Hardware Reference
In-Depth Information
11 Virtual instruments
PC-based instruments (i.e.
virtual instruments
) are rapidly replacing items of
conventional test equipment in many of today's test and measurement appli-
cations. This chapter provides readers with an introduction to the principles
and practice of these powerful, sophisticated, and highly cost-effective instru-
ments. One obvious use of virtual instruments is that of building automated test
systems but general laboratory, bench, and field-service applications are also
eminently possible.
Currently available PC instruments include digital storage oscilloscopes
(DSO), many of which incorporate additional features, such as spectrum
analysis, digital voltmeters and digital frequency meters, counters and timers,
waveform generators, arbitrary waveform generators (AWG), and logic analy-
sers. This chapter describes the facilities offered by modern high-specification
DSO and also shows how a low-cost sound card can be used to form the basis
of a simple oscilloscope for audio and general low-frequency applications.
Selecting a virtual
instrument
Several factors need to be considered when selecting a virtual instrument for a
particular application. These include:
•
Ease of use
: What level of expertise is required in order to make use of
the instrument and also whether the measurements are to be automated or
controlled by a human operator?
•
Flexibility
: Can the instrument be easily adapted to differing requirements
and can it be easily transferred from one PC to another?
•
Performance
: What performance criteria and specifications must be met?
•
Functionality
: Does the package offer a suitable range of functions and will
it interface correctly with an existing hardware/software configuration?
•
Cost
: Has the most cost-effective solution been chosen?
It is important to remember that virtual instruments comprise both hardware
and software. The hardware provides a means of interfacing to the PC and of
connecting external inputs. Additional controls may also be present (e.g. input
selection, trigger selection, attenuation, etc.). The software provides a means of
controlling the instrument, collecting data from it, processing the data, and then
displaying, analysing, and recording it. When purchasing a virtual instrument it
is important to ensure that
both
the hardware
and
the software fully meet your
requirements.
Instrument types
The following is a list of the main types of virtual instrument:
•
digital storage oscilloscopes;
•
digital counters, timers, and frequency meters;
