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Modular measurement equipment and its associated software are gaining ground, even as the number of different modular formats grows and users have more options for different applications. Test equipment for different types of analog, digital, and RF/microwave measurements can constitute a major investment for users—even military and aerospace users—to such a degree that modular test instrumentation has gained a great deal of favor from them over the past decade.

Fig. 1Modular measurement equipment offers tremendous flexibility and testing capabilities, with the potential to pack a great many different test functions within a small equipment space. Unfortunately, no single modular measurement has ever won over the electronics field, and end-users now have a choice of numerous modular instrumentation formats (including AXIe, PXIe, and VXI test equipment).

The VXI modular measurement format is the oldest modular instrumentation platform, and easily the most widely used of the different formats, with many major instrument suppliers offering some forms of VXI modular instruments or chassis. The organization behind the VXI format and standards, the VXIbus Consortium, was formed in 1987 with the goal of creating a universal instrument-on-a-card standard that would allow instruments from any number of different vendors to work together.

The VXI specification supported by the IEEE, IEEE 1155, was adopted in 1993, with the VXI plug&play Systems Alliance formed later that same year to pursue higher-level VXI instrumentation developments and advances in software to control the hardware. The VXI specification is based on the Versa Module Europa (VME) or VMEbus bus architecture.

The goals for the VXI modular format are still to produce instrument cards that will plug into any standard VXI chassis (Fig. 1) and enable instrument cards from any one supplier to work with instrument cards from any other supplier. A VXI system can be controlled by means of a remote general-purpose computer using a General Purpose Interface Bus (GPIB) or a Multisystem eXtension Interface (MXI) bus interface. In many cases, computers are embedded into a VXI chassis for direct control of the instrument modules.

The VXI format allows a test system that might have formerly occupied a floor-standing 19-in. rack-mount enclosure to fit within the slots within a single VXI chassis. VXI instruments can be operated by means of many different control interfaces, including Ethernet, Firewire, GPIB, and PCI. The standard is defined to be independent of computer controller, so that its instruments and software can outlast trends in computer technologies.

It is strongly supported by most major instrumentation manufacturers, as well as some firms that specialize in VXI. One notable example of the latter is VXI Technology, in business since 1990 and now known as VTI Instrumentation Corp. In addition, firms like VXI Global Solutions specialize in providing assistance to businesses wishing to develop and manage VXI test systems for their applications.

The VXI modular instrument format is well established with military and aerospace users, as well as in many high-volume manufacturing production facilities. That being said, a number of other modular instrument functions (such as AXIe) can tackle and adopt many of the functions still provided by VXI instrument modules. A growing number of analog, digital, and RF/microwave test and measurement functions are becoming available in compact modular formats, causing confusion for users in search of practical modular measurement solutions and wishing to know how the different instrument module formats compare.

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