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

3.7 Power rating. Resistors shall have a power rating based on continuous full load operation at an

ambient temperature of +25�C (see 3.1). This power rating is dependent on the ability of resistors to meet

the FR requirements specified in 3.19. For temperatures in excess of those specified above, the load shall

be derated in accordance with figure 1.

FIGURE 1. Derating curve for ambient temperatures.

3.8 Conditioning. When resistors are tested as specified in 4.8.2, there shall be no mechanical

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

3.9 DC resistance. When resistors are tested as specified in 4.8.3, the dc resistance shall be within the

specified tolerance of the nominal resistance (see 1.2.1.2 and 3.1).

3.10 Resistance temperature characteristic. When resistors are tested as specified in 4.8.4, the

resistance temperature characteristic shall not exceed �0.0030 percent per �C (30 ppm) for resistance

values of 20 ohms and higher and �0.0050 percent per �C (50 ppm) for resistance values from 1 ohm to

19.60 ohms and �0.0100 percent per �C (100 ppm) for resistance values below 1 ohm.

3.11 Dielectric withstanding voltage. When resistors are tested as specified in 4.8.5, there shall be no

flashover, show any evidence of mechanical damage, arcing, or insulation breakdown; the change in

resistance shall not exceed �(0.2 percent +0.01 ohm) as applicable..

3.12 Insulation resistance. When resistors are tested as specified in 4.8.6, the insulation resistance

shall not be less than 10,000 megohms.