Active ultrasonic room occupancy sensors are equipped with an ultrasonic transmitter having an output with a generally fixed amplitude. Ultrasonic occupancy sensors are sensitive to environmental noise such as forced air, e.g, from a HVAC vent, and other extraneous air pressure changes that may be interpreted by the ultrasonic receiver as a return ultrasonic signal representing an occupancy state. This type of environmental noise may cause a false trigger, as is known in the art, causing the controlled load to change state unintentionally. Typically, the false trigger noise is interpreted as occupancy, causing the controlled load to turn on and waste energy when there is no one in the monitored space.
USPTO Backgrounds
USPTO Backgrounds