| OCR Text |
Show (3) Flow rate control system Air Fuel Ratio Setter Air Flow Controller Square R<j>ot Extractor l J. l ~rfk\ KQ& AIR trffcs Differential Pressure Sensor G AS Orifice Flow Meter nW Control Butterfly Valve Gas Flow Controller Control Valve Fig. 4 Flow rate control system Flow rate control system, which applies flow rate control to both of fuel gas I ine and ai r I i ne, is shown i n Fig. 4. Th i s system has sever a I demer its as f o I lows. 1) Deviation in flow control increases at low flow rate condition, because of the increasing deviation of differential pressure at orifice. 2) Cost of temperature correction, cross limit, etc. is expensive 3) Usually temperature correction is not applied to gas line, but 30°C fluctuation, if any, results in flow rate error of about 5%. 4) Air ratio becomes temporari ly unstable in PID control, caused by feed back delay, etc. 5) Adoption of cross limit system would cause late response. 3.2 Control method adopted in Intelligent Burner System As mentioned above, it was difficult to control burner in a broad range with high accuracy by the conventional control system of high cost performance. Therefore we developed an original measuring control system which is called "Composite Throttle System". The composite throttle system, which basically applies the orifice measuring method, is a system developed to solve such a problem that the measuring method as ever used is unable to insure specific accuracy due to fine differential pressure in low flow rate. P0= Valve inlet pressure P2= Burner inlet pressure V= Valve flow rate characteristic va I ue N= Burner f I ow rate character i st i c va I ue Fig.5 Principle of Measuring Control |
