PROCESS CONTROLLER OF MULTI-VARIABLE SYSTEM

PURPOSE:To improve the stability for the transient response properties of the liquid level when the disturbance occurs, by combining a modern control with controls of P (proportion), I (integration) and D (differentiation) respectively and enabling the handling of >=2 operation quantities at one time. CONSTITUTION:The liquid level signal of a liquid level detector 37 is compared with the set liquid level (l) through a deviation operator 38 to obtain the liquid level deviation signal. This deviation signal is fed to a stage variable feedback controller 39 directly via an integrator 40. The controller 39 performs an operation to minimize both liquid level deviation signal and deviation integrating signal and obtains the operation quantity. The controller 39 executes the 1-input/1- output system control through a controller 41 with a range of control including the controller 39 in order to decide an optimum liquid level control system in which the supplied flow rate of liquid is defined as the disturbance and the flow rate of liquid is defined as the disturbance and the flow rate of heated steam defined as the operation quantity respectively. In such way, a simultaneous operation is possible for both heated steam flow rate and supplied liquid flow rate during a transient change.