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Interconnect solutions for aircr by fjzhangweiqun

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									       DefenseElectronics

         Interconnect solutions for aircraft
         Ethernet data networks
         Ethernet data networks in military and aerospace applications have mandated
         the implementation of a robust industry standard connector solution. Historically,
         low-cost solutions such as RJ45 packaging prove unacceptable in onboard,
         mission-critical Ethernet implementations. These robust requirements
         have resulted in the implementation of Quadrax contacts and standardized
         specifications.
         By James Yoshitake
            Design engineers face a considerable
         challenge in developing connectors for use
         in avionics Ethernet network applications.
         Initial evaluation of Ethernet networking
         system standards for commercial aircraft
         began with the formation of the aircraft
         data network (ADN) subcommittee of the
         ARINC Aircraft Electronic Engineering
         Committee (AEEC). The subcommittee
         created a multipart document addressing the
         ARINC 664 aircraft data network specification.
         The efforts of this subcommittee resulted in
         the creation of the Avionics full-duplex switch
         Ethernet (AFDX). The AFDX is based upon
         IEEE 803.2 Ethernet standards with the
         inclusion of specific deterministic network
         and bandwidth functionalities.
            The most popular connector for use in
         standard Ethernet networks and functionality
         is an 8P8C plug and jack known as RJ45.
         While ideal for the telecommunications in-
         dustry, the RJ45 connector is not suitable for
         the harsh environments found in aircraft, and
         in particular, military aircraft. The ADN
         subcommittee evaluated the rigorous envi-
         ronmental demands and identified the non-
         applicability of the RJ45 connector package.        Figure 1. Quadrax pin and socket contacts.
         Further evaluation revealed the necessity for       applications as the “Quadrax” connector,           each other and encased in an outer shell.
         blind mating in ARINC 600 LRU applica-              shown in Figure 1.                                 A polarization key assures proper mating
         tions. After obtaining substantial input from                                                          into ARINC 600 or similar connectors. The
         a sampling of connector manufacturers, the          Quadrax connector specifications                    polarization key also identifies the location
         ADN subcommittee identified the appropriate             The Quadrax connector comprises four            of contact 2, directly next to this contact.
         connector package for Ethernet data network         inner signal contacts that are insulated from      Similarly, the wiring key identifies both the

              Pin #              Cable End B               Cable End A               Cable End A              Cable End B            Cross-sectional
                                                                                                                                      Arrangement
          1                            Red                      Red                       Yellow                   Yellow                 R, Y, B, G
          2                           Yellow                   Yellow                      Red                      Red                   Y, R, G, B
          3                            Blue                     Blue                      Green                    Green                  Y, R, G, B
          4                           Green                    Green                       Blue                     Blue                  R, Y, B, G
          Polarization key   Adjacent to pin #2       Adjacent to pin #2         Adjacent to pin #2       Adjacent to pin #2                 N/A
          Wiring key         Between pins #1 and #2   Between pins #1 and #2     Between pins #1 and #2   Between pins #1 and #2             N/A
         Table 1. Color coding for the ARINC 664 standard for StarQuad cable assemblies.



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                                                                                designated StarQuad.
                                                                                The StarQuad assem-
                                                                                bly consists of four
                                                                                conductors and four
                                                                                shielded wires that
                                                                                are wound together in
                                                                                a spiral pattern with
                                                                                the cable assembly
                                                                                shield terminating to
                                                                                the outer shell of the
                                                                                Quadrax connector.
   Figure 2. ITT Electronic Components’ Quadrax termination.                       The ARINC 664
                                                                                standard identifies a
                                                                specific color coding for the StarQuad
                                                                cable assembly: red, green, blue and
                                                                yellow. Per the standard, color cod-
                                                                ing in the cable twist may be visually
                                                                used to identify both End A (clock-
                                                                wise rotation of red to green to blue
                                                                to yellow) and End B (clockwise
                                                                rotation of red to yellow to blue to
                                                                green). Table 1 outlines the color
   Figure 3. ITT’s completed Quadrax termination assembly.
                                                                coding portion of the standard.
                                                                   The combination of the StarQuad
                                                                and Quadrax designs increases the
                                                       complexity associated with designing and
                                                       handling military and defense aviation
                                                       Ethernet cables. Furthermore, the twist or
                                                       “lay” of the cables gives rise to specific
                                                       geometric relationships that require knowl-
                                                       edge of the cable ends, twist, and wire/
                                                       contact relationship. This relationship is most
                                                       critical when defining the final assembly and
                                                       termination.
                                                          The interrelationship between the contact
                                                       and the twist of the wire within that cable
                                                       has not been an issue with traditional wire
   Figure 4. Left to right--socket crimp termination   bundles that use standard (size 20 AWG
   and pin PWB termination.                            or 22 AWG) pins at the connector junc-
                                                                              tions. However, in cases
     Model Number 9-1C 17-2C 21-4C 23-6C 25-8C where an Ethernet link
    Number of Quadrax           1         2        4         6         8      contained connectors
    contacts                                                                  with Quadrax contacts,
                                                                              new guidelines were
    Size                      Size 9   Size 17 Size 21   Size 23 Size 25
                                                                              developed.
   Table 2. Contact arrangements for the MIL-DTL-38999 connector type.            To support this wire/
                                                                              contact relationship and
   position of contact 1 and contact 2, as it is aid in proper assembly procedures, the ARINC
   located directly between these two contacts. 664 committee defined the following color
   These two keys establish the proper mating of assignments: pin 1 = red, pin 2 = yellow,
   the Quadrax connector.                              pin 3 = blue, and pin 4 = green, as noted in
      Concurrent with the development of the Table 1. Within this nomenclature, only four
   Quadrax connector was the development of contact-number to wire-color combinations
   an aircraft Ethernet cable assembly design, may be used.

         Model Number              11Q11           6Q6               13Q2               64Q2
                                  (Metallic)     (Metallic)
     Number of Quadrax contacts        11             6                 2                  2
     Additional pins                  N/A            N/A        4 #20HD contacts    60 #22 contacts
     Additional pins                  N/A            N/A          3 #16 contacts     2 #16 contacts
     Additional pins                  N/A            N/A          4 #12 contacts     2 #16 contacts

    Table 3. Contact arrangements for the ARINC 600, MIL-C-83527 connector type.



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                       Model Number            33Q4M
                     Number of                    4
                     Quadrax contacts
                     Additional pins      25 #20HD contacts
                     Additional pins        4 #16 contacts
                    Table 4. Contact arrangements for the
                    ARINC 404, MIL-C-81658 connector type.

                       The ARINC 600 specifications
                    identify the external Quadrax con-
                    tact geometry, the orientation of the
                    Quadrax contact within the insert,
                    and the appropriate mating interface
                    location to ensure intermateability
                    of the connectors between various
                    suppliers. Furthermore, the ARINC
                    600 provides a list of electrical, me-
                    chanical, and thermal performance
                    requirements.
                       While early Quadrax connector
                    designs met the ARINC 664 standards,
                    many were not capable of terminating
                    a StarQuad cable. Additionally,
                    Quadrax connectors were initially used
                    in rack and panel products in different Figure 5. ARINC 600 LRU connector, receptacle, 11Q11
                                                              metallic insert with PWB termination Quadrax contacts.
                    types of aircraft applications using
                    circular connectors, but because different the Quadrax body, clip, metallic insert and
                    companies manufactured them, each Quadrax connector housing to the chassis. These
                    connector contained a different termination features make the connector perform as
                    method. One such termination approach is expected under the rigorous specifications
                    shown in Figure 2.                                 of military Ethernet networks.
                       ITT Electronic Components’ termination
                    process, for example, involves stripping Emergence of military-grade
                    the StarQuad cable and crimping the center connectors
                    contacts to the four discrete conductors.             Despite the fact that Quadrax contacts
                    The center contacts are then placed into initially found their home in rack and
                    the holder. The user inserts the holder, with panel applications for onboard Ethernet
                    terminated contacts, into the Quadrax networks, over time networking applica-
                    contact body assembly containing the inner tions migrated into other markets including
                    insulator. The final step involves securing industrial and military aircraft applications.
                    the StarQuad cable shield between the body This market migration necessitated the
                    and crimp ferrule using a standard hex crimp packaging of Quadrax contacts into other
                    tool. The completed Quadrax termination standardized connector configurations, such
                    assembly is shown in Figure 3.                     as MIL-DTL-38999 and ARINC 404.
                       The attachment of the cable shield to the          While conventional Quadrax connectors
                    Quadrax contacts provides several significant typically consist of separate contact, insulator
                    benefits including cable strain relief and a and housing components with the insulator
                    link to grounding the shield to the chassis via retaining a separate contact from the shell,
                    the connector housing. This is achieved by some Quadrax connectors integrate the
                    the retaining clip within the contact cavity. insulator with the connector housing,
                    Current then flows from the shield through providing maximum cable shielding to the




                    Figure 6. MIL-DTL-38999 type connector, 25-8 Quadrax layout with integral, metallic insert.




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                                                      38999 inserts are an integral part of the
                                                      shell.
                                                         As shown, the Quadrax connector design
                                                      provides design engineers with a number
                                                      of benefits when installed into Ethernet data
                                                      bus network applications, from meeting
                                                      standardization requirements to flexibil-
                                                      ity of design. The Quadrax contacts provide
                                                      an industry-standard ARINC 600 interface,
                                                      instant bonding of the cable shield upon
                                                      installation into the insert/connector, and
                                                      the MIL-DTL-38999 connectors prevent
   Figure 7. Box-mount MIL-DTL-38999 type con-        cracking of the insulators due to torsional
   nector, 23-6 Quadrax layout with socket Quadrax    loads when coupling.
   contacts, reversed gender, integral metallic          The same Quadrax contacts may also
   insert.
                                                      be used in a variety of connector types
                                                                           including ARINC
                                                                           600, ARINC 404 and
                                                                           MIL-DTL-38999. Ad-
                                                                           ditionally, the rear
                                                                           insertable, rear remov-
                                                                           able Quadrax with crimp
                                                                           termination and front in-
                                                                           sertable, front removable
                                                                           Quadrax with PWB ter-
                                                                           mination designs provide
                                                                           both ease of maintenance
                                                                           and reparability. Fur-
                                                                           thermore, by being able
    Figure 8. MIL-DTL-38999 type connector with 21-75 Quadrax insert       to use the same Quadrax
    layout.
                                                                           contacts in a variety
   housing. This type of connector also pro- of connector designs, as well as the same
   vides instant grounding of the cable shield connector being able to accommodate either
   upon locking of the Quadrax in the pin or socket Quadrax with PWB terminations,
   connector. ITT Electronic Components’ 38999 both inventory and manufacturing costs are
   Quadrax connector, for example, uses the decreased, while simplicity and ease of use
   latter design, providing the necessary ro- are increased.
   bustness and reliability needed for military          Connectors that meet the increasing
   environments.                                      market demands of high performance, ease
       Furthermore, the cable to the Quadrax of use, termination requirements, reliabil-
   connector is often terminated, but in some ity, and serviceability must be developed in
   cases the mating connector is installed on order to satisfy both the manufacturer and
   a box. Inside the box are devices to which application requirements. The wide range of
   the connector must connect, either through styles and flexibility of the connector design
   the cable or via a printed circuit board behind in terms of solder and crimp-style contacts,
   the connector, which then requires soldering shape, size and housing design allow the
   of the Quadrax to the board.                       Quadrax design to be designed in to the
       Alternative designs allow contacts to be continuously evolving applications using
   removed and/or replaced without having to Ethernet functionality.
   disassemble the entire box and all solder-
   ing points. This provides maximum ease
   in terms of field maintenance and contact
   reparability.
       Figures 4 through 8 show different standard
   connector packages using the Quadrax contact                ABOUT THE AUTHOR
   configuration in a size 8 contact.
                                                         James Yoshitake is a product manager
   Supporting connector diversity                        for ITT Electronic Components. He
       A number of contact arrangements are              joined the product management team
   available for the MIL-DTL-38999, ARINC                at ITT Cannon in 1985. He has been
   600, and 404 rectangular connectors.                  product manager of circular products
   These arrangements are presented in Tables            at ITT since 2002. James earned a B.S.
   2, 3 and 4, respectively. All insert arrange-         in business marketing from California
   ments provide electrical bonding of the               State University in 1982.
   cable shield to the housing, and MIL-DTL-


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