A liquid level detection device and method

Abstract

The present invention belongs to the technical field of liquid level detection, and particularly relates to a liquid level detection device and method. The liquid level detection device is used for measuring the liquid level of the liquid-phase medium inside a container, and includes a heating element, a temperature measuring element and a detection element arranged in a housing (11). The heating element is used to heat the gas-phase medium and the liquid-phase medium around the housing (11), the temperature measuring element is used to measure the temperature of the gas-phase medium or the liquid-phase medium, and the liquid level of the liquid-phase medium in the container is determined by combining the resistivity value and the resistance value of the detection element. By monitoring the change in the resistance of the detection element, the present invention completes the continuous detection of the container liquid level with a concise structure, reduces costs and simplifies the installation process; the functions of liquid level detection, heating and temperature measurement are synchronously realized by independent elements, broadening the demand application scenarios.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid level detection, and particularly relates to a liquid level detection device and method. Background Art

[0002] The demand for liquid level measurement is spread across various fields of industrial production. According to different usage environments, various detection instruments are adopted. Currently, there are already many mature liquid level detection methods, such as pressure method, electro method, ultrasonic method, nuclear radiation method, magnetoelectric method, optical method, and so on.

[0003] At present, the detection of continuous liquid level still generally relies on special instruments, and sensors based on various principles generally have exclusive requirements for the working space and environmental conditions. In some special application scenarios, such as a medium system working in a low-temperature environment, the performance requirements for all aspects of the detection equipment are strengthened. Using conventional equipment will inevitably increase the detection cost; at the same time, due to the particularity of the monitoring position, such as the liquid level monitoring point being at the bottom of a deep underground well, using conventional liquid level detection equipment will greatly increase the complexity of the installation process, resulting in a substantial increase in the input cost.

[0004] Therefore, for the need of liquid level detection in special environments, corresponding liquid level detection methods and devices need to be developed to simplify the installation process and reduce the detection cost. Summary of the Invention

[0005] The purpose of the present invention is to provide a liquid level detection structure and method, which have the functions of heating and temperature measurement, and can complete the continuous detection of the liquid level of the liquid-phase medium in the container with a concise structure, reduce the cost, and simplify the installation process.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is a liquid level detection device for measuring the liquid level of the liquid-phase medium inside a container, including a heating element, a temperature measurement element, and a detection element arranged in a housing. The heating element heats the gas-phase medium and the liquid-phase medium around the housing, the temperature measurement element measures the temperature of the gas-phase medium or the liquid-phase medium, and the liquid level of the liquid-phase medium in the container is determined by combining the resistivity value and the resistance value of the detection element.

[0007] Further, the liquid level detection device is divided into two major categories, namely the first type and the second type, both having the following same basic structure:

[0008] The housing is a cylindrical structure with heat conduction ability;

[0009] The heating element is composed of a first constantan wire, a first copper wire, a first heating auxiliary copper wire, and a second heating auxiliary copper wire. The top end of the first constantan wire is set within the top end of the housing, close to the top end of the housing. The top end of the first copper wire is set outside the top end of the housing. The top end of the first heating auxiliary copper wire is set outside the top end of the housing. The second heating auxiliary copper wire is set outside the top end of the housing. The bottom end of the first constantan wire and the bottom end of the first copper wire are connected and set within the bottom end of the housing, close to the bottom end of the housing. The tail end of the first heating auxiliary copper wire is connected to the top end of the first constantan wire, and the tail end of the second heating auxiliary copper wire is connected to the top end of the first copper wire. The top ends of the first heating auxiliary copper wire and the second heating auxiliary copper wire are used to connect the positive and negative electrodes of the power supply to form a heating circuit.

[0010] The first constantan wire is located at the axis position of the housing. When measuring the liquid level, the first constantan wire vertically penetrates the gas-phase medium and the liquid-phase medium. The specific form of the first constantan wire includes a straight shape or a spiral shape. When the first constantan wire is in a straight shape, the first constantan wire itself is located at the center of the entire liquid level detection device. When the first constantan wire is in a spiral shape, the center of the spiral structure coincides with the center of the entire liquid level detection device, so that the first constantan wire dissipates heat isotropically from the center of the liquid level detection device to the outside.

[0011] The temperature measuring element includes a liquid-phase temperature measuring point, and the liquid-phase temperature measuring point is the temperature measuring node of a T-type thermocouple composed of a copper wire and a constantan wire. The liquid-phase temperature measuring point is located near the bottom end of the housing and is used to obtain the temperature T of the liquid-phase medium. L ; The connection structure of the liquid-phase temperature measuring points is any way that can be firmly fixed to the same node, including arc welding, hydrogen arc welding, gas welding, and brine welding. After constructing the basic structure of the liquid-phase temperature measuring points to form a T-type thermocouple, the obtained liquid-phase temperature measuring points are calibrated to obtain an accurate liquid-phase medium temperature T during the subsequent medium temperature measurement process. L ;

[0012] The inside of the housing is filled with an insulating and heat-conducting substance, which is used to fix the detection element and the heating element and maintain their relative positions. Insulation measures are taken on the outside of the detection element and the heating element to ensure the insulation performance.

[0013] Further, on the basis of the basic structure, the first type of liquid level detection device is further subdivided into type 1-1, type 1-2, and type 1-3. The common structure of the first type of liquid level detection device is:

[0014] The temperature measuring element further includes a gas-phase temperature measuring point, which is the temperature measuring junction of a T-type thermocouple composed of a copper wire and a constantan wire; the gas-phase temperature measuring point is located inside the housing and above all possible liquid levels of the liquid-phase medium, and is used to obtain the gas-phase medium temperature T G ; The connection structure of the gas-phase temperature measuring point is any way that can be firmly fixed to the same junction, including arc welding, hydrogen arc welding, gas welding, and brine welding; after constructing the basic structure of the gas-phase temperature measuring point to form a T-type thermocouple, calibrate the obtained gas-phase temperature measuring point to obtain an accurate gas-phase medium temperature T during the subsequent medium temperature measurement process G ;

[0015] The detection element includes a first detection wire, a second detection wire, a first detection auxiliary copper wire, a second detection auxiliary copper wire, a third detection auxiliary copper wire, and a fourth detection auxiliary copper wire. The lengths, diameters D, and materials of the first detection wire and the second detection wire are exactly the same; the top end of the first detection wire is set inside the top end of the housing, and the distance between the top end of the first detection wire and the top end of the housing is greater than the distance between the top end of the first constantan wire and the top end of the housing. The top end of the second detection wire is set inside the top end of the housing, and the distance between the top end of the second detection wire and the top end of the housing is greater than the distance between the top end of the first constantan wire and the top end of the housing. The top end of the first detection auxiliary copper wire is set outside the top end of the housing, and the tail end of the first detection auxiliary copper wire is connected to the top end of the first detection wire. The top end of the second detection auxiliary copper wire is set outside the top end of the housing, and the tail end of the second detection auxiliary copper wire is connected to the top end of the first detection wire. The top end of the third detection auxiliary copper wire is set outside the top end of the housing, and the tail end of the third detection auxiliary copper wire is connected to the top end of the second detection wire. The top end of the fourth detection auxiliary copper wire is set outside the top end of the housing, and the tail end of the fourth detection auxiliary copper wire is connected to the top end of the second detection wire. The bottom ends of the first detection wire and the second detection wire are connected, and the connection point is near the bottom end of the housing. When measuring the liquid level, it penetrates the gas-phase medium and the liquid-phase medium to be detected from top to bottom to form a resistance measurement circuit; the first detection auxiliary copper wire and the second detection auxiliary copper wire are used as a group, and the third detection auxiliary copper wire and the fourth detection auxiliary copper wire are used as a group. They are respectively connected to a resistance measuring instrument from their top ends in a four-wire system to measure the resistance value of the detection element;

[0016] The arrangement of the detection element is divided into two types, and either one can be selected:

[0017] The first arrangement method is that except for the bottom parts where the first detection wire and the second detection wire are connected to each other, the rest are parallel straight lines

[0018] In the second arrangement, the first detection wire and the second detection wire overlap to form a co - helical shape with an equal pitch;

[0019] In both arrangements, the shortest distance from each point of the first detection wire and the second detection wire to the first constantan wire remains the same;

[0020] The materials used for the first detection wire and the second detection wire include Cu and Pt;

[0021] The distances from the gas - phase temperature measurement point, the first detection wire and the second detection wire to the first constantan wire are the same;

[0022] The resistance value of the detection element includes the total resistance R of the first detection wire and the second detection wire;

[0023] The resistivity value of the detection element includes a first resistivity value ρ G and a second resistivity value ρ L ; The first resistivity value ρ G refers to the resistivity value of the detection element in the gas - phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid - phase medium.

[0024] Furthermore, on the basis of the common structure of the first - type liquid - level detection device, the 1 - 1 type liquid - level detection device further has the following characteristics:

[0025] The temperature - measuring element includes a second constantan wire, a second copper wire, a third constantan wire and a third copper wire;

[0026] The top ends of the second constantan wire and the second copper wire are arranged outside the top end of the housing. The second copper wire is located near the top of the housing, and the bottom end of the second copper wire is arranged on the first constantan wire to form the gas - phase temperature measurement point; the bottom end of the second constantan wire is connected to the top end of the first constantan wire; the second constantan wire and the second copper wire together with the first constantan wire and the gas - phase temperature measurement point form a temperature - measuring circuit;

[0027] The top ends of the third constantan wire and the third copper wire are arranged outside the top end of the housing. The bottom end of the third constantan wire is connected to the top end of the first constantan wire, and the bottom end of the third copper wire is connected to the top end of the first copper wire. The bottom ends of the first constantan wire and the first copper wire are connected to form the liquid - phase temperature measurement point; the third constantan wire and the third copper wire together with the first constantan wire, the first copper wire and the liquid - phase temperature measurement point form a temperature - measuring circuit;

[0028] The tops of the second constantan wire, the second copper wire, the third constantan wire, and the third copper wire are connected to a temperature measuring instrument for detecting the temperature T of the gaseous medium G and the temperature T of the liquid medium L .

[0029] Furthermore, based on the common structure of the first type of liquid level detection device, the 1-2 type of liquid level detection device further includes the following features:

[0030] The temperature measuring element includes a second constantan wire, a second copper wire, a third constantan wire, and a third copper wire;

[0031] The tops of the second constantan wire and the second copper wire are disposed outside the top of the housing. The second copper wire is near the top of the housing. The bottom end of the second copper wire is disposed on the second constantan wire and forms the gaseous phase temperature measuring point. The gaseous phase temperature measuring point is below the top of the housing. The distance between the gaseous phase temperature measuring point and the top of the housing is greater than the distance between the top of the first constantan wire and the top of the housing. The second constantan wire, the second copper wire, and the gaseous phase temperature measuring point together form a temperature measuring circuit;

[0032] The tops of the third constantan wire and the third copper wire are disposed outside the top of the housing. The bottom end of the third constantan wire is disposed on the second constantan wire. The connection position between the bottom end of the third constantan wire and the second constantan wire is inside or outside the top of the housing. The bottom ends of the second constantan wire and the third copper wire are connected to form the liquid phase temperature measuring point. The liquid phase temperature measuring point is near the bottom end of the housing. The third constantan wire and the third copper wire together form a temperature measuring circuit through the second constantan wire and the liquid phase temperature measuring point;

[0033] The tops of the second constantan wire, the second copper wire, the third constantan wire, and the third copper wire are connected to a temperature measuring instrument for detecting the temperature T of the gaseous medium G and the temperature T of the liquid medium L .

[0034] Furthermore, based on the common structure of the first type of liquid level detection device, the 1-3 type of liquid level detection device further includes the following features:

[0035] The temperature measuring element includes a second constantan wire, a second copper wire, a third constantan wire, and a third copper wire;

[0036] The top ends of the second constantan wire and the second copper wire are arranged outside the top end of the housing. The second constantan wire and the second copper wire are located near the top of the housing. The bottom ends of the second constantan wire and the second copper wire are connected to form the gas-phase temperature measurement point, which is located below the top of the housing. The distance between the gas-phase temperature measurement point and the top end of the housing is greater than the distance between the top end of the first constantan wire and the top end of the housing. The second constantan wire, the second copper wire, and the gas-phase temperature measurement point together form a temperature measurement circuit.

[0037] The top ends of the third constantan wire and the third copper wire are arranged outside the top end of the housing. The bottom ends of the third constantan wire and the third copper wire are connected to form the liquid-phase temperature measurement point, which is located near the bottom end of the housing. The third constantan wire, the third copper wire, and the liquid-phase temperature measurement point together form a temperature measurement circuit.

[0038] The top ends of the second constantan wire, the second copper wire, the third constantan wire, and the third copper wire are connected to a temperature measurement instrument for detecting the temperature T of the gas-phase medium G and the temperature T of the liquid-phase medium L .

[0039] Further, on the basis of the basic structure, the second type of liquid level detection device is further subdivided into type 2-1 and type 2-2. The common structure of the second type of liquid level detection device is:

[0040] The detection element includes a first detection wire, a second detection wire, a third detection wire, a first detection auxiliary copper wire, a second detection auxiliary copper wire, a third detection auxiliary copper wire, a fourth detection auxiliary copper wire, a fifth detection auxiliary copper wire, and a sixth detection auxiliary copper wire.

[0041] The resistivity values of the detection element include a first resistivity value ρ G and a second resistivity value ρ L ; the first resistivity value ρ G refers to the resistivity value of the detection element in the gas-phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid-phase medium.

[0042] The diameters D and materials of the first detection wire and the second detection wire are exactly the same; the diameters D, lengths, and materials of the first detection auxiliary copper wire, the second detection auxiliary copper wire, the third detection auxiliary copper wire, and the fourth detection auxiliary copper wire are exactly the same; there is a difference ΔL in the lengths of the first detection wire and the second detection wire to generate a resistance difference ΔR, and the first resistivity value ρ is determined through the ΔR G ;

[0043] The arrangement of the detection elements is divided into two types, and either one can be selected:

[0044] In the first arrangement, the third detection wire is a bent straight copper wire. The straight part is parallel to the first constantan wire. The bent part is near the bottom end of the housing. The top end of the third detection wire is set inside the top end of the housing. The distance between the top end of the third detection wire and the top end of the housing is greater than the distance between the top end of the first constantan wire and the top end of the housing. The tail end of the third detection wire is inside the housing and above all possible liquid levels of the liquid-phase medium during liquid level measurement. The tail ends of the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire are connected to the top end of the third detection wire. The top ends of the first detection wire and the second detection wire are set inside the top end of the housing, close to the top end of the housing. The bottom ends of the first detection wire and the second detection wire are connected to the tail end of the third detection wire. The first detection wire and the second detection wire are in the gas-phase medium during liquid level measurement. The first detection wire is entirely routed in a bent manner. The middle part of the second detection wire is routed in a bent manner, and the rest is routed in a straight-line manner. The distance from the straight part of the third detection wire to the first constantan wire is r. At the same time, the first detection wire and the second detection wire are set on a cylindrical surface with a radius of r with the first constantan wire as the axis. The shortest distance from each point of the first detection wire and the second detection wire to the first constantan wire is r.

[0045] The second arrangement, the third detection wire is a straight copper wire parallel to the first constantan wire. The top end of the third detection wire is arranged within the top end of the housing. The distance between the top end of the third detection wire and the top end of the housing is greater than the distance between the top end of the first constantan wire and the top end of the housing. The tail end of the third detection wire is located near the bottom end of the housing. The tail ends of the first detection wire and the second detection wire are connected to the tail end of the third detection wire. The main parts of the first detection wire and the second detection wire are a spiral formed by their overlap, serving as a liquid level measurement section for measuring the liquid level of the liquid phase medium. The upper part of the first detection wire is a separately formed spiral, and the upper part of the second detection wire is a straight line. The bottom ends of the first detection wire and the second detection wire are connected to the tail end of the third detection wire. When measuring the liquid level, the non-overlapping parts of the first detection wire and the second detection wire in the upper part are in the gas phase medium. A part of the liquid level measurement section is in the liquid level of the liquid phase medium, and the liquid surface of the liquid phase medium cannot exceed the total height of the liquid level measurement section. The lengths of the first detection wire and the second detection wire used to form the liquid level measurement section are the same. There is a length difference ΔL between the non-overlapping parts of the first detection wire and the second detection wire in the upper part to generate a resistance difference ΔR, and the first resistivity value ρ is determined through the ΔR G ; The liquid level measurement section is wired in a coaxial spiral and equal pitch manner. The distance from the third detection wire to the first constantan wire is r. At the same time, the first detection wire and the second detection wire are arranged within a cylindrical surface with a radius of r centered on the first constantan wire. The shortest distance from each point of the first detection wire and the second detection wire to the first constantan wire is r;

[0046] The materials used for the first detection wire, the second detection wire, and the third detection wire include Cu and Pt. The detection element is divided into a first detection circuit and a second detection circuit. The total length of the first detection circuit is L L , which is composed of the first detection wire, the first detection auxiliary copper wire, the second detection auxiliary copper wire, the third detection wire, the fifth detection auxiliary copper wire, and the sixth detection auxiliary copper wire. The first detection auxiliary copper wire and the second detection auxiliary copper wire are grouped together, and the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire are grouped together. Copper wires are used to connect to a resistance measuring instrument in a four-wire system to obtain the total resistance R of the first detection circuit L ; The total length of the second detection circuit is L S, which is composed of the second detection wire, the third detection auxiliary copper wire, the fourth detection auxiliary copper wire, the third detection wire, the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire. The third detection auxiliary copper wire and the fourth detection auxiliary copper wire form a group, and the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire form a group. Copper wires are used and connected to a resistance measuring instrument in a four-wire system to obtain the total resistance R of the second detection loop S ; where L L -L S =ΔL, ΔL>0;

[0047] When performing liquid level detection, any one of the first detection loop and the second detection loop is selected to achieve liquid level detection;

[0048] When the first detection loop is selected as the liquid level detection loop, according to the total length L L and the total resistance R L of the first detection loop, the liquid level of the liquid phase medium in the container is determined;

[0049] When the second detection loop is selected as the liquid level detection loop, according to the total length L S and the total resistance R S of the second detection loop, the liquid level of the liquid phase medium in the container is determined.

[0050] Furthermore, on the basis of the common structure of the second-type liquid level detection device, the 2-1 type liquid level detection device further includes the following features: The temperature measuring element includes a third constantan wire and a third copper wire; The tops of the third constantan wire and the third copper wire are both located outside the top of the housing. The bottom end of the third constantan wire is connected to the top end of the first constantan wire, and the bottom end of the third copper wire is connected to the top end of the first copper wire. The bottom ends of the first constantan wire and the first copper wire are connected to form the liquid phase temperature measuring point; The third constantan wire and the third copper wire together with the first constantan wire, the first copper wire and the liquid phase temperature measuring point form a temperature measuring loop; The tops of the third constantan wire and the third copper wire are connected to a temperature measuring instrument for detecting the temperature T of the liquid phase medium L .

[0051] Furthermore, on the basis of the common structure of the second-type liquid level detection device, the 2-2 type liquid level detection device further includes the following features:

[0052] The temperature measuring element includes a third constantan wire and a third copper wire; the top ends of the third constantan wire and the third copper wire are arranged outside the top end of the housing, and the bottom ends of the third constantan wire and the third copper wire are connected to form the liquid-phase temperature measuring point; the third constantan wire, the third copper wire and the liquid-phase temperature measuring point together form a temperature measuring circuit; the top ends of the third constantan wire and the third copper wire are connected to a temperature measuring instrument for detecting the temperature T of the liquid-phase medium L 。

[0053] The present invention also discloses a liquid level detection method for the liquid level detection device of the above-mentioned 1-1 type, 1-2 type or 1-3 type and the detection element adopts the first arrangement method, including the following steps:

[0054] Step S1, vertically place the liquid level detection device into the container to be detected, the liquid-phase temperature measuring point is close to but does not touch the bottom of the container, ensuring that the liquid-phase temperature measuring point can always be submerged by the liquid-phase medium in the container during the test; ensuring that the gas-phase temperature measuring point is close to the top of the container and is always in the gas-phase medium during the test;

[0055] Step S2, connect the top ends of the first heating auxiliary copper wire and the second heating auxiliary copper wire to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire through the DC power supply to cause the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to change;

[0056] Step S3, connect the top end of the second constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument with a constantan wire, and connect the top end of the second copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument with a copper wire to form the first temperature measuring circuit, and measure and obtain the gas-phase medium temperature T through the gas-phase temperature measuring point G ; connect the top end of the third constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument with a constantan wire, and connect the top end of the third copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument with a copper wire to form the second temperature measuring circuit, and measure and obtain the liquid-phase medium temperature T through the liquid-phase temperature measuring point L ; or use T-type thermocouple compensating wires to connect the top ends of the second constantan wire, the second copper wire, the third constantan wire and the third copper wire to the temperature measuring instrument respectively to obtain the gas-phase medium temperature T G and the liquid-phase medium temperature T L ;

[0057] Step S4, collect the gas-phase medium temperature T G and the liquid-phase medium temperature T L, determining the first resistivity value ρ according to the resistivity-temperature relationship of the detection element G and the second resistivity value ρ L ;

[0058] Step S5, connecting the detection element to a resistance measuring instrument in a four-wire system, that is, using 2 copper wires respectively to connect the top of the first detection auxiliary copper wire and the top of the second detection auxiliary copper wire to one pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and connecting the top of the third detection auxiliary copper wire and the top of the fourth detection auxiliary copper wire to the other pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and measuring the total resistance R of the first detection wire and the second detection wire;

[0059] Step S6, according to the diameter D and the total length L of the detection element, determining the liquid level h1 of the liquid phase medium in the container according to the following formula

[0060]

[0061] R in the formula refers to the total resistance of the first detection wire and the second detection wire.

[0062] The present invention also discloses a liquid level detection method for the liquid level detection device of the above-mentioned 1-1 type, 1-2 type or 1-3 type and the detection element adopting the second arrangement method, including the following steps:

[0063] Step S1, vertically placing the liquid level detection device into the container to be detected, with the liquid phase temperature measurement point close to but not in contact with the bottom of the container, ensuring that the liquid phase temperature measurement point can always be submerged by the liquid phase medium in the container during the test; ensuring that the gas phase temperature measurement point is close to the top of the container and always in the gas phase medium during the test;

[0064] Step S2, connecting the top of the first heating auxiliary copper wire and the top of the second heating auxiliary copper wire to the two poles of a DC power supply respectively, and applying a constant electric heating power to the first constantan wire through the DC power supply to cause the temperatures of the gas phase medium and the liquid phase medium at the detection element to change;

[0065] Step S3, connecting the top of the second constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connecting the top of the second copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form the first temperature measurement loop, and measuring the gas phase medium temperature T through the gas phase temperature measurement point G; Connect the top end of the third constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument using constantan wire, and connect the top end of the third copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument using copper wire to form the second temperature measuring circuit, and obtain the temperature T of the liquid phase medium through the liquid phase temperature measuring point L ; Or use T-type thermocouple compensating wire to connect the top ends of the second constantan wire, the second copper wire, the third constantan wire, and the third copper wire to the temperature measuring instrument respectively to obtain the temperature T of the gas phase medium G and the temperature T of the liquid phase medium L ;

[0066] Step S4, collect the temperature T of the gas phase medium through the temperature detection instrument and the channel switch G and the temperature T of the liquid phase medium L , and determine the first resistivity value ρ according to the resistivity-temperature relationship of the detection element G and the second resistivity value ρ L ;

[0067] Step S5, connect the detection element to the resistance measuring instrument in a four-wire system, that is, use 2 copper wires respectively to connect the top ends of the first detection auxiliary copper wire and the second detection auxiliary copper wire to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the third detection auxiliary copper wire and the fourth detection auxiliary copper wire to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument to measure the total resistance R of the first detection wire and the second detection wire;

[0068] Step S6, determine the liquid level h1 of the liquid phase medium in the container according to the diameter D and total length L of the detection element according to the following formula

[0069]

[0070] R in the formula refers to the total resistance of the first detection wire and the second detection wire;

[0071] Step S7, further determine the liquid level h2 of the liquid phase medium in the container according to the corresponding relationship between the length of the unit pitch of the detection element and the vertical height. Specifically, if the length L of the unit pitch of the detection element C and the vertical height h C The relationship coefficient is α, that is, L C =α×h C , then The liquid level h2 is:

[0072]

[0073] The present invention also discloses a liquid level detection method for the liquid level detection device of the 2-1 type or the 2-2 type as described above and with the first arrangement mode of the detection element, including the following steps:

[0074] Step S1, vertically place the liquid level detection device into the container to be detected, with the liquid-phase temperature measurement point close to but not in contact with the bottom of the container, ensuring that the liquid-phase temperature measurement point can always be submerged by the liquid-phase medium in the container during the test; ensure that the part of the detection element with a length difference ΔL is close to the top of the container and is always in the gas-phase medium during the test;

[0075] Step S2, connect the top ends of the first heating auxiliary copper wire and the second heating auxiliary copper wire to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire through the DC power supply to cause the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to change;

[0076] Step S3, use a constantan wire to connect the top end of the third constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument, and use a copper wire to connect the top end of the third copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument to form a temperature measurement circuit, and measure and obtain the liquid-phase medium temperature T through the liquid-phase temperature measurement point L ; or use a T-type thermocouple compensating wire to connect the top ends of the third constantan wire and the third copper wire to the temperature measuring instrument respectively to obtain the liquid-phase medium temperature T L ;

[0077] Step S4, determine the second resistivity value ρ according to the resistivity-temperature relationship of the detection element L ;

[0078] Step S5, connect the detection element to a resistance measuring instrument in a four-wire system, that is, use 2 copper wires respectively to connect the top ends of the first detection auxiliary copper wire and the second detection auxiliary copper wire to one pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire to the other pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument; use 2 copper wires respectively to connect the top ends of the third detection auxiliary copper wire and the fourth detection auxiliary copper wire to one pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire to the other pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument; obtain the total resistance R of the first detection loop composed of the first detection wire and the third detection wire through the resistance measuring instrument and the channel switch L, and obtaining the total resistance R of the second detection circuit composed of the second detection wire and the third detection wire S ; determining the difference in resistance between the two circuits ΔR = R L -R S ;

[0079] Step S6, according to the diameter D of the detection element and the length difference ΔL between the first detection wire and the second detection wire, determine the first resistivity value ρ through the following formula G ;

[0080]

[0081] In the formula, S refers to the cross-sectional area of the first detection wire and the second detection wire;

[0082] Step S7,

[0083] According to the total length L L and the total resistance R L of the first detection circuit, the first resistivity value ρ G and the second resistivity value ρ L , determine the liquid level h1 of the liquid phase medium in the container through the following formula;

[0084]

[0085] Or, according to the total length L S and the total resistance R S of the second detection circuit, the first resistivity value ρ G and the second resistivity value ρ L , determine the liquid level h1 of the liquid phase medium in the container through the following formula;

[0086]

[0087] The present invention also discloses a liquid level detection method for a liquid level detection device of the above-mentioned 2-1 type or 2-2 type and the detection element adopting the second arrangement method, including the following steps:

[0088] Step S1, vertically place the liquid level detection device into the container to be detected, with the liquid phase temperature measurement point close to but not in contact with the bottom of the container, ensuring that the liquid phase temperature measurement point can always be submerged by the liquid phase medium in the container during the test; ensuring that the part with a length difference ΔL of the detection element is close to the top of the container and always in the gas phase medium during the test;

[0089] Step S2: Connect the top ends of the first heating auxiliary copper wire and the second heating auxiliary copper wire to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire through the DC power supply to cause changes in the temperatures of the gaseous medium and the liquid medium at the detection element.

[0090] Step S3: Connect the top end of the third constantan wire to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connect the top end of the third copper wire to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form a temperature measuring circuit. Measure the temperature T of the liquid medium through the liquid phase temperature measuring point. L ; Or use T-type thermocouple compensating wires to connect the top ends of the third constantan wire and the third copper wire to the temperature measuring instrument respectively to obtain the temperature T of the liquid medium. L ;

[0091] Step S4: Determine the second resistivity value ρ according to the resistivity-temperature relationship of the detection element. L ;

[0092] Step S5: Connect the detection element to a resistance measuring instrument in a four-wire system, that is, use 2 copper wires to connect the top ends of the first detection auxiliary copper wire and the second detection auxiliary copper wire to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; use 2 copper wires to connect the top ends of the third detection auxiliary copper wire and the fourth detection auxiliary copper wire to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the fifth detection auxiliary copper wire and the sixth detection auxiliary copper wire to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; obtain the total resistance R of the first detection loop composed of the first detection wire and the third detection wire through the resistance measuring instrument and the channel switch. L , and obtain the total resistance R of the second detection loop composed of the second detection wire and the third detection wire. S ; Determine the resistance difference ΔR between the two loops = R L - R S ;

[0093] Step S6: Determine the first resistivity value ρ according to the diameter D of the detection element and the length difference ΔL between the first detection wire and the second detection wire through the following formula. G ;

[0094]

[0095] In the formula, S refers to the cross-sectional areas of the first detection wire and the second detection wire;

[0096] Step S7,

[0097] According to the total length L L and the total resistance R L of the first detection circuit, G the first resistivity value ρ L and the second resistivity value ρ,

[0098]

[0099] the liquid level h1 of the liquid-phase medium in the container is determined by the following formula; S and the total resistance R S of the second detection circuit, G the first resistivity value ρ L and the second resistivity value ρ,

[0100]

[0101] Step S8, according to the correspondence between the length of the unit pitch of the liquid level measurement section detection element and the vertical height, the liquid level h2 of the liquid-phase medium in the container is further determined. Specifically, if the relationship coefficient between the length L C of the unit pitch of the liquid level measurement section and the vertical height h C is α, that is, L C = α×h C , then the liquid level h2 is:

[0102]

[0103] The beneficial effects of the present invention are as follows:

[0104] 1. By monitoring the resistance change of the detection element, the continuous detection of the container liquid level is completed with a concise structure, the cost is reduced, and the installation process is simplified.

[0105] 2. The functions of liquid level detection, heating and temperature measurement are synchronously realized by independent elements, broadening the demand application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 is a schematic diagram of the 1-1 type in the first type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the first arrangement method, and the first detection wire 3 and the second detection wire 4 are parallel straight lines);

[0107] Figure 2 isFigure 1 Axial sectional view of the 1-1 type liquid level detection device in it, showing an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0108] Figure 3 It is a schematic diagram of the 1-2 type in the first type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the first layout method, and the first detection wire 3 and the second detection wire 4 are parallel straight lines);

[0109] Figure 4 is Figure 3 Axial sectional view of the 1-2 type liquid level detection device in it, showing an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0110] Figure 5 It is a schematic diagram of the 1-3 type in the first type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the first layout method, and the first detection wire 3 and the second detection wire 4 are parallel straight lines);

[0111] Figure 6 is Figure 5 Axial sectional view of the 1-3 type liquid level detection device in it, showing an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0112] Figure 7 It is a schematic diagram of the 1-1 type in the first type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the second layout method, and the first detection wire 3 and the second detection wire 4 are spiral);

[0113] Figure 8 is Figure 7 Axial sectional view of the 1-1 type liquid level detection device in it, showing an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0114] Figure 9 It is a schematic diagram of the 2-1 type in the second type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the first layout method, and the middle parts of the first detection wire 3 and the second detection wire 4 are arranged in a bent wiring manner);

[0115] Figure 10 is Figure 9 Axial sectional view of the 2-1 type liquid level detection device in it, showing an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0116] Figure 11It is a schematic diagram of the 2-2 type in the second type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the first layout method, and the middle parts of the first detection wire 3 and the second detection wire 4 are arranged in a bent wiring manner);

[0117] Figure 12 It is Figure 9 an axial sectional view of the 2-2 type liquid level detection device in, giving an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0118] Figure 13 It is a schematic diagram of the 2-1 type in the second type of liquid level detection device described in the specific implementation part of the present invention (the detection element adopts the second layout method, and the main parts of the first detection wire 3 and the second detection wire 4 are a spiral formed by their overlap);

[0119] Figure 14 It is Figure 13 an axial sectional view of the 2-1 type liquid level detection device in, giving an example of the layout method that meets the conditions, and the specific layout method is not limited to this;

[0120] In the figure: 1 - first constantan wire, 2 - first copper wire, 3 - first detection wire, 4 - second detection wire, 5 - second constantan wire, 6 - second copper wire, 7 - third constantan wire, 8 - third copper wire, 9 - gas phase temperature measurement point, 10 - liquid phase temperature measurement point, 11 - outer shell, 12 - third detection wire, 1-1 - first heating auxiliary copper wire, 2-1 - second heating auxiliary copper wire, 3-1 - first detection auxiliary copper wire, 3-2 - second detection auxiliary copper wire, 4-1 - third detection auxiliary copper wire, 4-2 - fourth detection auxiliary copper wire, 12-1 fifth detection auxiliary copper wire, 12-2 - sixth detection auxiliary copper wire, P1 - the top end of the first constantan wire, P2 - the top end of the first copper wire, P3 - the top end of the first detection wire, P4 - the top end of the second detection wire, P5 - the connection position of the bottom end of the third constantan wire and the second constantan wire, P12-1 - the top end of the third detection wire, P12-2 - the tail end of the third detection wire. Specific implementation

[0121] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0122] Generally, the liquid phase heat capacity of the medium is significantly higher than the gas phase heat capacity. Absorbing the same amount of heat, the feedback speed of the gas phase temperature change is fast and the increase is significant. Near the boiling point, due to heating, liquid-gas phase conversion will occur, and the temperature change difference between the two phases is more significant.

[0123] Utilize the resistance-temperature characteristics of the detection element and the difference in heat capacities of the gas and liquid phases of a general medium. When heating the two phases of the medium simultaneously, a significant temperature difference will occur between the two phases near the heating element. By obtaining the resistivity values of the detection element located near the heating element in the gas and liquid phases of the medium in an appropriate manner and combining with the measurement of the total resistance value of the detection element, the length distribution of the detection element in the gas and liquid phases can be obtained, thereby indicating the liquid level of the medium.

[0124] According to the above characteristics, a liquid level detection device provided by the present invention is used for measuring the liquid level of the liquid-phase medium inside a container, and includes a heating element, a temperature measuring element, and a detection element arranged in a housing 11. The heating element heats the gas-phase medium and the liquid-phase medium around the housing 11, the temperature measuring element measures the temperature of the gas-phase medium or the liquid-phase medium, and the liquid level of the liquid-phase medium in the container is determined by combining the resistivity value and the resistance value of the detection element.

[0125] This liquid level detection device is divided into two major categories: the first type and the second type, both having the following same basic structure:

[0126] The housing 11 is of a cylindrical structure, having sufficient strength and heat conduction ability, and having insulation, corrosion resistance, and sealing performance;

[0127] The heating element is composed of a first constantan wire 1, a first copper wire 2, a first heating auxiliary copper wire 1-1, and a second heating auxiliary copper wire 2-1. The top P1 of the first constantan wire 1 is arranged inside the top of the housing 11, close to the top of the housing 11. The top P2 of the first copper wire 2 is arranged outside the top of the housing 11. The top of the first heating auxiliary copper wire 1-1 is arranged outside the top of the housing 11. The second heating auxiliary copper wire 2-1 is arranged outside the top of the housing 11. The bottom ends of the first constantan wire 1 and the first copper wire 2 are connected and arranged inside the bottom of the housing 11, close to the bottom of the housing 11. The tail end of the first heating auxiliary copper wire 1-1 is connected to the top P1 of the first constantan wire 1, and the tail end of the second heating auxiliary copper wire 2-1 is connected to the top P2 of the first copper wire 2. The top of the first heating auxiliary copper wire 1-1 and the top of the second heating auxiliary copper wire 2-1 are used to connect the positive and negative electrodes of the power supply (without a clear corresponding relationship) to form a heating circuit;

[0128] The first constantan wire 1 is located at the axis position of the housing 11. When measuring the liquid level, the first constantan wire 1 vertically penetrates the gas-phase medium and the liquid-phase medium. The specific form of the first constantan wire 1 is not limited, including a straight shape or a spiral shape. When the first constantan wire 1 is in a straight shape, the first constantan wire 1 itself is located at the center of the entire liquid level detection device. When the first constantan wire 1 is in a spiral shape, the center of the spiral structure coincides with the center of the entire liquid level detection device, so that the first constantan wire 1 dissipates heat isotropically from the center of the liquid level detection device to the outside.

[0129] The temperature measuring element includes a liquid-phase temperature measuring point 10, and the liquid-phase temperature measuring point 10 is the temperature measuring junction of a T-type thermocouple composed of a copper wire and a constantan wire; the liquid-phase temperature measuring point 10 is located near the bottom end of the outer shell 11 and is used to obtain the temperature T of the liquid-phase medium. L When performing liquid level measurement, the liquid-phase temperature measuring point 10 is located at the bottom of the container with the liquid level to be detected and is always below the liquid level of the liquid-phase medium during the measurement process; the connection structure of the liquid-phase temperature measuring point 10 can be any way that can be firmly fixed to the same junction, including arc welding, hydrogen arc welding, gas welding, and brine welding, etc.; after constructing the basic structure of the liquid-phase temperature measuring point 10 to form a T-type thermocouple, the obtained liquid-phase temperature measuring point 10 is calibrated to obtain the accurate temperature T of the liquid-phase medium during the subsequent medium temperature measurement. L ;

[0130] The inside of the outer shell 11 is filled with an insulating and heat-conducting substance, which is used to fix the detection element and the heating element and maintain their relative positions, so as to ensure the consistency of the resistivity of the detection element in the same-phase medium; both the detection element and the heating element are insulated to ensure sufficient insulation performance. The technical solution of the present invention is based on the fact that under the same heating conditions, there are differences in the resistance changes of the detection elements located in the gas and liquid phases, that is, the resistivity differences caused by temperature differences, for liquid level characterization. Therefore, the detection element parts located in the two phases need to each have the same resistivity, that is, the part of the detection element located in the gas phase has the same resistivity ρ G , and the part located in the liquid phase has the same resistivity ρ L . To ensure the consistency of the resistivity of the detection element in the same-phase medium, appropriate means need to be used to ensure the consistency of the relative positions of the detection element and the first constantan wire 1, that is, the positions of the detection element from the first constantan wire 1 in the same-phase medium are the same.

[0131] On the basis of the basic structure, the first type of liquid level detection device is further subdivided into type 1-1 (see Figure 1 , 2 , 7, 8), type 1-2 (see Figure 3 , 4 ) and type 1-3 (see Figure 5 , 6 ); the common structure of the first type of liquid level detection device is:

[0132] The temperature measuring element further includes a gas-phase temperature measuring point 9, and the gas-phase temperature measuring point 9 is the temperature measuring junction of a T-type thermocouple composed of a copper wire and a constantan wire; the gas-phase temperature measuring point 9 is located inside the outer shell 11 and (when performing liquid level measurement) is above all possible liquid levels of the liquid-phase medium and is used to obtain the temperature T of the gas-phase medium. G; The connection structure of the gas-phase temperature measurement point 9 can be any way that can be firmly fixed to the same node, including arc welding, hydrogen arc welding, gas welding, and brine welding, etc.; After constructing the basic structure of the gas-phase temperature measurement point 9 to form a T-type thermocouple, calibrate the obtained gas-phase temperature measurement point 9 to obtain the accurate gas-phase medium temperature T during the subsequent medium temperature measurement process. G ;

[0133] The detection element includes a first detection wire 3, a second detection wire 4, a first detection auxiliary copper wire 3-1, a second detection auxiliary copper wire 3-2, a third detection auxiliary copper wire 4-1, and a fourth detection auxiliary copper wire 4-2. The lengths, diameters D, and materials of the first detection wire 3 and the second detection wire 4 are exactly the same; The top end P3 of the first detection wire 3 is set inside the top end of the outer shell 11, and the distance between the top end P3 of the first detection wire 3 and the top end of the outer shell 11 is greater than the distance between the top end P1 of the first constantan wire 1 and the top end of the outer shell 11. The top end P4 of the second detection wire 4 is set inside the top end of the outer shell 11, and the distance between the top end P4 of the second detection wire 4 and the top end of the outer shell 11 is greater than the distance between the top end P1 of the first constantan wire 1 and the top end of the outer shell 11. The top end of the first detection auxiliary copper wire 3-1 is set outside the top end of the outer shell 11, and the tail end of the first detection auxiliary copper wire 3-1 is connected to the top end P3 of the first detection wire 3. The top end of the second detection auxiliary copper wire 3-2 is set outside the top end of the outer shell 11, and the tail end of the second detection auxiliary copper wire 3-2 is connected to the top end P3 of the first detection wire 3. The top end of the third detection auxiliary copper wire 4-1 is set outside the top end of the outer shell 11, and the tail end of the third detection auxiliary copper wire 4-1 is connected to the top end P4 of the second detection wire 4. The top end of the fourth detection auxiliary copper wire 4-2 is set outside the top end of the outer shell 11, and the tail end of the fourth detection auxiliary copper wire 4-2 is connected to the top end P4 of the second detection wire 4. The bottom ends of the first detection wire 3 and the second detection wire 4 are connected, and the connection point is near the bottom end of the outer shell 11. When performing liquid level measurement, it penetrates the gas-phase medium and liquid-phase medium to be detected from top to bottom to form a resistance measurement circuit; The first detection auxiliary copper wire 3-1 and the second detection auxiliary copper wire 3-2 are taken as a group, and the third detection auxiliary copper wire 4-1 and the fourth detection auxiliary copper wire 4-2 are taken as a group. They are respectively connected to a resistance measurement instrument in a four-wire system from their top ends to measure the resistance value of the detection element.

[0134] The arrangement methods of the detection element are divided into two types, and either one can be selected:

[0135] The first arrangement method: Except for the bottom parts that are connected to each other, the rest of the first detection wire 3 and the second detection wire 4 are parallel straight lines (see Figure 1 、 3 、5).

[0136] In the second arrangement, the first detection wire 3 and the second detection wire 4 overlap to form a co-helical shape with an equal pitch (see Figure 7 );

[0137] In both arrangements, the shortest distance from each point of the first detection wire 3 and the second detection wire 4 to the first constantan wire 1 remains the same;

[0138] The materials used for the first detection wire 3 and the second detection wire 4 can be Cu or Pt. In principle, metals with a significant resistance-temperature coefficient are used;

[0139] The gas-phase temperature measurement point 9, the first detection wire 3, and the second detection wire 4 are at the same distance from the first constantan wire 1 to ensure that the temperature measured at the gas-phase temperature measurement point 9 can represent the temperature of the detection element;

[0140] The resistance value of the detection element includes the total resistance R of the first detection wire 3 and the second detection wire 4;

[0141] The resistivity value of the detection element includes the first resistivity value ρ G and the second resistivity value ρ L ; The first resistivity value ρ G refers to the resistivity value of the detection element in the gas-phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid-phase medium.

[0142] Based on the common structure of the first-type liquid level detection device, the 1-1 type liquid level detection device (see Figure 1 , 2 ) also includes the following features:

[0143] The temperature measurement element includes a second constantan wire 5, a second copper wire 6, a third constantan wire 7, and a third copper wire 8;

[0144] The top of the second constantan wire 5 and the top of the second copper wire 6 are set outside the top of the housing 11. The second copper wire 6 is located near the top of the housing 11 and is in the gas-phase medium. The bottom of the second copper wire 6 is set on the first constantan wire 1 and forms the gas-phase temperature measurement point 9; The bottom of the second constantan wire 5 is connected to the top P1 of the first constantan wire 1; The second constantan wire 5 and the second copper wire 6 together with the first constantan wire 1 and the gas-phase temperature measurement point 9 form a temperature measurement circuit;

[0145] The top of the third constantan wire 7 and the top of the third copper wire 8 are set outside the top of the housing 11. The bottom of the third constantan wire 7 is connected to the top P1 of the first constantan wire 1, and the bottom of the third copper wire 8 is connected to the top P2 of the first copper wire 2. The bottom of the first constantan wire 1 and the bottom of the first copper wire 2 are connected to form the liquid-phase temperature measurement point 10; The third constantan wire 7 and the third copper wire 8 together with the first constantan wire 1, the first copper wire 2, and the liquid-phase temperature measurement point 10 form a temperature measurement circuit;

[0146] The tops of the second constantan wire 5, the second copper wire 6, the third constantan wire 7, and the third copper wire 8 are connected to a temperature measuring instrument for detecting the temperature T of the gas-phase medium G and the temperature T of the liquid-phase medium L .

[0147] Based on the common structure of the first-type liquid level detection device, the 1-2 type liquid level detection device (see Figure 3 , 4 ) also includes the following features:

[0148] The temperature measuring element includes a second constantan wire 5, a second copper wire 6, a third constantan wire 7, and a third copper wire 8;

[0149] The tops of the second constantan wire 5 and the second copper wire 6 are arranged outside the top of the outer shell 11. The second copper wire 6 is located near the top of the outer shell 11. The bottom end of the second copper wire 6 is arranged on the second constantan wire 5 and forms a gas-phase temperature measuring point 9. The gas-phase temperature measuring point 9 is located below the top of the outer shell 11, and the distance between the gas-phase temperature measuring point 9 and the top of the outer shell 11 is greater than the distance between the top P1 of the first constantan wire 1 and the top of the outer shell 11; the second constantan wire 5, the second copper wire 6, and the gas-phase temperature measuring point 9 together form a temperature measuring circuit;

[0150] The tops of the third constantan wire 7 and the third copper wire 8 are arranged outside the top of the outer shell 11. The bottom end of the third constantan wire 7 is arranged on the second constantan wire 5, and the connection position P5 between the bottom end of the third constantan wire 7 and the second constantan wire 5 is located inside or outside the top of the outer shell 11; the bottom end of the second constantan wire 5 and the bottom end of the third copper wire 8 are connected to form a liquid-phase temperature measuring point 10. The liquid-phase temperature measuring point 10 is located near the bottom end of the outer shell 11; the third constantan wire 7, the third copper wire 8, the second constantan wire 5, and the liquid-phase temperature measuring point 10 together form a temperature measuring circuit;

[0151] The tops of the second constantan wire 5, the second copper wire 6, the third constantan wire 7, and the third copper wire 8 are connected to a temperature measuring instrument for detecting the temperature T of the gas-phase medium G and the temperature T of the liquid-phase medium L .

[0152] Based on the common structure of the first-type liquid level detection device, the 1-3 type liquid level detection device (see Figure 5 , 6 ) also includes the following features:

[0153] The temperature measuring element includes a second constantan wire 5, a second copper wire 6, a third constantan wire 7, and a third copper wire 8;

[0154] The top ends of the second constantan wire 5 and the second copper wire 6 are arranged outside the top end of the outer shell 11. The second constantan wire 5 and the second copper wire 6 are located near the top of the outer shell 11 and are in the gas-phase medium. The bottom ends of the second constantan wire 5 and the second copper wire 6 are connected to form a gas-phase temperature measurement point 9, which is located below the top of the outer shell 11. The distance between the gas-phase temperature measurement point 9 and the top end of the outer shell 11 is greater than the distance between the top end P1 of the first constantan wire 1 and the top end of the outer shell 11; the second constantan wire 5, the second copper wire 6 and the gas-phase temperature measurement point 9 together form a temperature measurement circuit;

[0155] The top ends of the third constantan wire 7 and the third copper wire 8 are arranged outside the top end of the outer shell 11. The bottom ends of the third constantan wire 7 and the third copper wire 8 are connected to form a liquid-phase temperature measurement point 10, which is located near the bottom end of the outer shell 11; the third constantan wire 7, the third copper wire 8 and the liquid-phase temperature measurement point 10 together form a temperature measurement circuit;

[0156] The top ends of the second constantan wire 5, the second copper wire 6, the third constantan wire 7 and the third copper wire 8 are connected to a temperature measurement instrument for detecting the temperature T of the gas-phase medium G and the temperature T of the liquid-phase medium L .

[0157] For the 1-2 type and 1-3 type liquid level detection devices, when the overall spatial compactness requirement of the liquid level detection device is not high, the heating circuit and the temperature measurement circuit are in an independent structural form.

[0158] On the basis of the basic structure, the second type of liquid level detection device is further subdivided into the 2-1 type (see Figure 9 , 10 , 13, 14) and the 2-2 type (see Figure 11 , 12 ). The common structure of the second type of liquid level detection device is as follows:

[0159] The detection elements include the first detection wire 3, the second detection wire 4, the third detection wire 12, the first detection auxiliary copper wire 3-1, the second detection auxiliary copper wire 3-2, the third detection auxiliary copper wire 4-1, the fourth detection auxiliary copper wire 4-2, the fifth detection auxiliary copper wire 12-1 and the sixth detection auxiliary copper wire 12-2;

[0160] The resistivity values of the detection elements include the first resistivity value ρ G and the second resistivity value ρ L ; the first resistivity value ρ G refers to the resistivity value of the detection element in the gas-phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid-phase medium;

[0161] The diameters D and materials of the first detection guide wire 3 and the second detection guide wire 4 are exactly the same; the diameters D, lengths, and materials of the first detection auxiliary copper wire 3-1, the second detection auxiliary copper wire 3-2, the third detection auxiliary copper wire 4-1, and the fourth detection auxiliary copper wire 4-2 are exactly the same; there is a difference ΔL in the lengths of the first detection guide wire 3 and the second detection guide wire 4 to generate a resistance difference ΔR, and the first resistivity value ρ is determined through ΔR G ;

[0162] The arrangement methods of the detection elements are divided into two types, and either one can be selected:

[0163] The first arrangement method is as Figure 9 , 11 shown. The third detection guide wire 12 is a bent straight copper wire. The straight part is parallel to the first constantan wire 1, and the bent part is near the bottom end of the housing 11. The top end P12-1 of the third detection guide wire 12 is set inside the top end of the housing 11. The distance between the top end P12-1 of the third detection guide wire 12 and the top end of the housing 11 is greater than the distance between the top end P1 of the first constantan wire 1 and the top end of the housing 11. The tail end P12-2 of the third detection guide wire 12 is located inside the housing 11 and is above all possible liquid levels of the liquid-phase medium during liquid level measurement; the tail ends of the fifth detection auxiliary copper wire 12-1 and the sixth detection auxiliary copper wire 12-2 are connected to the top end P12-1 of the third detection guide wire 12; the top ends P3 of the first detection guide wire 3 and P4 of the second detection guide wire 4 are set inside the top end of the housing 11, close to the top end of the housing 11; the bottom ends of the first detection guide wire 3 and the second detection guide wire 4 are connected to the tail end P12-2 of the third detection guide wire 12. The first detection guide wire 3 and the second detection guide wire 4 are in the gas-phase medium during liquid level measurement; the first detection guide wire 3 is all wired in a bent manner, and the middle part of the second detection guide wire 4 is wired in a bent manner to generate a large length difference ΔL within a short vertical distance, and the rest is wired in a straight-line manner; the distance from the straight part of the third detection guide wire 12 to the first constantan wire 1 is r. At the same time, the first detection guide wire 3 and the second detection guide wire 4 are arranged within a cylindrical surface with a radius of r centered on the first constantan wire 1, and the shortest distance from each point of the first detection guide wire 3 and the second detection guide wire 4 to the first constantan wire 1 is r;

[0164] The second arrangement method is as Figure 13As shown, the third detection wire 12 is a straight copper wire parallel to the first constantan wire 1. The top end P12-1 of the third detection wire is set inside the top end of the housing 11. The distance between the top end P12-1 of the third detection wire 12 and the top end of the housing 11 is greater than the distance between the top end P1 of the first constantan wire 1 and the top end of the housing 11. The tail end P12-2 of the third detection wire 12 is near the bottom end of the housing 11. The tail ends of the first detection wire 3 and the second detection wire 4 are connected to the tail end P12-2 of the third detection wire 12. The main parts of the first detection wire 3 and the second detection wire 4 are in a spiral shape formed by the overlap of the two (the first detection wire 3 and the second detection wire 4), serving as a liquid level measurement section for measuring the liquid level of the liquid phase medium. The upper part of the first detection wire 3 is in a spiral shape formed separately, and the upper part of the second detection wire 4 is in a straight line shape. The bottom ends of the first detection wire 3 and the second detection wire 4 are connected to the tail end P12-2 of the third detection wire 12. When measuring the liquid level, the non-overlapping parts of the first detection wire 3 and the second detection wire 4 in the upper part are in the gas phase medium. A part of the liquid level measurement section is in the liquid level of the liquid phase medium, and the liquid surface of the liquid phase medium cannot exceed the entire height of the liquid level measurement section. The lengths of the parts of the first detection wire 3 and the second detection wire 4 used to form the liquid level measurement section are the same. There is a length difference ΔL between the non-overlapping parts of the first detection wire 3 and the second detection wire 4 in the upper part to generate a resistance difference ΔR, and the first resistivity value ρ is determined through ΔR G ; The liquid level measurement section is wired in a coaxial spiral and equal pitch manner. The distance between the third detection wire 12 and the first constantan wire 1 is r. At the same time, the first detection wire 3 and the second detection wire 4 are arranged within a cylindrical surface with a radius of r centered on the first constantan wire 1. The shortest distance from each point of the first detection wire 3 and the second detection wire 4 to the first constantan wire 1 is r;

[0165] The materials used for the first detection wire 3, the second detection wire 4, and the third detection wire 12 include Cu and Pt; in principle, metals with a significant resistance-temperature coefficient are used;

[0166] The detection element is divided into a first detection circuit and a second detection circuit. The total length of the first detection circuit is L L , which is composed of the first detection wire 3, the first detection auxiliary copper wire 3-1, the second detection auxiliary copper wire 3-2, the third detection wire 12, the fifth detection auxiliary copper wire 12-1, and the sixth detection auxiliary copper wire 12-2. The first detection auxiliary copper wire 3-1 and the second detection auxiliary copper wire 3-2 are taken as a group, and the fifth detection auxiliary copper wire 12-1 and the sixth detection auxiliary copper wire 12-2 are taken as a group. Copper wires are used and wired to the resistance measuring instrument in a four-wire system to obtain the total resistance R of the first detection circuit L ; The total length of the second detection circuit is L S, which is composed of a second detection guide wire 4, a third detection auxiliary copper wire 4-1, a fourth detection auxiliary copper wire 4-2, a third detection guide wire 12, a fifth detection auxiliary copper wire 12-1 and a sixth detection auxiliary copper wire 12-2. The third detection auxiliary copper wire 4-1 and the fourth detection auxiliary copper wire 4-2 form a group, and the fifth detection auxiliary copper wire 12-1 and the sixth detection auxiliary copper wire 12-2 form a group. Copper wires are used and connected to a resistance measuring instrument in a four-wire system to obtain the total resistance R of the second detection circuit S ; where L L -L S =ΔL, ΔL>0;

[0167] When performing liquid level detection, any one of the first detection circuit and the second detection circuit is selected to achieve liquid level detection;

[0168] When the first detection circuit is selected as the liquid level detection circuit, according to the total length L L and the total resistance R L of the first detection circuit, the liquid level of the liquid phase medium in the container is determined;

[0169] When the second detection circuit is selected as the liquid level detection circuit, according to the total length L S and the total resistance R S of the second detection circuit, the liquid level of the liquid phase medium in the container is determined.

[0170] On the basis of the common structure of the second-type liquid level detection device, the 2-1 type liquid level detection device (see Figure 9 , 10 , 13, 14) also has the following characteristics: The temperature measuring element includes a third constantan wire 7 and a third copper wire 8. The tops of the third constantan wire 7 and the third copper wire 8 are both located outside the top of the housing 11. The bottom end of the third constantan wire 7 is connected to the top end P1 of the first constantan wire 1; the bottom end of the third copper wire 8 is connected to the top end P2 of the first copper wire 2. The bottom ends of the first constantan wire 1 and the first copper wire 2 are connected to form a liquid phase temperature measuring point 10; The third constantan wire 7 and the third copper wire 8 together with the first constantan wire 1, the first copper wire 2 and the liquid phase temperature measuring point 10 form a temperature measuring circuit; The tops of the third constantan wire 7 and the third copper wire 8 are connected to a temperature measuring instrument for detecting the temperature T of the liquid phase medium L . The 2-1 type liquid level detection device can simplify the structure and save layout space by sharing the first constantan wire 1 and the first copper wire 2 for the temperature measuring element and the heating element.

[0171] On the basis of the common structure of the second-type liquid level detection device, the 2-2 type liquid level detection device (see Figure 11 , 12 ) also has the following characteristics:

[0172] The temperature measuring element includes a third constantan wire 7 and a third copper wire 8; the top ends of the third constantan wire 7 and the third copper wire 8 are arranged outside the top end of the housing 11, and the bottom ends of the third constantan wire 7 and the third copper wire 8 are connected to form a liquid-phase temperature measuring point 10; the third constantan wire 7, the third copper wire 8 and the liquid-phase temperature measuring point 10 together form a temperature measuring circuit; the top ends of the third constantan wire 7 and the third copper wire 8 are connected to a temperature measuring instrument for detecting the temperature T of the liquid-phase medium L .

[0173] When the overall spatial compactness requirement of the liquid level detection device is not high, the temperature measuring circuit and the heating circuit can be independent of each other. At this time, the heating circuit and the temperature measuring circuit of the 2-2 type liquid level detection device no longer share the first constantan wire 1

[0174] The present invention also provides a liquid level detection method (Method 1) for a liquid level detection device of the 1-1 type, 1-2 type or 1-3 type and with the detection element adopting the first arrangement method, including the following steps

[0175] Step S1, vertically place the liquid level detection device into the container to be detected, with the liquid-phase temperature measuring point 10 close to but not touching the bottom of the container, ensuring that the liquid-phase temperature measuring point 10 can always be submerged by the liquid-phase medium in the container during the test and has a representative liquid-phase medium temperature; ensure that the gas-phase temperature measuring point 9 is close to the top of the container and is always in the gas-phase medium during the test

[0176] Step S2, connect the top ends of the first heating auxiliary copper wire 1-1 and the second heating auxiliary copper wire 2-1 to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire 1 through the DC power supply to cause a sufficiently significant change in the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to meet the measurement requirements

[0177] Step S3, use a constantan wire to connect the top end of the second constantan wire 5 to the negative terminal of the wiring terminal of the temperature measuring instrument, and use a copper wire to connect the top end of the second copper wire 6 to the positive terminal of the wiring terminal of the temperature measuring instrument to form the first temperature measuring circuit, and measure and obtain the gas-phase medium temperature T through the gas-phase temperature measuring point 9 G ; use a constantan wire to connect the top end of the third constantan wire 7 to the negative terminal of the wiring terminal of the temperature measuring instrument, and use a copper wire to connect the top end of the third copper wire 8 to the positive terminal of the wiring terminal of the temperature measuring instrument to form the second temperature measuring circuit, and measure and obtain the liquid-phase medium temperature T through the liquid-phase temperature measuring point 10 L ; or use a T-type thermocouple compensating wire to connect the top ends of the second constantan wire 5, the second copper wire 6, the third constantan wire 7 and the third copper wire 8 to the temperature measuring instrument respectively to obtain the gas-phase medium temperature T G and the liquid-phase medium temperature T L ;

[0178] Step S4: Collect the temperature T of the gas-phase medium and the temperature T of the liquid-phase medium through a temperature detection instrument and a channel switch, and determine the first resistivity value ρ and the second resistivity value ρ according to the resistivity-temperature relationship of the detection element. G L G L ;

[0179] Step S5: Connect the detection element to the resistance measuring instrument in a four-wire system, that is, use 2 copper wires respectively to connect the top of the first detection auxiliary copper wire 3-1 and the top of the second detection auxiliary copper wire 3-2 to one pole of a group of measurement channels of the resistance measuring instrument in a four-wire system, and connect the top of the third detection auxiliary copper wire 4-1 and the top of the fourth detection auxiliary copper wire 4-2 to the other pole of a group of measurement channels of the resistance measuring instrument in a four-wire system to measure the total resistance R of the first detection wire 3 and the second detection wire 4.

[0180] Step S6: Determine the liquid level h1 of the liquid-phase medium in the container according to the diameter D and total length L of the detection element using the following formula. The R in the formula refers to the total resistance of the first detection wire 3 and the second detection wire 4.

[0181]

[0182]

[0183] The present invention also provides a liquid level detection method (Method 2) for a liquid level detection device of type 1-1, 1-2 or 1-3 with the detection element adopting the second layout method, including the following steps:

[0184] Based on steps S1 to S6 of Method 1, it further includes step S7: further determine the liquid level h2 of the liquid-phase medium in the container according to the corresponding relationship between the length of the unit pitch and the vertical height of the detection unit. Specifically, if the relationship coefficient between the length L of the unit pitch of the detection unit and the vertical height h is α, that is, L = α×h, then the liquid level h2 is: C C C C

[0185]

[0186] In Method 1 and Method 2, when the liquid level detection adopts a liquid level detection device with a compact structure as shown in Fig. (1-1) and Fig. (1-1), the heating circuit and the two temperature measurement circuits share the first constantan wire 1, and the heating and temperature measurement timing need to be strictly controlled to ensure measurement accuracy and instrument safety. Specifically, the heating period and the temperature measurement period should maintain a time interval of not less than the second level. Figure 1 Figure 7 ​​​

[0187] The present invention also provides a liquid level detection method (Method Three) for a liquid level detection device of Type 2-1 or Type 2-2 with the first arrangement of detection elements, including the following steps:

[0188] Step S1: Vertically place the liquid level detection device into the container to be detected. The liquid-phase temperature measurement point 10 is close to but does not touch the bottom of the container, ensuring that during the test, the liquid-phase temperature measurement point 10 can always be submerged by the liquid-phase medium in the container, having a representative liquid-phase medium temperature; ensuring that during the test, the part of the detection element with a length difference ΔL is close to the top of the container and is always in the gas-phase medium (in the technical solution where the third detection wire 12 is a bent straight copper wire, it refers to the first detection wire 3 and the second detection wire 4; in the technical solution where the third detection wire 12 is a straight copper wire parallel to the first constantan wire 1 and the main parts of the first detection wire 3 and the second detection wire 4 are a spiral formed by their overlap, it refers to the non-overlapping parts of the upper parts of the first detection wire 3 and the second detection wire 4);

[0189] Step S2: Connect the top ends of the first heating auxiliary copper wire 1-1 and the second heating auxiliary copper wire 2-1 to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire 1 through the DC power supply to cause a sufficiently significant change in the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to meet the measurement requirements;

[0190] Step S3: Use a constantan wire to connect the top end of the third constantan wire 7 to the negative terminal of the wiring terminal of the temperature measuring instrument, and use a copper wire to connect the top end of the third copper wire 8 to the positive terminal of the wiring terminal of the temperature measuring instrument to form a temperature measurement circuit, and measure the liquid-phase medium temperature T through the liquid-phase temperature measurement point 10 L ; or use a T-type thermocouple compensating wire to connect the top ends of the third constantan wire 7 and the third copper wire 8 to the temperature measuring instrument respectively to obtain the liquid-phase medium temperature T L ;

[0191] Step S4: Determine the second resistivity value ρ according to the resistivity-temperature relationship of the detection element L ; (that is, the resistivity value of the detection element in the liquid-phase medium)

[0192] Step S5, connect the detection element to the resistance measuring instrument in a four-wire system, that is, use 2 copper wires to connect the top of the first detection auxiliary copper wire 3-1 and the top of the second detection auxiliary copper wire 3-2 to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire 12-1 and the top of the sixth detection auxiliary copper wire 12-2 to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; use 2 copper wires to connect the top of the third detection auxiliary copper wire 4-1 and the top of the fourth detection auxiliary copper wire 4-2 to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire 12-1 and the top of the sixth detection auxiliary copper wire 12-2 to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; through the resistance measuring instrument and the channel switch, obtain the total resistance R of the first detection loop composed of the first detection wire 3 and the third detection wire 12 L , and obtain the total resistance R of the second detection loop composed of the second detection wire 4 and the third detection wire 12 S ; determine the resistance difference ΔR between the two loops = R L -R S ;

[0193] Step S6, according to the diameter D of the detection element and the length difference ΔL between the first detection wire 3 and the second detection wire 4, determine the first resistivity value ρ through the following formula G ;

[0194]

[0195] In the formula, S refers to the cross-sectional area of the first detection wire 3 and the second detection wire 4;

[0196] Step S7,

[0197] According to the total length L L and the total resistance R L of the first detection loop, the first resistivity value ρ G and the second resistivity value ρ L , determine the liquid level h1 of the liquid-phase medium in the container through the following formula;

[0198]

[0199] Or, according to the total length L S and the total resistance R S of the second detection loop, the first resistivity value ρ G and the second resistivity value ρ L , determine the liquid level h1 of the liquid-phase medium in the container through the following formula;

[0200]

[0201] The present invention also provides a liquid level detection method (Method Four) for a liquid level detection device of the 2-1 type or 2-2 type with the second arrangement of detection elements, including the following steps:

[0202] Based on steps 1 to S7 of Method Three, it further includes step S8. According to the correspondence between the length of the unit pitch of the liquid level measurement section detection unit and the vertical height, the liquid level h2 of the liquid phase medium in the container is further determined. Specifically, if the length L of the unit pitch of the liquid level measurement section detection element C and the vertical height h C have a relationship coefficient of α, that is, L C = α×h C , then the liquid level h2 is:

[0203] Or,

[0204] In Method Three and Method Four, when the liquid level detection uses the liquid level detection device shown in the attached Figure 2-1 type, the heating circuit and the liquid phase temperature measurement circuit share the first constantan wire 1. It is necessary to strictly control the heating and temperature measurement timing to ensure measurement accuracy and instrument safety. Specifically, the heating period and the temperature measurement period should maintain a time interval not less than the second level.

[0205] Compared with the linear structure, the detection element using a spiral structure can significantly improve the liquid level measurement accuracy. Because at the gas-liquid two-phase interface, the temperature of the detection element does not jump, but there is a temperature transition zone, which changes gradually. That is, from bottom to top, the temperature gradually rises from the liquid phase temperature to the gas phase temperature. The resistivity change here is the same as the temperature, from bottom to top, from the liquid phase resistivity ρ L gradually rising to the gas phase resistivity ρ G . However, in actual measurement, it is not possible to accurately describe this gradual process in the measurement calculation process, which will introduce measurement errors.

[0206] When using a spiral structure, the detection element has the same length of transition interval at the two-phase interface. However, the spiral structure has a large extension in the horizontal direction. That is, when using a spiral structure, the influence of the transition interval length at the two-phase interface on the vertical liquid level only becomes the projection height of the original transition interval length spiral line in the vertical direction, greatly weakening its influence on the vertical liquid level detection and significantly improving the measurement accuracy and accuracy.

[0207] The device described in the present invention is not limited to the embodiments described in the specific embodiments. Those skilled in the art can obtain other embodiments according to the technical solutions of the present invention, which also belong to the scope of the technical innovation of the present invention.

Claims

1. A liquid level detection device for measuring the liquid level of a liquid phase medium inside a container, characterized in that: it includes a heating element, a temperature measuring element and a detection element arranged in a housing (11). The gas phase medium and the liquid phase medium around the housing (11) are heated by the heating element, the gas phase medium or the liquid phase medium is measured for temperature by the temperature measuring element, and the liquid level of the liquid phase medium in the container is determined by combining the resistivity value and the resistance value of the detection element; this liquid level detection device is divided into two major categories, namely the first type and the second type, both having the following same basic structure: the housing (11) is of a cylindrical structure and has heat conduction ability; the heating element is composed of a first constantan wire (1), a first copper wire (2), a first heating auxiliary copper wire (1-1) and a second heating auxiliary copper wire (2-1). The top end (P1) of the first constantan wire (1) is arranged inside the top end of the housing (11), close to the top end of the housing (11). The top end (P2) of the first copper wire (2) is arranged outside the top end of the housing (11). The top end of the first heating auxiliary copper wire (1-1) is arranged outside the top end of the housing (11). The second heating auxiliary copper wire (2-1) is arranged outside the top end of the housing (11). The bottom end of the first constantan wire (1) and the bottom end of the first copper wire (2) are connected and arranged inside the bottom end of the housing (11), close to the bottom end of the housing (11). The tail end of the first heating auxiliary copper wire (1-1) is connected to the top end (P1) of the first constantan wire (1), and the tail end of the second heating auxiliary copper wire (2-1) is connected to the top end (P2) of the first copper wire (2). The top ends of the first heating auxiliary copper wire (1-1) and the second heating auxiliary copper wire (2-1) are used to connect the positive and negative electrodes of the power supply to form a heating circuit; the first constantan wire (1) is located at the axis position of the housing (11). When measuring the liquid level, the first constantan wire (1) vertically penetrates the gas phase medium and the liquid phase medium. The specific form of the first constantan wire (1) includes a straight line shape or a spiral shape. When the first constantan wire (1) is in a straight line shape, the first constantan wire (1) itself is located at the center of the entire liquid level detection device. When the first constantan wire (1) is in a spiral shape, the center of the spiral structure coincides with the center of the entire liquid level detection device, so that the first constantan wire (1) dissipates heat isotropically from the center of the liquid level detection device to the outside; The temperature measuring element includes a liquid-phase temperature measuring point (10), and the liquid-phase temperature measuring point (10) is a temperature measuring junction of a T-type thermocouple composed of a copper wire and a constantan wire; the liquid-phase temperature measuring point (10) is located near the bottom end of the housing (11) and is used to obtain the temperature T of the liquid-phase medium L ; the connection structure of the liquid-phase temperature measuring point (10) is any way that can be firmly fixed to the same junction, including arc welding, hydrogen arc welding, gas welding, and brine welding; after constructing the basic structure of the T-type thermocouple with the liquid-phase temperature measuring point (10), the obtained liquid-phase temperature measuring point (10) is calibrated to obtain an accurate liquid-phase medium temperature T during the subsequent medium temperature measurement L ; the inside of the housing (11) is filled with an insulating and heat-conducting substance to fix the detection element and the heating element and maintain their relative positions. Both the detection element and the heating element are insulated externally to ensure the insulation performance; The temperature measuring element of the first type of liquid level detection device further includes a gas-phase temperature measuring point (9), and the gas-phase temperature measuring point (9) is the temperature measuring junction of a T-type thermocouple composed of copper wire and constantan wire; the gas-phase temperature measuring point (9) is located inside the outer shell (11) and above all possible liquid levels of the liquid-phase medium, and is used to obtain the gas-phase medium temperature T G ; the connection structure of the gas-phase temperature measuring point (9) is any way that can be firmly fixed to the same junction, including arc welding, hydrogen arc welding, gas welding, and saline welding; after constructing the basic structure of the gas-phase temperature measuring point (9) to form a T-type thermocouple, calibrate the obtained gas-phase temperature measuring point (9) to obtain an accurate gas-phase medium temperature T during subsequent medium temperature measurement G ; on the basis of the above basic structure, the second type of liquid level detection device is further subdivided into type 2-1 and type 2-2. The type 2-2 liquid level detection device also has the following characteristics: The temperature measuring element includes a third constantan wire (7) and a third copper wire (8); the top ends of the third constantan wire (7) and the third copper wire (8) are arranged outside the top end of the housing (11), and the bottom ends of the third constantan wire (7) and the third copper wire (8) are connected to form the liquid-phase temperature measuring point (10); the third constantan wire (7), the third copper wire (8) and the liquid-phase temperature measuring point (10) together form a temperature measuring circuit; the top ends of the third constantan wire (7) and the third copper wire (8) are connected to a temperature measuring instrument for detecting the temperature T of the liquid-phase medium L .

2. A liquid level detection device according to claim 1, characterized in that, in Based on the basic structure, the first type of liquid level detection device is further subdivided into types 1-1, 1-2, and 1-3; the common structure of the first type of liquid level detection device is as follows: The detection element includes a first detection wire (3), a second detection wire (4), a first detection auxiliary copper wire (3-1), a second detection auxiliary copper wire (3-2), a third detection auxiliary copper wire (4-1), and a fourth detection auxiliary copper wire (4-2). The lengths, diameters D, and materials of the first detection wire (3) and the second detection wire (4) are exactly the same; the top end (P3) of the first detection wire (3) is set inside the top end of the housing (11), and the distance between the top end (P3) of the first detection wire (3) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11). The top end (P4) of the second detection wire (4) is set inside the top end of the housing (11), and the distance between the top end (P4) of the second detection wire (4) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11). The top end of the first detection auxiliary copper wire (3-1) is set outside the top end of the housing (11), and the tail end of the first detection auxiliary copper wire (3-1) is connected to the top end (P3) of the first detection wire (3). The top end of the second detection auxiliary copper wire (3-2) is set outside the top end of the housing (11), and the tail end of the second detection auxiliary copper wire (3-2) is connected to the top end (P3) of the first detection wire (3). The top end of the third detection auxiliary copper wire (4-1) is set outside the top end of the housing (11), and the tail end of the third detection auxiliary copper wire (4-1) is connected to the top end (P4) of the second detection wire (4). The top end of the fourth detection auxiliary copper wire (4-2) is set outside the top end of the housing (11), and the tail end of the fourth detection auxiliary copper wire (4-2) is connected to the top end (P4) of the second detection wire (4). The bottom ends of the first detection wire (3) and the second detection wire (4) are connected, and the connection point is near the bottom end of the housing (11). When measuring the liquid level, it penetrates the gas-phase medium and the liquid-phase medium to be detected from top to bottom to form a resistance measurement circuit; the first detection auxiliary copper wire (3-1) and the second detection auxiliary copper wire (3-2) are taken as a group, and the third detection auxiliary copper wire (4-1) and the fourth detection auxiliary copper wire (4-2) are taken as a group. They are respectively connected to a resistance measurement instrument in a four-wire system from their top ends to measure the resistance value of the detection element; The arrangement of the detection element is divided into two types, and either one can be selected: The first arrangement method: except for the bottom end parts that are connected to each other, the rest of the first detection wire (3) and the second detection wire (4) are parallel straight lines, In the second arrangement mode, the first detection wire (3) and the second detection wire (4) overlap to form a co - helical shape with an equal pitch; In both modes, the shortest distance from each point of the first detection wire (3) and the second detection wire (4) to the first constantan wire (1) remains the same; The materials used for the first detection wire (3) and the second detection wire (4) include Cu and Pt; The gas - phase temperature measurement point (9), the first detection wire (3) and the second detection wire (4) are at the same distance from the first constantan wire (1); The resistance value of the detection element includes the total resistance R of the first detection wire (3) and the second detection wire (4); The resistivity value of the detection element includes a first resistivity value ρ G and a second resistivity value ρ L ; the first resistivity value ρ G refers to the resistivity value of the detection element in the gas-phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid-phase medium.

3. A liquid - level detection device according to claim 2, characterized in that, on the basis of the common structure of the first - type liquid - level detection device, the 1 - 1 type liquid - level detection device further has the following characteristics: The temperature - measuring element includes a second constantan wire (5), a second copper wire (6), a third constantan wire (7) and a third copper wire (8); The top end of the second constantan wire (5) and the top end of the second copper wire (6) are arranged outside the top end of the housing (11). The second copper wire (6) is near the top of the housing (11), and the bottom end of the second copper wire (6) is arranged on the first constantan wire (1) to form the gas - phase temperature measurement point (9). The bottom end of the second constantan wire (5) is connected to the top end (P1) of the first constantan wire (1). The second constantan wire (5) and the second copper wire (6) together with the first constantan wire (1) and the gas - phase temperature measurement point (9) form a temperature - measuring circuit; The top end of the third constantan wire (7) and the top end of the third copper wire (8) are arranged outside the top end of the housing (11). The bottom end of the third constantan wire (7) is connected to the top end (P1) of the first constantan wire (1), and the bottom end of the third copper wire (8) is connected to the top end (P2) of the first copper wire (2). The bottom ends of the first constantan wire (1) and the first copper wire (2) are connected to form the liquid - phase temperature measurement point (10). The third constantan wire (7) and the third copper wire (8) together with the first constantan wire (1), the first copper wire (2) and the liquid - phase temperature measurement point (10) form a temperature - measuring circuit; The tops of the second constantan wire (5), the second copper wire (6), the third constantan wire (7) and the third copper wire (8) are connected to a temperature measuring instrument for detecting the temperature T of the gaseous medium G and the temperature T of the liquid medium L .

4. A liquid - level detection device according to claim 2, characterized in that, on the basis of the common structure of the first - type liquid - level detection device, the 1 - 2 type liquid - level detection device further has the following characteristics: The temperature - measuring element includes a second constantan wire (5), a second copper wire (6), a third constantan wire (7) and a third copper wire (8); The top end of the second constantan wire (5) and the top end of the second copper wire (6) are disposed outside the top end of the housing (11). The second copper wire (6) is located near the top of the housing (11). The bottom end of the second copper wire (6) is disposed on the second constantan wire (5) and forms the gas-phase temperature measurement point (9). The gas-phase temperature measurement point (9) is located below the top of the housing (11). The distance between the gas-phase temperature measurement point (9) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11). The second constantan wire (5), the second copper wire (6) and the gas-phase temperature measurement point (9) together form a temperature measurement circuit; The top end of the third constantan wire (7) and the top end of the third copper wire (8) are disposed outside the top end of the housing (11). The bottom end of the third constantan wire (7) is disposed on the second constantan wire (5). The connection position (P5) between the bottom end of the third constantan wire (7) and the second constantan wire (5) is located inside or outside the top end of the housing (11); The bottom end of the second constantan wire (5) and the bottom end of the third copper wire (8) are connected to form the liquid-phase temperature measurement point (10). The third constantan wire (7), the third copper wire (8) together with the second constantan wire (5) and the liquid-phase temperature measurement point (10) form a temperature measurement circuit; The tops of the second constantan wire (5), the second copper wire (6), the third constantan wire (7) and the third copper wire (8) are connected to a temperature measuring instrument for detecting the temperature T of the gaseous medium G and the temperature T of the liquid medium L .

5. A liquid level detection device according to claim 2, characterized in that, on the basis of the common structure of the first type of liquid level detection device, the 1-3 type of liquid level detection device further has the following characteristics: The temperature measuring element includes a second constantan wire (5), a second copper wire (6), a third constantan wire (7) and a third copper wire (8); The top end of the second constantan wire (5) and the top end of the second copper wire (6) are disposed outside the top end of the housing (11). The second constantan wire (5) and the second copper wire (6) are located near the top of the housing (11). The bottom end of the second constantan wire (5) and the bottom end of the second copper wire (6) are connected to form the gas-phase temperature measurement point (9). The gas-phase temperature measurement point (9) is located below the top of the housing (11). The distance between the gas-phase temperature measurement point (9) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11). The second constantan wire (5), the second copper wire (6) and the gas-phase temperature measurement point (9) together form a temperature measurement circuit; The top end of the third constantan wire (7) and the top end of the third copper wire (8) are disposed outside the top end of the housing (11). The bottom end of the third constantan wire (7) and the bottom end of the third copper wire (8) are connected to form the liquid-phase temperature measurement point (10). The third constantan wire (7), the third copper wire (8) and the liquid-phase temperature measurement point (10) together form a temperature measurement circuit; The tops of the second constantan wire (5), the second copper wire (6), the third constantan wire (7) and the third copper wire (8) are connected to a temperature measuring instrument for detecting the temperature T of the gaseous medium G and the temperature T of the liquid medium L .

6. A liquid level detection device according to claim 1, characterized in that, the common structure of the second type of liquid level detection device is: The detection element includes a first detection wire (3), a second detection wire (4), a third detection wire (12), a first detection auxiliary copper wire (3-1), a second detection auxiliary copper wire (3-2), a third detection auxiliary copper wire (4-1), a fourth detection auxiliary copper wire (4-2), a fifth detection auxiliary copper wire (12-1) and a sixth detection auxiliary copper wire (12-2); The resistivity value of the detection element includes a first resistivity value ρ G and a second resistivity value ρ L ; the first resistivity value ρ G refers to the resistivity value of the detection element in the gas-phase medium, and the second resistivity value ρ L refers to the resistivity value of the detection element in the liquid-phase medium; The diameters D and materials of the first detection guide wire (3) and the second detection guide wire (4) are exactly the same; the diameters D, lengths and materials of the first detection auxiliary copper wire (3-1), the second detection auxiliary copper wire (3-2), the third detection auxiliary copper wire (4-1) and the fourth detection auxiliary copper wire (4-2) are exactly the same; there is a difference ΔL in the lengths of the first detection guide wire (3) and the second detection guide wire (4) to generate a resistance difference ΔR, and the first resistivity value ρ is determined by the ΔR G ; The arrangement of the detection element is divided into two types, and either one can be selected: In the first arrangement, the third detection wire (12) is a bent straight copper wire, the straight part is parallel to the first constantan wire (1), the bent part is near the bottom end of the housing (11), the top end (P12-1) of the third detection wire is arranged inside the top end of the housing (11), the distance between the top end (P12-1) of the third detection wire (12) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11), the tail end (P12-2) of the third detection wire (12) is located inside the housing (11) and above all possible liquid levels of the liquid-phase medium during liquid level measurement; the tail ends of the fifth detection auxiliary copper wire (12-1) and the sixth detection auxiliary copper wire (12-2) are connected to the top end (P12-1) of the third detection wire (12); the top ends (P3) of the first detection wire (3) and the second detection wire (4) are arranged inside the top end of the housing (11), close to the top end of the housing (11); the bottom ends of the first detection wire (3) and the second detection wire (4) are connected to the tail end (P12-2) of the third detection wire (12), and the first detection wire (3) and the second detection wire (4) are in the gas-phase medium during liquid level measurement; the first detection wire (3) is entirely wired in a bent manner, the middle part of the second detection wire (4) is wired in a bent manner, and the rest is wired in a straight-line manner; the distance from the straight part of the third detection wire (12) to the first constantan wire (1) is r, and at the same time, the first detection wire (3) and the second detection wire (4) are arranged within a cylindrical surface with a radius of r centered on the first constantan wire (1), and the shortest distance from each point of the first detection wire (3) and the second detection wire (4) to the first constantan wire (1) is r; The second arrangement mode: the third detection wire (12) is a straight copper wire parallel to the first constantan wire (1). The top end (P12-1) of the third detection wire is arranged inside the top end of the housing (11). The distance between the top end (P12-1) of the third detection wire (12) and the top end of the housing (11) is greater than the distance between the top end (P1) of the first constantan wire (1) and the top end of the housing (11). The tail end (P12-2) of the third detection wire (12) is located near the bottom end of the housing (11). The tail ends of the first detection wire (3) and the second detection wire (4) are connected to the tail end (P12-2) of the third detection wire (12). The main parts of the first detection wire (3) and the second detection wire (4) are in a spiral shape formed by overlapping each other, serving as a liquid level measurement section for measuring the liquid level of the liquid-phase medium. The upper part of the first detection wire (3) is in a spiral shape formed separately, and the upper part of the second detection wire (4) is in a straight line shape. The bottom ends of the first detection wire (3) and the second detection wire (4) are connected to the tail end (P12-2) of the third detection wire (12). When measuring the liquid level, the non-overlapping parts of the first detection wire (3) and the second detection wire (4) in the upper part are in the gas-phase medium. A part of the liquid level measurement section is in the liquid level of the liquid-phase medium, and the liquid surface of the liquid-phase medium cannot exceed the total height of the liquid level measurement section. The lengths of the first detection wire (3) and the second detection wire (4) used to form the liquid level measurement section are the same. There is a length difference ΔL between the non-overlapping parts of the first detection wire (3) and the second detection wire (4) in the upper part to generate a resistance difference ΔR, and the first resistivity value ρ is determined through the ΔR. G ; The liquid level measurement section is wired in a coaxial spiral and equal pitch manner. The distance between the third detection wire (12) and the first constantan wire (1) is r. At the same time, the first detection wire (3) and the second detection wire (4) are arranged in a cylindrical surface with a radius of r centered on the first constantan wire (1). The shortest distance from each point of the first detection wire (3) and the second detection wire (4) to the first constantan wire (1) is r. The materials used for the first detection wire (3), the second detection wire (4) and the third detection wire (12) include Cu and Pt; The detection element is divided into a first detection circuit and a second detection circuit. The total length of the first detection circuit is L L , which is composed of the first detection wire (3), the first detection auxiliary copper wire (3-1), the second detection auxiliary copper wire (3-2), the third detection wire (12), the fifth detection auxiliary copper wire (12-1) and the sixth detection auxiliary copper wire (12-2). The first detection auxiliary copper wire (3-1) and the second detection auxiliary copper wire (3-2) are grouped together, and the fifth detection auxiliary copper wire (12-1) and the sixth detection auxiliary copper wire (12-2) are grouped together. Copper wires are used and connected to a resistance measuring instrument in a four-wire system to obtain the total resistance R of the first detection circuit L ; The total length of the second detection circuit is L S , which is composed of the second detection wire (4), the third detection auxiliary copper wire (4-1), the fourth detection auxiliary copper wire (4-2), the third detection wire (12), the fifth detection auxiliary copper wire (12-1) and the sixth detection auxiliary copper wire (12-2). The third detection auxiliary copper wire (4-1) and the fourth detection auxiliary copper wire (4-2) are grouped together, and the fifth detection auxiliary copper wire (12-1) and the sixth detection auxiliary copper wire (12-2) are grouped together. Copper wires are used and connected to a resistance measuring instrument in a four-wire system to obtain the total resistance R of the second detection circuit S ; where, L L -L S =ΔL, ΔL>0; During liquid level detection, any one of the first detection circuit and the second detection circuit is selected to achieve liquid level detection; When the first detection circuit is selected as the liquid level detection circuit, according to the total length L of the first detection circuit L and the total resistance R L , determine the liquid level of the liquid-phase medium in the container; When selecting the second detection circuit as the liquid level detection circuit, according to the total length L of the second detection circuit S and the total resistance R S , determine the liquid level of the liquid phase medium in the container.

7. A liquid level detection device according to claim 6, characterized in that, in Based on the common structure of the second type of liquid level detection device, the 2-1 type of liquid level detection device further has the following characteristics: The temperature measuring element includes a third constantan wire (7) and a third copper wire (8); the tops of the third constantan wire (7) and the third copper wire (8) are both located outside the top of the outer shell (11). The bottom end of the third constantan wire (7) is connected to the top end (P1) of the first constantan wire (1), and the bottom end of the third copper wire (8) is connected to the top end (P2) of the first copper wire (2). The bottom ends of the first constantan wire (1) and the first copper wire (2) are connected to form the liquid-phase temperature measuring point (10); the third constantan wire (7) and the third copper wire (8) together with the first constantan wire (1), the first copper wire (2), and the liquid-phase temperature measuring point (10) form a temperature measuring circuit; the tops of the third constantan wire (7) and the third copper wire (8) are connected to a temperature measuring instrument for detecting the temperature T of the liquid-phase medium L .

8. A liquid level detection method for a liquid level detection device as described in any one of claims 3, 4, or 5. For the liquid level detection device of the 1-1 type, the 1-2 type, or the 1-3 type and with the first arrangement mode of the detection element, the method includes the following steps: Step S1, vertically place the liquid level detection device into the container to be detected. The liquid-phase temperature measurement point (10) is close to but does not contact the bottom of the container, ensuring that the liquid-phase temperature measurement point (10) can always be submerged by the liquid-phase medium in the container during the test; ensure that the gas-phase temperature measurement point (9) is close to the top of the container and always remains in the gas-phase medium during the test; Step S2, connect the top ends of the first heating auxiliary copper wire (1-1) and the second heating auxiliary copper wire (2-1) to the two poles of a DC power supply respectively. Apply a constant electric heating power to the first constantan wire (1) through the DC power supply to cause the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to change; Step S3: Connect the top end of the second constantan wire (5) to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connect the top end of the second copper wire (6) to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form the first temperature measuring loop, and measure the gas phase medium temperature T through the gas phase temperature measuring point (9). G Connect the top end of the third constantan wire (7) to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connect the top end of the third copper wire (8) to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form the second temperature measuring loop, and measure the liquid phase medium temperature T through the liquid phase temperature measuring point (10). L Alternatively, use a T-type thermocouple compensating wire to connect the top ends of the second constantan wire (5), the second copper wire (6), the third constantan wire (7), and the third copper wire (8) to the temperature measuring instrument respectively to obtain the gas phase medium temperature T G and the liquid phase medium temperature T L ; Step S4, collect the temperature T of the gaseous medium through the temperature detection instrument and the channel switch G and the temperature T of the liquid medium L , determine the first resistivity value ρ according to the resistivity-temperature relationship of the detection element G and the second resistivity value ρ L ; Step S5, connect the detection element to a resistance measuring instrument in a four-wire system, that is, respectively use 2 copper wires to connect the top ends of the first detection auxiliary copper wire (3-1) and the second detection auxiliary copper wire (3-2) to one pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top ends of the third detection auxiliary copper wire (4-1) and the fourth detection auxiliary copper wire (4-2) to the other pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument to measure the total resistance R of the first detection wire (3) and the second detection wire (4); Step S6, according to the diameter D and total length L of the detection element, determine the liquid level h1 of the liquid-phase medium in the container according to the following formula In the formula, R refers to the total resistance of the first detection wire (3) and the second detection wire (4).

9. A liquid level detection method for a liquid level detection device as described in any one of claims 3, 4, or 5. For the liquid level detection device of the 1-1 type, the 1-2 type, or the 1-3 type and with the second arrangement mode of the detection element, the method includes the following steps: Step S1, vertically place the liquid level detection device into the container to be detected. The liquid-phase temperature measurement point (10) is close to but does not contact the bottom of the container, ensuring that the liquid-phase temperature measurement point (10) can always be submerged by the liquid-phase medium in the container during the test; ensure that the gas-phase temperature measurement point (9) is close to the top of the container and always remains in the gas-phase medium during the test; Step S2, connect the top ends of the first heating auxiliary copper wire (1-1) and the second heating auxiliary copper wire (2-1) to the two poles of a DC power supply respectively. Apply a constant electric heating power to the first constantan wire (1) through the DC power supply to cause the temperatures of the gas-phase medium and the liquid-phase medium at the detection element to change; Step S3: Connect the top end of the second constantan wire (5) to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connect the top end of the second copper wire (6) to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form the first temperature measuring loop, and measure the gas phase medium temperature T through the gas phase temperature measuring point (9). G Connect the top end of the third constantan wire (7) to the negative terminal of the wiring terminal of the temperature measuring instrument using a constantan wire, and connect the top end of the third copper wire (8) to the positive terminal of the wiring terminal of the temperature measuring instrument using a copper wire to form the second temperature measuring loop, and measure the liquid phase medium temperature T through the liquid phase temperature measuring point (10). L Alternatively, use a T-type thermocouple compensating wire to connect the top ends of the second constantan wire (5), the second copper wire (6), the third constantan wire (7), and the third copper wire (8) to the temperature measuring instrument respectively to obtain the gas phase medium temperature T G and the liquid phase medium temperature T L ; Step S4, collect the temperature T of the gaseous medium through the temperature detection instrument and the channel switch G and the temperature T of the liquid medium L , determine the first resistivity value ρ according to the resistivity-temperature relationship of the detection element G and the second resistivity value ρ L ; Step S5: Connect the detection element to a resistance measuring instrument in a four-wire system, that is, use 2 copper wires to connect the top of the first detection auxiliary copper wire (3-1) and the top of the second detection auxiliary copper wire (3-2) to one pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the third detection auxiliary copper wire (4-1) and the top of the fourth detection auxiliary copper wire (4-2) to the other pole of a group of measurement channels of the four-wire measurement of the resistance measuring instrument, and measure the total resistance R of the first detection wire (3) and the second detection wire (4); Step S6: Determine the liquid level h1 of the liquid phase medium in the container according to the diameter D and total length L of the detection element, according to the following formula In the formula, R refers to the total resistance of the first detection wire (3) and the second detection wire (4); Step S7, further determine the liquid level h2 of the liquid-phase medium in the container according to the correspondence between the length of the unit pitch of the detection element and the vertical height. Specifically, if the length L of the unit pitch of the detection element C and the vertical height h C have a relationship coefficient of α, that is, L C = α × h C , then the liquid level h2 is:

10. A liquid level detection method for a liquid level detection device as claimed in claim 7, for the 2-1 type or 2-2 type liquid level detection device with the detection element adopting the first arrangement method, includes the following steps: Step S1: Vertically place the liquid level detection device into the container to be detected, with the liquid phase temperature measurement point (10) close to but not touching the bottom of the container, ensuring that the liquid phase temperature measurement point (10) can always be submerged by the liquid phase medium in the container during the test; ensure that the part of the detection element with a length difference ΔL is close to the top of the container and is always in the gas phase medium during the test; Step S2: Connect the top of the first heating auxiliary copper wire (1-1) and the top of the second heating auxiliary copper wire (2-1) to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire (1) through the DC power supply to cause the temperatures of the gas phase medium and the liquid phase medium at the detection element to change; Step S3: Connect the top end of the third constantan wire (7) to the negative terminal of the wiring terminal of the temperature measuring instrument using constantan wire, and connect the top end of the third copper wire (8) to the positive terminal of the wiring terminal of the temperature measuring instrument using copper wire to form a temperature measuring circuit, and measure the temperature T of the liquid-phase medium through the liquid-phase temperature measuring point (10). L ; Or use a T-type thermocouple compensating wire to connect the top end of the third constantan wire (7) and the top end of the third copper wire (8) to the temperature measuring instrument respectively to obtain the temperature T of the liquid-phase medium. L ; Step S4, determining the second resistivity value ρ according to the resistivity-temperature relationship of the detection element L ; Step S5: Connect the detection element to the resistance measuring instrument in a four-wire system. That is, use 2 copper wires to connect the top of the first detection auxiliary copper wire (3-1) and the top of the second detection auxiliary copper wire (3-2) to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire (12-1) and the top of the sixth detection auxiliary copper wire (12-2) to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; use 2 copper wires to connect the top of the third detection auxiliary copper wire (4-1) and the top of the fourth detection auxiliary copper wire (4-2) to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire (12-1) and the top of the sixth detection auxiliary copper wire (12-2) to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; through the resistance measuring instrument and the channel switch, obtain the total resistance R of the first detection loop composed of the first detection wire (3) and the third detection wire (12) L , and obtain the total resistance R of the second detection loop composed of the second detection wire (4) and the third detection wire (12) S ; Determine the resistance difference ΔR between the two loops = R L -R S ; Step S6, according to the diameter D of the detection element and the length difference ΔL between the first detection wire (3) and the second detection wire (4), determine the first resistivity value ρ through the following formula G ; In the formula, S refers to the cross-sectional area of the first detection wire (3) and the second detection wire (4); Step S7 According to the total length L of the first detection circuit L and the total resistance R L , the first resistivity value ρ G and the second resistivity value ρ L , the liquid level h1 of the liquid-phase medium in the container is determined by the following formula; Alternatively, according to the total length L S and the total resistance R S of the second detection circuit, the first resistivity value ρ G and the second resistivity value ρ L are used to determine the liquid level h1 of the liquid-phase medium in the container through the following formula; 11. A liquid level detection method for a liquid level detection device as claimed in claim 7, for the 2-1 type or 2-2 type liquid level detection device with the detection element adopting the second arrangement method, includes the following steps: Step S1: Vertically place the liquid level detection device into the container to be detected, with the liquid phase temperature measurement point (10) close to but not touching the bottom of the container, ensuring that the liquid phase temperature measurement point (10) can always be submerged by the liquid phase medium in the container during the test; ensure that the part of the detection element with a length difference ΔL is close to the top of the container and is always in the gas phase medium during the test; Step S2: Connect the top of the first heating auxiliary copper wire (1-1) and the top of the second heating auxiliary copper wire (2-1) to the two poles of a DC power supply respectively, and apply a constant electric heating power to the first constantan wire (1) through the DC power supply to cause the temperatures of the gas phase medium and the liquid phase medium at the detection element to change; Step S3: Connect the top end of the third constantan wire (7) to the negative terminal of the wiring terminal of the temperature measuring instrument using constantan wire, and connect the top end of the third copper wire (8) to the positive terminal of the wiring terminal of the temperature measuring instrument using copper wire to form a temperature measuring circuit, and measure the temperature T of the liquid phase medium through the liquid phase temperature measuring point (10). L ; or use a T-type thermocouple compensating wire to connect the top ends of the third constantan wire (7) and the third copper wire (8) to the temperature measuring instrument respectively to obtain the temperature T of the liquid phase medium. L ; Step S4, determining the second resistivity value ρ according to the resistivity-temperature relationship of the detection element L ; Step S5: Connect the detection element to a resistance measuring instrument in a four-wire system. That is, use two copper wires to connect the top of the first detection auxiliary copper wire (3-1) and the top of the second detection auxiliary copper wire (3-2) to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire (12-1) and the top of the sixth detection auxiliary copper wire (12-2) to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; use two copper wires to connect the top of the third detection auxiliary copper wire (4-1) and the top of the fourth detection auxiliary copper wire (4-2) to one pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument, and connect the top of the fifth detection auxiliary copper wire (12-1) and the top of the sixth detection auxiliary copper wire (12-2) to the other pole of a set of measurement channels of the four-wire measurement of the resistance measuring instrument; through the resistance measuring instrument and the channel switch, obtain the total resistance R of the first detection loop composed of the first detection wire (3) and the third detection wire (12) L , and obtain the total resistance R of the second detection loop composed of the second detection wire (4) and the third detection wire (12) S ; Determine the resistance difference ΔR between the two loops = R L -R S ; Step S6, determine the first resistivity value ρ according to the diameter D of the detection element and the length difference ΔL between the first detection wire (3) and the second detection wire (4) through the following formula G ; In the formula, S refers to the cross-sectional areas of the first detection guide wire (3) and the second detection guide wire (4); Step S7, According to the total length L of the first detection circuit L and the total resistance R L , the first resistivity value ρ G and the second resistivity value ρ L , the liquid level h1 of the liquid-phase medium in the container is determined by the following formula; Alternatively, according to the total length L S and the total resistance R S of the second detection circuit, the first resistivity value ρ G and the second resistivity value ρ L , the liquid level h1 of the liquid-phase medium in the container is determined by the following formula; Step S8, further determine the liquid level h2 of the liquid-phase medium in the container according to the correspondence between the length of the unit pitch of the liquid level measurement section detection element and the vertical height. Specifically, if the length L of the unit pitch of the liquid level measurement section detection element C and the vertical height h C have a relationship coefficient of α, that is, L C = α × h C , then the liquid level h2 is: or

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