Portable direct current partial discharge current pulse group generating system and equipment detection method thereof

Abstract

The present application relates to a kind of portable direct current partial discharge current pulse group generation system and its equipment detection method, belong to direct current partial discharge test technical field, solve the problem that there is no portable direct current partial discharge current pulse group generation system and matched equipment detection method in prior art.A kind of portable direct current partial discharge current pulse group generation system, the generation system includes central processing unit, current pulse-time sequence generator and inductor;Wherein, central processing unit is used to load the algorithm file of abc equivalent model, constructs reference direct current TPRPD spectrum;Current pulse-time sequence generator is used to generate corresponding transient current pulse group according to the reference direct current TPRPD spectrum;Inductor is used to be connected in the test loop of direct current electrical equipment, and based on the transient current pulse group injected in inductor, simulate adjustable transient current pulse group in the test loop of direct current electrical equipment in direct current PD source output.

Description

Technical Field

[0001] This invention relates to the field of DC partial discharge testing technology, and in particular to a portable DC partial discharge current pulse group generation system and its testing method. Background Technology

[0002] During operation, the insulation systems of high-voltage direct current (HVDC) electrical equipment (such as converter transformers and DC cables) are susceptible to partial discharge (PD) due to various factors such as electrolytic corrosion, vibration-induced wear and cracking, thermal decomposition, and moisture absorption. Therefore, PD signals often contain information about the gradual process of insulation degradation and performance decline, making PD detection the core means of controlling the quality and operational status of such main equipment throughout its entire lifecycle. The PD source inside the equipment continuously generates single, nanosecond-level rising-edge current pulses. Detecting the current pulses generated by the DC PD source using ultra-wideband methods (including high-frequency methods) is currently the most common technique for routine live-line testing and online monitoring of converter transformers and DC cable equipment. These instruments and systems used for PD live-line testing and online monitoring are delivered to users after undergoing type tests and factory tests as required by relevant standards. However, for users such as power supply companies, there is a lack of relevant technical means to determine and evaluate whether the instruments and operational online monitoring systems are functioning properly and meet the requirements for DC PD testing.

[0003] A common method for assessment involves commissioning a professional organization to set up defects (such as sharp points, air gaps, and suspensions) in a laboratory setting, conducting high-voltage tests to induce stable discharge from the defects. This simulates the PD (Power Distribution) source formed by insulation defects, used to determine whether ultra-wideband (including high-frequency) DC PD instruments or online monitoring systems are functioning correctly, and whether the test results provided by the algorithm match the set defect model type. This approach is time-consuming and labor-intensive, requiring power supply companies to transport the equipment to the testing unit, and is not feasible for online monitoring systems already installed on-site.

[0004] Therefore, how to design a portable DC partial discharge current pulse group generation system and use it to realize the detection of PD detection instruments or online monitoring systems is a technical problem that urgently needs to be solved. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a portable DC partial discharge current pulse group generation system and its device detection method to solve the problem of the lack of a portable DC partial discharge current pulse group generation system and a matching device detection method in the prior art.

[0006] On one hand, the present invention provides a portable DC partial discharge current pulse group generation system, the system comprising a central processing unit, a current pulse-time sequence generator, and a sensor; wherein,

[0007] The central processing unit is used to load the algorithm file of the abc equivalent model and construct the reference DC TPRPD spectrum.

[0008] A current pulse-time sequence generator is used to generate a corresponding transient current pulse group based on the reference DC TPRPD spectrum.

[0009] An inductor is used to connect in the test circuit of a DC electrical equipment and, based on the transient current pulse group injected into the inductor, simulates the output of an adjustable transient current pulse group of a DC PD source in the test circuit of the DC electrical equipment.

[0010] Based on the above solution, the present invention also makes the following improvements:

[0011] Furthermore, the abc equivalent model refers to the abc equivalent model of the internal insulation defect air gap of DC electrical equipment.

[0012] Furthermore, by adjusting the amplitude of the transient pulse group injected into the sensor, a corresponding adjustable transient current pulse group is induced in the conductor or grounding wire of the test circuit of the DC electrical equipment.

[0013] Furthermore, the sensor is an ultra-wideband current transformer.

[0014] Furthermore, the generating system also includes a mobile terminal and a communication module; the mobile terminal is connected to the central processing unit via the communication module; wherein,

[0015] The mobile terminal is used to pre-store the algorithm file of the ABC equivalent model and transmit it to the central processing unit via the communication module.

[0016] Furthermore, the generating system also includes a power supply module and a human-machine interaction module; wherein,

[0017] The power module is used to supply power to the human-computer interaction module, the central processing unit, the current pulse-time sequence generator and the communication module.

[0018] The human-computer interaction module is used to acquire and display the status of the power module, central processing unit, current pulse-time sequence generator and communication module.

[0019] Furthermore, the power module, human-machine interaction module, central processing unit, current pulse-time sequence generator, and communication module form an integrated device; the integrated device is connected to the sensor via a coaxial cable and to the mobile terminal via a wireless or wired communication module.

[0020] On the other hand, the present invention also provides a device detection method based on the above-mentioned portable DC partial discharge current pulse group generation system, the device detection method comprising:

[0021] The PD testing instrument or online monitoring system used in the actual testing scenario of DC electrical equipment is taken as the device under test, and the sensor is selected according to the device under test;

[0022] The central processing unit loads the algorithm file of the abc equivalent model, constructs a reference DC TPRPD spectrum, and generates a transient current pulse group by a current pulse-time series generator, which outputs the transient current pulse group to the sensor.

[0023] Based on the received transient current pulse group, the sensor simulates the output of an adjustable transient current pulse group from a DC PD source in the test circuit of the DC electrical equipment.

[0024] The device under test detects adjustable transient current pulse groups and records the test DC PRPD spectrum; the device under test is judged to be working properly by comparing the reference DC TPRPD spectrum with the test DC PRPD spectrum.

[0025] Based on the above solution, the present invention also makes the following improvements:

[0026] Furthermore, the step of selecting and matching sensors based on the device under test, and then performing:

[0027] If the system under test includes multiple ultra-wideband current transformers, then one of them is selected as the inductor; if the system under test has only one ultra-wideband current transformer, then a card-mounted ultra-wideband current transformer is configured as the inductor.

[0028] Furthermore, by comparing the reference DC TPRPD spectrum with the test DC PRPD spectrum, the normal operation of the device under test is determined, and the following steps are performed:

[0029] Based on the given criteria, the difference between the reference DC TPRPD spectrum and the test DC PRPD spectrum is compared. If the difference between the two is not higher than the preset difference threshold, it indicates that the device under test is working normally; otherwise, the device under test is malfunctioning.

[0030] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0031] The portable DC partial discharge current pulse group generation system provided by this invention, through the cooperation of a central processing unit, a current pulse-time sequence generator, and sensors, enables the amplitude intensity of each transient current pulse in the transient current pulse group to be adjustable. It can realistically simulate the signal generated by a DC PD source in both the time and frequency domains, and the time distribution characteristics are consistent with those of a real DC PD source, thus accurately simulating the generation process of DC partial discharge current pulse groups. Furthermore, the system adopts a portable, integrated device form with a visual input window. Different sensors can be selected according to actual needs, and the transient current pulse group signal can be injected into the selected sensor. This allows it to adapt well to different working scenarios and meet on-site requirements, effectively solving the problem of the lack of portable DC partial discharge current pulse group generation systems in the prior art, and providing strong technical guidance for related technical fields.

[0032] Furthermore, this invention also provides a device testing method based on a portable DC partial discharge current pulse group generation system. The method utilizes the aforementioned generation system to induce adjustable transient current pulse groups, which are then detected by the device under test (a DC PD instrument based on the ultra-wideband method or an online monitoring system). The reference DC TPRPD spectrum is compared with the test DC PRPD spectrum to determine whether the device under test is functioning correctly. This provides a relatively fast device testing method and effectively solves the problem that power supply companies and other users lack the technical means to determine and evaluate whether their ultra-wideband (including high-frequency) DC PD instruments or online monitoring systems are functioning correctly and meet the requirements for DC PD testing.

[0033] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0034] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0035] Figure 1 This is a schematic diagram of the portable DC partial discharge current pulse group generation system provided in Embodiment 1 of the present invention;

[0036] Figure 2 This is the abc equivalent model of the internal insulation defect air gap of DC electrical equipment provided in Embodiment 1 of the present invention;

[0037] Figure 3 The DC TPRPD spectrum constructed using the abc equivalent model provided in Embodiment 1 of the present invention;

[0038] Figure 4 A schematic diagram of a single transient current pulse provided in Embodiment 1 of the present invention;

[0039] Figure 5 This is a schematic diagram of another portable DC partial discharge current pulse group generation system provided in Embodiment 1 of the present invention;

[0040] Figure 6 This is a flowchart of a device detection method based on a portable DC partial discharge current pulse group generator system provided in Embodiment 2 of the present invention;

[0041] Figure 7 This is a schematic diagram of the equipment detection connection relationship when the DC electrical equipment is a converter transformer.

[0042] Figure 8 This is a schematic diagram of the equipment detection connection relationship when the DC electrical equipment is a DC cable. Detailed Implementation

[0043] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0044] Specific embodiment 1 of the present invention provides a portable DC partial discharge current pulse group generation system, the structural schematic diagram of which is shown below. Figure 1 As shown, the system includes a central processing unit, a current pulse-time sequence generator, and sensors; the functions of each component are described below.

[0045] (1) Central processing unit, used to load the algorithm file of the abc equivalent model and construct the reference DC TPRPD spectrum.

[0046] The DC TPRPD spectrum, i.e., peak-time series (qt), is constructed by loading the algorithm file (.txt) of the abc equivalent model onto the central processing unit. To distinguish it from the DC TPRPD spectrum detected by PD testing instruments or online monitoring systems, the constructed DC TPRPD spectrum is referred to as the reference DC TPRPD spectrum. A schematic diagram of the abc equivalent model of the internal insulation defect air gap in DC electrical equipment is shown below. Figure 2 As shown below, the algorithm file for the ABC equivalent model of the internal insulation defect air gap in DC electrical equipment is described as follows.

[0047] The algorithm file for loading the abc equivalent model mainly consists of equations (1) to (4). It is assumed that no discharge occurs in the air gap during the pressurization process (one of the assumptions for solving the model; after the defect charging time is reached, the abc equivalent model will discharge, i.e., a voltage jump). Considering... Hybrid circuits in With a DC voltage source constantly connected, solve for the circuit's response to a step voltage. Zero-state response under excitation. Figure 2 In the diagram, b represents the defect, a is the insulating medium connected in series with the defect, and c is the other insulating medium besides a. The circuit equations shown below can be established:

[0048] (1)

[0049] in, , These represent the capacitances corresponding to a and b, respectively. , The voltage at both ends, , , , They represent the flow through , , , The current.

[0050] Equation (1) simplifies to:

[0051] (2)

[0052] In the formula: ; .

[0053] Solving equation (2) yields:

[0054] (3)

[0055] In the formula: This represents the defect charging time constant. .

[0056] Depend on much smaller Equation (3) can be simplified to:

[0057] (4)

[0058] This allows for the random setting of the occurrence time t, which subsequently forms a peak-time series (qt). The DC TPRPD spectrum q(i)-t(i) is a peak-time series, where the horizontal axis represents the occurrence time t(i) and the vertical axis represents the discharge quantity q(i). An example of a DC TPRPD spectrum is shown below. Figure 3 As shown.

[0059] (2) Current pulse-time sequence generator, used to generate corresponding transient current pulse groups based on the reference DC TPRPD spectrum.

[0060] Specifically, the current pulse-time series generator can generate the corresponding transient current pulse group as follows: Based on the DC TPRPD spectrum, the corresponding peak-time distribution characteristics are generated. All individual transient current pulses that satisfy the following conditions are selected: rise time of peak value less than 10 ns, half-peak width time less than 50 ns, and duration less than 100 ns. These are then combined to form a transient current pulse group, i.e., a current pulse-time series, which is output to the sensor. A schematic diagram of a single transient current pulse is shown below. Figure 4 As shown. Rise time Half-peak time Peak duration They are represented as follows:

[0061] (5)

[0062] (6)

[0063] (7)

[0064] in, This represents the peak value of the transient current pulse. express *0.5 corresponds to the second time point (ns); This represents the time (ns) corresponding to the apparent zero point of the transient current pulse. According to the equation of the straight line formed by the two points at 90% and 10% of the rising edge in formula (4):

[0065] (8)

[0066] We can obtain,

[0067] (9)

[0068] in, Indicates time, Indicates peak value; Indicates the peak value of the transient current pulse *0.1 corresponds to the second time point (ns). , These represent the amplitudes at 10% and 90% of the rising edge of the transient current pulse, respectively. , These represent the times corresponding to 10% and 90% of the rising edge of the transient current pulse, respectively.

[0069] (3) An inductor is used to connect to the test circuit of a DC electrical equipment and to simulate the output of an adjustable transient current pulse group of a DC PD source in the test circuit of the DC electrical equipment based on the transient current pulse group injected into the inductor.

[0070] In practice, an adjustable current pulse group, simulating the output of a DC PD source, can be generated in the test circuit of the DC electrical equipment using an inductor. This is known as an adjustable transient current pulse-time sequence. Specifically, by adjusting the amplitude of the transient pulse group injected into the inductor, a corresponding adjustable transient current pulse group is induced on the conductors or grounding wire of the DC electrical equipment's test circuit. The amplitude of the transient pulse group can be adjusted in the range of 5pC-50pC-500pC.

[0071] Preferably, the inductor is an ultra-wideband current transformer, consistent with the ultra-wideband current transformers used in PD testing instruments or online monitoring systems based on the ultra-wideband method (including the high-frequency method). For example, the ultra-wideband current transformer can be a Rogowski coil, with an operating frequency band of 20kHz~50MHz. Common inductors mainly include: clip-on Rogowski coils, high-frequency current transformers (HFCTs), and flexible wound current transformers. In specific implementation, an adaptive selection can be made according to the actual situation to facilitate the through-hole arrangement of the equipment's conductors or grounding wires. When a transient current pulse group is injected into the inductor, a corresponding adjustable transient current pulse group is induced on the conductors or grounding wires of the DC electrical equipment's test circuit.

[0072] Preferably, the generation system in this embodiment may further include a mobile terminal and a communication module; the mobile terminal is connected to the central processing unit via the communication module; wherein, the mobile terminal is used to pre-store the algorithm file of the abc equivalent model and transmit it to the central processing unit via the communication module.

[0073] Furthermore, the generation system in this embodiment may also include a power supply module and a human-machine interface module. The power supply module supplies power to the human-machine interface module, the central processing unit, the current pulse-time series generator, and the communication module; it can be charged via a common USB interface. The human-machine interface module acquires and displays the status of the power supply module, the central processing unit, the current pulse-time series generator, and the communication module.

[0074] For ease of practical application, the power supply module, human-machine interface module, central processing unit, current pulse-time sequence generator, and communication module are integrated into a single device. This integrated device connects to the sensor via a coaxial cable and to a mobile terminal via a wireless or wired communication module. The structural diagram of the generation system is shown below. Figure 5 As shown.

[0075] In practical applications, the human-machine interface module can be used to acquire and display the status of the power module, central processing unit, current pulse-time series generator, and communication module. It also provides a user interface for setting the status of the integrated device and displaying corresponding values, including the power module's battery level, and the operating status of the current pulse-time series generator and communication module. Furthermore, it provides manual input methods when the communication module cannot communicate with the mobile terminal, such as setting the integrated device to restart, pause, restart, or loop the current pulse-time series generator. In addition, the communication module supports data interaction between the integrated device and the mobile terminal, enabling users to understand the overall status of the integrated device, set parameters, and control the system via the mobile terminal. Data communication can typically be achieved via wired (serial or parallel I / O interfaces, fiber optics, etc.) or wireless (e.g., Rola, Wi-Fi, etc.). A mobile terminal can be a portable smart device such as a smartphone, tablet, or laptop computer equipped with software that maintains data communication with the integrated device. The software installed on it can load the DC TPRPD spectrum constructed from the algorithm file of the ABC equivalent model, facilitating operator observation. In addition to supporting the main data processing functions of the integrated device, the central processing unit can also be equipped with many additional functions, such as device self-testing, self-diagnosis, external environmental parameter monitoring, external process control recording, and data storage.

[0076] Embodiment 2 of the present invention discloses a device detection method based on a portable DC partial discharge current pulse group generation system, the flowchart of which is shown below. Figure 6 As shown, the detection method of this device includes the following steps.

[0077] Step S1: Select the PD testing instrument or online monitoring system used in the actual testing scenario of DC electrical equipment as the device under test, and select the appropriate sensor according to the device under test.

[0078] Specifically, in this embodiment, the DC electrical equipment can be a converter transformer and a DC cable. In actual testing scenarios for DC electrical equipment, the sensor can be selected based on the actual situation of the PD testing instrument or online monitoring system used in the ultra-wideband method (including the high-frequency method). Preferably, if the system under test includes multiple ultra-wideband current transformers, one of them is selected as the sensor; if the system under test has only one ultra-wideband current transformer, a card-mounted ultra-wideband current transformer is configured as the sensor.

[0079] In practical implementation, generally speaking, for PD testing instruments or online monitoring systems: if they include multiple ultra-wideband current transformers, one of them is selected as the sensor, and the remaining ultra-wideband current transformers are connected to the device under test as the test object. The device detection connection relationship at this time is as follows: Figure 7 As shown; if there is only one ultra-wideband current transformer, a card-mounted ultra-wideband current transformer can be configured as the sensor. The device detection connection relationship is as follows: Figure 8 As shown.

[0080] Step S2: The central processing unit loads the algorithm file of the abc equivalent model, constructs a reference DC TPRPD spectrum, and generates a transient current pulse group by a current pulse-time series generator, and outputs the transient current pulse group to the sensor.

[0081] Step S3: Based on the received transient current pulse group, the sensor simulates the output of an adjustable transient current pulse group from a DC PD source in the test circuit of the DC electrical equipment.

[0082] In practice, the maximum amplitude (peak value) of the transient current pulse group can be adjusted according to the discharge amount of 5 pC, 50 pC and 500 pC, thereby forming an adjustable transient current pulse group that simulates the generation of a DC PD source in the test circuit of the DC electrical equipment.

[0083] Step S4: The device under test detects the adjustable transient current pulse group and records the test DC PRPD spectrum; by comparing the reference DC TPRPD spectrum with the test DC PRPD spectrum, it is determined whether the device under test is working properly.

[0084] In practice, the difference between the reference DC TPRPD spectrum and the test DC PRPD spectrum can be compared according to the given discrimination criteria. If the difference between the two is not higher than the preset difference threshold, it indicates that the device under test has detected an air gap defect, is working normally, and can meet the requirements of PD testing; otherwise, the device under test is malfunctioning and cannot meet the requirements of PD testing. For example, the given discrimination criteria can be: the cumulative deviation (discharge quantity deviation) and (time deviation) of the two at all time points on the spectrum are not greater than 5%.

[0085] In addition, during the specific implementation process, after step S1, the following step can be added: using a mobile terminal to send the algorithm file of the above-mentioned abc equivalent model to the integrated device.

[0086] Based on the above equipment testing methods, it is possible to conveniently and quickly determine whether the tested equipment (i.e., DC PD testing instruments or online monitoring systems for DC electrical equipment) can work normally and meet the DC PD testing requirements.

[0087] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0088] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A portable DC partial discharge current pulse group generation system, characterized in that, The generating system includes a central processing unit, a current pulse-time sequence generator, and sensors; wherein... The central processing unit is used to load the algorithm file of the abc equivalent model and construct the reference DC TPRPD spectrum. A current pulse-time sequence generator is used to generate a corresponding transient current pulse group based on the reference DC TPRPD spectrum. An inductor is used to connect to the test circuit of a DC electrical equipment and, based on the transient current pulse group injected into the inductor, simulates the output of an adjustable transient current pulse group from a DC PD source in the test circuit of the DC electrical equipment; by adjusting the amplitude of the transient pulse group injected into the inductor, a corresponding adjustable transient current pulse group is induced on the conductor or grounding wire of the test circuit of the DC electrical equipment. The current pulse-time sequence generator generates the corresponding transient current pulse group as follows: Based on the DC TPRPD spectrum, it generates the corresponding peak-time distribution characteristics, and selects all individual transient current pulses that satisfy the following conditions: rise time of peak value less than 10 ns, half-width at half-maximum (FWHM) time less than 50 ns, and duration less than 100 ns, to form a transient current pulse group; where: Rise time Half-peak time Peak duration They are represented as follows: (1) (2) (3) in, , These represent the times corresponding to 10% and 90% of the rising edge of the transient current pulse, respectively. express The second time point corresponding to *0.

5. Indicates the peak value of the transient current pulse; This indicates the time corresponding to the apparent zero point of the transient current pulse; express *0.1 corresponds to the second time point.

2. The portable DC partial discharge current pulse group generation system according to claim 1, characterized in that, The abc equivalent model refers to the abc equivalent model of the internal insulation defect air gap of DC electrical equipment.

3. The portable DC partial discharge current pulse group generation system according to claim 2, characterized in that, The sensor is an ultra-wideband current transformer.

4. The portable DC partial discharge current pulse group generation system according to claim 3, characterized in that, The generating system also includes a mobile terminal and a communication module; the mobile terminal is connected to the central processing unit via the communication module; wherein, The mobile terminal is used to pre-store the algorithm file of the ABC equivalent model and transmit it to the central processing unit via the communication module.

5. The portable DC partial discharge current pulse group generation system according to claim 4, characterized in that, The generating system also includes a power supply module and a human-machine interaction module; wherein... The power module is used to supply power to the human-computer interaction module, the central processing unit, the current pulse-time sequence generator and the communication module. The human-computer interaction module is used to acquire and display the status of the power module, central processing unit, current pulse-time sequence generator and communication module.

6. The portable DC partial discharge current pulse group generation system according to claim 5, characterized in that, The power module, human-machine interaction module, central processing unit, current pulse-time sequence generator and communication module form an integrated device; the integrated device is connected to the sensor through a coaxial cable and to the mobile terminal through a wireless or wired communication module.

7. A device detection method based on a portable DC partial discharge current pulse group generation system according to any one of claims 1-6, characterized in that, The equipment testing method includes: The PD testing instrument or online monitoring system used in the actual testing scenario of DC electrical equipment is taken as the device under test, and the sensor is selected according to the device under test; The central processing unit loads the algorithm file of the abc equivalent model, constructs a reference DC TPRPD spectrum, and generates a transient current pulse group by a current pulse-time series generator, which outputs the transient current pulse group to the sensor. Based on the received transient current pulse group, the sensor simulates the output of an adjustable transient current pulse group from a DC PD source in the test circuit of the DC electrical equipment. The device under test detects adjustable transient current pulse groups and records the test DC PRPD spectrum; the device under test is judged to be working properly by comparing the reference DC TPRPD spectrum with the test DC PRPD spectrum.

8. The device detection method based on a portable DC partial discharge current pulse group generation system according to claim 7, characterized in that, The step involves selecting and matching sensors based on the device under test, and then performing the following: If the system under test includes multiple ultra-wideband current transformers, then one of them is selected as the inductor; if the system under test has only one ultra-wideband current transformer, then a card-mounted ultra-wideband current transformer is configured as the inductor.

9. The device detection method based on a portable DC partial discharge current pulse group generation system according to claim 7 or 8, characterized in that, The device under test is determined to be functioning correctly by comparing the reference DC TPRPD spectrum with the test DC PRPD spectrum. The following steps are performed: Based on the given criteria, the difference between the reference DC TPRPD spectrum and the test DC PRPD spectrum is compared. If the difference between the two is not higher than the preset difference threshold, it indicates that the device under test is working normally; otherwise, the device under test is malfunctioning.

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