MIL-PRF-39017G
4.8.6 Low temperature storage (see 3.12).
4.8.6.1 Mounting. Resistors shall be mounted in such a manner that there is a 1 inch of free 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.
4.8.6.2 Procedure. DC resistance shall be measured as specified in 4.8.3. Within one hour after this
measurement, the resistor shall be placed in a cold chamber at a temperature of -65°C ±2°C for a period
of 24 hours ±4 hours. The resistors shall then be removed from the chamber and maintained at a
temperature of 25°C ±5°C for a period of approximately 2 hours to 8 hours, the dc resistance shall again
be measured as specified in 4.8.3. Resistors shall be examined for evidence of mechanical damage.
4.8.7 Low temperature operation (see 3.13).
4.8.7.1 Mounting. As specified in 4.8.4a.
4.8.7.2 Procedure. Following the final measurement of dc resistance as specified in 4.8.3, the
resistors shall be placed in a cold chamber at room temperature. The temperature shall be gradually
decreased to -55°C +0°C, -5°C within a period of not less than one and one-half hours or for more than 2
hours. At the option of the manufacturer, the resistors may be placed in the cold chamber when the
chamber is already at the extreme low temperature. After one hour of stabilization at this temperature,
the full rated continuous working voltage (see 3.7) shall be applied for 45 minutes. The resistors may be
loaded individually or in parallel. Fifteen minutes +5 minutes, -0 minutes after removal of voltage, the
temperature in the chamber shall be increased to room temperature within a period of not more than 8
hours. The resistors shall be removed from the chamber, and maintained at a temperature of 25°C ±5°C
for a period not to exceed 24 hours. The dc resistance shall be measured as specified in 4.8.3.
Resistors shall then be examined for evidence of mechanical damage.
4.8.8 Short-time overload (see 3.14).
4.8.8.1 Mounting.
4.8.8.1.1 Qualification inspection. Resistors shall be mounted horizontally in free space with no object
closer than 3 inches to the resistor case, except the mounting base, which shall not be closer than 2
inches below the resistors. They shall be mounted in still air, with no circulation other than that caused by
the heat of the resistors being operated.
4.8.8.1.2 Conformance inspection. Resistors may be mounted in any position and allotted any size
space as deemed necessary by the manufacturer. Forced air cooling may be used to maintain a test
ambient temperature of 25°C ±10°C. The velocity of the forced air, if employed, shall not exceed 500 feet
per minute. When forced air is employed, there shall be no direct impingement of the forced air supply
upon the resistors.
4.8.8.2 Procedure. DC resistance shall be measured as specified in 4.8.3. Following this
measurement, a potential of 2.5 times the rated continuous working voltage, but not to exceed twice the
maximum voltage (see 3.1), shall be applied for 5 seconds to the resistor terminals. Thirty minutes +5
minutes, -0 minutes after the removal of the test potential, the dc resistance shall be measured as
specified in 4.8.3.
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