[Abstract] This article introduces the structural characteristics of fieldbus and its application in engine room monitoring and alarm systems. Keywords: Centralized monitoring and alarm, fieldbus, Distributed Control System (DCS), Fieldbus Control System (FCS) Fieldbus control systems (FCS) have been developed since the mid-1980s and have been widely used in various control fields such as automobiles, papermaking, textiles, petrochemicals, and power. Fieldbus is a digital bidirectional communication network with advantages such as strong anti-interference ability, simple equipment, and free configuration. Due to its high reliability, good structure, and strong controllability, it has also begun to be gradually applied in ship control and monitoring systems. It has great application value in ship centralized monitoring and alarm systems. 1 Structural Characteristics of Fieldbus 1.1 Definition and Characteristics of Fieldbus According to the IEC standard and the Fieldbus Foundation, fieldbus is a digital bidirectional transmission, multi-branch communication network that connects intelligent field devices and automation systems. By definition, fieldbus is a bidirectional digital communication protocol for interconnecting field automation devices and control systems. A fieldbus system (FCS) can be viewed as a distributed system composed of digital communication devices and monitoring devices. In fact, fieldbus is a computer network, and each node on this network is an intelligent device. Fieldbus consists of network communication, functional modules, object dictionary, network management, system management and other parts. It has the following characteristics: (1) Fully digital communication Traditional distributed control system (DCS) is a semi-digital system. Many I/O modules receive or send 4-20mA analog signals, while fieldbus control system (FCS) is a "pure digital" system. Signal transmission is fully digital, which improves the reliability and accuracy of signals and realizes error detection and correction functions. (2) Operability and interoperability Interoperability means realizing information transmission and communication between interconnected devices and systems, while interoperability means that devices with similar performance from different manufacturers can be interchanged. (3) Completely decentralized DCS is a "semi-decentralized" system. It uses multiple distributed control units to control multiple loops. Its control parts are distributed to some control boards, and each control board has multiple loops. Fieldbus adopts a completely decentralized system. Its control units are completely distributed in the field. In fieldbus, it also allows operation and adjustment in the control room using digital communication. 1.2 Basic Structure of Fieldbus A fieldbus system consists of the following parts: Master Controller: This can be a programmable logic controller (PLC) or personal computer, etc., which manages and controls the entire system through the bus interface. Bus Interface: Also known as the network manager. It is a card used as a gateway from the master controller to the bus, managing information from various devices on the bus and converting it into a data format that the master controller can understand before sending it to the master controller. Input/Output Devices: Called nodes. They are connected to the fieldbus. There are many types; depending on the control system, they may be sensors, digital instruments, and various modules, etc. Each node on the fieldbus requires power for information transmission and reception. Usually, the input channel and the internal chip share the same power supply, while the output channel uses a separate power supply. 2 Centralized Monitoring and Alarm System Constructed Using Fieldbus Technology 2.1 Characteristics of the FCS Centralized Monitoring and Alarm System The ship engine room monitoring and alarm system is a very important system in the engine room, mainly responsible for collecting data from various devices in the engine room, displaying the data on the computer screen in the central control room, and issuing over-limit alarms. An important condition for realizing a powerful centralized monitoring and alarm system is to have a communication system with a reasonable structure and high transmission speed. Traditional centralized computer monitoring and alarm systems mostly employ distributed systems. With the continuous development of fieldbus technology, it has begun to be gradually used in centralized monitoring and alarm systems for engine rooms. As mentioned above, fieldbus adopts a completely distributed architecture, with its control units (nodes) completely distributed throughout the engine room and freely configurable. It also allows for operation and adjustment via digital communication from the central control room. The FCS centralized monitoring and alarm system has significant advantages over DCS systems. It features a simple structure and convenient wiring: Control systems using fieldbus allow for easy networking of devices via twisted-pair cables. It also boasts a low failure rate and high communication baud rate. Design, installation, commissioning, and maintenance costs are significantly reduced: Previously cumbersome schematic and wiring diagrams are now simplified; standard modules simplify installation, and powerful fault diagnosis capabilities make system commissioning and maintenance much easier. Furthermore, the FCS control system has strong anti-interference capabilities, making it suitable for the harsh environment of ship engine rooms. 2.2 Hardware Structure of the FCS Centralized Monitoring and Alarm System The Department of Mechanical and Electrical Engineering at Qingdao Ocean Shipping Crew College introduced the STI-VC2100MA ship monitoring system from the Shanghai Ship Transportation Research Institute for centralized monitoring and alarm training in the automation laboratory. This system utilizes Lonworks fieldbus technology developed by Echelon Systems, Inc. It connects to a main microcomputer (the master controller) via a Lonworks network. Input modules (digital and analog modules) acquire field data, which is then transmitted to the main microcomputer for display, alarm, and management via the Lonworks network. Output data is sent to the controlled object via output modules, and the display terminal shows the measured parameters. The bus interface uses a Lonworks bus communication interface card, and all input devices and the network internals use a 24VDC power supply. The system structure is shown in Figure 1. This system uses a single main microcomputer as both the master controller and the display terminal. The input devices include a 16-channel digital input module, capable of connecting 16 channels of switch signals; a 4-20mA current input module, connecting 16 channels of 4-20mA signals; a resistance temperature detector (RTD) module, directly connecting 16 RTDs using a three-wire connection; and a thermocouple temperature measurement module, directly connecting 16 thermocouples with cold junction compensation. The output module is a grouped extended alarm board. All modules are connected to the main microcomputer via a Lonworks bus. The system's functions include: acquiring switch signals, analog signals, RTD signals, and thermocouple signals; converting the data via a Lonworks communication interface card; displaying the data on the main microcomputer; and providing audible and visual alarms for exceeding limits, as well as response and grouped extended alarm functions. 2.3 System Software Programming: The four input modules (nodes) directly receive signals of different natures from the field and are programmed using Intouch software. Wonderwarm Intouch is a newly developed software for monitoring systems, featuring a world-leading HMI (Human Machine Interface). It provides a single, integrated view for viewing and controlling information resources, enabling engineers, supervisors, administrators, and operators to monitor and react to operational conditions through graphical displays representing the production process. Intouch allows for easy setting of alarm limits and other parameters, plotting various graphs, and displaying measurement point tables, bar graphs, and secondary instrument simulation diagrams on the main microcomputer. When limits are exceeded, audible and visual alarms can be triggered using existing computer equipment through programmed instructions. Intouch's DDE (Dynamic Data Exchange) function allows data and graphs in the measurement point tables to change according to actual data changes in the field. Furthermore, it allows for various functions such as alarm delay, alarm interlocking, and wake-up through parameter settings and programming. Lonworks bus technology is well-suited for centralized ship monitoring and alarm systems. The modules and main microcomputer are networked via twisted-pair cables, making system design, installation, commissioning, and maintenance more convenient and significantly reducing costs. Simultaneously, the entire system's operation is intuitive and easy to understand. Furthermore, modules can be freely configured as needed, and their arrangement at the monitoring site is more flexible. Lonworks fieldbus networking is a free topology, meaning it can be networked in any way, with network cable lengths reaching 2700m, thus enabling long-distance networking. In practical teaching, resource sharing between laboratories can be achieved through simple networking. The advantages of fieldbus will undoubtedly lead to its increasingly widespread application in ship automatic control and monitoring systems. References: 1. Li Wen'an. Design and Implementation of Substation Monitoring Based on Fieldbus. <Electronic Technology Application>, 2000, No. 9. 2. Xu Qingxing. Fieldbus Control System and Application. <Electronic Times>, 2000, No. 8. (Original text available for download: Application of Fieldbus in Engine Room Monitoring and Alarm System.pdf)