| 摘要 |
PURPOSE:To measure an accurate volume flow rate by correcting the dynamic viscosity of gas according to information on at least either of the temperature of the gas and the external pressure outside a device. CONSTITUTION:An ultrasonic wave generated by an ultrasonic wave transmitter 5 is phase-modulated with a Karman's vortex street generated by air flowing through a passage 2 which has an air straightener and a Karman's vortex generation column and received by a receiver 6 to detect the air flow by 10. The output of the receiver 6 is amplified 12, phase-compared 9, and smoothed 16, and the waveform is shaped 17 and inputted to a frequency correcting circuit 89. The detected temperature of an air suction sound sensor 20 is A/D-converted 70B and inputted to a frequency correcting circuit 89 through a switch means 87. Further, the output of an atmospheric pressure sensor 21 is A/D-converted 71B and inputted to the frequency correcting circuit 87 through a switch means 88. The volume flow rate is found from the corrected frequency. Consequently, the measurement accuracy is improved. |
