Flowmeter

Abstract

The present invention provides a flowmeter, comprising: a rotating structure, a sensing component, and a processing circuit. The rotating structure has an axis, a rotating member, and a magnetic member, wherein the rotating member can be driven by the fluid in the pipeline to rotate around the axis, and the magnetic member is disposed on the rotating member with two magnetic poles parallel to the tangent of the rotation circumference of the rotating member. The sensing component is spaced apart from the rotating structure by a distance, and comprises a first sensing unit and a second sensing unit, which respectively sense the magnetic fields of the magnetic member in a first direction and a second direction to generate a first magnetic field component signal and a second magnetic field component signal. The processing circuit is connected to the sensing component and generates the angle of the rotating structure according to the first magnetic field component signal and the second magnetic field component signal.

Description

[0001] This invention claims the priority of a patent application in Taiwan, China, with a priority date of August 23, 2019 and an application number of 108130346. Technical Field

[0002] This invention relates to a flowmeter, and more particularly to a flowmeter with a rotating structure. Background Art

[0003] In order to monitor the state of fluids in pipelines, for different types of fluids, the prior art provides various flowmeters, including: ultrasonic flowmeters, variable area flowmeters, Coriolis flowmeters, paddle wheel flowmeters, positive displacement flowmeters, turbine flowmeters, laminar flowmeters, electromagnetic flowmeters, thermal mass flowmeters, etc.

[0004] Among various flowmeters, paddle wheel flowmeters, positive displacement flowmeters and turbine flowmeters include a rotating structure with magnetic components, a sensor and a processing circuit. The rotating structure is arranged in the pipeline, and the sensor is spaced from the rotating structure by a certain distance. When the fluid drives the rotating structure, the magnetic field intensity around the magnetic components changes periodically. The sensor senses the change in magnetic field intensity to generate a pulsed sensing signal, and the processing circuit generates a flow rate based on the pulsed sensing signal.

[0005] For the above-mentioned flowmeters with a rotating structure, the rotating structure needs to rotate at least 60 to 180 degrees to generate a pulsed sensing signal. When the rotation speed of the rotating structure is low (low flow rate), the number of pulsed sensing signals per unit time is small, and the processing circuit cannot generate reliable flow rate data. It is well known that the measurement error of the flowmeter at low flow rates can reach more than 5 times; furthermore, the processing circuit cannot judge the fluid flow direction from the pulsed sensing signal, nor can it distinguish whether the change in magnetic field intensity is due to fluid velocity change, wear of the rotating mechanism or external magnetic field interference, thus affecting the credibility of the flow rate data.

[0006] It is well known that flowmeters with a rotating structure have problems such as limited flow sensing range, inability to judge flow direction and abnormal rotating structure, and inability to distinguish between velocity change and external magnetic field interference. How to solve the various problems of the prior art and improve the flow sensing range, accuracy and credibility of flowmeters with a rotating structure is the main purpose of the development of this invention. Summary of the Invention

[0007] To achieve the above object, the present invention provides a flow meter, comprising: a rotating structure, a sensing component, and a processing circuit. The rotating structure has an axis, a rotating member, and a magnetic member, wherein the rotating member can be driven by the fluid in the pipeline to rotate around the axis, and the magnetic member is disposed on the rotating member with two magnetic poles parallel to the tangent of the rotation circumference of the rotating member. The sensing component is spaced apart from the rotating structure by a distance, and comprises a first sensing unit and a second sensing unit, which respectively sense the magnetic fields of the magnetic member in a first direction and a second direction to generate a first magnetic field component signal and a second magnetic field component signal. The processing circuit is connected to the sensing component and generates the angle of the rotating structure according to the first magnetic field component signal and the second magnetic field component signal.

[0008] In an embodiment, the number of the above-mentioned rotating members is plural, and each of the above-mentioned rotating members is provided with the above-mentioned magnetic member.

[0009] In an embodiment, the above-mentioned first direction and the above-mentioned second direction are perpendicular to each other.

[0010] In an embodiment, the above-mentioned processing circuit calculates the angle change amount of the above-mentioned rotating structure at two time points according to the above-mentioned first magnetic field component signal and the above-mentioned second magnetic field component signal to generate the angular velocity of the above-mentioned rotating structure, and generates the flow rate of the above-mentioned fluid according to the angular velocity of the above-mentioned rotating structure and the cross-sectional area of the above-mentioned pipeline.

[0011] In an embodiment, the above-mentioned processing circuit judges the flow direction of the above-mentioned fluid according to the angle change amount of the above-mentioned rotating structure.

[0012] In an embodiment, the above-mentioned flow meter further comprises: a display module, connected to the above-mentioned processing circuit, for displaying the flow rate of the above-mentioned fluid.

[0013] In an embodiment, the above-mentioned flow meter further comprises: a communication module, connected to the above-mentioned processing circuit, and transmits the angle of the above-mentioned rotating structure to a monitoring device by wire or wirelessly. The monitoring device calculates the angle change amount of the above-mentioned rotating structure at two time points to generate the angular velocity of the above-mentioned rotating structure, and generates the flow rate of the above-mentioned fluid according to the angular velocity of the above-mentioned rotating structure and the cross-sectional area of the above-mentioned pipeline.

[0014] In an embodiment, the above-mentioned processing circuit further generates a magnetic field intensity according to the above-mentioned first magnetic field component signal and the above-mentioned second magnetic field component signal.

[0015] In an embodiment, the above-mentioned processing circuit defaults a magnetic field intensity upper limit value and a magnetic field intensity lower limit value. When the above-mentioned magnetic field intensity is higher than the magnetic field intensity upper limit value, the above-mentioned processing circuit generates an abnormal information of external magnetic field interference; when the above-mentioned magnetic field intensity is lower than the magnetic field intensity lower limit value, the above-mentioned processing circuit generates an abnormal information of damage to the rotating structure.

[0016] Regarding the flowmeter of the present invention, the rotating structure has a magnetic member with two magnetic poles parallel to the tangent of the rotation circumference. The sensing component generates the first magnetic field component signal and the second magnetic field component signal of the magnetic member in different directions. The processing circuit can calculate a very small rotation angle change amount and magnetic field strength based on the two magnetic field component signals in different directions. Through the rotation angle change amount and magnetic field strength, the processing circuit can not only generate the fluid flow rate, but also further determine the fluid flow direction, whether the rotating structure is damaged, or whether there is abnormal external magnetic field interference, etc. Compared with the existing flowmeters, the flowmeter of the present invention can greatly improve the sensitivity and accuracy of measuring low flow rates, and reduce measurement errors and dead zones. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a block diagram of the flowmeter of the present invention;

[0018] Figure 2A is a cross-sectional view of the rotating structure of the flipper-wheel flowmeter of the present invention;

[0019] Figure 2B is a cross-sectional view of the rotating structure of the turbine flowmeter of the present invention;

[0020] Figure 2C is a cross-sectional view of the rotating structure of the gear flowmeter of the present invention;

[0021] Figure 2D is a cross-sectional view of the rotating structure of the turbine flowmeter of the present invention;

[0022] Figure 3 is a circuit diagram of the sensing component according to an embodiment of the present invention;

[0023] Figure 4A is a schematic diagram of the rotation angle and magnetic field strength signals according to an embodiment of the present invention;

[0024] Figure 4B is a schematic diagram of the rotation angle and magnetic field strength signals according to another embodiment of the present invention; and

[0025] Figure 5 is a schematic diagram of the magnetic field strength signal according to an embodiment of the present invention.

[0026]

SYMBOL DESCRIPTION

[0027] 1 Flowmeter

[0028] 11, 11a, 11b, 11c, 11d Rotating structure

[0029] 12 Sensing component

[0030] 13 Processing circuit

[0031] 111a, 111b, 111c, 111d Axis

[0032] Rotating members 112a, 112b, 112c, 112d

[0033] Magnetic members 113a, 113b, 113c, 113d

[0034] First sensing unit 121

[0035] Second sensing unit 122 Detailed implementation manners

[0036] The following further describes the implementation manners of the present invention in conjunction with the drawings and component symbols, enabling those with ordinary knowledge in the technical field to which the present invention pertains to implement the present invention after studying this specification.

[0037] Figure 1 It is a block diagram of the flowmeter of the present invention. As Figure 1 shown, the flowmeter 1 is, for example, a paddlewheel flowmeter, a turbine flowmeter, a (single / multi) nozzle impeller flowmeter, a gear flowmeter, etc., and includes: a rotating structure 11, a sensing assembly 12, and a processing circuit 13. The rotating structure 11 has a magnetic member and can generate a magnetic field change as the fluid in the pipeline flows. The sensing assembly 12 is separated from the rotating structure 11 by a distance (for example, one to dozens of millimeters) and is used to sense the magnetic field change of the rotating structure 11 to generate a sensing signal. The processing circuit 13 is connected to the sensing assembly 12 and generates the angle of the rotating structure 11 based on the sensing signal.

[0038] The processing circuit 13 can calculate the fluid flow rate in the pipeline by itself based on the angle of the rotating structure 11, or transmit the angle of the rotating structure 11 to a monitoring device equipped with a flow calculation program through a communication module. In one embodiment, the flowmeter 1 further includes a display module (not shown) connected to the processing circuit 13. The processing circuit 13 calculates the angle change amount of the rotating structure 11 at two time points to generate the angular velocity of the rotating structure 11, and then generates the fluid flow rate based on the angular velocity of the rotating structure 11 and the cross-sectional area of the pipeline. The display module displays the flow rate data generated by the processing circuit 13. In another embodiment, the flowmeter 1 further includes a communication module (not shown) connected to the processing circuit 13. The communication module transmits the angle of the rotating structure 11 to a monitoring device (not shown) by wire or wirelessly. The monitoring device calculates the angle change amount of the rotating structure 11 at two time points to generate the angular velocity of the rotating structure 11, and then generates the fluid flow rate based on the angular velocity of the rotating structure 11 and the cross-sectional area of the pipeline.

[0039] Figure 2A 、 Figure 2B and Figure 2C are respectively cross-sectional views of the rotating structures of the paddlewheel flowmeter, turbine flowmeter, and gear flowmeter of the present invention. As Figure 2A, Figure 2B and Figure 2C As shown, the rotating structures 11a, 11b, 11c have axles 111a, 111b, 111c, rotating members 112a, 112b, 112c and magnetic members 113a, 113b, 113c. The materials of the axles 111a, 111b, 111c and the rotating members 112a, 112b, 112c can be selected from metals and engineering plastics, and the materials of the magnetic members 113a, 113b, 113c can be selected from alloys with high magnetic permeability or ferrite materials. The number of the rotating members 112a, 112b, 112c is multiple, and they can be driven by the fluid to rotate around the axles 111a, 111b, 111c. According to the size of the rotation circumference of the rotating members 112a, 112b, 112c, the number of the magnetic members 113a, 113b, 113c can be one or more. For a smaller rotation circumference, each rotating member 112a, 112b, 112c is provided with a single magnetic member 113a, 113b, 113c, and the magnetic members 113a, 113b, 113c are arranged on one side of the rotating members 112a, 112b, 112c with two magnetic poles (N / S) parallel to the tangent of the rotation circumference of the rotating members 112a, 112b, 112c, so that the magnetic force lines of the magnetic members 113a, 113b, 113c (such as Figure 2A 、 Figure 2B and Figure 2C shown by the circular lines therein) surround the tangent of the rotation circumference.

[0040] Figure 2D is a cross-sectional view of the rotating structure of the turbine flowmeter according to another embodiment of the present invention. As Figure 2D shown, the rotating structure 11d has an axle 111d, a rotating member 112d and a magnetic member 113d. For a larger rotation circumference, each rotating member 112d is provided with multiple magnetic members 113d, which can enhance the output signal of the sensing component for sensing the change of the magnetic field.

[0041] The sensing component is an angular displacement magnetic field sensing component, which includes a first sensing unit and a second sensing unit. The first sensing unit and the second sensing unit can be selected from, but not limited to: anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), Hall sensors, etc. The first sensing unit and the second sensing unit are separated by an angle (such as, but not limited to, 45, 90, 135 degrees), and respectively sense the magnetic fields in the first direction and the second direction of the magnetic member, and generate a first magnetic field component signal and a second magnetic field component signal.

[0042] It is worth mentioning that in existing webbed-wheel flow meters, turbine flow meters and gear flow meters, the two poles of the magnetic member are arranged radially along the rotating member (i.e., webbed blades, vanes or gears, etc.), and the sensing component can only sense the change in the radial magnetic field intensity of each magnetic member to generate a pulsed sensing signal, and cannot generate magnetic field intensity signals in two different directions.

[0043] Figure 3 FIG. is a circuit diagram of a sensing component according to an embodiment of the present invention. As Figure 3 shown, in this embodiment, two sets of Wheatstone bridges are used as the first sensing unit 121 and the second sensing unit 122 of the sensing component 12. The first sensing unit 121 and the second sensing unit 122 are arranged perpendicular to each other. The first sensing unit 121 senses the intensity and direction of the magnetic field in the vertical direction (such as Figure 3 the Y-axis direction shown) to generate a first magnetic field component signal Vout-y; the second sensing unit 122 senses the intensity and direction of the magnetic field in the horizontal direction ( Figure 3 the X-axis direction shown) to generate a second magnetic field component signal Vout-x; the sensing component 12 transmits the first magnetic field component signal Vout-y and the second magnetic field component signal Vout-x to the processing circuit.

[0044] The processing circuit is, for example, a microcontroller or a system-on-chip that includes functions such as storage, analog / digital signal conversion, logic operation, and timing. Since the sensing component generates the first magnetic field component signal and the second magnetic field component signal in different directions, the processing circuit can perform an arctangent operation on the first magnetic field component signal and the second magnetic field component signal to obtain the rotation angle (Θi, i = 1 to n) of the rotating structure at the sensing time points (ti, i = 1 to n); the processing circuit or a monitoring device loaded with a flow calculation program can perform a difference operation on the rotation angles of two consecutive time points (Θn - Θn-1 / tn - tn-1) to obtain the angular velocity (ω) of the rotating structure; by converting the angular velocity (ω) of the rotating structure into the flow velocity (v) of the fluid in the pipeline and multiplying it by the preset pipeline cross-sectional area (A), the flow rate of the fluid in the pipeline can be obtained. In addition, an increase in the rotation angle of the rotating structure between two consecutive time points (Θn - Θn-1 > 0) is defined as counterclockwise rotation, and a decrease in the rotation angle of the rotating structure between two consecutive time points (Θn - Θn-1 < 0) is defined as clockwise rotation. The processing circuit can determine the flow direction of the fluid in the pipeline based on the change amount of the rotation angle (or the rotation direction of the angular velocity) of the rotating structure.

[0045] Figure 4ASchematic diagram of rotation angle and magnetic field strength signals according to an embodiment of the present invention. In this embodiment, a single magnetic member is provided in the rotation structure, and the processing circuit is pre-set to receive the magnetic field sensing signals of the single magnetic member. The magnetic member provided in the rotation structure and the sensing component are respectively defined as 0 degrees and 180 degrees at the nearest side and the farthest side on the same radial direction of the rotation circumference. As Figure 4A shown, the right vertical axis represents the magnetic field strength (0 to 1) of the sensing component calculated by the processing circuit, and the left vertical axis represents the rotation angle (Θi) of the magnetic member generated by the processing circuit calculating the first magnetic field component signal and the second magnetic field component signal of the sensing component. The horizontal axis represents the actual rotation angle (Θj) of the rotation structure. When the rotation structure actually rotates from 0 degrees to 180 degrees, the magnetic field strength (as shown by the dotted line in Figure 4A ) generated by the processing circuit calculating the first magnetic field component signal and the second magnetic field component signal of the sensing component sensing the magnetic member decreases from the peak value to the lowest value, and the rotation angle of the rotation structure (as shown by the solid line in Figure 4A ) increases from 0 degrees to 180 degrees; when the rotation structure actually rotates from 180 degrees to 360 degrees, the magnetic field strength generated by the processing circuit calculating the first magnetic field component signal and the second magnetic field component signal of the sensing component sensing the magnetic member increases from the lowest value to the peak value, and the rotation angle of the rotation structure increases from 180 degrees to 360 degrees, thereby generating the count data of one rotation of the rotation structure. The processing circuit can generate the rotation speed (ω) of the rotation structure according to the time of one rotation of the rotation structure or according to the rotation angle per unit time (for example, per second), and then generate the fluid flow rate with the rotation speed and the default pipeline cross-sectional area.

[0046] It should be noted that when measuring the flow rate of a large-diameter pipeline, a rotation structure with a relatively large size is usually used. The diameter of the rotation circumference of the large-size rotation structure is relatively large. If a single magnetic member is provided in the rotation structure, the lowest value of the magnetic field strength of the sensing component may be too small, thus increasing the error of the processing circuit calculating the flow rate data. Generally speaking, if the lowest value of the magnetic field strength of the sensing component calculated by the processing circuit is not less than 0.5, a rotation structure with a single magnetic member can be selected; if the lowest value of the magnetic field strength of the sensing component calculated by the processing circuit is not greater than 0.25, a rotation structure with multiple magnetic members can be selected to enhance the magnetic field strength of the sensing component sensing the magnetic member, which can effectively reduce the error of the processing circuit calculating the flow rate data and reduce the interference of the external magnetic field.

[0047] Figure 4B Schematic diagram of rotation angle and magnetic field strength signals according to another embodiment of the present invention. In this embodiment, two magnetic members are provided in the rotation structure relatively (i.e., separated by 180 degrees). The processing circuit is pre-set to receive the magnetic field sensing signals of the two magnetic members. The two magnetic members provided in the rotation structure are respectively defined as the first magnetic member and the second magnetic member. The first magnetic member and the sensing component are respectively defined as 0 degrees and 180 degrees at the nearest side and the farthest side on the same radial direction of the rotation circumference. AsFigure 4B As shown, the right vertical axis represents the magnetic field strength (0 to 1) of the processing circuit's operational sensing component, the left vertical axis represents the magnetic rotation angle (Θi) signal generated by the processing circuit's operational sensing component sensing the first and second magnetic field component signals of the first and second magnetic components, and the horizontal axis represents the actual rotation angle (Θj) of the rotating structure. When the rotating structure actually rotates from 0 degrees to 90 degrees, the magnetic field strength (as shown by the dashed line in Figure 4B ) generated by the processing circuit's operational sensing component sensing the first and second magnetic field component signals of the first and second magnetic components decreases from the peak value to the lowest value, and the processing circuit defines the rotation angle of the rotating structure (as shown by the solid line in Figure 4B ) increases from 0 degrees to 180 degrees; when the rotating structure actually rotates from 90 degrees to 180 degrees, the magnetic field strength generated by the processing circuit's operational sensing component sensing the first and second magnetic field component signals of the first and second magnetic components increases from the lowest value to the peak value, and the processing circuit defines the rotation angle of the rotating structure to increase from 180 degrees to 360 degrees; when the rotating structure actually rotates from 180 degrees to 270 degrees, the magnetic field strength generated by the processing circuit's operational sensing component sensing the first and second magnetic field component signals of the first and second magnetic components decreases from the peak value to the lowest value again, and the processing circuit defines the rotation angle of the rotating structure to increase from 0 degrees to 180 degrees again; when the rotating structure actually rotates from 270 degrees to 360 degrees, the magnetic field strength generated by the processing circuit's operational sensing component sensing the first and second magnetic field component signals of the first and second magnetic components increases from the lowest value to the peak value again, and the processing circuit defines the rotation angle of the rotating structure to increase from 180 degrees to 360 degrees; when the processing circuit defines the rotating structure to rotate twice from 0 to 360 degrees, the processing circuit generates count data for one full rotation of the rotating structure, and generates the rotation speed (ω) of the rotating structure based on the time for one full rotation of the rotating structure or based on the rotation angle per unit time (e.g., per second), and then generates the fluid flow rate based on the rotation speed and the default pipeline cross-sectional area.

[0048] Since the processing circuit generates the angle (rotation angle) and angular velocity (rotation speed) of the rotating structure based on the magnetic field component signals of the magnetic components in two directions, as long as the sensing component can sense the change in the magnetic field strength of the magnetic components, the processing circuit's calculation of the rotation angle has nothing to do with the magnetic field strength of the magnetic components, and can calculate extremely small changes in the rotation angle, greatly improving the sensitivity and accuracy of the flowmeter for measuring low flow rates.

[0049] Figure 5 This is a schematic diagram of the magnetic field strength of an embodiment of the present invention. In this embodiment, the processing circuit defaults the upper limit value and lower limit value of the magnetic field strength of the magnetic component. As shown in Figure 5As shown, the vertical axis represents the magnetic field strength (R) sensed by the sensing component for the magnetic component, and the horizontal axis corresponds to the rotation angle of the rotating structure for one full rotation. The processing circuit generates the magnetic field strength based on the first magnetic field component signal and the second magnetic field component signal of the magnetic component. If the magnetic field strength is higher than the upper limit value of the magnetic field strength (Rmax), it indicates external magnetic field interference. The processing circuit generates abnormal information about the external magnetic field interference to prompt the user to check the installation environment of the flowmeter. If the magnetic field strength is lower than the lower limit value of the magnetic field strength (Rmin), it indicates that the rotating structure has fallen off or worn out, and the processing circuit generates abnormal information about the damage of the rotating structure. Thus, the processing circuit can monitor the external magnetic field interference of the sensing component and the operating state of the rotating structure, effectively reducing the measurement error and blank window of the flowmeter.

[0050] In summary, the flowmeter of the present invention includes a rotating structure, a sensing component, and a processing circuit. The rotating structure has a magnetic component with two magnetic poles parallel to the tangent of the rotation circumference. The sensing component can generate the first and second magnetic field component signals of the magnetic component in different directions. The processing circuit can calculate a very small rotation angle change amount and the magnetic field strength based on the two magnetic field component signals in different directions. Through the rotation angle change amount and the magnetic field strength, in addition to generating the fluid flow rate, the processing circuit or the monitoring device can further determine the fluid flow direction, whether the rotating structure is damaged, or whether there is external magnetic field interference and other abnormalities. Compared with the existing flowmeters, the flowmeter of the present invention can greatly improve the sensitivity and accuracy of measuring low flow rates, and reduce the measurement error and blank window.

[0051] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this profession can modify and change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with professional knowledge in the technical field without departing from the spirit and technical principles disclosed by the present invention should still be covered by the patent application scope of the present invention.

Claims

1. A flowmeter, characterized in that, comprising: a rotating structure having an axis, a rotating member and a magnetic member, wherein the rotating member can be driven by the fluid in the pipeline to rotate around the axis, and the magnetic member is arranged on the rotating member with two magnetic poles parallel to the tangent of the rotation circumference of the rotating member; a sensing component spaced apart from the rotating structure by a distance, including a first sensing unit and a second sensing unit, respectively sensing the magnetic fields of the magnetic member in a first direction and a second direction to generate a first magnetic field component signal and a second magnetic field component signal; and a processing circuit connected to the sensing component, generating the angle of the rotating structure according to the first magnetic field component signal and the second magnetic field component signal, wherein the processing circuit further generates a magnetic field intensity according to the first magnetic field component signal and the second magnetic field component signal; and, the processing circuit defaults a lower limit value of the magnetic field intensity, and when the magnetic field intensity is lower than the lower limit value of the magnetic field intensity, the processing circuit generates an abnormal information that the rotating structure is damaged.

2. The flowmeter according to claim 1, characterized in that, the number of the rotating members is multiple, and each rotating member is provided with the magnetic member.

3. The flowmeter according to claim 1, characterized in that, the first direction and the second direction are perpendicular to each other.

4. The flowmeter according to claim 1, characterized in that, the processing circuit calculates the angle change amount of the rotating structure at two time points to generate the angular velocity of the rotating structure, and generates the flow rate of the fluid according to the angular velocity of the rotating structure and the cross-sectional area of the pipeline.

5. The flowmeter according to claim 4, characterized in that, the processing circuit judges the flow direction of the fluid according to the angle change amount of the rotating structure.

6. The flowmeter according to claim 4, characterized in that, further comprising: a display module connected to the processing circuit for displaying the flow rate of the fluid.

7. The flowmeter according to claim 1, characterized in that, further comprising: a communication module connected to the processing circuit, transmitting the angle of the rotating structure to a monitoring device by wire or wirelessly, the monitoring device calculates the angle change amount of the rotating structure at two time points to generate the angular velocity of the rotating structure, and generates the flow rate of the fluid according to the angular velocity of the rotating structure and the cross-sectional area of the pipeline.

8. The flowmeter according to claim 7, characterized in that, the processing circuit defaults an upper limit value of the magnetic field intensity, and when the magnetic field intensity is higher than the upper limit value of the magnetic field intensity, the processing circuit generates an abnormal information of external magnetic field interference.

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