A preliminary study on the operation and maintenance of I/A Series DCS control system

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1 Overview The automatic control system of the synthetic ammonia and urea plant of Chongqing Jianfeng Fertilizer Co., Ltd. is the I/A Series DCS distributed control system of the American FOXBORO Company. It adopts a hierarchical structure and local communication technology. It has rich function control, display, process alarm, report statistical management and other software packages, a super human-machine operation interface and high reliability. Since it was installed, commissioned and put into operation in 1992, it has been running continuously for 15 years. With the aging of some electronic components of the card, system defects and failures have increased year by year, affecting the safe and stable operation of the system. In recent years, with the continuous improvement and improvement of process production operation requirements and the continuous development of computer technology, the I/A Series DCS control system has been upgraded and transformed successively to improve the overall performance of the DCS system. * * Improve, while strengthening the daily maintenance of the system, timely discovering and handling system defects and faults, laying a solid foundation for the "stable, long-term, high-quality and excellent" operation of the system. 2 I/A Series DCS control system structure The communication network of the I/A Series DCS system is a standard network constructed according to the concept of local area network and is divided into 4 levels.: Broadband LAN, carrier band LAN, contact bus, field bus. The adopted I/A Series DCS control system consists of a two-layer network of redundant node bus and its components and field bus and its components. The specific structure is shown in Figure 1. http://www.nmtech.com.cn/jishuwang/upload/070601953481305.jpg 2.1 The structure of the node bus The I/A Series DCS system structure is based on the concept of contacts. The contacts operate independently to complete various functions of automatic control and can be connected to other non-FOXBORO contacts through a compatible network. “A "contact" is made up of a contact bus that connects together processor components called stations. Each component is independent and designed to complete some common functions in the system. I/A Series system processor components are connected to each other through a contact bus to form process management and control contacts. Each component can also be connected to external devices or other types of components through one or more communication links. The contact bus provides high-speed, redundant, point-to-point communication between various stations in the I/A Series DCS system (control processor CP, application processor AP, workstation processor WP, etc.), with excellent performance and security. 2.2 Fieldbus composition The fieldbus of the I/A Series DCS system is a single-master public line serial data communication bus that uses synchronous communication specifications and follows the EtA standard RS-485. All fieldbus data exchanges are initiated by the master station, and the connected fieldbus components are all slave stations. The field bus is hung on the control processor CP through the field bus isolation component FBI, and the field bus component FBM (Field Bus Module) is hung on the field bus to form a control system. The fieldbus component FBM provides an interface between field sensors/actuators and the redundant fieldbus. The fieldbus component has two signal types: analog and digital. 3. Upgrading of the DCS system. The I/A Series DCS control system was upgraded in 1997, 1999 and 2000 respectively to improve the overall performance of the DCS system. * * improve. 3.1 Upgrade of the operating station processor In 1997, three AP20 application processors were upgraded to AW51B, and the WP20 operating station was retained. ； In 1999, five WF20 operating stations were upgraded and transformed into WP51B operating stations, and the corresponding system software was also upgraded simultaneously. The performance comparison between AP20/WF20 before upgrade and WP51B/AW51B after upgrade is shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload/070601954432546.jpg As can be seen from Table 1, the upgraded operation station processor and application operation station processor have faster operation and data processing speeds and stronger functions. In particular, the image processing function and display driver function have been greatly improved. ； The upgrade of corresponding system software improves the overall performance of the DCS system. * * improve. After the upgrade, the external floppy disk drive and external tape recorder in the original system were eliminated. 3.2 Upgrading of the control processor In 2000, the control processor CP10 configured in the original system was an early product of FOXBORO Company, which had a long running time, aging products, backward technology, and reduced stability and reliability. To this end, 5 partially redundant CP40 series control processors were used to replace the 11 CP10 control processors in the original system configuration, and the corresponding control software was upgraded at the same time. The performance comparison between CP10 before upgrade and CP40 after upgrade is shown in Table 2. http://www.nmtech.com.cn/jishuwang/upload/070601955142606.jpg 3.3 The operating station processor WP51B was upgraded to the WP51F. During the overhaul in 2005, when the DCS system was powered off and put into operation after the overhaul and maintenance, it was discovered that the two operating station processors WP5101 and WP5103 could not start running normally, and it was later confirmed that the equipment hardware was damaged. To this end, the two WP51B models were upgraded to WP51F models, and corresponding system configuration modifications and software upgrades were made. 4 Daily fault diagnosis and processing The I/A Series DCS system provides a set of software packages (SYstem Monitor) for monitoring the working conditions of the system. Using its human-machine interface, you can easily diagnose and respond to the operation of each equipment in the system and system communication conditions. However, during actual operation, it was found that, in addition to the fact that the SYstem Monitor system can monitor field bus component FBM faults, sometimes when the field bus component FBM fails, the System Monitor system cannot diagnose the fault and does not have any fault response information. 4.1 FBM failure phenomenon. In 2005 and 2006, it was found many times that the fieldbus component FBM had actually experienced single-channel or multi-channel failures, but the Sys tern Monitor system did not respond to any failure and could not correctly diagnose the failure. It was found from the alarm information that the fault occurred instantaneously, returned to normal within 1 second, and occurred irregularly multiple times. 4.2 FBM fault inspection and diagnosis Due to the non-redundant configuration of the FBM card, once the FBM card fails, it will affect the fluctuation of its control loop and easily cause serious consequences. Therefore, it is very necessary to check and diagnose faults in a timely and accurate manner, and to troubleshoot and resolve faults in a timely manner to ensure stable operation of the system. When the above fault phenomenon occurs, first when inspecting the flow chart display screen, it can be found that some parameters are abnormally displayed with white characters on a red background, or the parameters fluctuate irregularly and abnormally. ； If there is a control loop, the control loop control mode system automatically switches the automatic mode to manual control mode. ； Secondly, query the process alarm information or historical alarm information, and you can find that the corresponding module alarm information prompt is "I/OBAD” ； If it is a multi-channel fault, it can be found that "I/OBAD" alarm information appears in different control loops of the same FBM card at the same time, and returns to normal within 1 second, and appears irregularly multiple times. Finally, prepare the corresponding technical plan for online replacement of the FBM card and process it. This FBM fault inspection and diagnosis method has been used to diagnose and deal with several FBM instantaneous faults such as 040301, 040308, 040804, 041008, etc., avoiding production accidents and ensuring the stable and long-term operation of the system. 5 Conclusion The I/A Series DCS control system has been put into operation since 1992. Through continuous upgrading and transformation of hardware and software, the system performance has become increasingly perfect. As the running time increases, the system failure rate increases significantly. How to detect faults promptly and accurately to ensure stable operation of the system is a topic that requires continuous and in-depth research and exploration.