An automation system implemented through a communication network (R) and comprising at least: - a first programmable logic controller (A) connected to said communication network and designed to execute a first automation application (app_A), - a first set of input/output modules (E/S_A) controlled by the first programmable logic controller (A) through the communication network (R), - a second programmable logic controller (B) connected to said communication network (R) and designed to execute a second automation application (app_B), - a second set of input/output modules (E/S_B) controlled by the second programmable logic controller (B) through the communication network (R), characterized in that it comprises: - a third programmable logic controller (D), called backup programmable logic controller, connected to said communication network (R) and designed to stand in for the first programmable logic controller (A) or the second programmable logic controller (B) when taken out of service, and in that - the backup programmable logic controller (D) comprises storage means storing both the first automation application (app_A) and the second automation application (app_B), and is designed to remain inactive as long as the first programmable logic controller and the second programmable logic controller are active, and to become active and execute the first automation application (app_A) for the purpose of standing in for the first programmable logic controller (A) and controlling the first set of input/output modules (E/S_A) through said communication network only when said first programmable logic controller is taken out of service, or to execute the second automation application (app_B) for the purpose of standing in for the second programmable logic controller (B) and controlling the second set of input/output modules (E/S_B) through said communication network only when said second programmable logic controller is taken out of service. - a first programmable logic controller (A) connected to said communication network and designed to execute a first automation application (app_A), - a first set of input/output modules (E/S_A) controlled by the first programmable logic controller (A) through the communication network (R), - a second programmable logic controller (B) connected to said communication network (R) and designed to execute a second automation application (app_B), - a second set of input/output modules (E/S_B) controlled by the second programmable logic controller (B) through the communication network (R), - a third programmable logic controller (D), called backup programmable logic controller, connected to said communication network (R) and designed to stand in for the first programmable logic controller (A) or the second programmable logic controller (B) when taken out of service, and in that - the backup programmable logic controller (D) comprises storage means storing both the first automation application (app_A) and the second automation application (app_B), and is designed to remain inactive as long as the first programmable logic controller and the second programmable logic controller are active, and to become active and execute the first automation application (app_A) for the purpose of standing in for the first programmable logic controller (A) and controlling the first set of input/output modules (E/S_A) through said communication network only when said first programmable logic controller is taken out of service, or to execute the second automation application (app_B) for the purpose of standing in for the second programmable logic controller (B) and controlling the second set of input/output modules (E/S_B) through said communication network only when said second programmable logic controller is taken out of service. <EOS>