【正文】 But soon technical and organizational problems were pushing the schedule to it’s limits which were determined by the HERA shutdown scheduled at that time. The final acceptance test at the vendors site showed dramatic performance problems. Two factors could be identified as the cause of these problems. The first one was related to the under estimated CPU load of the 6th grade polynomial temperature conversion running at 1 Hz. The second one was the additional CPU load caused by the plex functionality of the existing D/3 system. Here it was underestimated that each digital and analog input and output channel had it’s own alarm limits in the D/3 system. In a SCADA like system as Cube the base functionality of a channel is to read the value and make it available to the system. Any additional functionality must be added. Last not least the load on the network for polling all the alarm limits – typically for a SCADA system – was also driving the network to it’s limits. Finally the contract with Orosi was canceled and an upgrade of the D/3 system was the only possible solution. It was finally carried out in march 2003.In any case it should be mentioned that the Cube approach had the advantage of a homogeneous configuration environment (for the Cube front end controllers) – pared with heterogeneous environments for ‘pure’ SCADA systems.SCADA (PVSSII)The H1 experiment at the HERA accelerator decided to use PVSSII 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 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 Profuse (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 (ale) of the EPICS toolkit. In addition tools like the channel archive and the graphic display (dm2k) are used. The default name resolution (by UDP broadcast) and the directory server (name server) are used to connectclient 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 archive) 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 flavored 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。而這一切，很大程度上歸功于我的指導(dǎo)老師楊文方老師，在此，我對(duì)我的指導(dǎo)老師楊老師表示真摯的感謝！楊老師在平時(shí)中對(duì)我們非常認(rèn)真負(fù)責(zé)，給我們提供了很大的幫助，和我們畢業(yè)論文的完成有著密切的關(guān)系。這其中，雖然我遇到了很多問題，但通過查閱相關(guān)資料、請(qǐng)教老師和與同學(xué)討論將這些問題一一解決，從而使我對(duì)大學(xué)三年所學(xué)到得知識(shí)有了進(jìn)一步的加深和拓展，并且學(xué)會(huì)了西門子S7200是如何在溫度控制中應(yīng)用的，相信這一定會(huì)對(duì)以后走上工作崗位的我有很大的幫助。③模塊化程序設(shè)計(jì)，便于調(diào)試，并且方便功能的改進(jìn)。用PLC控制除了能解決以上問題以外，還具有以下特點(diǎn)： ①控制條理清楚，接線簡(jiǎn)單明了。針對(duì)大部分加熱鍋爐來說本系統(tǒng)將是一個(gè)比較理想的溫控系統(tǒng)。往MPI網(wǎng)添加一個(gè)新節(jié)點(diǎn)時(shí)，應(yīng)該切斷MPI網(wǎng)的電源?！?2Mbit/s，只有能夠設(shè)置為PROFIBUS 接口的MPI網(wǎng)絡(luò)才支持12Mbit/s的通信速率。MPI是多點(diǎn)通信接口（Multi plain Interface）的簡(jiǎn)稱。不同的獨(dú)立系統(tǒng)有傳輸線路互相交換數(shù)據(jù)便是通信，構(gòu)成整個(gè)通信的線路稱之為網(wǎng)絡(luò)，通信的獨(dú)立系統(tǒng)可以是計(jì)算機(jī)、PLC或其他有數(shù)據(jù)通信功能的數(shù)字設(shè)備，稱為DTE（Data Terminal Equipment)。控制程序流程圖如圖42所示：開始系統(tǒng)初始化綠燈亮，系統(tǒng)運(yùn)行取實(shí)際溫度變量TT是否滿足條件 YN PID調(diào)節(jié)Y調(diào)節(jié)是否成功 N紅燈/黃燈亮，喇叭響 圖42 控制程序流程圖 通信系統(tǒng)隨著計(jì)算機(jī)網(wǎng)絡(luò)通信技術(shù)的發(fā)展，自動(dòng)控制方式由傳統(tǒng)的集中控制向多級(jí)分布式方向發(fā)展，PLC的通信和聯(lián)網(wǎng)功能也越來越強(qiáng)。 程序設(shè)計(jì)本設(shè)計(jì)是鍋爐控制，以溫度控制為主，主要是控制鍋爐內(nèi)水的溫度達(dá)到控制溫度的目的。（3）系統(tǒng)診斷①快速瀏覽CPU的數(shù)據(jù)和用戶程序在運(yùn)行中的故障原因。（2）通信組態(tài)① 網(wǎng)絡(luò)連接的組態(tài)和顯示；② 設(shè)置用MPI或者PROFIBUSDP連接的設(shè)備之間的周期性數(shù)據(jù)傳送的參數(shù)。③ 模塊的參數(shù)設(shè)置。 7的硬件組態(tài)與診斷功能（1）硬件組態(tài)① 系統(tǒng)組態(tài)：選擇硬件機(jī)架，模塊分配給機(jī)架中希望的插槽。（4）STEP7的幫助功能按FI鍵便可以得到與它們有關(guān)的在線幫助。（2）符號(hào)表編輯器（3）增強(qiáng)的測(cè)試和服務(wù)功能設(shè)置斷點(diǎn)、強(qiáng)制輸入和輸出、多CPU運(yùn)行(僅限于57一400)，重新布線、顯示交叉參考表、狀態(tài)功能、.直接下載和調(diào)試塊、.同時(shí)監(jiān)測(cè)幾個(gè)塊的狀態(tài)等。（1）編程語(yǔ)言3種基本的編程語(yǔ)言:梯形圖(LAD)、功能塊圖(FBD)和語(yǔ)句表(STL)。ST