Electromagnetic Interference Classification

Electromagnetic Interference Classification Practically any electromagnetic phenomenon appearing within the broad frequency band could potentially affect the equipment operation. Depending on the source, electromagnetic interference falls under natural and artificial. Electromagnetic pulses caused by lightning are the most illustrative example of natural electromagnetic interference. Artificial interference can be generated by functional or non-functional sources. An interference source is a functional one if generated electromagnetic interference is a wanted signal for such source. Depending on propagation medium, electromagnetic interference are classified as inductive and conductive. Inductive electromagnetic interference propagates as electromagnetic fields in non-conducting media. Conductive electromagnetic interference takes the form of currents flowing through conducting elements and the Earth. Such inductive/conductive interference classification is a nominal one. In fact, there is a single electromagnetic process both in conducting and non-conducting media. When propagating, inductive interference can become conductive and vice versa. For example, alternating electromagnetic field can induce currents in cables that further propagate as regular conductive interference. On the other hand, currents in grounding cables and circuits generate electromagnetic fields i.e. inductive interference. Interference can be divided into inductive and conductive to a relatively strict extent within a low-frequency band only (up to dozens of kilo hertz) where capacitive and inductive couplings are low. Conductive interference occurring in circuits with more than one conductor is classified as common-mode interference and differential mode interference. When common-mode interference occurs, interference voltage is applied between each of circuit conductors and the Earth. In the other case, interference voltage is applied between different conductors in one circuit. Generally, differential-mode interference pose the highest hazard to equipment as they are applied similar to a wanted signal. Actually, interference generally combines common-mode and differential mode interference. Note that asymmetry of external signal transmission circuits and equipment input circuits may ...