Controlling a large Data Acquisition System using an industrial SCADA System

LHCb is one of the experiments currently under construction for the start-up of the Large Hadron Collider at CERN. It consists of various specific subsystems which themselves comprise a large amount of detectors requiring sophisticated readout electronics and a complex data acquisition system. To control the complete data acquisition system at the level of an expert system, an Experiment Control System is put in place, which is based on a commercial SCADA product (PVSS) and a controls Framework (JCOP) common to all experiments at LHC. We report here on the structured software layers of the whole system as well as its integration into the experiment. A focus is given on the protocols in use as well as the required hardware. The hierarchical structure which allows propagating commands down to the subsystems is explained. Via finite state machines an autorecovery scenario from error states can be defined. Before start-up, the configuration of all the registers is downloaded to the hardware via recipes depending on the type of run.