| 摘要 |
PROBLEM TO BE SOLVED: To provide a flowmeter for accurately measuring a flow rate from high to low with low power consumption, by determining the propagation time by executing the correction processing with a timer having improved time resolution. SOLUTION: The ultrasonic flowmeter includes a first timer 5 for counting reference clocks and performing time measurement, and a second timer 25 for performing time measurement from the measurement stop timing to the count-up timing of the reference clock. The second timer 25 includes a ring oscillator where a plurality of sets of signal generating means 5a-5g constituted by an inverting means 10, a delaying means 11, and a holding means 19 are interconnected in a ring shape, a counter 20 for counting the oscillations of the ring oscillator, and an arithmetic means 8 for correcting the measurement period of the first timer 5 with the period determined from the counted value of the counter 20. The output holding state of the holding means 19 can be selected according to a holding selection signal from a control section 4. By achieving the measurement mode according to the measurement application, the time resolution of the ring oscillator is improved. COPYRIGHT: (C)2008,JPO&INPIT |
