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The progression of MIL/Aero test systems.

During the 1970s and 1980s, each new weapon system that the DoD added required a unique automated test system (ATS), resulting in extensive ATS proliferation and redundancy. A 2003 government accountability office (GAO) audit of the U.S. Air Force's ATS inventory concluded that maintaining a collection of aging nonstandard testers was costing billions of dollars. (1)

A similar story could be told regarding the U.S. Navy, Marines, or Army, and each service has taken steps to correct the situation. A progression of improved, modular, and more general-purpose ATS has been defined and implemented with increasing success. COTS instruments and industry-proven software design have replaced nonstandard hardware and ATS languages in many cases.

Nevertheless, the need to continuously support the warfighter generally requires that new ATS provide backwards compatibility, which can be problematic. As stated in reference 1, the average age of the U.S. Air Force fleet is greater than 23 years, with some aircraft 50 years old. More than 20,000 proven test program sets (TPS) exist for these weapon systems and represent the bulk of the ATS investment. A TPS includes both the test fixture and special cables needed to connect the UUT to the test system and the software to run the test.

Early Air Force attempts at standardization designated the ATLAS programming language for TPS within the 1976 modular automatic test equipment (MATE) program. Many TPS were written in ATLAS, but it is not an accepted industry standard, nor is it taught as part of a software engineering curriculum. Although the MATE program's objectives were laudable, it failed to leverage industry standards. Today, it is not required for new ATS. (1)

Since 2007, the versatile depot automatic test station (VDATS) has been the favored ATS for any new Air Force weapon system. The original VDATS has been augmented by additional RF test capabilities and now addresses about 95% of the test requirements of legacy testers in the Warner Robins Air Logistics Center repair depot inventory. VDATS was developed at Warner Robins, and initial units were built there.

Beginning in 1994, the Navy has standardized on the consolidated automated support system (CASS), currently built in six models: basic hybrid, RF, high power, electrooptic, communications/navigation/interrogation, and the reconfigu-rable transportable RT-CASS. Beginning in 2016, 338 newly defined eCASS systems (Figure 1) will replace 553 CASS units. The Navy uses the bulk of these while the Marines and Air Force Special Operations Force work with some of the RT-CASS version. (2)

Although the Marines have RT-CASS units, this service, too, has a history of developing its own test systems. From the mid 1990s, the third echelon test system (TETS) provided depot or field repair and diagnostics test support. More recently, the VXI-based virtual instrument portable equipment repair/test (VIPER/T) system (Figure 2) has expanded the TETS capabilities.

The Army's standard ATS is the integrated family of test equipment (IFTE), which, as the name suggests, is several testers. The next-generation automatic test station (NGATS) addresses electronic and electrooptic weapon systems at the depot level. It is VXI-based and, according to a Northrup Grumman press release, backwards compatible with legacy IFTE versions. A description on the company's website states that the NGATS complies with the Joint Services NxTest architecture. On Feb. 24, 2011, Northrup Grumman was awarded a limited production contract calling for delivery of eight NGATS systems starting in July 2011.

Looked at broadly, the four services are in the second phase of ATS consolidation and rationalization. From the first phase with several hundred different test systems, today a few major ATS cover the bulk of the testing requirements. Ultimately, the DoD goal is to have a unified test system, termed NxTest when conceived in the late 1990s. This is the third phase of consolidation and still some years in the future.

The initial eCASS development contract was awarded on March 24, 2010, to Lockheed Martin Global Training and Logistics with first units to be deployed in 2016. Given a service life of at least 10 years, this puts off the actual implementation of NxTest to 2026 or later. And, as several recent papers emphasize, the lean defense budgets likely will demand even more conservation of existing test resources in the future.

There is a fifth ATS designation: the joint services electronic combat system tester (JSECST), designated as an acquisition category IV item. According to the DoD ATS website, a category IV item is not considered a major ATS acquisition and can be approved by the ATS manager in one of the four services.

NxTest Influences

Modularity is key to flexibility in a test system, so it is not surprising that VXI and PM are prominent in the newer ATS. However, in the late 1990s, modularity also was seen as a way to overcome obsolescence, the major downside of COTS hardware. Synthetic instruments (SIs) use software to coordinate a number of generic modules to function as a single higher-level instrument. A common example is that of a down-converter, digitizer, and display plus software combined to make a spectrum analyzer.

In addition to sponsoring the SI working group (SIWG), the DoD's NxTest Integrated Product Team (IPT) started the agile reconfigurable global combat support (ARGCS) program. This is a demonstration project that uses SI principles within a modern software design together with modular hardware to provide cross-agency test capabilities. The same core hardware and software are intended to support all branches of the U.S. services as well as those of NATO partners. Today, the NxTest IPT continues to gather information on new technologies to enable better cross-services ATS integration.

The ARGCS hardware is VXI-based, partially for reasons of compatibility. In addition, as Charles Greenberg, marketing manager at EADS North America Defense, commented, "The ARGCS system designers couldn't just procure all of the legacy instruments and assemble them into one gigantic tester that ran all legacy TPS. They needed a single core set of instruments and switching that was flexible enough to run legacy TPS from all supported legacy systems.... In this case, the depth of the VXI modules proved extremely helpful in building a group of switches that could reconfigure themselves into different legacy configurations." (3)

There are many specific test needs, so several smaller systems have been developed in parallel with ARGCS and other NxTest-related initiatives. CACI's common benchtop automatic test system (CBATS) is a PXI-based example that has been designed to replace a large number of legacy manual testers used in the repair shops in the Air Force maintenance depots.

As described by Richard McDonell, director, strategic and technical marketing at National Instruments (NI), CACI's primary role is to help depot maintenance shops reduce the number of individual pieces of test equipment that must be maintained to support the current workload by replacing them with a single hardware test solution. NI's LabVIEW, LabWin-dows/CVI, and TestStand software tools were used by CACI in the CBATS development for Hill Air Force Base.

"In this case," McDonell explained, "many legacy testers were replaced with a single, common tester for multiple line replaceable units (LRUs) for several end items such as F-15, F-22, and KC-135. It wasn't necessary to use modules that supported a legacy mode because all TPSs were redeveloped and each one was independently validated."

CBATS contains a DMM, a D/A module for dynamic analog stimulus, and a digital-to-synchro module. As noted in the CBATS brochure, a wide range of aircraft instruments can be tested including compass system amplifiers, liquid oxygen quantity indicators, steering computers, flight computers, and wheel-speed indicator transducers.

Nevertheless, the largest DoD ATS expenditures are associated with the major programs, and many instrumentation companies have become involved. Anirudh Narayanan, applications engineer at VTI Instruments, emphasized the continuing importance of VXI.

"We find many customers choose to retain VXI instrumentation because the larger cards offer higher density compared to PXUPXIe and still are an excellent platform for high channel-count applications. Also," he continued, "it is less expensive to change or add a card with similar functionality in a current VXI system than it would be to build an entirely new system on other platforms."

There has been significant progress in 3U PXI offerings, especially in the RF/microwave area. However, VXI remains a viable test system platform and retains several advantages for certain applications, as described by Fred Bloennigen, Bustec CEO. "Recently, Lockheed Martin selected our ProDAQ 3030 PCIe VXI 4.0 Controller for the Navy's eCASS ATS program. VXI was included in the system because many of the instrument resources needed to support the legacy TPS code only are available in VXI," he said.

"To maintain compatibility with the Teradyne Di-Series digital test instrument and other instruments previously selected, Bustec worked with Teradyne and Lockheed Martin," Bloennigen continued. "We also enhanced the software driver to allow seamless operation with non-Bustec VISA software, a request from customers still using 32-bit systems."

Similar to the way in which Bustec provides capabilities in either a VXI or LXI format but with identical commands, ZTEC develops instruments in VXI, PXI, PXIe, LXI, and PCI form factors. Christopher Ziomec, the company president, explained, "For the electronic system test set (ESTS) C 130 modernization, we provided the ZT452 and ZT412 VXI oscilloscopes that replace two obsolete HP instruments: a waveform digitizer and an oscilloscope. ZTEC's newer instruments have backwards-compatible functionality such as differential signaling, high voltage ranges, fast sample rates, and equivalent-time sampling that allowed them to be used in the same VXIbus slots as the discontinued instruments."

Ziomec added that legacy compatibility was the primary concern of the system integrator and military end customer for most MIL/Aero test systems. This emphasis also supported VTI's extension of the legacy CASS general-purpose interface (GPI) switching to route up to 1-G1-1z signals in the new eCASS system.

As described in a 2010 VTI press release, "The eGPI allows the Navy to maintain its large installed base of legacy TPS while creating the flexibility required to support next-generation platforms." The switch modification from GPI to eGPI was discussed in detail by Tom Sarfi, VTI Instruments' vice president business development, in the May 2011 EE-Evaluation Engineering article "Good Switching Maintains Good Signals."

To take advantage of the large variety of PXI and PXIe instruments, VTI Instruments has developed the CMX34 integrated 8U LXI/PXIe chassis, the same size as a 13-slot VXI chassis. Because of the similarities of the company's LXI switches and PXIe instruments to earlier VXI-based SMIP and VMIP designs, respectively, customers have an easy upgrade path from their existing VXI systems to an LXI/PXIe system.

Geotest-Marvin Test Systems is one of the few companies actively developing 6U PM modules. As with VXI, the larger form factor supports greater functional density. Mike Dewey, senior product marketing manager at the company, commented, "With the introduction of our GX5960 digital subsystem, in combination with software translation tools, we have been able to successfully offer a replacement for high-end VXI digital subsystems."

In a 2011 Autotestcon paper, Dewey and Jim Ginn, systems engineer at Astronics DME, described the development of a multiformat test system intended to highlight a more compact footprint, SI, improved digital performance, lower power, higher speed, and use of standard communications bus protocols: "A prototype system, the common off-the-shelf benchtop rapidly deployed advanced/tester (COBRA/T) has been developed ... to demonstrate how the current VIPER/T and TETS platforms can be downsized while retaining and even expanding the current capabilities. The system emulates the current VIPER/T functionality and employs cPCI, PXI, PXIe, and LXI instrument standards." (4)

The COBRA/T is about 50% smaller and lighter in weight than the VIPER/T. Further, it consumes about 50% less power at idle and has a significantly lower cost. Separately, Geotest-Marvin Test Systems has developed the PXI-based GBATS ATS (Figure 3) with similar capabilities to VDATS and RT-CASS.

TPS Migration

TPS issues so often drive ATS provisioning decisions that it is natural to question whether it is ever cost-effective to throw away the old TPS and start over. Indeed, NI's McDonell cited a few cases. In his experience, it made sense "when consolidating test of LRUs from multiple unique testers to a common tester or when the tester being replaced does not have a hardware abstraction layer (HAL). In this case, the redevelopment should include a HAL so future redevelopment is minimized when handling obsolescence events, upgrades, and the next generation of rehost."

McDonell also observed that creating new TPS seems to have been justified for the CBATS testers based on results of studies showing their effectiveness. Compared to UUTs tested on the earlier-generation testers, CBATS-tested UUTs remained in the field longer. CB ATS automated what previously were manual tests, so that alone could account for the UUT performance improvement.

In general, however, TPS migration to a new ATS is required. For example, Bill Ross, then deputy program manager for NAVAIR's Support Systems Group (PMA260), in 2008 said that about 1,300 of the currently active 3,000 TPS running on CASS will need to be transferred to eCASS. In the same article where Ross was quoted, the CASS systems are credited with saving $3.8bn by consolidating 30 different test systems. Moving to eCASS must retain that advantage and build on the $2bn already invested in CASS. (5)

Geotest's Dewey said, "We have developed several tools for TPS migration, specifically for digital test vector translation. We also have developed tools for translating digital test vectors from legacy VXI digital subsystems using XML as a common intermediate translation interface."

ZTEC's Ziomec explained that in some cases additional capabilities are required for newer military assets, such as more bandwidth or dynamic range. Providing the new capability is relatively straightforward with new instruments because there are no legacy compatibility issues.

Mike Rutledge, director of advanced programs at EADS North America Test and Services, commented on the benefits typically associated with system upgrades and the effect on TPS. "The new system reduced down time, maintenance costs, and obsolescence headaches. Generally, but not always, the new system improved throughput. Measurement conflicts are resolved by the automated allocation process inherent in our tool suite. It is cost-effective to obtain better measurements through technology insertion when the legacy system has problematic tests.

"Typically, the best migration path is to replicate the exact capability as the legacy component to minimize the validation 'activity. During this process, candidates for improvement can be identified and then later evaluated as to the cost/benefit of implementing a given improvement," he concluded.

Agilent Technologies' Jean Dassonville, digital wireless program manager, added that "because each TPS migration project is unique, a single platform or form factor rarely is the right answer for every scenario. One of the main elements in Agilent's strategy is to focus on the measurements that need to be performed and to identify the best solution. It has to address these measurements, backwards compatibility, and the need for flexibility so that the test platform can be easily updated as requirements change."

Bustec has taken perhaps the most straightforward approach possible by maintaining total TPS compatibility. That's not to imply it is easy. As Bloennigen commented, "Because of the work Bustec did at the hardware, firmware, and software levels of the product, all TPS can continue to communicate through the chosen vendor's VISA layer with no modifications."


A quote from the DoD clearly states the current ATS position."The intent [of the DoD'sATS policy] is to define an acquisition environment that makes DoD the smartest, most responsive buyer to meet our warfighters' needs while reducing the total cost of ownership. This will be accomplished through the use of ATS families as the preferred choice to satisfy automatic testing support requirements." (6)


(1.) Altham, J. M., "ATE and TPS Management," IEEE Autotestcon Proceedings, 2011, pp. 1-7.

(2.) Reagan, M. W., "Modernizing a DoD ATS Family Part IL" IEEE Autotestcon Proceedings, 2011, pp. 8-11.

(3.) Greenberg, C., "The VXI Bus: Well-Conceived for Demanding Test Applications," VXIbus Consortium Newsletter, Aug. 8, 2007.

(4.) Dewey, M. and Ginn, J., "Next Generation Test System Architectures for Depot and 0-Level Test," IEEE Autotestcon Proceedings, 2011, pp. 316-320.

(5.) Rosenberg, B., "Product Focus: Test Equipment," Avionics Magazine, September 2008.

(6.) "DoD Automatic Test Systems Master Pl an," DoD Automatic Test Systems Executive Directorate, 2009, p.7.

by Tom Lecklider, Senior Technical Editor
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Title Annotation:MODULAR TEST; military and aerospace
Author:Lecklider, Tom
Publication:EE-Evaluation Engineering
Geographic Code:1USA
Date:Feb 1, 2012
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