Mark Edwards Sales Director at Aim-TTi explores how LAN/LXi is shaping up as an ideal instrumentation control interface to replace GPIB systems
The cost of configuring a test system today can easily rival the cost of several instruments, making fast configuration more important than ever. LXI (LAN eXtensions for Instrumentation) combines the Ethernet and the Web enabling instruments to configure themselves by pulling information from the instrument’s web server or vendor site.
Instruments equipped with LXI capabilities may use open-source software, such as the Zero Configuration Networking (Zeroconf) discovery protocol or Apple’s open source Bonjour, to LXI test instrumentation. As a result simpler system integration, lower integration costs, and faster first measurement can be achieved.
LXI has been adopted by a steadily increasing number of the major test equipment manufacturers over the past few years. Initially targeted at volume manufacturing, LXI has also demonstrated great advantages to users of simpler test systems for whom the hardware burdens and complexity of GPIB have been a serious drawback.
Companies such as TTi have introduced the first in a range of lower cost products incorporating LXI. The company’s PL-P series of compact linear regulated DC power supplies offers RS232, USB and LAN (Ethernet) interfaces, the latter is designed to the LXI 1.2 standard.
Test systems need to provide stability and consistency to ensure they can test devices today and into the future. LAN speed increases have been the key enabler to making Ethernet attractive to the test and measurement community.
Ethernet has automatic discovery and setup, allows peer-to-peer communication, is compatible with familiar web interfaces, and offers network management tools previously unavailable to test engineers. With IEEE 1588, Ethernet introduces a sense of time.
The LXI Standard provides the common implementation needed to ensure interoperability. It defines a Unified Trigger Model that allows systems designers to use a common syntax when specifying hardwired triggers, LAN triggers, or time triggers. This gives programmers simplicity and flexibility when defining trigger actions. Because most real world systems consist of a variety of instruments, such as GPIB, VXI, and PXI, the Standard defines bridges and adapters to simplify hybrid systems, allowing integrators to use existing assets as they migrate to LXI.
Ethernet allows leverage of the network’s speed. The Ethernet industry continues to improve speed, which is important for systems transferring a lot of data between instruments or from instruments to the controller. For example, LXI has 16 times more bandwidth than GPIB. LXI scripting and peer-to-peer communication eliminates many of the speed and instrument-to-controller traffic concerns.
Ethernet is ideal for applications where large chunks of data is being transferred or those in which integrators, working on high channel count systems or distributed sensor networks, can leverage support for unlimited nodes. System designers have successfully multiplexed thousands of channels using LXI. Similarly, unlimited distance makes distributed networks simple compared to earlier test and measurement interfaces.
System integration is simplified by supporting automatic discovery, DHCP addressing, and network management tools developed by the Ethernet community. The web interface allows integrators and test engineers to configure test systems and troubleshoot from different locations.
Engineers working in regulated environments such as biomedical or aerospace fields, or engineers who must track a large number of test assets, appreciate the ability to poll the network for model number, serial number, firmware revision, and status.
LXI-compliant instruments provide peer-to-peer communication, multicast, scripting, and timing and synchronisation through IEEE 1588 PTP (Precision-Time Protocol). Peer-to-peer communication allows devices to communicate directly with one another, bypassing the controller and freeing it to perform higher-level tasks.
Combined with downloadable scripts that can start local test sequences, peer-to-peer and multicast communication can speed test operations well beyond traditional architectures by eliminating complex and time-consuming controller sequences.
Timing and synchronisation are a consistent challenge with which designers are faced. Typically they addressed settling times, cable lengths, and multiple channels by hand-tuning software with wait statements. The LXI Standard provides a common time reference that synchronises all nodes on a network using IEEE 1588, which coordinates actions across distributed nodes. In addition, the LXI specification expands upon IEEE 1588 by defining what to do with timing in a test environment and by defining a detailed API to apply time-based triggers.
IEEE 1588 optimises test system synchronisation based on specific time intervals rather than hand-tuned delays. As calibration and correction for trigger cable delays are no longer needed, it is easier to substitute instruments, as timing idiosyncrasies will not break the test programs.
Complex test systems have increased the challenges associated with the test engineer’s task but with the increasing power and convenience of Ethernet as the dominant test and measurement interface, these are being more and more effectively addressed.
Annual sales of LXI-equipped test and measurement equipment now exceed $200 million (US). With nearly 500 products certified as LXI Compliant, sales in excess of and a growing list of Class B and Class A products on the market and under development, LXI and network technologies are changing the face of test and measurement.
Aim-TTi
TTi Function Generator
