PLC外文文献翻译---工业控制系统和协同控制系统

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1、 1 INDUSTRIAL AND COLLABORATIVE CONTROL SYSTEMS - A COMPLEMENTARY SYMBIOSIS - Looking at todays control system one can find a wide variety of implementations. From pure industrial to collaborative control system (CCS) tool kits to home grown systems and any variation in-between. Decisions on the typ

2、e of implementation should be driven by technical arguments Reality shows that financial and sociological reasons form the complete picture. Any decision has its advantages and its drawbacks. Reliability, good documentation and support are arguments for industrial controls. Financial arguments drive

3、 decisions towards collaborative tools. Keeping the hands on the source code and being able to solve problems on your own and faster than industry are the argument for home grown solutions or open source solutions. The experience of many years of operations shows that which solution is the primary o

4、ne does not matter, there are always areas where at least part of the other implementations exist. As a result heterogeneous systems have to be maintained. The support for different protocols is essential. This paper describes our experience with industrial control systems, PLC controlled turn key s

5、ystems, the CCS tool kit EPICS and the operability between all of them. - INTRODUCTION Process controls in general started at DESY in the early 80th with the installation of the cryogenic control system for the accelerator HERA (Hadron-Elektron-Ring-Anlage). A new technology was necessary because th

6、e existing hardware was not capable to handle standard process controls signals like 4 to 20mA input and output signals and the software was not designed to run PID control loops at a stable repetition rate of 0.1 seconds. In addition sequence programs were necessary to implement startup and shutdow

7、n procedures for the complex cryogenic processes like cold boxes and compete compressor streets. Soon it was necessary to add interfaces to field buses and to add computing power to cryogenic controls. Since the installed D/3 system1 only provided an documented serial connection on a multibus board,

8、 the decision was made to implement a DMA connection to VME and to emulate the multibus boards functionality. The necessary computing power for temperature conversions came from a Motorola MVME 167 CPU and the field bus adapter to the in house SEDAC field bus was running on an additional MVME 162. T

9、he operating system was VxWorks and the application was the EPICS toolkit. Since this implementation was successful it was also implemented for the utility controls which were looking for a generic solution to supervise their distributed PLCs. 2 A SELECTION OF PROCESS CONTROL SYSTEMS AT DESY DCS (D/

10、3) As a result of a market survey the D/3 system from GSE was selected for the HERA cryogenic plant. The decision was fortunate because of the DCS character of the D/3. The possibility to expand the system on the display- and on the I/O side helped to solve the increasing control demands for HERA. T

11、he limiting factor for the size of the system is not the total number of I/O but the traffic on the communication network. This traffic is determined by the total amount of archived data not by the data configured in the alarm system. The technical background of this limitation is the fact that arch

12、ived data are polled from the display servers whereas the alarms are pushed to configured destinations like alarm-files, (printer) queues or displays. SCADA Systems with DCS Features (Cube) The fact that the D/3 system mentioned above had some hard coded limitations with respect to the Y2K problem w

13、as forcing us to look for an upgrade or a replacement of the existing system. As a result of a call for tender the company Orsi with their product Cube came into play 2. The project included a complete replacement of the installed functionality. This included the D/3 as well as the integration of th

14、e DESY field bus SEDAC and the temperature conversion in VME. The project started promising. But soon technical and organizational problems were pushing the schedule to its limits which were determined by the HERA shutdown scheduled at that time. The final acceptance test at the vendors site showed

15、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 complex functionality

16、of the existing D/3 system. Here it was underestimated that each digital and analog input and output channel had its 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 functio

17、nality 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 its limits. Finally the contract with Orsi was cancelled and an upgrade of the D/3 system was the only possible solution. It was finally carried

18、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) compared with heterogeneous environments for pure SCADA systems. SCADA (PVSS-II) The H1 experiment at the HERA accelerator de

19、cided to use PVSS-II for an upgrade of their slow control systems3. The existing systems were developed by several members of the H1 collaboration and were difficult to maintain. The 3 decision to use PVSS as a replacement was driven by the results of an extensive survey carried out at CERN by the J

20、oint 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)

21、 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

22、 SCADA systems PVSS comes with one basic feature: it provides a true object oriented API to the devices 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

23、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 its way to become the core application for the DESY utility group. In addition it is used whereve

24、r 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 its complete functionality. In total about 50 Input Output Controller (IOC) are operational processing about 25 thousand records

25、. 1 EPICS as a SCADA System The utility group ( water, electrical power, compressed air, heating and air conditioning) is using a variety of PLCs spread out over the whole DESY site. EPICS is used to collect the data from these PLCs over Profibus (FMS and DP) and over Ethernet (Siemens H1 and TCP).

26、The IOCs 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 defa

27、ult 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 arch

28、iver) 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 IOCs while the users can concentrate on the equipment being controlled.