plc控制的变频电梯系统的设计(1).docx
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1、外文翻译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 type
2、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 d
3、ecisions 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 one
4、 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 sys
5、tems, the CCS tool kit EPICS and the operability between all of them.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 commercial shall not be answer
6、ed here. We try to summarize here basic functionalities of different controls approaches.Front-end Controller One of the core elements of a control system is the front-end controller. PLCs can be used to implement most of the functions to control the equipment. The disadvantage is the complicated ac
7、cess to the controls properties. For instance all of the properties of a control loop like the P, I and D parameter, but also the alarm limits and other additional properties must be addressed individually in order to identify them in the communication protocol and last not least in the display-, al
8、arm- and archive programs. In addition any kind of modifications of these embedded properties is difficult to track because two or more systems are involved. This might be one strong argument why control loops are mainly implemented on the IOC level rather than PLCs. I/O and Control Loops Complex co
9、ntrol algorithms and control loops are the domain of DCS alike control systems. The support for sets of predefined display and controls properties is essential. If not already available (like in DCS systems) such sets of generic properties are typically specified throughout a complete control system
10、 (see namespaces). Sequence/ State programs Sequence programs can run on any processor in a control system. The runtime environment depends on the relevance of the code for the control system. Programs fulfilling watchdog functions have to run on the front-end processor directly. Sequence programs f
11、or complicated startup and shutdown procedures could be run on a workstation as well. The basic functionality of a state machine can be even implemented in IEC 61131. Code generators can produce C code which can be compiled for the runtime environment. Supported Hardware The support for field buses
12、and Ethernet based I/O is a basic functionality for SCADA type systems it is commercially available from any SCADA system on the market. The integration of specific hardware with specific drivers and data conversion is the hard part in a commercial environment. Open APIs or scripting support sometim
13、es help to integrate custom hardware. If these tools are not provided for the control system it is difficult if not impossible - to integrate custom hardware. New industrial standards like OPC allow the communication with OPC aware devices and the communication between control systems. One boundary
14、condition for this kind of functionality is the underlying operating system. In the case of OPC it is bound to DCOM which is a Microsoft standard. UNIX based control systems have a hard time to get connected. Only control systems supporting multiple platforms can play a major role in a heterogeneous
15、 environments. As a result the limited support for custom- or specialized hardware may give reason for the development of a new control system.1.Graphic Synoptic displays are the advertising sign for any control system. Commercial synoptic displays come with a rich functionality and lots of special
16、features. Starting to make use of all these features one will find out that all individual properties of the graphic objects must be specified individually. Since SCADA systems must be generic they cannot foresee that an input channel does not only consist of a value but also consists of properties
17、like display ranges and alarm values. Defining all of these properties again and again can be a pretty boring job. Some systems allow to generate prototypes of graphic objects. These prototype or template graphics are complex and need a specialist to generate them. DCS or custom synoptic display pro
18、grams can make use of the common set of properties each I/O point provides. This predefined naming scheme will fill in all standard property values and thus only require to enter the record or device name into the configuration tool. A clear advantage for control systems with a notion of I/O objects
19、 rather than I/O points.2.Alarming Alarms are good candidates to distinguish between different control system architectures. Those systems which have I/O object implemented also provide alarm checking on the front-end computer. Those systems which only know about I/O points have to add alarm checkin
20、g into the I/O processing. While the I/O object approach allows to implement alarm checking in the native programming language of the front-end system, I/O point oriented systems typically have to implement this functionality in their native scripting language. This is typically less efficient and e
21、rror prone because all properties must be individually configured. This leads to a flood of properties. Not only the error states for each I/O point wind up to be individual I/O points but also the alarm limits and the alarm severity of each limit must be defined as I/O points if it is desired to be
22、 able to change their values during runtime. Besides this impact on the configuration side the processing and forwarding of alarms makes the difference between SCADA and DCS systems. Since SCADA systems inherently do not know about alarms, each alarm state must be polled either directly from the cli
23、ent application or in advanced cases from an event manager which will forward alarm states to the clients. In any case a lot of overhead for just checking alarm limits. DCS system again have the advantage that clients can either register themselves for alarm states und thus get the information forwa
24、rded or are configured to send alarmchanges to certain destinations spread around the control system. The latter case is only possible for systems which in total are configured with all the nodes taking part in the controls network. 3.Trending and Archiving Trending has become an important business
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