MIL-STD-202H.pdf - 第93页
MI L - S TD - 202 - 112 4.6 .2.5 Light ing sourc e . A l i g ht i ng s o ur c e c a pab l e of pr od u c i ng at l ea s t 15 , 000 f oo t c a ndl es in air at a distance equal to t hat which the m o s t d i s t ant dev i…
MIL-STD-202-112
4.5.2.2 Filter. A filter shall be used which is capable of removing particles greater than 1 micron in size from the
fluid.
4.5.2.3 Magnifier. A 3X minimum magnifier or a stereo zoom microscope shall be used for observation of bubbles
emanating from the test specimens when immersed in the indicator fluid.
4.5.3 Precautions. The following precautions shall be observed:
a. Fluorocarbon liquids shall be filtered as specified in 4.5.2.2. Bulk filtering and storage is permissible. Leak
indicator fluids, which have accumulated observable quantities of particulate matter during use, shall be
discarded or reclaimed by filtration for reuse. Leak detecting fluids shall not be used for more than one
eight-hour shift without being refiltered.
b. The observation container shall contain sufficient fluid to assure coverage of the test specimen to a
minimum depth of two inches.
c. Illumination shall be a lighting source capable of providing at least 15,000 foot candles at the test specimen
position. The lighting source shall not require calibration but the light level shall be verified at the test
specimen position. The background behind the glass observation container should be a dull, non-reflective
black material.
d. The observation container should be covered at all times when not in use to minimize evaporation losses
and moisture adsorption.
e. Test specimens to be tested should be free from foreign material on the surface, including conformal
coatings and markings which may contribute to erroneous test results.
4.5.4 Procedure. The test specimens, mounted on specified fixtures to hold them in the fluid, shall be immersed,
with the uppermost portion at the minimum depth of 2 inches below the surface of the fluid, lid downward, one at a
time (or in such a configuration that a single bubble from a single specimen out of a group under observation may be
clearly observed as to its occurrence and source). The fluid shall be maintained at a temperature of 125°C ±5°C
(257°F ±9°F). The specimens shall be observed against a dull non-reflective black background through the magnifier
(see 4.5.2.3) from the instant of immersion until 20 seconds after immersion. Leakers will be identified by a single
bubble or a stream of bubbles. Specimens from which a single bubble is observed is considered to be a reject.
4.6. Test condition E.
4.6.1 Materials.
4.6.1.1 Fluorocarbon liquid. The fluids shall be D/80, FC-72 or PP-1 fluorocarbon detector fluids, and D02,
D02-TS, D03, FC-40, FC-43, PP-7 or PP-9 fluorocarbon indicator fluids.
4.6.2 Apparatus.
4.6.2.1 Heated fluid container. The container for the fluid shall be made of pyrex glass and shall be of sufficient
size to hold the test specimen in the fluid and to maintain a temperature of 125°C ±5°C (257°F ±9°F).
4.6.2.2 Filter. A filter shall be used which is capable of removing particles greater than 1 micron in size from the
fluid.
4.6.2.3 Magnifier. A magnifier with a magnification in the range between 3X to 30X for observation of bubbles
emanating from devices when immersed in the indicator fluid.
4.6.2.4 Chamber. A vacuum/pressure chamber for the evacuation and subsequent pressure bombing of device up
to 75 lbf/in
2
up to 10 hours.
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MIL-STD-202-112
4.6.2.5 Lighting source. A lighting source capable of producing at least 15,000 foot candles in air at a distance
equal to that which the most distant device in the bath will be from the source.
4.6.2.6 Instruments. Suitable calibrated instruments to indicate the test temperature pressures and times are as
specified.
4.6.2.7 Fixtures. Suitable fixtures to hold the device(s) in the indicator fluid.
4.6.3 Precautions. The following precautions shall be observed.
a. Fluorocarbon liquids shall be filtered as specified in 4.6.2.2. Bulk filtering and storage is permissible. Leak
indicator fluids, which have accumulated observable quantities of particulate matter during use, shall be
discarded or reclaimed by filtration for reuse. Leak detecting fluids shall not be used for more than one
eight-hour shift without being refiltered.
b. The observation container shall contain sufficient fluid to assure coverage of the test specimen to a
minimum depth of two inches (50.8 mm).
c. Illumination shall be a lighting source capable of providing at least 15,000 foot candles at the test specimen
position. The lighting source shall not require calibration but the light level shall be verified at the test
specimen position. The background behind the glass observation container should be a dull, non-reflective
black material.
d. The observation container should be covered at all times when not in use to minimize evaporation losses
and moisture adsorption.
e. Test specimens to be tested should be free from foreign material on the surface, including conformal
coatings and markings that may contribute to erroneous test results.
f. Precautions should be taken to prevent operator injury due to package rupture or violent evolution of bomb
fluid when testing large packages.
4.6.4 Procedure. The test specimens mounted on specified fixtures to hold them in the leak detecting fluid shall be
inserted into the combination vacuum-pressure vessel and the applied ambient pressure shall be reduced to less
than 5 torr for 1 hour. Then without breaking vacuum, a sufficient quantity of leak detecting fluid (see 4.6.1.1) to
cover the test specimens, shall be drawn into the vacuum/pressure vessel by inserting a transfer tube from the
vacuum/pressure vessel into a container of leak detecting fluid and opening a valve in the tube. For test specimens
with an internal cavity volume of 0.1 cm
3
or less, the pressure in the vessel shall be increased to 90 lbf/in
2
and
maintained at that pressure for 3 hours minimum. For test specimens with an internal volume in excess of 0.1 cm
3
,
the pressure shall be increased to 50 lbf/in
2
and maintained at that pressure for 3 hours minimum. After
pressurization, the pressure shall be released from the pressure vessel and the test specimens shall be removed
from the pressure vessel, and retained in a bath containing the leak detecting fluid. Then they shall be dried for 3 ±1
minutes in air prior to immersion in the indicator fluid. The test specimens shall be immersed with the uppermost
portion at a minimum depth of 2 inches (50.8 mm) below the surface of the indicator fluid, lid downward, one at a time
(or in such a configuration that a single bubble from a single specimen out of a group under observation may be
clearly observed as to its occurrence and source. The leak indicator fluid shall be maintained at a temperature of
125°C ±5°C (257°F ±9°F). The test specimens shall be observed against a dull non-reflective black background
through the magnifier (see 4.6.2.3) from the instant of immersion until 20 seconds after immersion. Leaks will be
identified by a single bubble or a stream of bubbles. Specimens from which a single bubble is observed is
considered to be a reject.
4.7. Test condition F.
4.7.1 Materials.
4.7.1.1 Fluorocarbon liquid. The fluid used shall be FC-84 or D/80 fluorocarbon detector fluid.
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MIL-STD-202-112
4.7.2 Apparatus.
4.7.2.1 Chamber. A vacuum/pressure chamber capable of the evacuation and subsequent pressure bombing of
devices up to 75 psig and maintaining pressure up to 12.5 hours.
4.7.2.2 Filter. A filtration system capable of removing particles greater than 1 micron in size from the fluorocarbon
fluid.
4.7.2.3 Detector. A fluorocarbon vapor detection system with a nominal sensitivity of 10
-5
atm cm
3
/s. The
sensitivity of the detector shall be better than 14 micrograms of FC84 or D/80. The detector shall have a linear
response to 280 micrograms and a response time of better than 1 second.
4.7.2.4 Instruments. Suitable calibrated instruments to indicate that test, pressure times and temperatures are as
specified. The detection system shall be calibrated using a calibration source of fluorocarbon at least once each shift
to an accuracy of at least ±15 percent.
4.7.3 Precautions. The following precautions shall be observed in conducting the fluorocarbon gross leak test.
a. Fluorocarbons shall be filtered through a filter system capable of removing particles greater than 1
micrometer prior to use. Bulk filtering and storage is permissible. Liquid that has accumulated observable
quantities of particulate matter during use shall be discarded or reclaimed by filtration for re-use.
Precautions shall be taken to prevent contamination.
b. Precautions should be taken to prevent operator injury due to package rupture or violent evolution of bomb
fluid when testing large packages.
4.7.4 Procedure. The devices shall be placed in a vacuum/pressure chamber and the pressure reduced to 5 torr
or lower and maintained for 30 minutes minimum. A sufficient amount of FC-84 or D/80 detector fluid shall be
admitted to the pressure chamber to completely cover the devices. The fluid shall be admitted after the 30 minute
minimum vacuum period but before breaking the vacuum. The devices shall then be pressurized in accordance with
table II. Upon completion of the pressurization period, the pressure shall be released and the devices removed from
the pressure chamber without being removed from the detector fluid for more than 20 seconds. When the devices
are removed from the fluid for testing, they shall be air dried for a minimum of 20 seconds and a maximum of 5
minutes prior to the test cycle. The devices shall then be tested with a fluorocarbon vapor detector in accordance
with the system operating instructions and as follows. Devices shall be admitted to the purge chamber and purged
(heated to remove any remaining surface fluorocarbon and to initiate vaporization of any internal fluorocarbon fluid).
Purge time shall be in accordance with table III. Test time shall commence immediately after purge either in the
same chamber (single chamber system) or an adjoining test chamber (dual chamber system). Test time shall be a
minimum of 3.5 seconds (unless the device is rejected earlier) with the fluorocarbon vapor detector purge and test
chambers at a temperature of 125°C ±5°C or 2.5 seconds minimum with the purge and test chambers at 150°C ±5°C.
During test time, the amount of fluorocarbon outgassing is measured and the total integrated value is compared to
the alarm level.
NOTE: Air dry, purge, and test time limits for each device shall be complied with in all cases, whether the device is
handled individually or in plastic or metal tubes.
4.7.4.1 Failure criteria. A device shall be rejected if the detector instrumentation indicates more than 280
micrograms of fluorocarbon gas.
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