Application of virtual instrument in the testing o

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Application of virtual instrument in relay testing

relay is one of the key components in automatic control system, remote control and telemetry system and communication system. It is widely used in aviation, aerospace, electronics, communication, machinery and other equipment. The reliability of relay directly affects the reliability of equipment and system composed of it. Relay testing is an important technology to ensure its reliability. Therefore, it is necessary to detect the characteristic parameters of relay, To meet the expected requirements. Traditional testing instruments have single function, huge volume, poor flexibility and difficult integration, which have been difficult to meet the needs of diversity and multi-function in the actual measurement work

the emergence of virtual instrument concept solves this problem

1 introduction to virtual instrument

1.1 concept of virtual instrument

virtual instruments (VI for short) is a new concept proposed by national instruments Corp. in 1986 based on the core idea of software is instrument. That is, on the hardware platform with computer as the core, a computer instrument system whose test function is defined by the user and realized by the test software. Its essence is to use the display function of computer display to simulate the control panel of traditional instruments and express the output results in various forms; Use i/O interface equipment to complete signal acquisition and control; Using the powerful software function of computer to realize the operation, analysis and processing of signal data, so as to complete a computer test system with various test functions. It is a new measurement technology that integrates electronic measurement, computer and network technology. While reducing the cost of the instrument, it greatly improves the flexibility and data processing ability of the instrument. It is a major breakthrough in the concept of traditional instruments

virtual mainly includes two meanings: first, the panel of virtual instrument is virtual: the functions completed by various devices on the traditional instrument panel are realized by various controls on the virtual instrument panel, such as various switches, keys, displays, etc. to realize the parameter settings such as turning on and off the input channel of the measured signal and the amplification factor of the instrument power supply; Numerical display and waveform display of measurement results. Second, the measurement function of virtual instrument is realized by software programming: supported by the hardware platform with oil resistance and PC as the core, the test function of the instrument is realized through software programming, and a variety of test functions can be realized through the combination of software modules with different test functions

1.2 software and hardware composition

the hardware platform of virtual instrument consists of two parts: (1) computer: generally a PC or workstation, which is the core of the hardware platform. (2) I/O interface equipment: it mainly completes the acquisition, amplification and analog-to-digital conversion of the measured input signal. Different i/O interface hardware devices can be used according to the actual situation, such as data acquisition card/board (DAQ), GPIB, PXI, VXI bus instrument module, serial port instrument, etc

the virtual instrument software consists of two parts: (1) application program: it includes two aspects of programs, the front panel software program that realizes the virtual panel function and the flow chart software program that defines the instrument test function. (2) I/O interface instrument driver: this kind of program is used to complete the expansion, drive and communication of specific external hardware devices

at present, there are many software development tools for virtual instruments, which can be roughly divided into two categories: text programming languages, such as C, VC +, VB, LabWindow proposed national rejuvenation s/CVI since taking office. Graphical programming languages, such as LabVIEW, HPVEE, etc. LabVIEW is the most widely used

2 relay action characteristic test based on virtual instrument

2.1 test principle

the action characteristic of relay refers to the measurement of relay action value (including pull in voltage and release voltage), in which the pull in voltage refers to the minimum voltage that can make the armature of its electromagnetic system reliably pull in to the final position, and the release voltage refers to the maximum voltage that can make the armature of its electromagnetic system reliably release to the starting position. This system takes LabVIEW as the software development platform, and uses Advantech PCL-818HG acquisition card to control the coil voltage change and monitor the contact action state at the same time. The digital output of pcl2818hg controls the forward and reverse rotation of the electric voltage regulator to realize the gradual increase/decrease of the relay coil voltage. When the pull in/off voltage value is reached, the relay contact is pulled in/off. The analog input channel of PCL-818HG collects the coil voltage in real time and monitors the contact action state with the digital input channel

2.2 software and hardware implementation

the test system integrated on the LabVIEW development platform with the acquisition card of Ni company is widely used in the industrial control field, and there are many introduction articles. In addition, this paper introduces an application of the test system integrated on the LabVIEW development platform with Advantech PCL-818HG acquisition card. This card is a 12 bit plug-in ISA bus multi-function high gain data acquisition card, 16 channel single ended AI, 1 channel Ao, 16 channel di/o, Stable performance with LabVIEW driver

the program made with LabVIEW is called a VI, which is composed of a front panel and a program block diagram. The former is that the user interface is equivalent to the instrument panel, which is composed of various controls and displays; The latter is the source code of LabVIEW program represented by graphics, which is composed of several nodes, data ports and connections. It is the program entity to realize the function of the instrument. As a data flow language, LabVIEW is different from the step-by-step execution of control program languages (such as basic and C). It is executed when and only when the data of all input ports of the node arrive. Therefore, multiple nodes can execute synchronously, that is, to achieve parallel and improve the execution efficiency of the program

after the PCL-818HG driver is installed in the LabVIEW environment, corresponding nodes are added to the user customization of the function template. Users can use these nodes to directly drive the board card to realize acquisition and control. It is very convenient to program with the function nodes in the function template

this program uses nodes to control the forward and reverse rotation of the electric voltage regulator to realize the rise and fall control of the coil voltage. It uses real-time reading of the status of each contact and displays it on the instrument panel in a graphical form. When the program detects that the state of any contact changes or the user manually presses the save data button, the event structure will trigger the execution of the save program, that is, the experimental data will be saved in text, word or excel format according to the user input save path (the user only needs to determine the suffix of the file, such as.Txt,.Word,.Excel), so as to facilitate the user or offline analysis of the data

3 conclusion

integrate the system with assembly, VB, VC and other text programming languages. Users must be familiar with the complex applications of these languages. This system draws the program like a flow chart, and the interface is more vivid and flexible, with reliable performance. It highlights the advantages of graphical programming language, and has been well used in relay performance testing. Through the research of this subject, we realize that virtual instrument technology can not only simplify the structure of the instrument system, but also effectively reduce the production cost and shorten the development cycle. The virtual instrument data acquisition system based on C machine, which takes p as the overall ecological use cost of automobile enterprises, not only has the measurement performance of high-end instruments, but also can well meet the diversity of measurement needs. It is a virtual instrument design scheme especially suitable for China's national conditions

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