Low-temperature liquid automatic supplementing circuit and low-temperature liquid container

Abstract

The invention provides a low-temperature liquid automatic supplementing circuit and a low-temperature liquid container. The low-temperature liquid automatic supplementing circuit comprises a power supply VCC, a high-level detection branch, a low-level detection branch, a logic judgment circuit and a driver. The high-level detection branch generates a first signal when the liquid level is higher than the highest line, and generates a second signal when the liquid level is lower than the highest line; the low-level detection branch generates a third signal when the liquid level is lower than the lowest line, and generates a fourth signal when the liquid level is higher than the lowest line; and the logic judgment circuit is electrically connected with the high-level detection branch and the low-level detection branch, and controls the connection state of the power supply VCC and the driver according to the first signal, the second signal, the third signal and the fourth signal. Liquid level judgment and liquid supplementing control are achieved through a pure hardware circuit, software or a microprocessor is not needed, and the problems of software crash, program errors or complex electromagnetic interference are avoided.

Description

Technical Field

[0001] This invention relates to, specifically, a cryogenic liquid automatic replenishment circuit and a cryogenic liquid container, and in particular, to a cryogenic liquid level sensor utilizing the self-heating effect of a thermal resistor and a matching automatic liquid replenishment device. Background Technology

[0002] Cryogenic liquids (such as liquid nitrogen) are widely used in scientific research, superconducting material testing, biological sample preservation, medical cryopreservation, and industrial cryogenic processing due to their low-temperature properties and relatively low preparation costs. During use, cryogenic liquids continuously evaporate and are consumed. If they are not replenished in time, the liquid level in the container will drop, leading to a series of problems. For example, in scientific research, insufficient cryogenic liquid levels may cause temperature runaway, affecting the accuracy of experimental data; in biological sample preservation, excessively low cryogenic liquid levels can cause sample failure or even permanent damage; in superconductor research and high-voltage applications, insufficient cryogenic liquid may cause superconductors to exit the superconducting state, triggering a resistive transition and damaging samples or experimental equipment. Therefore, the stable replenishment and maintenance of cryogenic liquid levels are crucial for experimental continuity and equipment safety.

[0003] Currently, there are two main types of methods for replenishing cryogenic liquids: the traditional method of manual monitoring and manual replenishment, and the automatic replenishment method that combines liquid level sensors with software control systems.

[0004] The basic procedure for traditional manual liquid replenishment is as follows: operators periodically observe changes in the liquid level in the container, and when the level drops to a certain critical value, they manually open the valve of the cryogenic liquid tank to replenish it. This method was widely used in the early days due to its simple structure and low equipment cost, but its shortcomings have become increasingly apparent in modern scientific research and industrial applications.

[0005] First, this method relies on the operator's subjective judgment, making it difficult to guarantee the timeliness and accuracy of monitoring. Cryogenic liquids evaporate rapidly at atmospheric pressure, especially under high-temperature, frequent opening of the lid, or high-power experimental conditions, where the liquid level may drop rapidly in a short period. If the operator fails to detect the drop in liquid level in time, the sample may be exposed to a non-cryogenic environment, causing experimental interruption or sample damage.

[0006] Secondly, manual operation is prone to introducing uncertainties and safety risks. If operators do not handle the injection of cryogenic liquids properly, they may add too much or too little, leading to excessive fluctuations in the liquid level and affecting the stability of the experiment. At the same time, the extremely low temperature environment for cryogenic liquid operations poses safety hazards such as frostbite and splashing of cryogenic liquids, increasing the workload and danger for experimental personnel.

[0007] Finally, in application scenarios requiring long-term unattended operation or continuous operation, manual testing and replenishment methods cannot meet the needs. Modern scientific research facilities, biological sample libraries, or industrial cryogenic equipment often require stable operation for extended periods, while manual methods require personnel to be on duty around the clock. This not only increases labor costs but also greatly limits the system's level of automation and efficiency.

[0008] For automatic liquid replenishment systems, the liquid level sensors currently used include photoelectric liquid level sensors, capacitive liquid level sensors, and weighing sensors.

[0009] Photoelectric liquid level sensors typically consist of a transmitter and a receiver. The transmitter emits a beam of light towards the liquid surface, which is reflected back. The receiver receives the reflected light and determines the liquid level by detecting the reflection time or the intensity of the reflected light. Its drawbacks are twofold: first, it is highly susceptible to light interference, leading to errors in low-light environments; second, due to material limitations, it cannot operate in the low-temperature environment of cryogenic liquids.

[0010] The basic principle of a capacitive liquid level sensor is to utilize the difference in dielectric constant between liquids and gases. Changes in liquid level cause changes in capacitance, which are then converted by a circuit to measure the liquid level. Its drawbacks are twofold: first, in extremely low-temperature environments with cold liquids, issues such as frost formation on the electrodes affect the accuracy and stability of the capacitance value, leading to a long response time; second, calibration is required before use to ensure the accuracy and repeatability of the measurement data, making the operation cumbersome.

[0011] A weighing sensor is disclosed in Chinese patent document CN120101028A, which describes an automatic liquid nitrogen replenishment device based on a high-purity germanium detector. This device employs a weighing sensor and solves the problems of measurement accuracy and stability caused by factors such as center of gravity shift, moisture, short circuits, and pressure changes due to liquid nitrogen evaporation. However, its limitation lies in its application scenarios; this device is specifically designed for automatically monitoring and replenishing the liquid nitrogen content in a high-purity germanium detector.

[0012] In addition, current thermometers such as resistance temperature detectors (RTDs), thermocouples, and semiconductor thermometers are simple, reliable, and mature in structure, and have high temperature measurement accuracy. However, the temperature difference between the liquid surface and the liquid level in a sealed storage tank is not significant, which means that conventional RTDs or other thermometers cannot be used to accurately measure the liquid level.

[0013] Given the numerous problems existing in the application of existing liquid level sensors for measuring the liquid level in cryogenic liquids, a new liquid level measurement method is needed to solve these problems. Summary of the Invention

[0014] To address the shortcomings of existing technologies, the present invention aims to provide an automatic cryogenic liquid replenishment circuit and a cryogenic liquid container.

[0015] The present invention provides an automatic cryogenic liquid replenishment circuit, comprising: a power supply VCC, a high-level detection branch, a low-level detection branch, a logic judgment circuit, and a driver;

[0016] The high-level detection branch generates a first signal when the liquid level is higher than the maximum line and a second signal when the liquid level is lower than the maximum line.

[0017] The low-level detection branch generates a third signal when the liquid level is below the minimum line and a fourth signal when the liquid level is above the minimum line.

[0018] The logic judgment circuit is electrically connected to the high-order detection branch and the low-order detection branch, respectively.

[0019] When the logic judgment circuit simultaneously acquires the first signal and the fourth signal, the control power supply VCC is disconnected from the driver.

[0020] When the logic judgment circuit simultaneously acquires the second and third signals, the control power supply VCC remains connected to the driver.

[0021] When the logic judgment circuit simultaneously acquires the second and fourth signals, the control power supply VCC is either disconnected from the driver or remains connected.

[0022] Preferably, the step of the logic judgment circuit simultaneously acquiring the second signal and the fourth signal includes:

[0023] When the liquid level changes from the highest level to the lowest level, the control power supply VCC is disconnected from the driver.

[0024] When the liquid level changes from the lowest to the highest level, the control power supply VCC remains connected to the driver.

[0025] Preferably, the high-level detection branch includes a voltage divider resistor R2, a high-level sensor, and an operational amplifier 2A;

[0026] The power supply VCC is connected to one end of the high-level sensor and the non-inverting input of the operational amplifier 2A after passing through the voltage divider resistor R2. The other end of the high-level sensor is grounded. The inverting input of the operational amplifier 2A is connected to the reference voltage. The output of the operational amplifier 2A outputs a first signal or a second signal.

[0027] Preferably, the low-position detection branch includes a voltage divider resistor R1, a low-position sensor, and an operational amplifier 1A;

[0028] The power supply VCC is connected to one end of the low-position sensor and the non-inverting input of the operational amplifier 1A after passing through the voltage divider resistor R1. The other end of the low-position sensor is grounded. The inverting input of the operational amplifier 1A is connected to the reference voltage. The output of the operational amplifier 1A outputs a third signal or a fourth signal.

[0029] Preferably, the reference voltage includes a voltage divider resistor R3 and a voltage divider resistor R4 connected in series, one end of the voltage divider resistor R3 is connected to the power supply VCC, and one end of the voltage divider resistor R4 is grounded;

[0030] The other ends of voltage divider resistor R3 and voltage divider resistor R4 are electrically connected and used as the output terminals of the reference voltage.

[0031] Preferably, the first and fourth signals are high-level signals, and the second and third signals are low-level signals.

[0032] Preferably, the logic judgment circuit includes relays K1, K2 and K3;

[0033] The output of operational amplifier 1A is electrically connected to one end of the control coil of relay K1, and the other end of the control coil of relay K1 is grounded. The output of operational amplifier 2A is electrically connected to one end of the control coil of relay K3 and one end of the control coil of relay K2, and the other ends of the control coils of relay K3 and relay K2 are connected and grounded. The switches of relays K2, K1, and K3 are connected in series. The power supply VCC is electrically connected to the solenoid valve after passing through the switches of relays K2, K1, and K3, and the other end of the solenoid valve is grounded. The output of operational amplifier 1A is electrically connected to the normally open terminal of the switch of relay K1.

[0034] Preferably, both the high-position sensor and the low-position sensor are resistance temperature detectors (RTD) sensors, specifically the PT100 model.

[0035] Preferably, the resistance values ​​of the voltage divider resistors R1 and R2 are 200Ω, and the resistance values ​​of the voltage divider resistors R2 and R4 are 10kΩ.

[0036] According to the present invention, a cryogenic liquid container employs the aforementioned cryogenic liquid automatic replenishment circuit.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. This invention uses pure hardware circuits (PT100, operational amplifier, relay, resistor, etc.) to realize liquid level judgment and liquid replenishment control. No software or microprocessor is required, which fundamentally avoids software crashes, program errors or complex electromagnetic interference problems. The system has extremely strong stability and anti-interference ability, and is particularly suitable for low temperature environments where no one is on duty for a long time.

[0039] 2. This invention incorporates hysteresis control logic. When the liquid level changes between high and low levels, the system determines the state of the solenoid valve based on whether the liquid level is "rising" or "falling." This fundamentally avoids the frequent opening and closing of the solenoid valve when the liquid level fluctuates near the critical point, protecting the equipment, extending its service life, and reducing the waste of liquid nitrogen.

[0040] 3. This invention utilizes the physical characteristic of thermistors to self-heat under high operating current, resulting in a significant temperature difference between the sensor and the "wet / dry" conditions, thereby generating an easily identifiable signal. The factory calibration is simple or unnecessary. Furthermore, the maximum / minimum limit setting can be completed on-site by replacing / fine-tuning the voltage divider resistor or the reference voltage, without the need for environmental modeling and periodic calibration as required by capacitive sensors.

[0041] 4. This invention consists only of a voltage divider circuit, an operational amplifier comparator circuit, and a relay self-locking / unlocking circuit. It eliminates the need for a microcontroller and its peripheral power supply, programming, and interface modules. Fewer components and shorter paths avoid problems such as program failure and initialization anomalies. Only one PT100 probe is needed at each of the high and low positions, resulting in small wiring holes and easy sealing. There is no need to drill large holes or add additional viewing windows to the container wall, nor does it alter the container's stress and support. The overall device is small in size, flexible in layout, and easy to integrate into narrow-necked Dewar flasks, cryogenic tanks, or experimental equipment, with low dependence on container shape and material.

[0042] 5. The core components of this invention are general-purpose PT100 diodes, resistors, general-purpose operational amplifiers, and relays, resulting in low material costs. It also eliminates the need for a microcontroller, A / D converter, voltage regulator, and isolation system. Compared to ultrasonic / optical probes that require cleaning and calibration, and digital systems that require software maintenance, this device significantly reduces the later-stage operation and maintenance costs.

[0043] 6. In this invention, the PT100 exhibits a large temperature jump during gas-liquid interface switching, and the voltage divider can quickly cross the threshold, resulting in a sensitive response. Through the hardware logic of "low-position triggering to open + relay self-locking to hold + high-position release self-locking to close," a clear upper / lower threshold and action sequence are formed, which is equivalent to "window + latch" hysteresis control. This can avoid frequent engagement of the solenoid valve caused by liquid surface fluctuations, boiling, or surges, significantly extending the life of the solenoid valve and relay.

[0044] 7. Compared to capacitive circuits, which are sensitive to changes in dielectric constant and are easily affected by frost / condensation; ultrasonic / optical circuits, which are easily affected by boiling, steam, and frost scattering; and digital systems, which are easily affected by EMI coupling and ground bounce noise, the judgment circuit of this device uses a low-impedance voltage divider with a fixed and clear comparison threshold; the operational amplifier can construct hysteresis, and the output drives the relay coil, resulting in a large signal amplitude and sufficient anti-interference margin; the system does not rely on the processing of weak signals with high impedance and high gain, nor does it require high-speed digital sampling. Attached Figure Description

[0045] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0046] Figure 1 This is a circuit diagram for the automatic cryogenic liquid replenishment in this invention;

[0047] Figure 2 This is a graph showing the resistance of the PT100 changing from a "wet to dry" state under different currents in this invention.

[0048] Figure 3 This is a graph showing the resistance of the PT100 changing from a "dry to wet" state under different currents in this invention. Detailed Implementation

[0049] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0050] This invention utilizes a cryogenic liquid level sensor based on the self-heating effect of a thermal resistor and a purely hardware circuit to achieve liquid level detection and automatic replenishment of cryogenic liquids. The core circuit components include a high-level sensor, a low-level sensor, operational amplifiers 1A and 2A, relays K1, K2, and K3, voltage divider resistors R1, R2, R3, and R4, a power supply VCC, and a solenoid valve. The high-level sensor is installed at the highest liquid level line, and the low-level sensor is installed at the lowest liquid level line.

[0051] In a preferred embodiment, the high-position sensor and the low-position sensor use the same resistance temperature detector (RTD) sensor. More preferably, the RTD sensor model is PT100, and PT100 will be used in the following description. It should be noted that the sensor type and specific model are only used as examples and are not intended to limit the scope of protection. Any scheme that uses a similar sensor to this application falls within the scope of protection of this application.

[0052] The core of this circuit is the detection of liquid level using two PT100 resistance thermometers. It utilizes a purely hardware circuit to implement the automatic opening and closing and self-locking functions of the solenoid valve. Based on the characteristics of the PT100, where resistance changes with temperature and its temperature measurement range reaches -200°C, and the self-heating effect of the resistance thermometer, the circuit uses the PT100 as a liquid level sensor. The liquid level is determined by the voltage division between the PT100 and another fixed-value resistor. The solenoid valve only opens to replenish the cryogenic liquid when the liquid level drops to its minimum height, stopping when the calibrated maximum height is reached. This invention is low-cost, has a fast response time, and allows for independent adjustment of the limit height.

[0053] The structure of this circuit will be explained in detail below.

[0054] Reference Figure 1 As shown, the voltage divider resistor R2, the high-level sensor, and the operational amplifier 2A constitute the high-level detection branch, which is responsible for generating a voltage signal when the liquid level is higher than the maximum line, thereby controlling the solenoid valve to close. The specific connection relationship is as follows: the power supply VCC is electrically connected to one end of the high-level sensor and the non-inverting input (+) of the operational amplifier 2A after passing through the voltage divider resistor R2, and the other end of the high-level sensor is grounded.

[0055] Voltage divider resistors R3 and R4 form a reference voltage source, providing a fixed comparison threshold voltage for the two operational amplifiers. The specific connection is as follows: power supply VCC, after passing through voltage divider resistor R3, is electrically connected to one end of resistor R4, the inverting input terminal (-) of operational amplifier 2A, and the inverting input terminal (-) of operational amplifier 1A.

[0056] The voltage divider resistor R1, the low-level sensor, and the operational amplifier 1A constitute the low-level detection branch, which is responsible for generating a voltage signal when the liquid level is below the minimum line, thereby controlling the solenoid valve to open. The specific connection relationship is as follows: the power supply VCC is electrically connected to one end of the low-level sensor and the non-inverting input (+) of the operational amplifier 1A after passing through the voltage divider resistor R1, and the other end of the low-level sensor is grounded.

[0057] Relays K1, K2, and K3 form a logic circuit responsible for controlling the solenoid valve based on the output signal of the operational amplifier. The specific connections are as follows: the output of operational amplifier 1A is electrically connected to one end of the control coil of relay K1, and the other end of the control coil of relay K1 is grounded; the output of operational amplifier 2A is electrically connected to one end of the control coil of relay K3 and one end of the control coil of relay K2, and the other ends of the control coils of relay K3 and K2 are connected and then grounded. The switches of relays K2, K1, and K3 are connected in series. The power supply VCC passes through the switches of relays K2, K1, and K3 and is then electrically connected to the solenoid valve, with the other end of the solenoid valve grounded. The output of operational amplifier 1A is electrically connected to the normally open terminal of the switch of relay K1, as shown in the reference diagram. Figure 1 As shown, the normally open terminal is the side of relay K1 that is electrically connected to relay K3.

[0058] Working principle of a resistance temperature detector (RTD) self-heating liquid level sensor:

[0059] The self-heating effect of a resistance temperature detector (RTD) refers to the temperature rise caused by the accumulation of Joule heat when an electric current is applied. The larger the current, the more pronounced the self-heating effect, manifested as a faster increase in resistance over time. In liquid level sensors, the self-heating effect of the PT100 is mainly manifested in the following two aspects.

[0060] One is the static characteristic: when the sensor is stably in a cryogenic liquid or air, the greater the applied current, the higher the initial temperature of the sensor, and the greater the measured resistance value.

[0061] Secondly, there is the dynamic characteristic: when the sensor is inside or above the liquid due to changes in the liquid level, the initial resistance value of the sensor varies due to the different applied currents, and the time required to reach or recover to the target resistance value also changes accordingly.

[0062] Liquid nitrogen was used as an example of a cryogenic liquid in the experiment.

[0063] The experiment first measured the process of the PT100 sensor being exposed from liquid nitrogen to above the liquid surface, i.e., undergoing a "wet-dry" change.

[0064] Before 10.44 seconds, the PT100 was stably immersed in liquid nitrogen. As shown in the figure, the sensor has its lowest initial resistance of 21.4Ω when operating at a standard 1mA current, indicating that the self-heating effect is almost negligible. The initial resistance gradually increases with increasing measuring current: at 50mA, the initial resistance reaches its maximum value of 39.2Ω, approximately twice the resistance at the standard operating current; the initial resistances at other currents are 22.4Ω, 23.6Ω, 26.8Ω, and 30.9Ω, respectively.

[0065] After 10.44 seconds, the PT100 sensor was fully exposed above the liquid surface. Figure 2 As can be seen, the resistance change rate at 10mA is close to that at a standard operating current of 1mA, indicating that the self-heating effect is still not significant. However, starting from a current of 20mA, the slope of the curve increases significantly, showing a clear difference from the resistance change rate at the standard operating current, indicating that the self-heating effect has a significant impact on the dynamic response.

[0066] For example, assuming a target resistance of 60Ω, the PT100 would take approximately 27.85 seconds to reach that resistance at a standard operating current of 1mA; while at 50mA, it would only take about 6.66 seconds. This phenomenon is the result of the self-heating effect acting on both static and dynamic characteristics: the higher the current, the more significant the self-heating effect, the higher the initial resistance, and the faster the resistance changes with temperature over time, thus shortening the response time and making the sensor more sensitive.

[0067] Next, the experiment measured the process of the PT100 sensor being re-immersed in liquid nitrogen from air, i.e., undergoing a "dry-wet" change. (Refer to...) Figure 3 As shown, 4 seconds before the sensor was stable in the air environment, consistent with the previous experiment, the initial resistance under different currents was significantly different: the initial resistance was the smallest at 1mA standard operating current, which was 110.6Ω; the initial resistance was the largest at 50mA current, which was 191.5Ω.

[0068] Four seconds later, the sensor was rapidly submerged in liquid nitrogen. Figure 3 As can be seen, the rate of change of resistance with time gradually decreases from 1mA to 50mA. This phenomenon indicates that as the current increases, the self-heating effect becomes more significant, leading to a slower cooling rate of the sensor and a delay in the resistance reduction process.

[0069] For example, when the target resistance is 60Ω, a PT100 operating at a standard current of 1mA takes approximately 3.32 seconds to reach that value, while at a current of 50mA it takes approximately 8.45 seconds. This indicates that during the "dry-wet" process, the self-heating effect manifests as follows: the higher the current, the higher the initial resistance, and the slower the resistance changes with temperature over time, thus extending the response time. Therefore, for the two sensors used to determine the lowest and highest liquid levels, the target resistance values ​​should be set appropriately based on actual requirements.

[0070] Basic working principle of circuit:

[0071] The operational amplifier is used as a comparator. Its non-inverting input is the voltage from either the high-level or low-level sensor (PT100), and its inverting input is the reference voltage. When the non-inverting input is greater than the inverting input, the operational amplifier outputs a high level; otherwise, it outputs a low level. Operational amplifier 1A is used to determine if the liquid level has reached its lowest point, and operational amplifier 2A is used to determine if the liquid level has reached its highest point.

[0072] The resistance values ​​of voltage divider resistors R1 and R2 are set according to actual needs, serving as auxiliary voltage divider resistors to help the PT100 liquid level sensor determine the liquid level.

[0073] When the liquid level is lower than the minimum set value, the resistance of the high-level sensor and the low-level sensor increases, the voltage drop increases, the operational amplifier 1A outputs a high level, the operational amplifier 2A outputs a high level, the relay K1 self-locks, the solenoid valve opens, and the cryogenic liquid is replenished.

[0074] When the liquid level rises to its maximum limit, the resistance of the high-level sensor and the low-level sensor decreases, the voltage drop decreases, the operational amplifier 2A outputs a low level, the operational amplifier 1A outputs a low level, the relay K1 self-locking is released, the solenoid valve closes, and the replenishment of cryogenic liquid stops.

[0075] Operating status 1: The liquid level is at the maximum limit.

[0076] When the circuit is working, since the resistances of both the high-level sensor and the low-level sensor are less than the voltage divider resistors, both operational amplifiers 1A and 2A output a low level, and relays K1, K2, and K3 are all in the open state, thus closing the solenoid valve.

[0077] Operating status 2: The liquid level is below the lowest point.

[0078] When the circuit is working, since the resistances of both the high-level sensor and the low-level sensor are greater than the voltage divider resistors, both operational amplifier A1 and operational amplifier 2A output high levels, and relays K1, K2, and K3 are all in the closed state, thus opening the solenoid valve.

[0079] Operating state 3: The liquid level is between the highest and lowest points.

[0080] 3.1 The liquid level is in a downward trend.

[0081] The high-position sensor is exposed to air, increasing its resistance. Operational amplifier 2A outputs a high-level signal, driving relays K2 and K3 to activate and close the relevant switches. Simultaneously, the low-position sensor remains in the cryogenic liquid, with lower resistance. Operational amplifier 1A outputs a low-level signal, and relay K1 is in the open state. Because the common terminal of relay K3 is connected to the normally open terminal of relay K1, and relay K1 is open, even if relay K3 is closed, there is no voltage or current in this circuit. Therefore, there is no voltage input to the solenoid valve, and it remains closed.

[0082] 3.2 The liquid level is rising.

[0083] The high-level sensor remains exposed to air, and operational amplifier 2A continuously outputs a high-level signal, keeping relays K2 and K3 closed. Simultaneously, the rising liquid level indicates that the low-level sensor was previously exposed to air, causing operational amplifier 1A to output an excessively high level, driving relay K1 to close. When the low-level sensor is re-immersed in the cryogenic liquid, although the output of operational amplifier 1A returns to a low level, relay K1 employs a self-locking circuit structure (e.g., ...). Figure 1 As shown, relay K1 and relay K2 are connected in series, and the normally open terminal of relay K1 is connected to its coil drive terminal. When relays K1 and K2 are closed simultaneously, the coil drive voltage of relay K1 is directly provided by this branch (no longer controlled by operational amplifier 1A), and relay K1 remains closed, ensuring that its circuit continuously receives power supply voltage. Under this condition, relay K3 and relay K1 are in the same circuit and are both closed, so the solenoid valve receives voltage input and is thus in the open state.

[0084] Complete working circuit principle:

[0085] Assume the initial state is that the liquid level is between the highest and lowest points.

[0086] When the circuit starts, the high-position sensor is in the air, its resistance increases, and operational amplifier 2A outputs a high level, closing relays K2 and K3. The low-position sensor is still in the cryogenic liquid, and operational amplifier 1A outputs a low level, thus opening relay K1. The common terminal of relay K3 is connected to the normally open terminal of relay K1. Because relay K1 is open, there is no voltage or current in the circuit containing relay K3, meaning there is no voltage or current across the solenoid valve, and the solenoid valve remains closed.

[0087] When the liquid level drops below the lowest point, since the resistance of PT100 is greater than the voltage divider resistance, the operational amplifier 2A outputs a high level, and at the same time, the operational amplifier 1A outputs a high level. Therefore, the relays K1, K2, and K3 are all closed, relay K1 is self-locked, and the solenoid valve is in the open state, and the cryogenic liquid is replenished.

[0088] When cryogenic liquid is replenished until the liquid level returns to between the highest and lowest points, the high-level sensor is still in the air, the operational amplifier 2A outputs a high level, and the relays K2 and K3 remain closed. The low-level sensor is immersed in the cryogenic liquid, its resistance decreases, the voltage drop decreases, and the operational amplifier 1A outputs a low level. However, due to the self-locking circuit design, the relay K1 remains closed, and the circuit containing the relay K3 remains below the supply voltage. That is, the solenoid valve still has a supply voltage and is in the open state, continuing to replenish cryogenic liquid.

[0089] When the liquid level rises to its highest point, the resistance of the high-level sensor decreases, the voltage drop decreases, and the operational amplifier 2A outputs a low level, causing both relays K2 and K3 to open. Since relay K2 is open, and the coil of relay K1 is driven by the voltage of the series branch of relays K1 and K2, the coil of relay K1 cannot be driven, so relay K1 opens, and the self-locking mechanism is released. Because relay K3 is open, there is no voltage or current across the solenoid valve, so the solenoid valve is closed, stopping the replenishment of cryogenic liquid.

[0090] The above cycle still applies when the initial state is that the liquid level is at or above the highest point and at or below the lowest point, the difference being the different circuit startup states. The former is operating state 1, and the latter is operating state 2.

[0091] The present invention also discloses a cryogenic container that adopts the above-described circuit structure.

[0092] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A cryogenic liquid automatic replenishment circuit, characterized in that, include: Power supply VCC, high-level detection branch, low-level detection branch, logic judgment circuit and driver; The high-level detection branch generates a first signal when the liquid level is higher than the maximum line and a second signal when the liquid level is lower than the maximum line. The low-level detection branch generates a third signal when the liquid level is below the minimum line and a fourth signal when the liquid level is above the minimum line. The logic judgment circuit is electrically connected to the high-order detection branch and the low-order detection branch, respectively. When the logic judgment circuit simultaneously acquires the first signal and the fourth signal, the control power supply VCC is disconnected from the driver. When the logic judgment circuit simultaneously acquires the second and third signals, the control power supply VCC remains connected to the driver. When the logic judgment circuit simultaneously acquires the second and fourth signals, the control power supply VCC is either disconnected from the driver or remains connected.

2. The cryogenic liquid automatic replenishment circuit according to claim 1, characterized in that, The condition when the logic judgment circuit simultaneously acquires the second signal and the fourth signal includes: When the liquid level changes from the highest level to the lowest level, the control power supply VCC is disconnected from the driver. When the liquid level changes from the lowest to the highest level, the control power supply VCC remains connected to the driver.

3. The cryogenic liquid automatic replenishment circuit according to claim 1, characterized in that, The high-level detection branch includes a voltage divider resistor R2, a high-level sensor, and an operational amplifier 2A; The power supply VCC is connected to one end of the high-level sensor and the non-inverting input of the operational amplifier 2A after passing through the voltage divider resistor R2. The other end of the high-level sensor is grounded. The inverting input of the operational amplifier 2A is connected to the reference voltage. The output of the operational amplifier 2A outputs a first signal or a second signal.

4. The cryogenic liquid automatic replenishment circuit according to claim 1, characterized in that, The low-position detection branch includes a voltage divider resistor R1, a low-position sensor, and an operational amplifier 1A; The power supply VCC is connected to one end of the low-position sensor and the non-inverting input of the operational amplifier 1A after passing through the voltage divider resistor R1. The other end of the low-position sensor is grounded. The inverting input of the operational amplifier 1A is connected to the reference voltage. The output of the operational amplifier 1A outputs a third signal or a fourth signal.

5. The cryogenic liquid automatic replenishment circuit according to claim 3 or 4, characterized in that, The reference voltage includes a voltage divider resistor R3 and a voltage divider resistor R4 connected in series. One end of the voltage divider resistor R3 is connected to the power supply VCC, and one end of the voltage divider resistor R4 is grounded. The other ends of voltage divider resistor R3 and voltage divider resistor R4 are electrically connected and used as the output terminals of the reference voltage.

6. The cryogenic liquid automatic replenishment circuit according to claim 3 or 4, characterized in that, The first and fourth signals are high-level signals, and the second and third signals are low-level signals.

7. The cryogenic liquid automatic replenishment circuit according to claim 6, characterized in that, The logic judgment circuit includes relays K1, K2, and K3; The output of operational amplifier 1A is electrically connected to one end of the control coil of relay K1, and the other end of the control coil of relay K1 is grounded. The output of operational amplifier 2A is electrically connected to one end of the control coil of relay K3 and one end of the control coil of relay K2, and the other ends of the control coils of relay K3 and relay K2 are connected and grounded. The switches of relays K2, K1, and K3 are connected in series. The power supply VCC is electrically connected to the solenoid valve after passing through the switches of relays K2, K1, and K3, and the other end of the solenoid valve is grounded. The output of operational amplifier 1A is electrically connected to the normally open terminal of the switch of relay K1.

8. The cryogenic liquid automatic replenishment circuit according to claim 3 or 4, characterized in that, Both the high-position sensor and the low-position sensor are resistance temperature detectors (RTD) sensors, model PT100.

9. The cryogenic liquid automatic replenishment circuit according to claim 5, characterized in that, The resistance values ​​of the voltage divider resistors R1 and R2 are 200Ω, and the resistance values ​​of the voltage divider resistors R2 and R4 are 10kΩ.

10. A cryogenic liquid container, characterized in that, The cryogenic liquid automatic replenishment circuit according to any one of claims 1 to 9 is adopted.

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