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Equipment Reliability
Institute |
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Does your test lab use ED or electrodynamic shakers? Three pictures here might illustrate a bad dream ..... overloaded driver coils. Can these shakers be saved? Yes, but each will take time and cost money to obtain repairs as in the fourth picture. All are courtesy of an old friend, Andy Grimaldi, www.acgdynamics.com, (203) 933-8000. I'm sure you don't want to damage your shaker. So read my article, "How can we get more PSD?". Don't blindly push more electrical power into your shaker, striving for greater force.
Here is a question for you to consider... "What can designer A learn from his vibration and shock testing?" collectively written by ERI's vibration and shock teachers. As long as you are paying for a test, maximize the benefit you obtain. Then I ask "Would you attend a “virtual” class?". We'd like your comments on this question. Finally, contributor Robert L. Renz of General Dynamics at Bloomington, Minnesota offers us four more of his "Test Lab Musings". Thanks, Robert. Will additional readers please offer their thoughts to our readers? Best wishes, |
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| How
can we get more PSD? Is there any way we can “beat”
Isaac Newton’s Second Law, that tells us that
Why do we need more A? A is usually stated as RMS g or the statistician’s standard deviation s (sigma), the square root of the mean square acceleration g2, which is calculated by multiplying required PSD (power spectral density, also known as ASD, autospectral density as well as acceleration spectral density) in g2/Hz times bandwidth in hertz. Our customer is demanding higher values of g2/H than we can “legally” achieve, based upon the published force rating for our shaker. Can we briefly increase F? Can we improve cooling? If we could more rapidly extract heat, burnout would be delayed. If our shaker were liquid cooled, we could probably quadruple applied power, thus doubling F and doubling the available PSD. If the liquid were chilled beforehand, we could further increase power and PSD. With the more common air-cooled shaker, we could blow refrigerated air into our shaker, somewhat increasing F and available PSD over where we commenced. Can we decrease M?
Can we possibly replace our shaker’s armature, quite likely cast from K1A (mostly magnesium) with a welded armature, saving a few ounces? Or could we use beryllium (unfortunately toxic)? Or a composite? What about the fixture? Might a design modification or another material save a few ounces? What about the device under test or DUT? Might a design modification or another material save a few ounces? Can we decrease A? Wayne Tustin, ERI's president, can be reached by e-mail or phone (805) 564-1260. Read more about Wayne at ERI's website. |
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| What
can designer A learn from his He can learn a great deal. Long before the test, even before his design is finalized, designer A meets with test engineers (in-house lab or outside commercial lab) to discuss
Designer A logically asks test personnel “Do you see any weaknesses in my tentative design? In what way do you think it is most likely to fail?” At the other extreme we have designer B who
Designer B does not recognize that lab personnel have witnessed many test failures and can make valuable suggestions that will enhance the design and possibly cut manufacturing costs. Designer B does not recognize that the lab knows more than one way to perform a given test, all perfectly “legal” but with different effect. One example is the location of the control accelerometer. Designer B does not recognize that the lab can provide him with much valuable information about is happening (during the test) and what happened (after the test).
Designer B may not recognize the importance of a good test fixture, custom designed for his test, experimentally evaluated, possibly modified and reevaluated. Designer B may use an intermediary for these negotiations, rather than visit the lab himself. This is shortsighted, but it happens. Designer B should be present to witness the test. He will make sure that photos document accelerometer locations, for example. He will ask for a low level sine sweep, meantime using a synchronized “strobe” light to watch his product flex in various response modes. Well, Mr. Designer, are you closer to A? Or to B? Designer B’s errors may not be deliberate. Possibly “that’s the way we’ve always done it.” Or possibly his manager doesn’t understand how the test lab can help his people. Or possibly Designer B is a recent graduate; testing was not mentioned on campus. |
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| Would
you attend a “virtual” class? Suppose that you ask your boss to send you to a short course. You explain why you need the training. Point out how much (time and money) it’s costing him for you to stumble along without that training. Suppose that he says, “OK, you can participate”. “In fact,” he continues, “you’ve convinced me that a number of your fellow design and test workers should also have that training. So let’s hold it in our own conference room. That way none of us violates Management’s ban on unnecessary travel.” You’re a little disappointed. It’s winter and you had hoped for a few days in Florida or California. But the idea of everyone participating is very attractive. “When will this happen?” you ask, “When will the instructor be here?” Now your boss smiles. “Well, strictly speaking, he isn’t coming here. This is going to be a 'virtual' class. He’ll be in his office, but we’ll see his image projected by a video projector. The program material, a series of several hundred Power Point slides, comes off the Internet into a PC here. A few slides contain animation or video clips; those “memory hogs” will be on a CD. A video camera will ‘pick up’ our instructor 'live' and we’ll see a small image (his face) in one corner of each slide. At the same time we’ll hear his voice either as a ‘voice over’ or via a telephone link.” “Will he see us, and hear our questions?” you ask. “Yes, we’ll have a video camera and a microphone, so he can see and hear us” your boss answers. “It won’t be quite the same as if he were here, teaching ‘live’. In some ways not so good, in some ways better.” “Better?” you ask. “Tell me one way it will be better.” “Well,” your boss answers, thoughtfully. “Do we want this course to meet for three long, full days? Do YOU want to sit there for all those hours? Wouldn’t it be nice if the course met for only 1 or 2 hours each day, for a few weeks, more like a college course?” “I see what you mean,” you answer. “Also, that would much less disrupt our testing programs. With virtual training his travel and living expenses will be zero. Are his prices less this way? I think this might work out very well.” Might that scenario “work out”
for the training your facility needs? Ask
ERI for a proposal on “virtual” training on some
subject that interests you. Visit my article/presentation
section at our Vibration & Shock website to see the visual portion
and read the audio portion of some very short sample virtual events
that I did in 2002 and 2003 for the IEST. Participants heard me
and I heard them via a telephone link. We posted what I was going
to say for people whom we thought might join late or might miss
the event. Wayne Tustin, ERI's president, can be reached by e-mail or phone (805) 564-1260. Read more about Wayne at ERI's website. |
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Test
Lab Musings (part 5)
Robert L. Renz of General Dynamics - Advanced Information Systems at Bloomington, Minnesota. |
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Wayne and Bob Jump at Honeywell
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Hello,
readers - 
Were
all three owners striving for increased force? Not necessarily.
Maybe cooling air was choked by dirt and debris. When did you clean
your shaker? Another all-too-common cause: one's "control accelerometer"
might fall off. Or it might have been placed at a bad location,
a node. Either way, lacking protective circuitry, the controller
might send full amplifier power to the driver coil.
If
you purchase fixtures, be sure the supplier installs spot-faced
10-32 accelerometer mounting pads in appropriate locations - if
you design your own, remember to install them. It’s a lot
easier to simply screw a mounting stud into a tapped hole than it
is to glue an adapter onto your fixture every time you use it. Also,
a tapped hole means that the accelerometer is always installed in
the same location, which helps test repeatability. If all else fails,
remember the machine shop. Don’t try to drill a mounting hole
with a hand drill: it won’t be square to the surface.
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Fixture Design course coming up |
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You can read about instructor Steve Brenner at our website. Steve admits to having designed some poor fixtures. Fortunately, he was able to gain some theoretical understanding of structural responses to vibration and shock, to study those unsatisfactory fixture, to improve them, and to avoid most mistakes on future designs. Here he will teach what he has learned on this subject. Most of Steve's presentation will use Power Point slides. A highlight on Day #3 will be a visit to a professional manufacturer of fixtures, Baughn Engineering, at LaVerne, California to see fixtures evolving from raw materials into finished, ready-to-ship fixtures. |
| Free sample of Chapter 1 |
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| Wayne at Honeywell |
During a recent vibration and shock test course at Honeywell's Federal Manufacturing and Technologies plant at Kansas City, Missouri, Wayne and class participants visited the environmental test laboratory. Bob Jump, environmental test leader, had arranged a demonstration on an electrodynamic shaker. Wayne and Bob posed for the photographer. |
| Optimizing Electronics Vibration |
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John E. Starr of CirVibe, Inc., Plymouth, Minnesota, will present his three-day lecturer/workshop "Optimizing Electronics Vibration - HALT, HASS, ALT and ESS" at Minneapolis September 14-16 and at Dallas October 19-21. John's course applies to vibration of electronics at system, box or circuit card level. Whether testing is HALT, HASS, ALT, ESS, Qualification or other type, understanding the product and also understanding how the test affects the product are both key to efficient testing. One step in the HALT process simply states "understand the root cause of failure". This is a fundamental part of all vibration testing but it is often avoided or inadequately covered due to its complexity. This course covers a giant leap in use of technology to visualize vibration damage and understand failure. |
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Switzerland Course |
| Another Vibration and Shock course will meet October 5-7 at Zug, Switzerland with Markus Dumelin teaching. Click here for more information. |
| Vibration and Shock courses coming up |
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August
24-26, 2004 September
28-30, 2004, October
5-7, 2004 November
1-3, 2004 December
7-9, 2004 2005 courses March
14-16, 2005 If none of these locations and dates meets your needs,
perhaps you’d like to have customized training presented at
your facility for your designers and test specialists. |
| Singapore course |
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| Contact information |
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Wayne Tustin tustin@equipment- Webmaster webmaster@equipment Websites http://www.vibrationand Copyright © 2000-2004 Equipment Reliability Institute. All rights reserved. |
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