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Solutions to exercises
from Chapter 7 Exercise 7.1 Smallest measurable distance
Ultrasonic proximity sensors which have only one ultrasonic transducer, operate
alternatively as an emitter and as a receiver. The ultrasonic transducer creates
oscillations by means of a connected alternating voltage and emits ultrasonic waves.
If the voltage is switched off, then the oscillation of the transducer dies out
exponentially. The transducer must stop oscillating before a reflecting signal can be
received. The final oscillation time is dependent on the size of the transducer. This
does not occur with designs which have separate emitter and receiver transducers.
However, neither type of proximity sensor should be used to detect objects at small
distances for another reason. Characteristically, the ultrasonic emission from these
proximity sensors produces secondary lobes in the near field adjacent to the main
emitting zone. If an object approaches laterally within the range of the near field,
sensing becomes highly irregular so that no predictab...
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- Spring '12