| 摘要 |
Received ultrasonic bursts of energy are rectified and converted into pulse trains and also envelope detected. The envelope is fed to a ramp generator whose output is threshold detected to provide an arrival delay signal corresponding in time to the peak amplitude of the received bursts. A regulator circuit varies the timing of the arrival delay signal to coincide with the next negative-going zero crossover of the pulse train. A timing generator provides a reference delay offset, relative to the transmission time of the ultrasonic bursts, by the expected transit time thereof. The timing of the reference signal is varied in the same manner as the arrival delay signal by the regulator circuit and compared with the positive-going zero-crossover in the pulse train next following the negative-going zero-crossover. This determines accurately the actual time of arrival of the bursts, using low components.
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