08-08-2012, 12:05 PM
virtual instrumentation system
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INTRODUCTION
Abstract
A virtual instrumentation system is computer software that a user would employ to develop a computerized test and measurement system, for controlling from a computer desktop an external measurement hardware device, and for displaying test or measurement data collected by the external device on instrument-like panels on a computer screen. Virtual instrumentation extends also to computerized systems for controlling processes based on data collected and processed by a computerized instrumentation system.
An instrument is a device designed to collect data from an environment, or from a unit under test, and to display information to a user based on the collected data. Such an instrument may employ a transducer to sense changes in a physical parameter, such as temperature or pressure, and to convert the sensed information into electrical signals, such as voltage or frequency variations.
The term instrument may also cover, and for purposes of this description it will be taken to cover, a physical or software device that performs an analysis on data acquired from another instrument and then outputs the processed data to display or recording means. This second category of instruments would, for example, include oscilloscopes, spectrum analyzers and digital multimeters. The types of source data collected and analyzed by instruments may thus vary widely, including both physical parameters such as temperature, pressure, distance, and light and sound frequencies and amplitudes, and also electrical parameters including voltage, current, and frequency.
Evolution of Virtual Instrumentation
History of Instrumentation Systems
Historically, instrumentation systems originated in the distant past, with measuring rods, thermometers and scales. In modern times, instrumentation systems have generally consisted of individual instruments, for example, an electro-mechanical pressure gauge comprising a sensing transducer wired to signal conditioning circuitry, outputting a processed signal to a display panel and perhaps also to a line recorder, in which a trace of changing conditions is inked onto a rotating drum by a mechanical arm, creating a time record of pressure changes.
Even complex systems such as chemical process control applications typically employed, until the 1980s, sets of individual physical instruments wired to a central control panel that comprised an array of physical data display devices such as dials and counters, together with sets of switches, knobs and buttons for controlling the instruments.
The introduction of computers into the field of instrumentation began as a way to couple an individual instrument, such as a pressure sensor, to a computer, and enable the display of measurement data on a virtual instrument panel, displayed in software on the computer monitor and containing buttons or other means for controlling the operation of the sensor. Thus, such instrumentation software enabled the creation of a simulated physical instrument, having the capability to control physical sensing components.
A large variety of data collection instruments designed specifically for computerized control and operation were developed and made available on the commercial market, creating the field now called “virtual instrumentation.”
Virtual Instruments versus Traditional Instruments
Stand-alone traditional instruments such as oscilloscopes and waveform generators are very powerful, expensive, and designed to perform one or more specific tasks defined by the vendor. However, the user generally cannot extend or customize them. The knobs and buttons on the instrument, the built-in circuitry, and the functions available to the user, are all specific to the nature of the instrument. In addition, special technology and costly components must be developed to build these instruments, making them very expensive and slow to adapt.
Virtual instruments, by virtue of being PC-based, inherently take advantage of the benefits from the latest technology incorporated into off-the-shelf PCs. These advances in technology and performance, which are quickly closing the gap between stand-alone instruments and PCs, include powerful processors such as the Pentium 4 and operating systems and technologies such as Microsoft Windows XP, .NET, and Apple Mac OS X. In addition to incorporating powerful features, these platforms also offer easy access to powerful tools such as the Internet. Traditional instruments also frequently lack portability,
whereas virtual instruments running on notebooks automatically incorporate their portable nature.
Engineers and scientists whose needs, applications, and requirements change very quickly, need flexibility to create their own solutions. We can adapt a virtual instrument to our particular needs without having to replace the entire device because of the application software installed on the PC and the wide range of available plug-in hardware.
Software in Virtual Instrumentation
Software is the most important component of a virtual instrument. With the right software tool, engineers and scientists can efficiently create their own applications, by designing and integrating the routines that a particular process requires. They can also create an appropriate user interface that best suits the purpose of the application and those who will interact with it. They can define how and when the application acquires data from the device, how it processes, manipulates and stores the data, and how the results are presented to the user.
An important advantage that software provides is modularity. When dealing with a large project, engineers generally approach the task by breaking it down into functional solvable units. These subtasks are more manageable and easier to test, given the reduced dependencies that might cause unexpected behavior. We can design a virtual instrument to solve each of these subtasks, and then join them into a complete system to solve the larger task. The ease with which we can accomplish this division of tasks depends greatly on the underlying architecture of the software.
LabVIEW ideal for creating Virtual Instruments
LabVIEW is an integral part of virtual instrumentation because it provides an easy-to-use application development environment designed specifically with the needs of engineers and scientists in mind. LabVIEW offers powerful features that make is easy to connect to a wide variety of hardware and other software.