Elego 37 SENSOR KIT - Page 79

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Component Introduction
Reed Switch and Reed Sensor Activation:
Although a reed switch can be activated by placing it inside an electrical coil, many reed
switches and reed sensors are used for proximity sensing and are activated by a magnet. As
the magnet is brought into the proximity of the reed sensor/switch, the device activates. As
the magnet is removed from the proximity of the reed sensor/switch, the device deactivates.
However, the magnetic interaction involved in activating the reed switch contacts is not
necessarily obvious. One way of thinking about the interaction is that the magnet induces
magnetic poles into the metal parts of the reed switch and the resulting attraction between
the electrical contacts causes the reed switch to activate.
Another equally valid way of thinking about the interaction between a magnet and a reed
switch is that the magnet induces magnetic flux through the electrical contacts. When the
magnetic flux is high enough, the magnetic attraction between the contacts causes the
reed switch to close.
The following are examples of typical reed switch and reed sensor activate distances.