series resonance network composed of the tunable element, the liquid level sensitive element and the load resistor is driven. The output detection device adopts a vector network analysis technology, extracts signals through a directional coupler, and comprehensively analyzes multiple parameters to accurately calculate the liquid level height. Liquid level detection is converted into frequency domain measurement, the precision, stability and full-scale performance of low-temperature liquid level measurement are remarkably improved, and the device is particularly suitable for storage tank liquid level monitoring of low-temperature media such as liquid nitrogen.

Description

Technical Field

[0001] This invention relates to the field of cryogenic liquid level detection technology, and more specifically to a resonant cryogenic liquid level sensor detection system. Background Technology

[0002] In the field of cryogenic liquid level detection, existing technologies such as differential pressure method, ultrasonic method, fiber optic method, superconducting method, and capacitance method have their own applications, but all have significant limitations. Among them, capacitive cryogenic liquid level sensors have been widely studied due to their good dynamic response, reliable mechanical structure, and strong environmental adaptability, but they face technical bottlenecks in high-precision cryogenic measurement.

[0003] In low-temperature environments, the relative permittivity of the medium is extremely low (e.g., 1.482 for liquid oxygen and 1.432 for liquid nitrogen), resulting in capacitance changes of only tens to hundreds of pF and extremely high output impedance. This makes the system poor in terms of load capacity and susceptible to interference, especially under low liquid level conditions. The liquid-immersed electrode area is small, the initial capacitance is extremely low (approximately tens of picofarads), the equivalent capacitive reactance is very large, the effective electrical signal is weak, and the signal-to-noise ratio deteriorates. Subsequent signal conditioning circuits struggle to extract the weak signal, creating a low liquid level detection blind zone and preventing accurate measurement across the entire range.

[0004] Therefore, there is an urgent need for a new type of detection system to improve the measurement reliability in low-temperature environments, in order to solve the problems of insufficient initial sensitivity, poor signal-to-noise ratio, and insufficient load capacity of capacitive low-temperature liquid level sensors in low-temperature measurement environments.

[0005] Existing capacitive liquid level detection solutions have not effectively solved problems such as excessive capacitive reactance, insufficient initial sensitivity, and noise suppression. There is an urgent need for an innovative system to improve the measurement reliability in low-temperature environments.

[0006] The present invention aims to overcome the above-mentioned technical shortcomings and proposes a resonant cryogenic liquid level sensor detection system to solve the problems of insufficient initial measurement sensitivity, poor signal-to-noise ratio, and insufficient load capacity of capacitive cryogenic liquid level sensors in low-temperature measurement environments, thereby achieving full-range, high-precision, and highly continuous liquid level detection in low-temperature environments. Summary of the Invention

[0007] The purpose of this invention is to provide a resonant cryogenic liquid level sensor detection system. By cascading a power amplification detection module and a series resonant network, the system converts the minute capacitance changes caused by the liquid level into resonant frequency shifts for measurement, significantly improving signal detection capability. This solves the problems of insufficient initial sensitivity, poor signal-to-noise ratio, and insufficient load capacity of capacitive cryogenic liquid level sensors in low-temperature measurement environments.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A resonant cryogenic liquid level sensor detection system includes a swept-frequency power supply module, a power amplification detection module, a series resonant network, and an output detection device, which are electrically connected in sequence, wherein: The frequency sweep power supply module is used to generate a broadband excitation signal with a scannable frequency. The power amplification and detection module is used to amplify, isolate, and perform impedance transformation on the excitation signal; The series resonant network includes a tunable element, a liquid level sensing element, and a load resistor, and is used to reflect changes in liquid level through resonant frequency shift; The output detection device is used to detect the response signal of the series resonant network and calculate the liquid level height; The series resonant network exhibits a low impedance state at the resonant frequency point.

[0009] Furthermore, the swept-frequency power supply module employs direct digital frequency synthesis technology and includes a DDS excitation signal source, an operational amplifier, and a bandpass filter connected in sequence, wherein: The DDS excitation signal source is used to generate a highly stable sine wave signal; The operational amplifier is used to increase signal amplitude and load capacity; The bandpass filter is used to suppress harmonics and out-of-band noise, and output a clean sweep signal.

[0010] Furthermore, the power amplification and detection module includes a power amplification and distribution submodule, a transformer balun, and an impedance transformation network connected in sequence, wherein... The power amplification and distribution submodule is used to amplify the power of the input signal; The transformer balun is used for the conversion of differential signals to single-ended signals and provides electrical isolation; The impedance transformation network is used to match the output impedance of the power amplifier detection module with the input impedance of the series resonant network.

[0011] Furthermore, the output detection device includes a directional coupler, a vector network analyzer, a liquid level display and processing device, and a matching terminal, wherein: The directional coupler is used to couple the forward transmission signal out of the main signal path; The vector network analyzer is used to measure the amplitude, phase, frequency, and impedance parameters of the forward transmission signal; The liquid level display and processing device is used to calculate the liquid level height according to a preset frequency-liquid level mapping model.

[0012] The matching terminal is used to absorb reflected signals to ensure measurement accuracy.

[0013] Furthermore, in the series resonant network, wherein: The tunable element is an inductor with adjustable inductance. The liquid level sensing element is a capacitive cryogenic liquid level sensor; The load resistor is a resistor element with a fixed resistance value, used to reduce the impedance at the resonant point.

[0014] Furthermore, the capacitance value of the capacitive cryogenic liquid level sensor changes with the liquid level height, and the resonant frequency is inversely proportional to the square root of the product of the capacitance value and the inductance of the inductive element.

[0015] Furthermore, the capacitive cryogenic liquid level sensor adopts an integrated coaxial cylindrical structure, including an outer electrode and an inner electrode that are respectively connected to the series resonant network through lead-out electrical connection lines.

[0016] Furthermore, the capacitive cryogenic liquid level sensor adopts a segmented structure, in which the inner and outer electrodes are constructed as multiple independent capacitor units arranged in a vertical direction, and the inner and outer electrodes are respectively connected to the series resonant network through lead-out electrical connection lines.

[0017] Furthermore, in the series resonant network, wherein: The tunable element is a capacitor element with adjustable capacitance; The liquid level sensing element is an inductive cryogenic liquid level sensor; The load resistor is a resistor element with a fixed resistance value, used to reduce the impedance at the resonant point.

[0018] Furthermore, the inductance value of the inductive cryogenic liquid level sensor changes with the liquid level height, and the resonant frequency is inversely proportional to the square root of the product of the inductance value of the inductive liquid level sensor and the capacitance of the capacitive element.

[0019] This invention provides a resonant cryogenic liquid level sensor detection system, which achieves a breakthrough in the field of cryogenic liquid level measurement through innovative design of the resonant detection system. The core of the system is based on the synergistic cascading of a power amplification detection module and a series resonant network, converting the minute capacitance changes (as low as a few tens of picofarads) caused by the liquid level into a significant shift in the resonant frequency for measurement. This fundamentally solves the problems of excessive capacitive reactance, weak signal, and noise interference in traditional capacitive cryogenic liquid level sensors under low-temperature environments. Specific technical effects are as follows: 1. Full-range high-precision detection and blind-zone-free measurement By introducing a tunable RLC series resonant network (composed of a tunable inductor, a liquid level capacitor, and a load resistor), the system achieves minimum impedance (only a few ohms) at the resonant point, significantly improving signal transmission efficiency. The cascaded system design enables the resonant frequency to accurately track changes in liquid level, achieving continuous measurement across the entire range and completely eliminating the low-level dead zone.

[0020] 2. Optimized signal-to-noise ratio and enhanced anti-interference capability The narrowband filtering characteristics of the series resonant network effectively suppress out-of-band noise, and combined with the pre-amplification function of the power amplifier module, the system signal-to-noise ratio is significantly improved. The capacitive cryogenic level sensor is directly immersed in the cryogenic liquid, and its initial capacitive reactance is greatly reduced through the load resistor, avoiding signal attenuation. Simultaneously, the multi-parameter extraction mechanism of the directional coupler and vector network analyzer further isolates environmental interference, ensuring reliability in complex liquid level sensing environments.

[0021] 3. Improved load capacity and power transmission efficiency The introduction of a load resistor reduces the system output impedance to the ohm level, resulting in high power transmission efficiency and overcoming the insufficient load-carrying capacity of traditional capacitive sensors. The power amplification detection module optimizes energy transfer through an impedance matching network, ensuring that weak liquid level signals do not significantly attenuate during transmission, making it suitable for long-distance cabling scenarios.

[0022] 4. Multi-parameter fusion and intelligent demodulation The output detection device fuses multi-dimensional information such as resonant frequency, S-parameters, phase, and impedance to construct a frequency-level mapping model, enabling multi-parameter calculation of the liquid level. This method combines contact capacitance measurement with non-contact vector analysis, significantly improving measurement consistency and disturbance resistance, and providing data support for intelligent monitoring of cryogenic storage tanks.

[0023] In summary, this invention, through its low-cost modular design, achieves a triple improvement in sensitivity, accuracy, and reliability of cryogenic liquid level detection, providing key technical support for high-end equipment in aerospace, medical MRI, and energy storage and transportation. Attached Figure Description

[0024] Figure 1 This is a system block diagram of the present invention; Figure 2 This is a schematic diagram of the sweep frequency power supply module of the present invention; Figure 3 This is a schematic diagram of the power amplification and detection module of the present invention; Figure 4 This is a schematic diagram of the structure of a capacitive cryogenic liquid level sensor according to Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the output detection device of the present invention; Figure 6 This is a schematic diagram of a series resonant network according to Embodiment 2 of the present invention; Figure 7 This is a schematic diagram of the segmented capacitive cryogenic liquid level sensor structure according to Embodiment 2 of the present invention; Figure 8 This is a schematic diagram of the series resonant network in Embodiment 3 of the present invention; Figure 9 This is a schematic diagram of the structure of an inductive cryogenic liquid level sensor according to Embodiment 3 of the present invention; In the picture: 1-Capacitive cryogenic liquid level sensor, 2-First measuring sealed liquid container, 3-Cryogenic medium storage container, 4-Cryogenic liquid, 5-Cryogenic gas, 6-Gas-liquid interface, 7-Isolation top cover, 8-First lead-out electrical connection line, 9-Second lead-out electrical connection line, 21-External electrode of segmented capacitive cryogenic liquid level sensor, 22-Internal electrode of segmented capacitive cryogenic liquid level sensor, 23-Measuring sealed liquid container, 24-Cryogenic medium storage container, 25-Isolation top cover, 26-First lead-out electrical connection line, 27-Second lead-out electrical connection line, 31-Inductive cryogenic liquid level sensor, 32-Measuring sealed liquid container, 33-Cryogenic medium storage container, 34-Cryogenic liquid, 35-Cryogenic gas, 36-Gas-liquid interface, 37-Isolation top cover, 38-First lead-out electrical connection line, 39-Second lead-out electrical connection line. Detailed Implementation

[0025] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0026] The core innovation of this invention, a resonant cryogenic liquid level sensor detection system, lies in the synergistic cascade design of a power amplification detection module and a series resonant network. This design converts the minute capacitance changes caused by liquid level into significant shifts in the resonant frequency for measurement, thereby solving the technical challenges of capacitive cryogenic liquid level sensors in low-temperature environments, such as excessive capacitive reactance, low initial liquid level measurement sensitivity, and poor signal-to-noise ratio. The system consists of a swept-frequency power supply module, a power amplification detection module, a series resonant network, and an output detection device, all cascaded sequentially. The swept-frequency power supply module provides a broadband excitation signal, the power amplification detection module amplifies, isolates, and preprocesses the signal, the series resonant network performs frequency selection filtering, forms a complex impedance modulated liquid level capacitance, and suppresses narrowband noise, the capacitive cryogenic liquid level sensor senses changes in the cryogenic liquid level, and the output detection device extracts multiple parameters, ultimately achieving a high-precision, full-range cryogenic liquid level detection system. The composition of this system is described in detail below.

[0027] 1. System Overall Structure and Working Principle like Figure 1As shown, the electrical connection sequence of the system of the present invention is as follows: the output terminal of the sweep frequency power supply module is connected to the input terminal of the power amplification and detection module, the output terminal of the power amplification and detection module drives the series resonant network, and the series resonant network is directly coupled to the capacitive cryogenic liquid level sensor; the response signal of the sensor is finally collected and processed by the output detection device.

[0028] The core of the system is an RLC series resonant network, consisting of tunable elements (such as an inductor with adjustable inductance, i.e., a tunable inductor ΔLs) and a liquid level sensing element (the liquid level capacitance ΔC of a capacitive cryogenic liquid level sensor). liquid It consists of a liquid level and a load resistor Rs. Its working principle is based on the detection of resonant frequency shift: when the liquid level changes, ΔC... liquid The change causes the resonant frequency of the resonant network to... Corresponding offset. The swept-frequency power supply module provides a wideband excitation signal, which is amplified by the power amplifier detection module and then drives the series resonant network. At the resonant point, the circuit impedance is minimal (mainly determined by Rs, with a resistance of only a few ohms), the signal transmission efficiency is highest, and out-of-band noise is suppressed by the high impedance, thus significantly improving the signal-to-noise ratio. The output detection device calculates the liquid level height in real time by detecting multiple parameters such as resonant frequency, phase, and impedance. This design not only solves the signal attenuation problem caused by high capacitive reactance but also avoids the limitations of analog signal processing through frequency domain measurement.

[0029] 2. Sweep frequency power supply module like Figure 2 As shown, the sweep frequency power supply module, serving as the system's excitation source, employs Direct Digital Synthesis (DDS) technology as its core, forming a complete three-stage signal generation and conditioning chain. This module first generates a highly stable, high-purity sinusoidal digital signal with precisely controllable frequency and linear sweeping from the DDS excitation signal source. This signal is then amplified in a buffer and driver stage composed of operational amplifiers to enhance the signal's voltage amplitude and load-carrying capacity, effectively driving subsequent circuits. Finally, the amplified signal undergoes spectral cleanup through a bandpass filter. This filter is precisely tuned to the system's required operating frequency band, significantly suppressing inherent harmonics and spurious signals from the DDS, noise introduced by the amplification circuit, and out-of-band interference, thereby outputting a "clean" and stable sweep frequency signal.

[0030] Its output frequency range is designed in the kHz to MHz range, ensuring that it can completely cover the liquid level capacitance ΔC caused by liquid level changes. liquid The corresponding expected resonant frequency range. This integrated design, from generation and amplification to filtering, ensures that the final output swept signal has excellent frequency accuracy, stable amplitude, and high spectral purity.

[0031] 3. Power Amplification Detection Module The power amplifier detection module is the core of the system's signal processing. Its multi-stage cascaded design is specifically designed to solve the problems of weak capacitive signals being easily interfered with by noise and having weak load-carrying capacity in low-temperature environments. For example... Figure 3 As shown, this module consists of a power amplifier and distribution submodule, a transformer balun, an impedance transformation network, etc. Its signal processing link is clear: the input of the detection module first receives the initial sweep frequency signal from the sweep frequency power supply module and sends it to the power amplifier and distribution submodule.

[0032] This submodule employs a high-performance Class AB or Class D power amplifier architecture to amplify the input signal, and its gain can be precisely adjusted according to actual needs. This amplification process significantly improves the signal power level, directly enhancing the ability to drive subsequent circuits and laying the foundation for improving the signal-to-noise ratio of capacitive cryogenic level sensors, effectively overcoming the bottleneck of weak and difficult-to-process signals.

[0033] The amplified signal is then fed into a transformer balun. This balun is a critical interface, marked with pins 1 to 5, indicating its complete differential-to-single-ended conversion capability. It efficiently converts any differential signal from the preceding stage into the single-ended form required by the subsequent stage, while simultaneously achieving electrical isolation through magnetic coupling. This feature effectively eliminates ground loops and significantly improves the overall detection system's resistance to common-mode interference.

[0034] Subsequently, the signal enters the impedance transformation network. This network, composed of inductors and capacitors in L-type or π-type topologies, is designed for impedance matching. It transforms the relatively low output impedance of the power amplification and distribution submodule (e.g., a standard 50 ohms) into a state that is conjugate-matched to the load impedance of the subsequent series resonant network. This precise impedance transformation minimizes signal reflection losses during transmission, enabling efficient power transfer from the detection module to the sensor network and ensuring that the excitation signal energy effectively acts on the liquid level capacitor.

[0035] Finally, the signal, after amplification, conversion, isolation, and matching optimization, is output from the detection module, providing high-quality, high-driving-capability excitation for the series resonant network, thereby ensuring the measurement accuracy and stability of the entire liquid level detection system.

[0036] 4. Series resonant network like Figure 1 As shown, the series resonant network serves as the core detection unit of the system, consisting of a tunable inductor ΔLs and a capacitive cryogenic liquid level sensor with a liquid level capacitance ΔC. liquid The resistor Rs and the load resistor Rs together form an RLC series circuit. The working principle of this network is that its resonant frequency... It will vary with the liquid level capacitance ΔC liquidThe frequency shifts with the change in liquid level, thus creating a precise mapping between the effective operating frequency of the resonant network and the liquid level height. At the resonant point, the circuit impedance reaches its minimum value, theoretically equal to the load resistance Rs (usually a few ohms). At this point, the signal transmission efficiency is the highest, and the voltage or current amplitude is the largest. For out-of-band noise, the network exhibits high impedance, thereby achieving significant frequency selectivity and strong noise suppression capabilities.

[0037] like Figure 4 As shown, the capacitive cryogenic liquid level sensor 1 used in Embodiment 1 is an integrated coaxial cylindrical structure. Its core part is installed inside a first sealed liquid measuring container 2, which is placed in a cryogenic medium storage container 3. The sensor's internal electrode is connected to a series resonant network via a first lead-out electrical connection line 8, and the sensor's external electrode is connected to the series resonant network via a second lead-out electrical connection line 9. The two are supported by insulating material to form a coaxial capacitor structure. The sensor is directly immersed in the cryogenic liquid 4, with cryogenic gas 5 above the liquid surface, and a clear gas-liquid interface 6 exists between the gas and the liquid. The top of the container is sealed by an insulating top cover 7, which also provides lead-out channels for the electrical connection lines.

[0038] Its liquid level capacitance ΔC liquid The mechanism of change is as follows: when the liquid level rises or falls, the effective area between the inner and outer electrodes, covered by the cryogenic liquid (whose dielectric constant is different from that of the cryogenic gas above), changes accordingly, thereby causing the equivalent capacitance ΔC between the two plates to change. liquid Changes occur. Under low liquid level conditions, the liquid coverage area is small, ΔC liquid The absolute change in capacitance is extremely small, only on the order of a few picofarads, resulting in a very high capacitive reactance. However, by introducing a series resonant network, at the resonant frequency, the capacitive reactance of the sensor cancels out the inductive reactance of the tunable inductor ΔLs, minimizing the impedance of the entire circuit to a minimum, leaving only the real impedance of the load resistance Rs, which is only a few ohms. This significantly reduces signal transmission loss and effectively solves the problem of difficulty in detecting the initial liquid level due to excessive capacitive reactance.

[0039] Therefore, the cascaded collaboration of the power amplification detection module and the series resonant network first amplifies and optimizes the weak signal, and then performs efficient extraction and noise filtering through the resonance mechanism. This significantly enhances the detection amplitude and processing capability of the entire system for weak capacitance signals caused by liquid level changes, providing a key guarantee for achieving high-precision, full-range cryogenic liquid level measurement.

[0040] 5. Output detection device like Figure 5As shown, the output detection device constitutes the signal demodulation and information processing terminal of this resonant detection system, which realizes the final extraction of liquid level information through precise microwave measurement technology. The connection relationship of the device is as follows: its input end is connected to the main signal path of the system through a directional coupler. The input end (In) of the coupler receives the return signal from the preceding series resonant network, and the output end (Out) is connected to a matching terminal to absorb residual energy and prevent reflection.

[0041] The directional coupler is the starting point of this process. It couples a portion of the forward transmission power signal (Fwd) from the complex signal returned by the series resonant network containing the capacitive cryogenic level sensor. This directional coupling characteristic ensures that the extracted signal accurately reflects the level-modulated resonant network response, while effectively isolating interference caused by the back-reflected signal. The coupled Fwd signal is then fed with high precision into a vector network analyzer.

[0042] The vector network analyzer, as a measurement unit, performs multi-parameter detection and extraction on the input Fwd signal. It can accurately measure the signal's fundamental characteristics such as amplitude, phase, and frequency, and further calculate key S-parameters (such as the forward propagation coefficient), the complex impedance characteristics of the resonant network at different frequencies, and the equivalent liquid level capacitance ΔC calculated through inversion. liquid This simultaneous acquisition of multi-domain parameters provides a rich and mutually verified data foundation for liquid level calculation. All measured data is transmitted in real time to the liquid level display and processing equipment via a digital interface.

[0043] The liquid level display and processing equipment is the final center for calculating and displaying liquid level information. Internally, it incorporates a frequency-liquid level mapping model pre-calibrated through experiments. The core algorithm of this equipment accurately tracks the position of the resonant frequency point by monitoring the transmission response of the series resonant network at different frequency sweeps (mainly manifested as the peak value of the S-parameter amplitude or the zero-crossing point of the phase). This resonant frequency is related to the liquid level capacitance ΔC. liquid As a definite functional relationship exists as described above, the liquid level height can be obtained indirectly and accurately. To further improve reliability and anti-interference capability, the calculation process does not rely solely on the single parameter of frequency, but deeply integrates multiple information such as harmonic distortion analysis, S-parameter curve shape analysis, phase change slope, and impedance real / imaginary part changes for data fusion and confidence judgment, and finally calculates and displays the current liquid level height in real time.

[0044] This vector analysis-based output detection method cleverly integrates the sensing mechanism of a contact-type capacitive cryogenic liquid level sensor with a non-contact microwave network multi-parameter domain measurement technology. This results in liquid level measurement accuracy, stability, and resistance to interference from complex electromagnetic environments that far surpasses traditional single-parameter detection methods that rely solely on absolute capacitance measurements. The presence of a matching terminal ensures impedance matching in the signal transmission link, avoiding measurement errors caused by mismatch, and is a crucial foundation for achieving the aforementioned high-precision measurements.

[0045] Example 1, taking liquid nitrogen storage tank level detection as an example, details the implementation steps of the present invention.

[0046] Select a coaxial cylindrical capacitive cryogenic liquid level sensor (such as...) Figure 4 The electrode material is 304 stainless steel, 1m in length, corresponding to a liquid level range of 0-100%. The sweep frequency power supply module uses an AD9850 DDS chip, with an output frequency range of 50kHz-10MHz and a sweep step of 100Hz. The power amplifier module gain is set to 30dB, and the impedance transformation network is tuned to VSWR<1.25. Series resonant network parameters: the initial value of the tunable inductor ΔLs is set to 50uH, and the load resistance Rs = 5Ω. The output detection device uses a commercial vector network analyzer (such as Keysight E5061B) connected via a directional coupler.

[0047] Then, system calibration and mapping model establishment were performed. For empty tank calibration, with the liquid level at 0%, ΔLs was adjusted to achieve a resonant frequency of 1.2MHz, which was recorded as f. min During full-tank calibration, with the liquid level at 100%, the resonant frequency shifted to 2.5MHz, recorded as f. max Establish a linear mapping model, where the liquid level height H = k·(f r -f min )+b, where k and b are fitted using the least squares method, and the measured fitting error is <±1%. Temperature compensation: In a liquid nitrogen environment at -196℃, the sensor capacitance temperature coefficient is recorded (-0.1% / ℃), and the software automatically compensates for frequency shift.

[0048] Testing begins with the sweep frequency power supply scanning at 100Hz / ms, and the power amplifier module outputs a signal to drive the sensor. A vector network analyzer samples the S-parameters every 100ms to extract the resonant frequency fr. The level display device calculates the level using a mapping model while simultaneously monitoring phase changes (threshold set at 5°) to verify data consistency; any phase anomalies trigger recalibration. A 4-20mA analog signal is output to the PLC system for closed-loop control. Testing in the 10% low level range shows a signal-to-noise ratio improved to 40dB (compared to only 20dB using traditional methods), with no blind spots. After 72 hours of long-term operation, level fluctuations are <±0.5%, verifying stability.

[0049] In addition, to maximize the versatility of the technical solution of this invention, Figures 6 to 9 This paper details several feasible design embodiments based on the same resonant detection principle. These embodiments demonstrate the core idea of ​​the invention: by constructing a series resonant network and converting liquid level changes into resonant frequency shifts for measurement, the invention can be flexibly adapted to different types of sensor structures, greatly enhancing the practicality and innovation of the technical solution.

[0050] Example 2, as Figure 6 As shown, an important improved topology is illustrated. This network still consists of a tunable inductor ΔLs, a load resistor Rs, and a level sensor connected in series. However, its core lies in the capacitive cryogenic level sensor, which employs a segmented structure. Its inner and outer electrodes are constructed as multiple independent capacitor units arranged vertically, and these inner and outer electrodes are connected to the series resonant network via lead-out electrical connections. Figure 7 As shown, the sensor consists of an external electrode 21 and an internal electrode 22 of a segmented capacitive cryogenic level sensor. The entire sensor is installed inside a sealed liquid container 23, which is placed within a cryogenic medium storage container 24, and the top is sealed by an isolation cap 25. The internal electrode 22 of the segmented capacitive level sensor is connected to the circuit via a first lead-out electrical connection line 26, and the external electrode 21 is connected to the circuit via a second lead-out electrical connection line 27. This segmented sensor features an innovative structure, with its internal and external electrodes designed as multiple independent capacitor units (C1 to C6) arranged vertically. This "segmented" structure transforms the continuous change in liquid level height into discrete activation of multiple capacitor units, effectively reducing measurement errors caused by edge effects and nonlinearity in traditional coaxial cylindrical capacitive sensors. By precisely designing the size and position of each capacitor unit, a superior linear relationship between the liquid level and the total capacitance can be achieved, significantly improving the overall linearity and segment recognition accuracy of the system, especially in large-range measurements.

[0051] Example 3: The universality of this invention is further demonstrated by its applicability to completely different sensing principles. For example... Figure 8 As shown, this design involves fundamental component replacements: the capacitive cryogenic level sensor is replaced with an inductive cryogenic level sensor 31, and the tunable element is replaced from the inductor ΔLs to a capacitor with adjustable capacitance ΔCs. In this case, the series resonant network consists of ΔCs, the inductive sensor, and Rs, and its resonant frequency formula becomes... , where △L liquid This represents the sensor inductance value that changes with the liquid level. For example... Figure 9As shown, the inductive cryogenic liquid level sensor 31 is connected to a series resonant network via the first lead-out electrical connection line 38 and the second lead-out electrical connection line 39. Figure 8 The sensor is installed inside a sealed liquid container 32, which is placed within a cryogenic medium storage container 33. The container contains cryogenic liquid 34 and cryogenic gas 35, with a clear gas-liquid interface 36 between them. The top is sealed by an insulating cap 37 to ensure the stability of the measurement environment. The inductive cryogenic liquid level sensor 31 is connected to the circuit via two lead wires. Its inductance varies depending on the immersion depth of the internal oxygen-free, highly conductive copper or other sensitive elements in the cryogenic liquid. This design is particularly suitable for conductive media or special scenarios where capacitive coupling interference needs to be avoided. It calculates the inductance change by measuring the resonant frequency to obtain liquid level information, fully demonstrating the wide applicability of the resonant detection mechanism of this invention.

[0052] In summary, whether employing a segmented capacitor structure to optimize performance or changing to an inductive sensing principle to adapt to different media, these transformation designs all share the same core technology: utilizing a tunable RLC series resonant network to highly sensitively convert changes in liquid level parameters (capacitance or inductance) into frequency signals for detection. The above embodiments demonstrate that the resonant detection system proposed in this invention is a powerful and flexible technical platform, rather than an isolated solution, with broad application prospects. This invention, through the synergistic cascading of frequency sweep excitation, power amplification, resonant frequency selection, and multi-parameter detection, transforms liquid level detection into frequency domain measurement, overcoming the limitations of traditional capacitance methods.

[0053] Contents not described in detail in this specification are prior art known to those skilled in the art. It is hereby indicated that the above description is intended to help those skilled in the art understand this invention, but does not limit the scope of protection of this invention. Any equivalent substitutions, modifications, improvements, or simplifications of the above descriptions that do not depart from the essential content of this invention fall within the scope of protection of this invention.

Claims

1. A resonant cryogenic liquid level sensor detection system, characterized by, The sweep frequency power supply module, the power amplification detection module, the series resonant network and the output detection device are connected in sequence. The sweep frequency power supply module is used for generating a broadband excitation signal with a frequency that can be swept. The power amplification detection module is used for amplifying, isolating and impedance converting the excitation signal. The series resonant network comprises a tunable element, a liquid level sensitive element and a load resistor, and is used for reflecting the liquid level change through resonant frequency shift. The output detection device is used for detecting the response signal of the series resonant network and calculating the liquid level height. The series resonant network presents a low impedance state at the resonant frequency point.

2. A resonant cryogenic liquid level sensor detection system according to claim 1, wherein, The sweep frequency power supply module adopts a direct digital frequency synthesis technology, and comprises a DDS excitation signal source, an operational amplifier and a bandpass filter connected in sequence. The DDS excitation signal source is used for generating a high-stability sine wave signal. The operational amplifier is used for improving the signal amplitude and the load capacity. The bandpass filter is used for suppressing harmonics and out-of-band noise, and outputting a pure sweep frequency signal.

3. A resonant cryogenic liquid level sensor detection system according to claim 1, wherein, The power amplification detection module comprises a power amplification distribution sub-module, a transformer balun and an impedance conversion network connected in sequence. The power amplification distribution sub-module is used for power amplifying the input signal. The transformer balun is used for converting the differential signal into a single-ended signal and providing electrical isolation. The impedance conversion network is used for matching the output impedance of the power amplification detection module with the input impedance of the series resonant network.

4. A resonant cryogenic liquid level sensor detection system according to claim 1, wherein, The output detection device comprises a directional coupler, a vector network analyzer, a liquid level display processing device and a matching terminal. The directional coupler is used for coupling the forward transmission signal from the main signal path. The vector network analyzer is used for measuring the amplitude, phase, frequency and impedance parameters of the forward transmission signal. The liquid level display processing device is used for calculating the liquid level height according to a preset frequency-liquid level mapping model. The matching terminal is used for absorbing the reflected signal to ensure the measurement accuracy.

5. A resonant cryogenic liquid level sensor detection system according to claims 1-4, characterized in that, The series resonant network comprises a tunable element, a liquid level sensitive element and a load resistor. The tunable element is an inductance-adjustable inductor. The liquid level sensitive element is a capacitance type cryogenic liquid level sensor. The load resistor is a resistor element with a fixed resistance value, and is used for reducing the impedance at the resonant point.

6. A resonant cryogenic liquid level sensor detection system according to claim 5, wherein: The capacitance value of the capacitance type cryogenic liquid level sensor changes with the liquid level height, and the resonant frequency is inversely proportional to the square root of the product of the capacitance value and the inductance of the inductor.

7. A resonant cryogenic liquid level sensor detection system according to claim 6, wherein: The capacitance type cryogenic liquid level sensor adopts an integrated coaxial cylindrical structure, and comprises an outer electrode and an inner electrode connected to the series resonant network through lead-out electric connection lines respectively.

8. A resonant cryogenic liquid level sensor detection system according to claim 6, wherein: The capacitance type cryogenic liquid level sensor adopts a segmented structure, and the inner electrode and the outer electrode are configured as a plurality of independent capacitive units arranged in the vertical direction.

9. A resonant cryogenic liquid level sensor detection system according to claims 1-4, characterized in that, The series resonant network comprises a tunable element, a liquid level sensitive element and a load resistor. The tunable element is a capacitance-adjustable capacitor. The liquid level sensitive element is an inductance type cryogenic liquid level sensor. The load resistor is a resistor element with a fixed resistance value, and is used for reducing the impedance at the resonant point.

10. A resonant cryogenic liquid level sensor detection system according to claim 9, wherein, The inductance of the inductive low temperature liquid level sensor varies with the liquid level height, and the resonance frequency is inversely proportional to the square root of the product of the inductance of the inductive liquid level sensor and the capacitance of the capacitive element.

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