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ITGlossary · Power quality
Electromagnetic Interference (EMI)
Unwanted electrical noise or interference that can disrupt electronic equipment operation.
Technical level:Intermediate
In practice, this noise comes from motors, lifts, air conditioners, switch-mode power supplies, LED lights with cheap drivers, or even distant lightning. It travels along the power cables or is radiated through the air, and shows up as interference on audio and video, computers freezing, or data errors.
That is why UPS units and voltage stabilizers include EMI/RFI filters at the input, and the units themselves must meet the emission limits of EN 62040-2 so that they do not disturb other equipment.
Tip: avoid running power cables tightly alongside network or signal cables over long distances, and make sure the installation is properly earthed; without a good earth the filters cannot do their job.
Questions that mention it
All frequently asked questionsWhat distance should be kept between a UPS and data processing systems?
Because the input/output cables cause electromagnetic interference, we recommend keeping some distance between the UPS and sensitive devices (e.g., medical equipment) to avoid interference.
Related terms
- Noise (Electrical)Unwanted high-frequency disturbances on the supply voltage, e.g. from motors or power supplies, which UPS systems and line conditioners filter out.
- RFI — Radio Frequency InterferenceA subset of EMI: high-frequency noise from electronic equipment that can disturb radio, Wi-Fi and other devices.
- EMC (Electromagnetic Compatibility)The ability of a device to work properly without being affected by electromagnetic interference and without causing any itself.
- Power ConditioningTechniques such as EMI/RFI filtering, surge protection and AVR that correct voltage problems before they reach the load.
- Static BypassAn electronic path inside the UPS that instantly and automatically transfers the load to the mains on overload or internal fault.
- Automatic Voltage Regulator (AVR)A device that automatically maintains a constant voltage level to protect electrical equipment from fluctuations.