PXI standard and technology tutorial

- a summary or tutorial about PXI (PCI extensions for Instrumentation) and the PXI standard for test instrumentation or test equipment for use with PC computers.

PXI tutorial includes:

In recent times the PXI bus and PXI standard has emerged as a major force in the test equipment and instrumentation industry. The PXI bus is a rugged PC based platform for use in automated test, data acquisition and many other applications. It successfully combines rugged mechanical elements with a high electrical performance specification and a low cost. Using standard PC technology, this makes PXI an ideal platform for a host of applications

PXI is based on CompactPCI and as such it is able provide the benefits of the PCI architecture - high level of performance, industry acceptance, wide availability of off the shelf units, etc. PXI adds a rugged Compact PCI mechanical form-factor, an there is an industry consortium that defines hardware, electrical, software, power and cooling requirements, enabling interconnectivity between items from different manufacturers. Then PXI adds integrated timing and synchronization that is used to route synchronization clocks, and triggers internally. A further advantage of PXI is that having been adopted by the industry it will remain in use for many years to come, thereby enabling any investment to be protected. These advantages make PXI an ideal standard for use as test equipment and for data acquisition applications.

PXI history

The history of the PXI standard can be traced back to 1993 with the release of the PCI specification on which PXI was later to be based. Realising that the PCI standard could be used for controlling test and data acquisition instrumentation, National Instruments developed a scheme based upon the PCI standard but modified for the needs of the test instrumentation industry. The first release of the PXI standard was issued in 1997.

The PXI standard is an industry open standard and it is now managed by the PXI Systems Alliance (www.pxisa.org). This quickly grew and by 1999 it has over 50 members. With the open architecture, and based around the PCI specification, this has enabled PXI technology to grow very rapidly. As a result a large number of products using PXI technology are available and the system has become an industry standard.

Wit the popularity of the PXI standard, work continued to improve the system. This resulted of the release of the Issue 2 of the PXI standard in 2000, and this was followed by a further revision in 2003 of issue 2.1 of the PXI standard.

With technology and standards moving forwards, while costs were reducing, the PXI standard kept in line. Using the PCI Express standard, the PXI standard was updated to provide PXI Express. This enabled a lower cost variant to be added to the already very successful PXI standard family.

PXI Hardware

The PXI hardware is platform on which the overall PXI standard is based. It forms the platform for running the software and for the individual instruments. It forms a particularly flexible scheme allowing a very wide variety of instruments to operate within a chassis environment.

There are three basic elements to a PXI system:

• PXI Chassis:   The PXI chassis is the most visible element of the PXI system. The PXI chassis literally provides the framework for the system and it normally can range in size from four slots up to eighteen. It contains a high performance backplane enabling the cards in the system to be able to communicate rapidly with one another and in addition to this timing and triggering lines are also included.
  
  To put this in context, a typical 3U PXI module measures approximately 100 x 160 mm (4x6 inches), and a typical 8-slot PXI chassis is 4U high and half rack width, full width PXI chassis contain up to 18 PXI slots.
• System controller:   A system controller card is located in left hand slot in the rack, or alternatively control can be undertaken by a remote PC. The use of a standard PC provides a particularly cost effective, but powerful option for many users. In this way the convenience of a standard PC can be combined with the power that they are able to offer these days. However the use of a controller module is also convenient in many applications and these leverage on the wide variety of PC cards and modules that are available.
• Modules or instruments that slot into the chassis:   There is a very wide variety of modules that are available. They include test instruments for taking a wide variety of measurements, e.g. voltage, current, frequency as well as signal and waveform generators. However modules are also available to perform other functions including boundary scan testing, digital or analogue input and output, image acquisition, power supplies, switching and much more.
  
  By choosing modules to meet the requirements of the overall PXI system it is possible to build up a flexible test or automation system that can be easily tailored to meet virtually any requirement.

PXI software

Many PXI instrument modules or cards are register based items. They use software drivers that can be hosted on the central controller PC and these configure in the way that the PXI modules are set up for the particular application in question. By adopting this technique it enables them to provide considerably more flexibility as the controller PC is able access the instrument directly and this simplifies the embedded software in the modules while enabling a high level of flexibility to be obtained. The open architecture allows hardware to be reconfigured to provide new facilities and features that are difficult to emulate in comparable bench instruments.

In addition to this a number of vendors offer software to run the automated tests and data acquisition applications. These proprietary products provide a high degree of sophistication, while being designed to operate with PXI. In addition to this they can be configured to meet the requirements of an individual application, be it for automated test, or data acquisition.

Major features of PXI technology

The PXI system boasts many features that make it a flexible platform for many applications. The highlight features of the PXI standard are detailed in the table below:

The PXI standard is a particularly successful open architecture test equipment standard that is widely used for a variety of applications. PXI can be used to provide automated test, as well as fulfilling a variety of other data acquisition requirements. This makes PXI an ideal standard to be considered where automated test and data-logging are needed.

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