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Magnetic system

The magnetic, coil system or motor unit is also called the energizing or primary side of a relay. lt consists of all the parts used to transform the electrical energy in the primary side into mechanical force to actuate the contacts and switch the secondary circuit.

Relay Magnetic System - The Coil
Relay Magnetic System – The Coil (on photo: Solid state electromagnetic recovery system)

Magnetic circuit

The magnetic circuit consists of non moving metal parts such as the core, yoke and a movable armature. and an air gap between the armature and the pole area of the core. The armature closes and opens under the influence of a magnetic held, its movement directly or indirectly operating the relay contacts.

The magnetic field is generated by a coil consisting of copper wire wound in layers around the bobbin in which there is an iron core.

If voltage is applied to the coil terminals a current (Ohms law l=U/R) flowing through the coil generates a magnetic field and hence magnetic flux. This induced magnetic held/flux is directly proportional to the coil current and the number of tums of the coil (H ≈ n*I, H=magnetic field, n=number of turns. I=coil current).

Due to the high permeability of the soft magnetic iron core in comparison with air. the magnetic field concentrates within the magnetic circuit (except the stray field).

Title: Relay Magnetic System – The Coil
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