VXI or PXI? Neither is the clear winner

At Autotestcon (October 15–17, 2002, in Huntsville, AL), leading lights in the test industry declared their positions in the VXI/PXI debate during a session entitled, "Advantages and Disadvantages of PXI and VXI Modular Instrumentation Platforms—A Panel Discussion."

Agilent Technologies (Palo Alto, CA) is firmly in the VXI camp, with no PXI products and no plans to develop them. Mike Granieri, Agilent program manager, brought down the house with his slide, "VXI Positioning Statement," featuring Mark Twain's quote, "Reports of my death have been greatly exaggerated."

Granieri pointed out that VXI is the world's leading modular instrument platform; more than 80 manufacturers build more than 1400 products. He added that for RF test applications, VXI is still the better choice by far: Few RF instrument modules are available in the PXI format, and VXI specs more clearly delineate the amount of interference a designer can expect between instrument modules. PXI, in contrast, is based on a specification meant for controlling the total emissions from a system.

Firmly on the PXI side of the fence was Loofie Gutterman, general manager of Geotest (Irvine, CA). Gutterman noted that 90% of Geotest's engineering budget now goes into developing PXI products and systems. "PXI is the future platform for test and measurement," he proclaimed.

One advantage that Gutterman claimed is the lower cost of PXI systems. He showed a slide comparing a system composed of VXI modules and a similar system composed of Geotest PXI modules. Not surprisingly, the VXI system was nearly twice as expensive ($67,030 vs. $36,405).

That drew protests from the other panelists, most notably Agilent's Granieri, who claimed the example was taken out of context. Without knowing the system application, you can't be sure the specified system would meet the requirements. Other panelists noted they could construct similar examples giving VXI the edge.

Another PXI advantage that Gutterman touted was size, noting that PXI modules generally are smaller than their VXI counterparts. On this point, Paul Dhillon, general manager of VXI Technology (Irvine, CA), spoke up, saying that this, too, was application dependent—some systems require many data-acquisition channels—and that VXI modules, in general, offer higher channel density. A PXI system with only 20 channels may be smaller than a similar VXI system, but a system with hundreds of channels would not have this advantage.

Despite the criticism, Gutterman was unshakable in his support for PXI. His view is that PXI has an undeniable price-performance advantage over VXI, so the majority of his customers will choose PXI in the future.

Other members of the panel were not as outspoken in their opinions. Chandran Nair, PXI/VXI product manager for National Instruments (Austin, TX), was one panelist straddling the fence. While leaning toward PXI from a technical viewpoint, Nair was not willing to abandon VXI entirely. Instead, he favored making the best choice for a particular application.

Bob Stasonis, a product manager for Teradyne (Westford, MA) and the president of the PXI Systems Alliance, was also squarely in the middle. Teradyne—after its acquisition of GenRad—sells both VXI- and PXI-based test systems.

Stasonis questions whether PXI offers sufficient advantages for the military to adopt it as the standard test platform. He noted, however, that PXI offers advantages for some applications. "If service depots suddenly had to be more mobile," he noted, "then smaller is beautiful," and PXI might be a good choice.

Racal Instruments (Irvine, CA) also favors choosing the platform that best meets the requirements. Racal's representatives described a jet-engine test system they built for the Navy that uses VXI modules for the data-acquisition subsystem and PXI modules for the throttle-control subsystem.

John Rosenwald, Racal's business development manager for military and aerospace solutions, said Racal chose the platform that best met the requirements. "Many of the specialty requirements for frequency measurement, vibration, and position sensing were not available in PXI, which was just emerging when our system was being designed," said Rosenwald. "The bottom line is that we chose the most advanced platform that best fit the requirements when design decisions had to be made."

For descriptions and a comparison of the VXI and PXI specs, see "PXI and VXI: the basics," on our Web site: www.tmworld.com/aatr.