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Test & Measurement World: VXI keeps hanging around

In 2002 I wrote “Don’t write off VXI”, where I noted that VXI was still a viable bus (Reference 1). Now over 20 years old, VXI remains entrenched in military and aerospace test applications. PXI, now more than 10 years old, has made inroads into commercial applications where VXI can’t go due to its higher cost. VXI remains strong in mil/aero testing because products in those industries have long life spans, with 15 to 20 years not being unusual.

Because VXI was the first industry standard for modular instruments, it was widely adopted, and with the cost of changing buses being so high, many companies are reluctant to swap their VXI systems for something newer. Although PXI—and PXI Express— and the more recent LXI buses use PC standard communications links, their software drivers differ from those used by VXI. Furthermore, VXI’s large card size lets test engineers put more components— usually switches—in a slot than is possible in smaller PXI slots.

Development of VXI modules continues, although a new VXI product doesn’t receive the fanfare that a PXI or LXI product receives. That’s because VXI equipment makers know their customers well. “VXI is a stable marketplace,” said Mike Granieri, vice president of advanced programs at Phase Matrix. “It has pragmatic users for whom performance specifications matter greatly.”

PC technology is coming to VXI, though. On 4th March 2008, National Instruments announced a cabled PCI Express link between a PC and a VXI slot-0 controller. (See “Cabled PCI Express link” below and Reference 2 for more on cabled PCI Express.)

Defense contractors are looking to complement VXI with other technologies. “At last year’s Autotestcon, there was considerable excitement over using new technologies such as software-defined radio with VXI,” said Richard McDonell, senior group manager for PXI and instrument control at National Instruments. “There’s a huge VXI infrastructure in place that contractors want to keep using.”

“Some VXI-based systems were deployed in the early 1990s, and they’re still in use today,” added Mark Morris, marketing manager at ZTEC Instruments. “They often need replacements for obsolete instruments.” Because of that need, ZTEC, VXI Technology, and others have developed replacements for modules originally from Hewlett-Packard (Agilent Technologies) and Tektronix. “We’re still seeing new test systems incorporating VXI,” said Morris.

 

Tom Sarfi, president of the VXIbus Consortium, points to the DoD’s Joint Strike Fighter program. “Design began in 2001 and the Lockheed Martin F-35 is yet to be deployed, but it uses VXI-based testers.”

Not everyone, however, is so excited about VXI. “We haven’t built a VXI-based system in several years,” said Tim Brooks, business development manager at National Technical Systems (formerly BB Technologies). “We’re steering our customers toward PXI. Some are replacing some rackand- stack systems with PXI, jumping over VXI because of the cost.”

Granieri counters that applications using VXI favor the measurement performance and larger card size of VXI over the bus speed of PXI or LXI. “We still sell microwave counters in GPIB,” he said, “because some customers don’t need the higher bus speeds of modular instruments.”