| 摘要 |
PURPOSE:To obtain precision by counting clock pulses and thus measuring the necessary time width up to the reception of a reflected signal with a maximum level by a count pulse signal. CONSTITUTION:When a pilot pulse is radiated, the start of clock pulses operated on the start contact of an FF circuit 18. Then, an ultrasonic wave is reflected by a reflecting layer and supplied to an input IN. A reference voltage signal SV is stepped-down 19 and inputted to a comparing amplifier 20 together with the input IN. Respective amplifiers 20 compare the signal SV with inputs IN to store 11 only pulses larger than the signal SV, and only one signal extracted by a maximum level extracting circuit 12 among pulses is applied to put only an AND circuit 21 in operation; and a signal passed through an OR circuit 22 is inputted to an FF circuit 18 to stop clock pulses in operation. This time difference is inputted to a counter 15 and processed together with the input from a clock circuit generating circuit 14 to measure the necessary time width. Then, this count result is inputted to a decimal counter 16, and counted as the distance and displayed 17. |
