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When to Choose PXI Instruments

 By: 

Why Customers Choose PXI

 By:  Murali Ravindran, PXI Product Manager, National Instruments

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This issue's focus is PXI Products. 
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Today’s test engineers can choose from a variety of instrumentation and instrumentation platforms – GPIB, LXI, VXI, and PXI – not to mention the PC- based offerings such as PCI, USB, Firewire, and LAN.  With all of these choices, how do you go about making the right choice? For starters, if you have a test requirement, or better yet a tester roadmap, one that maps to a product or a product family’s future roadmap you can start to define the key attributes needed in an instrument or a platform for both today and tomorrow’s test needs. Choosing an instrument platform involves both technical and financial considerations. Technical requirements include meeting the product’s test needs which translates into measurement performance / functionality, test throughput, and flexibility to adapt the architecture for future unit under test (UUT) variants.
  
From a financial standpoint, the acquisition cost of the instrumentation or platform is only one part of the overall equation.  Other factors to consider include footprint – why footprint you ask? Because factory floor space is an expense, just like any other resource and in today’s competitive electronics world, all costs are scrutinized, including floor space. Other financial aspects to consider is the idea that when you buy an instrument or select a platform, you are making an investment that will probably be in use much longer than the initial product that it is testing. Therefore, it’s important that you think about your choice of instrumentation as an investment and how this investment will be used and redeployed in future years.

Why the PXI Platform
With these requirements in mind, you can begin the process of evaluating and selecting instrumentation and an instrumentation platform.  The first major decision point is whether you select a card modular platform like PXI  / VXI or a “box” based implementation such as GPIB or LXI as your system core. For a variety of reasons including both the technical and financial ones detailed above, using a card modular architecture as a system core makes good financial and technical sense. And more specifically, for the vast majority of new systems employing a card modular architecture, (exclusive of some legacy military programs) PXI is the platform choice. This is also confirmed by market data from Frost and Sullivan (World PXI and VXI  Test
Equipment Markets, April 2005) which estimates that by the end of 2006 there will be over 10,000 PXI systems deployed which translates into almost 3 times as many PXI systems as VXI systems.  

Functional Density and System Footprint:
Functional density of a test system is directly related to how much real estate a tester will require. If system footprint is a primary concern, PXI is the winner hands-down.  . PXI offers both 6U and 3U module sizes, with the 6U format equal in width to a C-size VXI module and 3U modules half the size of a 6U module.  However, unlike VXI, the module pitch is .8 inches, allowing many more PXI instruments to be installed in a rack mount chassis when compared to a VXI platform. With  3U, 6U, and 3U/ 6U platforms such as those offered by companies like Geotest users are able to install up to 19 3U or 6U instruments into a single  chassis or optionally use a combination of 3U and 6U PXI/CompactPCI cards within a single chassis. The PXI platform with its compact form factor can deliver a 3x to 10x improvement in functional density when compared to a VXI or box based solution.  

Performance:
PXI is based on the PCI bus architecture and offers a high bandwidth data bus of 132 MB/s, which allows high data throughput for data intensive / streaming applications and instrumentation with the benefit being faster test execution and throughput.  And if 132 MB/s is not sufficient for your application, you can move to a PXI Express platform, which offers bus throughputs of up to 6 GB/s…. No other instrumentation platform offers this level of performance.

Availability and Breadth of Products:
Today, there are over 65 PXI vendors producing over 1400 different products and this does not even include all of the vendors producing 3U and 6U CompactPCI products which are fully compatible with the PXI architecture [www.pxisa.org]. With this many vendors and products, you can be assured that you will have access to variety of products and vendors offering competitive instruments and solutions. This makes the PXI platform the right choice and a sound investment for anyone using card modular architectures.

Since its introduction in 1998, the growth and acceptance of PXI in the market place has been phenomenal. Even with the architecture now 8 years old, the market continues to experience health growth with an estimated CAGR (compound annual growth rate) of over 25% from 2005 to 2010 (Frost & Sullivan, April 2005). The breadth of instrumentation and switching products is unmatched by any other platform, and with PXI’s adoption of PCI Express in 2005, it is anticipated that many more users will adopt the PXI platform.  For those users looking for instrumentation that addresses both the technical and business challenges for both today’s products and tomorrow’s technologies, PXI is the clear choice.

Why Customers Choose PXI

Murali Ravindran, PXI Product Manager, National Instruments

Selection Criteria

In selecting instrument platforms, customers look at certain criteria, such as throughput, reliability and expected test system cost.

Higher Throughput
Every application is unique and has very specific needs. However, bandwidth and latency are two important attributes of a platform for many applications. Latency tends to dominate single-point operations, such as digital multimeter/switch scanning, and bandwidth tends to dominate data streaming applications, such as waveform stimulus/response. PXI provides high speed for a wide range of applications with both high bandwidth and low latency via the PCI/PCI Express bus as shown in this figure: Bandwidth & Latency Specifications of Industry Standard Buses.

Timing and Synchronization
Many measurement and automation applications require advanced timing and synchronization capabilities that you cannot implement directly across PC standard I/O buses like PCI/PCI Express, Ethernet/LAN, USB, and so on. PXI offers advanced timing and synchronization features to meet your application needs:

• 100 MHz differential system reference clock

• 10 MHz reference clock signal

• Differential star trigger

• Star trigger bus with matched-length trigger traces to minimize intermodule delay and skew

• Trigger bus to send and receive high-speed timing and triggering signals

• Differential signals for multichassis synchronization

System Reliability
The PXI specification defines requirements that make PXI systems well-suited for harsh environments. PXI features the high-performance IEC (International Electrotechnical Commission) connectors and rugged Eurocard packaging system used by CompactPCI. The PXI specification also defines specific cooling and environmental requirements to ensure operation in industrial environments. Modularity makes it easy to configure, reconfigure, and repair your PXI systems, resulting in very low mean time to repair (MTTR). Because PXI is modular, you can update individual modules and components without replacing the entire system.

Lower System Costs
Because PXI is a PC based platform, it delivers the high-precision instrumentation, synchronization, and timing features at an affordable price. The low cost of PC components is only the beginning of the savings you gain from using PXI. With PXI, you use the same Operating System and application software such as Microsoft Excel and Word in your office and on the production floor. The familiarity of the software eliminates training costs and the need to retrain personnel every time you implement a new system. Because the foundation of PXI is PC technology, you benefit from low component costs, familiar software, and system reuse.

Expansion of the PXI Platform - PXI Express

PXI Express technology is the latest addition to the PXI platform. The PXI Express Specification integrates PCI Express signaling into the PXI standard, which increases backplane bandwidth from 132 MB/s to 6 GB/s, a 45X improvement. It also enhances PXI timing and synchronization features by incorporating a 100 MHz differential reference clock and differential triggers.

The PXI Express specification adds these features to PXI while maintaining backward compatibility, both software and hardware as follows:

Software: PCI Express uses the same operating system and driver model as PCI, resulting in complete software compatibility between PCI-based systems (such as PXI) and PCI Express-based systems (such as PXI Express).

You can use code you have written for previous PXI systems with PXI Express systems because PXI Express maintains complete software compatibility with PXI. Software compatibility includes Operating Systems such as Windows XP and Linux, application software such as Microsoft Office, and user code such as LabVIEW VIs and C++ projects.

This software compatibility is ensured by the PCI Special Interest Group (PCI-SIG), a group composed of member companies, such as Intel, who are committed to the development and enhancement of the PCI and PCI Express standards.

Hardware: PXI Express chassis provide hybrid peripheral slots that accept both PXI Express peripheral modules and hybrid slot-compatible PXI peripheral modules. These peripheral slots deliver signaling for both PCI and PCI Express.

Summary: PXI is the Industry Standard Platform for Instrumentation

PXI modular instrumentation defines a rugged computing platform for measurement and automation users that clearly takes advantage of the technology advancements of the mainstream PC industry. By using the standard PCI/PCI Express bus, PXI modular instrumentation systems can benefit from widely available software and hardware components. The software applications and Operating Systems that run on PXI systems are already familiar to users because they are already used on common desktop computers. PXI meets your needs by adding rugged industrial packaging, plentiful slots for I/O, and features that provide advanced timing and triggering capabilities.  To see a standard 8-slot PXI system, click here.

Related Links:

What is PXI

Build your own PXI system

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