EMI vs. EMC: What’s the Difference?

EMI filter

Electromagnetic interference (EMI) and electromagnetic compatibility (EMC) are both important considerations when working with electronic components. EMI is caused by electromagnetic emissions that can disrupt the function of electronic devices and radio frequency (RF) systems. These devices and systems must be properly shielded from electromagnetic radiation for them to work well. EMC measures how well these devices and systems can work in the presence of disruptive electromagnetic interference.

What is EMI?

Electromagnetic interference often manifests as undesirable noise. It may also lead to erratic or disrupted function of electrical, electronic, and RF systems. There are four types of EMI:

  • Conducted EMI EMI that flows through wires and is caused by physical contact with the source of EMI.
  • Common Mode EMI – A high-frequency EMI that flows in the same direction through one or more conductors.
  • Differential Mode EMI A low-frequency EMI that flows in an opposite direction though adjacent wires.
  • Radiated EMI The most common type of EMI, caused by radiating electromagnetic fields. Common manifestations of radiated EMI include static noise on AM/FM radio receivers and “snow” on TV monitors.

Here are some of the most common sources of EMI:

  • Power generating equipment and peripherals, such as generators, power supplies, voltage regulators, switches and relays, battery chargers, and high voltage electrical transmission lines.
  • Devices operating at high frequencies, like oscillators, computing devices, radios, radar, and sonar equipment.
  • Machines that use both high voltage and high frequencies, including motors and ignition systems.

What is EMC?

Electromagnetic compatibility of an electrical, electronic, or RF device has two facets:

  • The ability to work properly in the presence of electromagnetic radiation.
  • The ability to not generate additional EMI that affects the operation of other devices in its vicinity.

The EMC of a device can be improved through good design, shielding, and EMI filtering. A device’s EMC can be measured through compliance testing using dedicated test systems that consist of antennas, near field probes, and spectrum analyzers. Even though EMC testing can be expensive, it is essential to ensure that a design will function properly and won’t generate disruptive electromagnetic interference.

<Learn why EMI filters are critical in electric devices.>

EMI and EMC Compliance

EMI and EMC compliance standards are not uniform around the world. Different regulatory bodies each have their own specific standards. For example, the compliance standards in the European Union are different from those in the United States. To further complicate matters, the U.S. military uses stricter standards than commercial industries. Even commercial compliance standards often vary depending on the specific industry and the end use of the device.

For reference, here are some of the most common compliance standards that must be met:

  • FCC Part 15 specifies U.S. EMC testing standards for consumer devices.
  • Military EMC testing standards can be found in MIL-STD 461 and MIL-STD 464.
  • In the EU, specifications by the ISO, IEC, CISPR, and other similar agencies govern EMI and EMC compliance.

Testing for compliance has to cover both immunity and emissions:

  • Immunity testing covers the susceptibility of the device to EMI, and whether it functions as designed in the presence of EMI of specified intensities, both continuously and intermittently.
  • Emissions testing ensures that any EMI emanating from a device remains within specified limits so that it won’t cause ancillary devices to function incorrectly. Since EMI may occur through both conduction and radiation, a comprehensive emissions testing scenario must cover conducted EMI as well as radiated EMI.

What Is an EMI Filter?

EMI Solutions from Captor Corporation

Captor Corporation has been a leading supplier of electronic filters for aerospace, military, and other applications for more than 55 years. Our team of expert engineers and technicians specialize in all aspects of electronic filter design and manufacturing, including reverse engineering of electrical and electronic circuits. We frequently custom design filters to fix products that fail EMI and EMC compliance tests.

You can learn more about Captor’s capabilities for designing standard and custom EMI filters from these links:

For more information about EMI and EMC and appropriate filter solutions from Captor Corporation, please request a quote today.

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