FLOW METER

摘要

PURPOSE: A flow meter is provided to measure the flow rate of fluid flowing through a flow passage based on duration of propagation of ultrasonic wave along the flow passage by setting the reference voltage accurately and promptly without errors. CONSTITUTION: A flow meter for measuring the flow rate of fluid flowing through a passage(1) is composed of first and second oscillators(2,3) transmitting and receiving ultrasonic signals in the passage; a transmitter(5) driving the first and second oscillators; a converting unit(4) switching transmitting or receiving of the ultrasonic signal of the first and second oscillators; an amplifier(6) amplifying the receiving signal of the first and second oscillators; a flow rate calculating unit(11) outputting the flow rate based on propagation time of the ultrasonic signal between the first and second oscillators; a reference comparator(7) outputting the signal by comparing voltage of the amplified signal with the reference voltage; a decision unit(8) deciding the arrival time of the ultrasonic signal to the first and second oscillators and outputting the signal according to output from the reference comparator and the amplifier; a reference setting unit(13) having a propagation timer(13a) counting transmission time of the ultrasonic signal in the passage, and a voltage setting unit(13b) outputting reference voltage to the reference comparator by deciding reference voltage based on propagation time; a repetition unit(9) counting the signals from the decision unit and outputting the signal to a control unit(12); a counter(10) checking counting time according to the predetermined number; and the control unit controlling the transmitter and the amplifier corresponding to the signals from the flow rate calculating unit and the repetition unit.