| 摘要 |
An echo type rangefinding a system, preferably using ultrasonic energy bursts, includes a transducer for transmitting and receiving the energy burst and signal processing means for identifying a true echo of the energy burst (54) from a selected target. The signal processing means discriminates against spurious signals and electronic noise, some of which may be generated by the rangefinding system itself, by rejecting signals that do not persist for at least a predetermined period. Preferably, the system recognizes the leading edge of a true echo signal by sampling the integrated signal (156) at sampling intervals (158) which are small compared with the said predetermined period (for example 0.6 milliseconds). If the samples integrated signal voltage (Vc) steadily increases at at least a given minimum rate for at least the predetermined period then the signal processing means provides an "object detect" signal. The accuracy of the rangefinding system is improved firstly because of the improved signal discrimination, and secondly because the object detect signal is always produced at the same time after the beginning of the true echo signal. <IMAGE> |
