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

4.8.23 Rotational life (see 3.28).

4.8.23.1 Mounting. Resistors shall be suitably mounted in such a manner as to allow electrical connections to be

made to the terminals and concurrent contact arm actuation of each "pair" of resistors. The resistors, ganged in pairs,

and each pair shall be connected in series, as shown on figure 4, so that a nominally constant current flows through

the resistors, irrespective of the contact-arm position during the turning of the lead screw actuators.

4.8.23.2 Procedure. Total resistance shall be measured as specified in 4.8.5.1. A dc potential, equivalent to that

required to dissipate rated wattage across the entire resistive element of resistors having the same nominal total

resistance as those under test, shall then be applied as shown on figure 4. The operating shaft shall be continuously

cycled through 90 percent to 100 percent of the actual effective electrical travel, at the rate of one cycle for 2.5

minutes, for the multiturn units and 5 seconds to 2 minutes for single turn units, for a total of 200 cycles. A cycle shall

consist of travel through 90 to 100 percent of actual effective electrical travel and return to the starting point. At no

time during this test shall the contact arm be allowed to idle at either end of the travel. After rotation, total resistance

shall be measured as specified in 4.8.5.1. Resistors shall be examined for evidence of mechanical damage.

FIGURE 4. Rotational life test circuit.

4.8.24 Terminal strength (see 3.29).

4.8.24.1 Pull (applicable to all terminal types). Resistors shall be tested in accordance with method 211 of

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

Test condition: A. Applied force - 2 pounds. Resistors clamped by the resistor body, force applied to

each lead individually.

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

electrical continuity.