PXI (PCI eXtensions for Instrumentation) is a rugged PC-based platform for measurement and automation systems. PXI combines PCI electrical-bus features with the rugged, modular, Eurocard packaging of CompactPCI, and then adds specialized synchronization buses and key software features. PXI is both a high-performance and low-cost deployment platform for measurement and automation systems. These systems serve applications such as manufacturing test, military and aerospace, machine monitoring, automotive, and industrial test.
Developed in 1997 and launched in 1998, PXI was introduced as an open industry standard to meet the increasing demands of complex instrumentation systems. Today, PXI is governed by the PXI Systems Alliance (PXISA), a group of more than 70 companies chartered to promote the PXI standard, ensure interoperability, and maintain the PXI specification. For more information on the PXISA, including the PXI specification, visit www.pxisa.org.
2. Hardware Architecture
PXI systems are composed of three basic components - chassis, system controller, and peripheral modules.
Figure 1. A standard 8-slot PXI chassis contains an embedded
system controller and seven peripheral modules.
PXI chassis provides the rugged, modular packaging for the system. Chassis available in both 3U and 6U sizes, generally ranging in size from 4- to 18-slots, are available with special features such as DC power supplies and integrated signal conditioning. The chassis contains the high-performance PXI backplane, which includes the PCI bus and timing and triggering buses. Using these timing and triggering buses, users can develop systems for applications requiring precise synchronization.
As defined by the PXI Hardware Specification, all PXI chassis contain a system controller slot located in the leftmost slot of the chassis (slot 1). Controller options include remote controllers from a desktop, workstation, server, or a laptop computer and high-performance embedded controllers with either a Windows 2000/XP or a real-time OS (LabVIEW Real-Time)
PXI Remote Controllers
There are two types of PXI remote controllers:
- Laptop control of PXI
- PC control of PXI
Laptop Control of PXI
With ExpressCard MXI (Measurement eXtensions for Instrumentation) and PCMCIA CardBus interface kits, you can control PXI systems directly from laptop computers. During boot-up, the laptop computer recognizes all peripheral modules in the PXI system as PCI devices. Using ExpressCard MXI, you can control your PXI system with a sustained throughput of up to 214 MB/s.
ExpressCard MXI interface kit
PCMCIA CardBus interface kit
Figure 2. Laptop Control of PXI
You now have the advantage of mobile PXI systems for applications such as field tests, in-vehicle data logging, NVH and NDT with laptop control of PXI. You can purchase any ExpressCard MXI compatible laptop or PCMCIA CardBus compatible laptop to remotely control your PXI system. For more information, please refer to Laptop control of PXI.
PC Control of PXI
With MXI-Express and MXI-4 interface kits, you can control PXI systems directly from desktop, workstation, or server computers. During boot-up, the computer recognizes all peripheral modules in the PXI system as PCI devices.
Figure 3. Remote control with 2-port MXI-Express provides simultaneous
control of two PXI chassis with combined throughput of 160 MB/s.
Using MXI-Express you can control your PXI system with a sustained throughput of up to 832 MB/s. With the MXI-Express 2-port interface kit, you can control two PXI systems simultaneously from a single PC.
Figure 4. Remote control with MXI-4 provides PC control of PXI, as well as multichassis PXI systems.
MXI-4 interface kit comes with low-cost copper links or fiber-optic links for both extended distances and electrical isolation. As shown in Figure 4, you can build multichassis PXI systems with MXI-4 for high-channel-count applications. Using a MXI-4 link, you can implement either a daisy chain or a star topology to build multichassis systems. For more information on topologies for multichassis configurations, refer to the MXI-4 Series User Manual. You can purchase any desktop, workstation, or server computer, and then remotely control your PXI system using either MXI-Express or copper/fiber optic MXI-4 serial link. For more information, please refer to PC control of PXI.
With PXI remote controllers, you can maximize processor performance with minimized cost by using a desktop computer or laptop to remotely control a PXI system. Because all remote control products are software transparent, no additional programming is required.
PXI Embedded Controllers
Embedded controllers eliminate the need for an external PC, therefore providing a complete system contained in the PXI chassis. PXI embedded controllers are typically built using standard PC components in a small, PXI package. For example, the NI PXI-8105 controller has the 2.0 GHz Intel Core Duo T2500 dual-core processor, with up to 2 GB of DDR2 RAM, a hard drive, and standard PC peripherals such as ExpressCard, Hi-Speed USB, Ethernet, serial, parallel, and GPIB ports. There are two types of PXI embedded controllers
- PXI Embedded Controllers with Windows
- PXI Embedded Real Time Controllers
PXI Embedded Controllers with Windows:
PXI embedded controllers with windows come with standard PC features such as integrated CPU, hard-drive, RAM, Ethernet, video, keyboard/mouse, serial, USB, and other peripherals, as well as Microsoft Windows and all device drivers already installed. Because the controllers have Microsoft Windows, the user experience is no different than a PC or laptop computer. It has similar application software available in your PC or laptop computer such as Microsoft Office Word, Excel, and PowerPoint.
PXI Embedded Real Time Controllers:
PXI Embedded Real Time Controllers also come with standard PC features along with a Real-Time OS such as LabVIEW Real-Time or VxWorks to deliver real-time, deterministic, and reliable I/O for measurement, automation, and control. Because RT Series PXI controllers are configured and programmed over the Ethernet, you can distribute a real-time application across the network and remotely monitor it. These controllers are designed for applications requiring deterministic, reliable performance and can be run headless (that is, no keyboard, mouse, or monitor).
Figure 5. NI PXI-8105 2.0 GHz Dual-Core PXI Embedded Controller. Notice the familiar PC peripherals such as keyboard/mouse and monitor connections, as well as the hard drive, USB, Ethernet, serial, ExpressCard, and other standard PC peripherals. This controller runs standard Windows 2000/XP OSs, or with LabVIEW Real-Time.
Embedded controllers are ideal for portable systems and contained "single-box" applications where the chassis is moved from one location to the next. For more information please refer to PXI controllers.
PXI Peripheral Modules
National Instruments offers more than 100 different PXI modules; and because PXI is an open industry standard, nearly 1200 products are available from the 70+ members of the PXI Systems Alliance.
Because PXI is directly compatible with CompactPCI, you can use any 3U CompactPCI module in a PXI system. A categorized list of modules offered by National Instruments and our PXI product partners is available at ni.com/pxi.
PXI also preserves investments in stand-alone instruments or VXI systems by providing standard hardware and software for communication to these systems. For example, interfacing a PXI system to GPIB-based instrumentation is no different with a PXI-GPIB module than it is with a PCI-GPIB module. The software is identical. Additionally, a number of methods are available to build hybrid systems interfacing PXI, USB, LAN/LXI, VXI and stand-alone instruments. For more information, refer Integrating LXI, USB, PXI Express, and Other Standards into a Hybrid Test System.
3. Software Architecture
Because PXI hardware is based on standard PC technologies, such as the PCI bus, as well as standard CPUs and peripherals, the standard Windows software architecture is familiar to users as well. Development and operation of Windows-based PXI systems is no different from that of a standard Windows-based PC. Additionally, because the PXI backplane uses the industry-standard PCI/PCI Express bus, writing software to communicate with PXI devices is, in most cases, identical to that of PCI devices. For example, software to communicate to an NI PXI-6251 multifunction data acquisition module is identical to that of an PCI-6251 board in a PC. Therefore, existing application software, example code, and programming techniques do not have to be rewritten when moving software between PC-based and PXI-based systems.
Figure 6. Two different packages - one software standard. In software, communication
with a PXI module (bottom) is identical to that with a PCI board (top).
As an alternative to Windows-based systems, you can use a real-time software architecture for time-critical applications requiring deterministic loop rates and headless operation (no keyboard, mouse, or monitor). Additional information on using LabVIEW Real-Time with PXI systems is available at www.ni.com/realtime.
4. PXI - Industry Standard Platform
Every bus is unique and has its advantages. For example, USB is excellent for easy desktop connectivity; LAN/Ethernet is well-suited for distributed systems; and PCI and PCI Express provide high performance for ATE. For applications demanding a modular solution, users should expect reduced cost and size through a shared chassis, backplane, and processor; faster throughput through a high-speed connection to the host processor; and greater flexibility and longevity through user-defined software.
PXI, based on PCI and next-generation PCI Express, is the fastest-growing test and measurement standard since GPIB. PXI best meets modular instrumentation demands now and in the future, with more than 70 vendors in the PXI Systems Alliance, more than 1,200 products available today, and a projected 25 percent annual growth rate through 2011 (Frost & Sullivan, 2005). Primarily, all instruments in a PXI system share the same power supply, chassis, and controller. Alternative approaches duplicate power supply, chassis, and/or controller for every instrument, adding cost and size and decreasing reliability. With PXI, the controller can be a high-performance slot 0 embedded controller, desktop PC, laptop, or server-class machine. When you require faster processing, you can easily upgrade the controller of a PXI system. To reuse existing equipment, you can use PXI to control USB, GPIB, LAN/LXI, serial, and VXI instruments.
Figure 7. PCI and PCI Express provide the highest bandwidth and lowest latency, decreasing test time and delivering flexibility and longevity through user-defined software.
Modular instruments require a high-bandwidth, low-latency bus to connect instrument modules to the shared processor for performing user-defined measurements. PXI meets these needs with bandwidth up to 2 GB/s for each slot. Take a modular RF acquisition system for example. PXI can stream two channels of 100 MS/s, 16-bit IF data directly to a processor for computation. Neither LAN nor USB can meet these requirements, so these instruments always include an embedded, vendor-defined processor. Hence high-bandwidth standards such as PXI provide a truly software-defined approach required for modular instrumentation.
5. Why Customers Choose PXI
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 Figure 7.
Advanced 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
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 OS and application software such as MS 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.
6. 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:
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). 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.
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 OSs such as Windows XP and Linux, application software such as Microsoft Office, and user code such as LabVIEW VIs and C++ projects. For more information, please refer to PXI Express.
7. 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 OSs 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.
Visit ni.com/pxi for more information on PXI, including links to product pages, pricing, data sheets, and specifications. If you have any additional questions, you can contact an NI technical sales representative either by phone at (888) 280-7645 or via e-mail.
8. Relevant NI Products and Whitepapers
National Instruments, a leader in automated test, is committed to providing the hardware and software products engineers need to create these next-generation test systems.
- NI TestStand Test Management Framework
- LabVIEW Graphical Programming Environment
- Signal Express Interactive Measurement Software
- Modular Instruments (Oscilloscopes, Multimeters, RF, Switching, and More)
- Multifunction Data Acquisition
- PXI System Components (Chassis and Controllers)
- Instrument Control (GPIB, USB, and LAN)
NI offers a Designing Next Generation Test Systems Developers Guide. This guide is a collection of white papers designed to help you develop test systems that lower your cost, increase your test throughput, and can scale with future requirements. To download the complete developers guide (120 pages) , visit ni.com/automatedtest.