Active eddy current excitation thermocouple gradient liquid level detector

Abstract

The invention discloses an active eddy current excitation thermocouple gradient liquid level detector, relates to the technical field of industrial process detection, and aims to overcome the defects that a traditional thermocouple liquid level meter lags in response in a complex medium, and the measurement precision is limited by heat conduction characteristics. According to the scheme, a fusion mechanism of active eddy current excitation and distributed thermocouple gradient detection is innovatively provided. A miniature magnetofluid driven vortex generator is integrated in a coaxial nested detection rod, so that detected liquid is actively induced to generate directional vortex flow, and a static thermal boundary layer of a medium is broken; meanwhile, multiple stages of thermocouple arrays are precisely arranged in the axial direction, and dynamic temperature gradient jump signals at the liquid-steam interface under eddy current disturbance are captured in real time. The design breaks through the physical limit of passive heat conduction detection, the liquid level resolution is improved to the millimeter level, and the response time is shortened by more than 80%. Experiments show that in a 300 DEG C liquid sodium environment, the system measurement error is less than + / -1.5 mm, which is significantly superior to that of an existing contact type liquid level instrument.

Description

Technical Field

[0001] This invention relates to the field of industrial process detection technology, and in particular to an active eddy current disturbed thermocouple gradient liquid level detector. Background Technology

[0002] In nuclear reactor coolant circulation, molten salt energy storage systems, and metal smelting processes, the level monitoring of high-temperature liquid metal or molten salt media has long faced challenges under extreme operating conditions: Traditional thermocouple level gauges rely on the natural heat conduction of the medium, and in low Prandtl number media, the excessively thick thermal boundary layer leads to severe response lag (>2 seconds), and the measurement accuracy is significantly affected by interference such as medium stratification and bubble adhesion. In typical applications such as sodium-cooled fast reactors, the error can be as high as ±15mm. Existing improvement schemes, such as adding an auxiliary heater to the coaxial nested probe or using multi-sensor data fusion, have partially improved the response speed, but have introduced thermal disturbance noise and increased system complexity, and the reliability drops sharply in high-temperature environments above 480℃.

[0003] Chinese Patent Publication No. CN109520588A, entitled "A Multi-Point Thermocouple Liquid Level Detector with High-Frequency Induction Eddy Current Heating," includes a protective sleeve, a heating coil, an armored thermocouple, and a heated armored thermocouple. The heating coil, the armored thermocouple, and the heated armored thermocouple are all placed inside a pressure-bearing sleeve. The armored thermocouple is located at the bottom of the pressure-bearing sleeve. The heated armored thermocouple is installed inside the heating coil. The heated armored thermocouple is either filled with magnetically conductive metal in the hot end sleeve of the armored thermocouple, or a magnetically conductive metal block is welded onto the hot end sleeve, or the armored thermocouple itself is a magnetically conductive thermocouple. The armored thermocouple and the heated armored thermocouple constitute a thermocouple measuring pair for measuring the liquid level.

[0004] In light of existing technological bottlenecks, the core problem that this invention needs to solve is: how to overcome the limitations of the thermal boundary layer on the dynamic response of thermocouples without the need for complex algorithms, while also overcoming the measurement distortion caused by magnetohydrodynamic effects, bubble interference, and media stratification in liquid metals, and achieving continuous liquid level monitoring with an accuracy of ±1mm and a response of 200ms in environments with high temperatures above 550℃, high pressures of 20MPa, and strong electromagnetic interference. This has become a global challenge that urgently needs to be overcome in the fields of nuclear power and new energy. Summary of the Invention

[0005] In view of the aforementioned existing problems, the present invention is proposed.

[0006] Therefore, this invention provides an active eddy current disturbed thermocouple gradient liquid level detector to solve the problem of measurement distortion caused by magnetohydrodynamic effects, bubble interference and medium stratification in liquid metal.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] In a first aspect, the present invention provides an active eddy current-induced thermocouple gradient liquid level detector, comprising: a coaxial nested probe rod, a magnetohydrodynamic (MHD) driven eddy current generator, and a distributed thermocouple gradient array; the MHD driven eddy current generator is fixed inside the bottom end of the coaxial nested probe rod and generates directional helical eddies by driving a liquid metal medium through a rotating magnetic field; the thermocouple array is non-uniformly arranged along the axial direction of the coaxial nested probe rod, and the array node density increases with the distance from the MHD driven eddy current generator; the surface of the coaxial nested probe rod is processed with a micron-level turbulence-induced structure to enhance thermal boundary layer disturbance.

[0009] As a preferred embodiment of the active eddy current disturbed thermocouple gradient liquid level detector of the present invention, the coaxial nested detection rod is specifically constructed as follows: the inner heat-conducting core is a silicon carbide fiber-reinforced aluminum nitride ceramic matrix composite material sintered by hot isostatic pressing, wherein the volume fraction of silicon carbide fiber is 35±2%, and the fibers are axially oriented, so that the axial thermal conductivity of the composite material is stable in the range of 185~190W / (m·K), and the radial bending strength reaches 480MPa; the outer sheath is coated with a dense tungsten carbide layer with a thickness of 80±5μm on the surface of the heat-conducting core by chemical vapor deposition, the tungsten carbide layer has a Vickers hardness ≥2200HV, and the thermal expansion coefficient matches the inner aluminum nitride matrix with a deviation of less than 0.3×10. -6 / K; On the outer surface of the tungsten carbide layer, an equilateral pyramid-shaped microtexture array with a base width of 20±1.5μm and a height of 15±1μm is processed using picosecond laser etching. The center-to-center spacing of the pyramid units is 50μm, and the etching depth error is controlled within ±0.8μm. The distribution density Pr of the microtexture is dynamically adjusted according to the Prandtl number of the measured medium. When the medium is a low Prandtl number molten metal Pr<0.01, the texture coverage reaches more than 95%. When the medium is a high Prandtl number molten salt Pr>10, the coverage drops to 70%~75%, thereby optimizing the turbulence disturbance intensity and thermal boundary layer destruction efficiency.

[0010] As a preferred embodiment of the active eddy current-induced thermocouple gradient liquid level detector described in this invention, the magnetohydrodynamic driven eddy current generator comprises a stator electromagnetic coil group and a rotor permanent magnet impeller. Each stator electromagnetic coil group adopts a segmented Halbach array with alternating neodymium iron boron permanent magnets and permalloy soft magnetic pole shoes. The ends of the pole shoes are machined into arc-shaped protrusions with a radius of 1.2 mm, and the spacing between adjacent coils is precisely matched with a 45° mechanical angle. The coil frame is filled with nanocrystalline alloy magnetic filler, which generates a rotating magnetic field with a radial intensity of 0.85 ± 0.03 T at the air gap when a three-phase 10 kHz square wave with a peak current of 18 A is applied. The rotor permanent magnet impeller is a six-bladed asymmetric structure with samarium cobalt permanent magnets embedded in a tantalum-tungsten alloy frame. The blade root thickness is 2.5 mm, gradually thinning to 0.8 mm at the edges. Each blade pressure surface is designed with a Helmholtz resonance groove with a depth of 0.2 mm and a width of 1.5 mm, and the bottom of the groove transitions with a radius of 0.1 mm. The blade installation angle changes continuously from 30° at the leading edge to 60° at the trailing edge, and a micro-serration structure with a depth of 0.1 mm is machined on the trailing edge. The blade edge is provided with a Helmholtz eddy current enhancement groove with a depth of 0.2 mm. Six samarium cobalt permanent magnets are embedded in the impeller hub in an alternating N and N pole configuration, with the magnetization direction at a 17° angle to the rotation axis, achieving contactless transmission through magnetic coupling. When a three-phase 10 kHz high-frequency current is applied, the stator magnetic field rotates, driving the impeller to cut the medium at a speed of 8500 ± 200 rpm, forming a forced spiral eddy current around the coaxial nested probe with an axial extension distance of 5.2 times the pipe diameter, and the velocity gradient in the core region of the eddy current is ≥1200 s. -1 /

[0011] As a preferred embodiment of the active eddy current disturbed thermocouple gradient liquid level detector described in this invention, the distributed thermocouple gradient array employs 12 pairs of 0.1mm diameter tungsten-rhenium 26-tungsten-rhenium 5 heterojunction thermocouple wires. The thermal nodes are fixed to designated coordinate points on the outer surface of the coaxial nested detection rod via laser micro-welding. All thermal nodes are arranged in a logarithmic spiral spatial topology, with the bottom end of the coaxial nested detection rod as the coordinate origin. The axial position Zn of the nth node satisfies Zn = 8·ln(n+1), unit: mm, n = 1 to 12. The minimum bottom distance between adjacent nodes is 2.1mm, and the maximum top distance is 8.7mm. The thermocouple cold... The sealed cavity extends to the top of the coaxial nested probe rod. This cavity is filled with a phase change material with a eutectic composition of 52% indium and 48% tin. A closed-loop temperature control system is formed by a thin-film heater surrounding the cavity and a Pt100 temperature sensor to maintain the cold junction temperature within the range of the medium saturation temperature ±0.3℃. The signal wires of each thermocouple pair are twisted and shielded, passing through the inner hole of the coaxial nested probe rod. The ends are connected to a transimpedance differential circuit based on an instrumentation amplifier. The gain of this circuit is set to 500±5, and the bandwidth is 1MHz. It can synchronously output the natural temperature gradient curve in static mode and the dynamic gradient change signal in eddy current disturbance mode.

[0012] As a preferred embodiment of the active eddy current disturbed thermocouple gradient level detector of the present invention, the thermocouple signal is processed by a transimpedance differential amplifier circuit, which includes a static signal channel and a disturbance signal channel connected in parallel. The static signal channel adopts an inverting amplifier structure with a gain of 100, and a 10μF polypropylene film capacitor is connected in parallel at the input stage to form a high-pass filter with a cutoff frequency of 0.01Hz. After eliminating DC drift, it is amplified by a precision operational amplifier and outputs a temperature gradient baseline signal under natural thermal conduction. The disturbance signal channel has a differentiating circuit with a time constant of 15ms connected in series at the front end of the amplifier, and is amplified by an instrumentation amplifier at 500Hz. The transient thermoelectric potential change generated by the amplified eddy current disturbance is connected to the non-inverting input of a high-speed comparator. The static channel output signal is attenuated to 35.7% of its original value by a precision resistor voltage divider network before being input to the inverting input of the comparator. When the amplitude of the disturbance channel signal exceeds 2.8 times the reference voltage, the comparator outputs a high level to trigger the liquid level marking signal. Within a time window of 50 to 200 ms after the start of the magnetohydrodynamic driven eddy current generator, the comparator output signal is latched by a D flip-flop, and the RS485 interface is activated to output the liquid level coordinate value. The coordinate value is determined by the position of the thermocouple node that first triggers the comparator, with a position resolution of 0.1 mm.

[0013] As a preferred embodiment of the active eddy current-induced thermocouple gradient level detector described in this invention, the axial spacing between the magnetohydrodynamic (MHD) driven eddy current generator and the bottommost thermocouple node is configured as follows: a precision spiral guide rail with a lead of 0.5 mm is pre-installed inside the coaxial nested detection rod, and the MHD driven eddy current generator mounting base is axially moved by a closed-loop stepper motor with a step angle of 1.8°; during initial installation, the distance to the first-stage thermocouple hot node is measured using a laser rangefinder with the impeller tip as the reference surface, and the spacing is adjusted to the design value L; when the kinematic viscosity of the molten nitrate medium is detected to be ν = 1.2 × 10⁻⁶, the distance is adjusted accordingly. -6 m 2 When the outer diameter D of the coaxial nested probe is 25mm, and the impeller speed is set to 8500rpm, the corresponding impeller tip linear velocity V is... tip =22.3m / s, calculated L=8.02mm, the actual assembly spacing was calibrated to 8.0±0.05mm using a micrometer; after assembly, a vibration spectrum analyzer was used to verify that the vortex volume in the eddy core region is ≥1000s. -1 / Completely cover the first three thermocouple nodes, with a coverage deviation of less than 10% of the node spacing.

[0014] As a preferred embodiment of the active eddy current-induced thermocouple gradient level detector described in this invention, the following features are employed: a platinum-iridium 10 alloy wire with a diameter of 0.15±0.003mm (90% platinum / 10% iridium) is laid parallel to the axis of the coaxial nested detection rod at a position 0.8mm to the side of the thermocouple array; the length of the compensation wire is equal to the effective detection section of the coaxial nested detection rod, typically 300mm, and both ends are laser-welded to copper-nickel alloy leads with a diameter of 1mm; the leads are connected to a constant current source control module, which dynamically outputs a step compensation current based on the thermocouple time constant τ; when the magnetohydrodynamic driven eddy current generator is started, the control module synchronously outputs a negative step current with a pulse width of 50ms and an amplitude of 2.8A, causing the compensation wire to generate a temperature drop ΔT=1.7℃ within 0.5ms. This temperature drop compensates for the phase lag caused by the thermal inertia of the medium through heat conduction, compressing the effective response time of the thermocouple to 55% of the actual value.

[0015] As a preferred embodiment of the active eddy current disturbed thermocouple gradient liquid level detector described in this invention, the following features are described: a rectangular groove with a depth of 0.15±0.01mm is machined at the axial center of the outer sheath of the coaxial nested detection rod. A quartz crystal resonator with dimensions of 3.2×2.0×0.3mm is fixed in the groove at a 128° Y-axis tangent. The electrodes on both sides of the resonator are connected to a platinum microstrip antenna on a zirconia ceramic substrate via gold ball bonding with a diameter of 0.1mm. The antenna is designed with a serpentine topology, with a total length of 18mm, and the end is connected to a 125MHz oscillation circuit. A 0.2μm thick aluminum nitride piezoelectric film is sputtered onto the surface of the resonator, and an external polycrystalline diamond protective layer with a thickness of 5μm is covered by chemical vapor deposition. When bubbles adhere to the surface of the coaxial nested detection rod, the relationship between the resonant frequency offset Δf and the bubble coverage η is given by the calibration curve Δf=-0.0032η. 2 • f0 is determined, which is the base frequency of 125MHz. The frequency signal is down-converted to an intermediate frequency of 10.7MHz by a mixer, and then demodulated to produce a DC compensation voltage through a phase-locked loop. This voltage is input to the inverting terminal of the amplifier and superimposed on the original thermocouple signal to cancel the temperature measurement deviation caused by bubbles in real time.

[0016] As a preferred embodiment of the active eddy current-induced thermocouple gradient liquid level detector described in this invention, the driving control method of the magnetohydrodynamic driven eddy current generator in the liquid metal medium is as follows: the stator electromagnetic coil adopts a three-phase six-pole star connection, the input current is generated by a SiC MOSFET full-bridge inverter, the inverter carrier frequency is 40kHz, and the dead time is set to 1μs; the driving frequency f is controlled by a magnetic encoder in real-time feedback closed-loop control, and is forcibly locked at the magnetohydrodynamic critical threshold f. c More than 1.2 times, that is, f≥1.2×(σB) 2) / (2πρ), where σ is the dielectric conductivity in S / m, B is the air gap magnetic flux density in T, and ρ is the dielectric density in kg / m³. 3 When applied to molten lead-bismuth alloys, σ = 8.6 × 10⁻⁶ 4 S / m, ρ=10.5×10 3 kg / m 3 When B = 0.85T, f is calculated. c =708Hz, the actual drive frequency is configured as 850Hz±5Hz; frequency locking is achieved by a hardware comparator. When the encoder detects that the frequency corresponding to the rotational speed is lower than 840Hz, it immediately triggers an overmodulation pulse to increase the duty cycle to 95%, and recovers the target frequency within 0.5ms; simultaneously, an infrared temperature probe is installed at the rotor shaft end to monitor the permanent magnet temperature in real time. When the temperature exceeds 750℃, the drive frequency is linearly reduced to f. c 1.05 times that of samarium cobalt magnets, to prevent irreversible demagnetization of samarium cobalt magnets.

[0017] As a preferred embodiment of the active eddy current-induced thermocouple gradient liquid level detector described in this invention, the following is provided: an eddy current intensity-temperature gradient closed-loop control system is established; the temperature gradient magnitude is extracted from the excitation channel of the transimpedance differential amplifier circuit. The signal is converted to a true RMS value and outputs a 0-5V DC voltage Vg. This voltage is input to a comparator with a lower threshold set to 0.8K / mm (corresponding to 1.6V) and an upper threshold set to 1.2K / mm (corresponding to 2.4V). When Vg < 1.6V, the comparator outputs a low level to trigger a timer to generate a PWM wave with a linearly increasing duty cycle. The initial frequency is 1kHz, and the duty cycle is 40%. The PWM signal drives the three-phase inverter through optocoupler isolation, causing the impeller speed to increase in steps from a base of 8000rpm to 12000rpm. When... When the speed rises to 1.2K / mm, the speed is adjusted back to the reference 8000rpm, forming an anti-oscillation adaptive mechanism. When Vg > 2.4V, the comparator outputs a high level to activate the analog switch, locking the PWM duty cycle to the reference value of 40%. During speed regulation, the magnetic encoder provides real-time feedback of the actual speed and inputs it to the differential amplifier. After comparing it with the target speed, an error voltage is generated. This voltage is compensated for load fluctuations by an integral circuit with a time constant of 50ms, ensuring that the steady-state speed error is < ±15rpm. In the case of severe liquid level oscillation, the overload protection mode is forcibly activated: the power supply of the magnetohydrodynamic driven eddy current generator is cut off, and the spacing adjustment motor is activated to retract the magnetohydrodynamic driven eddy current generator by 5mm. The generator automatically recovers after the gradient signal stabilizes.

[0018] In a second aspect, the present invention provides a computer device including a memory and a processor, wherein the memory stores a computer program, wherein: when the computer program is executed by the processor, it implements any step of the active eddy current disturbed thermocouple gradient liquid level detector as described in the first aspect of the present invention.

[0019] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein: when the computer program is executed by a processor, it implements any step of the active eddy current disturbed thermocouple gradient liquid level detector as described in the first aspect of the present invention.

[0020] The beneficial effects of this invention are:

[0021] This invention actively breaks through the physical limitations of the thermal boundary layer by using a magnetohydrodynamic (MHD) driven eddy current generator. Combined with the logarithmic spiral topology of a distributed thermocouple gradient array and a cross-scale thermal capacity compensation mechanism, it achieves, for the first time, an absolute accuracy of ±0.8 mm and a dynamic response speed of 55 ms in high-temperature liquid metal level detection, representing an order of magnitude improvement over existing technologies. Specifically, it achieves three core breakthroughs: First, the innovatively designed asymmetric Helmholtz flute impeller, driven by a 0.85T rotating magnetic field, generates a forced eddy current (vortex quantity ≥ 1200 s⁻¹) extending axially up to 5.2 times the pipe diameter in molten sodium medium. -1The system employs several key technologies: First, it compresses the thermal boundary layer thickness from the natural 4.7 mm to 0.9 mm, completely solving the problem of thermal conduction hysteresis in low Prandtl number media. Second, the platinum-iridium alloy thermal capacity compensation wire generates a reverse heat flow through a negative step current with a pulse width of 50 ms and an amplitude of 2.8 A, offsetting the phase lag caused by the thermal inertia of the medium. This reduces the effective time constant of the tungsten-rhenium thermocouple from 15 ms to 8.3 ms, shortening the liquid level jump tracking delay to 1 / 4 of the traditional solution. Third, the 128° Y-cut quartz surface acoustic wave resonator works in conjunction with the hardware phase-locked loop demodulation circuit to output the compensation voltage corresponding to the bubble coverage rate in real time. Under molten salt boiling conditions, it suppresses the liquid level jump caused by bubble interference from ±12 mm to ±0.5 mm, reducing the false alarm rate to below 0.1%. These innovations simultaneously address eddy current attenuation caused by magnetohydrodynamic effects, gradient ambiguity due to medium stratification (dual-mode signal processing improves the signal-to-noise ratio to 78dB), and measurement instability caused by mechanical oscillations (eddy current intensity-temperature gradient closed-loop control compresses output fluctuations to ±0.2K / mm). In continuous operation verification on a sodium-cooled fast reactor (550℃ / 15MPa), the detector lifetime exceeded 60,000 thermal cycles, with a liquid level coordinate output standard deviation of 0.28mm, 10 times stricter than the highest accuracy level of the ISO 18213 international standard. Furthermore, the entire process is implemented based on hardware circuitry, avoiding the risk of software algorithm failure in nuclear radiation environments. This technology enables liquid level monitoring reliability to reach SIL-3 level in nuclear reactor coolant loss accidents, improves the energy storage efficiency of molten salt tanks in solar thermal power plants by 2.1%, and provides the first millimeter-level liquid level monitoring solution for extreme scenarios such as liquid lithium-lead cladding in fusion reactors and aluminum electrolytic cells. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a block diagram of an active eddy current disturbed thermocouple gradient liquid level detector in Example 1. Detailed Implementation

[0024] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0026] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0027] Example 1, referring to Figure 1 This is the first embodiment of the present invention, which provides an active eddy current-induced thermocouple gradient liquid level detector, comprising: a coaxial nested detection rod, a magnetohydrodynamic (MHD) driven eddy current generator, and a distributed thermocouple gradient array; the MHD driven eddy current generator is fixed inside the bottom end of the coaxial nested detection rod and generates directional helical eddies by driving the liquid metal medium through a rotating magnetic field; the thermocouple array is non-uniformly arranged along the axial direction of the coaxial nested detection rod, and the array node density increases with the distance from the MHD driven eddy current generator; the surface of the coaxial nested detection rod is processed with a micron-level turbulence-induced structure to enhance thermal boundary layer disturbance.

[0028] The specific structure of the coaxial nested probe is as follows: the inner heat-conducting core is a silicon carbide fiber-reinforced aluminum nitride ceramic matrix composite material sintered by hot isostatic pressing, wherein the volume fraction of silicon carbide fiber is 35±2%, and the fibers are axially oriented, so that the axial thermal conductivity of the composite material is stable in the range of 185~190W / (m·K), and the radial bending strength reaches 480MPa; the outer sheath is coated with a dense tungsten carbide layer with a thickness of 80±5μm on the surface of the heat-conducting core by chemical vapor deposition. The Vickers hardness of this tungsten carbide layer is ≥2200HV, and the coefficient of thermal expansion of this layer matches the inner aluminum nitride matrix with a deviation of less than 0.3×10. -6 / K; On the outer surface of the tungsten carbide layer, an equilateral pyramid-shaped microtexture array with a base width of 20±1.5μm and a height of 15±1μm is processed using picosecond laser etching. The center-to-center spacing of the pyramid units is 50μm, and the etching depth error is controlled within ±0.8μm. The distribution density Pr of the microtexture is dynamically adjusted according to the Prandtl number of the measured medium. When the medium is a low Prandtl number molten metal Pr<0.01, the texture coverage reaches more than 95%. When the medium is a high Prandtl number molten salt Pr>10, the coverage drops to 70%~75%, thereby optimizing the turbulence disturbance intensity and thermal boundary layer destruction efficiency.

[0029] The magnetohydrodynamic driven eddy current generator includes a stator electromagnetic coil group and a rotor permanent magnet impeller. Each stator electromagnetic coil group adopts a segmented Halbach array with alternating neodymium iron boron permanent magnets and permalloy soft magnetic pole shoes. The ends of the pole shoes are machined into arc-shaped protrusions with a radius of 1.2 mm. The spacing between adjacent coils is precisely matched with a 45° mechanical angle. The coil frame is filled with nanocrystalline alloy magnetic filler. When a three-phase 10kHz square wave with a peak current of 18A is applied, a rotating magnetic field with a radial strength of 0.85±0.03T is generated at the air gap. The rotor permanent magnet impeller is a six-bladed asymmetrical structure with samarium cobalt permanent magnets embedded in a tantalum-tungsten alloy skeleton. The blades are 2.5 mm thick at the root and gradually thin to 0.8 mm at the edges. Each blade pressure surface is designed with a Helmholtz resonance groove with a depth of 0.2 mm and a width of 1.5 mm, and the bottom of the groove transitions into an arc with a radius of 0.1 mm. The blade installation angle changes continuously from 30° at the leading edge to 60° at the trailing edge, and a micro-serration structure with a depth of 0.1 mm is machined on the trailing edge. The blade edge is provided with a Helmholtz eddy current enhancement groove with a depth of 0.2 mm. The six samarium cobalt permanent magnets are embedded in the impeller hub in an alternating N and N pole manner, with the magnetization direction at a 17° angle to the axis of rotation, achieving contactless transmission through magnetic coupling. When a three-phase 10kHz high-frequency current is applied, the stator magnetic field rotates, driving the impeller to cut the medium at a speed of 8500±200rpm. This creates a forced spiral vortex around the coaxial nested probe, extending axially by 5.2 times the pipe diameter, with a velocity gradient ≥1200s in the core region of the vortex. -1 /

[0030] The distributed thermocouple gradient array uses 12 pairs of 0.1mm diameter tungsten-rhenium-26-tungsten-rhenium-5 heterojunction thermocouple wires. The hot nodes are fixed to designated coordinate points on the outer surface of the coaxial nested probe rod via laser micro-welding. All hot nodes are arranged in a logarithmic spiral spatial topology, with the bottom of the coaxial nested probe rod as the origin. The axial position Zn of the nth node satisfies Zn = 8·ln(n+1), unit: mm, n = 1 to 12. The minimum bottom distance between adjacent nodes is 2.1mm, and the maximum top distance is 8.7mm. The cold junction of the thermocouples extends to the sealed cavity at the top of the coaxial nested probe rod. The cavity is filled with a phase change material with a eutectic composition of 52% indium and 48% tin. A closed-loop temperature control system is formed by a thin-film heater surrounding the cavity and a Pt100 temperature sensor to keep the cold junction temperature constant within the range of the medium saturation temperature ±0.3℃. The signal wires of each thermocouple pair adopt a twisted shielded structure and pass through the inner hole of the coaxial nested probe. The end is connected to a transimpedance differential circuit based on an instrumentation amplifier. The gain of this circuit is set to 500±5 and the bandwidth is 1MHz. It can synchronously output the natural temperature gradient curve in static mode and the dynamic gradient change signal in eddy current disturbance mode.

[0031] The thermocouple signal is processed by a transimpedance differential amplifier circuit, which includes a parallel static signal channel and a disturbance signal channel. The static signal channel uses a 100-gain inverting amplifier structure, with a 10μF polypropylene film capacitor connected in parallel at the input stage to form a high-pass filter with a cutoff frequency of 0.01Hz. After eliminating DC drift, the signal is amplified by a precision operational amplifier and outputs a temperature gradient baseline signal under natural thermal conduction. The disturbance signal channel has a differentiating circuit with a time constant of 15ms connected in series at the front end of the amplifier. The transient thermoelectric potential change generated by eddy current disturbance is amplified by an instrumentation amplifier with a gain of 500. The output terminal is connected to the non-inverting input terminal of the high-speed comparator; the static channel output signal is attenuated to 35.7% of its original value by a precision resistor voltage divider network before being input to the inverting input terminal of the comparator. When the amplitude of the excitation channel signal exceeds 2.8 times the reference voltage, the comparator outputs a high level to trigger the liquid level marking signal; within a time window of 50 to 200 ms after the start of the magnetohydrodynamic driven eddy current generator, the comparator output signal is latched by a D flip-flop, and the RS485 interface is activated to output the liquid level coordinate value. The coordinate value is determined by the position of the thermocouple node that first triggers the comparator, with a position resolution of 0.1 mm.

[0032] The axial spacing configuration method between the magnetohydrodynamic (MHD) driven eddy current generator and the bottommost thermocouple node is as follows: a precision spiral guide rail with a lead of 0.5 mm is pre-installed inside the coaxial nested probe rod. A closed-loop stepper motor with a step angle of 1.8° drives the MHD driven eddy current generator mounting base axially. During initial installation, using the impeller tip as the reference surface, the distance to the first-stage thermocouple hot node is measured with a laser rangefinder, and this spacing is adjusted to the design value L. When the kinematic viscosity of the molten nitrate medium is detected to be ν = 1.2 × 10⁻⁶... -6 m 2 When the outer diameter D of the coaxial nested probe is 25mm, and the impeller speed is set to 8500rpm, the corresponding impeller tip linear velocity V is... tip =22.3m / s, calculated L=8.02mm, the actual assembly spacing was calibrated to 8.0±0.05mm using a micrometer; after assembly, a vibration spectrum analyzer was used to verify that the vortex volume in the eddy core region is ≥1000s. -1 / Completely cover the first three thermocouple nodes, with a coverage deviation of less than 10% of the node spacing.

[0033] A platinum-iridium 10 alloy wire with a diameter of 0.15±0.003mm (90% platinum / 10% iridium) is laid parallel to the axis of the coaxial nested probe rod 0.8mm to the side of the thermocouple array. The length of the compensation wire is equal to the effective detection section of the coaxial nested probe rod, typically 300mm, and both ends are laser-welded to a 1mm diameter copper-nickel alloy lead wire. The lead wire is connected to a constant current source control module, which dynamically outputs a step compensation current based on the thermocouple time constant τ. When the magnetohydrodynamic driven eddy current generator is started, the control module synchronously outputs a negative step current with a pulse width of 50ms and an amplitude of 2.8A, causing the compensation wire to generate a temperature drop ΔT=1.7℃ within 0.5ms. This temperature drop cancels out the phase lag caused by the thermal inertia of the medium through heat conduction, compressing the effective response time of the thermocouple to 55% of the actual value.

[0034] A rectangular groove with a depth of 0.15±0.01mm is machined at the axial center of the outer sheath of the coaxial nested probe. A quartz crystal resonator with dimensions of 3.2×2.0×0.3mm is fixed in the groove, tangentially at 128°Y. The electrodes on both sides of the resonator are connected to a platinum microstrip antenna on a zirconia ceramic substrate via gold ball bonding with a diameter of 0.1mm. The antenna is designed with a serpentine topology, with a total length of 18mm, and a 125MHz oscillation circuit is connected to its end. A 0.2μm thick aluminum nitride piezoelectric film is sputtered onto the surface of the resonator, and a 5μm thick polycrystalline diamond protective layer grown by chemical vapor deposition is applied externally. When bubbles adhere to the surface of the coaxial nested probe, the relationship between the resonant frequency shift Δf and the bubble coverage η is given by the calibration curve Δf=-0.0032η. 2 • f0 is determined, which is the base frequency of 125MHz. The frequency signal is down-converted to an intermediate frequency of 10.7MHz by a mixer, and then demodulated to produce a DC compensation voltage through a phase-locked loop. This voltage is input to the inverting terminal of the amplifier and superimposed on the original thermocouple signal to cancel the temperature measurement deviation caused by bubbles in real time.

[0035] The drive control method for a magnetohydrodynamic (MHD) driven eddy current generator in a liquid metal medium is as follows: the stator electromagnetic coil adopts a three-phase six-pole star connection; the input current is generated by a SiC MOSFET full-bridge inverter with a carrier frequency of 40kHz and a dead time of 1μs; the drive frequency f is controlled by a real-time feedback closed-loop control via a magnetic encoder, and is forcibly locked at the MHD critical threshold f. c More than 1.2 times, i.e., f≥1.2×(σB2) / (2πρ), where σ is the dielectric conductivity in S / m, B is the air gap magnetic flux density in T, and ρ is the dielectric density in kg / m³. 3 When applied to molten lead-bismuth alloys, σ = 8.6 × 10⁻⁶ 4 S / m, ρ=10.5×10 3 kg / m 3 When B = 0.85T, f is calculated.c =708Hz, the actual drive frequency is configured as 850Hz±5Hz; frequency locking is achieved by a hardware comparator. When the encoder detects that the frequency corresponding to the rotational speed is lower than 840Hz, it immediately triggers an overmodulation pulse to increase the duty cycle to 95%, and recovers the target frequency within 0.5ms; simultaneously, an infrared temperature probe is installed at the rotor shaft end to monitor the permanent magnet temperature in real time. When the temperature exceeds 750℃, the drive frequency is linearly reduced to f. c 1.05 times that of samarium cobalt magnets, to prevent irreversible demagnetization of samarium cobalt magnets.

[0036] Establish a closed-loop control system for eddy current intensity and temperature gradient: extract the temperature gradient magnitude from the excitation channel of the transimpedance differential amplifier circuit. The signal is converted to a true RMS value and outputs a 0-5V DC voltage Vg. This voltage is input to a comparator with a lower threshold set to 0.8K / mm (corresponding to 1.6V) and an upper threshold set to 1.2K / mm (corresponding to 2.4V). When Vg < 1.6V, the comparator outputs a low level to trigger a timer to generate a PWM wave with a linearly increasing duty cycle. The initial frequency is 1kHz, and the duty cycle is 40%. The PWM signal drives the three-phase inverter through optocoupler isolation, causing the impeller speed to increase in steps from a base of 8000rpm to 12000rpm. When... When the speed rises to 1.2K / mm, the speed is adjusted back to the reference 8000rpm, forming an anti-oscillation adaptive mechanism. When Vg > 2.4V, the comparator outputs a high level to activate the analog switch, locking the PWM duty cycle to the reference value of 40%. During speed regulation, the magnetic encoder provides real-time feedback of the actual speed and inputs it to the differential amplifier. After comparing it with the target speed, an error voltage is generated. This voltage is compensated for load fluctuations by an integral circuit with a time constant of 50ms, ensuring that the steady-state speed error is < ±15rpm. In the case of severe liquid level oscillation, the overload protection mode is forcibly activated: the power supply of the magnetohydrodynamic driven eddy current generator is cut off, and the spacing adjustment motor is activated to retract the magnetohydrodynamic driven eddy current generator by 5mm. The generator automatically recovers after the gradient signal stabilizes.

[0037] The following is the workflow of an embodiment of an active eddy current disturbed thermocouple gradient liquid level detector:

[0038] After the detector is started, the magnetohydrodynamic driven eddy current generator first introduces a three-phase 10kHz square wave current, generating a 0.85T rotating magnetic field in the stator Halbach array. This magnetic field drives the asymmetric impeller to cut the liquid metal medium at a speed of 8500rpm, producing a helical forced eddy current with an axial extension of 130mm (eddy current ≥1200s). -1 / ); This eddy current actively disrupts the thermal boundary layer on the surface of the coaxial nested probe, causing the temperature gradient at the liquid-vapor interface to increase sharply by 3.8 times. The distributed thermocouple gradient array operates synchronously: the tungsten-rhenium 26-tungsten-rhenium 5 thermocouple nodes capture the dynamic temperature field, and their thermoelectric potential is transmitted to the transimpedance differential amplifier circuit via twisted-pair shielded wire. The excitation channel extracts the gradient abrupt change signal through a differentiating circuit with a 15ms time constant, while the static channel records the natural heat conduction baseline; when the gradient change rate output by the excitation channel... When the temperature exceeds 2.8 times the static channel value, the LT1016 high-speed comparator triggers the level marker, and the priority encoder locks the coordinates of the first responding thermocouple node (resolution 0.1mm). Simultaneously, a -2.8A step current is injected into the platinum-iridium alloy thermal capacity compensation wire, generating a 1.7℃ temperature drop to compensate for the phase lag caused by the thermal inertia of the medium. The surface acoustic wave resonator monitors the bubble attachment status in real time, and the frequency offset is demodulated by the phase-locked loop into a compensation voltage superimposed on the thermocouple signal. The closed-loop control system adjusts the temperature gradient magnitude... Dynamically adjust eddy current intensity: when The impeller speed is increased to 12000rpm, and when it exceeds 1.2K / mm, it is reduced back to 8000rpm. Under liquid level oscillation conditions, the magnetic fluid driven eddy current generator automatically retracts 5mm to protect the core components.

[0039] Example 2 is the second embodiment of the present invention. This embodiment provides an active eddy current disturbed thermocouple gradient liquid level detector, and the specific implementation is as follows:

[0040] 1. Structural Configuration

[0041] The coaxial nested probe consists of an inner silicon carbide fiber-reinforced aluminum nitride ceramic core (18mm×1200mm, axial thermal conductivity 185W / (m·K)) and an outer CVD tungsten carbide sheath (80μm thick). The surface is laser-etched with a pyramidal micro-texture (95% coverage) with a bottom edge of 20μm and a height of 15μm. The stator of the magnetohydrodynamic eddy current generator adopts an 8-pole segmented Halbach array, with neodymium iron boron permanent magnets (N52 grade) and permalloy pole shoes arranged alternately. The rotor is a tantalum-tungsten alloy six-bladed impeller (blade inclination angle gradually changing from 30° to 60°), with a 0.2mm deep Helmholtz groove machined on the pressure surface, and six samarium cobalt permanent magnets (SH28 grade) embedded in the hub at a 17° angle. Twelve pairs of 0.1mm tungsten-rhenium thermocouples are welded to the rod in a logarithmic spiral topology: the bottom node is 8.0mm from the impeller tip (2.1mm spacing), and the top node is 96mm from the bottom (8.7mm spacing).

[0042] 2. Control System Implementation

[0043] The eddy current driven inverter uses a C3M0065090K SiC module with a carrier frequency of 40kHz and a dead time of 1μs. A magnetic encoder (AS5048A) provides real-time speed feedback, and a hardware comparator forces the drive frequency to be locked at 1.2 times the critical threshold of the magnetohydrodynamics (850Hz in molten lead-bismuth alloy). The signal processing circuit consists of a static signal channel (OPA2188×100) and a disturbance signal channel (AD8421×500 + differential network), with the comparator threshold set to 35.7% of the static signal. A step current of -2.8A×50ms is applied to the thermal compensation wire (PtIr10, 0.15mm), implemented using a Buck-Boost topology constant current source. The output of the surface acoustic wave resonator (128° Y-cut quartz, fundamental frequency 125MHz) is demodulated by an ADF4351 phase-locked loop, and the bubble coverage η and frequency offset Δf satisfy Δf=-0.0032η. 2 ·f0, where f0 is the base frequency of 125MHz, and the compensation voltage is inverted by OPA2188 and added to the thermocouple signal.

[0044] 3. Operating parameter calibration

[0045] Perform three-point calibration in liquid sodium (550℃):

[0046] Zero-point calibration: When there is no eddy current, adjust the phase change thermostat cavity to make the cold end temperature equal to the saturation temperature of 546.8℃ ± 0.3℃;

[0047] Sensitivity calibration: Inject ±5mm liquid level step, optimize the time constant of the differentiating circuit to make Peak value reaches 1.5mV / mm;

[0048] Bubble compensation calibration: Attach a 2mm PTFE sheet and adjust the feedback resistor to make the temperature deviation < ±0.1℃;

[0049] Closed-loop control parameter settings: gradient modulus window 0.8~1.2K / mm (corresponding voltage 1.6~2.4V), speed regulation slope 5% duty cycle / second, overload protection threshold.

[0050] 4. Handling extreme operating conditions

[0051] Nuclear radiation environment: The critical circuits are coated with a 0.2mm thick boron polyethylene / lead composite shielding layer, and the chips are selected as RH1020 radiation-resistant models.

[0052] High pressure condition (20MPa): The coaxial nested probe is filled with fluorinated oil pressure compensation fluid, and the seal adopts double alumina ceramic rings + metal bellows.

[0053] Protection against media corrosion: The stator coil of the magnetohydrodynamic eddy current generator is impregnated with polyimide-nano-ceramic composite paint, and the thermocouple nodes are coated with a 0.1μm thick iridium coating.

[0054] In actual testing within the ITER liquid lithium experimental circuit (700℃, pulsed magnetic field 5T), the detector's performance degradation was less than 2% after 6000 hours of continuous operation, and the standard deviation of the liquid level output remained at 0.31mm.

[0055] Innovative Implementation Results

[0056] Accuracy verification: When ±3mm / 2Hz liquid level oscillation is applied in molten solder (Pr=0.002), the system tracking error is 0.82mm (traditional solution >8mm).

[0057] Response test: The delay from eddy current start-up to liquid level coordinate output is 55±3ms.

[0058] Reliability data: After 18 months of operation, the lead-cooled fast reactor (480℃ / 10MPa) had a false alarm rate of 0.02 times / thousand hours, and the spare parts replacement cycle was extended to 5 years.

[0059] Energy efficiency indicators: Total power consumption is 48W (40W for eddy current drive + 8W for electronic circuit), which is 62% lower than similar products, equivalent to an annual power saving of 34,000 kWh for a single nuclear power plant unit.

[0060] This implementation method, through the deep integration of physical layer innovation (active eddy current excitation + thermal capacity compensation) and hardware closed-loop control (gradient-speed feedback), pushes thermocouple liquid level detection technology into the millimeter-level era, providing core measurement support for major national projects such as fourth-generation nuclear reactors and fusion devices.

[0061] This embodiment also provides a computer device applicable to an active eddy current disturbed thermocouple gradient liquid level detector, including: a memory and a processor; the memory is used to store computer-executable instructions, and the processor is used to execute the computer-executable instructions to realize an active eddy current disturbed thermocouple gradient liquid level detector as proposed in the above embodiment.

[0062] The computer device can be a terminal, comprising a processor, memory, communication interface, display screen, and input devices connected via a system bus. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, carrier networks, NFC (Near Field Communication), or other technologies. The display screen can be an LCD screen or an e-ink screen. The input devices can be a touch layer covering the display screen, buttons, a trackball, or a touchpad on the computer device's casing, or an external keyboard, touchpad, or mouse.

[0063] This embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements an active eddy current-induced thermocouple gradient liquid level detector as described in the above embodiments. The storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0064] In summary, this invention actively breaks through the physical limitations of the thermal boundary layer by using a magnetohydrodynamic (MHD) driven eddy current generator. Combined with the logarithmic spiral topology of a distributed thermocouple gradient array and a cross-scale thermal capacity compensation mechanism, it achieves, for the first time, an absolute accuracy of ±0.8 mm and a dynamic response speed of 55 ms in high-temperature liquid metal level detection, representing an order of magnitude improvement over existing technologies. Specifically, this is manifested in three core breakthroughs: First, the innovatively designed asymmetric Helmholtz flute impeller, driven by a 0.85T rotating magnetic field, generates a forced eddy current (vortex quantity ≥ 1200 s⁻¹) extending axially up to 5.2 times the pipe diameter in the molten sodium medium. -1The system employs several key technologies: First, it compresses the thermal boundary layer thickness from the natural 4.7 mm to 0.9 mm, completely solving the problem of thermal conduction hysteresis in low Prandtl number media. Second, the platinum-iridium alloy thermal capacity compensation wire generates a reverse heat flow through a negative step current with a pulse width of 50 ms and an amplitude of 2.8 A, offsetting the phase lag caused by the thermal inertia of the medium. This reduces the effective time constant of the tungsten-rhenium thermocouple from 15 ms to 8.3 ms, shortening the liquid level jump tracking delay to 1 / 4 of the traditional solution. Third, the 128° Y-cut quartz surface acoustic wave resonator works in conjunction with the hardware phase-locked loop demodulation circuit to output the compensation voltage corresponding to the bubble coverage rate in real time. Under molten salt boiling conditions, it suppresses the liquid level jump caused by bubble interference from ±12 mm to ±0.5 mm, reducing the false alarm rate to below 0.1%. These innovations simultaneously address eddy current attenuation caused by magnetohydrodynamic effects, gradient ambiguity due to medium stratification (dual-mode signal processing improves the signal-to-noise ratio to 78dB), and measurement instability caused by mechanical oscillations (eddy current intensity-temperature gradient closed-loop control compresses output fluctuations to ±0.2K / mm). In continuous operation verification with a sodium-cooled fast reactor (550℃ / 15MPa), the detector lifetime exceeded 60,000 thermal cycles, with a liquid level coordinate output standard deviation of 0.28mm, 10 times stricter than the highest accuracy level of the ISO 18213 international standard. Furthermore, the entire process is implemented based on hardware circuitry, avoiding the risk of software algorithm failure in nuclear radiation environments. This technology enables liquid level monitoring reliability to reach SIL-3 level in nuclear reactor coolant loss accidents, improves the energy storage efficiency of molten salt tanks in solar thermal power plants by 2.1%, and provides the first millimeter-level liquid level monitoring solution for extreme scenarios such as liquid lithium-lead cladding in fusion reactors and aluminum electrolytic cells.

[0065] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An active eddy current-induced thermocouple gradient liquid level detector, characterized in that, include: The device comprises a coaxial nested probe rod, a magnetohydrodynamic (MHD) driven eddy current generator, and a distributed thermocouple gradient array. The MHD driven eddy current generator is fixed inside the bottom end of the coaxial nested probe rod and generates directional helical eddies by driving a liquid metal medium through a rotating magnetic field. The distributed thermocouple gradient array is non-uniformly arranged along the axial direction of the coaxial nested probe rod, and the array node density increases with the distance from the MHD driven eddy current generator. The surface of the coaxial nested probe rod is processed with micron-level turbulence-induced structures to enhance thermal boundary layer disturbance.

2. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 1, characterized in that: The specific structure of the coaxial nested probe is as follows: the inner heat-conducting core is a silicon carbide fiber-reinforced aluminum nitride ceramic matrix composite material sintered by hot isostatic pressing, wherein the volume fraction of silicon carbide fiber is 35±2%, and the fibers are axially oriented, so that the axial thermal conductivity of the composite material is stable in the range of 185~190W / (m·K), and the radial bending strength reaches 480MPa; the outer sheath is coated with a dense tungsten carbide layer with a thickness of 80±5μm on the surface of the heat-conducting core by chemical vapor deposition. The Vickers hardness of the tungsten carbide layer is ≥2200HV, and the coefficient of thermal expansion of the tungsten carbide layer matches the inner aluminum nitride matrix by less than 0.3×10. -6 / K; On the outer surface of the tungsten carbide layer, an equilateral pyramid-shaped microtexture array with a base width of 20±1.5μm and a height of 15±1μm is processed using picosecond laser etching. The center-to-center spacing of the pyramid units is 50μm, and the etching depth error is controlled within ±0.8μm. The distribution density Pr of the microtexture is dynamically adjusted according to the Prandtl number of the measured medium. When the medium is a low Prandtl number molten metal Pr<0.01, the texture coverage reaches more than 95%. When the medium is a high Prandtl number molten salt Pr>10, the coverage drops to 70%~75%, thereby optimizing the turbulence disturbance intensity and thermal boundary layer destruction efficiency.

3. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 2, characterized in that: The magnetohydrodynamic (MHD) driven eddy current generator comprises a stator electromagnetic coil assembly and a rotor permanent magnet impeller. Each stator electromagnetic coil assembly uses a segmented Halbach array with alternating neodymium iron boron permanent magnets and permalloy soft magnetic pole shoes. The pole shoe ends are machined into arc-shaped protrusions with a radius of 1.2 mm, and the spacing between adjacent coils is precisely matched with a 45° mechanical angle. The coil frame is filled with nanocrystalline alloy magnetic filler, generating a rotating magnetic field with a radial intensity of 0.85 ± 0.03 T at the air gap when a three-phase 10 kHz square wave with a peak current of 18 A is applied. The rotor permanent magnet impeller is a six-bladed asymmetric structure with samarium cobalt permanent magnets embedded in a tantalum-tungsten alloy frame. The blade root thickness is 2.5 mm, gradually thinning to 0.8 mm at the edges. Each blade pressure surface is designed with a depth of 0.2 mm. The impeller features a 1.5mm wide Helmholtz resonant groove with a 0.1mm radius arc transition at the bottom. The blade installation angle continuously changes from 30° at the leading edge to 60° at the trailing edge, with a 0.1mm deep micro-serration structure machined at the trailing edge. The blade edges are equipped with 0.2mm deep Helmholtz eddy current enhancement grooves. Six samarium-cobalt permanent magnets are embedded in the impeller hub in an alternating N / S pole configuration, with the magnetization direction at a 17° angle to the rotation axis, achieving contactless transmission through magnetic coupling. When a three-phase 10kHz high-frequency current is applied, the stator magnetic field rotates, driving the impeller to cut the medium at 8500±200rpm, forming a forced spiral eddy current around the coaxial nested probe with an axial extension distance of 5.2 times the pipe diameter. The velocity gradient in the eddy core region is ≥1200s. -1 / 4. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 3, characterized in that: The distributed thermocouple gradient array uses 12 pairs of 0.1mm diameter tungsten-rhenium-26-tungsten-rhenium-5 heterojunction thermocouple wires. The hot nodes are fixed to designated coordinate points on the outer surface of the coaxial nested probe rod via laser micro-welding. All hot nodes are arranged in a logarithmic spiral spatial topology, with the bottom of the coaxial nested probe rod as the origin. The axial position Zn of the nth node satisfies Zn = 8·ln(n+1), unit: mm, n = 1 to 12. The minimum bottom distance between adjacent nodes is 2.1mm, and the maximum top distance is 8.7mm. The cold junction of the thermocouples extends to the sealed cavity at the top of the coaxial nested probe rod. The chamber is filled with a phase change material with a eutectic composition of 52% indium and 48% tin. A closed-loop temperature control system is formed by a thin-film heater surrounding the chamber and a Pt100 temperature sensor to maintain the cold junction temperature within the range of the medium saturation temperature ±0.3℃. The signal wires of each thermocouple pair are made of twisted-pair shielding and pass through the inner hole of the coaxial nested probe. The ends are connected to a transimpedance differential circuit based on an instrumentation amplifier. The gain of this circuit is set to 500±5 and the bandwidth is 1MHz. It can synchronously output the natural temperature gradient curve in static mode and the dynamic gradient change signal in eddy current disturbance mode.

5. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 4, characterized in that: The thermocouple signal is processed by a transimpedance differential amplifier circuit, which includes a parallel static signal channel and a disturbance signal channel. The static signal channel employs a 100-gain inverting amplifier structure, with a 10μF polypropylene film capacitor connected in parallel at the input stage to form a high-pass filter with a cutoff frequency of 0.01Hz. After eliminating DC drift, the signal is amplified by a precision operational amplifier and outputs a temperature gradient baseline signal under natural thermal conduction conditions. The disturbance signal channel has a differentiating circuit with a time constant of 15ms connected in series at the front end of the amplifier. The transient thermoelectric potential change generated by eddy current disturbance is amplified by an instrumentation amplifier with a gain of 500. The output terminal is connected to the non-inverting input terminal of the high-speed comparator; the static channel output signal is attenuated to 35.7% of its original value by a precision resistor voltage divider network before being input to the inverting input of the comparator. When the amplitude of the excitation channel signal exceeds 2.8 times the reference voltage, the comparator outputs a high level to trigger the liquid level marking signal; within a 50-200ms time window after the start of the magnetohydrodynamic driven eddy current generator, the comparator output signal is latched by a D flip-flop, and the RS485 interface is activated to output the liquid level coordinate value. The coordinate value is determined by the position of the thermocouple node that first triggers the comparator, with a position resolution of 0.1mm.

6. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 5, characterized in that: The axial spacing configuration method between the magnetohydrodynamic (MHD) driven eddy current generator and the bottommost thermocouple node is as follows: a precision spiral guide rail with a lead of 0.5 mm is pre-installed inside the coaxial nested probe rod. A closed-loop stepper motor with a step angle of 1.8° drives the MHD driven eddy current generator mounting base to move axially. During initial installation, using the impeller tip as the reference surface, the distance to the first-stage thermocouple hot node is measured with a laser rangefinder, and this spacing is adjusted to the design value L. When the kinematic viscosity of the molten nitrate medium is detected to be ν = 1.2 × 10⁻⁶... -6 m 2 When the outer diameter D of the coaxial nested probe is 25mm, and the impeller speed is set to 8500rpm, the corresponding impeller tip linear velocity V is... tip =22.3m / s, calculated L=8.02mm, the actual assembly spacing was calibrated to 8.0±0.05mm using a micrometer; after assembly, a vibration spectrum analyzer was used to verify that the vortex volume in the eddy core region is ≥1000s. -1 / Completely cover the first three thermocouple nodes, with a coverage deviation of less than 10% of the node spacing.

7. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 6, characterized in that: A platinum-iridium 10 alloy wire with a diameter of 0.15±0.003mm (90% platinum / 10% iridium) is laid parallel to the axis of the coaxial nested probe rod 0.8mm to the side of the thermocouple array. The length of the compensation wire is equal to the effective detection section of the coaxial nested probe rod, typically 300mm, and both ends are laser-welded to a 1mm diameter copper-nickel alloy lead wire. The lead wire is connected to a constant current source control module, which dynamically outputs a step compensation current based on the thermocouple time constant τ. When the magnetohydrodynamic driven eddy current generator is started, the control module synchronously outputs a negative step current with a pulse width of 50ms and an amplitude of 2.8A, causing the compensation wire to generate a temperature drop ΔT=1.7℃ within 0.5ms. This temperature drop cancels out the phase lag caused by the thermal inertia of the medium through heat conduction, compressing the effective response time of the thermocouple to 55% of the actual value.

8. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 7, characterized in that: A rectangular groove with a depth of 0.15±0.01mm is machined at the axial center of the outer sheath of the coaxial nested probe. A quartz crystal resonator with a 128° Y-axis tangent and dimensions of 3.2×2.0×0.3mm is fixed in the groove. The electrodes on both sides of the resonator are connected to a platinum microstrip antenna on a zirconia ceramic substrate by gold wire ball bonding with a diameter of 0.1mm. The antenna is designed with a serpentine topology, with a total length of 18mm and a 125MHz oscillation circuit connected to its end. A 0.2 μm thick aluminum nitride piezoelectric film is sputtered onto the surface of the resonant plate, and then covered with a 5 μm thick polycrystalline diamond protective layer grown by chemical vapor deposition. When bubbles adhere to the surface of the coaxial nested probe, the relationship between the resonant frequency offset Δf and the bubble coverage η is given by the calibration curve Δf = -0.0032η. 2 • f0 is determined, which is the base frequency of 125MHz. The frequency signal is down-converted to an intermediate frequency of 10.7MHz by a mixer, and then demodulated to produce a DC compensation voltage through a phase-locked loop. This voltage is input to the inverting terminal of the amplifier and superimposed on the original thermocouple signal to cancel the temperature measurement deviation caused by bubbles in real time.

9. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 8, characterized in that: The drive control method for a magnetohydrodynamic (MHD) driven eddy current generator in a liquid metal medium is as follows: the stator electromagnetic coil adopts a three-phase six-pole star connection; the input current is generated by a SiC MOSFET full-bridge inverter with a carrier frequency of 40kHz and a dead time of 1μs; the drive frequency f is controlled by a real-time feedback closed-loop control via a magnetic encoder, and is forcibly locked at the MHD critical threshold f. c More than 1.2 times, i.e., f≥1.2×(σB2) / (2πρ), where σ is the dielectric conductivity in S / m, B is the air gap magnetic flux density in T, and ρ is the dielectric density in kg / m³. 3 When applied to molten lead-bismuth alloys, σ = 8.6 × 10⁻⁶ 4 S / m, kg / m 3 When B = 0.85T, f is calculated. c =708Hz, the actual drive frequency is configured as 850Hz±5Hz; frequency locking is achieved by a hardware comparator. When the encoder detects that the frequency corresponding to the rotational speed is lower than 840Hz, it immediately triggers an overmodulation pulse to increase the duty cycle to 95%, and recovers the target frequency within 0.5ms; simultaneously, an infrared temperature probe is installed at the rotor shaft end to monitor the permanent magnet temperature in real time. When the temperature exceeds 750℃, the drive frequency is linearly reduced to f. c 1.05 times that of samarium cobalt magnets, to prevent irreversible demagnetization of samarium cobalt magnets.

10. The active eddy current disturbed thermocouple gradient liquid level detector as described in claim 9, characterized in that: Establish a closed-loop control system for eddy current intensity and temperature gradient: extract the temperature gradient magnitude from the excitation channel of the transimpedance differential amplifier circuit. The signal is converted to a true RMS value and outputs a 0-5V DC voltage Vg. This voltage is input to a comparator with a lower threshold set to 0.8K / mm (corresponding to 1.6V) and an upper threshold set to 1.2K / mm (corresponding to 2.4V). When Vg < 1.6V, the comparator outputs a low level to trigger a timer to generate a PWM wave with a linearly increasing duty cycle. The initial frequency is 1kHz, and the duty cycle is 40%. The PWM signal drives the three-phase inverter through optocoupler isolation, causing the impeller speed to increase in steps from a base of 8000rpm to 12000rpm. When... When the speed rises to 1.2K / mm, the speed is adjusted back to the reference 8000rpm, forming an anti-oscillation adaptive mechanism. When Vg > 2.4V, the comparator outputs a high level to activate the analog switch, locking the PWM duty cycle to the reference value of 40%. During speed regulation, the magnetic encoder provides real-time feedback of the actual speed and inputs it to the differential amplifier. After comparing it with the target speed, an error voltage is generated. This voltage is compensated for load fluctuations by an integral circuit with a time constant of 50ms, ensuring that the steady-state speed error is < ±15rpm. In the case of severe liquid level oscillation, the overload protection mode is forcibly activated: the power supply of the magnetohydrodynamic driven eddy current generator is cut off, and the spacing adjustment motor is activated to retract the magnetohydrodynamic driven eddy current generator by 5mm. The generator automatically recovers after the gradient signal stabilizes.

Images