EP2178178A1 - Device for avoiding ground loops in data transfer systems - Google Patents

Abstract

The device (1) comprises a coupling device which acts as a direct current coupler, where a contact section (2.1,2.2) is arranged between a bush-shield contact of a plug-bush connection and a plug-shield contact of the plug-bush connection. A signal transmission system has the plug-bush connection. Independent claims are included for the following: (1) a method for reducing disturbing signals in a building wiring system; (2) a retrofit kit for avoiding the ground loops in a building wiring system; and (3) a tool for a device.

Description

The invention relates to a device for reducing interference in data transmission systems by avoiding ground loops and a tool and a device provided with a data transmission system.

Shielded cables - for example "screened twisted pair" (STP) - and otherwise unshielded cables - for example "unshielded twisted pair" (UTP) are available on the one hand for electrical signal transmission. The shielded systems provide good protection against an environment with electromagnetic interference signals, as they are often found especially in the high-frequency range from about 100 kHz. Therefore, especially for high data transmission rates, the shielded cabling systems are clearly preferable. In these, however, the so-called ground loops or "ground loops" are a serious problem. Earth loops arise when two points of grounding are connected to each other via different electrically conductive paths, that is, when there is a mass connection closed to a loop. Ground loops can lead to very large currents on the shield, which can also cause interference on the signal lines.

Two grounding concepts have prevailed in the industry: in the tree structure, different earth systems come from the defined collection point out separately, to prevent earth loops. In the mesh structure, the various earth points are meshed as close together as possible to minimize the influence of earth loops. It has been found that the tree structure is particularly suitable for low-frequency applications because there are no loops. The mesh structure has prevailed for high-frequency applications, because there are high-impedance grounding paths in the tree structure and it is advantageous in this regard to use as many as possible of all available ground connections.

It would be particularly desirable to have a device or system that combines the advantages of both approaches.

It has already been proposed to provide a decoupling device, which is arranged between the cable shield on the one hand and the shield contact of the plug on the other hand. Such a decoupling teaches, for example, the US 7,033,213 , A serious disadvantage of this solution is that in case of careless installation or handling, "floating" shielding paths can arise, which are not galvanically connected to the protective earth, which can lead to operational and personal safety problems. Also known are solutions in which a decoupling device is installed directly in the screen of a patch cable. The disadvantage here is that the protection is lost by simply replacing the patch cable by the (not necessarily trained) end user. A targeted, conceptual protection of selected lines by the IT or telecommunications manager is therefore not possible.

The US 6,092,910 teaches a cable adapter for BNC and other connectors, which is to be inserted between connections to be connected and galvanically isolates and capacitively couples the shields. The adapter has electrical connectors for the signal transmitting contacts on. A disadvantage of this solution is, inter alia, that between two devices to be connected due to the cable adapter two additional connectors are present, bring the corresponding transition losses.

It is therefore an object of the invention to provide a device which overcomes disadvantages of existing signal transmission systems in terms of "avoiding unwanted effects of ground loops" while minimizing additional transient losses. Preferably, the device should also be easy to retrofit in existing shielded systems, without complex installation work would be necessary.

This object is achieved by a device as defined in the patent claims.

In one aspect, the invention relates to a device for reducing spurious signals in shielded electrical signal transmission systems. The device is characterized in that it can be mounted within a plug-socket combination between a shield socket contact of the connector on the one hand and a shield connector contact of the connector on the other hand.

This is done so that the mutually corresponding signal-transmitting plug and socket contacts of the connector (plug-socket combination) are galvanically connected to each other and the shields of the two interconnected by the connector cables are Gleichstromentkoppelt.

A DC decoupling according to the definition used here is present when the DC resistance for small voltages is higher by at least one order of magnitude (and for example by at least a factor of 100) than the DC resistance via an electrical plug-socket contact. A Gleichstromentkopplung can be effected by a high-pass filter, for example. By a capacitor, but also by semiconductor elements. In this case, a high-resistance resistor or varistor connected in parallel with the capacitor or semiconductor switching element can allow further functionalities and should not be expressly excluded by the definition of direct current decoupling used here.

The connector may be a connector of a known, existing type, for example. A standardized connector.

The device thus removes the shield contact from the socket and directs it via a coupling device to the shield contact of the plug. For this purpose, it has a contact section which prevents (direct) electrical (galvanic) contact between the shield contacts and connects them to the coupling device.

The device is preferably shaped so that in the assembled state and when the plug is plugged into the socket, it does not touch the signal-transmitting socket nor the corresponding plug-in contacts. That is, the electrical contact between signal-carrying jack and plug contacts is unaffected by the device, as well as the relative position of the socket and the plug. Rather, the device is preferably arranged in the inserted state of the plug in spaces between the plug and socket, which may be present from the socket outstanding games. The - preferred - Procedure, according to which the contacting of the signal-transmitting plug and socket contacts is unaffected by the device, has the important advantage that no additional transition losses caused by the device.

For example, the coupling device - it may have a coupling element or a plurality of coupling elements as an electronic components (capacitor, semiconductor device, etc.) - arranged so that it is at least in the inserted state of the plug inside the socket. Alternatively, it may also have inside the socket engaging taps (contact parts), which are connected via electrical conductors to the outside of the socket arranged coupling device.

Often standardized plugs are designed so that they have a substantially flat, perpendicular to the plug axis end face. This applies, for example, among others for the RJ-45 connector. Between the front side of the plug and the parallel running base surface of the socket opening, a gap may be free; in the case of the RJ-45 connector, this distance is not required by the standard. According to one embodiment of the invention, the device is now designed such that the at least one capacitor and / or the at least one semiconductor component is located in this intermediate space between the socket base surface on the one hand and the plug end face on the other.

Shielded connectors, for example of the type RJ-45, have a metallic connector housing connected to the cable shield, which surrounds the electrically insulating contact housing in certain areas. The socket has a shielding plate with against the inside, projecting into the socket opening, resilient contact tabs which press against lateral sides of the plug housing. Accordingly, the contact portion of an inventive device for RJ-45 connector is designed so that it is guided along the two lateral sides of the plug housing and thus prevents direct electrical contact between the contact tabs and the plug housing. It has, for example, inside and outside contact surfaces, which are interconnected via the coupling device. For the purpose of mechanical stability, it is also advantageous for the device to have a base part which connects between the laterally extending contact parts and which extends at the end in relation to the plug. When the capacitor or other active elements as described above are arranged in the space between the socket base surface on the one hand and the plug end face on the other hand, the base part can carry these components. However, the base section is also useful if the electronic components are outside the socket. Instead of the base part or in addition thereto, the contact parts can also be connected in the plug at the back (proximal), ie outside the bushing extending fastening and / or stabilizing parts.

In sum, for preferred embodiments of the device a readily retrofittable, the connector neither the function nor the geometry affecting solution that is effective, easy to control in the application and is still inexpensive to manufacture.

Preferably, the device is designed so that the connection between the shields of the cable to be connected to each other via the connector acts as a high-pass filter. The high-pass filter is advantageously designed for many applications to block currents with frequencies of up to a few kHz. If the coupling device has a capacitor, it preferably has a capacitance of between approximately 0.2 μF and 20 μF, particularly preferably between 1 μF and 4 μF.

The plug-in connection is, for example, an RJ-45 plug-in connection or another standardized electrical plug-in connection, for example IEC 61076-3-110 "Connector for electronic equipment-product requirements", or another plug-in connection permeating the application.

The device may, for example, be attachable to or in the socket or on the plug. The coupling device of the device may comprise capacitors, protective elements and possibly further electronic components.

Particularly preferred is - this applies to each type of connector - the coupling device on a conductor carrier, for example. On a Flexprintfolie, i. a flexible printed circuit board applied. The conductor tracks of the conductor carrier may have the contact surfaces which remove the shield contacts of the socket and the plug. The conductor carrier is chosen so thin that it can be inserted in the existing space between the socket and plug, it runs, for example, in relation to the front side of the plug and can bear the front side of the electronic coupling elements of the coupling device.

In addition to the coupling device, which may be formed as mentioned on a conductor carrier, the device preferably also has a fastening device for mounting the device in a socket or on a plug. For reasons of optimal controllability, mounting in or on the bushing is particularly preferred. The fastening device may be, for example, a mounting frame, which is aufschlipbar on the outside of the socket and holds the inwardly projecting into the socket conductor carrier. In the case of mounting on the plug, the fastening device is, for example, designed as a mounting sleeve which can be placed around a housing of the plug.

A particular advantage of the inventive device is the excellent retrofitting. In an existing building cabling system, no sockets, plugs or even entire devices need to be replaced for retrofitting; no housing has to be screwed on and no solder joints need to be redone. Rather, only a device of the type described above must be mounted in a socket or on a plug, for example. By simple on or pushing.

A retrofit kit preferably also has, in addition to the actual device, a tool adapted to the device. This is particularly advantageous when the device is mountable in a socket and has a flexprint that is not dimensionally stable in itself. In addition to a handle, the tool can also have a guide part, which brings the flexprint film in the intended configuration into the socket opening.

For example, a typical cabling system includes a distributor (switch or the like) having a plurality of outputs connected by patch cords to a jack panel from which connections to the work stations are made. At the workplace there is a workplace socket (socket) to which the user can connect the terminal. A cabling system equipped with devices according to the invention has a plurality of devices according to the invention mounted in sockets of the socket panel or the divider or patch cables provided with devices according to the invention. In addition, also work sockets and / or other sockets and / or other plugs - depending on the need - be equipped with inventive devices.

• Fig. 1 eine erste Ausführungsform einer erfindungsgemässen Vorrichtung;
• Fig. 2 die Vorrichtung gemäss Fig. 1 ein einer RJ-45-Buchse montiert;
• Fig. 3 die Vorrichtung gemäss Fig. 1 mit einem Werkzeug für die Montage in einer RJ-45-Buchse
• Fig. 4 eine zweite Ausführungsform einer erfindungsgemässen Vorrichtung;
• Fig. 5 Teile einer Vorrichtung der in Fig. 4 gezeigten Art, wobei der besseren Übersichtlichkeit halber die Befestigungsmanschette nicht gezeichnet wurde;
• Fig. 6 ein Schaltschema einer Kopplungseinrichtung mit einem Kondensator und einem diesen schützenden Überspannungsschutzelement, z.B. einem Varistor;
• Fig. 7 ein Gebäudeverkabelungsschema mit erfindungsgemässen Vorrichtungen; und
• Fig. 8 die gemessene Transferimpedanz einer mit der erfindungsgemässen Vorrichtung ausgestatteten geschirmten Kabelverbindung (über eine geschirmte RJ-45-Buchse) in Funktion der Signalfrequenz.

Hereinafter, embodiments of the invention will be described in detail with reference to drawings. In the figures, the same reference numerals designate the same or analogous elements. Show it:

• Fig. 1 a first embodiment of an inventive device;
• Fig. 2 the device according to Fig. 1 mounted on an RJ-45 jack;
• Fig. 3 the device according to Fig. 1 with a tool for mounting in an RJ-45 socket
• Fig. 4 a second embodiment of an inventive device;
• Fig. 5 Parts of a device of in Fig. 4 shown kind, with the sake of clarity, the mounting sleeve was not drawn;
• Fig. 6 a circuit diagram of a coupling device with a capacitor and this protective overvoltage protection element, such as a varistor;
• Fig. 7 a building cabling scheme with inventive devices; and
• Fig. 8 the measured transfer impedance of a shielded cable connection equipped with the device according to the invention (via a shielded RJ-45 socket) as a function of the signal frequency.

The device 1 according to FIG. 1 has a fixed to a mounting frame 3 conductor carrier, namely a Flexprint 2. This has on the outside and inside each contact surfaces (in the figure, only the inside contact surface 4 is shown) for removing the female or Steckerschirmkontakte on. Of these lead tracks to the low-frequency decoupling, and high-frequency coupling capacitor 5 and an overvoltage protection 6, wherein the Flexprint 2 at least one via (via), so that the outside contact surfaces with the inside mounted capacitor 5 is connected can be.

The mounting frame is formed so that it can be fastened in front of an RJ-45 socket, such that the flexprint projects into the socket. The outer and inner contact surfaces are located on the lateral parts 2.1, 2.2 of the flexprint, which thereby form the contact area. The coupling elements 5, 6 are attached to the base section 2.3, which is in the inserted state of the plug between the end face of the plug and the base (the closed end) of the socket opening.

The flexprint is as known per se. Made of polyimide (PI) with a thickness of less than 50 microns, here of about 25 .mu.m, formed thereon with conductor tracks and contact surfaces made of copper. The very small thickness allows that the Flexprint is partially laterally between the inner wall of the socket 8 and the plug, which in FIG. 2 is apparent. The flexibility of the conductor carrier (ie the flexprint) is not a necessary feature of the device. Much more it results in the example described here from the small thickness of the conductor carrier.

The mounting frame 3 may be connected to the flexprint 2 in any suitable manner, for example by gluing. One possibility is also to provide the mounting frame in two parts with a base frame with attachment cams and a cover frame. The attachment cams can engage in corresponding mounting holes of an outwardly folded over the base frame mounting portion of the Flexprints, and what results after covering by the cover frame a firm connection. Depending on the type of mutual attachment of the base frame and cover frame so the flexprint can be solved.

The device as in Figures 1 and 2 shown can be inserted into an existing, standard-compliant RJ-45 socket and is then located between the socket and an existing, also compliant plug, here an RJ-45 connector.

FIG. 3 shows a device of the type described above with a tool 11, which in addition to a handle 11.1 also on the dimensioning of RJ-45 sockets matched guide webs 11.2. The tool 11 allows easy mounting / retrofitting of the inventive device in existing RJ-45 sockets 8. The tool is clipped by means of retaining clips 11.3 on the mounting frame 3 and can be solved easily after assembly. It is understood that the tool can also be used to disassemble the device from the socket. The tool can be optionally already clipped on delivery of the device and thus also ensure the stability of the device during transport and storage.

The embodiment of the device 1 according to FIG. 4 differs from the embodiment described above in that it can be mounted on a plug and not in a socket. For this purpose, the fastening means - here a fastening sleeve 3 '- designed so that it can be fastened to the outside of a connector housing. The flexprint 2 is for example designed so that it extends in the inserted state of the plug substantially in the same area, as is the case for the embodiment described above, in contrast to this, the Flexprint 2 preferably rests frontally on the plug and not as in Fig. 2 at the base of the socket opening.

The electronic components of the coupling device - the coupling elements capacitor 5 and overvoltage protection 6 - can be arranged as well as in the embodiment described above inside the connector, ie the front side relative to the plug (and thus preferably on the outside of the Flexprint 2). However, they can also lie according to the illustrated embodiment in the inserted state outside the socket, which is in FIG. 5 sees. FIG. 5 shows the device 1 according to FIG. 4 mounted on a plug 9, wherein the mounting sleeve 3 'is not shown. As you can see, the capacitor 5 and the overvoltage protection 6 with respect to the plug portion on the back, so arranged proximally on the side of the plug.

An arrangement of the elements (for example, capacitor, overvoltage protection) of the coupling device outside the actual socket opening is also possible in the embodiments in which the device is mounted in the socket and not on the plug.

FIG. 6 illustrates a circuit diagram of a coupling device for a device according to the invention. Terminals A and B are in contact with the screw contact of the plug or socket. As coupling elements, the coupling device, together with a capacitor 5, which acts as a high-pass filter, also has a parallel-connected overvoltage protection 6. This may be a varistor or another suitable protective element. In place of the varistor may also be a high-resistance of preferably at least 1 kΩ or at least 2 kΩ, for example, 5 kΩ or more.

The use of a varistor has the advantage that even high voltages can not destroy the capacitor. A high-impedance resistor has the advantage that the shield appears to be connected through testing of the network by means of a tester.

The electronic coupling components "capacitor" 5 and overvoltage protection 6, together with the conductor tracks and contact surfaces contacting them form the coupling device. Since RJ-45 sockets (and also sockets of other connector systems) have two mutually symmetrically arranged contact tabs for the shielding, due to the in Fig. 6 illustrated parallel circuit and the one contact tab on the capacitor 5 and the other via the overvoltage protection 6 to be connected to the male shield. The capacitor is then connected only via the socket and the connector shield with the surge protector; however, this also corresponds to the parallel, in Fig. 6 illustrated circuit.

FIG. 7 shows on the basis of a building cabling scheme a useful application for the inventive device. Often, the connection between a signal distributor ("switch") 21 and a Buchsenpaneel 22 by means of short so-called "patch cable" 23 accomplished. From Buchsenpaneel 22 from the connection is made with the workstations. The handling of these patch cables and thus the correct wiring are generally the task of the 1T responsible person of a company or the building technician. From the socket panel 22, the connection to the work station sockets 24 is via the building cabling 25. Both the switch 21 and the socket panel 22 and the user terminal (here a computer 26) are generally grounded, sometimes the work station socket 24 (ie the respective ones) Socket shield contacts are connected to the building earth). This would result in several ground loops without decoupling devices of the kind according to the invention.

The device 1 according to the invention with a coupling device can now be placed, for example, in the socket panel 22 or, alternatively, in the sockets of the switch 21, with one person responsible for equipping all the sockets of the switch or the socket panel, whether occupied or not, accordingly. As a further alternative, he / she can consistently work with patch cables, one plug is provided with a device mounted on the plug side.

Additionally or alternatively, the workstation sockets 24 or possibly device plug can be equipped with an inventive device 1, which is also in FIG. 7 is symbolically illustrated. This prevents another earth loop (between the socket panel and the terminal or between the workstation socket and the terminal).

Often the quality of the shield is expressed by the so-called "transfer impedance". This is a measure of what noise in the data conductor in Function of a current flowing in the shielding current is induced. The smaller the transfer impedance, the better.

In the field of building cabling according to ISO / IEC 11801, a limit value for the maximum tolerable transfer impedance exists for cabling components, in FIG. 8 shown as dashed line 31. An inventive device acts in the transfer impedance measurement as a series-connected capacitive element, thus increases the impedance at low frequencies. But it is easily possible to choose the capacity so that this has a significant effect only in the low-frequency range. In Fig. 8 the upper solid line 32 shows the measured course of the transfer impedance with device according to the invention. The lower solid line 32 shows the course without device according to the invention. As in Fig. 8 Without further ado, the transfer impedance 32, even with the device according to the invention, is below the predetermined limit value 31 at each frequency.

For applications with a predetermined maximum transfer impedance, it is thus possible to use capacitors whose capacitance does not fall below a minimum value of, for example, 0.2 μF, 0.5 μF or 1 μF. On the other hand, excessively high capacities are undesirable because, firstly, too much space is required and, secondly, the cutoff filter frequency of the disturbing ground loop hum signals is too low. Overall, for many applications, a capacitance anywhere in the range of between 0.2 μF and 20 μF is optimal. There are also conceivable applications for which the lower capacity limit is less critical, which therefore also work with comparatively smaller capacities.

Among other things, in connection with the limit value for the transfer impedance, the use of capacitors with deep Serieresonanz advantage. It It has been found that particularly chip capacitors and especially ceramic chip capacitors are particularly suitable for coupling devices according to the invention, they are also suitable in their dimensions to be arranged in the narrow space within the socket.

The embodiments described above represent only a few of many possible examples for implementing the invention. In particular, the concept is also readily applicable to connectors of other systems. For this purpose, the dimensioning must be adjusted accordingly and possibly the contact surfaces of the inventive device must be arranged differently according to differently on the flexprint-like or differently designed carrier of the coupling device.

Claims (12)

Device (1) for reducing interference signals in a shielded electrical signal transmission system, the signal transmission system having a plug-socket connection, and wherein the device has a coupling device acting as a DC decoupler, characterized in that the device further comprises a connection between a socket-shield contact of the connector Socket connection and a plug-shield contact the male-female connection arranged contact part (2.1, 2.2), which prevents a galvanic connection of the female shield contact with the male shield contact and connects the female shield contact and the male shield contact via the coupling means together the device (1) is formed such that it does not come into contact with signal-transmitting socket contacts or with signal-transmitting plug contacts in the case of a proper arrangement. Apparatus according to claim 1, characterized in that the male-female connection is an RJ-45 connector, wherein the exposed male contacts and latch define a Steckerober- and a -Unterseite and that the contact portion (2.1, 2.2) by a with respect to the top and bottom sides are formed on the lateral sides along the connector running conductor carrier (2), which is contacted by the female shield contact and the connector-shield contact. Apparatus according to claim 2, characterized in that the conductor carrier (2) is a Flexprint. Apparatus according to claim 2 or 3, characterized in that the conductor track carrier (2) has a base portion which extends frontally with respect to the plug and carries the electronic components (5, 6) of the coupling device. Device according to one of the preceding claims, characterized in that the coupling device acts as a high-pass filter. Apparatus according to claim 5, characterized in that the coupling device has at least one capacitor (5). Apparatus according to claim 6, characterized in that a capacitance of the coupling device is between 0.2 μF and 20 μF. Device according to claim 6 or 7, characterized in that the coupling device has an overvoltage protection (6) connected in parallel to the capacitor (5). Device according to one of the preceding claims, characterized by a fastening device (3, 3 ') adapted to the socket or the plug for mounting the device to the socket or the plug. A method of reducing spurious signals in a building cabling system having a plurality of existing, for example, standardized plug-to-socket connections, thereby characterized in that a plurality of devices are mounted in existing sockets and / or on existing plugs of the building cabling system. Retrofit kit for avoiding ground loops in a building cabling system, comprising a plurality of devices according to one of claims 1 to 9 and at least one adapted to the devices tool for mounting the devices to existing plugs (9) or sockets (8). Tool (11), adapted to a device according to one of claims 1 to 9, for mounting the device to a bushing (8), comprising a handle (11.1) and to the dimensioning of the bushing (8) adapted guide part (11.2) for Position the device inside the bushing opening.

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