| 摘要 |
PURPOSE:To make it possible to perform highly accurate measurement with a flowmeter having a small diameter, by obtaining an ultrasonic wave frequency in each direction of flow by using one VCO, thereby preventing the occurrence of a blind sector in a low flow speed region. CONSTITUTION:Under the state a PLL comprising circuits 1, 17, 16 and 3 is closed and the oscillating frequency of the VCO 1 is stabilized, a measuring control circuit 14 counts the oscillating frequency for a specified time. Then a measured value F1 is obtained. The value F1 is obtained under the state the ultrasonic wave is propagated in the forward direction with respect to the flow. Said value F1 is temporarily stored in an RAM in the circuit 14. Then, the direction of the signal with respect to transducers 8 and 9 is changed by the operation of a switching circuit 7. A measured value F2 is obtained under the state the ultrasonic wave is propagated in the reverse direction with respect to the flow and stored in the RAM. Then, the flow speed is obtained by a CPU in the circuit 14 based on the values F1 and F2. |
