PCB Tech - Discussion on PCB CS Control System and Its Application

1 Review of the development of the control system

In the industrial production process, the PLC that came out in 1969 and the DCS that came out in 1975 may be the two most influential computer control systems. The advent of PLC replaced devices such as relays, and realized the interlocking control and program control of switching values; the advent of DCS replaced instruments such as displays and regulators, and realized the indication, recording and PID loop adjustment of analog quantities. Function. In the late 1980s, with the development of computer technology, communication technology, integrated circuit technology, and smart sensor technology, the Fieldbus Control System (FCS) changed the structure of the original control system and made the control system by An important step has been taken from closed to open. In the mid-1990s, PC-Based Control System (PCB CS) began to appear. Many scholars believed that it would be the most promising new technology in the field of industrial automation. They combined PCB CS with PLC, DCS, (or plus FCS) and called the three major (or four major) control systems of industrial production processes. Some people even talked about "most people think that PC control will gradually replace traditional PLC or DCS in the next ten years" in an article four years ago. According to experts from PHOENIX CONTACT, Germany: Almost all consulting organizations believe that by 2005, PC-based control systems will account for more than 50% of the market share.

2 Structure of PCB CS

What is PCB board CS? Combine hardened PC hardware with control software to implement control functions usually performed by dedicated PLC or DCS, or "package" the control functions of PLC in software and run in the PC environment.

The PCB CS control system is mainly composed of the following three parts: PC; I/O components and their connectors; operating system software and application software.

The PC integrates the operation station and control station in the previous PLC and DCS control system, and has multiple functions such as implementation control, communication and operation display. The rapid development of computer technology enables the PC to provide a truly open platform, so that all the functions of the system are integrated on the unified and open platform of the PC to reduce installation space, save cables, and simplify complex communication connections. The Internet or the intranet of the enterprise can obtain important production information and realize the optimization of the production process. For the sake of reliability, PCs usually use industrial PCs. We know that the PC that appeared in the control system in the early days only had the function of a man-machine interface operation station. Later, the function was gradually increased. The PC can complete functions such as alarm, calculation, report, connection to the database, and connection to the office network. In the PCB CS control system, the PC has one more control function, the so-called PC-based control.

The I/O components are also completely open, and can support a variety of I/O hardware from multiple companies, including remote I/O and I/O substations of many PLCs. It can also be combined with fieldbus technology to connect the PC to the I/O device with fieldbus through the fieldbus interface. Since these I/O components are all equipment that has been tested in long-term on-site operation, their reliability is beyond doubt. It's just that it does not need to use a certain series of I/O components of a certain company like the early PLC and DCS control systems, and users can choose their favorite I/O components.

The upper layer is open to a variety of operating system software and application software. There are already a variety of commercial operating system software and application software, and users can also choose their favorite software.

From the above three components, it can be seen that the openness of the PCB CS system is comprehensive, so its current and future development speed will be very fast, and it will never be closed like the previous PLC and DCS control systems. Due to the long-term development lag due to its uniqueness and specificity, it will advance with the times and rapidly improve with the development of computer technology, communication technology, I/O component manufacturing technology, fieldbus technology and software technology.

3 Advantages of PCB CS

The advantages of the PCB board CS control system can be summarized as: low price; easy access to various control and business applications and information; excellent portability of software to new hardware platforms; control, man-machine interface and programming Functions are easy to integrate; it is easy to integrate process control, logic control, batch control and motion control into one; it does not rely on various proprietary control systems.

For example, PC has obvious advantages in CPU, memory, etc. When performing data processing (such as analog operation), the operation speed of PC is usually more than 10 times that of PLC and DCS. This is because the PC in PC BCS The machine can keep pace with the most advanced PC product technology. At the same time, the PCB CS control system can also save investment in CPU, power supply, rack, cabinet, wiring, etc.

German scholar Dr. Eberhard Grotz believes that the seven trends of PC-based automation control solutions are: more and more PCs are used in automation control technology; more and more PC-specific software, people can use PCs Programming and operation are like on a programmable controller; the application of system software that can complete real-time and control tasks on a PC is becoming more and more extensive; traditional PC programming has greatly promoted the production by using new programming techniques. Advances have led to the rapid development of PC-based automation control technology; PC-based automation standards are increasing; Internet technology is becoming more and more important in automation control technology; distributed systems will change the way of automation control.

4 PCB CS products

Major PLC manufacturers, such as Siemens, ROCKWELL automation, GE Fanuc, and Mitsubishi Electric have launched their own brand of PCB board CS control system products. The characteristic is that the controller has been changed to PC control. It communicates with each other through a control bus or communication interface. The original remote I/O component connection of each company indicates that the PLC manufacturer has accepted the technical route of PCB CS control. The Siemens Energy and Automation Group ISBU Center in Princeton, New Jersey, USA, focuses on PC-based automation. The controller in its PCB CS is SIMATIC WinAC (Windows Automation Center), which is fully compatible with SIMATIC S7 series PLCs. Complete PLC control function, its I/O interface uses communication module to connect Profibus-DP to realize SoftPLC control.

In 1995, the TCS (Tailored Control System, Flexible Control System) system proposed by Wayson Industrial Company has 7 structural types, one of which is to use a PC to directly bring the I/O module to the scene, which is used to run on the PC. The internal soft logic controller replaces the controller, which is used for occasions with more acquisition points but less control.

The American Entivity Company (formed by the merger of Think & Do and Steeplechase) uses an embedded operating system, Windows CE, to cooperate with hardware manufacturers to launch a new PCB CS product-WinPLC, which is a small PC mounted on the I/O substrate The computer, including the solidified Windows CE operating system and the Runtime environment of Think & Do application software, can run Think & Do application programs developed by ordinary PCs to realize the control of I/O modules on the same substrate. The WinPLC system can run independently from the development PC, and is suitable for small-scale control systems that do not require monitoring screens; when the system needs monitoring screens, a computer equipped with Think & Do software can also be connected to the WinPLC system via Ethernet Connect, use the computer as the upper operator station. According to some experts, traditional PLCs have hard real-time characteristics, which can guarantee the I/O scan cycle and interrupt response. The Windows NT/2000 operating system used by the PC is not a real-time system and cannot guarantee the interrupt response time or task execution cycle. Certainty. The emergence of Windows CE 3.0 makes PC-based control further in terms of real-time performance, even surpassing any PLC, ensuring accurate reading and writing cycles and program cycle cycles.

Some manufacturers that mainly produce I/O components have also joined the ranks of promoting PCB CS products. For example, the I/O products produced by the German Beckhoff company can be equipped with various field buses, such as PROFIBUS, INTERBUS, CAN, and ControlNet., DeviceNet, etc., his PCB CS products are composed of fieldbus system with I/O interface, Windows NT/2000 operating system, Beckhoff TwinCAT control software, and industrial PC. PHOENIX CONTACT, Germany, has been the first to propose and develop a PC-based control panel since 1995, and adopts the programming language of the PLC international standard IEC61131-3 to develop a complete set of control software based on PC technology. PC-WorX.. This set of software organically combines fieldbus management software, PLC control software, and monitoring software interface OPC, and can communicate directly with intelligent bus modules through INTERBUS or ETHERNET.

The ADAM-5510/P31 product launched by Advantech in May 1999 uses the Paradym-31 software package, which contains three languages: sequential function diagrams, ladder diagrams and function block diagrams specified in the IEC1131-3 standard. PCB CS products launched early.

The FOCS system of Beijing Hollysys currently has two structures: local type and compact type. The local system is composed of I/O modules with fieldbus, main controller, and operation station, and the compact system is composed of I/O modules with fieldbus and control station. The control station here is a PC, which completes the functions of the local system main controller and the operating station, such as monitoring, operation, control, networking, configuration programming, and so on. It can be seen that the compact system of FOCS is a PCB CS control system. Because of the first use of such technology, manufacturers are currently positioning the system as a low-cost data acquisition system and a control system with fewer adjustment loops. Both power supply and I/O modules can be configured redundantly. In fact, the FOCS compact system can still be used in occasions with high reliability requirements.