DCS System Tutorial

DCS Tutorial – The Latest DCS Operator Stations – General Operator Stations. The DCS system consists of three main components: controllers with I/O components, a communication network, and a human-machine interface. The human-machine interface includes the operation station, engineer station, and historian station. The controller’s I/O components are connected to the production process, while the operation stations are linked to humans; the communication network ties these two components together to form a system. Therefore, the operation station is an important component of DCS; the engineer station is used to configure the controllers and operation stations, while the historian station records the historical data from the production process. Human-machine interfaces developed in recent years also include dynamic data servers. 　　A DCS system controller and I/O components can typically operate for 16–20 years, while operation stations, due to their presence of moving parts such as hard drives, keyboards, CRTs, and floppy drives, are more prone to damage; the likelihood of failures increases after 6–8 years of use. As a result, operation stations are often replaced during the operation of a DCS system. 　　There are minor changes in the controllers of DCS. These changes are reflected in aspects such as 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. The operation stations have changed significantly. Operation stations from before the 1980s generally did not have hard drives or dynamic flowcharts, and the number of tags that could be displayed was relatively low, such as 500 tags (tags refer to logical relationships such as AI, DI, circuits, and digital switches). In the 1980s, operation stations that could display 5,000 tags appeared, and in the 1990s, those capable of displaying 30,000 tags came into use. At the same time, general-purpose display software that runs on Microsoft’s NT platform also emerged. Initially, general-purpose software was used only on the PLC operation stations, and later it was gradually applied to DCS as well. Its number of tags can reach 10,000 or even more. 　　The development process of DCS operation stations (taking the BAILEY operation station as an example) is as follows: 1. In the early 1980s, the N90 operation station belonged to the OIU series; it had no hard drive or dynamic flow charts, and the number of labels it could handle was 500. Later, hard drives and flowcharts were added, bringing the number of labels to 1,400–5,000. In the mid-1980s, the MCS series was introduced, with a capacity of 10,000 tags. In particular, the MCS PULS model featured a SCSI interface and could handle 30,000 tag points; it was at the forefront of the DCS market at that time. In 1986, BAILEY products accounted for one-third of the world’s DCS market. By 1988, a total of 8,500 units were in operation around the world. By the 1990s, the DCS market was highly competitive, and BAILEY was not as outstanding in terms of technology or sales as it had been in the 1980s. Thus, BAILEY Company sought to regain its glory by purchasing systems from companies such as FISCHER&PORTER and HARTMANN&BRAUN to sell them. 　　　　BAILEY has good controllers and communication networks, but its operation stations fall short when compared to those of its competitors. BAILEY’s latest operation station is Conductor NT, which is based on WINDOWS NT and standard microcomputers. In fact, this operation station was not developed for INFI-90; it is an operation station for FISCHER-PORTER’s System 6, created by embedding its monitoring software with drivers for communication with INFI-90. Due to low sales volume, there are few opportunities for testing, resulting in many problems and severe freezing issues. The operation stations of the OIS40 series run on DEC’s VMS platform. In fact, a driver software for communicating with VMS was still developed on the MTOS operating system platform of the MCS operation station, as both the OIU and MCS from the 1980s ceased to be sold by the end of that decade. BAILEY only sells the OIS20 series and the OIS40 series. 　　　　The OIS20 series was introduced to the market in the early 1990s; it is essentially an MCS, but it can communicate with INFI-90. Its development and manufacturing costs are relatively low, and its performance is good as well. The auxiliary stations in the OIS20 series do not use a network to transmit information; rather, an additional graphics card is installed on the main station to function as the auxiliary station. Later, due to high maintenance costs, both hard drives and floppy drives became difficult to obtain, leading to negative feedback from users. 　　　　Following the OIS20 series, BAILEY introduced the OIS41 and OIS42 models, adding Ethernet cards between the operation stations to create a backdoor network that enables printer sharing. The ability to transfer graphics to different host stations has also been improved, which in turn provides users with the opportunity to develop printing systems; that’s something for another time. Due to the poor performance of the hosts OIS40, OIS41, and OIS42, the performance improvement of the operation station is not significant. It was not until the emergence of the OIS43 Alpha chip that performance improved. Meanwhile, the Canadian company BAILEY developed PCV, an operation station based on PC that uses the QNX operating system. Due to its low number of labels, low cost, and stable performance, it is suitable for use in small systems. This is BAILEY’s OIS10 series; prior to version 5, it had only text and no graphics. Version 5 and later include both text and graphics. The OIS11 control stations are connected via ARCNET behind the back panels. OIS12 can be networked using either ARCNET or Ethernet. 　　　　Due to the complex software structure of the OIS40 series, its price is high. More importantly, DEC was acquired by COMPAQ, and production of the Alpha 255/233 models came to an end, which undoubtedly compounded the difficulties for BAILEY Corporation and its users. 　　　　II. In the mid-1980s, since the development of PLC operation stations was not very successful, some software companies developed generic monitoring software, which was quickly adopted by PLC manufacturers. Examples include FIX, INTOUCH, ONSPEC, etc. (there are over a hundred such types in total). Due to the favorable market prospects, software developers have created many more drive software programs for PLCs. In the 1990s, drive software for DCS was developed. The first to adopt general-purpose industrial control monitoring software was MOORE Company’s APEC system, which can use either INTOUCH or FIX. Since the INFI-90 system did not release any particularly excellent operation stations throughout the 1990s, PREVISE company developed the OpsCon operation station. 　　　　The OPsCon operation station runs on a PC hardware platform under the NT operating system; FIX is used as the monitoring software, and corresponding driver software capable of communicating with various DCS systems has been developed, supporting up to 10,000 tags. Since 90,000 units of the FIX software have been sold around the world, it works well with various PLCs, DCSs, and NT systems; this type of operation station can be used with a wide range of PLC and DCS operation stations. Thousands of units have been applied in the INFI-90 system. For example, a paper mill in New Zealand that was originally using CONDUCT NT eventually switched to OpsCon instead. 　　The advent of general-purpose operation stations has brought the following conveniences to DCS users: 1. There is no longer any need to worry about whether the original DCS manufacturer has gone out of business or been acquired, whether that particular product is no longer in production, or whether spare parts can be found. 　　2. Due to the wide range of applications for general-purpose operation stations, the relatively large production volume, and resulting cost reductions, it is possible to save users’ expenses. The maintenance costs are also relatively low. 　　3. Using a general-purpose system is simpler than employing various specialized systems, and it also allows users to reduce costs associated with staff training. 　　4. Easy to update and upgrade. 　　5. It has good openness, making it easy to establish a production management information system. 　　Therefore, the general-purpose operation station is the development direction of DCS. 　　 This post was last edited by an2 on 2008-9-20 12:56]

DCS Tutorial – Several Issues in DCS Selection Once the controlled object is determined, choosing the appropriate control system becomes an important issue. The decision is mainly based on the scale of the project and the investment budget. In terms of project implementation, there is not much difference between a DCS system based on digital technology and a control system made up of traditional analog instruments; what matters most are the project scale and investment budget. However, compared to analog instruments, DCS systems are more complex and require higher technical expertise. Now I will discuss several issues related to the selection of DCS systems. Theoretically, DCS can be used with different process processes; it is universal. However, the manufacturers of DCS specialize in a particular field. For example, HOMEYWELL is mainly used in the petrochemical industry, while BAILEY’s N90 and INFI90 are primarily used in power systems. ROSEMOUNT’s RS3 and Δ-V are mostly used in the chemical industry. However, it cannot be denied that different processing processes have certain specific requirements; for example, power plants must be equipped with voltage regulation devices and SOE, the petrochemical industry requires selective control, and the cement industry needs compensation for large time delays in control systems. These factors also need to be taken into account when making selections. 　　　　　　The second point is cost-effectiveness, which should be considered from the perspective of the DCS’s price and the expected benefits it will generate. There are domestic and imported DCS systems. For the same category, imported DCS systems have more robust control functions and incorporate advanced control algorithms such as Smith prediction and 3D matrix operations. Domestic DCS systems are much cheaper than imported ones, yet they can still meet the technical requirements. Structurally, the controllers of foreign DCS systems vary little among different manufacturers; the preset algorithms of these controllers differ slightly, and the way in which the controllers are connected to the I/O cards also varies. The operation stations, on the other hand, differ significantly. Some are based on PCs, while others are based on minicomputers; the operating system is generally a UNIX-based system. Minicomputers are much more expensive than PCs; imported minicomputer workstations cost over $40,000, and many models have been discontinued (such as DEC’s VAX and Alpha machines). The operation station for PCs costs less than 30,000 dollars; it uses the NT operating system, and its stability is not as good as that of UNIX. The mini-computer uses SCSI for its interfaces, with a transmission rate that is 8 times higher than that of serial connections. When using the NT operating system as the control station, the number of points required is lower; otherwise, frequent crashes occur. Domestic PCs are much cheaper, and by using PC-based control stations, the latest models can be employed. Operators also have greater familiarity with software installation, debugging, networking, and development. There are dedicated monitoring software solutions as well as general-purpose ones; general-purpose monitoring software offers better openness. Users should choose the appropriate option based on the scale of the project and the available budget. 　　　　　　In addition to the reasons mentioned above, another factor contributing to the high cost of DCS systems is the power supply system for the controllers; redundant power supply is typically used, and the installation of power supplies as well as heat dissipation are the main reasons for the high cost. There are significant differences among various DCS systems in this regard. 　　　　　　The communication network that connects the controller and the operation station also needs to be taken into consideration; if standard Ethernet is used, network cards and similar components are inexpensive, while dedicated network interfaces are costly, with prices reaching up to $20,000. 　　　　　　Therefore, cost-effectiveness is related to many factors; sometimes when a foreign supplier lowers its price for you, it’s actually just a change in certain aspects of the structure, and no real discount is given – in fact, their profit may even increase. A good approach at this time is to contact similar organizations in the country and seek advice from experienced experts. 　　　　　　The third point is the technical capabilities of the contractor, that is, their familiarity with specific process steps as well as the DCS system itself. If a contractor who is usually involved in chemical process control systems is tasked with developing control systems for rolling, he will not be very familiar with aspects such as loop control, coiling control, and tension control, and as a result the quality of the work he performs will not be very good. If the contractor is not familiar with the DCS itself, a crash can occur when the controllers are made too large. Many factories have purchased DCS systems from different manufacturers, a situation we refer to as the \"Eight-Nation Alliance\" scenario. In such cases, it is essential to choose an entity with strong technical capabilities to take overall responsibility, rather than selecting a single foreign manufacturer as the contractor. 　　　　　　The fourth point is after-sales service; foreign manufacturers usually charge high prices for accessories and spare parts, and fail to provide them in a timely manner. DCS users should choose manufacturers with strong capabilities, robust technical expertise, and excellent domestic technical support. Computer technology is developing rapidly, and DCS manufacturers also continuously update their products. It is essential that there be good compatibility between old and new products; otherwise, some manufacturers’ old and new systems are incompatible, which can result in significant losses during system upgrades. Domestic DCS manufacturers provide components and spare parts in a timely manner, and also offer good after-sales service. 　　　　　　The fifth point concerns the technical advancement of DCS, referring to the use of proven cutting-edge technologies in the system, as well as its potential for further development and vitality. This includes the openness and interconnectivity of DCS systems, the use of fieldbuses, and support from third-party software. It is important to note here that in order to gain a foothold in the market, some manufacturers introduced immature products to the Third World. For example, about five or six years ago, DCS lacked small-scale systems, so some manufacturers supplied users with such immature small-scale systems; as a result, all of these over 270 systems were retired ahead of schedule. As early as 1983, the DCS marketed by a foreign company exhibited arbitrary outputs from its controllers after a power failure and subsequent restoration of power; this meant that the position of the valves became dangerous. Such products should not have been released for sale, yet they were still sold to us**. As a result, the purchasing party hardly used them at all. 　　　　　　In short, DCS has been in use for over 20 years since 1975, and its reliability generally meets the required standards. Choosing the right type of system when establishing one is a very important step; we need to take into account not only the scale of the project and the budget available, but also a range of other factors. Whether the right choice is made often determines the future success of the system from the very beginning, so it cannot be taken lightly.

DCS Tutorial – DCS Dynamic Data Server. The DCS system falls under basic automation, while MIS systems are focused on office automation. There is a significant difference between the two in terms of response speed: DCS operates on a second-by-second basis, whereas MIS operates on a scale of hours or even longer periods of time. Therefore, there must be a isolation device between the two, and this isolation device is the dynamic data server. Its function is process monitoring ； Storage and management of historical data ； Statistical Quality Control ； Equipment preventive maintenance ； Equipment fault diagnosis ； Production optimization, etc. 　　　　　　The DCS and PLCs collect data on the production process on-site, and transmit this data to the operation station and the dynamic data server via a communication network. A dynamic data server collects analog or logical signals from the entire production process, so its data acquisition speed is extremely high. Data mining is required to send the signals to the production management department. 　　　　　　Typically, a company uses several different types of DCS and PLC systems, and to consolidate all these signals into a dynamic data server, it is best to choose a universal display platform. On this platform, signals from different models of DCS and PLCs are displayed. General display platforms can use software such as FIX, INTOUCH, KingView, and Synall to develop drive software for various DCS and PLC systems. 　　　　　　The DCS models produced recently use standard operation stations that run on the NT operating system; the monitoring software used is FIX and INTOUCH. Different DCS models employ different driver software. Signal transmission between various DCS systems is carried out via OPC servers, and a small number of signals can also be sent to the server of the MIS system. Software such as FIX and INTOUCH can store historical data; dozens of signals can be stored for up to 280 days. To store more historical data, the OSI historical database can be used, as it is capable of storing data for over three years. These general monitoring software products all have OSI interfaces. The operation stations of older-generation DCS systems use dedicated operating systems and monitoring software, making communication with other systems very difficult. To establish inter-system connectivity, a dynamic data server is created through a computer interface unit; the monitoring software can still use standard versions that run on the NT platform, but its data can only be sent in one direction, not in the other. When designing a MIS system, it is advisable to use dynamic data servers; do not send DCS and PLC data directly to the Web, as this can affect the proper operation of the DCS and PLC. As for exactly how many dynamic data servers are needed, it is determined by the amount of data that needs to be collected and data security considerations. Under normal circumstances, it can reach 10,000 points. 　　 DCS Tutorial – Multi-screen operation stations and the backdoor network of operation stations. A DCS system can have several operation stations, and each station can display either the same content or different content. For power plants, for a 300MV generator set with a relatively centralized process flow, it is considered appropriate to use two operation stations in a redundant configuration. However, for large units, due to the large number of input and output points, one monitor is not sufficient; it is better to have multiple monitors. At this point, the monitoring software should be able to support multiple screens. Early DCS systems used split-screen cards connected to the host computers in the operation stations; for example, cards that allowed for 2 or 4 split screens, enabling connection to 2 or 4 CRT monitors respectively. Use this method to enhance the human-machine interface. For production processes other than power plants, such as cement plants and steel mills, the production process is long and spread over a large area; it is controlled by a DCS system with a large number of input and output points. To save on investment, one operation station is usually assigned to handle part of the production process. For example, in a cement plant, the rotary kiln and the grinders are far apart, so the control stations can be installed in two different locations. At this time, one printer is configured per operation station. If the host of one of the operation stations fails, the content displayed on that operation station will disappear. To ensure the safe operation of the system, an overlapping configuration of tags is employed. If the system has two operation stations, namely Station A and Station B, and it contains 2000 tags, then Stations A and B need to be configured with 1300 tags each, of which 300 tags are common to both stations. Even if Operation Station A fails, as long as Operation Station B is functioning properly, the system will continue to work as usual. Because the important labels are all available at Operation Station B. It is worth noting that overlapping configurations can also have negative effects. It will result in unclear responsibilities for the managers at stations A and B. 　　　　Thanks to the rapid development of network technology, the number of human-machine interfaces can be unlimited. The operation station is divided into a master station and a slave station. The master station is connected to the DCS network. Data from the controller database is read directly from the DCS network via 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 displaying the flowchart, the master station shows the complete process image, while the slave stations display the process image from the master station. The number of slave stations is unlimited. Both the master station and the slave stations are connected via a backdoor network. With a backdoor network, text copying can be performed between various operation stations during system maintenance. When the system is in operation, even if one of the main control stations fails, its secondary station can function as a secondary station for the other main station. In a network, connected to a print server, the server has multiple channels, and several workstations share one or several printers. This network that connects the master station and the slave stations has no relation to the DCS network. That’s why it is called a backdoor network. Early backdoor networks used ARCNET; later, as the operator station hosts in some DCS systems adopted DEC minicomputers, backdoor networks switched to DECNET or Ethernet. When configuring tags at the operation station, it is up to the user to decide whether to configure important I/O points in an overlapping manner. 　　　　With the adoption of a universal operation station, the system becomes open; the master stations and slave stations are connected via Ethernet, with no limit on the number of slave stations. To improve the reliability of backdoor networks, and due to the low cost of Ethernet, dual networks are usually employed. Remote operation is possible. Using a network in localized areas brings great convenience. If process control is connected to the Internet, it can be invaded by viruses or hackers. It is necessary to implement security levels, one-way data transmission, and firewalls. 　　　　The protocols between Ethernet devices follow the seven-layer protocol of the OSI model (Open System Interconnection). The seven layers of the protocol are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer. 　　　　The physical layer describes the transmission medium, connectors, and signal pulse standards. A repeater or hub is also a device at the physical layer, and it is independent of the specific content of the information frames being transmitted. A frame is a set of digital pulses sent onto the medium. Used to transmit information. The size of a frame is 64-1518 bytes. A frame includes a pre-synchronization signal, a message header, data information, and a frame checksum sequence. A repeater or hub simply amplifies the electrical signal in the wires and sends it on its way. 　　　　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 fibers) and multiple network layer standards. It connects the physical aspects of a network (cables and digital pulses) with the abstract world of software and data streams. Information transmitted over a network is sent in frame format. A frame has a header and a trailer, with datagram packets enclosed within it. Detection error; adjust data traffic. A frame message consists of the source and destination media access control (MAC) addresses, and a CRC trailer is generated using this information along with the content of the data area. The data link layer sends frames in accordance with the topology rules of the network, forwarding them to the physical layer (network cables). Bridges and switches are devices at the data link layer. Because they are frame-supporting. Both use the information in the frame header to regulate traffic. The frame header is responsible for identifying who sent the message and where it is being sent. The frame header contains two fields used to identify the source and destination of the transmission, which are the node addresses of the source and destination systems. The size of the frame header is always 14 bytes. 　　　　The network layer describes how systems on different network segments find each other, and it also defines web addresses. A website address is a name or number assigned to a group of physically connected systems. It is the cornerstone of all upper layers; the unit is the datagram. Protocols such as the IP datagram transmission protocol in networks are examples of the functions of the network layer. The term “website” varies in name depending on the protocol used. When IP is used, it is called a subnet. 　　　　The transport layer handles the actual processing of data and prepares it for transmission over the network. If the data is too large to be transmitted as a single frame, the transport layer breaks it down into smaller parts and assigns sequence numbers to them; these sequence numbers allow the transport layer on other systems to reassemble the data into its original form. The CRC verification for frames is performed at the data link layer, while the transport layer can serve as a backup verification mechanism. The functions of the transport layer include IP’s transport protocol (TCP), with the unit being a segment. 　　　　The session layer handles the establishment and maintenance of connections between two or more systems. It ensures the proper completion of specific service requests. 　　　　If the system is running multiple network applications, the session layer is responsible for maintaining the correct order of communication, ensuring that incoming data is directed to the appropriate application. 　　　　The presentation layer ensures that the data is received in a format suitable for use by applications. Its task is encoding and decoding. 　　　　The task of the application layer is to determine when to request access to network resources. 　　　　

DCS Tutorial – Interconnection of heterogeneous systems, time synchronization, and SDSL technology. A company, especially medium and large-sized ones, has many process streams, each of which operates with relative independence. Depending on the period of construction or the timing of technical upgrades, different models of DCS systems will certainly be used, while various models of PLC systems will be employed for equipment interlocks and control. To establish a comprehensive management information system within an enterprise, the interconnection and time synchronization of heterogeneous systems become very important issues. In the early days, the interconnection between DCS and PLCs was achieved by using the PLC as an input card for the DCS; the DCS had a dedicated interface card designed for communication with the PLC, which was connected to the same I/O bus as the DCS’s own I/O cards. The controller reads the signals from the PLC and sends those signals to the DCS operation station via the DCS network. A major drawback of this interconnection method is that the fast signals from the PLC are displayed on the DCS operation stations, which have a slower response time. It has been determined that it takes several seconds or more for the operation of a microswitch to be reflected on the DCS operator station. Some DCS even require 8 seconds. Another method of interconnection is to connect the individual signals from the PLC using hard wires to the input board of the DCS; this results in a small number of input points, but the cost is relatively high. Some DCS systems design a node on the DCS network, which is dedicated to reading signals from PLCs. It is relatively difficult to feed PLC signals into the DCS network. The downside is that the cost of developing the interface is very high. Even if development is successful, the interfaces often fail. A typical example is a power plant that generates electricity using gas turbines and boilers; the gas turbines are imported from the United States or other countries, and their control systems (PLCs) are supplied as part of the main equipment, while the control system for the boilers is chosen by the user themselves. The user desires to display information from both systems on a single control station. To develop this operation station, the development costs exceeded several tens of thousands of dollars. Even when developed successfully, failures often occur. 　　　　For PLCs, dedicated operation stations were developed in the mid-1970s, but they were not very successful. Later, no dedicated operation station was developed; at that time, PLCs handled only digital signals, and the digital display on the controller served as a human-machine interface, which was sufficient. The controller of the PLC is connected to the I/Os via a network. By the late 1980s and 1990s, analog control was introduced into PLCs. Users found that human-machine interfaces based on CRTs to be very inconvenient; therefore, they opted for general-purpose monitoring software that runs on the NT platform, using ordinary computers as the hardware foundation. Driver software for each PLC was developed, thereby providing an operation station for those PLCs as well. For commercial reasons, some PLC manufacturers also developed monitoring software in the 1990s. And it attempts to become a general-purpose monitoring software for industrial control. Due to the late development stage, there are very few driver software options for various PLCs, and the market is also dominated by other software. 　　　　For general monitoring software, communication protocols developed by Microsoft such as DDE (DYNAMIC DATA EXCHANGE), Fast DDE, and Network DDE are all supported. 　　　　DDE allows machines running under Windows to establish client/server relationships, send and receive data, as well as issue commands. The server provides data and receives requests for data of interest sent from other machines in use. The machine that sends requests is the client, while the one that sends data is the server. 　　　　u Quick DDE allows many DDE messages to be packed into a single DDE message. Packaging improves efficiency by reducing the DDE data transmitted between servers and clients. 　　　　U-Network DDE extends the capabilities of standard DDE, including communication over local area networks via serial ports. The extension of the network allows different computers connected to it to function as servers or clients for DDE connections. For example, network DDE supports DDE between IBM-compatible computers connected to a LAN or modem, and PC-based platforms in operating environments such as VMS and UNIX. 　　　　u SuitLinkK is used for TCP/IP-based protocols and is designed to meet industrial requirements such as data integrity, high throughput, and easy diagnosis. This protocol standard is only applicable to Windows NT 4.0 and later. 　　　　The u OPC (OBJECT LINK EMBED PROCESS CONTROL) client can retrieve data from the server. Comply with the TCP/IP protocol. 　　　　Due to the market demand for monitoring software, many manufacturers have developed general-purpose monitoring software; in the 1990s, there were over 100 such products, including FIX, INTOUCH, PARAGON, ONSPEC, CIMPLICITY, and others. In China, there are products such as KingView and SYNALL. For monitoring software, if many driver programs for DCS and PLCs are developed, along with various network kits for networking, it becomes a general-purpose monitoring software. Among them, FIX and INTOUCH have the most driving software. On the NT platform, if software such as FIX and INTOUCH is used, they can act as either servers or clients to each other, allowing them to exchange data. 　　　　When DCS was introduced in the 1970s, computer technology was still relatively underdeveloped, and there were few components available on the market. The operation stations developed by DCS manufacturers come equipped with a dedicated operating system, specialized monitoring software, dedicated interface hardware and CRTs, as well as dedicated printers, hard drives, and floppy drives. Even the cables and plugs, sockets used for connection are specialized. Of course, this does not rule out the possibility that DCS manufacturers are considering it in order to achieve maximum commercial benefits. Due to the rapid development of computer technology, DCS has not progressed as fast as computers and is now in a relatively stable stage of development. Later on, there were many various microcomputer components available on the market, but they could not be connected to DCS systems; heterogeneous systems were even less capable of interconnecting. Moreover, DCS manufacturers did not modify their software in response to changes in the market, so DCS systems became true isolated islands in terms of automation. DCS users find it very inconvenient, and moreover, the operation stations are more prone to damage than the controllers. Its lifespan is about 7-8 years. Since components such as hard drives and floppy drives are unavailable, many users decide not to use the operation stations provided by the original DCS manufacturer when replacing them, as these stations are expensive and their spare parts are hard to find. Using PCs and NT platforms, general monitoring software is installed, along with driver software specific to a particular DCS, to create a universal operation station that replaces the original dedicated operation station. 　　　　Some DCS manufacturers simply eliminate the dedicated operation stations and use general-purpose operation stations instead. For example, Moore Company’s APACS system used INTOUCH software in 1996 (FIX could also be used); Moore Company only provided the driver software for APACS along with the hardware configuration requirements, while the hardware was selected by the user themselves. After use, it works very well. It’s a bit better than the monitoring software developed by MOORE Company itself. This may be related to the fact that DCS manufacturers have fewer software developers than software companies that develop general-purpose software. Similarly, the operation station of MEASUREX also uses general-purpose monitoring software. Currently, the most common alternative operation stations are the two general types: FIX and INTOUCH. 　　　　In the early days of DCS, manufacturers developed their own dedicated monitoring software. When writing a program, the driver software and display software for the controller are not developed separately. If general-purpose microcomputers and NT platforms are used, their CPU usage is lower compared to general-purpose software, and their hardware requirements are less stringent than those of general-purpose systems. However, since they are sold as part of a complete system, the sales volume is low, and the issues related to the software itself have not been fully exposed. If the hardware can meet both general and specialized requirements, the problem of operation station crashes with specialized monitoring software is more severe than that with general-purpose software. It is understood that in a certain DCS system, where the hardware consists of PCs and the operating system is NT, along with operation stations equipped with specialized monitoring software, the system crashes several times per day. With the upgrade of software versions, crashes are on the increase. Several re-nailing attempts were made within a year, yet the freezing issue persisted. Compared to general-purpose software, dedicated software is still more closed at present. It is used on the network, but there is no network suite software yet. If general monitoring software is used, the human-machine interfaces of DCSs with each other, DCSs and PLCs, as well as PLCs with each other, can be interconnected. Any Microsoft WINDOWS interface can serve as a client, using DDE, Fast DDE, and Suitelink to read data. They can function as either servers or clients. A comprehensive management information system can be established within a company. To ensure the safe operation of the control station, a separate HMI can be used for interconnection. General monitoring software usually comes in a network version; after configuration, it can be used over the network to form a server/client setup for transmitting real-time information to remote locations. On the client side, it is possible to view in real time the data in the database of the dynamic data server created by general-purpose software. It can also send information into the standard databases of MIS systems (such as SQL, SYBASE, ORACLE). General monitoring software also includes Web software in its suite; it is installed as a Web server, and operations are carried out through that Web server. Browse the data in the dynamic data server. It is not real-time data. At the same time, the Web can also be accessed through Microsoft’s GLANZE software. Browse the data in the MIS database. Using a web server to browse data is slower than the server/client approach. 　　　　The advantages of using a general-purpose operation station are as follows: 　　　　● Low cost 　　　　● DCS functionality expansion 　　　　● User familiarity 　　　　Time synchronization across various systems is also an important issue. A network time server is a high-quality device for time synchronization across all online workstations. Under normal circumstances, the absolute time of a DCS system is generated at the operation station (human-machine interface), while the controllers only have relative time. For time synchronization, satellite time GPS (GLOBAL POSITION SYSTEM) can be used as a reference to calibrate the DCS time. The specific implementation method is as follows: Through a satellite receiving antenna, the time server receives the atomic clocks of various satellites in the GPS system, and then sends the time signals to the dynamic data server or the operation station of the DCS. The time signal is sent to the DCS network via the drive software of the dynamic data server or the operator station. It turns out that Ethernet is less commonly used in DCS networks, but it is useful now as well. Because it is relatively inexpensive. It is widely used in Management Information Systems (MIS). Ethernet also employs a broadcast protocol, but it differs from token networks. It uses random-access link control. In an Ethernet network, nodes can transmit data randomly. But when two or more nodes send data simultaneously, a data transmission conflict occurs. All nodes involved in the conflict retreat, and after using a random delay algorithm, they resume sending. That is, carrier sense multiple access technology is used. There are many algorithms for random delay, all of which are currently used in Ethernet. 　　　　Currently, the MIS system has been integrated with DCS and PLCs to form one system. The data from DCS and PLCs is sent to the Ethernet via a dynamic data server, with fiber optics being the primary medium used for transmission. The control room is usually the central area, from which a star-shaped network structure is formed. Servers are installed in the central area. Such as ORACLE, SYBASE, SQL, etc. Software is stored on the server, and the software is structured in the form of sub-modules. Such as the financial management sub-module, personnel management sub-module, raw materials sub-module, etc. Place the signals from DCS and PLC within the production real-time subsystem module. 　　　　The data generated in real time is massive, including both real-time and historical data. All general monitoring software comes with a historical data platform. Consider a server; it can function as an independent system. Finally, it is connected to the database of the MIS system; for data security, a firewall should also be in place. Currently, optical fibers are also the most common transmission medium. The cost of laying optical fibers is relatively high (about 20,000 RMB per kilometer). In MIS systems that use optical fibers as the transmission medium, there may be areas that are far from the central area, but some data still needs to be sent to the center for display; in such cases, optical fibers are not necessarily required, and telephone lines can be used instead. There is very little data from areas such as balance of plant, coal transportation, and water treatment. As long as a special router is connected to the switch of the telephone exchange, it has an Ethernet interface. With a MODEM as the information source, only slight adjustments are needed in the wiring. The costs of routers and MODEMs are not very high. At this time, fiber optic cables and telephone lines can be used for Ethernet simultaneously. This is the SDSL (Symmetric Digital Subscriber Line) technology. The feature of SDSL technology is that it allows both phone calls and data transmission simultaneously. As long as the phone connection is established, the network connection is also established. This technology is applied to factories and mines that already have telephone lines and a telephone switchboard. It is now widely used in factory networks abroad. If the company is small, fiber optic cables may not be necessary; telephone lines can be used instead, with a communication speed of 2.3M. Whether it is data being read from the information side or commands being sent to it, the rate is the same. The distance between the router and the MODEM can be 7,000 feet. When in use, the distance can be increased by not using the phone at the same time. For specific application wiring, see the figure below. 　　

DCS Tutorial – The Basic Structure of DCS and the Differences from PLC DCS is the abbreviation for Distributed Control System (TOTAL DISTRIBUTED CONTROL SYSTEM). It refers to the control of hazard dispersion, management, and centralized display. In the late 1960s, programmable controllers for performing logical operations were developed. Abbreviated as PLC. It is mainly used in the automotive manufacturing industry. In the mid-1970s, DCS systems with analog control were introduced to the market, replacing analog instrument control based primarily on PID calculations. The concept of DCS was first proposed by the original manufacturers of measuring instruments, and it was initially used primarily in the chemical industry. Later, the computer industry got involved in the development of DCS. 　　　　In the 1970s, microcomputer technology was not yet mature, and computer technology was not sufficiently developed. The operation station, controllers, I/O boards, and network interface boards are all developed by the DCS manufacturers themselves; in other words, all components are proprietary. 　　　　In the early 1970s, people used minicomputers such as the PDP/1124 to replace the previously used centrally installed analog instruments for control. There are many cables connected to the central control room. If a minicomputer is used as both the controller and the CRT connected to it as the display device (i.e., the human-machine interface). A minicomputer is required to receive signals from thousands of transmitters or other sensors, and to perform calculations for hundreds of circuits. Obviously, the risks are somewhat concentrated. There are as many cables connected to the analog instruments, and once the minicomputer fails, both control and display functions are lost. Digital control did not achieve the intended purpose. 　　　　Later, someone proposed separating control from display. One computer handles the control and calculation tasks, while another computer handles the display tasks. Furthermore, a process as a controlled object may have many points that need to be displayed and controlled; some of these require closed-loop control or logical operations. The various components of such a process can be relatively independent of each other and can be divided into several separate units. The input and output points that need to be monitored and controlled within these individual units can then be distributed across multiple computers. Thus, the computational tasks that were previously handled by a single minicomputer can now be carried out by several or even dozens of computers (controllers). If one of the machines breaks down, it does not affect the overall system. The so-called tactic of “using wolves to replace tigers” means dispersing the risk. It brings together management functions such as display, operation, and printing, and uses a network to connect these control and display components into a single system. At that time, some people called this system a distribution system. 　　　　To what extent should the risk be distributed to be considered appropriate? This is related to the level of development of computer technology at that time. In the mid-1970s, complete decentralization meant that a single controller handled the calculations for one circuit. At that time, since people were not very familiar with digital technology and were accustomed to analog instruments, loop controllers were popular in the late 1970s and 1980s. These controllers were designed to look almost identical to the original analog instruments, so as not to change users’ operating habits, while the PID calculations were carried out digitally inside. One instrument (a computer) performs the control tasks for one circuit. Its price is relatively high, but the risk is spread out. Then, a communication network is used to connect the various controllers and the CRT-based human-machine interface into a single system. At this time, the network structure is usually star-shaped. The manufacturing cost of the controller for this circuit is too high, resulting in a poor price/performance ratio. Later, to reduce costs, two-channel and four-channel controllers were introduced, which offered a slightly better cost/performance ratio. For large and medium-sized systems, the price/performance ratio of DCS is better than that of systems composed of circuit controllers. In some special cases, circuit controllers are still needed. 　　　　If too many circuits need to be processed, such as when a controller collects data from thousands of points and performs calculations for hundreds of circuits, the risk becomes extremely high. In this case, the danger must be dispersed. With the development of computer technology, the computing power, storage capacity, and reliability of computers have been continuously improving, allowing computers to handle more tasks. Completed tasks can also be consolidated. In addition, redundancy technologies such as controllers and networks have also been developed, allowing control operations to be centralized to some extent. 　　　　Based on current DCS systems, a single controller is capable of performing calculations for dozens of loops and collecting data from hundreds of points, along with carrying out appropriate logical operations; in practical use, this approach yields good results. This raises the issue of controller upgrade. Sometimes the distance between the controller and the sensing elements is quite large, which has promoted the development of fieldbuses. Fieldbuses such as CAN, LOONWORKS, FF, etc., as well as HART protocol receiving boards, are all used in DCS systems. 　　　　DCS is divided into three main parts: the controller with I/O boards, the communication network, and the human-machine interface (HMI). It is connected directly to the production process via an I/O board and a terminal block to read signals from sensors. There are several different types of I/O boards, and each type comes with its own terminal board. 　　　　Analog input: standard 4-20 milliampere signal board and a millivolt signal board for reading thermocouples ； 4-16 channels, varying amounts ； 　　　　An analog output is typically a standard signal of 4-20 milliamps; it usually has a limited number of channels, ranging from 4 to 8 channels ； 　　　　l Digital input ； 16–32 channels:　　　　l Digital output; digital input and output are also available on boards with different voltage levels, such as 24 volts and 125 volts DC ； AC 220 volts or 115 volts, etc ； 8-16 channels, varying amounts ； 　　　　l Pulse input, used for the signal of acquisition rate ； 4-8 channels, varying ； 　　　　l Quick interrupt input ； 　　　　l HART protocol input board ； 　　　　l Fieldbus I/O board ； 　　　　Each I/O board is connected to the I/O bus. To ensure the safety and integrity of the signal, it must be processed before entering the I/O board. This processing includes checking upper and lower limits, performing temperature compensation, and applying filtering. These tasks can be carried out on the terminal board or separately; the boards used for this signal processing are now sometimes referred to as signal conditioning boards. 　　　　The I/O bus is connected to the controller. In the 1980s, due to the limited computing power of the controllers in DCS systems, in order to increase the number of I/O points, the controller tasks were divided; in fact, there were three types of controllers. That is: a controller that performs closed-loop operations, an analog data collector, and a logic operator. They each have their own I/O bus, and the I/O buses of different DCS systems vary from one another. If speed is required, a parallel bus is the best choice. Serial buses are generally used more often. Especially when there are many RS485 buses, the I/O count of analog data collectors and logic operators can be higher. 　　　　Closed-loop controllers, analog data collectors, and logic operators can be directly connected to the human-machine interface over a communication network, with each individual controller on the network acting as an independent node. Each node performs a different function. They should all have network interfaces. Some DCS systems, in order to save on network interfaces, connect all the devices used for process control – namely closed-loop controllers, analog data acquisition units, and logic operators – to the control bus in advance, which are referred to as process control stations. This can increase the number of I/O points that the process control station can receive, while also saving on interfaces. It is then connected to the network via an interface, and linked to the human-machine interface. With the development of computer technology, the computing power of controllers has been continuously improving. For example, a controller based on a PC possesses strong capabilities, being able to handle both analog calculations and digital logic operations. A controller becomes a node on the network. Connected to a human-machine interface via the network. 　　　　The controller is the core component of a DCS; it is equivalent to a PC. In some DCS systems, the controllers themselves are PCs. It mainly consists of chips such as CPU, RAM, E2PROM, and ROM, as well as two interfaces: one that receives signals from the I/O bus, and another that sends signals to the network to connect with the human-machine interface. ROM is used to store the control algorithms that carry out various operational functions (in some DCS systems, this is referred to as a function block library). Store functional blocks in the library, such as control algorithms like PID, PID with deadband, integral-separate PID; arithmetic operations including addition, subtraction, multiplication, division, squaring, square root; function operations such as first-order filtering, sine, cosine, X-Y function generators; as well as lead-lag functions ； More advanced algorithms include Smith prediction, C language interface, matrix addition, and matrix multiplication ； Logical operations include logical AND, logical OR, logical NOT, and logical NAND, among others. Typically, station function blocks not only combine analog and digital signals but also connect people. The more function blocks there are, the easier it is for users to write applications (i.e., configure them). The configuration involves connecting functional blocks according to the process requirements to form a control scheme. Store the control scheme in E2PROM. Since E2PROM can be erased and written, and the configuration needs to change as the manufacturing process changes, the configuration is stored in E2PROM. Different users have different configurations. During configuration, the user selects the desired function blocks from the function block library, enters the parameters, and connects the function blocks together. The formation control scheme is stored in the E2PROM. At this time, the controller is in configuration mode; once it is put into operation, it switches to operation mode. The controller is equipped with an operating system, function block configuration software, and communication software. 　　　　To ensure the safe operation of the system, the closed-loop controllers must operate in a redundant manner, with one in use and one as a backup, and this backup is hot-swappable. To ensure successful redundancy, the following points should be noted: the hardware and software versions of the two controllers must be identical ； Check whether the send-receive chip is intact ； Whether the redundant chip is intact. Check whether the settings of the two modules are the same, as well as whether a manual operation station is available, etc. 　　　　The communication network connects the process stations and the human-machine interface into a system. Communication networks have several different structural formats. Such as bus, ring, and star topologies (see figure). In logic, a bus topology is also circular. Star shapes are only suitable for small systems. Whether it is ring or bus topology, broadcast is generally used. Some other protocol methods are used less frequently. The speed of communication networks is around 10M and 100M. 　　　　The human-machine interface has four different types of nodes: the operation station, the engineer workstation, the historical trend station, and the dynamic data server. 　　　　The u operation station is equipped with an operating system, monitoring software, and driver software for the controllers. Displays system labels, dynamic flowcharts, and alarm information. 　　　　The engineer workstation is used for configuring controllers (CAD), as well as for configuring operation stations (to create dynamic flowcharts). If the monitoring software has strong graphing capabilities, the graphing task can be completed independently by it. Another function of the engineer station is to read the controller’s configuration, which is used for controller upgrades and fault detection. We call it the reverse engineering station. 　　　　The historical trend station is used to store historical data, usually with disk arrays (referred to as RAID technology). 　　　　The u dynamic data server serves as an interface between DCS and MIS systems, as well as a device that isolates DCS from the Web. 　　　　The design principles of DCS and PLC differ significantly. PLCs were developed by mimicking the control principles of traditional relays; PLCs in the 1970s had only digital logic control, and they were first applied in the automotive manufacturing industry. It stores instructions for performing logical operations, sequential control, timing, counting, and arithmetic operations ； And various machines or production processes are controlled through digital input and output operations. The control programs developed by the user reflect the technological requirements of the production process, and are stored in the user program memory of the PLC in advance. During operation, it executes each instruction according to the content of the stored program in order to carry out the operations required by the process flow. The CPU of a PLC contains a program counter that indicates the storage address of the current program step. As the program runs, this counter increases by 1 with each step executed; the program proceeds sequentially from the starting step (with a step number of zero) to the final step (usually the END instruction), after which it returns to the starting step to repeat the cycle. The time required for a PLC to complete one cycle of operation is called a scan period. For different models of PLCs, the cycle scanning time ranges from 1 microsecond to several dozen microseconds. Loop operations such as the program counter are something that DCS does not have. This is also why the redundancy of PLCs is inferior to that of DCS. DCS was developed based on operational amplifiers. All functions and the relationships between various process variables are represented as function blocks (some DCS systems refer to them as expansion blocks). DCS in the mid-1970s had only analog control. In a system like the TDC2000, one controller can perform calculations for 8 PID loops per second. The first industry to apply it is the chemical industry. The main difference between DCS and PLC lies in the logical processing of digital signals and the calculation of analog values; even though there has been some overlap between the two over time, differences still exist. After the 1980s, in addition to logical operations, PLCs also had algorithms for use in control circuits; however, performing some complex calculations remained difficult. PLCs are programmed using ladder diagrams, and performing arithmetic operations on analog values is not very intuitive in such programming, making it rather cumbersome. However, in terms of computation logic, it boasts a speed advantage; it takes less than 1 millisecond to compute a 1K logic program, on the order of microseconds. It treats all inputs as digital signals, with 16 bits (or 32 bits) constituting one analog signal. DCS treats all inputs as analog values, with 1 bit representing a digital signal. Solving a logic problem takes anywhere from a few hundred microseconds to several milliseconds. It takes the PLC a few dozen milliseconds to perform a PID calculation, which is on par with the computation time of a DCS. Large PLCs use another CPU to perform analog calculations. Send the calculation results to the PLC controller. Different models of DCS take varying amounts of time to compute the PID, but all are in the range of several tens of milliseconds. Like the early TDC2000 system, it completes control calculations for 8 circuits in 1 second. With the advancement of chip technology, the time required to compute an algorithm is decreasing. The time required to solve an algorithm depends on the arrangement and configuration of the functional blocks. 　　　　In terms of ground resistance, the requirements may not be high for PLCs, but for DCS it must be below a few ohms (usually below 4 ohms). Analog isolation is also very important. In areas with explosion hazards, intrinsically safe barriers should be installed. 　　　　For systems with the same number of I/O points, using a PLC is cheaper than using a DCS (approximately 40% in cost savings). PLCs do not have dedicated operation stations; the software and hardware they use are standard, which means their maintenance costs are much lower than those of DCS. A PLC controller can handle thousands of I/O points (up to over 8,000 I/Os). The controllers of DCS can only handle a few hundred I/O points (no more than 500 I/Os). If the controlled objects mainly involve equipment interlocks with few circuits, a PLC is more appropriate. If it is mainly analog control with many functional operations, a DCS is the best choice. In terms of redundancy in controllers, I/O cards, communication networks, etc., as well as advanced calculations and industry-specific requirements, DCS is far superior to PLC. Due to the use of general monitoring software, PLCs make it easier to design management information systems for enterprises. 　　　　It is particularly important to note that a dedicated operation station for DCS is not an inherent necessity. It was formed for historical reasons. If DCS manufacturers fail to make the operation stations connected to the factory’s management information system, certain DCS systems risk disappearing from the market. 　　　　With the emergence of new technologies, negative impacts follow as well. With the introduction of new operation stations, viruses and hackers can more easily invade the system. When designing, set a password at the operation station, and implement additional isolation and firewalls for the system. Minimize the negative impacts.

DCS Tutorial – Multi-screen operation stations, the backdoor network of operation stations, and dual-machine dual-network configuration. A DCS system can have multiple operation stations, and each station can display the same information; this is known as redundant operation. It can also be different content. For power plants, for a 300MV generator set with a relatively centralized process flow, it is considered appropriate to use two operation stations in a redundant configuration. However, for large units, due to the large number of input and output points, one monitor is not sufficient; it is better to have multiple monitors. At this point, the monitoring software should be able to support multiple screens. Early DCS systems used additional display cards installed on the host computers at the operation stations, such as 2 or 3 display cards. It can connect 2 CRTs or 3 CRTs respectively. Use this method to enhance the human-machine interface. For production processes other than power plants, such as cement plants and steel mills, the production process is long and spread over a large area; it is controlled by a DCS system with a large number of input and output points. To save on investment, one operation station is usually assigned to handle part of the production process. For example, in a cement plant, the rotary kiln and the grinders are far apart, so the control stations can be installed in two different locations. At this time, one printer is configured per operation station. If the host of one of the operation stations fails, the content displayed on that operation station will disappear. To ensure the safe operation of the system, an overlapping configuration of tags is used to achieve safe operation. If the system has two operation stations, namely Station A and Station B, and it contains 2000 tags, then Stations A and B need to be configured with 1300 tags each, of which 300 tags are common to both stations. Even if Station A fails, the system can still operate normally by using only Station B for monitoring. Because the important labels are all available at Operation Station B. It is worth noting that overlapping configurations can also have negative effects. When a malfunction occurs during operation, it results in unclear responsibilities for the managers at stations A and B. 　　　　Thanks to the rapid development of network technology, the number of human-machine interfaces can be unlimited. The operation station is divided into a master station and a slave station. The master station is connected to the DCS network. Data from the databases of various controllers is read directly from the DCS network via 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 displaying the flowchart, the master station shows the complete process image, while the slave stations display the process image from the master station. The number of slave stations is unlimited. Both the master station and the slave stations are connected via a backdoor network. With a backdoor network, text copying can be performed between various operation stations during system maintenance. When the system is in operation, even if one of the main control stations fails, its secondary station can function as a secondary station for the other main station. In a network, connected to a print server, the server has multiple channels, and several workstations share one or several printers. This network that connects the master station and the slave stations has no relation to the DCS network. That’s why it is called a backdoor network. Early backdoor networks used ARCNET; later, as the operator station hosts in some DCS systems adopted DEC minicomputers, backdoor networks switched to DECNET or Ethernet. When configuring tags at the operation station, it is up to the user to decide whether to configure important I/O points in an overlapping manner. 　　　　Thanks to the development of network and database technologies, there are new ways for human-machine interfaces to connect to DCS networks. Connect the server to the DCS network. The server and the human-machine interface form a server/client architecture, with an Ethernet connection between them; due to the low cost of Ethernet, a dual-network setup is often used. To enhance the security of servers, redundancy is employed, which is known as dual-server dual-network configuration. Remote operation is possible. The client includes an operation station, an engineer station, a historical trend station, and an MIS system interface. The databases in the server can be configured. 　　　　Transmitting information over a network in a localized area brings great convenience. 　　　　The DCS systems of Beijing HollySys, as well as ABB’s PROCONTROL P, have such a structure. See the figure below. If process control is connected to the Internet, it can be invaded by viruses or hackers. Be sure to set up a security level and a firewall. In terms of usage, domestic DCS systems have reached a high level in terms of structure and hardware manufacturing. Further efforts are needed in the development of functional blocks. 　　　　The protocols between Ethernet devices follow the seven-layer protocol of the OSI model (Open System Interconnection). The seven layers of the protocol are the physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer. 　　　　The physical layer describes the transmission medium, connectors, and signal pulse standards. A repeater or hub is also a device at the physical layer, and it is independent of the specific content of the information frames being transmitted. A frame is a set of digital pulses sent onto the medium. Used to transmit information. The size of a frame is 64-1518 bytes. A frame includes a pre-synchronization signal, a message header, data information, and a frame checksum sequence. A repeater or hub simply amplifies the electrical signal in the wires and sends it on its way. 　　　　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 fibers) and multiple network layer standards. It connects the physical aspects of a network (cables and digital pulses) with the abstract world of software and data streams. Information transmitted over a network is sent in frame format. A frame has a header and a trailer, with datagram packets enclosed within it. Detection error; adjust data traffic. A frame message consists of the source and destination media access control (MAC) addresses, and a CRC trailer is generated using this information along with the content of the data area. The data link layer sends frames in accordance with the topology rules of the network, forwarding them to the physical layer (network cables). Bridges and switches are devices at the data link layer. Because they are frame-supporting. Both use the information in the frame header to regulate traffic. The frame header is responsible for identifying who sent the message and where it is being sent. The frame header contains two fields used to identify the source and destination of the transmission, which are the node addresses of the source and destination systems. The size of the frame header is always 14 bytes. 　　　　The network layer describes how systems on different network segments find each other, and it also defines web addresses. A website address is a name or number assigned to a group of physically connected systems. It is the cornerstone of all upper layers; the unit is the datagram. Protocols such as the IP datagram transmission protocol in networks are examples of the functions of the network layer. The term “website” varies in name depending on the protocol used. When IP is used, it is called a subnet. 　　　　The transport layer handles the actual processing of data and prepares it for transmission over the network. If the data is too large to be transmitted as a single frame, the transport layer breaks it down into smaller parts and assigns sequence numbers to them; these sequence numbers allow the transport layer on other systems to reassemble the data into its original form. The CRC verification for frames is performed at the data link layer, while the transport layer can serve as a backup verification mechanism. The functions of the transport layer include IP’s transport protocol (TCP), with the unit being a segment. 　　　　The session layer handles the establishment and maintenance of connections between two or more systems. It ensures the proper completion of specific service requests. 　　　　If the system is running multiple network applications, the session layer is responsible for maintaining the correct order of communication, ensuring that incoming data is directed to the appropriate application. 　　　　The presentation layer ensures that the data is received in a format suitable for use by applications. Its task is encoding and decoding. 　　　　The task of the application layer is to determine when to request access to network resources

DCS Tutorial – Loop Controllers and DCS Systems. In the 1970s, since instrument engineers working on site were not very familiar with digital control, they wanted the digital control panels to look similar to the traditional analog instruments, so as not to change operating habits; additionally, this was done to spread risks, which led to the development of loop controllers. Examples include HONEYWELL’s KMM series, FOXBORO’s SPEC 200, and Japan’s Hokushin (which later merged with Yokogawa)’s HOMAC series. These systems feature bar graphs on the panel showing process variables (PV), setpoints, and control outputs (CO), as well as pointer displays for the process values, along with functions for switching between manual and automatic mode and confirming alarms. This digital instrument, capable of performing PID-based loop control, has only one or two loops (two single loops). At that time, some people referred to such instruments as programmable regulators in order to avoid confusion with programmable logic controllers (PLCs). By the 1980s, a range of digital instruments emerged, including two-circuit (capable of operating as two cascade circuits) and four-circuit controllers, 32-channel data collectors, and paperless recorders. These instruments retained bar graphs and manual/auto switch options on their panels, using digital displays instead of pointer displays; all such digital instruments were collectively referred to as circuit controllers. 　　　　So far, there are many types of such instruments. What sets it apart is its ability to communicate with a higher-level system, namely the human-machine interface, to form a complete system. Each module can be connected to a field bus, and the I/O capabilities can be expanded as needed. The algorithms used within it are pre-programmed in the form of functional blocks and stored in ROM. It can be configured according to the required control strategy (not programmed). For example, the 353 product from the American company MOORE consists of over 80 functional blocks; control configuration is achieved through configuration maps, and it connects to the human-machine interface via MODBUS. The monitoring software for the human-machine interface can be either IFIX or INTOUCH. Because both of these software packages have driver software for such programmable regulators. As long as domestic monitoring software has driver software for such programmable regulators, it can also be used as monitoring software for this type of system. Otherwise, it won’t be able to connect. The 353 itself has only 4 AIs and 2 AOs, which means it can control 2 PID loops. If a control loop is to be added, a fieldbus should be used, as it has a LONWORKS interface that allows LONWORKS modules to be connected to this bus. When assembling the system, software ** is required. For data security, optoelectronic converters are added between the table and the bus. This system is shown in Figure 1. Another example is the circuit controllers from FOXBORO and SMAR companies, which come in multi-circuit versions. It also has an interface with programmable logic controllers (PLCs), which is why it is widely used in our country as well. 　　　　If there are several analog outputs, it is called a controller with several circuits. There can be more analog inputs than analog outputs. There can also be a small number of digital input and output channels. 　　　　Another type is those that cannot be connected to a fieldbus; their number of I/O points cannot be expanded, but they can still form a system together with higher-level communication devices. Products of this type include UDC from the American company HONEYWELL, other products from FOXBORO, Fisher’s 900 series, as well as similar products from Japanese companies such as Yokogawa, Fuji, and Toshiba, and from the European company ABB. The most representative product is **Euroland’s System 6000, which incorporates circuit controllers from various British manufacturers, programmable controllers from the United States, and monitoring software from the same country; these components are integrated together to form the S6000 system. . Due to its strong sales network, it is widely used on the mainland. It is particularly widely used in the pharmaceutical industry. 　　　　Digital meters, whose sheer abundance can be described as overwhelming, implement the PID algorithm in a fixed manner; once the process variable (PV) is connected to the meter’s terminals and set values are entered manually, the meter can output the control value (CO). In other words, a meter has only one functional block, namely PID; there are already many such products both domestically and abroad. For example, Chino in Japan produces such meters, as does Asahi. In China, companies such as Tianchen, Tianjin Instrument Factory, and the instrument manufacturers in various coastal provinces also produce such products. In China, they are sometimes called S-series instruments. The appearance of the product is shown in Figure 3. Its function is very simple; a single watch can only perform one function. The feature is that it cannot be configured. The price of each watch is only a few hundred yuan. But imported ones also cost around 4,000 yuan. 　　　　Overall, the circuit controller has very few input and output points. If there are hundreds of I/O points and dozens of PID control loops need to be managed, with each panel requiring a housing and a gauge display, the cost is much higher compared to plug-in modules. Furthermore, it has far fewer functional blocks compared to DCS controllers, as its memory is limited; this makes it even less suitable for use as a loop controller when there is a large amount of analog data to be collected, along with digital signals and complex calculations. If there is no upper-level display, it feels less intuitive. Systems integrated by loop controllers, along with CRT-based human-machine interfaces, are much more expensive than DCS systems made up of modules. There is another drawback: systems composed of loop controllers generally use MODBUS to connect to the human-machine interface, and can only adopt a star topology, meaning there is only one master station. For power plants that require redundant operation stations, this is a flaw. Therefore, it is only suitable for relatively small systems, namely those control objects with a small number of I/O points but many control loops. Pharmaceutical factories that produce antibiotics are quite suitable for this. Furthermore, especially for some chemical companies that often carry out operations outdoors, it has unique advantages. Just like the bypass systems in power plants, it is also appropriate to use them. In other words, it also holds a certain market share. Their design principle is no different from that of DCS. Combining the DCS controller with its corresponding operator station results in a programmable regulator. Therefore, the loop controller is a component of the DCS system and, in essence, still belongs to the DCS. 　　　　DCS, PLCs, and programmable regulators are all computer-based control systems. What they have in common is that their basic structures are similar; there are several essential components, with only slight differences depending on the scale of the system and the nature of the process being controlled. To read the on-site signals into the control system, first connect the sensor’s signal wires to the terminals. If there is more than one sensor, it has additional signal wires and requires some signal preprocessing, in which case a terminal block is needed. To convert analog signals into digital signals, an analog input board is required. After calculation and output, to convert the digital signal into an analog signal, an output board is required, followed by a terminal board. Finally, the signal is sent to the actuator (such as a valve). Due to the development of communication technology, in control systems only the computing component (i.e., the controller) can be considered; if a Fieldbus Foundation is used, this component can be omitted. Store the function blocks for arithmetic operations in the memories of the sensors and actuators respectively. It is invoked over the network during configuration. At present, due to the limited number of functional blocks that have been developed and the interests of various manufacturers, this type of bus is not yet widely used. FISHER-ROSEMOUNT has done a lot of work on fieldbuses. 　　　　For larger systems, it is essential to have a human-machine interface based on CRTs (or LCDs) in order to make them more user-friendly. For users, a DCS tutorial that requires low investment, is easy to use, and comes with comprehensive functions is the one that’s suitable – data acquisition systems, as well as soft DCS and soft PLCs. A data acquisition system merely collects field signals and transfers them to a control computer; it does not have any circuit control functions within the computer. It is only for display on the human-machine interface. It can be said to be relatively simple. As for the hardware structure, it can be divided into three levels or two levels. They are the I/O board, controller, and human-machine interface, respectively. Simply put, it can be divided into I/O boards and human-machine interfaces. However, some industries have certain special requirements. For example, the control systems in power plants often separate boiler control from the data acquisition system. The boiler control uses a DCS, while the others use a Data Acquisition System (DAS). There are also many manufacturers worldwide that produce data acquisition systems. Under normal circumstances, there are no technical issues with data acquisition systems, but power plants have some special requirements. There are some aspects in power plants where it is necessary to record the sequence of events. It has a fast interrupt function (usually 2 milliseconds). There aren’t many such points; it’s around 100 digital inputs and outputs. The resolution of the input board should be in milliseconds. Its difficulty lies in event sequence recording (SOE). The input panel should have a function to store historical data. When the human-machine interface is displayed for viewing, it can show the chronological order of the events. SOE (SEQUENCE OF EVENT) is manufactured by specialized manufacturers. Some DCS systems designed specifically for power plants also have such functions. 　　　　A commonly used data acquisition system is the OPTO22 product from the United States; it consists of small modules, with ones for digital signals (DI, DO) and analog signals (AI, AO). A total of 42 types of small modules are available for users to choose from, with different voltage levels and more. When in use, the small modules are installed on a large board (i.e., Board B1 and Board B2); there are 8 analog modules per board and 16 digital modules per board. In addition to these small modules, Boards B1 and B2 also have serial communication ports. Then install these two types of panels on a rack, and mount the rack inside the cabinet. The CRT-based human-machine interface runs on the WINDOWS platform. Monitoring software equipped with MODBUS driver software is used; previously PAREGON software was employed, but it is less used these days. FIX and INTOUCH are more commonly used now. The human-machine interface can read the I/O signals from the small modules and display them on the CRT. There are over 20 factories in the United States that produce similar products. It is in the same category as STD bus products. Products based on the STD bus have gradually disappeared from the market because they require a large amount of work from users during use. 　　　　In some purely acquisition-based systems, OPTO products are widely used. The main advantage is low maintenance requirements. If closed-loop control is required, a controller similar to that of a PC (LC4) is added between the human-machine interface and the I/O. This controller contains several functional blocks that allow for the configuration of various control strategies. Under normal circumstances, since the number of function blocks is relatively small, OPTO22 is not often used in large control systems with thousands of I/O points. 　　　　The most common application of OPTO digital signal small modules is as isolation modules for DCS digital input modules. Protect the DCS itself from lightning interference. Due to its relatively simple manufacturing process, domestic modules have received positive feedback from users regarding their performance, and their price is less than half that of imported ones. 　　　　In the early 1990s, due to the development of computer technology, it was argued that ordinary microcomputers (PCs) were already highly mature, as their processing speed and memory capacity were sufficient to meet the requirements for control tasks. Operation is divided into front and back ends. Neither DCS nor PLC requires controllers; transferring the function codes and ladder diagrams from DCS and PLC controllers to PCs running the NT operating system is a rather difficult task. It is directly connected to the I/O board by a microcomputer. Since the control algorithm is already available on the PC, the PC serves both as a human-machine interface and as a controller; some people refer to them as soft DCS or soft PLC. American company AB has soft PLCs. The PCs are connected to each other via Ethernet. So far, its application is still not very widespread. Some small systems use SOFT DCS and SOFT PLC. 　　　　

DCS Tutorial – Function Blocks in DCS Controllers DCS not only can perform the functions of traditional analog instruments, but it also **exceeds them**. This is because it utilizes four key technologies: advanced computer technology, communication technology, CRT technology, and control technology. With digital control, the algorithms stored in ROM within the controller are virtually unlimited, with each algorithm representing a specific function. In analog meters, these functions are implemented using analog circuits, and they are subject to the limitations of components such as drift, resistance, and capacitance in those circuits. Creating an analog meter with very high precision is costly, and in fact almost impossible. And the digital control algorithms are implemented through programs. Use programs to replace the functions that simulated circuits can perform. Theoretically, it is infinite, which is a significant advancement. The principle is the same for various DCS systems. Various algorithms are commonly referred to as functional blocks. The assembly of function blocks is called a function block library. 　　　　The controller of a DCS is mainly composed of a CPU, ROM, RAM, E2PROM, address setting switches, etc. The CPU performs calculations, while ROM is used to store the operating system and function block libraries. The arrangement of function blocks in ROM is fixed and cannot be changed by the user. RAM is used to store the CPU’s calculation results and I/O signals. Control scheme formed by E2PROM storage function blocks. When power is turned off, the control scheme is not lost. Not only that, but if the control scheme is inappropriate, it can also be modified. The modification is carried out using ultraviolet irradiation to erase the contents in the E2PROM. The controller should have an address in the network, which is set by these address switches. The arrangement of function blocks in ROM is referred to by some DCS systems as a function code. The order of the codes corresponds to the addresses of the function blocks in the library. Different manufacturers’ DCS systems vary in the way they handle calculation algorithms, which is why their names differ as well. Some DCS systems refer to these algorithms as internal instruments, but in reality they are all just programs, and their essence is the same. When using these functional blocks, it is necessary to indicate the relationship between the inputs and outputs of the block, as well as the various parameters required for the calculations. When a user determines a control strategy to formulate a control scheme based on the controlled object, they select the functional blocks required for control from the function block library, clarify the connection relationships between these blocks, and first define their addresses in the E2PROM; the connections to other functional blocks are also represented through addresses. Enter the required parameters at the same time. These tasks are called configuration, to distinguish them from programming in a language. During configuration, it can be done using graphical methods, that is, the CAD approach. There is a CAD software that can draw the functional blocks required for each control loop, as well as their interconnections. It is called the engineer station. Use it to configure the controller. During configuration, first draw a SAMA diagram or an ISA diagram. When using small functional blocks, draw a SAMA diagram; when using large functional blocks, draw an ISA diagram. 　　　　The most important function block in the function block library is the PID function block. The relationship between its output Y(t) and input X(t) is based on the proportional-integral-differential principle; it plays an extremely important role in process control. The PID function block must be used when implementing closed-loop control. 　　　　　 　　　　The PID function block containing PV-SP performs proportional-integral-derivative calculations on the difference between the process variable (PV) and the setpoint (SP); its parameters include the setpoint, the process variable, and the coefficients for proportional, integral, and derivative actions. Its output is usually sent to the address on the terminal board of the output board. Finally, the output is sent to the valve. Generally, the PID function block includes the PV-SP calculation. Some PID function blocks do not have subtraction operations for SP and PV, which is to allow other operations to be performed before the PID. Such as adding a dead zone. Another important functional block in the function block library is the station functional block. It cannot express the direct relationship between inputs and outputs using mathematical formulas; it serves to facilitate communication between humans and machines, by transmitting the set values determined by humans to the control loop, as well as the conditions under which the control loop should be activated and the conditions for switching between manual and automatic mode. 　　　　The PID function blocks in some DCS systems are almost all-inclusive, with over 100 parameters. 1. First, ask where the PV comes from; the address of the PV needs to be entered ； The PV value comes from an analog input module or terminal block ； 2. The address of SP; the address of SP is usually the address of the station ； 3. Is there a dead zone? If there is no dead zone, then there’s no need to worry about this aspect; if there is a dead zone, the width and height of that dead zone need to be specified ； 4. Is integration required? Yes, it is. What is the integration constant? 5. Is differentiation required? Yes, it is. What is the differentiation constant? ； 6, what is the ratio? ； 7. Whether to use a dead zone: if yes, the width and height of the dead zone need to be entered. 8. Should a Smith estimate be used? If so, the parameters of the Smith estimator need to be filled in ； 9. Where does the output of the PID function block go? For example, to an analog output module or to the function blocks on the terminal board. Its output is directly to the valve. The output can also be sent to memory, but an address must be specified. At this point, the output of the PID function block becomes the input of another function block. In cascade control, for example, the output of the first PID serves as the setpoint for the second PID. In this case, there are two PV values, and two station function blocks are used; however, only one of these station function blocks has a manual/auto switching feature. The manual control station and the operation station communicate directly with this function block, with the priority of the manual control station being higher than that of the operation station. 　　　　Arithmetic operations such as addition, subtraction, multiplication, division, squaring, and taking square roots are essential in DCS. Next are function operations, trigonometric geometry operations, matrix operations, C language interface blocks, and Basic language interface blocks, etc. Function blocks connected to hardware, such as those for reading analog and switch inputs, functions blocks for analog and switch outputs, function blocks for reading analog and switch values from the network, and function blocks for sending analog and switch values to the network. 　　　　As a DCS controller, the functional blocks that must be available include: there are usually 4 functional blocks for connecting to the hardware, and this depends on the type of input board ； It includes analog input function blocks, analog output function blocks, digital input function blocks, and digital output function blocks. Each functional block must be connected to a specific terminal board. If there are signals from the field bus to be received, a functional block for receiving those field bus signals is also required. There are also 4 functional blocks connected to the network. They are respectively: analog network input, analog network output, digital network input, and digital network output. Next are the PID function blocks and station function blocks, followed by arithmetic operations (addition, subtraction, multiplication, division). Then come function operations (single filtering, lead-lag, 2D curves, etc.), trigonometric operations (sine, cosine, tangent, cotangent, etc.), and 3D matrix operations. Some advanced operations, such as fuzzy logic and model control, are optional, but they serve as criteria for assessing the strength of a DCS system’s performance. As for the functions of the subjects under investigation in certain industries, they require some special hardware support; for example, the SOE function in power plants necessitates a hardware input board with fast interrupt capabilities. 　　　　To increase the number of I/O points on the controller and to allow it to be placed at a greater distance from the field, a field bus can be used to connect the controller, such as the LonWorks bus; in this case, the controller should have functional blocks for connecting to LonWorks. The modules on the Lonworks bus have separate input/output boards and a processing board, which also contains a small number of functional blocks. 　　　　

DCS Tutorial – Interconnection of heterogeneous systems, time synchronization, and SDSL technology. A company, especially medium and large-sized ones, has many process streams, each of which operates with relative independence. Depending on the period of construction or the timing of technical upgrades, different models of DCS systems will certainly be used, while various models of PLC systems will be employed for equipment interlocks and control. To establish a comprehensive management information system within an enterprise, the interconnection and time synchronization of heterogeneous systems become very important issues. In the early days, the interconnection between DCS and PLCs was achieved by using the PLC as an input card for the DCS; DCS experts designed an interface card for the PLC, which was connected to the DCS’s own I/O cards on the same I/O bus. The controller reads the signals from the PLC and sends those signals to the DCS operation station via the DCS network. A major drawback of this interconnection method is that the fast signals from the PLC are displayed on the DCS operation stations, which have a slower response time. It has been determined that it takes several seconds or more for the operation of a microswitch to be reflected on the DCS operator station. Some DCS even require 8 seconds. Another method of interconnection is to connect the individual signals from the PLC using hard wires to the input board of the DCS; this results in a small number of input points, but the cost is relatively high. Some DCS systems design a node on the DCS network, which is dedicated to reading signals from PLCs. It is relatively difficult to feed PLC signals into the DCS network. The downside is that the cost of developing the interface is very high. Even if development is successful, the interfaces often fail. A typical example is a power plant that generates electricity using gas turbines and boilers; the gas turbines are imported from the United States or other countries, and their control systems (PLCs) are supplied as part of the main equipment, while the control system for the boilers is chosen by the user themselves. The user desires to display information from both systems on a single control station. To develop this operation station, the development costs exceeded several tens of thousands of dollars. Even when developed successfully, failures often occur. 　　　　For PLCs, dedicated operation stations were developed in the mid-1970s, but they were not very successful. Later, no dedicated operation station was developed; at that time, PLCs handled only digital signals, and the digital display on the controller served as a human-machine interface, which was sufficient. The controller of the PLC is connected to the I/Os via a network. By the late 1980s and 1990s, analog control was introduced into PLCs. Users found that human-machine interfaces based on CRTs to be very inconvenient; therefore, they opted for general-purpose monitoring software that runs on the NT platform, using ordinary computers as the hardware foundation. Driver software for each PLC was developed, thereby providing an operation station for those PLCs as well. 　　　　For general monitoring software such as INTOUCH, it supports communication protocols developed by Microsoft, including DDE (DYNAMIC DATA EXCHANGE), Fast DDE, and Network DDE. 　　　　DDE allows machines running under Windows to establish client/server relationships, send and receive data, and issue commands to one another. The server provides data and receives requests for data of interest sent from other machines in use. The machine that sends requests is the client, while the one that sends data is the server. 　　　　u Quick DDE allows many DDE messages to be packed into a single DDE message. Packaging improves efficiency by reducing the DDE data transmitted between servers and clients. 　　　　U-Network DDE extends the capabilities of standard DDE, including communication over local area networks via serial ports. The extension of the network allows different computers connected to it to function as servers or clients for DDE connections. For example, network DDE supports DDE between IBM-compatible computers connected to a LAN or modem, and PC-based platforms in operating environments such as VMS and UNIX. 　　　　u SuiteLinkK is used for TCP/IP-based protocols and is designed to meet industrial requirements such as data integrity, high throughput, and easy diagnosis. This protocol standard is only applicable to Windows NT 4.0 and later. 　　　　The u OPC (OBJECT LINKING AND EMBEDDING PROCESS CONTROL) client can retrieve data from the server. Comply with the TCP/IP protocol. 　　　　Due to the demand for monitoring software, many manufacturers have come to develop it. In the 1990s, there were over 100 such systems, including FIX, INTOUCH, PARAGON, ONSPEC, CIMPLICITY, and others. In China, there are products such as KingView and SYNALL. Various monitoring software vendors have developed numerous driver programs for DCS and PLC systems, among which FIX and INTOUCH offer the most such drivers. On the NT platform, if FIX and INTOUCH software are used, they can function as either servers or clients to each other, allowing them to exchange data. 　　　　When DCS was introduced in the 1970s, computer technology was still relatively underdeveloped, and there were few components available on the market. The operation stations developed by DCS manufacturers come equipped with a dedicated operating system, specialized monitoring software, dedicated interface hardware and CRTs, as well as dedicated printers, hard drives, and floppy drives. Even the cables and plugs, sockets used for connection are specialized. This also does not rule out the possibility that DCS manufacturers consider it in order to achieve maximum commercial benefits. They are the sole providers of DCS software and hardware; they can only ensure that their own systems can communicate with each other, and despite much effort, it is still not possible to connect them to other systems. Some compare dedicated systems to religious organizations, as they are almost incompatible with others, and each business tries to maintain a market shared with its loyal followers. We often use the term “religious war” to describe discussions between supporters of two different proprietary products or operating systems. 　　　　Due to the rapid development of computer technology, DCS has not progressed as fast as computers and is now in a relatively stable stage of development. Later on, there were many various microcomputer components available on the market, but they could not be connected to DCS systems; heterogeneous systems were even less capable of interconnecting. Moreover, DCS manufacturers did not modify their software in response to changes in the market, so DCS systems became what might be called \"automation islands\". DCS users find it very inconvenient; moreover, compared to controllers, the operation stations are more prone to damage. After approximately 7–8 years of use, since components such as hard drives and floppy drives are not available, many users decide to avoid using the original DCS manufacturer’s operation stations when replacing them, as they are expensive and their spare parts are hard to find. Using PCs and NT platforms, general monitoring software is installed, along with driver software specific to a particular DCS, to create a universal operation station that replaces the original dedicated operation station. 　　　　Some DCS manufacturers simply eliminate the dedicated operation stations and use general-purpose operation stations instead. For example, Moore Company’s APACS system used INTOUCH software in 1996 (FIX could also be used); Moore Company only provided the driver software for APACS along with the hardware configuration requirements, while the hardware was to be assembled by the user themselves. After use, it works very well. It’s a bit better than the monitoring software developed by MOORE Company itself. This may be related to the fact that there are fewer software developers at DCS manufacturers compared to those in general software development companies. Similarly, the operation station of MEASUREX also uses general-purpose monitoring software. Currently, the most common alternative operation stations are the two general types: FIX and INTOUCH. 　　　　In the early days of DCS, manufacturers developed their own dedicated monitoring software. When writing a program, the driver software and display software for the controller are not developed separately. If general-purpose microcomputers and NT platforms are used, their CPU usage is lower compared to general-purpose software, and their hardware requirements are less stringent than those of general-purpose systems. However, since they are sold as part of a complete system, the sales volume is low, and the issues related to the software itself have not been fully exposed. If the hardware can meet both general and specialized requirements, the crash phenomenon is more severe in specialized cases than in general ones. It is understood that in a certain DCS system, where the hardware consists of PCs and the operating system is NT, along with operation stations equipped with specialized monitoring software, the system crashes several times per day. As the software version updates, crashes continue to increase. Several re-nailing attempts were made within a year, yet the freezing issue persisted. Compared to general-purpose software, dedicated software is still more closed at present. It is used on the network, but there is no network suite software yet. If general monitoring software is used, the human-machine interfaces of DCSs with each other, DCSs and PLCs, as well as PLCs with each other, can be interconnected. Any Microsoft WINDOWS interface can serve as a client. Data is read using DDE, Fast DDE, and Suitelink. They can function as either servers or clients. A comprehensive management information system can be established within a company. To ensure the safe operation of the control station, a separate HMI can be used for interconnection. General monitoring software usually comes in a network version; after configuration, it can form a server/client setup over the network to transmit real-time information to remote locations. On the client side, it is possible to view in real time the data in the database of the dynamic data server created by general-purpose software. It can also send information into the standard databases of MIS systems (such as SQL, SYBASE, ORACLE). General monitoring software also includes Web software in its suite; it is installed as a Web server, and operations are carried out through that Web server. Browse the data in the dynamic data server. It is not real-time data. At the same time, Web can also be accessed through Microsoft’s Glance software. Browse the data in the MIS database. Using a web server to browse data is slower than the server/client approach. 　　　　The advantages of using general-purpose operation stations are as follows: 　　　　● Low cost 　　　　● Expansion of DCS functions 　　　　● Familiarity to users 　　　　Networking of different types of machines also requires compliance with the OSI seven-layer model; general-purpose monitoring software is used, and all network components are developed according to open standards. Using general monitoring software can also have negative effects, as some specific functions may not meet the requirements. 　　　　Time synchronization across various systems is also a very important issue. A network time server is a high-quality device for time synchronization across all online workstations. Under normal circumstances, the absolute time of a DCS system is generated at the operation station (human-machine interface), while the controllers only have relative time. For time synchronization, satellite time GPS (GLOBAL POSITION SYSTEM) can be used as a reference to calibrate the DCS time. The specific implementation method is as follows: through a satellite receiving antenna, the time server receives the atomic clocks of various satellites in the GPS system, and then sends the time signals to the dynamic data server or the operation station of the DCS. The time signal is sent to the DCS network via the drive software of the dynamic data server or the operator station. It turns out that Ethernet was less commonly used in DCS networks, but it is now also used because it is relatively inexpensive. It is widely used in Management Information Systems (MIS). Ethernet also uses a broadcast protocol, but it differs from token ring. It uses random-access link control. In an Ethernet network, nodes can transmit data randomly. But when two or more nodes send data simultaneously, a data transmission conflict occurs. All nodes involved in the conflict retreat, and after using a random delay algorithm, they resume sending. That is, the carrier sense/collision detection multiple access technology is used. There are many algorithms for random delay, all of which are currently used in Ethernet. Gigabit networks now support point-to-point communication. 　　　　Currently, the MIS system has been integrated with DCS and PLCs to form a single system. The data from DCS and PLCs is sent to the Ethernet via dynamic data servers, with fiber optics or coaxial cables being the most common transmission media. Coaxial cables are vulnerable to lightning strikes. The control room is usually the central area, from which a star-shaped network structure is formed. Servers are installed in the central area. Such as ORACLE, SYBASE, SQL, etc. Various sub-modules are stored in the server. Such as the financial management submodule, the personnel management submodule, etc. The signals from DCS and PLC come within the real-time production subsystem module. The data generated in real time is massive; it can form its own system with its own servers, which can then be connected to the database of the MIS system. Currently, the transmission medium is also fiber optic or coaxial cable. The cost of laying optical fibers is relatively high (about 20,000 RMB per kilometer). In MIS systems that use optical fibers as the transmission medium, there may be areas that are far from the central area, but some data still needs to be sent to the center for display; in such cases, optical fibers are not necessarily required, and a telephone line transmission network can be used instead. There is very little data from areas such as balance of plant, coal transportation, and water treatment. All that is needed is to add a special Ethernet router to the switch of the telephone exchange, a MODEM at the data source, and make slight adjustments to the wiring. Ethernet routers and “modems” are relatively inexpensive. At this time, fiber optic cables and telephone lines can be used for Ethernet simultaneously. This is the SDSL (Symmetric Digital Subscriber Line) technology. Its significant advantage is that when the phone connection is good, the network connection is also good. Thus, it is easy to maintain. Furthermore, this technology can be used with existing telephone exchanges, eliminating the need for additional wiring costs. 　　　　SDSL (Symmetric Digital Subscriber Line) technology is now widely used in factory networks abroad. If the company is small, fiber optic cables may not be necessary; telephone lines can be used instead, with a communication speed of 2.3M. The rate at which data is read from the information side or commands are sent to it is the same.

DCS Tutorial – Tips for Replacing Components in DCS Operation Stations and DCS Printing Systems. According to incomplete statistics, as many as nearly 3,000 sets of DCS systems of over 20 different models were imported from abroad before 1995; these systems came from the United States, Japan, and Europe. Some systems are dedicated; they come to our country along with the main equipment. Some control systems used in paper mills, such as Measurex ODX, may be introduced into our country along with the main papermaking equipment. Most DCSs enter our country directly. Another example is the Euro mainland System 6000, which is an integrated DCS system. The loop controller is used for process control, and the human-machine interface employs PARAGON software as the monitoring software. Use the serial port of a PC to connect the PLC to the HMI as well. The same manufacturer offers several different models of DCS, which are systems designed for system upgrades or varying system scales. Group those from the same manufacturer together to observe the usage of several DCS systems in China. Users with dozens or more of the following systems include: TDC3000 (TDC2000, R150, S9000), μXL, (CENTUM), I/A (SPECTRUM), N90 (INFI90), PROVAX, RS3(ΔV), APACES, MOD300 (MODⅢ), AC450 (AC210, AC500), WDPF, HIACS, TELEPUM, and MAX-1 (MAX-1000). There are also some systems with fewer than 10 users; for example, there are only 4 units of PROCONTROL P14 in the country, 5 units of D/3, and a limited number of users for the TOSDIC system as well. Regardless of whether there are many or few users in China, what these DCS systems have in common is that many of the components of their human-machine interfaces are purchased from third parties rather than being produced internally; currently, the production of most of these components has ceased. If some DCS operation station hosts use DEC’s VAX or α machines, DEC was acquired by COMPAQ in 1996, and these machines have been out of production for 5 years now; not only are they no longer manufactured, but the chips for them are also no longer produced. If such DCS are still imported now, obtaining spare parts will be very difficult. 　　　　 　　　　For example, the hard drives used in operation stations typically have interfaces such as ST412 (like ST225, ST4096, ST4097, XT1085, etc.) or IDE interfaces; these hard drives are large in size but have small storage capacities. It has been out of production for many years. When the hard drive in the control station is damaged, it can be difficult to purchase an original hard drive; instead, a hard drive from the same series as the original one, with slight modifications to the BIOS, has to be used as a replacement. It is easier to purchase hard drives with a small number of SCSI interfaces. There are also low-resolution CRTs, which generally use RGB input. The CRTs available on the market today cannot be connected to most DCS control stations; once a CRT fails, the control station becomes unusable. The solution is to use a converter in order to connect the current monitor to the DCS operation station, thereby allowing the information from the DCS system to be displayed. For example, ARCHIVE tape drives and TEAC floppy drives are also unavailable for purchase. Finding old products is a difficult task. Even if it’s found, it may not be useful. If it is a hard drive, it may also require formatting or initialization. 　　　　 　　　　If you still want to use the original control station host, you need to equip it with compatible hard drives, CRTs, keyboards, etc. DCS imported in the 1980s sometimes cannot have some spare parts supplied, even by the manufacturers of that DCS. It is available sometimes, but the delivery time is extremely long, making it impossible to meet urgent requests. Its price can be described as exorbitant. Since the DCS manufacturers also purchase these components from third parties, they have to seek them out as well, which results in a long supply time. Each component, such as hard drives, CRTs, tape drives, etc., costs tens of thousands or even hundreds of thousands of yuan. If a new server is needed, it will cost hundreds of thousands of yuan. Therefore, a new approach is needed to purchase these components. When replacing the host, it is sometimes even better to remove the original operation station and replace it with a new generic one. 　　　　 　　　　It is worth mentioning the dedicated printers for various DCS systems; for example, the GENICON printer that can print graphics, whose print heads and ink cartridges are difficult to find. Another example is the alarm printer that was originally included with the DCS system: whenever an alarm occurs, the printer keeps printing continuously. Moreover, the order in which the alarms occur is not recorded, so it’s impossible to determine which alarm happened first; as a result, useful information gets lost among a large amount of irrelevant data. It not only wastes a large amount of printing paper, but it is also difficult to extract useful information. 　　　　 　　　　The printing system was developed against the aforementioned background, with printing software used for the printing management systems of various DCS systems. This printing system can be connected to the operation stations of various DCS systems to form a printing information management system, which includes online alarm records, screen copies, and event lists. It can not only completely replace dedicated printers but also has functions such as storage and querying, making it more suitable for field use. Each printing system can be connected to 4 DCS operation stations. 　　　　 　　　　The core of a printing management system is the printing management software, which is installed on a regular PC and runs on the WINDOWS platform. To ensure data security, RAID technology is employed, with dual hard drives operating in redundancy. This software is a print information management system developed to improve the printing functions of computer-based DCS operation stations, as well as to enhance the capabilities for storing, retrieving, and copying information. It features strong functionality, a user-friendly interface, and easy operation. Using it can fundamentally prevent the loss of information that often occurred in the past when only printers were used due to printer failures, and it can also prevent useful information from being overwhelmed by a large amount of useless information. It allows the print output from the operation station to be saved in file format on the hard drive for an extended period of time (depending on the hard drive’s capacity and the amount of print information, this can be several months or even years), and it is also possible to copy it to other storage devices (such as optical discs). 　　　　 　　　　The printing system can automatically identify elements such as alarm records, control operations, statistical reports, event-triggered reports, screen copies, and configuration lists in the operator station information, and process them separately. With it, it is possible to view in real time the alarm records of the operation station, control operations, statistical reports, event-triggered reports, screen copies, and configuration lists, and to process them accordingly ； It also allows for real-time monitoring of alarm records at the control station, as well as of data and status that require immediate attention, such as control operations; in addition, it makes it easy to view all records that have been received. It is possible to use “offline printing” to selectively print the information that has already been received, as well as to use “online printing” to send the content from the operator station to the printer immediately. 　　　　 　　　　The working principle of printing systems is that printers manufactured by various printer manufacturers all come with drivers that are compatible with the WINDOWS operating system. Meanwhile, the operating systems of most of the control stations in the original DCS were proprietary, containing drivers only for a few specific types of printers. Common printers available on the market don’t have drivers, so they can’t be connected. In fact, the task of the printing system software is to develop reverse driver software for the WINDOWS operating system, so that signals from the DCS control stations can be recognized in a WINDOWS environment. Then, common printers are connected using WINDOWS drivers. The printing system software needs to be able to recognize different data formats, as printers connected to DCS control stations of various models have their own data formats, such as ANSI format and IBM format. Before the printing system is connected to the control station, it is necessary to determine its data format so that it can function within the WINDOWS environment. The printing system software should be programmed to include `reverse driver software for various data formats`. Furthermore, the software for printing graphics and printing text differs greatly. It only prints text; its software is relatively simple, while printing graphics is more complex. For example, when using an HP printer to print graphics, it is first necessary to determine whether it is in dot matrix format or page scan format. Most Hp printers use page scanning; the software interprets PCL commands, allowing the printer to print the graphics on the operator station screen. If it’s not an HP printer, other instructions need to be explained.