| 摘要 |
PURPOSE:To enable accurate and stable long-term measurement with a simple structure even over a short distance by driving an oscillating element at a differentially processed pulse of short pulse width or eliminating an unnecessary electric wave-receiving signal with the assistance of NAND circuit. CONSTITUTION:An oscillating output from an oscillation circuit 1 dries an oscillating element 13 in the form of a narrow width pulse coverted by a differentiation circuit consisting of a condenser 11 and a resistance 12. As a result, an ultrasonic pulse of narrow-width ultrasonic pulse synchronized to an oscillating output is transmitted from a wave transmitter 13. This pulse is received by means of a wave receiver 19 after reflecting a target. Because of a short ultrasonic wave existence time, an accurate short-distance measurement is carried out. In the meantime, an oscillating output from this circuit 1 sets FF17 starting time counting and at the same time, closing NAND gate. Consequently, even if a transmitted ultrasonic wave from the wave transmitter 13 is received directly by the wave receiver 19, an output from the gate 16 won't turn to a high level, and FF17 also won't be reset, thus eliminating an unnecessary received wave signal substantially. Accordingly, it is possible to make an accurate, stable measurement for a long period even over a short distance under a simple structure. |
