Depth adjustable bimetallic thermometer

Abstract

This invention discloses an adjustable-depth bimetallic thermometer, belonging to the field of thermometers. The adjustable-depth bimetallic thermometer includes a sensing rod mounted on the bimetallic thermometer, with a movable metal probe coaxially sleeved on the sensing rod. The movable probe has a hollow structure and an inner tube coaxially fixed thereon. The inner tube is made of a heat-conducting material and its diameter is smaller than that of the movable probe. Multiple through holes are opened at both ends of the inner tube. A piston, fixed to the bottom end of the sensing rod, is slidably connected to the inner wall of the inner tube. The annular space between the movable probe and the inner tube, as well as the interior of the inner tube, are filled with a heat-conducting medium. A connecting tube is fixed to the top of the movable probe, and the connecting tube has a first sealing component, a second sealing component, and a positioning component. This invention, through the adjustable structure of the movable probe, can adapt to different installation depth requirements, ensuring that the sensing end is always in the optimal measurement position, thereby improving measurement accuracy and enhancing versatility and applicability while adapting to various working conditions.

Description

Technical Field

[0001] This invention relates to the field of thermometers, and particularly to an adjustable depth bimetallic thermometer. Background Technology

[0002] A bimetallic thermometer is an instrument that measures temperature by utilizing the thermal expansion properties of a bimetallic strip. Its working principle is based on the combination of two metals with different coefficients of thermal expansion. Its core temperature-sensing element is a multi-layered spiral-wound metal strip. When the temperature changes, the two metals bend and deform due to their different coefficients of expansion, thereby driving the pointer to indicate the temperature value. This instrument features strong shock resistance, high mechanical strength, and clear readings, and is widely used in environmental monitoring in industries such as petroleum, chemical, and metallurgy.

[0003] Currently, most bimetallic thermometers on the market have a fixed structure, and the length of their sensing tube (or probe, insertion tube) is determined at the factory. In practical applications, operators need to select the appropriate specification based on the diameter of the pipe or equipment and the depth of the mounting flange or threaded interface.

[0004] However, on-site conditions are often complex and variable, and the pre-selected length may not perfectly match the actual installation depth: if the probe is too long, it may touch the pipe wall or the opposite side, or even be damaged due to bending; if the probe is too short, the temperature sensing element cannot be in the required measurement position, which may lead to the measured value not accurately reflecting the true temperature and producing a large error. In addition, in some situations where it is necessary to change the temperature measuring point, a fixed-length thermometer cannot be well adapted to temperature measuring holes of different depths. Replacing the entire thermometer after disassembly increases the cost and inconvenience of use. Summary of the Invention

[0005] This invention provides an adjustable depth bimetallic thermometer, which can solve the problem in the prior art where the fixed length of the temperature sensing rod is difficult to adjust the insertion depth flexibly according to actual working conditions.

[0006] An adjustable depth bimetallic thermometer includes a temperature sensing rod mounted on the bimetallic thermometer. A movable metal probe is coaxially sleeved on the temperature sensing rod. The movable probe has a hollow structure inside and an inner tube is coaxially fixed thereon. The inner tube is made of a heat-conducting material and has a diameter smaller than that of the movable probe. Multiple through holes are opened at both ends of the inner tube. A piston fixed to the bottom end of the temperature sensing rod is slidably connected to the inner wall of the inner tube. The annular space between the movable probe and the inner tube, as well as the inside of the inner tube, are filled with a heat-conducting medium. The top of the movable probe is fixedly provided with a connecting pipe, and a first sealing component and a second sealing component are respectively provided inside the connecting pipe and near the top and bottom ends. A positioning component is symmetrically provided on the connecting pipe between the first sealing component and the second sealing component. The positioning component is used to restrict the relative sliding between the movable probe and the temperature sensing rod when locked.

[0007] Preferably, the first sealing assembly includes an inflatable sealing ring fixed to the inner wall of the connecting pipe and an air bladder portion formed on the inflatable sealing ring. A first mounting tube is fixed near the top of the connecting pipe, and the air bladder portion extends into the interior of the first mounting tube. A push plate for compressing the air bladder portion is provided inside the first mounting tube.

[0008] Preferably, a first screw is threaded onto the first mounting tube, and one end of the first screw is rotatably connected to the push plate.

[0009] Preferably, the second sealing assembly includes a first sealing element sleeved on the temperature sensing rod, the first sealing element contacting the outer wall of the temperature sensing rod.

[0010] Preferably, the positioning component includes a second mounting tube fixed to the connecting tube, a fixing plate fixed to the inner wall of the second mounting tube, and a second screw threaded to the fixing plate, one end of the second screw being able to contact the outer wall of the temperature sensing rod.

[0011] Preferably, a pressure plate is rotatably connected to the end of the second screw near the temperature sensing rod, and an anti-slip pad is fixed on the side of the pressure plate near the temperature sensing rod.

[0012] Preferably, a protective tube coaxially arranged with the first screw is fixed on the first mounting tube, and a plug assembly is provided at the end of the protective tube away from the connecting tube and the end of the second mounting tube away from the connecting tube.

[0013] Preferably, the plug assembly includes screws, all of which are threaded onto the corresponding protective tube or the second mounting tube.

[0014] Preferably, a limiting ring is fixed on the inner wall of the inner tube at a position in the upper middle part.

[0015] Preferably, the heat-conducting medium is heat-conducting oil or liquid metal.

[0016] This invention provides an adjustable depth bimetallic thermometer, which has the following beneficial effects: 1. When the movable probe is inserted into the measured medium, heat is transferred through the probe wall to the heat-conducting medium within the annular space. The medium then conducts the heat through the through-holes in the inner tube to the interior of the inner tube, where it is finally absorbed by the sensing rod, thus achieving a temperature response. During adjustment, the through-holes at both ends of the inner tube allow the heat-conducting medium to flow freely between the annular space and the interior of the inner tube, ensuring smooth piston sliding. This adjustable movable probe structure better adapts to different installation depth requirements, ensuring the sensing end is always in the optimal measurement position, thereby improving measurement accuracy and enhancing versatility and applicability while adapting to varying operating conditions.

[0017] 2. A dual-sealing structure is adopted. The first sealing component serves as the main seal, achieving a long-term reliable static seal through an adjustable inflatable sealing ring. The second sealing component serves as an auxiliary seal, ensuring a dynamic seal during adjustment. The positioning component is located inside the protected area of ​​the first sealing component, avoiding contact with external heat-conducting media and ensuring the long-term flexibility and reliability of the locking mechanism. The combination of each sealing component and the positioning component guarantees the sealing between the movable probe and the temperature sensing rod.

[0018] 3. Screws are installed at the operating points of the first and second screws. The screws are threaded onto the protective tube or the second mounting tube to seal their external ports. In conjunction with the second sealing element, the end face of the connection is sealed to prevent the external test medium from entering the operating area of ​​the first and second screws and affecting subsequent operations. Attached Figure Description

[0019] Figure 1 A schematic diagram of the structure of an adjustable depth bimetallic thermometer provided by the present invention. Figure 1 ; Figure 2 A schematic diagram of the internal cross-sectional structure of the movable probe and connecting tube of an adjustable depth bimetallic thermometer provided by the present invention; Figure 3 This invention provides an adjustable depth bimetallic thermometer. Figure 2 Enlarged structural diagram at point A in the middle; Figure 4 This invention provides an adjustable depth bimetallic thermometer. Figure 3 Enlarged structural diagram at point B; Figure 5 A schematic diagram of the movable probe and inner tube of an adjustable depth bimetallic thermometer provided by the present invention; Figure 6 The present invention provides a schematic diagram of the structure of a first seal, an inflatable sealing ring, a screw, and a second screw in an adjustable depth bimetallic thermometer.

[0020] Explanation of reference numerals in the attached figures: 100. Temperature sensing rod; 200. Movable probe; 201. Inner tube; 202. Through hole; 203. Piston; 300. Connecting tube; 301. First seal; 400. Limiting ring; 500. First mounting tube; 501. First screw; 502. Push plate; 503. Protective tube; 600. Inflatable sealing ring; 602. Airbag part; 700. Second mounting tube; 701. Fixing plate; 702. Second screw; 703. Pressure plate; 800. Screw; 801. Second seal. Detailed Implementation

[0021] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0022] like Figures 1 to 6 As shown in the figure, an adjustable depth bimetallic thermometer provided by an embodiment of the present invention includes a temperature sensing rod 100 disposed on the bimetallic thermometer. A movable probe 200, which can slide along its axial direction, is coaxially sleeved on the temperature sensing rod 100. The movable probe 200 is made of metal and has a hollow structure inside, with an inner tube 201 coaxially fixed thereon. The inner tube 201 is made of a thermally conductive material and has a diameter smaller than that of the movable probe 200, thereby forming an annular space between the movable probe 200 and the inner tube 201. Multiple through holes 202 are opened at both ends of the inner tube 201. A piston 203 is slidably connected to the inner wall and fixed to the bottom end of the temperature sensing rod 100. The annular space between the movable probe 200 and the inner tube 201, as well as the interior of the inner tube 201, are filled with a heat-conducting medium. A connecting tube 300 is fixedly provided at the top of the movable probe 200. A first sealing component and a second sealing component are respectively provided inside the connecting tube 300 and near the top and bottom ends. A positioning component is symmetrically provided on the connecting tube 300 and between the first sealing component and the second sealing component. The positioning component is used to restrict the relative sliding between the movable probe 200 and the temperature sensing rod 100 when locked.

[0023] The bimetallic thermometer involved in this application is a conventional technology in the field. It is an industrial instrument that measures temperature based on the difference in thermal deformation between two metals with different coefficients of linear expansion. The core component is a multi-layered spiral-wound metal strip, which drives the pointer reading through bending deformation caused by temperature changes. It is suitable for various industrial scenarios such as pipelines and containers. The temperature sensing rod 100 (or probe, insertion tube) is a key peripheral component, and its core function is to isolate the temperature sensing element from the measured medium. The bottom end of the temperature sensing rod 100 is inserted into the inner tube 201 and fixedly connected to the piston 203. The outer edge of the piston 203 slides and seals against the inner wall of the inner tube 201. To reduce thermal resistance, the annular space between the movable probe 200 and the inner tube 201, as well as the interior of the inner tube 201, are filled with a heat-conducting medium. This structure forms a closed and efficient heat conduction loop: when the movable probe 200 is inserted into the medium being measured, heat is transferred through the tube wall of the movable probe 200 to the heat-conducting medium in the annular space. The medium then conducts the heat through the through hole 202 of the inner tube 201 to the inside of the inner tube 201, and finally it is absorbed by the temperature sensing rod 100, thereby achieving a response to temperature.

[0024] After adjusting the extension length of the movable probe 200, it is locked by the positioning component to restrict the relative sliding between the movable probe 200 and the temperature sensing rod 100; the first sealing component and the second sealing component are used to seal the inside of the movable probe 200 to prevent the leakage of the internal heat-conducting medium and the infiltration of the external medium to be tested.

[0025] When adjusting the insertion depth of the movable probe 200, the operator releases the positioning assembly and pulls the movable probe 200 away from the bimetallic thermometer head. During this process: The piston 203 slides upward relative to the inner tube 201, and the heat-conducting medium above the piston 203 is compressed. Part of the medium flows into the annular space through the through hole 202 at the upper end of the inner tube 201. The heat-conducting medium in the annular space is filled into the remaining area as the movable probe 200 extends, ensuring that the newly added movable probe 200 and temperature sensing rod 100 areas also have heat-conducting capabilities.

[0026] Conversely, when a shorter insertion depth is required, push the movable probe 200 towards the head of the meter: The piston 203 slides downward relative to the inner tube 201, and the volume of the heat-conducting medium located above the piston 203 inside the inner tube 201 increases. The medium is replenished from the annular space through the through hole 202 and enters the area below the inner tube 201.

[0027] During adjustment, the through holes 202 at both ends of the inner tube 201 allow the heat transfer medium to flow freely between the annular space and the interior of the inner tube 201, ensuring smooth sliding of the piston 203. This adjustable structure of the movable probe 200 can better adapt to different installation depth requirements, ensuring that the temperature sensing end is always in the optimal measurement position, thereby improving measurement accuracy and enhancing versatility and applicability while adapting to various working conditions.

[0028] like Figure 2 and Figure 3 As shown, a connecting tube 300 is fixedly connected to the top of the movable probe 200, and the connecting tube 300 is sleeved on the outside of the temperature sensing rod 100. A first sealing assembly and a second sealing assembly are respectively provided inside the connecting tube 300, near its top and bottom ends, to create a sealed adjustment chamber between the connecting tube 300 and the temperature sensing rod 100. A positioning assembly is symmetrically provided on the connecting tube 300, located between the first and second sealing assemblies. This positioning assembly is used to lock the movable probe 200 after its extension length has been adjusted, preventing relative sliding between the movable probe 200 and the temperature sensing rod 100.

[0029] In some specific implementation plans, such as Figure 3 and Figure 4 As shown. The first sealing assembly includes an inflatable sealing ring 600 fixed to the inner wall of the connecting pipe 300 and an air bladder portion 602 formed on the inflatable sealing ring 600 and communicating with its interior. The inflatable sealing ring 600 has multiple raised sealing lips at the part that contacts the temperature sensing rod 100 to improve the sealing pressure. A first mounting pipe 500 is fixed near the top of the connecting pipe 300. The air bladder portion 602 extends into the first mounting pipe 500. The first mounting pipe 500 has a push plate 502 for compressing the air bladder portion 602 inside. A first screw 501 is threadedly connected to the first mounting pipe 500. One end of the first screw 501 is rotatably connected to the push plate 502.

[0030] By turning the first screw 501, the push plate 502 can be pushed to compress the air bladder 602, thereby causing the air-filled sealing ring 600 to expand and tightly hug the temperature sensing rod 100, achieving a reliable static seal and preventing the external medium from seeping in along the temperature sensing rod 100.

[0031] To ensure the sealing reliability and service life of the gas-filled sealing ring 600 under varying temperature conditions, it is made of fluororubber (FKM). Fluororubber possesses excellent high-temperature resistance, chemical corrosion resistance, and low compression set, maintaining stable elasticity over a wide temperature range, making it suitable for most industrial temperature measurement scenarios. When the thermometer is used in extremely high-temperature environments or involves specific chemical media, it is made of perfluoroelastomer (FFKM). FFKM is resistant to almost all chemical corrosion and has good temperature resistance, ensuring the long-term effectiveness of the sealing structure under extreme conditions.

[0032] In some specific implementation plans, such as Figure 2 As shown. The second sealing assembly is located below the first sealing assembly, inside its protected area, to prevent direct contact with the external heat-conducting medium and effectively protect it. The second sealing assembly includes a first sealing element 301 sleeved on the temperature sensing rod 100. The first sealing element 301 contacts the outer wall of the temperature sensing rod 100 and uses a contact seal, such as a mechanical seal or a Glyd ring. It mainly serves to further seal the movable probe 200 during dynamic adjustment, preventing leakage of the heat-conducting medium or infiltration of the external medium being tested.

[0033] In some specific implementation plans, such as Figure 3 As shown. The positioning assembly is also located inside the protection area of ​​the first sealing assembly to avoid contact with the external heat-conducting medium. The positioning assembly includes a second mounting pipe 700 fixed to the connecting pipe 300, a fixing plate 701 fixed to the inner wall of the second mounting pipe 700, and a second screw 702 threadedly connected to the fixing plate 701. A pressure plate 703 is rotatably connected to one end of the second screw 702 near the temperature sensing rod 100, and one end of the second screw 702 abuts against the outer wall of the temperature sensing rod 100 through the pressure plate 703. To increase friction and prevent slippage, an anti-slip pad, such as a patterned rubber pad, is fixed to the side of the pressure plate 703 near the temperature sensing rod 100, so that the deformation of the anti-slip pad can better fit against the outer wall of the temperature sensing rod 100.

[0034] By turning the second screw 702, the pressure plate 703 can be driven to move toward the temperature sensing rod 100 and abut against its outer wall to position the movable probe 200 and prevent the movable probe 200 from slipping during normal use.

[0035] In some specific implementation plans, such as Figure 3 , Figure 4 and Figure 6As shown, to prevent external test media from entering the operating points of the first screw 501 and the second screw 702, a protective tube 503 coaxially arranged with the first screw 501 is fixed on the first mounting tube 500. A plug assembly is provided at one end of the protective tube 503 away from the connecting tube 300 and at one end of the second mounting tube 700 away from the connecting tube 300. The plug assembly includes screws 800, each screw 800 being threaded onto the corresponding protective tube 503 or the second mounting tube 700 to seal its external port. A second sealing element 801 is fixedly provided at the end of the protective tube 503 and the second mounting tube 700 near the screw 800 to seal the end face of the screw 800 connection.

[0036] In some specific implementation plans, such as Figure 2 and Figure 5 As shown. A limiting ring 400 is fixed on the inner wall of the inner tube 201 at the upper middle position. The limiting ring 400 serves to limit the distance between the piston 203 and the top of the movable probe 200 to prevent it from being too short. When the movable probe 200 is adjusted upward to the limit position, the piston 203 will abut against the limiting ring 400.

[0037] The heat from the external medium being measured is primarily transferred through the contact between the heat-conducting medium and the temperature-sensing rod 100. Specifically, the amount of heat-conducting medium in the area between the piston 203 and the top of the movable probe 200 affects the heat transfer efficiency. Therefore, the stroke range of the piston 203 is optimized to ensure the effective heat transfer volume of the heat-conducting medium, thereby guaranteeing the accuracy and response speed of the temperature measurement. Specifically, the area enclosed between the piston 203 and the top of the movable probe 200 is the main heated area of ​​the heat-conducting medium. The volume of heat-conducting medium in this area directly determines the efficiency of heat transfer to the temperature-sensing rod 100. If the amount of heat-conducting medium in this area is too small, it may lead to insufficient heat capacity, thus affecting the effective heat transfer and causing temperature response lag or measurement errors.

[0038] In some specific implementation schemes, to ensure effective heat transfer, materials with high thermal conductivity, such as heat transfer oil or liquid metal, are selected as the heat transfer medium.

[0039] When the temperature of the measured medium is low, a high-temperature heat transfer oil, such as a biphenyl-diphenyl ether mixture or an alkylbenzene type heat transfer oil, is selected as the heat transfer medium. This oil has good thermal stability and can quickly transfer heat from the inner wall of the movable probe 200 to the inner tube 201 and the sensing rod 100. When the temperature of the measured medium is high or when extremely fast response speed is required, a liquid metal, such as gallium, gallium-indium alloy, or gallium-indium-tin alloy, is selected as the heat transfer medium. Liquid metals have a higher thermal conductivity than heat transfer oils, enabling better heat conduction and shortening the thermometer's hysteresis time.

[0040] In some specific implementation schemes, to ensure long-term stable operation in corrosive environments, components that may come into contact with the tested medium, such as the movable probe 200, connecting pipe 300, first mounting pipe 500, second mounting pipe 700, and screws 800, are all made of stainless steel. Since stainless steel has poor thermal conductivity, the wall thickness of the movable probe 200 should be as small as possible (1.0-1.5mm; too thin a wall may result in insufficient strength) to shorten the heat transfer distance and accelerate the temperature response. The inner tube 201 is made of a high thermal conductivity material, such as aluminum alloy or copper alloy. The high thermal conductivity of the inner tube 201, combined with the heat-conducting medium, further reduces contact thermal resistance, achieving a balance between corrosion resistance and thermal conductivity for the movable probe 200.

[0041] To facilitate understanding of the embodiments of this solution by those skilled in the art, the working principle of this solution will now be briefly explained in conjunction with specific application scenarios: During on-site installation, the operator first loosens the positioning component on the connecting pipe 300 according to the required effective insertion depth and then pulls the movable probe 200 out to the predetermined length. The heat-conducting medium in the space of the movable probe 200 automatically fills the newly extended area. After adjustment, it is locked again, and the heat-conducting medium re-establishes a stable heat conduction path in the new position. After adjustment, the second screw 702 is tightened, and the pressure plate 703 presses firmly against the outer wall of the temperature-sensing rod 100 to achieve locking. The temperature of the medium to be measured is first transferred to the outer wall of the movable probe 200. Due to the extremely thin wall thickness, the heat passes through the stainless steel wall and is transferred to the heat-conducting medium in the annular space. Through conduction, the heat is transferred to the heat-conducting medium inside the inner tube 201. The heat-conducting medium inside the inner tube 201 comes into contact with the temperature-sensing rod 100, and the heat is transferred to the temperature-sensing rod 100. Finally, the temperature-sensing rod 100 conducts the heat to the temperature-sensing element of the bimetallic thermometer, driving the pointer to rotate and display the current temperature value.

[0042] After adjustment, screw the first screw 501 to push the push plate 502 to compress the air bladder 602, causing the inflation sealing ring 600 to expand and tighten around the temperature sensing rod 100, forming a reliable static seal to prevent contact between the internal components and the medium being measured. This, in conjunction with the second sealing assembly, reliably seals the interior of the movable probe 200. Finally, screws 800 are threaded onto the corresponding protective tube 503 or the second mounting tube 700 to seal their external ports.

[0043] By adjusting the extension length of the movable probe 200 as described above, the depth of the bimetallic thermometer is adjustable, which better adapts to different installation depth requirements and ensures that the sensing end is always in the optimal measurement position, thereby improving measurement accuracy and enhancing versatility and applicability while adapting to various working conditions.

[0044] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An adjustable depth bimetallic thermometer, comprising a temperature sensing rod (100) disposed on the bimetallic thermometer, characterized in that, A movable metal probe (200) is coaxially sleeved on the temperature sensing rod (100). The movable probe (200) has a hollow structure inside and an inner tube (201) is coaxially fixed thereon. The inner tube (201) is made of heat-conducting material and has a diameter smaller than that of the movable probe (200). Multiple through holes (202) are opened at both ends of the inner tube (201). A piston (203) fixed to the bottom end of the temperature sensing rod (100) is slidably connected to the inner wall of the inner tube (201). The annular space between the movable probe (200) and the inner tube (201) and the inside of the inner tube (201) are filled with heat-conducting medium. The top of the movable probe (200) is fixed with a connecting pipe (300), and the connecting pipe (300) is provided with a first sealing component and a second sealing component at the positions near the top and bottom ends, respectively. A positioning component is symmetrically provided on the connecting pipe (300) between the first sealing component and the second sealing component. The positioning component is used to restrict the relative sliding between the movable probe (200) and the temperature sensing rod (100) when locked.

2. The adjustable depth bimetallic thermometer as described in claim 1, characterized in that, The first sealing assembly includes an inflatable sealing ring (600) fixed on the inner wall of the connecting pipe (300) and an airbag portion (602) formed on the inflatable sealing ring (600). A first mounting pipe (500) is fixed near the top of the connecting pipe (300). The airbag portion (602) extends into the interior of the first mounting pipe (500). A push plate (502) for compressing the airbag portion (602) is provided inside the first mounting pipe (500).

3. The adjustable depth bimetallic thermometer as described in claim 2, characterized in that, The first mounting tube (500) is threaded with a first screw (501), and one end of the first screw (501) is rotatably connected to the push plate (502).

4. The adjustable depth bimetallic thermometer as described in claim 3, characterized in that, The second sealing assembly includes a first sealing element (301) sleeved on the temperature sensing rod (100), the first sealing element (301) being in contact with the outer wall of the temperature sensing rod (100).

5. The adjustable depth bimetallic thermometer as described in claim 2, characterized in that, The positioning assembly includes a second mounting tube (700) fixed on the connecting tube (300), a fixing plate (701) fixed on the inner wall of the second mounting tube (700), and a second screw (702) threadedly connected to the fixing plate (701). One end of the second screw (702) can contact the outer wall of the temperature sensing rod (100).

6. The adjustable depth bimetallic thermometer as described in claim 5, characterized in that, The second screw (702) is rotatably connected to a pressure plate (703) at one end near the temperature sensing rod (100), and an anti-slip pad is fixed on the side of the pressure plate (703) near the temperature sensing rod (100).

7. The adjustable depth bimetallic thermometer as described in claim 6, characterized in that, A protective tube (503) coaxially arranged with the first screw (501) is fixed on the first mounting tube (500). A plug assembly is provided at one end of the protective tube (503) away from the connecting tube (300) and at one end of the second mounting tube (700) away from the connecting tube (300).

8. The adjustable depth bimetallic thermometer as described in claim 7, characterized in that, The plug assembly includes screws (800), all of which are threaded onto the corresponding protective tube (503) or the second mounting tube (700).

9. The adjustable depth bimetallic thermometer as described in claim 1, characterized in that, A limiting ring (400) is fixed on the inner wall of the inner tube (201) at the upper middle position.

10. The adjustable depth bimetallic thermometer as described in claim 9, characterized in that, The heat-conducting medium is heat-conducting oil or liquid metal.

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