THERMAL MANAGEMENT AND EMC Understanding the


complexities of EMC testing EMC compliance is a mandatory requirement in most global markets.


I


n the EU, most electrical products must comply with the EMC Directive 2014/30/EU, as well as other relevant Directives, before they can carry the CE marking. In the UK, the equivalent is the Electromagnetic Compatibility Regulations 2016 and products must comply with this before they can carry the UKCA mark.


The standards set strict limits for emissions and immunity. Emission limits control the amount of electrical interference that a device produces that might interfere with radio and television reception, mobile phones, Bluetooth, WiFi and the host of other wireless technologies that we use today. Immunity limits require the product to operate in its intended electromagnetic environment without upset or degradation to its intended functions. Equipment must therefore be designed and manufactured so that the electromagnetic disturbance it creates is not excessive, as well as ensuring a reasonable level of immunity to electromagnetic disturbances. While a single item of equipment might meet these limits, there is no guarantee if you combine multiple items or additional components, that for example, the overall emission levels will still be satisfactory. Therefore, the final integrated product must be assessed against EMC standards.


Not only does EMC testing ensure that products meet regulatory requirements, it reduces the risk of costly non-compliance, which could require product recalls or cause significant time-to-market delays for new products. Third-party EMC tests and conformity assessments help to ensure that a product maintains its desirable features when exposed to adverse conditions (immunity test) and does not cause undue interference (emission test). This can help to strengthen a brand’s competitive position in the market due to improved product performance and reliability by reducing the chances of failures in use. The two key drivers of brand loyalty and product quality can therefore both be beneficially influenced by such tests, helping to ensure that the product maintains its desirable features when exposed to adverse conditions.


For immunity testing there are three performance criteria, A, B and C, that are specified in the EMC standards and each immunity test has one criterion specified. Criteria A requires the product to continue operating as normal at all times and applies to tests for continuous EMC phenomena, like immunity to adjacent mobile phones. Criteria B allows some degradation during the test condition and applies to tests for transient immunity, so infrequent events, such as electrostatic discharge due to someone touching the equipment. Criteria C allows temporary loss of function and applies to severe transient immunity which is very infrequent, such as a power surge or supply voltage interruptions. Permanent loss of function will be a failure.


Manufacturers can minimise the costs and time associated with EMC testing by proper preparation for test. A test laboratory sees many thousands of products each year; they will not be familiar with your product, so you must brief them fully. A successful testing programme is the result of you disclosing as much information to your chosen EMC test laboratory about the equipment under test (EUT) as early as possible in the project cycle, with a special focus on: •


Block diagrams of the test


configurations and details of any support equipment to exercise or monitor the EUT


• •


Mode of operation for emissions testing to maximise potential interference and highest internal operating frequencies


Mode of operation for immunity to exercise critical functions and method of monitoring to determine if function is upset or degraded


• •


• Power supply requirements


List of signal interface ports, type and cable lengths


Grounding arrangement


This information will help the laboratory to develop a realistic test plan, enabling you to more accurately anticipate time and costs for testing.


Consideration of EMC at earliest stage in the design process will help manufacturers to minimise test failures and the time and cost for reworking their design and retesting. A product lifecycle review will also highlight any design measures required to maintain a product’s compliance. This will help manufacturers increase the return- on-investment that they get from their EMC testing, help to ensure that the EMC integrity of products lasts a lifetime and enhance a brand’s reputation for product reliability.


JULY/AUGUST | ELECTRONICS FOR ENGINEERS 41


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