Virtual instrumentation
for different apps
By Benny Xu
Technical Marketing Engineer
E-mail: benny.xu@ni.com
June Zhu
Marketing Manager
E-mail: june.zhu@ni.com
National Instruments Corp.
The concept of virtual instrumentation has now been widely
adopted in the automated test
and measurement industr y.
Virtual instrumentation allows
users to create a user-defined
system by combining modular hardware, development
software and PC technologies.
The software-defined approach
affords greater flexibility than
vendor-def ined box instruments, and because it is built
on PC technologies, it has advanced in capability at a much
faster rate. With this, engineers
and scientists can create automated test systems that fit their
unique needs.
The result is a test done
in a shorter period of time,
shortened time-to-market and
guaranteed product quality.
Virtual instrumentation’s modular architecture also preserves
investment by allowing you to
buy what you need, and flexibility to expand and upgrade
functionalities.
An example of a test system
that leverages the virtual instrumentation concept is PXI, a
standard for modular I/O built
on PC technologies. It adds
(a)
Figure 1: PXI is a platform hosting a 24bit resolution digitizer (NI PXI-5922), 8GSps high speed digitizer (Acqiris
DC282), 15bit and 1.25GSps arbitrary waveform generator (Agilent 6030A), 7-digit FlexDMM (NI PXI-4071) etc.
integrated timing and synchronization, industrial ruggedness
and increased channel count to
a PC-based architecture. PXI
is now a multivendor standard
supported by more than 70
companies across the world.
The core internal bus for data
transfer between the modular
instruments and CPU is the
high-speed PCI bus with maximum bandwidth of 132MBps.
In addition, the PXI specification requires a dedicated timing
and triggering bus designed
specifically for synchronization
between modules. With the PXI
architecture, you automatically benefit from lower cost,
ease of use and flexibility of
PC technology. Whether you
are building an instrumentation platform, automated test
system, industrial automation
system or data acquisition system, PXI can help you reduce
overall system cost and development time, increase system
performance and bandwidth,
ease system integration, and
protect your investment with
open-industry standard.
PXI is governed by the PXI
Systems Alliance (PXISA), a
group of more than 70 companies worldwide chartered
to promote the PXI standard,
ensure interoperability and
maintain the PXI specification.
With PXI becoming a standard
platform, some test system suppliers are also transferring their
test solutions to PXI platform.
From the PXISA member
companies, more than 1,200
PXI peripheral modules are
available, including modules
for analog and digital I/O, high-
speed instrumentation, vision,
motion, and many bus interfaces. PXI is a platform hosting
a 24bit resolution digitizer (NI
PXI-5922), 8GSps high-speed
digitizer (Acqiris DC282),
15bit and 1.25GSps arbitrary
waveform generator (Agilent
6030A) and 7.5-digit FlexDMM
(NI PXI-4071) (Figure 1).
Considerable investments have
been made in new PXI products.
National Instruments releases
new PXI products at an average rate of one per week. Major
players Agilent and Aeroflex
have also added new RF products for PXI systems.
According to World VXI &
PXI Test Equipment Markets
Estimate conducted by Frost &
Sullivan (April 2005), CAGR
for PXI is 25.1 percent, compared to the industrial average
(b)
Figure 2: (a) For Microsoft’s Xbox 360, NI PXI-5124 12bit, 200MSps digitizer was used for USB communication interface analysis and PXI-4472 dynamic
signal acquisition module for vibration feedback motor test; (b) With NI PXI-5660 vector signal analyzer and software developed with LabVIEW environment, Huari developed the HR-100, a patent-pending wideband radio receiver and monitoring system.
100MHz
differential CLK
PXI
PXI Express
SYNC 100
Star
trigger
PXI
peripheral
Hybrid
peripheral
PXIe
peripheral
PXIe system
timing
controller
PXIe
system
controller
10MHz
CLK
Differential star
triggers
PXI trigger bus (8 TTL triggers)
Figure 3: PXI Express provides additional timing and synchronization features to achieve greater measurement accuracy.
of 4 percent, making it the fastest growing instrumentation
standard since the growth of
general-purpose interface bus
(GPIB) in the mid-1970s.
PXI is now being used in a
wide range of industries—from
consumer electronics to military, and aerospace to medical
device testing. PXI is also a
suitable platform to serve an
array of applications within
each industry. PXI has products
fit to different needs for different tasks such as developing
benchtop applications in design
validation, rack mount applications in manufacturing test, or
portable or embedded systems
for in-vehicle data logging.
Applications
In May 2005, Microsoft announced its latest innovation for
digital entertainment and gaming, the Xbox 360, along with
a new line of Xbox 360 wired
and wireless controllers. The
Xbox 360 controller-functional
test system demanded higherperformance signal capture to
qualify the signal integrity of
the new controller and ensure
high-quality user experience.
With the PXI platform and the
latest NI modular instruments,
the increased functional test
requirements for the Xbox 360
controller were fulfilled. NI PXI5124 12bit, 200MSps digitizer
was used for USB communication interface analysis and PXI4472 dynamic signal acquisition
module for vibration feedback
motor test. With the LabVIEW
graphical development environment, more than 100 tests were
created, Ethernet communication was implemented, and a
data storage interface was incorporated into Microsoft SQL
Server database (Figure 2a).
Another example is Chengdu
Huari Telecommunications Co.
(Huari Telecom). It required a
solution to improve measurement speed for spectral monitoring, directional finding and
signal identification.
With NI PXI-5660 vector
signal analyzer and software
developed with LabVIEW environment, Huari developed
the HR-100, a patent-pending
wideband radio receiver and
monitoring system. This system
can be used as both a radio receiver and an RF vector signal
analyzer to monitor modern
wideband digital telecom signals and conventional narrowband analog broadcast signals.
Moreover, this system can be
configured as a single-channel
receiver or a multiple-channel
directional finding system.
Because the new system uses
an open software-defined radio
platform, HR-100 can perform
standard and custom measurements that previously required
several dedicated, standalone
instruments. The company
can make system updates to
meet future needs of wireless
standards, which is critical
as wireless standards rapidly
change (Figure 2b).
Technology forecast
With the modular architecture
of PXI, it can incorporate the
most advanced technology to
expand the test system’s capability. Because of its high-speed
performance and compatibility
with PCI, PCIe is a bus suited for
test and measurement applications. It provides low latency and
higher bus bandwidth—and unlike PCI, LAN, USB and GPIB, it
is not shared among devices.
A digitizer based on PCIe
will have a 1GBps direct path
to the CPU module, which is approximately 8x the throughput
of 32bit, 33MHz PCI today. To
translate this into real measurement terms, a high-resolution
16bit IF digitizer could potentially stream up to 500MHz
bandwidth continuously to
the CPU without bus limits
or sharing bandwidth with
adjacent modules. This higher
bandwidth will enable many
new applications. With PCIe,
users can take advantage of a
basic communication lane of
250Mbps in each direction with
x1 implementation up to 4Gbps
and with x16 implementation,
an increase of 24x over PCI. In
addition, PCIe also improves
peer-to-peer communication,
enabling instruments within
the system to communicate with
one another quickly and easily.
Lastly, PCIe was designed with
compatibility needs in mind.
With a layered architecture,
it ensures compatibility with
future generations and software
compatibility with PCI.
New apps
With its higher performance,
modular hardware architecture
and compatibility, PCIe has the
capability to solve many new test
and measurement applications.
Some of these used to be served
only by expensive and proprietary hardware, including high
bandwidth IF instruments for
communications systems test,
interface to high-speed digital
protocols such as LVDS-based
proprietary protocols, FireWire
and large-channel-count data
acquisition systems.
Historically, in the case of
high-speed video acquisition,
users had to settle with the
lower bandwidth available and
rely on less dependable data to
make a decision or use a very
expensive, proprietary system
to meet bandwidth needs. With
the greater bandwidth provided
by PCIe, developers can acquire
high-speed video with a more
accurate and complete representation of the real-time event
without the cost of a proprietary
system. For instance, using the
NI PCIe-1429 image acquisition card enables users to acquire data at a rate of 680MBps
compared with using banks of
expensive onboard memory
that could acquire images only
for short periods of time.
Integration
By taking advantage of PCIe
technology in the backplane, PXI
Express increases the available
PXI bandwidth from 132MBps
to 6GBps for a bandwidth improvement of more than 45x,
while maintaining software and
hardware compatibility with
PXI modules. Building on exist-
ing timing and synchronization
capabilities in PXI, PXI Express
provides the additional timing
and synchronization features of
a 100MHz differential system
clock, differential signaling and
differential star triggers (Figure
3). By using differential clocking and synchronization, PXI
Express systems benefit from
increased noise immunity for
instrumentation clocks and the
ability to transmit at higher-frequency clocks.
With the software compatibility of PCIe, the standard software framework provided by PXI
will carry into PXI Express. To
provide hardware compatibility,
the new PXI Express specification defines a new hybrid slot
that enables engineers to install
modules with either a PXI or PXI
Express architecture in a slot.
With this technology, engineers
and vendors can preserve their
existing investments in PXI
systems and products through
both hardware and software
compatibility.
As a standard platform for
test and measurement applications, PXI takes advantage of
commercial technologies to
help increase the performance
and lower the cost of test systems. Commercial standards
have also contributed to PXI’s
adoption rate in different applications ranging from test
to control. Aggressive new
product investments by many
vendors in the PXISA are fueling continuous PXI growth
and clearing the way for new
applications as the functionality continues to expand. The
future evolution of PXI based
on PCIe technology will expand
the platform to serve more applications while maintaining
backward-compatibility.