The Pros and Cons of Windows for DAS

The need for a new PC-based data acquisition system (DAS) has been established. You know the nature of the input data and are ready to configure the system. The immediate question that comes to mind is: How do I want to present the data?

Since an estimated 80% of all IBM-compatible PCs are running on MS-Windows, it seems obvious that the data acquisition software should be MS-Windows-based. But Windows has certain shortcomings, especially for some real-time data acquisition applications, so the pros and cons must be carefully considered. And sometimes Windows is overqualified. The Windows graphical user interface (GUI) may be a time-saver at an engineer’s desk or lab, but nonessential for a DAS that is part of an unattended industrial control system.

The Good Points

The majority of PC-based applications used in offices today, and many currently used in labs, are running on Windows. All these applications have the same look and feel. After you are familiar with the operational procedures of one, you probably can master the basic manipulative skills required for all. Consequently, the learning curve is shorter.

Usually, acquiring data is only the first step. It is almost always followed by analysis, conclusions and reports.

“A typical application may require you to use a data acquisition program to acquire data, a spreadsheet such as Microsoft Excel or Lotus 1-2-3 to perform calculations on the data, and Microsoft Word to create a final report,” said Carolyn Carter, Senior Product Specialist at Fluke. “Obviously, it would be more productive to use the same environment for all these tasks. And since nearly everyone has converted to Windows, more and more customers are insisting that the software they purchase be Windows-compatible.”

Some DOS enthusiasts may counter this point. They argue that almost any DOS program can be run from the DOS prompt in the Windows program and data can be transferred between DOS and Windows applications. However, mixed DOS/Windows operation doesn’t facilitate effective data sharing, made possible by Window’s Dynamic Data Exchange (DDE) facility, or efficient multitasking.

Another advantage of selecting Windows-based DAS software is the inherent peripheral support provided for Windows. “With a Windows-based package, you can be fairly sure that your printer, video card and mouse are all supported, since the peripheral manufacturers always supply Windows drivers,” said Rick Daniel, Vice President Product Management at Intelligent Instrumentation. “With a DOS package, the application-package supplier must provide support for all the peripherals, and the likelihood that he has missed yours is much higher.

“Windows also frees the DAS software developer from the 64k memory boundary that exists under DOS. This means that Windows applications can be much bigger, with more functionality than you will be likely to find under DOS,” Mr. Daniel concluded.

The availability of many Windows-based analytical, presentation- and graphics-oriented applications, as well as software generation tools, also benefits the Windows-based DAS software developer or user. The advantage of easily integrating and using the best of many off-the-shelf post-acquisition analysis packages is obvious. But the features and functionality that can be created with Windows-oriented programming tools are equally important.

“Not all applications require all-encompassing graphical acquisition and analysis packages,” said Ron Gilbert, Marketing Communications Manager at IOtech. “But users increasingly expect hardware products to be provided with hardware-specific no-programming-required Windows applications programs that typically contain GUIs for setting up analog and digital I/O.”

Often, applications which don’t need graphical assistance can be readily created with minimal code generation by using available indigenous programs and Windows programming tools, such as Visual Basic.

With Windows compatibility comes a certain degree of obsolescence protection. “Today, most software vendors place their major efforts into their Windows applications and let their older, DOS-based packages wither on the vine,” said Mr. Daniel. “If you find a bug in a DOS-based package, you may have trouble getting your supplier to fix it.”

The Negatives

Some software developers and users express strong reservations about today’s widely used Windows version. “Windows 3.l still has bugs and undocumented requirements, takes too much memory, and slows everything down,” said Jim Hayes, Technical Director/President of Fotec. “We prefer DOS.”

These facts are undisputed: Programs run faster in DOS and Windows requires more memory. Even worse, some of today’s PC-based test or data acquisition applications require speeds which are just too fast for Windows.

While there are ways to get around these limitations, they may be appropriate for only certain applications. For instance, “If you absolutely must have Windows for high speed applications, then run the board in the postprocessing mode,” suggested Bob Leonard, Product Marketing Manager at DATEL. “First collect the data to disk under DOS, then run the Windows application and use the data files as input.”

Alternatively, some boards contain extensive buffering and preprocessing facilities to handle all speed-sensitive operations, relegating only the GUI tasks to Windows. In either case, added complexity and cost are potential deterrents to these solutions.

Another disadvantage of Windows 3.1, in contrast to Windows NT, is its nonpreemptive programming environment. This means that once a task is running, it cannot be interrupted by another task. This results in an unpredictable response time to external events, a potentially serious shortcoming for many real-time data acquisition applications.

Selection Considerations

Windows-based programs are easy to use, but not always easy to generate. Developing a Windows-based DAS programming environment entails costs which must be passed on to the user. Whether this cost can be justified depends on the end-use purpose or operational requirements of the DAS.

As to end use, “Windows is nice for the user sitting at a terminal, but not necessarily best for every data acquisition application,” said Jerry Mercola, President of ICS Electronics. “It is slower than DOS and harder to program. And why bother with it when the end result is to generate a compiled program for the test department?”

Similarly, the final operational requirements play an important role in deciding whether a Windows environment is desirable. “MS-Windows requires both visual and tactile sensory contact to operate. The operator must glue his eyes to the monitor and have a free hand to operate,” said Susan McCafferty, Marketing Assistant at R.C. Electronics.

“In many real-world environments, such as a plant process-control system or during in-vehicle data acquisition, the operator has to look at other dials or watch the road, making it impossible to operate in the Windows environment,” Ms. McCafferty continued. “In DOS, you can simply put your finger on the right key and operate while you focus and synchronize with other external parameters.”

Software, as well as hardware, selection must always be based on the mission and performance charter of the total system. “If sustained data rates are slow and data blocks are small, there are numerous user advantages to Windows compatibility,” said Dick Boring, Director of Engineering at ADTEK.

“But if the mission and charter encompass high sustained data rates and large blocks of data or even seamless data acquisition at 10 MB/s rates, the Windows environment is prohibitively slow,” Mr. Boring continued. “Being inhibited by unpredictable interrupt latencies and an unwillingness to allocate large blocks of contiguous memory on 32-bit boundaries makes Windows an unsuitable environment for low-cost, high-performance data acquisition systems.

“Hopefully, Windows 95 will alleviate the unpredictable interrupt latency and memory allocation problems that exist with Windows 3.1. If so, Windows 95 compatibility is a definite plus because it will allow project engineers to mix and match multivendor data acquisition software and hardware in a high-performance, reliable and user-friendly graphical interface environment,” Mr. Boring concluded.

Portability is particularly important to the engineer, who must plan for expansion, and the multiproject program developer. “Although Windows is the most popular platform today, computer technologies and software continue to change rapidly, as do system requirements,” said John Graff, Corporate Marketing Manager at National Instruments. “Make sure that the software vendor you select has a track record of providing portability not only from one software version to another but also from platform to platform.

“Another important consideration this year is whether selected PC plug-in cards are Microsoft Plug & Play-compatible,” added Mr. Graff. “Plug & Play, which is fully integrated into Windows 95, will greatly simplify system configuration and remove the headache of setting jumpers and switches that plague most PC hardware today.”

These companies provided information for this feature:

Analog Digital Technology (ADTEK) (818) 597-1578

DATEL, Inc. (508) 339-3000

Fluke Corp. (800) 44-FLUKE

Fotec, Inc. (800) 537-8254

ICS Electronics Corp. (408) 263-5500

Intelligent Instrumentation (800) 685-9911

IOtech, Inc. (216) 439-4091

National Instruments (512) 794-0100

R. C. Electronics (805) 685-7770

Signalogic, Inc. (214) 343-0069

Copyright 1995 Nelson Publishing Inc.

May 1995

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