EMC Basics
Inductive Coupling Mechanism Inductive coupling - or sometimes known as transformer coupling - is a coupling via the magnetic field. This occurs between lines running parallel to one another. Current changes in a wire cause a fluctuation in the magnetic field. The resulting magnetic field lines affect parallel running wires and induce an interference voltage there. A current now flows which overrides the useful signal as an interference signal. Inductive coupling is caused in parallel running lines in cables, wire harnesses and cable ducts. Well known sources of interference are: Conductors and electrical equipment with high and fluctuating operational and interfering currents (short circuit currents) Lightning discharge currents Capacity switching Welding current generators
The following circuit diagram shows the construction of inductive coupling. Current changes in circuit 1, which are caused by switching large loads or those that are caused by a short circuit, are producing a fluctuation in the magnetic field.
Size of the interference The interference voltage caused by the inductive coupling depends on the coupling inductivity MK between the two conductors and the current change time di/dt on the power line:
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