Flow measurement

The frequency of rotation of a turbine, anemometer or other rotary mechanism immersed in the passing fluid is linearly related to the flow rate over a range of flow rates.

Another method of measurement is to constrict the flow in some fashion, and measure the differential pressure that results across the constriction. This method is widely used to measure flow rate in the transmission of gas through pipelines, and has been used since Roman Empire times.

Measurement of the pressure within a pitot tube in the flowing fluid, or the cooling of a heated element by the passing fluid are two other methods that are used. These types of sensors are advantageous in that they are rugged, so not easily damaged in a hostile environment.

Modern innovations in the measurement of flow rate incorporate electronic devices that can correct for varying pressure and temperature conditions, and for the characteristics of the fluid.

Measurement of the doppler shift resulting in reflecting an ultrasonic beam off the flowing fluid is another recent, accurate innovation made possible by electronics.