【正文】 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 munication 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 plex sequences as well as plex graphics. Compared with other SCADA systems PVSS es 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 overe 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 bee 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 plete 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, pressed 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 Ether (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 handler and the archiver) provides a flexible configuration scheme. At DESY the utility group has developed a set of tools to create IOC databases and alarm configuration files from Oracle. This way the controls group provides the service to maintain the EPICS tools and the IOC?s while the users can concentrate on the equipment being controlled. 2 EPICS as a DCS System Besides the basic ponents of a SCADA system EPICS also provides a full flavoured Input Output Controller (IOC). The IOC provides all of the function a DCS system requires, such as: a standard set of properties implemented in each record, built in alarm checking processed during the execution of each record。此外，在實現(xiàn)對復雜的低溫 冷藏系統(tǒng)的開閉過程中，頻率項目顯得尤為重要。但是因為 HERA 試驗原定時間是有限制的，所以技術(shù)問題和組織問題也迫使計劃提前。其核心元素叫做事件管理器。所有這些都是基本的 SCADA功能。但是，在極少數(shù)情況下，只通過商業(yè)的立場時難以回答的。所有 SCADA 系 統(tǒng)在市場商業(yè)運作中是可行的。編碼發(fā)電機可以產(chǎn)生 C 代碼。 PLC’ s 和智能 I / O 子系統(tǒng)的差別正在消失。此外，如通道歸檔和圖形顯示（ dm2k） 會 被使用。在 CERN 由聯(lián)合控制項目 [4]進行的廣泛調(diào)查促使他們做出 使用 PVSS 作為代替品的決定。這包括 D / 3，以及德國電子同步加速器研究所的集成總線 SEDAC 和 VME 的溫度轉(zhuǎn)換器。這項新技術(shù)是必需的，因為但是現(xiàn)有的硬件沒有能力來處理標準過程控制信號，如 4 至 20 毫安的電流輸入和輸出信號。 control records like PID etc.。 有必要增加接口解決總線問題并增加運算能力，以便于低溫控制。在供應(yīng)商網(wǎng)站上的最后驗收測試又出現(xiàn)了戲劇性的性能問題。它收集的數(shù)據(jù)主要是由 I/ O 設(shè)備提供。所有的配置文件（圖形工具，報警處理程序和歸檔）提供了一種靈活的配置方案。在這里，我們試圖總結(jié)不同控制方法的基本功能。配置特定驅(qū)動器和數(shù)據(jù)轉(zhuǎn)換器的集成硬件在商業(yè)環(huán)境中是一個難點。國家機器的基本功能在 IEC 61131 中得到了落實。 PLC’ s 對于分布式 I / O 已不再重要。 IOC 向客戶提供接口并采集數(shù)據(jù)。 現(xiàn)有的系統(tǒng)是由 H1 合作組的幾名成員開發(fā)的，而現(xiàn)在卻難以維持了。該項目包括安裝功能的完全更換。 引言： 80 年代早期，隨著為 HERA(HadronElektronRingAnlage)加速器安裝低溫控制系統(tǒng)，德國電子同步加速器研究所普遍開始研究過程控制。 configuration tools for the processing engine. The flexible naming scheme and the default display and alarm properties for each record ease the connection between the operator tools and the IOC?s. The flexible data acquisition supports the poll mode as well as the publish subscribe mode. The latter reduces the traffic drastically. PLC?s PLC?s provide nowadays the same rich functionality as it was known from stand alone control systems in the past. Besides the basic features like the periodic execution of a defined set of functions they also allow extensive munication over Ether including embedded servers and different sets of munication programs. Besides the munication processors, display processors can be linked to PLC?s to provide local displays which can be prised as touch panels for operator intervention and value settings. These kind of PLC?s are attractive for turn key systems which are missioned at the vendors site and later integrated into the customers control system. Intelligent I/O New developments in I/O devices allow to ?cluster? I/O in even smaller groups and connect theses clustered I/O channels directly to the control system. PLC?s are not any more necessary for distributed I/O. Simple munication processors for any kind of field buses or for Ether allow an easy integration into the existing controls infrastructure. Little local engines can run IEC 61131 programs. The differences between PLC?s and intelligent I/O subsystems fade away. FUNCTIONALITY The ever lasting question why control systems for accelerators and other highly specialized equipment are often home grown or at least developed in a collaboration but only in rare cases mercial shall not be answered here. We try to summarize here basic functionalities of different controls approaches. Frontend Controller One of the core elements of