Instrumentation design is a competitive field, and manufacturers are constantly striving to increase functionality while simultaneously reducing both time-to-market and cost. To meet these demands, instrumentation systems have evolved to more closely leverage existing, off-the-shelf technologies. The PXI modular instrumentation standard, adopted in 1998, is itself a study in leveraging existing technology to deliver high performance, low cost modular instrumentation. It is these qualities that drove 38 percent growth of the PXI market in 2001, according to an industry report by Frost and Sullivan, a year when most other test platforms saw large declines.

Two key elements of a modular instrumentation standard are the module interconnect and the packaging (or form factor). In this most recent generation of instruments, designers turned to the Peripheral Component Interconnect (PCI) Bus because of its speed, its 132 Mbytes/sec burst transfer rate is nearly 10 times that of previous standards, and its numerous modes for module control. Another benefit of using PCI was that designers could draw from the vast personal computer (PC) marketplace for software and low cost components.

Although the PC was an excellent resource, the desktop PC packaging was not suited to the demanding industrial environments envisioned for new instrument designs. PCs were not designed for industrial environments, and therefore do not provide the connectivity, cooling support, EMI resistance, and the slot capacity needed for many high-performance instrumentation systems. To solve these problems, designers adopted the ruggedized Euro-Card standard for packaging. This allowed access to the long design history and broad vendor support for board and enclosure designs. With minor interconnect and packaging changes, the CompactPCI standard was proposed and has since gained increasing market acceptance.

However coordination of multi-module operations demanded additional functionality. The VMEbus eXtensions for Instrumentation (VXI) standard, a previous modular instrument standard, showed the advantage of including auxiliary signals such as a common system frequency reference, controlled timing triggers, and generic system signaling flags. Again with some modification, the VXI auxiliary signal set was added to the CompactPCI standard to form the PCI eXtensions for Instrumentation (PXI) standard. By design, most PXI products are fully inter-operable with CompactPCI products.

With its roots in the dynamic personal computer (PC), rugged Euro-Card, and legacy VXI markets, the PXI specification is providing the guidance for a new generation of higher performance, lower cost test equipment.

How do I use PXI?
PXI modules are designed to implement specific functions, such as analog signal capture, RF signal analysis, or waveform generation. In order to control these functions, a CompactPCI or PXI chassis and a system controller are needed. As mentioned before most PXI modules can be freely mixed with CompactPCI modules, but the PXI auxiliary signals such as the common frequency reference will not be available. Two configurations are available: slave chassis operation with a desktop host or standalone chassis operation with an embedded controller. In development and bench top instrument applications, the most economical way to use PXI instruments is with a desktop PC for control and a host-to-slave link for connection to the PXI modules. The host-to-slave link acts as a normal PCI bridge and the PXI modules appear as normal PCI devices under the PC hardware device manager. This configuration allows full access to the PC environment at a relatively inexpensive price.

For many other applications, the PXI instruments will ultimately reside in a rack with other equipment such as on a factory floor or remote site or portable operation is desired. In these settings the use of desktop PCs is not feasible and an embedded PC must be used. A monitor and keyboard may be attached to the controller for development or debug and then removed or replaced with a LAN connection for later use. This configuration is somewhat higher in cost but allows the most flexibility in operational setting and smaller system size. (Adapted from an article by ZTEC Inc. Visit the ZTEC Web site at www.ztec-inc.com)