Patent ID: 6178827
Filing Date: 2001-01-30
Classification: G01F

Abstract:
A transit-time flow sensor for measuring an acoustic propagation time difference between upstream and downstream acoustic transmissions in a fluid and for determining the flow rate of the fluid therefrom, wherein the fluid wets a probe portion of the sensor, the probe portion comprising;first and second transducers, each of the transducers having a respective transmitting functional state and a respective receiving functional state, each of the transducers adapted to transmit acoustic energy at a first frequency along an axis parallel to a direction of flow of said fluid when said each transducer is in its respective transmitting state, each transducer adapted to receive said acoustic energy transmitted by the other transducer when said each transducer is in its receiving state; anda reflector adapted to convey said acoustic energy between said transducers;the sensor further comprising:means for alternating the transmitting and receiving states of the transducers so as to always have one of the two transducers in its respective transmitting state and the other of the two transducers in its respective receiving state, the means for alternating adapted to act at a second frequency substantially less than the first frequency;means for providing a continuous carrier signal at the first frequency to the transmitting one of said transducers; anda phase detector containing a low pass filter for providing an output signal responsive to a phase difference between electrical signals corresponding to, and of the same frequency as, the transmitted and received acoustic energy.