Measuring Gas Velocity with the D-FL 100 Differential Pressure Bar

D−FL 100 Seite 2Fig. 1:Diagram of a Pitot tubeIn a Pitot tube, the total reference pressure P ges is measured at the tip of the differential pressure bar,and the static pressure P stat is measured via lateral openings. However, the influence of the velocitysquared (v 2 ) component makes obtaining an accurate measurement difficult in the case of gases withvery slight differential pressures and slight pressure variations.The differential pressure is therefore increased by using a reference pressure that is lower than thestatic pressure. A low-pressure area created through a vortex effect behind an object in the path of theflow can be used as a reference. The correction of the dynamic pressure according to Bernoulli (Eq. 2)is achieved with a so-called k -factor. The mathematical relation between the differential pressure andthe gas velocity is therefore as follows:(Eq. 2)VAkmass flowduct/stack cross-sectioncorrection factorWhen correcting volume or mass flow for temperature and absolute pressure, the density of themeasured medium is taken into account. Equation 3 shows how the density depends on the twoparameters of an ideal gas:(Eq.3)ρ n normal density under standard conditionsP n standard pressure = 1,013 * 10 5 PaP operating pressure in PaT n standard temperature = 0 ° CT operating temperature in °CGmbH