nfiguration environment (for the Cube front end controllers) - compared with heterogeneous environments for 'pure' SCADA systems.
SCADA (PVSS-II)
The H1 experiment at the HERA accelerator decided to use PVSS-II for an upgrade of their slow control systems[3]. The existing systems were developed by several members of the H1 collaboration and were difficult to maintain. The decision to use PVSS as a replacement was driven by the results of an extensive survey carried out at CERN by the Joint Controls Project [4]. PVSS is a 'pure' Supervisory And Data Acquisition System (SCADA). It provides a set of drivers for several field buses and generic socket libraries to implement communication over TCP/IP. The core element is the so called event manager. It collects the data (mostly by polling) from the I/O devices and provides an event service to the attached management services like: control manager, database manager, user interface, API manager and the built in HTTP server. The PVSS scripting library allows to implement complex sequences as well as complex graphics. Compared with other SCADA systems PVSS comes with one basic feature: it provides a true object oriented API to the device's data.
One major disadvantage of SCADA systems is the fact that two databases, the one for the PLC and the one for the SCADA system must be maintained. Integrated environments try to overcome this restriction.
EPICS
EPICS has emerged at DESY from a problem solver to a fully integrated control system. Starting from the data collector and number cruncher for the cryogenic control system, EPICS made it's way to become the core application for the DESY utility group. In addition it is used wherever data is available through VME boards or by means of Industry Pack (IP) modules. For those cryogenic systems which are not controlled by the D/3 system EPICS is used with it's complete functionality. In total about 50 Input Output Controller (IOC) are operational processing about 25 thousand records.
1 EPICS as a SCADA System
The utility group ( water, electrical power, compressed air, heating and air conditioning) is using a variety of PLC's spread out over the whole DESY site. EPICS is used to collect the data from these PLC's over Profibus (FMS and DP) and over Ethernet (Siemens H1 and TCP). The IOC's provide the interfaces to the buses and collect the data. The built in alarm checking of the EPICS records is used to store and forward alarm states to the alarm handler (alh) of the EPICS toolkit. In addition tools like the channel archiver and the graphic display (dm2k) are used. The default name resolution (by UDP broadcast) and the directory server (name server) are used to connect
client and server applications over TCP. All of these are basically SCADA functions.
The textual representation of all configuration files ( for the IOC, the graphic tool, the alarm handl