MIL-PRF-22097 Resistors, Variable, Nonwirewound, Adjustment Type, General Specification ForThis specification covers the general requirements for multi-turn lead screw actuated and single turn nonwirewound, variable resistors with a contact bearing uniformly over the entire surface of the entire resistive element, when positioned by the actuator. These resistors are capable of full load operation \(where maximum resistance is engaged\) at a maximum ambient temperature of 70 Degrees C and 85 Degrees C, and are capable for continuous operation when properly derated, at a maximum temperature of 125 Degrees C and 150 Degrees C \(see figure 1\). These resistors have a resistance of ┬▒10 percent \(see 3.1\).

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MIL-PRF-22097J

3.4.3.1 Terminal identification and circuit diagram.

3.4.3.1.1 Terminal identification.

3.4.3.1.1.1 Terminals P, S, W, X, and Y. For terminals P, S, W, X, and Y type resistors identification shall be by

one of two methods. The numerals designating terminal identification may be marked adjacent to the terminals or the

circuit diagram (see 3.4.3.1.2) may be used, provided that such identification clearly indicates the applicable

terminals.

3.4.3.1.1.2 Terminals L. For terminal L type resistors, the insulation of the flexible leads shall be color coded as

shown on figure 2.

FIGURE 2. Circuit diagram.

3.4.3.1.2 Circuit diagram. The circuit diagram shall be marked on any surface of the resistor in a legible manner,

as shown on figure 2.

3.4.3.1.3 Legibility. Marking shall remain legible after all test.

3.4.3.2 Solder dip (retinning) leads (not applicable to terminal L). The manufacturer may solder dip/retin the leads

of product supplied to this specification provided the solder dip process (see appendix A) has been approved by the

qualifying activity.

3.4.3.2.1 Tin plated finishes. The use of pure tin, as an underplate or final finish is prohibited both internally and

externally. Tin content of resistor components and solder shall not exceed 97 percent, by mass. Tin shall be alloyed

with a minimum of 3 percent lead, by mass (see 6.13).

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

specified herein.

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

electrical parts of the resistor. The operating shaft head shall be slotted as specified (see 3.1).

3.4.6 Contact arm assembly. Uniform 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.

3.4.7 Mechanical limits.

3.4.7.1 Clutches (applicable only to multiturn lead-screw actuated units, unless otherwise specified) (see 3.1).

Clutches shall be furnished to permit the contact arm to idle at either end of the resistance element without electrical

or mechanical malfunctions (see 3.12.2).