MIL-PRF-19E
3.4.9 Protective housing or enclosure (when applicable see 3.1). The resistance element of the completed
resistors shall be protected by a housing, or an enclosure, or both, which shall cover the exterior of the resistance
element. The protective housing or enclosure shall be free from holes, fissures, chips, or other faults, and shall be
such as to minimize the establishment of leakage paths between terminals, resulting from collection of moisture film
on the exterior surface of the housing or enclosure. If the housing is made from an aluminum alloy, it shall be
properly protected against corrosion, and all fasteners shall be plated. Unplated copper alloy metals shall not be used
in contact with aluminum.
3.4.10 Shaft and panel seals. When shaft and panel seals are specified (see 3.1), the panel seal may be an
integral part of the resistor or may be detachable.
3.5 Voltage Rating. The theoretical calculated rated continuous working voltage or the voltage equivalent to proper
rating (rated wattage) shall be determined from the following formula:
E=
PR
Where:
E = Rated or root mean square (rms) continuous working voltage.
P = Power rating.
R = Nominal total resistance.
3.6 Power rating. The resistors shall have a power rating based on continuous full-load operation at the ambient
temperature of +40OC. The power rating is dependent on the ability of the resistors to meet the requirements
specified in the life test. For temperatures in excess of that specified, the load shall be derated as shown in figure 4.
Power rating as specified (see 3.1) is applicable only when the maximum resistance is engaged in the circuit. When
only a portion of the resistance element is engaged in the circuit, the power rating is reduced in approximately the
same proportion as the engaged resistance.
3.7 Dielectric withstanding voltage. When resistors or switches, as required, are tested as specified in 4.7.2, there
shall be no evidence of damage, arcing, or breakdown. The leakage current shall not exceed 1 milliampere (mA).
3.8 DC resistance (see 4.7.3).
3.8.1 Total resistance. When resistors are tested as specified in 4.7.3.1, the total direct-current (dc) resistance
shall equal the nominal resistance value plus or minus the resistance tolerance.
3.8.2 Resistance taper. A linear resistance taper is one having a constant change of resistance with angular
rotation. A nonlinear resistance taper is one having variation or lack of constancy in the change of resistance with
angular rotation. When resistors are tested as specified in 4.7.3.2, the resistance taper shall conform in general
shape to the nominal curve shown on figures 2 or 3, as applicable. The angle at which any percent of measured
resistance is effective shall be within ±5 percent of the total effective electrical rotation of the specified position as
3.8.3 Minimum resistance. When resistors are tested as specified in 4.7.3.3, the resistance measured between the
rotating contact arm terminal and the adjacent resistance-element terminal shall not exceed the applicable value
listed in table VI.
3.8.3.1 Resistance value deviations. All maximum deviations as specified in this section are to be considered
absolute limits with the exception of the contact resistance adjustment.
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