Screened cable terminating ferrule

Abstract: A terminating ferrule (10) for connecting a screen (34) of a screened cable (30) to an electrical connector (46) and a method for its installation. The ferrule (10) comprises inner (12) and outer (14) tubular portions defining a cavity (22) into which the screen (34), or screen (34) and jacket (32), of the screened cable (30) can be inserted to make electrical contact with the screen (34) thereby to permit engagement of the ferrule (10) with a connector body (56, 60) to provide an electrical connection between the screen (34) and body (56, 60).

Description: The present invention relates to a connector and a screened cable with a connector and to a method for connecting a screen of a screened cable to an electrical connector. Screened cables, for example screened twisted pairs (STP) and coaxial cables, commonly have their screen terminated by one or more crimped ferrules. In the case of STP cables the screen is in the form of a foil such as a plated plastics material. The foil screen commonly includes a drain wire running along the length of the cable in contact with the foil. Termination of a foil screen is commonly performed by stripping back both the foil and jacket of the cable, folding the exposed drain wire back over the jacket and crimping a ferrule around the jacket and over the drain wire. The purpose of the screen is to prevent communication of electrical disturbances external of the cable from communicating with the twisted pairs by electrostatic or electromagnetic coupling to avoid interference with wanted signals carried by the twisted pairs. In an alternative termination employed with coaxial cable, the cable is prepared prior to termination by stripping back a section of the cable's jacket to reveal the screen. A first cylindrical ferrule is slid onto the cable over the jacket and the screen is then wrapped back over the first ferrule. A second, slightly larger ferrule is then slid over the first and the screen and is crimped into place. The crimping force secures the wrapped back screen between the two ferrules and also secures the first ferrule to the jacket. Signal carrying element(s) of the cable is/are then terminated to a connector, the body of which is connected to the ferrules to continue the screening. In this case the screen continuity is primarily intended to maintain the characteristic impedance of the cable. The screen can consist of a plurality of fine wires woven into a hollow cylinder disposed between the signal carrying element(s) of the cable and the jacket. Both of the above described termination procedures result in a drop in the screening performance of the cable at the cable-connector interface. In the case of crimping the screen between two ferrules, the crimp does not produce a uniform connection between the ferrules and the screen. In the case of the drain wire, whilst the cable is completely screened about its circumference by the foil, the screen-connector interface is formed by a single wire crimped to a ferrule. The connection is formed only by a few millimetres of contact between the wire and ferrule and screening performance is therefore greatly reduced. Furthermore, in both cases there is a gap in the screening at the cable connector interface allowing leakage at the terminated end of the cable. An alternative we explored to overcome these problems involved wrapping the foil screen back over the jacket of the cable and crimping a connector body over the wrapped back foil. The foil is commonly in the form of a sheet wrapped around the signal carrying element(s) normally with a longitudinal seam. The sheet when wrapped back over the jacket is not sufficiently wide to completely encircle the cable and therefore results in a gap such that the screening performance in this region is still reduced. Furthermore, the foil commonly tears and kinks during wrapping back, therefore reducing screening effectiveness. US4239313 discloses a connector having a body portion which comprises inner and outer tubular portions defining a cavity. The screen and jacket of a screened cable is inserted to make electrical contact with the screen. The screened cable comprises a central conductor surrounded by an insulating sheath, and with a braided surrounding screen (a single core braided conductor). The inner tubular portion acts to spread out the braiding and for this purpose, the tip of the inner tubular portion has a sharpened part. The present invention seeks to provide a screen terminating ferrule for connecting a screened cable to a connector, the connection between the screen, ferrule and connector having improved performance over those described. The present invention also seeks to provide a method for the termination of screened cables using the screen terminating ferrule. According to an aspect of the present invention, there is provided a connector including an electrically conductive connector body and terminating ferrule, the ferrule comprising inner and outer tubular cylindrical portions defining a cavity into which the screen, or screen and jacket, of a screened cable can be inserted to make electrical contact with the screen, wherein the ferrule is engageable with the connector body to provide an electrical connection between the screen and the body. The ferrule is formed from a single hollow cylinder drawn back over itself to form the inner and outer tubular portions and the annular portion. The ferrule is constructed so as to permit it to completely enclose the screen, or screen and jacket, of the inserted cable. The ferrule may be engaged with a projection which may be an elongate tongue, securable to the ferrule by a crimp ring. The projection may be a sleeve having an annular cross section securable to the ferrule by crimping the projection around the ferrule. The connector may include a ground plate adapted for connection to the connector body and to the ferrule. The ground plate may have a semi-cylindrical projection that engages the ferrule at a position opposite the tongue. The connector may be engageable with the ferrule by a 360° connection about a centre axis of the cable. According to a further aspect of the present invention, there is provided a method of connecting a screen of a screened cable to an electrical connector using a connector including an electrically conductive connector body and terminating ferrule, the ferrule comprising inner and outer tubular cylindrical portions defining a cavity into which the screen, or screen and jacket, of a screened cable can be inserted to make electrical contact with the screen, the method including the steps of: a) making an incision of a predetermined length through the jacket at the stripped end of the cable; b) sliding the ferrule over the stripped portion of the cable; d) inserting the screen, or screen and jacket, of the cable into the cavity of the ferrule; and f) bending a drain wire of the stripped portion of the cable back over the ferrule; g) trimming the wire flush with an end of the ferrule furthest from the terminated end of the cable. h) engaging the ferrule with a connector body for effecting an electrical connection therebetween. The incision may be made parallel to the cable axis. The method may include any of the steps of; c) revolving the ferrule and the stripped portion of the cable relatively to the jacket about a centre axis of the held cable thereby opening the incision to form a bellmouth at the jacket end; e) crimping the outer tubular portion of the ferrule around the screen, or screen and jacket, of the cable; The step (h) of engaging the ferrule with a connector body may include the steps of: i) attaching a ground plate to the connector body; and ii) engaging the ferrule with the ground plate. The invention also provides a screened cable terminated with a connector body which makes electrical contact to the screen of the screened cable, the termination comprising a terminating ferrule having inner and outer tubular portions defining a cavity into which the screen, or screen and jacket, of the screened cable is inserted to make electrical contact with the screen, and wherein the ferrule engages with the connector body to provide an electrical connection between the screen and the body, characterised in that the screened cable comprises a screened twisted pair cable, the screen of which comprises a foil sleeve. and in that the outer surface of the inner tubular portion has a substantially constant diameter corresponding substantially to the diameter of the foil sleeve and in that whereby said ferrule is formed from a single hollow cylinder drawn back over itself to form the inner and outer tubular portions and an annular portion, which electrically and mechanically joins the tubular portions. In order that the invention and its various other preferred features may be understood more easily, some embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:- Figure 1 is an isometric view of a terminating ferrule constructed in accordance with the invention, Figure 2 is an opposite isometric view of the ferrule of Figure 1, Figure 3 is a cross sectional view of the ferrule of Figures 1 and 2 with a screened cable inserted, Figures 4 and 5 are isometric views of the ferrule of Figures 1 to 3 and a prepared screened cable, Figure 6 is an exploded view of a connector assembly incorporating the ferrule of Figures 1 to 3, and Figure 7 is an isometric view of a further connector incorporating the ferrule of Figures 1 to 3. Throughout the Figures, like reference numerals are used for corresponding or similar elements. Referring to Figures 1 and 2, there is shown a ferrule 10 comprising an inner tubular portion in the form of a cylinder 12 and an overlapping outer tubular portion in the form of a cylinder 14. The cylinders 12, 14 are electrically and mechanically joined at one of their common ends 16 by an annulus 18. The inner surface of the inner cylinder 12 defines a through hole 20 extending between the two ends 15, 16 of the cylinders 12, 14. The outer surface of the inner cylinder 12 in combination with the inner surface of the outer cylinder 14 and the annulus 18 define a cavity 22 at the end 15 of the cylinders 12, 14. The ferrule 10 is formed from an electrically conducting material. It is formed by drawing back an end of a hollow cylinder over itself in an overlapping manner to form the inner cylinder 12 joined at one end 16 to the outer cylinder 14. Referring to Figure 3, the ferrule 10 is shown with a cable 30 inserted. The cable 30 includes a jacket 32, shield 34 and signal carrier, or signal carrier twisted pairs, 36. The cable 30 is inserted into the ferrule 10 so that the jacket 32 and shield 34 are slid into the cavity 22, whilst the signal carrier 36 and any insulating element between the signal carrier 36 and shield 34 is/are slid through the through hole 20. It is preferable that the jacket 32 and shield 34 are stripped back by a predetermined length to allow a sufficient amount of the signal carrier 36 to extend out of an end of the through hole 20 at the end 16 of the cylinders 12, 14 for termination to a contact of a connector. By using a ferrule of this configuration it is possible to ensure that a connection is made to all 360° of the circumference of the inner surface of the cable screen and continue this complete screening through the body of a connector. Where a drain wire is present, it is not stripped back with the jacket 32 and shield 34. To facilitate insertion into the ferrule 10, it is preferable that the drain wire is temporarily wrapped around the signal carrier 36 and any plastic film that may be present. Subsequent to insertion into the ferrule 10, the drain wire is unwrapped from the signal carrier 36 and bent back over the ferrule 10. The wire is then trimmed flush with an end of the ferrule 10 furthest from the stripped end and may subsequently be terminated to a connector with the ferrule 10. In the case of coaxial cable having a braided shield 34, there is usually sufficient flexibility in the braid 34 and jacket 32 for them to be slid straight into the cavity 22. In cables such as twisted pairs, there may be less flexibility in the jacket 32 and it may be necessary to make one or more incisions at the insertion end of the jacket 32 to allow the shield 34 and jacket 32 to pass over the inner cylinder 12. It is preferable that any incisions be enlarged into bellmouths as is illustrated in Figures 4 and 5. Once the incisions are made, the ferrule 10 is slid over the signal carrier 36 and any drain wire or film present. The jacket 32 is then held at a predetermined distance, preferably 20mm, from an end of the jacket 32. The ferrule 10, signal carrier 36 and any drain wire or plastic film are then revolved about the centre axis of the held cable 30 in clockwise and anticlockwise directions as is shown in Figure 4 to create the bellmouth 31 shown in Figure 5. In Figure 6, an 808 connector assembly 40 is shown in an exploded, pre-terminated, view. The cable 30 is inserted into the ferrule 10 as described previously. A crimp ring 42 is then fed onto the cable past the ferrule. The signal carrier 36 of the cable 30 is terminated to a contact 44 of a connector 46 by inserting stripped wires and closing a lid 48. The length of the stripped wires are predetermined such that, once the wires are terminated, the ferrule 10 is positioned in contact with a projecting tongue 50. A ground plate 52 is attached to the connector 46 over the lid 48. The ground plate 52 has a semi cylindrical projection 54 that engages the ferrule 10 at a position opposite the tongue 50. The crimp ring 42 is slid back up the cable to a position where it encircles the tongue 50, the semi cylindrical projection 54 and the ferrule 10. The crimp ring 42 is then tightened to clamp everything together. An outer conducting body 56 is then slid over the connector 46 to complete the termination of the cable 30 to the connector assembly 40. The outer body 56 is in contact with portions of the tongue 50 and the ground plate 52 and is therefore connected to the screen 34 of the cable 30 via the ferrule 10. Referring to Figure 7, an enhancement of the 808 connector assembly 40 of Figure 6 is shown where the ground plate 52, the crimp ring 42, the tongue 50 and the outer body 56 are replaced by a single screening body 60 having a cylindrical projection 62. The screening body 60 is slid onto the cable 30 which cable 30 is then terminated to the ferrule 10 and connector 46 as described previously. The screening body 60 is slid up the cable 30 and over the connector 46 so that the projection 62 overlaps the ferrule 10. The projection is then crimped around the ferrule to secure the connector assembly 40 to the cable and also to connect the screen 34 of the cable 30 to the screening body 60 via the ferrule 10. It will be appreciated that the example embodiments illustrated are susceptible of modification and the inventive principle involved is applicable to any cables having a screen for connection to any form of compatible connector such as coaxial cables and connectors. It should also be appreciated that the invention is applicable to connectors presently in use. By replacing a pair of crimped ferrules used in the prior art with the terminating ferrule of the present invention, the connection between a connector and screen should be improved. By also using a ground plate 52 to provide further contact between the connector and ferrule 10, the connection may be further improved. The connection assembly shown in Figure 6 shows a known 808 connector adapted for improved screening connection. The design of the ground plate 52 could be varied according to the connector it is to be used with and how it is to be attached. It is preferable that the construction of the ferrule 10 be such that the outer cylinder 14 deforms under a crimping force whilst the inner cylinder 12 remains substantially unaffected. In this way, the ferrule 10 may be crimped to the cable 30 without any disruption to the signal carrier 36 and in the case of twisted pairs will not affect the lay of the cable thereby resulting in no change in the cable data transmission performance.

Claims: A connector including an electrically conductive connector body (56, 60) and terminating ferrule (10), the ferrule (10) comprising inner and outer tubular cylindrical portions (12,14) defining a cavity (22) into which the screen (34), or screen and jacket (34,32), of a screened cable can be inserted to make electrical contact with the screen (34), wherein the ferrule is engageable with the connector body (60) to provide an electrical connection between the screen and the body, wherein the ferrule (10) is constructed so as to permit it to completely enclose the screen, or screen and jacket, of the inserted cable and comprises, characterised in that the ferrule (10) is formed from a hollow cylinder drawn back over itself to form the inner and outer tubular portions and the annular portion. A connector as claimed in claim 1, wherein the body (60) has a sleeve (62) projecting from the body and having an annular cross section, and the ferrule (10) is engageable with the sleeve (62) to provide an electrical connection between the screen and the body, the sleeve being adapted for crimping around the ferrule to provide connection between the sleeve and the ferrule. A connector as claimed in claim 1, wherein the body (56) has an elongate conductive tongue (50) projecting from the body, and the tongue (50) is engageable with the outside of the ferrule (10) to provide an electrical connection between the screen and the body, wherein the connector further comprises a ground plate (52) for connection to the connector body and to the ferrule, the ground plate having a substantially semi-cylindrical projection that engages the outside of the ferrule at a position opposite the tongue, a crimp ring (42) being provided for securing the tongue and projection to the ferrule. A screened cable (30) terminated with a connector body (56,60) which makes electrical contact to the screen (34) of the screened cable, the termination comprising a terminating ferrule (10) having inner and outer cylindrical tubular portions (12,14) defining a cavity (22) into which the screen (34), or screen and jacket (34,32), of the screened cable is inserted to make electrical contact with the screen (34) and comprising an annular portion (18) which electrically and mechanically joins the inner and outer tubular portions (12,14), and wherein the ferrule (10) engages with the connector body to provide an electrical connection between the screen (34) and the body (56,60) the inner surface of the cable screen contacting the surface of the inner cylindrical tubular portion (12) within the cavity (22), characterized in that the screened cable comprises a screened twisted pair cable, the screen (34) of which comprises a foil sleeve, and the ferrule (10) is formed from a hollow cylinder drawn back over itself to form the inner and outer tubular portions and the annular portion. A method of connecting a screen of a screened cable to an electrical connector using a connector including an electrically conductive connector body and terminating ferrule engageable with the connector body, the ferrule comprising inner and outer cylindrical tubular portions defining a cavity into which the screen, or screen and jacket, of a screened cable can be inserted to make electrical contact with the screen and comprising an annular portion (18) which electrically and mechanically joins the inner and outer tubular portions (12,14), whereby said ferrule (10) is formed from a hollow cylinder drawn back over itself to form the inner and outer tubular portions and the annular portion, characterised in that the method includes the steps of: a) making an incision of a predetermined length through the jacket at the stripped end of the cable; b) sliding the ferrule over the stripped portion of the cable; d) inserting the screen, or screen and jacket, of the cable into the cavity of the ferrule; f) bending a drain wire of the stripped portion of the cable back over the ferrule; g) trimming the wire flush with an end of the ferrule furthest from the terminated end of the cable; and h) engaging the ferrule with a connector body for effecting an electrical connection therebetween. A method as claimed in claim 5, wherein the incision is made parallel to the cable axis. A method as claimed in claim 5 or 6, including the step of; c) revolving the ferrule and the stripped portion of the cable relatively to the jacket about a centre axis of the held cable thereby opening the incision to form a bellmouth at the jacket end. A method as claimed in claim 5, 6 or 7, including the step of; e) crimping the outer tubular portion of the ferrule around the screen, or screen and jacket, of the cable. A method as claimed in any one of claims 5 to 8, wherein the step (h) of engaging the ferrule with a connector body includes the steps of: i) attaching a ground plate to the connector body; and ii) engaging the ferrule with the ground plate.

Inventors: BROWN ALAN PETER, BROWN, ALAN PETER
Applicants: ITT MFG ENTERPRISES INC, ITT MANUFACTURING ENTERPRISES, INC.
Application year: 1998
Main classification: H01R9
IPC codes: H01R9, H01R4