Abstract: This paper develops an intelligent testing system for pulse detonation engines based on virtual instrument technology, utilizing computer hardware and software resources to replace a large amount of hardware in traditional testing instruments. This system can realize multi-channel data acquisition, real-time data processing and display, post-analysis and processing of test data, and generation and printing of test reports. The paper introduces the overall composition and working principle of the system and presents the design methods for the relevant hardware and software. Keywords: LabWindows/CVI; virtual instrument; MATLAB; data processing [b][align=center]Development of Intelligent Measurement System for Pulse Detonation Engine MO Yong-xin YAO Rong-Bin WANG Yu[/align][/b] Abstract: With the computer's software and hardware resources to replace the hardware of traditional measurement systems, an intelligent measurement system for PDE based on virtual instruments is developed. This system can be applied to achieve functions such as real-time multi-channel data acquisition, data processing, and display, etc. The working principle and basic structure are presented. The design method of the hardware and software development technology is also presented. Key words: LabWindows/CVI; virtual instrument; MATLAB; Data processing 1. Introduction Under the urgent need for large-scale, automated, and intelligent measurement and control systems, the combination of computer technology, instrument technology, and communication technology has created a new milestone in instrumentation—virtual instrument technology. Virtual instruments rely on the powerful data processing capabilities and rich graphics display capabilities of computers, combined with a good virtual instrument software platform, to realize various hardware functions in traditional instruments. Its advantage lies in the fact that users can define their own dedicated instrument system, and it is flexible in function, easy to build, and easy to upgrade. In a sense, "software is the instrument". Based on the PC and multi-functional data acquisition card hardware platform, this paper uses LabWindows/CVI and MATLAB software as development tools to develop an intelligent test system for pulse detonation engines based on virtual instrument technology and laser diagnostic technology. The system can monitor the temperature, pressure and concentration of various combustion product components of the pulse detonation engine in real time, effectively solving the shortcomings of traditional measurement methods. 2. Brief description of the test system 2.1 Introduction to pulse detonation engine and optical diagnostic technology The pulse detonation engine (PDE) is a new concept of power device that uses high-temperature and high-pressure gas generated by intermittent or pulse detonation waves to generate thrust. PDE has the advantages of high cycle thermal efficiency, low fuel consumption rate, simple structure, light weight, high thrust-to-weight ratio, large specific impulse and adjustable thrust, and has become a major research hotspot in the field of engines today [1-3]. Pulse detonation combustion is a type of unsteady-state combustion, characterized by high-frequency changes in parameters such as pressure, temperature, combustion products, and component concentrations within the combustion chamber. Rapidly and accurately obtaining the patterns of these parameter changes is crucial for studying pulse detonation engines. Optical diagnostic techniques (optical absorption/high-temperature radiation combination method) are a rapid, non-contact measurement method with minimal disturbance to the measured object, making it particularly suitable for measuring various parameters of pulse detonation engines. A laser diode and a photodiode are symmetrically placed on either side of the engine under test (with quartz windows on both sides of the PDE). When no laser light enters the detector, the detector receives the radiation energy from the high-temperature flame; when laser light enters the detector, the energy received consists of the superposition of the transmitted laser energy and the infrared energy radiated by the high-temperature flame. The temperature of the combustion gas can then be obtained by combining Planck's blackbody radiation law and Kirchhoff's laws. The incident laser beam is modulated to switch at a specific frequency, thus combining the aforementioned optical radiation and absorption methods. In addition, due to the advantages of lasers such as high intensity, good collimation, and narrow bandwidth, they can perform absorption spectrum measurements with very high resolution. Combining Beer-Lambert's law, based on the relationship between the transmittance and incident amount of narrowband light after passing through a uniform medium of length L, the ratio of the absorption coefficients of the two spectra can be obtained from the measured absorption spectrum, and the corresponding temperature can be calculated. Then, the concentration of each combustion product can be calculated from the temperature and the spectral absorption coefficient [1~3]. 2.2 Overall Structure of the Test System Based on the above principles, the multi-parameter measurement system developed for the PDE model machine mainly consists of a semiconductor laser (pulse modulation output), an optical sensor, a piezoelectric sensor, a signal conditioning circuit, a multi-functional data acquisition card, a computer, and related software. The overall system structure block diagram is shown in Figure 1. [align=center] Figure 1 Test System Block Diagram[/align] 3 System Hardware Design 3.1 Photoelectric Receiving Circuit The photoelectric receiving circuit is an important part of the PDE test system. The photoelectric receiving circuit consists of a photoelectric conversion device and a signal conditioning circuit, and its performance has an important impact on the measurement results. Because the photodiode photocurrent is very small and the received modulated light frequency is relatively high, the circuit design must consider the requirements of high gain, low noise, and bandwidth. The designed circuit consists of three parts: a preamplifier (also used for I/V conversion), a driver amplifier, and a power amplifier. The operational amplifier selected is the OPA627 with high input impedance and low offset current to improve the signal-to-noise ratio and bandwidth of the signal conditioning circuit. 3.2 Charge Amplifier The charge signal output by the piezoelectric sensor is relatively weak and cannot be directly sent to the data acquisition card. A charge amplifier must first convert the weak charge signal into a voltage signal compatible with the data acquisition card. A charge amplifier is an amplifier whose output voltage is proportional to the input charge. Its core is an operational amplifier with capacitive negative feedback and high input impedance and gain. This system uses the YE5850 charge amplifier, which has a built-in bandpass filter with adjustable upper and lower limits. 3.3 The multi-functional data acquisition card is a self-made eight-channel multi-functional data acquisition card. Its analog input signal dynamic range is ±5V, sampling pass rate is 10MHz, A/D conversion resolution is 12bit, and it provides multiple triggering modes to meet the needs of signal waveform analysis. Figure 2 shows the block diagram of the multi-functional data acquisition card. This circuit mainly consists of a multi-channel analog switch, A/D conversion circuit, buffer circuit, control circuit, control signal output circuit, and PC bus interface circuit. Various signals within the PDE, such as the output of the piezoelectric sensor, are connected to the YE5850 charge amplifier. Optical signals are converted to photoelectric signals and then sent to the signal conditioning circuit, where they are converted into signals matching the acquisition card. These signals are then sent to the respective input terminals of the data acquisition card, selected by a multiplexer, and sequentially acquired under the control of the controller. The data is then sent to the storage buffer, read into memory by the computer, processed, and the results are output. Simultaneously, the acquired data can be saved to the hard drive for future research. Synchronous control of the PDE ignition device can be achieved through the control signal output (DO) terminal of the acquisition card. [align=center] Figure 2 Block diagram of data acquisition card[/align] 4. System software design Through comparison of commonly used virtual instrument development platforms, and considering that the data acquisition card used in this system is self-made, LabWindows/CVI was chosen as the main development platform. LabWindows/CVI is an interactive development environment based on standard C language developed by NI, with a good user interface, which can easily perform low-level operations on non-NI boards. At the same time, through the interface with MATLAB, it greatly improves programming efficiency [4-6]. The system software adopts a modular design concept, mainly including user interface design (instrument soft panel), data acquisition and processing, result output and display, etc. The basic structure of the software is shown in Figure 3. [align=center] Figure 3 System software structure[/align] 4.1 Main interface of the software The main interface of the system operation (instrument soft panel) is designed using the user interface editor provided by LabWindows/CVI. The user interface includes buttons corresponding to the function modules such as data acquisition card parameter setting; data acquisition and control; analysis, processing and saving of measurement data; dynamic display and printing of results. Users can call each module through the control buttons on the main interface. Figure 4 shows the front panel interface of this measurement system. [align=center] Figure 4 System front panel operation interface[/align] 4.2 Data Acquisition and Preprocessing Before acquisition, the acquisition card needs to be set, such as selecting continuous or single signal acquisition, setting the acquisition channel, windowing mode, and observing the time domain and frequency domain values ​​of the signal by moving the cursor. For the triggering mode, parameters such as trigger source, trigger level, trigger edge, and number of points to be reserved before triggering can be selected. When the user starts the data acquisition card, the data acquisition card will cyclically acquire each incoming signal according to the pre-set parameters and read the acquired data into memory or store it on the hard drive. At the beginning of acquisition, due to the limitations of certain components, the quality of the first few acquired data points is not very good, so the first 8 data points were removed during programming. To further remove abnormal data caused by external interference, data smoothing, filtering, and other preprocessing are performed. LabWindows/CVI includes many signal processing functions that can be directly called. Figure 5 shows the waveforms before and after preprocessing. [align=center] Figure 5 Signals before and after processing[/align] 4.3 Data analysis and processing Data processing is the core of the measurement system, realizing various calculations, analyses and processing of the collected data, and finally obtaining the parameters such as pressure, temperature and combustion product component concentration of PDE. The various library functions provided by LabWindows/CVI can meet most of the calculation requirements, but for some complex time domain and frequency domain analyses, such as wavelet analysis, the programming workload is very large. When designing data processing software, if the various signal processing toolboxes provided by MATLAB can be used, the programming efficiency can be effectively improved. However, as a high-level language that runs in an interpreted manner, MATLAB has low execution efficiency. Considering that both MATLAB and LabWindows/CVI programming languages ​​have good openness, this system shares MATLAB software toolkits in LabWindows/CVI in order to realize virtual instruments based on the latest signal analysis and processing technology, thereby achieving the goal of having both powerful numerical calculation capabilities and high execution efficiency in the programming environment [6]. The implementation method is to realize the function of calling MATLAB in the LabWindows/CVI environment and running the program in the MATLAB environment through the interface function between LabWindows/CVI and MATLAB. The essence of the above process is to establish an ActiveX service control for data exchange in the LabWindows/CVI environment, transferring data information from the LabWindows/CVI platform to the MATLAB environment to achieve the purpose of calling MATLAB function calls, executing MATLAB programs, and returning MATLAB results. Because DLL files execute quickly, are highly portable, and convenient for users to call, the ActiveX service functions are re-encapsulated into easily callable high-level functions in the specific implementation, and then DLL files for these functions are created. More complex signal processing in the system, such as wavelet analysis, is implemented using this method. Experiments have proven that these methods are feasible and can effectively shorten system development time and reduce costs. The results of data analysis and processing, such as parameter values ​​and curves, can be directly displayed on the computer monitor or output through printers and other methods. 5. Conclusion This paper utilizes virtual instrument technology to develop a multi-parameter intelligent testing system for pulse detonation engines. It can adapt to the testing needs of the specific PDE environment, and the test results are reliable. Furthermore, the entire testing system is low-cost, small in size, easy to use, and easy to modify and upgrade, demonstrating the advantages of virtual instruments. Leveraging the strengths of LabWindows/CVI and MATLAB, this paper combines the rich control resources and high execution efficiency of LabWindows/CVI with the powerful data processing function library of MATLAB. This successfully enables the rapid application of new signal analysis and processing technologies within the system, improving programming efficiency and quality. This has significant guiding value for practical engineering applications. The author's innovation lies in the fact that the development of pulse detonation engines, as the power plant for next-generation aerospace vehicles, is still in its early stages in my country, lacking automated and intelligent testing methods. To accelerate the development of PDEs (Power Detonation Engines), it is essential to improve testing capabilities. This paper introduces virtual technology into the field of multi-parameter testing of pulse detonation engines, combining it with optical diagnostic technology and employing a self-made high-speed data acquisition card to develop an intelligent testing system for pulse detonation engines. This system can acquire, process, and display measurement results in real time and can also process previous test data. Furthermore, the use of hybrid programming with LabWindows/CVI and MATLAB shortens the system development cycle and facilitates upgrades and maintenance. 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