With today's tighter customer
deadlines and ruthlessly
competitive industry,
designers can't delay in getting their products to market. Fortunately, new testing options are accelerating the process.
The PXI modular instruments and the
new LXI instruments let engineers
assemble economical test systems optimized for their needs.
But don't let that similar "XI" ending
fool you. These instruments aren't necessarily competitive. Actually, they're different systems that address different situations, giving test engineers a bountiful
choice of test options that will keep them
in the race to market.
PXI Came First
PXI is a modular
instrument platform based on the Compact PCI bus. Test engineers can plug
over 1200 test instrument modules from
many different vendors into its standard
chassis to build the perfect test system
for their needs.
These systems combine hardware,
software, and communications to produce a system that not only meets target
needs but also provides similar flexibility,
throughput, and synchronization previously available only with more expensive
traditional bench instruments.
Standards set by the PXI Systems
Alliance (www.pxisa.org) ensure compatibility and interoperability. National Instruments first introduced PXI in 1997. Now,
over 65 other companies who are members of PXISA support the standard as
well. Instruments that meet the standards are allowed to use the PXI logo.
The typical PXI test chassis consists of
a built-in system controller, which is typically a powerful dual-core embedded PC
running at 2 GHz or more (). Versions that use an external PC or laptop
are also available. The chassis contains a
power supply and a PXI backplane that
comprises the PCI bus and a special trigger bus for timing and triggering operations. The chassis has slots for seven
instrument modules chosen to meet the
desired test needs.
PXI instruments are virtual instruments. The plug-in modules serve as signal conditioning, data capture, and storage media. Using software like National
Instruments' LabVIEW, the internal or
external PC does the actual instrument
processing and display.
The newer PXI systems use the PCI
Express (PCIe) super-fast serial version of
PCI to boost throughput and cut latency.
PCIe uses two or more unidirectional pairs
or lanes to transmit data across the bus at
speeds from 2.5 to 5 Gbits/s in the newer
versions. With x4, x8, or x16 lanes, the total
throughput can be as much as 45 times
greater than the basic PXI parallel bus.
These faster versions of PXI suit the systems for some of the more challenging test
situations, such as wireless and RF.
The PXI instrument business is doing
well, with wide use in the communications, military, aerospace, and automotive industries. Nine of the top 10 contract manufacturers use PXI systems.
Furthermore, 17 of the top 20 electronic
companies use PXI. Research firm Frost &
Sullivan forecasts a 23% compound
annual growth rate for PXI through 2012.
LXI: The Newcomer
LXI (LAN
eXtension for Instrumentation) is the
newest system in test and measurement.
The LXI Consortium (www.lxistandard.org) first developed it in 2004 and
released the first version of it in September 2005. Since then, over 150 LXI
instruments have been developed and
standardized.
LXI is based on Ethernet, the ubiquitous local-area network (LAN) technology,
including the wireless versions. It uses
TCP/IP and Web-based interface and program control. All LXI instruments have a
Web page that users can access with any
browser to view instrument outputs and
change instrument parameters. Also, LXI
instruments are designed for rack
mounts. They don't have a traditional
front panel. And, an external PC controls
them via Ethernet.
One way to view the new LXI instruments is to see them as standalone
measuring equipment that can be linked
to other equipment and PCs as well as
into complete systems using Ethernet as
the replacement for the General Purpose
Interface Bus (GPIB).
Hewlett-Packard (now Agilent) developed the first programmable instruments
and interconnection platform in the late
1960s. Known originally as the HP Interface Bus (HPIB), it was later renamed
GPIB and supported by almost all test
instrument companies to some degree.
GPIB was subsequently standardized by
the IEEE as IEEE 488 in 1975.
The standard has been maintained
and updated with the additions of codes,
formats, protocols, and common instrument commands that come together in
the Standard Commands for Programmable Instrumentation (SCPI). Most instruments comply with SCPI.
The IEEE 488 interface is an 8-bit parallel bus with a maximum speed of 1
Mbyte/s. An 8-Mbyte/s version is also
available, but length limitations (20 m
max) restrict its use in some applications.
While the IEEE 488 interface is still
around and widely used, it's gradually giving way to faster and more flexible and
powerful systems based on LXI.