Abstract: This paper mainly discusses the data acquisition of the SBE 37-SI MicroCAT temperature, salinity, and depth sensor, which can accurately measure seawater temperature, conductivity, pressure, depth, salinity, sound velocity, density, and other state parameters, and can well meet the requirements of submersible navigation and control. However, due to the difference between its data output format and that of navigation equipment, it cannot directly exchange data with the navigation system. Therefore, it is necessary to design a data acquisition circuit interface to enable data exchange with the navigation system. Keywords: temperature and salt depth sensor; navigation; submersible[b][align=center]The Application of A New Type CTD In The Submarine Li Xue-cong, Wan Pin, Deng qinghua, Li Jun[/align][/b] Abstract: This paper mainly introduces the type CTD of SBE 37-SI MicroCAT, which is able to bear the high pressure and can measure exact value of such states as the temperature, conductivity, pressure, depth, salinity, velocity of sound , density of seawater. The characteristic can meet the design of the Integrated Navigation System (INS) in the submarine. Because there are differences in the output form of its data and the data form of general navigation equipment, its data can't be sent to INS in the submarine directly. So it is necessary to design transformation of serial interface. It makes the SBE 37-SI MicroCAT to communicate with INS of the submarine directly. Key words: CTD; Navigation; Submarine; 0 Introduction With the development of industrial and defense technologies, diving equipment, especially in military applications, demands increasingly sophisticated and advanced detection technologies. Submersibles, of paramount importance in the technological development of various diving equipment, fully embody this trend. To enhance their deep-diving capabilities, submersibles are equipped with integrated navigation, display, and control systems to ensure precise navigation and successful completion of various underwater tasks. Due to the size and payload limitations of submersibles, the sensors used in these integrated navigation, display, and control systems must be small, lightweight, and pressure-resistant, while also being able to quickly and accurately obtain the submersible's navigation parameters. The SBE 37-SI MicroCAT temperature, conductivity, pressure, depth, salinity, sound velocity, and density sensor integrates the measurement of these seven seawater parameters, and its accuracy, size, and weight perfectly meet the system design requirements, making it an ideal sensor for use on submersibles. The following discussion concerns the data acquisition process of the SBE 37-SI MicroCAT CTD sensor in a submersible. Addressing the issue of incompatible transmission formats hindering direct transmission, a feasible design scheme and approach are proposed, along with an example of its application. 1. Application of the SBE 37-SI MicroCAT CTD sensor in a submersible The integrated navigation and display control system of a submersible primarily utilizes combined navigation technology and information fusion technology to organically integrate various navigation devices. Without altering the individual navigation devices, filtering technology is employed to process various navigation information, allowing them to complement each other and improve navigation and positioning accuracy. Through centralized display, control, and processing of navigation information, the effectiveness of each piece of navigation information can be maximized, providing comprehensive and optimal navigation information to the user equipment in real time. The CTD sensor measures various state parameters of seawater in real time, such as temperature, conductivity, pressure, depth, salinity, sound velocity, and density, and transmits these parameters to the integrated navigation and display control system for display or use by other equipment. To ensure the safety of submersible navigation and the completion of salvage and search and rescue missions, the measurements from the sensors on the submersible must meet navigation requirements; the data refresh rate must meet the submersible's requirements; and the measured data must be stable and reliable. The SBE 37-SI MicroCAT temperature, salinity, and depth sensor meets all these performance requirements, satisfying the navigation system's requirements. [align=center] Figure 1 SBE 37-SI MicroCAT Temperature, Salinity, and Depth Sensor[/align] The SBE 37-SI MicroCAT temperature, salinity, and depth sensor is currently mostly used in submersibles and submarines abroad, but its application in China is still rare. As shown in Figure 1, its dimensions are 43.69 cm in length, 13.97 cm in maximum height, 10.8 cm in maximum width, and it weighs approximately 2.9 kg. The SBE 37-SI MicroCAT temperature, salinity, and depth sensor has very high measurement accuracy; for example, in a temperature range of -5 to 30°C, its accuracy reaches 0.0001°C, and it can measure the required precise navigation information even under high pressure conditions at a depth of 7000 meters. The SBE 37-SI MicroCAT communicates with other devices primarily via asynchronous serial communication according to the NMEA-0183 standard, exchanging data bidirectionally. Its external interface is EIA RS-232, with selectable transmission baud rates ranging from 1200 bit/s to 38400 bit/s. The transmitted character code is ASCII, and the transmission rate of measurement data can also be selected by the output parameters. The time interval between each measurement data output ranges from 1.15 seconds to 22.19 seconds. The SBE 37-SI MicroCAT interface circuit design differs from common formats used in navigation devices, such as GPS: $PASHR,POS,n,……,tt.t，vvvv＊cc[CR][LF], which includes a start character $, data content, code and flags *, code and cc, and data terminator [CR][LF]. However, the SBE 37-SI MicroCAT output data format lacks a start character, code and flags, and code and . Another significant feature is the SBE 37-SI MicroCAT temperature, salinity, and depth sensor's output level protection. When it restarts after a power outage, the output level is zero, and it will not automatically send measurement data. It requires a trigger signal (data transmission command) to activate. This trigger signal consists of two carriage return and line feed bytes (0x0D and 0x0A), but they cannot be sent consecutively; they must be sent in two separate, two-second intervals to activate the sensor and enable it to send data according to the set format and rate. To ensure that the data format output by the temperature, salinity, and depth sensor is consistent with that of commonly used navigation devices, a data format conversion interface circuit must be designed. This circuit must perform the following tasks: first, receive an external command or generate its own trigger command to send to the sensor; then, receive external commands to change the baud rate and update rate of the SBE 37-SI MicroCAT output data; receive data from the sensor, adding start characters, codes, and flags; if spaces are present in the data, replace them with zeros; and finally, output the data to the integrated navigation display console. Thus, the data format conversion interface circuit must handle control command interrupts and change the sensor's baud rate and data update rate, while also communicating serially with the sensor. 3. Practical Application Examples Because the RS232 data format provided by the SBE 37-SI MicroCAT temperature, salinity, and depth sensor differs from the data format of commonly used navigation equipment, it cannot be directly connected to the submersible integrated navigation display and control console system for data exchange. To facilitate communication, the authors designed a data format conversion circuit board for a practical engineering application. The circuit structure is shown in Figure 2. [align=center]Figure 2 Design of SBE 37-SI MicroCAT Data Format Conversion Circuit Board[/align] In Figure 2, the communication control microcontroller is responsible for receiving data, converting the received ASCII characters representing seawater state parameters into numeric types, determining the sign of the numeric type, replacing corresponding spaces with zeros, converting it back to ASCII character types, adding the start character $ and the first letter of each data (i.e., T, C, P, D, S, V, R), calculating the code sum of all characters after $, adding the code sum flag, code sum, carriage return, and line feed, and finally outputting it to the integrated guidance and display control console via RS232. On the other hand, it receives commands from the integrated guidance and display control console and sends them to the SBE 37-SI MicroCAT temperature, salinity, and depth sensor, and the sensor's response is completely returned to the integrated guidance and display control console. Therefore, the integrated guidance and display control console can change the output data, data output interval, and its state of the temperature, salinity, and depth sensor at any time, and can also receive data in a universal format. This example uses the commonly used and reliable AT89C51 microcontroller. The AT89C51 is a low-voltage, high-performance CMOS 8-bit microprocessor with 4KB of flash programmable and erasable read-only memory (FPEROM). This device is manufactured using Atmel's high-density non-volatile memory technology and is compatible with the industry-standard MCS-51 instruction set and output pins. By combining a multi-functional 8-bit CPU and flash memory on a single chip, Atmel's AT89C51 is a highly efficient microcontroller, providing a flexible and cost-effective solution for many embedded control systems. Due to its relatively simple programming, assembly language is used instead of a high-level language to improve development efficiency. In environments with high reliability requirements, RS232 serial port programming uses only three signal lines: transmit, receive, and ground. This ensures that data can be sent and received at any time, improving reliability. Figure 3 shows the designed and used SBE 37-SI MicroCAT data format conversion circuit. The circuit design is ingenious, small in size, easy to install, and the signal lines are easy to plug and unplug. The SBE 37-SI MicroCAT temperature, salinity, and depth sensor outputs data directly from air measurements in the following format (adding one bit if the data is negative): xxx.xxxx,xx.xxxxx,xxxx.xxx,xxxx.xxx,xxxx.xxx,xxxxx.xxx,xxx.xxxx[CR][LF] 24.7798, 0.00068, -0.310, -0.307, 0.0130, 1496.123, -2.8873[CR][LF] The interface circuit receives data from the sensor (with three negative values) and outputs data from the interface (replacing spaces with zeros): $Txxx.xxxx,Cxx.xxxxx,Pxxxx.xxx,Dxxxx.xxx,Sxxxx.xxxx,Vxxxxx.xxx,Rxxx.xxxx＊cc[CR][LF] $T024.7798,C00.00068,P-0000.310,D-0000.307,S0000.0130,V01496.123,R-002.8873＊66[CR][LF] [align=center]Figure 3 SBE 37-SI MicroCAT Format Conversion Circuit Board[/align] 4 Conclusion The author's innovation: The performance, size, weight, and reliability of the SBE 37-SI MicroCAT temperature, salinity, and depth sensor meet the design requirements of the integrated navigation and control console system in submersibles. It can accurately measure the temperature, conductivity, pressure, depth, salinity, sound velocity, density, and other state parameters of seawater required by the submersible. Because its output data format differs from the commonly used format of navigation equipment, direct connection is not possible. Therefore, a separate data format conversion circuit must be connected to its interface to obtain a conventional data output format, enabling faster development of communication and data acquisition software and control and communication of the data acquisition system through a human-machine interface. The hardware and software implementation methods of the example system introduced in this article are relatively simple, highly reliable, and have wide applicability. References: [1] Ma Zhongmei, Ji Shunxin, He Limin. C Language Programming of Microcontrollers [M]. Beijing: Beijing University of Aeronautics and Astronautics Press, 1999. 57-73. [2] Zhao Yunpeng. Application of MATLAB Serial Communication in Data Acquisition, Microcomputer Information, 2006, No. 1-1, P111-112 [3] Luo Xinglong, Huang Longsheng. Design of 0.01℃ Digital Display Thermometer Based on AT89C51 Control, Microcomputer Information, 2006, No. 5-2, P70-72 [4] Yang Baoqing, Song Wengui. Practical Circuit Handbook. Beijing: Machinery Industry Press, 2002 [5] Wu Jinshu, Shen Qingyang, Guo Tingji. 8051 Microcontroller Practice and Application. Beijing: Tsinghua University Press, 2001 [6] Sea-Bird Electronics, Inc. User's Manual of SBE 37-SI MicroCAT