| 摘要 |
<p>A device for measuring distances which is one embodiment will allow an echo of a transmitted acoustic signal to be identified in a noisy environment and in second embodiment is more suited for less noisy environments. The device comprises a phased locked loop circuit (5, 6, 1, 2) which provides a reasonant frequency to a transducer (4) to result in a frequency modulated tone burst being transmitted. A received signal is cross-correlated by storing samples of the transmitted signal in a first storage location (10) and samples of the received signal in a second storage location (40). The samples are compared by EXCLUSIVE OR gate (120) to determine if there is correlation between the received signal and transmitted signal. The number of correlations are counted in counter (130) and the number is displayed as a peak or an A scan. The larger the peak the greater the correlation. Hence when a large peak is displayed there is indication of receipt of the echo and the time between transmission and receipt may be read from the time base of the A scan and the distance calculated. In a second embodiment filter (74) is synchronised with a constant transmitted tone burst so that a received echo will charge capacitors C1...Cn in the same manner during each cycle of the received echo indicating receipt of the echo. The received signal is then applied to an A scan in a similar manner to that described above so that large peaks will be indicative of receipt of the echo and time between transmission and receipt may be used to calculate the distance between the object and the receiving location. </p> |
