MIL-DTL-15109D
3.4.2.3 Interpolating. When interpolating rheostats (see 6.4.5) are required to obtain the necessary fineness of
control, the resistance of the interpolating plate shall be not less than the three steps of the main plate, having the
highest ohmic value. The ohms per step shall not exceed 0.4 percent of the total resistance of the main plate.
3.4.2.4 Interchangeability. In no case shall parts be physically interchangeable or reversible unless such parts are
also interchangeable or reversible with regard to function, performance and strength.
3.5 Operational requirements.
3.5.1 Life. Resistors and rheostats shall be capable of withstanding the required electrical and mechanical life
tests without a resistance change in excess of 10 percent (see 4.5.8).
3.5.1.1 Electrical life. Continuously rated resistors and rheostats shall withstand 100 cycles of operation at 125
percent of the continuous duty watt rating of the resistor or rheostat. Each cycle shall consist of 2 hours on and 2
hours off. Intermittently rated devices shall withstand 100 cycles of operation at 125 percent of the intermittent duty
watt rating for the duty cycle specified.
3.5.1.2 Mechanical life. Rheostats, mechanically operated or motor driven, shall withstand 25,000 cycles of
operation at rated load. Each operation shall cover at least 90 percent of the movement possible.
3.5.2 Salt spray. Resistors and rheostats shall withstand exposure to salt spray (see 4.5.9). The change in
resistance shall not exceed 25 percent.
3.5.3 Vibration. Resistors and rheostats shall withstand type I vibration tests of MIL-STD-167-1, without
mechanical damage or malfunctioning (see 4.5.10).
3.5.4 Shock. Resistors and rheostats shall withstand the shock tests specified in MIL-S-901 (see 4.5.11).
3.5.5 Insulation resistance. Insulation resistance, after completion of the electrical life and vibration tests, shall be
not less than 50 megohms for resistors and 5 megohms for rheostats.
3.6 Identification and information plates. Rheostats and resistors or rheostat assemblies shall be provided with an
identification plate containing the manufacturer's name and catalog number, voltage, maximum and minimum
amperes and ohms. Plates shall be brass or corrosion-resistant steel marked by etching, engraving, or stamping not
less than 0.003 inch deep. Alternate methods of marking individual resistors shall be approved by the Command or
agency concerned. Such marking shall contain the manufacturer's name or trademark, ohms, and watts.
3.7 Recycled, recovered, or environmentally preferable materials. Recycled, recovered, or environmentally
preferable materials should be used to the maximum extent possible provided that the material meets or exceeds the
operational and maintenance requirements, and promotes economically advantageous life cycle costs.
3.8 Workmanship. Resistors shall be processed in such a manner as to be uniform in quality and shall be free
from cracked or displaced parts, sharp edges, burrs, and other defects which will affect life, serviceability, or
appearance.
4. VERIFICATION
4.1 Classification of inspections. The inspection requirements specified herein are classified as follows:
(a) Qualification inspection (see 4.2).
(b) Retention of qualification inspection (see 4.3).
(c) Conformance inspection (see 4.4).
4.2 Qualification inspection. Qualification inspection shall consist of the applicable examination and tests of
table I. Inspection shall be conducted at a laboratory satisfactory to the qualifying activity.
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