Ultrasonic flow sensor

A transit time flow sensor for determining a flow rate of a fluid from a measurement of an acoustic propagation time difference between upstream and downstream acoustic transmissions in the fuid, wherein the fluid wets a probe portion of the sensor, the probe 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, when in its transmitting state, acoustic energy at first, controllable, frequency, the acoustic energy transmitted along an axis parallel to a direction of flow of said fluid, each transducer further adapted to receive said acoustic energy transmitted by the other transducer when said each transducer is in its receivg state;
• and
• a reflector adapted to convey said acoustic energy between said transducers;
• the sensor further comprising:
• means for repeatedly 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 controllable frequency;
• means for providing a continuous carrier signal at the controllable frequency to that one of said transducers that is in its transmitting state;
• a 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, said transmitted and received acoustic energy;
• and
• a phase locked loop adapted to act responsive to the output signal to control the controllable frequency, so that said phase detector operates, on the average, at a center of its operating range.

A transit-time flow sensor for sensing 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 perpendicular to a direction of flow of said fluid when said each transducer is in its respective transitting state, each transducer adapted to receive a portion of the acoustic energy transmitted by the other transducer when said each transducer is in its receiving state;
• the sensor further comprising:
• means for repeatedly alternating the transmitting and receiving states of said 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;
• and
• means responsive to a change in time between said transmitted and said received acoustic energy for indicating a flow rate component that is not along the axis.

A transit-time flow sensor for measuring an acoustic propagation time difference between upstream and downstream acoustic transmissions in a fluid and for determining a 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 when said each transducer is in its respective transmitting state, each transducer adapted to receive acoustic energy transmitted by the other transducer when said each transducer is in its receiving state;
• and
• a reflector adapted to convev said acoustic energy between said transducers;
• the sensor further comprising:
• a bluff body for generating a Karman vortex street in said fluid and for therebv producing a plurality of vortices that pass through at least one acoustic pathlsl betveen said reflector and said transducers;
• and
• means responsive to a change in time between said transmitted and said received acoustic energy caused by said Karman v ortex street for generating an electrical signal with a frequency representative of said flow rate.