MIL-PRF-19E
4.7.8 Load life (see 3.13).
4.7.8.1 Test conditions. During this test, resistors with a diameter of 2 inches (51 mm) or less shall be mounted
with their terminals positioned downward on a 4 inch (102 mm) square, 0.050 inch (1.27 mm) thick, steel panel in still
air. Still air is surrounding air with no circulation other than that created by the heat of the resistor being operated.
Shielding shall be located no closer than 12 inches (304 mm) from the panel. This test shall be conducted at a
temperature of +40OC ± 5OC, whenever possible.
4.7.8.2 Procedure. Following a measurement of resistance within the chamber, at test temperature, rated wattage
(see 3.1) shall be applied 1 hour (30 minutes "on", 30 minutes "off") for a total of 1000 hours through the contact arm
and one resistance element terminal, so that rated wattage is dissipated across the entire resistive element.
Adequate precautions shall be taken to maintain constant wattage on resistors under test. Resistance measurements
shall be made at the end of the 30 minute "off" periods after 100 hours ± 8 hours, 200 hours
± 8 hours, 500 hours ± 12 hours, 1000 hours ± 12 hours have elapsed.
4.7.9 Salt spray (corrosion) (see 3.14). Resistors shall be mounted on an aluminum panel (2S), with there
terminals positioned downward and tested in accordance with tested method 101, test condition A (salt solution 5
percent) of MIL-STD-202. At the conclusion of the test, resistor covers, if any, shall be removed, the resistors shall
be thoroughly rinsed in clear tap water, and then permitted to dry for 24 hours ± 4 hours at +40OC ± 2OC. Resistors
shall be then examined for evidence of damage and corrosion. The resistors shall be tested for electrical continuity
between the end terminals and contact arm terminal and each end terminal over the total mechanical rotation.
MIL-STD 202. The following details and exceptions shall apply:
a.
Mounting: On a noncorrosive metal panel with operating shaft in a horizontal position and radial terminals
pointed downward.
Initial measurements: Resistance shall be measured as specified in 4.7.3 and insulation resistance shall be
b.
measured as specified in 4.7.14.
Load: During steps 1 and 4, a dc voltage corresponding to 65 percent rated wattage (see 3.1) shall be
c.
applied for the first 2 hours of each step to all resistors. The voltage shall be applied across the left
terminal and contact arm, with the operating shaft rotated to the maximum clockwise position
(see figure 1).
d.
Final measurements: At the end of the last cycle and while the resistors are still in the test chamber at the
high humidity condition, total resistance shall he measured as specified in b. above. Following this
measurement of total resistance and for purposes of performing the insulation resistance and dielectric
withstanding voltage tests, the test chamber may be opened in order to make the necessary electrical
connections. These tests shall be performed after chamber has been returned to the high humidity
condition for at least 1 hour. Insulation resistance shall be measured between all the resistor terminals
connected together and the mounting bushing, using a dc potential of 100 volts. Dielectric withstanding
voltage shall be tested as specified in 4.7.2.1 except that the test potential applied to the resistors shall he
250 volts. The subsequent 24 hour conditioning period and measurements do not apply.
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