Detlef Swoboda/CERN
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The LHC experiments and the CERN IT/CO group agreed to collaborate extensively in order to conceive a common kernel for a detector control system (DCS). ALICE is participating in this effort and has based the concept of its control system architecture on the proposals for standardized communication systems, interfaces and hardware.
The control and monitoring of the detectors require the exchange of information with external systems like the LHC accelerator and technical services but also with sub-systems within the experiment, i.e. magnets, DAQ control, etc. 
The Alice experiment will include more than 10 individual detectors of different technologies and with specific operating conditions. The instrumentation required to run and control the operation of each sub-detector will include commercial and custom hardware of various standards.
It is, however, assumed that there is no fundamental difference with respect to the functional requirements for an industrial process control system. Consequently, the possibility of building the DCS with commercial hardware and software has been investigated and the design choices have been verified with prototype development.
In order to minimize the number of different communication interfaces, the architecture of the DCS for ALICE is based on a complete vertical separation between sub-detectors. This implies the absence of direct communication between equivalent functions of different sub-detectors. The resulting DCS structure of three layers is divided into the process field parameters, which include the front end hardware for monitoring and actuation, the process control level, which handles the parameters from the process field and communicates with the general supervisory and control system (SCADA).
The SCADA system will be used by each individual sub-system to monitor and control the related parameters during commissioning, maintenance and for fault detection. It will in addition manage all interactions between sub-systems. During experiment operation, the SCADA system will be used for integrated operation of all active sub-detectors and provide the data exchange with other systems like DAQ control, LHC accelerator, safety system and magnet control.
The prerequisite for this concept is the capability of all connected instrumentation to provide a common communication interface and protocol between the process control and the SCADA layer. The trend for industrial hardware to converge to public standards can be noted. It is the strategy of ALICE to use commercial hardware wherever this is reasonable and to encourage the developers of specialized instrumentation to adopt communication interfaces compatible with the present mainline.
Detailed explanation is given of the technologies which will be used for the controller level hardware and the software options and, the current development status and experience with small-scale prototypes used to verify design choices.

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The Alice experiment will include more than 10 individual detectors of different technologies and with specific operating conditions. The instrumentation required to run and control the operation of each sub-detector will include commercial and custom hardware of various standards. 
The detector control system (DCS) for the ALICE experiment will allow a hierarchical consolidation of the participating systems to obtain a fully integrated detector operation. This goal will be achieved by clearly defined interfaces between system layers. In addition, sub-detectors will continue to be able to access their equipment independently from other sub-detectors for maintenance, upgrading and debugging. The architecture will, therefore, be based on partitioning into self-contained sub-systems, which can be separately developed, maintained and operated. Horizontal communication between sub-systems will consequently be avoided. 
The DCS will use, where possible, commercial hardware components and software. 
The clear vertical separation and hierarchical structure of the system should also allow implementing of a single user interface to the experiment, which can access the DAQ control and the DCS.
The technologies which will be used for the controller level hardware and the software options are explained. Also described is the current development status and the experience to date with the small-scale prototypes that are used to verify design choices.

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