Networking RF Tests With LXI

May 20, 2009
The latest version of the LXI Standard provides a great deal of flexibility for manufacturers designing compliant instruments that also contain custom features.

Automatic-test-equipment (ATE) systems have operated with a wide range of control schemes over the years, from standards such as the General Purpose Interface Bus (GPIB) to customized interfaces. The LAN eXtensions for Instrumentation (LXI) standard, however, is an attempt to use proven network practices over a Local Area Network (LAN) to link and control electronic test equipment. Developed by the member companies of the LXI Consortium, which recently announced a new president, the latest version of the LXI Standard, Version 1.3, provides a great deal of flexibility for firms developing test instruments for compatibility with the standard.

The new LXI Consortium President, Von Campbell, was introduced earlier this year. A 26-year veteran of Agilent Technologies, he acts as that company's liaison for a number of industry consortia, including the LXI, VXI, IVI, and PXI organizations. He joined the firm when it was originally part of Hewlett- Packard Co., and holds a Bachelor of Science (BS) degree in Electrical Engineering from Purdue University and a Master of Science degree in Electrical Engineering from Stanford University. He noted that "As more and more test systems incorporate the power of Ethernet and the Web, the standardization and extended functionality offered by LXI-compliant instruments become even more compelling."

In addition to naming Campbell as the group's new president, the LXI Consortium's Board of Directors also elevated the Technical Working Group, which is responsible for certifying instruments as LXI compliant, to the status of a Board Committee. Jochen Wolle, Head of Research and Development for SoftwareSpectrum and Network Analyzers at Rohde & Schwarz, will serve as the chairperson. This committee is responsible for approving all conformance applications.

The IEEE 1588 precision time protocol, which provides for submicrosecond synchronization of real-time clocks in a networked distributed measurement system, is standard in LXI Classes A and B and optional in Class C compliant devices. This standard, which is highly useful for telecommunications and mulimedia equipment developers, is now available for any system designer who is interested in synchronizing instruments with a master clock and in simplifying troubleshooting operations. Version 1.3 of the LXI Standard features the adoption of the Multicast Domain Name System (mDNS) as an additional discovery protocol for instruments connected to a LAN. This avoids polling every instrument and speeds discovering of a connected instrument.

The new version of the LXI Standard also allows instrument manufacturers to create customized Class C LXI Instruments, expanding the definition of the standard for Class C well beyond the initial limits, in order to meet custom requirements. The LXI Standard supports Class A, B, and C instruments. Class C provides LAN and web server functionality while Classes B and A provide progressively expanded functionality. Class C instruments can include selected features of Classes A and B. Any included features are tested to ensure that LXI interoperability is maintained across all compliant instruments.

For Class C instruments, the latest version of the LXI Standard supports the use of a trigger bus as a standardized method of connecting LXI devices that allows them to exchange hardware trigger signals with low timing uncertainty. This is particularly critical for high-speed applications such as in military and aerospace systems. The new version of the LXI Standard also supports IEEE 1588 synchronization for Class C, with submicrosecond synchronization of real-time clocks in a networked distributed measurement system.

In addition, Version 1.3 of the LXI Standard supports time-stamped data for Class C instruments, allowing samples to be correlated among many different instruments within an LXI networked environment. It also incorporates event logs so that actions within an instrument, such as a received trigger, are recorded for analysis and troubleshooting purposes. The new standard also captures event messages, so that alarms or messages sent to other LXI devices are recorded for further analysis.

The LXI Consortium has enjoyed significant growth over the past year, with 1178 products certified as LXI compliant, more than double the number available a year ago. LXI-compliant instruments cover a wide range of product types, including spectrum analyzers, function generators, power meters, power suppliers, power meters, switches, signal generators, RF/microwave downconverters, power analyzers, system source meters, IF digitizers, and oscilloscopes. Companies in the consortium fall into one of four groups: strategic companies, participating firms, advisory companies, and informational companies. The first group includes Agilent Technologies, Keithley Instruments, Pickering Interfaces Ltd., Rohde & Schwarz GmbH, and VTI Instruments Corp. Participating companies include Aeroflex, Kepco, National Instruments, and The MathWorks. Advisory companies include TDK-Lambda and ZTEC Instruments. Informational companies include COM DEV Ltd., Dow-Key Microwave, LeCroy, TEGAM, Teradyne, and Yokogawa Electric Corp.

This kind of high-level support would imply a healthy future for the LXI Standard and recent market studies from notable firms such as Frost & Sullivan point to a growth rate for LXI instruments that greatly exceeds the overall market for test and measurement equipment. In its 46-page report from December 2008, "World LXI Test and Measurement Equipment Markets," the market research firm reported that the worldwide LXI-enabled test and measurement equipment market generated $220.0 million in sales in 2007, or an 83.3 percent increase over 2006. The report also included a forecast that the size of the world LXI market will grow as large as $650.0 million by 2012 at a compound annual growth rate of 24.2 percent. These numbers are in sharp contrast with the predicted growth in sales for GPIB instrumentation, which likely will be limited to just 3-4 percent a year in growth. LXI Consortium President Campbell commented that "with 730 instruments and 109 product families included in the LXI offering, the case for building your next system around LXI architecture has never been more compelling."

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