Software Design Of Virtual Instrument Development Workbench LabScene

Scientific instruments have an extremely important role in the national life and production; moreover, virtual instrument is exactly the direction in which the instrument is developed in future. Graphic language is an advance programming language to develop virtual instrument. Comparing to developed country, technology gap is more and more great. In order to narrow the gap immediately and realize great-leap-forward development, LabScene was developed independently. In introduction, this paper introduce the basic conception of virtual instrument in total is that it combines the all-purpose computer and functional hardware together through the application program at first. Users can operate this computer through the friendly figure interface, just the same as operating an individual instrument that is defined and designed by oneself, thereby finish collecting, analyzing, judging, displaying, storing test value. And then introduce its current situation and development trend according to software and hardware system frame of the virtual instrument. In the chapter of building the LabScene basic system frame, analyze real hardware how about making up at first and draw a conclusion that it have two aspects to implement for building a virtual instrument. One is simulating user mutual interface of real hardware, the other is simulating and implementing the six basic elements which are abstracted in circuit diagram. It formed the mechanism of module encapsulation at the same time. Then propose the message drives dataflow graphic language running model according to the general graphic language developing platform that is base for the dynamic pure dataflow, however, it can't integrate to operating system which is driven by message very well. This model has three basic elements: visual element, message, message pool and rule. The visual elements transmit data and information through messages and execute one's own function according to different rules at the same time. Assembling these three kinds of elements in the model can finish general execution, the control of circulation, the choice of the branch and realize the nested module execution by regarding SubVI as a kind of special visual element. In the chapter of implement graphic language in LabScene, at first, introduce LabScene's basic frame is three mutual interfaces in multi-document: user mutual panel (front panel), data flow designing panel (diagram), toolbox panel. User can design the dataflow in the diagram through the toolbox panel and input or output data in the front panel. Then introduce the implement of controls in user mutual panel in detail. It must have some conditions to implement these controls such as emulation, beauty, interaction, editor. There are three kinds of special objects in these controls: local variable, array and cluster. Local variable make one control in the front panel have many corresponding nodes in the diagram and this kind of node not only can write value but also can read value. Array is many data that have same type and it may be one dimension or multidimensional. Cluster is be made up by many kinds of data type and formed a whole. Then introduce the implement graphic code in LabScene. Function node is a functional core of graphic code and represent implement of the function. Function node is equal to pieces of function in the text language. The types of nodal function node in LabScene have numeric, logic, string, file , graphical display , array , cluster , time , dialog , signal , advanced controller , outside procedure transferring , instrument and equipment ,etc.. Container node can hold function node and container node. Container node which represents some kind of control function is made up frame and indiscerptible concomitant function node. For circulation and While circulation which are both container node are used to control circulation. Sequence can realize the order control and CaseStructure can finish branch's choosing. The formula node is a kind of special container node which can parse the formula written in C program language and run in system. Pin is a certain display area in node and has two kinds of type: input pin, output pin. The distribution algorithm of pin is confirmed by some distribution rules. Wire connect pin with pin through joint which is a special element and form the integrate dataflow diagram. Introduce the concept of module design and edit function of graphic code at last. As system software, design of LabScene should be flexible, expanded and reusable. Therefore it is inevitable to use design patterns to design LabScene. This chapter has summarized some patterns which are often used. Some are object building pattern, others are object behavior pattern. Command pattern gain two function through encapsulating command. One is offering the strong flexibility in designing virtual instrument for users, the other is supporting undo and redo. Singleton pattern guarantee that class has only one instance in LabScene and offer a global point to call. Dispatcher pattern drive task executing in a different way. Builder pattern separate the construction of complicated object from its expression, which make the same construction course to establish different expression. Factory pattern build object in a flexible way. Observer pattern in LabScene on the one hand make...