Patent ID: 7628081

Claim:
A time of flight flow meter for measuring flow of a fluid along a flow direction, the meter comprising: at least one acoustic source comprising two electrodes separated by a gap through which the fluid flows when the meter is in use, the at least one source operable responsive to a high voltage input to supply an acoustic pulse; two capacitive acoustic detectors spaced apart along the flow direction, each of the acoustic detectors comprising: a respective fixed plate exposed to the fluid and facing the acoustic source; and a respective movable plate interposed between the respective fixed plate and the acoustic source, each movable plate spaced apart from the associated respective fixed plate by means of a respective insulator interposed therebetween, each movable plate having a respective front surface and a respective rear surface, each rear surface facing the respective fixed plate and each front surface facing the acoustic source, both the front and the rear surfaces of the respective movable plate exposed to the fluid; and a circuit operable to selectively detect respective changes in electrical capacitance occurring when the acoustic pulse arrives at each of the acoustic detectors; to determine a time of flight difference between the respective changes, and to calculate therefrom the rate of flow of the fluid.