Test Connections
- March 2012

Next Generation Test System Architectures for Depot and O-Level Test

Beginning in the mid-1990s, the USMC developed an electronics support strategy that focused on providing repair and diagnostics test capability in a depot level or field environment. Based on these requirements, the Third Echelon Test System (TETS), developed by ManTech provided a transportable electronics test system that could be used at both repair shop and in field forward applications.

Expanded capabilities and requirements to support USMC electronics systems resulted in the development of the Virtual Instrument Portable Equipment Repair/Test (VIPER/T) system, a VXI-based system designed and manufactured by Astronics DME. (Figure 1)


Figure 1: Viper/T

A Next Generation Architecture – Requirements

The on-going need to support the repair and diagnosis of electronic assemblies at both the depot and field or O-level, coupled with the requirement to support existing test programs yields a demanding set of requirements for next generation test systems. Specifically, these requirements include:
  • Significantly smaller foot print and corresponding weight
  • Improved reliability with lower total power dissipation
  • Retain TETS and  VIPER/T legacy test capabilities and provision for new / next generation test needs

In addition, a next generation test platform needs to address new and emerging electronics systems and communication technologies. As an example, modern communication systems require test instrumentation and systems that can support both analog and digital modulation technologies as well as address new communication systems that operate at frequencies up to 26 GHz. All of these test needs drive the use of flexible and cost effective instrumentation solutions.

Implementing a Next Generation Test Platform

Beginning with the TETS system and subsequently the VIPER/T which are largely based on the VXI card modular architecture, these systems offered the required flexibility and technical capabilities for depot and O-level test support when they were initially fielded over 10 years ago. However, for current and next generation test needs, the card modular PXI standard offers several key features and benefits that meet the needs for complex test systems such as VIPER/T. Compared to VXI and other instrument standards, PXI offers:
  • High "functional density"
  • A compact footprint
  • A wide range of baseband, analog and RF products including high performance digital subsystems

As demonstrated by VXI and subsequently by PXI, card modular instrument vendors have demonstrated the ability to achieve high levels of instrument functionality and density on a single card, resulting in high levels of "functional density" compared to "box" implementations.

In conjunction with the high functional density of PXI, PXI’s card modular architecture offers the ability to decrease the overall size of a test system. With a maximally configured 19 inch rack supporting up to 20 PXI slots (19 peripheral and one controller) a compact system footprint can be achieved. In addition, with the flexibility to combine both 3U and 6U PXI cards in a single chassis (Figure 2), system designers have the option to exploit the capabilities associated with 6U cards while retaining a small system footprint.

Compact PXI Chassis for 6U and 3U

Figure 2: Compact PXI chassis for 6U and 3U modules

Using the PXI platform as the core architecture, a prototype system, the Common Off-the-Shelf Benchtop Rapidly deployed Advanced / Tester (COBRA/T) has been developed as an IR&D effort for the purpose of demonstrating how the current VIPER/T and TETS platforms can be downsized while retaining and even expanding the current capabilities of the VIPER/T. The system emulates the current VIPER/T functionality, employs cPCI, PXI, PXI Express and LXI instrument standards and offers the following capabilities:
  • A PXI-based, performance digital I/O subsystem supporting 50 MHz data rates, offering 144 channels with per pin timing capability. The digital subsystem provides equivalent functionality to the existing TETS and VIPER/T test systems while offering much lower power dissipation and improved thermal management.
  • PXI-based RF measurement instrumentation offering capabilities compliant with the VIPER/T and TETS systems with the added ability to operate at frequencies up to 26.5 GHz and supporting both digital and analog modulation schemes.
  • A switching subsystem and baseband instrumentation using LXI and PXI commponents.
  • Multiple DC Power Supplies for UUT power.  Eight (8) programmable power supplies with compatible voltages and currents for VIPER/T and TETS systems.

Figure 3 details the COBRA/T system.

COBRA/T System

Figure 3: COBRA/T System

When compared to the existing TETS and VIPER/T systems, the new platform features:
  • A more compact footprint - the system requires less space/weight (two transit cases and one storage case) versus three or four (TETS) transit cases and two storage cases.
  • Incorporatoin of synthetic instrumentation offering RF stimulus and analysis capabilities to 26.5 GHz
  • Improved Digital instrument performance: The existing TETS digital subsystem is based on VXI and offers a 25 MHz data rate, 32 kbits of memory per channel with a limited programming range for digital levels from -2 to +5 V. For the COBRA/T, Geotest’s GX5960 PXI digital subsystem was selected which offers a higher data rate - 50 MHz instead of 25 MHz; more channel memory (256 kbits); wider programmable voltage levels, -11 to +15 V, and equivalent functionality to the current digital subsystem simplifying TPS migration and re-hosting of test programs. Additionally the GX5960’s Green Power technology offers significantly lower power consumption and thermal loading compared to prevous generation digital subsystems.
  • Higher performance instrument control bus

TPS Migration

The next generation TETS / VIPER/T platform has been architected to support existing test programs and fixtures. The COBRA/T platform’s test interface accepts existing test fixtures and replicates existing test instrumentation and switching capabilities. Many of the TETS & VIPER/T test programs include the use of digital test resources. A majority of these digital test programs are LASAR - based and provide both go / no-go and fault (guided probe) diagnostic. A comprehensive tool set was developed that provided the means to migrate existing digital bursts or LASAR .tap files to the PXI digital subsystem. A summary of this process is detailed in Figure 4.

Program Conversion Tools

Figure 4: Program Conversion Tools

As shown in Figure 4, the migration tools provide the ability to convert legacy binary digital files (.dtb files) to a binary format that is compatible with the COBRA/T digital subsystem via the use of the XML intermediate file format. Additionally, tools have been developed that allow LASAR .tap files to be converted into digital bursts for the new digital subsystem. For guided probe applications, this latter strategy is the preferred methodology.
The effectiveness of this tool set was demonstrated by migrating an existing TPS to the COBRA/T platform. The resulting conversion required no manual "tweaking" of the digital test program. Additonal testing is in process to confirm the robustness of the tools and the platform.


The development of the COBRA/T platform has shown that by employing PXI, a depot / field deployable test system can be developed that offers several key benefits:
  • Smaller system size and weight: Compared to the VIPER/T this platform offers approximately 50% smaller size and 50% less weight.
  • New generation instrumentation and architectures such as synthetic instruments offer the flexibility and a lower cost solution to address current and emerging communication technologies and standards.
  • Lower power dissipation: Compared to the current VIPER/T at idle, this platform offers a power reduction of  greater than 50% which translates into not only lower operational costs but lower internal operating temperatures resulting in increased overall system reliability and up time.
  • Lower recurring acquisition costs: The use of the PXI architecture provides the opportunity to significantly lower the acquisition cost of test systems. For comparable instrument functions, PXI instrumentation can be 50% less than a VXI version of the same instrument and for some high end instruments such as digital cards, the per channel cost for PXI vs VXI can be 60% less.

To learn more about how PXI can offer high performance digital and mixed signal test solutions, click here to download the complete paper.