Keywords: PLC; valve remote control; liquid level telemetry DOI: 10.16640/j.cnki.37-1222/t.2017.22.111
In the contemporary shipbuilding industry, controlling the hull balance is an important issue. When the ship is loading and unloading goods, it is necessary to adjust the ballast water. For example, when the ship is loading, the hull is bound to tilt in the direction of loading. At this time, the water in the ballast tank corresponding to the loaded cabin needs to be discharged; At that time, the ballast water is injected into the ballast tank corresponding to the unloading tank. Modern ship control systems have the advantages of automation, integration, safe operation, and good stability. This article designs and develops the valve remote control and liquid level telemetry system on the basis of PLC.
1 system hardware structure design Valve remote control and telemetry system is divided into three layers structure: electro-hydraulic valve drive head and sensor unit, control module, monitoring and control panel MIMIC. From the perspective of the control system, decentralized control of all parts of the ship is carried out and centralized management is carried out on the control room and monitoring platform. The system structure is shown in Figure 1.
1.1 The power source of valve electro-hydraulic drive head and sensor unit valve switch is provided by hydraulic oil. The transmission mechanism consists of hydraulic pump, motor and control accessories. The signal collected by the PLC controls the on and off of the solenoid valve. The integrated hydraulic circuit of the hydraulic part can avoid incomplete pipeline connection. It has the advantages of integral structure and convenient maintenance. Each valve corresponds to an electro-hydraulic drive head, so each control unit is independent and does not affect each other, so it can improve its reliability.
The design uses a pressure-type liquid level sensor, which is suitable for level measurement of various ballast vessels, fuel tanks and liquid cargoes. The sensor converts the collected liquid level, ship draught, and temperature signals into a 5-20 mA reference current as the PLC input signal.
1.2 Intermediate Control Module The intermediate control module consists of 8 Siemens 7S-200 series PLCs and corresponding expansion modules, of which one is connected to the Ethernet expansion module. The PLC master station communicates with the monitoring machine through the switch. The PLC slave station uses 7 PLCs. The PLC master station and slave station, PLC slave station use RS485 interface to connect. The digital input/output module connected to PLC1-PLC5 is used to collect the status of the valve from the site, the pump's running status signal, and the digital output control relay remotely operates the valve, and the level, temperature, and pumping of each compartment. The pressure of the outlet is collected by the analog input module; the digital input/output module connects the PLC6 and PLC7 to obtain the switching state of the valve and the start-stop control signal on the MIMIC analog panel. According to these signals, the output drives the valve switch and also controls Pump operation indicator on the MIMIC analog panel.
2 System Software Design and Implementation 2.1 Design and Implementation of Monitoring Software This design achieves modular and hierarchical design through man-machine interface, can dynamically display the flow of liquid in the pipeline, and can be opened and closed on the valve using a mouse or keyboard. Interface, complete pump start and stop, can also monitor the real-time status of valves, pumps, easy to find and analyze the fault.
2.2 PLC program design and realization Monitoring and PLC master station use Ethernet module to communicate between PLC master station and PLC slave station and PLC slave station using RS485 serial communication interface. The PLC free port protocol communicates and sets the PLC special function registers accordingly to define the start and stop conditions for message transceiving.
3 System Working Principles and Functions In this design, PLC1-PLC5 is responsible for collecting the on/off status of each valve, the liquid level of the tank, temperature and other signals. The PLC sequentially collects the status of all input terminals as data when the program is running. The PLC master station receives the input signal from the acquisition and communicates with the monitoring machine. The information is transmitted to the monitoring machine so that the monitoring machine can monitor the state of the valves, pumps, etc. In addition, PLC master station sends and receives the information to PLC6 and PLC7, carries on the corresponding operation according to the received information, the output control MIMIC analog screen indicator, the valve and the pump condition also may display on the MIMIC simulation screen. Remote control of the valve can be performed on the monitor and the MIMIC analog panel, but not at the same time. When the valve is remotely operated on the MIMIC analog panel, the corresponding valve control signal is collected by PLC6 or PLC7 and sent to the PLC master station, and then sent to the corresponding PLC1-PLC5 slave station to realize the remote control of the valve and the slave station status feedback. To monitor and MIMIC analog control panel. When the monitor remotely operates the valve, the control signal is transmitted through the mouse to the PLC master station using the Ethernet switch. The remote operation of the valve is performed by the MIMIC analog panel. Its working principle is shown in Figure 2.
4 Conclusion The system is stable, reliable operation, friendly man-machine interface, is an important part of the ship to achieve remote monitoring, can reflect the development trend of ship automation.
Zhan Zhanguang. Microcomputer system control scheme of multi-functional ship valve remote control system[J].Marine Technology,2014,23(03):130-133.
 Zhang Xingbiao. Economy and reliability research of tank valve control system [M]. Dalian: Dalian Maritime University Press, 2004.
About the author: Qin Fuzhen (1981-), female, master, associate professor, main research direction: electrical control.
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