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Automatic XBT Launch And Measurement System

By Ya-bin Men • Dr. He-quan Sun

Sketch map of automatic XBT launch and measurement system.

A seawater temperature profile is a basic marine environmental parameter to describe ocean thermal conditions. Since it influences the velocity and path of underwater acoustic propagation, it is very important for the surveillance, scientific research and exploitation of marine resources and for military oceanography.

The expendable bathythermograph (XBT) is a measuring device that releases the probe over board and measures the water temperature during the rapid submergence. XBT probes can be launched by hand or remote control by an automatic launch system.

It is very complicated for an experienced engineer to launch a probe manually. Only one probe can be launched at a time, which is time-consuming and labor-intensive with a low success rate. Launching is also influenced by sea conditions, which can lead to wrong location and timing for a probe.

The automatic XBT launch and measurement system, which was developed by the National Ocean Technology Center of China, is a new water temperature profile measurement system that can group launch up to six probes. Water temperature is measured during the rapid descent after launch. The system can be used in severe sea conditions to acquire hydrological data quickly and can be operated easily by a crew.

System Structure
The automatic XBT launch and measurement system comprises control and real-time data-processing software, data acquisition and control box, automatic launch device, remote display terminals and other accessories, such as communication cables. The system is divided into two major parts: deck unit and observation room.

The deck unit is installed on the ship deck, including fixed launchers, data acquisition and control box, the display terminal and connecting cables. The frame of the launchers is fixed near the shipboard on the stern using three G-shaped clamps. The launchers are located outside the frame, stretching out toward the sea. The data acquisition and control box on deck is located under the frame and grounded to the ship hull. This box can receive instructions to detect the probe state, control the frame motor to open or close the probe valves, and launch the probes. The system status, relative position of the valve, motor running current, temperature inside the box and CPU temperature are monitored in real time. The alarm will set off when an anomaly occurs.

The system can communicate with a remote display terminal, collect GPS data and acquire the water temperature information after launching the XBT probes. The display terminal is connected to the data acquisition and control box with RS-485 cable.

The observation room is located inside the ship cabin with the data-processing system, including the embedded computer and software. The software is programmed to send the control instructions, process the data acquisition feedback information, receive GPS data, and acquire and plot water temperature data. Data communication with the remote data center can also be done with the Ethernet interface.

The system's hardware comprises the AC power supply, switch power supply unit, main control board, stepper motor, valve position sensor, XBT data-receiving unit, Ethernet communication modules and other accessories. The system self-test, status display, motor control, motor position detection, display terminal interaction and data communication are mainly completed by the data acquisition and control board. The signal transmitted from the XBT probe is modulated and amplified by the XBT data receiver unit. The digital data can be obtained by using an A/D converter, processed and stored by the microprocessor. The measurement results are transmitted to the data processor via the serial port.

The XBT probes are released by the main control panel, with the control instructions sent by the data processor via an RS-485 cable. Meanwhile, the real-time temperature data and GPS message are sent to the data processor with RS-422 and RS-232 cables. In general, there are at least three kinds of communication cables. To reduce the amount of cabling and improve communication reliability, the serial port server of NPort IA5000A produced by Moxa (Brea, California) is used, which can convert three serial ports to the Ethernet interface that connects with the data processor. The server can protect the system from electrical noise or voltage changes with surge protection technology. To continue this article please click here.

Ya-bin Men is a senior engineer at the National Ocean Technology Center of China. He has been working on the development of a marine monitoring instrument since he received his master's degree in 2003.

Dr. He-quan Sun received his Ph.D. degree in port, coastal and offshore engineering from Dalian University of Technology in China. He has been working at Dalian Naval Academy, China as an associate professor since 2008. His research includes applied mathematics, software design and noncontact measurement of flow field.

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