The OPERA Spectrometer Slow Control System

OPERA is a long-baseline neutrino experiment at the Gran Sasso underground laboratories (LNGS), to observe $\nu _{\tau} $ appearance in a $\nu _{\mu} $ neutrino beam produced at CERN. The detector is a structure of two super modules, each built-up of a massive lead/nuclear-emulsion target complemented by electronic detectors and a magnetic spectrometer. The two magnets are instrumented by 1000 Resistive Plate Chambers (RPCs) detectors for a total surface of about 3200 ${\rm m}^{2}$. The slow control system has been designed to monitor and control all the critical parameters for the proper functioning of the spectrometers. The different hardware (Magnet and RPC High Voltage power supplies, RPC current meters, Magnet and RPC temperature sensors, RPC timing boards) is read out via CAN bus connections by several distributed clients. The clients write the data to a relational database (PostgresSQL) which is the heart of the system: it gives persistence to the data and allows to perform correlations useful to debug possible system malfunctioning. Among the various tools (histograms and XML Configuration Managers), a controller process checks for possible failures of the system using data from the database and generates warnings/alarms for people on shift.