【正文】 s), and rear wall (RW), is established through the difference in fluid density between the subcooled water in the downers 14 and the steam/water mixture in the heated furnace circuits 18. The fluid velocity in the wall tubes prising the furnace circuits must be sufficient to cool the furnace wall tubes 18, which are typically exposed to bustion gases B whose temperature may reach 3500176。s) 14 provided with downer bottles (DCB39。 (3) in certain controls under the system to obtain the PID controller through the formula putation the parameter. Chart 6 will be forever the great programmable foreword controller PID subprogram gives an example. Chart 6 forever great programmable foreword controller PID partial procedure charts Except for this for guaranteed the boiler movement the security, when carries on the automation control system design, to the boiler water level, the boiler dome pressure and so on the important parameter should establish the conventional measuring appliance and the alarm device, guaranteed the water level and the dome pressure have the dual even tertiary alarm device, this is essential, in order to avoid the boiler has the significant accident. 5 concluding remark Because used PLC to carry on the control, system function perfect, structure advanced reasonable, energy consumption small, expansion nimble, was advantageous for the maintenance, and the reliability was high, moreover also enormously enhanced enterprise39。 Kc (gain) =D4005/Pb) En: n the time error = supposes the definite value (SP) n the time process to change the value (PVn) Ki: Constant of integration (scope: 0 ~ 9,999, is equal to ~ Repeats/Minute) Td: Fluxionary calculus timeconstant (scope: 0 ~ 9,999, is equal to ~ ) PVn: n the time process changes the value PVn1: n the time previous process changes the value Ts:PID operation time interval (scope: 1 ~ 3,000, unit: ) Bias: Bias output (scope: 0 ~ 16,383) Adds on the micro subitem the controller, the goal lies in the elimination program control system excessively to respond that, then enables the program control system steadily to relax achieves stably. Although the micro subitem has the above merit, but because it is quite keen to the output contribution, the majority of applications do not need to use the micro subitem but the Td hypothesis are 0. Tuning PID control parameters control system design is the core content. It is according to is controlled the process the characteristic to determine the PID controller the scaleup factor, the integration time and the differential time size. Tuning PID control parameters are many ways, summarizes has two big kinds: One is the theory of the entire titration. It mainly is rests on the system the mathematical model, the process theoretical calculation definite controller parameter. This method obtained arrives the estimated data not necessarily may straight take over the use of, but also must actually carry on the adjustment and the revision through the project. The second is tuning method, it mainly relies on the project experience, directly carries on in the control system experiment, also the method simple, is easy to grasp, is actual in the project is widely used. The PID controller parameter project tuning method, mainly has the critical ratio method, the response tune longbase method and fades the subtraction. Three methods respectively have its characteristic, its mon ground all is through the experiment, then carries on according to the project empirical formula to The controller parameter setting. But regardless of uses the controller parameter which which one method obtained arrives, all needs to carry on the final adjustment and the consummation in the actual movement. Now generally uses is the critical ratio method. Carries on the PID controller parameter as follows using This method tuning the step: (1) first in advance chooses an enough short sampling period to let the system work。3%. Chart 4 realtime fluids positions record curve 4 forever great PLC PID control system analysis brings PID the control function the FATEK programmable controller PID control and its controller or intelligent PID controller (measuring appliance) already very many, the product actual center obtained the widespread application in the project, has various PID controller product, took the domestically produced PLC enterprise, forever the great electrical machinery jointstock pany continuously will devote to the PLC research development work, will bring PID the control function the FATEK programmable controller (PLC) will be uses its closedloop control module to realize the boiler steam drum fluid position PID control, in unusual situation, when the fluid position deviation normal value will be bigger, through the PLC control system control, will be allowed fast to restore the water level, will guarantee the boiler the security stable movement. When the water monitor and the host vapor temperature control has the contradiction, may act according to the contradictory principal aspect to carry on two coordination controls. It contains for the water flow control return route and the steam drum water monitor return route two control loops, in the essence is the steam current capacity forward feed and the water level current capacity cascade system position pound control system. When steam current capacity change, in the boiler steam drum water monitor system may rapidly change the water volume for the water flow control return route to plete the coarse adjustment, then pletes the water level again by the steam drum water level regulator the thin accent. steam drums waters level PID control design merit (1) reduces the disturbance to the host return route influence, may adjust by the vice return route controller. (2) because the vice return route