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Introduction to the CE Mark and EMC Compliance.
If you make or supply things with electricity in them they must comply with the EMC Directive This is now law in all EC Countries. If you don't like it, emigrate, but be warned the rest of the world is gradually following suit. To comply, the product must have a CE mark. In order to qualify for a CE mark some responsible person within your organisation must sign a Declaration of Conformity which states that the product complies with the appropriate EMC standards. Generally this will mean testing the product to ensure that it really is compliant.
Introduction to the CE Mark
The CE Mark is the symbol as shown on the top of this page. The letters "CE" are the abbreviation
of French phrase "Conformité Européene" which literally means "European Conformity". The term
initially used was "EC Mark" and it was officially replaced by "CE Marking" in the Directive
93/68/EEC in 1993. "CE Marking" is now used in all EU official documents. "CE Mark" is also in use,
but it is NOT the official term.
Introduction to EMC Compliance and Testing.
Selecting the correct standards for your product is the first critical hurdle. Some product families may have a number of applicable standards particularly if it’s a new product which has not been seen on the market before. However, irrespective of which standard is used for testing the EMC compliance of your product the substance of the testing will remain similar. The sections below give an overview of equipment classification and of the testing that will be carried out.
Equipment classification determines the level and severity of testing and
decides which specific procedure is applied for testing the equipment under test.
Emissions testing is done to determine the levels of Radio Frequency noise being generated by the equipment being tested. These emissions could be harmful to other legitimate communications on the airwaves. This testing takes two forms as described below:
Conducted emissions:The RF conducted back down the mains lead or other leads entering the equipment being tested is measured. Problems occur when the equipment being tested injects or induces noise onto the cables entering (from outside) the equipment being tested. Noise measurements go down to 150KHz.
Radiated emissions:This type of emission occurs when the equipment being tested is emitting noise into the environment via interconnecting leads, poorly earthed enclosure, unscreened cables, noisy control electronics etc. Measurement of this type of emission requires the use of a broadband antenna to measure the level of RF energy radiated from the product into ‘space’. Ideally an Open Area Test Site (OATS) or equivalent should be used. Many test houses use an anechoic chamber
Immunity testing is carried out to ensure the effects of electromagnetic disturbances will not damage the equipment or render it inoperable.
Surge and Electrical Fast Transients:Surges can be considered as the net result of a lightning discharge to the National Electricity distribution grid. This lightning impulse is then severely filtered by the low-frequency response of the grid, arriving at the consumer as a low frequency (but high energy) surge.
Fast Transients can be loosely considered as 'equivalent' to the effect of switch or relay bounce.
Voltage interruptions and Voltage fluctuations:Variations to the level of mains voltage or complete loss of that voltage is covered in this testing. One test will cycle the mains power on and off over a period. Malfunction of the equipment is assessed against a pass fail criteria.
Radiated immunity.Radiated immunity testing requires that the equipment under test(EUT) operates satisfactorily when subject to a strong electromagnetic field. This requires a frequency scan at a certain fixed level of field strength (specified by the standard). The 'scan' will comprise a series of 'steps' in frequency. Each step is specified as a percentage of current frequency value. This percentage is variable from 0.5% to 5%.
At each step, the frequency is held, the level adjusted to the required field strength (V/m) as measured by a field sensor, a prescribed modulation mode is initiated and then the conditions held for a 'dwell' time. The EUT should be monitored to detect faulty operation during the test. Typical values for field strength are 3 V/m for domestic and 10 V/m for industrial products. These fields are so intense that this test must be carried out in a screened room or test cell.
ESD ( Electrostatic discharge).ESD testing simulates the effect of a user touching the EUT and discharging a high voltage onto the accessible part of the EUT. Testing requires points to be tested which are accessible to the user in normal operation. Installation and/or setup is unlikely to fulfil one or both of these conditions. Maintenance and installation are not regarded as "normal operation".