1. Introduction Missile aiming equipment integrates optics, precision mechanics, and electronics, and is an important component of missile weapon systems. Its performance and accuracy directly affect the lateral accuracy of the missile. During use, transportation, and storage, factors such as vibration, impact, temperature changes, and internal stress variations cause changes in the equipment's accuracy and key performance indicators, directly affecting missile aiming accuracy and weapon combat effectiveness. Therefore, it is essential to conduct regular verification and pre-use re-inspection of the aiming equipment. Currently, most traditional metrological verification systems are bulky, complex to operate, have low automation, poor versatility, and cannot provide accompanying or proactive metrological support. Therefore, this paper designs and implements a novel virtual metrological verification system for missile aiming equipment based on the design concepts of PXI bus and virtual instruments, discussing the system's hardware composition, detection principle, and system software. 2. Introduction to PXI Bus PXI (PCI eXtension for Instrumentation) is a modular instrument bus specification released by National Instrumentation (NI) in 1997. Its core is to integrate all the superior performance of the high-speed PCI bus and the Compact PCI module structure. The PXI bus features 32/64-bit data transfer capabilities and data transfer speeds of up to 132MB/s and 264MB/s respectively. It also supports PCI-PCI bridge expansion and plug-and-play functionality. Dedicated system reference clocks, trigger buses, star trigger lines, and inter-module local buses are added to meet high-precision timing, synchronization, and data communication requirements. Besides using embedded computers, PXI can expand its system control via the MXI-3 interface, including external PC control, multi-chassis expansion, and longer-distance control, broadening its application scope. Not only can eight expansion cards (one system module and seven instrument modules) be inserted into a single PXI rack, but multiple PXI chassis can also be connected in star or daisy-chain configurations via the MXI-3 expansion interface. To meet the needs of the measurement and control module, the PXI bus not only provides a 33MHz system clock, but also a 10MHz TTL reference clock signal, a TTL trigger bus, and a 12-pin local bus. This allows the signal lines for synchronization, triggering, and clocking functions to be directly obtained from the PXI bus, eliminating the need for numerous cables. PXI offers synchronization and timing characteristics at an affordable price, previously only found on high-precision instruments on expensive test platforms (such as VXI). PXI module instruments can provide high-performance testing, measurement, and data acquisition without compromising measurement accuracy and saving development costs. 3. System Scheme 3.1 System Hardware Composition Based on the characteristics of the missile aiming equipment under test and the requirements of various test parameters, and considering various factors, this system selects PXI products from National Instruments (NI) as the system acquisition device to construct the hardware platform for the verification system. The system adopts an external control computer scheme based on the PXI bus. The hardware consists of three main modules: a portable industrial computer, optical testing equipment, and electronic testing equipment, as shown in Figure 1. [img=500,439]http://image.mcuol.com/News/080801132550920.jpg[/img] Figure 1 System Hardware Composition The industrial notebook computer is the main control unit of the system. It connects to the PXI bus via the MXI-3 control kit and controls the electronic and optical testing equipment through the various function cards in its expansion slots and the bus, completing the acquisition of various signals. Through the virtual metrology software system built using Visual Basic and Measurement Studio, it completes the analysis, processing, and display of test data. The electronic testing equipment mainly consists of PXI module instruments, PCL720 digital I/O modules, signal converters, and other accessories and cables. The PXI module instruments include the PXI-1002 chassis, the MXI-3 control kit, the PXI-6052E multi-function data acquisition module, and the NI-4060 digital multimeter module. The MXI-3 control kit connects the main control computer and the PXI testing instrument. The multi-functional data acquisition module and digital multimeter module complete signal acquisition and processing. The signal converter handles the conversion between dedicated and general interfaces and controls the time-division multiplexing of multiple input signal channels via the PCL720 module. 3.2 System Software In the development of the platform system software, a hybrid programming approach using the object-oriented development tools Visual Basic 6.0 plus the Measurement Studio 6.0 standard software package and Visual C++ 6.0 was chosen. Visual Basic 6.0 and Measurement Studio 6.0 were used to develop the main system program, while Visual C++ 6.0 was used to develop the dynamic link library. The metrological verification system needs to verify various types of aiming equipment, and the methods and requirements for verifying each different piece of equipment vary. To ensure the system software has good reliability, maintainability, and scalability, a hierarchical design method was adopted in the software programming design, following the principles of standardization and modularization. The software system module structure is shown in Figure 3-2. [align=center]Figure 2 Software Functional Structure Diagram[/align] The system is divided into multiple model series, each containing multiple different aiming device calibration modules. In the software design, calibration procedures, initialization and self-testing, database queries, and help/guidance modules are designed for each type of weapon system. Each calibration procedure module is further divided into sub-modules for I/O control, database calls, data processing and analysis, calibration result display and output, calibration table generation, and printing. In this modular program structure, each program module is an independent functional unit. If a calibration item needs to be modified, only the corresponding program module needs to be modified without affecting other program modules. Moreover, this modular structure facilitates functional expansion of the calibration program and integration with other systems. 3.3 System Testing Principle The aiming equipment needs to detect two types of signals: electrical quantity and time/frequency. During system operation, the main control computer, following a prescribed testing procedure, controls the relays in the signal transfer box to sequentially connect the signal channels of the tested point to the corresponding test module. The signal from the tested electronic device is transferred through the dedicated and general interfaces on the signal transfer box to the PXI-6052E data acquisition module and NI-4060 digital multimeter module in the PXI chassis for acquisition, real-time measurement of the tested point's operating status. The measurement data is sent to the main control computer for processing via the MXI-3 interface card. After analysis, calculation, and comparison by the software program, the test results are displayed in real-time. When multiple different state indicators (voltage, current, frequency) at the same point need to be tested, the relays in the signal transfer box can be controlled to split the signal into multiple paths, which are then input to the corresponding test modules for testing. For aiming electronic devices requiring a dedicated signal source for external signal testing, the MXI-3 controller controls the function generator module to apply an external excitation signal to the test channel, while simultaneously detecting the signal response of that channel. This flexible control method makes the entire automatic detection process very simple and reliable, realizing real-time detection at multiple points, multiple channels, and multiple states. 4. Conclusion This metrological verification system is small in size, easy to carry, and low in cost. Its hardware equipment has high detection accuracy and complete functions, capable of acquiring and processing various signals. Moreover, it has good versatility and expandability; by appropriately adding some hardware interfaces and developing corresponding software, it can realize the detection of other types of aiming equipment. It has achieved the tasks of accompanying metrological support and front-line metrological support, and its application prospects are very broad. References: 1. Zhou Hong. Design of Software Structure for Virtual Instrument System. Computer Automatic Measurement and Control. No.1 2000 2. Liu Junhua. Modern Detection Technology and Test System Design. Xi'an Jiaotong University Press. 2001 3. Liu Junqi. Fault Diagnosis System for Electrical Equipment Based on PXI Bus Technology. China Ship Repair. No.5 2001 4. Liu Ya. Construction Technology of Virtual Instrument. Computer Automatic Measurement and Control. 1999 5. Lin Zhengsheng. 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