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Derating is a method of reducing stress and/or making
quantitative allowances for a part’s functional degradation. Consequently,
derating is a means of reducing failures, extending part life, and increasing
reliability (not quality). In addition, derating helps protect parts from
unforeseen application anomalies and overstresses.
Part derating may sometimes be difficult to achieve
in some instances but is critical for systems being procured by the military
today. When non-military parts are employed they often need protection from
environmental conditions and/or need derating more than military parts. In
addition, non-military parts are not expected to perform for as long as military
parts. These concerns make derating crucial to every application.
The following definitions are adopted for
a. Derate – To reduce the voltage, current, or power
rating of a part to improve its reliability or to permit operation at high
b. Derating – The reduction in rating of a part
especially the maximum power-dissipation rating at higher
c. Derating factor – The factor by which the ratings
of parts are reduced to provide additional safety margins in critical
applications or when the parts are subjected to extreme environmental conditions
for which their normal ratings do not apply.