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|  MIL-M-48640 (AR)
3 .5.6 Eyepiece focus measurement. The eyepiece setting shall
be -0.75 + 0.25 diopters.
3.5.7 Magnification. The requirement for magnification of 7X
plus or minus 0.14X.
3.5.8 Field of view (FOV). The FOV shall be 6 degrees minimum.
3.6 Purging. The MBD shall be purged with dry nitrogen for a
period of time until it is determined that the dew point is at least
-25 degrees F at atmospheric pressure. The unit shall be sealed
immediately after purging.
3.7 Sealing. Care will be utilized to keep MBD internal
atmosphere purged. The MBD shall show no evidence of leakage in
excess of 0.1 PSI when subjected to an internal pressure of 5 PSIG
plus or minus 0.1 PSI for a period of one hour. The interior
atmosphere of the accepted MBD shall contain nitrogen having a dew
0
point at least as low as minus 25 F at a pressure of between 0.25
and 0.50 PSIG.
3.8 Interchangeability verification. All MBD's shall be
interchangeable (see 4.7.6.1) .
3.9
Environmental.
3.9.1 Storage temperature. The MBD shall show no evidence of
cement separation, glass breakage, or other physical failure and
shall meet the requirements of this specification at standard
temperature (plus 15 degrees C to 32 degrees C) after having been
exposed and thermally stabilized at temperatures of plus 71 degrees
C and minus 62 degrees C.
3.9.2 Operating temperatures. The MBD shall be mechanically
operable while thermally stabilized at plus 65 degrees C and minus
40 degrees C. The rate of temperature change shall not exceed 10
degrees C/hour.
3.9.3 Vibration. The cased MBD shall be capable of
withstanding vibration when subjected to Test Method 514.2,
Procedure X, Curve AV, Equipment Category G, of M1L-STD-810.
3.9.4 Shock. The MBD shall withstand shock in accordance with
Test Method 516.2, Procedure I, Figure 516.2-2, Time Duration 11
milliseconds, of MIL-STD-810, except that the peak acceleration
shall be 40 g's.
4
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