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

4.6.5 Group B inspection. Group B inspection shall consist of the examinations and tests specified in

table IX, in the order shown. ER parts shall be performed on inspection lots, that have been subjected to

and have passed group A inspection. Sample units selected shall be of the highest resistance value in the

lot.

TABLE IX. Group B inspection (ER only).

Inspection

Requirement

Test method

Sample

paragraph

size

Subgroup 1 1/

Visual and mechanical

3.1 and 3.24

4.8.1

examination (when applicable)

Subgroup 2 2/

13 (highest

3.10

4.8.4

Resistance temperature

value)

characteristic

1/ Only applicable when marking inspection is not performed in group A inspection.

No defects shall be permitted. Marking shall remain legible at the end of all tests.

2/ If the manufacturer can demonstrate that this test has been performed five consecutive

times with zero failures, the frequency of this test, with the approval of the qualifying activity,

can be performed on an annual basis. If the design, material, construction or processing of

the part is changed, or if there are any quality problems or failures, the qualifying activity

may require resumption of the original test frequency.

4.6.5.1 Sampling plan (ER only). 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. Style grouping is not permitted in cases where group B inspection is being performed on an

annual basis.

4.6.5.2 Subgroup 1. A sample of 13 parts shall be randomly selected. If one or more defects are found,

the lot shall be rescreened and defects removed. A new sample of 13 parts shall be randomly selected. If

one or more defects are found in this second sample, the inspection lot shall be rejected and shall not be

supplied to this specification.

4.6.5.3 Subgroup 2. A sample of 13 parts (highest value) shall be randomly selected. If one or more

defects are found, the lot shall be rescreened and defects removed. A new sample of 13 parts (highest

value) shall be randomly selected. If one or more defects are found in this second sample, the inspection

lot shall be rejected and shall not be supplied to this specification.

4.6.5.4 Disposition of sample units. Sample units which have been subjected to group B, subgroup 1

and subgroup 2 inspections may be delivered on the acquisition document provided they are within

resistance tolerance and meet requirements of group B inspection.