MIL-STD-690-SUP Failure Rate Sampling Plans and ProceduresThis standard provides procedures for failure rate FR qualification, sampling plans for establishing and maintaining FR levels at selected confidence levels, and lot conformance inspection procedures associated with FR testing for the purpose of direct reference in appropriate military electronic parts established reliability ER specifications. Figures and tables throughout this standard are based on exponential distribution. Weibull distribution will be acceptable in certain components such as capacitors. Use of Weibull distribution for any component must be approved by the qualifying activity. This standard also provides guidance to specification writers in the use of this standard see appendix A and references material for users of ER parts.

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MIL-STD-690D

q. Screening. A process for inspecting items to be removed, that are unsatisfactory, or those likely to exhibit early failure. Inspection included visual examination, physical dimension measurement and functional performance measurement under specified environmental conditions.

r. Test, acceptance. A test conducted under specified conditions by, or on behalf of, the Government, using delivered or deliverable items, in order to determine the item's compliance with specified requirements. (includes acceptance of first production units).

s. Test measurement and diagnostic equipment (TMDE). Any system or device used to evaluate the condition of an item to identify or isolate any actual or potential failures.

t. Test qualification (design approval). A test conducted under specified conditions, by or on behalf of the Government, using items representative of the production configuration, in order to determine compliance with item design requirements as a basis for production approval. (also known as a "Demonstration.")

u. True failure rate. This term describes the failure rate that would be measured if all units of a controlled process were, in fact, tested. A "controlled process" is one in which FR variation about its mean is due to chance causes.

v. Truncation. Truncation is a "cutoff" point for life test data, that establishes a precise point in time in which the manufacturer can choose the elimination of previous extended life test data when:

(1) A life test failures has occurred and the manufacturer has determined the cause and implemented corrective action acceptable to the qualifying activity.

(2) The manufacturer seeks an extension of failure rate on the basis of new design improvements, occurring after a life test failure or failures.

The truncation point is not a random event. There must exist a clear distinction between the "old" less reliable and the "new" improved design (see 5.5).