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Conceptual through-beam system to detect unauthorized access to a secure door. If the beam is interrupted, the detector triggers an alarm. A photoelectric sensor is a device used to determine the distance, absence, or presence of an object by using a light transmitter, often infrared, and a photoelectric receiver. They are largely used in ...
An optical beam smoke detector is a device that uses a projected beam of light to detect smoke across large areas, [1] typically as an indicator of fire. [2] They are used to detect fires in buildings where standard point smoke detectors would either be uneconomical [ 3 ] or restricted for use by the height of the building.
One category of presence sensing devices is Photoelectric Sensors. Light Curtains also fall into this category. Light curtains use many infrared light beams to form a perimeter around machinery. When two or more consecutively adjacent beams are interrupted, a kill-switch stops the machine until the boundary is reset.
In common (non-SLR) digital cameras, the sensor system is often retroreflective. Researchers have used this property to demonstrate a system to prevent unauthorized photographs by detecting digital cameras and beaming a highly focused beam of light into the lens. [26] In movie screens to allow for high brilliance under dark conditions. [27]
Although photoelectric alarms are highly effective at detecting smoldering fires and do provide adequate protection from flaming fires, fire safety experts and the NFPA recommend installing what are called combination alarms, which are alarms that either detect both heat and smoke or use both the ionization and photoelectric smoke sensing methods.
This is often connected to an electrical trigger. The trigger reacts to a change in the signal within the light sensor. An optical sensor can measure the changes from one or several light beams. When a change occurs, the light sensor operates as a photoelectric trigger and therefore either increases or decreases the electrical output.
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