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

RX TEST SPECIMEN

OSCILLOSCOPE OR TEST CIRCUIT BANDWITH: DC TO 500 KILOHERTZ MINIMUM.

MINIMUM INPUT IMPEDANCE: 1.0 MEGOHM AT 400 HERTZ.

FIGURE 3. Peak noise measuring circuit.

4.8.4 Total resistance (see 3.10). Resistors shall be tested in accordance with method 303 of

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

a. Measuring apparatus: Different types of measuring test equipment (multimeters, bridges, or

equivalent) are permitted to use, provided the equipment is the same style, model, or if it can be

shown that the performance of the equipment is equivalent to or better.

b. Measure energy for electronic test equipment: The measure energy applied to the unit under test

shall not exceed 10 percent of the 25�C rated wattage times 1 second.

Test for bridges: Measurements of resistance shall be made using the test voltages specified in

table X. The test voltage chosen, whether it is the maximum or a lower voltage which would still

provide the sensitivity required, shall be applied across the terminals of the resistor. This same

voltage shall be used whenever a subsequent resistance measurement is made.

TABLE X. Total resistance test voltages.

Resistance, nominal

Test potential

Volts

Ohms

10 to

100 inclusive

1.5

100 to 1,000 inclusive

3.0

Over 1,000 to 20,000 inclusive

10.0

4.8.4.1 Total resistance. Total resistance shall be measured as specified in 4.8.4, between the

resistance element end terminals (terminal 1 and terminal 3 of figure 1), with the contact arm positioned

against a stop. The positioning of the contact arm and terminal shall be the same for all subsequent

measurements of the total resistance on the same specimen (see 3.10.1).

4.8.4.2 Absolute minimum resistance. The contact arm shall be positioned at one end of the

resistance element, so that a minimum value of resistance shall be measured as specified in 4.8.4

between the contact arm and the corresponding end terminal. The same procedure shall be followed for

the other end of the resistance element. Rated current through the resistance element shall not be

exceeded during this measurement (see 3.10.2).