The terms Electromagnetic interference (EMI) and electromagnetic compatibility (EMC) are often used interchangeably when referring to the regulatory testing of electronic components and consumer goods.
EMI can be defined as electromagnetic energy which affects the functioning of an electronic device. Sources of EMI can sometimes be naturally occurring environmental events, such as electrical storms and solar radiation. However, most commonly the EMI source is another electronic device or electrical system.
Cellphones, welders, motors and LED screens are especially apt to create disturbances.
Because it is rare for electronics to operate in isolation, products are generally engineered to function in the presence of some amount of EMI. This is particularly important in military-grade and avionics equipment, as well as devices requiring superior reliability in all situations.
EMC, on the other hand, 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.
Evaluating how a device will react when exposed to electromagnetic energy is one component of this, known as immunity (or susceptibility) testing. Measuring the amount of EMI generated by the device’s internal electrical systems ( emissions testing) is another.
Emissions testing requires the use of EMI measurement equipment. Typical equipment would be receiving antennas, amplifiers and spectrum analyzers. Working together, these tools provide an accurate measurement of the amount and type of noise generated by a device. This can be done either on an open area test site or in a shielded, anechoic (or semi-anechoic), test chamber.
Immunity (or susceptibility) testing involves determining the ability of a device to tolerate noise from external sources. In order to do this, it is necessary to have tools that can simulate and measure electromagnetic energy specific frequencies. The nature of the device, its intended application and any regulatory requirements will determine which type of testing equipment is required.
The commercial and military aerospace sectors are particularly prone to testing equipment for aircraft electromagnetic compatibility.
EMC testing is regulated. The two primary guidelines in the U.S.:
- FCC Part 15 rules define limits for the amount of unlicensed radio frequency interference that can be produced by consumer electronics and other devices.
- MIL-STD 461 and MIL-STD 464, which outline EMC and environmental requirements for components/subsystems and systems for military applications.
Outside of the U.S., various ISO, IEC, CISPR and other standards define acceptable limits of EMI and overall EMC.
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