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.
1．系统设计
测试系统要实现包括压力阀、流量阀和方向阀等3类比例阀的压力偏移和压力振摆、稳态压力控制特性、稳态负载（等压力）特性、稳态流量特性、输入/输出特性、动态过程检测等6项特性的测试。测试系统设计包括硬件和软件设计两部分。整个系统以Windows为系统平台，LabWindows/CVI为开发工具，以PCL-818L数据采集卡作为转换元件，利用计算机强大的数据处理、显示、存储和打印功能，将试验数据以曲线形式显示出来，以文件形式进行存储，并可进行打印。测试系统框图如图33所示。
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.
采用数据采集卡是虚拟仪器中常用获取数据的方法。数据采集卡为I/O接口设备，对I/O接口设备的驱动是通过相应库函数实现的。实现数据采集的软件驱动I/O接口数据采集卡有两种情况：①对于NI公司生产的数据采集卡，可利用LabWindows/CVI自带的驱动函数驱动，只需要正确设置输入参数，就可以实现数据采集的任务，而不需编写代码程序；②对于非NI公司生产的数据采集卡，可利用编程直接驱动的方法来实现采集卡的软件驱动。
系统使用的是数据采集卡PCL-818L卡，不是NI公司的产品。PCL-818L卡采用标准ISA接口，直接插在计算机主板的扩展ISA插槽即可，通过DIP开关可以设定卡的I/0地址，占用计算机的空闲I/0段即可，一般设为0×300，并将其设为基地址，其他控制或数据地址全在该地址上加上固定的偏移量即可。
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.
