A device and method for measuring low temperature of permanent magnetic material

Abstract

The present invention discloses a low-temperature measurement device and method for permanent magnetic materials, wherein a corresponding constant temperature pole head is arranged on a pole, a heat preservation cover is arranged outside the constant temperature pole head, a J-H coil is arranged between two constant temperature pole heads, a sample is arranged inside the J-H coil, the output end of the J-H coil is respectively connected to the input end of a J measurement integrator and the input end of an H measurement integrator, the output end of the J measurement integrator and the output end of the H measurement integrator are connected to the input end of an industrial computer, the output end of the industrial computer is connected to the input end of an electromagnet electric control, the control output end of the electromagnet electric control is connected to the control input end of the pole, and a constant temperature unit is arranged inside the heat preservation cover. The present invention solves the problem of accurate temperature control within the range of -40°C to room temperature in the measurement of magnetic properties of rare earth permanent magnet closed magnetic circuits, and meets the needs of closed magnetic circuit low-temperature measurement of rare earth permanent magnet production and use enterprises.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic material magnetic measurement, and in particular to a low-temperature measurement device and method for permanent magnetic materials. Background Art

[0002] The magnetic properties of rare earth permanent magnet materials are related to the temperature range. Different operating temperature environments have different performances and are nonlinear. -40℃~150℃ is the temperature range for the conventional service of permanent magnets, so permanent magnet material manufacturers and users need to master the magnetic properties within this temperature range. At present, the temperature of the sample near room temperature can only be achieved by running the indoor air conditioner. For high temperature measurements, it is achieved by electrically heating the pole head. For low temperature measurements, there is a method of obtaining a low temperature environment by cooling the pole head with liquid nitrogen, but this method is not easy to obtain accurate and stable temperature. The low temperature measurement equipment currently available at home and abroad include SQUID magnetometers and pulsed magnetic field magnetometers (PFM), but these are open magnetic circuit measurement methods.

[0003] Whether it is national standards or international standards, in fact, it is almost impossible to measure within the operating temperature range of 0-20℃, and no substantial work has been invested in low-temperature closed magnetic circuit measurement. So far, there is no instrument that can achieve low-temperature closed magnetic circuit measurement to meet the needs of domestic and foreign customers. Therefore, a permanent magnetic material low-temperature measurement device and method is needed. Summary of the invention

[0004] The object of the present invention is to provide a permanent magnetic material low temperature measurement device and method for measuring the closed magnetic circuit temperature characteristics of rare earth permanent magnetic materials.

[0005] To achieve the above object, the present invention is implemented according to the following technical solutions:

[0006] The present invention comprises a refrigerator, an excitation power supply, an electromagnet electric control, a J measurement integrator, an H measurement integrator, a JH coil, a constant temperature pole head, a temperature measurement unit and an industrial computer, wherein the pole is provided with a corresponding constant temperature pole head, a heat preservation cover is provided outside the constant temperature pole head, a JH coil is provided between two constant temperature pole heads, a sample is provided inside the JH coil, the output end of the JH coil is respectively connected to the input end of the J measurement integrator and the input end of the H measurement integrator, the output end of the J measurement integrator and the output end of the H measurement integrator are connected to the input end of the industrial computer, the output end of the industrial computer is connected to the input end of the electromagnet electric control, the control output end of the electromagnet electric control is connected to the control input end of the pole, a constant temperature unit is provided inside the heat preservation cover, and the measuring device is provided inside An embedded integrator self-calibration module comprises a crystal oscillator, a time frequency divider, a solid-state switch, a voltage divider circuit, a single-chip microcomputer, a J measurement integrator, an H measurement integrator and an industrial computer. The output end of the crystal oscillator is connected to the input end of the time frequency divider, the output end of the time frequency divider and the output end of the precision reference voltage are respectively connected to the first end of the solid-state switch, the second end of the solid-state switch is connected to the input end of the voltage divider circuit, the output end of the J coil is connected to the input end of the J measurement integrator, the output end of the H coil is connected to the input end of the H measurement integrator, the output end of the voltage divider circuit is respectively connected to the input end of the J measurement integrator and the input end of the H measurement integrator through a switching switch, the switching switch is provided with a single-chip microcomputer, and the output end of the single-chip microcomputer is connected to the industrial computer.

[0007] Furthermore, the constant temperature unit includes a heating and refrigeration circulator, a temperature sensor and a constant temperature pole, the temperature sensor is arranged on the constant temperature pole, the temperature sensor includes a first temperature sensor and a second temperature sensor, the output end of the first temperature sensor is connected to the input end of the pole temperature measurement, the output end of the pole temperature measurement is connected to the input end of the industrial computer, the output end of the second temperature sensor is connected to the input end of the heating and refrigeration circulator, and the control signal output end of the industrial computer is connected to the control end of the heating and refrigeration circulator to ensure that the temperature of the constant temperature pole in the insulation cover is constant.

[0008] Furthermore, the excitation power supply is connected to the electromagnet to form a magnetizing device for generating a continuously changing magnetic field.

[0009] Furthermore, the heating and refrigeration cycle machine and the constant temperature pole head cool and control the temperature of the sample.

[0010] A temperature control method for low-temperature measurement of permanent magnetic materials, comprising the following steps:

[0011] AWhen measuring permanent magnets, the magnet is placed on the electromagnet pole head, and the magnet, electromagnet constant temperature pole head, electromagnet pole column, and yoke form a closed magnetic circuit;

[0012] B. Constant temperature control of the permanent magnet is performed to make the sample under test reach -40°C;

[0013] C modifies the values ​​of the turn area and resistance of the H coil and J coil under changing temperature conditions.

[0014] The turn area of ​​the H coil is corrected using the following formula:

[0015] (NS) H,T =(NS) H,0 (1+2α L (T-T0))

[0016] Where:

[0017] (NS) H,T ——H coil turn area at temperature T, m 2 ;

[0018] (NS) H,0 ——Temperature T0 (room temperature) coil turn area, m 2 ;

[0019] α L ——Linear expansion coefficient of coil material or frame, ppm / ℃;

[0020] T——temperature during measurement, °C;

[0021] T0——room temperature, ℃.

[0022] The turn area of ​​the J coil is corrected using the following formula:

[0023] (dNS) J,T =(dNS) J,0 (1+2α L (T-T0))

[0024] Where:

[0025] (dNS) J,T ——Remaining turns area of ​​coil J at temperature T, m 2 ;

[0026] (dNS) J,0 ——Remaining turn area of ​​coil J at temperature T0 (room temperature), m 2 ;

[0027] α L ——Linear expansion coefficient of coil material or frame, ppm / ℃;

[0028] T——temperature during measurement, °C;

[0029] T0——room temperature, °C;

[0030] D. First, place the coil in a zero magnetic field environment, set the fluxmeter to zero, and then perform sample measurement. Then, place the coil in a zero magnetic field environment and correct the fluxmeter drift of the JH coil.

[0031] E uses the temperature calculation function to correct the temperature to establish the corresponding relationship between the sample temperature and the pole head temperature. By fitting the temperature curve, the correction coefficients a and b of the temperature function are calculated respectively. The calculation formula is as follows:

[0032]

[0033] Where:

[0034] T s1 ——The sample temperature when setting the first temperature, °C;

[0035] T s2 ——The sample temperature when setting the second temperature, °C;

[0036] T p1 ——The pole temperature when setting the first temperature, °C;

[0037] T p2 ——The pole temperature when setting the second temperature, °C;

[0038]

[0039] In this way, the corrected sample temperature calculation function is obtained, as shown in the following formula.

[0040] T s =α+b·T p

[0041] Where:

[0042] T s ——Sample temperature, °C;

[0043] T p ——Pole temperature, °C;

[0044] After obtaining the correction coefficient of the sample temperature, the measurement is performed and the result is output.

[0045] Further, the JH coil includes an H coil and a J coil, which are respectively connected to two independent flux meters, wherein the H coil is used to measure the magnetic field intensity, and the J coil is used to measure the magnetic polarization intensity of the sample;

[0046] When the temperature changes from room temperature to a certain temperature, the corresponding coil resistance correction of the H coil and the J coil is calculated using the following formula;

[0047] R J,T =RJ,0 (1+α(T-T0))

[0048] Where:

[0049] R J,T ——Resistance of coil J at temperature T, Ω;

[0050] R J,0 ——Resistance of coil J at temperature T0 (room temperature), Ω;

[0051] α——Temperature coefficient of coil resistance, ppm / ℃;

[0052] T——temperature during measurement, °C;

[0053] T0——room temperature, ℃:

[0054] R H,T =R H,0 (1+α(T-T0))

[0055] Where:

[0056] R H,T ——Resistance of coil H at temperature T, Ω;

[0057] R H,0 ——Resistance of coil H at temperature T0 (room temperature), Ω;

[0058] α——Resistance temperature coefficient of the coil, ppm / ℃;

[0059] T——temperature during measurement, °C;

[0060] T0——room temperature, °C;

[0061] 7. A temperature control method for low-temperature measurement of permanent magnetic materials according to claim 5, characterized in that the flux meter drift is corrected according to the following formula;

[0062]

[0063] Where:

[0064] ΔΦ t ——Magnetic flux drift per unit time, Wb / s;

[0065] Φ2——Fluxmeter value after completing sample measurement, Wb;

[0066] t——total measurement time, s;

[0067] The correction of H channel flux and J channel flux is carried out according to the following formula;

[0068]

[0069] Where:

[0070] Φ i '——The measured magnetic flux of the ith measuring point of the hysteresis loop after drift correction, Wb;

[0071] Φ i ——The magnetic flux at the i-th measuring point of the hysteresis loop, Wb;

[0072] Φ2——Fluxmeter value after completing sample measurement, Wb;

[0073] t i ——The measurement time of the ith measurement point of the measured hysteresis loop, s;

[0074] t——total measurement time.

[0075] Furthermore, when the integrator is self-calibrated, the J measurement integrator and the H measurement integrator are connected to the pulse voltage output end of the voltage divider circuit in sequence; the acquisition card is used to control the range switching of the J measurement integrator and the H measurement integrator; the integrator drift is automatically adjusted to the minimum, and the standard magnetic flux signal Φ0 is generated after the integrator is zeroed, and the magnetic flux signal Φ measured by the integrator is recorded, and then fed back to the computer to correct the integrator range coefficient using the software correction algorithm, so as to realize the self-calibration of the J measurement integrator and the H measurement integrator, and the integrator self-calibration module is embedded in the measuring device.

[0076] Furthermore, the correction formula of the integrator self-calibration module is:

[0077]

[0078] Where k 1,old is the original range coefficient of the integrator; k 1,new is the new range factor of the integrator.

[0079] 10. A temperature control method for low-temperature measurement of permanent magnetic materials according to claim 1, characterized in that the method of using a temperature function to correct the temperature comprises using a permanent magnetic sample with a high-precision temperature probe buried in the center as a sample temperature measurement point, placing it between the upper and lower poles, and connecting it to a temperature display device, closing the upper and lower poles, setting the device to a first temperature, and measuring the sample temperature T at the same time. s1 and the pole temperature T p1 ; Set the second temperature and measure the sample temperature T s2 and the pole temperature T p2 ; Set multiple commonly used temperature points in sequence, obtain two groups of corresponding temperatures, and draw them into a temperature curve.

[0080] The beneficial effects of the present invention are:

[0081] The present invention is a device and method for measuring low temperature of permanent magnetic materials. Compared with the prior art, the present invention has the following technical effects:

[0082] The invention solves the problem of accurate temperature control in the range of -40°C to room temperature in the measurement of magnetic properties of rare earth permanent magnet closed magnetic circuits, and meets the needs of rare earth permanent magnet production and use enterprises for closed magnetic circuit low-temperature measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 It is a structural schematic diagram of a low-temperature measurement device for permanent magnetic materials of the present invention;

[0084] Figure 2 A schematic diagram of demagnetization curves at different temperatures in a temperature control method for low-temperature measurement of a permanent magnetic material according to the present invention;

[0085] Figure 3 It is a structural schematic diagram of an integrator self-calibration module in rare earth permanent magnet closed magnetic circuit measurement of the present invention; DETAILED DESCRIPTION

[0086] The present invention is further described below with specific examples. The illustrative examples and descriptions of the present invention are used to explain the present invention but are not intended to limit the present invention.

[0087] like Figure 1 As shown, the measuring device includes an excitation power supply, an electromagnet electronic control, a J measurement integrator, an H measurement integrator, a JH coil, a constant temperature pole, a refrigerator, a heat preservation cover, a temperature measurement unit, an industrial computer and a measurement software. The high-power excitation power supply is connected with the electromagnet electronic control to form a magnetization device for generating a continuously changing magnetic field; the J integrator is used to measure the magnetic flux density or the magnetic polarization intensity; the H measurement integrator is used to measure the magnetic field; and the JH coil is used to sense the magnetic flux and magnetic field signals.

[0088] The sample temperature is achieved by cooling the thermostatic pole with a refrigerator. The operating temperature of the refrigerator is -60℃ to 200℃, and the cooling medium is silicone oil.

[0089] Silicone oil circulates in the series path composed of the refrigerator, the upper pole and the lower pole. The PT100 platinum resistor connected to the refrigerator is installed on the lower pole, and the working temperature of the refrigerator is set and adjusted by the PT100. Another PT100 temperature measuring platinum resistor is installed on the upper pole and connected to the temperature measuring head to measure the temperature of the upper pole, which represents the sample temperature. The first temperature sensor is located on the left side of the constant temperature pole, and the second temperature sensor is located on the right side of the constant temperature pole.

[0090] An insulation cover is installed between the upper and lower coils around the constant temperature pole, which plays a role of heat insulation and sealing, isolates the heat exchange between the low temperature environment and the external environment, ensures the uniformity and stability of the pole temperature, and also prevents frost during low temperature measurement.

[0091] In addition, the equipment also includes an automatic electromagnet electric control lifting mechanism control device to realize the automatic opening and closing of the electromagnet electric control. Because the sample needs to be taken and placed during measurement, the insulation cannot be completely closed, and the convenience of taking and placing the sample needs to be considered. In particular, the magnet must be saturated magnetized before measurement, and the design of the insulation structure increases the difficulty of sample placement.

[0092] Because the present invention is a closed magnetic circuit design, the temperature control method is still based on the electromagnet pole head. The refrigerator used in the present invention is a constant temperature oil tank, that is, the refrigerant medium circulates in the electromagnet electric control pole head to achieve temperature control. The advantages of this method are that the temperature can be controlled by feedback, and the refrigerant medium can be recycled, and it is highly safe, simple and economical.

[0093] The overall solution of the present invention is implemented in a constant temperature bath, and the refrigerator itself is a constant temperature oil tank (that is, it can provide a constant temperature). The low temperature environment is obtained by a refrigerator, which uses liquid refrigeration, and the refrigerant medium is silicone oil. The refrigerator, the lower pole head, and the upper pole head are connected in series into a loop through a low temperature resistant pipeline. Silicone oil circulates in the pipeline as a refrigerant medium to achieve cooling of the pole head. During measurement, the sample is placed between the upper and lower pole heads and is in direct contact with the surface of the pole head, because the temperature of the pole head can be quickly transmitted to the sample, so that the sample can be quickly cooled.

[0094] The refrigerator used in the present invention can provide a constant temperature in the range of -60°C to 200°C, but because the present invention is to cool the electromagnet pole, there is heat loss in the refrigeration pipeline and the electromagnet electronic control, especially the electromagnet electronic control is made of a large volume of electrical pure iron, so there is a large heat loss, resulting in a large temperature difference between the working temperature of the refrigerator and the actual temperature of the pole, and the temperature of the refrigerator cannot replace the pole temperature and the sample temperature. In order to obtain an accurate sample temperature, the present invention installs a PT100 temperature measuring platinum resistor at the lower pole, and this platinum resistor is connected to the refrigerant. When measuring, the working mode of the refrigerant is set to external PT100 feedback, thereby ensuring that the working temperature of the refrigerator is close to the pole temperature. Another PT100 is installed on the upper pole, and a temperature measuring head is connected to measure the temperature of the upper pole, which represents the sample temperature.

[0095] Calculation of temperature compensation

[0096] When measuring at low temperature, the detection coil of the permanent magnet measurement also reaches low temperature. Due to the change in temperature, the detection coil constant and resistance will change, which will have a significant impact on the measurement results. The present invention proposes to improve the measurement accuracy of magnetic properties by correcting the detection coil constant and resistance, as well as the fluxmeter drift.

[0097] (1) Temperature correction of coil resistance

[0098] The detection coil includes an H coil and a J coil, which are connected to two independent flux meters respectively. The H coil is used to measure the magnetic field strength, and the J coil is used to measure the magnetic polarization strength of the sample.

[0099] When the temperature changes from room temperature to a certain temperature, the corresponding resistance of the H coil and the J coil is calculated using the following formula.

[0100] R J,T =R J,0 (1+α(T-T0))

[0101] Where:

[0102] R J,T ——Resistance of coil J at temperature T, Ω;

[0103] R J,0 ——Resistance of coil J at temperature T0 (room temperature), Ω;

[0104] α——Temperature coefficient of coil resistance, ppm / ℃;

[0105] T——temperature during measurement, °C;

[0106] T0——room temperature, ℃.

[0107] R H,T =R H,0 (1+α(T-T0))

[0108] Where:

[0109] R H,T ——Resistance of coil H at temperature T, Ω;

[0110] R H,0 ——Resistance of coil H at temperature T0 (room temperature), Ω;

[0111] α——Resistance temperature coefficient of the coil, ppm / ℃;

[0112] T——temperature during measurement, °C;

[0113] T0——room temperature, ℃.

[0114] (2) Temperature correction of coil turn area

[0115] The turn area of ​​the H coil is corrected using the following formula:

[0116] (NS) H,T =(NS) H,0 (1+2α L (T-T0))

[0117] Where:

[0118] (NS) H,T ——H coil turn area at temperature T, m 2 ;

[0119] (NS) H,0 ——Temperature T0 (room temperature) coil turn area, m 2 ;

[0120] α L ——Linear expansion coefficient of coil material or frame, ppm / ℃;

[0121] T——temperature during measurement, °C;

[0122] T0——room temperature, ℃.

[0123] The turn area of ​​the J coil is corrected using the following formula:

[0124] (dNS) J,T =(dNS) J,0 (1+2α L (T-T0)) where:

[0125] (dNS) J,T ——Remaining turns area of ​​coil J at temperature T, m 2 ;

[0126] (dNS) J,0 ——Remaining turn area of ​​coil J at temperature T0 (room temperature), m 2 ;

[0127] α L ——Linear expansion coefficient of coil material or frame, ppm / ℃;

[0128] T——temperature during measurement, °C;

[0129] T0——room temperature, ℃.

[0130] (3) Correction of sample temperature

[0131] Since the measured permanent magnetic material has obvious temperature characteristics, especially NdFeB magnets have a large temperature coefficient. During the magnetic measurement of the sample, due to the obvious temperature gradient between the sample and the environment, there will be a large deviation between the sample temperature and the pole temperature, and the pole temperature cannot accurately reflect the actual temperature of the sample. This temperature measurement error will bring a large error to the measurement result and needs to be corrected.

[0132] The present invention uses a temperature function to correct the temperature to establish a corresponding relationship between the sample temperature and the pole head temperature. Specifically, it includes using a permanent magnetic sample with a high-precision temperature probe buried in the center as the sample temperature measurement point, placing it between the upper and lower pole heads, and connecting it to a temperature display device, closing the upper and lower pole heads, setting the device to a first temperature, and measuring the sample temperature T at the same time. s1 and the pole temperature T p1 ; Set the second temperature and measure the sample temperature T s2 and the pole temperature T p2 ; Set multiple commonly used temperature points in sequence, obtain two groups of corresponding temperatures, and draw them into a temperature curve.

[0133] By fitting the temperature curve, the correction coefficient of the sample temperature can be obtained, and the correction formula of the sample temperature can be obtained to improve the accuracy of sample temperature measurement.

[0134] For example, for a certain type of high-precision temperature measurement device, there is a linear relationship between two sets of temperatures. In this case, only two temperature points with a large span, such as temperature 1 and temperature 2, need to be set, and the correction coefficients a and b of the temperature function can be calculated using the following formulas.

[0135]

[0136] Where:

[0137] T s1 ——The sample temperature when setting the first temperature, °C;

[0138] T s2 ——The sample temperature when setting the second temperature, °C;

[0139] T p1 ——The pole temperature when setting the first temperature, °C;

[0140] T p2 ——The pole temperature when setting the second temperature, °C;

[0141] In this way, the corrected sample temperature calculation function is obtained, as shown in the following formula.

[0142] T s =α+b·T p

[0143] Where:

[0144] T s ——Sample temperature, °C;

[0145] T p ——Pole temperature, °C;

[0146] It is also possible to perform a linear fit on the entire temperature range to obtain a correction formula for the sample temperature and the pole temperature.

[0147] This formula is stored in the computer to realize real-time correction of sample temperature and improve the accuracy of sample temperature measurement.

[0148] In addition, in the case of nonlinear relationships, curve fitting can be used, or the temperature interval can be divided into segments and then a series of temperature points can be measured to obtain the temperature correspondence within each temperature interval. Each temperature interval is corrected according to the above linear algorithm and used as a temperature correction function to achieve temperature correction within the entire temperature interval, thereby improving the accuracy of sample measurement.

[0149] In addition to being used at low temperatures, the correction method of the present invention can also be applied to heating conditions. For example, when the pole temperature is heated from room temperature to a maximum of 200°C, or even to a maximum of 500°C, the sample temperature can still be corrected according to this method.

[0150] (4) Correction of fluxmeter drift

[0151] During the measurement process, the influence of fluxmeter drift on the measurement results cannot be ignored. For the measurement of permanent magnetic materials, the following measurement method is used for flux correction. Before starting the measurement, first place the coil in a zero magnetic field environment, such as a magnetic shielding tube or an environment where the magnetic field effect can be ignored, and set the fluxmeter to zero; then measure; after completing the sample measurement, quickly place the coil in a zero magnetic field environment. The total measurement time is t, and the fluxmeter value is recorded as Φ2. The fluxmeter drift is corrected according to the following formula,

[0152]

[0153] Where:

[0154] ΔΦ t ——Magnetic flux drift per unit time, Wb / s;

[0155] Φ2——Fluxmeter value after completing sample measurement, Wb;

[0156] t——total measurement time, s.

[0157] The correction of H channel flux and J channel flux is carried out according to the following formula:

[0158]

[0159] Where:

[0160] Φ i '——The measured magnetic flux of the ith measuring point of the hysteresis loop after drift correction, Wb;

[0161] Φ i ——The magnetic flux at the i-th measuring point of the hysteresis loop, Wb;

[0162] t i ——The measurement time of the ith measurement point of the measured hysteresis loop, s;

[0163] t——total measurement time.

[0164] like Figure 2 As shown, since the integrators commonly used in the measurement device have a certain temperature coefficient, it will cause errors in the measurement results. The following table shows the demagnetization curves at different temperatures at a certain time:

[0165]

[0166] (5) Self-calibration of integrator

[0167] The present invention embeds an integrator self-calibration module in the measuring device. The circuit principle is shown in Figure 3 , including a crystal oscillator, a time frequency divider, a solid-state switch, a voltage divider circuit, a single-chip microcomputer, a J measurement integrator, an H measurement integrator and an industrial computer. The output end of the crystal oscillator is connected to the input end of the time frequency divider, the output end of the time frequency divider and the output end of the precision reference voltage are respectively connected to the first end of the solid-state switch, the second end of the solid-state switch is connected to the input end of the voltage divider circuit, the output end of the voltage divider circuit is connected to the input end of the single-chip microcomputer, the output end of the single-chip microcomputer is respectively connected to the input end of the J measurement integrator and the input end of the measurement integrator, the output end of the J measurement integrator, and the output end of the measurement integrator is connected to the industrial computer, including a standard magnetic flux signal generating unit, which has the advantages of high precision and high stability, and is used for automatic calibration of the integrator magnetic flux. The crystal oscillator generates a standard time signal, which is divided by the clock to obtain a series of set time widths, such as 0.01s, 0.1s, 1s, 10s, etc. The precision voltage reference generates a standard DC voltage. The single-chip microcomputer connected to the computer controls the solid-state switch output to generate a series of pulse width voltages, which are then combined with the pulse width time through a voltage divider circuit to obtain the set pulse voltage-time output as a standard flux signal. This end is the standard flux signal output end, which is used for the calibration of the integrator.

[0168] The integrator is connected with a switch, which can be connected to the measuring coil or the standard magnetic flux signal output terminal respectively by controlling the switch through the single chip microcomputer. When the integrator switches to the measuring coil, the sample magnetic flux is measured; when the integrator switch is switched to the standard magnetic flux signal output terminal, the standard magnetic flux signal is measured to perform self-calibration of the integrator.

[0169] (1) When measuring a sample, the J measurement integrator and the H measurement integrator are connected to the J measurement coil and the H measurement coil respectively.

[0170] (2) During the self-calibration of the integrator, the switching switch is controlled by the single-chip microcomputer connected to the computer, and the J measurement integrator and the H measurement integrator are connected to the pulse voltage output end (i.e., the standard flux signal output end) of the voltage divider circuit in sequence; first, the acquisition card is used to control the range switching of the J measurement integrator and the H measurement integrator; then the integrator drift is automatically adjusted to the minimum, and then the integrator is reset to zero; then the standard flux signal Φ0 is generated, the flux signal Φ measured by the integrator is recorded, and then fed back to the computer, and the software correction algorithm is used to correct the integrator range coefficient. The correction formula is as follows to realize the self-calibration of the J measurement integrator and the H measurement integrator.

[0171]

[0172] Where:

[0173] k 1,old —-Original range coefficient of integrator;

[0174] k 1,new —-New range coefficient of integrator;

[0175] Implementation Results

[0176] Table 1 shows the temperature reached at different time periods after the thermostatic pole head is installed on the electromagnet electronic control and connected to the refrigerator. As can be seen from Table 1, after 50 minutes, the pole head can reach -43.66°C from 18.09°C, indicating that the method of the present invention can reach the target temperature and has a good cooling effect.

[0177] Table 1 Comparison of cooling effects of thermostatic poles

[0178]

[0179] Table 2 Correspondence between sample temperature and pole head temperature

[0180] Sample temperature (℃) Pole temperature (℃) 20.01 20.5 10.44 10.91 0.06 0.66 -8.8 -8.75 -18.6 -19.39 -28 -29.4 -37.83 -39.51

[0181] The correction formula of sample temperature and pole temperature is that after linear correction, the maximum temperature error is within 0.5℃ in the whole temperature range. Compared with the uncorrected temperature, the measurement accuracy of sample temperature is significantly improved.

[0182] T s =0.9584·T p -0.0631

[0183] Figure 3 Demagnetization curves of a N35M sample with a diameter of 10mm and a height of 10mm measured at different temperatures. The test temperatures are 20℃, -0℃, -20℃, and -40℃.

[0184] 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, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A temperature control method for low temperature measurement of permanent magnetic materials, characterized in that: The following steps are involved: AWhen measuring permanent magnets, the magnet is placed on the electromagnet pole head, and the magnet, electromagnet constant temperature pole head, electromagnet pole column, and yoke form a closed magnetic circuit; B. Constant temperature control of the permanent magnet is performed to make the sample under test reach -40°C; C modifies the values ​​of the turn area and resistance of the H coil and J coil under changing temperature conditions. The turn area of ​​the H coil is corrected using the following formula: (NS) H,T =(NS) H,0 (1+2α L (T-T0)) Where: (NS) H,T ——H coil turn area at temperature T, m 2 ; (NS) H,0 ——Temperature T0 (room temperature) coil turn area, m 2 ; α L ——Linear expansion coefficient of coil material or frame, ppm / ℃; T——temperature during measurement, °C; T0——room temperature, °C; The turn area of ​​the J coil is corrected using the following formula: (dNS) J,T =(dNS) J,0 (1+2α L (T-T0)) Where: (dNS) J,T ——Remaining turns area of ​​coil J at temperature T, m 2 ; (dNS) J,0 ——Remaining turn area of ​​coil J at temperature T0 (room temperature), m 2 ; α L ——Linear expansion coefficient of coil material or frame, ppm / ℃; T——temperature during measurement, °C; T0——room temperature, °C; D. First, place the coil in a zero magnetic field environment, set the fluxmeter to zero, and then perform sample measurement. Then, place the coil in a zero magnetic field environment and correct the fluxmeter drift of the JH coil. E uses the temperature calculation function to correct the temperature to establish the corresponding relationship between the sample temperature and the pole head temperature. By fitting the temperature curve, the correction coefficients a and b of the temperature function are calculated respectively. The calculation formula is as follows: Where: T s1 ——The sample temperature when setting the first temperature, °C; T s2 ——The sample temperature when setting the second temperature, °C; T p1 ——The pole temperature when setting the first temperature, °C; T p2 ——The pole temperature when setting the second temperature, °C; In this way, the corrected sample temperature calculation function is obtained as follows: T s =a+b·T p Where: T s ——Sample temperature, °C; T p ——Pole temperature, °C; After obtaining the correction coefficient of the sample temperature, the measurement is performed and the result is output.

2. According to claim 1, a temperature control method for low-temperature measurement of permanent magnetic materials is characterized in that: The JH coil includes an H coil and a J coil, which are respectively connected to two independent flux meters, wherein the H coil is used to measure the magnetic field intensity, and the J coil is used to measure the magnetic polarization intensity of the sample; When the temperature changes from room temperature to a certain temperature, the corresponding coil resistance correction of the H coil and the J coil is calculated using the following formula; R J,T =R J,0 (1+α(T-T0)) Where: R J,T ——Resistance of coil J at temperature T, Ω; R J,0 ——Resistance of coil J at temperature T0 (room temperature), Ω; α——Temperature coefficient of coil resistance, ppm / ℃; T——temperature during measurement, °C; T0——room temperature, ℃: R H,T =R H,0 (1+α(T-T0)) Where: R H,T ——Resistance of coil H at temperature T, Ω; R H,0 ——Resistance of coil H at temperature T0 (room temperature), Ω; α——Resistance temperature coefficient of the coil, ppm / ℃; T——temperature during measurement, °C; T0——room temperature, ℃.

3. The temperature control method for low-temperature measurement of permanent magnetic materials according to claim 1, characterized in that: The fluxmeter drift is corrected according to the following formula: Where: ΔΦ t ——Magnetic flux drift per unit time, Wb / s; Φ2——Fluxmeter value after completing sample measurement, Wb; t——total measurement time, s; The correction of H channel flux and J channel flux is carried out according to the following formula; Where: Φ i '——The measured magnetic flux of the ith measuring point of the hysteresis loop after drift correction, Wb; Φ i ——The magnetic flux at the i-th measuring point of the hysteresis loop, Wb; Φ2——Fluxmeter value after completing sample measurement, Wb; t i ——The measurement time of the ith measurement point of the measured hysteresis loop, s; t——total measurement time.

4. The temperature control method for low-temperature measurement of permanent magnetic materials according to claim 1, characterized in that: During the self-calibration of the integrator, the J measurement integrator and the H measurement integrator are connected to the pulse voltage output end of the voltage divider circuit in sequence; the acquisition card is used to control the range switching of the J measurement integrator and the H measurement integrator; the integrator drift is automatically adjusted to the minimum, and the standard magnetic flux signal Φ0 is generated after the integrator is zeroed, and the magnetic flux signal Φ measured by the integrator is recorded, and then fed back to the computer to correct the integrator range coefficient using the software correction algorithm, so as to realize the self-calibration of the J measurement integrator and the H measurement integrator, and the integrator self-calibration module is embedded in the measuring device.

5. The temperature control method for low-temperature measurement of permanent magnetic materials according to claim 4, characterized in that: The correction formula of the integrator self-calibration module is: Where k 1,old is the original range coefficient of the integrator; k 1,new is the new range factor of the integrator.

6. The temperature control method for low-temperature measurement of permanent magnetic materials according to claim 1, characterized in that: The method of correcting the temperature using the temperature function includes using a permanent magnetic sample with a high-precision temperature probe buried in the center as the sample temperature measurement point, placing it between the upper and lower poles, and connecting it to a temperature display device, closing the upper and lower poles, setting the device to a first temperature, and measuring the sample temperature T at the same time. s1 and the pole temperature T p1 ; Set the second temperature and measure the sample temperature T s2 and the pole temperature T p2 ; Set multiple commonly used temperature points in sequence, obtain two groups of corresponding temperatures, and draw them into a temperature curve.

7. A permanent magnetic material low temperature measurement device, used to implement a temperature control method for low temperature measurement of a permanent magnetic material according to any one of claims 1 to 6, characterized in that: It includes an excitation power supply, an electromagnet electric control, a J measurement integrator, an H measurement integrator, a JH coil, a constant temperature pole head, a temperature measurement unit and an industrial computer. A corresponding constant temperature pole head is arranged on the pole, a heat preservation cover is arranged outside the constant temperature pole head, a JH coil is arranged between the two constant temperature pole heads, a sample is arranged inside the JH coil, the output end of the JH coil is respectively connected to the input end of the J measurement integrator and the input end of the H measurement integrator, the output end of the J measurement integrator and the output end of the H measurement integrator are connected to the input end of the industrial computer, the output end of the industrial computer is connected to the input end of the electromagnet electric control, the control output end of the electromagnet electric control is connected to the control input end of the pole, a constant temperature unit is arranged inside the heat preservation cover, and the measuring device has an embedded integrator. The calibration module includes a crystal oscillator, a time frequency divider, a solid-state switch, a voltage divider circuit, a single-chip microcomputer, a J measurement integrator, an H measurement integrator and an industrial computer. The output end of the crystal oscillator is connected to the input end of the time frequency divider, the output end of the time frequency divider and the output end of the precision reference voltage are respectively connected to the first end of the solid-state switch, the second end of the solid-state switch is connected to the input end of the voltage divider circuit, the output end of the J coil is connected to the input end of the J measurement integrator, the output end of the H coil is connected to the input end of the H measurement integrator, the output end of the voltage divider circuit is respectively connected to the input end of the J measurement integrator and the input end of the H measurement integrator through a switching switch, the switching switch is provided with a single-chip microcomputer, and the output end of the single-chip microcomputer is connected to the industrial computer.

8. A permanent magnetic material low temperature measuring device according to claim 7, characterized in that: The constant temperature unit includes a heating and refrigeration circulator, a temperature sensor and a constant temperature pole. The temperature sensor is arranged on the constant temperature pole. The temperature sensor includes a first temperature sensor and a second temperature sensor. The output end of the first temperature sensor is connected to the temperature measurement input end of the constant temperature pole. The temperature measurement output end of the constant temperature pole is connected to the input end of the industrial computer. The output end of the second temperature sensor is connected to the input end of the heating and refrigeration circulator. The control signal output end of the industrial computer is connected to the control end of the heating and refrigeration circulator to ensure that the temperature of the constant temperature pole in the insulation cover is constant.

9. A permanent magnetic material low temperature measuring device according to claim 7, characterized in that: The excitation power supply is connected with the electromagnet to form a magnetizing device for generating a continuously changing magnetic field.

10. A permanent magnetic material low temperature measuring device according to claim 8, characterized in that: The heating and cooling circulator and the thermostatic pole are used to cool and control the temperature of the sample.

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