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Unformatted text preview: .2.3 Detecting a magnetic field
The most simple and usual method of detecting a magnetic field is to use a reed
switch. Two soft magnetic metal reeds are brought into contact by means of an
external magnetic field and an electrical contact is established. Closing of this
contact is however not bounce-free. Fig. 11.2.4 illustrates the switching behaviour of
this contact. ON OFF
t1 t2 t Fig. 11.2.4: Switching characteristic of bouncing mechanical contacts © Festo Didactic GmbH & Co. KG • FP 1110 169 11. Physical fundamentals Furthermore, it should be noted that this switch has two or three switching zones
depending on the direction of the magnetic pole axis. If the pole axis points
vertically in the plane of the switching reeds, then two switching zones will always
be obtained (Fig. 11.2.5). This is due to the shape of the magnetic flux pattern. When
the magnet passes, the field strength which is required to trigger the switch is
obtained twice. If the pole axis is parallel to the switching reeds, t...
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