AbstractRFX employs a centralized approach to the tasks of control, monitoring, data acquisition and machine protection. In this paper we describe the requirements, the structure, the components, and the operation of the corresponding systems of RFX.To guarantee a high degree of reliability, a strict subdivision has been imposed from the very start, between the control, monitoring and data acquisition system SIGMA (“sistema di gestione, monitoraggio ed acquisizione dati”) and the global fast machine protection system SGPR (“sistema generale di protezione rapida”).SIGMA has been designed for the following signals: about 5000 slow, mostly digital, signals, which provide non-shot-related information from the plant and commands to the plant, and about 1000 channels of fast (2 kHz–1 MHz), shot-related data from the plant, which produce up to 20 Mbytes of data per shot. In addition, fast plant-wide timing signals (precision better than 10 μs) have to be provided.SIGMA employs two distinct technologies: industrial-type programmable controllers (PLCs) handle the slow signals; a centralized VAX-VMS computer cluster with front end according to the CAMAC standard takes care of the fast system components. The CAMAC-based system covers both the fast data acquisition and the timing requirements. Workstations are used as operator consoles for the fast part of the system; personal computers are used as consoles to the PLCs. All components of the system communicate via a single, fibre optic Ethernet. A single PLC acts as supervisor of the entire shot sequence.The PLCs are programmed in an assembler-type language at the lower level and in a language according to the grafcet standard at the higher level. The PC-based consoles employ a commercial package for plant monitoring and control. The VAX-based systems run a purpose-developed software package, known as mds-plus, which provides integrated operation of timing and fast data acquisition. mds-plus is a joint software development with the MIT Plasma Fusion Center and the Los Alamos National Laboratory.The machine protection system SGPR has to deal with up to 50 possible requests for fast intervention and to distribute the corresponding command signals with an overall reaction time of 1 ms. SGPR is based on dedicated hardware which implements decision logic for intervention requests of four different urgency levels. It despatches the intervention commands to the corresponding protective devices in the various local units. All signal paths and the decision logic are duplicated with continuous automatic checks for integrity. Single transmission from the sensors and to the protective devices is by duplicated fibre optic lines with continuous self-test.Operation of RFX is under complete control of SIGMA from a single, central control room. It houses the supervisor console, all subsystem consoles (PCs and workstations) as well as some additional equipment (SGPR display, printers, television equipment, etc.). Shot execution follows a strict sequence, which is implemented as a unique state machine on all subsystems (PLCs and VAX computers). The supervisor console is the operator interface to the system-wide state machine which controls the shot sequence.The performance of the system is considered satisfactory with scope for further improvement. The cycle time of the PLCs is below 200 ms; the picture update time on the PC-based consoles is below 3 s. The fast system acquires all channels (at the moment around 15 Mbytes of uncompressed data per shot) within around 10 min. This time includes the display of several hundreds of measurement channels on different workstations in the central control room, and the automatic execution of a number of data analysis programs.