Liquid level detection device, liquid nitrogen circulating system and liquid level control device thereof

Abstract

The present application aims at the deficiency in the prior art that the detection device cannot accurately measure the liquid level of unstable liquid surface and cannot accurately control the liquid nitrogen inflow in the separator when gas-liquid separation is performed on liquid nitrogen, and provides a liquid level detection device, a liquid nitrogen circulation system and a liquid level control device thereof, wherein the liquid level detection device comprises a guide member, a float and a detector, the float comprises an upper float and a lower float connected by an elastic member, the float moves up and down along the guide member with the liquid surface, the upper float has small fluctuation due to the fact that the elastic member absorbs most of the liquid surface fluctuation, and the detector accurately detects the liquid level value through the position of the upper float; in the liquid nitrogen circulation system and the liquid level control device thereof, the controller controls the opening and closing angles of the liquid proportional valve and the gas proportional valve according to the liquid level information provided by the liquid level detection device and the pressure information in the liquid nitrogen separator provided by the pressure sensor, so that the inflow and the exhaust in the separator are kept in dynamic balance and the liquid level fluctuation in the separator is reduced.

Description

Technical Field

[0001] This invention relates to the field of liquid gas separation technology, and particularly to a liquid level detection device, a liquid nitrogen circulation system, and a liquid level control device thereof. Background Technology

[0002] When injecting liquid into a container, the liquid level needs to be detected to control the injection volume. However, in practice, especially when injecting liquid into a closed container, it is difficult for the operator to see the liquid level with the naked eye. Therefore, level gauges or floats are usually used for level detection. Existing technologies mostly use capacitive level gauges or mechanical floats. Capacitive level gauges are very susceptible to interference and influence from external electric and magnetic fields, resulting in unstable measurements. Moreover, the liquid injection port is usually above the liquid level, and the injection process causes surface fluctuations, leading to inaccurate measurements. When using a mechanical float for level detection and control, its output digital signal is 0 and 1, and the corresponding valve can only open and close. When the output signal is 1, the valve opens, allowing a large influx of liquid, inevitably causing significant level fluctuations; when the output signal is 0, the valve closes, and liquid stops flowing in, until the output signal becomes 1, then the next cycle begins. Besides causing inaccurate measurements, surface fluctuations also cause frequent valve movements, increasing the valve's workload.

[0003] Especially in the field of liquid nitrogen gas-liquid separation technology, liquid nitrogen is transported to a liquid nitrogen separator through pipelines, and then the liquid nitrogen separator supplies liquid nitrogen to the MBE to maintain the normal operation of the MBE, while gaseous nitrogen is discharged into the atmosphere. However, due to the extremely low boiling point of liquid nitrogen, the surface of the liquid nitrogen in the separator is almost in a "boiling" state, and the liquid level is extremely unstable. It is difficult to accurately measure the liquid level using traditional capacitive level gauges or mechanical floats, which leads to the inability to control or accurately control the liquid nitrogen inflow. This further leads to the inability to control the pressure in the separator, causing large fluctuations in liquid nitrogen, thus failing to provide a stable supply of liquid nitrogen to the MBE and maintain the normal operation of the MBE. Summary of the Invention

[0004] The purpose of this invention is to provide a liquid level detection device to address the shortcomings of existing technologies, where detection devices cannot accurately measure unstable liquid levels when injecting liquid into containers, especially closed containers. Another objective of this invention is to address the shortcomings of existing technologies in accurately controlling the amount of liquid nitrogen entering the separator during gas-liquid separation of liquid nitrogen, by providing a liquid nitrogen circulation system and its liquid level control device.

[0005] The objective of this invention is achieved through the following technical solution: A liquid level detection device includes a guide member, a float, and a detector for detecting the position of the float. The float is movably connected to the guide member body by reciprocating along its length. The float includes an upper float, a lower float, and an elastic member disposed between the upper float and the lower float. The two ends of the elastic member are fixedly connected to the upper float and the lower float, respectively. When the float is in the liquid, the upper float and at least a portion of the elastic member are above the liquid surface. The detector is used to detect the position information of the upper float. The detector includes one or more signal detection elements. When it includes one signal detection element, the fixed height of the signal detection element corresponds to the height of the liquid level to be detected. When it includes multiple signal detection elements, the multiple signal detection elements are arranged in a straight line along the depth direction of the liquid level. When the detector includes multiple signal detection elements, the multiple signal detection elements are fixedly mounted on the fixed plate, and the fixed plate can be moved up and down. The detection element is a contact sensor or a proximity sensor. The contact element that works with the contact sensor and the sensing element that works with the proximity sensor are both fixedly mounted on the upper float. When a proximity sensor is used, the sensor is a Hall sensor that detects displacement. The Hall sensor includes multiple Hall elements, each with independent coded information. A permanent magnet, which serves as a sensing element, is fixedly installed on the upper float corresponding to the position of the Hall sensor. The permanent magnet corresponds to different Hall elements as the upper float rises and falls. The surface area of ​​the permanent magnet on the side opposite the Hall sensor is larger than the surface area of ​​a single Hall element, and it can interact with at least two Hall elements to make them emit signals; The permanent magnet is fixedly connected to the upper float via a bracket; A liquid nitrogen circulation system level control device includes a pressure sensor for measuring the internal pressure of a separator, a liquid proportional valve for controlling the liquid inlet flow rate of the separator, a gas proportional valve for controlling the gas outlet flow rate of the separator, a controller for controlling the opening and closing angles of the liquid proportional valve and the gas proportional valve, and a level detection device for any one of the above. The pressure sensor, liquid proportional valve, gas proportional valve, and level detection device are respectively electrically connected to the controller. The controller controls the opening and closing angles of the liquid proportional valve and the gas proportional valve based on the level information sent by the level detection device and the pressure information sent by the pressure sensor. A liquid nitrogen circulation system includes a liquid nitrogen tank, a separator, and an MBE system. The liquid nitrogen tank and the separator are connected by an inlet pipe, and the MBE system is connected to the separator by an outlet pipe. An exhaust pipe is also provided at the end of the separator. The system is characterized by further including a liquid nitrogen circulation system level control device, a pressure sensor installed at the top of the separator, a liquid proportional valve installed on the inlet pipe, a gas proportional valve installed on the exhaust pipe, a level detection device installed in the inner cavity of the separator, a guide member installed vertically with its lower end fixedly connected to the bottom of the separator, and a signal detection member installed on the inner wall of the separator. A return pipe is also installed between the MBE system and the separator. The inlet end of the return pipe is connected to the upper end of the MBE system, and the outlet end of the return pipe is located at the lower end of the inner cavity of the separator.

[0006] In the liquid level detection device provided by this invention, the float includes an upper float and a lower float, which are connected by an elastic element. When the float is placed in the liquid, the lower float floats in the liquid, while the upper float and at least a portion of the elastic element are above the liquid surface. Because the elastic element has a buffering effect, its fluctuation is less than that of the liquid surface, thus the upper float can maintain a relatively stable state. The upper float sends its position information to the controller via a position detector. The controller determines the position of the upper float by reading the position information data, thereby measuring the liquid level height. Since the position of the upper float is relatively stable, the position information sent by the position detector to the controller is relatively accurate, thus allowing for a relatively accurate determination of the liquid level height.

[0007] The liquid nitrogen circulation system and liquid nitrogen circulation system level control device provided by this invention are as follows: a liquid proportional valve is installed on the inlet pipe of the liquid nitrogen separator, and a gas proportional valve is installed on the exhaust pipe. The controller reads the liquid level height using the liquid level detection device provided by this invention, and then controls the opening and closing angle of the liquid proportional valve according to the liquid level height, thereby controlling the amount of liquid nitrogen entering the separator; simultaneously, based on the pressure value detected by the pressure sensor in the liquid nitrogen separator, the opening and closing angle of the gas proportional valve is controlled to control the exhaust volume, so that the inlet and exhaust volumes in the separator are kept in dynamic balance, reducing the liquid level fluctuation in the separator and keeping the liquid nitrogen in the separator in a relatively stable state. Since the liquid nitrogen in the MBE is supplied by the separator, when the liquid nitrogen in the separator is relatively stable, the liquid nitrogen supplied to the MBE is also relatively stable. Stable liquid nitrogen can maintain the normal operation of the MBE. Experiments have shown that the more stable the liquid nitrogen level in the separator, the higher the temperature stability of the MBE system outlet and the less liquid nitrogen loss. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the principle structure of the liquid nitrogen circulation system of the present invention; Figure 2 This is an enlarged view of the schematic diagram of the liquid level detection device of the present invention; Figure 3 This is a schematic top cross-sectional view of an embodiment of the rod-shaped member in this invention; Figure 4 This is a schematic top cross-sectional view of another embodiment of the rod-shaped member in this invention.

[0009] Explanation of reference numerals in the attached figures 1. Liquid nitrogen tank; 201. Inlet pipe; 202. Outlet pipe; 3. Return pipe; 4. Separator; 403. Separator sidewall; 404. Safety valve; 405. Liquid level; 5. Liquid level detection device; 501. Lower float; 502. Upper float; 503. Support; 504. Hall element; 505. Permanent magnet; 506. Rod-shaped component; 507. Spring; 508. Controller; 601. Liquid proportional valve; 602. Gas proportional valve; 603. Pressure sensor; 7. Manual valve; 8. Exhaust pipe; 9. MBE system; 10. Vacuum pump. Detailed Implementation The present invention will be further described below with reference to specific embodiments: like Figures 1-4 As shown, the present invention provides a liquid level detection device, a liquid nitrogen circulation system containing the liquid level detection device, and a liquid nitrogen circulation system liquid level control device.

[0010] The liquid level detection device of this invention includes a float, a guide, and a detector for detecting the position of the float. The float includes an upper float 502 and a lower float 501, positioned above and below each other. The center lines of the upper and lower floats coincide. The lower float can be shaped like a cube or a sphere, while the upper float 502 is preferably shaped like a cube. The upper float 502 and the lower float 501 are connected as a single unit by an elastic element, using a spring 507 as the elastic element. The spring is preferably vertically positioned, with one end connected to the upper end of the lower float and the other end connected to the lower end of the upper float. Several springs can be evenly distributed. Depending on the number of springs, different distribution structures can be adopted: when one spring is used, the center line of the spring coincides with the center line of the float; when two springs are used, the two springs are symmetrically arranged about the center line of the float; when three or more springs are used, the line connecting the center lines of the springs forms a regular polygon, and the center line of the regular polygon coincides with the center line of the float. This spring design not only keeps the float's center of gravity in a constant position, preventing it from shifting due to uneven spring distribution, but also ensures that the tension of the spring on the lower surface of the upper float is uniform, thereby enhancing the stability of the upper float and preventing it from tilting during movement.

[0011] The float is movably connected to a guide member, which can be a rod-shaped component or a combination of a slide and a slider. When using a slide and slider combination, the slide is vertically fixed, the slider is connected to the slide, and the float is fixedly connected to the slider. When the float rises and falls with the liquid level, it can drive the slider to slide up and down along the slide. Preferably, a rod-shaped component 506 is used as the guide member. The rod-shaped component has a certain length, such as... Figure 3 , Figure 4 As shown, the cross-section of the rod-shaped member can be set as an arc or a polygon. When set as an arc, the intersection of the straight line and the arc is rounded. When set as a polygon, it is preferably a quadrilateral, and the intersection of adjacent sides is rounded. Preferably, the sides of the quadrilateral are set as non-concentric arcs, with the side of the arc facing outward.

[0012] Two connection structures are preferred for the float and the rod-shaped member 506. One structure involves through holes at the centers of the upper and lower floats, matching the cross-sectional shape and size of the rod-shaped member 506. The float is fitted onto the outside of the rod-shaped member 506 through these through holes. The other structure involves a collar horizontally fixed on the same side of the upper and lower floats. The inner wall shape of the collar matches the cross-sectional shape of the rod-shaped member. Whether the through hole or the inner hole of the collar mates with any surface on the rod-shaped member, there is a certain gap to ensure smooth sliding of the float. The gap on one side is preferably less than or equal to 3mm. Furthermore, since the contact surface between the rod-shaped member and the through hole or the inner hole of the collar on the float is mainly an arc surface, the smoothness is good, which better prevents jamming. The rod-shaped component guides the float, directing it along its length and preventing it from drifting on the liquid surface or overturning. The cross-sectional shape of the rod effectively prevents the float from rotating around it. Due to the small gap between the rod and the float or collar, the rod provides good restraint for the float, especially the lower float 501, preventing it from swinging excessively with the liquid surface. When the lower float swings less, it helps the upper float 502 maintain better stability.

[0013] The position detector of the float includes a signal detection element, which is preferably a position sensor. The position sensor can be a contact sensor or a proximity sensor. When a contact sensor is used, a limit switch can be used; when a proximity sensor is used, an electromagnetic sensor, a photoelectric sensor, a Hall effect sensor, etc., can be used.

[0014] The working principle of this invention will be explained below using a rod-shaped guide as an example. During operation, the rod-shaped member 506 is vertically fixed, and the float is sleeved on the rod-shaped member 506. Under the guidance of the rod-shaped member 506, the float moves up and down along the length of the rod-shaped member as the liquid level rises and falls. The lower float floats in the liquid, while the upper float and at least part or all of the spring are above the liquid surface. Because the spring has a buffering effect, it can absorb some of the energy from the liquid surface fluctuations. Therefore, the spring's vibration is less than the liquid surface fluctuation, thus keeping the upper float in a relatively stable state. When a limit switch is used to detect the position of the upper float, the limit switch is fixed to the inner wall of the container. A collision member corresponding to the limit switch is fixedly installed on the upper float on the side corresponding to the limit switch. The collision member can be rod-shaped or plate-shaped, and it faces the limit switch. When liquid is injected into the container, the float rises with the liquid level. When the collision member contacts the limit switch, the limit switch sends the position signal of the upper float to the controller, thereby determining the liquid level. When using a proximity sensor to detect the position of the float, taking a photoelectric sensor as an example, the structure and working principle of the proximity sensor are explained as follows: The photoelectric sensor includes a light source and a photoelectric receiver. The light source and the photoelectric receiver are fixedly positioned relative to each other on the inner wall of the container. When the float rises with the liquid level in the container to the same height as the light source and the photoelectric receiver, the float is located between the light source and the photoelectric receiver. The float blocks part or all of the light flux emitted by the light source. At this time, the sensor sends the information of the float to the controller to obtain the liquid level height.

[0015] The liquid level detection device provided by this invention, when used to detect the highest position of the liquid level, has the sensor fixed at a position adapted to the highest position of the liquid level; when used for real-time detection of the liquid level, multiple sensors need to be set up, and the multiple sensors are arranged vertically in a straight line. When the upper float rises with the liquid level, it corresponds to the sensor at different heights. The sensors at different heights send out different position signals to the outside, thereby realizing real-time detection of the liquid level.

[0016] The liquid level detection device provided by this invention can be applied in wastewater treatment, nitrogen gas-liquid separation, and other fields. When applied in wastewater treatment, the sensor can be a common sensor such as a limit switch, electromagnetic sensor, or photoelectric sensor. However, when applied in nitrogen gas-liquid separation, due to the extremely low temperature of liquid nitrogen, the sensor used must be able to operate stably for extended periods at ultra-low temperatures (-196°C), and common sensors cannot meet these requirements. Furthermore, because the liquid level is extremely unstable after entering the separator, real-time monitoring of the liquid level is necessary to control its stability. Therefore, a Hall effect sensor is preferred in nitrogen gas-liquid separation. The following section uses a Hall effect sensor as an example to describe in detail the structure employed when using the liquid level detection device provided by this invention to monitor the liquid nitrogen level in a liquid nitrogen separator in real time.

[0017] The Hall sensor includes multiple Hall elements 504, each with an independent information code. These independent Hall elements are vertically fixed in a straight line on the surface of a long, narrow fixed plate facing the float. Each Hall element is electrically connected to the controller. The fixed plate is preferably movable up and down on the side wall 403 of the liquid nitrogen separator via a connecting structure to accommodate different liquid levels. The connecting structure can employ existing technology, for example, a sliding structure combined with a locking structure. The sliding structure can use a slider and a track, and the locking structure can use a set bolt. The track is vertically positioned on the inner wall of the separator. The track body can be rectangular. The slider is positioned on the fixed plate on the side opposite to the Hall elements. The slider can be U-shaped, with the U-shaped opening size matching the width of the track. A set screw is vertically positioned on at least one side of the U-shaped wall of the slider. The set screw is threaded to the U-shaped wall. When the U-shaped slider moves the sensor along the track to a predetermined position, the set screw is tightened, so that the end of the set screw rests against one side of the track, thereby fixing the sensor.

[0018] The liquid level detection device is installed inside the liquid nitrogen separator. A rod-shaped member 506 is vertically positioned, with its lower end fixedly connected to the bottom of the separator. A float is sleeved on the outside of the rod-shaped member 506. A Hall sensor needs to be used in conjunction with a sensing element, which is a permanent magnet. Since the upper float is relatively stable, the permanent magnet 505 is fixedly mounted on it. Preferably, the permanent magnet 505 is connected to the upper float via a bracket 503. The bracket 503 is preferably inverted L-shape, with its lower end fixedly connected to the upper float and its upper end bent towards the Hall sensor. The permanent magnet 505 is located at the bent end of the bracket 503. The surface area of ​​the permanent magnet 505 facing the Hall sensor is larger than the surface area of ​​a single Hall element 504. As the float rises and falls vertically with the liquid surface, the permanent magnet 505 rises and falls with it. During this process, the permanent magnet 505 corresponds to different Hall elements 504. Since the surface area of ​​the permanent magnet 505 is larger than that of a single Hall element, the permanent magnet can correspond to at least two Hall elements simultaneously, preferably 3-5 Hall elements. These 3-5 Hall elements simultaneously send signals to the controller. Because each Hall element 504 has independent encoded information, the controller knows which encoded Hall element is generating Hall current. Through optimized calculations, the controller determines the specific position of the float, thereby reducing information deviation caused by the fluctuation of the permanent magnet with the float. The controller is preferably a PLC controller, and a MicroLogix 1100 Programmable Controller is a suitable model.

[0019] The liquid nitrogen circulation system level control device provided by the present invention includes a pressure sensor 603 for measuring the internal pressure of the separator, a liquid proportional valve 601 for controlling the liquid inlet flow rate of the separator, a gas proportional valve 602 for controlling the gas outlet flow rate of the separator, a controller 508 for controlling the opening and closing angles of the liquid proportional valve 601 and the gas proportional valve 602, and a level detection device 5. The pressure sensor 603, the liquid proportional valve 601, the gas proportional valve 602, and the level detection device are respectively electrically connected to the controller. The controller controls the opening and closing angles of the liquid proportional valve and the gas proportional valve based on the level information received from the level detection device 2 and the pressure information received from the pressure sensor, thereby controlling the liquid inlet flow rate and the gas outlet flow rate in the separator.

[0020] The liquid nitrogen circulation system provided by this invention includes a liquid nitrogen tank 1, a separator 4, an MBE system 9, and a liquid nitrogen circulation system level control device. The upper end of the separator 4 is connected to the liquid nitrogen tank 1 through an inlet pipe 201, and the lower end is connected to the MBE system 9 through an outlet pipe 202. An exhaust pipe 8 is also provided at the upper end of the separator 4. Liquid nitrogen enters the separator from the liquid nitrogen tank through the inlet pipe 201. The nitrogen gas in the separator is discharged into the atmosphere through the exhaust pipe 8, and the liquid nitrogen in the separator enters the MBE system 9 through the outlet pipe 202. After the liquid nitrogen enters the separator, the liquid nitrogen level is extremely unstable. Therefore, the liquid nitrogen circulation system level control device controls the opening and closing angles of the liquid proportional valve 601 and the gas proportional valve 602 to maintain a dynamic balance between the liquid inflow and the exhaust flow in the separator, thereby maintaining a relatively stable pressure in the separator. When the pressure in the separator 4 is stable, the pressure of the liquid nitrogen supplied to the MBE system is also relatively stable. Stable liquid nitrogen pressure is beneficial for maintaining the normal operation of the MBE system.

[0021] Furthermore, to reduce liquid level fluctuations in the separator, the following measures are taken: A manual valve 7 is installed on the outlet pipe 202. After opening the manual valve, liquid nitrogen flows from the separator into the MBE system. Since the manual control of the liquid inlet flow of the MBE system 9 is not precise enough, when there is an excess of liquid nitrogen in the MBE system 9, the liquid nitrogen will flow back into the separator 4 through the return pipe 3. In this invention, the outlet end of the return pipe 3 is inserted from the upper end to the lower end of the separator 4, and the returned liquid nitrogen enters from the bottom of the separator, which can reduce the liquid level fluctuations caused by the returned liquid. Vacuum jackets are provided on the pipe walls of the inlet pipe 201 and the outlet pipe 202. The vacuum jacket is evacuated to a vacuum state by the vacuum pumping device 10 to prevent the liquid nitrogen from absorbing heat during transportation and aggravating the fluctuations of the liquid nitrogen level 405. In addition, a safety valve 404 is also provided at the upper end of the separator 4 to prevent the pressure inside the separator 4 from becoming too high and causing danger in the event of a system failure.

Claims

1. A liquid level detection device, characterized in that, The liquid level detection device is used to detect fluctuating liquid levels. It includes a guide, a float, and a detector for detecting the float's position. The float is movably connected and reciprocates along the length of the guide body. The float includes an upper float (502), a lower float (501), and an elastic element (507) disposed between the upper float (502) and the lower float (501). Both ends of the elastic element (507) are fixedly connected to the upper float (502) and the lower float (501), respectively. When the float is in the liquid, the upper float (502) and at least a portion of the elastic element (507) are above the liquid surface. The detector is used to detect the position information of the upper float. The elastic element is a spring, with multiple springs arranged symmetrically at the center. Multiple signal detection elements are arranged in a straight line along the depth direction of the liquid surface; A rod-shaped member (506) is used as a guide member. The cross-section of the rod-shaped member (506) is arc-shaped or polygonal. The gap on one side between the float and the rod-shaped member is ≤3mm. The detection element is a proximity sensor, and the sensing element that cooperates with the proximity sensor is fixedly installed on the upper float; The elastic element has a buffering effect and can absorb some of the energy of the liquid surface fluctuation. The vibration of the elastic element is less than the fluctuation of the liquid surface. The sensor is a Hall sensor for detecting displacement. The Hall sensor includes multiple Hall elements (504), each with independent encoding information. A permanent magnet (505) is fixedly installed on the upper float (502) corresponding to the position of the Hall sensor, serving as a sensing element. The permanent magnet (505) corresponds to different Hall elements (504) during the rise and fall of the upper float (502). The surface area of ​​the side of the permanent magnet (505) opposite to the Hall sensor is larger than the surface area of ​​a single Hall element (504), and it can interact with at least three Hall elements simultaneously to make them emit signals. The controller can then know which encoded Hall element is generating Hall current, thereby determining the specific position of the upper float. The permanent magnet (505) corresponds to 3-5 Hall elements (504) simultaneously. The controller calculates the specific position of the upper float based on the encoding information of the 3-5 Hall elements through optimization.

2. The liquid level detection device as described in claim 1, characterized in that, Through holes matching the cross-sectional shape and size of the rod-shaped member (506) are provided at the center of the upper and lower floats. The floats are sleeved on the outside of the rod-shaped member (506) through the through holes, or a collar is horizontally fixed on the same side of the upper and lower floats. The inner wall shape of the collar is adapted to the cross-sectional shape of the rod-shaped member. When the through holes or the inner hole of the collar are matched with each surface of the rod-shaped member, there is a certain gap to ensure that the floats can slide smoothly.

3. The liquid level detection device as described in claim 2, characterized in that, When the detector includes multiple signal detection elements, the multiple signal detection elements are fixedly mounted on a fixed plate, and the fixed plate is movable up and down.

4. The liquid level detection device as described in claim 1, characterized in that, The center lines of the upper and lower floats coincide, and the lower float is cube-shaped or sphere-shaped.

5. The liquid level detection device as described in claim 1, characterized in that, The permanent magnet (505) is fixedly connected to the upper float (502) via a bracket (503).

6. A liquid nitrogen circulation system level control device, characterized in that, The system includes a pressure sensor (603) for measuring the internal pressure of the separator, a liquid proportional valve (601) for controlling the liquid inlet flow rate of the separator, a gas proportional valve (602) for controlling the gas outlet flow rate of the separator, a controller (508) for controlling the opening and closing angles of the liquid proportional valve (601) and the gas proportional valve (602), and a liquid level detection device (5) as described in any one of claims 1-5. The pressure sensor (603), the liquid proportional valve (601), the gas proportional valve (602), and the liquid level detection device (5) are electrically connected to the controller (508). The controller (508) controls the opening and closing angles of the liquid proportional valve (601) and the gas proportional valve (602) based on the liquid level information sent by the liquid level detection device (5) and the pressure information sent by the pressure sensor (603).

7. A liquid nitrogen circulation system, comprising a liquid nitrogen tank (1), a separator (4), and an MBE system (9), wherein the liquid nitrogen tank (1) and the separator (4) are connected by an inlet pipe (201), the MBE system is connected to the separator (4) by an outlet pipe (202), and an exhaust pipe (8) is provided at the upper end of the separator (4), characterized in that, It also includes the liquid nitrogen circulation system level control device as described in claim 6, wherein the pressure sensor (603) is disposed at the top of the separator (4), the liquid proportional valve (601) is disposed on the inlet pipe (201), the gas proportional valve (602) is disposed on the exhaust pipe (8), the level detection device (5) is disposed in the inner cavity of the separator (4), the guide is vertically disposed and its lower end is fixedly connected to the bottom of the separator (4), and the signal detection device is disposed on the inner wall of the separator (4).

8. A liquid nitrogen circulation system as described in claim 7, characterized in that, A return pipe (3) is also provided between the MBE system (9) and the separator (4). The inlet end of the return pipe (3) is connected to the upper end of the MBE system (9), and the outlet end of the return pipe (3) is located at the lower end of the inner cavity of the separator (4).

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