MIL-DTL-27723F
shall be less than 2 minutes. At the end of this time, the indicated temperature of the
temperature-sensing element shall return to within 1°C of the reading before the ice was allowed
to accumulate. If temperature fluctuations exist in the icing wind tunnel, the average of several
test runs may be used. After the ability of the probe to deice properly has been demonstrated,
rated power shall be continually applied for an additional 15 minutes. There shall be no re-
accumulation of ice on the probe that would affect the temperature indication.
4.6.8 Conduction and radiation errors. The conduction and radiation errors of the probe
shall be determined by dynamic conditions, by analytical means, or by comparison of similarity
to other temperature probes. The approval of such methods and results shall be made by the
contracting officer. The conduction and radiation errors of the probe as shown by one or more of
the above methods shall meet the requirements of 3.6.8.
4.6.9 Deicing heater error. The probe shall be subjected to an internal airflow of mach
0.3 at room temperature and pressure with the deicing heater element de-energized. When the
temperature-sensing element has reached the stabilized condition, the deicing heater element
shall be energized. After a period of 3 minutes, the temperature indicated shall be no more than
1°C above the temperature indicated with the heater de-energized. If the temperature fluctuations
exist in the air stream, the average of several tests may be used.
4.6.10 Deicing heater element life. The heater power consumption (see 4.6.17) shall
change no more than 10 percent after a life test consisting of 40 hertz of 10 hours with power on
and 2 hours with power off. One-hundred of the 400 hours of operation shall be run in still air at
room temperature. The other 300 hours of operation shall be run with the probe in an airflow at
room temperature and with a velocity no greater than 50 knots. The probe shall meet the deicing
heater element life requirements of 3.6.10.
4.6.11 Insulation resistance of deicing heater element. Following the test of 4.6.2, a
potential of 500V rms, 60 hertz, shall be applied between any electrical pin contact of the deicing
heater element (pin B or F) and any ground part of the probe. The deicing heater element shall
meet the insulation resistance requirements of 3.6.11.
4.6.12 Still air operation. The deicing heater element shall be energized at rated voltage
for 5 minutes in still air. At the end of the 5 minute period, the heater power consumption shall
be less than 200w; the application of power shall cause no damage to the probe. The resistance
of the temperature-sensing element shall be determined at 0° and 100°C, and shall not differ from
the resistance values before this test by more than the equivalent of 0.2°C. The resistance
calibration at 0° and 100°C need not be made if this test is conducted prior to the temperature
sensing. The probe shall meet the insulation still air operation requirements of 3.6.12.
4.6.13 Low temperature and power consumption. The probe shall be subjected to a
temperature of -70°C for a period of 15 hours. Rated voltage shall then be applied to the heater
element through a 5-amp fuse and shall not be of such duration as to render the fuse inoperative.
Power shall be determined after rated voltage is initially applied, after 5 seconds and after 20
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