Unique PXI Application Support
by Tom Lecklider, Senior Technical Editor
With more than 1,500 available modules and chassis, the popularity of PXI is obvious. As new applications are addressed, the number of unusual PXI products continues to grow. Some of these products began as custom solutions for a major customer, eventually finding broader appeal. Others were developed because a vendor perceived an unfilled opportunity. And, a few are prospective efforts to encourage adoption of the latest specification enhancements.
When we contacted manufacturers for information, we simply asked them to describe their unusual PXI products. It was up to them to decide what was meant by unusual. Speed, flexibility, unique capabilities, and a combination of high-performance characteristics were among the interpretations. The modules and chassis they listed are important because they facilitate PXI solutions for new applications or support improvements to existing systems.
Unusual Functionality
V, R, F, Standards
Mike Dewey, senior product marketing manager at Geotest-Marvin Test Systems, described the company’s GX1034 PXI Standards Module. “The GX1034 features NIST-traceable voltage, resistance, and frequency standards. Initial accuracy is established at the time of manufacture by using a NIST-traceable 8.5-digit standard. Values for each of the standards are measured and then loaded into the card’s nonvolatile memory,” he explained. “These values are used by the instrument’s driver to create accurate and traceable standards within the PXI system. The design of the card has focused on minimizing long-term drift, allowing this card to provide 6.5-digit accuracy for a period of up to two years.”
According to Mr. Dewey, the GX1034 allows system designers to develop a recertification strategy that uses only internal system resources. You can recertify a system’s source and measure baseband instrumentation, which simplifies support and maintenance logistics and improves system availability.
RF Mux-DeMux
Aeroflex has introduced the Model 3066 RF Multipath Active Combiner that enables higher utilization of expensive test equipment. Up to four mobile communications devices can be simultaneously tested using a single vector signal generator (VSG) and vector signal analyzer (VSA).
The company’s Tim Carey, product manager for PXI systems, explained, “For receiver testing, this two-slot-wide PXI module enables the output from a VSG to be broadcast to or multiplexed between up to four full-duplex test interfaces. The output level at each test port can be adjusted independently. For transmitter testing, it provides power combining or multiplexing between up to four full-duplex test ports and a single VSA. Path loss values between each of the test ports and the RF out port are stored within the module and can be queried and used to compensate measurement results.”
In one case, the 3066 module facilitates testing multiple transceivers synchronized to a common broadcast downlink. In another application, the I/O ports on the 3066 are connected to the various RF I/O ports on a single smartphone. The module eliminates complex switching arrangements that otherwise would be required and reduces measurement uncertainty. LTE, cdma2000, and Wi-Fi devices using diversity or MIMO technology also can benefit from the multiple ports and switching.
 |
|
Figure 1. PXI-C1553 Bus Test and Simulation Module
|
Configurable 1553
Avionics communications testing based on MIL-STD-1553 has a long history and still is required for modern aircraft. Avionics Interface Technologies (AIT) developed the PXI-C1553 Bus Test and Simulation Module (Figure 1) as part of the company’s range of test and simulation instrumentation. The FPGA-based design accommodates one, two, or four dual-redundant 1553 interfaces and can simultaneously simulate a bus controller, up to 31 remote terminals, and a chronological bus monitor on each channel.
Troy Troshynski, vice president of product development at the company, described how the C1553 solved an important customer’s problem, “On one of Lockheed Martin’s projects, the basic MIL-STD-1553 physical interface was being used but with a different protocol. A team of AIT engineers modified the FPGA firmware on the PXI-C1553 to meet the unique standards of the protocol and add custom functionalities, such as the capability to introduce and detect protocol errors.”
AIT modules are recommended by National Instruments (NI), with whom AIT recently signed a long-term cooperation agreement. NI can directly supply many source, analysis, and switching modules needed in a test system, but it makes sense to use qualified third-party products for specialized applications such as avionics.
JTAG Hardware Assist
The ScanWorks PXI-100 Controller Module from ASSET InterTech functions as a boundary-scan test controller in circuit board test applications. It provides 16 individually controllable digital I/O lines that, according to Kent Zetterberg, product manager for boundary-scan test at the company, allow test engineers to set constraints and control board-level lines such as resets and watchdogs during test.
Typically, the module is integrated into a PXI-based board test system. In many cases, these are based on NI LabVIEW or use NI TestStand test executives. ScanWorks and the PXI-100 module are fully compatible with these products. The PXI-100 also supports in-system programming for NOR and NAND Flash, PLD, and FPGA devices.
Filling the Gaps
Hi-Res Analog I/O
Jacky Lin, product marketing manager for measurement and automation products at ADLINK, discussed a customer’s application that used a PCI-9527 Dynamic Signal Acquisition and Generation Module. “Our customer incorporated the PCI-9527 into production test equipment. The customer performed harshness testing and measured THD and SNR on MP3-type electronic devices,” he said.
The 9527 features two 24-bit input channels simultaneously sampled at rates from 2 kS/s to 432 kS/s, programmable in 455-µs increments. A 4,096-sample FIFO is shared between the two input channels. There also are two simultaneously sampled 24-bit analog outputs, but these have a 1-kS/s to 216-kS/s update rate programmable in 227-µs increments. The input amplitude range is from ±40 V to ±0.316 V and the output from ±10 V to ±0.1 V. Each output channel has an associated 2,048-sample FIFO.
Critical performance specifications quantify the fidelity you can expect. Input bandwidth is 130 kHz for signals up to 10-V amplitude and falls off to 30 kHz at 40 V. The analog output THD+noise is specified at -101 dB for 1-V and 10-V signals, increasing to -89 dB for 0.1-V signals. Several types of triggers, built-in offset and gain error calibration, and wide temperature and humidity operating ranges complete the features. A PXI version is in development.
Fault Injection
Hardware in the loop (HIL) refers to system simulation that includes at least some of the actual hardware. This technique has become very popular because it supports a development process that can start with a totally simulated system and gradually transition to a more conventional prototype as actual hardware becomes available. The hardware modules take the place of simulation routines. Testing is accelerated because many problems can be found and corrected during simulation before committing to the design.
Nevertheless, many critical systems are sufficiently complex and subject to liabilities associated with failures that you really need to prove how they will react under a range of fault conditions. Simulation is not good enough. Pickering Interfaces makes a range of PXI Fault Insertion Switch Modules for just this purpose.
According to Bob Stasonis, sales and marketing manager at the company, several modules have been developed, ranging from the high-density BRIC module to high-current solid-state units with 120-A surge capability. Originally, a test was conducted using a go, no-go strategy. But with the increasing use of HIL-based development, fault injection has become increasingly important.
The Model 40-190B 2A Fault Insertion Switch is intended for automotive and avionic applications and available with 32, 64, or 74 fault insertion channels and one or two fault buses. In operation, a signal on one of the channels can be interrupted, causing an open circuit. Alternatively, you can short that signal to any other signal. Finally, the original signal can be connected to one of the fault buses that may be connected to ground, power, or an ignition signal.
Fast Digitizer
The PXIe-5186 Digitizer resulted from collaboration between NI and Tektronix. NI’s Chetan Kapoor, group manager for PXI platform product marketing, picks up the story: “Codeveloped with Tektronix, the NI PXIe-5186 achieves 5-GHz bandwidth and 12.5-GS/s sample rates. The NI PXIe-5185 has the same high sampling rate but 3-GHz bandwidth.”
At these speeds, it is not surprising that the digitizer has 8-bit resolution and 50-Ω inputs. However, the maximum 1-V input amplitude confirms the modular nature of the product. If signal conditioning or even attenuation is required in your test system, it will have to be separately provided. The detailed specifications are complete, covering crosstalk, SFDR, THD, SINAD, and ENOB at a variety of frequencies and under different conditions. In addition, curves are included to show typical pulse response, frequency response, VSWR, and insertion loss.
Advanced Arb Features
Closed-case calibration, a 1-ppm internal frequency reference, and combined fixed and arbitrary function generator (Arb), sequencer, and pulse/modulation generator performance distinguish Tabor Electronics’ Model TE5251. The 250-MS/s generator provides sine and square waves to 100 MHz, 16-bit amplitude resolution, and AM, FM, FSK, PSK, frequency hop, and sweep modulation. The 10 built-in functions are sine, triangle, square, pulse, ramp, sinc, Gaussian, exponential, noise, and DC.
The 2-Mpoint Arb memory can be segmented into from one to 10k parts as small as 16 points. The segments may be linked and repeated in a user-specified order with up to 4,096 steps, advancing either on a command or a counter value. Each segment can be looped up to a million times. Typical applications include simulation of signal distortion, power-line cycle dropouts, video signals, component failures, and power supply transients.
Multicomputing Opportunities
PXImc, the latest update to the PXI specification, adds a multicomputing capability. According to the PXI Systems Alliance, PXImc provides interoperable communications between multiple controllers or systems. It also supports the use of multiple processors within a single chassis. The technology underlying PXImc is based on nontransparent bridges between PCI domains.
Of course, there are many applications that do not need this capability. According to Pickering Interfaces’ Mr. Stasonis, “PXImc multicomputing has had no impact on our business and is unlikely to do so in the future. PXImc requires a PXI module to have a PCI/PCIe interfaced controller running its own set of programs and a nontransparent bridge as a ‘blind’ interchange for information between that controller and the system controller (or the next controller up the chain). Most modules and applications, especially in the area of switching, do not require the PXImc cost overhead or its complexity.”
Nevertheless, multicomputing attracts innovative approaches. Geotest’s Mr. Dewey commented, “We have not really seen that much call for multicomputing via the PXImc standard. We find that customers are creating their own intelligent instruments using FPGAs with computer cores that provide on-board computing capability. To effectively use multicomputing, you need to ensure the PXIe infrastructure can support the PXImc capabilities. For example, if peer-to-peer communications are planned, the chassis must support it, and this capability is related to having the relevant PXIe slots controlled via the same PCIe switch,” he concluded.
 |
|
Figure 2. GX3700e PXIe Flex DIO FPGA Module |
Geotest’s GX3700e Flex DIO FPGA Module (Figure 2) allows you to create your own custom circuitry totally within the single-slot 3U form factor. An Altera® Stratix® III FPGA is included along with RAM, a DMA capability, an on-board 80-MHz oscillator, 16-MB of flash memory, and access to PXI triggers and clocks. Various FPGA IP design cores are available from Altera and third parties.
PXIe Chassis
Agilent Technologies is one of the more prominent PXImc proponents, having produced the M9018A PXIe Chassis with 16 hybrid slots. As described by Jean Manuel Dassonville, software and modular solutions outbound manager at the company, “Our focus is on letting customers benefit from a chassis in which each module can operate at up to 4 GB/s slot-to-slot and up to 8 GB/s from a slot to the system module. To increase flexibility, the hybrid slots are broken into two segments, each served by its own PCIe-to-PCI bridge.
“To ensure that module-to-module communications can be performed without impacting the overall backplane performance, the chassis backplane is based on advanced switch fabrics,” he continued. Any peripheral slot can communicate with any other peripheral slot without utilizing the system slot PCIe links.
Several of Agilent’s PXIe modules can make use of the chassis’ high-speed capabilities. For example, the M9392A Microwave Vector Signal Analyzer has up to a 250-MHz bandwidth and can continuously stream data at a 500-MB/s rate to ensure transferring at least 100-MHz signal bandwidth.
 |
|
Figure 3. NI PXIe-6674T Timing Module |
Timing and Synchronization
Special-purpose modules are required to take full advantage of the PXIe specification, one of them being a timing module. NI’s PXIe-6674T Timing Module (Figure 3) was described by the company’s Mr. Kapoor. “It generates and routes clocks and triggers between devices in a PXIe chassis. It also can externally route signals to other PXI and PXIe chassis or third-party instrumentation,” he said.
“The timing module generates two types of clock signals. The first is a highly stable 10-MHz clock based on an on-board precision OCXO reference with a 50-ppb accuracy. The second is a clock up to 1 GHz with micro-Hertz resolution from the direct digital synthesis (DDS) clock generation circuit. The 6674T also features advanced trigger and timing routing with PXIe_DSTAR differential star trigger lines that offer less than 500-ps skew and 10-ns delay,” Mr. Kapoor explained.
Conclusion
The applications addressed by PXI and PXIe systems continue to increase in variety. In part, this growth has been facilitated by the availability of modules with unusual capabilities. Without these special functions, test systems would have to interface to benchtop instruments or instruments in some other format such as VXI.
However, as shown by the examples presented here, a wide range of functionality is available if you know where to look. The best place to start is the website for the PXI Systems Alliance (www.pxisa.org), the consortium tasked with promoting and maintaining the PXI standard. One way it does this is by organizing plugfests during which new PXI modules are thoroughly exercised to ensure interoperability. The organization’s website lists the member companies along with a brief description of the types of products manufactured and each company’s ULR.
Find out why engineers are choosing National Instruments and the PXI platform for their automated test needs.