Magnet system with opening and closing operations implemented on-line on an electrobalance experimental device

Abstract

The application discloses a magnet system capable of implementing opening and closing operation on an electric balance experimental device, wherein a unique horizontal opening and closing surface is arranged at the position close to the air gap of a BIPM magnet, the BIPM magnet is divided into a first magnet and a second magnet which are asymmetrically coaxially arranged in the up-down direction, one of the first magnet and the second magnet is used as a fixed part and the other is used as a movable part, the opening and closing of the BIPM magnet is realized by applying a mechanical force to the movable part to make the movable part axially move relative to the fixed part, and the partial electromagnetic force generated when the BIPM is opened and closed is offset by using the gravity of the movable part, so that the mechanical force required for the opening and closing of the BIPM magnet is minimized. The application can solve the problem that the BIPM magnet of the electric balance experimental device is difficult to realize online operation due to the excessive electromagnetic attraction force, and the offline operation seriously interferes with the coil collimation measurement system, and can greatly improve the convenience of the operation of the electric balance experimental device and the stability of the measurement.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic measurement and precision instrument technology, and specifically relates to a magnet system that can be opened and closed online on an electric balance experimental device. Background Technology

[0002] The magnet system is one of the core devices for reproducing the kilogram, a unit of mass, using the electric balance method. Generally, the magnet system is required to provide uniformity (vertically) better than 5 × 10⁻⁶ within a measurement range of 10 mm or more. -4 The magnetic field. Currently, the magnetic system required for electric balance experiments all adopts a "permanent magnet + yoke" design. This involves using a high-permeability yoke to guide the magnetic field lines of the permanent magnet through a uniform air gap between the inner and outer yokes, thus generating a relatively uniform radiating magnetic field in the vertical direction within this air gap. Currently, the most commonly used magnetic circuit design for electric balance experimental apparatus internationally is the BIPM type magnetic circuit system proposed by the International Bureau of Weights and Measures.

[0003] Because the BIPM type magnet uses a closed magnetic circuit design, it faces the following main problems during experiments: It requires mechanical forces of several kN or even exceeding 10 kN to open or close the magnet. Furthermore, if adjustments are needed to the coils or optical components of the suspension system, the magnet must first be removed from the electric balance apparatus, and then opened using a specially designed mechanical device. Removing the magnet typically requires disassembling the main optical components and electrical wiring, inevitably causing interference to the measurement system, especially the coil collimation measurement system. Moreover, after the magnet is reinstalled into the electric balance apparatus, the coil collimation measurement system needs to be readjusted and reset, making the entire readjustment process extremely cumbersome, time-consuming, and labor-intensive. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of this invention is to provide a magnet system that can be opened and closed online on an electric balance experimental device. This solves the problem that the BIPM type magnet in the electric balance experimental device is difficult to operate online due to excessive electromagnetic attraction, while offline operation seriously interferes with the coil collimation measurement system. This significantly improves the ease of operation and measurement stability of the electric balance experimental device.

[0005] According to an embodiment of the present invention, a magnet system capable of online opening and closing operations on an electric balance experimental device has a unique horizontal opening and closing surface optimizedly provided on the BIPM type magnet near the air gap end. The horizontal opening and closing surface divides the BIPM type magnet into an asymmetrically coaxially arranged first magnet and second magnet in the vertical direction. One of the first magnet and the second magnet serves as a fixed part and the other as a movable part. The fixed part is used to fix it to the balance experimental device. The opening and closing of the BIPM type magnet is achieved by applying a mechanical force to the movable part, causing the movable part to move axially relative to the fixed part. By utilizing the gravity of the movable part to counteract part of the electromagnetic force generated when the BIPM is opened and closed, the mechanical force required for the opening and closing of the BIPM type magnet is minimized.

[0006] According to an embodiment of the present invention, a magnet system capable of online opening and closing operations on an electric balance experimental device, by optimizing the horizontal opening and closing surface, utilizes the gravity of the movable part to counteract some of the electromagnetic forces, such as attractive or repulsive forces, generated when the BIPM-type magnet opens and closes. This minimizes the mechanical force required for the opening and closing of the BIPM-type magnet within a certain range. Thus, without affecting the realization of other measurement systems or functions of the electric balance experimental device, the opening or closing operation of the BIPM-type magnet can be completed using conventional mechanical auxiliary devices such as mechanical guide rails and low-power motors, realizing online adjustment of the coil or magnetic field characteristics of the magnet system of the present invention. The magnet system capable of online opening and closing operations on an electric balance experimental device according to the present invention solves the problem that the BIPM-type magnet in an electric balance experimental device is difficult to operate online due to excessive electromagnetic attraction, while offline operation seriously interferes with the coil collimation measurement system. This significantly improves the convenience of operation and the stability of measurement of the electric balance experimental device.

[0007] In some embodiments, the first magnet includes a first cover, a first inner yoke, a first permanent magnet, and a first outer yoke. The first permanent magnet is fixed between the first cover and the first inner yoke, and the first outer yoke surrounds the outer periphery of the first permanent magnet and the first inner yoke and is fixed to the first cover. The second magnet includes a second cover, a second inner yoke, a second permanent magnet, and a second outer yoke. The second permanent magnet is fixed between the second cover and the second inner yoke. The second outer yoke surrounds the outer periphery of the second permanent magnet and the second inner yoke and is fixed to the second cover. The second outer yoke and the second inner yoke are respectively axially aligned with the first outer yoke and the first inner yoke, and the horizontal contact surface when the first magnet and the second magnet are in contact is the horizontal opening and closing surface.

[0008] In some embodiments, the horizontal opening surface is located on one side of the central horizontal plane of the BIPM type magnet.

[0009] In some embodiments, the BIPM type magnet is assembled in one of the following four ways, which are as follows: Assembly method 1: The horizontal opening and closing surface is located above the central horizontal surface, the second magnet is the fixed part, and the first magnet is the movable part; Assembly method two: The horizontal opening and closing surface is located above the central horizontal plane, the first magnet is the fixed part, and the second magnet is the movable part; Assembly method three: The horizontal opening and closing surface is located below the central horizontal surface, the second magnet is the fixed part, and the first magnet is the movable part; Assembly method four: The horizontal opening and closing surface is located below the central horizontal surface, the first magnet is the fixed part, and the second magnet is the movable part.

[0010] In some embodiments, with the central horizontal plane A as a reference, the vertical coordinates of the central horizontal plane A are... z =0mm, the distance from the central horizontal plane to the horizontal opening and closing surface is z o The distance between the first magnet and the second magnet when the BIPM type magnet is in the open state is Δ. z The electromagnetic force between the first magnet and the second magnet is f (Δ z And define attractive force as negative, repulsive force as positive, and gravity of the first magnet as... G 1. The gravity of the second magnet is G 2. The maximum mechanical force required is Δ f Therefore, under assembly method one, assembly method two, assembly method three, and assembly method four, the maximum required mechanical force is respectively characterized as follows: (1) Δ f= Max| f (Δ z )- G 1|; (2) Δ f= Max| f (Δ z )+ G 2|; (3) Δ f= Max| f (Δ z )- G 2|; (4) Δ f= Max| f (Δ z )+ G1|.

[0011] In some embodiments, for any h min / 2< z o < h a / 2, where, h min To obtain the minimum uniform region of the magnetic field required for measurement, h a To determine the height of the air gap, Δ can be obtained through numerical calculation or estimation using electromagnetic field finite element simulation tools. f With Δ z The changing characteristic curve; in different z o Within the range of values, take Δ f ( z o The position of the point with the minimum value is taken as the position of the horizontal opening and closing surface.

[0012] In some embodiments, the BIPM type magnet is obtained by comprehensively comparing the Δ under the four assembly methods. f ( z o The size and z o The most suitable assembly method is selected based on the magnitude of the impact on the uniform magnetic field region.

[0013] In some embodiments, when both conditions cannot be met simultaneously z o > h min / 2 and to ensure that the magnetic field in the uniform region is not damaged, then take z o = h min / 2.

[0014] In some embodiments, a mechanical auxiliary device is used to traction the movable part, and the traction radius is greater than the average radius of the air gap of the BIPM type magnet.

[0015] In some embodiments, a mechanical guide rail is arranged on the outer periphery of the BIPM type magnet. The mechanical guide rail includes a linear slide rail and a movable member. The extension direction of the linear slide rail is consistent with the axial direction of the BIPM type magnet. The linear slide rail is fixed to the fixed part, and the movable member is fixed to the movable part. The movable member can slide along the linear slide rail.

[0016] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of half assembly of the magnet system when the horizontal opening and closing plane is located above the center horizontal plane according to an embodiment of the present invention; Figure 2 This is a schematic diagram of half assembly of the magnet system when the horizontal opening and closing plane is located below the central horizontal plane according to an embodiment of the present invention; Figure 3 This is one of the schematic diagrams showing the setting position of the horizontal opening and closing surface in an embodiment of the present invention; Figure 4 This is a second schematic diagram showing the setting position of the horizontal opening and closing surface in an embodiment of the present invention; Figure 5 The electromagnetic force for opening and closing of a BIPM-type magnet in one example of this invention. f Follow z o and Δ z The changing characteristic curve; Figure 6 In one example of this invention, Δ is calculated under four assembly scenarios. f Position of horizontal opening and closing surface z o The changing characteristic curve.

[0018] Figure label: BIPM type magnet 100; first magnet 1; first cover 101; first inner yoke 102; first outer yoke 103; first permanent magnet 104; second magnet 2; second cover 201; second inner yoke 202; second outer yoke 203; second permanent magnet 204; mechanical guide rail 3; linear slide rail 301; moving part 302; center horizontal plane A; horizontal opening and closing surface B. Detailed Implementation

[0019] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0020] The following is combined with Figures 1 to 6 This invention describes a magnet system that can be opened and closed online on an electric balance experimental apparatus, according to an embodiment of the present invention.

[0021] like Figure 1 and Figure 2As shown, according to an embodiment of the present invention, a magnet system capable of online opening and closing operations on an electric balance experimental apparatus has a unique horizontal opening and closing surface B optimizedly provided on the BIPM type magnet 100 near the air gap end. The horizontal opening and closing surface B divides the BIPM type magnet 100 into an asymmetrically coaxially arranged first magnet 1 and second magnet 2 in the vertical direction. In particular, it divides the inner and outer magnetic yokes of the BIPM type magnet 100 into asymmetrical upper and lower parts. The axial dimension of the first inner magnetic yoke 102 is smaller than the axial dimension of the second inner magnetic yoke 202, and the first inner magnetic yoke 102 and the second inner magnetic yoke 202 are asymmetrical vertically. The axial dimension of the first outer magnetic yoke 103 is smaller than the axial dimension of the second outer magnetic yoke 203, and the first outer magnetic yoke 103 and the second outer magnetic yoke 203 are asymmetrical vertically. The horizontal opening and closing surface B is the horizontal contact surface when the first magnet 1 and the second magnet 2 are in contact. One of the first magnet 1 and the second magnet 2 serves as a fixed part and the other as a movable part. The fixed part is used to fix it to the balance experimental apparatus. For example, the first magnet 1 is fixed to the balance experimental apparatus as the fixed part, and the second magnet 2 is connected to a conventional mechanical auxiliary device as the movable part. Alternatively, the second magnet 2 is fixed to the balance experimental apparatus as the fixed part, and the first magnet 1 is connected to a conventional mechanical auxiliary device as the movable part. The opening and closing of the BIPM type magnet 100 is achieved by applying mechanical force to the movable part through a conventional mechanical auxiliary device, causing the movable part to move axially relative to the fixed part. The purpose of optimizing the horizontal opening and closing surface B is to use the gravity of the movable part to counteract some of the electromagnetic forces, such as attractive or repulsive forces, generated when the BIPM type magnet 100 is opened and closed, so that the mechanical force required for the opening and closing of the BIPM type magnet 100 within a certain range is minimized. In this way, without affecting the realization of other measurement systems or functions of the electric balance experimental device, the opening or closing operation of the BIPM type magnet 100 can be completed using conventional mechanical auxiliary devices such as mechanical guide rail 3 and low-power motor, so as to realize the online adjustment of the coil or magnetic field characteristics of the magnet system of the present invention.

[0022] The magnet system of the present invention, which can be opened and closed online on the electric balance experimental device, can solve the problem that the BIPM type magnet 100 of the electric balance experimental device is difficult to operate online due to excessive electromagnetic attraction, while offline operation seriously interferes with the coil collimation measurement system. It can greatly improve the convenience of operation and the stability of measurement of the electric balance experimental device.

[0023] In some embodiments, such as Figure 1 and Figure 2As shown, the first magnet 1 includes a first cover 101, a first inner yoke 102, a first permanent magnet 104, and a first outer yoke 103. The first permanent magnet 104 is fixed between the first cover 101 and the first inner yoke 102. The first outer yoke 103 surrounds the outer periphery of the first permanent magnet 104 and the first inner yoke 102 and is fixed to the first cover 101. The second magnet 2 includes a second cover 201, a second inner yoke 202, a second permanent magnet 204, and a second outer yoke 203. The second permanent magnet 204 is fixed between the second cover 201 and the second inner yoke 202. The second outer yoke 203 surrounds the outer periphery of the second permanent magnet 204 and the second inner yoke 202 and is fixed to the second cover 201. The second outer yoke 203 and the second inner yoke 202 are respectively axially aligned with the first outer yoke 103 and the first inner yoke 102.

[0024] When the BIPM type magnet 100 is closed, the second outer magnetic yoke 203 and the second inner magnetic yoke 202 are in axial contact with the first outer magnetic yoke 103 and the first inner magnetic yoke 102 respectively, and the space gap enclosed by the second outer magnetic yoke 203, the second inner magnetic yoke 202, the first outer magnetic yoke 103, and the first inner magnetic yoke 102 constitutes the air gap of the BIPM. When the BIPM type magnet 100 is opened, the second outer yoke 203 and the second inner yoke 202 are axially separated from the first inner yoke 102 and the second outer yoke 203, respectively. This allows for convenient online adjustment of the coil or magnetic field characteristics of the first permanent magnet 104 coil and the second permanent magnet 204.

[0025] In some embodiments, such as Figure 1 and Figure 2 As shown, the horizontal opening and closing surface B is located on one side of the central horizontal surface A of the BIPM type magnet 100. That is to say, the horizontal opening and closing surface B can be located above the central horizontal surface A or below the central horizontal surface A. The central horizontal surface A can be understood as the centrally symmetrical plane of the BIPM type magnet 100. In this way, the first magnet 1 and the second magnet 2 are asymmetrically coaxially arranged in the vertical direction.

[0026] In some embodiments, the BIPM type magnet 100 is assembled in one of the following four ways, as follows: Assembly method 1: The horizontal opening and closing surface B is located above the central horizontal surface A, the second magnet 2 is the fixed part, and the first magnet 1 is the movable part; Assembly method two: The horizontal opening and closing surface B is located above the central horizontal surface A, the first magnet 1 is the fixed part, and the second magnet 2 is the movable part; Assembly method three: The horizontal opening and closing surface B is located below the central horizontal surface A, the second magnet 2 is the fixed part, and the first magnet 1 is the movable part; Assembly method four: The horizontal opening and closing surface B is located below the central horizontal surface A. The first magnet 1 is the fixed part, and the second magnet 2 is the movable part.

[0027] In some embodiments, such as Figure 1 and Figure 2 As shown, with the central horizontal plane A as a reference, the vertical coordinates of the central horizontal plane A are... z =0mm, the distance from the center horizontal plane A to the horizontal opening and closing plane B is z o When the BIPM type magnet 100 is in the open state, the distance between the first magnet 1 and the second magnet 2 is Δ. z (Generally on the order of cm), the electromagnetic force between the first magnet 1 and the second magnet 2 is f (Δ z And define the attractive force as negative and the repulsive force as positive, and the gravity of the first magnet 1. G 1. The gravity of the second magnet 2 is G 2. The maximum mechanical force required is Δ f Then, under assembly method one, assembly method two, assembly method three, and assembly method four, the maximum required mechanical force is respectively represented as follows: (1) Δ f= Max| f (Δ z )- G 1|; (2) Δ f= Max| f (Δ z )+ G 2|; (3) Δ f= Max| f (Δ z )- G 2|; (4) Δ f= Max| f (Δ z )+ G 1|.

[0028] It should be noted that when the first magnet 1 and the second magnet 2 are in the closed state, the resultant force of the electromagnetic force and the gravity of the movable part points towards the fixed part. Therefore, the BIPM type magnet 100 can remain in the closed state without mechanical assistance.

[0029] In some embodiments, such as Figure 3 As shown, for any h min / 2< z o < h a / 2, where,h min To obtain the minimum uniform region of the magnetic field required for measurement, h a The height of the air gap (i.e., the sum of the axial heights of the first inner magnetic yoke 102 and the second inner magnetic yoke 202) can be obtained by numerical calculation or estimation using electromagnetic field finite element simulation tools. f With Δ z The changing characteristic curve; in different z o Within the range of values, take Δ f ( z o The position of the horizontal opening and closing surface B is defined as the point with the minimum mechanical force. In other words, each of the four assembly methods of the BIPM type magnet 100 has a corresponding minimum mechanical force and its own position of the horizontal opening and closing surface B.

[0030] In some embodiments, the BIPM type magnet 100 compares the Δ values ​​under four assembly methods. f ( z o The size and z o The most suitable assembly method is selected based on the magnitude of the impact on the uniform magnetic field region.

[0031] In some embodiments, such as Figure 4 As shown, when it is not possible to satisfy simultaneously z o > h min / 2 and to ensure that the magnetic field in the uniform region is not damaged, then take z o = h min / 2.

[0032] The following is a specific example, in which the outer diameter of the magnetic circuit is 300 mm, and the height of the BIPM type magnet 100 in the closed state is 210 mm. The permanent magnet uses samarium cobalt (Sm2Co). 17 The inner yoke is made of soft magnetic material and provides a magnetic field source for the entire magnetic circuit. The height of the inner yoke is 70 mm, its outer diameter is 200 mm, and its inner diameter is 50 mm. The inner diameter of the outer yoke is 240 mm, and its outer diameter is 300 mm. The air gap formed by the inner and outer yokes is 20 mm. The average magnetic induction intensity of the magnetic field in the air gap is 0.4 T. The inner and outer yokes are made of soft magnetic material and operate in the linear region of magnetization characteristics without obvious local saturation.

[0033] In this example, h min / 2=10mm, therefore zo The value range is 10mm to 35mm (at the end of the air gap), Δ z The value range is 0mm to 30mm. First, using electromagnetic field finite element simulation analysis software, the electromagnetic force between the first and second magnet parts is calculated. f Follow z o and Δ z The distribution of variation is characterized by the corresponding characteristic curves, as shown in the attached figure. Figure 5 As shown. It is not difficult to see that electromagnetic force f Follow z o The change in Δ z It exhibits high sensitivity under relatively small values; electromagnetic force varies with... z o and Δ z Changing characteristic curve f (Δ z (Approximately from) z o > Starting at 18mm, and with the electromagnetic force having a zero-crossing point, it indicates that the electromagnetic force is an attractive force within a certain range, while it is a repulsive force within other ranges.

[0034] In this example, the volume of the second magnet 2 is greater than the volume of the first magnet 1, and the weight of the second magnet 2 is... G 2 = 500N, the weight of the first magnet 1 is G 1 = 300N; due to electromagnetic force in different z o and Δ z The calculated values ​​and the maximum mechanical force Δ required to open or close the magnet. f Based on the relationships satisfied under different assembly conditions, Δ can be calculated for the four assembly conditions of the BIPM type magnet 1000. f Position of the opening and closing plane of the magnet z o The characteristic curves of the change are shown in the attached figure. Figure 6 As shown. Under four assembly conditions of the BIPM type magnet 1000, the optimal position and minimum mechanical force of its horizontal opening and closing plane are respectively... (1) z o =18mm, Δ f =250N; (2) z o =27mm, Δ f =880N; (3) z o =16mm, Δ f =220N; (4) z o =25mm, Δ f =690N.

[0035] Note that in the above four situations, the BIPM type magnet is in the off state, i.e., Δ z When the magnetic field diameter is 0 mm, the resultant force of the electromagnetic force and the gravity of the movable part both point towards the fixed part of the magnet. Under this condition, the BIPM type magnet 100 can remain closed without mechanical assistance. In terms of the magnitude of the resultant force, (1) and (3) have smaller mechanical forces, but the position of the horizontal opening and closing surface B has a greater impact on the uniform magnetic field area; conversely, (2) and (4) have higher mechanical forces, but have less impact on the uniform magnetic field area. The final selection and determination of which of the above four optimal positions of the horizontal opening and closing surface B should be determined according to the specific assembly requirements of the magnet in the electric balance experimental device (choose one of the four). However, in general, if the position of the horizontal opening and closing surface B obtained according to the optimization idea is designed, the mechanical force will be significantly lower than before optimization (>3kN). This can solve the problem that the electric balance experimental device uses a closed magnetic circuit magnet, which is difficult to operate online due to excessive attraction, while offline operation seriously affects the collimation measurement of the magnet system coil. This can greatly improve the convenience of operation and the stability of measurement of the electric balance experimental device.

[0036] In some embodiments, a mechanical auxiliary device is used to pull the movable part, and the traction radius is greater than the average radius of the air gap of the BIPM type magnet 100, so as to facilitate the insertion and removal of the coil; the mechanical auxiliary device is used to pull the movable part to open or close the BIPM type magnet 100, and the operation of opening or closing the BIPM type magnet 100 is performed directly on the electric balance experimental device, and the operation process does not cause significant interference to other measurement systems or functions of the electric balance experimental device.

[0037] In some embodiments, a mechanical guide rail 3 is arranged on the outer periphery of the BIPM type magnet 100. The mechanical guide rail 3 includes a linear slide rail 301 and a movable member 302. The extending direction of the linear slide rail 301 is consistent with the axial direction of the BIPM type magnet 100. The linear slide rail 301 is fixed to the fixed part, and the movable member 302 is fixed to the movable part. The movable member 302 can slide along the linear slide rail 301. For example, as Figure 1 and Figure 2 As shown, there are three mechanical guide rails 3, and the three mechanical guide rails 3 are arranged at 120 degrees. 。The mechanical guide rails 301 are spaced apart on the outer periphery of the BIPM type magnet 100. The linear guide rail 301 is fixedly connected to the second cover 201 of the second magnet 2 (which is a fixed part), and the movable part 302 is fixedly connected to the first cover 101 of the first magnet 1 (which is a movable part). By arranging the mechanical guide rails 3 on the outside of the BIPM type magnet 100, the axial movement of the movable part can be guided, ensuring smooth movement of the movable part.

[0038] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A magnet system capable of online opening and closing operation on an electric balance experimental apparatus, characterized in that, A unique horizontal opening and closing surface is provided on the BIPM type magnet near the air gap end. The horizontal opening and closing surface divides the BIPM type magnet into an asymmetrically coaxially arranged first magnet and second magnet in the vertical direction. One of the first magnet and the second magnet serves as a fixed part and the other serves as a movable part. The fixed part is used to fix it to the balance experimental device. The opening and closing of the BIPM type magnet is achieved by applying mechanical force to the movable part, causing the movable part to move axially relative to the fixed part. By using the gravity of the movable part to counteract part of the electromagnetic force generated when the BIPM is opened and closed, the mechanical force required for the opening and closing of the BIPM type magnet is minimized. The first magnet includes a first cover, a first inner yoke, a first permanent magnet, and a first outer yoke. The first permanent magnet is fixed between the first cover and the first inner yoke, and the first outer yoke surrounds the outer periphery of the first permanent magnet and the first inner yoke and is fixed to the first cover. The second magnet includes a second cover, a second inner yoke, a second permanent magnet, and a second outer yoke. The second permanent magnet is fixed between the second cover and the second inner yoke. The second outer yoke surrounds the outer periphery of the second permanent magnet and the second inner yoke and is fixed to the second cover. The second outer yoke and the second inner yoke are respectively axially aligned with the first outer yoke and the first inner yoke, and the horizontal contact surface when the first magnet and the second magnet are in contact is the horizontal opening and closing surface. The horizontal opening and closing surface is located on one side of the central horizontal plane of the BIPM type magnet.

2. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to claim 1, characterized in that, The BIPM type magnet is assembled in one of the following four ways, as follows: Assembly method 1: The horizontal opening and closing surface is located above the central horizontal surface, the second magnet is the fixed part, and the first magnet is the movable part; Assembly method two: The horizontal opening and closing surface is located above the central horizontal plane, the first magnet is the fixed part, and the second magnet is the movable part; Assembly method three: The horizontal opening and closing surface is located below the central horizontal surface, the second magnet is the fixed part, and the first magnet is the movable part; Assembly method four: The horizontal opening and closing surface is located below the central horizontal surface, the first magnet is the fixed part, and the second magnet is the movable part.

3. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to claim 2, characterized in that, With the central horizontal plane as a reference, the vertical coordinates of the central horizontal plane z =0mm, the distance from the central horizontal plane to the horizontal opening and closing surface is z o The distance between the first magnet and the second magnet when the BIPM type magnet is in the open state is Δ. z The electromagnetic force between the first magnet and the second magnet is f (Δ z And define attractive force as negative, repulsive force as positive, and gravity of the first magnet as... G 1. The gravity of the second magnet is G 2. The maximum mechanical force required is Δ f Therefore, under assembly method one, assembly method two, assembly method three, and assembly method four, the maximum required mechanical force is respectively characterized as follows: (1)D f= Max| f (D z )- G 1|; (2)D f= Max| f (D z )+ G 2|; (3)D f= Max| f (D z )- G 2|; (4)D f= Max| f (D z )+ G 1|。 4. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to claim 3, characterized in that, For any h min / 2< z o < h a / 2, where, h min To obtain the minimum uniform region of the magnetic field required for measurement, h a To determine the height of the air gap, Δ can be obtained through numerical calculation or estimation using electromagnetic field finite element simulation tools. f With Δ z The changing characteristic curve; in different z o Within the range of values, take Δ f ( z o The position of the point where the minimum value is is taken as the position of the horizontal opening and closing surface.

5. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to claim 4, characterized in that, The BIPM type magnet is obtained by comprehensively comparing the Δ under the four assembly methods. f ( z o The size and z o The most suitable assembly method is selected based on the magnitude of the impact on the uniform magnetic field region.

6. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to claim 5, characterized in that, When both conditions cannot be met z o > h min / 2 and to ensure that the magnetic field in the uniform region is not damaged, then take z o = h min / 2.

7. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to any one of claims 1-6, characterized in that, The movable part is tractioned by a mechanical auxiliary device, and the traction radius is greater than the average radius of the air gap of the BIPM type magnet.

8. The magnet system capable of online opening and closing operation on an electric balance experimental apparatus according to any one of claims 1-6, characterized in that, The outer periphery of the BIPM type magnet is provided with a mechanical guide rail, which includes a linear slide rail and a movable component. The extension direction of the linear slide rail is consistent with the axial direction of the BIPM type magnet. The linear slide rail is fixed to the fixed part, and the movable component is fixed to the movable part. The movable component can slide along the linear slide rail.

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