The Automated Test Blog

PXI is celebrating its 10 year anniversary in 2007. Richard Quinnell at Test and Measurement World recently wrote about PXI’s anniversary, highlighting the compatibility it has achieved during this time. For me, its been remarkable to see the growth and changes in this marketplace over the past 10 years, especially all the times that PXI vendors achieved “the impossible”. Here are a few of my favorites:

• 1999 - 50 members and over 200 products. The first few years of the standard saw a rapid adoption by vendors and the release of a lot of products. Grow exceeded expectations in every dimension.
• 2002-PXI’s entry ito RF. Prior to the release of products by National Instruments and Aeroflex, certain vendors had been outspoken that “you could never do RF in PXI”. Last year, Phase Matrix announced that they are taking PXI all the way up to 26.5 GHz!
• 2003 - PXI systems shipments exceed VXI. By 2006, PXI vendors shipped over 10,000 systems per year - 3 times larger than VXI at its peak. Naysayers claimed modular systems would never be mainstream.
• 2004- A 512 Cross-Point Switch. With the release of the PXI-2532, National Instuments put to rest those that claimed the Achilles heal of PXI was switch density.
• 2005-PXI Express. The PXI Systems Alliance did a remarkable job incorporating new technology to achieve a 45-fold increase in bandwidth while preserving backward compatibility. Those that claimed PCI Express would break compatibility become suddenly quiet.
• 2007 - Agilent joins the PXISA. Agilent Technolgies joined other big name vendors such as Advantest, Aeroflex, Keithley, National Instruments, Rohde & Schwarz, and Teradyne. So much for not having any big name companies in PXI!

I just saw another example of what we call a VBA, a “van-based acquisition”. It turns out that in RF applications, virtual instrumentation is particularly common when customers need portability and real-time data streaming. There aren’t a lot of commercial products to solve this application, but a PXI-based system can handle most of these requirements at a very low cost. Here is the latest example I just received of a VBA:

“The customer was looking for a completely mobile RF spectral monitoring application. They want to have a DC-based system mounted in their vehicles and they want to drive through areas and monitor a band of secure radio channels and signal strengths for those channels. The main requirements of the system are portability, quick spectral acquisition and storage (stream-to-disk) and time/location stamping for each spectral sweep.

This is a unique application that requires a small form-factor, stream-to-disk capabilities and GPS stamping. It can solved today with commercial off the shelf PXI products”

Other PXI-based VBAs are deployed in military applications (either looking for “signals of interest” or jamming them), ground-based transceiver testers, commercial spectral monitoring systems, and cell-phone coverage mapping applications.

I’ve recently been using the term Instrumentation 2.0 to refer to the changes happening in the architecture and use of test instrumentation. Rick Nelson, Editor of Test and Measurement World, wrote about this trend in his recent editorial and blog, I’d like to clarify what this concept means in terms of architecture and usage, for the two are related, but can be independent.

The internal architecture of test instruments is changing. Rapidly improving capability of PC processors, bus technology, and FPGAs have changed the architecture of both standalone instruments as well as modular devices such as PXI. Standalone oscilloscopes, for example, used to use proprietary technology from the front-end conditioning, through digitization, memory, storage, and display. Instrumentation companies were once the pioneers of early display technology, like the DVBST CRT in the Tektronix 4014. Signal processing on these devices has often been done using custom Digital Signal Processors, or DSPs. The investment in commercial PC and consumer electronics technology has created a compelling alternative to these proprietary architectures, however. Increasingly, standalone instruments use commercial operating systems, displays, memory, and storage. Indeed, most high-performance modern instruments contain a standard PC motherboard, transfer data over a commercial bus such as PCI, and run the Windows operating system. Increasingly, I believe the digitization and signal processing capability inside standalone instruments will also migrate to commercial technologies. Commercial A/Ds, driven by applications such as direct conversion for cellular base stations, are now available up to several GS/s. And studies have show that for many applications general-purpose processors and FPGAs can outperform dedicated DSPs. Modern instruments, will, in fact, start to look a lot more like a PC, at least architecturally speaking. A typical standalone instrument will have a acquisition block connected over a commercial high speed bus, such as PCI Express, to a general purpose processor. This processor will both run Windows and drive the display, as well as perform the signal processing necessary for real time measurements. In the highest performance instruments, FPGAs will be used to augment the analysis capability of the processor.

The change is architecture, combined with evolving needs of design and test engineers, has led to a change in usage. Increasingly, users require flexibility in their measurement systems and desire the ability to define capability specific to their application. This trend towards ever increasing customization and the ability through technology to capture this demand, is well articulated by Chris Anderson in his blog and book, both titled The Long Tail. He focuses on the trend in media markets such as music and film, but examples of long tail demand abound in test and measurement as well. Wireless technologies, for example, continue to evolve at a fast pace, and devices often include more than one wireless link. The model of a “one-box” tester specific to a single wireless protocol, therefore, has become a dinosaur. Users need a common platform where they can deploy measurements for new standards as they are deployed, without replacing their hardware. The relationship between these two trends is that the ability of users to define their own measurement capability is enabled by the architectural changes noted above. Instruments built on a PC architecture that use commercial technolgy components can enable users to write their own algorithms in software for processing the acquired data. Even better if they can switch out the acquisition front-end when the requirements necessitate it.

Of course, modular, or PC-based, instrumentation has been at the forefront of this trend. By their nature, these devices build on PC busses and processors and separate the acquisition from the measurement analysis. And the rapid evolution of converters, buses, and PC processors, has increased the capability of this approach over recent years, so that in many cases it is equal to or greater than the alternative standalone instrument. Software tools such as LabVIEW have been used for many years to create customized analysis for measurement applications. Newer developments, such as LabVIEW FPGA actually target LabVIEW programs to FPGA components in a test system to create very powerful embedded processing that is still defined by the user to their needs.