Synthetic instrumentation (SI) offers a different approach
to test and measurement. It uses a collection of basic hardware
and software building blocks in a flexible, open, and
modular architecture to synthesize the stimulus and measurement
functions required by a given test application. So, why do
we need it?
As electronic products become increasingly integrated and
dependent on software, testing procedures get more complex
and time-consuming. Instruments have kept pace with these
testing needs, but costs have soared since test systems are built
for singular, special needs.
Automatic test systems (ATSs) speed up and simplify testing,
as well as automate the process and squeeze out some
test costs, especially in high-volume devices like cell phones.
To some extent, modular test systems using the PXI bus have
helped along these lines. However, many test systems capable
of producing the desired cost and throughput goals become
dead-end investments that can’t be used for other current
products or even next-generation products.
This problem of investing in new test systems for just one
product has become particularly acute in the military and
aerospace sector—so much so that the government issued
guidelines to create a more modular, generic, and flexible test
approach that can be quickly reconfigured for different products
and systems. Say hello to synthetic instrumentation.
While the early systems adopted by the aerospace and military
proved successful, the techniques have yet to significantly
impact the consumer and commercial sectors. Nonetheless, SI
shows lots of promise. Its usage continues to grow, costs are on
the decline, and more companies are beginning to build test
products. As a result, it’s likely that SI will eventually impact
your own world.
CLARIFYING THE DEFINITIONS
You know what traditional instruments are—multimeters,
oscilloscopes, signal generators, and vector signal analyzers.
These benchtop units are devoted to a specific purpose, such
as measuring voltage or power, observing voltage waveforms
versus time, generating test signals, looking at power versus
frequency, or performing a complex modulation analysis.
In many cases, these same instruments or modified versions
thereof also become part of production test systems. Rackand-
stack traditional instruments do their jobs well, but they
must be organized, sequenced, and programmed to carry out
their task. GPIB, LXI, and other interconnections ensure communications
between instruments, and specialized software
organizes the measurement process and data collection.
Once the test system is successfully built, its performance
is superior. But on the downside, as mentioned, the system
typically targets just one job. Also, it often contains redundant
elements (multiple displays, keyboards, digitizers, frequency
converters, etc.), which results in an expensive, larger, and heavier system. Changing the applications
requires new interconnections and programming
to use the same equipment in a
new test system.
The instruments’ high cost and the time
involved in reconfiguring and preprogramming
is significant. A system made
to test radar sets for the Air Force can’t
be used to test missile hardware for the
Navy, though many of the same tests may
need to be run. As the largest customer of
T&M equipment in the world, the Department
of Defense (DoD) wants to change
that to save money and extend the life of
test systems.
FROM NI’S VI TO SI
In the mid-1980s, a new approach called
virtual instrumentation (VI) came along.
Virtual instruments are built-in software
executed on a PC or laptop. National
Instruments (NI), the inventor of VI,
defines it as a software-defined system in
which software based on user requirements
defines the functionality of generic measurement
hardware.
The instrument is built around modular
I/O and data-conversion hardware using
PXI modules, while software does all of
the processing and measuring. Even the
front panel of the specialized instrument
with its display and controls is softwaredefined.
Software programs the system.
NI also created the software known as
LabVIEW. It makes programming a snap
by using a graphical user interface with
icons and interconnections in a dataflow
format. Because the software actually carries
out the measurement, the instrument
is easily customized and rapidly changed.
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