Investigation of the pressure response of different Pitot tubes

Pitot tubes are commonly used to measure gas flow in ducts. The integration of the velocity profile which allows the calculation of the gas flow is described in several international standards such as ISO 3966 or ISO 10780. The common working principle of Pitot tubes is based on the measurement of the differential pressure between the two different pressure taps. The gas velocity is related to this differential pressure through a flow coefficient depending on the Pitot tube type. In case of stable flow, in a pressurized duct, fluctuations of the in-line pressure, even low, can occur. If the response times of the two pressure lines (static and total) between the Pitot tube head and the differential pressure sensor are not equal, these fluctuations can be seen as fluctuations of the measured differential pressure and then of the calculated velocity. This phenomenon is investigated for different design of Pitot tubes and the difference in behaviour of the two pressure lines is highlighted.