| 摘要 |
PURPOSE:To prevent malfunction due to an ultrasonic wave noise and to improve reliability while detecting only a necessary objective body by outputting a detection signal only when a received signal is present for a specified time after its transmission. CONSTITUTION:By a switch 25 driven in accordance with a transmission and reception switching signal Sb having a period T0 from a switching circuit 23, a transmitter and receiver 21 transmits a pulse ultrasonic wave Ut. A reflected signal Ue from a body 1 is compared with a set level; and the comparison output signal is supplied to a malfunction preventing circuit 3 and gate signals Sc and Sd are supplied to the circuit 3. On the other hand, at every time when pulse ultrasonic wave transmission from a generating circuit 29 is repeated (n) times, a reset signal Se and a latch signal Sf are outputted to the circuit 3. Further, when the body is present in a detection area, a comparison output signal Sh is supplied to the circuit 3. Consequently, the circuit 3 outputs a detection signal Sl only when a received signal within prescribed time width after its transmission is present successively for plural times and the received signal is not present for a prescribed time after the transmission. |
