5 Myths of Modular Instruments

Keysight Technologies

Five Myths of Modular Instruments

Article Reprint

NP Communications grants Keysight Technologies permission to distribute the article “Five Myths of Modular Instruments” posted July 15, 2014, in the Web Exclusives section of the EE-Evaluation Engineering website.

Five Myths of Modular Instruments

by Tom Lillig, Agilent Technologies*

July 15, 2014

As modular test equipment continues to grow in popularity, so have the abundance of myths surrounding the advantages and disadvantages of modular compared to traditional “box” instruments (Figure 1 and Figure 2, respectively).

Myths are often quite fantastic, yet within each myth reality and fiction tend to co-exist. Myths originate to explain complex things in a simpler way, using familiar language and well-understood concepts. Choosing the best test and measurement gear for your application is also a complex thing, so we shouldn’t be surprised that myths have formed as a way to simplify the choice. Agilent has been developing box instruments for over 75 years and modular instruments for over 30 years, and we proudly offer the best of both. Because we know that choosing between the two can be difficult, we thought it would be a good idea to sort the facts from the fiction, to help you make a choice that’s ideal for your application. So, let take a look at some of the myths that have developed and set the record straight.

Myth #1: Modular instruments are inherently less expensive than box instruments.

This myth exists because when you see a box instrument, it looks expensive. You see a complete, self-contained instrument with buttons and a front-panel display, which may be critical in some R&D environments (Figure 3), but are unnecessary overhead in most automated test environments. The expensive elements of modular instruments are more hidden, giving the impression that they may be inherently less expensive. For example, a modern PXI backplane supports 4 GB/s to 18 slots. This adds to the cost in the form of expensive connectors, switches, and backplane material (Figure 4). A chassis that is fully loaded with instruments that all need high-bandwidth connections will fully leverage these costs while providing additional flexibility—thereby resulting in lower costs over its lifetime. But for other applications, these costs are unnecessary overhead. As a result, a PXI system with a single instrument can be 10 to 40% more costly than the same “box” instrument.

Regarding Figures 3 and 4, which one looks more expensive? And where is the truth in myth #1?

While box instruments may be less expensive as a standalone item, modular solutions are typically less expensive when multiple instruments are combined into a single chassis. This is due to the fact that the overhead costs can be spread across several instruments. Typically, the break-over point happens with 2-4 instruments in a chassis.

Furthermore, there is a difference between the cost to manufacture the instruments and the price the user pays. Several vendors are entering test and measurement markets with modular approaches. As a way to gain market traction, some of them are willing to lower their price below the market price, eliminating a profit margin, in order to gain share. Of course, this is not sustainable over the long-run.

Myth #2: Modular is inherently able to offer higher throughput.

This myth probably arose because modular systems often have fast backplanes. In reality, the choice of backplane used in a box or modular instrument solution comes down to the need to balance cost and required capabilities for the intended usage. In other words there is no inherent reason why a modular instrument needs to have a faster backplane than a box instrument. The decision is purpose driven. For example, with a box instrument, it is easier to connect the acquisition part of the instrument to the computing part of the instrument with a high-bandwidth backplane, because only a point-to-point connection is needed.