Simplifying the Modular Puzzle

The task of configuring and building a PXI, VXI, or AXIe test system can seem complex. While building a modular system is seldom as straightforward as building a system from boxes, it is very satisfying to build a system that exactly fits your needs. Here are a few tips to help simplify the process.

Tip 1: Use modular instruments where they make sense for your application. Modular systems work best in highly automated environments and may be difficult to use in semi-automated environments where interactive debugging is critical. In automated environments, consider the match of the instrument to the architecture. Power supplies don’t work well in modular formats and should be considered only in the most limited of circumstances.

Tip 2: If in doubt, choose a larger chassis and go hybrid for flexibility. Each of the three major modular architectures offers different size mainframes. PXI also has two variants: PXI and PXI Express. Newer PXI chassis contain hybrid slots to accept either format.

As you are adding up all the modules, counting slots, power budgets, and card types, consider simplifying by upsizing. Many of the smaller mainframes have limited power supplies (and cooling). The larger PXI mainframes have more flexibility in accepting both PXI and PXI Express card types. A larger mainframe eliminates the power calculations and may provide a few extra slots when you are reconfiguring your test system on the next project.

Tip 3: Bundle instruments when appropriate. The major modular vendors have begun bundling modules together to make virtual instruments. This can be any number of preconfigured devices including switch matrices, vector signal analyzers, arbitrary waveform generators, and vector signal generators. There are several benefits from these bundles including a single driver and front panel. Bundles are known to work together and can be calibrated as a unit. Connections between the modules of the bundle usually are provided as well.

Tip 4: Use modules with a universal driver type. Having a universal driver type will significantly speed and simplify your software programming efforts and give you the most flexibility. The most universal driver type today is the IVI driver. IVI-C or IVI-COM drivers work with virtually any programming language and will give you a consistent programming interface. A vendor that does not provide a universal driver should be eliminated from consideration.

A standard dynamic link library (DLL) is not sufficient to ensure smooth programming in modern system development. Most vendors have a driver library on the web where you can check to see what they provide.

Tip 5: Assemble your chassis in stages. While this may seem like a slow process, I recommend you assemble your system one or two modules at a time, especially when integrating modules from different vendors. It can be very confusing to assemble a chassis with five or six modules because Windows will try to find the drivers for all of them simultaneously.

While you should have all the driver software in place and ready to go, I prefer a much simpler approach of booting up a couple of modules at a time, loading their drivers and soft front panels, then verifying operation before proceeding to the next modules. Of course, this means you will be watching Windows boot messages after each step.

I’m sure there are plenty of other tricks for successfully assembling a modular system. I hope these help you when you begin.

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