Proximity Sensor Basics

A proximity sensor is a device which detects objects when they get within a certain distance from the sensor. The proximity sensor will then usually send a signal to an electronic circuit to perform a simple action, such as opening a door, turning on a light or sounding an alarm Many proximity circuits detect anything that comes too close. Others are designed to pick up on a particular type of object and ignore everything else. Proximity switches are devices which detect when an object is nearby. When an object gets within a certain distance, they will turn on a circuit to perform some basic function, such as opening a door or turning on a light or an alarm. Some proximity switches are designed to detect certain kinds of objects, while others will detect pretty much anything.

Active Proximity Sensors

Active proximity sensors actively hunt for an object. They typically send out some sort of signal and wait for it to be reflected back. By measuring the time between sending the signal and getting a reflection, they can determine how far away the nearest object is. For example, the proximity sensors on automatic doors send beams of infrared light out at an angle that will intercept anyone walking within a few feet of them. When someone walks up to the door, the light bounces off of him and back to the sensor. The sensor then tells the door to open.

Passive Proximity Sensors

Passive proximity switches work by absorbing information from their environment. When a particular change occurs, they note the change, and send a signal to a circuit. For example, outdoor safety lights use a carefully tuned infrared sensor to look for people. Everything emits infrared light, but the frequency of the light depends on the object. The human body emits a particular frequency which the sensor is tuned to recognize. When it registers that frequency of infrared, the sensor turns on the light.