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

3.24 Life. When tested as specified in 4.6.19, resistors shall meet the following requirements:

The change shall not exceed 2 percent plus the specified nominal

Resistance between end, terminals

resolution (see 3.1) between the initial measurement and each of the

with the contact arm in the position

for setting stability:

succeeding measurements.

Change shall not exceed 2 percent of the total applied voltage plus

Setting stability:

the specified nominal resolution (see 3.1).

Total resistance:

Change shall not exceed 2 percent.

Dielectric withstanding voltage

As specified in 3.12.

(at atmospheric pressure):

Starting torque:

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

Independent linearity tolerance:

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

Visual examination:

There shall be no evidence of mechanical damage.

3.25 Low-temperature operation. When tested as specified in 4.6.20, 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).

Starting torque:

Shall not exceed 150 percent of specified starting torque (see 3.15).

Total resistance:

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

Visual examination:

There shall be no evidence of mechanical damage.

3.26 High-temperature exposure. When tested as specified in 4.6.21, resistors shall meet the following

requirements:

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

Setting stability:

the specified maximum resolution (see 3.1).

Total resistance:

Change shall not exceed �3 percent.

Starting torque:

Shall not exceed 150 percent of specified starting torque (see 3.15).

Dielectric withstanding voltage

As specified in 3.12.

(at atmospheric pressure):

Insulation resistance:

Shall not be less than 1,000 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.

3.27 Rotational life. When resistors are tested as specified in 4.6.22, the change in total resistance between initial

and any succeeding measurement shall not exceed �3 percent; and there shall be no mechanical damage. The

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

3.28 Terminal strength. When resistors are tested as specified in 4.6.23, there shall be no evidence of mechanical

damage, and resistors shall be electrically continuous.