Evaluation Engineering - December 2008 - (Page 16)

TEST SOFTWARE models, but let’s assume a typical testsystem consists of three interdependent components: the hardware computer, the software, and the instrument or device, as shown in Figure 1. Interfacing technologies exist between these hardware and software components to integrate them as a system. The purpose of this test system is to characterize, validate, and compare both parametric and functional capabilities of a UUT to a known standard. When a UUT must last for 25 years, the test program sets (TPSs) written in software components need to evolve to match upgrades in the UUT. Often the test hardware or the software becomes obsolete and needs to be updated as well. Standardized interfaces between these components and the UUT can help manage change throughout the test system. To use an IVI driver, you must write a program using a software programming language such as C#, C++, C, Visual Basic .NET, Visual Basic, MATLAB, LabVIEW, LabWindows/CVI, or VEE Pro to access various function calls of the instrument or device of interest. A test executive typically sequences this program and other similar programs as a TPS. Math algorithms also manipulate the data. Normally, IVI drivers sit on top of another software I/O interface called Virtual Instrument Software Architecture (VISA). The two main versions of VISA are NI-VISA from National Instruments or Agilent’s VISA. There are two IVI driver standards: IVI-C and IVI-COM. These replaced the previous VXI plug-and-play driver standards. In addition, there are programming language-speciﬁc drivers that enable an easy-to-use experience native to each respective language. The LXI instrument protocol was invented in 2005, and the test and measurement-speciﬁc VXI-11 protocol over TCP/IP was developed in the early 1990s based on the Ethernet/LAN bus that has been around since 1969. Both the PXI backplane and LXI bus standards are used for the creation of SIs today. Figure 2. Expanded System SIs Block Diagram With IVI Drivers Emerging Standards Standard software I/O interfaces for SIs are just emerging. For example, the U.S Navy is taking the lead for DoD since it has a large quantity of test stations with the strictest requirements for space. Accordingly, the original goals for moving in the direction of SIs were to reduce the total cost of ownership, the time to develop and ﬁeld new or upgraded automated test systems (ATS), and the overall footprint and provide greater flexibility through interoperable ATSs. Now in 2008, these goals have further played out as both onshore and afloat CASS test stations using approximately 1,300 TPSs for automated avionics/electronics testing are approaching the end of their useful service life. In addition, a recent Request For Information by the Naval Air Systems Command describes the goals for replacing existing CASS test stations with a next-generation test station solution called electronic CASS or eCASS.2 These systems need to emulate existing functionality as well as take advantage of new capabilities, use standardized interfaces, and be ﬂexible enough to resolve obsolescence issues that appear in the future. The IEEE ATML Group incorporated the SIWG’s charter and research into the Instrument Description Stand- ard P1671.2, which now is in the IEEE balloting process. 3 This will be the standard for Exchanging Automatic Test Equipment and Test Information via XML. It is much broader than SIs and intended to provide one overall description language for all instruments, including VME, VXI, GPIB, LAN, LXI, PCI, cPCI, PXI, RS-232, and USB. This allows for interoperability and the exchange of ATML-defined components. The IVI Foundation approved charters for two SI IVI driver working groups about a year ago. One group is developing the SI digitizer and SI waveform generator driver speciﬁcation. The other group is addressing the SI up-converter and SI down-converter speciﬁcation. Prototyping will be followed by an IVI Foundation review before the SI interfaces become ofﬁcial. Types of SIs and Related IVI Drivers Let’s walk through each SI instrument and the IVI driver that is likely to emerge to support it. Figure 2 shows that the SI digitizer converts analog data to digital data through sampling and can acquire time-varying voltage waveforms. Typical functionality includes setting the channel, the acquisition, and the triggering subsystems when configuring a waveform for 1 6 • E E • December 2008 www.e v al u a ti o n e n g i n e e r i n g . c o m http://www.evaluationengineering.com

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Evaluation Engineering - December 2008 Contents Editorial Product Briefing Test Software C-V Measurements Nanoelectronics Test Product Guide Company Guide Machine Vision EMC Test Index of Advertisers

Evaluation Engineering - December 2008

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