MIL-PRF-39035 Resistor, Variable, Nonwirewound \(Adjustment Type\), Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), multiturn lead-screw actuated, and single-turn, nonwirewound, variable resistors with a contact bearing uniformly over the surface of the entire resistive element, when positioned by an actuator. These resistors are capable of full-load operation \(when the maximum resistance is engaged\), at a maximum temperature of 150 Degrees C, with a resistance tolerance of ??10 percent. The ER resistors will have life failure rate levels ranging from 1.0 to 0.001 percent per 1,000 hours \(see 1.2.1.5\). These failure rate levels are established at a 60 percent confidence level maintained at 10 percent producer\'s risk on the basis of the life tests.

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MIL-PRF-39035E

4.7.1 Sampling plan. If more than 1,000 resistors of any style or style grouping are produced over the

maintenance period, the group B tests shall be performed as specified. If the production rate is less than 1,000

resistors for any style or style grouping over the maintenance period then the monthly, quarterly, or semi-annual

group B inspection may be postponed until at least 1,000 resistors of that style or style grouping are produced (except

for the monthly life test). In any case, the monthly tests shall be performed at least once every 3 months. The

quarterly tests shall be performed at least every 6 months and the semi-annual tests shall be performed at least once

every year. This is waived if the semi-annual tests shall be performed at least once every year. This requirement is

waived if the manufacturer has obtained a reduced inspection status through the qualifying activity.

All qualified styles may be grouped together in a single sample. This can be accomplished by proportion based on

manufacturing percentages by styles, equally divided by style, or by establishing an alternating style sequence. In

order to incorporate a style sample grouping, a written description must be presented and approved by the qualifying

activity. This plan must assure that the grouping only combines styles of the same basic design, encapsulation

material, and the same element type.

4.7.2 Quarterly.

4.7.2.1 Subgroup 1. Samples shall be accumulated from each inspection lot and placed on extended life

(see 4.8.25) of for the full 10,000 hour life test. A sufficient number of samples shall be selected from each lot by the

manufacturer so that the maintenance of FR requirements are complied with, within the specified maintenance period.

In any event, a minimum of 5 samples shall be selected from each lot. As far as practicable, the manufacturer shall

select the resistance values so that all resistance decades produced during the maintenance period are represented.

4.7.2.2 Subgroup 2 and subgroup 3. Quarterly, the specified number of sample units shall be subjected to the

tests specified in table X.

4.7.3 Semiannual. Sample units and tests shall be as specified in table X.

4.7.4 Disposition of sample units. Sample units which have been subjected to group B inspection shall not be

delivered on the contract or purchase order.

4.7.5 Noncompliance. If a sample fails to pass group B inspection, the manufacturer shall notify the qualifying

activity and the cognizant inspection activity of such a failure and take corrective action on the materials or processes,

or both, as warranted, and on all units of product which can be corrected and which were manufactured under

essentially same materials and processes, and which are considered subject to the same failure. For ER level,

acceptance and shipment of the product shall be discontinued until corrective action, acceptable to the qualifying

activity has been taken. For C level, stop shipment may not be necessary depending on the nature of the failure.

After corrective action has been taken, group B inspection shall be repeated on additional sample units (all

inspections, or the inspection which the original sample failed, at the option of the qualifying activity). Group A

inspection may be reinstituted; however, final acceptance and shipment shall be withheld until the group B inspection

has shown that the corrective action was successful.

4.8 Methods of inspection.

4.8.1 Visual and mechanical examination. Resistors shall be examined to verify that the materials, design,

construction, physical dimensions, marking, and workmanship are in accordance with the applicable requirements

(see 3.1, 3.3, to 3.3.2 inclusive, 3.4 to 3.5.11 inclusive, and 3.33 to 3.34 inclusive).