1. Introduction Modern ship equipment systems are becoming increasingly high-performance and modular in structure. The engine room monitoring system is an essential system in ocean-going vessels, crucial for their safe and reliable operation. It accurately and reliably monitors the operating status and parameters of various power equipment within the engine room. When equipment malfunctions, it automatically issues audible and visual alarms and prints alarm records. It also periodically prints and tabulates relevant operating parameters. In an automated engine room, the operating status, parameter values, and fault alarm status of equipment are all displayed on the monitoring screen in the control room. Engineers no longer need to patrol the engine room; they can access the operating status and parameter values ​​of all equipment from the central control room, thus reducing the workload of engine management personnel, improving working conditions, promptly detecting equipment malfunctions, and enhancing equipment reliability. Therefore, this paper introduces a PLC-controlled engine room monitoring system for ocean-going vessels and develops a monitoring software solution within a configuration environment. 2. System Introduction Ocean-going vessel equipment consists of subsystems such as the main engine system, oil purifier system, fuel tank system, air compressor system, steering gear system, boiler system, waste oil incinerator, generator set, emergency generator system, and pumps. Each piece of equipment operates 24 hours a day without interruption. For example, the main engine system is the heart of the ship, and its reliable and stable operation during navigation must be ensured. During this period, the monitoring system is required to constantly monitor the main engine system's speed, cooling water temperature, fuel inlet and outlet temperatures, lubricating oil inlet and outlet temperatures, and main engine exhaust temperature. These parameters involve temperature signals of 4-20mA above 600℃ and temperature signals below 600℃, resulting in a wide variety of signals and increasing the system's complexity. The system's framework is shown in Figure 1. Figure 1 shows the engine room monitoring and alarm system. Various types of sensors (switching signals, 4-20mA, PT100, RTD, etc.) collect various signals and continuously send them to the display unit (microcomputer LCD) to display the current values ​​of each monitoring channel. Once a monitoring limit is exceeded, an alarm signal is sent to the extended alarm control unit, the printing and recording unit, and the alarm control unit. The printing and recording unit can immediately print the parameter values ​​of the alarm. The alarm control unit activates the speakers in the control room and engine room to alert the engine room management personnel. Simultaneously, it activates the extended alarm device and outputs audible and visual alarm signals in public areas, the chief engineer's cabin, and the watchkeeping engineer's cabin. Audible and visual alerts are also output on the alarm monitoring screen on the bridge. Both the main power supply and emergency power supply have self-testing functions. After an alarm occurs, it can be answered in the control room, with silencing and flashing signals. 3. Hardware Implementation This monitoring system includes the display and alarm functions for the main operating parameters of a 14-cylinder main engine, three generators, a boiler, an incinerator, two air compressors, and a steering gear, as well as indications of the operating status of other equipment. The system monitors a total of 118 analog signals and 128 digital signals. Therefore, an S7-200CN PLC 226 was used as the system's main controller, expanded with seven 16-I/O EM223 CN digital input modules. The analog signal acquisition module uses an Advantech ADAM and communicates with the PLC via a 485 bus. The monitoring host computer uses an Advantech UNO-2160 embedded industrial PC, forming a network via PPI to achieve real-time monitoring of the ship's engine room equipment. Its system architecture diagram is shown in Figure 2. Figure 2 Framework diagram of PLC-based ship engine room monitoring system. When the system is monitoring and alarming, all switch quantity modules are collected and input through Siemens S7-200CN PLC expansion module EM223 CN. Three types of analog quantities, 4-20mA, temperature signals above 600℃ and temperature signals below 600℃ are collected and input through ADAM, and then sent to Siemens S7-200CN PLC through 485 bus. The PLC is centrally processed and then sent to the host computer and other devices, such as indicator lights and speakers. In addition, external buttons can issue commands through Siemens S7-200CN PLC to start and stop various pumps and other corresponding equipment. As an indispensable system for ocean-going ships, it mainly has the following functions: (1) Fault alarm: When the system detects a fault, the system issues an audible and visual alarm. After the response, the system stops the sound output and the indicator light is flat; after the alarm is cleared, the indicator light goes out. (2) Parameter display and alarm indication: The current monitored parameter values ​​can be viewed on the system's software interface, and the parameters that are normal or not are displayed in different colors. (3) Printing records: The system is connected to an alarm record printer. When an alarm is generated, the system starts the printer at the same time to print the current alarm, which is convenient for the engine management personnel to view and record in the logbook. (4) Delayed alarm: When an alarm such as temperature or liquid level is generated, the system outputs the alarm after a delay of a few seconds to prevent false alarms. (5) Lockout alarm: This function is used when the system is under maintenance, and it can be checked individually. (6) Extended alarm: The system can extend the alarm information to the cabins of each engine officer and transmit the alarm information to the relevant engine management personnel. (7) Negligence alarm: When an alarm occurs and no engine personnel respond within a certain period of time, the system will generate a ship-wide alarm to remind the watch personnel of their negligence. (8) Functional test: The system has a self-test function. 4 Monitoring System Software Implementation The control logic flowchart implemented in Siemens S7-200CN PLC is shown in Figure 3. Figure 3 Control Logic Flowchart of Ship Engine Room Monitoring System The system monitoring software is implemented on the Windows platform in the KingSCADA development environment. KingSCADA has a visual operation interface, rich library, highly flexible animation connection; it has comprehensive script and graphic animation functions. It can save a part of the screen for later analysis or printing. Variable import and export function supports distributed storage of real-time and historical data. Powerful script language processing fully supports screen publishing, real-time data publishing, historical data publishing and database data publishing. Convenient recipe processing, rich equipment support library, supports common PLC equipment, smart instruments and smart modules. The system software has the following functions: (1) Parameter list display, displaying all engine room parameter items in sequence or group. Including parameter number, name, current value, unit, upper limit value, lower limit value and alarm status. And can be continuously displayed by flipping screen. (2) Parameter chart display, displaying relevant parameters of main/auxiliary machine in the form of virtual instrument. Regarding the exhaust temperature and cooling water temperature of the main engine, and the pressure and temperature of the generator set of the auxiliary machine. (3) Curve display: The relevant parameters are described separately as real-time and historical curves. The real-time curve depicts a curve with corresponding values ​​on the interface as time goes by. The historical curve allows the operator to view the parameter changes of a certain parameter in the past two days, and thus reproduce the working conditions of the past two days. (4) Alarm query function: When an alarm exceeds the limit at a certain monitoring point, the system automatically pops up an alarm window, and the relevant information of the monitoring point can be queried in the window. (5) User management function: The system has three types of users: system administrator, chief engineer, and operator. The system administrator is used by the company management level such as the chief engineer. Its operation authority is the highest. It can set up chief engineer and operator users and modify relevant parameters, such as alarm upper and lower limits. The chief engineer is used by the ship's chief engineer. Its operation authority is the second highest. It can also modify relevant parameters. The operator is used by the ship's general watch crew. It cannot modify relevant parameters and set up users. Its authority is the lowest. 5. Conclusion The main controller of this system uses a Siemens S7 200CN PLC. Its compact structure, good expandability, and powerful instruction functions, along with its use of the 485 standard communication port for information transmission and a self-designed interface, fully utilize the hardware resources of this micro PLC and leverage its software advantages. The input/output uses a differential method, improving anti-interference capability. Furthermore, the main unit and multiple terminals can be connected in parallel on a single twisted-pair cable for multi-machine communication, saving on transmission lines. Therefore, this system is small yet fully functional and stable, providing great convenience to users. No failures have occurred in nearly two years of actual operation, playing a crucial role in the safe and reliable navigation of ships and bringing significant economic benefits to shipping companies. The ship engine room monitoring and alarm system designed in this paper is suitable for various ocean-going vessels. Actual operation shows that the system is stable and reliable, fully meeting the requirements of ocean-going vessels, and has high promotional value. References: [1] Lü Jinhua, Jiang Hanhong. Ship engine room monitoring system based on PLC [J]. Microcomputer Information. 2005, 21(12-1) 76-77, 133. [2] Wan Manying, Liu Sanshan, Tang Jie. Design of engine room monitoring system and data acquisition module based on CAN bus [J], Transportation and Computer. 2001, 19(5) 46-48. [3] Chen Yihui, Pu Xiaolian. Real-time monitoring and alarm system for ship engine room based on PLC [J]. Journal of Shanghai Maritime University. 2005, 26(2) 67-70. 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