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

4.8.2 Conditioning (see 3.8). Resistors shall be conditioned in accordance with method 108 of MIL-STD-202. The

following details and exceptions shall apply:

Method of mounting: Supported by their terminals (resistors not mounted on life test chassis). 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 on the resistors.

25OC, +10OC, -5OC.

Temperature and tolerance:

Initial measurements: Initial total resistance shall be measured at 25OC, +10OC, -5OC after mounting as

specified in 4.8.5.1. This initial measurement shall be used as the reference temperature for all

subsequent measurements.

Operating condition: DC continuous working voltage or a continuous working voltage from an ac supply at

commercial line frequency and waveform equivalent to 1.5 times the specified wattage (see 3.1), shall be

applied between the end terminals intermittently 1.5 hours "on" and 0.5 hour "off" for a minimum of 50

hours +8 hours, -0 hours at a temperature of 25OC, +10OC, -5OC. Each resistor shall dissipate 1.5 times

the rated wattage, but not to exceed the maximum voltage specified for each style (see 3.1).

Measurement after conditioning: Total resistance shall be measured at the end of the 50 hours+8 hours, -

0 hours as specified in 4.8.5.1 after load has been removed and the resistors stabilized.

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

Test duration: 50 hours +8 hours, -0 hours.

4.8.3 Contact resistance variation (see 3.9). Contact resistance variation shall be measured with the measuring

circuit shown on figure 3, or its equivalent. The operating shaft shall be rotated in both directions through 90 percent

of the actual effective-electrical travel for a total of 6 cycles. If the product passes on any one of the first three cycles,

then the product is acceptable. Only the last 3 cycles shall count in determining whether or not a contact resistance

variation is observed at least twice in the same location, exclusive of the roll-on or roll-off points where the contact

arm moves from the termination, on or off, the resistance element. Group A, subgroup 1, product acceptance may be

determined based on one cycle minimum where compliance to the specification is demonstrated. The rate of rotation

of the operating shaft shall be such that the wiper completes 1 cycle in 5 seconds, minimum, to 2 minutes, maximum.

4.8.4 Integrity of shaft (see 3.10).

4.8.4.1 Mounting. Resistors shall be mounted on an appropriate mounting fixture with their bodies restrained from

movement.

4.8.4.2 Pull force. A force of 5 pounds (for styles RJR12 and RJR24) and 2 pounds (for styles RJR26 and RJR28)

shall be applied along the axis of the operating shaft, away from the body of the resistor. The force shall be

maintained for a minimum of 1 minute.

4.8.4.3 Perpendicular force. A force of 2 pounds shall be applied in a direction perpendicular to the axis of the

operating shaft for a minimum of 1 minute.

4.8.4.4 Examination after test. Resistors shall be examined for evidence of shaft breakage.