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ERG (Equipment Reliability Group) lists specialists who provide consulting. Go to our Specialists page to learn more about each consultant.

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ERI / V&S can be contacted by postal mail, by phone, by FAX or by email:
Equipment Reliability Institute
1520 Santa Rosa Avenue
Santa Barbara, California
93109, USA
Phone: (805) 564-1260
FAX: (805) 966-7875
e-mail: info@vibrationandshock.com

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This is a mechanical engineering term referring to a shaking or quivering that travels through structures (aircraft, automobiles, buildings, etc.). It resembles sound which travels through air and liquids. Our ears sense sound. Microphones measure sound. Our fingertips sense vibration. Accelerometers and other sensors attached to the structure measure vibration.

Random vibration is unpredictable. An example: the unpredictable mechanical inputs from the terrain (roads or off-roads) into the suspension of your automobile.

Another example: the structural quivering of a rocket or high-performance aircraft, especially during trans-sonic flight due to highly turbulent air flow. We must distinguish between unpredictable random vibration and the repeatable and predictable vibration from automobile engines, drive trains and airplane propellers.

A shaker or vibration exciter is a controllable source of vibratory force, which is useful for vibration testing and for environmental stress screening (ESS). Shakers can be mechanical, electrohydraulic (servo-hydraulic), electrodynamic (electromagnetic), piezoelectric or pneumatic.

Sir Isaac Newton taught us that force is equal to mass times acceleration, or F = MA. Shaker vibratory force must be at least total vibratory mass [armature + fixture + device under test (DUT)] times desired acceleration. The vibrating table size should accommodate the size of the DUT.

Well, yes, but it's not very practical. See Test Engineering and Management, June/July 1994, "We Made Our Own Shaker". Better yet, consult one of the shaker manufacturers.

This definition refers to mechanical (not electrical) shock: an abrupt (occurring in a short time interval - compared with hardware natural frequencies) change in position or motion. Dropping a piece of hardware onto the floor provides us with an example of shock.

When we perform an environmental test on a sample of equipment, we simulate one or more environments that may be harmful to that equipment. This should be done during the development of a new product. Our aim is to increase the reliability and durability of that new product. Call that sample our DUT or device under test.

We can place our DUT  in a climatic environmental chamber for a climatic test. There we will stress it with varying altitude, temperature and humidity. In other chambers we can stress it with sand-and-dust, with salt, fog, sunshine, etc. to simulate in-service or in-transport conditions.

We can place our DUT onto a shaker or a shock test machine for a vibration or shock dynamic test. There we will stress it with vibration and/or shock - dynamic tests.

Although ESS may use chambers and shakers resembling those used for an environmental test, the purpose is different. In ESS we stimulate just-produced or just-overhauled equipment (usually an electronic assembly or subassembly), usually using rapid thermal ramping and broad-spectrum random vibration.

Our aim is to precipitate any latent or hidden defects so that the equipment malfunctions in ways we can observe. We prefer that malfunctions occur close to the production line rather than downstream at final assembly or (heaven forbid) when a customer is using the final product. Malfunctioning equipment goes to failure analysis, then to repair or to scrap.

ESS is not a test. Equipment does not 'pass' or 'fail'. Most observers understand thermal ramping, typically over 100°C temperature range at 20°C to 50°C per minute. However, they have some difficulty understanding random vibration at, say 0.04g²/Hz spectral density.

According to MIL-STD-810F, 6 March 1998, an EES is one who is skilled in one or more environmental engineering areas. Areas include, but are not limited to: natural and induced environments and their effects on materiel; expertise in measuring and analyzing field environmental conditions; formulating environmental test criteria; determining when environmental laboratory tests are appropriate/valid substitutes for natural field/fleet environmental tests; and evaluating the effects of specific environments on materiel.

These are the peculiar units in which intensity of random vibration is measured. The quantity is called ASD or Auto Spectral Density. Alternatively, it is known as PSD or Power Spectral Density. ASD or PSD are plotted vertically against frequency in hertz plotted horizontally.

A message board (a.k.a. forum) is a place where you and other visitors can view and post messages. A forum typically has an index page (a list where message titles are displayed), a message page (where individual messages can be read), and a post form (where someone can enter a message).

No, you don't. But you might want to register with Network54.com (V&S' message board host) to be able to use other features.

To post a new topic, click on the Post Now link. This will take you to a page where you can enter your name, e-mail address (optional), message and subject title. When finished, you can choose to preview your topic by clicking on the Preview button (next to the Post! Button).

If you decide to enter your e-mail address, you might want to check "Also send responses to my email address" to receive replies straight to your e-mail account. This option is located below the message text box.

To post a reply to a message, click on the Respond to this message link. That will take you to a page where you can enter your name, e-mail address (optional), your message and your subject title. You can choose to preview your reply by checking the Preview button (next to the Respond! Button).

Note: If you want to clear all of the fields, click the Clear Fields button. All the information you have placed in the boxes will be cleared and you can start over.

Only the original author, administrator or moderator can edit a post on V&S' message boards. Remember! You can edit your message only before you post it.

Perhaps you have a technical difficulty concerning (for example) vibration or shock. Share your difficulty by posting a message at the subject-related board. It will be seen by many people who share your interests. Some of them will post their comments and one of those comments may solve your difficulty.

Nothing. It's one more benefit ERI/V&S offers to visitors! Good luck!!