MIL-PRF-23648F
c. Loading: During the first two hours of step 2 and step 5 of MIL-STD-202, a test potential which will
maintain the thermistors at their maximum power specified (see 3.1), shall be applied to 50
percent of the thermistors. The remaining 50 percent of the thermistors will be tested without any
application of voltage.
d. Final measurements: Upon completion of step 6 of MIL-STD-202 of the final cycle, the thermistors
shall be held at the high humidity state conditions and a temperature of 25°C ±2°C for a period of
one and one-half hours to three and one-half hours. Thermistors shall be removed from the
chamber, and within 24 hours the insulation resistance measured (see 4.8.6). Zero power
resistance tests shall be performed as specified in 4.8.2 within 24 hours. The sample units shall
not be subjected to forced circulating air during tests.
202. The following details and exceptions shall apply:
a. Method of mounting: Mounting shall be as specified in 4.8.2.3.a and 4.8.2.3b. Thermistor location
shall be arranged so that the temperature of any one thermistor shall not appreciably influence the
temperature of any other thermistor. There shall be no circulation of air over the thermistors other
than that caused by the heat of the thermistors.
b. Ambient test temperature and tolerance: 25°C +5°C, -0°C.
c. Initial measurement: Zero power resistance shall be measured at temperature of 25°C in
accordance with 4.8.2.
d. Test circuit: See figure 1.
e. Operating conditions: Apply the maximum power specified (see 3.1) intermittently, one and one-
half hours on and one-half hour off for 1,000 hours.
f. Test condition letter: D.
g. Measurements during test: The zero power resistance shall be measured as specified in 4.8.2, at
the end of each of the one half hour off periods, after 250 hours ±12 hours, 500 hours ±12 hours,
750 hours ±12 hours, and 1,000 hours ±12 hours have elapsed.
h. Inspection after test: Thermistors shall be inspected for evidence of mechanical damage.
4.8.18 High temperature exposure (see 3.20). Thermistors shall be maintained at the applicable
maximum temperature (see 3.1) for 1,000 hours +20 hours, -0 hours. Zero power resistance will be
measured at 25°C after 100 hours +10 hours, -0 hours, and at the end of the test. These measurements
shall be taken after stabilization at 25°C not to exceed 72 hours.
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