MIL-PRF-18546G
FIGURE 1. Derating curves for high ambient temperatures.
4.7.11 Life (see 3.15).
4.7.11.1 Test conditions. Life test shall be conducted at an ambient temperature of +25°C ±2°C. The
resistor shall be centrally mounted by normal mounting means on an aluminum chassis of the dimensions
specified (see 3.1). The resistor shall be mounted with the longitudinal axis of the resistor parallel to the
longitudinal axis of the chassis. The chassis shall be horizontally supported by a material having a low
thermal conductivity. Resistors shall be so arranged that the temperature of any one resistor shall not
appreciably influence the temperature of any other resistor. There shall be no circulation of air over the
resistors other than that caused by the heat of the resistors. The voltage used shall be the rated
continuous working voltage (see 3.5) from an ac supply at commercial line frequency and waveform, and
adequate precaution shall be taken to maintain constant voltage on resistors under test.
4.7.11.2 Procedure. Following a measurement of resistance (see 4.7.2), the test potential shall be
applied intermittently, 1 hour 30 minutes on, and 30 minutes off, for a total of 1,000 hours ±12 hours.
Resistance measurements (see 4.7.2) shall be made at the end of the 30 minutes off periods after the
following hours have elapse:
250 hours +72 hours, - 24 hours
500 hours +72 hours, - 24 hours
750 hours +72 hours, - 24 hours
1,000 hours +72 hours, - 24 hours
Resistance and insulation resistance as specified in 4.7.2 and 4.7.7, respectively, shall be measured.
Resistors shall then be inspected for evidence of mechanical damage. Measurement shall be made as
near as possible to the specified time but may be adjusted so that measurements need not be made
during other than normal weekdays.
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