Proximity Sensors

Proximity sensors are discrete sensors that sense when an object has come near to the sensor face. They are able to detect the presence of nearby objects without any physical contact. A proximity sensor emits a beam of electromagnetic radiation and looks for changes in the field or return signal. Proximity sensors are commonly used on Smartphone’s to detect accidental touch screen taps when held to the ear during a call. Typical applications include the detection, position, inspection and counting on automated machines and manufacturing systems. There are four fundamental types of proximity sensors Inductive proximity sensor, Capacitive proximity sensor, Ultrasonic proximity sensor and the Photoelectric or Opto-electronic Sensors.

Inductive proximity sensors respond to ferrous and non - ferrous metal objects. They will also detect metal through a layer of non - metal material. Inductive proximity sensors consist of a coil wound around a soft iron core. The inductance of the sensor changes when a ferrous object is in its proximity. This change is converted to a voltage-triggered switch. Capacitive sensors respond to a change in the dielectric medium surrounding the active face without necessarily making physical contact and can thus be tuned to sense almost any substance. Capacitive sensors can also sense a substance through a layer of glass, plastic or thin carton.

Photoelectric sensors offer non-contact sensing of almost any substance or object up to a range of 10 meters. It consists of a light source (usually an LED, light emitting diode, in either infrared or visible light spectrum) and a detector (photodiode). Ultrasonic sensor utilizes the reflection of high frequency (20 KHz) sound waves to detect parts or distances to the parts. Ultrasonic sensors are the best choice for transparent targets.