| 摘要 |
PURPOSE:To discriminate a normal transmission wave pulse or not to prevent erroneous detection due to a reflected wave and noise an to shorten the length of juxtaposition by juxtaposing photoelectric sensors which detect the same material synchronously with the detection timing of a receiver which receives the ultrasonic wave transmitted from a transmitter. CONSTITUTION:When a pulse (a) having a preliminarily set transmission wave pulse width l is oscillated out from an oscillating circuit 3 from a time t1 to a time t2, a transmission wave pulse (c) which is synchronized with the pulse (a) and has the transmission wave pulse width l is transmitted from an ultrasonic oscillator 5 for transmission. A light projecting circuit 11 detects the rise and the fall of the oscillated pulse (a) and controls the light projection of a light projecting element 12 in accordance with times t1 and t2 to output two light projection pulses correspondingly to the transmission wave pulse l. These light projection pulses are received by a photodetector 13 to obtain two photodetector outputs in total. They pass an amplifier 14 and are delayed by a delay circuit 15 and are outputted to a signal processing circuit 8. Meanwhile, the transmission wave pulse (c) is received by an oscillator 6 and is sent to the circuit 8, and it is discriminated whether the pulse is the normal transmission wave pulse or not according as both input signals are synchronized or not. |
