| 摘要 |
The distance of an object is measured by using and measuring the time at which reflected waves 20b, 30b are detected. The waves are observed from the instant at which direct waves might possibly appear. If a wave is detected after the detection of a previous wave has ended, the measurement is repeated with a sensitivity updated to a higher level and, when the same wave is detected, this is considered as the reflected wave. If it is observed that the same waves are reflected by the same object with several different sensitivities, the value corresponding to the highest sensitivity is adopted. The transmitted level of the ultrasonic waves is regulated by using the mechanical properties of an ultrasonic transmitter through adjustments to the number of pulses or frequency of a binary signal which actuates the ultrasonic transmitter. If either the reflected waves or the direct waves are not detected at the predetermined time, the device is taken to be faulty. Application to the detection of objects from motor vehicles. <IMAGE> |
