Understanding functions and performance criteria for EMC compliance testing
By Engaged ExpertJames Daniels
James Daniels is the General Manager of Element’s Connected Technologies business in the UK, currently responsible for Operations in our Hull, Skelmersdale, Malvern, Wimborne and Oxford laboratories.
Knowledge of the EMC compliance testing process and the EMC performance criteria against which a product is assessed is essential to success when preparing for EMC testing. Compliance is determined by how a product operates and performs during testing.
EMC emissions testing
Emissions testing is the measurement of the generation of electromagnetic energy by a source and its release into the environment. When testing for emissions your device must be exercising all parts of the circuit fully.
The limits for emissions vary by product type and geographical region. In addition, specific industries such as military, automotive, or aerospace will usually have more rigorous and demanding requirements.
EMC immunity testing
Immunity testing is the ability of equipment to function correctly in the presence of Electromagnetic Interference (EMI). When testing for immunity some tests will use continuous (usually modulated) waves and others will involve very short bursts (transient) phenomena.
A wide range of tests are available dependent on the type of immunity to which you are testing. These include radiated radio frequency, magnetic field, Electrostatic Discharge (ESD) conducted radio frequency, electrical fast transients (EFT), surges, and voltage dips/interruptions.
EMC criteria A, B, and C
If testing to commercial standards for the European Union (EU), your device must comply with one of the following summarized general performance criteria.
Performance criteria A
No degradation of performance or loss of function is allowed below a minimum performance level specified by the manufacturer (or what the user may reasonably expect) when the equipment is used as intended.
Criteria A means that your product has performed normally and within specifications that have usually been outlined in the product manual, both during and after the test.
Performance criteria B
No degradation of performance or loss of function is allowed, after the application of the phenomena below a performance level specified by the manufacturer (or what the user may reasonably expect) when the equipment is used as intended.
Criteria B means that the product may have had a temporary loss of function or degradation of performance but after the test has finished, recovers to its normal performance without operator intervention.
Performance criteria C
During and after testing, a temporary loss of function is allowed, provided the function is self-recoverable or can be restored by the operation of the controls or cycling of the power to the EUT by the user in accordance with the manufacturer’s instructions.
Criteria C is similar to B, but the test includes an allowance for operator intervention. For example, this might mean that you need to turn the device back on to resume normal performance.
Which of these three performance criteria you will need to test will depend upon the test standard that applies to your particular product.
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