A series of screens are conducted under environmental stresses to disclose weak parts and workmanship defects which require corrections and this requires and understanding of burn-in testing and ESS of which both techniques identify weak points and eliminate them by motivating early failures. Burn-in is usually a long process of operating under load(s) and at fixed temperature (in short, this is a special case of ESS) or it can be operated at varying loads and accelerated temperatures to achieve a shorter burin-in period, whereas ESS is a scientifically planned and conducted test which is usually conducted under accelerated loads to produce the same test/use results in a shorter period of time by increasing the stress on the components or assemblies. The objective of these screens is to produce a failure free product when released into operations. ESS is not intended as a test to validate compliance to a design, however it is intended to force latent defects into becoming defects before the end user finds them in day-to-day usage.
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
Comments
There are no comments for this article yet. Why not add one?