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Magnetic
proximity sensors are actuated by the presence of a permanent magnet.
Their operating principle is based on the use of reed con-tacts,
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 par-ticularly suitable
for low current or high inductive circuits. Magnetic sensors compared
to traditional mechanical switches have the following advantage:
- 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
Outputs:
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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