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The lowdown on reigning instrument standards

22 Dec 2015  | Larry Desjardin

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That said, VXI development has slowed considerably. With a large installed base, but few new products, VXI is in a state of suspended animation. PXI gives VXI vendors and system integrators a migration path for the functionality that fits. But what about functionality that can't be downsized to the small PXI format?

That's where AXIe may come in...

4. AXIe: A wild card among the standards
AXIe (ATCA eXtensions for Instrumentation) is the newest of the modular standards. Coined as the "big brother to PXI" in 2009, it has a board area slightly larger than VXI, but with the same PCIe backplane as PXI. At 200 watts/slot, it has been largely targeted at high speed digital and data converter applications. Keysight is the major vendor, and has delivered leading-edge products in this format. With the recent Giga-tronics unveiling of an electronic warfare and radar test system based on AXIe, it has been slowly picking up critical mass for wider adoption.

The latest efforts of the AXIe Consortium focus on low-cost. AXIe-0, the name of a low cost derivative standard, was recently announced, and purports to offer the large board size needed for switching, loads, and custom instrumentation, but at a cost similar to that of PXI. Based on LAN, AXIe-0 modules are actually simple LXI devices, forming an interesting crossroads between the modular world and traditional instruments. It may be just the ticket for VXI vendors looking at migrating large-size assemblies to a modern modular format.

Keysight, Aeroflex, and Guzik have all taken a similar tact: Using AXIe to create solutions based largely from their own products. This eliminates the chicken and egg issue of critical mass of modules and vendors. Giga-tronics was the first to deliver a solution that explicitly relied on other vendors' modules.

I've called AXIe a wild card, as it is impossible to predict its ultimate growth. It is just one or two vendors away from achieving critical mass on its own regards, where modules are mixed and match by end users, much as they are now with PXI. If so, it would further expand the footprint of modular instruments.

But all of these standards require software. That's where IVI comes in...

5. IVI aids instrument programmability
The IVI Foundation is the keeper of all things related to instrument programming. IVI is short for Interchangeable Virtual Instruments, which is quite a mouthful, but it actually supports traditional and modular instruments. For example, VISA, the standard I/O library, supports ASCII and memory-mapped communication. The SCPI standard (Standard Commands for Programmable Instruments) is hosted by IVI, and standardises ASCII commands across instruments for similar functions.

Modular instruments generally rely on memory-mapped read/writes, so SCPI isn't applicable. That's where the IVI drivers come in. At the top they offer a standard driver interface for similar functions. Think of it as similar to SCPI in that regards, but much of the parsing and error checking is done at compile time, decreasing latency. At the bottom, they execute the high-speed memory accesses via the VISA I/O library. These compiled drivers offer the fastest execution speed of any interface method, but with a standardised API. IVI continues to grow supported instrument classes, with the AC power supply class being the most recent.

If you are integrating a test system, chances are you are already using some of these standards.

About the author
Larry Desjardin is President of Modular Methods LLC, a consulting company focused on the rapidly growing modular instrument industry. Larry joined Hewlett Packard (now Agilent Technologies), serving in several R&D and executive management positions. As an R&D Manager, Larry received the John Fluke Sr. Memorial Award in recognition of his contribution to the creation of the VXIbus. Most recently, he was General Manager of Agilent's Modular Product Operation before retiring in 2011. Larry holds a BS Engineering from CalTech, and an MS Electrical Engineering from Stanford University..

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