Design of ship engine room alarm system based on LabVIEW and OPC

O Introduction
The ship engine room monitoring system is the most basic and important system in modern automated ships. At present, most of the centralized monitoring systems of ships adopt distributed structures, and the centralized and distributed control and distributed control of ship automation monitoring systems will gradually be replaced by centralized monitoring systems based on fieldbus, so as to maximize the safety, reliability and economy of ship navigation. Compared with the long cycle, slow running speed, and difficult debugging and maintenance of the engine room monitoring system developed in the traditional development environment (VB, VC++, C, etc.), the system uses LabVIEW as the programming language. It is efficient, flexible, and object-oriented. Its powerful graphical programming capabilities and visual programming environment are favored by many software developers. As one of the important pillars of modern control technology, PLC is widely used in modern control systems for its high reliability and strong anti-interference ability. It can adapt to the harsh environment of the ship engine room. Combining LabVIEW with PLC and applying it to the ship engine room system has great application value and prospects.
The system uses Profibus fieldbus control, adopts an OPC-based Lmb-VIEW implementation method for real-time communication between PC and SIEMENS PLC S7-300, combines virtual instrument technology with PLC technology to develop a ship engine room host computer control system to achieve a good human-machine interface and reliable system control. Realizing real-time and stable data exchange between LabVIEW and PLC S7-300 is the key and difficulty of the system.

l System Implementation
1.1 System Hardware and Software Conditions
Software: LabVIEW 8.2, SIMATIC NET (OPC Include), Step7 v5.3 SQL database. LabVIEW8.2 is used for host computer programming, SIMATIC NET is used to configure communication and configure OPC Server, and Step 7 v5.3 is used to program SIE-MENS PLC S7-300.
Hardware: PC, SIEMENS PLC S7-300 (CPU315-2DP), SIEMENS CP5611 communication card, Profibus bus. Profibus bus is a field bus used for industrial control by SIEMENS, with a communication rate of up to 12 Mb/s within a range of 100 m. CP5611 is a PCI communication card used to connect PC to Profibus.
1.2 System Flowchart
The system design uses cabin alarm and extended alarm to complement each other. The whole monitoring system has 84 working parameters, including 71 switch quantities and 13 analog quantities. 71 switch quantities such as exhaust gas boiler comprehensive failure, emergency switchboard DC24 V power failure, No. 1 left fuel tank high position and all 13 analog quantities such as fuel oil inlet pressure, lubricating oil inlet main bearing pressure, cylinder cooling high temperature fresh water outlet temperature are directly connected to the PLC input and output module, and the signal is read into the PLC data image area in real time through the sensor. The PLC and PC (RS 232 standard serial port) are connected with PPI cable. The upper computer PC monitoring software is written in LabVIEW program. All switch quantity and analog quantity data are taken out from the PLC through the interface between LabVIEW and PLC to realize data display, alarm, storage, real-time curve and historical curve analysis, fault diagnosis and other functions. The system can also send instructions to the PLC through the upper computer program to realize remote control of the equipment. The system structure flow is shown in Figure 1.

1.3 Communication scheme and implementation
1.3.1 Communication scheme
Under the above hardware conditions, the key to achieving real-time communication between PC and PLC in LabVIEW is how to drive the SIEMENS CP5611 communication card in the LabVIEW programming environment. After the CP5611 is driven, the PC can connect to the Profibus bus through the CP5611 and read data from or write data to the PLCS7-300 address block. SIEMENS CP5611 currently does not have a LabVIEW driver. If you want to develop a higher-level control system for SIEMENS PLC in the LabVIEW environment, you can take two approaches:
(1) The developer develops the CP5611 driver by himself, starting from the underlying dynamic link library;
(2) Find and install the SIEMENS OPC Server application, and use NI's OPC Client to interact with it. [page]

Obviously, the second solution is more convenient and faster for developers, so this article uses the second solution. OPC (OLE for Process Control) is an extension of COM/DCOM interface based on Windows NT technology. Its essence is that OPC Client communicates with OPC Server in an open and standardized communication method. The standard interface defined by OPC specification makes it easy to integrate hardware and software from different manufacturers. When using third-party hardware, as long as the hardware developer provides OPC Server, software developers do not need to write low-level drivers, and can interact with it through the OPC Client of user software.
1.3.2 Establishing data communication between LabVIEW and PLC
(1) Configuration of OPC Server
The OPC Server interface provided by SIEMENS for S7-300/S7-400 is integrated in the SIMATIC NET software package. In this system, Siemens S7 system provides OPC Server, and LabVIEW is used as OPC Client for data communication.
(1) First, OPC configuration is required. After successfully installing the drivers of SIMATICNET and CP5611, restart the computer and start using SIMATIC NET software to configure PC Station.
(2) After configuration, connect the OPC Server to CPU315-2 DP in Step7v5.3.
(3) After connection, download, pay special attention to the setting of access points, Options—PG/PCINTERFACE, download to the local server, select the local access point PC internal (1ocal), download to CPU315-2 DP, and change the access point to CP5611.
(4) Set the local IP address in the properties, such as 192.168.6.174. The partner is CP5611, and its IP address must also be set, such as 192.168.6.132. In this way, after configuration is completed, if the small icon in PCStation turns to color, it means that the OPC Server is configured.
(2) Communication between DataSocke and OPC
The graphical programming platform of LabVIEW integrates various advanced software development technologies in the current measurement and control field, and can use a variety of solutions to access the OPC server. Since the LabVIEW software platform supports DataSocket technology, DataSocket can realize real-time data sharing. This paper uses DataSocket technology to access the OPC server. DataSocket technology is based on Microsoft COM and ActiveX, originates from the TCP/IP protocol and highly encapsulates it. It is oriented to measurement and automation applications and is used to share and publish real-time data. It is an easy-to-use high-performance data exchange programming interface. However, it does not need to convert data into unstructured byte streams like TCP/IP programming. Instead, it transmits various types of data in its own unique encoding format, including strings, numbers, Boolean quantities, and waveforms. It can also establish connections between field data and user-defined attributes and transmit them together. Although the implementation principles of DataSocket and OPC are different, DataSocket and OPC are similar in system. Both are client/server models in structure, and both define their own transmission protocols for cross-network data transmission, and access server data items in the form of URLs. In LabVIEW, DataSocket VIs on the DataSocket VI function sub-template can support OPC applications. In LabVIEW, connecting to an OPC Sever is achieved by calling the DataSocketOpen Connection.vi icon and passing the corresponding OPC server URL to the Vi. The basic structure of OPC URL is: OPC://host name//OPC server name/data item/refresh rate.
l.4 Monitoring system interface
The real-time parameter values ​​of the 5 parameters of the 1# host displayed in the upper computer can be displayed in real time and stably by using DataSocke and OPC. In the dashboard, green means that the parameter is running in a safe state; yellow means that the parameter is in a critical state and is about to reach the state of exceeding the limit; and red means that the parameter has exceeded the limit. When the parameter exceeds the limit, the alarm light under the instrument will turn red. The third instrument in Figure 3 has already alarmed, showing that the speed of the 1# host has exceeded the limit. At this time, instructions can be sent to the PLC as required, or the PLC can be programmed to automatically switch or stop. After processing, the PLC can return the processing results to LabVIEW for display and storage. The three curves under the header use the powerful data display function of LabVIEW to set the real-time data curve for the current period of time by setting the display data history length, as shown in Figure 3.

Combined with the database, users can query logs, alarm records, control processing results, and the historical operating status of each device. Figure 4 is the historical curve display analysis interface of the host. The historical trend of system parameters can be seen from the historical curve. After analysis, it can be concluded that the overall trend of the curve is flat, and each parameter is within the normal range most of the time. Some individual points are different from other points, indicating that there were parameter alarms in the past.

2 Conclusion
The system has a short development cycle, an intuitive and friendly human-machine interface, reliable control, and easy maintenance. The use of LabVIEW's built-in DataSocket and OPC communication is real-time and reliable, and is suitable for almost all communication buses and communication cards of SIEMENS. If different communication buses and different types of communication cards are used, the corresponding bus model and communication card model can be selected during configuration. OPC is used as the interface for data exchange, which is scalable and can integrate other systems to form a comprehensive monitoring system. Practice has proved that this system has been running on Tongsha Ferry No. 5 for more than a year, with stable performance, greatly improving the level of ship engine room automation.