Interference immunity (EMC)

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In high-frequency technology, electromagnetic immunity refers to the desired resistance of a system to be tested to be able to work undisturbed up to a certain level or setpoint against an external source of interference.

Definition and description

The interference immunity SF describes the degree of ability of a system to continue to work without malfunction or failure and unaffected by a specific and defined interference variable acting on the test object. The level of the disturbance variable during an EMC measurement is generally selected to be greater than an operating situation of the system that occurs in practice could achieve this.

In the theoretical ideal case, the external source of interference could generate an infinite amount of energy without any noticeable influence on the system to be tested.

In English, electromagnetic susceptibility (EMS) is often used instead of the term for immunity . The translation of immunity to electromagnetic immunity is more precise .


The immunity to interference cannot generally be described by a single number or unit, but rather has to be defined by a number of parameters before the measurement, so that after the measurement it can be quantitatively recognized whether the test has been fulfilled, for example:

  • "The system must withstand an interference immunity level of 360 volts / meter with an amplitude modulation of 1 kilohertz at an 80 percent degree of modulation in the frequency range from 1 to 1000 megahertz with a horizontal antenna position."
  • "The system may show a malfunction Y when a disturbance variable X is applied, but must then automatically return to its normal state after Z seconds without external intervention."

In general, it must be described what the system must be able to do and not what it cannot .

See also


  • Georg Durcansky: EMC-compliant device design. Franzis, Poing 1995, ISBN 3-7723-5386-X
  • Adolf J. Schwab: Electromagnetic Compatibility , Springer Verlag, ISBN 3540607870

Individual evidence

  1. Strictly speaking, the English term actually means the exact opposite of interference immunity, namely susceptibility or susceptibility to interference. Since this property is expressly not desired, everyone seems to know in practice what is really meant.
  2. The name Electromagnetic Susceptibility suggests something in common with electrical and magnetic susceptibility. While the latter describe physical materials, the term electromagnetic susceptibility is aimed at entire systems.