For decades, the venerable Hewlett-Packard-derived IEEE-488/GPIB (General Purpose Interface Bus) served well in small- and medium-sized test systems, with VXI-based testers meeting the needs of high channel-count applications. Time marches on. Test engineers now seek high-bandwidth systems that are relatively easy to configure and are low in cost.
Some system architects are turning to USB (Universal Serial Bus), and USB certainly has a niche in test racks. Others use standards-based communications approaches and buses such as PCI and PXI, but LXI (LAN eXtensions for Instrumentation) is ascending beyond these implementations.
Spurred in 2004 by Agilent Technologies and VXI Technology, LXI is based on industry-standard Ethernet technology. It uses standard I/O based on the popular IEEE-802.3 specs for networking.
LXI also uses standard TCP/IP (Internet Protocol) sockets, VXI-11 instrument discovery, and IVI-COM drivers.
To synchronize Ethernet interfaces, an auxiliary trigger bus can be used, or you can rely on the NTP (Network Time Protocol), or the IEEE-1588 Clock Synchronization Protocol for Networked Measurement and Control Systems.
IEEE-1588, often referred to as PTP (Precision Time Protocol), can sync test instruments with clocks of different precision, resolution, and stability, and do it with sub-microsecond accuracy.
LXI also relies on standard 1U-sized and 2U-sized racks, with mechanical depths of 13.6-in., 16.6-in., or 25-in. There's also no cardcage or Slot 0 requirements.
Many LXI Wares
With a leg up on competitors, Agilent is in the forefront of productization. Since LXI's debut, it's fair to say that the company has released more LXI-compatible products than its competitors. Agilent now offers LXI-equipped modular power sources, arbitrary waveform generators, faceless oscilloscopes, synthetic microwave instruments, RF generators,
DMMs (digital multimeters), signal analyzers, and even automotive seatbelt restraint testers, to name a few.
Look at Agilent's LXI Class C-compliant 6000L Series of DSOs (digital storage oscilloscopes). They offer four channels in compact rack-mountable 1U-high form-factors.
Replete with remote capabilities and graphical Web interface, these scopes provide up to 1-GHz of bandwidth. The concept of an oscilloscope without local controls and a front-panel display may be unsettling to traditionalists, but in most engineering enterprises the benefits of space-saving 6000L Series DSOs will soon outweigh any discomfort.
Significantly, all of Agilent's faceless 1U-sized 6000L Series scopes are entirely software compatible with the firm's predecessor 6000A benchtop (or 5U-sized rack-mounted) scopes. You can use the benchtop versions on your bench, and then the LXI equivalents in production. Moreover, the 6000L scopes pack additional features optimized for ATE (automatic test equipment) as typically located on the factory floor.
These scopes also feature built-in Web servers. The servers permit remote access and control of the instruments using any Java-enabled browser. Using the Web browser, you can set up measurements, monitor waveforms, capture screen images, and operate the instrument remotely.
Click here for a previous eeProductCenter review, and additional information on these LXI-networked oscilloscopes.
Or, search www.eeProductCenter.com for Article ID: 193500287
LXI-Based Switching And Control
Agilent also has a number of LXI Class C instruments for switching and control applications. Packaged as 1U-sized half-rack instruments, Agilent's L4400 Series are can be placed close to applications. Remote capabilities and graphical Web interfaces ease the configuration of design verification and functional test systems.
For low frequency switching apps, Agilent offers three products. Its L4421A is a 40-channel armature multiplexer is for general purpose scanning. The L4421A includes a built-in temperature reference, and has low thermal offset characteristics. It can make temperature measurements in conjunction with an external DMM at a 100-channel/s scan rate.
Another LXI instrument in the series is the L4433A. It's a dual/quad 4 x 8 reed matrix that offers a flexible connection path between a DUT (device under test) and other test gear. It can let different instruments be connected to multiple points on a DUT at the same time.
Multiple high-speed reed-relay matrices can be combined through an analog buses connector to create a larger matrix, too. For its part, Agilent's L4437A is a 32-channel simultaneous channel-switching device that can be used to cycle power to DUTS, control status lights, and actuate relays and solenoids.
If you need to process digital I/O, need analog outputs, and can use a dual counter, Agilent's L4450A is a 64-bit digital I/O unit with memory and triggering. Its 64 bi-directional lines can be configured as eight 8-bit channels, with each channel programmable for polarity and thresholds.
The L4450A's 128-kbytes of memory can also be used for simulating and capturing digital patterns up to 10-MHz. The unit's two counter channels can be used to count events, frequency, period, duty cycle, pulse width and totalize.
Agilent's L4451A is a 4-channel isolated 16-bit DAC (digital-to-analog) converter with memory. The DACs can operate at up to 200-kHz update rates, delivering sine, square, and ramp waves, or your own custom wave shapes with over 500,000 points.
For high frequency switching, Agilent's L4445A is a microwave switch/attenuator driver. As a driver, it lets you control microwave switches and attenuators, with the ability to place the switching elements close to your DUT (lower loss, better impedance matching).
Click here for a previous eeProductCenter review, and additional information on these switch-control units.
Or, search www.eeProductCenter.com for Article ID: 183702219
More Switching Matrices
Another vendor of LXI switching sub-systems is UK-based Pickering Interfaces. Its PXI switching modules are high-density 40-581 1-A 2-pole matrices, packaged in single-slot PXI modules. Thse modules are supported by Pickering's LXI-compatible Modular Switching Chassis.
In an LXI system, each 40-581 module packs up to 264 crosspoint switches organized in a 33 x 8 matrix. This matrix is able to switch up to 1-A signals at up to 150-V in amplitude.
The 40-581 comes with Windows 98, Windows 2000, Windows NT, and Windows XP drivers. These VISA/IVI drivers let you write words to the card to set relay patterns, write bits to operate individual relays, and provide relay status reporting and card identification.
You also get Pickering's PI-MXT diagnostic tool. PI-MXT is a Windows-hosted relay self-test application that can be used to control and monitor remote systems.
Click here for a previous eeProductCenter review, and additional information on these switching systems.
Or, search www.eeProductCenter.com for Article ID: 190400302
For its part in the LXI gambit, VXI Technology recently rolled out its EX1629 High-performance Remote Strain Gage Measurement Unit. The EX1629 is slated for structural and fatigue testing of aircraft, satellites, and rocket assemblies, as well as general-purpose bridge measurements. Using LXI, the VXI Tech platform can handle distributed static and dynamic strain measurements.
The 48-channel EX1629 uses independent 24-bit A/D (analog-to-digital) converters/channel, along with software-selectable filtering. Set-up times and maintenance are reduced thanks to precision programmable internal excitation sources with built-in monitoring capabilities.
You also get self-calibration features that eliminate the need for additional external signal conditioning or sources. The unit also supports TEDS (Transducer Electronic Data Sheets).
The EX1629's 1.5-in. high chassis supports programmable bridge completion, excitation changes, and extensive calibration hooks. These features add up to a system that spares you from having to re-configure any hardware when it comes time to make sensor and measurement changes to your application. VXI Technology's platform can be expanded in an open and networked manner.
Multiple EX1629s can be synchronized using an external trigger bus, with various units controlled by a single host computer in a Master/Slave configuration. You can actually configure an application with literally thousands of input channels.
Programming the EX1629 is handled by an internal Ethernet controller, and the unit provides plug-and-play function calls. High-level commands let you configure a bridge, list the parameters of a strain gauge or excitation voltage, and initiate a scan that produces measurement results in desired engineering units.
You can also write your own code using unique constants for linearization. You can also program the EX1629 to save raw bridge output voltages needed for post-processing on your PC.
Click here for a previous eeProductCenter review, and additional information on these measurement units.
Or, search www.eeProductCenter.com for Article ID: 178601809
Another top-tier test-and-measurement house introducing LXI gear is Keithley Instruments. The company has a number of pieces of RF test spanning 400 MHz through 2.5 GHz.
Software-Defined Radio Meets LXI
In 2006, Keithley rolled out its first LXI product, its Model 2910 RF Vector Signal Generator. Based on an SDR (software-defined radio) architecture, this instrument uses a patent-pending synthesizer and power-leveling scheme. As an SDR design using an intuitive user-interface, software will adapt it to your test requirements.
Whether switching between frequencies, amplitude levels, or waveforms, the 2910 exhibits switching speeds as great as 10X faster than competitors. The 2910 can settle in 1.5-ms, and a sync-out source-settled indicator will only be set when a source is settled. This will eliminate the need to slow down tests by adding wait-states to your executables to ensure the signal generator has settled.
Also, a 64-Msample arbitrary waveform generator supports simultaneous loading of multiple signal waveforms, switching between them in less than 5-ms.
The 2910 also gives you optional signal-generation personalities for cellphone formats, including GSM, GPRS, EDGE, W-CDMA, cdmaOne, and cdma2000 formats. The unit's arbitrary waveform generator also lets you download virtually any externally-generated waveform, with up to 40-MHz of bandwidth.
The 2910 can also generate an RF signal with up to a 200-MHz bandwidth from analog baseband I/Q (in-phase and quadrature) signals.
Click here for a previous eeProductCenter review, and additional information on these Keithley RF generators.
Or, search www.eeProductCenter.com for Article ID: 177103922
For More Information
Agilent Technologies Inc., 395 Page Mill Rd., Palo Alto, Calif. 94303. Phone: 800-829-4444. Fax: (650) 752-5300.
Agilent Technologies, 650-752-5000, www.agilent.com
Keithley Instruments, Inc., 28775 Aurora Road, Cleveland, Ohio 44139-1891. Phone: 800-688-9951 or 440-248-0400. Fax: 440-248-6168. E-mail: email@example.com.
Keithley Instruments, 800-688-9951, www.keithley.com
Pickering Interfaces, 12 Alfred St., Suite 300-3, Woburn, Mass. 01801. Phone: 781-897-1710. Fax: 781-897-1701.
Pickering Interfaces, 781-897-1710, www.pickeringtest.com
VXI Technology, 2031 Main Street, Irvine, CA 92614. Phone: 949-955-1VXI or 949-955-1894. Fax: 949-955-3041
VXI Technology, 949-955-1894, www.vxitech.com