Five Things to Consider When Selecting an IVI Driver
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Instrument drivers eliminate the need to learn low-level instrument commands by providing a high-level interface for instrument programming. Interchangeable Virtual Instrument (IVI) drivers are sophisticated and specifically designed to improve performance and flexibility in your test systems. However, it is important to note that not all IVI drivers are created equal, so bear in mind the following five criteria when selecting your next driver.
Usability in Your Application Development Environment (ADE)
There are two types of IVI drivers: IVI-C based on the ANSI C standard and IVI-COM based on the Microsoft Component Object Model (COM) technology. With two driver options, it is best to choose the one that delivers the best experience for your ADE. IVI-C offers native support for the C programming language and, through the use of language-specific wrappers, provides first-class support for NI LabVIEW and Microsoft Visual Studio .NET programming languages. IVI-COM, best used in Visual Basic 6.0, delivers secondary support for LabVIEW through ActiveX automation and Visual Studio .NET using interoperability assemblies. To address the needs of those programming in .NET languages, the IVI Foundation is actively working on a new IVI .NET standard.
Source Code Availability
IVI drivers are not always perfect, and in some cases you may want to add functionality or tweak performance. If source code is provided, you can make the changes yourself without having to wait for an update from the instrument vendor.
Usability in IVI-Based Software Products
While many of the IVI capabilities are meant for high-end test systems, the development of these drivers has led to the creation of interactive tools such as NI LabVIEW SignalExpress and NI Switch Executive that further simplify instrument control. With the interchangeability of IVI, these tools can provide a single point-and-click interface that works with multiple instruments, regardless of manufacturer. To take advantage of these tools, look for IVI-C drivers that conform to the scope, DMM, function generator, switch, or power supply classes.
Consistent API Design
IVI drivers provide both a generic instrument class and an instrument-specific interface for programming. To ensure consistency, the IVI specification states that the instrument-specific interface should be consistent with the class-compliant capabilities whenever possible. However, in many IVI-COM drivers this is not followed. With two ways to program an instrument with the same driver, you may end up writing code that prevents instrument interchangeability. To facilitate interchangeability, request that the driver-specific interface conforms to the class specifications.
Full Implementation of the IVI Standard
State caching and range checking are two key features that enable the advanced performance and reliability in IVI drivers; however, they are not required for a driver to be IVI certified. Confirm with your driver provider that these features are implemented to ensure the best system performance.
Download IVI drivers for your instruments.
This article first appeared in the Q4 2007 issue of Instrumentation Newsletter.
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