Measurements of the average flow velocity with the Pitot-Prandtl tube

Author: W. Cierniak

The input signal to the Pitot-Pradtl tube is the pressure difference between the tube inlet and side openings, which is proportional to the squared velocity. In the course of further processing the quantity is first averaged and then the square root is sought, hence the indicated average velocity value will be overstated.

Conduits connecting the tube with the pressure difference transducers and the measuring chamber make up/act as a low-pass filter.

Beyond the upper transmission limit, the filter implements the averaging procedure, thus generating certain errors.

The paper explores the correlation theory in stochastic processes to introduce relevant formulas to compute the average velocities, taking into account the properties of the Pitot-Prandtl tube and dynamic behaviours of a pressure gauge and conduits, described with a linear differential equation of the first order.