When Is It Best To Use VXI, PXI, Or GPIB For Your System?

Andy Toth

ED Online ID #7495

Article Rating: Not Rated

DESIGN VIEW is the summary of the complete DESIGN SOLUTION contributed article, which begins on Page 2.

Choosing the right platform (or combination of platforms) for your ATE system can save you money and labor—plus improve measurement results. You can assemble an instrumentation system in several different ways. One option is to "rack and stack" standalone boxes and connect them to a computer via the well known General Purpose Interface Bus (GPIB), also called the IEEE-488 bus. This makes it simple to swap out instruments and create new configurations quickly and easily.

Another route is to use instruments on VME eXtensions for Instrumentation (VXI) and PCI eXtensions for Instrumentation (PXI) cards that plug into a backplane. Such a solution seems ideal, with the computer and the instruments it controls all in the same card cage. However, not all instruments are availlable as plug-in cards.

Experience has shown that it's seldom possible to put together a complete system using all bus-based or all standalone instruments. Generally, there will be some of both.

This article reviews each of the platforms in detail, discussing their benefits and limitations. It also gets into the mixing and matching of the buses for an optimal solution.

With so many choices, it's possible to put together a system to meet just about any need. It's nice to know, too, that these technologies will stick around for a long time.

HIGHLIGHTS:
GPIB	The General Purpose Bus Interface is a byte-serial, bit-parallel bus that can connect up to 15 devices to one controller. GPIB has a huge installed base, making instrument connection a snap. It's primary drawback is limited bandwidth.
VXI	VXI, which is based on the VMEbus, works with signals ranging from low-level analog to microwave. It offers the advantages of performance and ruggedness, but it could cost two to three times more than alternatives
PXI	PXI, based on CompactPCI, falls midway in complexity between GPIB and VXI. PXI lets users standardize cards and card cages. And because it's based on the PC architecture, software is readily available. Limitations include space inside the enclosure, as well as power and density. Also, GPIB equipment is often needed to complete a test setup.
Combining Buses	Mixing and matching standalone boxes, VXI, and PXI is probably the most optimal solution. Because systems can connect to each other via GPIB and to the world via Ethernet, this circumvents VXI's and PXI's inability to supply or handle enough power.

Full article begins on Page 2