| 摘要 |
PURPOSE:To prevent an erroneous action when an air layer of a different temperature from a room temperature exists in a detection area, by interposing an amplifier having gain-time change characteristics between a wave-receiving element and an output circuit. CONSTITUTION:First, an ultrasonic wave is converted to an electric signal by means of a wave-receiving element 6 and a relationship between the reflection distance of an ultrasonic wave and a wave-receiving output level, is set below a prearranged value against a detection level by means of gain-time change type amplification circuit consisting of voltage time change circuit 8 and self-bias amplification circuit 9. As a result, gain-time change characteristics are obtained, amplifying a conversion signal and detecting 11 the existence of wave-receiving pulse inside a detection gate after pulse shaping 10. Then an output circuit 12 is driven by means of detection output. At that time, inside the circuit 8, boot strap circuit which causes an integrating condenser to be discharged at a reset signal from a pulse preparation circuit 2 driving a transmission oscillation circuit 3, a transistor circuit for voltage detection with plural pieces of the series diode inversely connected and RC integration circuit are provided. |
