MIL-PRF-94G
4.7.10 Moisture resistance. Resistors shall be tested in accordance with method 106 of MIL-STD-202. The
following details and exceptions shall apply (see 3.13):
a.
Mounting: Resistors shall be mounted by their bushings on a metal panel with the operating shaft in
a horizontal position and the radial terminals pointed downward. Vibration shall be performed either in a
vertical or horizontal plane.
b.
Initial measurements: Total resistance shall be measured between terminal 1 and the contact arm terminal
with the operating shaft rotated to the maximum clockwise position (see figure 2).
c.
During steps 1 and 4, rated (100 percent) wattage or maximum rated dc voltage, whichever is smaller, shall
be applied for the first 2 hours of each step.
d.
Method of applying load voltage: Across terminal 1 and the contact arm terminal, with operating shaft
rotated to the maximum clockwise position (see figure 2).
e.
Final measurements: At the end of the final cycle and while the resistors are still in the humidity chamber at
the high humidity condition, total resistance shall be measured as specified in 4.7.10b. above. Following this
measurement, the humidity chamber may be opened in order to make the necessary electrical connections
to perform the dielectric withstanding voltage (see 4.7.4) and the insulation resistance shall be specified in
table III. The chamber shall then be returned to the high humidity condition and maintained at this condition
for at least 1 hour prior to these test. Dielectric withstanding voltage shall be tested as specified in 4.7.4.1
except that the operating shaft shall not be rotated during the test, electrification time shall be 2 minutes, and
then test potential applied to styles RV5 and RV6 shall be 500 volts. Insulation resistance shall then be
measured between the resistor terminals tied together and mounting bushing, using a dc potential of 500
volts. The subsequent 4 hour to 24 hour conditioning period and measurements do not apply.
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4.7.11 Low temperature storage. The total resistance shall be measured at 25 C +10 C, -5 C. Within 1 hour
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after this measurement, resistors shall be placed in a chamber at a temperature of 25 C +10 C, -5 C. The
temperature in this chamber shall be lowered to -63OC +0OC, -2OC within a minimum period of 3 hours. Twenty fours
hours after the resistors have reached this temperature, the temperature of the chamber shall be gradually raised to
25OC +10OC, -5OC within a maximum period of 8 hours. Resistors shall then be removed from the chamber and
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maintained at 25 C +10 C, -0 C for a period of approximately 24 hours, after which the total resistance shall be
measured (see 3.14).
4.7.12 Low temperature operation. The resistors shall be measured at 25OC, +10OC, -5OC. The resistors shall
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then be placed in a chamber at 25 C, +10 C, -5 C and the temperature in the chamber shall be lowered to -55 C
+0OC, -5OC with a minimum period of 1.5 hours. After 1 hour ±15 minutes of stabilization at this low temperature,
rated continuous working voltage (see 3.1), shall be applied for 45 minutes across the resistance element between
one end terminal and the contact arm. The resistors shall then be allowed to stabilize for 1 hour ±15 minutes and the
torque necessary to effect rotation of the contact arm shall be measured. Following this measurement, the
temperature shall be gradually raised to 25OC +10OC, -5OC within a period of 8 hours. The resistance shall then be
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removed from the chamber and maintained at 25 C +10 C, -5 C for approximately 24 hours, after which the total
resistance shall be measured (see 3.15).
4.7.13 Thermal shock. (see 3.16).
4.7.13.1 Mounting. Resistors shall be mounted by their mounting bushings in such a manner that there is at least
one (1) inch of free air space around each resistor, and with the mounting in such a position with respect to the air
stream that it offers the least obstruction to the flow of the air across and around the resistors.
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