Apparatus for measuring the flow velocity of fluids

Claim 1

Apparatus for measuring a flow velocity or velocity component of a fluid, which apparatus comprises first and second units arranged spaced apart to define a single path extending through the fluid in the direction in which flow velocity or flow velocity component is to be measured, each of which units comprises a single transducer capable of operating as a transmitter and as a receiver of pressure wave pulses, first pulse generator means operative, when triggered, to cause the said first unit to transmit a pressure wave pulse, second pulse generator means operative, when triggered, to cause the said second unit to transmit a pressure wave pulse, means for retriggering the said first pulse generator means upon reception of a pressure wave pulse by the second unit, means for retriggering the said second pulse generator means upon reception of a pressure wave pulse by the first unit, means inhibiting said re-triggering except during a predetermined period embracing the expected reception of a pulse, means for introducing, when necessary, delay in the re-triggering of the pulse generator means to avoid simultaneous transmission and reception of a pulse by either of said units, whereby in operation the first and second units each transmit and receive continuously trains of pressure wave pulses travelling over the same path in the fluid but in opposite directions without clash at either unit between the moment of reception of an individual pulse at a said unit and the moment of transmission of a pulse from that unit, and means for indicating the difference in frequency of pulse repetition of the first unit from the second.