EMC vs EMI Testing, What’s the Difference, and What do I Need to Consider?

Electromagnetic compatibility (EMC) & electromagnetic interference (EMI) mean different things, frequently referred to when discussing testing and compliance of electronic and electrical products. While they are closely related, it is important to understand that EMC and EMI are not the same things.

EMI meaning

EMI is the interference caused by an electromagnetic disturbance that affects the performance of a device. Sources of EMI can be environmental, such as electrical storms and solar radiation but more usually will be another electronic device or electrical system. If the interference is in the radio frequency spectrum it is also known as radio frequency interference or RFI.

EMC meaning

EMC is a measure of a device's ability to operate as intended in its shared operating environment while, at the same time, not affecting the ability of other equipment within the same environment to operate as intended.

The importance of early consideration

Electromagnetic compatibility (EMC) and interference (EMI) are both extremely important design considerations. Failing to consider them in the initial stages of product development can result in the time-consuming and costly need to redesign the product at a later stage to meet EMC/EMI specification tests and prevent product failure or safety risk.

However, different requirements in the US and the European Union (EU), as well as differing interpretations of the meanings of EMC and EMI, often cause confusion when it comes to testing. In addition, specific industrial or military standards will apply to the product depending on its target market and therefore also need to be considered.

EMI & EMC emissions and immunity

Evaluating how a device will react when exposed to electromagnetic energy is known as susceptibility or immunity testing and involves determining the ability of a device to tolerate noise from external sources.Meanwhile, emissions testing measures the amount of EMI generated by the device that could affect other electrical products and can provide an accurate measurement of the amount and type of noise generated by a device. This is called an EMC level. 

Determining which test to use

The device’s intended application will determine the exact type of testing required. 

Key questions to ask are:

• Where is this product going to be used?
• With what/whom is it going to interfere?
• How will the energy travel from the product to its “victim”?

The two key methods that electromagnetic activity or ‘energy’ can reach a product are through the air (radiative coupling) or via the cabling (conductive coupling). The standards used are therefore based primarily on radiated and conducted tests.

How to design for EMI & EMC to minimize risk

If a product has to be redesigned, it can be prohibitively expensive and result in delays to market and a loss in consumer confidence.

Bad product design (from an EMC or EMI perspective) would be when earthing, filtering, and shielding have not been considered. The result of this would include product failure during tests and in the real world would mean that the product would be unreliable and not work as intended.

Good product design incorporates the application of basic EMC principles such as effective shielding, earthing, and filtering will simultaneously improve electromagnetic immunity and reduce electromagnetic emissions, whilst minimizing risk.