| | Q: Why must we achieve EMC?
A: Other than the fact that products which do not comply cannot be marketed legally in the EC, more disruptive manifestations exist that can affect the way in which we lead our lives. These encompass health and safety issues, the security of data processing, and the functioning of electronic equipment. ABS braking systems, engine management systems, telecommunications and data transfer plus the security of both commercial and military data could all be readily compromised without adequate screening. |
| | Q: What are the main sources of EMC problems ?
A: In all cases there has to be a source and a victim for a path to exist thereby permitting a radiated or conducted coupling. RF interference (sometimes referred to as RFI), more correctly known as Electromagnetic Interference (EMI), results from the operation of electrical or electronic devices involving rapidly changing voltage or current levels and which cause the generation of electromagnetic energy at discrete frequencies and over frequency bands. |
| | Q: What is defined as a "direct function"?
A: A direct function is defined by the Commission as "any function of a component or a finished product which fulfils the intended use specified by the manufacturer in the instructions for use for an end user. This function can be available without further adjustment or connections other than simple ones which can be performed by any person not fully aware of the EMC implications." |
| | Q: What are some sources of electromagnetic emissions (EME)?
A: There are two main sources of emissions: Radiated Emissions (Examples: power lines, pulsed circuits, and improperly designed electronic systems). Conducted Emissions (Examples: switching transients, motor noise on the power lines, RF on the power leads). |
| | Q: What is conducted interference?
A: These interference signals move from one point to another on the power supply leads between a source and a receptor. Two possible sources of these signals are (1) the circuits within the device and (2) radiated energy induced onto the wires of the device. |
| | Q: What is radiated interference?
A: Radiated Interference: These interference signals are transferred via an electromagnetic (EM) field produced by a signal source over a propagation path through the air. The source of these signals can be external (e.g., radio and TV stations) or internal (e.g., unshielded radio frequency (RF) circuits and switching power supplies) to an electronic system. |
| | Q: What is written in the EMC Directive?
A: The EMC Directive 89/336/EEC is a policy statement published by The Council of the European Communities. It declares two essential requirements- "Apparatus" sold within the European Union (EU) "Will be constructed such that the electromagnetic disturbance it generates does not exceed a level allowing radio and telecommunications equipment and other apparatus to operate as intended" and "Will have an adequate level of intrinsic immunity of electromagnetic disturbance to enable it to operate as intended". |
| | Q: What is an "Apparatus"?
A: An "Apparatus" is defined in the EMC directive as "all electrical and electronic appliances together with equipment and installations containing electrical and/or electronic components." Note: The word "Installations" has been removed from the requirements because installations are stationary and are not part of free trade. |
| | Q: How can I determine if my product is an "Apparatus" or a "Component"?
A: For a product to be classified as an apparatus it must meet four criteria: 1) It must be a finished product. 2) It is intended to be placed on the market as a single commercial unit. 3) It presents EMC hazards against which protection is justified. 4) It delivers a direct function. Additional clarification may be found in the guidlines to the EMC Directive 89/336/EEC. |
| | Q: What constitutes a sub-assembly and what are the rules regarding a sub-assembly?
A: Guidance from the Commission has clarified the definition, and items which are designed, manufactured and intended to form part of an item of apparatus do not have to comply with the directive (only the finished product must so do). If, however, the item would perform a "direct function" for an end user, and is placed on the market, then it is covered by the requirements of the directive. |
| | Q: Is a custom-made one-off item "placed on the market"?
A: The UK Regulations make use of the concept of supply rather than placing on the market, which makes the position clearer. Even one-off items are covered by the directive, when they are supplied for an end user. |
| | Q: Is reconditioned second-hand equipment covered?
A: If the EMC performance of the product is unaffected, it may be considered second-hand, and the EMC Directive does not apply. If in the process of reconditioning, the product is brought up to latest specification, or the EMC characteristics are worsened to a material degree, then the reconditioner becomes a manufacturer and therefore responsible for compliance with the directive. |
| | Q: Do software upgrades affect the validity of the CE Mark?
A: There has been much debate on this subject, and the consensus to date suggests that software changes should be considered in assessing whether a re-evaluation for EMC is necessary. On the emissions side, the apparatus should always be tested in the worst-case senario, with equipment being exercised to it's maximum extent. However, changes in software can have a large affect on susceptibility, particularly to transients. |
| | Q: What is EMC?
A: Electromagnetic compatibility is an essential feature of any specification for electrical equipment. It is defined as the ability of electrical and electronic equipments, sub-systems and systems to share the electromagnetic spectrum and perform their desired functions without unacceptable degradation from or to the specified electromagnetic environment. |
