Virtual test system of proportional valve
Virtual test system of proportional valve
In the test technology of hydraulic components, the test of proportional valve is more difficult. Its working condition changes continuously, and the test results are also continuous. Generally, the test results are reflected by the characteristic curve. The conventional test process of proportional valve is: use the signal generator to generate oblique wave, triangular wave and other control signals according to the test requirements and connect them to the proportional valve, and the proportional valve moves under working conditions. The controlled pressure, flow and other operating parameters are recorded on the X-Y recorder through the corresponding sensors. In this way, the characteristic curve reflecting the performance of the proportional valve between the controlled parameters (pressure, flow, etc.) and the control signal (current, etc.) can be obtained.
With the development of computer technology, the proportional valve computer-aided test system began to appear. The hardware system of signal generation and acquisition was composed of "microcomputer +ad/da acquisition card" and corresponding sensing and transformation circuits, and the proportional valve test system was composed of special software to replace the signal generator and X-Y recorder.
Virtual test instrument takes PC computer as the unified hardware platform of the instrument, realizes the functions, panels and controls of the test instrument with corresponding software, and stores them in the software library of PC in the form of text. At the same time, it is equipped with the corresponding modular hardware interface card that can realize data exchange in the computer bus slot. The function of virtual test instrument is to make the test function software, control software, output software of the instrument in the library and the interface card input the data in the computer, and operate under the unified command and coordination of computer system management.
The hardware design becomes very simple because of the integrated data acquisition card PCL-818L, and the performance is stable and reliable. PCL-818L is an efficient and multifunctional data acquisition card, which is suitable for industrial computers. It can carry out 12 bit a/d, d/a conversion, 16 bit digital input, output and 16 bit timing / counting. The a/d conversion frequency can reach 40KHz, which is enough to meet the measurement requirements of general physical quantities.
2. Software design
The software development platform of the system adopts the 32-bit virtual instrument software development platform for computer measurement and control field developed by National Instruments Corporation of the United States using virtual instrument technology - virtual instrument programming language labwindows/cyi (cfor virtual instruments), which can run under multi operating systems (such as windowsnt/2000, Mac OS and Unix). It takes ansic as the core, and organically combines the powerful and flexible C language platform with professional measurement and control tools for data acquisition, analysis and expression. Its integrated development platform, interactive programming method, rich function panels and library functions greatly enhance the functions of C language, and provide a theoretical software development environment for developers who are familiar with C language to establish detection system, automatic measurement environment, data acquisition system, process monitoring system, etc.
The virtual test system of proportional valve adopts labwindows/cvi5.5 for program design. Because the programming technology of labwindows/cvi mainly adopts event driven mode and callback function mode, the programming method is simple and easy to learn. When using labwindows/cvi to design the system software, the project file is the main framework, which includes three parts: C source code file (*.c), header file (*.h), user interface file (*.uir).
After all the software is debugged, the project files can be generated into application files (*.exe). Labwindows/cvi integrates source code editing, 32-bit ansic compilation, linking, debugging and standard ansic library into an interactive development environment, which can quickly and easily write, debug and modify applications to form executable files. At the same time, the virtual instrument designed can be separated from the development environment, and the user will eventually see an operation panel similar to the actual hardware instrument.
3. Data acquisition card driver
The hardware platform of virtual instrument consists of computer and i/o interface equipment. The i/o interface equipment mainly performs the tasks of signal input acquisition, amplification and data conversion. For a single system, the i/o interface device involved in lab windows/cvi is a data acquisition card. The data obtained through it is usually used in the measurement system to achieve data acquisition between instruments. The driving of i/o interface equipment is the basis of virtual instrument to realize the acquisition of real physical signals. After data acquisition and exchange, the software analyzes and processes the data, and then realizes a certain measurement function to obtain the measurement results. Therefore, i/o interface device driver is an important part of virtual instrument system.
The proportional valve virtual test system based on lahwindows/cyi platform has the advantages of stable and reliable performance, high test efficiency, convenient and fast instrument loading and unloading in practical application.