- Why Ethernet instruments?
- Is any instrument with a LAN port an LXI instrument?
- Can anybody develop LXI modules?
- How does LXI differ from rack and stack instruments?
- What is the LXI consortium?
- Does LAN latency make LXI devices inherently slower?
- Does LXI replace PXI?
1. Why Ethernet instruments?
Ethernet is the logical choice. PC-standard technologies offer clear advantages
to instrument applications, as the PC industry employs far more engineers than the
test industry to develop, improve, and cut costs on PC-standard technologies. It
simply makes sense to stick to PC-standard technologies where possible and focus
test engineering resources on what they do best, make great measurements.
Ethernet is by far the most widely accepted communications interface in use today;
nearly every computer is manufactured with an integrated Ethernet interface and
networking hardware is becoming increasingly inexpensive. Ethernet speeds have increased
three orders of magnitude in the past fifteen years, yet backward compatibility
is preserved; GPIB and MXI have not matched this feat. Further, many of the attributes
that make Ethernet so popular to the computer industry are also attractive to the
instrumentation community, yet instrument IO standards like MXI and GPIB have not
kept pace. Rather than replicate what the Ethernet community has developed, it makes
far more sense to leverage Ethernet engineering.
Technical advantages such as TCP/IP error checking and fault detection, long inter-device
connectivity, and peer-to-peer communications clearly exceed the limitations of
parallel bus and other serial based interfaces. The TCP/IP stack provides error
detection and correction that will typically not interfere with throughput rates,
especially when a dedicated test system network is used. 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
Some advantages of Ethernet include:
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- UPnP, SNMP, DHCP, etc. enable automatic discovery, addressing, asset management,
and network management
- Serve up web pages, UI, manuals, and support. Local or server based—it is
invisible to the user. New use models, including remote desktop, instrument sharing,
and multi-site collaboration are possible
- Unlimited range, unlimited number of nodes.
- Multiple media choices, from CAT5 cable to wireless to glass, giving integrators
unprecedented connectivity and isolation options
- LAN cables cost pennies per meter, compared to GPIB and MXI cables that cost $100
per meter or more
- All PCs have a standard LAN port. No special cards are needed.
- Speed scales with processor
- Simple linkage to enterprise software and peripherals.
2. Is any instrument with a LAN port an LXI instrument?
The short answer is no. To ensure interoperability among suppliers, standards must
define what LXI is and is not. Failure to adhere to the specifications will result
in poor interoperability and user frustration.
The LXI standard strives for simplicity. It relies heavily on industry-standard
definitions such as 802.3, IVI, IEEE 1588, etc. While these go a long way toward
ensuring interoperability, there are many instrument-specific requirements that
must be addressed before Ethernet based devices can be accepted as the next generation
platform for modular instruments. Some of these include:
- Interrupt Handling
- Mechanical Interfaces
- Multiple Device Synchronization
- Software Interfaces
- Network Routing, Switching
The most challenging aspects of LXI implementation involve instrument synchronization
and timing, test network architecture, and software interoperability. The LXI specification
outlines different implementation approaches to address these issues.
The LXI Consortium will develop detailed technical specifications over the coming
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3. Can anybody develop LXI modules?
The LXI Consortium is open to any company interested in expanding LAN-based instrument
capabilities. We have several levels of participation, so most companies should
find a level that fits their interests and budget.
To ensure interoperability and a consistent user experience, LXI is a trademarked
brand that may only be used by Consortium members.
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4. How does LXI differ from rack and stack instruments?
From a measurement perspective, LXI and rack and stack instruments are identical.
They use the same measurement science, boast the same specs, and offer the same
features, and run the same software.
The difference is in how it is packaged. Standard rack and stack instruments are
designed to be used standalone (without a PC) from their user-friendly front panels.
By removing handles, bumpers and feet these same instruments can be mounted into
a rack and run with a PC. LXI modules, on the other hand, are controlled with a
PC and mounted into a test system. They do not have a front panel so they have all
the signal connections on the front and all the power and communications signals
on the back. They are optimized to run over high-speed LAN.
LXI offers some advantages not found in rack-and-stack instruments. By using LAN,
LXI supports peer-to-peer operation, which opens the door for synthetic instruments
and simultaneous operation, speeding measurements, reducing redundancy, and driving
The test industry learned a few things from VXI, PXI, and MMS, and we applied these
lessons to LXI. Since modular instruments represent a subset of the overall test
equipment market, making specialized modular instruments can be expensive and inefficient.
Inevitably, the industry wants the capabilities and price of high volume instruments,
yet low volumes make that impossible. Rigid footprints often require custom-engineered
instruments that have little in common with rack-and-stack counterparts, leaving
little room for leverage. Development costs are spread across a small base and unique
supply chain footprints fail to generate scale economies. We saw this with VXI scopes
that cost many times more than their rack and stack counterparts because the VXI
products were essentially custom engineered products, sharing few parts with their
rack/stack counterparts. In the case of LXI, the boards and software are identical
to the rack/stack versions, giving customers the same performance, software, and
costs they get in high-volume rack/stack versions. The result is greater product
availability, improved compatibility with full-featured bench instruments, and generally
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5. What is the LXI consortium?
The LXI Consortium is a not-for-profit (501c3) corporation made up of leading companies
in the Test and Measurement Industry. The group’s goal is to ensure interoperability
and a consistent user experience by developing, supporting, and promoting the LXI
standard. Since announcement in September 2004, many companies have expressed support
for a LAN-based T&M standard. Please see the Company Directory for the latest
list of members.
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6. Does LAN latency make LXI devices inherently slower?
Test system performance consists of multiple factors, and achieving the best performance
requires understanding those factors. You will discover that although the fastest
I/O interface provides clear benefits for some applications, the dominating performance
factors for test systems include physics - such as signal and power supply settling
times, measurement times, interconnection switching times, and synchronization between
The following are some key assertions about test system performance. For more information,
refer to the LXI Consortium’s paper on
Maximizing Performance of LXI-Based Test Systems.
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- I/O latency has very little impact in most test systems
- Distributed intelligence allows overlap processing that can greatly improve performance
- There are a handful of best practices providing better performance for any test
- LXI provides additional features to improve test system development and integration,
such as LXI Clock Synchronization, LXI LAN Events, LXI Wired Trigger Bus. These
are optional functionality not present in all LXI Devices, but are present on key
products that can make good use of them.
7. Does LXI replace PXI?
The LXI Consortium includes some major PXI players. LXI will complement PXI for
customers that need more accuracy, resolution, bandwidth, and functionality than
is possible in PXI. Since LXI leverages technology from rack/stack, it offers cutting
edge performance not normally found in modular formats. LXI is a solution aimed
at customers performing automated tests on electronic devices, while PXI is a better
solution for many lower-end data acquisition applications.
The LXI Consortium looked at the ubiquity and low cost of LAN. LXI does not require
special cards or cables since every PC now comes standard with LAN. LAN-based LXI
supports synthetic instruments and peer-to-peer networking, enabling some unique
capabilities not presently available to the test engineer in any format.
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