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

3.16.2 Clutch. When resistors are tested as specified in 4.8.10.2, the contact arm shall idle against the

stop without electrical ohmmeter discontinuity or evidence of mechanical damage. The travel of the

contact arm shall also be capable of reversing direction.

3.17 Thermal shock. When resistors are tested as specified in 4.8.11, the change in total resistance

shall not exceed �1 percent for resistance values of 100 ohms or greater �(1.0 percent +0.05 ohm) for

values below 100 ohms. The change in setting stability shall not exceed �0.5 percent plus the specified

maximum resolution (see 3.1). Resistors shall meet the requirements of 3.10.1 and there shall be no

evidence of mechanical damage.

3.18 Solderability (applicable to terminals P, W, X, and Y only). When resistors are tested as specified

in 4.8.12, they shall meet the criteria for wire lead terminal evaluation in the test method.

3.19 Resistance temperature characteristic. When resistors are tested as specified in 4.8.13, the,

resistance temperature characteristic, referred to an ambient temperature of 25�C, shall not exceed

�0.005 percent per degree Celsius (50 PPM/�C) (see table X and table XI). This measurement is made

with the contact arm against the stop.

3.20 Moisture resistance. When resistors are tested as specified in 4.8.14, resistors shall meet the

following requirements:

Change shall not exceed �1 percent for resistance values of 100 ohms

Total resistance:

or greater, and �(1.0 percent +0.05 ohm) for values below 100 ohms.

Shall not be less than 100 megohms.

Insulation resistance:

There shall be no evidence of mechanical damage.

Visual examination:

3.21 Shock (specified pulse). When resistors are tested as specified in 4.8.15, the change in total

resistance shall not exceed �1 percent for resistance values of 100 ohms and greater and �(1.0 percent

+0.05 ohm) for values below 100 ohms. The change in setting stability shall not exceed �0.5 percent plus

the specified maximum resolution (see 3.1) and there shall be no electrical discontinuity or evidence of

mechanical damage.

3.22 Vibration, high frequency. When resistors are tested as specified in 4.8.16, there shall be no

electrical discontinuity and resistors shall meet the following requirements:

Change shall not exceed 0.5 percent plus the specified maximum

Setting stability:

resolution (see 3.1).

Total resistance:

Change shall not exceed �1 percent for resistance values of 100 ohms

or greater, and �(1.0 percent +0.05 ohm) for values below 100 ohms.

Visual examination:

There shall be no evidence of mechanical damage.

3.23 Salt spray (corrosion). When resistors are tested as specified in 4.8.17, there shall be no

evidence of mechanical damage.

3.24 Resistance to soldering heat (applicable to terminals P, W, X, and Y). When resistors are tested

as specified in 4.8.18, the change in total resistance shall not exceed �1 percent for resistance values of

100 ohms or greater, and �(1.0 percent +0.05 ohm) for values below 100 ohms. There shall be no

evidence of mechanical damage.