| 摘要 |
PROBLEM TO BE SOLVED: To realize an ultrasonic flow meter capable of accurately measuring the velocity of a fluid near a probe and at distant positions. SOLUTION: Control signals C1, C2, C3 are outputted from a control part 103 according to a gate time T corresponding to a measurement distance. The gain of a transmitting amplifier 105 is controlled by the control signal C1 so that a received wave R has a desired S/N ratio. The attenuation factor of a variable attenuator 106 and the gain of a preamplifier 107 are controlled by the control signals C2, C3, respectively, so that the preamplifier 107 is not saturated and that the output level of the preamplifier 107 falls within the dynamic ranges of a mixer 108 and of the circuits following it.
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