Thermocouple verification furnace

Abstract

The invention provides a thermocouple verification furnace which is a vertical verification furnace and comprises a furnace core assembly, a one-way atmosphere protection device and a thermocouple positioning device. Through the design of the heat insulation layer, the highest temperature can reach 1800 DEG C, the upper limit of 1600 DEG C of a traditional high-temperature verification furnace is broken through, platinum and other high-melting-point materials can be melted, verification is carried out when the temperature exceeds 1600 DEG C, calibration is carried out through a fuse method by utilizing pure metal materials, and the calibration precision is improved; a vertical furnace is adopted to solve the problem of high-temperature deformation in the gravity direction of a furnace tube of a common horizontal thermocouple verification furnace; in the verification process, the whole process is protected by using the protective gas, so that the detected thermocouple is prevented from being oxidized under the high-temperature verification condition.

Description

Technical Field

[0001] This invention belongs to the field of metrology and testing equipment technology, and specifically relates to a thermocouple calibration furnace. Background Technology

[0002] With the development of industrial technology, the demand for calibration at temperatures above 1500℃ has increased dramatically. Calibration using pure metal materials via the fused wire method has significant advantages, such as platinum with a melting point of 1768℃. However, the current upper temperature limit of high-temperature thermocouple calibration furnaces is 1600℃, which cannot provide the temperature environment required for platinum melting. Furthermore, most high-temperature thermocouple calibration furnaces are horizontal structures; prolonged use at high temperatures causes the furnace tubes to deform due to gravity, affecting the uniformity of the temperature field and making the furnace tubes difficult to replace. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a vertical high-temperature thermocouple calibration furnace with atmosphere protection. This invention solves the problems existing in the prior art.

[0004] The technical solution of this invention:

[0005] A thermocouple calibration furnace, wherein the thermocouple calibration furnace is a vertical calibration furnace, comprising a furnace core assembly, a one-way atmosphere protection device, and a thermocouple positioning device.

[0006] The one-way atmosphere protection device includes a gas cylinder containing protective gas and a vent pipe connected to the gas cylinder through a gas passage. During the calibration process, the vent pipe fills the furnace tube with protective gas.

[0007] The thermocouple positioning device is installed above the furnace tube and is used to fix the vent pipe, temperature control thermocouple, thermocouple to be calibrated, and standard thermocouple.

[0008] The furnace core assembly includes a furnace tube, a heating device, a temperature-controlling thermocouple, a heat insulation layer, and a heat preservation layer. The heating device includes at least one heating rod and a power source to provide energy to the heating rod. The furnace tube is installed vertically to the ground and is a refractory furnace tube that is closed at the bottom and open at the top. The closed end is located inside the heat insulation layer, and the open end is located on the upper surface of the heat insulation layer. A vent pipe and a temperature-controlling thermocouple from a one-way atmosphere protection device are installed inside the furnace tube. The temperature-controlling thermocouple is used to detect and control the temperature of the furnace tube. The heating rod is a U-shaped heating rod placed around the furnace tube. The heat insulation layer is a cylindrical sealed space surrounded by refractory bricks, including a circular limiting brick, an annular brick, and a bottom circular brick. The furnace tube is installed at the geometric center of the heat insulation layer. The circular limiting brick has limiting holes for the furnace tube and the heating rod. The sealed space side of the heat insulation layer is polished and then sprayed with a high-reflectivity coating. The heat preservation layer wraps around the annular brick.

[0009] Furthermore, the heating rod is a U-shaped heating rod made of silicon molybdenum, including a heating end and an electrode end. The heating end is placed on the outer periphery of the furnace tube, and the electrode end is installed on the limiting hole by a clamp. The power supply is connected to the electrode end by a power cord.

[0010] Furthermore, the thermocouple positioning bracket has a test thermocouple limiting hole at its geometric center, through which the tested thermocouple and the standard thermocouple are radially and axially limited.

[0011] Furthermore, the temperature-controlling thermocouple is a non-standard platinum-rhodium 40-platinum-rhodium 20 thermocouple, with a temperature control upper limit of 1800℃.

[0012] Furthermore, the axial depth of the refractory vent pipe is close to the bottom of the closed end of the furnace tube, and a one-way airflow valve is installed at the upper end of the refractory vent pipe.

[0013] Furthermore, the insulation layer consists of two layers, including a first insulation layer that is in contact with the heat insulation layer and a second outer insulation layer. The thermal conductivity of the first insulation layer is one order of magnitude greater than that of the second insulation layer.

[0014] Furthermore, the formulas for calculating the thickness of the first insulation layer and the second insulation layer are as follows:

[0015] d1 = r2 - r1, d2 = r3 - r2, where d1 is the thickness of insulation layer one and d2 is the thickness of insulation layer two. r1: Outer radius of the refractory brick, i.e., the inner radius of the insulation layer, in meters; r2: Outer radius of the first insulation layer, in meters; r3: Outer radius of the second insulation layer, in meters; T i T is the temperature inside the borehole. max T0 is the maximum operating temperature of insulation layer 2, T2 is the ambient temperature, k2 is the thermal conductivity of insulation layer 2, and k1 is the thermal conductivity of insulation layer 1.

[0016] Preferably, the first insulation layer is made of high-alumina felt made of alumina fiber and zirconium oxide fiber, and the second insulation layer is made of ceramic fiber cotton.

[0017] Furthermore, the thermocouple calibration furnace also includes a cooling device, which includes a furnace shell and a cooling fan. The furnace shell is cylindrical and is wrapped around a heat insulation layer and a heat preservation layer, with a gap between the furnace shell and the heat insulation layer and the heat preservation layer. The cooling fan is installed on the furnace shell.

[0018] Preferably, the furnace shell has a hollow structure.

[0019] The beneficial effects of this invention compared to the prior art are as follows:

[0020] 1. This invention, through the design of the heat insulation layer, can reach a maximum temperature of 1800℃, breaking through the traditional high-temperature calibration furnace upper limit of 1600℃. It can melt high-melting-point materials such as platinum, thereby improving the calibration accuracy by using pure metal materials and the fused wire method for calibration at temperatures exceeding 1600℃.

[0021] 2. This invention uses a vertical furnace to solve the problem of high-temperature deformation of furnace tubes under gravity in common horizontal thermocouple calibration furnaces;

[0022] 3. This invention uses a protective gas to provide full protection during the calibration process, preventing the thermocouple under test from oxidizing under high-temperature calibration conditions;

[0023] 4. This invention, through the design of the insulation layer, uses the optimal combination thickness of two layers of insulation cotton of different materials to maximize the insulation of the furnace tube, so that the temperature can reach 1800℃.

[0024] 5. This invention achieves rapid cooling after high-temperature testing through the design of a cooling device. Attached Figure Description

[0025] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0026] Figure 1 A cross-sectional view of a thermocouple calibration furnace provided according to an embodiment of the present invention is shown.

[0027] Figure 2 This image shows a front view of the outer casing of a thermocouple calibration furnace provided according to an embodiment of the present invention.

[0028] Figure 3 This illustration shows a schematic diagram of the structure of the furnace tube, temperature control thermocouple, and ventilation device provided according to an embodiment of the present invention.

[0029] Figure 4 A schematic diagram of a circular limiting brick structure provided according to an embodiment of the present invention is shown;

[0030] Figure 5 The diagram shows a schematic of a heating rod structure according to an embodiment of the present invention.

[0031] The above figures include the following reference numerals:

[0032] 1. Furnace tube; 2. Heating rod; 3. Temperature control thermocouple; 4. Circular limiting brick; 5. Ring brick; 6. Insulation layer; 7. Vent pipe; 8. One-way airflow valve; 9. Thermocouple positioning bracket; 10. Furnace shell; 11. Cooling fan. Detailed Implementation

[0033] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0035] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0036] like Figure 1 As shown, according to an embodiment of the present invention, a thermocouple calibration furnace is provided. The thermocouple calibration furnace is a vertical calibration furnace, including a furnace core assembly, a one-way atmosphere protection device, and a thermocouple positioning device.

[0037] The one-way atmosphere protection device includes a gas cylinder containing protective gas and a vent pipe connected to the gas cylinder through a gas passage. During the calibration process, the vent pipe fills the furnace tube with protective gas.

[0038] The thermocouple positioning device is installed above the furnace tube to fix the vent pipe, temperature control thermocouple, thermocouple to be calibrated, and standard thermocouple;

[0039] The furnace core assembly includes a furnace tube, a heating device, a temperature-controlling thermocouple, a heat insulation layer, and a heat preservation layer. The heating device includes at least one heating rod and a power source to provide energy to the heating rod. The furnace tube is installed vertically to the ground and is a refractory furnace tube that is closed at the bottom and open at the top. The closed end is located inside the heat insulation layer, and the open end is located on the upper surface of the heat insulation layer. A vent pipe and a temperature-controlling thermocouple from a one-way atmosphere protection device are installed inside the furnace tube. The heating rods are U-shaped heating rods and are evenly placed around the furnace tube. The heat insulation layer is a cylindrical sealed space surrounded by refractory bricks. The furnace tube is installed at the geometric center of the heat insulation layer and includes a circular limiting brick, an annular brick, and a bottom circular brick. The circular limiting brick is provided with limiting holes for the furnace tube and the heating rod. The sealed space side of the heat insulation layer is polished and then sprayed with a high-reflectivity coating. The heat preservation layer is wrapped around the annular brick.

[0040] With the above-mentioned device, the maximum temperature can reach 1800℃, breaking through the traditional 1600℃ upper limit of high-temperature calibration furnaces. It can melt high-melting-point materials such as platinum, thus enabling calibration at temperatures exceeding 1600℃. The calibration is performed using pure metal materials and the fused wire method, improving the accuracy of calibration. The vertical furnace solves the problem of high-temperature deformation of furnace tubes under gravity in common horizontal thermocouple calibration furnaces. By using protective gas throughout the calibration process, oxidation of the thermocouple under test is prevented under high-temperature calibration conditions.

[0041] In a further embodiment, the heating rod is a U-shaped heating rod made of silicon molybdenum, including a heating end and an electrode end. The heating end is placed on the outer periphery of the furnace tube, and the electrode end is mounted on a limiting hole by a clamp. The power supply is connected to the electrode end via a power cord. In a preferred embodiment, three heating rods are evenly arranged on the outer periphery of the furnace tube. The U-shaped arrangement improves heating efficiency and ensures that the furnace tube temperature reaches 1800 degrees Celsius.

[0042] In a further embodiment, a test thermocouple limiting hole is provided at the geometric center of the thermocouple positioning bracket, and the thermocouple under test and the standard thermocouple are radially and axially limited through the limiting hole at the geometric center of the thermocouple positioning bracket.

[0043] In a further embodiment, the temperature-controlled thermocouple is a non-standard platinum-rhodium 40-platinum-rhodium 20 thermocouple with a temperature control upper limit of 1800°C.

[0044] In a further embodiment, the axial depth of the refractory vent pipe is close to the bottom of the closed end of the furnace tube, and a one-way airflow valve is installed at the upper end of the refractory vent pipe. This arrangement ensures that the furnace tube is filled with protective gas, preventing oxidation of the thermocouple under test under high-temperature calibration conditions and avoiding irreversible damage.

[0045] In a further embodiment, the insulation layer consists of two layers: a first insulation layer in contact with the heat insulation layer and a second outer insulation layer. The thermal conductivity of the first insulation layer is one order of magnitude greater than that of the second insulation layer.

[0046] In a further embodiment, the thickness calculation formulas for insulation layer one and insulation layer two are as follows:

[0047] d1 = r2 - r1, d2 = r3 - r2, where d1 is the thickness of insulation layer one and d2 is the thickness of insulation layer two. r1: Outer radius of the refractory brick, i.e., the inner radius of the insulation layer, in meters; r2: Outer radius of the first insulation layer, in meters; r3: Outer radius of the second insulation layer, in meters; T i T is the temperature inside the borehole. max T0 represents the maximum operating temperature of insulation layer two, T2 represents the ambient temperature, k2 represents the thermal conductivity of insulation layer two, and k1 represents the thermal conductivity of insulation layer one. By setting these parameters, the optimal combination of insulation layer one and insulation layer two is achieved, ensuring the best insulation performance.

[0048] In one preferred embodiment, the first insulation layer is made of high-alumina felt made of alumina fiber and zirconium oxide fiber, and the second insulation layer is made of ceramic fiber cotton. In other embodiments, other materials that meet the actual usage requirements can be selected, which will not be described in detail here.

[0049] In a further embodiment, the thermocouple calibration furnace also includes a cooling device, which includes a furnace shell and a cooling fan. The furnace shell is cylindrical and is wrapped around a heat insulation layer and a heat preservation layer, with a gap between the furnace shell and the heat insulation layer and the heat preservation layer. The cooling fan is installed on the furnace shell.

[0050] In a preferred embodiment, the furnace shell has a hollow structure.

[0051] To gain a better understanding of the thermocouple calibration furnace provided by the present invention, a detailed description is provided below with reference to specific examples and accompanying drawings.

[0052] The technical solutions in the embodiments of this invention will now be fully described with reference to the accompanying drawings:

[0053] See attached document Figure 4The circular limiting brick 4 is provided with furnace tube limiting holes and heating rod limiting holes. The furnace tube limiting hole is located at the geometric center of the circular limiting brick 4, realizing radial limiting of the furnace tube 1. The three heating rod limiting holes are equidistantly arrayed around the geometric center, realizing radial limiting of the heating rod 2.

[0054] See attached document Figure 3 The furnace tube 1 is closed at one end and open at the other, positioned vertically at the geometric center of the furnace body. Compared to a horizontal calibration furnace, maintaining the vertical orientation of the furnace tube 1 avoids deformation in the direction of weight. The closed end is located inside the furnace body, and the open end is located on the upper surface of the furnace shell. Inside the furnace tube 1 are placed a refractory vent pipe 7, a temperature-controlled thermocouple 3, a standard thermocouple, and the thermocouple under test. During the calibration process, the furnace tube 1 is filled with a protective gas to prevent the thermocouple under test from oxidizing under high-temperature calibration conditions, thus preventing irreversible damage to the thermocouple under test.

[0055] See attached document Figure 5 Heating rod 2 is a U-shaped heating rod made of silicon molybdenum, with the heating section placed around the furnace tube. The electrode end is installed on the limiting hole through a clamp to achieve axial limiting of heating rod 2. Heating rod 2 is powered by a 40V DC power supply. The connection between the power cord and the heating rod is made of a stress-free conductive stainless steel strip to avoid deformation of the conductive stainless steel strip during heating, which would cause stress on the electrode end of the heating rod. Stress can easily damage the electrode end structure of the heating rod under high temperature conditions.

[0056] See attached document Figure 1 The thermocouple positioning bracket 9 is located at the top of the calibration furnace. Multiple limiting holes are provided on the bracket. The geometric center of the thermocouple positioning bracket 9 is the limiting hole for the calibration thermocouple. The thermocouple under test and the standard thermocouple are radially and axially limited through the limiting hole at the geometric center of the thermocouple positioning bracket 9. Three thermocouples can be inserted into the limiting hole at the same time, namely two thermocouples under test and one standard thermocouple, so as to realize the simultaneous measurement of two thermocouples.

[0057] See attached document Figure 3 The radial and axial limiting of the temperature-controlled thermocouple 3 is achieved through the limiting holes of the temperature-controlled thermocouple. The temperature-controlled thermocouple 3 is a non-standard thermocouple of platinum-rhodium 40-platinum-rhodium 20, with an upper limit of temperature control of 1800℃. A refractory vent pipe limiting hole is provided symmetrically at the limiting holes of the temperature-controlled thermocouple to achieve radial and axial limiting of the refractory vent pipe 7. The axial depth of the refractory vent pipe 7 is close to the bottom of the closed end of the furnace tube, ensuring that while protective gas is transported inside the furnace tube 1, the protective gas can overflow the entire furnace tube, achieving 100% filling of the furnace tube with protective gas during the calibration process. A one-way airflow valve is installed at the upper end of the refractory vent pipe 7 to ensure a stable flow of gas into the furnace tube 1.

[0058] See attached document Figure 2The furnace consists of five layers of annular refractory bricks, with the bottom layer being a solid, disc-shaped refractory brick. Hollow annular refractory bricks are then stacked one on top of this solid disc-shaped refractory brick, surrounding the heating zone formed by the heating rod 2 and furnace tube 1. The top of the stacked annular refractory brick layers is inlaid with circular limiting bricks. Through the circular limiting bricks, the annular refractory brick layers, and the bottom solid disc-shaped refractory brick, a high-reflectivity enclosed furnace and efficient heat insulation barrier are formed, breaking through the existing temperature limit of 1600℃ for high-temperature thermocouple calibration furnaces and achieving 1800℃ high-temperature calibration. This effectively insulates the heating zone formed by the heating rod 2 and furnace tube 1. The cylindrical sealed space provides insulation for the heating zone formed by the heating rod 2 and furnace tube 1. Compared to a conventional rectangular furnace, the cylindrical furnace eliminates radiation dead zones, allowing heat radiated from the heating rod to reach the furnace tube with fewer reflections and a higher proportion, reducing energy loss during transfer. Cylindrical structures can focus circumferentially distributed energy onto the central axis, while rectangular structures tend to disperse energy within a local plane, which is not conducive to forming a uniform axial temperature field.

[0059] Polishing is performed on the sealed space formed by each layer of refractory bricks to smooth and flat the rough and porous inner surface of the refractory bricks, reducing the amount of diffuse reflection on the rough surface. The heat is then reflected directionally to the furnace tube area through mirror reflection, thereby increasing radiant heat and achieving better heat preservation.

[0060] A high-reflectivity coating was applied to the sealed space formed by each layer of refractory bricks. The coating was made by mixing alumina micro powder and alumina sol in a 1.5:1 ratio to form a uniform slurry. The slurry was then sprayed onto the sealed space formed by the refractory bricks using a spray gun, with the coating thickness controlled between 0.1 mm and 0.5 mm. The coating was first dried at 100℃ to 150℃, and then sintered at high temperature during the initial heating of the calibration furnace to 1800℃, forming a robust and durable high-reflectivity coating.

[0061] Given that the emissivity of the furnace inner wall without coating is ε1 = 0.85, and with coating, the emissivity is ε1 = 0.20, and the emissivity of the furnace tube surface is ε1 = 0.80; the furnace inner wall temperature is T1 = 1200℃, the furnace tube surface temperature is T2 = 1100℃, the furnace inner radius is R1 = 0.1m, the furnace tube outer radius is R2 = 0.02m, and the furnace length is L = 1m, calculate the overall radiation exchange factor under different conditions using the following formula. The overall radiation exchange factor without coating is F. 12-no =0.52, the overall radiation exchange factor with coating is F 12-with =0.05.

[0062]

[0063] The effectiveness of the high-reflectivity coating was verified by calculating and comparing the net radiative heat flow in the furnace with and without the coating. The calculation process is as follows:

[0064]

[0065] Among them: Q f Net radiative heat flux, W / m 2 ;

[0066] σ: Stefan-Boltzmann constant, 5.67 × 10⁻⁶ -8 W / (m 2 ·K 4 );

[0067] A1: Surface area of ​​the furnace inner wall, m² 2 ;

[0068] T1: Absolute temperature of the furnace, K;

[0069] T2: Absolute temperature of the furnace tube, K;

[0070] F 12 Total radiation exchange factor.

[0071] The net radiative heat flux Q without coating was calculated. f =33800W / m 2 With coating, net radiative heat flux Q f =3100W / m 2 Calculations show that without a coating, the furnace absorbs a large amount of heat and transfers it to the furnace tubes via high radiation; that is, most of the heat is absorbed by the furnace and not reflected. With a coating, the furnace absorbs a small amount of heat and transfers it to the furnace tubes via low radiation; that is, most of the heat is reflected by the furnace and not absorbed. High-efficiency heat preservation is achieved through a high-reflectivity coating process.

[0072] See attached document Figure 1 The annular refractory brick layer is wrapped with an insulation layer 6 of different materials. The insulation layer material in contact with the annular refractory brick layer is a high-alumina felt made of alumina fiber and zirconium oxide fiber. The outer layer of the high-alumina felt is wrapped with ceramic fiber cotton with a thermal conductivity one order of magnitude lower. The double-layer insulation cotton with different thermal conductivity effectively reduces the heat exchange between the furnace interior and the outside air. Through the structure of gradient change in thermal conductivity, a high-efficiency thermal insulation barrier is achieved. The high-reflectivity closed furnace is combined with the high-efficiency thermal insulation barrier.

[0073] To determine the optimal thickness of double-layer insulation cotton of different materials, the optimal insulation thickness is calculated and confirmed by minimizing heat loss (i.e., maximizing thermal resistance) while ensuring that the insulation cotton does not exceed its temperature resistance limit. The calculation process is as follows: For a cylindrical furnace, the unit heat flux is calculated using the cylindrical thermal resistance formula:

[0074]

[0075] Where: L: furnace length, m;

[0076] r1: Outer radius of the refractory brick, i.e., the inner radius of the insulation layer, in meters;

[0077] r2: Outer radius of the first insulation layer, in meters;

[0078] r3: Outer radius of the second insulation layer, in meters;

[0079] h i : Internal surface heat transfer coefficient, W / (m2·K);

[0080] h0: External surface heat transfer coefficient, W / (m2·K);

[0081] T i : Inner surface temperature, K;

[0082] T0: Ambient temperature, K;

[0083] k1: Thermal conductivity of the inner high-alumina felt, W / (m·K);

[0084] k2: Thermal conductivity of the outer ceramic fiber cotton, W / (m·K).

[0085] Assuming that heat exchange between the inner and outer surfaces of the insulation layer has a relatively small impact, and that the main thermal resistance is the thermal resistance of the insulation layer, the heat exchange between the inner and outer surfaces of the insulation layer is ignored, and the formula for calculating unit heat flux is approximated as follows:

[0086]

[0087] Under optimal insulation conditions, the heat flux Q should be minimized and the thermal resistance R should be maximized. The formula for calculating the thermal resistance is as follows:

[0088]

[0089] Let d1 be the thickness of the inner high-alumina felt, then d1 = r2 - r1; d2 be the thickness of the outer ceramic fiber cotton, then d2 = r3 - r2; d t For the total thickness of the insulation cotton, then d t =d1+d2=r3-r1. The temperature inside the furnace is known to be T. i =1200℃, ambient temperature T0 = 25℃, refractory brick outer radius r1 = 0.15m, inner high-alumina felt thermal conductivity k1 = 0.25W / (m·K), outer ceramic fiber cotton thermal conductivity k2 = 0.025W / (m·K), furnace length L = 1m, the maximum operating temperature of the outer ceramic fiber cotton is T max =800℃, based on the interface temperature relationship, the following formula is obtained:

[0090]

[0091] Based on the above formula, the thickness of the inner high-alumina felt is 80mm, and the thickness of the outer ceramic fiber cotton is 20mm.

[0092] See attached document Figure 2 The furnace shell 10 adopts a hollow structure, and the distance between it and the insulation cotton is 5cm to ensure that the insulation cotton layer can fully exchange heat with the outside air. When the furnace tube temperature is heated to 1800℃, the temperature of the outermost shell is 200℃. Two cooling fans 11 are installed on the furnace shell 10. After the high-temperature test is completed, the cooling fans 11 are activated to increase the convection heat exchange between the furnace body and the outside, so as to achieve rapid cooling after the high-temperature test is completed.

[0093] In summary, the thermocouple calibration furnace provided by this invention has at least the following advantages compared to the prior art:

[0094] 1. This invention, through the design of the heat insulation layer, can reach a maximum temperature of 1800℃, breaking through the traditional high-temperature calibration furnace upper limit of 1600℃. It can melt high-melting-point materials such as platinum, thereby improving the calibration accuracy by using pure metal materials and the fused wire method for calibration at temperatures exceeding 1600℃.

[0095] 2. This invention uses a vertical furnace to solve the problem of high-temperature deformation of furnace tubes under gravity in common horizontal thermocouple calibration furnaces;

[0096] 3. This invention uses a protective gas to provide full protection during the calibration process, preventing the thermocouple under test from oxidizing under high-temperature calibration conditions;

[0097] 4. This invention, through the design of the insulation layer, uses the optimal combination thickness of two layers of insulation cotton of different materials to maximize the insulation of the furnace tube, so that the temperature can reach 1800℃.

[0098] 5. This invention achieves rapid cooling after high-temperature testing through the design of a cooling device.

[0099] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the device as described in the figures. For example, if the device in the figures were inverted, a device described as "above" or "on top of" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0100] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0101] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A thermocouple calibration furnace, characterized in that, The thermocouple calibration furnace is a vertical calibration furnace, comprising a furnace core assembly, a one-way atmosphere protection device, and a thermocouple positioning device. The one-way atmosphere protection device includes a gas cylinder containing protective gas and a vent pipe (7) connected to the gas cylinder through a gas passage. During the calibration process, the vent pipe (7) fills the furnace tube (1) with protective gas. The thermocouple positioning device is installed above the furnace tube (1) to fix the vent pipe (7), the temperature control thermocouple (3), the thermocouple to be tested and the standard thermocouple; The furnace core assembly includes a furnace tube (1), a heating device, a temperature-controlled thermocouple (3), a heat insulation layer, and a heat preservation layer (6). The heating device includes at least one heating rod (2) and a power source that provides energy to the heating rod (2). The furnace tube (1) is installed vertically to the ground and is a refractory furnace tube (1) that is closed at the bottom and open at the top. The closed end is located inside the heat insulation layer, and the open end is located on the upper surface of the heat insulation layer. A vent pipe (7) of a one-way atmosphere protection device and a temperature-controlled thermocouple (3) are installed inside the furnace tube (1). The temperature-controlled thermocouple (3) is used for detection and control. The temperature of the furnace tube (1) is controlled by the heating rod (2), which is a U-shaped heating rod (2) and placed around the furnace tube (1). The heat insulation layer is a cylindrical sealed space surrounded by refractory bricks, including a circular limiting brick (4), an annular brick (5) and a bottom circular brick. The furnace tube (1) is installed at the geometric center of the heat insulation layer. The circular limiting brick (4) is provided with limiting holes for the furnace tube (1) and the heating rod (2). The sealed space side of the heat insulation layer is polished and then sprayed with a high reflectivity coating. The heat insulation layer (6) is wrapped around the annular brick (5).

2. The thermocouple calibration furnace according to claim 1, characterized in that, The heating rod (2) is a U-shaped heating rod (2) made of silicon molybdenum, including a heating end and an electrode end. The heating end is placed on the outer periphery of the furnace tube (1), and the electrode end is installed on the limiting hole by a clamp. The power supply and the electrode end are connected by a power line.

3. A thermocouple calibration furnace according to claim 2, characterized in that, The thermocouple positioning bracket (9) has a test thermocouple limiting hole at its geometric center. The test thermocouple and the standard thermocouple are radially and axially limited through the limiting hole at the geometric center of the thermocouple positioning bracket (9).

4. A thermocouple calibration furnace according to claim 3, characterized in that, The temperature-controlled thermocouple (3) is a non-standard platinum-rhodium 40-platinum-rhodium 20 thermocouple with a temperature control limit of 1800℃.

5. A thermocouple calibration furnace according to claim 1, characterized in that, The axial depth of the refractory vent pipe (7) is close to the bottom of the closed end of the furnace tube (1), and a one-way airflow valve (8) is installed at the upper end of the refractory vent pipe (7).

6. A thermocouple calibration furnace according to claim 1, characterized in that, The insulation layer (6) consists of two layers, including a first insulation layer in contact with the heat insulation layer and a second outer insulation layer. The thermal conductivity of the first insulation layer is one order of magnitude greater than that of the second insulation layer.

7. A thermocouple calibration furnace according to claim 6, characterized in that, The formulas for calculating the thickness of the insulation layer (6) one and the insulation layer (6) two are as follows: d1 = r2 - r1, d2 = r3 - r2, where d1 is the thickness of insulation layer one and d2 is the thickness of insulation layer two. r1: Outer radius of the refractory brick, i.e., the inner radius of the insulation layer, in meters; r2: Outer radius of the first insulation layer, in meters; r3: Outer radius of the second insulation layer, in meters; T i T is the temperature inside the borehole. max T0 is the maximum operating temperature of insulation layer 2, T2 is the ambient temperature, k2 is the thermal conductivity of insulation layer 2, and k1 is the thermal conductivity of insulation layer 1.

8. A thermocouple calibration furnace according to claim 6 or 7, characterized in that, The first insulation layer is made of high-alumina felt made of alumina fiber and zirconium oxide fiber, and the second insulation layer is made of ceramic fiber cotton.

9. A thermocouple calibration furnace according to claim 1, characterized in that, The thermocouple calibration furnace also includes a cooling device, which includes a furnace shell (10) and a cooling fan (11). The furnace shell (10) is cylindrical and is wrapped around the heat insulation layer and the heat preservation layer (6), with a gap between it and the heat insulation layer and the heat preservation layer (6). The cooling fan (11) is installed on the furnace shell (10).

10. A thermocouple calibration furnace according to claim 9, characterized in that, The furnace shell (10) has a hollow structure.

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