DCS ENTRY TO MASTER THE DETAILED TUTORIAL, YOU ARE WORTH COLLECTING!
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www.plc-module.com1.DCS INTRODUCTION
Since the advent of DCS in 1975,there have been about three major changes.In the 1970s,the hardware,operating system and monitoring software of the operation station were all dedicated,developed by the DCS manufacturers themselves,and there was no dynamic flow chart.The communication network was basically polling;In the 1980s,it was different.The communication network mostly used token mode;In the 1990s,universal systems appeared in the operation stations.At the end of the 1990s,some communication networks complied with TCP/IP protocols,and some began to use Ethernet.In general,the changes are mainly reflected in I/O boards,operation stations and communication networks.The change of controller is relatively small.The operation station mainly changes from a dedicated computer to a general-purpose computer,such as the application of PC and minicomputer.But at present,its operating system is generally UNIX,and some small systems are NT.Compared with UNIX,its stability is better,and NT has a crash.I/O board is mainly reflected in the introduction of field bus into DCS system.
Theoretically,a DCS system can be used in various industries,but each industry has its own particularity,so DCS also has different branches,sometimes due to the limitations of the process knowledge of DCS manufacturers'technicians.For example,HONEYWELL is familiar with petrochemical industry,and its products are widely used in the petrochemical industry,while BAILEY's products are widely used in the power industry.When selecting DCS,users should pay attention to whether their technicians are familiar with the production process;Then it depends on how large the system is suitable for,for example,the NT operating system is suitable for smaller systems;The last is the price.The prices of different combinations will vary greatly.The price of domestic DCS system is at least half lower than that of imported DCS,and the price of spare parts is much lower.
DCS consists of four parts:I/O board,controller,operation station and communication network.
The technical level of the I/O board and the DCS manufacturers in the world are not far different.If there are some differences,it is the number of algorithms in the controller and the combination of algorithms.The difference between the I/O board is that some have intelligence and some have no,but the controller must complete a cycle in one second to read all I/O data;The operating stations are quite different.The main differences are PC or minicomputer,UNIX or NT operating system,and special or general monitoring software.When the operating system and monitoring software are well coordinated,the crash can be reduced;The biggest difference is the communication network,the worst is the polling method,and the best is the exception reporting method.According to our experiment,the speed is seven or eight times different.
2.DCS GENERAL OPERATION STATION
DCS system includes three parts:controller with I/O components,communication network and human-machine interface.Man machine interface includes operation station,engineer station and history station.The controller I/O components are connected with the production process,and the operation station is connected with people.The communication network connects these two parts into a system.Therefore,the operation station is an important part of DCS.The engineer station configures the controller and operation station,and the history station records the historical data of the production process.The human-computer interface developed in recent years also has a dynamic data server.
A DCS system controller and I/O components can normally operate for 16-20 years,while the operation station is relatively easy to be damaged due to its moving parts,such as hard disk,keyboard,CRT,floppy drive,etc.The probability of failure is relatively high after 6-8 years of operation,so there are many updates of the operation station during DCS operation.The controller of DCS has little change.Its changes are shown in the arrangement of control algorithms,the number of control algorithms,the number of I/O points accessed and the size of memory.Operating systems are generally dedicated.Operating stations have changed a lot.Before the 1980s,operating stations generally did not have hard disks and dynamic flow charts,and the number of labels that could be displayed was relatively small,such as 500 labels(labels refer to the logical relationship between AI,DI,loops,switching values,etc.).In the 1980s,operating stations that could display 5000 labels appeared,and in the 1990s,operating stations that could display 30,000 labels appeared.At the same time,there also appeared general display software running on Microsoft's NT general platform.At first,the general software was only used on the operation station of PLC,and later it was gradually applied to DCS.Its number of tags can reach 10000 or more.
The development process of DCS operation station(taking BAILEY operation station as an example)is as follows:
1、In the early 1980s,the operating station of the N90 was the OIU series.At that time,it had no hard disk and no dynamic flow chart,with 500 labels.Later,hard disks and flow charts were added,with 1400-5000 labels.In the mid-1980s,the MCS series was launched with 10000 labels,especially MCS PULS,which is a SCSI interface and can have 30000 label points.At that time,it was in a leading position in the DCS market.In 1986,BAILEY products accounted for 1/3 of the world DCS market.By 1988,a total of 8500 sets were operating in various countries.In the 1990s,the DCS market was fiercely contested,and BAILEY was not as brilliant in technology or sales as it was in the 1980s.So BAILEY wants to rebuild its brilliance by purchasing FISCHER&PORTER,HARTMANN&BRAUN and other companies to sell their systems.
The controller and communication network of BAILEY are relatively good,but on the operation station,BAILEY can not compare with its competitors.The latest operation station of BAILEY is Conductor NT based on Windows NT and general microcomputer.In fact,this operation station is not developed for INFI-90.It is the operation station of FISCHER-PORTER system 6,which is built by embedding its monitoring software into the driver software for communication with INFI-90.As the sales volume is not large,there are few opportunities for running in,there are many problems,and the crash is serious.OIS40 series operation stations run on the VMS platform of DEC.In fact,it still developed a driver software to communicate with VMS on the MTOS operating system platform of the MCS operating station,because OIU and MCS in the 1980s had stopped selling at the end of the 1980s.BAILEY only sells OIS20 series and OIS40 series.
OIS20 series was introduced to the market in the early 1990s.It is essentially MCS,but it can communicate with INFI-90.Its development and manufacturing costs are relatively low,and its performance is relatively good.The auxiliary station of OIS20 series does not use the network to transmit information,but adds an additional video card to the main station to realize the auxiliary station.Later,due to the high maintenance cost,hard disks and floppy disks were difficult to buy,and users complained badly.
Following OIS20 series,BAILEY Company introduced OIS41 and OIS42,and added Ethernet cards between operation stations to form a backdoor network,which can realize printer sharing.The ability to transmit graphics to different master stations has also been enhanced,which also provides users with space to develop printing systems.The performance of OIS40,OIS41,and OIS42 hosts is poor,so the performance of the operation station is not significantly improved.The performance was not improved until OIS43 Alpha chip appeared.At the same time,Canadian BAILEY Company has developed PCV,which is a PC based operating station and uses QNX operating system.Because of its small number of labels,low price and stable operation,it is suitable for small systems.This is the OIS10 series of BAILEY.Before version 5,only text without graphics.After version 5,there are both text and graphics.ARCNET is used for networking between the back doors of OIS11 operation station.OIS12 can be networked with ARCNET or Ethernet.
Because of the complex structure of OIS40 series software,the price is high.More importantly,DEC was merged by COMPAQ,and Alpha 255/233 stopped production,which undoubtedly made it worse for BAILEY and its users.
2、In the mid-1980s,because the development of PLC operation stations was not very successful,some software companies developed general monitoring software,which was soon adopted by PLC manufacturers.For example,FIX,INTOUCH,ONSPEC,etc.(there are hundreds in total).Because of the good market prospects,software developers have developed many PLC driver software.In the 1990s,DCS driver software was developed.The first to use general industrial control monitoring software is MOORE's APEC system,which can use both INTOUCH and FIX.Since the INFI-90 system has not introduced an excellent operation station in the 1990s,PREVISE has introduced the OPsCon operation station.
The OPsCon operating station runs on the PC hardware platform and NT operating system,uses FIX as the monitoring software,and develops the corresponding driver software that can communicate with various DCS,with 10,000 tags.Because FIX software has sold 90000 sets all over the world,it runs well with various PLC,DCS and NT systems.This kind of operation station can be used on a variety of PLC and DCS operation stations.There have been thousands of applications on INFI-90 system.For example,a paper mill in New Zealand used to operate the PRODUCT NT,but later it switched to OPsCon.
The appearance of general operation station brings the following convenience to DCS users:
1.There is no need to worry about whether the original DCS manufacturer has closed down or merged,whether this type of product has stopped production,and whether spare parts can be found.
2.Due to the wide application scope of the general operation station,the relative production volume is large,and the cost is reduced,the user's expenses can be saved.Maintenance costs are also relatively low.
3.It is simpler to use a general system than various special systems,and users can also reduce the cost of personnel training.
4.Easy to update and upgrade.
5.It is open and easy to establish production management information system.
Therefore,the general operation station is the development direction of DCS.
3.SEVERAL PROBLEMS IN DCS SELECTION
After the controlled object is determined,what kind of control system to choose becomes an important problem.It is mainly considered according to the project scale and investment budget.The control system composed of digital technology based DCS system and early analog instruments has little difference in essence from the implementation of the project.The project scale and investment budget are mainly considered.However,compared with analog instruments,DCS is more complex and has higher technical requirements.Let me talk about several problems in the selection of DCS system.Theoretically,DCS can be used in different processes.It is universal.However,DCS manufacturers are specialized in a certain field.For example,HOMEYWELL is mainly used in the petrochemical sector,BAILEY's N90 and INFI90 are mainly used in the power system,ROSEMOUNT's RS3Δ-V is mostly used in chemical systems.However,it cannot be denied that different process processes will have some special requirements,such as:power plants must have power regulation equipment and SOE,petrochemical departments must have selective control,cement industry must have large pure lag control compensation,etc.These factors must also be considered when selecting models.
The second point is economy,which should be considered from the perspective of DCS price and expected benefits.DCS is made in China and imported.For the same grade,imported DCS has stronger control function and some advanced control algorithms,such as Smith prediction,three-dimensional matrix calculation,etc.The price of domestic DCS is much lower than that of imported DCS,which can also meet the technical requirements.From the perspective of structure,there is not much difference between the manufacturers of DCS controllers abroad,the preset algorithm of the controllers is slightly different,and the connection mode between the controllers and I/O boards is also different.The operating stations are quite different.Some are PC based,others are minicomputer based,and UNIX type systems are generally selected as operating systems.The price of minicomputers is much higher than that of PCs,and the price of imported minicomputer operation stations is more than 40000 dollars,and many models have been discontinued(such as the VAX machines andαMachine).The operating station of PC is less than 30000 dollars.Its operating system is NT,and its stability is not as good as UNIX.The interface of the minicomputer adopts SCSI,and the transmission rate is as much as 8 times that of the serial.If the NT operating system is used as the operating station,the number of points should be less.Otherwise,the system will crash frequently.The domestic PC is much cheaper.If the PC operating station is used,the latest model can be used.The operators should be much more familiar with the installation,debugging,networking and development of software.The monitoring software can be either special or general.The general monitoring software has better openness.Users should choose to use it according to the scale and budget of the project.
The reason why DCS is expensive is that in addition to the above reasons,there is also the power system of the controller,which usually uses redundant power supply.The introduction of power supply and heat dissipation are the main reasons for the high price.Each DCS system is quite different in this respect.
The communication network connecting the controller and the operation station should also be considered.If the general Ethernet is used,the price of the network card is very low,and the dedicated network interface is very expensive,up to$20000.
Therefore,the economy is related to many factors.Sometimes a foreign businessman offers you a lower price,which actually changes the structure without giving you any preferential treatment,or even increases his profits.At this time,it is advisable to contact similar units in China and consult experienced experts.
The third point is the technical strength of the contractor,that is,which process and DCS the contractor is familiar with.For example,if a contractor who often works as a chemical control system works as a rolling control system,he is not familiar with looper control,crimp control and tension control,and will not do a good job.If the contractor is not familiar with DCS itself,the controller will crash if it is too large.Many factories have purchased DCS systems from different manufacturers,which we call the"Eight Nations Alliance"status.At this time,it is more important to select a unit with strong technical strength to focus on the general management,rather than a foreign manufacturer as the contractor.
The fourth point is after-sales service.Foreign manufacturers usually supply accessories and spare parts at high prices and cannot provide them in time.DCS users should choose manufacturers with strong strength,strong technical force and good domestic technical support.With the rapid development of computer technology,DCS manufacturers will continue to update their products.The compatibility between old and new products is good.Some manufacturers are not compatible with old and new systems,causing great losses when upgrading systems.The DCS manufacturers in China provide timely accessories and spare parts,and the after-sales service is also good.
The fifth point is about the progressiveness technology of DCS,which means that the system has adopted the latest proven technology and has a bright future and vitality,including the openness and interconnection of DCS system,the application of field bus,the support of third-party software,etc.One thing to note here is that in order to occupy the market,some manufacturers have pushed some immature products to the third world.For example,five or six years ago,DCS lacked small systems,and some manufacturers pushed immature small systems to users.As a result,more than 270 sets of systems have been retired in advance.As early as 1983,the DCS promoted by a foreign company,when the power supply failed and was restored,the output of the controller was arbitrary.At this time,the position of the valve was very dangerous.This product could not be delivered,but it was sold to our country.As a result,the buyer basically did not operate.
In a word,DCS has been used for more than 20 years since the seventy-five years,and its reliability can basically meet the requirements.When establishing the system,model selection is a very important link.We not only mainly consider the project scale and investment budget,but also consider a series of other factors.Whether the model selection is appropriate often determines the future fate of the system from the beginning,so we must not be careless.
4.DCS DYNAMIC DATA SERVER
DCS system belongs to basic automation,while MIS system focuses on office automation.There is a big difference in the speed of reflection between the two.DCS belongs to the second level,while MIS is based on hours or more.Therefore,there must be an isolation device between the two,which is the dynamic data server.Its function is production process monitoring;Storage and management of historical data;Statistical quality control;Preventive maintenance of equipment;Equipment fault diagnosis;Production optimization,etc.
DCS and PLC collect the on-site production process data and transmit the data to the operation station and dynamic data server through the communication network.Dynamic data server collects analog signals or logic signals in the whole production process,so its acquisition speed is massive.The signal shall be sent to the production management department after data panning.
Generally,an enterprise often has several DCS and PLC of different brands.To centralize these signals in the dynamic data server,it is better to choose a general display platform.The signals of DCS and PLC of different models are displayed on this platform.The general display platform can use FIX,INTOUCH,Kingview,Synll and other software to develop various DCS and PLC drive software.
The recently delivered DCS adopts the general operation station,which adopts the NT operating system.The monitoring software is FIX and INTOUCH Different DCS models use different drive software.OPC server is used for signal transmission between various DCS,and a small amount of signals can also be sent to the server of MIS system.FIX,INTOUCH and other software can store historical data,and dozens of signals can be stored for up to 280 days.If you want to store more historical data,you can use the OSI historical database,which can store more than three years.These general monitoring software have OSI interfaces.The operating station of the old generation DCS system is dedicated to both the operating system and the monitoring software,and it is very difficult to communicate with other systems.If the interconnection between systems is to be established,the dynamic data server is to be established through the computer interface unit.The monitoring software can still be used in general and run on the NT platform,but its data can only be uplink,not downlink.In the process of designing the MIS system,it is better to use the dynamic data server,and do not send the DCS and PLC data directly to the Web,otherwise the normal operation of the DCS and PLC will be affected.How many dynamic data servers need to be established depends on the amount of data to be collected and the data security.Generally,it can reach 10000 points.
5.BACK DOOR NETWORK OF MULTI SCREEN OPERATION STATION AND OPERATION STATION
A DCS system can have several operation stations,each of which can display the same content or different content.For a power plant,a 300MV generator set has a relatively centralized process,and it is generally considered appropriate to adopt redundant operation of two operation stations.However,for large units,due to the large number of input and output points,one display is not enough,and it is better to have multiple displays.At this time,the monitoring software should support multiple screens.Early DCS used split screen cards on the host of the operation station,such as two split screen cards and four split screen cards,which can connect two CRTs or four CRTs respectively.This method is used to increase the man-machine interface.For production processes other than power plants,such as cement plants and iron and steel plants,a production process is long,geographically dispersed,and controlled by a set of DCS systems.It has many input and output points.In order to save investment,an operation station often corresponds to some production processes.For example,the rotary kiln and the mill in the cement plant are far away,and the operation station can be installed in two places.At this time,one operation station is configured with one printer.If the host of one of the operation stations is broken,the content displayed by this operation station will disappear.For the safe operation of the system,the overlapping configuration of tags is adopted.If the system has two operation stations,station A and station B,the system has 2000 labels,and operation stations A and B need to configure 1300 labels respectively,of which 300 labels are overlapped.Even if Operation Station A fails,the system will work normally only if Operation Station B operates normally.Because the important labels are on the B operation station.It is worth noting that overlapping configurations can also have negative effects.It will make the responsibilities of the management personnel of operation stations A and B unclear.
Due to the rapid development of network technology,the number of human-computer interfaces can be unlimited.The operation station is divided into master station and slave station.The master station is connected to the DCS network.Read the data in the controller database directly from the DCS network through the DCS network interface.The number of master stations is determined by the number of interfaces.The slave station is connected to the master station.It has no database.When the flow chart screen is displayed,the master station displays the complete process screen,while the slave station displays the process screen of the master station.The number of slave stations is unlimited.Both the master station and slave station are connected by backdoor network.With the backdoor network,when maintaining the system,each operation station can make a copy of the text.When the system is running,even if one of the master operating stations fails,its slave can be used as the slave of the other master.In the network,when connected to the print server,the server has many channels,and several operation stations share one or more printers.The network connecting master station and slave station has no relationship with DCS network.So it is called backdoor network.ARCNET was used in the early backdoor network.Later,because some DCS operating station hosts used DEC minicomputers,DECNET or Ethernet was used in the backdoor network.During tag configuration in the operation station,whether important I/O point overlapping configuration should be determined by the user.
After the universal operation station is adopted,the system will become open.All master stations and slave stations will be connected with Ethernet,and the number of slave stations is unlimited.In order to improve the reliability of the backdoor network and the low cost of Ethernet,dual networks are usually used.Remote operation is possible.Using the network in local areas will bring great convenience.If the process control is connected to the INTERNET network,it will be invaded by viruses or hackers.The security level,one-way data transmission and firewall must be added.
The protocols between Ethernet networks follow the seven layer protocol of the OSI model(Open System Interconnection).The seven layer protocols are physical layer,data link layer,network layer,transport layer,session layer,presentation layer and application layer.
The physical layer describes the transmission medium,connector and signal pulse standard.The repeater or hub is also a device in the physical layer,which is independent of the specific content of the information frame transmitted.A frame is a group of digital pulses sent to a medium.Used to transmit information.The frame size is 64-1518 bytes.The frame includes pre synchronization signal,message header,data information and frame check sequence.A repeater or hub merely amplifies the electrical signal in the wire and continues to transmit it forward.
The data link layer describes the topology and communication standards between local systems.Ethernet can work with multiple physical layer standards(twisted pair cables,optical cables)and multiple network layer standards.Connect the physical aspects of the network(cables and digital pulses)to the abstract world of software and data flows.The information transmitted in the network is transmitted in frame format.There are message headers and footers in the frame,and datagrams are packaged into the frame.Detect errors and adjust data flow.The frame message consists of source and target media access control MAC addresses,and uses this information and the content of the data area to establish the CRC tail.The data link layer uses topology rules according to the network to send frames to the physical layer(network cable).Bridges and switches are devices at the data link layer.Because they support frames.Both use the information in the frame header to regulate traffic.The frame header is responsible for identifying who sent the information and where the information was sent.The frame message header contains two areas,which are used to identify the source and target of the transmission.They are the node addresses of the source and target systems.The size of the frame header is always 14 bytes.
The network layer describes how systems on different network segments look for each other,and also defines the web address.A web address is a system name or number assigned to a group of physical connections.It is the cornerstone of all the upper layers.The unit is datagram.For example,the IP datagram delivery protocol of the network is an example of network layer functions.The term web address is called differently depending on the protocol used.IP is adopted,which is called subnet.
The network layer describes how systems on different network segments look for each other,and also defines the web address.A web address is a system name or number assigned to a group of physical connections.It is the cornerstone of all the upper layers.The unit is datagram.For example,the IP datagram delivery protocol of the network is an example of network layer functions.The term web address is called differently depending on the protocol used.IP is adopted,which is called subnet.
The session layer handles the establishment and maintenance of connections between two or more systems.It ensures that specific service requests are completed correctly.
If the system is running multiple network applications,the session layer is responsible for maintaining the correct communication order and ensuring that the incoming data is introduced to the correct application.
The presentation layer ensures that data can be received in the form of applications.Its task is encoding and decoding.
The task of the application layer is to determine when access to network resources is required.
6.INTERCONNECTION OF HETEROGENEOUS SYSTEMS,TIME SYNCHRONIZATION AND SDSL TECHNOLOGY
An enterprise,especially large and medium-sized enterprises,has many technological processes,each of which is relatively independent.In different periods of construction or technical transformation at different times,different models of DCS systems will be used,and several different models of PLC systems will be used for equipment interlocking and control.In order to establish an integrated management information system in an enterprise,the interconnection and time synchronization of heterogeneous systems become very important issues.In the early days,the interconnection between DCS and PLC used PLC as an input board of DCS.DCS specialists designed an interface board with PLC,which was connected to the same I/O bus with the I/O board of DCS itself.The controller reads the signal from the PLC and sends the PLC signal to the DCS operation station through the DCS network.This interconnection method has a big disadvantage:the fast signal of PLC is displayed on the operation station of the slow response DCS.It is measured that the action of a microswitch can only be displayed on the DCS operation station after several seconds.Some DCS even takes 8 seconds.Another interconnection method is to connect the individual signals of PLC to the input board of DCS by hard wire,so there are few input points and the cost is relatively high.Some DCS designs a node on the DCS network,which is specially used to read PLC signals.It is difficult to send the PLC signal to the DCS network.The disadvantage is that the cost of developing interfaces is very high.Even if the development is successful,the interface often fails.A typical example is the power plant with gas turbine and boiler for combined power generation.The gas turbine is imported from the United States or other countries.The control system(PLC)of the gas turbine and the main equipment are configured together,while the control system of the boiler is selected by the user himself.The user wants to display the information of both on one operation station.To develop this operation station,the development cost is more than tens of thousands of dollars.Even if the development is successful,failures often occur.
For PLC,a special operation station was developed in the mid-1970s,but it was not very successful.Later,it did not develop a dedicated operation station.At that time,PLC only handled switching value,and the digital display on the controller as a human-computer interface could also meet the requirements.The PLC controller and I/O are connected by network.In the late 1980s and 1990s,analog quantity control entered PLC,.The user felt that it was inconvenient not to have a CRT based human-computer interface.The user selected a general monitoring software,which ran on the NT platform,and used a general microcomputer as the hardware platform.The driver software of each PLC was compiled,so that the PLC also had an operating station.For commercial reasons,some PLC manufacturers also developed monitoring software in the 1990s.And try to become a general monitoring software for industrial control.Because of the late development time,not only the drive software of each PLC is too few,but also the market is occupied by other software.
For general monitoring software,Microsoft developed communication protocol DDE(DYNAMIC DATAEXCHANGE),fast DDE,network DDE,etc.are supported.
U DDE allows each machine used in the Windows environment to establish a client/server relationship,send and receive data,and then send instructions.The server provides data and receives interested data requests from other machines.The machine that sends the request is the client,and the server that sends the data.
U Fast DDE provides many DDE information packaged into a single DDE information.Packaging improves efficiency and reduces DDE data transferred between servers and clients.
U Network DDE extends the standard DDE functions,including LAN communication through serial ports.The extension of the network allows different computers connected to the network to connect as DDE running server and client applications.For example,network DDE supports connecting to LAN,or DDE between IBM compatible computers on modem and non PC based platforms in VMS,UNIX and other operating environments.
U SuitLinkK is used for TCP/IP based protocols and is designed to meet industrial needs,such as data integrity,high throughput and easy diagnosis.This protocol standard is only applicable to Windows NT4.0 and above.
U OPC(OBJACT LINK EMBED PROCESS CONTROL)client can fetch data from the server.Comply with TCP/IP protocol.
Since the market needs monitoring software,many manufacturers have developed general monitoring software,such as FIX,INTOUCH,PARAGON,ONSPEC,CIMPLICITY and more than 100 others in the 1990s.China has Kingview,SYNALL,etc.For monitoring software,if many DCS and PLC driver software are developed,and there are many network suites when networking,it will become a general monitoring software.Among them,FIX and INTOUCH drive the most software.On the NT platform,if FIX,INTOUCH and other software are used,they can be used as servers or clients to exchange data with each other.
When DCS came out in the 1970s,the computer technology level was still relatively low,and there were few spare parts available in the market.The operation station developed by the DCS manufacturer has special operating system,special monitoring software,special interface hardware and CRT,special printer,special hard disk and floppy drive.Even the cables,plugs and sockets used for connection are also special.Of course,it cannot be ruled out that DCS manufacturers are considering it in order to obtain the maximum commercial benefits.Due to the rapid development of computer technology,DCS is in a relatively stable stage of development.Later,there were many kinds of microcomputer components on the market,but DCS could not be connected,and there was no way to interconnect heterogeneous systems.DCS manufacturers did not modify their own software according to market changes,so DCS became a veritable"island"of automation.DCS users feel very inconvenient,and the operation station is more easily damaged than the controller.Its service life is about 7-8 years.Because the operation station can not buy hard disks,floppy drives,etc.,many users decide not to use the original DCS manufacturer's operation station when replacing the operation station,because it is expensive and hard to sell spare parts.PC and NT platform are used to install general monitoring software,and drive software with a specific DCS is developed to make a general operation station instead of the original special operation station.
Some DCS manufacturers simply remove the special operation station and provide a general operation station.For example,the APACS system of MOORE Company adopted INTOUCH software(FIX can also be used)in 1996.MOORE Company only provides APACS driver software and hardware configuration requirements,and the hardware is selected by the user.After use,it runs well.It is better than the monitoring software developed by MOORE Company.This may be because the software developers of DCS manufacturers are less than those of general software development companies.For example,the operation station of MEASUREX also adopts general monitoring software.At present,the most common alternative operation stations are FIX and INTOUCH.
In the early DCS,the manufacturers developed their own special monitoring software.When programming,the driver software and display software of the controller are not written separately.If the general-purpose microcomputer and NT platform are used,compared with the general-purpose software,they have less CPU overhead and lower requirements for hardware than the general-purpose software.However,because they are sold together with the system,the sales volume is very small,and the problems of the software itself are not fully exposed.If the hardware can meet the general and special requirements,the crash of the operation station of the special monitoring software is more serious than that of the general.It is understood that the hardware of a certain DCS system is a PC,the operating system is NT,and the operating station assembled with special monitoring software crashes several times a day.As the software version is upgraded,the crash phenomenon is increasing.A few times a year,there is still a crash.Compared with the special software and the general software,the special software is still more closed than the general software.There is no network suite software for network use.If the general monitoring software is used,the human-computer interfaces between DCS and DCS,between DCS and PLC,and between PLC and PLC can be interconnected.As long as the Windows interface of Microsoft is used,it can be used as a client to read data using DDE,fast DDE and Suitelink.They can be both servers and clients.Comprehensive management information system can be formed in the enterprise.In order to ensure the safe operation of the operation station,a separate HMI can be used for interconnection.The general monitoring software usually has a network version of software.After configuration,it can form a server/client format through the network to transmit real-time information to the remote.In the client,you can view the data in the dynamic data server database made of general software in real time.It can also send information into the standard database of the MIS system(such as SQL,SYBASE,ORACLE).Common monitoring software also includes Web software in their suite software,which is installed as a Web server through the Web server.Browse the data in the dynamic data server.It is not real-time data.At the same time,you can also connect to the Web through Microsoft's GLANZE software.Browse the data in the MIS database.Using a Web server to browse data is slower than using a server/client.
The advantages of using general operation station are summarized as follows:
●Low price
●DCS function expansion
●User maturity
Time synchronization of various systems is also a very important issue.The network time server is a high-quality time synchronization device for all network workstations.Generally,the absolute time of DCS system is formed on the operation station(human-machine interface),and there is only relative time in the controller.For time synchronization,the GPS(GLOBAL POSITION SYSTEM)can be used as a benchmark to calibrate the DCS time.The specific implementation method is as follows:through the satellite receiving antenna,the time server receives the atomic clock of each satellite in the GPS system,and then sends the time signal to the dynamic data server or DCS operation station.The time signal is sent to the DCS network through the dynamic data server or DCS driver software of the operation station.Originally,Ethernet was rarely used in DCS network,but it is also useful now.Because it's cheaper.It is widely used in management information network(MIS).Ethernet also adopts broadcast protocol,but it is different from token network.It adopts random access link control.In the Ethernet network,each node can send data randomly.However,when two or more nodes send data at the same time,data transmission conflicts will occur.All the nodes in conflict are returned and sent again after using a random delay algorithm.That is,the carrier sense multiple access technology is adopted.There are many kinds of random delay algorithms,which are currently applied to Ethernet.
Time synchronization of various systems is also a very important issue.The network time server is a high-quality time synchronization device for all network workstations.Generally,the absolute time of DCS system is formed on the operation station(human-machine interface),and there is only relative time in the controller.For time synchronization,the GPS(GLOBAL POSITION SYSTEM)can be used as a benchmark to calibrate the DCS time.The specific implementation method is as follows:through the satellite receiving antenna,the time server receives the atomic clock of each satellite in the GPS system,and then sends the time signal to the dynamic data server or DCS operation station.The time signal is sent to the DCS network through the dynamic data server or DCS driver software of the operation station.Originally,Ethernet was rarely used in DCS network,but it is also useful now.Because it's cheaper.It is widely used in management information network(MIS).Ethernet also adopts broadcast protocol,but it is different from token network.It adopts random access link control.In the Ethernet network,each node can send data randomly.However,when two or more nodes send data at the same time,data transmission conflicts will occur.All the nodes in conflict are returned and sent again after using a random delay algorithm.That is,the carrier sense multiple access technology is adopted.There are many kinds of random delay algorithms,which are currently applied to Ethernet.
Real time production data is massive,both real-time and historical.For general monitoring software,there is a historical data platform.Set up a server,which can form its own system.Finally,it is connected to the database of the MIS system.For data security,there should also be a firewall.At present,most of the transmission carriers are optical fibers.The cost of laying optical fiber is relatively high(about 20000 yuan/km).In the MIS system with optical fiber as the carrier,some places may be far away from the central area,but a few data are also expected to be sent to the center for display.At this time,optical fiber is not necessarily used,but telephone lines can be used.There are few data in places such as weighbridge,coal handling and water treatment.As long as a special router is connected to the switchboard,it has an Ethernet interface.In the information source plus cat(MODEM),the wiring should be adjusted slightly.The cost of routers and MODEMs is not very high.At this time,optical fiber and telephone line can be used for Ethernet at the same time.This is the SDSL(Symmetric Digital SubscriberLine)technology.The characteristic of SDSL technology is that it can not only communicate with telephone,but also transmit network.As long as the phone is connected,the network is also connected.This technology is applied to factories and mines that already have telephone lines and telephone exchanges.Now it has been widely used in the factory network abroad.If the enterprise is relatively small,it can use telephone lines instead of optical fiber,and the communication rate is 2.3M.Whether the data is read from the information terminal or the instructions are sent to the information terminal,the rate is the same.The distance between routers and MODEMs can be 7000 feet.When in use,the distance can be extended without using the telephone at the same time.
