MIL-DTL-27190C
4.5.15 Effect of lead length. The indicator shall not change more than 1 degree of arc
when the lead length between the indicator and the transmitter is changed from 5 feet to 500 feet
of number 20 AWG gage wire. Equivalent resistances may be substituted for the added wire
length. The ground lead shall be kept short.
4.5.16 Temperature-altitude. The temperature-altitude test shall be conducted in
accordance with MIL-STD-810, method 504, procedure I (except the temperature shall be -55 °C)
with a chamber pressure equivalent to an altitude of 100,000 feet. The rate of pressure change
shall exceed an average of 3 psi per second while under these conditions and at the end of a
1-hour period, the scale error and friction test shall be conducted. The errors shall not exceed the
tolerances specified in tables II and III. This test may be conducted concurrently with the low
temperature exposure test.
4.5.17 Low temperature exposure. The indicator shall be subjected to a temperature of
-65 °C ± 2 °C for a period of 48 hours. While at this temperature, the indicator shall be operated
to ensure that the pointer moves over the entire scale range without exhibiting sticky or erratic
characteristics. The temperature shall then be raised to -55 °C ± 2 °C and held for a period of
24 hours. While at this temperature, the indicator shall be subjected to the scale error and friction
test, except that in every case, the indicator shall not require more than 4 seconds to come within
the tolerances of tables II and III. All parts of the indicator shall then be maintained at room
temperature for a period of not less than 4 hours and the indicator is again subjected to the scale
error and friction test. The scale error and friction shall not exceed the tolerances specified in
tables II and III. There shall be no damage or deterioration that will affect subsequent operation.
4.5.18 High temperature exposure. The indicator shall be subjected to a temperature of
71 °C for a period of 24 hours and then tested at this temperature for scale errors as specified in
4.5.4. The scale error tolerances and friction shall not exceed the tolerances specified in tables II
and III. All parts of the indicator shall then be maintained at room temperature for a period of not
less than 4 hours and the indicator shall then be subjected to the scale error and friction test. The
scale errors observed shall not exceed the tolerances specified in table II. There shall be no damage
or deterioration that might affect subsequent operation.
4.5.19 Thermal shock. The indicator shall be subjected to eight cycles of immersion in
water at a temperature of 85 °C ± 2 °C and then in water at a temperature of 5 °C ± 2 °C without
evidence of moisture penetration or damage to the coating or the case. The length of time for each
immersion shall be 30 minutes, with not more than 5 seconds between immersions. After eight
continuous cycles have been completed, the indicator shall be subjected to the test specified in 4.5.6.
4.5.20 Salt fog. The indicator shall be subjected to a salt fog test for a period of 48 hours
in accordance with MIL-STD-810, method 509, procedure I. There shall be no evidence of
external corrosion or deterioration that might affect subsequent operation. The scale errors after
this test shall not exceed the tolerances specified for the room temperature scale error.
4.5.21 Radio noise interference. The indicator shall be subjected to a radio noise
interference test in accordance with MIL-STD-461 except that the frequency range for radiated
noise shall be within 0.15 megacycle to 150 megacycles. During this test, the synchro shall be
operated at 30 revolutions per minute (rpm) ± 5 rpm.
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