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

4.8.13 Resistance temperature characteristic (see 3.19). Resistors shall be tested in accordance with

method 304 of MIL-STD-202. The following details shall apply:

a. Test temperatures: As specified in table XI.

b. Measurements at the end of each period: Total resistance shall be measured as specified in

4.8.4.1, (wiper against stop, measured through end terminals) at temperature maintained during

the period.

TABLE XI. Resistance-temperature characteristics.

Temperature 1/

Sequence

�C �3�C

2/ 25

3/ 2

-15

-55

2/ 25

3/ 5

150

1/ At the option of the manufacturer, the reverse

sequence may be as follows:

1: 25�C � 3�C.

2: 65�C � 3�C.

3. 150�C � 3�C.

4: 25�C � 3�C.

5: -15�C � 3�C.

6: -55�C � 3�C.

2/ This temperature shall be considered the reference

temperature for each of the succeeding temperatures.

3/ Not applicable in conformance inspection.

4.8.14 Moisture resistance (see 3.20). Resistors shall be tested in accordance with method 106 of

MIL-STD-202. The following details and exceptions shall apply:

a. Mounting: Clamped, or otherwise mounted with the terminals exposed on a stainless steel panel

of sufficient size to extend beyond the resistor extremities, and in such a manner as to allow

electrical connections to be made to the terminals. Mounting means shall also be provided for the

insulation resistance test (see 4.8.8.1a).

b. Initial measurement: Immediately following the initial drying period, total resistance shall be

measured as specified in 4.8.4.1.

c. Steps 7a and 7b are not applicable.