Frequently Asked Questions

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 are used.

Some advantages of Ethernet include:

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:

Cooling
Triggering
Interrupt Handling
Mechanical Interfaces
Discovery
Multiple Device Synchronization
Software Interfaces
Network Routing, Switching
EMI/RFI

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 months.

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.

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 cost savings.

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 lower costs.

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.

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 instruments.

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.

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 system
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.