EMC Part 53. Electromagnetic Compatibility: Understand Radiated & Conducted EMI/EMS Classification.

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Conducting the Electromagnetic Interference, EMI & Electromagnetic Susceptibility, EMS tests are a crucial step when introducing a new product to the market. Generally, these tests can be categorized into two main categories: Emission and Immunity testing.

Emission testing measure the amount of electromagnetic generated by a device during normal operation. The purpose of these tests is to ensure that any emission from the device are below the relevant limits defined for that device type. This, in turn, will ensure that there is reasonable assurance that the device will not cause damaging interference with other devices operating within the expected environment.

Immunity testing assesses how a device reacts when exposed to disturbances such as electromagnetic noise. The purpose of these tests is to ensure reasonable confidence that the device will perform as intended within its expected operating environment.

Why we need to Test Both Emission & Immunity

Testing all four aspects, RE, CE, RI & CI give your product the best chance to meet EMC standards and thrive in its intended environment. Fortunately, a product that is well designed in one aspect tends to perform well in the others, and improving either emissions or immunity performance can give the other aspects a boost as well.

2 Ways for Electromagnetic Wave to Propagate

Conducted Emissions testing involves measuring the energy exiting your product via power supply, data input and output ports and any cables through which current flows. This measurement is typically conducted at lower frequencies. Conversely, Conducted Immunity testing evaluates your product's resistance to RF energy entering the system through the same ports and cabling.

In contrast, Radiated Emissions testing reveals the electromagnetic waves that emanate from the operating product via air as medium, and usually measured at higher frequencies. Radiated Immunity testing demonstrates the product's resilience when exposed to EM waves at specific field strengths through the medium air.

How EMC Labs Measure Emissions and Immunity

Conducted Emissions and Conducted Immunity are usually measured in Volts and Amps, but they are often expressed in decibel (dB) form.

Radiated Emissions limits and Radiated Immunity levels are measured in Volts and Amps per meter—but they are often also expressed in dB form.

Why there is a difference?
Radiated testing concerns the field strength of electromagnetic waves, using antennas to measure or transmit those electromagnetic waves respectively. The “per meter” qualifier is a fundamental aspect of describing wave behavior. Without it, the measurements mean nothing.

EMC Standards, Levels, and Limits

There are a variety of EMC standards committees responsible for determining acceptable immunity levels and emissions limits. This decision is based on a mix of known and expected electromagnetic environmental conditions in which the product is expected to operate seamlessly.

The harsher the environment, the stricter the requirements. However, the same product can have different EMC emissions and immunity requirements if it is used in more than one environment. In such a case, you can simply target the most stringent requirement; it’s always better to have exceptional performance in less stringent environments than to fall short of the standard where it matters most.