Saturday, March 31, 2012

Motion Light Sensors

As technology becomes more stylish and unobtrusive, with increasingly compact phones and computers offering an expanding number of features, other industries have followed suit. The desire to accomplish more with less has extended into security systems, where devices such as motion light sensors provide high levels of security while taking up little space and using less energy than older security systems. The technology itself, however, isn’t anything new—the detection of infrared energy, the primary mechanism in a light sensor, has been used in numerous other applications prior to its application in security devices and in-home lighting systems.

How Motion Light Sensors Work

The process by which a motion light sensor detects motion and triggers a response is contingent upon a passive infrared detector (PIR or PID). The word passive indicates that the sensor doesn’t emit infrared, rather receives infrared data—a PID picks up on the infrared energy (light) emitted by an object, such as a person. The difference in temperature, as detected by the PID, is the primary element in triggering a response.

A PID motion sensor is typically composed of a printed circuit board with a pyroelectric sensor chip, housed within a mounting structure, which is placed in a location where the sensor is completely unobstructed. The printed circuit board serves as the decoding device, and interprets the signals the pyroelectric chip receives. The chip responds to temperature, and when the amount of infrared surpasses a pre-set limit, the pyroelectric chip will release a signal, thus activating a light or an alarm.

In order for infrared light to reach the chip sensor, a small window is built into the mounted structure, directly exposing the sensor to the designated, monitored area. If a person enters the given area, the change in infrared as a result of their body temperature is detected by the sensor, through the small window. The window is transparent for infrared light, so it doesn’t block any signals, but it also helps protect the device form dust and bugs, both of which can trigger a false response.

In order to further avoid false responses, care must be taken in selecting an installation area. Avoiding contact with air vents, such as HVAC vents, can help prevent fluctuations in air temperature from activating the sensor.

Motion Light Sensor Applications

A motion sensor light triggers a response when motion is detected. They can be installed indoors, on walls, ceilings, and in doorways, or outside, on the exterior of buildings and homes. Some kinds of motion sensor lights, called occupancy sensors, operate by turning off lights in unoccupied rooms and spaces. When motion is detected, the sensor triggers the light; when motion stops being detected, the sensor shuts off the light. Occupancy sensors are one low-maintenance method for cutting down on electricity bill charges from lights left on when no one is home or in a room.

Occupancy sensors can be controlled and adjusted to meet the user’s needs. Typically, two forms of control are offered: sensitivity and time delay. A sensitivity setting enables the user to adjust the magnitude of motion that must occur to trigger the sensor. If properly set, a person walking in a room with a motion sensor should trigger the sensor, but a fly passing through shouldn’t result in turning on the lights. A time delay setting allows the user to determine how long the lights should remain on after the sensor is triggered, if no further motion is detected.

Motion light sensors can also be used in external applications, on the outside of homes and buildings, to sound an alarm or to turn on an outside light to announce a person’s presence.

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