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Principle

Proximity Ditectors Provide information on the displacement of a body with respect some boundary, the output of a proximity sensor is thus binary in nature.

Theory

Proximity sensor-

 Like range sensors, proximity detectors make use of an energy source and detector.The detector is a device whose output changes between two states when the magnitude of the incident
reflected energy exceeds a certain threshold level. A common from of proximity sensor uses an infrared light-emitting diode (LED) source and a photo transistor. Light triggers the transistor
into a conducting state when the LED is within a certain distance from a reflective boundary and the reflected light exceeds a threshold level.this system is physically small, occupying a volume
of only a few cubic centimeters. If even this small volume is obtrusive, then fiber-optic cables can be used to transmit light from a remotely mounted LED and photo transistor. the sensor contains a high-frequency oscillator oscillator output is demodulated and fed via a trigger circuit to amplifier output stage.The oscillator output radiates through the surface of the sensor and,
when the sensor surface becomes close to an electrically or magnetically conductive boundary, the output voltage is reduced because of the interference with the flux paths.
    

Conclusion

Inductive sensor can be adjusted to change state at displacements in the range of 1 to 20mm. A third from of proximity sensor uses the capacitive principal. these can operate in similar conditions to inductive types. The threshold level of displacement detected can be varied between 5 and 40mm. Such devices are particularly suitable for operation in aggressive environmental conditions and they can be mode.

Published Date

28 Feb, 2018