Abstract: This paper designs an integrated testing system based on virtual instrument technology to meet the testing requirements of ship degaussing equipment. The design scheme and implementation method of the system are introduced from both hardware and software perspectives. The system adopts a USB universal serial bus and features an oscilloscope, signal generator, and general measurement functions. Fault tree analysis and an expert system are used to perform functional testing and fault analysis of each component of the equipment, and performance analysis of the degaussing equipment can be performed based on feedback control theory. Application in production and maintenance processes shows that this testing system improves testing accuracy and efficiency. Keywords: Virtual Instrument; Ship Degaussing Equipment; Integrated Test System; Universal Serial Bus; Feedback Control Abstract: For the need of testing ship degaussing apparatus, an integrated test system based on virtual instrument technology has been designed. This paper describes the hardware and software, and the design and implementation method of the system based on VI technology. This system adopts a USB bus. It can be used as an oscillograph, waveform generator, and multimeter. The functions of the degaussing apparatus modules were tested, and faults were found using fault analysis theory and a diagnosis expert system. Feedback control theory is also used to analyze the performance of the ship degaussing apparatus. Application in testing indicates that the precision and efficiency have been improved. Key words: Virtual Instrument, ship degaussing apparatus, integrated test system, USB, feedback control 1 Introduction Virtual Instrument (VI) is a new type of instrument formed by the application of computer technology in the field of instrumentation. Virtual instruments consist of a computer, application software, and instrument hardware. The software integrates all the functions of instrument acquisition, control, data analysis, result output, and user interface. Functions can be modified by adding or removing elements through software changes, embodying the concept of "software is the instrument." It also possesses intelligence and good system scalability, representing the future direction of instrument technology development. In military applications, ships are equipped with degaussing devices to eliminate the induced magnetic field of the hull in response to magnetic weapons. The production and maintenance of degaussing equipment requires various types of instruments, resulting in complex operation and low testing efficiency and accuracy. This paper, based on the signal characteristics and performance indicators of degaussing equipment, fully utilizes the advantages of virtual instrument technology to design an integrated testing system for the maintenance and performance testing of degaussing equipment. 2. Overall Design of the Testing System This testing system uses the USB 2.0 bus, which offers advantages such as high speed, good versatility, plug-and-play functionality, and hot-swappability, meeting the requirements of automated industrial field measurement. The hardware of the degaussing equipment testing system consists of a computer and an instrument testing box, connected via a USB bus (the system hardware structure is shown in Figure 1). The computer sends commands to the microcontroller inside the instrument box via the USB bus to control signal input/output, excitation, and conditioning. The USB-9201 data acquisition card acquires the conditioned signals to complete various testing and measurement functions, and the software performs data analysis. All testing functions are performed through operation of the testing software interface on the computer screen. The USB-9201 is a data acquisition card manufactured by National Instruments, using a USB 2.0 interface, with a signal input range of ±10V, a resolution of 12 bits, a maximum sampling rate of 500kS/s, and the ability to simultaneously acquire 8 channels of analog signals. [align=center] Figure 1 System Hardware Structure[/align] 3 Software and Testing Function Design The software used in the virtual instrument system, in addition to the basic software such as the operating system required by the computer, also requires device driver software and user applications. Compared with traditional instruments, the biggest feature of virtual instruments is that they simulate the instrument panel on the computer screen, and all operations are performed entirely by software. Currently, commonly used programming tools include Visual Basic, Visual C++, NI LabVIEW, Aglientive VEE, and other visual programming software, each with its own advantages and disadvantages in terms of specific functional characteristics. This paper uses the object-oriented Microsoft Visual C++ 6.0 software development platform and utilizes NI's Measurement Studio Component Works integrated ActiveX controls to develop a user-friendly and easy-to-operate test program. The system's software structure consists of basic measurement control functions, component testing, system performance testing, and information management, as shown in Figure 2. [align=center] Figure 2 System Software Functional Structure Diagram[/align] 3.1 Basic Measurement Control Functions For basic measurement control, various commonly used test functions of multimeters, oscilloscopes, and signal generators are integrated into a single panel. Users can easily select various functions for measurement, fully demonstrating the advantages of virtual instruments. During measurement, the system can automatically control the gain based on the signal input amplitude to select the most suitable measurement range, improving measurement accuracy. The measurement interface is shown in Figure 3. [align=center] Figure 3 Measurement Interface[/align] This system utilizes a data acquisition card to design a dual-channel virtual oscilloscope. With dual-channel acquisition, the sampling rate is 250 kS/s per channel; with single-channel acquisition, a sampling rate of 500 kS/s can be achieved, meeting actual testing requirements. The functional structure of the virtual oscilloscope is shown in Figure 4. [align=center] Figure 4 Functional Structure Diagram of Virtual Oscilloscope[/align] 3.2 Component Testing Function The entire degaussing equipment is composed of various functional components. For each component's function, a combination of a diagnostic expert system and fault tree analysis is used to generate a knowledge base for the diagnostic expert system, guiding users in equipment maintenance and automatically measuring relevant signals, thus realizing fault diagnosis and fault location for the degaussing equipment system components. 3.3 System Dynamic Index Testing Function The degaussing equipment controller belongs to a feedback control system. The time response of a control system can be divided into two processes: dynamic and steady-state. The dynamic process, also known as the transient process, refers to the system's response process from its initial state to near its final state. The steady-state process refers to the system's output state when time t approaches infinity. It is generally considered that tracking and reproducing step actions are relatively stringent operating conditions for the system. Therefore, step response is often used to define time-domain performance indicators and measure the quality of system control performance. The unit step response performance index of the control system is shown in Figure 5. [align=center]Figure 5 Performance Indicators of Unit Step Response of Control System[/align] The figure shows six dynamic performance indicators: rise time tr, peak time tp, delay time td, settling time ts, overshoot σ%, and steady-state error ess. These indicators basically reflect the characteristics of the system's dynamic process. tr, td, and tp reflect the speed of the initial stage of the system response. Settling time ts reflects the overall speed of the system response. Overshoot σ% reflects the smoothness of the system response process. Steady-state error reflects the final control accuracy of the system in reproducing the input signal. Among these six indicators, the most important are overshoot σ%, settling time ts, and steady-state error ess, which respectively evaluate the smoothness, speed, and steady-state accuracy of the system's unit step response. This system, targeting the control process of demagnetizing equipment, generates a configurable step excitation signal input to the demagnetizing equipment control loop, collects its output signal waveform, and calculates overshoot σ%, settling time ts, and steady-state error ess to evaluate its dynamic and steady-state performance. The software test waveform and data calculation interface are shown in Figure 6. [align=center]Figure 6 Transient Process Test Waveform[/align] 3.4 Information Management Function The information management function module realizes functions such as tester permission management, system parameter setting, equipment measurement record archiving, and can print relevant reports. 4 Conclusion The virtual instrument-based integrated test system for demagnetizing equipment designed in this paper achieves high accuracy in basic signal measurement and dynamic performance testing, meeting the test requirements. The system has undergone metrological testing at the Institute of Metrology and Testing and passed environmental testing. Application in actual production and maintenance processes shows that the system is stable and reliable, improving the automation level, test accuracy, test efficiency, and information management level of demagnetizing equipment maintenance. It has significant advantages compared to traditional testing using multiple ordinary instruments. This system is designed based on virtual instrument technology, possessing good versatility, compatibility, and scalability. By adding corresponding software modules, various test functions can be expanded, making it applicable to a wide range of fields. The innovative points of this paper are: 1. Virtual instrument technology is applied to the testing of demagnetizing equipment, integrating multiple testing functions into one; 2. Functional testing and fault location of demagnetizing equipment components are realized using expert systems and fault tree theory; 3. A configurable step signal source is used to test the dynamic performance of demagnetizing equipment; 4. This testing system has good versatility and scalability. References: [1] Tang Jianfei, Gui Yongsheng, Jiang Nengjun. Overview of submarine degaussing system [J]. Marine Electrical Technology, 2005.6:1-3. 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