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

FIGURE 1. Circuit diagram

3.5.3.1.3 Legibility. Marking shall remain legible after all tests.

3.5.4 Securing of screw-thread assemblies. Screw-thread assemblies shall not loosen as a result of the tests

specified herein.

3.5.5 Operating shaft. The operating shaft shall be of corrosion-resistant material with the head insulated from all

electrical parts of the resistor.

3.5.6 Contact-arm assembly. Contact pressure on the resistance element shall be maintained by positive pressure

and shall permit smooth electrical and mechanical control of the resistor over the entire range. The moving contact

shall have continuous electrical contact with its terminal throughout the entire mechanical travel and shall be insulated

from the operating shaft head and case.

3.5.7 Mechanical limits.

3.5.7.1 Clutches (applicable only to multiturn adjustment type units, unless otherwise specified). Clutches shall be

furnished to permit the contact arm to idle at either end of the resistance element without electrical or mechanical

malfunction (see 3.1 and 3.16.2).

3.5.7.2 Stops (applicable to single turn units, unless otherwise specified). Stops employed to limit the mechanical

rotation of the contact arm assembly may be part of, but shall not complete an electrical circuit

3.5.8 Riveting. When riveting is required, the operation shall be carefully performed to insure that the rivets are

tight and satisfactorily headed. Riveting shall not be used in assembling two or more current-carrying parts to an

insulating material.

3.5.9 Flux and cleaning agents. Flux for soldering of electrical connections shall be resin or resin and alcohol. No

acid or acid salts shall be used in preparation for or during soldering; however, exception is permitted for preliminary

tinning of electrical connections and for tinning or soldering of mechanical joints not used to complete electrical

circuits. Acid or acid salts shall not be used where they can come in contact with insulation material. Where acid or

acid salts are used, as permitted herein, they shall be completely neutralized and removed immediately after use.

3.5.10 Process. Soldering connections shall be neat. There shall be no sharp points or rough surfaces resulting

from insufficient heating. The solder shall feather out to a thin edge, indicating proper flowing and wetting action, and

shall not be crystallized, overheated, or underheated. The minimum necessary amount of flux and solder shall be

used for electrical connections. Excess resin shall be removed without damage to the solder connection. Insulation

material that has been subjected to heating during the solder operation shall be undamaged and parts fastened

thereto shall not have become loosened.