LXI meets challenge of test systems
01 January 2007
LXI is the LAN-based architecture standard for automated test systems.
Bidding to have a place over GPIB (general purpose interface bus), PXI (Peripheral Component Interconnect eXtension for Instrumentation) and VXI (Virtual Memory Environment eXtension Interface) standards, LXI includes classic instruments, faceless modular instruments and functional building block modules, also called synthetic instruments or SIs. The standard is intended to deliver compact, flexible, high-speed I/O equipment which uses LAN (local area networks) for aerospace, military and satellite applications.
LAN eXtensions for Instrumentation is a test system architecture based on widely used standards, such as Ethernet. By interacting with these standards, LXI promises to enable fast, efficient and costeffective creation and reconfiguration of test systems. The same instruments can be used, preserving investment by leveraging test system software across R&D, design validation, manufacturing and service teams.
Class distinctions
There are three classes of LXI, which implement the standard’s capabilities in increments, with Class A through to Class C. These classes define the requirements of different applications and bear no relation to the physical size of devices. Class C devices provide a standardised LAN and web browser interface, compliant with the LXI standard. Class B devices provide a standardised LAN interface and support for the timing parts of IEEE 1588. Finally, Class A devices provide a standardised LAN interface, IEEE 1588 operation and have a physically wired trigger interface.
The standard was released in 2005 and ratified in August 2006 by the LXI Consortiu (www.lxistandard.org). LXI uses the USB and LAN interfaces already built into computers as a measurement interface. The consortium was established by Agilent Technologies and VXI Technology to combine the high throughput of LAN and the high performance measurements of GPIB. It currently has 50 members. Version 2.0 which will include enhanced security features is already being worked on. Six working groups have been established to refine other parts of the specifications relating to LAN interfaces, web interfaces, driver behaviours, physical considerations, trigger and synchronisation capabilities and hardware-based triggering.
A single system architecture makes it more efficient for users to use, to combine or share source, measure, power and RF/microwave capabilities. The standard is also intended to reduce overheads, as there is a finite capacity, unlike in cardcages, where once capacity is reached, any additions require a new cardcage to be added.
LXI uses IEC-standard rack dimensions and recommends that specific connections should be placed on the front and rear panels. The standard uses the IEE 802.3 standard to define Ethernet connections, protocols, speeds, addresses, configuration and default conditions for consistent operation. All LXI devices must have an IVI (Interchangeable Virtual Instrument) driver to enable users to use a preferred programming language or development environment. Similarly, each LXI device has to serve a web page that provides information such as serial number and MAC address. There also has to be a browser-accessible configuration page that lets the user change IP address, host name and other parameters. The LAN and (2002) IEEE 1588 time-synchronised protocol provides peer-topeer and time-based triggering modes.
The logic of LXI
By enabling intelligent instruments to talk to each other and operate in parallel, LXI can open up opportunities that would not be possible in traditional rack-and-stack or cardcage systems. The standard allows devices to remain synchronised through IEEE 1588, LAN-based trgigers, peer-to-peer and multicast messaging and a hardware trigger bus. The IEEE 1588 standard speeds up the throughput using time-based triggering, which initiates instrument operations at a specific time rather than after a trigger, a command or a wait state.
Companies like Agilent
(www.agilent.com) have adopted LXI as part of the company’s Open concept, which is designed to simplify the entire testing process, with the use of PC-standard I/O and open software tools. GPIB instruments can be incorporated into LAN and USBbased systems, with a choice of interface gateways and converters. Agilent Open is a combination of test-system hardware, I/O and software tools, offering a choice of measurements, connectivity and programming.
Agilent has introduced what it claims is the industry’s first half-rack format, switch and control instruments for LXI in the L4400 series and the first benchtop function/arbitary waveform generator, the LXI-compliant 33220A. There are also digital storage oscilloscopes, the 6000L series with four channels and up to 1GHz bandwidth, packaged in a 1U form factor.
LXI oscilloscope
In some industries, like aerospace, military, automotive, communications, medical and computers, engineers are demanding more digitiser channels in less rack space.
The 6000L digital storage oscilloscope is claimed to be the first LXI class C-compliant oscilloscope family which has been optimised for use in test systems. It offers four channels of measurements in a compact, rack-mountable 1U form factor and delivers up to 1GHz performance. The units have remote capabilities and graphical web interfaces to reduce set-up time. These features also help with troubleshooting in time-sensitive and mission-critical applications from design verification and functional testing in these industries.
The oscilloscopes offer 100MHz, 500MHz and 1GHz analogue bandwidth and sample rates of up to 4Gsample/sec. The three models in the range all have 8Mpoints MegaZoom III deep memory to capture long, non repeating signals and maintain high sample rates with timing resolution.
LAN, GPIB and US interfaces are standard and there is also an additional front panel USB port to store data, scope set-ups and screen images on standard USB memory sticks. The scopes are software compatible with the company’s 6000A portable oscilloscopes. There is also an upgrade facility to include the capabilities of a mixed signal oscilloscope for use with analogue and digital circuitry.
Another option in this series is the secure environment mode which adds a level of security by ensuring the internal memory is clear of all set-up and trace settings, complying with National Industrial Security Program Operating Manual, Chapter 8 information-system security requirements.
LXI options
The company has also added LXI Class B compliance options to the MXA signal analyser and the MXG signal generator. LXI Class B provides synchronisation and IEEE 1588 precision time capabilities. The two models are currently LXI Class C-compliant.
The N9020A MXA signal analyser is claimed to be the industry’s fastest signal analyser with the highest accuracy among mid-range analysers. The MXA platform allows flexible signal and spectrum analysis measurements for the design and manufacture of wireless communications to existing and emerging standards.
The N5181A and N5182A MXG analogue and vector signal generators have simplified self-maintenance and can be used in manufacturing teams to produce components and receivers for communications systems, as well as highperformance, basestation MCPA (multicarrier power amplifier) design and lowvolume manufacturing.
Acquisition
The drive and competition to deliver systems is leading to a shift in the test world’s dynamics. Europe has established itself as a wireless R&D centre, for example. At last year’s Electronica, the company also announced its acquisition of Acquiris, producer of acquisition, data conversion digitisers. Finalised in December 2006, the acquisition is expected to introduce technology for future acquisition products to be added to the company’s portfolio of spectrum analysis, signal generation, wireless and wireline test, network analysers, basestation testers and VoIP assurance and test products.
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