MIL-PRF-39015 Resistors, Variable, Wirewound, \(Lead Screw Actuated\), Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), lead screw actuated; wirewound variable resistors with a contact bearing uniformly over the surface of the entire resistive element, wound linearly, when positioned by a multiturn lead screw actuator. These resistors are capable of full load operation \(when the maximum resistance is engaged\), at a maximum temperature of 85OC and are capable for continuous operation, when properly derated, at maximum temperature of 150OC \(see 3.6\), with a resistance tolerance of ??5 percent. The ER resistors have life failure rate \(FR\) levels ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.4\). These FR levels are established at a 60 percent confidence level on the basis of life tests.

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MIL-PRF-39015E

4.4.2 Test routine. Sample units shall be subjected to the qualification inspection specified in table V,

in the order shown. Sample test routine shall be as indicated in the appendix A. The qualification of

other than "P" type terminals shall be only applicable at the time of the original submission (see table A-I).

The manufacturer shall not submit all of one terminal type at original submission and request

qualification extension to a different terminal by partial submission at a later date. The qualification life

sample shall be continued on test for 10,000 hours. The requirement of 3.31.2 shall apply for FR data

accumulation.

4.4.3 Defectives. Defectives in excess of those allowed in table V shall be cause for refusal to grant

qualification approval.

4.4.4 FR qualification. FR qualification shall be in accordance with the general and detail requirements

of MIL-STD-690 and the following details:

a. Procedure I: Qualification at the initial FR level. Level M (1.0 percent of FRSP-60) shall apply.

Sample units shall be subjected to the qualification inspection specified in group VII, table V (see

4.4.2). Entire life test sample shall continue on test to 10,000 hours as specified in 4.8.25, upon

completion of the 2,000 hour qualification.

b. Procedure II: Extension of qualification to lower FR levels. To extend qualification to the "R"

level (0.01 percent) and "S" (0.001 percent) FR level unit hours, two or more styles of similar

construction may be combined. Style combination shall be as described for lot formation (4.6.2).

Procedure III: Maintenance of FR level qualification. Maintenance period "B" of FRSP-10 shall

apply. Regardless of the number of production lots produced during this period, the specified

number of unit hours shall be accumulated to maintain qualification (see 4.7).

4.4.5 PPM level verification. The contractor is responsible for establishing a quality system to assess

the PPM level of lots that are subjected to group A inspections. The PPM defect level shall be based on

a 6 month moving average.

4.5 Verification of qualification . Every 6 months, the manufacturer shall provide verification of

qualification to the qualifying activity. Continued qualification is based on meeting the following

requirements.

b. Design of resistor has not been modified.

Lot rejection for group A (subgroup 1 and subgroup 3) does not exceed 10 percent or one lot,

whichever is greater.

d. Periodic group B inspection.

e. FR levels.

PPM assessment (NOTE: Grouping of style is permitted).

g. Continued qualification to non-ER ("C") shall be based on continued maintenance of qualification

for the ER part (minimum "M" FR level maintained).