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|  MIL-R-19365D
4.7.8 Thermal shock (see 3.13). Resistors shall be mounted on a rack of low heat conducting material.
Following a measurement of total resistance (see 4.7.1.1), rated wattage from an ac supply at commercial
line frequency and waveform shall be applied until thermal stability has been reached. The power shall
then be removed and, within 8 second to 12 second, the resistors shall be subjected to an air temperature
of -55C 5C for a period of not less than 15 minutes nor more than 30 minutes. Total resistance shall
again be measured not less than 2 hours after final exposure. Resistors shall then be examined for
evidence of mechanical damage and change in any part of the resistors.
4.7.9 Short time overload (see 3.14). Resistors shall be mounted by their normal mounting means.
Following a measurement of total resistance (see 4.7.1.1), a potential from an ac supply at commercial
line frequency and waveform which will result in 10 times the rated wattage (see 3.1) shall be applied to
the resistors for 5 seconds. In no case shall this voltage exceed 6,000 volts. Total resistance shall again
be measured after the resistors have cooled to room temperature. Resistors shall then be examined for
evidence of mechanical damage, arcing, burning, and charring.
4.7.10 Moisture resistance (see 3.15). Resistors shall be tested in accordance with method 106 of
MIL-STD -202. The following details and exceptions shall apply:
a. Mounting: All resistors shall have their adjustable terminal positioned within 5 percent of
electrical center. Resistors under load shall be mounted horizontally not less than 2.5 inches apart
and with their terminals pointing upward, as follows:
(1) One half of the resistors shall be mounted by means of their associated hardware (see 3.1),
with supplementary insulation.
(2) The remaining half of the resistors shall be mounted, witho ut supplementary insulation,
between two metal plates normal to the longitudinal axis of the resistor (one plate at each end)
held firmly against the ends of the resistor by through bolts. These plates shall be of sufficient
size to extend beyond the extremities of the resistor terminals.
b. Initial measurements: Resistance between adjustable terminal and fixed end terminals, total
resistance, and insulation resistance shall be measured as specified in 4.7.1, 4.7.1.1, and 4.7.6,
respectively.
c. Load and polarization: One half of the resistors shall be subjected to load (see 4.7.10a.1) and the
remaining half to polarization (see 4.7.10a.2).
(1) Load: During the first 2 hours of each of steps 1 and 4, one half the rated wattage from a dc
supply, der ated in accordance with the derating curve shown on figure 1 to the temperature
attained at the end of the 2 hour period, shall be applied to each half of the resistor with the
positive lead connected to the adjustable terminal, and a negative lead to each of the fixed
end terminals. The negative terminals shall be electrically grounded to the mounting surface.
(2) Polarization: During steps 2 and 3, and 5 and 6 a potential of 100 volts dc shall be applied
with the positive lead connected to the terminals tied together, and the negative lead
connected to the mounting hardware.
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