If you are interested in the design or development of electronic appliances, then it is important to understand basic EMC regulations and testing. EMC and EMI are two terms that crop up a lot in the world of electronics – both consumer goods and components. They are closely related, but not as interchangeable as some usages may suggest.
EMC stands for Electromagnetic Interference, and EMI stands for Electromagnetic Compatibility. They are both important terms, and they refer to the regulatory testing that all consumer electronics sold in the United States must undergo. Here, we will discuss the differences between EMI and EMC and also look at the requirements for each set of tests.
What are EMI and EMC
Electronic devices will always generate some electromagnetic radiation. We have a perception of electronics as being a form of a self-contained system – but while electrical energy travels along wires, it is not a completely effective way of transmitting energy. Some energy does escape into the air and into other wires, as electromagnetic interference or disturbance voltage. It is important that when new devices are made, the EMC and EMI fits within the required specifications because an appliance that puts out too much interference could prevent essential devices from working properly and an appliance which cannot cope with a reasonable amount of interference could lose data or malfunction at an inopportune time.
Some appliances do put out more interference than others. High-powered motors, for example, put out a lot of interference. Cell phones can also produce a lot of interference – something that you may hear from time to time as a buzzing or whine when an older phone is being used near a TV, for example. In addition, there are some devices that you might not expect to cause interference, such as LED-based screens.
Electronic devices rarely get used in isolation, so essential devices should be made to withstand a decent amount of EMI. Things such as avoinics or medical equipment, in particular, must be able to cope with EMI.
A devices EMC rating is a measure of how well it can cope with interference. EMC can be tested with specialist equipment, and these tests are a good indicator of how a device would operate under real-world conditions.
When an appliance is being developed it should be tested for both EMI and EMC. Emissions can be tested using antennas, spectrum analyzers, and amplifiers. These can be used in an open test area, or in a shielded chamber, depending on the precision of the testing required and the nature of the device.
Electronic devices must tolerate interference but also submit to it in certain circumstances. There is a range of equipment which can be used to generate noise on different frequencies, in order to simulate real-world interference. It is important that the testing that is performed matches the type of device and the application for which the device is intended.
Regulations Regarding EMC Testing
Military devices are tested according to the MIL-STD 461 and another standard, MIL-STD 464. These specify the environmental and EMC requirements for appliances, subsystems, and components. Military-grade components are held to a much higher standard for both interference resistance and output than other components would be.
Consumer appliances and other devices are tested to FCC Part 15, which restricts the amount of unlicensed RF interference that such devices can put out. These regulations exist, in part, to ensure that consumer-grade appliances do not interfere with critical electronics in places such as hospitals or airports where proper functioning of electronics is vital.
In other countries, there are standards set by organisations such as ISO, IEC, and CISPR. These define similar limits for EMI and EMC. Not all markets have made the standards mandatory, however, so it is important to confirm whether parts or appliances are compliant before purchasing them or using them in your own devices.
If you are making or designing an appliance, then make EMC testing a part of your processes from as early on in the system as possible. Precompliance testing can save a lot of time and stress by helping to ensure that your appliance or component is in compliance with the regulations.