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Building virtual instruments that meet the changing demands of scientific and engineering applications.

The key is the software; it must support all aspects of an instrumentation system including data acquisition and control

In the past, many laboratories have relied on unautomated instrumentation systems for their test and measurement systems. Engineers and scientists gathered test data by hand, performed analysis with calculators, and wrote the results into a report. These steps were tedious and time-consuming, leaving considerable room for clerical errors. Today, computer technology is radically changing instrumentation systems and offering greater accuracy and efficiency.

The key to an instrumentation system model is the software. Instrumentation software should support all aspects of an instrumentation system, including data acquisition and control, data analysis, and data presentation. with this type of software you can build your own instruments to exactly match a particular application using virtual instruments (VIs).

A VI is a software module that presents the look and feel of an instrument on a

computer and usually consists of a software front panel and a body of program code. The software front panel serves as the interface for the user to supply the inputs for and observe the outputs of the VI, while the program code implements the functionality of the VI.

In a data acquisition system, a VI most commonly controls an external instrument, acquires data through an analogue or digital interface board, or manipulates data already within the computer. In the first case, the VI is a driver for the external instrument; in the second, the VI is a handler for the plug-in board; and in the third, the VI is a software program that manipulates the data.

In each case, the software module and the associated hardware function like an instrument.

Most modern instruments have some type of programmable interface for remote control by a computer -- typically, the interface is RS-232 or IEEE 488 (also known as GPIB). For many years, the user wrote programs in conventional, text-based languages to implement the remote communication.

Over the years, add-on application software with higher level calls aided this programming process by removing the burden of understanding the bus protocol details from the user. However, both programming and operating the system remained text-based. Recently, software vendors have incorporated advances in the graphics of modern personal computers to create application software that adequately animates instrument-like controls and indicators on the computer screen.

By implementing the intelligence of the data acquisition system on the computer, the data is stored in the computer where it is available for analysis, presentation, and permanent storage -- and can take advantage of the latest PC technology.

In a PC-based data acquisition system, most of the application is specified in the program code of the VI, so the user can define its functionality. In the engineering and scientific markets where application needs often change as research develops, the user has a distinct advantage because he can modify VIs in his data acquisition system to meet the everchanging requirements of the application.

Graphical computing is a critical element

Graphical programming is a relatively new programming technology that takes full advantage of graphical computing environments, such as Windows and the Macintosh OS, by giving users a graphical development environment to develop and debug programs. For the engineer and scientist, graphical programming is ideal because the visual representation of the program is very similar to the diagram of the instrumentation system. Stated another way, you design a graphical program the same way you would design an instrumentation system.

Like graphical computing, graphical programming has been in use for several years. For example, for test and measurement applications, engineers have been using National Instruments' LabVIEW for the Macintosh since 1986. LabVIEW is a graphical programming system for instrumentation that is now available for Microsoft Windows based PCs and UNIX-based Sun SPARCstations.

LabVIEW is used for all types of test, measurement, and control applications, which typically incorporate some type of data acquisition and control, data analysis, and data presentation.

By building their own VIs, engineers and scientists can create instruments that are easy to configure, easy to use, and match their specialized needs in the laboratory or on the factory floor, Fig. 1.

Graphical programming for graphical computing

As the computer industry begins its second decade of personal computing, attention has moved away from pure processing power to a focus on the ability of software to harness that processing power. A 50-MHz 486 PC is roughly equivalent in processing power to a low-end RISC workstation. But the real measure of the PC lies in the usefulness of the operating system and applications that run on it. Historically, software for the PC has lagged behind the technological innovation of PC-based hardware and thus limited the industry's ability to deliver its final product, personal computing.

The second decade of personal computing, however, has begun with a major advancement in PC-based software -- graphical computing. The importance and need for this innovation in software was made clear by the dramatic announcement and overwhelming support of Microsoft Windows 3.0. Although Windows was not the first operating system to introduce graphical computing, its debut in May 1900 introduced graphical computing to the masses. Industry analysts, in fact, predict that by year's end over 12 million (Dataquest Research) users will have adopted Windows, Fig. 2.

So is Windows the solution to all of the PC-industry's software woes? No, but it is an excellent start.

Graphical computing delivered by Microsoft Windows and other operating systems such as the Macintosh OS from Apple Computer and Solaris 2.0 from Sun Microsystems offers several key technologies necessary for true personal computing. Most obvious, is the graphical user interface (GUI). Operating systems and applications that incorporate a GUI are much easier to use and are much less intimidating than software that uses a command line interface.

While the GUI is the most visible attribute of graphical computing, there are several other important features. Memory management that gives applications access to large amounts of memory is critical. Multi-tasking and interapplication communications are equally important so that multiple applications can run concurrently and share data. And, finally, a standard mechanism for networking multiple PCs together is needed so that multiple users can share information across multiple computers.

The corporate computing world has already enjoyed substantial productivity gains from the adoption of graphical computing. Virtually every major software vendor has a GUI version of a spreadsheet, word processor, data base, or desktop publishing application. And, unlike many of their DOS predecessors, the Windows versions are very easy to use.

All of the benefits of graphical computing for the corporate computing world apply equally as well to the instrumentation industry. Although the Macintosh computer is technically capable of supporting most laboratory and manufacturing applications, Apple Computer's penetration into the scientific and engineering industry is relatively weak. The PC with the technical robustness of Windows, however, is already accepted as a standard platform for virtually any computing application.

While not a revolutionary technological innovation, Windows has opened the door to technological innovation and provided a standard platform on which products like LabVIEW can flourish, LabVIEW is used primarily by scientists and engineers for programming instrumentation, but as graphical programming becomes a standard, its application use will extend well beyond science and engineering market and possibly become as common as C, Basic, and, Pascal.

VIs at work

At the Lawrence Livermore National Laboratory, they are experimenting with directed energy devices such as electron accelerators and ultraviolet flashlamps for destruction of chlorinated solvent vapors in air streams to reduce dependency on carbon.

Evaluation of these experimental systems, and development of optimum operation requires on-site monitoring systems capable of giving investigators rapid quantitative analysis of vapor concentrations and convenient display of relevant physical parameters from the extraction system.

They also need to modify the configuration of both hardware and software rapidly, as dictated by experimental findings. To achieve this flexibility, they used a suite of design and programming tools, including LabVIEW, that make excellent use of the integrated graphical computing environment of the Macintosh.

At Marion Merrell Dow Inc., LabVIEW was selected to control and monitor a data acquisition system for an instrumental tablet press. They needed to design a data acquisition system that provided a compressed learning curve and was flexible for user-specific applications requiring critical and comprehensive data from the tableting process. One experimental study used the system to measure and evaluate the relative chemical and physical performance of several granulations in manufacturing tablets on a rotary press.

Jack Barber, LabVIEW Marketing Manager and Ray Almgren, Software Marketing Manager, National Instruments, Austin, TX.
COPYRIGHT 1993 Chemical Institute of Canada
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Title Annotation:includes related article
Author:Barber, Jack; Almgren, Ray
Publication:Canadian Chemical News
Date:May 1, 1993
Words:1419
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