A PID based MIMO control system of the CMS tracker thermal screen

The tracker is one of the CMS (compact muon solenoid experiment) subdetectors to be installed at the LHC (Large Hadron Collider) accelerator at CERN (European Organization for Nuclear Research). The tracker is operated at a temperature of -10 /spl deg/C in order to reduce the radiation damage on the silicon detectors; hence, an insulated environment has to be provided by means of a screen that introduces a thermal separation between the tracker and the neighbouring detection systems. The control system design includes a description of the process by means of a thermodynamic model and the electrical equivalence. The transfer function is inferred by the ratio of the temperature outside the tracker and the heat generated (which is the controlled variable). A PID (proportional integral derivative) controller has then been designed. The MIMO (multiple input multiple output) approach and the relative gain array showed that mutual interactions are negligible. The results achieved so far prove that this methodology is rigorous and effective; every step of the procedure is well defined, simplifying the debugging and updating phases. Besides, the first field tests show a good accordance of the model to the real system.