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

4.3 Inspection conditions and precautions.

4.3.1 Inspection conditions. Unless otherwise specified herein, all inspections shall be in accordance with the test

4.3.2 Precautions. Adequate precautions shall be taken during inspection to prevent condensation of moisture on

resistors, except during moisture resistance test. Precautions shall also be taken to prevent damage by heat when

soldering resistor leads to terminals.

4.4 Qualification inspection. Qualification inspection shall be performed at a laboratory acceptable to the

Government (see 6.3) on sample units produced with equipment and procedures normally used in production.

4.4.1 Sample size. The number of sample units comprising a sample of resistors to be subjected for qualification

inspection shall be as specified in the appendix A to this specification.

4.4.2 Inspection routine. Sample units shall be subjected to the qualification inspection specified in table IV, in the

order shown. Thirty enclosed sample units shall be subjected to the inspection of group I. The sample shall then be

divided equally into five groups of five units each, for group II to VI, inclusive, and subject to the inspection for their

particular group. Three of the remaining five enclosed sample units shall be subjected to the inspection of group VII

only. The remaining two enclosed sample units shall be subjected to the visual and mechanical examination of

group I. Ten additional sample units shall be subjected to group VIII. Qualification shall be extended to other

terminal types of the same style by submission of samples to additional testing in accordance with table A-I.

4.4.3 Defective. Failure of a resistor in one or more tests of a group shall be charged as a single failure. No

failures shall be allowed for groups I, VII, and VIII. One failure shall be allowed for groups II, III, IV, V and VI,

combined. Failures in excess of those allowed shall be cause for refusal to grant qualification.

4.5 Retention of qualification. Every 6 months, the manufacturer shall verify the retention of qualification to the

qualifying activity. In addition, the manufacturer shall immediately notify the qualifying activity whenever the group B

inspection results indicate failures of the qualified product to meet the requirements of this specification. Verification

shall be based on meeting the following requirements:

The manufacturer has not modified the design of the item.

The specification requirements for the item have not been amended so far as to affect the character of the

item.

Lot rejection for group A inspection does not exceed the group A sampling plan.

The requirements for group B inspection are met.

When group B requirements were not met and the manufacturer has taken corrective action satisfactory to the

Government, group B inspection retesting shall be instituted.

4.6 Conformance inspection.

4.6.1 Inspection of product for delivery. Inspection of product for delivery shall consist of group A and group B

inspections.

4.6.1.1 Inspection lot. An inspection lot, as far as practicable, shall consist of all resistors of the same style

produced in a period not to exceed 30 days, produced under essentially the same conditions, and offered for

inspection at one time.

4.6.1.2 Group A inspection. Group A inspection shall consist of the examination and tests specified in table V and

shall be made on the same set of sample units, in the order shown.