Product Focus: PXI Coming Of Age

Small test cards based on the PCI bus technology used in desktop computers emerged six years ago. But the PXI (PCI eXtensions for Instrumentation) standard caught on slowly in the military/aerospace market. Now, however, PXI appears to be poised for takeoff, as products reach a critical mass. Advocates claim that PXI offers not only a smaller footprint, but also lower-cost implementations and faster design cycle time than the more established VXI (VME eXtensions for Instrumentation) standard, based on VMEbus technology.

PXI reportedly offers more than 1,000 products, and military/aerospace is a major growth area, says Fred Bode, executive director of the approximately 60-member PXI Systems Alliance. PXI’s progress in the military/aerospace market owes much to its widening array of wares, including switching and radio frequency (RF) products, high-accuracy digital multimeters (DMMs) and digital input/output (I/O) cards. PXI’s growing foothold in functional test applications, is due in part to the availability of high-density switch cards, Bode says.

The latest figures from market analyst Prime Data show revenues growing apace. Bode cites Prime Data’s forecast of a 25 percent compound annual growth rate over the next five years, compared with the older VXI standard’s 5.2 percent growth rate. (VXI boasted sales in 2003 of $500 million, based on shipments worldwide, compared with PXI’s $94 million.)

Frost & Sullivan, meanwhile, estimates shipments of 4,100 PXI chassis in 2003 vs. 3,100 VXI systems, says Greg Caesar, PXI marketing group manager with National Instruments (NI). Frost & Sullivan forecasts PXI chassis shipments of 5,600 units in 2004 vs. 3,300 for VXI.

Says Doug Ullah, director of sales and marketing with data bus specialist, AIM UK: "We’re being brought into [PXI] more and more each day by the customer." AIM offers data bus interface cards in the compact PCI (cPCI) format, which uses the same connector as PXI.

In some cases, military officials are specifying PXI, says Loofie Gutterman, president of Geotest-Marvin Test Systems, Irvine, Calif. He cites Geotest’s customer, the U.S. Air Force Maverick missile program. PXI also plays a role in the F-16 avionics intermediate shop program, as part of a BAE Systems tester, Gutterman adds. Cameras linked to PXI systems also can be used to test head-up displays (HUDs), Caesar says.

PXI’s primary 3U form factor–3.9 by 6.3 inches (10 by 16 cm)–is very attractive, considering the premium on board real estate. However, a bigger, 6U format also is available–9.2 by 6.3 inches (23.3 by 16 cm)–if more board space is required.

Based on the rugged cPCI format, PXI uses the cPCI pin-in-socket connector. The instrumentation spec simply defines additional functions for pins that are undefined on the cPCI connector. PXI also calls out a dedicated 10-MHz system reference clock, eight bussed trigger lines, and slot-to-slot local buses for timing and synchronization. And PXI adds electromagnetic compatibility testing and active cooling to the cPCI mechanical spec.

While it’s impossible to list PXI products one by one, here are a few examples:

Switching: UK-based Pickering Interfaces offers PXI-format RF switching cards. NI likewise provides RF switching up to 4 GHz.
DMMs: NI supplies DMMs and high-speed digital I/O cards, among other products. Geotest, which helped pioneer the PXI military/aerospace market, offers DMMs, as well as up to 100-MHz, multichannel digital I/O cards, and time interval counters up to 2 GHz.
RF: NI offers RF vector analyzers and signal generators; Aeroflex provides a suite of RF synthesizer, digitizer and combiner products.
Arbitrary waveform generator: Racal Instruments recently introduced an arbitrary waveform generator with sample rates of up to 100 mega samples/s and 2 megabytes of waveform memory. Racal also supplies a 6U PXI IndustryPack carrier module hosting up to four daughter card-like modules for custom interfacing to the units under test.

Compact PCI Interface Cards

Numerous aviation test and simulation cards also are available in PXI-compatible cPCI format. In Mil-Std-1553, Data Device Corp. (DDC), Condor Engineering, Excalibur Systems, Ballard Technology and AIM-USA have cPCI cards for PXI. North Atlantic Industries provides PXI-compatible synchro/resolver products.

DDC announced earlier this year that it had developed the software to become a PXI-certified vendor of 1553 tester/simulator cPCI boards, such as the BU65570T and BU65572T 1553 products. DDC application engineer George Los attributes much of the increased interest in PXI to the availability of commercial off-the-shelf (COTS) software to program the cards and the shortened design cycle that COTS software entails.

National Instruments’ Caesar also claims ease-of-use advantages to being on the PCI bus. The speed of the bus, for example, allows users of NI’s arbitrary waveform generator to download large waveforms quickly. And the learning curve for engineers new to the standard is shorter than it is with VXI, Caesar says. When you’re learning VXI, "Chapter 1" is databases, address spaces and configuration registers, he says. "Nobody learns that for PCI because the PXI driver framework takes care of that."

AIM also offers AFDX/ARINC 664 interface cards in cPCI. (AFDX stands for avionics full-duplex Ethernet switch.) "For us, compact PCI and PXI are one and the same," says Ken Bisson, technical marketing engineer with AIM-USA. "We’re not addressing the additional lines that differentiate cPCI and PXI. We’re only passing data, using the standard PCI bus."

PXI specialist, Geotest, claims an up to 50 percent price differential between PXI and VXI. "There’s nothing VXI can do that we can’t do cheaper," Gutterman says. AIM-USA cites a 20 percent differential in a particular case.

Bisson nevertheless views PXI as a niche market. While "a lot of VXI applications are moving to PXI," PXI is more appropriate for smaller programs, testing two or three items, not for big test benches, he says. A manufacturer might use a PXI-based system to test the AFDX link and some discrete lines for a display, for example.

Bode sees less of a price difference between the two standards. The only VXI component that is not mass-produced is the one that decodes the VME protocol, he says. For multiple-chassis test solutions, the tendency is to go with VXI, simply because more functionality can be squeezed into the larger format.

COMPANIES

Advantest www.advantest.co.jp/en-index

Aeroflex www.aeroflex.com

AIM www.aim-online.com

AMPOL Technologies Ltd. www.ampol-tech.com

ASCOR Inc. www.ascor-inc.com

Avionica Inc. www.avionica.com

Ballard Technology Inc. www.ballardtech.com

BCF Designs Ltd. 44 (0)1285 642434

BMC Communications Corp www.bmccorp.com

Condor Engineering Inc. www.condoreng.com

Data Device Corp. www.ddc-web.com