PLUG

Abstract: The invention relates to a plug (1) comprising: a body portion (2); an elongated conductive connector (3) projecting from the body portion for receiving one or more conductors, at one end of which connector are arranged means (8) for bringing said conductor into contact with a connector in a plug counterpart; a tubular capacitor (4) threaded around the connector (3) so as to couple an inner surface forming a first pole of the tubular capacitor to the connector; and grounding means (5, 6, 17) coupled to an outer surface forming a second pole of the tubular capacitor (4), the grounding means being arranged to ground said second pole of the tubular capacitor. To facilitate the assembly of the plug, the grounding means comprise a flexible conductive element (6) which is arranged to press like a spring against the outer surface of the tubular capacitor (4) to ground said second pole of the capacitor.

Description: Plug The invention relates to a plug comprising: a body portion, an elongated conductive connector projecting from the body portion for receiving one or more conductorε, at one end of which connector are arranged means for bringing said conductor into contact with a con¬ nector in a plug counterpart, a tubular capacitor threaded around the connector so as to couple an inner surface forming a first pole of the tubular capacitor to the con¬ nector, and grounding means coupled to an outer surface forming a second pole of the tubular capacitor, the grounding means being arranged to ground said second pole of the tubular capacitor. The term "elongated connector" as used herein re¬ fers to e.g. a needle-shaped fairly long connector whose length is sufficient for a tubular capacitor to be thread¬ ed thereon. This invention relates to a disturbance shielded plug adapted for use in environments with a relatively strong interfering electromagnetic field. The plug according to the invention is adapted for use with e.g. telecommunications equipment, radio transmitters and the like. If a conventional non-shielded plug, to which e.g. a conventional multipolar cable is connected, were used in the strong RF field surrounding radio transmitters, the field surrounding the plug and the cable would cause such strong interference that hardly any useful signal could be transmitted via the cable and the plug. It is known to utilize a conventional non-shield¬ ed plug with a shielded cable in places with a strong interfering electromagnetic field. In this case " a multi¬ polar cable is commonly used, with e.g. an aluminium foil layer arranged under an insulating material layer forming the external armature of the cable. For practical reasons a shielded cable cannot, however, be used in all places, and its cost is also relatively high compared with conven¬ tional cables. Additionally, it is known to utilize a shielded so-called D-plug with a conventional non-shielded cable in places with a strong interfering electromagnetic field. In this case tubular capacitors are arranged around the elongated connectors in the plug. In this solution a first pole of the tubular capacitors, formed by their inner sur- faces, is soldered to the connector around which that par¬ ticular tubular capacitor is arranged. Furthermore, the outer surface forming a second pole of the tubular capaci¬ tors is soldered to a grounding plate in the plug. When the tubular capacitors are correctly designed, they can be used to filter e.g. interference caused by an external RF field, thus allowing the utilization of a non-shielded cable with said plug. The most significant disadvantage of the above known shielded plug is that it is complicated to assemble. This is because each tubular capacitor must be separately soldered both to that particular connector around which it is arranged and to the grounding plate in the plug. As a plug may comprise several connectors, e.g. 64, this would result in the number of necessary solders being 128. Owing to the small size of the tubular capacitors (diameter e.g. approx. 1 to 2 mm, and height e.g. approx. 2 mm) and the lack of space in the plug, providing soldering to the right places requires extreme accuracy. Thus, the assembly of the plug is slow and expensive. The object of this invention is to solve the above problem and to provide a shielded plug that is sig¬ nificantly simpler to assemble than known solutions. This goal is achieved with the plug according the invention, which is characterized in that the grounding means coiti- prise a flexible conductive element which is arranged to press like a spring against the outer surface of the tubu¬ lar capacitor to ground said second pole of the capacitor. The invention is based on the idea that once the grounding means of a plug are provided with a springlike portion which presses against the outer surface forming a second pole of the tubular capacitor, the outer surface of the tubular capacitor can be grounded without soldering. If the springlike portion is also designed so that the force it directs to the tubular capacitor is such that the tubular capacitor presses with considerable force towards a connector penetrating through it, so that the inner surface forming a first pole of the tubular capacitor is brought into contact with the outer surface of the connec¬ tor, there is no need to solder the inner surface of the tubular capacitor to the connector. The most significant advantage of the plug according the invention is thus that it is significantly simpler, faster and less expensive to assemble than known plugs, as the number of necessary sol- derings is significantly lower than in known solutions. Advantageously, the tubular capacitors can be installed into the plug without any soldering. In a preferred embodiment of the plug according to the invention, the plug comprises a cover portion, sep¬ arate from the body portion and provided with apertures through which the ends of the connectors can penetrate. The cover portion is connected to the body portion so that the cover portion and the body portion are pressed against the end surfaces of the tubular capacitors, whereby the tubular capacitors can be locked in place.- This prevents the tubular capacitors from moving under the influence of e.g. vibration, which would impair the contact between them and the connectors. In another preferred embodiment of the plug ac¬ cording to the invention, the above flexible element is arranged so that placing the cover portion in place causes the flexible element to press against the tubular capacitor. Thus the flexible element can be formed such that it does not direct any notable force against the tu¬ bular capacitor until the cover portion is in place. This simplifies further the assembly of the plug as placing a small tubular capacitor in place may be difficult if a springlike portion is pressed against it during assembly. The preferred embodiments of the plug according to the invention are disclosed in the attached dependent claims 2 through 7. The invention is described further hereinafter, by way of a few preferred embodiments of the plug accord¬ ing to the invention with reference to the accompanying drawings, in which: Fig. 1 illustrates the use of a plug according to the invention, Fig. 2 illustrates a first preferred embodiment of the plug according to the invention, Fig. 3 is a partial section of the plug of Fig. 2, Fig. 4 illustrates a second preferred embodiment of the plug according to the invention, and Fig. 5 is a partial section of the plug of Fig. 4. Fig. 1 illustrates the use of _a plug according to the invention. The plug 1 in Fig. 1 is connected to e.g. a base station in a cellular radio system. Thus there is a strong RF-field in a casing 12 inside which the plug 1 is arranged. The RF-field would cause interference for a non- shielded plug and cable. The plug 1 is, however, shielded, and a conventional non-shielded multipolar cable 11 can be used in connection thereto. A metal texture net 13 is ar¬ ranged on the outer surface of the cable 11 inside the casing 12, the net being grounded to the casing 12 by means of connectors 14, and also coupled to the metal casing of the plug 1. The plug 1 is preferably encased in a metal casing. Fig. 2 illustrates a first preferred embodiment of the plug according to the invention. The plug 1 pres- ented in Fig. 2 may be e.g. a 64-pole Euro connector. A body portion 2 of the plug 1 is attached by means of screws 15 to a metal casing 16. The metal casing comprises an aperture through which the cable 11 is led to the plug. The cable 11 consists of a plurality of separate conductors each of which is connected by means of the con¬ nectors of the plug (cf. Fig. 3) to a contact 8. Thus the contacts 8 connect the conductors to the contacts in a counterpart (not shown) of the plug. The left edge of the plug comprises a metal grounding contact 5 designed so that it is grounded when the plug 1 is connected to its counterpart. The concept "grounded when the plug is connected to its counterpart" as used herein suggests that when the plug is inserted in a counterpart of a plug in an electric appliance, the grounding contact is grounded either once it comes into contact with a grounding contact in the counterpart or alternatively once it comes directly into contact with the body of the electric appliance. Fig. 3 shows the plug of Fig. 2 in partial sec- tion taken on the line III - III. In Fig. 3 the parts of the plug 1 are, however, shown apart to simplify the distinction of one from the other. Fig. 3 thus illustrates also the assembly of the plug 1. The body portion 2 of the plug 1 can be e.g. of plastic. The body portion comprises elongated metal con¬ nectors 3 to the right end (in Fig. 3) to which one or more cable 11 conductors are connected. Metal contacts 8 are arranged at the left ends of the connectors, by means of which the cable 11 conductors are brought into contact with a plug 1 counterpart. In Fig. 3, a sleeve-like tubular capacitor 4 is threaded on the upper connector 3. Such a tubular capacitor is preferably threaded on each connector, i.e. even on the lower connector 3 shown in Fig. 3. The tubular capacitor 4 is formed of a tubular capacitor known per se and the inner surface forming its first pole can be e.g. of a mixture of lead and tin. Cor¬ respondingly, the outer surface forming the second pole of the capacitor can be e.g. of a mixture of lead and tin. Between the inner and outer surfaces formed of the mixture of lead and tin is arranged a third layer of e.g. some ce¬ ramic material. If the plug of Fig. 3 is used e.g. in such circumstances in which the frequency of the interfering field surrounding it is 0 to 2 MHz, and the frequency of the signal transmitted through the connector 3 is approx. 2 MHz, 120 pF tubular capacitors can be chosen for the plug 1, whereby the form of the pulses transmitted through the plug does not change significantly. The plug of Fig. 3 comprises additionally a lid portion 9 made of plastic, with apertures 10 through which the connectors 3 penetrate when the lid portion 9 is being connected to the body portion 2. This is when the tubular capacitors 4 are locked in place between the lid portion and the body portion. The whole lid portion 9 fits into the metal casing 16 of the plug 1 once the plug is as¬ sembled. Hence the lid portion is not shown in Fig. 2. The lid portion 9 is provided with a metal grounding plate 17 parallel to its surface, the plate covering essentially the whole surface facing its body portion. However, a plastic projection 18 projecting from the plate 17 so that there is no contact between the end surfaces of the tubular capacitors 4 and the plate 17, is arranged in connection with each aperture 10. At each aperture 10 a flexible metal projection 6 projects from the grounding plate 17, the projection being arranged to press against the outer surface of its re¬ spective tubular capacitor 4 when the lid 9 and the body portion 2 are connected. In addition, the grounding con¬ tact 5 shown in the background of Fig. 3 (in partial sec- tion) projects from the grounding plate 17. The operation of this contact is described in connection with Fig. 2. In an assembled plug the flexible metal projec¬ tions 6 press in a spring-like manner towards the outer surfaces of the tubular capacitors 4, the outer surfaces being thus grounded through the grounding plate 17 and the grounding connector 5. In addition, the radial force dir¬ ected to the tubular capacitors 4 brings the inner sur¬ faces of the tubular capacitors 4 into contact with the connector 3. Most advantageously, the tubular capacitors need not be soldered at all. Fig. 3 further shows the metal casing 16 of the plug 1 with an aperture 19 for receiving the cable 11. When the plug is being assembled, the body portion 2 and the lid portion 9 are pressed together once the tubular capacitors 4 have been mounted and thereafter the body portion 2 is fastened by means of e.g. screws 15 to the casing 16. Fig. 4 illustrates a second preferred embodiment of the plug according to the invention. Fig. 4 shows a body portion 2' of a plug 1' in partial section. In Fig. 4 the ends of -connectors 3, to which the conductors are supposed to be connected, project towards the reader. As may been seen from Fig. 4, a tubular capacitor 4 is threaded around each connector 3. The embodiment of Fig. 4 differs from that of Fig. 2 and 3 in that in Fig. 4 the plug 1' comprises only two flexible elements 6' through which all tubular capacitors 4 of the plug 1' are grounded. The flexible elements 6' can be formed of e.g. spiral springs arranged to contact the outer surfaces of the tubular capacitors 4. Fig. 5 is a partial section of the plug of Fig. 4 taken on the line V - V. However, a lid 9' and a metal casing 16', not shown in Fig. 4, have been added to Fig. 5. Even in the embodiment of Fig. 5 the connectors 3 are connected to contacts 8 which thus connect the con¬ ductors to be connected to the left ends of the connectors to contacts in a counterpart (not shown) of the plug 1'. As is evident from Fig. 5, the spiral springs 6' have been compressed when the lid portion 9' has been put in place. The lid portion 9' remains in place owing to friction between itself and the connectors 3. The spiral springs 6' are shown as ellipses in contact with the tubu¬ lar capacitors 4. Fig. 5 further shows that the plug 1' does not comprise a separate grounding plate; instead the two-piece metal casing 16' of the plug 1' functions as a grounding element against which the spiral springs press when the lid portion 9' is in place. Thus the metal casing 16' com- prises a grounding contact (not shown) through which it is grounded to a grounding contact in the counterpart of the plug 1' or alternatively directly to the jbody of an elec¬ tric appliance. It will be understood that the purpose of the above description and the accompanying drawings is only to illustrate the present invention. It will be obvious for those skilled in the art that various variations and modi¬ fications of the invention are possible without departing from the scope and spirit of the invention disclosed in the attached claims.

Claims: Claims 1. Plug (1, 1') comprising: a body portion (2, 2'), an elongated conductive connector (3) projecting from the body portion for receiving one or more conduct¬ ors, at one end of which connector means (8) are arranged for bringing said conductor into contact with a connector in a plug counterpart, a tubular capacitor (4) threaded around the con¬ nector (3) so as to couple an inner surface forming a first pole of the tubular capacitor to the connector, and grounding means (5, 6, 6', 16', 17) coupled to an outer surface forming a second pole of the tubular capaci- tor (4) , the grounding means being arranged to ground said second pole of the tubular capacitor, c h a r a c t e r ¬ i z e d in that the grounding means comprise a flexible conductive element (6, 6') which is arranged to press like a spring against the outer surface of the tubular capacitor (4) to ground said second pole of the capacitor. 2. Plug as claimed in claim 1, c h a r a c ¬ t e r i z e d in that the plug comprises a plurality of connectors (3) and a plurality of tubular capacitors (4) , with a tubular capacitor threaded around each connector, the first pole of which capacitor is connected to a con¬ nector, and the second pole of which capacitor is arranged to be grounded by said grounding means (5, 6, 6', 16', 17) when the plug is connected to a counterpart. 3. Plug as claimed in claim 2, c h a r a c - t e r i z e d in that the grounding means comprise per each tubular capacitor a separate conductive flexible ele¬ ment (6) which presses against a second pole of its re¬ spective tubular capacitor (4) for grounding of the pole. 4. Plug as claimed in claim 2, c h a r a c - t e r i z e d in that the grounding means comprise a con- ductive flexible element (6') which is arranged to press against the outer surface of a plurality of tubular capa¬ citors (4), said flexible element (6') thus grounding the second poles of said plurality of capacitors. 5. Plug as claimed in any of claims 1 to 4, c h a r a c t e r i z e d in that the plug (1, 1' ) com¬ prises a lid portion (9, 9') which is separate from the body portion and provided with an aperture or apertures (10) and connected to the body portion (2, 2') so that the connector or connectors (3) project through the apertures in the lid portion, whereby the body portion (2, 2') and the lid portion (9, 9') , when connected to each other, are pressed against the end surfaces of the tubular capacitors (4) that surround the connectors to lock the tubular capacitors in place. 6. Plug as claimed in claim 5, c h a r a c ¬ t e r i z e d in that the flexible element (6) or corres¬ pondingly the flexible elements are arranged in connection with the lid portion (9) . 7. Plug as claimed in claim 5 or 6, c h a r a c - t e r i z e d in that arranging the lid portion (9, 9') in place causes the flexible elements (6, 6') to be press¬ ed against the tubular capacitors causing the spring-like elements to yield elastically so that internal tension is formed under the influence of which the elements are pressed against the tubular capacitors (4) .

Inventors: ELORANTA OLLI, LEINONEN ISMO, ELORANTA, OLLI, LEINONEN, ISMO
Applicants: ELORANTA OLLI, LEINONEN ISMO, NOKIA TELECOMMUNICATIONS OY, ELORANTA, OLLI, LEINONEN, ISMO
Application year: 1996
Main classification: H01R13
IPC codes: H01R13