Equipment Reliability Institute
ERI News - your reliability newsletter
November 2003 - volume 13

Hello, readers.

Our first article encourages combining EMC tests with climatic and with dynamic tests. Traditional laboratory (benign environment) EMC tests don’t reflect the “real world”, where electrical interference, climatic and dynamic stresses occur simultaneously.

The second major article is by ESD (electrostatic discharge) specialist Gene Bliley. If you are asking “Who is Gene Bliley?”, visit his ERI page. His article deals with cloth wristbands (used for ESD protection).

Then we have four more helpings of Bob Renz’s Test Lab Musings.

Hey, readers: have you a question? ERI specialists can help you out! Please take a look at our current "Should we buy or build our fixtures?" below.

Would you like to see an earlier issue of this Newsletter? Visit our Resources section for a listing of the topics in 12 earlier issues.

We’re glad you could join us. If you plan to write an article dealing with reliability, please consider publishing it with us. Send a draft to our editor.

Best wishes,
Wayne Tustin

Combining EMI/EMC/EME tests with Environmental Tests
by William H. Parker and Wayne Tustin
also Tony Masone

Abstract
Most EMC (electromagnetic compatibility, sometimes called RFI or radio frequency interference and less often EME for electromagnetic effects or EMI for electromagnetic interference) problems are just nuisances, such as an electric shaver interfering with radio reception. But some interference problems are more serious, so that, for example, airline passengers may not use their laptop computers at certain critical times in each flight. To control interference problems the U.S. Federal Communications Commission or FCC, the Canadian Standards Association or CSA and the European Union or EU require tests that prove that equipment manufacturers meet intersystem EMC standards. Commercial aircraft and military EMC standards are discussed. Such testing is traditionally conducted under rather benign and clean laboratory climatic conditions. Temperature, humidity and altitude are moderate. There is no condensation, no contamination. There are no dynamic stresses (mechanical shocks, vibration).

But equipment, especially military equipment, is used under field conditions where any or all of these and possibly other environments can temporarily or permanently degrade our protections against RFI.

This article expresses concern that traditional (benign environment) EMC testing fails to reveal certain intersystem problems. We propose that all future test standards call for climatic and dynamic environmental tests to precede EMC tests or, for greater realism, be conducted simultaneously with EMC tests.

Quick Review: EMI/EMC/EME and Testing
Situation #1: You are involved with electronic equipment that you discover is vulnerable to (cannot tolerate) electrical interference. Solution #1: You might place your equipment inside a metal box (sometimes called a Faraday cage). If your equipment is battery powered and the metal box is completely closed, your equipment will be able to withstand quite high levels of radiated electromagnetic fields from any direction.

Situation #2: You are involved with electronic equipment that, unfortunately, along with "doing its job", radiates strong electromagnetic fields. These fields can interfere with other services. Solution #2: If your equipment is battery-powered, and if you place it inside a metal box (Faraday cage) and if the box is completely closed, the radiated electromagnetic fields from your equipment will be significantly reduced, and most likely will not affect even nearby sensitive equipment.

Unfortunately, in a "real world" environment, Solutions 1 and 2 can't be fully achieved. Most equipment operates from power brought in via cables from external power sources. Most equipment communicates to other equipment via interface cabling. Test standards (relative to Situation #1) dictate the measure of radiated electromagnetic emissions and electromagnetic susceptibility under which your equipment (which is probably not battery powered and probably not inside a completely closed metal box) must operate properly. Such tests may be performed in an Electromagnetic Interference (EMI) chamber. Most EMI chambers will attenuate RF signals as much as 80dB over the frequency range 10 kHz to 10 gHz. Other test standards (relative to Situation #2) limit how much electromagnetic radiation - both the wanted signals and the unwanted "noise" - you are permitted to generate.

Box May Leak
It is very difficult to build a box that keeps 100% of the RF inside (Situation #1) or outside (Situation #2), particularly (as is common) if the box has openings. Instructors often cite the somewhat comparable difficulty you would have in building an airtight house for your family. Even Columbia University's famed "sealed" Biosphere 2 near Oracle, AZ had an annual atmosphere exchange rate near 10%; see http://www.bio2.edu.] A practical house needs doors for human and equipment access. It needs ventilation for life support and cooling. It needs penetrations for pipes and cables, for fluids, for electrical and communications connections.

Let's consider the doors to our RF enclosure. They will never fit perfectly, so we will add gaskets. But climatic stresses such as solar radiation, salt fog also sand and dust can degrade gaskets. Further, metal surface treatments (intended to conduct current) can corrode. Finally, dynamic environments (vibration and shock) can degrade EMI gaskets.

Penetrations and Cabling
Cables are usually necessary, usually with disconnects from connectors that actually pass through the skin of boxes or racks of equipment. We don't want our cables to bring in or to carry out unwanted RF energy. We can use ferrite attenuators or add braided shielding over individual conductors or over entire cable harnesses. We can install filters that pass useful signals but that block unwanted RF "noise". How well will these shields, filters and attenuators work in service? What will be the reliability of individual components and manufacturers' materials in the "real world" that includes climatic and dynamic stresses? Are components mounted securely or is potting used? Environmental testing is far more useful than attempts at reliability prediction.

Boxes And Racks Deform
Our box (or rack supporting several boxes) may be attached to some sort of vehicle or fixed structure. Vehicles (such as your automobile or an Army tank, or a ship or a helicopter) deform as they move. Less obviously, even supposedly fixed structures move and deform. Think about the effects of building machinery, elevators, wind loading, nearby highway inputs. Any of these structural deformations can exert force on our box or rack, might result in relative motion along originally tight metal seams. Further, our stressed box may move relative to its unstressed doors. Apertures will lose their "RF tightness".

Quick Review: Vibration and Resonances
Electrical engineers use the letter "Q" as a measure of voltage magnification at resonance. Mechanical engineers us it as a measure of vibration magnification at resonance. Resonance occurs when a forcing frequency matches a natural frequency . That is, when =. As a very simple example of resonance, place a favorite child onto a playground swing. Experiment. Vary the timing of your pushes. Very quickly you will find that you get greatest magnification "Q" when your matches the swing's .

That playground swing is deceptively simple. It only has one natural frequency . Vehicles and buildings respond strongly at their several twisting and flexing natural frequencies to vibratory inputs at various forcing frequencies .

In your automobile, those forces come from the engine, drive train, wheels, etc. On an Army tank, these forces are joined by "clanking" of the treads. A ship's propeller is a strong vibration source. A helicopter's rotors create much vibration.

Recognize that your box or rack has numerous twisting and flexing natural frequencies . If any of these s is excited by any of the forcing frequency s you will have a resonance that significantly magnifies your RF leakage problems perhaps 100 times.

Shall we wait for these problems to appear in service? No! We will discover them by simultaneously performing vibration and EMC tests.

Combined Environment Test Example
A client recently asked Garwood Testing Laboratories to pass 100 watts of RF (band reaching from 12 to 18 gHz) through a cable that was heated to 110^oC and to do this at a simulated altitude of 60,000 feet. The cable survived. The EMC technicians had some difficulty sealing the cable penetration into the thermal test chamber but the altitude test specialists knew exactly what to do.

Loss of Cooling
Electronic systems depend upon cooling to prevent heat-caused performance degradation or outright failure. They are designed to operate under certain ambient altitude and air flow conditions. In a vacuum (at altitude) fans cannot move much air and cannot extract much heat. Heat received from some other source may compound the difficulty. Temperature conditions can degrade the performance of components and circuits. As a Situation #1 example, component values in a power supply filter may change (at temperature or altitude) causing the filter, which performed properly at ambient conditions, to lesser attenuate power line noise. RF interference from outside may disrupt normal operation of the device. As a Situation #2 example, component value shifts can increase radiation from a device and can interfere with other systems nearby or sharing the same power bus. These possibilities call for combined EMC (both Radiated and Conducted Emissions and Susceptibility Tests) and thermal testing.

Intermittent Chassis Grounds
Unwanted RF signals (noise) is usually directed (filtered) to chassis ground. But what happens if the impedance of that ground connection degrades from near-zero ohms to some higher value? This degradation can be caused by climatic environments such as temperature, moisture condensation, corrosion, etc. It can also be caused by vibration loosening, say, a bolted connection. The result, depending upon where this occurs, can be an increase in RF susceptibility or in unwanted RF emissions.

Current flow through an intermittent ground can cause arcing, which can generate large amounts of broadband RF energy and can disturb the operation of nearby equipment. Two examples follow.

A pilot once complained about navigation and communication equipment on his plane becoming inoperable when flying through rain. Studies have shown that when an aircraft flies through rain, static electricity on aircraft skin can exceed 100,000 volts. In the hanger, they simulated this situation by isolating the aircraft from ground and, using a high voltage power supply, they charged the aircraft skin to approximately 100,000 volts. Then they used a portable RF receiver to locate the source of broadband RF noise. It turned out to be arcing between poorly bonded aircraft surfaces.

Author Tony Masone recalls a flight test to document a similar problem. The test involved flying EMI specialists into a storm. Immediately upon entering the storm, Masone heard a high-pitched squealing sound from the pilot's headset, so severe that the pilot had to remove his headset. The navigation display then went black. All navigation and communication equipment was inoperable, in a whiteout condition with freezing rain and snow! Fortunately the pilot was well experienced, and there were no other aircraft in their flight path. Upon exiting the storm, all navigation and communication functions returned to normal operation. Back at the hanger, high voltage testing led to finding a poor bond between two surfaces on the horizontal stabilizer.

We are not proposing climatic or vibration tests on entire aircraft. These two examples were used because they were known to one of us. But please recognize that similar poor bonds can occur in and on your boxes and racks of equipment, resulting in similar difficulties. Bonding problems will be exacerbated by vibration, shock and corrosion. Corrosion in turn will be exacerbated by combinations of temperature, humidity (condensation), salt fog, etc. Better to find your product's bonding problems in the test lab than in service.

Power Switches
On-off power switches are common. They all work in ambient conditions. But under temperature, altitude or vibration situations, contact arcing may occur; this can generate broadband RF noise.

Intermittent Cover Plate Bonding
RF emissions were once observed to increase intermittently during a vibration test. The difficulty was traced to a cover plate losing its continuous RF bond. Somewhat similar loss of cover plate bond can be caused by differences in coefficients of thermal expansion (CTE) between box and cover plate materials.

Such difficulties are relatively easy to fix, if the difficulties are known. Better to find difficulties in the test lab than to find them in service.

Commercial Aircraft and Military Environmental and EMC Test Standards
Consider DO-160E, the current issue of "Environmental Conditions and Test Procedures for Airborne Equipment". Source: RTCA - Radio Technical Commission for Aeronautics, Washington, DC http://www.rtca.org. This is the aerospace standard for commercial aircraft. EMC concern ranges from dc to 18 gHz. Other standards are extended to 40 gHz.

In the military world, MIL-STD-461D/462D is most commonly cited, although MIL-STD-461E will eventually supersede.

Conclusion
In neither world is EMC testing combined with climatic nor dynamic (vibration and shock) testing. We decry this lack. This article encourages combining the RF tests (Audio Frequency Conducted Susceptibility - Power Inputs Test, Induced Signal Susceptibility Test, Radio Frequency Susceptibility Test, Emission of Radio Frequency Energy Test) with climatic (temperature, altitude, humidity, waterproofness test, fluid susceptibility test, sand and dust test, fungus resistance test, salt spray test) and with dynamic (sawtooth mechanical shock, sine and random vibration, explosion proof) tests.

William H. Parker is an ERI specialist in EMC & Test Services. For more information please visit his page at ERI's website.

Tony Masone is the EMC Manager of Garwood Testing Laboratories in Pico Rivera, California. Contact Tony at tonym@garwoodtestlabs.com.

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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Testing the Integrity of Cloth Wristbands
by Gene Bliley, Bliley Consulting

The cloth style wristbands represent a serious reliability issue because the elastic band may lose its conductive properties over time. When this condition occurs, the operator is not grounded if the metal buckle loses contact with the wrist. A simple pinch test can detect this condition, and the defective band can be removed from service before the quality and reliability of electrostatic discharge sensitive (ESDS) products are jeopardized.

I first became aware of this condition several years ago while serving as the ESD program manager at the Lucent Technologies manufacturing facility in Columbus, OH. At that time, cloth wristbands were optional in the ESD prevention program, and a mixture of cloth and metal style bands existed.

Internal ESD audits revealed a large number of cloth wristbands that were not functional. ESD assessments conducted at equipment manufacturers' facilities revealed that the problem was widespread. In one case, 53% of the cloth wristbands sampled failed the cuff conductivity requirement. As a result, a decision was made to allow only metal, expansion type wristbands in the process.

Cloth Wristbands
To the casual observer, it may appear that the only purpose of the elastic band is to hold the metal buckle against the operator's wrist. The elastic band servers a dual role. The interior of the elastic band that contacts the wrist has conductive fibers knitted into the surface to assure complete circumferential contact. This construction technique can be seen in Figure 1.

Figure 1 - Typical Cloth Wristband Construction

The interior cuff resistance limit is specified in ESD Association ESD-S1.1 Standard for Protection of Electrostatic Discharge Sensitive Items: Personnel Grounding Wrist Straps. The cuff resistance testing procedure is found in paragraph 5.2. Table 1 of the document states that the interior cuff resistance must be 100 kW . This is a laboratory test for measuring the performance of new wristbands or for evaluating a new supplier's product.

It typically is not conducted as part of an ESD audit and I have never seen it used as part of the daily process check of the wristband system. It is for these reasons that many defective cloth wristbands are being used in ESD processes.

Analysis
As the cloth wristband is used repeatedly, two failure mechanisms occur:

1. The interior surface of the band becomes soiled.

2. The band loses its elasticity, and the interior surface becomes less conductive because the fibers breakdown due to stretching. It is difficult to estimate when this failure will occur. Some cloth bands seem to lose their conductivity faster than others because construction techniques, quality of materials and properties of the conductive strip vary with manufacturers.

Eventually, the interior surface of the band becomes nonconductive, and the operator is grounded only while the metal buckle is contacting the wrist. The metal buckle can easily separate from the wrist when the operator pulls against the coiled wrist strap grounding cord. During this time, the person is no longer grounded, and ESD damage becomes a possibility.

Figure 2 shows the voltage on an operator vs. time for grounded and ungrounded conditions. During the time that the operator is connected to ground, the body voltage is zero. When the connection loses ground, the voltage on the operator rapidly rises and falls to the approximate values shown in Figure 2. This potential represents a risk to ESDS devices and assemblies.

Figure 2 - Graph of Body Voltage: Grounded vs. Ungrounded Operator

While the time intervals on the graph seem short, it is important to realize that they are extremely long with respect to an ESD event. A typical human body model (HBM) pulse has a rise time of less than 10ns and a decay time constant of 50ns to 300ns.

Pinch Test
The pinch test identifies defective cloth wristbands. It utilizes a typical wrist strap tester and can be performed in a few seconds. It is also applicable to wristbands used in conjunction with continuous workstation monitors.

The following procedure is used to test the conductivity of the cloth wristband: The wrist strap assembly (wristband and coiled grounding cord) is plugged into the wrist strap tester, as it normally would be to conduct a standard verification test. The wrist strap is not worn during this portion of the test. Instead, the operator pinches the band between the thumb and forefinger. One finger will be on the outside of the band and the other will be in contact with the interior or conductive surface of the band.

With the other hand, the operator activates the wrist strap tester as usual. Do not touch the metal buckle or allow it to contact the hand holding the wristband. This procedure is shown in Figure 3.

Figure 3 - Procedure for Testing Cuff Conductivity

A passing condition on the wrist strap tester indicates that the conductive portion of the band is functional. A failing condition means that either the band has lost its conductivity or the ground cord is defective.

Touching the metal buckle and repeating the test can easily validate the ground cord. If a passing condition is achieved but the pinch test failed, the band is defective and should be removed from service.

Conventional Testing
Once it has been determined that the band is functional, the wrist strap assembly should be tested as recommended by the manufacturer or your company's specific instructions, to ensure that a continuous path to ground is present. A high resistance failure indicates a possible dry skin condition or a loose fitting wristband.

Lotion formulated for the electronic manufacturing environment should be applied to the skin beneath the wristband to improve conductivity. A wristband should fit snugly on the wearer's wrist and does not slip during normal use.

To complete the wrist strap assembly test, the coiled ground cord must be lightly stressed by flexing the snap connector and the banana plug to verify that no intermittent condition exists.

Continuous Monitors
A defective band can produce momentary alarm conditions when normal activity at the station causes separation of the metal buckle and the operator's wrist. Continuous monitors that operate at a sample frequency may not detect this condition.

These monitors typically check for a properly grounded condition at 2 s to 3 s intervals. If ground is lost during the monitor's off period, the ungrounded condition can go undetected.

Continuous Monitors (Single Wire)
The pinch test can be performed on cloth style wristbands connected to continuous workstation monitors using the following procedure: The operator removes the wristband from his/her wrist. The band should still be connected to the grounding cord and constant monitor. The monitor will indicate an alarm condition because the person is no longer grounded.

The operator performing the test should pinch the band between the thumb and forefinger and hold for approximately 10 s. One finger will be on the outside of the band, and the other will be in contact with the interior surface. The monitor should then indicate a passing condition.

If the constant monitor continues to indicate a failing condition, the wristband has lost its conductivity and should be removed from service. This can be quickly verified by touching the metal buckle. If the monitor indicates a passing condition, the failure of the wristband has been confirmed.

Dual Wire
For two wire resistive and body voltage sensing continuous monitoring systems, the testing procedure must be modified slightly. It is necessary to realize that the wristband consists of two halves, each connected to the constant monitor by a separate wire.

To evaluate these bands, make contact with both halves of the band simultaneously. This can be easily accomplished by having the operator performing the test pinch one half of the band with the thumb and forefinger of the left hand and the other half of the band with the thumb and forefinger of the right hand. This procedure is shown in Figure 4.

Figure 4 - Testing Wristband Connected to a Continuous Monitor

Within approximately 10 s, the monitor should indicate a passing condition. If a passing condition cannot be obtained, the band has lost its conductivity. This can be quickly determined by touching both halves of the metal buckle. If the monitor indicates a passing condition, the failure of the wristband has been confirmed and the band should be removed from service.

Conclusion
If you use cloth style wristbands in your ESD prevention program, collect data by incorporating the pinch test into your auditing practices to determine if a cuff continuity problem exists. If a significant number of defective cloth wristbands are found, consider incorporating the cuff conductivity test into the daily process check of the wristband system. By doing so, you can verify that the wristband is performing its intended function of safeguarding the quality and reliability of your products.

Gene Bliley is a member of the ESD Association and offers ESD engineering consultation, factory assessments, and training to the manufacturing community. He's also an ERI specialist. You can read more about Mr. Bliley at ERI's website. To contact Mr. Bliley: bliley@equipment-reliability.com.

Test Lab Musings (part 2)
by Robert L. Renz

How about standardizing on a few lengths of bolt? Just because they are available in increments of 1/4" doesn't mean that we need to stock every length in the book. And when you design and build a new fixture, why not stamp the fixture description / part number into it, as well as the number of bolts and the size? You can also use a ring of paint to mark the inside of the hole to indicate the bolt length (for instance - blue = 1.5", red = 2", yellow = 2.5", black = 3").

While we're at it, if your lab is frequently used by many people, get into the habit of periodically removing the slip table from the slab, and look at the bottom of it. I'll bet you'll find some spots where the bolt was a little too long, but it was used anyway, and it pushed down a bump of magnesium. First, this means that your slip table is no longer held down by the oil film, and your testing will start to have many more variables in it than it used to. Second, it might be time to start a bolt length marking program right now (or else, change the lock on the lab door). Meanwhile, haul the slip table to the machine shop and clean up the bumps.

While we're on the topic of slip tables, periodically take a tap and clean up the threads on the table inserts. If someone used a bolt with damaged threads somewhere along the line (another reason to throw out old bolts), you probably have an insert that needs help. Inserts can be removed and replaced if needed, but be sure that the new insert is the same thread as the rest (don't laugh - I've seen a coarse thread insert replaced with a fine thread insert because someone put the wrong insert in the right drawer in the stockroom.)

I like to have a wall mounted tool board by each tester. The board is designed to have the right tools placed in the marked spot. For instance, the hex wrenches that are needed to connect the slip table, rotate the shaker, install the head expander, and install the fixtures all have their specific locations. It's a whole lot easier than digging in a tool box trying to locate the 1/4" hex driver. Likewise for socket wrenches and extensions. Each shaker usually needs only a few sizes.

Robert L. Renz of General Dynamics - Advanced Information Systems at Bloomington, Minnesota.

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Questions our readers have asked...

This section of our newsletter was created for you, reader! Feel free to send questions or suggestions to the webmaster. One of our specialists will respond.

Q: Should we buy or build our fixtures?

Unless you are employed by a commercial environmental testing laboratory,
your testing laboratory probably doesn't need very many new fixtures. What - three or four per year? Then your firm has probably not developed fixture expertise.

You are likely to "spin your wheels" a bit in deciding which type of fixture best suits your particular combination of (1) DUT or device under test, (2) shaker limitations, (3) test plan and (4) frequency range. One example of fixture type is the "bookend" or "ell" fixture sketched in Figure 1.

Figure 1

A competent professional fixture firm might spend five minutes on that decision.

You are likely to attempt thin cross-sections, perhaps attempting to save fixture weight. 1/4 inch thickness rarely if ever is sufficient. A competent professional fixture firm would use 1 inch or more, and would have the requisite material already in stock, whereas you would have to procure it. And would have the necessary skills to appropriately cut the material.

You are likely to attempt to bolt a number of plates together, as in the
center sketch of Figure 2.

Figure 2

A competent professional fixture firm would know from experience that bolted fixtures rarely if ever work well. At the higher test frequencies, relative motion between bolted plates greatly distorts shaker waveform. Bonding can help, but a competent professional fixture firm would immediately suggest casting (so that highly damped K1A alloy of magnesium may be used) or welding of magnesium or aluminum tooling plate. That decision may well hinge upon your schedule. Welding is faster.

Even though your firm or agency has designers and fabricators competent in other products, fixture design Is different.

Even if you know enough to weld your fixtures, you are likely to waste effort chamfering parts as in Figure 3(a) so that welding can achieve full penetration.

Figure 3

Why bother? This is not a pressure vessel. A competent professional fixture firm would quickly clamp the parts, "tack weld" each side of the juncture and then lay a heavy weld bead along each side. Upon cooling, the resulting fillet gives great bending rigidity. The resulting fixture is likely to be somewhat warped; your experienced fixture firm would quickly machine the surfaces so they are square. And then would quickly locate and drill holes for mounting the DUT to the new fixture and the new fixture to your shaker. And would remember to install inserts as suggested by Figure 4 or appropriate studs for securing the DUT to the soft fixture material.

Figure 4

If, as sometimes happens, when you experimentally evaluate your new fixture, you find unwanted fixture resonances, your experienced fixture firm is likely to know what remedies work well.

I've not answered the title question, "Should we build or buy our vibration test fixtures?", have I? Only you can answer it, depending upon your circumstances (including your budget). Hopefully, I've helped you to recognize some preliminary questions that need to be worked out before you decide the title question for yourself.

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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My new text is titled "Random Vibration and Shock Testing, HALT, ESS and HASS". We're describing it as "A minimal-mathematics introduction to the fundamentals of Random Vibration and Shock Testing, HALT, ESS and HASS also Measurements, Analysis and Calibration, with applications in the fields of aeronautical, automotive, seismic and shipboard design and production". It is shown here, alongside my 1984 text "Random Vibration in Perspective", which is updated, greatly expanded and in color.

Click on the image to enlarge

The book will be approximately 300+ pages, letter size and it will include a CD-ROM, which carries a number of video clips and animations that illustrate vibratory and shock motion. One of my favorites shows the highly repetitive motions inside an automobile engine. Another shows cantilever beams responding to random vibration.

Prepublication Sale Deadline
You can order the book for only $150 if your funds reach us by December 31, 2003. And we'll pay the shipping. After that the price will be $250.00 + shipping. We expect to ship the book by February 1, 2004.

New dates for John Starr's courses

For any design, HALT, ESS or HASS vibration requirement, circuit card life is limited by the failure distributions of a few components on that card. Starr teaches how to add "Point of Failure" analysis to the design process as a vital step in identifying any vibration-weak areas. John Starr has 4 courses scheduled for 2004:

February 17-19, 2004
Santa Barbara, California

April 21-23, 2004
Las Vegas, Nevada
(Registration required by March 1, 04)

May 18-20, 2004
Minneapolis, Minnesota

June 8-10, 2004
Santa Barbara, California

Can some reader assist me with Chapter 27 of my new vibration text?
The figure below is an attempt to show what I seek.

The Adapter bolts (not
shown) to the armature of an electrodynamic shaker adjusted for shaking
horizontally. The slip plate slides on an oil film or possibly on hydrostatic bearings. Two flat plates which clamp the slip plate are welded to the adapter. These are not ordinary bolts but rather are segmented pins that expand and fill the holes through which they pass, so that there can be no relative motion between clamping plates and slip plate.

I'm trying to find out the details. Where can these pins be obtained?
Precisely how are they used? Reader assistance will be appreciated. Please e-mail me or call me at (805) 564-1260.

Modal Testing course
Save the dates March 22-25, 2004 for the upcoming course in Modal Testing with Lee Smith. Please check ERI's website for more details soon.

Message Boards
Have you visited ERI's message boards? They are free and easy to use. You can discuss or ask about situations, difficulties and experiences in the fields of equipment reliability and durability as well as in the field of dynamics.

Acoustics Consultant Wanted
We'd like to hear from an acoustics consultant who is willing to travel and to teach short courses to groups of engineers and consultants, possibly in non-industrialized countries.

ERI - Equipment Reliability Institute
1520 Santa Rosa Ave.
Santa Barbara - CA - 93109
Tel: (805) 564-1260
Our fax number:
(805) 966-7875

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reliability.com

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