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|  MIL-R-19365D
c. Nature of potential: Alternating current (ac ) supply at commercial line frequency and waveform.
d. Points of application of test voltage: Between the terminals tied together, and the mounting
hardware and plates.
e. Examination and measurements: Total resistance shall be measured before and after the test. At
the conclusion of the test, resistors shall be examined for evidence of mechanical damage, arcing,
and insulation breakdown.
4.7.6 Insulation resistance (see 3.11). Resistors shall be tested in accordance with method 302 of
MIL-STD -202. The following details shall apply:
a. Test condition letter: A.
b. Special preparations: As specified in 4.7.5a.
c. Points of measurement: As specified in 4.7.5d with the positive lead connected to the winding and
the negative lead to the mount ing hardware.
4.7.7 Power rating (see 3.12). The adjustable terminal shall be positioned at one end as close to the
fixed end terminal as possible while still engaging the bare resistance wire. The resistors shall be
mounted horizontally with the expos ed portion facing downward. Total resistance shall be mounted as
specified in 4.7.1.1. The resistors shall be supported without mounting hardware by means of their
terminals in free space and still air (see table II) at an ambient temperature of 25C +5C, -0C (See
4.7.7.1). If the power rating is measured at any ambient temperature other than 25C, a power rating
correction factor with reference to 25C +5C, -0C ambient temperature shall be applied in accordance
with the derating curve shown on figure 1. Rated wattage from an ac supply at commercial line frequency
and waveform shall be applied to the fixed end terminals until thermal stability has been reached. During
the test, added precaution shall be taken to determine the possibility of intermittent open circuiting in the
winding. The hotspot surface temperature shall be determined by the use of a thermocouple. (see
4.7.7.2). Measurements of resistance shall be made not less than 2 hours after removal of the load
potential.
4.7.7.1 Measurement of ambient temperature. The ambient temperature shall be measured on a level
with, and at a point 12 inches from, the nearest resistor under test.
4.7.7.2 Thermocouple. The thermocouple junction shall rest on the hotspot, and the thermocouple
wires shall hang down on opposite sides of the resistor. Precaution shall be taken that the thermocouple
wire does not touch the exposed portion of the resistor. Weights of at least 2 ounces on each wire lead
shall provide the pressure of the thermocouple junction against the surface of the resistor under test. The
thermocouple shall be composed of wire .010 inch (0.25 mm) in diameter (AWG size 30), or smaller. The
thermocouple wire shall not extend more than .125 inch (3.18 mm) beyond the junction. A negligible
difference of potential may exist between the thermocouple and the resistor winding so as to prevent a
possible dielectric failure of the coating.
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