SWEL developed a new occupancy sensor based on the Ultrasound-Echo-Principle. Impulse transmission and echo reception correspond to the conventional echo sounding principle. The processing of received "echo images" mimics the orientation-function of the bat.
1. Impulse Transmission:
First the sensor transmits a short ultrasonic impulse train. This impulse train "flies" at the speed of sound through the air. Depending on the frequency and construction of the transducer the sensor has a certain directive effect.
2. Echo Reception:
If the impulse encounters an object, it will be partially reflected and then be registered as an echo by the sensor. The time interval between impulse transmission and echo reception can be used to deduce the distance of the object. If there are several objects their echoes overlap, forming complex signals. The geometrical parameters of the scanned domain are coded in these complex signals.
3. Scanning Echoes:
The received echoes are sampled and stored in digital form in the sensor. The result is a pattern image of the scanned domain.
4. Detecting Motion:
The impulse echo scanning is repeated at short intervals (2-3 times per sec.). A comparison of sequential images provides information on motion of an object. For each detected motion it is also checked if it occurred inside the specified range. In order to prevent false turning on, several measurements are summarized and analyzed. The turn-off delay is done by a timer.