Environmental testing is a highly specialized industry, which means the engineers and technicians who perform them need specialized training. Environmental tests are performed on prototypes of electronic and other hardware that must operate reliably in spite of severe usage environments. Consider extremes of temperature, altitude (including space), Arctic cold, pressure (as in deep underwater), humidity (as in jungles), sand and dust (as in a desert). These often are grouped as climatic environments, with tests performed in various sizes of climatic chambers. For one example, temperature extremes are found in chambers that might be compared to the household oven and refrigerator. Probably the largest, at Eglin AFB in Florida, will accommodate an entire airplane.
Consider also extremes of vibration, intense noise, and mechanical shock (as occur in missile launch and explosive stage separation, as well as on military and other vehicles operating off-road). These are often grouped as dynamic environments. Vibration tests are performed on shakers, sources of controllable vibration that can mimic land vehicle vibration caused by the vehicle itself (engine and drive train) and by the road or off-road terrain. Or mimic shipboard vibrations. Or mimic helicopter and fixed wing aircraft, UAV, and rocket liftoff and in-flight vibrations.
Environmental test laboratories are maintained by all three U.S. military services and their counterparts abroad, by NASA, and by manufacturers of high-reliability equipment. Alternately, many manufacturers go “outside” to commercial environmental testing labs.
A Form of Insurance
These important but little-known laboratory tests can be thought of as insurance against failure in service, where equipment failure can doom a mission or cost lives. So we perform
climatic tests in chambers (temperature, altitude, pressure, humidity) and dynamic tests on shakers, shock test machines, and intense noise chambers. We sometimes meet testing standards, such as Military Standard 810G and overseas equivalents.
When it comes to testing, laboratory failures are useful and even desirable. Lab technician Bill may be a bit surprised, after an unexpected end to, say, a vibration test, when supervisor Ed claps him on the shoulder and says “Good for you, Bill. You broke it.”
Ed is happy. His lab is doing its job, causing failures to occur in the laboratory where analysts can determine the root cause. Redesign or a production change may be indicated. Then the lab can retest the hardware. Further redesign may be needed. Or further production changes. Eventually, the product passes the test. It has survived all the required environmental tests. “High fives” all around.
Consider Benefits of Additional Testing
Are we finished in the lab? Many people would say, “Yes. We’re assured of the contract. Let’s close the lab and go home for the weekend.”
But I urge you to consider a little more testing at almost zero additional cost, since the DUT is already mounted on the shaker (or in the chamber) with all instrumentation in place. Let’s find out what our margins are. Let’s increase test time by 10 percent. Let’s increase bandwidth by 10 percent. Let’s increase intensity 10 percent. Let’s go 10 degrees hotter. Let’s go 10 degrees colder.
Knowing that out product can survive longer, over a wider frequency range, with greater intensity, hotter, colder, our product can command a higher price. It can be sold for use in even more severe environmental locations.
Specialized Training Needed
Military service, manufacturer, and laboratory training directors often face a laboratory staffing problem: When they hire newly graduated mechanical and electrical engineers for these laboratories, they often must provide them with specialized training. Why? Because environmental testing rarely is taught in universities.
When questioned, a recently graduated and hired mechanical engineer may say, “Yes, in my last year, I signed up for a course that was labeled ‘Vibration,’ but it was really an advanced math course. Nothing practical, nothing that might assist me in performing my present job. Why, until I came here, I’d never seen (nor heard of) a shaker or a climatic chamber.”
Can They Learn From Their Peers?
Sometimes supervisors and coworkers can assist the neophyte. But don’t count on it. Supervisors and coworkers may not have time or talent to teach. The neophyte may be reluctant to expose his ignorance. Outside formal training is usually best.
Wayne Tustin has been teaching about vibration testing since 1960. The president of Equipment Reliability Institute (ERI), he’s coauthored several texts and soon will publish through Apple Bookstore a series of 33 iBooks dealing with vibration and shock basics, measurement, analysis, calibration and testing. For more information, visit www.equipment-reliability.com.
