An ultra-low temperature cascade refrigeration device

Abstract

The application discloses an ultralow-temperature cascade refrigeration device and belongs to the technical field of refrigeration devices, and solves the problem that when a low-temperature-stage screw compressor continuously operates below-80 DEG C, trace moisture and organic acid generated by hydrolysis of ester lubricating oil form a gelatinous deposit with metal scraps, increase the slide valve resistance and cause displacement lag, and the problem that the bearing is finally worn or the energy efficiency is reduced because the sensor can only feedback an instruction signal and cannot be monitored by a controlled system. The application comprises a screw compressor and a slide valve state monitoring circuit arranged in the screw compressor. The application uses a double-frequency laser interference to measure the actual displacement of the slide valve in real time, combines with a surface acoustic wave frequency shift to analyze the thickness of the gelatinous substance, calculates a fault index after dynamic compensation, and gives an early warning when the index exceeds a limit, so that the blind area of a traditional sensor is eliminated, and the bearing of the compressor is diagnosed in advance to avoid wear.

Description

Technical Field

[0001] This invention relates to the field of refrigeration equipment technology, and in particular to an ultra-low temperature cascade refrigeration device. Background Technology

[0002] Ultra-low temperature cascade refrigeration systems, also known as cascade freezers, are cryogenic devices that operate through a two-stage cascade cooling cycle. The low-temperature stage typically uses a screw or piston compressor with refrigerant such as R23, while the high-temperature stage often uses a screw compressor with refrigerant such as R404A. The two stages are thermally coupled via a condenser-evaporator. Its electrical system includes a main controller, temperature and pressure sensors, a compressor inverter module, solenoid valves, and safety interlock circuits, allowing for precise control of the operating parameters of both stages. This equipment is suitable for refrigeration requirements from -40℃ to -150℃ and is widely used in fields such as pharmaceutical freezing and low-temperature material testing. It achieves ultra-low temperature output through two-stage relay refrigeration, combining high efficiency and stability.

[0003] When the cryogenic screw compressor of a cascade refrigeration unit operates continuously in an ultra-low temperature environment below -80°C, trace amounts of residual moisture in the system will undergo a hydrolysis reaction with ester-based synthetic lubricating oil, generating low-molecular-weight organic acids. These acidic substances combine with metal debris generated by compressor wear to form a viscous, gel-like polymer, which gradually deposits in the gap between the slide valve guide and the sealing surface. As operating time accumulates, the gel-like substance significantly increases the sliding valve's moving resistance, causing a mechanical hysteresis deviation between the displacement command issued by the controller and the actual displacement.

[0004] However, because the valve position sensor only feeds back command signals rather than actual mechanical displacement, the control system cannot detect displacement deviation. This makes the gel-like deposition process an unmonitored "gray box" until abnormal wear of the compressor bearings or a significant drop in energy efficiency occurs.

[0005] Therefore, an ultra-low temperature cascade refrigeration device is proposed to solve or alleviate the above problems. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing an ultra-low temperature cascade refrigeration device.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] An ultra-low temperature cascade refrigeration device includes a screw compressor and a slide valve status monitoring circuit installed in the screw compressor. The slide valve status monitoring circuit detects the deviation between the actual displacement of the slide valve and the command value in real time through dual-frequency laser interferometry, and analyzes the thickness of the gel deposit by combining the surface acoustic wave resonant frequency shift analysis. After dynamic compensation by multi-physics field parameters, the deposition fault index is calculated. When an abnormal increase in displacement hysteresis or an excessive deposition thickness is detected, a simulated early warning signal is triggered in stages.

[0009] Preferably, the slide valve status monitoring circuit includes a dual-frequency laser interferometry displacement module, a surface acoustic wave material analysis module, a multi-physics field compensation module, a data fusion processor module, an industrial interface module, and a power supply module;

[0010] The dual-frequency laser interferometric displacement module is used to acquire real-time phase difference signals; the surface acoustic wave material analysis module is used to acquire resonant frequency signals; the multi-physics compensation module is used to acquire temperature, stress, and air pressure parameters to compensate for temperature drift of the frequency signals; the data fusion processor module is used to calculate the absolute difference between the controller command displacement and the actual compensated displacement as displacement hysteresis; calculate the difference between the compensated frequency and the fundamental frequency divided by the product of the material constant and the square of the fundamental frequency as deposition thickness; calculate the percentage of the sum of the amplitudes of the third to fifth harmonics to the amplitude of the fundamental frequency as motion nonlinearity; weight the normalized displacement hysteresis, deposition thickness, and nonlinearity according to weight coefficients; dynamically adjust the weight coefficients and threshold parameters according to the running time; divide the fault state into four levels according to the fault index value range and set the judgment conditions; the industrial interface module is used to transmit the fault state to the host computer; and the power supply module supplies power to each module.

[0011] Preferably, the phase difference voltage output terminal of the dual-frequency laser interferometric displacement module is connected to the analog signal input channel of the data fusion processor module via a shielded wire; the serial peripheral interface bus of the surface acoustic wave material analysis module is connected to the synchronous clock line, serial data line, and chip enable line of the data fusion processor module via a ribbon cable; the analog-to-digital conversion output of the multiphysics compensation module is connected to the clock line, data output line, and data input line of the data fusion processor module; the internal integrated circuit interface of the multiphysics compensation module is connected to the serial clock line and serial data line of the data fusion processor module via a twisted pair cable; the digital output channel of the data fusion processor module is connected to the isolated input channel of the industrial interface module; the output terminal of the industrial interface module is used to connect to a host computer; and the output terminal of the power supply module is connected to the power input terminal of each module.

[0012] Preferably, the dual-frequency laser interferometric displacement module includes a first distributed feedback laser DFB-1550, a second distributed feedback laser DFB-1550, a polarization beam combiner, a polarization beam splitter, a reference mirror, a measuring mirror, a balanced photodetector, and an AD8302 phase detection chip. The reference mirror is fixedly connected to the housing of the screw compressor, and the measuring mirror is fixedly connected to the slide valve push rod in the screw compressor. The positive terminals of the first and second distributed feedback lasers DFB-1550 are connected to the output terminal of the power supply module, and the negative terminals of the first and second distributed feedback lasers DFB-1550 are grounded. The laser output of the first and second distributed feedback lasers DFB-1550 is... The output ends are respectively connected to the first optical signal input end and the second optical signal input end of the polarization beam combiner. The combined light output end of the polarization beam combiner is connected to the optical signal input end of the polarization beam splitter. The reference light output end of the polarization beam splitter is used to connect to the incident surface of the fixed reflector. The measurement light output end of the polarization beam splitter is used to connect to the incident surface of the sliding valve reflector. The reference light signal input end of the balanced photodetector is used to connect to the reflected light path of the fixed reflector. The measurement light signal input end of the balanced photodetector is used to connect to the reflected light path of the sliding valve reflector. The in-phase signal output end of the balanced photodetector is connected to the in-phase voltage input end of the AD8302 phase detection chip. The phase difference voltage output end of the AD8302 phase detection chip is connected to the analog signal input channel of the XC7A100T field-programmable gate array chip in the data fusion processor module.

[0013] Preferably, the surface acoustic wave (SAW) material analysis module includes an HMC583LP5 microwave oscillator, a circulator, a SAW sensor, an ADL6012 detector, and an ADF4351 frequency synthesizer. The RF signal output of the HMC583LP5 microwave oscillator is connected to the RF input port of the circulator. The RF output port of the circulator is connected to the signal input port of the SAW sensor. The reflection signal port of the circulator is connected to the RF signal input of the ADL6012 detector. The envelope signal output of the ADL6012 detector is connected to the signal input of the ADF4351 frequency synthesizer. The serial peripheral interface clock line of the ADF4351 frequency synthesizer is connected to the first clock signal terminal of the XC7A100T field-programmable gate array (FPGA) chip in the data fusion processor module. The serial data output of the ADF4351 frequency synthesizer is connected to the first data receiving terminal of the XC7A100T FPGA chip in the data fusion processor module.

[0014] Preferably, the multiphysics compensation module includes a PT1000 platinum resistance temperature sensor, a REF200 constant current source chip, an AD8420 instrumentation amplifier, an ADS1248 analog-to-digital converter, a CEA-13 strain gauge full-bridge, an HX711 bridge ADC, and a BMP388 barometric pressure sensor. The positive terminal of the current excitation of the PT1000 platinum resistance temperature sensor is connected to the current output terminal of the REF200 constant current source chip. The positive terminal of the voltage sensing of the PT1000 platinum resistance temperature sensor is connected to the non-inverting input terminal of the AD8420 instrumentation amplifier. The signal output terminal of the AD8420 instrumentation amplifier is connected to the analog input channel of the ADS1248 analog-to-digital converter. The serial clock input terminal of the ADS1248 analog-to-digital converter is connected to the XC7A100T field-programmable gate array in the data fusion processor module. The second clock signal terminal of the array chip is connected to the second data receiving terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module. The full-bridge output terminal of the CEA-13 strain gauge full bridge is connected to the input terminal of the HX711 bridge ADC. The clock terminal and output terminal of the HX711 bridge ADC are both connected to the XC7A100T field-programmable gate array chip in the data fusion processor module. The serial clock signal terminal of the BMP388 barometric pressure sensor is connected to the third clock signal terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module. The serial data output terminal of the BMP388 barometric pressure sensor is connected to the serial data terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module.

[0015] Preferably, the data fusion processor module includes an XC7A100T field-programmable gate array (FPGA) chip, an IS61WV102416BLL static random access memory (SRAM), and a SIT5356 crystal oscillator. The address bus, data bus, and control signals of the IS61WV102416BLL SRAM are all connected to the XC7A100T FPGA chip, and the output terminal of the SIT5356 crystal oscillator is connected to the clock input terminal of the XC7A100T FPGA chip.

[0016] Preferably, the industrial interface module includes an ADuM1410 digital isolator, an MCP2515 controller LAN controller, and a TJA1050 controller LAN transceiver. The digital signal input terminal of the ADuM1410 digital isolator is connected to the digital output terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module. The digital signal output terminal of the ADuM1410 digital isolator is connected to the MCP2515 controller LAN controller. The outgoing terminal of the MCP2515 controller LAN controller is used to connect to the host computer through the TJA1050 controller LAN transceiver.

[0017] The present invention has the following beneficial effects:

[0018] In the cascade refrigeration device of this invention, the status of the slide valve is detected in real time by dual-frequency laser interferometry to detect the nanometer-level deviation between the actual displacement of the slide valve and the command value. Combined with the analysis of the frequency shift of surface acoustic wave resonance, the thickness of the gel deposit is calculated. After dynamic compensation of multiple physical field parameters, the deposition fault index is calculated. When an abnormal increase in displacement hysteresis or excessive deposition thickness is detected, a simulated early warning signal is triggered in stages. This allows for the identification of the problem of mechanical hysteresis monitoring blind spot caused by traditional displacement sensors only feeding back command values ​​in ultra-low temperature environments. This enables early diagnosis of gel deposits and avoids abnormal wear of the compressor bearings in the cascade refrigeration device of this invention. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a structural block diagram of the present invention.

[0021] The diagram shows: 1. Dual-frequency laser interferometric displacement module; 2. Surface acoustic wave material analysis module; 3. Multiphysics compensation module; 4. Data fusion processor module; 5. Industrial interface module; 6. Power supply module. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the description of this invention, it should be understood that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] Furthermore, the terms "first," "second," and "third" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0027] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] An ultra-low temperature cascade refrigeration device includes a screw compressor and a slide valve status monitoring circuit installed in the screw compressor. The slide valve status monitoring circuit detects the deviation between the actual displacement of the slide valve and the command value in real time through dual-frequency laser interferometry, and analyzes the thickness of the gel deposit by combining the surface acoustic wave resonant frequency shift. After dynamic compensation by multi-physics field parameters, the deposition fault index is calculated. When an abnormal increase in displacement hysteresis or an excessive deposition thickness is detected, a simulated early warning signal is triggered in stages.

[0029] like Figure 1As shown, the slide valve status monitoring circuit includes a dual-frequency laser interferometric displacement module 1, a surface acoustic wave material analysis module 2, a multi-physics field compensation module 3, a data fusion processor module 4, an industrial interface module 5, and a power supply module 6. The phase difference voltage output terminal of the dual-frequency laser interferometric displacement module 1 is connected to the analog signal input dedicated channel of the data fusion processor module 4 through a shielded wire. The serial peripheral interface bus of the surface acoustic wave material analysis module 2 is connected to the synchronous clock line, serial data line, and chip enable line of the data fusion processor module 4 through a ribbon cable. The analog-to-digital conversion output of the multi-physics field compensation module 3 is connected to the clock line, data output line, and data input line of the data fusion processor module 4. The internal integrated circuit interface of the multi-physics field compensation module 3 is connected to the serial clock line and serial data line of the data fusion processor module 4 through a twisted pair cable. The digital output channel of the data fusion processor module 4 is connected to the isolated input channel of the industrial interface module 5. The output terminal of the industrial interface module 5 is used to connect to the host computer. The output terminal of the power supply module 6 is connected to the power input terminal of each module.

[0030] The dual-frequency laser interferometric displacement module 1 includes a first distributed feedback laser DFB-1550, a second distributed feedback laser DFB-1550, a polarization beam combiner, a polarization beam splitter, a reference mirror, a measuring mirror, a balanced photodetector, and an AD8302 phase detection chip. The reference mirror is fixedly connected to the housing of the screw compressor, and the measuring mirror is fixedly connected to the slide valve push rod in the screw compressor. The positive terminals of the first and second distributed feedback lasers DFB-1550 are connected to the output terminal of the power supply module 6, and the negative terminals of the first and second distributed feedback lasers DFB-1550 are grounded. The laser outputs of the first and second distributed feedback lasers DFB-1550 are... The output ends are respectively connected to the first optical signal input end and the second optical signal input end of the polarization beam combiner. The combined light output end of the polarization beam combiner is connected to the optical signal input end of the polarization beam splitter. The reference light output end of the polarization beam splitter is used to connect to the incident surface of the fixed reflector. The measurement light output end of the polarization beam splitter is used to connect to the incident surface of the sliding valve reflector. The reference light signal input end of the balanced photodetector is used to connect to the reflected light path of the fixed reflector. The measurement light signal input end of the balanced photodetector is used to connect to the reflected light path of the sliding valve reflector. The in-phase signal output end of the balanced photodetector is connected to the in-phase voltage input end of the AD8302 phase detection chip. The phase difference voltage output end of the AD8302 phase detection chip is connected to the analog signal input channel of the XC7A100T field programmable gate array chip in the data fusion processor module 4.

[0031] The surface acoustic wave (SAW) material analysis module 2 includes an HMC583LP5 microwave oscillator, a circulator, a SAW sensor, an ADL6012 detector, and an ADF4351 frequency synthesizer. The RF signal output of the HMC583LP5 microwave oscillator is connected to the RF input port of the circulator. The RF output port of the circulator is connected to the signal input port of the SAW sensor. The reflection signal port of the circulator is connected to the RF signal input of the ADL6012 detector. The envelope signal output of the ADL6012 detector is connected to the signal input of the ADF4351 frequency synthesizer. The serial peripheral interface clock line of the ADF4351 frequency synthesizer is connected to the first clock signal terminal of the XC7A100T field-programmable gate array (FPGA) chip in the data fusion processor module 4. The serial data output terminal of the ADF4351 frequency synthesizer is connected to the first data receiving terminal of the XC7A100T FPGA chip in the data fusion processor module 4.

[0032] The multiphysics compensation module 3 includes a PT1000 platinum resistance temperature sensor, a REF200 constant current source chip, an AD8420 instrumentation amplifier, an ADS1248 analog-to-digital converter, a CEA-13 strain gauge full-bridge, an HX711 bridge ADC, and a BMP388 barometric pressure sensor. The positive terminal of the PT1000 platinum resistance temperature sensor's current excitation is connected to the current output terminal of the REF200 constant current source chip, and the positive terminal of the PT1000 platinum resistance temperature sensor's voltage sensing is connected to the non-inverting input terminal of the AD8420 instrumentation amplifier. The signal output terminal of the AD8420 instrumentation amplifier is connected to the analog input channel of the ADS1248 analog-to-digital converter, and the serial clock input terminal of the ADS1248 analog-to-digital converter is connected to the XC7A100T field-programmable gate array chip in the data fusion processor module 4. The second clock signal terminal of the ADS1248 analog-to-digital converter is connected to the second data receiving terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module 4. The full-bridge output terminal of the CEA-13 strain gauge full bridge is connected to the input terminal of the HX711 bridge ADC. The clock terminal and output terminal of the HX711 bridge ADC are both connected to the XC7A100T field-programmable gate array chip in the data fusion processor module 4. The serial clock signal terminal of the BMP388 pressure sensor is connected to the third clock signal terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module 4. The serial data output terminal of the BMP388 pressure sensor is connected to the serial data terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module 4.

[0033] The data fusion processor module 4 includes an XC7A100T field-programmable gate array (FPGA) chip, an IS61WV102416BLL static random access memory (SRAM), and a SIT5356 crystal oscillator. The address bus, data bus, and control signals of the IS61WV102416BLL SRAM are all connected to the XC7A100T FPGA chip, and the output of the SIT5356 crystal oscillator is connected to the clock input of the XC7A100T FPGA chip.

[0034] Industrial interface module 5 includes an ADuM1410 digital isolator, an MCP2515 controller LAN controller, and a TJA1050 controller LAN transceiver. The digital signal input terminal of the ADuM1410 digital isolator is connected to the digital output terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module 4. The digital signal output terminal of the ADuM1410 digital isolator is connected to the MCP2515 controller LAN controller. The outgoing terminal of the MCP2515 controller LAN controller is used to connect to the host computer through the TJA1050 controller LAN transceiver.

[0035] The dual-frequency laser interferometric displacement module 1 is used to acquire real-time phase difference signals, multiply the real-time phase difference by the laser wavelength and then divide by four times the constant of pi. The surface acoustic wave material analysis module 2 is used to acquire resonant frequency signals, and add the fundamental frequency to the product of the material constant and the deposition thickness.

[0036] The multiphysics compensation module 3 is used to collect temperature, stress and air pressure parameters to perform thermal expansion compensation, stress compensation and air pressure refractive index compensation on displacement signals, and temperature drift compensation on frequency signals.

[0037] The specific displacement compensation is the original displacement value multiplied by a compensation coefficient that includes temperature deviation, stress and air pressure deviation. The temperature deviation coefficient is -9 x 10 to the power of -7 per degree Celsius, the stress coefficient is -3 x 10 to the power of -8 per microstrain, and the air pressure deviation coefficient is +7.6 x 10 to the power of -7 per hectopascal.

[0038] The specific frequency compensation is the original frequency value multiplied by one minus the product of the temperature drift coefficient and the temperature deviation, where the temperature drift coefficient is 10 to the power of negative six per degree Celsius.

[0039] The data fusion processor module 4 is used to calculate the absolute difference between the controller command displacement and the actual compensation displacement as the displacement hysteresis, calculate the difference between the compensation frequency and the fundamental frequency divided by the product of the material constant and the square of the fundamental frequency as the deposition thickness, and calculate the percentage of the sum of the third to fifth harmonic amplitudes to the fundamental frequency amplitude as the motion nonlinearity.

[0040] The normalized displacement hysteresis, deposition thickness, and nonlinearity are summed by weighted coefficients, and the weighting coefficients and threshold parameters are dynamically adjusted according to the running time. The deposition failure index is calculated by multiplying the quotient of displacement hysteresis divided by its maximum threshold by a weight of 0.6, adding the quotient of deposition thickness divided by its maximum threshold by a weight of 0.3, and adding the motion nonlinearity by a weight of 0.1. The weighting coefficients are dynamically optimized by increasing the displacement hysteresis weight by 0.1 times over time by the hyperbolic tangent function value, where the independent variable of the hyperbolic tangent function is 1 / 100th of the running time. The threshold is self-tuned by setting the maximum displacement hysteresis threshold to 20 micrometers initially, increasing by 0.5 micrometers every 1,000 hours of operation.

[0041] The fault states are divided into four levels based on the fault index range, and judgment conditions are set accordingly. The specific judgment conditions are as follows:

[0042] When the fault index is less than 0.3, it is considered to be in a normal state, which requires that the displacement hysteresis is less than 5 micrometers and the deposition thickness is less than 1 micrometer.

[0043] When the fault index is greater than or equal to 0.3 and less than 0.5, it is judged as a warning state, and the displacement lag continues to rise for ten consecutive minutes.

[0044] When the fault index is greater than or equal to 0.5 and less than 0.7, it is judged as a moderate fault, with a deposition thickness greater than 10 micrometers or a motion nonlinearity greater than 15%.

[0045] A fault index greater than or equal to 0.7 is considered a serious fault, with a displacement hysteresis greater than 15 micrometers and a deposition thickness greater than 30 micrometers.

[0046] Industrial interface module 5 is used to transmit fault status to the host computer, and power module 6 provides power to each module.

[0047] More specifically,

[0048] When the cryogenic cascade refrigeration device operates continuously in a cryogenic environment of minus 80 degrees Celsius, the first and second distributed feedback lasers in the dual-frequency laser interferometric displacement module 1 emit orthogonally polarized laser beams with a wavelength of 1,550 nanometers, respectively. After being combined by a polarization combiner, they enter a polarization beam splitter to be divided into a reference optical path and a measurement optical path. The reference optical path returns through a reference mirror, and the measurement optical path is reflected back by a measurement reflector magnetically adsorbed on the slide valve push rod. The two beams interfere in the balanced photodetector and are transmitted to the in-phase input and quadrature input of the phase detection chip through the in-phase signal output terminal and the quadrature signal output terminal. The phase difference voltage output terminal of the phase detection chip outputs an analog signal proportional to the displacement of the slide valve in real time.

[0049] Meanwhile, the microwave oscillator RF signal output terminal in the surface acoustic wave material analysis module 2 generates a 433 MHz excitation signal, which is input through the first port of the circulator and output through the second port to the RF signal port of the surface acoustic wave sensor.

[0050] When the gel deposits on the slide valve rail, the change in the surface wave velocity of the surface acoustic wave sensor causes a shift in the resonant frequency of the reflected signal. This signal is transmitted to the radio frequency signal input of the detector via the third port of the circulator, and its envelope signal output transmits the frequency shift characteristics to the signal input port of the frequency counter.

[0051] The multiphysics compensation module 3 collects the temperature of the slide valve area through a platinum resistance temperature sensor. Its excitation current positive terminal is connected to the current output positive terminal of the constant current source chip, and the sensing signal positive terminal is connected to the non-inverting input terminal of the instrumentation amplifier. The signal output terminal of the instrumentation amplifier sends the amplified temperature signal to the first analog input channel of the analog-to-digital converter. The strain gauge full bridge is attached to the housing of the screw compressor, and its full bridge output positive terminal is connected to the non-inverting input channel of the bridge ADC to monitor mechanical stress. The pressure sensor transmits the pressure data to the data fusion processor module 4 through the internal integrated circuit interface.

[0052] The field-programmable gate array chip in the data fusion processor module 4 acquires the phase difference voltage through the dedicated analog signal input channel, calculates the real-time displacement value after internal analog-to-digital conversion, and obtains the compensation frequency output by the frequency counter through the clock line and data line of the first serial peripheral interface. Combined with temperature stress and air pressure parameters, it performs multi-physics compensation.

[0053] The displacement value is compensated by applying a thermal expansion compensation coefficient of -9 x 10 to the power of -7 per degree Celsius, a stress compensation coefficient of -3 x 10 to the power of -8 per microstrain, and a gas pressure refractive index compensation coefficient of +7.6 x 10 to the power of -7 per hectopascal. The surface acoustic wave frequency is compensated by applying a temperature drift coefficient of 10 to the power of -6 per degree Celsius.

[0054] In the feature extraction stage, the absolute difference between the controller command displacement and the compensation displacement is calculated by the field programmable gate array chip as the displacement hysteresis. The deposition thickness is obtained by dividing (compensation frequency minus 433 MHz) by the product of 2.3 x 10 to the power of -10 and the square of the fundamental frequency. At the same time, the motion nonlinearity is calculated by analyzing the ratio of the amplitude of the third to fifth harmonics of the vibration spectrum to the amplitude of the fundamental frequency.

[0055] During the data fusion phase, the normalized displacement hysteresis is divided by the dynamic threshold (initially 20 micrometers, increasing by 0.5 micrometers every thousand hours), the deposition thickness is divided by the 50-micrometer threshold, and the motion nonlinearity is fused using a weighting coefficient of 0.6:0.3:0.1 to generate a deposition fault index. When the value of the deposition fault index exceeds 0.3, the fault diagnosis logic is activated: a continuous increase in displacement hysteresis for ten minutes is considered a warning state; when the deposition thickness is greater than 10 micrometers or the motion nonlinearity is greater than 15%, it is upgraded to a moderate fault; and when the displacement hysteresis exceeds 15 micrometers and the deposition thickness exceeds 30 micrometers, it is considered a severe fault.

[0056] As a result, the screw compressor in this refrigeration unit can achieve early detection of gelatinous deposits at the level of one micrometer in an environment of minus 85 degrees Celsius, and the displacement hysteresis detection accuracy is ±0.5 micrometers. This solves the problem of blind spots in monitoring mechanical hysteresis deviation caused by traditional displacement sensors that only feed back command values, and provides early warnings to avoid malfunctions such as abnormal wear of compressor bearings.

[0057] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A cryogenic cascade refrigeration device, characterized in that, The system includes a screw compressor and a slide valve status monitoring circuit installed in the screw compressor. The slide valve status monitoring circuit detects the deviation between the actual displacement of the slide valve and the command value in real time through dual-frequency laser interferometry. After analyzing the gel deposit thickness by combining the surface acoustic wave resonant frequency shift, it calculates the deposition fault index after dynamic compensation of multi-physics field parameters. When an abnormal increase in displacement hysteresis or excessive deposition thickness is detected, a simulated early warning signal is triggered in stages. The valve status monitoring circuit includes a dual-frequency laser interference displacement module (1), a surface acoustic wave material analysis module (2), a multi-physics field compensation module (3), a data fusion processor module (4), an industrial interface module (5), and a power supply module (6). The dual-frequency laser interferometric displacement module (1) is used to acquire real-time phase difference signals; the surface acoustic wave material analysis module (2) is used to acquire resonant frequency signals; the multi-physics compensation module (3) is used to acquire temperature, stress, and air pressure parameters to perform thermal expansion compensation, stress compensation, and air pressure refractive index compensation on the displacement signals, and temperature drift compensation on the frequency signals; the data fusion processor module (4) is used to calculate the absolute difference between the controller command displacement and the actual compensated displacement as the displacement hysteresis; calculate the difference between the compensated frequency and the fundamental frequency divided by the product of the material constant and the square of the fundamental frequency as the deposition thickness; calculate the percentage of the sum of the amplitudes of the third to fifth harmonics to the amplitude of the fundamental frequency as the motion nonlinearity; weight the normalized displacement hysteresis, deposition thickness, and nonlinearity according to the weight coefficients; and dynamically adjust the data fusion processor module according to the running time. The system integrates weighting coefficients and threshold parameters, classifies four levels of fault states according to the fault index range, and sets judgment conditions. The judgment conditions are as follows: when the fault index is less than 0.3, it is judged as a normal state, and the displacement hysteresis must be less than 5 micrometers and the deposition thickness must be less than 1 micrometer; when the fault index is greater than or equal to 0.3 and less than 0.5, it is judged as a warning state, and the displacement hysteresis must maintain an upward trend for ten consecutive minutes; when the fault index is greater than or equal to 0.5 and less than 0.7, it is judged as a moderate fault, and the deposition thickness must be greater than 10 micrometers or the motion nonlinearity must be greater than 15%; when the fault index is greater than or equal to 0.7, it is judged as a serious fault, and the displacement hysteresis must be greater than 15 micrometers and the deposition thickness must be greater than 30 micrometers. The industrial interface module (5) is used to transmit the fault state to the host computer, and the power supply module (6) supplies power to each module. The phase difference voltage output terminal of the dual-frequency laser interference displacement module (1) is connected to the analog signal input channel of the data fusion processor module (4) through a shielded wire. The serial peripheral interface bus of the surface acoustic wave material analysis module (2) is connected to the synchronous clock line, serial data line, and chip enable line of the data fusion processor module (4) through a ribbon cable. The analog-to-digital conversion output of the multi-physics compensation module (3) is connected to the clock line, data output line, and data input line of the data fusion processor module (4). The internal integrated circuit interface of the multi-physics compensation module (3) is connected to the serial clock line and serial data line of the data fusion processor module (4) through a twisted pair cable. The digital output channel of the data fusion processor module (4) is connected to the isolated input channel of the industrial interface module (5). The output terminal of the industrial interface module (5) is used to connect to the host computer. The output terminal of the power supply module (6) is connected to the power input terminal of each module respectively.

2. The cryogenic cascade refrigeration device according to claim 1, characterized in that, The dual-frequency laser interferometric displacement module (1) includes a first distributed feedback laser DFB-1550, a second distributed feedback laser DFB-1550, a polarization beam combiner, a polarization beam splitter, a reference mirror, a measuring mirror, a balanced photodetector, and an AD8302 phase detection chip. The reference mirror is fixedly connected to the housing of the screw compressor, and the measuring mirror is fixedly connected to the slide valve push rod in the screw compressor. The positive terminals of the first and second distributed feedback lasers DFB-1550 are connected to the output terminal of the power supply module (6), and the negative terminals of the first and second distributed feedback lasers DFB-1550 are grounded. The laser output of the first and second distributed feedback lasers DFB-1550 is... The output ends are respectively connected to the first optical signal input end and the second optical signal input end of the polarization beam combiner. The combined light output end of the polarization beam combiner is connected to the optical signal input end of the polarization beam splitter. The reference light output end of the polarization beam splitter is used to connect to the incident surface of the fixed reflector. The measurement light output end of the polarization beam splitter is used to connect to the incident surface of the sliding valve reflector. The reference light signal input end of the balanced photodetector is used to connect to the reflected light path of the fixed reflector. The measurement light signal input end of the balanced photodetector is used to connect to the reflected light path of the sliding valve reflector. The in-phase signal output end of the balanced photodetector is connected to the in-phase voltage input end of the AD8302 phase detection chip. The phase difference voltage output end of the AD8302 phase detection chip is connected to the analog signal input channel of the XC7A100T field programmable gate array chip in the data fusion processor module (4).

3. The cryogenic cascade refrigeration device according to claim 1, characterized in that, The surface acoustic wave (SAW) material analysis module (2) includes an HMC583LP5 microwave oscillator, a circulator, a SAW sensor, an ADL6012 detector, and an ADF4351 frequency synthesizer. The RF signal output of the HMC583LP5 microwave oscillator is connected to the RF input port of the circulator. The RF output port of the circulator is connected to the signal input port of the SAW sensor. The reflection signal port of the circulator is connected to the RF signal input of the ADL6012 detector. The envelope signal output of the ADL6012 detector is connected to the signal input of the ADF4351 frequency synthesizer. The serial peripheral interface clock line of the ADF4351 frequency synthesizer is connected to the first clock signal terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4). The serial data output terminal of the ADF4351 frequency synthesizer is connected to the first data receiving terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4).

4. The cryogenic cascade refrigeration device according to claim 1, characterized in that, The multiphysics compensation module (3) includes a PT1000 platinum resistance temperature sensor, a REF200 constant current source chip, an AD8420 instrumentation amplifier, an ADS1248 analog-to-digital converter, a CEA-13 strain gauge full bridge, an HX711 bridge ADC, and a BMP388 barometric pressure sensor. The positive current excitation terminal of the PT1000 platinum resistance temperature sensor is connected to the current output terminal of the REF200 constant current source chip. The positive voltage sensing terminal of the PT1000 platinum resistance temperature sensor is connected to the non-inverting input terminal of the AD8420 instrumentation amplifier. The signal output terminal of the AD8420 instrumentation amplifier is connected to the analog input channel of the ADS1248 analog-to-digital converter. The serial clock input terminal of the ADS1248 analog-to-digital converter is connected to the XC7A100T field-programmable gate array chip in the data fusion processor module (4). Two clock signal terminals: the serial data output terminal of the ADS1248 analog-to-digital converter is connected to the second data receiving terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4); the full-bridge output terminal of the CEA-13 strain gauge full bridge is connected to the input terminal of the HX711 bridge ADC; the clock terminal and output terminal of the HX711 bridge ADC are both connected to the XC7A100T field-programmable gate array chip in the data fusion processor module (4); the serial clock signal terminal of the BMP388 barometric pressure sensor is connected to the third clock signal terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4); and the serial data output terminal of the BMP388 barometric pressure sensor is connected to the serial data terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4).

5. The cryogenic cascade refrigeration device according to claim 1, characterized in that, The data fusion processor module (4) includes an XC7A100T field-programmable gate array chip, an IS61WV102416BLL static random access memory, and a SIT5356 crystal oscillator. The address bus, data bus, and control signals of the IS61WV102416BLL static random access memory are all connected to the XC7A100T field-programmable gate array chip. The output terminal of the SIT5356 crystal oscillator is connected to the clock input terminal of the XC7A100T field-programmable gate array chip.

6. The cryogenic cascade refrigeration device according to claim 1, characterized in that, The industrial interface module (5) includes an ADuM1410 digital isolator, an MCP2515 controller LAN controller, and a TJA1050 controller LAN transceiver. The digital signal input terminal of the ADuM1410 digital isolator is connected to the digital output terminal of the XC7A100T field-programmable gate array chip in the data fusion processor module (4). The digital signal output terminal of the ADuM1410 digital isolator is connected to the MCP2515 controller LAN controller. The outgoing terminal of the MCP2515 controller LAN controller is used to connect to the host computer through the TJA1050 controller LAN transceiver.

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