Developing a PXI-Based Flight-Line Test Set

PXI technology can provide the platform for testing missile systems anywhere in the world.

Initial Design Phase
The development of the test set started in 2001 with these basic design goals:

• A state-of-the-art architecture to ensure long life.
• Maximized use of commercial off-the-shelf (COTS) products to reduce initial and life-cycle costs.
• A portable, rugged design to allow field use in any operational theater.
• Support for all Maverick missile system components including missiles, missile sections, launchers, and missile-launcher clusters.

Architecture Evaluation and Selection
The first task of the design team was to determine the architecture for the new test set. Portability, the third requirement, eliminated GPIB as a viable architecture and dictated that the test set would be based on an instrument-on-a-card architecture which led to three options, VXI, custom design, and PXI, all capable of meeting the fourth design goal.

VXI seemed to be the most viable. It is an established standard and has been used in the past in portable, rugged testers for military applications. However, even with its relative small footprint, the use of VXI would have resulted in a bulky and heavy test set with the cables alone estimated to weigh more than 70 lb. Two additional factors that worked against VXI were the high cost and possible obsolescence on the VXI horizon.

A custom design of all required electronics wasn t an option due to the desire to use COTS products. The previous tester was based on proprietary technology that significantly increased the development costs as well as the cost of ownership. For that reason, the custom design option wasn t seriously considered.

At the time of initial design, the PXI platform still was in its early adoption stage and used predominantly by commercial test and data acquisition applications. However, PXI, although not previously used by military testers, was the natural selection for this application due to its small size and footprint, high performance, low cost, and a COTS industry standard.

The conclusion of the evaluation was to use PXI because it met all four basic design requirements.

The Detailed Design Phase
Once the basic architecture had been selected, the next step was to consider the detailed architecture that includes support for both current and future versions of the missile system. The current configuration of the AGM-65 is predominantly analog; however, future versions will be digital, taking advantage of MIL-STD-1760 technology. For that reason, the test set's architecture required the resources to test analog products with limited digital capabilities that could be expanded in the future to support digital electronics. The result of these requirements was the functional block diagram shown in Figure 1.

The hardware selection for a portable and rugged test set for military field applications is not an easy task. While the design team was quite familiar with the ruggedization process of COTS hardware, some functions cannot be improved.

The test set was required to operate at extreme cold and hot temperatures to allow operation anywhere in the world. For the extreme cold-temperatures requirement, a heater was selected along with temperature sensors to control heater operation. However, to accommodate the high-temperature requirement, the design team could not use heat exchangers or air conditioning due to the costs and weight associated with these products.

Additionally, the test set was supposed to operate under extreme vibrations as well as in high relative humidity, requirements that typically are not met by commercial products. That led to a creative design in which COTS products were slightly modified or screened to demonstrate compliance with the requirements. Examples of such modifications include the conformal coating of all boards to meet the humidity requirement, using RTV to secure components and connectors to meet the humidity and vibration requirements, and in some extreme cases, replacing susceptible components on the COTS product.

While the test set's size was limited due to the portability requirement, UUT channel count was high, a fact that dictated many switching channels. To accommodate both requirements, the design team decided to use a combination PXI backplane with seven 6U slots and seven 3U slots for the following reasons:

• The 6U slots would provide the necessary density to accommodate the high channel count.
• The 3U slots would meet both the current and future requirements for test instrumentation.
• The relatively small size of the combo backplane would keep the overall test-set size small while providing sufficient capabilities.
• This backplane was available as a COTS product.

The Command and Control Subsystem
The control subsystem needed to provide all command and control capabilities for the test set. To meet this requirement, the subsystem should include a CPU, the necessary peripheral interfaces, and the operating software.

Continuing on the path of COTS hardware, a 6U PXI embedded controller was selected as the system's computer. This card was a standard Pentium 4-based CPU capable of operating at 2.4 GHz. However, the version of this COTS CPU that can operate at extreme temperatures is limited to 1.7 GHz, a speed that was more than sufficient to meet the UUT test requirements. This standard PXI embedded controller provided the necessary peripheral interfaces including serial ports, USB, VGA, and Ethernet.

One of the main reasons for selecting a COTS CPU was the desire to use COTS development software. Windows XP was chosen as the operating system, and ATEasy was selected as the test development software and test executive. ATEasy can reduce the development cycle time and support future Maverick components with a minimum investment.

The Maverick missile outputs analog video that must be displayed as part of the test procedure. Unlike the obsolete tester in which the video was routed to a dedicated second display, the design team selected a frame grabber and displayed the live video using an ATEasy control. Control over the seeker was accomplished via a virtual joystick as opposed to the analog joystick used by the obsolete tester.

The user interface had to be simple and intuitive because the test set was to be used by technicians rather than engineers. Due to the field operation of the test set, the use of a keyboard or a mouse was ruled out, and the design team selected a combination of an SVGA LCD screen and a touch screen as the only user interface.

The remote control and display unit can be detached and used up to 25 ft away from the test set. Since no off-the-shelf unit met the design criteria, a display manufacturer was contracted to develop this semicustom display.

Air Force personnel use Tech Orders (T.O.) to operate equipment. While a T.O. was developed for this new tester, the design team wanted to simplify the operation and practically eliminate the need for the T.O. during normal operation. As a result, online help was developed to make the tester easy to operate by any personnel.

Figure 2 illustrates the online help and the simplified operation for cable connections. In Figure 2a, the operator is instructed to connect several cables between the tester and the UUT. The tester then automatically attempts to detect if the cables are connected properly and proceeds with the test once proper connection is verified.

If the operator needs a graphic illustration of how the cables must be connected, touching the SHOW CONNECTIONS button will display an interconnect diagram (Figure 2b). If the operator needs help in identifying the cables, touching the SHOW CABLE button will display a picture of the required cables (Figure 2c).

System Configuration
In addition to the command and control subsystem, other tester components include the stimuli, measurement, digital, and switching subsystems. The stimuli subsystem comprises a two-channel D/A converter and an eight-channel precision DC source. An eight-channel A/D converter and a 6 -digit DMM are used in the measurement subsystem.

The digital subsystem has a 96-channel TTL digital I/O card and slots to support future Maverick functions. Four 6 32 switch matrices and two high-current relay cards with 45 channels, each capable of switching 7 A per channel, make up the switching subsystem.

System Interface
Typical test systems have a mainframe where instruments are installed, a mass interconnect interface routing the system's resources to a central location, and interface test adapters (ITAs) routing these resources to various UUTs. This concept works very well for most laboratory-type testers that support many UUTs.

This concept, however, is flawed when it comes to portable testers. Bulky ITAs add weight and most likely will be damaged during flight-line use. For this reason, the design team selected circular military connectors as the interconnect interface for the new tester. Consequently, all the circuitry typically found in the ITA is inside the tester, and no external circuitry or adapters are required.

The tester is designed to execute several hundred tests on each UUT. Unlike most field testers, it is not a go, no-go tester since it performs full parametric testing. The results of the tests are displayed during run time and automatically stored for future trend analysis. The tester also provides troubleshooting information using ATEasy's Fault Library toolkit.

The result of this development effort was the MTS-206, an ultra-rugged PXI-based tester that can operate anywhere in the world (Figure 3). While the MTS-206 is fully qualified and meets the requirements of MIL-STD-461 for EMI and EMC and MIL-STD-810 for environmental conditions, it mostly is made of COTS PXI products.

The use of COTS products reduced the cost of the MTS-206 to about half of the cost of the obsolete tester. In fact, the price is so attractive that, in many cases, it is more cost-effective to replace the obsolete tester with an MTS-206 than to repair it.

About the Author
Loofie Gutterman, co-founder of Geotest-Marvin Test Systems, has more than 20 years of experience designing, managing, and implementing test-equipment programs for military and commercial applications. At Geotest, he has served in many positions ranging from vice president of systems engineering to COO and now president. Previously, Mr. Gutterman studied electrical engineering at Tel Aviv University and was employed at RSI for several years as a program manager, COO, and technical director. Geotest-Marvin Test Systems, 17570 Cartwright Rd., Irvine, CA 92614, 949-263-2222, e-mail: [email protected]

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