MIL-PRF-27208 Resistor, Variable, Wirewound, Nonprecision General Specification ForThis specification covers the general requirements for multiturn, lead-screw actuated and single turn wirewound, variable resistors with a contact bearing uniformly over the entire surface of the entire resistive element, wound linearly, when positioned by an actuator. These resistors are capable of full load operation \(where maximum resistance is engaged\) at maximum ambient temperature of 85 Degrees C, and are capable for continuous operation when properly derated, at a maximum temperature of 150 Degrees C \(see figure 2\). These resistors have a resistance tolerance of ┬▒5 percent \(see 3.1\).

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MIL-PRF-27208F

3.16 Moisture resistance. When tested as specified in 4.7.11, resistors shall meet the following requirements:

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

Total resistance:

Insulation resistance:

Shall be not less than 100 megohms.

Visual examination:

There shall be no evidence of mechanical damage.

3.17 Shock (specified pulse). When resistors are tested as specified in 4.7.12, the change in total resistance shall

not exceed �(1 percent +0.05 ohms). The change in setting stability shall not exceed 1 percent plus the specified

maximum resolution (see 3.1), and there shall be no electrical discontinuity or evidence of mechanical damage.

3.18 Vibration, high frequency. When resistors are tested as specified in 4.7.13, there shall be no electrical

discontinuity, and resistors shall meet the following requirements.

Setting stability:

Change shall not exceed 1 percent plus the

maximum specified resolution (see 3.1).

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

Total resistance:

Operating voltage:

Shall not exceed 150 percent of the specified

operating torque (see 3.1).

Visual examination:

There shall be no evidence of mechanical damage.

3.19 Salt spray (corrosion). When resistors are tested as specified in 4.7.14, there shall be no appreciable

corrosion.

3.20 Resistance to soldering heat (applicable to terminal type P,W,X, and Y). When resistors are tested as

specified in 4.7.15, the change in total resistance shall not exceed �(1 percent +0.05 ohms) and there shall be no

evidence of mechanical failure.

3.21 Life. When tested as specified in 4.7.16, resistors shall meet the following requirements:

Resistance between end terminals,

Change shall not exceed 2 percent plus the specified

maximum resolution (see 3.1) between the initial

with the contact arm in the position

measurements and each of the succeeding measurements.

for setting stability:

Setting stability:

Change shall not exceed 2 percent plus the specified

maximum resolution (see 3.1).

Total resistance

Change shall not exceed 2 percent.

Dielectric withstanding voltage at

As specified in 3.11.

atmospheric pressure:

Operating torque

Shall not exceed 150 percent of the specified operating

torque (see 3.1).

Visual examination:

There shall be no evidence of mechanical damage.