Test & Measurement
Understanding the complexities of EMC testing
By Nicholas Forsyth, senior engineer at TÜV SÜD, a global product testing and certification organisation E
lectromagnetic compatibility (EMC) testing measures the ability of equipment or systems to function satisfactorily in their electromagnetic environment without causing or
being affected by electromagnetic interference. As the number of connected devices grows, so does the need for testing. This is especially true for devices that are heavily reliant on software and communication between multiple components. For example, smart products that have connectivity features such as cellular modems or Wi-Fi chipsets to enable remote monitoring and functionality enhancements. This includes industrial control systems, smart home appliances, and connected vehicles. EMC testing is therefore a critical part of any good design and compliance is a mandatory requirement in the majority of global markets. In the EU, 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. 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 therefore 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).
EMC testing of immunity and radiated emissions is performed in an anechoic chamber, a specialised room designed to provide a stable environment for the measurement of field strengths of electromagnetic waves emitted from the device under test. The chamber is a shielded room that blocks any outside interference that could affect the measurements, and the walls and ceiling are lined with radiation absorbent material (RAM), preventing internal reflections from affecting testing.
The standards set strict limits for emissions and immunity. Emissions may radiate from
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the product or be conducted over power leads. Emission limits control the amount of electrical interference that a device produces that might interfere with radio and television reception, mobile phones, Bluetooth, Wi-Fi and the host of other wireless technologies that we use today. Emission tests primarily focus on the ability of the product not to emit radio frequency energy but also include low frequency tests for mains harmonics and to avoid lighting flicker.
Immunity limits require the product to operate in its intended electromagnetic environment without upset or degradation to its intended functions. Immunity tests ensure that the product functions correctly in the presence of radiated fields from transmitters, conducted interference via cables and a range of transient interference events such as electrostatic discharges, power surges due to lightning or fast transients due to power switching.
Equipment must therefore be designed and manufactured so that the electromagnetic disturbance it creates is not excessive, and
Components in Electronics
so that it has 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.
Key EMC tests
There are six major areas of EMC testing: 1. Radiated RF Emissions (RE): Unintended emission of RF energy from electronic devices or systems.
2. Conducted RF Emissions (CE): Unintended emission of RF energy travels along conductive paths, such as power lines, signal cables, or other wiring connected to an electronic device or system.
3. Conducted Transient Emissions (CTE): Unintended emission of transient electrical disturbances, such as voltage or current spikes, through conductive paths.
4. Electrostatic Discharge (ESD): A sudden
flow of electricity occurs between two electrically charged objects due to their differing electrical potentials.
5. Radiated RF Immunity (RI): Ability of an electronic device or system to resist and function correctly when exposed to external RF electromagnetic fields. This ensures that the device can operate without performance degradation or malfunction when EMI is present.
6. Conducted Transient Immunity (CTI): Ability of an electronic device or system to withstand and continue to function properly when exposed to transient electrical disturbances from conductive paths. For immunity testing there are three performance criteria A, B and C that are specified in the EMC standards. Criteria A requires the product to continue operating as normal at all times and must not suffer any degradation due to electromagnetic interference. Criteria B allows some degradation during the test condition but most recover to normal operation, without operator intervention. Criteria C allows
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