MIL-PRF-49465C
4.8.7 Low temperature storage (see 3.13).
4.8.7.1 Mounting. Resistors shall be mounted in such a manner that there is at least 1 inch of fine air space
around each resistor, and in such a position with respect to the air stream that the mounting offers substantially no
obstruction to the flow of air across and around the resistors.
4.8.7.2 Procedure. DC resistance shall be as specified in 4.8.2. Within 1 hour after this measurement, the
resistors shall be placed in a cold chamber at a temperature of -55 C ±2 C for a period of 24 hours ±4 hours. The
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resistors shall then be removed from the chamber and maintained at a temperature of 25 C ±5 C for a period of
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approximately 2 hours to 8 hours; the dc resistance shall again be measured as specified in 4.8.2. Resistors shall
then be examined for evidence of mechanical damage.
4.8.8 Short time overload (see 3.14). DC resistance shall be measured as specified in 4.8.2. The resistors shall
then be mounted by means other than soldering and shall be subjected to an overload voltage which will result in 5
times rated wattage for a 5 second duration. DC resistance shall again be measured after the resistors have cooled
to room temperature. Care should be taken so as not to exceed the maximum overload current rating (see 3.1).
4.8.9 Dielectric withstanding voltage (see 3.15).
4.8.9.1 Atmospheric pressure. Resistors shall be tested in accordance with method 301 of MIL-STD-202. The
following details and exceptions shall apply:
a.
Special preparation:
(1)
Axial lead resistors shall be placed in a conductive material which will conform to the resistor surface
so that at least 90 percent of the outer periphery is contacted. The resistor leads shall be so
positioned that one of the points of contact of the periphery of the resistor with the V-block is the point
at which the distance from the surface of the resistor leads to the periphery of the resistor body is a
minimum. The minimum distance to the periphery of the resistor body shall be measured from the
point of emergence of the resistor lead.
Initial measurement: DC resistance shall be measured as specified in 4.8.2.
b.
c.
Magnitude of test voltage: 1,000 volts rms.
d.
Nature of potential: An alternating current (ac) supply at commercial line frequency and waveform.
e.
Duration of application of test voltage: 1 minute for qualification and group B inspection.
f.
Rate of application of voltage: The test voltage shall be raised from zero to the application value as
uniformly as practicable, at the rate of 100 volts rms per second for group B and qualification testing.
g.
Points of application of test voltage: Between the resistor terminals connected together and the mounting
hardware, or the V-block, as applicable.
h.
Measurement during the test: The leakage current shall be monitored during the application of the test
voltage.
Measurement after test: The dc resistance shall be measured as specified in 4.8.2.
i.
j.
Examinations after test: Resistors shall be examined for evidence of flashover, mechanical damage, arcing,
and insulation breakdown.
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