Valve Measurement Air Controller To burner Valve Gas Measurement From teınP,era.ture controller Figure 1. mixed and combusred. (In the case ofa nozzle mix burner, rhese processes occıır simulraneously). A profile of rhe required furnace temperature conrrols the gas valve allowing mor<: or less gas co the burner. The ratio control system then detects the change in gas flow and adjusts rhe air flow rate to the burner by means ofa valve. Precise measuremenr and conrrol of thc air/gas flows in therefore required. An incorrect AGR at the burner may lead co a deteriorarion in product quality and may also cause the emission ofunwanred gase� to the atmosphere. In some applications, one ratio conrrol sysrem may supply air/gas to several burners. Currenr commercially available conrrol systems are mosrly based on mechanical or electro mechanical technology and are often unable ro produce the performance that is required in a modern system; this being due parrly to rhe inrroducrion of improved thermal insulation materials. DDilAL GA?. DERGiSi SAYL 27 le is belived, however rhar rhe major source of rhe AGR problem arises from rhe non-linear effecrs wirhin rhe air/gas valves and rhe inadequacies of rhe conrrol srraregies co accommodare such effecrs. in addressing rhis problem, rhe paper presenrs resulrs obrained from an industrial rest rig. This highlighrs rhe problems rhar are inherenr in many of rhe commercially available valves. Merhods ofmodelling rhe valves and rheir esrimared model paramerers are also considered. 2. STATEMENT OF THE PROBLEM Essentially, rhe problem considered is rhar of derecting an imbalance in rhe flows from rhe required air/gas rario (AGR) and subsequenrly correcring rhe AGR by adjusrmenr of rhe air, or gas, flow valve. in a gas led system such a mechanism assumes that the gas flow valve is conrrolled independenrly via an exrernal temperature demand profile. A summary of rhe problem definition is given in (3}. (It must be nored, however, that other systems exist which are led by rhe air flow valve.) in either case, the problem is extenuared when it becomes necessary ro measure and conrrol the AGR ar extremely low flow rares, such as is the case when arrempting to achieve a greater TDR; the problem being futher compounded when dealing with multi-burner instalarions. A typical configurarion which is applicable for a range of AGR systems is shown schematicly in Figure 1. With reference to Figure 1, it should be noted that the conrroller output ro the air valve may comprise a fıxed mechanical linkage or an electrical signal. With the rapid developrnenrs in microprocessor technology it is considered that an 'inrelligenr' conrrol system should provi83 l ı r 0�
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