MIL-PRF-94G
FIGURE 5. Rotational life test circuit.
4.7.8 Switch life (not applicable to locking bushing type resistors). A 3.0 ampere current, slowing through a carbon
lamp or a wire-wound resistor load with an ac, rms potential of 117 volts ±10 percent applied, shall be interrupted
5,000 times by the operation of the switch. Switch contact resistance shall be measured both before and after the
test (see 3.11). This test may be conducted concurrently with the rotational load life test specified in 4.7.7.
4.7.9 Load life. Resistors shall be tested in accordance with method 108 of MIL-STD-202. The following details
and exceptions shall apply (see 3.12):
a.
Method of mounting: Resistors shall be mounted by their bushings with terminals positioned downward, in
the center of a vertical No. 16 gauge, steel panel, 4 inches square in still air. Still air is surrounding air with
no circulation other than that created by the heat of the resistor being operated. No shielding shall be
located closer than 12 inches from the panel.
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Test temperature and tolerance: 70 C ±5 C
b.
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Initial measurement: Minimum resistance at 25 C +10 C, -5 C (see 4.7.2.3). Following this measurement,
c.
the ambient temperature shall be held at the test temperature for 24 hours ±4 hours without load. At the end
of this period, total resistance shall be measured. This measurement shall be the initial test measurement
that shall be used as a reference for all future measurements of total resistance.
Operation conditions: Rated dc continuous working voltage as specified in (see 3.1), shall be applied
d.
intermittently 1.5 hours "on" and 0.5 hours "off" for a total of 1,000 hours through the contact arm located
against either stop and one resistance element terminal for taper A, and against the stop at the low end and
one resistance element for tapers C and F, so that the rated wattage is dissipated across the entire element.
Adequate precautions shall be taken to maintain constant voltage on resistors under test.
e.
Test condition : D.
f.
Measurements during test: Resistance measurements shall be made at the end of the 0.5 hour off periods
after 100 hours ±8 hours, 200 hours ±8 hours, 500 hours +48 hours, -0 hours have elapsed and compare to
the similar readings taken in 4.7.9c.
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Measurements after the test: The resistors shall be returned to an ambient temperature of 25 C +10 C,
g.
-5OC, and the minimum resistance shall be measured within not less than 2 hours nor more than 4 hours.
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