MIL-PRF-39009 Resistors, Fixed, Wire-Wound \(Power Type, Chassis Mounted\), Nonestablished Reliability, Established Reliability, General SpecificationThis specification covers the general requirements for nonestablished reliability \(non-ER\), and established reliability \(ER\), power type, wire wound, fixed resistors which utilize the principal of heat dissipation through a metal mounting surface. These resistors have initial resistance tolerances of ??1 percent. These resistors are suitable for continuous full load operation at an ambient temperature of +25 degrees C, and when derated up to +250 degrees C \(see figure 1\). These resistors should not be used in circuits where their ac performance is of critical importance in the operation of such circuits. However, provisions have been made in particular styles to minimize inductances \(see 3.1\). These resistors will have life failure rate levels \(FRL\) ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.4\). These FRL are established at a 60 percent confidence on the basis of the life tests. The FRL, identified by the appropriate symbol, is referred to operation at full rated wattage at +25 degrees C, with a permissible change in resistance of ??2 percent as the criteria for failure.

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MIL-PRF-39009E

4.4.1 Samples. The number of samples units comprising a sample of resistors to be submitted for

qualification inspection shall be as specified in the appendix to this specification. The samples shall be

taken at random from a production run and shall be produced with equipment and procedures normally

used in production.

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

in the order shown. All sample units shall be selected to the inspection of group I and group IA. The 252

sample units shall then be divided as specified in table V for group II to group V inclusive, and subjected to

the inspection for their particular group. In addition, 10 sample units each shall be subjected to group VI.

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

qualification.

4.4.4 FR level and product level verification (ER only).

4.4.4.1 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 VI of table V (see

4.4.2). Entire life test sample shall continue on test to 10,000 hours as specified in 4.8.13, upon

completion of the 2,000 hour qualification.

b. Procedure II: Extension of qualification to lower FR levels. To extend qualification to the R (0.01

percent) and S (0.001 percent) FR levels unit hours from different resistance values within a style

may be combined. Style combinations shall be as described for lot formation (see 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, periodic group C

inspection).