Proximity Sensor basics
Proximity sensor basically convert movement of person or thing into electrical form without
having any physical contact.Proximity sensor is defined in Japanese standard JIS C 8201, part-5 , Section-2.
There are three types of such detection systems as described below based on their functionality.
Proximity sensors are of three types inductive, capacitive and magnetic.
Inductive type detects metallic objects such as aluminium, iron, copper and brass etc. Here coupling condition of transformer is basically replaced by impedance change. This impedance change occurs due to eddy current losses. This impedance change is similar to inserting resistance in series with the object being sensed.
Capacitive type detects metallic object as well as non metallic objects such as liquids(water),resins,powders etc. The capacitance change is measured between sensor and object. The value depends on distance as well as size of the object.
Magnetic type: detects presence of magnets. Here reed end of the switch is triggered by magnet. Proximity Sensor will be on when the reed switch gets on.
How to make a proximity sensor of inductive type
Figure depicts inductive type of proximity sensor which works on inductance principle. It is simple to make this type of sensor. There are four basic components needed viz. coil, oscillator, detection circuitry and output circuitry. Oscillator will produce fluctuating magnetic field around the coil. This coil is positioned near the device to be detected. Eddy current produced on the metal object reduce the sensor's own oscillating fields. Detection circuit will monitor this strength of oscillator and will trigger the output when it goes below threshold.
Siemens proximity sensor is one such sensor which measures object coming at distance of about o-3mm at 250Hz frequency. The model simatic-PXI920 has M12 frame size and possess IP67 degree protection. It produces output voltage within range 0-10V proportional to the distance of the object from the sensor.
Sensor RELATED LINKS
Also refer IoT compliant sensors which includes ambient light sensor, optical sensor, gesture sensor, proximity sensor, touch sensor,
fingerprint sensor etc.
Refer Sensors and transducers article which covers types, basic functions and provide links to sensors and transducers. It include temperature sensor, humidity sensor, strain sensor, proximity or occupancy sensor, force or load sensor, voltage and current sensor, pressure sensor, speed sensor, resistance sensor, power sensor, level sensor, event or state sensor etc.