It is not unusual today to find test systems populated with a variety of technologies¾ GPIB, VXI, and PCI. Each technology provides unique capabilities to address the overall requirements of a system. GPIB offers performance not available in the others, VXI has its modularity, and PCI is lower cost.
Test-system developers mix and match these technologies to come up with a system that has just the right performance at the lowest possible cost. It might include three or four GPIB instruments, a couple of 13-slot VXI crates, and some PCI cards. Whatever the configuration, the system is under the direction of the test program.
The test program is written around the specific instruments, modules, and cards that make up the system. But what happens if you have to change out one instrument for another? More than likely, the test program will have to be modified in some way to accommodate the new instrument.
Or worse yet, what if you wanted to replace a GPIB instrument with a VXI module? The test source code would have to be changed and the program recompiled. This effort could be time-consuming and costly.
To combat this loss of time and money, National Instruments has developed the IVI Driver Library. The library helps eliminate test-program modifications whenever hardware is replaced in a test system.
Here’s how it works. The library is comprised of instrument driver tools that allow you to develop test programs independent of system hardware. The tools are based on standard instrument programming specifications as defined by the Interchangeable Virtual Instruments (IVI) Foundation.
The IVI standard assigns instruments into classes, such as oscilloscopes, digital multimeters, and function generators. It doesn’t matter if an oscilloscope is a GPIB instrument, a VXI module, or a PCI card—it is included in the oscilloscope class. By defining a generic programming interface for each class, test programs can be written without regard to what hardware is in the system.
Included in the IVI Driver Library are standard drivers, simulation drivers, and soft front panels for five classes of instruments. The instrument classes are oscilloscopes, DMMs, arbitrary waveform generators/function generators, switches/multiplexers/matrices, and power supplies.
The class drivers communicate with an instrument through its specific instrument driver. Instruments can be interchanged in a system by just replacing the instrument and its driver. IVI-compatible drivers can be written using the Instrument Driver Development Wizard in LabWindows/CVI 5.0.
Class simulation drivers are also included in the driver library. With these drivers, programmers can develop test programs when the instruments are not available. The simulation drivers are available in source code so they can be customized for a particular application.
The library also includes a soft front panel for each instrument class. This tool can interactively control any IVI-compatible instrument, regardless of vendor, and verify its proper operation.
About IVI
The IVI Foundation is an open consortium of user companies, systems integrators, and an instrument manufacturer working together to define interchangeable instrument drivers for test-system developers. These drivers augment the current VXIplug&play driver standards and the VISA I/O library.
IVI categorizes instruments into classes or types. A class is defined as a collection of instrument attributes and functions and a standard API. Attributes and functions of a particular class are common to all instruments within that class. A class driver written for an oscilloscope, for example, will work with any oscilloscope from any vendor.
Because not all instruments have identical functionality and capability, the IVI instrument class specifications are broken down into fundamental capabilities and extensions. The fundamental capabilities define the attributes and functions that are common to most instruments in the class. The extensions specification handles those functions and attributes that are special to instruments in the class.
Complete interchangeability among all instruments and all vendors would make system developers very happy. We are not there yet; however IVI could be one step in that direction.
Current membership in the IVI Foundation includes Boeing, GEC Marconi Test Systems, GenRad, Lockheed Martin, Lucent Technologies, Marconi North America, National Instruments, Northrop Grumman, and Raytheon TI Systems. The charter document and five interchangeable instrument specification documents are available on the foundation’s web site at www.ivifoundation.org.
Pricing for the IVI Driver Library for Windows NT/98/95 and the Sun Solaris is $1,495. National Instruments, (800) 258-7022.
Copyright 1998 Nelson Publishing Inc.
|
|