Abstract: A plant control system includes at least one control apparatus, and an engineering apparatus for changing a security state of the control apparatus. The control apparatus includes: a security management part for accepting a security level change request downloaded from the engineering apparatus and changing a security level of the control apparatus by referring to a password held by the control apparatus; and a change permission part for permitting a change in the security level by the security management part.

Abstract: A safety control system includes a plurality of safety control stations connected to a control bus to communicate with each other and with a distributed control system including a plurality of control stations connected to the control bus, wherein each of the plurality of safety control stations has an interface through which each of the plurality of safety control stations is connected to the control bus for transmitting own data of each of the plurality of safety control stations to all other safety control stations by broadcasting at a fixed cycle via the control bus and for receiving by each safety control station transmitted data from all other safety control stations, and wherein the interface implements a safety layer used to generate and diagnose safety information.

Abstract: A safety control system includes a plurality of safety control stations connected to a control bus to communicate with other, and a link transmission communicating means having a function of transmitting own data to other safety control station at a fixed cycle via the control bus every safety control station and also receiving transmitted data from other safety control station.

Abstract: A plant control system includes at least one control apparatus, and an engineering apparatus for changing a security state of the control apparatus. The control apparatus includes: a security management part for accepting a security level change request downloaded from the engineering apparatus and changing a security level of the control apparatus by referring to a password held by the control apparatus; and a change permission part for permitting a change in the security level by the security management part.