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Virtual Instrumentation

This chapter first discusses the virtual instrumentation first and then presents a Pipeline Liquefied Petroleum Gas Network (PLPGN) monitoring system based upon the virtual instrument architecture. Starting from the introduction of development requirements and environment for the monitoring system, this chapter discusses its hardware configuration and software functionalities in detail. Practical application has demonstrated that the virtual-instrument-based structure is very effective and the obtained monitoring system is highly flexible.

2.1 INTRODUCTION

The rapid development of microprocessor and VLSI technologies has a revolutionary impact on the field of electronic industrial measurement and instrumentation. In the industrial measurement system, the requirements on instrument intelligence become higher than ever in order to satisfying more and more demanding user requirements. As the microprocessor plays a more important role in the industrial measurement system, the modern instrument system behaves like a microprocessor system in many regards. Furthermore, with the widespread use of microprocessors and intelligent instruments, there are more and more redundant components in an industrial measurement system, but unfortunately they lack the capability of fault tolerance. Therefore, it is highly necessary to systematically consider the relationship between the instrument and computer. As a result, the modular instruments used together with personal computer appeared in the early 1980s.

Distinguished from the traditional instruments, modular instruments do not contain instrument control panels; instead, they are provided with the graphical environment and other functionality supported by a personal computer to build the graphical virtual instrument panels. The most significant difference between a virtual instrument and a traditional instrument is that a personal computer is used in the virtual instrument for all of user interactions and operations. Most traditional instruments do not have sufficiently powerful computational capability to deal with the demanding applications in modern industrial measurement systems. On the contrary, in the virtual instruments, personal computer is an integral part of the instrumentation system, so its strong computational and control capabilities can be applied to deal with various industrial measurement tasks. In addition, the graphical front panels provided by the computer can markedly ease the user operations.

Traditionally, for different industrial measurement purposes, several standalone instruments are chosen and connected to each other for constructing the desired measurement systems. Because such instrument systems normally have no powerful computation capability, the operators have to do most of the calculation work manually, which is, however, not desired in the hostile and stressful industrial field environments. The stressed engineers may be required to do too much work within a short period such that they are more prone to make mistakes. Furthermore, whenever the measurement purpose or target changes, a new measurement system has to be constructed from scratch in order to meet the new measurement requirements. Fortunately, the concept of virtual instrumentation has resulted in a completely innovative type of measurement system, by which the engineers are able to deal with different measurement targets and demands in a more efficient and cost-effective fashion. The virtual instrument system comprises a set of measurement devices with strong data acquisition capability together with the analysis software with powerful computation and presentation capabilities. Virtual instrument systems are able to automate the whole measurement process including data acquisition, analysis, and presentation. As the measurement equipment is tightly integrated with the measuring and controlling software which runs in the computer, the rich resources provided by the personal computer can be fully utilized, which include comprehensive data manipulation functions, multimedia display, networked control, real-time communication, and many others.