| 摘要 |
PURPOSE:To measure even a long time interval with high precision by counting frequency-divided clocks between ultrasonic wave transmission and reception, and extending a time of shorter than frequency-divided clock wavelength and counting clocks. CONSTITUTION:A clock CLK which is frequency-divided at a frequency division ratio (m) from a frequency divider 9 while passed through an AND gate 4 opened by the Q output of an FF1 set and reset according to ultrasonic transmitting and receiving signals P and R to output a counted value A. The period of the Q output of an FF2 which is set by the signals P and R and reset by the frequency-divided clock is multiplied by M through an extending circuit 3 to control an AND gate 5, and an up/down counter 7 which counts up and down according to the Q output of the FF1 counts up and down the clock CLK to output a counted value B-C during the extended period of a deviation period of shorter than the wavelength of the frequency-divided clock. Then, an ultrasonic-wave propagation time (t) based upon an equation I is determined precisely regardless of the frequency of the clock to measure even a long time interval with high precision. |
