CN115902378A - Solving method of interference of fluxgate sensor on ultra-large current characteristic - Google Patents
Solving method of interference of fluxgate sensor on ultra-large current characteristic Download PDFInfo
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Abstract
The invention belongs to the technical field of leakage detection, and discloses a method for solving the interference of a fluxgate sensor on the characteristics of ultra-large current, which comprises the following steps of S1, selection and design of a magnetic core: the magnetic ring is composed of a superconducting magnetic core, and the magnetic circuit of the magnetic core is designed in a balanced manner to control the highest disturbed point of the magnetic core; s2, performing hardware filtering on the interference of the rest part: processing the signal by a small amplitude coupling interference square wave signal through an RC filter; and S3, sampling through the MCU module to perform debounce, amplitude limiting, frequency limiting and integral processing. The magnetic core has the advantages that the magnetic core design achieves the balance of a magnetic circuit induction loop, controls the highest interfered point, and greatly suppresses and shields interference ripples; the interference of the instantaneous impact pulse to the coil can be greatly reduced, the rest small interference is subjected to hardware filtering, and amplitude limiting, frequency limiting and integration processing are performed through sampling of the MCU, so that the most effective high-precision sensor application is realized.
Description
Technical Field
The invention relates to the technical field of leakage current detection, in particular to a method for solving the interference of a fluxgate sensor on the characteristics of ultra-large current.
Background
The leakage current sensor is widely applicable to the measurement of alternating current leakage current, power and electric energy with high precision and small phase error in the fields of electric power, communication, meteorology, railways, oil fields, buildings, measurement, scientific research and teaching units, industrial and mining enterprises and the like, can be connected with various high-precision digital multimeters or data recorders, and is very convenient to use.
Numerous disturbances have always affected the measurement accuracy of the sensor, such as: the field has more energy-consuming devices, and particularly, the starting and stopping of a high-power inductive load can cause the power grid to generate spike pulse interference of hundreds of volts or even thousands of volts; under-voltage or over-voltage of an industrial power grid often reaches about 35% of rated voltage, and the severe condition sometimes lasts for several minutes, hours or even days; various signal wires are bound together or a same multi-core cable is laid, so that signals can be interfered, and particularly, the signal wires and the alternating current power wires are interfered in a long pipeline which is laid together; the performance of the multi-way switch or the keeper is poor, and channel signal interference can be caused; the normal operation of the sensor can be interfered by the changes of various electromagnetic and meteorological conditions, lightning and even the geomagnetic field in the space;
in addition, the changes of the field temperature and humidity can cause the circuit parameters to change, and the reliability of the sensor can be influenced by the actions of corrosive gas, acid, alkali, salt, wind, sand, rain, even the damage of mice and insects in the field.
The leakage current sensor generally processes small signals, and has the problems of small signal amplification, processing, shaping and anti-interference, namely, the weak signals of the sensor are amplified to required uniform standard signals (such as 1 VDC-5 VDC or 4 mADC-20 mADC) and reach required technical indexes. This requires that the designer must be aware of the tamper resistance problem.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to solve the problem that the high power interferes with the accuracy of the sensor, including the continuous interference and the instant start-stop impact interference of a large-current loop.
In order to realize the purpose, the invention provides the following technical scheme:
a method for solving the interference of the fluxgate sensor about the ultra-large current characteristic is characterized by comprising
S1, selection and design of a magnetic core: the magnetic ring is composed of superconducting magnetic cores, the magnetic circuits of the magnetic cores are designed in a balanced mode, and the highest disturbed point of the magnetic cores is controlled;
s2, performing hardware filtering on the interference of the rest part: processing the signal by the small amplitude coupling interference square wave signal through an RC filter;
s3, carrying out debounce, amplitude limiting, frequency limiting and integral processing through sampling of the MCU module: the jitter removal and the amplitude limiting can shield interference within 2ms and filter abnormal waveforms with overhigh instantaneous energy; the frequency limitation and integration are because the measured current can reflect that the frequency is too high after exceeding the measuring range, and the real current state is identified through integration and the effective average current value is calculated in continuous regular oscillation.
Further, the magnetic core is formed by smelting permalloy 1J 85; annealing the alloy cold-rolled thin strip at 1300 ℃ in a hydrogen atmosphere, keeping the temperature, controlling the cooling speed to about 300 ℃, discharging and air cooling, and increasing the high-temperature annealing time and adopting secondary medium-temperature annealing at 500 ℃;
si and alloy with adjusted components and alloy containing Ca and Ba are added in the later stage of alloy smelting, which is beneficial to the aggregation and floating of inclusions, the floating inclusions are removed to increase the purity of the alloy, the size of the aggregated inclusions is far away from the size of a magnetic domain wall of about 1 mu m, the influence on the rotation and movement of the magnetic domain wall is reduced, and thus the magnetic performance is increased.
Furthermore, when the magnetic core is selected and detected, the magnetic core is detected through automatic screening equipment, the automatic screening equipment comprises a functional PCBA board with a built-in sensor, a base, a probe assembly, a U-shaped copper bar, a cylinder and a motor, the probe assembly comprises 10 groups of probes arranged on the inner side and the outer side of the base, the 10-turn effect of winding of a coil is simulated and the probe assembly is connected with the functional PCBA, and a complete sensor state with the replaceable magnetic core is formed;
fixing the magnetic core on the base, pressing down the cylinder and driving the probe to contact with the magnetic core, and making the copper bar pass through the magnetic core, applying 30A triangular wave current on the copper bar to simulate the interference current to pass through, controlling the copper bar to rotate every 36 degrees in the current applying process by the motor, scanning different interference values of every angle, judging whether the maximum interference value of the whole circle of magnetic core meets the requirement limit after finishing the whole 360-degree scanning, and combining the actual range of the product with the size of the relative interference, and whether the accuracy error allowance is met.
Furthermore, when a large load current passes through the magnetic core coil, high-frequency pulse interference generated instantly is coupled to the oscillation square wave signal through the magnetic core coil, when the signal coupled with the high-frequency pulse is processed through the RC low-pass filter, the high-frequency part is attenuated and filtered, and the sampling signal with the recognizable frequency range is collected, processed and judged by the MCU-ADC;
the cutoff frequency of the RC filter is calculated as: f (cutoff) = 1/(2 π RC)
The low-pass filter is configured, and the frequency response characteristic of the sensor is combined, so that effective test in a bandwidth range and reliable processing of an ultra-wide range are guaranteed.
Further, the effective current in the bandwidth is mainly used for comprehensively identifying alternating current, direct current, two-phase rectification, three-phase rectification and pulsating direct current through the duty ratio and the frequency of the square wave; further collecting 16 calculated values in each period (20 ms), wherein each value is calculated by collecting peak values of 4 continuous points by the ADC; and analyzing and processing the 16 values, identifying the average amplitude difference of each point, judging the effectiveness, calculating to confirm the actual leakage size and type, and making a product action logic.
Furthermore, the current characteristics outside the bandwidth and the current state after RC low-pass filtering are all attenuated to the minimum amplitude, and in the standard requirement frame without misoperation, the actual high-frequency leakage is all very small current displayed in software sampling, so that the alarm range cannot be reached, and the risk of false tripping of the sensor cannot be caused.
By adopting the technical scheme, the invention has the beneficial effects that: the magnetic core design achieves the balance of a magnetic circuit induction loop, controls the highest interfered point and greatly suppresses and shields interference ripples; the interference of the instantaneous impact pulse to the coil can be greatly reduced, the rest small interference is subjected to hardware filtering, and amplitude limiting, frequency limiting and integration processing are performed through sampling of the MCU, so that the most effective high-precision sensor application is realized.
Drawings
Fig. 1 is a schematic frame diagram of the leakage sensor.
Fig. 2 is a waveform of the operation of the fluxgate.
Fig. 3 shows the principle of the change of the current-sensing parameter.
Fig. 4 shows the ac ripple of the disturbed analog output.
FIG. 5 is a graph of the relationship between the preferred perturbation point of the magnetic core and the current being measured.
Fig. 6 is a schematic diagram of instantaneous high-frequency pulse interference during high-current start and stop.
FIG. 7 is a frame diagram of MCU data sampling period.
Fig. 8 is a graph of the square wave processing state and data analysis and results of the RC low pass filter.
Fig. 9 is a diagram of interference data processed by the MCU from transient impulse interference.
FIG. 10 is a sensor frequency response curve characteristic.
Fig. 11 is a schematic structural view of an automatic screening apparatus.
Detailed Description
Embodiments of the present invention are further described with reference to fig. 1 to 11.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and those skilled in the art should be able to make general changes and substitutions within the technical scope of the present invention.
The invention mainly aims to solve the problem of high power interference on the accuracy of the sensor, including continuous interference and instant start-stop impact interference of a large-current loop. The invention aims to realize the invention by solving the problems of (1) key materials, (2) hardware design and (3) software design.
The three main problems to be solved relate to the following principles:
as shown in fig. 1, the leakage current sensor is based on the fluxgate principle, the magnetic field of the magnetic ring probe is alternately saturated through the square wave excitation source, and once the magnetic field is saturated, the driving level of the excitation source is automatically turned over through detection control (fig. 2); even if the leakage current is in mA level, the induction coil continuously superposes induced electromotive force in a certain direction, so that the output signal is asymmetric, and the leakage current protection judgment is achieved (figure 3).
The core mainly relates to a key material superconducting magnetic core shown in (1) of fig. 1, and the characteristic of the core is that self-excited driving square waves pass through a magnetic core coil to achieve the effect of charging and fast saturation and overturning, so that the detection capability of the fluxgate is completed.
The detection capability of the fluxgate comprises rectification waves, pulsating waves, alternating currents, direct currents, complex waves, superposed waves and the like within the range of the micro currents and the range which can be reached by the design; the corresponding square wave can effectively and accurately identify the type and the current size of the square wave through the change of the duty ratio and the frequency of the square wave; when the super-large current loop passes through the detection coil, the generated sharp pulse interference is detected and sensed by the fluxgate, and is expressed to the output end through analog modulation, so that the existence of large alternating current ripples can be obviously seen, the large ripples can be expressed into an effective alternating current leakage state on the final data processing, and the precision is seriously influenced!
The invention aims to solve the problems that: namely the continuous spike interference generated by a large current loop when the fluxgate works. By simulating the actual interference environment, researching the induction characteristic change of the coil and improving the optimization scheme, the problem of precision disturbance is solved.
In the above large-current loop interference simulation environment, a triangular pulse wave (power frequency 50 Hz-30A) similar to large-current interference is modulated mainly by a programmable power supply and a high-power load, the large-current loop passes through the coil, and the simulated pulse waveform is continuously applied to the loop, so that an alternating current ripple (fig. 4) which is still output and coupled to the sensor after sampling modulation can be obviously found, and the effective value of the alternating current ripple is enough to cause precision deviation.
The alternating current ripples are distributed on the same magnetic core in different disturbed degrees, and the magnetic core of the alternating current ripples is closely related to the distance and the angle of a current loop to be measured. Therefore, the current loop is eccentrically arranged in the coil, and the coil is uniformly rotated for 360 degrees (fig. 5), so that the coil is obviously found to have a highest disturbed point, and the highest point is perpendicular to the line surface of the current loop and is disturbed most seriously when being close to the line surface of the current loop, therefore, two key points need to be controlled when the magnetic core is designed: firstly, a magnetic circuit is designed in a balanced manner; secondly, the highest disturbed point is controlled, so that the overall disturbed condition can be effectively improved;
the solution of the present invention is: the impact interference of instant start and stop of large current is the interference. The method mainly depends on hardware filtering combined with software processing to achieve effective filtering and real current identification and complete the anti-interference processing method.
The above-mentioned impact interference of instant start-stop of large current is mainly reflected in that when the large current suddenly switches on the load, the instantaneous high-frequency pulse generation (fig. 6) including the occurrence of inductive or capacitive load influences the sampling waveform identification of the MCU in the parasitic and detection feedback loop, resulting in accuracy deviation.
The detection loop and the MCU sampling (figure 7) are cycles of square wave oscillation and charge-discharge saturation current feedback of the fluxgate. Mainly relates to a Vin-self-excitation square wave driving end, a Vcom saturation current feedback end, a coil, an LN-tested current loop and an MCU AD sampling end; combining the change of the duty ratio and the frequency of the square wave (shown in figures 2 and 3) caused by the influence of the electric leakage, and finishing accurate judgment of the electric leakage and action alarm through sampling, filtering and data operation of the MCU;
the sampling change of the square wave plays a vital role in ensuring the information integrity and precision of the whole system. When (fig. 6) the instantaneous high-frequency pulse interference at start and stop is sampled by the coil and coupled to the square wave, the high-frequency and continuous interference wave cannot be subjected to effective de-jittering filtering on software analysis, and system misjudgment or data precision deviation is caused (fig. 9).
The concrete solving method of the invention is as follows:
the magnetic core design achieves the balance of a magnetic circuit induction loop, controls the highest interfered point, and has great suppression and shielding on interference ripples. And the interference of the instantaneous impact pulse to the coil can be greatly reduced, so that only the residual small part of interference is required to be subjected to hardware filtering in the aspect of hardware design, and amplitude limiting, frequency limiting and integration processing are performed through sampling of the MCU, so that the most effective high-precision sensor application is realized.
The above hardware filtering mainly processes the signal into a clean state by a small-amplitude coupling to the interfering square wave signal through an RC filter, and although each square wave inversion is affected by RC replay electricity, the authenticity of actually required sampling data is not damaged while the interfering waveform is filtered out (fig. 8);
the methods for removing jitter, limiting amplitude, limiting frequency and integrating, which are related to the above, are software filtering, processing analysis, solving interference and ensuring current precision and waveform accuracy. In the face of the initial stage of the instantaneous impact current and the surge test impact, the same characteristics exist, the time is short, and the energy is large, so that even though the clutter can be filtered by hardware filtering, the actual impact energy still enters an AD sampling end, the jitter removal and the amplitude limiting can shield the interference within 2ms and filter the abnormal waveform with overhigh instantaneous energy; the frequency limitation and integration are because the measured current can reflect that the frequency is too high after exceeding the measuring range, and the real current state is identified through integration and the effective average current value is calculated in continuous regular oscillation.
In conclusion, the interference suppression of the front-end magnetic core, the interference filtering of the middle-end and the shielding, filtering, analysis, processing, identification, calculation and output of the back-end software are systematically ensured. The whole invention method is completed.
Processing and selecting a magnetic core:
permalloy 1J85 melting
(1) In the smelting process, the time of smelting and refining is increased, the alloy components are homogenized as much as possible, the alloy yield, the inclusion carrying source and the inclusion carrying amount are summarized and counted aiming at different smelting furnaces, and the available alloy component control method for each furnace is realized.
(2) Carrying out long-time annealing treatment on the alloy cold-rolled thin strip at high temperature (1300 ℃) in hydrogen atmosphere, keeping the temperature, controlling the cooling speed to about 300 ℃ and discharging for air cooling, and accurately controlling the cooling speed; the high-temperature annealing time can be prolonged, and a heat treatment system of secondary medium-temperature annealing at 500 ℃ and then rapid cooling can be adopted. Impact, vibration and other forces should be avoided during use.
(3) Reasonable smelting, refining and heat treatment processes are adopted to control the grain size and grain size of the alloy, such as increasing annealing temperature in heat treatment, prolonging heat preservation time in annealing, adopting two-stage continuous annealing and the like.
(4) In addition to Si and alloy for adjusting components, alloy containing Ca and Ba is also recommended to be added in the later stage of smelting, so that the aggregation and floating of inclusions are facilitated, the floating inclusions are removed to increase the purity of the alloy, the size of the aggregated inclusions is far away from the size of a magnetic domain wall of about 1 mu m, the influence on the rotation and movement of the magnetic domain wall is reduced, and the magnetic performance is improved.
The angular distribution automatic screening equipment (figure 11) equivalent to the model of figure 5 is designed, and the interfered alternating effective value extraction of figure 4 is realized by combining the equipment control and the upper computer software (attached page 2) for data reading, the screening limit of the automatic equipment is set, and the effective guarantee of the application process is realized.
The automatic screening equipment comprises a tool structure and matched upper computer software. The tool structure mainly sets up the magnetic core base through the function PCBA board of built-in sensor, and 10 groups of probes are placed to the base inside and outside, simulate the 10-turn effect of coil coiling, and connect with function PCBA, form the complete sensor state of a removable magnetic core.
Fixing the magnetic core on the base, the probe contact is accomplished through the air lever to the frock pushing down, the bar copper becomes the U type and passes the magnetic core, apply 30A's triangular wave current simulation interference current at the bar copper and pass through, apply the in-process frock motor and pass through the rotatory bar copper of host computer software control every 36 at the electric current, scan the different interference value of its every angle, judge whether its biggest interference value of whole round magnetic core meets the requirement and limits after accomplishing whole 360 scans, the size that its standard combines the actual range of product to receive the interference relatively, whether satisfy the precision error and allow.
Example (c): a leakage current sensor with a 500mA measuring range is applied to a load product of 30A, the gain of the leakage current sensor is 4mV/mA, the precision is 2% of the full measuring range, if the disturbance limit of a screening tool is set to be less than 8mV/AC, the maximum actual influence is 2mA, and compared with the precision of 2%, the influence of a controlled magnetic core on the precision meets the standard requirement.
With reference to fig. 6, the oscilloscope performs actual measurement and analysis, the yellow line is used for carrying out leakage sampling on the current clamping table, all the LN return lines are placed in the test clamp, and the actual state of leakage when a large load passes is monitored; meanwhile, the red line is a sensor oscillation sampling square wave;
when a load is connected, high current starts instant high-frequency pulse interference to generate, interference existing in a loop is fed back by the clamp current, and meanwhile, high-frequency interference is coupled to an oscillation waveform of the sensor.
In the detection loop (fig. 7), when a large load current passes through the magnetic core coil, the instantaneously generated high-frequency pulse interference is coupled to the oscillation square wave signal through the magnetic core coil, when the signal coupled with the high-frequency pulse is processed through the RC low-pass filter (fig. 8), the high-frequency part is attenuated and filtered, and the sampling signal with the identifiable frequency range is collected, processed and judged by the MCU-ADC.
Referring to the characteristic of a frequency response curve of a sensor (figure 10), the sensor is designed to be 700Hz bandwidth, and the bandwidth is in accordance with-3 db attenuation limit, meanwhile, after 700Hz, linear attenuation occurs due to bandwidth limit, abnormal fluctuation occurs when the bandwidth exceeds 15K, and meanwhile, signals are mistakenly judged as effective current during final sampling judgment.
The cutoff frequency of the RC filter is calculated as: f (cutoff) = 1/(2 π RC).
The method sets R =1K and C =10nF
By the formula F =15923.6hz
The high-frequency signal after 15KHz is subjected to amplitude attenuation minimum waveform by the configuration of an effective low-pass filter and the combination of the frequency response characteristics of the sensor, so that the effective test of software processing in a bandwidth range and the reliable processing of the over-range of an over-bandwidth are ensured;
the software processing modes mainly comprise a method for judging and calculating the effective current in the bandwidth and a method for processing the out-of-bandwidth overrange.
The effective current in the bandwidth is mainly characterized by comprehensively identifying alternating current, direct current, two-phase rectification, three-phase rectification, pulsating direct current and the like through the duty ratio and frequency of square waves; further collecting 16 calculated values in each period (20 ms), wherein each value is calculated by collecting peak values of 4 continuous points by the ADC; and analyzing and processing the 16 values, identifying the average amplitude difference of each point, judging the effectiveness of the average amplitude difference, calculating to confirm the actual leakage magnitude and type, and making a product action logic.
The effectiveness is mainly characterized in that abnormal fluctuation coupled in when large-current high-frequency pulses occur is distinguished, shielding processing is carried out after the abnormal fluctuation is directly calculated and judged by the peak value of each point, a sampling period is restarted, and the shielding and filtering effects of instantaneous high-frequency large current are effectively finished.
The current characteristics outside the bandwidth, including the current states of 700Hz-15kHz and 15kHz after RC low-pass filtering, are attenuated to the minimum amplitude, within the standard: in the framework of requirement that current is not mistakenly operated from 20mA to 200mA at high frequency of 15K to 150K, the actual high-frequency leakage is very small current displayed in software sampling, the alarm range cannot be reached, and the risk of false tripping of the sensor cannot be caused.
Claims (6)
1. A method for solving the interference of the fluxgate sensor about the characteristics of the ultra-large current is characterized by comprising the following steps
S1, selection and design of a magnetic core: the magnetic ring is composed of a superconducting magnetic core, and the magnetic circuit of the magnetic core is designed in a balanced manner to control the highest disturbed point of the magnetic core;
s2, performing hardware filtering on the interference of the rest part: processing the signal by a small amplitude coupling interference square wave signal through an RC filter;
s3, carrying out debouncing, amplitude limiting, frequency limiting and integral processing through sampling of the MCU module: the jitter removal and the amplitude limiting can shield interference within 2ms and filter abnormal waveforms with overhigh instantaneous energy; the frequency limitation and integration are because the measured current can reflect that the frequency is too high after exceeding the measuring range, and the real current state is identified through integration and the effective average current value is calculated in continuous regular oscillation.
2. The method for solving the problem of the interference of the characteristics of the over-current of the fluxgate sensor as set forth in claim 1, wherein the magnetic core is formed by melting permalloy 1J 85; annealing the alloy cold-rolled thin strip at 1300 ℃ in a hydrogen atmosphere, keeping the temperature, controlling the cooling speed to about 300 ℃, discharging and air cooling, and increasing the high-temperature annealing time and adopting secondary medium-temperature annealing at 500 ℃;
si and alloy with adjusted components and alloy containing Ca and Ba are added in the later stage of alloy smelting, which is beneficial to the aggregation and floating of inclusions, the floating inclusions are removed to increase the purity of the alloy, the size of the aggregated inclusions is far away from the size of a magnetic domain wall of about 1 mu m, the influence on the rotation and movement of the magnetic domain wall is reduced, and thus the magnetic performance is increased.
3. The method for solving the interference of the fluxgate sensor with respect to the characteristic of the ultra-large current according to claim 2,
when the magnetic cores are selected and detected, the magnetic cores are detected through automatic screening equipment, the automatic screening equipment comprises a functional PCBA board with a built-in sensor, a base, a probe assembly, a U-shaped copper bar, a cylinder and a motor, the probe assembly comprises 10 groups of probes arranged on the inner side and the outer side of the base, 10 turns of winding effects of a coil are simulated and connected to the functional PCBA, and a complete sensor state with the replaceable magnetic cores is formed;
fixing the magnetic core on the base, pressing down the cylinder and driving the probe to contact with the magnetic core, and making the copper bar pass through the magnetic core, applying 30A triangular wave current on the copper bar to simulate the interference current to pass through, controlling the copper bar to rotate every 36 degrees in the current applying process by the motor, scanning different interference values of every angle, judging whether the maximum interference value of the whole circle of magnetic core meets the requirement limit after finishing the whole 360-degree scanning, and combining the actual range of the product with the size of the relative interference, and whether the accuracy error allowance is met.
4. The solving method of the interference of the fluxgate sensor with respect to the characteristic of the extra large current according to claim 1,
when a large load current passes through the magnetic core coil, high-frequency pulse interference generated instantly is coupled to the oscillation square wave signal through the magnetic core coil, when the signal coupled with the high-frequency pulse is processed through the RC low-pass filter, the high-frequency part is attenuated and filtered, and a sampling signal with an identifiable frequency range is collected, processed and judged by the MCU-ADC;
the cutoff frequency of the RC filter is calculated as: f (cutoff) = 1/(2 π RC)
The low-pass filter is configured, and the frequency response characteristic of the sensor is combined, so that effective test in a bandwidth range and reliable processing of the over-range of the super-bandwidth are guaranteed.
5. The solving method of the interference of the fluxgate sensor with respect to the characteristic of the extra large current according to claim 1,
the effective current in the bandwidth is mainly characterized by comprehensively identifying alternating current, direct current, two-phase rectification, three-phase rectification and pulsating direct current through the duty ratio and frequency of square waves; further collecting 16 calculated values in each period (20 ms), wherein each value is calculated by collecting peak values of 4 continuous points by the ADC; and analyzing and processing the 16 values, identifying the average amplitude difference of each point, judging the effectiveness of the average amplitude difference, calculating to confirm the actual leakage magnitude and type, and making a product action logic.
6. The solving method of the interference of the fluxgate sensor with respect to the characteristic of the extra large current according to claim 1,
the current characteristic outside the bandwidth and the current state after RC low-pass filtering are attenuated to the minimum amplitude, and in a standard requirement frame without misoperation, the actual high-frequency leakage shows that all currents are very small in software sampling, so that the alarm range cannot be reached, and the risk of false tripping of the sensor cannot be caused.
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