What is SCADA?
Axel Daneels, Wayne Salter , IT/CO
An industrial SCADA system will be used for the development of the controls of the four LHC experiments. This paper describes the SCADA systems in terms of their architecture, their interface to the process hardware, the functionality and the application development facilities they provide. Some attention is also paid to the industrial standards to which they abide, their planned evolution as well as the potential benefits of their use.
On 20 Sept. 2000, the Finance Committee approved the proposal to negotiate a contract with ETM A.G. (Eisenstadt, Austria) for the supply of PVSS - ETM's SCADA - for developing the control systems of ALICE, ATLAS, CMS and LHCb. In addition the SCADA Working Group, that was set up by the CERN Controls Board, recommends PVSS as one of the SCADA products for the development of future control systems at CERN. These decisions are the accomplishment of around thirteen person-years (FTE) of effort - spanning over more than three years - to identify and evaluate a proper industrial control system that copes with the extreme requirements of high energy particle physics experiments such as those of the LHC. Widely used in industry for Supervisory Control and Data Acquisition of industrial processes, SCADA systems are now also penetrating the experimental physics laboratories for the controls of ancillary systems such as cooling, ventilation, power distribution, etc. More recently they were also applied for the controls of smaller size particle detectors such as the L3 muon detector and the NA48 experiment, to name just two examples at CERN. SCADA systems have made substantial progress over the recent years in terms of functionality, scalability, performance and openness such that they are an alternative to in house development even for very demanding and complex control systems as those of physics experiments. 2. What does SCADA MEAN?
SCADA stands for Supervisory Control And Data Acquisition. As the name indicates, it is not a full control system, but rather focuses on the supervisory level. As such, it is a purely software package that is positioned on top of hardware to which it is interfaced, in general via Programmable Logic Controllers (PLCs), or other commercial hardware modules. SCADA systems are used not only in industrial processes: e.g. steel making, power generation (conventional and nuclear) and distribution, chemistry, but also in some experimental facilities such as nuclear fusion. The size of such plants range from a few 1000 to several 10 thousands input/output (I/O) channels. However, SCADA systems evolve rapidly and are now penetrating the market of plants with a number of I/O channels of several 100 K: we know of two cases of near to 1 M I/O channels currently under development. SCADA systems used to run on DOS, VMS and UNIX; in recent years all SCADA vendors have moved to NT and some also to Linux. 3. Architecture
This section describes the common features of the SCADA products that have been evaluated at CERN in view of their possible application to the control systems of the LHC detectors , . 3.1 Hardware Architecture
One distinguishes two basic layers in a SCADA system: the "client layer" which caters for the man machine interaction and the "data server layer" which handles most of the process data control activities. The data servers communicate with devices in the field through process controllers. Process controllers, e.g. PLCs, are connected to the data servers either directly or via networks or fieldbuses that are proprietary (e.g. Siemens H1), or non-proprietary (e.g. Profibus). Data servers are connected to each other and to client stations via an Ethernet LAN. The data servers and client stations are NT platforms but for many products the client stations may also be W95 machines. Fig.1. shows typical hardware architecture.
Figure 1: Typical Hardware Architecture
References: Note: this article is based on a very similar one that has been published in the Proceedings of the 7th International Conference on Accelerator and Large Experimental Physics Control Systems, held in Trieste, Italy, 4 - 8 Oct. 1999.
 A.Daneels, W.Salter, "Technology Survey Summary of Study Report", IT-CO/98-08-09, CERN, Geneva 26th Aug 1998.
 A.Daneels, W.Salter, "Selection and Evaluation of Commercial SCADA Systems for the Controls of the CERN LHC Experiments", Proceedings of the 1999 International Conference on Accelerator and Large Experimental Physics Control Systems, Trieste, 1999, p.353.
 G.Baribaud et al., "Recommendations for the Use of Fieldbuses at CERN in the LHC Era", Proceedings of the 1997 International Conference on Accelerator and Large Experimental Physics Control Systems, Beijing, 1997, p.285.
 R.Barillere et al., "Results of the OPC Evaluation done within the JCOP for the Control of the LHC Experiments", Proceedings of the 1999 International Conference on Accelerator and Large Experimental Physics Control Systems, Trieste, 1999, p.511.
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