LAN eXtensions for Instrumentation
LAN eXtensions for Instrumentation (LXI) is a standard developed by the LXI Consortium, an industry consortium that maintains the LXI specification, promotes the LXI Standard, and ensures interoperability. The LXI standard defines the communication protocols for instrumentation and data acquisition systems using Ethernet. Ethernet is an accessible and versatile interface that must be implemented against a standard for instrumentation to communicate effectively.
The LXI Consortium provides the structure that ensures instrumentation developed by various vendors works effectively as long as the instruments are compliant. The LXI Consortium ensures that the LXI standard complements test and measurement systems, such as existing GPIB and PXI systems.
Introduced in 2005 by Agilent Technologies and VTI Instruments (formerly called VXI Technology), the LXI instrumentation platform combines Ethernet-enabled instrumentation with the ubiquity of the World Wide Web and applies them to test and measurement applications. Small, modular instruments, using low-cost, open-standard LAN (Ethernet) are the system backbone. LXI-compliant instruments offer the size and integration advantages of modular instruments without the cost and constraints of card-cage architectures. LXI supports synthetic instruments and peer-to-peer networking, which provides number of unique capabilities to the test engineer. Utilizing Ethernet communications, permits flexible packaging, high-speed I/O, and standardized use of LAN connectivity addresses a broad range of commercial, industrial, aerospace, and military applications.
Typically, LXI modules have no front panel or display, using the host PC and Ethernet connections to present setup and results. DUT connectivity is reserved for the front of the module, with line power and Ethernet IO on the rear panel. LXI modules utilize self-contained power supplies to improve reliability, and lower costs. This also enables widely distributed system architectures. Measurement IP may reside on the module, in the PC, or both.
LXI devices can communicate with devices that are not themselves LXI compliant, as well as instruments that employ GPIB, VXI, and PXI, into heterogeneous configurations. In order to simplify communication with non-LXI instruments, the standard mandates that every LXI instrument must have an Interchangeable Virtual Instrument (IVI) driver. The IVI Foundation defines a standard driver application programming interface (API) for programmable instruments. There are currently two IVI driver formats: IVI-COM for working with COM-based development environments and IVI-C for working in traditional programming languages. Most LXI instruments can be programmed with methods other than IVI, so it’s not mandatory to work with an IVI driver; developers can use other driver technologies or work directly with SCPI commands.
The LXI Standard has three functional attributes: A standardized LAN interface that provides a framework for web based interfacing and programmatic control. The LAN interface can include wireless connectivity, as well as physically connected interfaces. The interface supports peer-to-peer operation, as well as master/slave operation. A trigger facility based on the IEEE 1588 Precision Timing Protocol that enables modules to have a sense of time, which allows modules to time stamp actions and initiate triggered events over the LAN interface. More information on the IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems is available from NIST. A physical wired trigger system based on an Multipoint Low-Voltage Differential Signaling (M-LVDS) electrical interface that tightly synchronizes the operation of multiple LXI instruments. More information on the M-LVDS Standard is available in a white paper available from the LXI Consortium.
The LXI Consortium is a not-for-profit (501c3) corporation made up of test and measurement companies. The Consortium’s primary purpose is to promote the development and adoption of the LXI Standard, an open, accessible standard identifying specifications and solutions relating to the functional test, measurement, and data acquisition industry. The Consortium is open to all test and measurement companies, and participation by industry professionals, systems integrators, and government representatives is encouraged. The first Consortium meeting was held November 17–18, 2004. Membership is divided into four levels: Strategic (Agilent Technologies, Pickering Interfaces and Rohde & Schwarz), Participating, Advisory, and Informational.
Consortium members meet several times a year at PlugFests held around the world where conversations regarding the LXI Standard are discussed face-to-face meetings in working groups. The public is invited to attend tutorials intended for users and manufacturers interested in joining the LXI ranks. PlugFests keep LXI instrument manufacturers current with changes in the specification, test implementations. It also provides an opportunity for to certify new products as LXI conformant via an independent testing lab.
The Consortium’s standard development efforts are performed by volunteers working through a number of committees and technical working groups (WGs), which include Compliance WG, LAN and Web WG, Physical WG, Programmatic Interface WG, Resource Management WG, Specification Revisions, Technical Committee, and Timing and Synchronization.
In September 2005, the LXI Consortium released Version 1.0 of the LXI Standard. Just one year later, Version 1.1 followed with minor corrections and clarifications. In October 2007, the Consortium adopted Version 1.2; its major focus was discovery mechanisms. A discovery mechanism allows the test system to recognize and register a new instrument plugged into the system so the user and other instruments can work with it. Specifically, LXI 1.2 included enhancements to support plug-and-play identification of LXI devices. Version 1.3 incorporates the 2008 version of IEEE 1588 for synchronizing time among instruments, so systems using LXI Class A and Class B devices will synchronize with each other based on the 1588-2008 Precision Time Protocol (PTP) standard.
In addition to XML-based discovery, Version 2.0 of the Standard will incorporate even more significant changes. This functionality include the extension of LXI device Web pages to support instrument configuration and interactive testing of different LXI trigger capabilities such as LAN peer-to-peer messages, IEEE 1588 time events, or the wired trigger bus of LXI Class A devices. Logging of all the events in LXI devices will improve as will the ease of troubleshooting LXI-based test systems. Resource Management is another major extension that enables management and allocation of LXI devices in a network with more than one controller accessing instruments. Yet another working group is dealing with the standardization of script downloads into LXI devices. Execution of custom scripts can be done without the system controller, simplifying the development of test software and increasing the throughput of test systems. The most current version of the standard (version 1.4) is available on the LXI Consortium’s website.
LXI test market
World LXI Test and Measurement Equipment Markets, a recent research report (December 2008) from Frost & Sullivan forecasted a growth rate for the LXI test market that far exceeds the overall test market going forward. F&S reported that the worldwide LXI-enabled test and measurement (T&M) equipment market generated $220.0 million in sales in 2007, which represents 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.
After a company joins the LXI Consortium, it can gain access to the Consortium’s Conformance Test Suite software, which they can use as a pre-test before submitting the product to the Consortium for compliance testing. Once a product is ready to submit, a company can choose to have its product tested at a PlugFest or tested using an approved, privately arranged testing house. The LXI Consortium offers detailed instructions on how to get an LXI product certified. Dates of upcoming PlugFests are available on the Consortium’s website.
Overview of device classes
The latest LXI standard no longer categorises devices into class A, B or C.
Legacy Device Classes
Class C was the baseline for devices with LAN capabilities, a Web interface, and IVI drivers. Class B added expanded triggering, such as multicast and peer-to-peer communications between instruments and time-based trigger events. The time-based triggering is made possible by implementing the PTP, which can distribute a precision timing source across many Class A and B devices over a LAN. Class A devices build upon Class B devices by adding a wired trigger bus for precision triggering.
The number of LXI-compliant instruments has grown dramatically, starting from a handful of products from just two vendors in December 2005. This expansion in instrument availability is seen as likely to speed widespread acceptance of the LXI platform and encourage migration to LXI from older instrument platforms. As of March 2009, the Consortium had certified 1,117 instruments from 22 manufacturers as compliant with the Standard. The latest information on compliant instruments is available on the LXI Consortium’s website.
- LXIConneXion magazine
- Test & Measurement World magazine
- Interchangeable Virtual Instrument (IVI) Foundation website
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