MIL-PRF-19E
4.7.4.2 Operating (see 3.9.1). The torque required to rotate the contact arm on the resistance element shall be
determined throughout the entire range of mechanical rotation by the torque wrench method or by any other method
satisfactory to the qualifying activity.
4.7.4.3 Stop (see 3.9.2). Resistors shall be mounted on a metal panel by their normal mounting means. The
contact arm shall then be rotated to each extreme limit of mechanical rotation and the specified torque (see 3.1)
applied through the operating shaft to the stops.
4.7.4.4 Locking (see 3.9.3). Resistors shall be mounted on a metal panel by their normal mounting means and set
at approximately 40 percent of the resistance value (measured between the counterclockwise end terminal and the
center tap). The locking device shall be tightened with a torque not greater than that specified. With the locking
device tightened, the operating shaft is to withstand the specified torque (see 3.1). Movement of the shaft shall be
checked visually and resistors shall be examined for evidence of damage. The total resistance shall be measured.
4.7.5 Low temperature storage (see 3.10). The total resistance shall be measured at +25OC +10OC, -5OC
within 1 hour after this measurement, resistors shall be placed in a chamber at a temperature of +25OC +10OC,
-5OC. The temperature in this chamber shall be lowered to -63OC, +0OC, -2OC within a minimum period of 3 hours.
Twenty four 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 maintained at +25OC +10OC, -0OC for a period of approximately 72 hours, after which the total
resistance shall be measured.
4.7.5.1 Conformance inspection. At the option of the manufacturer, the sample units may be placed in or removed
from the test chamber while the chamber is at the extreme low temperature.
4.7.6 Low temperature operation (see 3.11). The total resistance shall be measured at +25OC +10OC, -5OC. The
resistors shall then be placed in a chamber at +25OC +10OC, -5OC and the temperature in the chamber shall be
lowered to -55OC +10OC, -5OC within a minimum period of 1 hour and 30 minutes. 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, with the contact arm against the
opposite stop. 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 24 hours. The resistors shall then be removed from the chamber and
maintained at +25OC +10OC, -5OC. For approximately 24 hours, after which the total resistance shall be measured.
4.7.6.1 Conformance inspection. At the option of the manufacturer, the extreme low temperature may be
-63OC, 0OC, -2OC and the sample units may be placed in or removed from the test chamber while the chamber is at
the extreme high or low temperature.
4.7.7 Thermal shock (see 3.12). Resistors shall be tested in accordance with method 107 of MIL-STD-202. The
following details and exceptions apply:
a.
Test condition letter: A.
b.
Measurement before cycling: Total resistance shall be measured as specified in 4.7.3.1
Measurements after cycling: Total resistance shall be measured as specified in 4.7.3.1, continuity of the
c.
contact arm shall be verified by connecting a vacuum tube voltmeter or other indicating device, between the
contact arm terminal and the counterclockwise end terminal. The applied voltage shall be in accordance
with table XIII.
d.
Examination after test: Resistors shall be examined for evidence of mechanical damage.
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