Reconfigurable virtual instrument testing technology teaching platform

1 Introduction

Testing technology is a professional basic course for engineering majors in colleges and universities in my country. The course content and name vary slightly with different majors, such as testing technology, mechanical engineering testing technology, thermal energy and power engineering testing technology, etc. Except for the different application backgrounds, the teaching content of these courses is basically the same, mainly introducing the measurement principles of common physical quantities such as temperature, force, and noise and the analysis methods of test signals. At present, the main problem in the teaching of testing technology courses is that there are no physical objects in the classroom teaching of the sensor part. Various different sensors are the same in the eyes of students, and the similar principle introduction makes them feel boring and tedious; while the signal analysis theory part is too profound and difficult for students to understand. In response to these problems, we propose a visual teaching method for testing technology courses with virtual instrument demonstration experiments and engineering cases as the main line; the specific approach is to select several sensors and use measurement experiments to present the working principles of sensors; select several measurement instrument analysis functions and use virtual instrument technology to show the role of signal analysis; select several engineering cases and combine them to introduce the application of testing technology in industry. Use experiments and engineering cases to bring vitality to boring content and give image to abstract theories, change the single book-based teaching model, mobilize students' enthusiasm and initiative in learning, and improve teaching quality.

For the teaching of test technology courses, the most ideal way is to put the classroom in the laboratory, and the teacher explains the theory while operating the test instrument, but this is not realistic. In order to solve the problem of creating an experimental teaching environment in the classroom, we used the reconfigurable virtual instrument technology developed in the National Natural Science Foundation project "Reconfigurable Measurement Theory for Manufacturing" to develop a reconfigurable virtual instrument experimental teaching platform (Dynamic Reconfigurable Virtual Instrument Platform) with independent intellectual property rights for the needs of experimental teaching of test technology courses. And according to the teaching knowledge points, more than 30 experiments were designed to form a virtual instrument experimental teaching environment. In class, teachers can use virtual instrument demonstration experiments to visualize and animate knowledge points to liven up the classroom atmosphere; after class, students can use virtual instrument experiments to verify the learned theories and deepen their understanding of knowledge. DRVI has been used for many years in the national excellent courses "Foundations of Engineering Test Technology" and "Engineering Test and Information Processing" (online) for undergraduates, and the teaching effect is good. At present, more than 150 universities in China have adopted this platform for teaching test technology courses and experimental teaching, and have achieved good social benefits.

2 Design considerations for teaching applications

Teaching virtual instrument experimental platforms and scientific research and industrial virtual instrument platforms have commonalities in technology, but they also have their own special requirements. For example, they must be easy to learn and use; they should be easy to install and carry; they should be easy to organize teaching and knowledge point demonstrations, etc. Perfect and powerful functions are not the main goals pursued during design.

2.1 Software Breadboard Modular Plug-in Assembly Environment

In hardware circuit experiments, teachers and students often use breadboards to connect electronic components and construct experimental circuits. There are many small holes on the breadboard for plugging in electronic components. By plugging the pins of the components into the small holes, a simple experimental circuit can be quickly built using the breadboard, which is very convenient. Drawing on its concept, we use the pipeline of computer inter-process communication to simulate soft wires, and then use a container component containing a group of soft wires to construct a software breadboard; then use the pipeline component to encapsulate the virtual instrument function into a soft component that is easy to plug in, thereby constructing a virtual instrument plug-in assembly development environment similar to a hardware breadboard that is suitable for teaching applications. When applied, teachers and students can quickly assemble a virtual instrument experimental system on the software breadboard like building blocks. Figure 1 is the structure of the virtual instrument software breadboard.

The system adopts a component-based development method in technical implementation. Its advantage is that there is no need for compilation and connection links in the development process of the virtual instrument experiment, and the plug-and-play and hot-swappable of soft components can be realized, which is convenient for teachers and students to operate and try; in addition, the size of the virtual instrument development platform can be made very small. For example, the size of the DRVI platform is less than 5M, and it is green and free to install. Teachers and students can easily use a USB flash drive to copy it to computers in classrooms, dormitories and other places for use.

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Figure 2 Typical signal spectrum analysis experiment assembly diagram

2.2 Browser/virtual instrument dual-screen display structure

In the teaching design, we selected more than 30 virtual instrument experiments according to the test technology course architecture and knowledge points. There are about 100 electronic files in total, including experimental scripts, experimental instructions, theoretical references, etc. The most ideal way is to manage these files in the form of hyperlinks of web page files, and to classify, organize and search the experiments according to the teaching system. However, virtual instruments and browsers are two things with different technical implementation forms. It is difficult to make virtual instruments support browsers, and it is also not easy to make browsers support virtual instruments. For this reason, we use the feature that IE browser can be embedded as an ActiveX control as a whole, and embed IE browser in the virtual instrument interface. In order to ensure that the browser interface and the virtual instrument interface do not conflict, when reading web page files such as experimental instructions, the IE control is maximized and the virtual instrument interface is hidden; when doing virtual instrument experiments, the virtual instrument interface is activated, and the IE control is minimized and hidden; that is, the so-called browser/virtual instrument dual-screen display structure is realized.

In addition, to facilitate automatic switching between virtual instruments and browsers, we added a hyperlink control to the virtual instrument. When clicking on a hyperlink in the virtual instrument, it can automatically switch to the browser interface and load the linked web page file. In the browser, we use the hook function to add hyperlink content recognition and filtering functions. When clicking on a hyperlink in the browser, the browser first determines whether it is a web page or a virtual instrument experiment script. If it is a web page, it will be displayed by the browser. If it is an experiment script, it will be processed by the virtual instrument. As shown in Figure 3.

Figure 3 Using the browser/virtual instrument dual-screen structure to achieve operation linkage

By utilizing the browser/virtual instrument dual-screen display structure, teachers and students can read the experiment catalog, experimental content and other information in the browser embedded in the platform during the experiment. By clicking on the link in the web page, they can directly call up the relevant virtual instrument experiment for operation, which is very convenient to use.

2.3 Composite Virtual Instrument Documentation

In the design of test technology teaching experiments, a knowledge point may be decomposed into several related virtual instrument experiments. For example, when explaining the knowledge point of signal modulation and demodulation, the main contents include synchronous modulation and demodulation of signals, bias modulation and demodulation of signals, and the influence of carrier frequency, etc. If these contents are placed in a virtual instrument interface, they often cannot be displayed. If they are treated as different virtual instrument experiments, the virtual instrument scripts need to be loaded back and forth when used.

To this end, we took advantage of the technology that Windows compound documents can store multiple files, and combined several virtual instrument scripts in the same knowledge point to form a compound virtual instrument document. When loading a virtual instrument compound document, the relevant virtual instrument experiments are loaded at the same time and displayed in a layered manner in the virtual instrument window in the form of page frames. Click the page frame selection button on the right side of the virtual instrument interface to quickly switch between virtual instrument experiments in the group.
Figure 4 shows the display of the virtual instrument compound document of the signal modulation and demodulation knowledge point. During the experiment, page frames can be used to quickly jump between signal synchronization modulation and demodulation experiments, bias voltage influence experiments, and carrier frequency influence experiments.

Figure 4 Signal modulation and demodulation knowledge point virtual instrument composite document display interface

2.4 Signal Basic Scripting Language

Another characteristic of the virtual instrument platform for teaching is that it must be more open. In addition to directly using the virtual instrument functional modules integrated in the platform, such as waveform signal generators and spectrum analysis, students must also be able to understand how they are implemented in the virtual instruments; that is, students can design their own virtual instrument analysis functions based on the mathematical formulas they have learned, such as effective value calculations and related function calculations.

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To achieve this goal, we used the VBScript scripting language provided by the Windows platform, integrated it into the virtual instrument platform, and added common signal analysis functions such as FFT and FIR, hardware operation functions such as sound cards and cameras, and graphic function functions such as drawing lines and circles, to form a special scripting language that meets the teaching needs of testing technology courses, called Signal Basic.

Figure 5 Sine wave signal generator Signal Basic code and interface

For example, the mathematical formula for a sine wave signal is:
(1)

Where A is the amplitude of the sine wave signal, f is the frequency, and is the initial phase. This formula is not unfamiliar to students, but after students design a sine wave signal generator by themselves, their understanding of the knowledge will be completely different. Figure 5 is an example of a sine wave signal generator designed using the Signal Basic scripting language, which can be completed with just a few simple lines of code. The Document.xxx functions in the figure are the special functions we extended in VBScript, and the regular language elements such as the Sin function and the For statement are the inherent functions of VBScript.

2.5 Experimental process AVI screen capture and curve bolding demonstration mode

In teaching, it is often necessary to use virtual instrument experiments to demonstrate some difficult-to-understand theoretical content. On-site virtual instrument experiment operation and demonstration is time-consuming and error-prone. To this end, we used the video file reading and writing technology provided by the Windows DirectX multimedia development library and integrated the AVI screen capture function in the virtual instrument experiment teaching platform, which can directly save the virtual instrument experiment process as an AVI video file.

There is another problem when using virtual instruments to demonstrate experiments. The lines of waveforms, spectra and other curves are thin, and it is difficult for students in the back row of the classroom to see them clearly after projection. For this reason, we set up a curve bolding demonstration mode. In this mode, the waveforms, spectra and other curves in the experiment are displayed with bold lines. This is very similar to the display difference between PPT files and Word files after projection. Although this is just an inconspicuous technical improvement, it can greatly improve the teaching demonstration effect.

3 Application of testing technology in teaching

3.1 Visualized experimental teaching of signal analysis theory

Signal analysis theories such as waveform analysis, spectrum analysis, and correlation analysis are difficult points in the teaching of test technology courses. Fourier transform formulas and convolution theorems often give students a headache. In order to improve the teaching effect, we use virtual instrument experiments to visualize these theoretical knowledge. The following is a directory of virtual instrument experiments with a composite document structure designed in teaching. Each experiment contains several small experiments:

1) Typical signal time domain waveform analysis experiment
2) Typical signal spectrum analysis and application experiment
3) Typical signal correlation analysis and application experiment
4) Typical signal probability density analysis and application experiment
5) Error and improvement method experiment in FFT spectrum analysis
6) Digital filter design and application experiment
………

For example, Figure 6 is a signal synthesis and decomposition experiment in the form of a virtual instrument designed by us. Through intuitive experience, students can have a deeper understanding of the engineering significance of Fourier transform and stimulate their interest in learning.

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Figure 6 Waveform synthesis and decomposition experiment

3.2 Physical teaching based on PC test resources

Compared with the test experiments conducted in the laboratory, the virtual instrument experiment has a shortcoming, which is the lack of physical experiments. In fact, the PC running the virtual instrument software itself is a device with rich test resources. For example, the optical mouse on the computer is a photoelectric sensor, the microphone is a capacitive sensor, the camera is a CCD sensor, and the computer sound card is a dual-channel A/D card + D/A card.

We have made full use of this favorable condition in the design of the test technology virtual instrument experimental teaching platform, integrating the sound card and camera driver into the platform to form a PC-based test laboratory. Students can use the PC mouse to do the photoelectric sensor principle experiment, use the microphone to do the capacitive sensor principle experiment, use the camera to do the CCD principle experiment, and use the sound card to do the A/D and D/A card working principle experiment. This solves the problem that the teaching of sensors and test systems in the classroom is boring and tedious due to the lack of real objects.

Figure 7 Signal generator based on PC sound card

In this way, we can build a powerful test laboratory with physical objects and hardware on the PC where teachers teach and students surf the Internet without spending any additional hardware costs. Through it, teachers can show students the principles and applications of test technology in class; after class, students can also do experiments and design small measurement devices by themselves, integrate the knowledge they have learned in practice, and cultivate their ability to observe and solve problems. Figure 7 is the signal generator interface we designed using the sound card.

3.3 Experimental teaching based on engineering cases

In order to combine theory with practice and broaden students' academic horizons, we also took advantage of the fact that the course group members had undertaken a large number of scientific research projects. We abstracted 16 engineering measurement cases from the scientific research projects, such as bridge natural frequency measurement, gearbox vibration fault source analysis, and automobile engine acceleration process noise analysis, and designed them into virtual instrument simulation modules, which were integrated into the virtual instrument experimental teaching platform. Figure 8 shows the rotor test bench model and the axis trajectory measurement experiment designed with it.

Figure 8 Rotor test bench model and its application in axis trajectory measurement experiment

4 Conclusion

“Teaching is the main theme of the school, and improving teaching quality is the eternal theme of the school”. In order to improve the teaching level and quality of the test technology course, the course group has made full use of its scientific research advantages in the field of virtual instruments and developed the DRVI reconfigurable virtual instrument experimental teaching platform, which makes the sensor principle part of the test technology course, which is boring and tedious due to the lack of physical objects, become concrete and vivid, and makes the signal analysis theory part, which is abstract and difficult to learn, become intuitive and vivid, and the quality and effect of course teaching are greatly improved.