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

4.8.24.2 Push (applicable to all terminals except type L). Resistors shall be tested in accordance with method 211 of

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

Test condition: A, except force shall be applied in the direction toward the resistor body, force applied to

each terminal individually.

Measurement after test: Resistors shall be examined for evidence of mechanical damage, and tested for

electrical continuity.

4.8.24.3 Bend (applicable to terminal types P, W, X, and Y only). Resistors shall be firmly clamped and each

terminal shall be bent through 90O at a point .125 inch from the body of the resistor, with the radius of curvature at the

bend approximately .03125 inch. The pin shall be returned to the original position, bent 90O in the opposite direction,

and again returned to the original position. At the conclusion of the test, the resistors shall be examined for evidence

of mechanical damage and tested for electrical continuity.

4.8.25 Life (see 3.30). Resistors shall be tested in accordance with method 108 of MIL-STD-202. The following

details and exceptions shall apply:

Method of mounting: Resistors shall be mounted by their normal mounting means on a .0625-inch thick,

glass base, epoxy laminate. The resistors shall be so arranged that the temperature of any one resistor

shall not appreciably influence the temperature of any other resistor. There shall be no undue draft over

the resistors.

Test temperature and tolerance: 85OC � 5OC.

Initial measurement: Total resistance shall be measured as specified in 4.8.5.1.

Operating conditions: Rated dc or ac working voltage at commercial line frequency and waveform

(see 3.1) shall be applied intermittently to terminals 1 and 3 of the resistor, 1.5 hours "on" and 0.5 hours

"off" the time duration specified in 4.8.25f at the test temperature. Each resistor shall dissipate rated

wattage, but shall not exceed maximum voltage. Adequate precaution shall be taken to maintain the

constant voltage on the resistor.

Test condition: 2,000 hours for qualification with all samples continued to 10,000 hours.

Measurements during test:

(1) Qualification inspection: Resistance (see 4.8.5), shall be measured at the end of the 0.5 hour "off"

periods after 168 hours +72 hours, -24 hours; 504 hours +72 hours, -24 hours; 1,008 hours +72

hours, -24 hours; and 2,016 hours +96 hours, -24 hours have elapsed. Units continued on test shall

be measured at intervals above 2,000 hours in accordance with 4.8.25f(2).

(2) Extended life testing: Resistance (see 4.8.5), shall be measured at the end of the 0.5 hour "off"

periods after 168 hours +72 hours, -24 hours; 504 hours +72 hours, -24 hours; 1,008 hours +72

hours, -24 hours; 2,016 hours +96 hours, -24 hours; and every 2,000 hours +96 hours, -24 hours

thereafter until the required extended life period (10,000 hours +120 hours, -0 hours) have elapsed.

Measurements shall be made as near as possible to the specified time but may be adjusted so that

measurements need not be made during other than normal working days.

Examination after test: Resistors shall be examined for evidence of mechanical damage.