What is PXI tutorial

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

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 the PXI bus 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

Launched in 1998 the PXI standard was introduced as an open industry standard and today it is managed by the PXI Systems Alliance (PXISA) that promotes the PXI standard. More than 60 companies are members of the Alliance, indicating the considerable degree of interest within the industry.

Although relatively new when compared to other standards including GPIB, the PXI standard has been adopted by many users as well as the manufacturing industry. The standard enables traditional measurement capabilities to be incorporated into a standard that can interface easily with computer controllers. VXI has very successfully addressed the high end of the measurement market, finding markets in mainly in military and aerospace applications. By contrast PXI uses mainstream PC technology and using this approach is able to benefit from some significant economies of scale.

Accordingly PXI provides a broad measurement platform that can be used in a variety of test automation and data acquisition applications. It is widely used in manufacturing ATE systems as well as in design verification and factory automation applications. In these applications and others it has proved itself as a cost effective solution to many requirements.

PXI Hardware

There are three basic elements to a PXI system:

• PXI Chassis



• System controller



• Modules or instruments that slot into the chassis.

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 and instruments     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 from the wide variety that are available 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 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.

PXI system operation

A PXI system will consist of a PXI chassis into which the PXI modules may be plugged. The PXI chassis may include its own controller that can run a variety of different operating systems. Alternatively the may employ a PCI to PXI bridge that provides a high speed link to a PC which can act as the controller. It is also possible to link multiple PXI racks together. In this way large systems comprising of many instruments can be built up for the more demanding applications.

PXI modules provide a specific function in the same way that individual items of test equipment provide them. Analogue capture, RF generator, or waveform generator, etc would all be implemented on separate cards, and a system can be built up using a variety of different PXI cards to provide the required capabilities. In view of the fact that the PXI standard defines the capabilities for the system, it is possible to mix modules and chassis from different manufacturers. It is also possible to mix most PXI modules with CompactPCI modules, but under these circumstances the PXI auxiliary signals such as the common frequency reference will not be available

It is possible to configure a PXI system in two ways:

• Standalone PXI chassis operation



• Slave PXI chassis operation

The two different methods of configuring a PXI system can be used to advantage under different conditions.

The standalone configuration uses an embedded controller in the chassis and does not require an external PC. This approach is often preferred for remote or data acquisition applications, or for use on a shop floor where space and ergonomics are of importance. A monitor and keyboard may be attached to the controller for development and debug, although they may disconnected if they are not be required for later use. The system may also be attached to a local area network (LAN) and the data returned to a data logging system where any results can be held.

For applications in a development arena, the approach using an external PC is normally preferred. A host to slave connection is required and this link acts as a normal PCI bridge. The PXI modules then appear as normal PCI devices and this configuration allows full access to the PC environment. This approach is particularly flexible and cost effective and is normally used where space is not at a premium.

Summary

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