CN109188152B - Method for detecting common-mode disturbance of grounding circuit - Google Patents
Method for detecting common-mode disturbance of grounding circuit Download PDFInfo
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- G01R31/001—Measuring interference from external sources to, or emission from, the device under test, e.g. EMC, EMI, EMP or ESD testing
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Abstract
The method for detecting the common-mode disturbance of the grounding circuit adopts time domain analysis combined with frequency domain analysis, and realizes the purpose of definitely judging the disturbance condition of the equipment or the system in the grounding circuit by testing the disturbance of the grounding circuit between any two grounding points and covering 0Hz to 150KHz, and is finally used for supporting the selection and the confirmation of the grounding points with electromagnetic compatibility. The method comprises the following steps of acquiring parameter characteristics of a detection target system or equipment, including a normal working electrical parameter range and a sensitive frequency range of a sensitive component, a transmitting frequency range and an alternative equipotential grounding point; the testing stage comprises a time domain test and a frequency domain test, and disturbance signals in a required frequency range are obtained through the time domain test and the frequency domain test; and an analysis stage, wherein the electromagnetic interference risk is analyzed and judged, and whether the grounding loop has conducted disturbance or not and disturbance intensity corresponding to different disturbance frequencies are judged so as to select the grounding point supporting electromagnetic compatibility.
Description
Technical Field
The invention discloses an analysis and judgment method for electromagnetic compatibility grounding of electrical equipment and an integrated system based on a time domain and frequency domain signal detection means, and belongs to the field of electronics and electricity.
Background
With the rapid development of rail transit technology, the types and functions of electrical equipment are more and more, and accordingly the equipment pays more attention to the protection grounding, but the design and compliance verification of the existing protection grounding are relatively simple and do not meet the innovative requirements of the existing technology.
The grounding design is a complex concept, and design concepts such as a protective ground, a functional ground and electromagnetic compatibility grounding are compatible. Generally, the electromagnetic compatibility ground is the most abstract, and in practical design and production, a ground wire is often shared with the protection ground, the selection of the butt joint place is often neglected, or the ground point is selected according to experience, and the actual grounding effect is difficult to correct. In order to realize the functional design of the product, the N line of the alternating current power line and the negative line of the direct current power line are usually directly grounded or grounded through series resistors, so that the electromagnetic disturbance of the working circuit is inevitably led into the grounding circuit.
At present, the technical requirement of the selection of grounding points for electromagnetic compatibility grounding is essentially established according to the principle of minimum impedance of a loop. This principle is not problematic in itself, but in practice often ignores the impedance characteristics at different frequencies. Further, in an integrated system or an integrated device, it is difficult to determine only a relatively accurate minimum dc impedance path between two points of potential connection of a certain ground loop or ground equipotential due to a gap or discontinuity in metal bonding. Some industry standards, such as GB4824-2013 electromagnetic disturbance characteristic limit and measuring method of industrial, scientific and medical (ISM) radio frequency equipment, GB9254-2008 radio disturbance limit and measuring method of information technology equipment, and 9KHz-150KHz conducted disturbance limit are not clearly defined. The conducted disturbance before 9KHz is also defined by the harmonic emission which does not relate to the working loop of the earth circuit, and the current situation causes the vacancy of the earth disturbance test of partial low-frequency bands.
In view of this, the present patent application is specifically proposed.
Disclosure of Invention
The invention discloses a method for detecting common-mode disturbance of a grounding circuit, which aims to solve the problems in the prior art and provides a new testing means, wherein time domain analysis and frequency domain analysis are adopted, and the disturbance condition of the grounding circuit of equipment or a system is definitely judged by testing the disturbance of the grounding circuit between any two grounding points and covering 0Hz to 150KHz, and the method is finally used for supporting the selection and the confirmation of electromagnetic compatible grounding points.
In order to achieve the design purpose, the method for detecting the common mode disturbance of the grounding loop mainly comprises the following steps:
in the investigation stage, parameter characteristics of a detection target system or equipment are obtained, wherein the parameter characteristics comprise a normal working electrical parameter range and a sensitive frequency range of a sensitive component, a transmitting frequency range and an alternative equipotential grounding point;
the testing stage comprises a time domain test and a frequency domain test, and disturbance signals in a required frequency range are obtained through the time domain test and the frequency domain test; the time domain test equipment is an oscilloscope or an equivalent time domain signal test device, and the frequency domain test equipment is a spectrum analyzer or an oscilloscope with a Fourier analysis function; therefore, the strength acquisition and the spectrum characteristic acquisition of the grounding test value with the frequency characteristic are realized, and the low impedance characteristic under different frequency characteristic conditions is judged;
and an analysis stage, namely judging whether the ground circuit has conducted disturbance and disturbance intensities corresponding to different disturbance frequencies according to disturbance signal data acquired in the test stage, analyzing and judging electromagnetic interference risks by combining parameter characteristics of a target system or equipment acquired in the investigation stage, and selecting a ground point supporting electromagnetic compatibility.
As in the basic design above, the test means includes two parts, time domain testing and frequency domain testing. The time domain waveform obtained by the time domain test is mainly used for judging whether the detected loop has obvious electromagnetic disturbance; and the frequency domain waveform obtained by the frequency domain test is used for specifically analyzing the disturbance intensity corresponding to different disturbance frequencies.
The further refinement and the preferred scheme are that the test stage tests the electromagnetic disturbance between different grounding points in the same grounding loop.
The main difference between the testing method and the traditional testing means is that the electromagnetic disturbance frequency spectrum and the electromagnetic disturbance intensity of the grounding loop are judged by testing the electromagnetic disturbance between different grounding points.
The more optimized technical scheme is that a test fixture with a probe and a grounding clamp structure is adopted for testing two grounding points and detecting electromagnetic disturbance of voltage characteristics of a grounding loop.
Generally, a voltage probe can be installed through a spectrum analyzer, a certain spectrum is set, the probe is connected with one point of a grounding point, a grounding clip is connected with a second point of the grounding point, and the electromagnetic disturbance intensity of the voltage characteristic under the spectrum is tested.
Or, a voltage probe can be installed through an oscilloscope, the probe is connected with one point of the grounding point, the grounding clamp is connected with the second point of the grounding point, the time domain waveform intensity in the time period is tested, whether the grounding loop has potential difference and periodic or transient disturbance waveform is judged, and meanwhile, Fourier analysis can be carried out through frequency domain analysis software carried by the oscilloscope;
based on the same design concept, aiming at the test between two grounding points, when the electromagnetic disturbance of the current characteristic of a grounding loop is detected, a test fixture with a probe in an annular structure is adopted.
Through the test to the ground wire, can install the current probe through the spectrum analyzer, set for certain frequency spectrum, the earth connection is blocked to the current loop, tests the electromagnetic disturbance intensity of the current characteristic under this frequency spectrum. Or, a current probe can be installed through the oscilloscope, the time domain waveform intensity in the time period is tested, whether the grounding loop has periodic or transient current pulses or not is judged, and meanwhile, Fourier analysis can be carried out through frequency domain analysis software carried by the oscilloscope.
In summary, the method for detecting common mode disturbance of the ground loop has the advantages that:
1. the application relates to a test and analysis method for judging common-mode ground disturbance of a ground circuit, which is suitable for judging and confirming the common-mode ground disturbance of equipment and system levels, even large-scale integrated systems. By the method, whether the grounding loop has conducted disturbance, disturbance frequency and corresponding disturbance intensity can be clearly judged by means of testing equipment such as an oscilloscope, a spectrum analyzer and the like, and test data obtained by the method can be analyzed to support selection and confirmation of the electromagnetic compatibility grounding point.
2. The applicable frequency range is wide, and the test can be started from 0Hz as long as the effective test range of the test equipment allows.
3. The detection mode is a test means aiming at conducted emission, and the test frequency band is different from the test of radiation emission. The method is more suitable for large-scale integrated systems with obvious disturbance on metal shells and grounding loops, and is convenient for selecting the grounding point with low electromagnetic disturbance risk.
4. The design verification means of time domain and frequency domain signal analysis is integrated, and the method is safe, simple and convenient and has strong operability.
Drawings
FIG. 1 is a schematic view of a detection process;
FIG. 2 is a schematic ground diagram of an integrated system;
FIG. 3 is a schematic diagram of an oscilloscope voltage probe;
FIG. 4 is a disturbance waveform diagram of a time domain signal;
FIG. 5 is a frequency plot of a frequency domain signal for a first ground point;
FIG. 6 is a frequency plot of a frequency domain signal for a second ground point;
FIG. 7 is a schematic diagram of a spectrum analyzer acquiring a frequency domain signal by a voltage probe;
as shown in fig. 1 to 7, the electronic device 1 of the sensitive characteristic, the electronic device 2 of the transmitting characteristic, the common ground 3 of the integrated system, the first ground 4, the second ground 5, the electronic device ground 6 of the transmitting characteristic, the oscilloscope probe 7, the oscilloscope grounded alligator clip 8, the horizontal axis 9 representing time in fig. 4, the vertical axis 10 representing signal disturbance intensity in fig. 4, the horizontal axis 11 representing each frequency characteristic in fig. 5 and 6, the disturbance signal intensity 12 corresponding to different frequencies in fig. 5 and 6, the horizontal axis 13 representing each frequency characteristic in fig. 7, and the voltage disturbance amplitude 14 corresponding to different frequencies in fig. 7.
Detailed Description
Example 1 the present invention will be described in further detail below with reference to the accompanying drawings.
As shown in fig. 1, the method for detecting common mode disturbance of the ground circuit includes the following steps:
in the investigation stage, parameter characteristics of a detection target system or equipment are obtained, wherein the parameter characteristics comprise a normal working electrical parameter range and a sensitive frequency range of a sensitive component, a transmitting frequency range and an alternative equipotential grounding point; in the investigation stage, relevant factors such as typical sensitive frequency, typical emission frequency, equipment structure, possible equipotential ground, normal working electrical parameters of sensitive components and the like are confirmed and clarified through parameter investigation of a target system or equipment in the investigation stage. The method is used as a technical support for electromagnetic compatibility risk judgment in a subsequent analysis stage.
The testing stage comprises a time domain test and a frequency domain test, and disturbance signals in a required frequency range are obtained through the time domain test and the frequency domain test; the time domain test equipment is an oscilloscope or an equivalent time domain signal test device, and the frequency domain test equipment is a spectrum analyzer or an oscilloscope with a Fourier analysis function;
an analysis stage, namely judging whether the ground circuit has conducted disturbance and disturbance intensities corresponding to different disturbance frequencies according to disturbance signal data acquired in the test stage, analyzing and judging electromagnetic interference risks by combining parameter characteristics of a target system or equipment acquired in the investigation stage, and selecting a ground point supporting electromagnetic compatibility;
the stage of rectification optimization confirmation is generally design optimization which is carried out again under the condition that the electromagnetic compatibility risk exists, the test at the stage is retested according to the previous test steps, the obtained test data is compared with the data before rectification optimization, whether the rectification effect or the rectification direction is proper is judged, and meanwhile, the electromagnetic interference risk analysis is carried out according to the limitation of the investigation stage. If the risk of electromagnetic interference is still considered high, this step will be repeated until the risk of electromagnetic interference is considered low or no risk of electromagnetic interference exists.
In the system integration shown in fig. 2, through parameter investigation, the electronic device 1 with cognitive sensitivity characteristics is a sensitive device which is easy to interfere, and the electronic device 2 with emission characteristics is a disturbance source with typical emission frequency characteristics. A typical transmission frequency of the electronic device 2 for the confirmation and the clear transmission characteristics is 40 KHz; the typical sensitive frequency of the electronic equipment 1 with sensitive characteristics is 40KHz, the equipment structure is a steel structure box body, an equipotential mechanism body is formed by adopting welding connection, a 5V sensitive voltage chip is arranged in the equipment structure, the rated working voltage range is 3.3VDC-6.7VDC (5 +/-1.7 VDC), and the 5V sensitive voltage chip is provided with a grounding pin. The equipment belongs to the field of medical equipment in the industry and the science, and the emission limit value of the equipment meets the electromagnetic disturbance characteristic limit value and the measurement method of industrial, scientific and medical (ISM) radio frequency equipment in GB4824-2013, namely the requirement of no disturbance voltage limit value before 150KHz, but the test can be limited by referring to the maximum quasi-peak value of 110dBuV (converted into the level value of about 0.32V) required by 9KHz-50KHz specified in Table 8 in GB 4824-2013.
The common ground point 3 of the integrated system is confirmed by using the principle that the outside of the box is grounded nearby.
And according to the dc impedance method, the electronic device 1 with sensitive characteristics has two possible low impedance electromagnetic compatible grounding points, i.e. a first grounding point 4 and a second grounding point 5.
Because the electronic equipment 1 with sensitive characteristics is sensitive to the transmission frequency of the electronic equipment 2 with transmission characteristics, the grounding point of the electronic equipment 1 with sensitive characteristics is reasonably selected, so that the ground disturbance noise generated by the electronic equipment 2 with transmission characteristics is released to the common grounding point 3 of the integrated system as conveniently as possible, and the electronic equipment 1 with sensitive characteristics is not connected in series as far as possible.
As shown in fig. 3, the above-mentioned detection method is applied, and a common grounding point 3 of the integrated system and a grounding point 6 of the electronic device with emission characteristics are tested by using a voltage probe, so as to obtain the frequency spectrum and the disturbance intensity of the path of the emission source. Then, when the electronic device 1 with the acquired sensitive characteristics is at different grounding points, namely a first grounding point 4 and a second grounding point 5, respectively aiming at a common grounding point 3 of the integrated system, frequency spectrums on a grounding path and disturbance intensity thereof; comparing the test waveforms, selecting the grounding point with less influence of the emission source path on the electronic equipment 1 with sensitive characteristics under the sensitive frequency, and judging whether the risk of electromagnetic interference exists.
Specifically, when an oscilloscope with a fourier function is used, the oscilloscope probe 7 is connected to the electronic equipment grounding point 6 of the emission characteristic, and the oscilloscope grounding crocodile clip 8 is connected to the common grounding point 3 of the integrated system. A time domain disturbance waveform map as shown in figure 4 may be obtained.
This shows that there is a significant electromagnetic disturbance in the ground loop with frequency characteristics and disturbance intensity. The equipment is also explained to be subjected to a targeted further electromagnetic compatibility grounding design so as to prevent disturbance signals from mixing in the public ground due to poor grounding point selection.
The frequency characteristics of the frequency domain signal can be analyzed using the fourier analysis function of an oscilloscope, as shown in fig. 5.
And acquiring frequency characteristics obtained by measuring points in the graph 4 and corresponding disturbance signal intensities under different frequencies, wherein the main emission frequency is 40KHz, and the corresponding disturbance intensity is 7V and is far greater than 0.32V.
By the same detection method, the oscilloscope probe 7 is connected with the first grounding point 4, and the oscilloscope grounding crocodile clip 8 is still connected with the common grounding point 3 of the integrated system. If the frequency characteristics and the strength acquired by the first grounding point 4 are shown in fig. 4 and 5, it is shown that disturbance of the electronic equipment 2 with emission characteristics can be connected in series into the electronic equipment 1 with sensitive characteristics through the first grounding point 4, at this time, the disturbance strength of the first grounding point 4 still has a disturbance strength of approximately 7V at 40KHz, by combining data in a previous investigation stage, the equipment of the electronic equipment 1 with sensitive characteristics is sensitive equipment, the sensitive frequency is 40KHz and is exactly the same as or close to the frequency of disturbance emission, and the fluctuation range of the rated working voltage of the internal 5V sensitive voltage chip is +/-1.7 VDC, and the disturbance voltage amplitude can enable the voltage fluctuation to be approximately 7V, so that the normal operation of the voltage chip can be influenced by grounding completely, therefore, the electromagnetic compatibility correction optimization is required to be performed when the analysis result is "high risk of electromagnetic interference", and the result of the correction optimization is retested and verified.
If the grounding point of the electronic device 1 with changed sensitive characteristics, i.e. the grounding point, is changed to a second grounding point 5, the oscilloscope probe 7 is connected to the second grounding point 5, and the oscilloscope grounding crocodile clip 8 is still connected to the common grounding point 3 of the integrated system. The testing is carried out again according to the steps, the frequency characteristics and the strength obtained by the second grounding point 5 and the common grounding point 3 of the integrated system are as shown in fig. 6, the emission quantity corresponding to the sensitive frequency is greatly attenuated, the disturbance strength at the sensitive frequency of 40KHz is lower than 0.2V, the requirement of a GB4824-2013 limit value is met, the voltage amplitude is lower than 1.7V, even if a voltage sensitive pin is connected in series, the voltage sensitive pin is within a normal working voltage range, so the analysis is that the electromagnetic interference risk is low, and the testing is finished.
Similarly, the frequency characteristics of the frequency domain signal can be obtained by using a mode that the voltage probe is installed on the spectrum analyzer.
As shown in fig. 2, a voltage probe is used between a common grounding point 3 of the integrated system and a grounding point 6 of the electronic equipment for transmitting characteristics, and the electronic equipment for transmitting characteristics 2 obtains the transmission intensity corresponding to each frequency point from 9KHz to 100 MHz; this test waveform is saved as a background value. Then, a voltage probe is used for testing between the first grounding point 4 shown in fig. 2 and the common grounding point 3 of the integrated system in the same method, so that a waveform shown in fig. 7 can be obtained, the waveform comprises a background waveform (between the common grounding point 3 of the integrated system and the electronic equipment grounding point 6 with the emission characteristic) and a current grounding point waveform (between the first grounding point 4 and the common grounding point 3 of the integrated system), and the emission intensity of a measuring point at a corresponding frequency can be visually compared to judge whether the electromagnetic disturbance of a grounding loop between the two points meets the requirement or not.
Similar technical solutions can be derived from the solutions given in the figures and the description, as described above. However, any modification, equivalent change and modification of the shape, size, connection mode and installation structure of the above-described components and slight adjustment of the positions and structures of the components according to the technical essence of the present invention, such as sealing the centering device with a rubber dust-proof boot, and sealing the rear side of the centering device based on the existing structure, still belong to the scope of the technical solution of the present invention.
Claims (3)
1. A method for detecting common mode disturbance of a grounding loop is characterized by comprising the following steps: comprises the following steps of executing the following steps,
in the investigation stage, parameter characteristics of a detection target system or equipment are obtained, wherein the parameter characteristics comprise a normal working electrical parameter range and a sensitive frequency range of a sensitive component, a transmitting frequency range and an alternative equipotential grounding point;
the testing stage comprises time domain testing and frequency domain testing; the time domain waveform obtained by the time domain test is used for judging whether obvious electromagnetic disturbance exists in the tested loop, and the frequency domain waveform obtained by the frequency domain test is used for specifically analyzing disturbance intensity corresponding to different disturbance frequencies; the time domain test equipment is an oscilloscope or an equivalent time domain signal test device, and the frequency domain test equipment is a spectrum analyzer or an oscilloscope with a Fourier analysis function;
an analysis stage, namely judging whether the ground circuit has conducted disturbance and disturbance intensities corresponding to different disturbance frequencies according to disturbance signal data acquired in the test stage, and analyzing and judging electromagnetic interference risks and selecting a grounding point supporting electromagnetic compatibility by combining parameter characteristics of a target system or equipment acquired in the investigation stage;
in the testing stage, a common grounding point of the integrated system is determined by utilizing the principle of the local grounding outside the box body, and two possible low-impedance electromagnetic compatibility grounding points of the electronic equipment with sensitive characteristics are determined according to a direct-current impedance method; in the time domain test process, respectively obtaining the time domain waveform intensity between a first grounding point and a common grounding point and between a second grounding point and the common grounding point in the two electromagnetic compatible grounding points so as to judge whether obvious electromagnetic disturbance exists; in the frequency domain test process, respectively obtaining frequency spectrums and disturbance intensities between a first grounding point and a common grounding point and between a second grounding point and the common grounding point in the two electromagnetic compatibility grounding points;
in the analysis stage, the frequency spectrums between two electromagnetic compatibility grounding points and a common grounding point obtained by frequency domain test and the disturbance intensity thereof are compared with the normal working voltage to judge the electromagnetic interference risk; by comparing frequency domain test waveforms formed by grounding loops where two electromagnetic compatibility grounding points are located, the grounding point with sensitive characteristics, which is less affected by a transmission source path under sensitive frequency of the electronic equipment, is selected.
2. The method for detecting the common-mode disturbance of the ground circuit according to claim 1, characterized in that: when detecting the electromagnetic disturbance of the voltage characteristics of the grounding loop, the test fixture with the probe and the grounding clamp structure is adopted.
3. The method for detecting the common-mode disturbance of the ground circuit according to claim 1, characterized in that: when detecting the electromagnetic disturbance of the current characteristics of the grounding loop, a test fixture with a probe in an annular structure is adopted.
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| CN111781457A (en) * | 2020-07-24 | 2020-10-16 | 上海擎度汽车科技有限公司 | Test system and method for EMC conduction emission of electronic product |
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Address after: No.86, Jinhong East Road, Chengyang District, Qingdao City, Shandong Province Patentee after: Qingdao Sifang Alstom railway transportation equipment Co.,Ltd. Address before: No.86, Jinhong East Road, Chengyang District, Qingdao City, Shandong Province 266111 Patentee before: BOMBARDIER SIFANG (QINGDAO) TRANSPORTATION Ltd. |