Device and method for measuring temperature coefficient of permanent magnetic material based on nuclear magnetic resonance principle

Abstract

The present invention discloses a device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance, belonging to the technical field of measuring the magnetic properties of permanent magnet materials. The device includes a high-uniform magnetic system in a magnetic shielding space, a dual-temperature control system, a magnetic field detection system, a temperature test system, a mobile trolley, and a magnetic shielding space. The method for measuring the temperature coefficient of a permanent magnet using the above device is as follows: the nuclear magnetic resonance magnetometer probe is used to detect the change in the magnetic field, and the detected value is output through a computer; the temperature sensor outputs the temperature of the permanent magnet to be measured through a computer; then, based on the formula, the change in the magnetic field value corresponding to different temperatures is calculated and processed to obtain the temperature coefficient of the permanent magnet to be measured. The present invention uses a nuclear magnetic resonance magnetometer to accurately measure the high-uniform magnetic field generated by the permanent magnet. By changing the temperature of the permanent magnet, the relationship between the magnetic field of the permanent magnet and the temperature is obtained, realizing the high-precision measurement of the temperature coefficient of permanent magnet materials, and the measurement accuracy can reach the order of ×10<supgt;‑7< / supgt; / ℃.

Description

Technical Field

[0001] The invention relates to the technical field of permanent magnetic material magnetic property measurement, and in particular to a device and method for measuring the temperature coefficient of a permanent magnet based on the nuclear magnetic resonance principle. Background Art

[0002] The temperature stability of permanent magnetic materials is an important characteristic parameter of permanent magnetic materials. It is particularly important in the application of permanent magnetic materials, especially in inertial navigation devices and various electric vacuum devices. The temperature coefficient of permanent magnetic materials is an important indicator to measure temperature stability. If the temperature coefficient of permanent magnetic materials can be accurately measured, it can provide support for the development of permanent magnetic materials with high temperature stability.

[0003] At present, the main methods for measuring the temperature coefficient of permanent magnetic materials are: superconducting quantum susceptibility meter (Squid), magneto-optical method, magnetoresistance, vibrating sample magnetometer, magnetic balance, fluxgate, Hall effect, fluxmeter method, electron paramagnetic resonance, nuclear magnetic resonance measurement method, etc. Among them, the worst accuracy is about 10 for superconducting quantum susceptibility meter, magneto-optical method and magnetoresistance method. -2 / ℃ level, while the fluxmeter method can reach (100~10)×10 -6 / ℃ level. The most accurate method is the nuclear magnetic resonance measurement method, which can reach (10~1)×10 -6 / ℃ level.

[0004] There are many reports on the measurement of temperature coefficient of permanent magnetic materials, such as:

[0005] CN202735500U "Device and method for measuring temperature characteristics of permanent magnets and permanent magnetic materials in an open magnetic circuit" uses the principle of electromagnetic induction and a detection coil to measure the magnetic flux of the sample; CN1036835A "Device for measuring the thermal magnetic characteristics of rare earth permanent magnets" uses a magnetometer to measure the magnetic flux density of the test sample at different temperatures; CN203759233U "A permanent magnet temperature coefficient open circuit measurement device" and CN103887036A "A gradient field electromagnet for open circuit measurement of permanent magnet temperature coefficient" both use a magnetic balance method to measure the temperature coefficient. The common problems of the above methods are: low accuracy and low repeatability, and it is difficult to meet the test requirements of ultra-low temperature coefficients.

[0006] The fluxmeter method has a relatively high measurement accuracy, with a maximum of 5 significant digits. The measurement accuracy needs to be further improved. In addition, the measurement method is to obtain the flux signal by cutting the magnetic field lines relative to the test coil through the sample to be tested, and then obtain the test result through multiple processes of amplifiers and integrators. These processing processes inevitably introduce detection errors, which have a great impact on high-precision testing.

[0007] Siemens has studied the temperature coefficient of permanent magnetic materials. The patent publication number is CN101109720A, "Method and device for measuring the temperature change characteristics of magnetic induction intensity of magnetic materials". Although it is a measurement method based on nuclear magnetic resonance, it has at least the following problems: First, this method puts the magnetic material to be measured into the nuclear magnetic resonance device, which will destroy the uniformity of the high uniform magnetic field (usually 20-30ppm) of the nuclear magnetic resonance; then, it requires the probe to be very close to the material, which will inevitably lead to a large difference in the magnetic field at the probe site, thereby reducing the accuracy of magnetic measurement; in addition, the patent cannot avoid the disturbance of the magnetic field by the heating current, which leads to a reduction in the accuracy of magnetic measurement. Summary of the invention

[0008] One of the purposes of the present invention is to provide a device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance to solve the above-mentioned problem.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows: a device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance, the device comprising a high uniform magnetic system, a dual temperature control system, a magnetic field detection system, a temperature testing system, a mobile pallet and a magnetic shielding space, wherein:

[0010] The high uniform magnetic system is composed of a permanent magnet to be tested, a magnetic yoke, a pole head, and a base. The permanent magnet to be tested is connected to the magnetic yoke by magnetic force, and the pole head is connected to the magnetic yoke by a magnetic conductive connector. The high uniform magnetic system is placed in the middle of the mobile cart.

[0011] The dual temperature control system comprises an upper temperature control chamber, a lower temperature control chamber and a middle insulation layer between the upper temperature control chamber and the lower temperature control chamber. The high uniform magnetic system is placed in the dual temperature control system as a whole. The permanent magnet to be tested is in the lower temperature control chamber, and the pole head is in the upper temperature control chamber. The middle insulation layer is used to separate the permanent magnet to be tested from the pole head. That is, the dual temperature control system has two sets of temperature control systems. The upper temperature control chamber belongs to the magnetic field measurement chamber, which controls the temperature to room temperature and keeps it constant. The lower temperature control chamber belongs to the high and low temperature chamber, which is used to change the temperature of the permanent magnet to be tested. The dual temperature control system is located in the magnetic shielding space, that is, the entire test system is placed in the magnetic shielding space. During the entire measurement process in the magnetic shielding space, the magnetic shielding space realizes magnetic shielding.

[0012] The magnetic field detection system includes a nuclear magnetic resonance magnetometer probe and a host. The nuclear magnetic resonance magnetometer probe is fixed in a high uniformity area at the center of the two poles to detect magnetic field changes and output the detection value through a computer;

[0013] The temperature testing system comprises a temperature sensor and a computer, wherein the temperature sensor is attached to the center of the surface of the permanent magnet to be tested.

[0014] As a preferred technical solution: it also includes a probe fixing and adjusting system, and the nuclear magnetic resonance magnetometer probe is fixed by the probe fixing and adjusting system. The probe fixing and adjusting system is used to adjust the nuclear magnetic resonance magnetometer probe and to adjust the balance of the pole head.

[0015] As a preferred technical solution: an annular or square pit is arranged on the pole head.

[0016] The circular or square pits play a role in regulating the magnetic field, which can significantly improve the uniformity of the magnetic field in the air gap, making its magnetic field uniformity reach PPm level, and the magnetic field inhomogeneity reaches 10 in the required uniform area. -3 / cm. Providing a pit on the pole head is an important invention of the present invention. Figure 2 It is a schematic diagram of the cross section of the pole structure. Figure 2 A scheme for setting a pit is shown in FIG. 1 ; if the pole head is not provided with a pit, the magnetic field uniformity generated by the pole head is poor and cannot meet the basic conditions for the oscillation of the nuclear magnetic resonance magnetometer probe, so the test data cannot be obtained.

[0017] As a preferred technical solution: the permanent magnet to be tested is a rare earth cobalt or neodymium iron boron permanent magnet.

[0018] As a preferred technical solution: the yoke and the pole head are made of soft magnetic alloy materials, such as Q235, DT4, etc.

[0019] As a preferred technical solution: the mobile trolley and the probe fixing and adjusting system are made of non-magnetic materials, such as 2A12, 304 stainless steel, etc.

[0020] The second object of the present invention is to provide a method for measuring the temperature coefficient of a permanent magnet using the above-mentioned device, the technical solution adopted is as follows:

[0021] The nuclear magnetic resonance magnetometer probe is used to detect the magnetic field change, and the detection value is output through a computer;

[0022] The temperature sensor outputs the temperature of the permanent magnet to be measured through a computer;

[0023] The computer processes the changes in magnetic field values ​​corresponding to different temperatures based on formula (1) through a calculation unit to obtain the temperature coefficient of the permanent magnet to be measured:

[0024] (1).

[0025] The high-precision nuclear magnetic resonance method is used to directly measure the magnetic field generated by the permanent magnetic material, and then find the relationship between the magnetic field and temperature.

[0026] As a preferred technical solution: the permanent magnet to be tested is pre-stabilized before testing. The function of the pre-stabilization treatment is to remove the irreversible loss of the permanent magnet sample to be tested, thereby improving the accuracy of subsequent temperature-magnetic field measurement.

[0027] As a further preferred technical solution: the pre-stabilization treatment process: treatment at 250°C for 2h.

[0028] It should be noted that although both Siemens' CN101109720A and the present application adopt the principle of nuclear magnetic resonance, there are essential differences between them. Specifically:

[0029] 1. CN101109720A uses a background uniform magnetic field and places the magnetic material to be tested in the background uniform magnetic field, which will seriously affect the uniformity of the magnetic field. However, this application directly uses the permanent magnet to be tested to generate a high uniform magnetic field, and the nuclear magnetic resonance magnetometer probe directly tests the uniform magnetic field generated by the permanent magnet to be tested;

[0030] 2. The heating source used in CN101109720A is close to the magnetic material to be tested. The heating source itself has a great influence on the uniformity of the magnetic field, thereby affecting the oscillation of the nuclear magnetic resonance magnetometer. However, the present application adopts a double temperature control test box, and the permanent magnet to be tested is completely placed in the atmosphere, far away from the heating source, and is not affected by this.

[0031] 3. The probe of CN101109720A is close to the magnetic material to be measured, which will cause a large difference in the magnetic field at the probe site, thereby reducing the accuracy of magnetic field measurement. However, the present application measures the magnetic field generated by the permanent magnet to be measured, which has little disturbance on the highly uniform magnetic field, so the measurement accuracy is higher.

[0032] Compared with the prior art, the advantages of the present invention are as follows: the present invention uses a nuclear magnetic resonance magnetometer to measure the high uniform magnetic field generated by a permanent magnet with high precision, and by changing the temperature of the permanent magnet, the relationship between the permanent magnet magnetic field and the temperature is obtained, thereby realizing high-precision temperature coefficient measurement of the permanent magnet material, and the measurement accuracy can reach ×10 -7 / ℃ level. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention;

[0034] In the figure: 1. High uniform magnetic system; 1-1. Permanent magnet to be tested; 1-2. Magnetic yoke; 1-3. Pole head; 1-4. Base; 2. Dual temperature control system; 2-1. Upper temperature control chamber; 2-2. Lower temperature control chamber; 2-3. Middle insulation layer; 3. Magnetic field detection system; 3-1. Nuclear magnetic resonance magnetometer probe; 3-2. Main unit; 4. Temperature test system; 4-1. Temperature sensor; 5. Probe fixing and adjustment system; 6. Mobile cart; 7. Magnetic shielding space;

[0035] Figure 2 It is a schematic diagram of the cross section of the pole head structure;

[0036] Figure 3 This is the structural diagram of the probe fixing and adjustment system.

[0037] In the figure: 5-1, probe fixing system; 5-1-1, probe fixing knob; 5-2, probe adjustment system; 5-2-1, X-axis adjustment knob; 5-2-2 Y-axis adjustment knob; 5-3, pole head positioning fixture. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings.

[0039] Embodiment 1:

[0040] A device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance, such as Figure 1 As shown, it includes a high uniform magnetic system 1, a dual temperature control system 2, a magnetic field detection system 3, a temperature test system 4, a probe fixing and adjusting system 5, a mobile pallet 6 (the uniform magnetic field structure is placed on the mobile pallet 6 for easy movement) and a magnetic shielding space 7, wherein:

[0041] The highly uniform magnetic system 1 is composed of a permanent magnet 1-1 to be tested, a yoke 1-2, a pole head 1-3, and a base 1-4. The permanent magnet 1-1 to be tested is connected to the yoke 1-2 by magnetic force, the pole head 1-3 is connected to the yoke 1-2 by magnetically conductive screws, and the base 1-4 is connected to the yoke 1-2 by screws. The highly uniform magnetic system 1 is placed in the middle of the mobile cart 6;

[0042] The dual temperature control system 2 includes an upper temperature control chamber 2-1, a lower temperature control chamber 2-2 and a middle insulation layer 2-3 between the upper temperature control chamber 2-1 and the lower temperature control chamber 2-2. The high uniform magnetic system 1 is placed in the dual temperature control system 2 as a whole. The permanent magnet 1-1 to be measured is in the lower temperature control chamber 2-2, and the pole head 1-2 is in the upper temperature control chamber 2-1. The middle insulation layer 2-3 is used to separate the permanent magnet 1-1 to be measured from the pole head 1-3; that is, the dual temperature control system of this embodiment has two sets of temperature control systems, the upper temperature control chamber 2-1 belongs to the magnetic field measurement chamber, controls the temperature to room temperature and keeps it constant, and the lower temperature control chamber 2-2 belongs to the high and low temperature chamber, which is used to change the temperature of the permanent magnet 1-1 to be measured; the dual temperature control system 2 is located in the magnetic shielding space 7, and the magnetic shielding space 7 realizes magnetic shielding during the entire process of measurement in the magnetic shielding space 7;

[0043] The magnetic field detection system 3 includes a nuclear magnetic resonance magnetometer probe 3-1 and a host 3-2. The nuclear magnetic resonance magnetometer probe 3-1 is fixed in the high uniformity area at the center of the two pole heads 1-3 through a probe fixing and adjusting system 5, and is used to detect magnetic field changes and output the detection values ​​through a computer (i.e., a host + display screen, the computer here mainly records and saves data, reads the surface temperature of the permanent magnet, etc.);

[0044] The temperature testing system 4 includes a temperature sensor 4-1 and a computer, wherein the temperature sensor 4-1 is attached to the center of the surface of the permanent magnet 1-1 to be tested;

[0045] In this embodiment, the structure diagram of the probe fixing and adjusting system 5 is as follows: Figure 3 As shown, the pole head positioning fixture 5-3 is clamped in the groove of the pole head, which determines that the axes of the two pole heads are on the same axis. The nuclear magnetic resonance magnetometer probe is fixed by the probe fixing system, and is clamped and fixed by rotating the probe fixing knob 5-1-1. The position of the nuclear magnetic resonance magnetometer probe in the uniform area is finely adjusted by rotating the X-axis adjustment knob 5-2-1 and the Y-axis adjustment knob 5-2-2 of the probe adjustment system 5-2;

[0046] The method for measuring the temperature coefficient of a magnet using the above device is as follows:

[0047] First, the saturated magnetized permanent magnet 1-1 to be tested is pre-stabilized, the temperature sensor 4-1 is attached to the center of the surface of the permanent magnet 1-1 to be tested, the permanent magnet 1-1 to be tested is connected to the yoke 1-2 by magnetic force, the pole head 1-3 is connected to the yoke 1-2 by magnetically conductive screws, the base 1-4 is connected to the yoke 1-2 by screws, and the high uniformity magnetic system 1 is assembled;

[0048] Then, the high uniform magnetic system 1 is placed in the middle of the mobile pallet 6, and pushed into the dual temperature control system 2 as a whole, the permanent magnet 1-1 area to be tested is in the lower temperature control chamber 2-2, and the pole head 1-3 is in the upper temperature control chamber 2-1, separated by the middle insulation layer 2-3, and the nuclear magnetic resonance magnetometer probe 3-1 is extended into the center position of the two pole heads 1-3 through the reserved hole, and fixed by the probe fixing system 5, and the whole test system is placed in the magnetic shielding space 7;

[0049] The temperature sensor 4 - 1 outputs the temperature of the permanent magnet 1 - 1 to be tested through the computer, and the magnetic field detection value is output through the computer. The computer processes the magnetic field value changes corresponding to different temperatures based on formula (1) through the calculation unit to obtain the temperature coefficient of the permanent magnet to be tested.

[0050] (1)

[0051] In this embodiment, the permanent magnet is a 2:17 type samarium cobalt permanent magnet material, and is measured three times at temperatures of -55°C, 80°C, and 100°C. The measurement results are shown in Table 1.

[0052] The temperature coefficient measurement repeatability of the present invention is calculated by formula (2).

[0053] (2)

[0054] Comparative Example 1

[0055] The conventional fluxmeter method was used to measure the same sample as the permanent magnet 1-1 to be measured in the above-mentioned embodiment 1. The measurements were performed three times at -55°C, 80°C and 100°C respectively. The measurement results are shown in Table 1.

[0056]

[0057] It can be seen from Table 1 that the accuracy of measuring magnetic field value can reach 1×10 -7 / ℃ level, much higher than 1×10 -3 / ℃ level, the temperature coefficient measurement repeatability reaches 10 -6 The above magnitude is one order of magnitude higher than the comparative example.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance, characterized in that: The device includes a high uniform magnetic system, a dual temperature control system, a magnetic field detection system, a temperature test system, a mobile pallet and a magnetic shielding space, wherein: The high uniform magnetic system is composed of a permanent magnet to be tested, a magnetic yoke, a pole head, and a base. The permanent magnet to be tested is connected to the magnetic yoke by magnetic force, and the pole head is connected to the magnetic yoke by a magnetic conductive connector. The high uniform magnetic system is placed in the middle of the mobile cart, and a pit for adjusting the magnetic field is arranged on the pole head. The dual temperature control system comprises an upper temperature control chamber, a lower temperature control chamber and a middle heat insulation layer between the upper temperature control chamber and the lower temperature control chamber. The high uniform magnetic system is placed in the dual temperature control system as a whole. The permanent magnet to be tested is in the lower temperature control chamber, and the pole head is in the upper temperature control chamber. The permanent magnet to be tested is separated from the pole head by the middle heat insulation layer. The dual temperature control system is located in the magnetic shielding space. The magnetic field detection system comprises a nuclear magnetic resonance magnetometer probe and a host. The nuclear magnetic resonance magnetometer probe is fixed in a high uniformity zone at the center of two poles through a probe fixing and adjusting system to detect magnetic field changes, and the detection value is output through a computer; the probe fixing and adjusting system comprises a probe fixing knob, a probe adjusting system and a pole head positioning fixture, the pole head positioning fixture is clamped in a groove of the pole head to ensure that the axes of the two poles are on the same axis, and the probe is clamped and fixed by rotating the probe fixing knob, and the position of the nuclear magnetic resonance magnetometer probe in the uniformity zone is finely adjusted by rotating the X-axis adjusting knob and the Y-axis adjusting knob of the probe adjusting system; The temperature testing system comprises a temperature sensor and a computer, wherein the temperature sensor is attached to the center of the surface of the permanent magnet to be tested.

2. The device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance according to claim 1, characterized in that: The pit is annular or square.

3. The device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance according to claim 1, characterized in that: The permanent magnet to be tested is a rare earth cobalt or neodymium iron boron permanent magnet.

4. The device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance according to claim 1, characterized in that: The magnetic yoke and the pole head are made of soft magnetic alloy material.

5. The device for measuring the temperature coefficient of a permanent magnet based on the principle of nuclear magnetic resonance according to claim 1, characterized in that: The movable trolley and the probe fixing and adjusting system are made of non-magnetic conductive materials.

6. A method for measuring the temperature coefficient of a permanent magnet using the device according to any one of claims 1 to 5, characterized in that: The steps include: The nuclear magnetic resonance magnetometer probe is used to detect the magnetic field change, and the detection value is output through a computer; The temperature sensor outputs the temperature of the permanent magnet to be measured through a computer; The computer processes the changes in magnetic field values ​​corresponding to different temperatures based on formula (1) through a calculation unit to obtain the temperature coefficient of the permanent magnet to be measured: （1）。 7. The method according to claim 6, characterized in that: The permanent magnet to be tested is pre-stabilized before testing.

8. The method according to claim 7, characterized in that: The pre-stabilization treatment method is: treating at 250° C. for 2 hours.

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