A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact.
Principles of Operation for Inductive Proximity Sensors
Inductive proximity sensors are designed to operate by generating an
electromagnetic field and detecting the eddy current losses generated when ferrous and nonferrous metal target objects enter the field. The
sensor consists of a coil on a ferrite core, an oscillator, a trigger-signal level detector and an output circuit. As a metal object advances into the field, eddy currents
are induced in the target. The result is a loss of energy and a smaller amplitude of oscillation. The detector circuit then recognizes a specific change in
amplitude and generates a signal which will turn the solid-state output “ON” or
OFF"
WORKING
The DC supply generates AC in the internal coil, which in
turn causes an alternating magnetic field.
If no conductive materials are near the face of the sensor, the
only impedance to the internal AC is due to the inductance of the coil.
If, however, a conductive material enters the magnetic
field, eddy currents are generated in the conductive material, resulting in increase
in impedance to the AC in the proximity sensor.
A current sensor present in the sensor, detects when there
is a drop in the internal AC current due to increased impedance.
The current sensor controls a switch providing the output. Similar
to other sensors, proximity sensors also have built in hysteresis. The sensor’s
output goes on when a conducting material is inside the sensing range and will
goes off if the material just moves away from the sensing range.
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