| 摘要 |
PURPOSE:To accurately and stably remove only noises and to accurately detect a vortex frequency by setting the charging and discharging time constant of an f-V converting circuit by a resistance, an arithmetic circuit, and a capacitor. CONSTITUTION:An ultrasonic wave which crosses a flow of a Karman vortex street is received by a ultrasonic wave receiver 5, whose output is inputted to a phase comparator 9 through a waveform shaping circuit 8. The output of the phase comparator 9 is sent out through a low-pass filter 11, a variable frequency filter 12, and a waveform shaping and amplifying circuit 13. This output is supplied to the f-V converting circuit 14, whose output is used to control the frequency band of the filter 12. The f-V converting circuit 14 has a charging path formed of a 1st resistance and an operational amplifier forming an imaginary short circuit and a discharging path formed of a 2nd resistance and a capacitor so that quick charging is performed at the time of high frequency generation and slow discharging is performed at the time of low frequency generation. |
