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

D−FL 100 Seite 3The output signal at the D-FL 100-10 Display can be corrected so that the current value of the volume ormass flow is displayed. To do this, the signals (4 - 20 mA) for absolute pressure and temperature mustbe accessible to the D-FL 100-10 Display.The equation between the standard volume flow and the flow is:(Eq. 4)Taking the eqauations 2, 3 and 4 into account, the standard volum flow can be obtained by the followingequation:(Eq. 5)Fig. 2 shows a diagram of a differential pressure bar spanning the entire diameter of a stack. The twochamberdifferential pressure bar senses the impact and static pressures, and transfers them separatelyto the differential pressure transmitter.Fig. 2:Diagram of a differential pressure bar inside a stackAs the gas velocity is not evenly distributed in a duct/stack, an average speed is derived to calculate gaspressure. With completely laminar flow patterns, a single differential pressure measurement wouldsuffice to calculate average gas velocity. This, however, requires very long input and output paths,which are usually not present.The average velocity is measured by means of the differential pressure bar placed across the entirediameter of the duct/stack. The duct/stack is divided into rings of equal areas, and measuring points areGmbH