at first, EMC became a problem in the military environment, especially on large ships that had to successfully operate many electronic devices that were close to each other. In such an environment, communication, navigation and data processing electronic devices all need to operate synchronously in a strong RF field. These RF fields are generated by two-way communication equipment, radar transmitter and microprocessor control equipment. In addition, in this "complex" environment, it is necessary to add warship regulations or shipborne explosives and aircraft fuel. In such an environment, it is obvious that every kind of equipment should have electromagnetic compatibility with its environment, and it cannot be shown that it is unusable or unsafe in this environment. In addition, every kind of equipment added in this environment can't emit stray radiation that doesn't play any role unnecessarily or aimlessly. As can be seen from the foregoing, the two main origins of EMC are emission and immunity.
due to the wide application of electronic equipment in the global non-military field, it is becoming more and more important for EMC to maintain with civilian settings. Residential and commercial environments may contain many applications controlled by microprocessors, such as gas stoves, video tape recorders, televisions, bread makers, personal computers and so on. All electronic devices using microprocessor technology will generate radio frequency. For example, a 1 MHz computer has an electronic clock running in a microprocessor through its programs. In this case, the clock frequency falls into the spectrum allocated by the United States for FM radio broadcasting. If PC manufacturers do not take protective measures, it will interfere with nearby radio receivers. If the harmonic or frequency doubling of this frequency is not suppressed, it may cause interference to other radio receivers, such as those used by emergency medical personnel and TV receivers. Therefore, manufacturers of digital electronic equipment should ensure that their products will not be incompatible with or damage other electronic equipment.
EMC and the United States
Due to the wide application of information technology equipment (ITE) and other electronic devices controlled by microprocessors, F.C.C (the authoritative organization with jurisdiction in the United States) imposed restrictions on RF radiation generated by digital devices in the 197s. Digital devices dedicated to the living environment are classified as "B" devices. All "B" equipment must comply with the restrictions specified in Part 15 of the F.C.C Rules for Space Radiation and Conducted Radiation. "B" equipment must meet the requirements of the F.C.C rules before it can be sold in the United States. At present, there is no requirement for immunity testing in the United States. Equipment dedicated to the industrial, scientific and medical fields in the United States has now obtained exemption from these restrictions. These devices are classified as "A" devices and cannot be used in residential environment.
EMC and EU
Products sold in the EU must bear the "CE" mark, which means that the product manufacturer complies with all applicable harmonic directives and standards. Electronic equipment shall comply with EMC directive 89/392/ EEC. Article 4 of this document states: "The structure of the instrument shall meet the following requirements: (a) The EMC interference generated shall not exceed the level that allows the normal operation of radio and communication equipment and other instruments; (b) The instrument shall have sufficient inherent immunity to EMC interference to ensure normal operation. " Obviously, it is necessary to evaluate the radiation and anti-interference characteristics of products to comply with the basic requirements of the EU EMC directive. In particular, products used in commercial, light and heavy industries must comply with these requirements.
the inherent immunity requirements indicate that electronic equipment will not be affected by its normal electromagnetic environment, resulting in performance degradation. For example, for a European consumer, if the nearby ambulance personnel talk to their local dispatcher through two-way radio communication equipment, the consumer has the right to demand that the digital security system monitoring his residence will not malfunction. This directive indicates that the products designed by manufacturers should not only have immunity to radiated RF fields, but also have this characteristic for other electromagnetic phenomena.
the specific immunity test is carried out one by one according to the conventional and product-specific European specifications or standards. This means that the performance of the equipment will at least not be adversely affected by the following factors: (1) radio frequency fields, such as radio and television broadcasting stations and licensed two-way radio equipment; (2) Electrostatic discharge event (ESD); (3) Electrical Fast Transient (EFT). To test the immunity of products by imitating the real world environment, the manufacturer should show that it complies with Article 4 (b) of the EMC Directive. Some specific standards and the 1997 general immunity standard require additional immunity tests. These additional tests include: conducted RF immunity; Lightning immunity; Power frequency magnetic field immunity; Voltage sag and interruption immunity; Immunity of pulsed radio frequency field.
CE compliance
the manufacturer or its authorized representative must declare compliance with the basic requirements of the EMC directive. This process can be completed by issuing a document called "Declaration of Conformity" (DOC). It is the manufacturer's responsibility to obtain and keep the technical evidence supporting the "conformity" statement of all products. This supporting evidence will be compiled into a construction technical document (TCF). Every product sold in the EU has TCF. Compliance verification (testing) can be performed by the manufacturer or a third-party testing organization. But in all cases, the test must be carried out according to the international IEC test standard. The results of EMC tests (such as test reports issued by test laboratories) should be included in TCF.
products that meet the requirements of applicable "product-specific standards" or general standards instead of "product-specific standards" are assumed to meet the basic requirements of the EMC directive. In addition to EMC instructions, electronic equipment may have to meet other instructions. Compliance with all applicable directives must be verified and documented. Only after all the requirements are met can the "CE" mark be obtained. Ten years after entering the European market, the supporting technical documents (TCF) must be recorded and can be consulted by authorized representatives of the European Union.
Benefits
It conforms to the EMC directive of the European Union and can continuously improve products, quality and customer satisfaction. For example, ESD (electrostatic discharge) immunity test can quickly reveal any weakness of products under these standards, and provide improvement measures to show the immunity of products to such situations in the real world. As a result, reliable and genuine products can work trouble-free for many years, thus improving customer satisfaction.
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