Proximity Sensor and its types

A proximity sensor is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation (infrared, for instance), and looks for changes in the field or return signal.

Proximity Sensors are widely used in industrial and manufacturing applications, especially for safety and inventory management applications. In an automated production line, for example, it is used for object detection, positioning, inspection and counting. It is also used for part detection in an industrial conveyor system.

Proximity sensors can also be found in consumer devices. In smartphones, proximity sensors are used to detect if a user is holding their phone near their face. They are also used as capacitive touch switches on consumer electronics products.

Infrared Proximity Sensor offered at Seed

Based on the SHARP GP2Y0A21, this IR proximity sensor is a popular choice that I’m recommending for anyone that’s looking for accurate distance measuring beyond your alternatives.

Packed in a small package with low power consumption, this IR proximity sensor allows for continuous distance reading with a range of 10cm to 80cm!


  • Corresponding analog voltage range from 3V when an object is 10cm (4″) away and 0.4V when the object is 80cm (30″) away.
  • Grove interface compatible
  • Wide supply voltage range: 2.5V-7V

Inductive Proximity Sensor

This sensor operates under the electrical principal of inductance where a fluctuating current induces an electromotive force(EMF) in a target object. These non-contact proximity sensors detect ferrous targets, ideally mild steel thicker than one milli-metre. They consist of four major components: a ferrite core with coils, an oscillator, a Schmitt trigger, and an output amplifier. This sensor has 2 main versions and they are,

  • Unshielded: Electromagnetic field generated by the coil is unrestricted, allowing for wider and greater sensing distances
  • Shielded: Electromagnetic field generated is concentrated in the front, where sides of the sensor coil are covered up

The oscillator creates a symmetrical, oscillating magnetic field that radiates from the ferrite core and coil array at the sensing face. When a ferrous target enters this magnetic field, small independent electrical currents (eddy currents) which are induced on the metal’s surface.

An inductive proximity sensor has the frequency range from 10 to 20 Hz in ac, or 500 Hz to 5 kHz in dc. Because of magnetic field limitations, inductive sensors have a relatively narrow sensing range like from fractions of millimetres to 60 mm on an average.

Due to this, load will be caused on the sensor that decreases the electromagnetic field amplitude. If the metal object moves towards the proximity sensor, the eddy current will increase accordingly. Thus, the load on the oscillator will increase, which decreases the field amplitude.

The schmitt trigger block monitors the amplitude of the oscillator and at particular level (predetermined level) the trigger circuit switches on or off the sensor. If the metal object or target is moved away from the proximity sensor, then the amplitude of the oscillator will increase.

Advantages of Inductive Proximity Sensors

  • Contactless detection
  • Environment adaptability- resistant to common conditions seen in industrial areas such as dust and dirt
  • Capable and versatile in metal sensing
  • High switching rate
  • No moving parts, ensuring a longer service life

Disadvantages of Inductive Proximity Sensors

  • Lack in detection range, averaging a max range of up to 60 mm
  • Can only detect metal objects
  • External conditions like extreme temperatures, cutting fluids or chemical affects on the performance of the sensor.

Capacitive Proximity sensor

Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the Sensor. As per the name, capacitive proximity sensors operate by noting a change in the capacitance read by the sensor.

The amount of capacitance varies depending on the size and distance of the sensing object. An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the capacity of the two plates detected.

The oscillator circuit starts oscillating and changes the output state of the sensor when it reaches certain amplitude. As the object moves away from the sensor, the oscillator’s amplitude decreases, switching the sensor back to its initial state.

The capacitive proximity sensor detects the larger dielectric constant of a target easily. This makes possible the detection of materials inside non metallic containers because the liquid has a much higher dielectric constant than the container, which gives the sensor ability to see through the container and detect the liquid.

Advantages of Capacitive proximity sensors

  • Contactless detection
  • A wide array of materials can detect
  • Able to detect objects through non-metallic walls with its wide sensitivity band
  • Well-suited to be used in an industrial environment
  • Contains potentiometer that allows users to adjust sensor sensitivity, such that only wanted objects will be sensed
  • No moving parts, ensuring a longer service life

Disadvantages of Capacitive proximity sensors

  • Relative low range, though incremental increase from inductive sensors
  • Higher price as compared to inductive sensors

Ultrasonic Sensor:

Ultrasonic sensors work by sending out a sound wave at a frequency above the range of human hearing. The transducer of the sensor acts as a microphone to receive and send the ultrasonic sound. Our ultrasonic sensors, like many others, use a single transducer to send a pulse and to receive the echo. The sensor determines the distance to a target by measuring time lapses between the sending and receiving of the ultrasonic pulse.

This HC-SR04-Ultrasonic Range Finder is a very popular sensor which is found in many applications where it requires to measure distance and detect the objects.

The module has two eyes like projects in the front which forms the Ultrasonic transmitter and Receiver. The HC-SR04 ultrasonic sensor uses sonar to determine the distance to an object like bats or dolphins do.

IR Proximity sensor :

IR sensor is an electronic device, that emits the light in order to sense some object of the surroundings. An IR sensor can measure the heat of an object as well as detects the motion. Usually, in the infrared spectrum, all the objects radiate some form of thermal radiation. These types of radiations are invisible to our eyes, but infrared sensor can detect these radiations. The emitter is simply an IR LED (Light Emitting Diode) and the detector is simply an IR photodiode . Photodiode is sensitive to IR light of the same wavelength which is emitted by the IR LED. When IR light falls on the photodiode, the resistances and the output voltages will change in proportion to the magnitude of the IR light received.


Proximity sensors have number of applications. The very basic is the detection of objects. This application of proximity is hugely use. For example in cell phones the proximity sensors are the essential parts. In different projects of engineering different proximity sensors are use for various functionalities. Proximity sensors are also use in parking lots, sheet break sensing and conveyor systems.

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