MIL-DTL-15109D
4.5.7 Temperature rise. The test methods to be employed and the precautions to be observed in conducting
temperature rise tests shall be in accordance with NEMA ICS 1 and the following:
4.5.7.1 General. Temperature rise tests shall be made under conditions equivalent to normal operating conditions
at rated voltage, frequency load, and the duty specified to determine that the rises specified in 3.3.6 are not
exceeded.
4.5.7.2 Ambient temperature. Resistors and rheostats shall be tested at any convenient room temperature above
10 C, but whatever the value of this ambient temperature, the maximum permissible temperature rises specified
herein shall not be exceeded.
4.5.7.3 Ambient measurement. The ambient temperature shall be measured by means of two or more
thermometers placed at different points around and on a level with the resistor or rheostat and at a distance of 3 to 6
feet therefrom. The thermometers shall be inserted in oil filled cups not less than 1 inch in external diameter and 2
inches high, and shall be protected from drafts and from heat radiation from the item under test or from outside
sources. The value to be adopted for the room temperature during the test shall be the mean of the readings of the
several thermometers, placed as stated, taken at four equal intervals of time during the last quarter of the duration of
the test. The resistor or rheostat under test shall be protected from drafts and from heat radiation from outside
sources.
4.5.7.4 Ambient variations. A variation of more than 10 C, during a period of 6 hours, or a proportional change for
runs of shorter duration, shall not be permitted. If the ambient variations are excessive or if the ambient changes
rapidly at the end, the test shall be repeated.
4.5.7.5 Starting temperature. Temperature rise tests shall not be started if the ambient differs more than 5 C from
the ambient where the equipment has stood during the preceding 2 hours.
4.5.8 Life. Life tests shall be as specified in 3.5.1. The resistance of the resistor or rheostat shall be measured
and recorded at the end of the tests.
4.5.9 Salt spray. Resistors and rheostats shall be exposed to 4 hours of salt spray in accordance with ASTM B
117, washed in tap water, external surfaces dried and the resistance measured immediately. After completion of this
4-hour test, resistors and rheostats shall be exposed to 100 hours of salt spray in accordance with ASTM B 117. The
condition of the finish shall be recorded at the end of this test.
4.5 10 Vibration. Resistors and rheostats shall be subjected to the vibration tests specified in MIL-STD-167-1,
type I tests, under load. Rheostats shall be adjusted to approximately the mid-position. Operation shall be checked
at each frequency of vibration.
4.5.11 Shock. Shock tests shall be conducted under load. Rheostats shall be adjusted to approximately the mid-
position. MIL-S-901 and the following apply:
4.5.11.1 Method of mounting.
4.5.11.1.1 Resistors. Standard mounting for electrical controller components (contacts, relays, resistors, and so
forth) type C lightweight equipment figure of MIL-S-901 shall be used for individual resistors or sub-assemblies. The
number of resistors to be tested at one time shall depend on the size of the panel and the condition that there be
sufficient clearance between adjacent resistors to prevent impact between samples under shock. Individual resistors
shall be supported at one end, mounted on brackets supplied by the manufacturer or mounted on sharp-edge L-
shaped brackets of at least 0.094 inch thickness or heavier, as necessary, to prevent bracket distortion under shock.
The choice of brackets is dependent upon the manner in which the resistors are normally mounted. Standard
mounting for bulkhead mounted equipment type A test lightweight equipment figure of MIL-S-901 shall be used for
resistor assembly's intended for bulkhead mounting.
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