| Infrared |
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| Active Infrared Devices: |
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| Active devices that use infrared technology have an infrared diode, which constantly or periodically emits infrared waves. Concurrently there is a receiver, which monitors the reflected wave levels .The absence of a reflected wave or a change in its properties (wavelength or amplitude) will indicate to the receiver that something has changed in the detection zone. In the case of a door sensor this change will cause a relay to trip. |
| Passive Infrared Devices: |
| Passive Infrared devices monitor a certain area for the presence of infrared rays, which are emitted by humans in the form of body heat. |
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Ultrasonic |
Ultrasonic devices constantly emit inaudible sound waves. At the same time the device is scanning for reflected waves, which are reflected at a preset speed. The speed corresponds to the height of the door and if a faster reflected wave is detected it indicates that something or someone has entered the monitored space. This triggers the door to open.
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| Microwave |
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Microwave devices constantly emit inaudible microwaves. Concurrently, there is a receiver, which monitors the reflected waves, which are reflected from objects. The change of reflected waves' parameters indicate that something or someone has entered the monitored space. This triggers the door to open. Microwave technology is different from ultrasonic one by waves' length. Microwaves are shorter than ultrasonic waves.
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Radio Transmission (Initiated by a touch-sensitive device) |
When the device is activated a radio wave is transmitted along a preset path to a nearby receiver. The receiver then activates a control circuit, which carries out an action (e.g. Opening the door) based on the presence of the signal or the results of signal analysis.
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