第4章-COMPUTER-CONTROL-SYSTEMS.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,2014-9-17,#,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,2014-9-17,#,CHAPTER 4,COMPUTER CONTROL SYSTEMS,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Consider the level control system shown in schematic form in Figure 4.1.1.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.2 Block diagram of level control system.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.3 Block diagram for realisation of analogue control loop.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Assume that the dp cells output is one of a number of 4,20 mA channels handled by the card,the circuit for which is as depicted in Figure 4.1.4.,4.1.1 Input Interface,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,The following equation is used universally for linear scaling.For brevity,a 10-bit A/D converter is assumed:,4.1.2 Input Scaling,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,A typical algorithm,written in structured text,for implementing it would be:,4.1.2 Input Scaling,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,The most common type of filter is the simple first order lag,which is of the form:,4.1.3 Filtering,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Using Eulers first order explicit method of numerical integration:,4.1.3 Filtering,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,A typical algorithm for implementing the filter would be,4.1.3 Filtering,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,The PID function block of Figure 4.1.3 represents the routine for a 3-term controller.It operates on the output of the FIL function block.In particular,a discretised version of the absolute form of the classical PID controller with derivative feedback was developed.Typical algorithms,written in structured text,for implementing this controller would be,4.1.4 PID Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,The following equation is used extensively for output scaling.The range of the controller output is normally 0,100%and,for brevity,an 8-bit A/D converter is assumed:,4.1.5 Output Scaling,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,The output q0 is stored in the database as a bit pattern.The algorithm used for the output scaling is typically,4.1.5 Output Scaling,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.5 Analogue output channel.,4.1.6 Output Interface,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.6 depicts the construction of the quasi analogue signal.,4.1.6 Output Interface,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.6 depicts the construction of the quasi analogue signal.,4.1.6 Output Interface,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.1 Fundamentals of Computer Control,Figure 4.1.6 depicts the construction of the quasi analogue signal.,4.1.6 Output Interface,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.1 Advisory control system.,4.2.1 Advisory Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.2 Supervisory control system.,4.2.2 Supervisory Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.3 Direct digital control(DDC)system.,4.2.3 Direct Digital Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.4 Integrated control system(ICS).,4.2.4 Integrated Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.5 Dual integrated control system.,4.2.4 Integrated Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.6 Multi-drop type of distributed control system(DCS).,4.2.5 Distributed Control,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.2 Computer Control System Architecture,Figure 4.2.7 Programmable logic controller(PIC)system.,4.2.6 Programmable Logic Controllers,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,The first programmable controller,introduced in 1970,was developed in response to a demand from General Motors for a solid-state system that had the flexibility of a computer,yet could be programmed and maintained by plant engineers and technicians.These early programmable controllers took up less space than the relays,counters,timers,and other control components they replaced,and they offered much greater flexibility in terms of their re-programming capability(Figure 4.3.1).,4.3.1 Programmable Controllers Defined,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,Figure 4.3.1 Basic PLC components.,4.3.1 Programmable Controllers Defined,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,The initial programming language,based on the ladder diagrams and electrical symbols commonly used by electricians,was key to industry acceptance of the programmable controller(Figure 4.3.2).,4.3.1 Programmable Controllers Defined,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,The success of the programmable controller has spurred innovation in a number of competing technologies.Below is a brief review of these technologies,which may in some cases be successfully applied as an alternative to programmable controllers.,4.3.2 Alternatives to Programmable Controllers,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,PC-Based Control,Distributed Control System,Relay-Based Control,Single-Board Controllers,4.3.2 Alternatives to Programmable Controllers,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,Figure 4.3.3 Relay logic control,4.3.2 Alternatives to Programmable Controllers,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.3 Programmable Controllers,Table 4.3.1 Evaluation of control methods for the application.,4.3.2 Alternatives to Programmable Controllers,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.4 Distributed Control System(DCS),Figure 4.4.1 Multi-drop type of distributed control system(DCS).,4.4.1 Introduction and Architecture of DCS,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.4 Distributed Control System(DCS),The operators control station(OCS)is a term which refers to the hardware used by an operator.It typically consists of a colour graphics VDU,a keyboard,and some processor capacity for handling the operators control program(OCP).In essence the OCP is the software with which the operator interacts.It enables access to the systems database and handles the various displays.,4.4.2 Operator Station,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.4 Distributed Control System(DCS),Figure 4.4.2 Typical card,rack and frame structure.,4.4.3 Physical Structure,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.4 Distributed Control System(DCS),Figure 4.4.3 Connections between cards and back plane.,4.4.3 Physical Structure,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.4 Distributed Control System(DCS),4.4.4 Card Types,I/O cards,1,System cards,2,Coms cards,3,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.1 Messages,Figure.4.5.1 IEEE802 type of frame.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.2 Local Area Networks,The most commonly used type of communications system is the local area network(LAN).The IEEE has developed standards for LANs which are generally adhered to by systems suppliers.The three LANs of particular interest for process control purposes are Ethernet,token bus and token ring.The essential difference between them is the method by which messages on the LAN,known as traffic,are controlled.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.3 Token Systems,The token bus is a LAN,often referred to as a highway,to which the IEEE 802.4 standard applies.Token bus topology,which is essentially the same as for Ethernet,has an open structure as depicted in Figure 4.5.2.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.3 Token Systems,Token ring is another type of LAN to which the IEEE 802.5 standard applies.It is essentially the same as token bus,except that the ends of the bus are physically connected to form a ring,as depicted in Figure 4.5.3.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.4 Protocols,The open systems interconnection(OSI)protocol,known as the OSI model,published in ISO 7498-1(1995)for reference purposes,has seven layers whose functionality is as summarised in Table 4.5.1.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.5 Network Access,Access concerns gaining control of the network in order to transmit messages.The three layered access model of IEEE 802 is depicted in Figure 4.5.4 and relates to both Ethernet and token bus types of network.,CHAPTER 4,COMPUTER CONTROL SYSTEMS,4.5 Computer Control System Communications(1),4.5.5 Network Access,Node management provides the functionality that fragments and/or reconstructs messages into/from frames of data which are of the correct length for transmission.The three layers are:,Logic link control(LLC)layer:,this puts the source and destination addresses,the data to be transmitted and the checksum into the frame.,Media access control(MAC)layer:,this handles collisions and imposes random waits for Ethernet type LANs,or handles the token/flags and enables repeats for token bus type LANs.,Physical layer:,this handles the encoding and decoding of data,if necessary,and the transmission and/or receipt of messages between nodes.,