Build Ethernet-based test systems with LXI
LXI offers many advantages over traditional GPIB implementations.
Rick Nelson, Editor in Chief -- Test & Measurement World, 11/24/2010 11:23:59 AM
Böblingen, Oct. 26th, 2010:
Many engineers are building test systems on based on Ethernet/LAN platforms. LXI standardizes and extends Ethernet LAN technology to serve test-and-measurement applications, supporting instant and uniform discovery of instruments on a network and providing for time synchronization among geographically dispersed instruments. LXI also provides for debugging and interoperability of instrument systems, and it offers the consistency of a uniform standard across multiple sites and test systems.
LXI offers many advantages over traditional GPIB implementations, which have a theoretical maximum bus speed of 1 Mbyte/s. In addition, GPIB supports a maximum of 14 instruments on the bus at one time, maximum cable length is 2 m, and cables cost over $100. GPIB systems also require a GPIB controller card or a USB adapter.
In contrast, Ethernet supports bus speeds of 10 Mbps, 100 Mbps, 1000 Mbps, and soon 10 Gbps-all with PC industry-standard support and availability. And keep in mind that Ethernet ports are standard and essentially free on almost all PCs, and Ethernet can take advantage of long cables in custom lengths that are inexpensive and easy to buy or make.
Of course, Ethernet networks have their own drawbacks when it comes to test-and-measurement applications. For example, adding an instrument to existing networks can be complicated, LAN hardware such as switchers and routers can introduce latencies, and LAN-based instrument systems present issues related to firewalls, viruses, and security.
The LXI enhancements to LAN address such issues, standardizing, for example, on how to configure an IP address and on instrument-hosted Web page configuration facilities. LXI also supports trigger and synchronization capabilities, including support for IEEE 1588 and a wired programmable parallel trigger bus for the highest-speed applications.
In the Webcast "How to Build Better Ethernet-Based Test Systems with LXI," sponsored by the LXI Consortium and Test & Measurement World and which I moderated, representatives of Keithley Instruments, VTI Instruments, LXinstruments, and Agilent Technologies commented on compelling reasons to consider LXI. Those reasons include cost (see the table below), flexibility, connectivity, and performance. Specifically, participants addressed how to optimize system performance, how to enable the next generation of distributed test, how to put together an open test-and-measurement platform based on LXI, and how to lower instrument system deployment costs. You can view the archived Webcast at www.tmworld.com/webcasts.
Instrument-system cost comparison
| |
VXI
13-slot
|
PXI
14-slot
|
GPIB
|
LAN
|
Interface card
|
$2432
(FireWire)
|
$2085
(MXI-4)
|
$653
|
$53
|
Cable
|
$111
|
$167
|
$111
|
$6
|
Card cage
|
$5934
|
$4864
|
$0
|
$0
|
Total
|
$8477
|
$7116
|
$764
|
$59
|
Source: LXinstruments
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