A data acquisition and experimental control system for the OPAL experiment at the CERN LEP collider

The OPAL data acquisition (DAQ) system is a distributed multi-processor environment for the collection, processing and data-flow management of the signal generated by 14 independent subdetectors whose purpose is to record e+e- interactions near and above the Zo mass. The diversity of detection techniques is reflected b the wide range of front-end read-out hardware implemented using the CAMAC, FASTBUS, and VME standards. To facilitate the management of the data from the subdetectors by utilising standard software throughout the system, a standard architecture was imposed at the Local System Crate (LSC) and above thereby providing a uniform interface with the central OPAL DAQ chain. Each LSC consists of a VME crate containing a standard arrangement of commercial and purpose-built modules including 68000 series CPU's running the OS-9 operating system. Triggering and data-flow beyond the LSC is managed by similar VME crates and bulk data transfer from the detector to the OPAL On-line VAX 8700 uses an optical fibre link. The raw data are recorded onto IBM 3480 cartridges from the VAX for subsequent off-line processing. (orig.)