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Air Leakage:
The measure of gas ingress across an hermetic
barrier. Total air leakage is the sum of the gas
which passes through the seal itself, through
permeable shell materials or via cracks or gaps
in the mounting area.
Black Box:
Electronic assembly or subassembly which can
be easily installed or removed from a larger
system through the use of connectorized circuits
and detachable fittings. Box-mounted hermetic
receptacles see wide use on black box equipment
designed for use in high-pressure differential
applications.
Body:
As in connector body, the main cylindrical or
rectangular housing used to hold contacts, glass
seals, insulators and other connector components
in exact position and alignment. The
connector body is tooled or machined to receive
the necessary mounting hardware and connector-to-connector coupling technologies.
Bonding:
In hermetic glass-to-metal sealing, the permanent
fusing of the constituent connector parts—contacts, connector body and glass seal—to
one another using surface preparation techniques
and high-heat.
Co-efficient of Expansion:
A mathematically derived value describing the
dimensional change of a material when subjected
to a measured change in temperature.
Factored into hermetic connector fabrication to
insure the glass and metal materials return to
a known state of compression after the heating
and cooling process is completed.
Compression Seal:
The most effective glass-to-metal sealing. It is
created by using metal shell and contact materials
which expand at a greater rate than the
glass during heating. During cooling, the metal
materials contract back into the already solidifying
glass to form a robust compression bond.
Also called "mismatched" sealing.
Environmentally Sealed:
A class of interconnect components, such as
connectors or backshells, which are sealed
against moisture ingress through the use of gaskets,
O-rings, grommets or other means. Many
applications that could use costlier hermetically-sealed
connectors can be adequately protected
using simpler environmental sealing techniques.
The decision to use hermetics is generally made
when the ability to withstand high-pressure differentials
(1000 psi and up) is added to the application
performance specifications.
Feedthrough:
A double-sided receptacle connector device,
mounted in a bulkhead or wall, used in interconnect
systems to pass wires through barriers
without creating an entry point for moisture, dust
or chemical pollutants. Hermetic feedthrough
connectors are used when the compartments on
either side of a bulkhead must be maintained at
different pressure levels. Feedthroughs may be
supplied with pin-to-pin, pin-to-socket or other
contact gender combinations to suit the configuration
of the interconnecting plugs.
Flange:
Disc-shaped projection extending from or
around the periphery of a receptacle connector
designed to house O-ring sealing devices,
fasteners or other mounting hardware. A flange
may also be used to provide a greater surface
area of metal material to aid in weld or solder
mount attachment of receptacle connectors to
bulkheads. The provision of various shapes
and diameters of connector flanges is a common
requirement in custom hermetic connector
designs.
Hermeticity:
The measure of a connector's permeability to gas
ingress. In general terms it means how "airtight"
the device is when measured in air-leakage tests.
Since all materials are ultimately permeable to
gas ingress at some point, hermeticity ratings are
used to define acceptable performance levels as
required by each individual application.
Hermetic Connector:
Any of various forms of interconnect devices
which are outfitted with specialized seals
to prevent moisture and gas from passing
through the connector and damaging sensitive
electronic equipment. Glass sealed hermetic
connectors are the most effective, with compression-glass sealed connectors providing
the highest levels of protection from severe
levels of environmental contaminants and
high-pressure differentials.
Kovar®:
An iron-nickel-cobalt alloy made by Westinghouse
with a co-efficient of expansion closely
matched to certain glass seals used in hermetic
connector manufacturing. The material is used
in the fabrication of both connector bodies and
contacts.
Matched Seals:
A category of glass-to-metal sealing. In
matched seals, the co-efficient of expansion for
the glass seal, contacts and connector body are
relatively the same, resulting in a finished product
with little or no built-in stress between the
constituent parts.
Mismatched Seals:
Also known as compression sealing, the different
material co-efficient of expansion values
in the glass and metal materials result in an
hermetic seal that is under signifi cant compression
stress after cooling. Hermetics of this type
can withstand higher-pressure differentials than
matched seals.
Passivation:
In the manufacture of stainless steel interconnect
components, a light surface oxidation of the
stainless steel material is effected to seal the
part against ongoing oxidation from corrosive
environmental conditions. In hermetic connector
manufacture, finish plating and surface fi nishes
for connector bodies and contacts takes place
after the exothermic firing process.
Permeability:
The measure of gas or liquid leakage through a
material or hermetic barrier. Refers both to the
potential for leakage in the sealing technology
as well as the other materials (shells, contacts,
etc.) used in the fabrication of the part.
Pressure Differential:
The difference in pressure between the inside
and outside of a sealed connector, the compartments
on either side of a wall or bulkhead, or
the outside atmosphere and a sealed equipment
housing or ship. It is this pressure differential
that leads to leakage across the sealed barrier
and ultimately to contamination of sensitive electronic
equipment.
Weld Mount:
One of the most common mounting confi gurations
for hermetic connectors, especially for
electronic equipment such as switches and
transducers. Unlike jam-nut mounted connectors
(the other most common mounting style),
weld mount hermetics are permanently attached
to the pressurized bulkhead, typically with lazer,
TIG or MIG welding technology.
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