MIL-DTL-27188C
f.
Temperature altitude (see 4.5.14).
g.
Low temperature exposure (see 4.5.15).
h.
High temperature exposure (see 4.5.16).
i.
Thermal shock (see 4.5 17).
j.
Salt fog (see 4.5.18).
k.
Radio noise interference (see 4.5.19).
l.
Unit torque gradient (see 4.5.20).
4.5 Test methods.
4.5.1 Examination of product. The indicator shall be inspected to determine compliance with
the requirements specified herein with respect to materials, workmanship, and markings. Prior to
assembly, dials, pointers, and synchros shall be inspected as to markings, dimensions, and finishes.
4.5.2 Dielectric strength. A potential of 200V at a commercial frequency shall be applied
between any pin of the electrical receptacle and the case of the indicator for a minimum period of
5 seconds. There shall be no breakdown of the insulation.
4.5.3 Electrical zero. The electrical zero test and the verification of leads shall be
accomplished on the completed indicator with the case removed. A voltage of 26V ± 1V single
phase shall be applied to the rotor of the synchro with leads designated R1 and R2. R2 shall be
connected to the ground or low potential side of the power input. With a lead designated S2
connected to R2, the following conditions shall exist at electrical zero:
a. The voltage between the remaining stator terminals designated S1 and S3 shall be
minimal.
b. The voltage between R1 and S3 shall be near the low null and shall reach the low null
when the rotor is rotated clockwise approximately 30 degrees from electrical zero.
4.5.4 Scale error and friction. The indicator shall be tested for scale error at ambient
temperature at the test points specified in table II. The indicator shall be lightly tapped or
vibrated before each reading to remove normal instrument friction. The scale errors shall not
exceed the tolerances specified in table II. The friction error test may be conducted in
conjunction with the scale error tests. The difference between the readings before and after the
indicator is tapped or vibrated shall constitute the friction error. The friction error shall not
exceed the tolerances specified in table III. This procedure shall be accomplished both up-scale
and down-scale at the test points specified.
4.5.5 Position error. The indicator pointer shall be positioned at the electrical zero
reference mark with power applied. The change pointer position when the indicator is held in any
position shall not exceed the value specified in table III.
4.5.6 Sealing. The indicator case shall be tested for leaks by means of a mass
spectrometer type helium leak detector. The detected leak rate shall not exceed 0.1 micron cubic
foot per hour at a pressure differential of 1 atmosphere with a 10 percent helium fill medium.
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