| 摘要 |
PROBLEM TO BE SOLVED: To accurately judge a property of a fuel by a method wherein the effect of a noise except a primary reflection wave in a detected signal detected by an ultrasonic wave sensor is eliminated and a detection time from a transmission wave to the primary reflection wave is accurately measured, then a concentration of the fuel is calculated based on the detection time. SOLUTION: A signal processing circuit 21 is comprised of a transmission wave generation circuit 22, a time region selection circuit 23 and a detection time measuring circuit 24. The transmission wave generation circuit 22 consists of an ultrasonic wave oscillator 25, a divider circuit 26, a timing signal generation circuit 27 and a transmission wave output circuit 28. The time region selection circuit 23 consists of four switching circuits 30, 31, 32, 33 which are controlled by means of a dividing signal from the divider circuit 26. The time region selection circuit 23 selectively outputs a time region having a carrier wave and a primary reflection wave to the detection time measuring circuit 24 to accurately detect a detection time, thereby judging a property of the fuel. |
