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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