MIL-DTL-83361B
4.5.2.1 Visual comparison. The prime standard and the indicator under test shall be
placed side-by-side at eye level. The two indicators shall be viewed from a distance of 2 feet
within a sighting cone of 30 degrees from normal to the surface of the coverglass. The prime
standard lighting circuit shall be energized with 2.50 V ± 0.01 V and the lighting circuit of the
indicator under test shall be energized with 2.60 V ± 0.01 V. The overall brightness level of the
dial and pointer of the indicator under test shall equal or exceed the brightness of equivalent
areas of the prime standard. The voltage applied to the indicator under test shall be decreased to
2.40 V ± 0.01 V. The brightness levels of the dial and pointer of the prime standard shall be
equal to or less than the brightness of the equivalent areas of the indicator under test. A voltage
of 4.50 V ± 0.01 V shall be applied to both the prime standard and the indicator under test. The
two units shall be compared for white color and shall appear the same. All indicators that fail
this test shall have the questionable areas measured with a photometer. If they also fail the
photometer test, the indicators shall be rejected.
4.5.3 Dielectric strength. The dielectric strength test shall be conducted in accordance
with MIL-STD-202, Method 301, "Dielectric Withstanding Voltage", after the indicator has
reached its normal operating temperature. A voltage of 500 V AC at commercial frequency shall
be applied between the external connections of each mutually insulated circuit and between each
external connection and the case. Any arc-over, breakdown, or current flow that constitutes a
transient or steady increase in leakage current at the specified test voltage shall be cause for
rejection. This test shall not include the lighting circuit.
4.5.4 Electrical zero. A voltage of 26 V ± 1 V AC single-phase power shall be applied
to the rotor leads designated as R1 and R2 (see figure 3). R2 shall be connected to the ground or
low potential side of the 26 V AC power supply. With the S2 lead connected to the R2 lead, the
following conditions shall exist at electrical zero (50 psi):
a. The S3S1 voltage shall be minimum, shall be in-phase with voltage R2R1, and shall
remain approximately in-phase as the synchro rotor is rotated from a position corresponding to
50 psi, decreasing to a position corresponding to -6 psi.
b. The R1S3 voltage shall be near minimum at a rotor position corresponding to 50 psi
and shall reach minimum when the synchro rotor is rotated to a position corresponding to
59.375 psi.
c. Rotation of the synchro rotor from a position corresponding to 50 psi increasing to
59.375 psi shall produce an increasing S3S2 voltage and a decreasing S2S1 voltage.
4.5.5 Scale and friction error. The indicator shall be tested for scale error 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 test. 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.
4.5.6 Position error. The indicator pointer shall be positioned at electrical zero reference
mark with power applied. The change in pointer position when the indicator is held in any
position shall not exceed the value specified in table III.
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