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

4.7 Periodic Group C inspection (ER only). Periodic inspection shall consist of group C inspection tests

specified in table X, in the order shown. They shall be performed on sample units selected from lots that

have passed group A and group B inspection. Except where the results of these inspections show

noncompliance with the applicable requirements (see 4.7.6), delivery of products which have passed

group A and group B inspections shall not be delayed pending the results of these periodic inspections.

4.7.1 Sampling plan. If more than 1,000 resistors of any style or style grouping are produced over the

maintenance period, the group C tests shall be performed as specified. If the production rate is less than

1,000 resistors for any style or style grouping over the maintenance period then the monthly, quarterly or

semi-annual group C inspection may be postponed until at least 1,000 resistors of that style or style

grouping are produced (except for the monthly life test). In any case, the monthly tests shall be performed

at least once every 3 months. The quarterly tests shall be performed at least every 6 months and the

semi-annual tests shall be performed at least once every year. This requirement is waived if the

manufacturer has obtained a reduced inspection status through the qualifying activity.

All qualified styles may be grouped together in a single sample. This can be accomplished by proportion

based on manufacturing percentages by style, equally divided by style, or by establishing an alternating

style sequence. In order to incorporate a style sampling grouping, a written description must be presented

and approved by the qualifying activity. This plan must assure that the grouping only combines styles of

the same basic design, encapsulation material, and the same element type.

4.7.2 Monthly.

4.7.2.1 Monthly (subgroup 1). A minimum of five samples shall be selected from each inspection lot

and placed on extended life test of 4.8.13 once a month for the full 10,000-hour life test. A sufficient

number of samples shall be selected from each lot by the manufacturer so that the maintenance of the FR

requirements is complied within specified maintenance period. As far as practicable, the manufacturer

shall select the resistance values so that the full range of all resistance decades produced during the

maintenance period is represented. The accumulated data shall be used for maintenance or extension of

FR qualification (see 3.19.2).

4.7.2.2 Monthly (subgroup 2 and subgroup 3). Each month the specified number of sample units shall

be subjected to the inspections of table X.

4.7.3 Quarterly. Sample units and tests shall be as specified in table X.

4.7.4 Annual. Sample units and test shall be as specified in table X.

4.7.5 Disposition of samples. Sample units which have been subjected to group C inspection shall not

be delivered on the contract or order.