A virtual instrument (VI) at its simplest consists of a circuit board that plugs into a PC and software that makes the board perform much like traditional stand-alone test instruments or data-acquisition equipment. This basic definition of a VI has expanded over the years to encompass a wide range of systems. VI systems today range from simple USBconnected devices to sophisticated packages made up of specialized modules plugged into isolated chassis networked to a PC.
The newest wrinkle in VI systems is to do away altogether with the concept of a VI as a test instrument. Instead, VI technology is now beginning to appear as the foundation block in a new series of machine monitors and controls replacing more conventional control systems. The same technology that let VI-equipped PCs mimic oscilloscopes and DVMs makes it possible to field compact computer systems able to handle industrial control tasks. These systems generally reside in their own industrially hardened enclosure and work as well as traditional embedded controllers.
The key difference between ordinary embedded controllers and this new generation of VI technology is in the development software. Graphical programming techniques get much of the credit for making VIs a widely used technology. With the advent of VI hardware able to handle embedded computing, the same graphical programming can be used to develop embedded systems in fields ranging from automotive engine control to mechanized packaging machinery.
The graphic programming techniques now finding their way into embedded systems were pioneered by National Instruments Corp., Austin, Tex., a company whose name has become synonymous with virtual instrumentation. The firm's LabView software lets developers define the functions of VIs by manipulating icons on a screen that represent instrument functions.
LabView's graphic-user interface links software modules as easily as drawing a line on paper or, more specifically, on the computer screen. System developers link modules together by literally dragging a line from the output of one module to the input of another. Developers add control knobs, buttons, dials, charts, and graphs using the same technique to get readings or controls. A human-machine interface designer constructs an operator display screen the same way, placing virtual status lights, readouts, graphs, or other display features on the screen.
The key to this versatility is the function library. Software modules for each function are written in such manner to make them fully compatible with a wide number of hardware systems from many different suppliers. Promoting compatibility between vendors of VI systems is the Interchangeable Virtual Instrument (IVI) Foundation.
The IVI Foundation is an open consortium founded to promote specifications for programming virtual test instruments that simplify interchangeability, provide better performance, and help reduce costs of test program development and maintenance. Its membership includes end users, instrument vendors, software vendors, system suppliers, and system integrators.
The IVI sees two factors in today's world hindering efficient test system setup and support. First is the high cost of developing and maintaining test system software. Second, rapidly evolving technology is continually forcing development of new measuring requirements. The IVI addresses these needs by defining new driver technology for quality, complete-ness, usability, and functionality to reduce test system development and ownership costs. And IVI drivers simplify upgrading or replacing components in complex test systems intended to be used over long periods of time.
VI Without Readouts
Computerized control systems require digitized process parameters. Digitization of those parameters uses the same commercial hardware found in many VIs. So the idea of using embedded VI as part of the design is a natural extension. Coupled with embedded Webserver software and wireless connectivity, VI programming allows any laptop system to become a machine control panel or diagnostic display.
At the enterprise level, the same technology creates a portal for data acquisition and machine monitoring and control rivaled only by large, custom-designed systems.