Overall Scheme Design of Fault Diagnosis for Complex Electronic Systems

Traditional manual testing methods are no longer able to meet the maintenance needs of modern shipboard fire control system board-level circuits. Therefore, the development of intelligent and universal automatic test systems has become an important issue for shipboard fire control system fault detection. This article analyzes the performance and functional requirements of the automatic test system, develops the automatic test system based on PXI bus instruments, and designs an overall solution with signal time-frequency analysis capabilities that can carry out intelligent fault diagnosis for a variety of board-level circuits. On this basis, the design of hardware circuit and software solution is completed. The automatic test system was analyzed on hardware indicators and software functions. On the hardware side, the hardware resource selection was completed based on the hardware indicator requirements. On the software side, the overall software architecture design and the design of each functional module were completed based on the system software functional requirements. Finally, the composition and functions of each module of the system software and the overall operation process are introduced.


Introduction
With the development of science and technology, the structure of board-level circuit becomes more and more complex.Compared with traditional manual test methods, automatic test system has faster test speed and higher measurement accuracy, so automatic test system has been widely used in industrial production, aerospace, military development and other fields.Fault diagnosis method is an important part of automatic test system, it is the technical basis of fault diagnosis and location, and it is also the difficulty of automatic test technology development, so it has gradually become one of the emphases of automatic test system research in recent years [1][2].At present, ATS mainly rely on the way of joint programming, using professional data processing software to solve the above problems, but in the joint programming, professional signal processing often needs to occupy a lot of computer resources, so when large-scale ATS detect complex circuits, the hardware equipment is often difficult to meet the real-time and stability requirements of the test [3].
Based on the engineering background of fault diagnosis of complex electronic system, this paper develops the design of automatic test system.In complex electronic system, there are many kinds of board-level circuits and complex structures, so fault detection has the characteristics of long time, difficulty and low efficiency.To solve the above problems, this paper will develop an automatic test system based on PXI bus instrument, and design a set of automatic test system with signal timefrequency analysis ability, which can carry out intelligent fault diagnosis for various board-level circuits [4][5].

System Requirements Analysis
The automatic test system intends to take the frequency domain characteristics of circuits as the basis for fault diagnosis to the test board-level circuits.Its basic working principle is shown in figure 1.The user controls the automatic test equipment through the test software, provides the necessary power supply signal and test excitation signal to the circuit under test, collects and analyzes the output response signal of the circuit under test, obtains the frequency domain characteristics of the circuit under test, and realizes the fault diagnosis of the circuit under test by analyzing the frequency domain characteristics of the board-level circuit [6].

Hardware Resource Selection
The hardware index of this system is required to be high, so it is necessary to complete the selection of hardware resources according to the hardware index requirements of the system.PXI bus is a measurement and control instrument bus standard introduced by NI Company in 1998.As shown in table 1, the bus has a faster transmission rate and higher data throughput than previous buses.In addition, instruments developed on the basis of PXI bus are small in size and light in weight, and many instruments provide VI driver samples corresponding to functions, making software development less difficult.To sum up, PXI bus test instruments are selected to build automatic test system in this project.

Hardware Overall Connection
The overall electrical connection diagram of the system is shown in figure 2. The chassis provides power supply and PXI communication bus for the main controller and each instrument module.The main controller and each instrument are connected to the overall system through PXI bus.All devices share a PXI bus to ensure the power supply and clock synchronization of each module.
The main controller located in the zero slot of the chassis is used as an upper computer and is connected with each instrument board card through a bus to control each instrument board card to carry out test tasks and acquire signals for data analysis [7].The adapter circuit is an important part of this automatic test system.The actual interface of the tested object is various, and most test instruments are 3 difficult to connect directly with the signal port of the tested object [8][9].At this time, it is necessary to make the adapter circuit, through the interface circuit, adapt to the port of the tested object, so that the instrument can correctly connect the signal to the tested circuit and read the response signal of the circuit.
As the hub of the acquisition module and the upper computer in the drive circle, it is responsible for This automatic test system uses a variety of card instrument models, and the interface models provided by the card are also different, which leads to a large number of cable types required during the use of the instrument, and the wiring work of the instrument before the test is more troublesome.And more instruments use high-density DB interface, this kind of plug is not easy to plug, and after many times of insertion and drawing easily lead to pin bending, connector damage, which undoubtedly greatly increases the cost of later maintenance.Therefore, this system designs the transfer circuit, connecting all instrument ports to the transfer circuit, the transfer circuit is classified according to the signal type, signal quality, input and output of the instrument port, and led to different high-quality blind connectors respectively.Blind plug interface connection is simple and firm, can withstand multiple plug-in, through the original connection into a unified blind plug connector, can the difficulty reduce of the connection in the test process, but also reduce the difficulty of the design of the board level circuit adapter board to be tested in the later stage.

Hardware Overall Connection Mode
Therefore, this system designs the transfer circuit, connecting all instrument ports to the transfer circuit, the transfer circuit is classified according to the signal type, signal quality, input and output of the instrument port, and led to different high-quality blind connectors respectively.Blind plug interface connection is simple and firm, which can withstand multiple insertion, through the original connection into a unified blind plug connector, can reduce the difficulty of the connection in the test process, but also reduce the difficulty of the design of the board level circuit adapter board to be tested in the later stage.The connection between each instrument and the transfer circuit can be divided into three categories: (1) Direct connection (2) Connected via matrix switch The module of function generator (PXI-5413) utilized as a commonly used source instrument, oscilloscope (PXI-5114) and multimeter (PXI-4065) utilized as a commonly used sink instrument, their signal channels are used very frequently, but the number of ports of these three instruments is limited.If there are multiple test points that need to be input signals or multiple test points that need to be connected, it is necessary to pause the test frequently and manually change the connection to switch the test points.This greatly increases the workload required for the test and is not conducive to the rapid development of the test.
Therefore, in order to reduce manual operation and increase test accuracy, the input and output ports of the above three instruments are connected with matrix switches (PXIe-2534), played the role of bridges to connect to the transfer circuit.As shown in figure 3, the signal ports of the signal source, oscilloscope and multimeter are connected to the R terminal of the matrix switch.By adjusting the switch on or off, connections between R port and C port of the matrix switch can be realized.Qscilloscope and multimeter to the R terminal of the matrix switch, and connect the test point to the C terminal of the matrix switch.When the test point needs to be tested, just open the corresponding switch and connect the test point to the corresponding instrument for testing.In this way, the signal source, oscilloscope and multimeter can be integrated into a small module to realize the customization function of the C port of the matrix switch.
(3) Connected by C-type switch The programmable power supply (PXIe-4112 and PXI-4110) and DA(PXI-6723) used in this system have large output power.In order to prevent the high-power signal output by this kind of instrument from affecting the safety of the system, this kind of instrument is connected to the C switch (PXI-2570), and then connected to the transfer circuit.

System Software Module Composition
The design of software part of this automatic test system adopts modular and structural design concept.According to the functional requirements of system use, the software is divided into several corresponding functional modules.Different modules are interrelated and mutually contained to form the overall automatic test system software architecture [9].
(1) User management module: The system provides login verification interface, users need to use account password to log in the system, users are divided into junior users and advanced users, different users have different access rights.Junior users have the right to carry out tests, edit new test programs, save and read their own test data, etc., different users' test data and records are saved in different paths.In addition to the full privileges of the initial user, advanced users also have the right to add new test accounts and query test data and records of other users.
(2) Instrument driver module: The system can establish communication between the host computer and each instrument board, so as to control the function generator, oscilloscope, multimeter and other instruments, realize the transmission of excitation signals, the measurement of signals to be tested, the communication of data interfaces, etc., and monitor the working state of the instrument in real time.
(3) Signal processing module: The ability to analyze and process the signals collected by the instrument.Users can perform various forms of signal processing such as Fourier transform, waveform identification, waveform comparison, noise filtering, etc., based on the collected data according to test needs.
(4) Test program editing module: Users are allowed to modify or create new test programs.Users can design new test programs according to their own test requirements, and load them into the test program.At the same time, users can save the test program as an independent file and export it.
(5) Test flow control module: The system shall provide pause, end, continue and other control options to control the test flow.Users can select "automatic test mode" to complete the test at one time, or select "semi-automatic test mode" to perform step test.
(6) Display interactive module: The system can operate a single instrument through a virtual panel to observe the running state of the instrument, or monitor the progress of the test during the running process of the test program to observe the electrical characteristics of the tested object.
(7) Self-test module: provide self-test and initialization function of system instrument resources, which can self-test the test instrument resources and test channels of the whole equipment.After selftest, it will give the information of faulty instruments in the system for maintenance.
(8) Data management module: The system can store, analyze, import and export all kinds of data in the test process.
(9) Auxiliary function modules: In addition to the above function modules, the system also has auxiliary functions such as file report editing and printing.

System Software Operation Flow
In the process of using the system, the software operation flow is shown in figure 4.After starting the system, the user first enters the account password to log in, and the user management module verifies the user information according to the account password, and endows the user with use rights.After entering the system, the system background will call the self-test module to initialize and self-test each instrument to ensure the reliability of the test instrument resources and test channels in the whole equipment.Then the user can choose the completed test program in the system or choose to use the test strategy generation module to design a new test scheme.
The test flow is mainly composed of instrument drive control and signal processing analysis, so the control process of test flow control module in the system is actually the process of system calling instrument drive module and signal processing module.During the test operation, the user realizes the real-time control of the test flow through the test flow control module, the system invokes the instrument driving module and the signal processing module according to the current test steps, and monitors the test progress through the display interaction module.Data management module is responsible for data communication in the test process.It can obtain data from external or instrument drive module and transmit data to signal processing module for processing.When completion of the test, the test results are edited and printed through the affiliated function modules [10].

Conclusion
This article mainly designs the framework of the fault diagnosis automatic test system for complex circuit systems, provides guidance for the complex circuit fault diagnosis system, and meets the realtime and stability requirements of the test.The specific content is based on the system requirements analysis of the automatic test system based on the maintenance requirements of the modern shipboard fire control system board-level circuit.Based on the requirements analysis, the hardware index analysis and software function analysis are carried out, and on this basis, the overall hardware scheme design and software are completed.Overall design.Among them, in terms of hardware, hardware resource selection, switching circuit design, and overall solution design were completed based on hardware index requirements; in terms of software, based on system software functional requirements, the overall software architecture design and the design of each functional module were completed.

Figure 1 .
Figure 1.Basic working principle of automatic test system.

Figure 3 .
Figure 3. Schematic diagram of port switching design.

4 .
Overall Design of System Software Scheme LabWindows/CVI is selected to develop the software of automatic test system.LabWindows/CVI is an interactive C language test software development platform developed by NI Company.Different from LabVIEW, another graphical programming language based on development software of NI Company, LabWindows/CVI is a text-based programming language software.It combines C language with professional tools in the field of testing.It can be widely used in the development of various testing, control, fault analysis and information processing software.Development tasks for large complex test systems.EPES-2023 Journal of Physics: Conference Series 2731 (2024) 012031 IOP Publishing doi:10.1088/1742-6596/2731/1/0120315

Figure 4 .
Figure 4.The relationships among functional modules.

Table 1 .
Transmission rate of different buses.