September 2004
For more than 40 years,
the functional test and data acquisition community has been
instrumental in the development of many industry standards ranging
from the definition of communication protocols to instrumentation
backplanes. Agilent (formerly Hewlett-Packard) started automated
test in 1972 with the invention of HP-IB (now called GPIB) or
IEEE-488. GPIB addressed a wide variety of applications from
small benchtop prototype testing to large, multi-vendor, electronic
functional test applications. Agilent helped create VXI in 1985
to reduce the size of instrumentation for the military and improve
performance for those high channel-count applications.
Today, test and measurement-developed interfaces
such as GPIB are now challenged by the industry's need for increasing
bandwidths, faster data transfer rates and lower cost. Many
standards have been advertised as the next generation replacement
for GPIB such as USB, Firewire, CAN bus, PCI and PXI, but none
of these have met wide acceptance within the test and measurement
industry. As a result of this need, Agilent Technologies and
VXI Technology, Inc. have combined engineering resources to
develop the LXI standard.
LXI (LAN extensions for instrumentation) is
the next generation instrumentation platform. LXI is based on
industry standard Ethernet technology and provides the flexibility
and performance, commonplace on larger VXI systems, to small-
and medium-sized systems. The new standard is managed by a not-for-profit
corporation called the LXI Consortium. This consortium is comprised
of leading companies in the test & measurement industry.
The group's goal is to develop, support, and promote the LXI
standard. LXI combines built-in measurement science and PC-standard
I/O connectivity from rack-and-stack instruments with the modularity
and size reduction of cardcage-based systems. LXI's compact,
flexible package, high-speed I/O and reliable measurements meet
the needs of R&D and manufacturing engineers delivering
electronics for the aerospace/defense, automotive, industrial,
medical and consumer electronics markets.
Ethernet: The Logical Choice
Ethernet (LAN) is integrated into nearly every
computer, making it the most widely accepted communications
interface in use today. As a result of ongoing, industry wide
R&D, networking hardware is becoming less expensive and
LAN speeds continue to increase. LAN also offers unique peer-to-peer
communications not available in other point-to-point interface
standards.
Ethernet's technical advantages include high-speed
communications, error-checking and fault detection. Furthermore,
Ethernet connections can span 100 meters point-to-point, encompass
a radius of 200 meters with the use of a hub, switch, or router,
or extend to thousands of kilometers if fiber interfaces are
used.
LXI increases the acceptance of Ethernet for
next-generation modular instruments by addressing instrumentation-specific
requirements such as EMI/RFI, mechanical interfaces, cooling,
triggering, device synchronization, software interfaces and
network behavior. Performance areas such as mechanical interfacing
and cooling do not represent significant technical challenges.
Others, including device synchronization, test network architecture
and software offer greater challenges. LXI addresses these issues
through hardware and software, all based on industry standard
sizes, interfaces and protocols.
For example, the synchronization and control
of multiple instruments is a prerequisite for most functional
test applications that are dependent on event detection, stimulus/response
handshaking or phase relationships. Engineers can choose the
synchronization approach, which could include an auxiliary trigger
subsystem (TriggerBus), or IEEE 1588, which ever best suits
their application requirements.
The Benefits of LXI
LXI test and measurement modules are optimized
for use in all phases of automated testing - from design validation
to manufacturing. In addition, because LXI modules use the same
software and test routines developed on standard bench instruments,
LXI offers seamless migration from product development through
manufacturing deployment. Unlike PXI modules that require a
cardcage with an expensive power supply, backplane, computer
controller and cables, LXI modules are self-contained with their
own processor, LAN connections, power supply and trigger inputs.
This maximizes flexibility and reduces cost for engineers designing
test systems. They can add new LXI modules as needed without
worrying about calculating proper cooling and power in the cardcage,
purchasing a larger cardcage or changing to a new test system
architecture. LXI-based systems can start with one module and
build up as needs change. They can also be mixed into an existing
system with other LAN-based or GPIB-based instruments.
From a measurement perspective, LXI modules
use the same measurement science and have the same high-performance
specifications as rack-and-stack instruments, so they offer
accurate measurements and advanced features. They also offer
a big advantage for automated test systems with packaging that
reduces the overall footprint of the test system.
Rack-and-stack instruments are designed to
be used standalone from the buttons, dials and displays on their
user-friendly front panels. For this reason, they tend to be
full-rack width (19") and greater than two rack units tall.
In contrast, LXI modules are either one- or two-rack units tall
in full- or half-width, making it simple to mix and match functionality.
In addition, because LXI modules are designed to be controlled
with a computer and mounted into a test system, they are faceless
to reduce their size, not performance. Signal inputs and outputs
are located on the front, and LAN and input AC power cord are
located on the rear of each LXI module. LXI modules are optimized
to run over high-speed LAN, use IVI-COM drivers for communications,
and serve up information and troubleshooting screens viewable
by standard web browsers to ease system integration. In addition,
by using LAN, LXI supports peer-to-peer operation which opens
the door to synthetic instruments and simultaneous operation
for faster measurements.
LXI Applications
LXI combines the best of VXI and GPIB-based
instruments to better solve the needs of test system builders
in a variety of industries. For example:
- Aerospace/defense engineers need the latest
measurement technology in a small form factor, linked together
with industry standard I/O and software. They often deploy
test systems all over the world, so small size is important.
The test systems need to last for 25 years, so reliability
is very important. They also need to be built with industry-standard
I/O and software to reduce the cost of getting replacement
hardware to work in aging systems. LXI brings size reduction,
the reliability of proven instruments and industry-standard
I/O and drivers.
- Communications engineers need the latest
measurement technology in a form that can be used on the bench
and in manufacturing. Time-to-market is critical, so they
hope to leverage software between R&D and manufacturing.
LXI gives them the same measurement technology on their bench
and in manufacturing.
- Engineers developing products for the
medical industry require highly reliable measurements. LXI
gives them state-of-the-art, reliable measurements with the
additional benefit of operating on a high-speed LAN to give
them more throughput than possible with their existing systems
built with GPIB instruments.
- Automotive and industrial engineers are
looking for cost-effective measurements in a small form factor.
LXI is more cost effective than typical cardcage products
because LXI modules don't require a cardcage, controller or
special interface in the computer. They are smaller than bench
instruments, reducing the space required for the test system.
And because LXI modules are optimized for use in a system,
throughput is improved through a combination of fast measurements,
parallel operations (multiple modules operating simultaneously)
and faster I/O.
- Engineers developing consumer electronics
require low-cost test systems that are small in size. LXI
reduces cost by eliminating the cardcage, controller and interface
card, and is smaller than instruments and cardcage products.
The system can be sized to fit the need.
Conclusion
LXI is the next logical step in the progress
of open standard instrumentation for test systems. The LXI standard,
managed by the LXI Consortium, will provide the necessary framework
for the test & measurement industry to develop, support,
and promote the LXI standard. With LXI, engineers are able to
leverage the software and measurement accuracy they currently
have from their GPIB instruments to the test system. The LXI
standard provides a basis for long life cycle instrumentation
implementations that are not limited by bandwidth, software
or computer-dependent architectures.
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Contacts:
Janet Smith, Agilent
+1 970 679 5397
janet_smith@agilent.com
Jon Semancik, VXI Technology
+1 216 447-8950
jons@vxitech.com
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