【正文】 cts such as loops and conditional code to create a graphical editing and multitasking execution environment. In order to deliver the performance required by large applications, LabVIEW included a piler that created 68K machine code directly from the diagram and executed it, rather than interpreting the diagram as did LabVIEW 1. The aim of the third generation of LabVIEW was to achieve a portable system. From 1990 to 1993, the LabVIEW application was pletely redesigned to isolate processor and operating system dependent code from the rest of the platformindependent code. At the same time, the internal architecture, especially the platform independent code, was improved once again. Currently, LabVIEW also supports Windows NT, PowerPC and HPUX. This section presents a case study from the field of nondestructive testing and discusses various usability aspects of LabVIEW. One of the most important techniques of nondestructive testing is the ultrasonic examination of ponent parts and specimens. Until recently the ultrasonic technique has been primarily carried out by experts and performed by hand. Rapid progress in ultrasonic and puter hardware has changed the situation dramatically, allowing experts to design systems which can assist in both data collection and analysis. The reliance on domain experts has not diminished since automated ultrasonic testing requires an extensive background in a number of disciplines such as image processing, protocol generation, motion control, and fast data transfer. The plex nature of systems which can handle such tasks has mandated the use of textbased languages which were considered to be the only tools appropriate for projects of such magnitude. The ideal designer of an automated nondestructive testing system should be an engineer with expertise in the discipline, but engineers often have little knowledge of puter science, and can rarely work with textbased programming languages without the involvement of a software engineer. In 鞍山科技大學本科生畢業(yè)設(shè)計(論文) 第 24 頁contrast to this, the engineers in this case study have been able to effectively deal with the plexity of such systems using LabVIEW which both allows the engineer to exploit the natural visual aspects of the problem and is vastly easier to use than traditional textbased programming languages. The nondestructive testing team of BASF (Ludwigshafen, Germany) has developed two ultrasonic scanners. The programming environment chosen was LabVIEW, a decision which was strongly influenced by the availability of the product on the Apple Macintosh platform. The logical structure of the two scanners is shown in figure 1. The main ponents are: ultrasonic equipment, DC stepper motor, motion control, digital oscilloscope, spectrum analyzer, digital image processing, protocol generator and user interface. A Macintosh IIfx (20 MB RAM, 160 MB hard drive) equipped with 3 mercially available plugin cards (NBDSP2300 digital signal processing board, NBMIO16H multifunction data acquisition board, NBDMA2800 GPIB Interface with DMA capability) is used to control the scanner. The entire project was realized from scratch in the rather short period of two months. This is remarkable because the team had no experience with LabVIEW or other visually oriented languages before the project.One of the most obvious strengths of LabVIEW, although not strictly tied to the graphical nature of the language, is the ease in which the user interface can be constructed. A graphical interface is an integral part of any LabVIEW module or VI. To be more precise, the amount of development time for this important, and often time consuming, part of the project is negligible. Further interface changes at any stage during the life cycle of the program are equally simple. The separation of a LabVIEW program into block diagram (the program from the classical point of view) and front panel makes it easy to build up a new user interface without redesigning, in fact without changing in any way, the underlying block diagram. The user is of course free to redesign the block diagram for the sake of clarity for instance, independent of the user interface LabVIEW39。s hierarchical visual programming paradigm also proved to be an enormous benefit during the development of the software. LabVIEW provides a very important abstraction mechanism that helps to increase the readability and understandability of a program. The diagram of a VI can optionally have an 鞍山科技大學本科生畢業(yè)設(shè)計(論文) 第 25 頁icon that suggests its functionality. The icon associates a number of the interactive control inputs with wiring connections on the icon so that data can be passed to and from the VI diagram, and thus creates a graphical reference to the diagram’s functionality. Multiple instances of the icon can be placed within another diagram to execute the VI in different situations with different dataflow input and output parameters. This allows easy reuse of LabVIEW modules and supports the hierarchical position of structured dataflow diagrams. Complex diagrams can be made more manageable by breaking them into modular pieces. It seems that this approach seems very natural and intuitive to most users. People who have never had any contact with a visual language like LabVIEW, need only a small amount of time (one week on average) for learning the do’s and don’ts of LabVIEW. The main problem is not the visual concept of LabVIEW, rather, the dataflow programming style collides with the ideas taught in schools, universities, and in the industry. Indeed, experienced controlflow programmers seem to have more difficulty in adjusting to dataflow programming than nonprogrammers.Another property of LabVIEW is its suitability for pure experimental work. This is especially true if the experiment is realized under time constraints forbi