EMC test conditions determined by the test method. Specific test methods are divided into the laboratory conditions in the test bench method and in the actual use of conditions in the field method. To simulate the field may encounter all the interference phenomenon is impossible, especially the field method 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, the international recommendation is to first use the test bench method, unless it can not be carried out in the laboratory, generally do not use the field method.
The main method of immunity testing is in accordance with the electromagnetic environment conditions in which the equipment, 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 testing, 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.
The electromagnetic environment of the electromagnetic nuisance source, electromagnetic nuisance source of the coupling mode of the equipment, the sensitivity of the equipment to electromagnetic harassment, and the user of the work site of the protective measures directly related to the severity of the level. 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 environment conditions:
1 level, with a well-protected environment, such as the computer room;
2 level, protected environments, such as factories and power plants, control room or terminal room;
1 level, with good protection;
2 level, protected environments, such as factories and power plants, control room or terminal rooms in factories and power plants;
Class 3, typical industrial environments, such as industrial process installations, power plants and open-air high-voltage transformer substations in relay rooms and other places;
Class 4, severe industrial environments, such as power stations, industrial process equipment without special mounting measures, outdoor areas, and so on.
IEC801-5 for the source of the surge for the power switching transient or indirect lightning flash transient, the installation conditions of the equipment and protection facilities are classified as follows (applicable surge):
Class 0: well-protected, primary and secondary overvoltage protection of electrical environments, usually in special rooms, the surge voltage will not exceed 25V;
Category 1: locally protected, with primary overvoltage protection of the electrical environment, the surge voltage does not exceed 500V;
Category 2: power lines and other lines separated from the electrical environment, cable isolation is good, the surge voltage does not exceed 1kV;
Category 3: power cables and signaling cables laid in parallel with the electrical environment, the surge voltage does not exceed 2kV;
Category 4: interconnecting wires laid along the power cable as outdoors, and electronic and electrical circuits are used in the cable electrical environment, the surge voltage does not exceed 4kV;
Category 5: non-populated areas of electronic devices connected to the telecommunications cables and overhead power lines in the electrical environment.
No surge test for category 0. General power supply products in Category 1 or 2 electrical environment, you can choose the severity level of Class 1 or 2.
It must be noted that the environment as a correlation of immunity testing is an important feature of immunity testing. Because if you ignore these relevant, do not take into account the application of the device working environment conditions, but that the device should be "independent", should be suitable for insertion into any kind of combination of devices (or systems), will result in all devices under test must be subjected to the full range of items of the interference test, and to achieve the highest degree of severity of the wrong conclusions. This not only imposes an unreasonably high and stringent limit on the devices to be used, but also imposes a significant financial burden in terms of the large number of tests that need to be carried out.
In addition, immunity testing involves high-voltage signals, in addition to strict compliance with relevant safety regulations, it is also necessary to carry out safety tests on the equipment after the immunity test.
For AC voltage regulator such as high-power electrical products, selected from the utility imports of high-frequency, high-energy as the characteristics of the immunity program, and choose a higher degree of severity than other electrical and electronic products to be higher level, is necessary.
Another important feature of immunity testing is the test generator technical parameters to make strict and clear provisions. In order to compare the immunity performance of equipment, there should be a way to produce a more consistent and repeatable reproduction of the test device, 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.
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.
Harmonic conduction interference test is a test of the power supply of the equipment into the end of the frequency current harmonics; measured below 40 times the maximum value of the current harmonics of the three-phase power supply should also be tested in the middle of the line of the current harmonics. In the AC regulated power supply performance project to the source current relative harmonic content to assess this project.
The conducted interference test of AC regulated power supply is the same as that of other electronic products, GB6833-86 electromagnetic compatibility test specification for electronic measuring instruments (with reference to the standard of HP or GB9254-88 information technology equipment, radio interference limit values and measurement methods (the equivalent of the CISPR?22), the CISPR?22 test specification is the same as that of other electronic products, and the CISPR?22 test specification is the same as that of other electronic products. 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 grid to achieve RF isolation, 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 using peak detector, GB9254 quasi-peak detector.
RF radiation interference test is more complex, involving the test site, antenna, test line connection and other test issues. Test site for the field open, background electromagnetic noise level at least 6dB smaller than the permissible limit. this requirement is difficult to achieve, the standard also recommended that electromagnetic shielding room (and such as wave dark room) 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.