| 摘要 |
A distance indicating system, particularly for a vehicle, includes a transmitter (8) to transmit a signal beam, and two receivers (10) and (12) one on either side of the transmitter (8) The transmitter and the receivers are mounted on the front of a vehicle, and if an object (24) is directly in front of the vehicle the transmitted signal beam will be reflected by the object (24) and received simultaneously by the receivers (10) and (12). A coincident gate (16) is actuated only in response to signals received simultaneously by the receivers (10) and (12), and the actuated gate (16) sends an output signal to an echo delay measuring circuit (18). This circuit (18) operates an audio tone generator (20) and an audio output indicator (22) thereby providing an aural warning for the vehicle driver of the presence of the object (24). A clock (14) switches the transmitter (8) and the receivers (10) and (12) on and off in a suitable sequence to prevent a transmitted signal being passed directly from the transmitter (8) to the receivers (10) and (12) and being passed to the coincident gate (16). The audio output (22) is not operated in response to signals reflected from objects to the left or right of the vehicle because the reflected signals do not arrive simultaneously at the receivers (10) and (12), and consequently the coincident gate (16) is not actuated.
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