Magnetic core mounting and potting method of high-precision open-loop Hall current sensor

Abstract

The invention discloses a magnetic core mounting and potting method for a high-precision open-loop Hall current sensor, and aims to solve the problem that the precision and stability are obviously insufficient at extreme temperature in the prior art. A pre-mounted magnetic core is fixed by potting epoxy resin; a Hall element and a plurality of electronic components are welded on a PCB (Printed Circuit Board), and the welded PCB is arranged in a sensor shell fixed with a magnetic core; waveform testing and amplitude debugging are carried out on the assembled Hall current sensor, after debugging is completed, polyurethane or two-component silicone rubber is adopted for reencapsulation, reencapsulation is used for completely fixing the magnetic core, the PCB and the sensor shell to enable the magnetic core, the PCB and the sensor shell to form a whole, and soft rubber can effectively protect the PCB and electronic components. The Hall current sensor manufactured by the method has the characteristics of high measurement precision, wide temperature range operation and high stability.

Description

Technical Field

[0001] The present application relates to the technical field of current sensors, and in particular to a method for installing and encapsulating a magnetic core of a high-precision open-loop Hall current sensor. Background Art

[0002] With the continuous advancement and improvement of electronic technology and the continuous expansion and deepening of its application fields, the performance requirements for Hall effect current sensors have far exceeded the current market standards. The operating temperature of open-loop Hall effect current sensors on the market is typically -25°C to 85°C, with an output temperature drift of 4mV / °C. While existing open-loop Hall effect current sensors can meet application requirements within a certain range, their operating temperature range and output temperature drift characteristics have gradually become bottlenecks that limit their application in wider and more extreme environments. In particular, in applications requiring high-precision measurement, highly reliable operation, and extreme temperature conditions (-40°C to 125°C or higher), the performance of existing products seems to be insufficient. With market competition intensifying and customer application complexity and requirements increasing, the development of a Hall effect current sensor with high measurement accuracy, wide temperature range operation, and high stability has become increasingly urgent. Summary of the Invention

[0003] The present application provides a method for installing and potting the magnetic core of a high-precision open-loop Hall current sensor, aiming to solve the dilemma that the existing technology has obviously insufficient accuracy and stability under conditions requiring high-precision measurement, high-reliability operation, and extreme temperatures (-40°C to 125°C or higher), and to provide a method for installing and potting the magnetic core of a Hall current sensor with high measurement accuracy, wide temperature range operation, and high stability.

[0004] In a first aspect, a method for mounting and encapsulating a magnetic core of a high-precision open-loop Hall current sensor is provided. The Hall current sensor includes a sensor housing and a magnetic core, a PCB, a Hall element, and multiple electronic components installed in the sensor housing. The method includes:

[0005] The pre-installed magnetic core is encapsulated and fixed with epoxy resin;

[0006] Solder the Hall element and multiple electronic components onto the PCB, and then install the soldered PCB into the sensor housing with the magnetic core fixed.

[0007] The assembled Hall current sensor is subjected to waveform testing and amplitude debugging. After debugging, it is re-potted with polyurethane or two-component silicone rubber. The re-potting is used to completely fix the magnetic core, PCB board and sensor housing to form a whole, effectively protecting the PCB board and electronic components.

[0008] In the above scheme, optionally, the welding height of the Hall element is determined according to the size of the magnetic core. The larger the magnetic core size, the higher the welding height of the Hall element. The welding height of the Hall element refers to the straight-line distance measured from the welding surface of the PCB board to the top of the Hall element body after the Hall element is fixed to the PCB board through its pins.

[0009] In the above solution, further optionally, the welding height of the Hall element is based on the body of the Hall element being located exactly in the middle of the air gap of the magnetic core.

[0010] In the above solution, optionally, the step of encapsulating and fixing the pre-installed magnetic core with epoxy resin includes: determining the height of the encapsulation and fixing with epoxy resin according to the height of the magnetic core, while ensuring that the Hall element does not touch the epoxy resin colloid after being installed in the air gap of the magnetic core.

[0011] In the above solution, further optionally, when the epoxy resin is used for potting and fixing, the height of the potting and fixing should not exceed half of the height of the magnetic core.

[0012] In the above solution, optionally, the magnetic core is made of silicon steel sheets through cutting, winding, aging and cutting processes.

[0013] In the above solution, further optionally, the silicon steel sheet has a thickness of 0.23 mm or 0.1 mm.

[0014] In the above solution, optionally, the magnetic core is made of Permalloy material through cutting, winding, aging and cutting processes.

[0015] In a second aspect, a high-precision open-loop Hall current sensor is finally manufactured by the above-mentioned magnetic core mounting and potting method of the high-precision open-loop Hall current sensor.

[0016] Compared with the prior art, this application has at least the following beneficial effects:

[0017] Based on further analysis and research of existing technical issues, this application recognizes that changes in the air gap of the magnetic core of a Hall current sensor are the key reason for the decline in Hall current sensor test accuracy, and temperature is the key factor causing the air gap change. By adopting two glues and a double potting technique, namely, after the magnetic core is installed, epoxy resin is used for the first potting to fix it, and then the Hall element and other components are soldered to the PCB board. The soldered PCB board is installed in the sensor housing with the fixed magnetic core. After the assembled Hall current sensor is subjected to waveform testing and amplitude debugging, a second potting is performed. The second potting is performed using relatively soft polyurethane or two-component silicone rubber. This double potting method can not only completely fix the magnetic core, but also effectively protect the PCB board and electronic components. By producing multiple samples and repeating experiments, this application verifies that the air gap cutout size of the magnetic core fixed with epoxy resin does not change significantly when the ambient temperature fluctuates significantly (temperature change of 165°C), which can greatly improve the measurement accuracy of open-loop Hall current sensors.

[0018] The present applicant also discovered that the Hall effect current sensors on the market generally have an output deviation of 1% or even 2% due to installation position deviation, which seriously affects the measurement accuracy of the sensor. Through further research and analysis, the present applicant realized that increasing the welding height of the Hall effect element can greatly improve this problem. By continuously increasing the welding height of the Hall effect element to conduct sensor position error tests and comparisons, it was found that the size of the magnetic core determines the final welding height of the Hall effect element. The larger the magnetic core size, the higher the Hall effect welding height. The present applicant ultimately determined that the best welding height of the Hall effect element is when the main body of the Hall effect element is exactly in the middle of the magnetic core.

[0019] This application uses new magnetic core installation and potting technology to increase the operating temperature of the current sensor to -40°C to 125°C, and the output temperature drift of the current sensor is controlled within 0.4mv / °C, greatly improving the measurement accuracy and measurement stability of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of an open-loop Hall current sensor provided in one embodiment of the present application.

[0021] Figure 2 A schematic diagram of a magnetic core provided for one embodiment of the present application.

[0022] Figure 3 This is a finished image of the magnetic core installation and potting process provided in one embodiment of the present application.

[0023] Figure 4 A cross-sectional view of a finished magnetic core installation and potting product provided in one embodiment of the present application.

[0024] Figure 5 A schematic diagram of the welding height of a Hall element provided in one embodiment of the present application.

[0025] In the figure, 1, Hall element; 2, magnetic core; 3, housing; 4, PCB board. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0027] In the description of this application: unless otherwise specified, "a plurality of" means two or more. Expressions such as "include", "comprising", "having" and the like also mean "not limited to" (certain units, components, materials, steps, etc.).

[0028] The present application provides a method for installing and potting the magnetic core of a high-precision open-loop Hall current sensor, which can be used for installing and potting the magnetic core of a high-precision open-loop Hall current sensor.

[0029] refer to Figure 1 The principle of the open-loop current sensor is: when the primary current I P When current flows through a long wire, a magnetic field is generated around the wire. The magnitude of this magnetic field is proportional to the current flowing through the wire. The generated magnetic field is concentrated in the magnetic ring, that is, the magnetic core. At this time, the Hall element in the air gap of the magnetic core senses the magnitude of the magnetic field and outputs a voltage signal, which is usually a weak voltage of tens of millivolts. After being amplified by the amplifier circuit, the output is generally rated at 4V. The output voltage can accurately reflect the primary side measurement current I P size.

[0030] A Hall element is a semiconductor device based on the Hall effect principle that can convert magnetic signals into electrical signals. Table 1 below shows a comparison of how Hall elements convert magnetic signals into electrical signals.

[0031] Table 1

[0032]

[0033] With the continuous development and improvement of electronic technology, as well as the complexity and increasing demands of customer applications, a Hall effect current sensor with high measurement accuracy, wide temperature range and high stability is needed.

[0034] So how to improve the measurement accuracy of the sensor? According to the principle of open-loop Hall current sensor and magnetic circuit theorem, the measuring current is proportional to the magnetic field size of the magnetic core air gap. The Hall element senses the magnetic field size and outputs a voltage signal. If the magnetic field in the air gap changes, the voltage signal output by the Hall element will change. After being amplified by the amplifier circuit, the output voltage of the Hall current sensor will eventually deviate significantly.

[0035] So what causes the change of the magnetic field in the air gap of the magnetic core? According to the magnetic circuit theorem and the principle of Hall current sensor, the size of the air gap of the magnetic core will change the size of the magnetic field in the air gap. Therefore, the change of the air gap of the magnetic core is the key reason for the decrease in the test accuracy of the current sensor.

[0036] The core size and air gap size are pre-calculated. The core of an open-loop Hall effect current sensor is made of silicon steel sheets, typically 0.23mm thick, through cutting, winding, aging, and other processes. The core air gap size deviation can typically be controlled within 0.1mm, so the core air gap size generally remains constant. In some embodiments, the core material can be replaced with a superior Permalloy material; the core can also be made of 0.1mm thick silicon steel sheets or Permalloy. This application does not impose specific restrictions on the core material and thickness.

[0037] So, what exactly causes or under what circumstances the air gap changes? After long-term research and repeated experiments, we found that temperature is the key factor causing air gap variation. The experimental process: Place the magnetic core in the sensor housing and secure it in place, then pot it (commercially available sensors typically use polyurethane or silicone rubber, which are relatively soft). After the glue is completely cured, place it in a high-temperature chamber. The chamber is set to -40°C (minus 40 degrees Celsius) for four hours. After the time is up, use a digital caliper to immediately measure the air gap size and record it. Then, set the chamber to 125°C for another four hours. After the time is up, immediately measure the air gap size and record it. After producing a large number of samples and repeated experiments, we concluded that the air gap size increases at high temperatures and decreases at low temperatures. This concludes that temperature is the key factor causing air gap size variation.

[0038] The key to this research is how to ensure that the core air gap remains constant despite significant changes in ambient temperature. Commercially available Hall effect current sensors typically use polyurethane or two-component silicone rubber for a one-time potting process. Both of these relatively soft adhesives protect the electronic components within the Hall effect current sensor. In other words, the entire current sensor is potted with the same adhesive. This upgrade to the existing core mounting and potting technology utilizes two adhesives and a two-step potting process. After the core is mounted, epoxy resin (a hard, rock-hard adhesive after curing) is used for the first potting step to secure it. The potting height is approximately 2 to 8 mm (depending on the core height, ensuring that the Hall effect element does not contact the adhesive after being installed and placed within the core air gap). The Hall effect element and other components are then soldered to the PCB, which is then installed within the sensor housing containing the fixed core. After waveform testing and amplitude debugging of the assembled Hall effect current sensor, a second potting step is performed. This second potting step uses a relatively soft polyurethane or two-component silicone rubber. This second potting step completely secures the magnetic core, PCB, and sensor housing, forming a single unit. The soft colloid effectively protects the PCB and electronic components. This double potting method not only completely secures the magnetic core, preventing temperature fluctuations from affecting the air gap size, thus improving the sensor's measurement accuracy and stability, but also effectively protects the PCB and electronic components with the soft colloid, preventing stress damage during subsequent use.

[0039] In one embodiment, reference Figure 3 and Figure 4 , provides a method for installing and potting a magnetic core of a high-precision open-loop Hall current sensor. The Hall current sensor includes a sensor housing and a magnetic core, a Hall element, and multiple electronic components installed in the sensor housing. The potting method includes the following steps:

[0040] The pre-installed magnetic core is encapsulated and fixed with epoxy resin;

[0041] Solder the Hall element and multiple electronic components onto the PCB, and then install the soldered PCB into the sensor housing with the magnetic core fixed.

[0042] The assembled Hall current sensor is subjected to waveform testing and amplitude debugging. After debugging, it is re-potted with polyurethane or two-component silicone rubber. The re-potting is used to completely fix the magnetic core, PCB board and sensor housing to form a whole. The soft colloid can effectively protect the PCB board and electronic components.

[0043] In this embodiment, based on further analysis and research on the existing technical problems, it is recognized that if only epoxy resin is used for one-time potting, since epoxy resin is very hard after curing, the hard epoxy resin glue will cause stress damage to the PCB board with precision devices such as Hall elements welded thereon during subsequent use; if only polyurethane or two-component silicone rubber or other soft potting glue is used for one-time potting, although it can protect the electronic components inside the Hall current sensor, in an extremely high or extremely low temperature environment, due to thermal expansion and contraction, the air gap cut of the magnetic core will change, and the output value of the Hall current sensor will change significantly, affecting the accuracy of the Hall current sensor. This application uses a method of two-time potting with two glues to increase the operating temperature of the current sensor to -40℃~125℃, and the output temperature drift of the current sensor is controlled within 0.4mv / ℃, which greatly improves the measurement accuracy and stability of the sensor.

[0044] In this embodiment, the pre-installed magnetic core is potted and fixed with epoxy resin, including: the height of the epoxy resin potting and fixing is determined according to the size of the magnetic core height, while ensuring that the Hall element does not touch the epoxy resin colloid after being installed in the air gap of the magnetic core. The height of the epoxy resin potting and fixing refers to the process of pouring a certain amount of potting colloid into the shell from the inner bottom surface of the shell (that is, the surface that the magnetic core is directly in contact with during installation and fixing) through the potting process. The height of this colloid, that is, the vertical distance from the bottom surface of the shell to the top surface of the colloid, is the so-called "epoxy resin potting and fixing height", refer to Figure 2 .

[0045] In one embodiment, reference Figure 2 and Figure 4 When using epoxy resin for potting and fixing, the potting height should not exceed half of the core height, so as not to affect the sensing part of the Hall element, that is, the middle position of the body placed in the air gap of the core.

[0046] In one embodiment, the height of the magnetic core is 8 mm, and when epoxy resin is used for potting and fixing, the height of the potting and fixing should not exceed 4 mm.

[0047] In one embodiment, the height of the magnetic core is 10 mm, and when epoxy resin is used for potting and fixing, the height of the potting and fixing should not exceed 5 mm.

[0048] In one embodiment, the height of the epoxy resin for potting and fixing is generally 2 to 8 mm.

[0049] An experimental verification was conducted on the magnetic core that had undergone the first potting process. The core casing, potted with epoxy resin, was placed in a high-temperature test chamber and set to -40°C for 4 hours. After the time was up, the core's air gap dimensions were measured with a digital caliper and recorded. The high-temperature test chamber was then set to 125°C for 4 hours. Once the temperature was reached, the core's air gap dimensions were immediately measured with a digital caliper and recorded. Multiple samples were prepared and the experiment was repeated multiple times. The experimental conclusion was that the air gap dimensions of the core fixed with epoxy resin did not change significantly when the ambient temperature fluctuated significantly (a temperature change of 165°C). Because the epoxy resin is as hard as stone after curing, it can firmly fix the core and prevent the core's air gap from changing, thus meeting the experimental requirements.

[0050] Next, conduct high and low temperature testing on the finished product: Place the secondary potting finished current sensor in a high and low temperature test chamber for the finished product high and low temperature testing. First, set the temperature to 25°C for 4 hours. Once the time is up, immediately test the current sensor's electrical performance and record the results. Second, set the temperature to -40°C for 4 hours. Once the time is up, immediately test the current sensor's electrical performance and record the results. Third, set the temperature to 125°C for 4 hours. Once the time is up, immediately test the current sensor's electrical performance and record the results. The test data is shown in Tables 3 and 4. Table 3 shows the high and low temperature test data for the 1000A finished product, and Table 4 shows the high and low temperature test data for the 1500A finished product. The maximum temperature drift of the Hall effect current sensor's output voltage is 23mV, significantly improving the sensor's test accuracy. The performance table of a well-known imported Hall effect current sensor is shown in Table 2 below.

[0051] Table 2

[0052]

[0053] The output voltage of this imported current sensor is 4V at room temperature of 25℃, and the output voltage temperature drift is 0.1% / K of the output voltage, that is, 4mv / ℃.

[0054] The output voltage temperature drift of a Hall effect current sensor refers to the offset error in the current sensor's output voltage due to changes in ambient or operating temperature. Table 2 shows the rated output and output temperature drift performance parameters of an imported current sensor. The Hall effect current sensor has an output voltage of 4V, and the output voltage temperature drift is 0.1% / K. The calculated temperature drift is 4V * 0.1% / K = 4mV / k = 4mV / °C (K refers to the Kelvin temperature unit, which is equivalent to the Celsius unit, °C. When expressing temperature differences and temperature intervals, 1K = 1°C). Therefore, for large temperature changes (-40 to 85°C), the output change is 125 * 4 = 500mV, a significant deviation. 500mV / 4V = 12.5%, indicating a sensor error of at least 12.5%, seriously affecting measurement accuracy. The Hall current sensor, which has undergone technological upgrades, has a maximum output deviation of 23mV when the ambient temperature changes greatly (-40 to 85°C). 23mV / 4V = 0.576%. The sensor output deviation is less than 1% when the maximum ambient temperature changes, greatly improving the measurement accuracy of the sensor. Refer to the high and low temperature test data table of the 1000A finished product shown in Table 3 below and the high and low temperature experimental data of the 1500A finished product shown in Table 4 below.

[0055] Table 3

[0056]

[0057] Table 4

[0058]

[0059] A Hall-effect current sensor is an indirect measurement device. It detects the current flowing through a copper busbar or cable by passing it through the sensor's central hole. However, due to the varying sizes of the copper busbar or cable used by end users, the sensor's hole may not be fully occupied. This can cause the busbar or cable to be misaligned within the sensor hole, often tilted upward, downward, left, or right. This deviation in mounting position often results in output deviations of 1% or even 2% for commercially available Hall-effect current sensors, severely impacting measurement accuracy. Effectively addressing this issue is the second key technology discovered in this research.

[0060] Through a large number of technical experiments, we concluded that such problems can be greatly improved by increasing the welding height of the Hall element. How much should the height of the Hall element be increased? The Hall welding height of various types of open-loop current sensors on the market is usually 4 to 7 mm. Then, by continuously increasing the welding height of the Hall element, we conducted sensor position error tests and comparisons. Ultimately, we determined that the ideal welding height of the Hall element is within the range of 8 to 15 mm. Finally, the final welding height of the Hall element is determined based on the size of the magnetic core. The larger the magnetic core size, the higher the Hall welding height. For specific experimental data, please refer to Table 5, which is a comparison table of the effects of different welding heights of the Hall element on the sensor output accuracy.

[0061] Table 5

[0062]

[0063] In one embodiment, the soldering height of the Hall element is determined according to the size of the magnetic core. The larger the magnetic core size, the higher the soldering height of the Hall element. The soldering height of the Hall element refers to the straight-line distance from the soldering surface of the PCB to the top of the Hall element body after the Hall element is soldered to the PCB through its pins. Figure 4 and Figure 5 , Figure 5 Schematic diagram of the welding height of the Hall element.

[0064] In one embodiment, the welding height of the Hall element is preferably such that the body of the Hall element is located exactly in the middle of the magnetic core, so as to ensure that the sensing part (body) of the Hall element is close to the center of the magnetic core under different sizes.

[0065] In one embodiment, the height of the magnetic core is 8 mm, the center portion thereof is 4 mm, and the reserved size is 2-3 mm, so the welding height of the Hall element is 6-7 mm.

[0066] In one embodiment, the height of the magnetic core is 10 mm, the center portion thereof is 5 mm, and the reserved size is 3 mm, so the welding height of the Hall element is 8 mm.

[0067] In one embodiment, the welding height of the Hall element is 8 to 15 mm to ensure that the sensing portion of the Hall element, ie, the black body portion, reaches the center of the magnetic core as much as possible.

[0068] In this embodiment, based on further analysis and research on the problems of the prior art, it is recognized that in the prior art, the welding height of the Hall element is usually relatively short (4 to 7 mm), and the welding height of the present application is relatively high (8 to 15 mm). After a large number of experiments, this embodiment found that when the sensing part of the Hall element, that is, the black body part, reaches the center position of the magnetic core as much as possible, the output value of the Hall current sensor will be more stable, and the middle part of the air gap of the magnetic core will be closer to the uniform magnetic field. At this time, the measurement accuracy of the Hall current sensor is the highest, which solves the problem of large deviations in the measurement of Hall sensors on the market.

[0069] In one embodiment, a high-precision open-loop Hall current sensor is provided. The sensor is finally manufactured by the magnetic core installation and potting method of the high-precision open-loop Hall current sensor provided in one embodiment of the present application.

[0070] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for installing and encapsulating a magnetic core of a high-precision open-loop Hall current sensor, wherein the Hall current sensor comprises a sensor housing and a magnetic core, a PCB, a Hall element, and multiple electronic components installed in the sensor housing, characterized in that: The pre-installed magnetic core is encapsulated and fixed with epoxy resin; Solder the Hall element and multiple electronic components onto the PCB, and then install the soldered PCB into the sensor housing with the magnetic core fixed. The assembled Hall current sensor is subjected to waveform testing and amplitude debugging. After debugging, it is re-potted with polyurethane or two-component silicone rubber. The re-potting is used to completely fix the magnetic core, PCB board and sensor housing to form a whole, effectively protecting the PCB board and electronic components.

2. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 1, characterized in that: The soldering height of the Hall element is determined by the size of the magnetic core. The larger the magnetic core size, the higher the soldering height of the Hall element. The soldering height of the Hall element refers to the straight-line distance measured from the soldering surface of the PCB to the top of the Hall element body after the Hall element is soldered and fixed to the PCB via its pins.

3. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 2, wherein: The welding height of the Hall element is based on the fact that the body of the Hall element is located exactly in the middle of the air gap of the magnetic core.

4. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 1, wherein: The method of potting and fixing the pre-installed magnetic core with epoxy resin includes: The height of the epoxy resin potting and fixing is determined according to the height of the magnetic core, while ensuring that the Hall element does not touch the epoxy resin colloid after being installed in the air gap of the magnetic core.

5. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 4, characterized in that: When epoxy resin is used for potting and fixing, the height of the potting and fixing should not exceed half of the height of the magnetic core.

6. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 1, wherein: The magnetic core is made of silicon steel sheets through cutting, winding, aging and cutting processes.

7. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 6, characterized in that: The silicon steel sheet has a thickness of 0.23 mm or 0.1 mm.

8. The method for installing and encapsulating the magnetic core of a high-precision open-loop Hall current sensor according to claim 1, wherein: The magnetic core is made of Permalloy material through cutting, winding, aging and cutting processes.

9. A high-precision open-loop Hall current sensor, characterized in that: The high-precision open-loop Hall current sensor is finally manufactured by the magnetic core installation and potting method of claim 1.

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