Fieldbus: more than a communication link

Abstract

A virtual instrument alone is nonsensical. Measuring a voltage or a current with a multi-meter is much simpler, faster, and cheaper than using a virtual measurement environment. A dedicated instrument can perform more accurate and reliable measures than any virtual instrument. On the other hand, if a measurement is a combination of different data, if it has to be mathematically manipulated, or transmitted, or recorded, or displayed...for these situations, virtual instruments prove their worth. The concept can extend to virtual controllers. A hardware controller can easily implement a single PID control loop, but virtual devices are much more flexible in implementing multiple control strategies. Virtual devices give the best results when solving complex measurement and control tasks. Let's define the meaning of the two words that comprise virtual system. A system has specific characteristics: 1) integration of multiple actuators and sensors; 2) flexibility in defining the measurement or control target; 3) integration of different subsystems; 4) capacity of performing multiple tasks; and 5) interface with other systems. To summarize, when we speak of a virtual instrument, what we actually mean is "an instrument based on digital technology" that is a hardware platform, an operating system, and a development environment. In a sense, it may be preferable to speak of "intelligent systems" rather than of virtual systems. In the I&M world, the terms "intelligent" and "virtual" can roughly be considered synonyms. An instrument is intelligent if its human designer is intelligent. Innovation rests with the capacity of transforming physical principles into reliable field devices. The virtual instrument defined in the fieldbus profile is a representation that is necessary for interfacing the instrument with the data acquisition or control system, but it has nothing to do with the instrument itself. Through fieldbus it is possible to create a really distributed virtual measurement system. The instrument interface is virtual (digital and programmable), but the instrument itself is all but virtual.