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

TABLE V. Qualification inspection - Continued.

1/ See appendix A for details.

2/ Failure of a single resistor in one or more tests of a group shall be charged as a single defective.

3/ Group I tests need not be performed if manufacturer presents certified data proving tests have

been previously performed on the qualification sample units.

4/ Nondestructive tests.

5/ Marking shall be considered defective only if illegible or missing. Marking shall remain legible at

the end of all tests.

6/ Test shall not be performed if manufacturer certifies that all external materials are fungus

resistant.

4.6 Conformance inspection.

4.6.1 Inspection of product for delivery.

4.6.1.1 Non-ER resistors. Inspection of product for delivery shall consist of the requirements in 4.6.3.1.

4.6.1.2 ER resistors. Inspection of product for delivery shall consist of group A inspection (see

4.6.2 Inspection and production lot.

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

style, characteristic, and protective enclosure or coating and manufactured under essentially the same

process and conditions during a manufacturing period of 1 month maximum. For purposes of lot formation

all terminal types may be included in the same lot; however, all lead types which are combined shall have

the same method of terminal attachment. All leads in the lot shall be represented in a similar proportion by

samples selected for inspection. Non-ER and ER lots shall be kept separate.

4.6.2.2 Production lot. A production lot shall consist of all resistors of the same characteristic, style,

nominal resistance value, and resistance tolerance. Manufacture of all parts in the lot shall have been

started, processed, assembled, and tested as a group. Lot identity shall be maintained throughout the

manufacturing cycle. Non-ER and ER lots shall be kept separate.

4.6.3 Group A inspection.

4.6.3.1 Non-ER resistors. The manufacturer shall establish and maintain an inspection system to

verify resistors meet visual/mechanical, peak noise, total resistance, immersion, and solderability

requirements. In-line or process control may be part of such a system. The inspection system shall also

include criteria for lot rejection and corrective actions. The inspection system shall be verified under the

overall MIL-STD-790 QPL system. NOTE: Since the non-ER (C level) is the ER design without the mandatory

conformance inspection and FR level assessment, this product is still expected to meet the environmental

qualification type requirements (e.g., moisture resistance, shock, vibration, etc.).

4.6.3.2 ER resistors. Group A inspection shall consist of the inspections specified in table VI, in the

order shown.