flow meter

flow meter

Device that measures the velocity of a gas or liquid. It has applications in medicine as well as in chemical engineering, aeronautics, and meteorology. Examples include pitot tubes, venturi tubes, and rotameters (tapered graduated tubes with a float inside that is supported by the flowing fluid at a level that depends on the flow rate). Ultrasonic flow meters, in which reflecting ultrasound off a flowing liquid leads to a Doppler shift (see Doppler effect) that is calibrated to provide the flow rate of the liquid, have important industrial applications and have also been used to measure arterial blood flow.

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A device that measures the movement of liquid in a pipe. "Invasive" flow meters are coupled into the pipe and derive the flow rate from the rotation of a turbine or paddle wheel that is moved by the liquid.

"Non-invasive" meters use two ultrasonic transducers that clamp on the outside of the pipe at a prescribed distance from each other based on the pipe's composition and diameter. They derive the flow rate based on the transit time of ultrasonic pulses sent from transmitter to receiver. In liquids with high solid or gaseous content, rather than measuring transit time, the amount of frequency shift is detected (see Doppler effect).