MIL-PRF-39015 Resistors, Variable, Wirewound, \(Lead Screw Actuated\), Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), lead screw actuated; wirewound variable resistors with a contact bearing uniformly over the surface of the entire resistive element, wound linearly, when positioned by a multiturn lead screw actuator. These resistors are capable of full load operation \(when the maximum resistance is engaged\), at a maximum temperature of 85OC and are capable for continuous operation, when properly derated, at maximum temperature of 150OC \(see 3.6\), with a resistance tolerance of ??5 percent. The ER resistors have life failure rate \(FR\) levels ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.4\). These FR levels are established at a 60 percent confidence level on the basis of life tests.

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MIL-PRF-39015E

4.8.8 Dielectric withstanding voltage (see 3.14).

4.8.8.1 Atmospheric pressure. Resistors shall be tested in accordance with method 301 of

MIL-STD-202. The following details shall apply:

a. Special preparations: Resistors shall be mounted on metal plates of sufficient size to extend

beyond the resistor extremities, and in such a manner that measurements can be made between

the terminals tied together and any other external metal parts.

b. Magnitude of test voltage: 900 volts rms.

Nature of potential: From an alternating current (ac) supply at commercial line frequency and

waveform.

d. Points of application of test voltage: Between the resistor terminals connected together and the

metal portions of the resistors and metal mounting plate.

e. Examinations and measurements: During the tests, the leakage current shall be monitored and

the resistors examined for evidence of arcing and breakdown. At the conclusion of the test,

resistors shall be examined for evidence of damage.

4.8.8.2 Barometric pressure. Resistors shall be tested in accordance with method 105 of

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

a. Method of mounting: As specified in 4.8.8.1a.

b. Test condition: C.

Period of time at reduced pressure prior to applicable of potential: One minute.

d. Test during subjection to reduced pressure: A potential of 350 volts rms from an ac supply at

commercial line frequency and waveform shall be applied for 1 minute.

e. Points of application: As specified in 4.8.8.1d.

Examinations and measurements: As specified in 4.8.8.1e.

4.8.9 Insulation resistance (see 3.15). Resistors shall be tested in accordance with method 302 of

MIL-STD-202. The following details shall apply:

a. Special preparation: As specified in 4.8.8.1a.

b. Test condition: A or B, whichever is more practicable.

Points of measurement: As specified in 4.8.8.1d.