MIL-DTL-27190C
4.5.22 Unit torque gradient. The indicator shall be connected to the master transmitter
synchro and the master transmitter locked in the electrical zero position. The synchro rotors shall
then be energized with rated voltage and frequency ±1 percent. Weights shall be applied to a
torque pulley which is positioned on the rotor shaft to rotate the shaft in a counter clockwise
direction through an angle of 5 degrees of arc. The torque tending to return the shaft to its
original position shall be computed and shall be no less than 2,000 milligram-millimeters per
degree of displacement.
4.5.23 Lighting. Lighting tests shall be conducted in accordance with sampling plan B
tests of MIL-L-27160, except the dielectric test shall not be conducted.
4.5.24 Reliability. Seven indicators shall be tested for reliability. Recording, data
handling, and reporting shall be performed for the government. MIL-HDBK-781 may be used for
guidance.
4.5.24.1 Reliability test. The test equipment and fixtures shall include provisions for
vibration and temperature cycling at the periodic intervals specified herein. During this test,
input signals shall be applied to the indicator at a rate of 2 to 3 cycles (minimum and maximum)
per minute from 0 percent to 85 percent of full scale and return. The test shall begin when rated
power is applied. After completion of 4 hours of operation with rated power on, which shall
include at least 480 cycles of operation, the power shall be turned off and shall remain off for a
period of 10 minutes. For at least 10 minutes out of every hour of ON time, the indicator shall
be vibrated at 2.2g ± 10 percent peak acceleration value at any non-resonant frequency between
20 cps and 60 cps measured at the mounting points on the equipment. The duration of vibration
shall be at least 10 minutes during each hour of equipment operating time. The temperature
cycles shall be conducted in the following sequence: 4 hours at -20 °C, 14 minutes for
temperature change to 50 °C at a minimum rate of 5 °C per minute; 4 hours at 50 °C, 14 minutes
for temperature change to -20 °C, and 4 hours at -20 °C. In case of malfunction, the malfunction
shall be recorded and the test interrupted while repairs are made. Upon completion of each
250 hours of cycling, the indicator shall be checked for scale error. The scale error shall not
exceed 150 percent of the tolerance in table II at room temperature. No recalibration shall be
performed on the units during this test. The test may be interrupted for weekend shutdown. The
contractor shall prepare a report that contains test procedures, details of any malfunctions, and
corrective actions taken. MIL-HDBK-781 may be used for guidance.
4.5.24.2 Longevity. At the completion of the reliability test, testing of three of the
indicators shall be continued for a total of 3,000 hours each. The test time accumulated during
the reliability test shall be applied to this test.
4.6 Maintenance of qualification. At specified intervals determined by the qualifying
activity, the manufacturer must be able to demonstrate that the company still has the capabilities
and facilities necessary to produce the QPL items in accordance with this specification and the
provisions governing qualification specified in SD-6.
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