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August 15, 2018

Why ruggedness testing matters

Ruggedized mobile computing gear costs more than standard consumer technology, but in the long run it often costs less. That’s because rugged computers don’t break down as often, they last longer, and there isn’t as much downtime. What that means is that despite the higher initial purchase price, the total cost of ownership of rugged equipment is often lower.

That, however, only works if ruggedized products indeed don’t break down as often, indeed last longer, and indeed do not cause as much downtime. Ruggedness, therefore, isn’t just a physical thing. It’s an inherent value, an implied promise of quality and durability. And that makes ruggedness testing so important.

Interestingly, ruggedness testing is entirely voluntary. While computers must pass stringent electrical testing before they can be sold, ruggedness testing isn’t officially required anywhere. It isn’t regulated. Electrical testing makes sure a computer adheres to standards, will not interfere with other equipment, and meet a wide range of other requirements. Why not ruggedness?

It’s probably because electric interference can affect third party equipment and systems, and possibly do harm, whereas ruggedness “only” affects the customer. And it’s also because unlike electrical interference standards that are absolutes, the degree of ruggedness required depends on the intended application. In that sense, the situation is similar to the automotive field where there are strict governmental testing requirements for safety and emissions (which affect third parties) but not for performance, comfort or handling (which only affect the customer).

Given the voluntary nature of ruggedness testing, how should it be conducted, and how relevant are the results of that testing?

For the most parts, testing is performed as described in the United States Department of Defense’s “Environmental Engineering Considerations and Laboratory Tests,” commonly known as MIL-STD-810G. In some areas, testing is done in accordance with a variety of different standards, such as IEC (International Electrotechnical Commission), ANSI/ISA and others. By far the most often mentioned is the MIL-STD-810G.

So what, exactly, is the MIL-STD-810G? As far as its scope and purpose go, the document says, “This standard contains materiel acquisition program planning and engineering direction for considering the influences that environmental stresses have on materiel throughout all phases of its service life.” Minimizing the impact of environmental stresses, of course, is the very purpose of rugged design, so using the MIL-STD-810G as a guide to accomplish and test that makes sense.

How does the MIL-STD-810G go about its mission? In the document’s foreword, it says that the emphasis is on “tailoring a materiel item's environmental design and test limits to the conditions that the specific materiel will experience throughout its service life, and establishing laboratory test methods that replicate the effects of environments on materiel, rather than trying to reproduce the environments themselves.”

The MIL-STD-810G is huge and often very technical, as you’d expect from a document whose purpose is to provide testing for everything that may be used by the US Department of Defense. The operative term, therefore, is “tailoring.” Tailoring the tests to fit the conditions a specific item or device may encounter through its service life. That means it’s up to manufacturers to knowledgeably pick and choose the tests to be performed.

It also means that simply claiming “MIL-STD-810G approved” or MIL-STD-810G certified” or even “designed in accordance with MIL-STD-810G” means absolutely nothing. Not even “passed MIL-STD-810G testing” means anything unless accompanied by an exact description what testing was performed, to what limits or under what conditions.

So how do we go about ruggedness testing that truly matters? First by determining, as the MIL-STD-810G suggests, the conditions that a specific device will experience in its service life. Let’s think what could happen to a rugged handheld computer.

It could get dropped. It could get wet. It could get rattled around. It could be exposed to saltwater. It could get crushed. It could be used in very hot or very cold weather. It could get scratched. It could be used where air pressure is different.

That’s the important stuff. There may be other environmental conditions, but for the most part, this is what might happen to a handheld. And it must be able to handle those conditions and events while remaining functional.

It’s instantly obvious that it’s all a matter of degree. From what height can it fall and survive? How much water can it handle until it leaks? How much crunching force before it cracks? How hot or cold can it be for the device to still work? How much vibration before things break loose? And so on. It’s always a matter of degree.

So how does one determine the degree of ruggedness required? Deciding that requires thinking through possible use scenarios and then, applying common sense, arrive at the appropriate level of protection. Too little and it may break, which is bad for both the customer and the reputation of the manufacturer. Too much and it may become too bulky, heavy and expensive.

Ruggedness is a compromise. Nothing is completely invulnerable, freak accidents can and will happen, and figuring out how rugged is rugged enough is an educated judgement call, one based on knowledge and experience. Facilitating the desired degree of ruggedness is an act of balance and good design. And that, again, requires experience.

So how might one go about determining the proper degree of ruggedness? Here are some of the considerations:

A handheld computer will get dropped. It’s just a matter of time. What’s the height it may get dropped from? I am six feet tall. When I stand and use a handheld, the device is about 54 inches above ground, 4-1/2 feet. If it falls out of my hands while I use it, it’ll fall 4-1/2 feet to whatever surface I am standing on. That could be grass or a trail with pebbles and rocks on it, or anything between. And a user may be taller or shorter than I am. So one might conclude that if the device can reliably survive repeated falls from 5 feet to a reasonably unforgiving surface, such as concrete, we’d be safe. The device could, of course, fall so that its display hits a pointy rock. Or it could slip out of your hands while you’re standing on a ladder. But those are exceptions.

So now we check the MIL-STD-810G on how to conduct a test where a device is dropped from five feet to concrete, and, surprise, there is such a test. If the device passes that test, described in Method 516.6, Procedure IV, all is (reasonably) well.

But do consider that MIL-STD-810G Method 516.6 alone consists of 60 pages of math, physics, statistics, graphs, rules, descriptions, suggestions and rather technical language. Simply claiming “MIL-STD-810G” is not nearly enough. The device specs must describe the summary result, and supporting documentation should describe the reasoning, specifics, and sign-offs.

Now let’s look at another example. Sealing. How well can a device keep liquids from getting inside (which is almost always fatal to electronics)? Since rugged handhelds are used outdoors, they obviously must be able to handle rain. But that’s not enough. Working around water means that eventually it will fall into water. What degree of protection is reasonable? Given that most consumer phones are now considered waterproof, rugged handhelds should be as well. The question then becomes what degree of immersion the device can handle, and for how long.

Here again, much is common sense. No one expects a device to fall off a boat into a deep lake and survive that. But if it falls into a puddle or a shallow stream, it should be able to handle that. The most often used measure of sealing performance is IEC standard 60529, the IP Code. IP67, for example, means a device is totally sealed against dust, and can also survive full immersion to about three feet. Unfortunately, the IP rating is imperfect. Several liquid protection levels are qualified with a “limited ingress permitted.” Electronics cannot handle any degree of ingress. Amount of liquid, pressure of liquid, and time of exposure all matter. And what happens if a protective plug is not seated properly? So here again, specs should include the summary, with the exact testing procedure in supporting documentation.

I will not go through every single environmental threat, as the approach is always the same: What is the device likely to encounter? How is it protected against that threat? How was resistance tested? Who tested it? And what was the result?

Ruggedness testing is about common sense. If it is likely that a device will be used in an unpressurized aircraft, how high will that aircraft fly? Determine that and then test operation under that pressure.

If a device is likely to be used in very cold or very hot climates or conditions, determine how hot and cold it might get, then test whether it will work at those temperatures, for how long, and without an unreasonable drop in performance.

Test procedures for most environmental conditions can be found in the MIL-STD-810G or some other pertaining standards. I say “most” because some are not included. For example, I’ve often wondered why some rugged devices use shiny, gleaming materials that are certain to get scratched and dented on first impact. It will not affect performance, but no one likes their costly rugged device to be all scratched up after a week on the job. Scratch and dent resistance should be part of ruggedness testing.

The big picture is that serious, documented ruggedness testing, based on common sense and tailored for the device and application at hand, matters. The ability to hold up on the job is what sets rugged handhelds apart. Testing that ability is an integral part of the product, one that benefits vendors and customers alike. -- Conrad H. Blickenstorfer, Ph.D., RuggedPCReview.com

Posted by conradb212 at 7:18 PM