| 摘要 |
PROBLEM TO BE SOLVED: To obtain an ultrasonic flow meter for gases that is improved in practical use by expanding a measurement limit about flow rates. SOLUTION: An arrival point is considered to be displaced by a distance w/2, after an in-tube propagation period of time T; and since the parallel component of a fluid flow rate is Va×cosαon the condition that Va is the fluid flow rate, and an ultrasonic beam from a transceiver 2 on the transmitting side is drifted so as to arrive at an edge area, on the downstream side of a transceiver 3 so as to be a straight line B, and the drift in the arrival point of the principal axis becomes w/2=T×Va×cosα. Meanwhile, the time T is represented by T=d/(C×cosα), where C is the velocity of sound in the gas, obtaining Va=wC/2d. The angleθa is w×cosα/2d, the angle to be deflectedθfor the flow rate to be measured V is given byθ=θa×V/Va, and the delay timeτi, to be applied to an i pieces of the vibrators of the transceiver 2, is obtained based on the angleθ. The delay timeτi can be calculated by using an expression: (i-1)p×sinθ/C, where p is the spacing of the vibrator, and accordingly, the principal axis of the ultrasonic beam is made to reach the center of the transceiver 3, by deflecting the ultrasonic beam through the angleθ. COPYRIGHT: (C)2008,JPO&INPIT
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