At the beginning of the electronics age early in the 20th century, the paradigm of the box form factor for measuring instrumentation was born. Based on the technology, functionality and use models at the time there was really no alternative. With controls and displays on the front panel, a box instrument could be placed on a bench top or easily stacked and bolted into a rack (hence the term “rack ‘n’ stack”).
The need for repeatability and efficiency brought about the demand for automation. Hewlett-Packard initially entered the computer business solely to enable automated control of their test equipment and to provide post-processing of test data. Communication between the computer controller and the instrument was facilitated by the introduction of the General Purpose Instrument Bus (GPIB — originally HPIB or Hewlett-Packard Instrument Bus) and later with universal serial bus (USB) and by Ethernet LAN connectivity — which developed into standardized LAN extensions for Instruments (LXI)
Over the last 20 years, many different types of software applications have evolved to help relieve the test engineer from spending huge blocks of time writing code. Today, software products exist to create waveforms, analyze vector signals and make highly accurate measurements using advanced methodologies. These software tools can be integrated into a larger automated test environment and many instruments are now PC-based so the applications can now run directly on the instrument. These applications also provide a user interface separate from the instrument which supports more flexibility and detail.
With the ability to remotely control instruments and display data it became clear that the box instrument would be one of several form factors, based upon the use model. When modular instruments entered the market they addressed the use models that included higher speed data bus, smaller size, flexibility in configuration, and a lower overall cost of test.
With modular instruments, such as the PXI form factor, data transfer rates can be very fast, providing benefits in speed of test and data transfer. This is due to the PCI and PCI Express (enabling peer to peer communications) bus performance. The smaller size benefits in reducing rack space and making deployment in confined spaces such as on ships, submarines and aircraft much easier. Mixing and matching of modules of different function and from different vendors plus the ability to easily reconfigure test systems means improved flexibility. Costs often are lower as well which can include initial expenditure, test development, service and support. The evolution of instrumentation bus architectures is shown in Figure 1.
The next big thing to come along in modular instrumentation is the introduction of products using the new open standard AdvancedTCA Extensions for Instrumentation and Test (AXIe®). AXIe shares the same fast PCIe bus interface but has six times the cooling and board area for high power modular instruments. AXIe will open the door to many new modular products including microwave sources and analyzers.
So what else does the future hold for test instrumentation? Naturally, basic performance will continue to improve with advances in lower noise, higher power and better accuracy. The cost of test will be steadily driven lower, particularly in non-military commercial applications. Eventually, we may arrive at integrating test instrumentation into operational equipment on a much wider scale than we see today. Built-in-Test (BIT) would require low cost board level instruments eliminating the need for test systems and providing the ability to remotely troubleshoot failures to the board, if not device, level using sophisticated de-embedding techniques. We shall see.
John S. Hansen, Agilent Technologies