LXI: The Solution for Data Acquisition
LXI (LAN eXtensions for Instrumentation), based on industry-standard Ethernet technology, offers many benefits for data acquisition over traditional PXI or PCI systems. LXI technology makes system configuration simple using the widely-adopted Ethernet. In addition, the widespread adoption of LXI to replace GPIB is driving the development of high-performance, LXI-based tools for a variety of applications. With LXI, engineers can add modularity, flexibility, and performance to new and existing systems, which provide new possibilities in their applications. Bustec LXI products bring the benefits of LXI to data acquisition applications for test and measurement engineers.
This FAQ addresses the following commonly-asked questions about LXI technology:
- Ubiquity – For several decades, Ethernet has been the de facto standard for home and enterprise network infrastructure. Due to its mainstream adoption, commonly-used products such as cables, routers, and switches are readily available and inexpensive, resulting in significant savings compared to using alternative buses.
- Ease of Use – Since every computer today is built with an RJ-45 Ethernet connector, Ethernet data acquisition reduces configuration and integration time by omitting the traditional need for installing and configuring PC plug-in cards. Plus, these systems easily can take advantage of other Ethernet benefits, such as automatic discovery, error detection and correction, and security.
- Access Over Long Distances – Distributed systems for data acquisition often can require input and output signals that span over large distances, such as systems required for structural testing of wind turbine blades. With the use of built-in web interfaces, an unlimited number of measurement nodes can be accessed and controlled from virtually anywhere in the world.
The widespread adoption of LXI to replace GPIB is driving the development of high-performance, LXI-based tools for PC-based data acquisition. LXI adds several features on top of the Ethernet standard to specifically address the needs of test and measurement applications, including synchronization, flexibility in form factor, and longevity.
- Synchronization – The LXI platform offers automatic synchronization of devices with only 20 ns jitter using the IEEE 1588 Precision Time Protocol over standard Ethernet cables. Traditional LXI instruments have additional transparent clocks to enable synchronization and triggering, but with Bustec LXI products, engineers can reap the benefits of synchronization and triggering using standard switches. For example, a system with Bustec ProDAQ 6100-AA LXI Class B Function Card Carriers, Ethernet boxes that hold function cards and connect via Ethernet cables to a switch or PC can achieve up to 100 MB/s throughput with 20 ns synchronization accuracy. The Bustec ProDAQ 6100-BA Class A Function Card Carrier, which uses the daisy-chain Wired Trigger Bus (WTB) LXI cable system, provides synchronization capability in the picosecond range and adds extended triggering capabilities.
- Flexibility – LXI is not limited by the real estate constraints inherent in platforms with smaller form factors such as PCI, PCI Express (PCIe), PXI, or PXI Express (PXIe). As long as they include an Ethernet port, LXI devices can come in many shapes and sizes, allowing for custom form factors and higher I/O density. Plus, with greater real estate freedom, engineers can attain proper power supply voltage and adequate power conditioning, an essential component for accurate data acquisition systems.
- Longevity – While PC-based technologies change quickly and require new hardware, LXI technology is based on Ethernet, which has been in active use for decades and offers staying power to protect investments for the future. For example, Ethernet technology has made significant performance improvements in terms of physical media interfaces and magnitudes of speed, from 10 Mbit/s to 1 Gbit/s, yet still maintains backward compatibility.
With Gigabit Ethernet connectivity a standard feature of PCs, Ethernet-based data acquisition systems now can deliver sustained throughput of over 100 MB/s, and this will continue to increase as 10 GB Ethernet and future generations of Ethernet become the norm. LXI adds benefits to Ethernet, such as triggering and synchronization as precise as 20 ns over standard Ethernet cables. LXI also adds more precise triggering and synchronization options, as discussed later in this document.
The first byte latency associated with the Ethernet packetization process is often in question for engineers when considering LXI data acquisition. For high-volume production test systems that need to take multiple measurements from multiple instruments in as little time as possible, the overhead of initiating each test step is more important than data throughput in order to minimize test cycle time for each UUT. For a data acquisition system taking data at a prescribed rate, the opposite is true – reliable throughput of data is more important than the relatively small proportion of time spent sending the first byte, because of the need to avoid data loss regardless of how demanding the required throughput. The first byte latency for a Bustec system is on the order of 100 to 150 μs
Computer bus technologies – such as ISA, EISA, Micro Channel (MCA), PCI, PXI, PCIe, and PXIe – constantly emerge and subsequently become obsolete without maintaining compatibility with each other, making long-term or lifetime support for existing systems extremely difficult. LXI is based on standard TCP/IP Ethernet, a network bus with long-lasting adoption, millions of users, and performance improvements that preserve backward compatibility.
LXI provides seamless interoperability between vendors, giving users the flexibility to select the most suitable LXI products for their specific application. Plus, the standard complements existing test and measurement systems, working with GPIB, VXI, PCI, and PXI standards.
LXI promotes ease-of-use with easily configurable LAN options, VXI-11 instrument discovery, and connectivity between test and measurement software, including VISA and IVI drivers to instruments. This technology also provides coordination activities using IEEE 1588 and the IVI LxiSync API for managing the arming, triggering, and event functionality of LXI devices.
Because LXI offers numerous benefits as an emerging technology, and will continue to play a role in data acquisition applications where flexibility and seamless integration are critical application needs. Many companies have adopted LXI technology, which has been in existence since 2004. Read about the History of LXI.
Common industries where LXI technology is used include:
- Power generation
- Medical devices
- Consumer electronics
While there are many viable platform options for data acquisition systems, each with its unique features and benefits, LXI distinguishes itself with its flexibility in size and power as well as accessibility in its use of ubiquitous Ethernet technology.
Because LXI systems are not based on cards that must fit inside a PC, they are not limited by the power and real estate constraints of PCI and PXI-based systems. The ADCs in traditional PCI and PXI instruments do not have optimal headroom for taking accurate 10 V measurements. LXI products, on the other hand, have the real estate to use a 15 V power supply for analog power rails, which allows for more accurate measurements without having to alter the original signal.
With an LXI-based data acquisition system, setup and results data are typically displayed via Ethernet connectivity on the host PC. As long as they include an Ethernet port, LXI instruments have much flexibility in physical size and shape, whereas PCI and PXI boards must fit into standard-sized slots and chassis. Although most LXI devices are designed for rack mounting, some devices may use a smaller form factor to support portable, stand-alone form factors. With Bustec LXI data acquisition systems, signals enter and exit the module from its front panel while connectors for Gigabit Ethernet, power, and trigger cables are found on the back of the module. DUT connectivity is reserved for the front of the module, with line power and the RJ-45 Ethernet port on the rear panel.
Without the need for mainframes or slot-0 controllers, LXI systems can provide considerable cost savings compared to chassis-based platforms. LXI modules feature self-contained power supplies to improve reliability, lower costs, and provide widely distributed system architectures.
Why should I use Bustec LXI products for my data acquisition system?
Bustec has a long history in high channel-count data acquisition systems, starting in the 1990s on the VXI platform. With hundreds of deployed systems in critical applications, such as mil/aero test applications and nuclear power plant monitoring and control systems, Bustec continues to invest in R&D to develop new technologies that lower costs and increase performance.
Bustec systems are known for their high throughput, channel density, and accuracy. A system comprised of Bustec ProDAQ 6100 LXI function card carriers can reach up to 100 Mbytes/s throughput for streaming waveform data, with 20 ns synchronization accuracy between separate LXI devices. Their function card line includes 24-bit resolution analog input cards with an absolute accuracy of 50 μV typical for the 10 V range. In addition, over 384 digital I/O channels or 192 analog input channels can fit in 1U of rack space.
For flexibility, Bustec offers data acquisition solutions for LXI and VXI using the same function card modules in carriers for both platforms. The company addresses applications where accuracy is critical, such as those that include static signals (voltage, temperature, pressure, etc.) and dynamic signals acquired at higher speeds, as well as closed-loop control and simulation.
View our complete LXI product line.