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Next-Generation LXI Platform Delivers Benefits of Modular Test System with High-Speed LAN Connectivity

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.


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.

September 2004