How to choose the equipment EMC test level?

The test relies on three factors: method, technology, equipment. Methods by the principle of measurement and the use of test equipment to determine the two, technology is in order to get the correct test results (high accuracy) and take all the means of testing, equipment is the embodiment of the above two factors for the test of all technical devices. These must be standardized to ensure that the test is reproducible and true. \x0d\\\x0d\\ EMC test conditions are determined by the test method. Specific test methods are categorized into the test bench method, which is conducted under laboratory conditions, and the field method, which is conducted under actual conditions of use. It is impossible to simulate all interference phenomena that may be encountered in the field, and the field method in particular has insurmountable limitations. However, through standardized testing can be more comprehensive access to information on how the EMC performance of the device under test. For this reason, it is internationally recommended that the test bench method be used first, and the field method is generally not used unless it cannot be carried out in the laboratory. The main method of \x0d\\\x0d\\ immunity test is in accordance with the electromagnetic environmental conditions in which the equipment is located, combined with the measures taken by the user of the equipment, select the appropriate level of severity, in accordance with the relevant test methods for the test, and finally, according to the product standards put forward by the qualified judgement conditions to assess whether the test results are qualified. This is the main difference between immunity testing and other tests. \x0d\\\\x0d\\\ electromagnetic environment in the electromagnetic nuisance sources, electromagnetic nuisance sources on the coupling mode of the equipment, equipment on the electromagnetic nuisance of the sensitivity of the user on the work site of the protection measures are directly related to the level of severity. That is, the use of the environment determines the form of interference, the installation of protective conditions determines the interference of the severity level. GB/T13926.4 specifies the electromagnetic environment and the severity level corresponding to the equipment under the work of the electrical environmental conditions: \x0d\\\\x0d\1 level with a well-protected environment such as a computer room; \x0d\2 level with a protected environment, such as factories and power plants control rooms or terminal rooms; \x0d\3 level, typical industrial environments, such as industrial process installations, relay rooms in power plants and open-air high voltage substations and other places; \x0d\4 level, severe industrial environments, such as power stations, industrial process installations without special mounting measures, and outdoor areas. \x0d\ IEC801-5 for the source of the surge for power switching transient or indirect lightning flash transient, the installation conditions and protective facilities of the equipment are categorized as follows (applicable to the surge): \x0d\0 class 0: well-protected, primary and secondary overvoltage protection of electrical environments, usually in special rooms, the surge voltage will not exceed 25V; \\ \x0d\1 category: locally protected electrical environment with primary overvoltage protection, surge voltage will not exceed 500V; \x0d\2 category: electrical environment where the power lines are separated from other lines and the cables are well isolated, surge voltage will not exceed 1kV; \x0d\3 category: electrical environment where the power cables are laid in parallel with the signal cables, surge voltage will not exceed 2kV; \x0d\4 category: interconnecting wires are laid along the power cables like outdoors, and the electrical environment where both electronic and electrical circuits use cables, with a surge voltage not exceeding 4kV; \x0d\ Category 5: Electrical environment where electronic installations are connected to telecommunication cables and overhead power cables in a non-densely populated area. \x0d\ to Category 0 does not do surge testing. Generally power supply products are in Class 1 or Class 2 electrical environments and can be selected with a severity level of Class 1 or Class 2. \x0d\\\\\x0d\ It is important to note that the use of the environment as a correlation condition for immunity testing is an important feature of immunity testing. This is because if these correlations are ignored, and the working environmental conditions of the application of the device are not taken into account, and the device is considered to be "independent" and suitable for insertion into any kind of combined device (or system), then this will lead to the erroneous conclusion that all the devices to be tested must be subjected to the full range of interference tests and must reach the highest level of severity. This would not only impose an unreasonably high and stringent limit on the devices to be used, but would also necessitate a significant financial burden due to the large number of tests that would have to be performed. \x0d\\\\x0d\\ Furthermore, immunity testing involves high-voltage signals, and in addition to the fact that the relevant safety regulations should be strictly adhered to, it is also necessary to carry out safety tests on the equipment after the immunity test. \x0d\\\\x0d\\ For high power electrical products such as AC voltage stabilized power supplies, it is necessary to select the immunity items imported from the utility power supply which are characterized by high frequency and high energy, and to select a higher severity level than other electrical and electronic products. Another important feature of \x0d\\\x0d\\ immunity testing is the strict and clear specification of the technical parameters of the test generator. In order to compare the immunity performance of equipment, it is necessary to have a test device that produces a relatively consistent and repeatable reproduction, which is the interference simulation generator. Obviously must specify the generator's output resistance, output waveform requirements, open-circuit voltage amplitude and error; to ensure that the test results are consistent and repeatable. Otherwise, due to the different source impedance of different equipment under test, the generator impedance matching different and can not make the generator under load output waveform or amplitude is the same. In fact, impedance mismatch is an effective means of suppressing electromagnetic nuisance. \x0d\\\x0d\\ AC regulated power supply to the outside world (through the utility network) electromagnetic harassment test items are: harmonic conducted interference test, high frequency conducted interference test. \x0d\\\x0d\\ harmonic conduction interference test is to test the power inlet line of the equipment into the end of the power frequency current harmonics; measured below 40 times the maximum value of the current harmonics of the various times, the three-phase power supply should also be tested for current harmonics of the center line. In the AC regulated power supply performance program to source current relative harmonic content to assess this project. \x0d\\\x0d\\ AC regulated power supply conducted interference test with other electronic products, can be used GB6833-86 electronic measuring instruments electromagnetic compatibility test specification (with reference to the use of HP standards or GB9254-88 information technology equipment radio interference limit values and measurement methods (equivalent to the use of)) CISPR?22?1985). High-frequency conducted interference test in an important test device is to use artificial power supply network (ArtificialMainNetwork), in the U.S. standard is known as the power impedance stabilization network (LineImpedanceStabilizationNetwork,LISN). This is due to different power conditions, utility power in different equipment power inputs present high-frequency impedance is not the same, in order to make the test results reflect the real situation, must be in the test equipment and its power terminals indirectly into the network that meets the requirements of the network, the network not only enables the equipment and the realization of the radio frequency isolation between the grid, but also for the equipment to provide a stable high-frequency impedance. The number of branches of the artificial power supply network is the same as the number of lines in the power supply system, and the connection between the network and the interference measurement instrument should ensure impedance matching (50Ω/50μH), and each power line is tested separately, and the measurement is the value of the interference voltage.GJB152-86 recommends that the current probe method to measure the conduction interference current; which connects a 10 μF core-piercing capacitor between the power line and the ground. μF through-center capacitor is connected between the power line and the ground, which serves the same function as LISN. Current probe method is easy to use, rapid measurement, easy to field test, closer to the actual situation, may be measured in the future to its main. In addition, the military standard uses a peak detector, and GB9254 uses a quasi-peak detector. \x0d\\\x0d\\ RF radiated interference testing is more complex, involving test sites, antennas, test line connections and other testing issues. Test site for the field open, background electromagnetic noise level is at least 6dB smaller than the allowable limit value. this requirement is difficult to achieve, the standard also recommended that electromagnetic shielded room can be used (there are also such as radio wave dark room, etc.) as a replacement. Test radiation field strength of the equipment under test should be strictly in accordance with the actual mode of operation wiring, power lines, signal lines are not allowed to deliberately curled, contraction, to reflect the authenticity.