MIL-PRF-94 Resistors, Variable, Composition General Specification ForThis specification covers the variable resistors having a composition resistance element shaped in an arc, and a contact bearing uniformly thereon, so that a change in resistance is produced between the terminal of the contact and the terminal of either end of the resistance element when the operating shaft is turned. These resistors are capable of full load operation \(where maximum resistance is engaged\) at a maximum ambient temperature of 70 degrees C and are capable for continuous operation when properly derated, at a maximum temperature of 120 degrees C \(see 6.9\).

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MIL-PRF-94G

4.6.1.3.2 Disposition of sample units. Sample units which have passed all the group B inspection may be

delivered on the contract or purchase order, if the lot is accepted.

4.7 Methods of examination and test.

4.7.1 Visual and mechanical examination. Resistors shall be examined to verify that the materials, design,

construction, physical dimensions, marking, and workmanship are in accordance with the applicable requirements

4.7.2 DC resistance. Resistors shall be tested in accordance with method 303 of MIL-STD-202. The following

details shall apply (see 3.5).

Measuring apparatus: Different types of measuring test equipment (multimeter, bridges, or equivalent) are

permitted to be used on the initial and final readings of this test, provided the equipment is the same style

and model, or it can be shown that the performance of the equipment is equivalent. The supplier shall

establish and maintain a calibration system in accordance with NCSL Z540-1, ISO 10012-1, or equivalent

system as approved by the qualifying activity.

Measurement energy for electronic test equipment: The measurement energy applied to the unit under test

shall not exceed 10 percent of the 25 C rated wattage times 1 second.

Limit of error of measuring apparatus. Shall not exceed �0.5 percent for qualification inspection nor �1

percent for conformance inspection.

Test voltage for bridges: Measurements of resistance shall be made using the test voltage specified in

table XIV. The test voltage chosen, whether it be the maximum or lower voltage which would still provide

the sensitivity requires, shall be applied across the terminals of the resistor. This voltage shall be used

whenever a subsequent measurement is made.

TABLE XIV. DC resistance test voltage.

Total resistance,

Maximum

nominal

test voltage

ohms

volts

100 to

999 incl

1,000 to

9,999 incl

10,000 to 99,999 incl

0.1 megohm and over

4.7.2.1 Total resistance. The total resistance of resistors shall be measured between the terminals of the

resistance of element with the contact arm against either stop of taper A and against the stop at the low resistance

end for tapers C and F. The resistance value obtained shall be compared with the specified nominal total resistance

4.7.2.2 Resistance taper. Following the measurement of total resistance measurement shall be made at 50

percent of the electrical rotation. The contact arm may be varied �3 percent of the total electrical rotation from the

specified angle of 50 percent to meet the resistance tolerance of �20 percent (see 3.5.2).

4.7.2.3 Minimum resistance. The contact arm shall be rotated to its extreme counterclockwise limit of mechanical

rotation. With the arm in this position, the resistance between the counterclockwise terminal and the rotating contact

terminal shall be measured. The contact arm shall then be rotated to its extreme clockwise limit of mechanical

rotation. With the arm in this position, the resistance between the clockwise terminal and the rotating contact terminal

shall be measured (with the switch "on") at the exact point where the shaft actuator makes contact with the switch