October 13, 2013

What are proximity sensors?

A proximity sensor is a device that detects objects when they get within a certain distance from the sensor. It usually works through sending a signal to an electronic circuit to perform actions such as opening a door or turning on light.

Active proximity sensors actively hunt for an object. They typically send out some sort of signal and wait for it to be reflected back. By measuring the time between sending the signal and getting a reflection, they can determine how far away the nearest object is. For example, the proximity sensors on automatic doors send beams of infrared light out at an angle that will intercept anyone walking within a few feet of them. When someone walks up to the door, the light bounces off of him and back to the sensor. The sensor then tells the door to open.

Passive proximity switches work by absorbing information from their environment. When a particular change occurs, they note the change, and send a signal to a circuit. For example, outdoor safety lights use a carefully tuned infrared sensor to look for people. Everything emits infrared light, but the frequency of the light depends on the object. The human body emits a particular frequency which the sensor is tuned to recognize. When it registers that frequency of infrared, the sensor turns on the light.

Working:

An Inductive Proximity Sensor consists of an oscillator, a ferrite core with coil, a detector circuit, an output circuit, housing, and a cable or connector. The oscillator generates a sine wave of a fixed frequency. This signal is used to drive the coil. The coil in conjunction with ferrite core induces a electromagnetic field. When the field lines are interrupted by a metal object, the oscillator voltage is reduced, proportional to the size and distance of the object from the coil. The reduction in the oscillator voltage is caused by eddy currents induced in the metal interrupting the field lines. This reduction in voltage of the oscillator is detected by the detecting circuit.

Types of Proximity Sensors

There are several types of proximity sensor which are used according to the need, material detection and many other things. To classify them here are its types:

Inductive Proximity Sensors

Device which generates output signal or electrical signal when metal objects are either inside or entering into its sensing area from any direction. The metal objects above includes iron, aluminum, brass, copper, etc with varied sensing distances

Other factors which affect Proximity sensors: flat targets are preferable, targets larger than the sensing face may increase the sensing distance. First inductive proximity sensor was introduced in the mid 60’s.

Capacitive Proximity Sensors

t can also detect metals but along with it can also detect resins, liquids, powders, etc. This sensor working can vary accordingly covering material, cable longness, noise senstivity. Its sensing distance also vary according to factors such as the temperature, the sensing object, surrounding objects, and the mounting distance between Sensors. Its maximum range of sensing is 25 mm.

Magnetic Proximity Sensors

Name is saying its sensing object – magnets. Magnetic Proximity Sensors have no electrical noise effect and it can work on DC, AC, AC/DC, DC. Again sensing distance can vary due to factors such as the temperature, the sensing object, surrounding objects, and the mounting distance between Sensors. This type of sensors have highest sensing range upto 120 mm.[divider]

These sensors has been used in various devices like mobile phones, tablets, security appliances, etc. These days its mostly used on mobile phones in order to make it more functional, responsive and useful.

Proximity sensors is provided by many brands including Omron, Autonics, Balluff, Turck, Dolphin etc.

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What are proximity sensors?

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