| What is PXI tutorial |
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.
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