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Developing automatic test systems for extended duty

Posted: 10 Feb 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Department of Defense? weapons? virtual instrument software architecture?

Since redevelopment of these TPSs is costly, ATS systems designed with an abstraction layer between the TPS and the test station hardware assets offer a significant advantage in reducing the expense of obsolescence events. A hardware abstraction layer, sometimes referred to as a software wrapper or simply a wrapper, makes it possible to develop tests with generic commands for controlling test assets instead of using vendor unique syntax. Separating the commanding functionality from unique syntax protects the TPS investment when an obsolescence or upgrade event occurs.

An example of hardware abstraction is using common function calls for instrument classes such as those defined by the interchangeable virtual instruments (IVI) specification.2 IVI drivers abstract the generic instrument functionality from the unique hardware implementation, replacing unique manufacturer calling syntax with common instrument command syntax (table 1).

Table 1: List of common test instruments for which IVI defines instrument classes. This abstraction provides a layer of protection against the obsolescence of a specific manufacturer's instrument.

Modular abstraction layer
While IVI provides a layer of TPS protection for the listed instruments, test stations nearly always include additional instrument types and other test assets. These other station elements also become obsolete or may need to be replaced in order to provide new capability as the ATS workload changes. Another key element in ATS design is thus the development of a comprehensive, modular abstraction layer that encompasses all of the current test station assets and is also open for further development when required later in the ATS program.

Another useful abstraction to incorporate into a system's design is the use of modular subsystems such as synthetic instrumentation. A synthetic instrument is defined as a reconfigurable system that ties together a series of elemental software and hardware components, with standardized interfaces, for the purpose of generating signals or performing measurements using numeric processing techniquesa modular, software-defined instrument.3 This is another powerful tool for addressing the typical mismatch between instrumentation lifecycles and test system lifespans (figure 2).

Figure 2: Modular, software-defined instrumentation allows the user to customize the instrument functionality to the specific test application.

Because these instruments are software-defined, integrating them into a system will typically lead to greater cost savings and greater system flexibility because each synthetic instrument:

???Replaces multiple traditional instruments
???Can emulate obsolete instruments
???Can be more easily upgraded to address new requirements
???Is more readily customizable to specific test needs

Testing over multiple generations of electronics
The past experiences of support organizations have proven how expensive it is to operate unique testers for the maintenance of different subsystems or even for separate weapons platforms. As a result, the trend is to consolidate to common support equipment whenever possible. Although this approach can reduce cost, it also presents additional challenges to providing ATS solutions.

Combined with the forces of platform life extension, consolidation significantly increases the range of electronics technologies that platform support ATSs must be capable of testing. This creates an extremely high-mix test application environment compared to most commercial counterparts. The additional complexity and greater number of UUTs tend to increase the frequency of obsolescence events. They also heighten the impact that these obsolescence events have on the ATS programs and the missions they support. Here again, modular instrumentation platforms, abstraction layers, and software-defined instrumentation prove to be invaluable design elements, yielding differentiating capabilities for ATSs that integrate them.

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