Reuse Extends Test InvestmentsReuse Extends Test Investments

Avoid development tool obsolescence
Engineers should think of their software development tools as a "free ticket" to software reuse. Using a programming language and software tools that will remain in use-and that vendors will support-for many years helps guard against obsolescence. Engineers want a software development "environment" to exist for their test system's lifetime-often a decade or more. That doesn't happen often, though. Recently, Microsoft shifted its emphasis from tools, such as Visual Basic 6, to Visual Studio .NET. That move will leave many VB6 developers high and dry. The .NET tools may last for five or six years. But who knows? Engineers should adopt tools that offer longevity.

Integrate design and test tools
Seek software tools engineers can apply equally well in a development lab or on a production line. When design engineers and test engineers define their test software needs in parallel, they can develop a common test strategy that uses one set of software tools. In addition to saving time and money, using one test development tool includes hidden benefits. First, design and test engineers can use each other's code. Second, design engineers can help troubleshoot problems in production, and test engineers can assist design engineers to ensure sufficient-but not excessive-production test coverage during product design.

Choose easy-to-use tools
Software development tools should be easy to use, even for novices or engineers who use the tools infrequently. These latter users should not have to relearn menu choices and other operational details to set up test applications. Ease of use encompasses the "connection" of application software to test-and-measurement hardware. Tools should simplify the configuration of hardware and make it easy for engineers to transfer data to and from data acquisition modules, digital I/O boards, signal generators, and so on. And drivers should shield engineers and users from hardware-implementation details.

Develop reusable modules
Mention reuse of software and most developers think only of standard, proven code they can insert in a program as needed. But software reuse extends farther. Developers interested in maximizing software reuse should use software tools that produce "modules" that can operate in two ways. First, they can run on their own to test a specific function on a device under test (DUT). Second, modules should operate-without modification-within a larger test management program. Not all software tools produce reusable modules of this type.

Employ test management software
Test management software, also known as a test executive, handles system-level tasks, such as powering a DUT, getting the DUT to a specific state, and reporting test results. This overarching test management software controls and "connects" the modules that perform specific tests on the DUT. Separating management and test functions makes it easy to change and reuse individual tests. Combining management and test routines in a single, inflexible program can force software developers to dig through lots of code to gain access to the software for individual tests.

Adapt to new buses
Engineers must keep an eye on new technologies, such as the LAN eXtensions for Instrumentation (LXI) that may make older buses obsolete. By configuring test systems to use the Virtual Instrument System Architecture (VISA) specification and Interchangeable Virtual Instrument (IVI) drivers, developers can insulate themselves-and users-from bus changes. Thus, software can control instruments regardless of the hardware bus that connects them to a host controller. And, in most cases, adhering to IVI-driver and VISA specs means adopting a new bus requires little or no change to application code. Move a DMM from an IEEE 488 bus to an Ethernet cable, for example, and the DMM and the application will continue to operate properly. Thus, engineers can reuse instruments and software even as bus technologies change.

Rely on standard hardware
The use of standard hardware increases the reuse possibilities of test systems. Because vendors have invested a great deal in a broad offering of hardware based on USB, PXI, IEEE 488, and other buses, engineers can count on long-term support. So, as testing needs change, engineers can count on a wide array of instrument and control hardware that will keep their test systems up to date. Reuse involves changing hardware functions instead of building a new test system. The PXI bus, in particular, builds on the Compact PCI-bus spec, so in addition to test instruments, developers can buy PXI motion and vision controllers, and many other special-purpose cards.
Longevity has its limits, though. Because the VXI-bus community focused solely on test applications, the market stayed small. Today, few engineers base new test systems on this bus. But the VXI bus continues to find use in test systems, particularly those employed by the military.

Mix and match test equipment
To maximize the potential for hardware reuse, design a test system that will accommodate a variety of instruments and buses. Then, older-but still useful-instruments can quickly drop into a system. It's easier to use existing test instruments than to get approval for a capital equipment purchase.

Seek multifunction equipment
A test instrument or module that can solve several problems helps designers reuse hardware in new test systems. A switch card, for example, supplies a matrix of contacts. Cards with a fixed matrix adapt poorly to changing test needs. On the other hand, a card that will change its switch configuration under software control can operate as, say, a 4 x 64-switch matrix today, or as a 16x16 matrix tomorrow. Thus, one card provides many switch configurations, which makes it easy to reuse, as test needs change.
Measuring instruments also combine functions so one box or card will measure current, voltage, temperature, inductance, and capacitance, and other quantities, depending on the code that controls it. That capability lets engineers reuse an instrument in a new test system, or they can extend the capabilities of an existing system at no extra cost.