| 摘要 |
PROBLEM TO BE SOLVED: To enlarge rangeability of an ultrasonic flowmeter up to an equal or higher level, compared with a diaphragm gas meter. SOLUTION: A pair of ultrasonic transceiver 2, 3 are arranged oppositely with a distance L both on an upstream part and on a downstream part in a channel 1. A flow velocity and a flow rate are measured from propagation times t1 , t2 of the sound wave both in the following direction along the direction of the flow velocity V and in the reverse direction to the flow velocity V of the gas to be measured. In a low or medium flow-velocity range, a flow-velocity range of 1 cm/s to 15 m/s, the flow velocity and the flow rate are measured from the both times t1 , t2 , of the following and the reverse directions, by using a time reciprocal subtraction method. In a high flow-velocity range, 15 m/s to 60 m/s, the flow velocity and the flow rate are measured by measuring only either propagation time, t1 or t2 , of the times in the following direction or in the reverse direction, and also by performing a sound-velocity correction. The sound velocity, necessary for the sound-velocity correction, is obtained from the measured times t1 , t2 in the low flow-velocity range. |
