EMI and EMC are two terms which are thrown around a lot when discussing the regulatory testing of electronic goods and components. EMI stands for Electromagnetic Interference, and EMC stands for Electromagnetic Compatibility. The two terms are related, but they do refer to different things and it is worth learning the differences.
In this article, we will look at what EMC and EMI actually mean, and explain the different testing techniques which are used with them as well as the requirements for electronic components and for consumer goods.
Electronic devices generate some electromagnetic radiation – the amount depends on the type of the device and the amount of power it uses. Electronics are, ideally, a closed system – but the electricity that flows through a circuit is not completely contained within those wires. The electricity will also propagate through the air in the form of electromagnetic radiation, and it can also reach other I/O or power cables, creating what is known as disturbance voltage. It is important that consumer goods generate as little radiation as possible so that they do not interfere with the functioning of other appliances or essential law enforcement/ medical/rescue equipment.
EMI is defined as electromagnetic energy that has an impact on the functioning of other electronic devices.
EMI can include both interference from other devices, and interference from storms and solar radiation or another natural, environmental events. Some equipment – such as a cell phone or a high-powered motor – is more likely to create EMI than other types of equipment.
Electronic devices do not usually get operated in isolation, so it is important that appliances are shielded so that they can cope with EMI. This is particularly true for avionics equipment and medical equipment where proper functioning in a real-world environment is mission-critical.
EMC is the measure of how well a device will operate in its intended environment, without interfering with the functioning of other equipment in that environment. It is important that EMC is measured accurately because it is one of the most important engineering considerations when a new device is being produced. If the EMC is not anticipated correctly, then the device could pose a significant safety risk – leading to failure of that product or others, or data loss.
EMC and EMI testing and monitoring is something that is a full industry now.
Emissions testing requires the use of an EMI tool – such as a spectrum analyzer or a receiving antenna. These can be used to give an idea of the amount, and kind of electromagnetic noise that a device generates. Depending on the type of device and the intended application, this can be done in an open test site or a shielded chamber.
The immunity of the device is tested using some EMC testing equipment, and the basics of EMC testing involve using tools that will simulate and measure different frequencies and subject the device being tested to different levels of noise. The goal is to ensure that the device can withstand emissions at a reasonable level. The definition of “reasonable” depends on the type of device.
There are regulatory guidelines that everyone who is interested in the basics of EMC should learn.
FCC Part 15 defines the limits in terms of the amount of RF interference that consumer electronics and other devices can put out. The MIL-STD 461 and 464 standards outline the EMC Requirements for systems and subsystems or components that are being used in military applications.
In other parts of the world, the ISO, IEC and CISPR standards are commonly used to define interference requirements. Some industries and some territories consider compliance with these standards to be voluntary, so consider carefully whether equipment imported from abroad would be safe.
Pre-compliance EMC testing is a frequently-used technique for predicting or identifying potential EMC issues during the product development cycle. It is a good idea to do some in-house testing at each stage of your product design and development so that you can be confident that your products are compliant with the EMC and EMI regulations, and that they will work well in the kind of environment that they are likely to be exposed to.