You have heard about proximity sensors in your daily life that are commonly used in mobile or smartphones, tablets, etc. Proximity sensors are commonly used on mobile devices to detect if someone is in nominal range. A proximity sensor is a type of sensor which is able to detect the presence of nearby objects without any physical contact. The maximum distance that a proximity sensor can detect is defined as “nominal range“.

International Electrotechnical Commission (IEC) 60947-5-2 defines the technical details of proximity sensors.

These sensors are of three types:

  1. Acoustic proximity sensor
  2. Capacitive proximity sensor
  3. Inductive proximity sensor

1. Acoustic proximity sensor

This sensor working is based on the principle of SONAR ranging. In this, acoustic signals are sent out, with the time of echo return being a measure of distance to an obstacle/target. This requires accurate circuitry so acoustic sensors require a processor of some sort to drive them.

2. Capacitive proximity sensor

When power is applied to the sensor, an electrostatic field is generated and reacts to changes in capacitance caused by the presence of a target. The disadvantage of this type of proximity sensor is that its usefulness is dependent on properties of the target/obstacle object it is sensing i.e. dielectric constant. The higher the dielectric constant, the more sensitive a capacitive proximity sensor is to that target/obstacle.

3. Inductive proximity sensor

This proximity sensor emits an electromagnetic field or a beam of electromagnetic radiation (infrared) and looks for changes in the field or return signal. The object being sensed is often referred to as the proximity sensor’s target or an obstacle. The primary problem with this method is that it is largely confined to sensing metallic objects.

Advantages of Proximity Sensors

Proximity sensors can have a high reliability and long functional life because of the absence of mechanical parts and lack of physical contact between the sensor and the sensed object or obstacle.

Applications of Proximity Sensors

These sensors find applications in the following

  1. Parking sensors, systems mounted on car bumpers that sense the distance to nearby cars for parking.
  2. Ground proximity warning system for aviation safety.
  3. Vibration measurements of rotating shafts in machinery.
  4. Sheet break sensing in a paper machine.
  5. Anti-aircraft warfare
  6. Roller coasters
  7. Conveyor systems
  8. Improvised Explosive Devices or IEDs
  9. Mobile devices
  10. 3D Touch will come true with the aid of proximity sensing elements.
  11. Automatic Faucets
Proximity Sensors | Working & Applications

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