A flue gas flow meter principles set `triangle columnar vortex shedder in the fluid, from the vortex of both sides alternately produce two columns regular vortex, the vortex is called Karman vortex street, as shown in (a) of the show. Load capacitance detection probe or piezoelectric detection probe in the vortex shedder in and the corresponding matching circuit, can constitute a capacitance detection type flue gas flow meter / sensor or piezoelectric sensor detects flue gas meter. Figure (a) listed in the vortex shedder vortex downstream arranged asymmetrically. Set the frequency of the vortex is f, the average speed measured medium to flow is V, the vortex shedder welcome stream surface width d, table body diameter is D, based on the principle of Karman vortex street, there is the following relationship: f = St.V / [(1-1.25d / D) d] where: f- Karman vortices occur resulting frequency side of the average velocity d- St- Strouhal number V- fluid flow cylinder surface width D- pipe diameter Figure (b) in the curve table St = straight section 0.17, the frequency and velocity is proportional to the release of the vortex, namely the flue gas flow meter measuring range of the sensor. As long as the detected frequency f can be obtained within a tube of fluid flow rate, volume flow rate calculated by the velocity V. Second, the flue gas flow meter installation requirements: 1, the flue gas flow meter can be installed indoors or outdoors. When installed in ground wells, and there is the possibility of flooding, you should choose submersible sensor or transmitter. 2 to the flue gas flowmeters horizontal, vertical or inclined installation in the pipeline, but when measuring liquids, the pipeline must be filled with liquid. Thus flue gas flow meter installed on a vertical or inclined pipes, the flow direction of the liquid to be bottom-up. 3, the upstream and downstream sides of the flue gas meter should be left long straight pipe upstream and downstream straight pipe length requirements with piping conditions vary. Flue gas upstream of the meter installation should avoid regulating valve or half open valves or valve should be installed after the half-open valve downstream of the meter 5D. 4, the installation of flue gas flow meter pipe diameter must be consistent with the meter diameter, otherwise it must be adjustable. 5, in the design of the pipeline, the upper end of the sensor or transducer should stay at least 500mm of space to facilitate debugging and maintenance.