Patent ID: 6772643
Filing Date: 2004-08-10
Classification: G01F

Abstract:
A flow meter for measuring a flow rate of fluid flowing through a flow passage, said flow meter comprising:first and second oscillators provided across said flow passage for transmitting and receiving an ultrasonic wave; a transmitter for driving said first and second oscillators; a switching unit for switching transmission of said ultrasonic wave between said first and second oscillators; an amplifier for amplifying a signal received from said first and second oscillators; a flow-rate calculator for calculating said flow rate based on a duration of propagation of said ultrasonic wave between said first and second oscillators; a reference comparator for comparing a voltage of said amplified signal with a reference voltage to output a signal which indicates a time point where a relationship between said voltage of said amplified signal and said reference voltage changes; a judging unit for detecting an arrival time of said ultrasonic wave at said first and second oscillators based on said signal output from said reference comparator and said signal output from said amplifier to output a signal which indicates said arrival time; and a reference setting unit including a propagation measuring unit for measuring a duration of propagation of said ultrasonic wave along said flow passage from a start of transmission of said ultrasonic wave to said arrival time detected by said judging unit, and a voltage setting unit for determining said reference voltage based on said duration of propagation and for said reference voltage to said reference comparator.