A number of years ago, a professor was researching the impact of drugs on human tissue. A presentation he gave one day included a slide of a computer-generated strip-chart recorder illustrating data from a biological monitoring system. "I can't even program my name in BASIC [programming language]," he told his audience, then showed them the virtual instrument he'd created and data he'd obtained...
A number of years ago, a professor was researching the impact of drugs on human tissue. A presentation he gave one day included a slide of a computer-generated strip-chart recorder illustrating data from a biological monitoring system. "I can't even program my name in BASIC [programming language]," he told his audience, then showed them the virtual instrument he'd created and data he'd obtained using software, a PC, and an analog-to-digital converter board. "It's a lot easier than you think," he smiled.
Indeed, monitoring, measuring, and analyzing using computer-based instrumentation has only gotten easier. The application of virtual devices continues to grow and advancements and improvements in computer technology are making the concept increasingly simpler, more effective, and more popular.
By any other name...
Just what is a virtual instrument? For that matter, what is a virtual anything? Once defined simply as "existing in essence, not in actual fact, form, or name," [ American Heritage Dictionary], virtual is now more frequently used to describe things that mimic their "real" equivalents. Virtual has come to be applied in a computational sense to things simulated by a computer: virtual memory, virtual machine, virtual reality. "Over time," says Tim Ludy, product marketing manager, Data Translation, "the adjective has come to be applied to things that are created or carried on by means of computers. Using a PC and software in place of an instrument gives you the ability to re-create that instrument."
Using a PC to mimic an instrument differs from simply talking to an instrument using a PC, he explains. "From our [Data Translation's] perspective, end users use a DAQ board for test and measurement or for diagnostics or R&D functions. People take a board and some software and create an instrument-like device on a PC. One reason they might do this is because the instrument itself is too costly. Instead of buying a $15,000 oscilloscope, they use a DAQ board and PC to create what they need for less than $1,000. Depending on what is needed—in precision, accuracy, speed—this option might be more cost effective than purchasing an instrument outright." (Data Translation offers data acquisition boards for PC plug-in primarily for test and measurement applications. A DAQ board will perform operations similar to many types of instruments.)
Beyond capital cost, there's time savings, suggests Bill Glover, product manager for BizWare Direct: "With virtual instrumentation, a customer uses existing computer equipment to provide instrument readings instead of adding all the specialized equipment needed to maintain, record, and log data in a traditional way. For example, people used to read meters manually and record data into a notebook, an approach that was error prone and not always timely. Data are a lot more reliable in a virtual format."
Virtual instruments (right) tend to be more user-definable, while traditional instruments (left) more often have fixed functionality. Although the two types have many architectural components in common, traditional instruments provide a software and measurement circuitry package with a finite list of fixed functions. A virtual instrument uses software for customizing acquisition, analysis, storage, sharing, and presentation functionalities. (Illustration courtesy of National Instruments)
Virtual instrumentation (VI), explains Ray Almgren, vice president of product marketing and academic relations at National Instruments, grew out of the capability to define a system by combining PC-based hardware that performs measurement and control with a software tool that lets a user define system capabilities through that software. NI is credited by many as responsible for conceiving and developing the concept with its LabView product.
"In 1986," Almgren recalls, "the notion of saying there's an instrument in the software was a strange one. The term 'virtual instrumentation' helped users understand the device is virtual, not physical."
Make it your own
VI lets users configure instrumentation to meet specific needs. Its primary benefit, says Almgren, "is customization. A virtual instrument does not have to interface to hardware. It may be pure simulation (software) or connected to an actual instrument. A single interface can be created to control one or a whole system of instruments through a single point of operation. [See this article online at controleng.com for an example.] The term doesn't mean you're not actually making measurements," he stresses. "You're using a tool to define the capability of an instrument the way you want it to be."
Creating a virtual instrument can be done at many levels, from using graphical representations of instruments provided in a software package to text-based programming on a more sophisticated level. Graphically based programs typically are easier to use. While text-based systems offer more precision and control, they require more programming knowledge and are more complicated to use. Today, most firms involved with virtual instrumentation strive to build ease of use, customization, and control into subsequent software editions.
Ethernet/LAN-based virtual instrumentation system provides a low-cost, moderate-throughput method for exchanging data and control commands over distances, enabling remote test system control, distributed I/O, and enterprise data sharing. (Illustration courtesy of National Instruments)
"Our Measure Foundry software," says Data Translation's Ludy, "lets a user drag instrument-like objects from a toolkit to a workspace screen on your PC and configure a board to accept data from different channels in different ranges in whatever type of display you like. You virtually create an instrument to meet your specific needs. It's a custom operation."
Customization is also readily apparent in BizWare Direct's DataNetOPC Professional, an OPC client that runs in a Web browser. The product brings the virtual concept to the water and wastewater industries by providing an economical way to record and monitor multiple values—in particular turbidity—using modern technology but presenting it in the old, familiar way.
"This industry is still accustomed to seeing data in circular pin chart formats," points out Bill Glover. "The old traditional paper charts were difficult to use and hard to read. So we put it all in electronic format. We have circular pin charts in our software. Since the software is Web based, all a user needs to do is go to the appropriate URL and obtain any information in a familiar format. They can select, customize, and talk to all the instruments in a system."
A 'virtual' boon
While few believe a virtual instrument can replace a traditional one, all agree the virtual concept will become more pervasive. In systems where measurements are highly automated, virtual instruments dominate. Few buy traditional instruments for automated test-and-control systems today, preferring instead to use devices that are highly programmable and highly modular.
VI augments rather than replaces existing process control systems. Programmable automation controllers are often indistinguishable from virtual instrumentation, observes NI's Almgren, noting that both are programmable devices, with VI focusing on the measurement side and PACs on the control side.
In addition, the embedded area is poised to benefit enormously from VI, where more functions are plug-and-play, software tools are more standardized, costs are lower, and the expertise required to build systems is, relatively speaking, much lower.
In the opinion of Shahzad Sarwar, director of industrial and real-time solutions, Averna Technologies Inc., VI is playing a key role in helping engineers increase performance, productivity, and quality. "Honeywell's APU test cell automation (see accompanying sidebar) is one example where a customer achieved an immediate return on investment due to virtual instruments, as well as many intangible efficiency benefits. With its technical and business advantages, VI will continue its exponential growth for years to come."
A VI system can embrace all kinds of devices, and therein lies a crucial strength. Recent moves by organizations such as the Interchangeable Virtual Instrument Foundation and the LXI Consortium promote standardization, strengthening the concept.
IVI Foundation is an open consortium, founded in 1998, to address interchangeability issues with new driver technology. It promotes specifications for programming test instruments that simplify interchangeability, provide better performance, and reduce cost of program development and maintenance. It builds on existing industry standards to create specifications that simplify interchanging instruments and provide better performance and simplified maintenance.
The LXI Consortium promotes development and adoption of the LXI Standard, an open, accessible standard identifying specifications and technologies for the functional test, measurement, and data acquisition industry. LXI, or LAN eXtensions for Instrumentation, is an instrumentation platform based on industry-standard Ethernet technology and designed to provide modularity, flexibility, and performance to small- and medium-sized systems. Defining such a standard—essentially by extending GPIB (general purpose interface bus) to LANs—is expected to make PC/instrument communications easier and less costly.
To someone approaching VI for the first time, NI's Almgren advises: "Software defines the instrument in a virtual instrumentation system. It is the instrument. Gaining an understanding of what's possible with the software tools is what will really empower a virtual instrumentation system designer to maximize the benefits of VI. Once you have that understanding and capability, you can pick whatever device matches your needs. Focus on the software. Understand how you can use it and how to develop a proficiency in it. Don't be afraid of it. Many of these tools are really easy to use."
Virtual instruments help automate test facility, increase productivity
Automating auxiliary power unit (APU) data acquisition and control equipment at a Honeywell APU test facility involved using NI's SCXI and LabView platforms to integrate signals and measurements needed for APU testing. (APUs are used on jet engines, military vehicles, rockets, and spacecraft.) The automated system provides acquisition, control, configuration, calibration, test sequence automation, report generation, and test process mapping, resulting in a paperless test execution and increasing facility throughput by 600%, compared to the unautomated process.
Averna Technologies, a production technology provider, directed the project. The company implements automation systems and provides solutions in such areas as test, measurement, automation and control, vision, robotics, and manufacturing productivity software.
A typical test facility manages hundreds of process signals and transducers. The signals are related to control and measurement of engine fuel, power, and speed. Additional measurements involve ambient and engine temperatures, pressures, communication, and vibration monitoring. The non-automated process took up to 12 hr of shift work for a single unit.
Averna used NI's SCXI platform, which interfaced with the current test infrastructure without transducer or cabling changes. One 12-slot SCXI chassis houses a set of signal conditioning modules providing more than 100 I/O channels. Desktop LabView software and a multifunction DAQ card were used to read and control the APU test facility signals. The dashboard (see illustration) acquires and displays process data and allows the operator to interactively control testing. Test operation and test management are significantly simplified.
The virtual instrumentation dashboard saves hours of manual configuration time by automatically configuring the hardware in seconds. It also provides single-window access to all process measurements and allows interactive control and operation of the test set-up. Built-in networking capabilities allow monitoring from multiple and remote locations.
In addition, full programmatic control of test hardware from other Microsoft Windows applications is done using
Proligent, a process-mapping collaborative framework that manages all product documentation, test procedure definitions, facility hardware calibration, communication standards, and more. A complete test sequence can be run without operator intervention.
Information for this application was provided by Shahzad Sarwar, director of industrial and real-time solutions, Averna Technologies Inc.; and National Instruments.
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