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

4.8.7 Low temperature operation (see 3.13). Resistors shall be mounted as specified in 4.8.13a.

Following a measurement of resistance (4.8.3), rated voltage from an ac supply at commercial-line

frequency and waveform (see 3.6) shall be applied until thermal stability has been reached. The potential

shall be removed, and within 8 seconds to 12 seconds, the resistors shall be subjected to an air

temperature of -55�C, +0�C, -5�C for a period of not less than 15 minutes or more than 30 minutes.

Resistance (see 4.8.3) shall again be measured not less than 2 hours after final exposure. Resistors shall

then be examined for evidence of mechanical damage.

4.8.8 Short time overload (see 3.14). Resistors shall be mounted as specified in 4.8.13a. One of the

resistor terminals shall be grounded to the resistor housing during the test. Following a measurement of

resistance (see 4.8.3), a test potential from an ac supply at commercial line frequency and waveform

which will result in five times the rated wattage (see 3.1), but not to exceed the specified voltage used for

dielectric withstanding voltage test (atmospheric pressure) (see 3.1), shall be applied to the resistors for 5

seconds. Resistance (see 4.8.3) shall be measured after the resistors have stabilized at room

temperature. Resistors shall then be examined for evidence of arcing, burning, and charring.

4.8.9 Moisture resistance (see 3.15). Resistors shall be tested in accordance with method 106 of MIL-

STD-202. The following details and exceptions shall apply:

a. Mounting: Resistors under load shall be mounted as specified in 4.8.13a. Resistors under

polarization shall be mounted as specified in 4.8.5.1a.

b. Initial measurements: Resistors shall be measured as specified in 4.8.3.

Load and Polarization: One-half of the resistors shall be subjected to load and the remaining half

to polarization.

(1)

Load: During the first 2 hours of step 1 and step 4, the rated dc continuous working voltage

(see 3.6), derated in accordance with figure 1 to the temperature attained at the end of the

two hour period, shall be applied to the resistors. The negative terminals shall be

electrically grounded to the mounting surface.

(2)

Polarization: During steps 1 to 6 inclusive, a 100 volt dc potential shall be applied with the

positive lead connected to the resistor terminals tied together, and the negative lead

connected to the mounting plate.

d. Final measurements and examination: At the end of the final cycle, the resistors shall be removed

from the chamber, conditioned at room ambient conditions, and the dc resistance and insulation

resistance shall be measured as specified in 4.8.3 and 4.8.6, respectively, within 8 hours of

removal from the chamber. The resistors shall not be wiped or forced air dried prior to these

measurements. Resistors shall then be examined for evidence of breaking, cracking, loosening of

terminals, and corrosion. (The subsequent 4 hour to 24 hour conditioning period and

measurements do not apply).

e. Step 7b: Vibration subcycle, step 7b is not required to be performed.