Everyone knows that testing is an essential part of the manufacturing process, but no one wants to spend a lot of money on it. This is mostly because it doesn't add any tangible features to the product that can justify an increase in cost. Nonetheless, testing must be done. And while it can't be done for free, with PCI eXtensions for instrumentation (PXI), testing can be performed for less.
Engineers first automated test equipment with PCs as a way to spend less on testing. Now with PXI modular instrumentation technologies, it's possible to downsize automated test equipment (ATE) in unprecedented ways and reduce overall test costs. Downsizing ATE with PXI modular instrumentation doesn't only mean lower component costs and a smaller footprint. It also amounts to lower maintenance costs, faster test times, faster development times, and better test coverage. It's not the ideal approach for every aspect of testing, however. In many cases, a hybrid test approach leveraging the strengths of PXI modular instrumentation, VXI modular instrumentation, and standalone GPIB instrumentation is the best way to go.
Companies such as Hewlett-Packard (now Agilent Technologies), GenRad, and Tektronix pioneered much of the first test equipment with instruments such as oscilloscopes, digital multimeters, and arbitrary waveform generators. While these devices proved extremely useful, the benefit of controlling and monitoring these instruments from a PC was apparent. In the late 1960s, the general-purpose interface bus (GPIB), or IEEE-488 bus, was developed as a way to allow instruments to communicate with each other.
With the rise of the PC in the late seventies and early eighties, GPIB was expanded to not only communicate between instruments, but to communicate between instruments and PCs as well. This enabled the creation of ATE systems that completed complicated tests quickly and efficiently.
While GPIB had improved the performance and functionality of test systems, it was obvious that ATE systems needed to be downsized to be smaller and less expensive. At the same time, they had to improve in performance. In 1987, the VXI Consortium was formed. The consortium defined an open industry standard to combine elements of the VME bus and GPIB to create a powerful modular instrumentation platform. VXI allowed for tighter synchronization between instruments, faster data transfer, and a reduction in size. Plus, it marked a shift from standalone box instruments to modular instrumentation.
Standalone box instruments require their own processors, input devices (knobs and dials), and display devices (CRT or LCD). Modular instrumentation, on the other hand, eliminates these costly and bulky individual components. This is because all of the instruments can leverage off one processor, one input device, and one display device.
As PC technology progressed, it became possible to create PC-based instruments. PC-based instruments take advantage of the low cost and small size of PCs while achieving higher data throughput rates than VXI or GPIB instruments. But PCs are not ideal for ATE applications. They typically have only three or four peripheral slots and aren't built for a rugged rack-mount environment. Another drawback is that PCs don't have standards for passing timing and synchronization between instruments. Nevertheless, because of its performance and flexibility, PC technology remains highly desirable on manufacturing floors.
CompactPCI arose in an effort to address some of the shortcomings of PCs. CompactPCI is an open industry standard that features rugged, modular Eurocard packaging like that found in VME and VXI. It combines this packaging with a high-speed PCI bus and high-performance connectors that allow for eight slots without a PCI-to-PCI bridge.
But CompactPCI didn't address the needs of ATE systems. So in 1997, National Instruments created the open PCI eXtensions for Instrumentation (PXI) specification. The following year, the PXI Systems Alliance was established and took the next step by ad-opting ownership of the specification.
PXI adds dedicated timing and synchronization lines, environmental and EMC testing requirements, and system-level specifications that simplify integration of CompactPCI. In addition, it maintains complete interoperability with CompactPCI while adding the features necessary to build successful, high-performance ATE systems. It also allows for downsizing of ATE systems never before realized. PXI-based ATE systems can be built at a lower cost and use significantly less space than either GPIB or VXI-based systems.
PXI defines both a 3U and 6U form factor. Yet most PXI products are 3U, which is a quarter of the size of the VXI 6U form factor. The 3U size takes maximum advantage of the miniaturization of electronic components to create small, high-performance instruments. This smaller footprint offers manufacturers two options. They can either create ATE systems that test more products in the same amount of space, or use the extra space for more profitable areas of their manufacturing processes. With PXI, it's possible to implement a system into a single PXI chassis (7 by 11 by 15 in.) that would normally require an entire rack of GPIB and VXI instruments. These chassis can then be integrated into a complete ATE system (Fig. 1).