Target flow meter

A target flow meter is a device in which a target is installed at the center of the pipeline under measurement, facing the direction of the flow velocity; it measures the flow rate by detecting the forces acting on the target. The force transducer in the new type of target flow meter is a strain-type one, and it possesses many excellent features such as high accuracy (total flow measurement accuracy of ±0.5% to ±1%), a wide range (50:1), no moving parts, a simple structure, easy maintenance, and the possibility of periodic calibration using the deadweight method. It can be expected that target flow meters will become an important type of device for measuring natural gas flow, capable of indicating the approximate speed of flow; however, their accuracy is relatively low and their errors are typical for this category of devices.

When the medium flows through the measuring tube, its kinetic energy creates a pressure difference with the target plate, resulting in a force exerted on the target plate that causes it to move slightly. The magnitude of this force is proportional to the square of the flow velocity of the medium; the mathematical formula for this is: F = Cd·A·ρ·V²/2. Here, F represents the force acting on the target plate, Cd is the coefficient of fluid resistance, A is the area of the target plate as projected along the axis of the measuring tube, ρ is the density of the medium under the given conditions, and V is the characteristic flow velocity of the medium within the measuring tube. The force acting on the target plate is transmitted through the target rod, causing a slight deformation of the elastic element in the sensor; this deformation is then converted into an electrical signal via an electronic circuit.

This post was last edited by different Radial tee on 2009-5-14 at 14:04. The images were found online at http://www.xabolt.com/jishu.asp; they should be clear enough to understand!