A proximity sensor is an electronic sensor that can sense the presence of objects without any physical contact. In order to detect objects, the proximity sensor radiates a beam of electromagnetic radiation (infrared light) and senses reflected radiations. The object being sensed is called the proximity sensor’s target. Proximity sensors are highly reliable and have a long life because of the lack of moving parts. It has fast responded to the target object. Proximity sensors are widely used in many manufacturing fields like packaging, production, printing, plastic molding, metal working, food processing, etc
Types of Proximity Sensors
- Inductive Proximity Sensors
- Capacitive Proximity Sensors
- Ultrasonic Proximity Sensor
- Optical Proximity Sensor
- Inductive Proximity Sensor
This is an electronic proximity sensor, which detects the metallic object without any physical contact. Operating principle of Inductive Proximity Sensors are based on the high-frequency oscillator and a coil which creates a field
The main components of proximity sensors include coil, oscillator, detector and output circuit. The coil develops a high-frequency magnetic field. When the magnetic object comes in the field, it absorbs some of the energy. It affects the oscillator field. This cause a change in the output of sensors
Capacitive Proximity Sensors
This type of sensor is used to detect the presence of both metallic and non-metallic objects. Capacitive proximity sensor uses the change of capacitance between the sensors and object being detected.
Main components of the capacitive proximity sensor are a plate, oscillator, threshold detectors, and output circuits. Plate inside the sensor act as one of the plates of capacitor and object that has to be detecting act as another plate of the capacitor. When the object comes close to the plate inside the sensor, the electronic circuit inside the sensor begins to oscillate. This causes output in this sensor.
Optical Proximity Sensor
Optical proximity sensor includes a transmitter (light emitting diode) and a receiver (photo diode) to detect the light. Light emitted by the light emitting diode. Transmitter lens helps to focus the light on to the object surface. This light gets reflected from the surface of object. The reflected light is received by photodiode through receiver lens. Receiver lens used to focus the light on the receiver.
Ultrasonic proximity sensors
Ultrasonic proximity sensors are similar to the optical proximity sensor. Instead of using the light beam, a high-frequency sound wave is used to detect the presence of the object. The frequency of this sound wave is above normal hearing frequency. Ultrasonic proximity sensors detect the presence of the object in any of two methods. Based on these ultrasonic sensors are classified into two
In Reflective sensors, the transmitter and receiver are arranged together. When an object is present in front of it, the sound waves (ultrasonic waves) from the transmitter will strike on the object and are reflected back to the receiver.
In Opposed sensors have the transmitter and receiver arranged in different places facing each other. When an object enters the sensing range of the ultrasonic sensor, it blocks the transmitted sound waves from the transmitter to the receiver and generates an output.
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