Magnetic Proximity Sensors0 pages

Magnetic
OPERATING PRINCIPLES FOR MAGNETIC SENSORS
Magnetic sensors are actuated by the presence of a permanent magnet. Their operating principle is based on the use of reed contacts, whose thin plates are hermetically sealed in a glass bulb with inert gas. The presences of a magnetic field makes the thin
plates flex and touch each other causing an electrical contact. The plate’s surface has been treated with a special material particularly suitable for low current or high inductive circuits. Magnetic sensors compared to traditional mechanical switches have the
following advantage:
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Contacts are well protected against dust, oxidization and corrosion due to the hermetic glass bulb and inert gas; contacts are
activated by means of a magnetic field rather than mechanical parts
Special surface treatment of contacts assures long contact life
Maintenance free
Easy operation
Reduced size
When using the NO (normally open) type the open reed contact closes as the magnet approaches. NO Magnetic sensors are two
wires. When using the NO+NC type both NO (normally open) and NC (normally closed) functions are made available by means of
a single glass bulb. NO+NC Magnetic sensors are supplied with three wires, one is in common, one is NO and one is NC
TYPICAL REED CONTACT PROTECTIONS
The lifespan of a magnetic sensor at low values of voltage and current depends on the mechanical characteristics of the contact
while for higher values the operating life depends on the characteristics of the load. In these cases, it is suggested to apply some
form of external protection at the sensor output.
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