MIL-PRF-39002 Resistors, Variable, Wirewound, Semi-Precision, General Specification ForThis specification covers the general requirements for semi-precision, wirewound, variable, resistors having a resistance element of wire, wound on an arc shaped insulated form, so that a contact bears uniformly on the resistance element, when adjusted by a contact shaft. The electrical output \(in terms of percent of applied voltage\) is linear with respect to the angular position of the contact arm. These resistors are capable of full-load operation \(when the maximum resistance is engaged\) at a maximum ambient temperature of 85 Degrees C, and are suitable for continuous operation, when properly derated, at a maximum temperature of 135 Degrees C. These resistors have a tolerance of ??5 percent.

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MIL-PRF-39002C

3.15.2 Stop. When tested as specified in 4.6.10.2, resistors shall withstand the specified stop torque without

damage to the contact arm and stop.

3.15.3 Locking. When tested as specified in 4.6.10.3, resistors with locking bushings shall withstand the specified

locking torque without damage to the bushing, thread, and nonturn device. The contact arm shall not move when

subjected to the test.

3.16 Thermal shock. When resistors are tested as specified in 4.6.11, the change in total resistance shall not

exceed �(1 percent +0.05 ohm); the change in setting stability shall not exceed 1 percent, of the total applied voltage,

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

mechanical damage. The independent linearity tolerance shall not exceed 150 percent of specified value (see 3.13).

3.17 Resistance-temperature characteristic. When resistors are tested as specified in 4.6.12, the resistance-

temperature characteristic, at each of the test temperatures specified in table VII, referred to an ambient temperature

of 25 C, shall not exceed �0.007 percent (�70 ppm/ C) for resistance values of 50 ohms and above. For resistance

values below 50 ohms the resistance-temperature characteristic shall not exceed �0.020 percent (�200 ppm/ C).

3.18 Moisture resistance. When tested as specified in 4.6.13, resistors shall meet the following requirements:

Total resistance:

Change shall not exceed �3 percent.

Insulation resistance:

Shall be not less than 100 megohms.

Shall not exceed 150 percent of specified value (see 3.13).

Independent linearity tolerance:

Visual examination:

There shall be no evidence of mechanical damage.

3.19 Acceleration. When resistors are tested as specified in 4.6.14, the total resistance shall not exceed �(1

percent +0.05 ohm); the change in setting stability shall not exceed 1 percent of the total applied voltage plus the

specified nominal resolution (see 3.1); there shall be no electrical discontinuity or evidence of mechanical damage.

3.20 Shock, specified pulse. When resistors are tested as specified in 4.6.15, the change in the total resistance

shall not exceed �(1 percent +0.05 ohm); the change in setting stability shall not exceed 1 percent of the total applied

voltage plus the specified nominal resolution (see 3.1); and there shall be no electrical discontinuity or evidence of

mechanical damage.

3.21 Vibration, high frequency. When tested as specified in 4.6.16, there shall be no electrical discontinuity, and

resistors shall meet the following requirements:

Change shall not exceed 1 percent of the total applied voltage plus

Setting stability:

the specified nominal resolution (see 3.1).

Total resistance:

Change shall not exceed �(1 percent +0.05 ohm).

Starting torque:

Shall not exceed 150 percent of specified starting torque (see 3.1).

Shall not exceed 150 percent of specified value (see 3.13).

Independent linearity tolerance:

3.22 Salt spray (corrosion). When resistors are tested as specified in 4.6.17, there shall be no evidence of

corrosion of the base metal; and the resistors shall be mechanically operative.

3.23 Resistance to soldering heat. When resistors are tested as specified in 4.6.18, the change in total resistance

shall not exceed �(1 percent +0.05 ohm); and there shall be no evidence of mechanical damage.