PROBLEM TO BE SOLVED: To provide a replacement method of plant monitoring controllers which allows to perform a replacement work in continuing plant operation or while stopping plant operation, and to provide a data converter to be used for the replacement. SOLUTION: Replacement of plant monitoring controllers is performed by arranging an existing plant monitoring controller and a newly installing plant monitoring controller in a line via a data converter, and connecting them to a process input/output device. Then, the existing plant monitoring controller and the newly installing plant monitoring controller perform monitoring the plant state and control to a state signal supplied via the data converter, while the newly installing plant monitoring controller uses the state signal converted to the data format suitable to the device via the data converter. Both plant monitoring controllers adjust the newly installing plant monitoring controller until the same process result is obtained to the supplied state signal. After the completion of the adjustment, the connection of the existing plant monitoring controller is disconnected. COPYRIGHT: (C)2004,JPO
