PCI eXtensions for Instrumentation
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PCI eXtensions for Instrumentation (PXI) is one of several modular electronic instrumentation platforms in current use. These platforms are used as a basis for building electronic test equipment, automation systems, modular laboratory instruments in science, and the like. PXI is based on industry-standard computer buses and permits flexibility in building equipment. Often modules are fitted with custom software to manage the system.
PXI Systems Alliance
PCI eXtensions for Instrumentation (PXI) is a modular instrumentation platform originally introduced in 1997 by National Instruments. PXI is promoted by the 54-member PXI Systems Alliance (PXISA), whose sponsor members are (in alphabetical order) ADLINK, Aeroflex, Agilent Technologies, Geotest, Gigatronics, National Instruments, Pickering Interfaces and Teradyne. (Sep 2010) 
Executive Members of the alliance include Alfautomazione, BAE Systems, CHROMA ATE Inc, GOEPEL electronic, LeCroy, MAC Panel, Virginia Panel Corp, and ZTEC Instruments. Another 40 associate member organizations that do not have voting rights are supporting PXI and use the PXI logo on their products and marketing material. (Sep 2010) 
Two major players in 2006
- Acqiris; was acquired by Agilent Nov 2006.
- PXIT; an early PXI entrant (acquired by Agilent Nov 2006).
- Keithley Instruments; launched a range of 35 Data Acquisition and Instrumentation PXI cards in Nov 2006.
The PXI worldwide market size, estimated in 2007, was 284 million USD and was expected to grow to over 520 million USD by 2010. The PXI market is also larger than the VME eXtensions for Instrumentation (VXI) market at an estimated size in 2007 of 233.2 million USD. The LAN eXtensions for Instrumentation (LXI) standard has grown to 200 million USD within 2 years.[dubious ].
PXI is designed for measurement and automation applications that require high-performance and a rugged industrial form-factor. With PXI, one can select the modules from a number of vendors and integrate them into a single PXI system, over 1150 module types available in 2006. A typical 3U PXI module measures approximately 100 x 160 mm (4x6") in size, and a typical 8-slot PXI chassis is 4U high and half rack width, full width chassis contain up to 18 PXI slots.
PXI uses PCI-based technology and an industry standard governed by the PXI Systems Alliance (PXISA) to ensure standards compliance and system interoperability. There are PXI modules available for almost every conceivable test, measurement, and automation application, from the ubiquitous switching modules and DMMs, to high-performance microwave vector signal generation and analysis. There are also companies specializing in writing software for PXI modules, as well as companies providing PXI hardware-software integration services.
PXI is based on CompactPCI, and it offers all of the benefits of the PCI architecture including performance, industry adoption, COTS technology. PXI adds a rugged CompactPCI mechanical form-factor, an industry consortium that defines hardware, electrical, software, power and cooling requirements, leaving nothing to chance. Then PXI adds integrated timing and synchronization that is used to route synchronization clocks, and triggers internally. PXI is a future-proof technology, and is designed to be simply and quickly reprogrammed as test, measurement, and automation requirements change.
Most PXI instrument modules are register-based products, which use software drivers hosted on a PC to configure them as useful instruments, taking advantage of the increasing power of PCs to improve hardware access and simplify embedded software in the modules. The open architecture allows hardware to be reconfigured to provide new facilities and features that are difficult to emulate in comparable bench instruments. PXI system data bandwidth performance easily exceeds the performance of the older VXI test standard. There is debate within the technical community as to whether newer standards such as LXI will surpass PXI in both performance and overall cost of ownership.
PXI modules providing the instrument functions are plugged into a PXI chassis which may include its own controller running an industry standard operating system such as Windows XP, Windows 2000, or Linux (which is not yet PXI System Alliance approved), or a PCI-to-PXI bridge that provides a high-speed link to a desktop PC controller. Likewise, multiple PXI racks can be linked together with PCI bridge cards, to build very large systems such as multiple source microwave signal generator test stands for complex ATE applications.
CompactPCI and PXI products are interchangeable, i.e. they can be used in either CompactPCI or PXI chassis, but installation in the alternate chassis type may eliminate certain clocking and triggering features. So for example you could mount a CompactPCI Network interface controller in a PXI rack to provide additional network interface functions to a test stand. Conversely, a PXI module installed in a CompactPCI chassis would not utilize the additional clocking and triggering features of the PXI module.
PXI Express is an adaptation of PCI Express to the PXI form factor, developed in 2005. This increases the available system data rate to 6 GByte/s in each direction. PXI Express also allows for the use of hybrid slots, compatible with both PXI and PXI Express modules.
An MXI link provides a PC with direct control over the PXI backplane and connected cards using a PXI card and a connected PCI/CompactPCI card. This interface provides a maximum data throughput of 208 MByte/s using fiber-optic or copper cabling, and can support a maximum length of 200 metres (660 ft) using a fiber-optic connection.
PXI MultiComputing (PXImc)
PXImc is an interconnection standard that allows multiple PXI systems to be linked together, with each system potentially including both instrumentation and processing. Using PXImc, data gathered from one system can be processed in parallel on multiple computing nodes, or a single PC can access instruments in several PXI chassis.
- Fountain, T.; McCarthy, A.; Peng, F. (2005). "PCI Express: an Overview of PCI Express, Cabled PCI Express and PXI Express". 10th ICALEPCS Int. Conf. on Accelerator & Large Expt. Physics Control Systems.
- PXI Systems Alliance (2005). PXI Express Hardware Specification (Standard). PXI-5.
- "PC Control of PXI". National Instruments. Retrieved 18 June 2014.
- Rowe, Martin (1 December 2009). "PXI expands to multiple processors". Test & Measurement World. Archived from the original on 22 February 2012.
- pxisa.org - Overview of PXI
- pxionline.com - PXI Test and Technology magazine
- pickeringtest.com - PXImate Book provides overview of the PXI Standard, module types and cabling
- PXI / PXI Express / PXImc tutorial