Detector Control System for the ATLAS Transition Radiation Tracker - architecture, development techniques and operational issues

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three sub-systems of the ATLAS Inner Detector at the Large Hadron Collider at CERN. With ~350000 thin-wall drift tube proportional counters (straws) filled with stable active gas mixture and high voltage biased it provides precise quasi continuous tracking and particles identification.
The Detector Control System (DCS) running on 11 computers as PVSS (industrial SCADA) projects and fully integrated with the ATLAS DCS enables safe, coherent and efficient operation of the TRT.
Standard industrial and custom developed server applications and protocols are used for reading detector hardware parameters. Higher level control system layers based on the CERN JCOP framework allow for automatic control procedures, efficient error recognition and handling and provide a synchronization mechanism with the ATLAS data acquisition system. Different data bases are used to store the detector online parameters, the configuration parameters and replicate a subset of them used to flag data quality for physics reconstruction.
High voltage settings of ~2500 channels are periodically modified at distinct detector topological regions by closed-loop regulation mechanism to ensure a constant gaseous gain independent of drifts of atmospheric pressure, local detector temperatures and gas mixture composition.
Low voltage system powers front-end electronics via ~1700 channels. Special algorithms provide fine tuning procedures for detector-wide discrimination threshold equalization to guarantee uniform noise figure for whole detector.
Detector, cooling system and electronics temperatures are continuously monitored by ~3000 temperature sensors, as well as active gas parameters and infrastructure (cooling system, racks, VME crates and LV hardware interlock system).
The DCS system has been operational since the beginning of LHC operation and operates the detector in a very stable and reliable way.
This contribution presents system architecture, professional tools and techniques used during the development, some operational issues and current status.