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Historically, connectors were only considered a hardware
item with little attention paid to the concerns of today’s sophisticated system
requirements. Connectors must be carefully selected through an assessment
process that considers all applicable electrical, mechanical, and environmental
stresses as well as the design’s requirement for size function, reliability, and
at a price that is cost effective.
Connector designs and technologies are too vast and changing for all to
be addressed in this narrative. The following are general requirement guidelines
that should be supplemented with current information from the connector
manufacturer, specific to the application and product.
General
Characteristics
Electrical connectors usually consist of a mating pair (plug & receptacle * below) each with electrically conductive male (pins) or female
(sockets) contacts, and one of the connector halves, or inserts/contacts must
always be floating. The contacts are often beryllium copper or phosphor
bronze-plated with gold or some other non-corrosive, highly conductive metal.
The contacts are contained by an insulator (insert) of adequate dielectric
material, and when necessary, housed in an enclosure (shell), often die-cast or
sheet aluminum, plated or anodized for corrosion protection. The contacts may be
captive or removable with a special tool. The electrical connection into the
system at the contact terminal is either a crimp or solder connection. The seal
between the shell and insert may be moisture resistant or hermetic. The inserts
in each connector half must be oriented for correct mating, and the shell or
insert usually contains a keying feature to prevent mis-mating, which could
damage the connector and/or result in a electrical problem. Cable clamps and mounting hardware may be
provided and used as required. The mated halves are usually secured by a locking
mechanism to prevent untimely disengagements.
*NOTE: The terms referenced in
parenthesis are names in general usage and are not necessarily appropriate
nomenclature for some connector designs, e.g. flat male and flat female contacts
are called “blade” contacts, not “pins
and sockets”.
Connectors are precision mechanical
devices whose interfaces are critical and
subject to mechanical wear, more so than most other electrical
components. They may be required to make-and-break contact frequently, are often
subjected to vibration or repeated physical affect, which contribute to fatigue,
abrasion or galling of the contact materials. These life stresses cause
degradation of electrical conductivity, and can result in opens, intermittents,
or high contact resistance. In some installations, these stresses can also
adversely affect the integrity of the securing apparatus. Another concern is
chemical activity from the environment, for instance. oxidation and sulfide
formation that adversely affect conductivity. These concerns, when applicable to
the intended usage, need be to addressed in the connector assessment and test
program.
MIL-SPEC
Connectors
MIL-SPEC connectors, originally designed for severe and/or critical
tactical applications, are sometimes used in automotive (e.g. under-hood),
aviation, industrial, marine, and special commercial applications. As a
convenient reference, a partial listing of available military connectors are
shown in Table 1. Complete listings are available
from DSCC (Defense Supply Center
Columbus) 3990 E. Broad St., Columbus, Ohio, 43216-5000.
Non-MIL-SPEC
Connectors
Alternative procurement can be achieved through product
identification by Performance Specifications or by using CIDs (Commercial
Identification Drawings). See Tables 2 & 3
for a representative list. DSCC can
also be contacted for a more complete listing of these documents.
Connector performance specifications are intended to
describe product that is essentially the same quality previously defined by
familiar military specifications, but with the QML,
product/supplier controlled system rather than the QPL system.
Connector CIDs
are specifications that describe products as defined by the connector
manufacturer’s specification. These products may not be suitable for
environmentally severe and/or critical, communication or tactical military
applications. In cases where the product is found suitable through an assessment
process, periodic re-assessments are recommended and a contractual requirement
for change notification should be considered. These items may be an acceptable
cost effective choice in less demanding applications.
Table 1. Common Military
Connectors
Military Standard
|
Description
|
Class
|
Application
Considerations
|
MIL-C-28840
|
Circular threaded, high density, high
shipboard
|
D
|
Intended for use with a jacket cable in shipboard
applications.
|
MIL-C-22992
|
Cylindrical, heavy duty
|
C
|
Intended for heavy duty, rough service applications such
as in shelters, vans, buildings, missile launch sites,
etc.
|
|
|
R
|
Intended for heavy duty, rough service applications such
as in shelters, vans, buildings, missile launch sites,
etc.
|
|
|
L
|
Intended for power connections (60 to 200A) with heavy
duty jacketed cables.
|
|
|
N
|
Intended for applications where EMI must be held to low
levels to prevent interference with nearby sensitive
electronics.
|
|
|
H
|
Intended for applications where atmospheric pressures
must be contained by the connectors across the wall or panels they are mounted
on.
|
MIL-C-28731
|
Rectangular, removable contact, formed blade, fork
type
|
N/A
|
General use connector for rack and panel
mounting.
No active QPL
source
|
MIL-C-28804
|
Rectangular, high density, polarized center jackscrew,
rack and panel mounting
|
G
|
Intended for non-environmental resisting applications
where operating temperature is -55 to
125oC.
|
|
|
E
|
Intended for non-environmental applications. Have a
provision for sealing around wire at rear of
connector.
|
MIL-C-81659
|
Rectangular, environment resistance, crimp
contacts
|
N/A
|
ARINC type connector for rack and panel
mounting.
|
MIL-C-83733
|
Rectangular, miniature, back to panel,
|
N/A
|
Environmental resisting, high continuous operating
temperatures (up to +200oC).
|
MIL-C-21097
|
Edge card
connector
|
N/A
|
General-purpose connector intended to be mounted to
printed wiring board.
|
MIL-C-55302
|
Printed circuit subassembly and
assembly
|
N/A
|
General purpose for printed wiring board and other
assemblies. No restrictions
apply.
|
MIL-C-39024
|
Test point, panel, or printed wiring
type
|
N/A
|
Intended to be used as test point connector. No restrictions
apply.
|
WC-596
|
Plug, receptacles and cable outlet,
power
|
N/A
|
Intended for high power applications. Grounding type and
non-armored, front construction.
|
MIL-S-83502
|
Round sockets
“TO” style
|
N/A
|
Intended for printed circuit
boards.
|
MIL-S-83505
|
Individual
sockets
|
N/A
|
Intended for insertion through printed circuit boards
|
MIL-S-83734
|
IC DIPs
Plug-in
|
N/A
|
Intended for printed circuit
boards.
|
MIL-S-12883
|
Sockets, Relay and
Misc.
|
N/A
|
Intended for plug-in electrical components e.g. relays
crystals, batteries, capacitors, coils,
etc.
|
Table 2. Military
Connector Performance Specifications
Performance
Specification
|
Description
|
Comments
|
MIL-PRF-24308
|
Rectangular,
miniature, polarized shell, rack and
panel
|
Non
–environmental with range of -55°c to
+125°C
|
MIL-PRF-31031
|
Coaxial, plugs and receptacles,
RF
|
High reliability, for flexible and semi-rigid
cables
|
MIL-PRF-38999
|
Circular, miniature, quick disconnect, bayonet, threaded
or breech coupling
|
Environmental, high density, with either removable crimp
or hermetic solder contacts
|
MIL-PRF-39012
|
Coaxial, RF
|
Intended to be used with flexible RF cables and coaxial
transmission lines. Intended for high
frequency applications.
|
MIL-PRF-49142
|
Triaxial,
RF
|
For triaxial cable
applications
|
MIL-PRF-55339
|
Coaxial adapter,
RF
|
For use between and within
series
|
MIL-PRF-83513
|
Rectangular, micro-miniature polarized
shell
|
For limited space allocation
applications
|
MIL-PRF-49291
|
Optical, fiber,
metric
|
For fiber optics cable
applications
|
MIL-PRF-85045
|
Fiber optics
cable
|
For use with above
connectors)
|
Table 3. CIDs
(Commercial Item Description) – Connectors
CIDs
|
Description
|
Comments
|
A-A-55094
|
Rectangular, miniature, plugs, 24 pos.
polarized shell
|
Meets IEEE 488 Interface Std, cable terminating, bail
locking
|
A-A-55138
|
Rectangular, miniature, receptacle, 24 pos. polarized
shell
|
Meets IEEE 488 Interface Std, cable terminating, screw/bail locking, thick
flange
|
A-A-55139
|
Rectangular, miniature, receptacle, 24 pos. polarized
shell
|
Meets IEEE 488 Interface Std cable terminating, screw/bail locking, thin
flange
|
A-A-55140
|
Rectangular, miniature, receptacle, 24 pos. polarized shell, shielded,
pre-assembled,
|
Meets IEEE 488 Interface Std, flat cable
terminating, screw
locking,
|
A-A-55141
|
Rectangular, miniature, receptacle, 24 pos. polarized shell, low
profile
|
Meets IEEE 488 Interface Std, flat cable terminating,
panel mount
|
A-A-55144
|
Rectangular, miniature, receptacle, 24 pos. polarized shell,
shielded
|
Meets IEEE 488 Interface Std, printed circuit board
terminating, screw locking
|
A-A-55145
|
Rectangular, miniature, receptacle, 24 pos. polarized shell, right angle,
shielded
|
Meets IEEE 488 Interface Std, printed circuit board
terminating, screw locking
|
A-A-55146
|
Rectangular, miniature, receptacle, 24 pos. polarized shell, right angle,
shielded
|
Meets IEEE 488 Interface Std, printed circuit board
terminating, bail locking
|
A-A-55147
|
Rectangular, miniature, plug, 24 pos. polarized shell, low
profile
|
Meets IEEE 488 Interface Std, flat cable terminating,
screw locking
|
A-A-55148
|
Rectangular, miniature, 24 pos. polarized shell
|
Meets IEEE 488 Interface Std, cable terminating, back to
back interface, screw locking
|
A-A-55155
|
Rectangular, miniature, receptacle, 24 pos. polarized
shell, shielded, loose piece const.
|
Meets IEEE 488 Interface Std, flat cable terminating,
screw locking.
|
A-A-55463
|
Power, receptacle housing,
polarized
|
Power
applications
|
A-A-55464
|
Power, plug housing,
polarized
|
Power
applications
|
A-A-55513
|
Rectangular, miniature, plug, 24 pos. polarized shell, EMI
shielded
|
Meets IEEE 488 Interface Std, cable terminating, screw
locking
|
A-A-55528
|
Telecommunication, plug, male, polarized shell, solder
contacts
|
Rack and panel applications, screw
locking
|
A-A-55529
|
Telecommunication, receptacle female, polarized shell,
solder contacts
|
Rack and panel applications, screw
locking
|
A-A-55530
|
Telecommunication, plug, male, polarized shell, solder
contacts
|
Rack and panel applications, side entry shield, screw
locking
|
A-A-55531
|
Telecommunication, receptacle, female, polarized shell,
solder contacts
|
Rack and panel applications, side entry cover, screw
locking
|
A-A-55532
|
Telecommunication, plug, male, polarized shell, solder
contacts
|
Printed circuit board applications, screw
locking
|
A-A-55533
|
Telecommunication, receptacle, female, polarized shell,
solder contacts
|
Printed circuit board applications, screw
locking
|
A-A-55558
|
Receptacle, electrical, power, utility receptacle with
cover
|
15 amp, 125 volts, 50/60 Hz. power
applications
|
Closing
Comments
When choosing a connector, provide for additional future
circuits and circuit changes by selecting a style that has a few extra
contacts. Consider using standard styles
that are more likely to remain viable in the market place. Consider carefully
the cost of the style in comparison to its expected use. For a room ambient, permanent installation,
where seldom disconnects are required, a less costly, lower quality design may
be cost effective and substantially reliable. In addition to the recommendations
already provided for specific connectors and applications, caution is urged in
the consideration of new and untried designs, commercial quality product, and
product from new, unfamiliar sources and/or installations involving new or
unfamiliar applications, which may justify more frequent inspections and
preventative maintenance. Also risky, is continued procurement without periodic
re-assessment, availability of a special/unique design from a single source, and
dealing with a supplier that is having financial difficulties.