The automatic testing system for airborne electronic equipment requires functional testing of hundreds of components, involving a large variety and quantity of signals. These signals are categorized by frequency (low-frequency and high-frequency), time-domain characteristics (continuous and discrete), and form (electrical and non-electrical signals, such as temperature, speed, altitude, air pressure, and heading). To meet these complex testing requirements, we employ virtual instrument technology. The system hardware design utilizes PXI modular instruments, which offer advantages over GPIB, VXI, and RS232 instruments in terms of speed, size, and expandability, making them the core hardware component. Conventional signal sources and signal measurement modules are then selected, and dedicated and self-developed equipment is expanded via GPIB and RS232 buses. The overall system hardware principle is shown in Figure 1. Due to the large number of PXI modules and for future expansion, an 18-slot PXI-1045 chassis was chosen. To further improve the system platform integration, a PXI-8187 zero-slot embedded controller was selected, abandoning the previous method of using an industrial computer as the main controller via an MXI-2. The PXI-8187 features a GPIB interface, facilitating the expansion of GPIB bus devices. Since some instrument resources and components require serial communication, the PXI-8421 was chosen to expand four serial ports. 1. Signal Acquisition The 6 1/2-inch digital multimeter PXI-4070 and the 5 1/2-inch digital multimeter PXI-4060 are commonly used test modules, capable of measuring voltages from 0 to 300V, currents from 0 to 1A, and resistances from 0 to 100MΩ. The oscilloscope PXI-5112 (2-channel 8-bit resolution, 100MHz bandwidth) and the analog input PXI-6070E (16 single-ended inputs/8 differential inputs, 12-bit resolution, 1.25MHz sampling rate) are used together to meet the acquisition needs of commonly used continuous wave and single-point voltage signals. During data acquisition, the PXI-6070E connects two SCXI-1125 chips to the front end for signal conditioning (10kHz or 4Hz low-pass filtering and attenuation). Additionally, the PXI-6070E can be used for communication between the controller and the SCXI chassis. The high-speed DIO PXI-6534 can acquire and output high and low-speed discrete signals. Acquisition and processing of special and complex signals utilize GPIB devices and self-developed RS232 devices, such as a spectrum analyzer. 2. Signal Output The function generator PXI-5421 (16-bit resolution, 100MS/s sampling rate, 43MHz bandwidth) and the high-speed analog output PXI-6733 (8-channel output, 16-bit resolution, 1MHz refresh rate) work together to meet the output needs of commonly used continuous wave and single-point voltage signals; the SCXI-1124 is used to isolate analog voltage and current outputs. The output of special and complex signals utilizes GPIB and self-developed RS232 equipment, such as AC/DC power supplies, RF signal sources, atmospheric data testing systems, and simulators. 3. Signal Routing Due to the large number of signals from most airborne electronic devices, it is impossible to connect all signals directly to resources simultaneously; switching must be performed via a relay matrix. Therefore, the relays must have sufficiently fast response times to switch large signals. Two relay matrix modules, SCXI-1129, and accessories SCXI-1333 and SCXI-1339, were selected and combined to form a suitable relay matrix (maximum switching capacity 150Vdc/A, 150Vrms/250mA). During signal connection and disconnection, to achieve automatic selection of the optimal path and safety protection (avoiding source-to-source connections), the relay matrix driver was rewritten, achieving satisfactory results in practical use. 4. Resource Interfaces and Adapters The resource interface is a collection of all resource interfaces. Each component connects to some resources as needed via an adapter. One or more UUTs share one adapter; therefore, the test system can configure one or more adapters based on the signal characteristics of the UUTs. The system software design uses CVI (Computer-Instrument-Virtual) as a virtual instrument development software, adding instrument control and tool function libraries to the standard C language (Ansi C). It provides many practical examples, a user-friendly graphical interface, and C language is a familiar and easy-to-use development tool. Therefore, choosing CVI can accelerate the development of test programs (TPs). The system software principle is shown in Figure 2. Figure 2 System Software Architecture. To facilitate and standardize TP writing, the TP development management software automatically generates the test program code framework and instrument operation code based on the input test information. After the test program is written, it is compiled to generate a dynamic library, which is called and managed by the test program execution management software. In the test program development process, instrument operation and the development of the virtual instrument interface are two key aspects. 1 Development and Use of IVI Instrument Drivers The purpose of instrument drivers is to program and control instruments, simplifying the operation of instruments for test program developers. Traditional instrument drivers are too tightly coupled with the instrument; if the instrument changes, the driver must be rewritten, and consequently, the test program using this driver must also be rewritten and compiled. Interchangeable Virtual Instruments (IVI) drivers employ the concept of class drivers, enabling interchangeability between instruments of the same class. They also enhance instrument simulation and state caching capabilities, improving the efficiency of test program development and debugging. CVI provides convenient IVI driver development tools, allowing the use of IVI drivers to control instruments during test program development. Currently, the IVI driver standard only releases class drivers for eight major instrument categories. To ensure interchangeability and simulation capabilities for non-IVI standard instruments within a certain range, we have developed a custom IVI driver, drawing inspiration from the standard IVI driver mechanism. Using IVI drivers, we successfully achieved interchangeability between NI's PXI-4070 card multimeter and AGILENT's HP34401 GPIB benchtop multimeter, as well as interchangeability between single-phase and three-phase AC power supplies from different companies. IVI drivers utilize logical names and XML configuration files. When hardware resource descriptions change, only the configuration file needs modification; no changes or recompilation of the test program are required to ensure its normal operation. Without IVI drivers, all test programs using function generators would have to be modified, significantly delaying project progress. Furthermore, utilizing the simulation capabilities of IVI-driven systems allows test program developers to perform simulation debugging on computers without any hardware installed, improving platform efficiency and test program development efficiency. 2. Development of Virtual Instrument Interfaces Virtual instrument interfaces provide a human-machine interface, allowing operators to apply signals and monitor them in real time as needed. CVI provides user interface resource files (*.uir) and various control and display controls for developing virtual instrument interfaces to simulate actual instrument interfaces. Currently, NI LabVIEW, CVI, and HP VEE are the most outstanding and user-friendly virtual instrument interface development software. Figure 3 shows one of the virtual instrument interfaces in TPS. Figure 3. Virtual Instrument Interface Based on Magnetic Sensor. In this example, when the excitation switch is turned on, the PXI-6733 continuously outputs a 1.5V RMS sine wave at a frequency of 400Hz as the excitation for the magnetic sensor. The three analog input channels of the PXI-6070E simultaneously acquire the three heading signals (maximum amplitude less than 100mV, frequency 800Hz) output from the magnetic sensor and display them in the same waveform display control. The angle is then calculated using an algorithm and displayed on the dial control. By adding the signal conditioning board SCXI-1125 and the terminal board SCXI-1313, the test range of the PXI-6070E is extended to 2.5mV to 300V, thus accurately measuring the small signal output by the magnetic sensor and calculating the precise angle. Application Results Using NI PXI modules, CVI, IVI tools, MAX management software, and third-party equipment, we have successfully built multiple general-purpose, open automatic test systems for airborne electronic equipment. These systems have been used to successfully develop over 300 different TPS (Test Platform) models, enabling users to perform rapid scheduled inspections and maintenance of UUTs (Unmanned Underground Test Units). Compared to building test benches with traditional instruments, automated testing systems have significantly improved efficiency and quality, providing strong support for airborne electronic equipment.