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

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

mechanical damage and the change in resistance shall not exceed �0.5 percent for resistance values of

100 ohms or greater, and �(0.5 percent +0.05 ohm) for values below 100 ohms.

3.9 Peak noise. When resistors are tested as specified in 4.8.3, the peak noise resistance shall not

exceed 500 ohms, with the following exceptions:

In group I of table V:

Shall not exceed 100 ohms.

In group IV of table V:

Shall not exceed 200 ohms.

Shall not exceed 100 ohms.

3.10 DC resistance.

3.10.1 Total resistance. When measured as specified in 4.8.4.1, the total direct current (dc) resistance

shall not deviate from the specified nominal (see 3.1) by more than �5 percent.

3.10.2 Absolute minimum resistance. When measured as specified in 4.8.4.2, the absolute minimum

resistance shall not exceed 0.25 percent of the nominal total resistance value, or 1 ohm, whichever is

greater.

3.10.3 End resistance. When measured as specified in 4.8.4.3, the end resistance shall not exceed 2

percent of the nominal total resistance value, or 1 ohm, whichever is greater.

3.10.4 Resistance value deviations. All maximum deviations as specified in this section are to be

considered absolute limits with the exception of the contact resistance adjustments.

3.11 Immersion (not applicable to L terminals). When resistors are tested as specified in 4.8.5, no

continuous stream of bubbles shall emanate from any concentrated point of the resistor. When resistors

are subjected to the dye penetrate test, there shall be no evidence of dye in the internal cavities.

3.12 Continuity. When resistors are tested as specified in 4.8.6, the change in voltage or resistance

shall be smooth and unidirectional throughout the effective electrical travel.

3.13 Actual effective electrical travel. When resistors are tested as specified in 4.8.7, the number of

turns of the operating shaft necessary for the contact arm to traverse the resistance element shall be as

specified (see 3.1).

3.14 Dielectric withstanding voltage. When resistors are tested as specified in 4.8.8, there shall be no

evidence of damage, arcing, or breakdown. The leakage current shall not exceed 1 milliampere.

3.15 Insulation resistance. When resistors are tested as specified in 4.8.9, the dry insulation

resistance shall not be less than 1,000 megohms.

3.16 Torque.

3.16.1 Operating. When resistors are tested as specified 4.8.10.1, the torque required to move the

contact arm shall be as specified (see 3.1).