Photoelectric Motion Sensors
Photoelectric Motion Sensors

Some homeowners use devices that detect motion as a security measure. These sensors survey areas and trigger other security measures, such as alarms, when they detect motion. One such system, photoelectric sensors, projects beams of light between two points.

They trigger other measures such as alarms when the beam of light is broken. As most systems use infrared filters that render the light beams invisible to the naked eye, so the common intruder cannot see them. Thus, photoelectric sensors constitute effective security measures.

Design a Photoelectric Motion Sensor

These systems consist of transmitters and receivers. The transmitter sends a beam of focused light to the receiver. Receivers are equipped with light-sensitive diodes that register changes in light patterns. If a change does not fall within operating parameters (usually ninety percent of the light transmission for as little as seventy-five milliseconds), the processing unit registers the change and relays a signal to another security component such as an alarm.

Most systems can cast a beam over one-hundred meters. As an intruder may effectively step over or under a single beam of light and thus bypass the system, some people use mirrors to reflect the beam across a wide space in several different directions. It is also possible to use more than one beam vertically. Several beams set vertically make crossing virtually impossible.

Another conceivable way to bypass the system is to reflect another light into the receiver's diode. Systems counteract this method by modulating light frequencies at rate of up to 1,000 changes per second. Changes not recognized by the system or failure of the receiver to register the correct change trigger alarms or other measures.

Places to Use Photoelectric Motion Detectors

Most systems are best used indoors. Outdoor usage is possible, however any object breaking the beam, such as a bird or a leaf blown by the wind, may cause false alarms. Some people adjust the tolerance level breakage duration, but they risk intrusion by quickly moving intruders.

Also, dust collecting on lens covers or mirrors will cause the light to scatter and interfere with the system's operation. Weather conditions such as fog and mist as well as smoke may also interfere with the system. In addition, direct sunlight shining into the transmitter or receiver will block transmission.

However, some systems are especially designed for outdoor usage. Among the features offered by these systems include blockage tolerance up to ninety-nine percent, as well as monitors that gradually adjust operating parameters to changing weather patterns, and sealed optics. As one may expect, the more sophisticated systems are also more expensive.

In general, these systems offer reliable warnings of trespassing. They may be used in conjunction with other systems or alone. Usage outdoors requires special features, but indoor usage, even at a basic level, may be highly effective.