I recently spent an afternoon as a guest at General Dynamics Itronix at its new facilities in Spokane, Wash., to learn about the design, materials and testing that produce cop-resistant computers. The specifics in this article pertain to their products only, but the broad strokes are similar for other vendors in this market.
A day spent at most police trade shows will include one or more encounters with so-called ruggedized computers. These devices have been hardened to withstand the abuse that cops, their patrol vehicles and their environment will inflict on them during their service lives. Common hazards in the police setting include dust, moisture, vibration, shock, temperature extremes, the occasional high-speed projectile and that most deadly enemy of patrol car electronics, the Big Gulp Slurpee.
I can never discuss this topic without a nod to a former Northern California police officer, Alec Gagne. In the early days of in-car computers, Alec had devised a homegrown basic mobile data network for his agency. In discussing this and the unexpected problems he had to contend with in designing and maintaining the system, he mentioned what I have since come to call Gagne s First Law: Any horizontal surface in a patrol car, no matter how costly, will be used as a coffee cup holder. For vendors, the lesson here is to never assume your equipment will receive the tender loving care you think is due. Any piece of gear you give to a cop will be beaten like a rented mule, and there s not a thing you can do about it.
My primary guide at Itronix was a mechanical test engineer named Chad Treffry. Chad showed me a wall chart with print modeled on the annual statement of terms and conditions I get from my credit card company. This detailed the various standards that each of their products was held to, depending on its application and customer.
Most of these standards are derived from some portion of MIL-STD 810F, which sets out tests prescribed by the U.S. Army s Developmental Test Command to ensure equipment will function in environmental extremes. The 810F will soon be replaced by MIL-STD 810G, presently in draft form. Treffry had a copy of it. It fills a three-ring binder about 2.5'' thick with both sides of the paper used. According to Treffry, 810G clears up some ambiguous issues of 810F and previous versions by providing the foundation and rationale for most of the test standards.
Many of the test requirements aren t as stringent as they might appear at first examination. For instance, one drop test used at this facility requires 26 drops of the test unit from a height of 30 to 36 inches onto a 2'' thick piece of plywood over a 4'' inch concrete pad. The drops have to vary corners and faces, meaning a unit will be dropped on each of its four corners, all four edges, and both sides in varying combinations, and still work.
This sounds like an extremely rigorous test until you learn that the military standard allows for as many as five units to be used through the drop sequence, and the units may not be operating during the test. So, under this scenario, if a unit broke during the 26-drop sequence, it could be replaced up to four times and would still pass, so long as there was at least one working unit at the end. The idea is to test for resistance to damage, no matter how the computer lands. No one is encouraging you to drop a computer repeatedly just to see what happens.
Treffry advocated that many applications don t require the toughest device available, and to buy technology you don t need is false economy. You can overengineer any component and get something that will survive about any test, but it's probably going to be too heavy and too expensive. By producing components that do what they need to do and no more, you get a more cost-effective product.
Almost everything breaks the first time it s tested, Treffry said. You go back and see what broke, improve the design or materials, and repeat the cycle until you have a product that meets the standard with a safety margin you can live with.
An example of getting an appropriate level of hardiness is in the difference between what some companies label as "semi-rugged" or vehicle-rugged, and fully rugged, Fully rugged devices are typically tested while operating, while the semi-rugged get tested with the power off. A fully rugged computer might have to operate in the open during a downpour, where a vehicle-rugged machine would have the same resistance to vibration, but not to water. The expectation is that a computer intended to operate inside a vehicle won t get rained on, although it may be doused lightly now and again.
The five most critical standards for police computers center on vibration, temperature, screen viewability, drops and moisture. Exposure to drops is mostly determined by the policies and practices at the point of use. Some computers are installed in their car mounts and stay there until they need repair or replacement. Others are taken out of the car regularly, and will occasionally be dropped on the pavement or left on a roof or trunk lid as the car drives off. All car-mounted machines are going to be exposed to nearly continuous vibration, and exposure to rain might come from a cloud or a Styrofoam cup, so you have to be ready for it either way.
Drop, Bump & Crash
For computers built to be vehicle-rugged, drop tests are usually conducted with the power off. The process is drop and boot, drop and boot, Treffry told me. They drop the computer onto the wood-over-concrete surface, using a test stand designed specifically for this, then boot up the machine. If it works, they shut it off and go to the next drop test. Some drops-while-operating are done for design purposes.
Some commercial notebook manufacturers advertise sensors in their computers that detect when the machine is in free-fall and park the hard drive heads before impact so the hard drive is undamaged and no data loss occurs. Writing to the hard drive is the most sensitive process the computer performs. If the machine impacts while the drive is writing data, you ll be fortunate if all you lose is data. You ll probably crash the hard drive, Treffry said.
Unless the fall is a very long one (which would probably destroy the computer on impact anyway), there just isn t any process that will sense the fall and park the drive heads in time to do any good. The same is true of hardened computers, even if their materials and design are drop-resistant. A rugged machine will survive a drop that a commercial one won t, but you ve got to hope that even the rugged device isn t writing to the drive when it hits.
The here it comes! software and hardware that parks the drive can be added by the manufacturer to any computer with the necessary accelerometer sensors, but if the sensitivity is set too high, it will park the drive heads every time the vehicle hits a pothole or goes over a driveway apron, interrupting whatever process was ongoing at the time. The user might see his computer going into paralysis every few minutes, which is likely to produce user-imposed impact damage.
Another process determines if the computer will stay in its dock during a 30-mph impact. There s a shock tower at the Spokane facility, but the final test takes place on a vertical sled in California. The machine has to survive 20 Gs for 120 milliseconds. The difference between pass and fail can hinge on the tiniest of details. One dock mount was failing until a small dovetail joint was machined into a center post.
The survivability of these computers is enhanced by the materials used in them. Polycarbonate is one of the best rigid plastics for casings because of its thermal stability, and many of the metal parts are made of AZ-91, an alloy of 90 percent magnesium, 9 percent aluminum and 1 percent zinc. Some casings are combinations of AZ-91, rubber and thermoplastic elastomer (TPE). The result is a compound that is light, yet highly resistant to shock and fracture.
The soft, flexible port covers that keep dust and moisture out are made of Poron cellular urethane or a silicone rubber. Hard-drive cushions can be shock-absorbing vinyl elastomer, carefully molded to maximize the capacity of the material to soak up kinetic energy. Hinges and other seemingly insignificant parts can put the computer on the disabled list if they fail unexpectedly, so nothing can be regarded as trivial.
Thermal & Moisture Testing
Computers left inside patrol cars will experience oven-like heat and freezing cold, though seldom back-to-back. But back-to-back thermal extremes are exactly what they are exposed to in the electronic torture chambers. One device exposes computers to 140 degrees F and -9 degrees F (five days on the high end, one on the low end), while the machine is running test software the entire time. Any failure display, processor or hard drive and the test is over.
An even nastier box, the Highly Accelerated Life Test, cycles the computers from up to 392 degrees F to -148 degrees F continuously while the computers are constantly shaken with forces between up to +125 and -125 Gs in six different axes. The thermal shock rate (the change between temperature extremes) is 212 degrees F per minute, helped along with some liquid nitrogen, and the machines are tested to failure. A typical test duration is two to three months.
Another oven-like test box exposes the computers to temperature and humidity extremes. Constant humidity levels are difficult to maintain with temperature changes because humidity is a function of temperature, but the test environment is kept very close to 95 percent humidity during the entire test cycle. The environment is varied between 140 degrees F and 86 degrees F every 48 hours, with eight hours at the high end and 36 hours at the low. This test runs for 10 days while the computers run test software the entire time.
Treffry invited me to stick my hand through an access port in the side of this test chamber while it was running at the high end of the temperature range. It felt like the muggiest, most miserable day imaginable.
Water resistance is harder to test. Few computers are designed to run while immersed in water (for those that are, see the comments above on overengineering), but without subjecting them to that, it s difficult to know where moisture will seep in. MIL-STD 810 requires that water used in spray testing be at least 50 degrees F colder than the computer. When the water hits it, the air in the computer s interior cools and contracts, creating a partial vacuum. This draws air and more moisture inside, challenging the engineers efforts to keep water out.
Vehicle-rugged computers aren t normally tested with water sprays. The fully-rugged machines that are tested get hit with sprays that vary in intensity from a kitchen faucet to a small fire hose. The spray times can range from an hour to five minutes, with the shorter test times getting the heavier sprays.
One of the more recent additions to the testing suite at General Dynamics Itronix is a huge vibration table. The test device gets its own soundproof room, with warning signs about hearing protection posted all around. The vibration table doesn t have the deflection range of the other impact tests, but has more amplitude and a broader test range from 2000 Hz Treffry told me. The table vibrates so fast that whatever is mounted on it becomes a blur. It has three axes of movement (back-and-forth, side-to-side, and up-and-down), although only one at a time.
For specific applications, it s possible to use a recorder equipped with multiple accelerometers to precisely duplicate the stresses a device might experience while mounted in a vehicle operating on a test course. Once those recordings are available, the vibration table can, in essence, play back that same vibration pattern for as long as the test engineer deems necessary.
Displays on ruggedized computers present a special problem: They not only have to be tough, but extra-bright to remain visible in outdoor daylight. Shock mounting is critical, as is stiffening of the casing so the display can t be flexed and broken. Many displays are touch screen-enabled, so the surface material must withstand repeated presses, often in the same spot where a software button appears.
Some manufacturers improve their daylight visibility by overdriving the backlights of the displays, heating them up, reducing their service life, and drawing down the battery. A more reliable method is to use cooler, lower-voltage LED illumination and multi-layer technology to improve light transmission through the display.
The Bottom Line
No one will build the computer that can t be broken, and even if they could, you could neither afford nor lift it. But by doing a proper needs assessment to see just how much and what kind of special protection you need for the devices you re deploying, you can save money and get the degree of ruggedness necessary and no more.