y standard. At the time Directive. They are divided into standards for immunity (EN50082) of writing it covers electrostatic discharge, radiated RFI and fast and emissions (EN50081), each of which has separate parts for transients, with draft parts in circulation covering switching and different environment classes. lightning surges and conducted RFI. Also, EN55020 lays down Where a relevant product specific standard exists, this takes pre- requirements for the immunity of radio and TV receivers to RFI. A cedence over the generic standard. The tests defined in the generic further standard (EN55101, to be renumbered EN55024) is in prep- standards are based only on internationally approved, already exist- aration to cover the immunity of information technology equip- ing standards. For each electromagnetic phenomenon a test proce- ment. dure given by such a standard is referenced, and a single test level or limit is laid down. Since the referenced standards are undergoing revision to incorporate new tests, these are noted in an 'informative 23.10.2.3 The generic standards annex' in each generic standard. A particular problem with immunity is that the equipment under There are many industry sectors for which no product-specific test may exhibit a wide variety of responses to the test stimulus. To standards have been developed. This is especially SO for immunity. account for this variety, the generic immunity standard includes Class A Europe & Japan Class B 100MHz 30MHZ 88MHz 216MHz 230MHz Frequency Figure 23.19 Radiated emission limits (CISPR16 quasi-peak detector, normalised (1/d) to a measuring distance of 10m) Interference coupling mechanisms 23/15 Radiated, case to mains cable Source equipment Peripheral Conducted, through common mains impedance Radiated, Radiated cable to cable Conducted case to case through common earth impedance Input Victim equipment External mains interference Figure 23.20 Coupling mechanisms three generalised performance criteria for the purpose of evaluating emissions standards regulate t