シーケンス制御系の設計修正に伴う機能変化の検証

Abstract

The design of industrial sequence control systems, such as power plants, is often carried out by the modification of an old design. The paper describes a new method to verify whether the functional change caused by the modification may influence the unmodified portion or not.Assume that a portion A of an original system is modified to A', and the remaining unmodified portion is B. The portion A and the modified portion A' include a controller part and controlled devices.Both A and A' are converted into timed petri nets: TPN (A) and TRN (A'). TPN (A) and TPN (A') have inputs I which are signals from B and outputs O which are signals to B. As B is affected by the outputs O, the change of outputs O is examined.In order to check the difference between A and A', TPN (A) and TPN (A') are converted into automata with the reachability tree. In this conversion, only stable markings, in which no transition is ‘firable’ if the inputs (I) never change, are selected as the states of the automata. The inputs, the state transitions and the outputs of the automata are obtained from the inputs (I), the change of markings and the outputs (O) of TPN (A) and TPN (A'), respectively.The paper shows that the functional change is easy to verify by comparing the automata's output functions of the old design and the new one. Besides, the automata are used to generate test inputs to check the functional change.