| 摘要 |
PROBLEM TO BE SOLVED: To provide an accurate and highly reliable flow velocity measurement method and a device therefor, and a gas meter which can prevent an interference against accurate measurement and an unfair intervention to flow velocity measurement due to that the frequency of ultrasonic wave is read by an outside obstructor. SOLUTION: A frequency change circuit 16 changes the frequency of the ultrasonic wave used for measurement of fluid velocity by propagating into fluid to be measured to a different frequency at a predetermined cycle or an irregular cycle. Therefore, even if the frequency of the sonic wave used in a certain timing is read by an external heckler, as a different frequency is used after the cycle, intentional interference or unfair intervention using the stolen frequency can be prevented and constant mixing of noises can be also prevented. COPYRIGHT: (C)2004,JPO |
