Abstract: The setting of parameters of signal quality bit will cause the failure on demand or spurious failure of digital control system(DCS) in nuclear power plant. To solve this problem, limitations of general scheme based on the current design status are analyzed. A new design method is proposed. The function of DCS is confirmed by the status of nuclear power plant. It not only solves the problems caused by quality bit setting, but also simplifies the operator’s operation to a certain extent. It improves the safety and availability of the nuclear power plant and promotes intelligence and unmanned developments in the nuclear power plant. Thermal physical parameters in the steady state and manual operation in the process of state transition are used to identify the state of the nuclear power plant. It helps DCS to perform expected functions. And it can avoid the occurrence of unexpected events.

Key words: quality bit; digital control system (DCS); status of nuclear power plant