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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