PXI turns 20: How long do standards last?

-March 07, 2017

Twenty years ago this year, National Instruments announced PXI, PCI eXtensions for Instrumentation. The following year the PXISA (PXI Systems Alliance) was formed to manage the specification. Today, PXI represents a $700M market, growing at or near double-digit rates. How long do standards last?

If we are asking about test and measurement standards, the answer is a very long time.  The figure below outlines the major standards that dominate test and measurement.

Figure 1 These major standards dominate the test and measurement industry.

Figure 1 shows that GP-IB was announced in 1972, and is still being deployed in today’s test systems. Certainly LXI and USB have encroached into its space, and GP-IB is declining in size, but it still exists.

VXI was announced in 1987. As with GP-IB, it has taken a hit in market share from its more recent brethren, PXI and AXIe, but anyone who has walked the floor of Autotestcon will know that VXI still has a major role in mil/aero maintenance systems.

The SCPI (Standard Commands for Programmable Instrumentation) standard was announced in 1990, and is the mainstay of traditional instrument programming today, whether over GP-IB, LAN, or USB.  That’s 27 years.

AXIe, the new kid on the block, is nearly eight years old. It is growing handsomely, but that could be expected from a relatively new standard.

Why such long lifetimes? Especially in the light of shorter and shorter consumer electronic lifetimes.  The answer is threefold.

1.    Test and measurement has naturally long lifetimes.  The lifetimes of test instrumentation is naturally longer than those in the electronic industry it serves. For the most part, test and measurement is a derivative industry to the entire electronic manufacturing industry.  As such, the investments and product replacements must be less frequent than the primary market. Coupled with that is the fact that many pieces of test equipment are deployed in systems that last many years. If you consider mil/aero maintenance systems, they need to last the lifetimes of the vehicles and systems they support, which can be decades. This is certainly the reason behind the staying power of VXI, and will have a similar longevity effect on PXI.

2.    Standards last longer than products.  We know this from real life. How long has the AC power outlet been around? Since the 19th century. There’s a synergy between products and standards that stretches the lifetimes of standards. There are so many products deployed to a given standard at any given time, that when a replacement product needs to be defined, the existing standard has a high priority. Besides, many of the standards are not dependent on a certain technology from a certain point in time. Take the SCPI standard, for example. It defines numerous English-like commands that are sent as ASCII characters to an instrument. At the time of introduction, a popular instrument processor for interpreting SCPI was the Motorola 68000. Now there are Intel processors that are a hundred times faster. Why change SCPI? English technical terms are the same. ASCII is the same. The instruments are just faster. Being a properly layered standard, SCPI works just fine over modern interfaces, such as LXI or USB. Expect SCPI to be around for a long time.

Figure 2 The ability to support older PCI-based cards, as well as each speed increase with PCI Express, positions PXI for continued growth. Source: National Instruments

3.    Specific to PXI- it’s hardly the same standard. The original PXI specification relied on the original parallel PCI bus, essentially a 33 MHz 32-bit wide bus. In the early 2000s, serial technology was proving to be much faster than parallel clocked systems, and PCIe (PCI Express) was born. In 2005, the PXISA published the first PXI Express specification that incorporated PCIe. Borrowing a trick deployed in CompactPCI, it defined a hybrid slot that could accept the older cards as well as the newer ones. But by transitioning to PCIe, something else happened: the speed upgrades came automatically without updating the specification. While the original PCIe was “Gen 1”, at 2.5 GT/sec, PCIe brought an autonegotiation protocol that allowed speed upgrades to occur automatically. If any of the devices operated at the lower Gen 1 speed, that would be the speed for that link. However, if all the devices could operate at Gen 2, the speed of that specific link would upgrade to Gen 2. Each successive generation of PCIe doubled the speed. A device could also choose the width of the link, from one lane (x1) to eight (x8). In the past year two vendors have announced PCIe Gen 3 PXI chassis, and the industry is pursuing PCIe Gen 4. Essentially, PXI can upgrade itself by following the PCIe speed curve.

4.    Keysight Technologies joining National Instruments to offer PXI gave PXI a boost.  Did I say three reasons? There was a forth reason – Keysight, which was Agilent Technologies at the time, joined PXI in a big way in 2010. Standards are dependent on critical mass. This is not to say that NI wouldn’t be pursuing PXI just as vigorously today without Keysight; they most certainly would be. But having a second major vendor added a degree of confidence in the standard, and the competition has been nothing but upside to the users and system integrators.

These factors aligned to make PXI a healthy growing standard 20 years after its inception. PXI is predicted to continue its above market average growth for the next several years, as 5G communications becomes a reality. The needs of 5G match the capabilities of PXI- a high bandwidth low latency system with the modularity to match the multi-channel nature of 5G. Toss in the continual speed upgrades and the large installed base, and you can expect PXI to thrive for the foreseeable future.

PXI at 30, anyone?

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