Why: The extremes of operating conditions such as high power levels, high temperatures, high vibration levels, etc. produce failures not anticipated from testing at nominal conditions. Generally ESS is directly applicable and interpreted to be applicable to electrical/electronic equipment, however the same issues/concepts apply to mechanical equipment when the stressing conditions are loads/pressures/temperatures/vibrations/thermal shocks/etc., so as for all reliability issues-think broadly!

When: When acquiring data, the tests are done upfront of production. When controlling early failures that would be discovered by the end user, these test are done as a portion of the production process to eliminate week units to control warranty costs and improve customer satisfactions

Where: Some tests are conducted in the laboratory for quick results and then the data is used to control product testing/release for the purpose of limiting costs and preventing the loss of customers from unsatisfactory performance in the field.

These definitions are written by H. Paul Barringer and are also posted on his web site at www.barringer1.com

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