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|  MIL-T-46311B(MU)
3.4 Sealing and purging.
3.4.1 Optical assembly area.- The telescope optical assembly area
shall be capable of sustaining an internal pressure of 5.0 0.1 psi for
a period of 2 hours minimum without loss of pressure in excess of 0.2 psi.
3.4.2 Counterbox area.- The counterbox area of the telescope shall
be capable of sustaining an internal pressure of 2.0 .2 psi for a period
of 2 hours minimum without loss of pressure in excess of 0.2 psi.
3.4.3 Purging.- The optical assembly portion of the telescope shall
be purged with dry nitrogen supplied at a pressure of 5 1/4 psi until
the dew point of the emergent gas is no higher than -25F. Purging
apertures shall be quickly and positively closed to minimize intermingling
of external atmosphere upon disconnection of purging equipment.
3.5 Cleanliness.
3.5.1 Dirt.- Inspection for dirt and foreign particles (classed as
dirt) shall be made from the eye end only. The maximum size of any particle
appearing on the reticle shall be a reticle line width. The maximum number
of dirt particles appearing within a central field of view of 50 mils
diameter shall be three (3). The maximum number of dirt particles appearing
outside this field of view shall be three (3). The minimum angular separation
between dirt particles shall be 15 mils. Dirt particles smaller than 1/4
reticle line width shall be ignored regardless of distribution.
3.5.2 Other defects.- There shall be no evidence of moisture, grease,
fingerprints, condensates, fractures, and adhesive separations when viewing
through the objective and eye end of the instrument.
3.6 Orientation.- The requirements of 3.7 to 3.8.3.3.2, inclusive,
shall be met with the flat mounting surface of the telescope horizontal,
the elbow assembly within 2 of the center of the swing stops, the head
elevation indices indicating zero, the azimuth and reset counters indicating
3200 mils, the gunner's aid counters set at zero, and the five mil click
lead knob set for "Indirect" fire (out of detent).
3.7 Accuracy.
3.7.1 Collimation.
3.7.1.1 Pre-vibration setting.- Prior to meeting the requirements of
3.3.3, the line of sight shall be adjusted horizontal and perpendicular to
the locating keyways within 0.25 mil.
3.7.1.2 Post-vibration.- Subsequent to meeting the requirements of
3.3.3, the line of sight shall be within 0.25 mil of the position established
in 3.7.1.1 excluding backlash.
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