MIL-PRF-22E
4.7.3 DC resistance. Resistors shall be tested in accordance with method 303 of MIL-STD-202. Measuring
instruments used for initial and final readings of this test, can be of different styles or models provided performance is
equivalent or better (see 3.6).
4.7.3.1 Initial resistance. The contact arm shall be rotated 25 cycles to remove any foreign material which may
have accumulated on the resistance element of the resistor (see 3.6.1.1) .
4.7.3.1.1 Total resistance of a resistor with an electrical off position. The total resistance of a resistor with an
electrical off position shall be the resistance between its terminals when the movable contact is located at the position
introducing the total resistance element of the resistance (see 3.6.2).
4.7.3.1.2 Total resistance of a resistor without an electrical off position. The total resistance of a resistor without
an electrical off position shall be the resistance between the end terminals when the movable contact is at the
extreme counterclockwise end of the total resistance element.
4.7.3.2 Minimum resistance. The contact arm shall be rotated to its extreme counterclockwise limit of rotation.
With the arm in this position, the resistance between the counterclockwise terminal and rotating contact terminal shall
be measured. The contact arm shall then be rotated to its extreme clockwise limit of rotation. With the arm in this
position, the resistance between the clockwise terminal and the rotating contact terminal shall be measured. If one
terminal is an electrical off position, this test shall not apply (see 3.6.2).
4.7.4 Torque (see 3.7).
4.7.4.1 Operating. The torque required to rotate the contact arm on the resistance element shall be determined
throughout the entire range of mechanical rotation by the torque wrench method or by any other method satisfactory
to the Government.
4.7.4.2 Stop. The contact arm shall be rotated to each extreme limit of rotation, and the specified torque (see 3.1)
shall be applied to the operating shaft. Resistors shall then be examined for damage to the contact arm, stop, and
nonturn device, as applicable.
4.7.4.3 Locking (when applicable). Resistors shall be mounted on a metal panel by their normal mounting means
and the locking device tightened with a torque wrench not greater than 8 inch-pounds. With the locking nut tightened,
a 20 ounce-inch torque shall be applied to the operating shaft. Movement of the shaft shall be checked visually, and
resistors shall be examined for damage to the bushing, threads, and nonturn device.
4.7.5 Low temperature exposure. Resistors shall be mounted on a panel in a refrigeration chamber. Low heat
conducting extension shafts shall be placed through holes in the chamber such that rotation of the contact arm may
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be affected from outside the chamber. The chamber shall then be cooled to -55 C +0 C, -3 C and held at this
temperature for 1 hour. At the expiration of the hour, the amount of torque required to rotate the contact arm shall be
determined by the method specified in 4.7.4.1. continuity, electrical connections, loosening of rivets, and effect of
lubrication shall be checked. Resistors shall be examined for electrical and mechanical damage (see 3.8).
4.7.6 Power rating (when applicable) (see 3.1).
4.7.6.1 Mounting. Resistors shall be centrally mounted with terminals pointing downward on a vertical steel panel
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of the dimensions specified in still air at an ambient temperature of 25 C 5 C (see 3.1). No shielding shall be closer
than 12 inches to the panel. Still air is surrounding air with no circulation other than that created by the heat of the
resistor being operated.
4.7.6.2 Procedure. Rated power shall be applied with the contact arm in the position introducing total resistance.
The hot spot shall be determined by the use of a thermocouple with 0.010030 inch diameter (No. 30 AWG) or smaller
wire, after thermal stability has been reached. After determination of the hot spot, the thermocouple shall be
cemented immediately adjacent to the exposed portion of the winding, using a minimum quantity of cement, and the
hot spot temperature rise shall be measured. For the purpose of this test, thermal stability will have been reached
when no further change in temperature is observed between to successive measurements taken at 5 minute
intervals. The hot spot is the point or elemental area of maximum temperature on the exposed surface of the
winding.
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