Virtual instrument is
that in the general computer platform, users define and design the testing
functions of equipment according to requirements, making users operate the
machine like operate the same equipment designed by them. The emergence of the
concept of virtual
instruments,
breaking the traditional definition of equipment from manufacturers, users can
not change the work mode, users can make according to its own needs, design
their own instrument system, in the testing system and equipment design to make
full use of software instead of hardware, take full advantage of computer
technology and expansion of the traditional test systems and equipment
functions. "Software is equipment" is the simplest concept of virtual
instrument also is the most essential expression. Virtual machines cannot work
without computer control; design software of virtual instrument is the most
important and most complex part.
Usually
instrumentation manufacturers provide specific functions to given architecture
and fixed interfaces for measuring devices, and thus limit the application domain
of these devices. In actual use much time is required for adjusting the
measuring range and for saving and documenting the results. The advent of
microprocessors in the measurement and instrumentation fields produced rapid
modifications of measuring device technology, soon followed by the appearance
of computer-based measurement techniques. A single user controls the system,
which runs exclusively on a piece of hardware. The measurement consists of
three parts, as shown in Fig.7.1, acquisition of measurement data or signals, conditioning
and processing of analysis of measurement signals and presentation of data
Figure
7.1: measurement of data
The
concept of virtual instrument is frequently used in industrial measurement
practice, but not always with precisely the same meaning. For some people,
virtual instruments are based on standard computers and represent systems for
storage, processing and presentation of measurement data. For others, a virtual
instrument is a computer equipped with software for a variety of uses including
drivers for various peripherals, as well as analogue to digital and digital to
analogue converters, representing an alternative to expensive conventional
instruments with analogue displays and electronics. Both views are more or less
correct. Acquisition of data by a computer can be achieved in various ways and
for this reason the understanding of the architecture of the measuring
instrument becomes important.
A
virtual instrument can be defined as an integration of sensors by a PC equipped
with specific data acquisition hardware and software to permit measurement data
acquisition, processing and display. A virtual instrument can replace the
traditional front panel equipped with buttons and display by a virtual front
panel on a PC monitor. Virtual instruments are a means of integration of the
display, control and centralization of complex measurement systems. Industrial
instrumentation applications, however, require high rates, long distances, and
multi- vendor instrument connectivity based on open industrial network protocols.
In order to construct a virtual instrument it is necessary to combine the
hardware and software elements which should perform data acquisition and
control, data processing and data presentation in a different way to take
maximum advantage of the PC. It seems that in the future the restrictions of
instruments will move more and more from hardware.
7.1
BASIC COMPONENTS OF SYSTEM
The
basic components of all virtual instruments include a computer and a display,
the virtual instrument software, driver software and the instrument hardware.
1.
Computer and Display
The
computer and the display are the heart of virtual instrument systems. These
systems are typically based on a personal computer or workstation with a high
resolution monitor, a keyboard, and a mouse. It is important for the chosen
computer to meet the system requirement specified by the instrumentation
software packages. Rapid technological advancements of PC technology have
greatly enhanced virtual instrumentation. Moving from DOS to Windows gave to PC
users the graphical user interface and made 32-bit software available for
building virtual instruments. The advances in processor performance supplied
the power needed to bring new applications within the scope of virtual instrumentation. Faster
bus architectures (such as PCI) have eliminated the traditional data transfer
bottleneck of older buses. The future of virtual instrumentation is tightly
coupled with PC technology.
2. Software
If
the computer is the heart of the virtual instrument systems, the software is
their brain. The software uniquely defines the functionality and personality of
the virtual instrument system. Most software is designed to run on industry
standard operating systems on personal computers and workstations. Currently
the most popular way of programming is based on the high-level tool software.
With easy-to-use integrated development tools, design engineers can quickly
create, configure and display measurements in a user-friendly form, during
product design, and verification. The most known, popular tool is LabVIEW
(Laboratory Virtual Instrument Engineering Workbench) | is a highly productive
graphical programming language for building data acquisition and
instrumentation systems. To specify the system functionality one intuitively
assembles block diagrams a natural design notation for engineers. Its tight
integration with measurement hardware facilities gives rapid development of
data acquisition, analysis and presentation of solutions.
3.
Instrument Hardware
The
preceding subsection on interfaces also touches on the attributes found in each
of the respective instrument hardware products. One note is worth to be repeated:
Virtual instrumentation never eliminates the instrument hardware completely. To
measure the real world there will always be some sort of measurement hardware,
sensor, transducer and conditioning circuit, but the physical form factor of
this instrumentation may continue to evolve.
4.
Driver software
Today
drivers for most instruments, as well as interfacing hardware are available
either free or nominal cost. This reduces the cost and development time for
application utilising these products. In today’s environment, it is almost
mandatory for an instrument developer to provide a driver on one or more of VI
platforms. To cater to popular hardware where manufacture does not provide
support for VI, there is now a very large number of small vendors splicing in
the development of these drivers. Many of examples, labVIEW drivers are
available as downloads for almost all instrument of Tektronix, AAGILENT etc.
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