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

3.13 Low temperature operation. When resistors are tested as specified in 4.8.7, there shall be no

evidence of mechanical damage which will result in degradation of performance. The change in

resistance shall not exceed �(0.3 percent +0.01 ohm).

3.14 Short time overload. When resistors are tested as specified in 4.8.8, there shall be no evidence of

mechanical damage; the change in resistance shall not exceed �(0.3 percent +0.01 ohm).

3.15 Moisture resistance. When resistors are tested as specified in 4.8.9, there shall be no evidence of

breaking, cracking, loosening of terminals, or corrosion; the change in resistance shall not exceed �(0.5

percent +0.01 ohm). In addition, the insulation resistance shall not be less than 1,000 megohms.

3.16 Terminal strength. When resistors are tested as specified in 4.8.10, there shall be no evidence of

mechanical damage. The change in resistance shall not exceed �(0.2 percent +0.01 ohm).

3.17 Shock (specified pulse). When resistors are tested as specified in 4.8.11, there shall be no

evidence of mechanical or electrical damage; the change in resistance shall not exceed �(0.2 percent

+0.01 ohm). There shall be no electrical discontinuity during the test. Resistors shall meet the dielectric

withstanding voltage requirements specified in 3.11.

3.18 Vibration, high frequency. When resistors are tested as specified in 4.8.12, there shall be no

evidence of mechanical damage; the change in resistance shall not exceed �(0.2 percent +0.01 ohm).

There shall be no electrical discontinuity during the test. Resistors shall meet the dielectric withstanding

voltage requirements specified in 3.11.

3.19 Life.

3.19.1 Qualification inspection. When resistors are tested as specified in 4.8.13, there shall be no

evidence of mechanical damage to the resistance element, coating, or enclosure. The change in

resistance between the initial measurement and any succeeding measurement up to and including 2,000

hours shall not exceed �(1.0 percent +0.01 ohm).

3.19.2 FR determination (extend FR test). When resistors are tested as specified in 4.8.13, there shall

be no evidence of mechanical damage to the resistance element, coating, or enclosure. The change in

resistance between the initial measurement shall not exceed �(2.0 percent +0.01 ohm). This single failure

criteria shall be applicable to all measurements during the life test for purposes of determining FR level

qualification and is applicable as a parallel requirement with 3.19.1 to the measurement made during the

life tests specified for qualification inspection.

3.20 High temperature exposure. When resistors are tested as specified in 4.8.14, there shall be no

evidence of mechanical damage and the change in resistance shall not exceed �(1.0 percent +0.05 ohm).

3.21 Solderability. When resistors are tested as specified 4.8.15, the flat portion of the terminal shall be

considered as the solderable area, and meet the criteria for lug or tab terminal evaluation in the test

method.

3.22 Low temperature storage. When resistors are tested as specified in 4.8.16, there shall be no

evidence of mechanical damage. The change in resistance shall not exceed �(0.3 percent +0.01 ohm).