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

4.8.10.2 Clutch (see 3.16.2). The contact arm shall be adjusted to each extreme limit of mechanical travel, and

sufficient torque shall be applied to the lead-screw actuator to permit the contact arm to idle for 25 complete

mechanical turns of the lead-screw actuator. During idle, a suitable electrical indicating device connected between

the contact-arm terminal and the adjacent end terminal shall be observed for electrical continuity. After idle, the

operating shaft shall be rotated in the opposite direction and the indicating device observed to determine if the contact

arm reversed direction.

4.8.10.3 Stop (when applicable) (see 3.16.3). Resistors shall be mounted by their normal mounting means. The

contact arm shall then be rotated to each extreme limit of mechanical rotation, and the specified torque (see 3.1),

applied through the operating shaft to the stop.

4.8.11 Thermal shock (see 3.17). Resistors shall be tested in accordance with method 107 of MIL-STD-202. The

following details and exceptions shall apply:

Test condition: F.

Measurements before cycling: Total resistance and setting stability shall be in as specified in 4.8.5.1 and

4.8.12, respectively.

Measurements after cycling: Setting stability, total resistance, and continuity shall be measured as

specified in 4.8.12 and 4.8.5.1, respectively. Continuity of the contact arm shall be verified by connecting

a vacuum-tube voltmeter or suitable indicating device, between the contact arm terminal and the

counterclockwise end terminal. The applied voltage shall be in accordance with table XI.

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

4.8.12 Setting stability. The contact arm shall be set at approximately 40 percent of the actual effective electrical

travel. An adequate dc test potential shall be applied between the end terminals. The voltage between the end

terminals, and the voltage between one end terminal and the contact arm, shall be measured and applied to the

following formula:

E1 X 100

Setting in percent =

Where:

E1 = Voltage across one end terminal and the contact arm terminal.

E2 = Voltage across the end terminals.

The difference between the initial measurements made before the environmental test and the measurement made

after the test indicates the setting stability in percent.

4.8.13 Solderability (see 3.18). Resistors shall be tested in accordance with method 208 of MIL-STD-202. All pin

terminals of each resistor shall be tested.

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

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

Test temperatures: As specified in table XII.

Measurements at the end of each period: Total resistance shall be measured as specified in 4.8.5.1,

(wiper against stop, measured through end terminals) at temperature maintained during the period.