GB1570165A

GB1570165A - Electrical equipment practices

Info

Publication number: GB1570165A
Application number: GB1844578A
Authority: GB
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC
Priority date: 1978-05-09
Filing date: 1978-05-09
Publication date: 1980-06-25

Description

154) IMPROVEMENT IN OR RELATING TO ELECTRICAL EQUIPMENT PRACTICES .-!1) We, STANDARD TELE PHONES AND CABLES LIMITED, a British Company, of 190 Strand, London WC2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to electrical equipment practice, especially for electronic equipment.

In current systems such as automatic telecommunication exchanges and data processing systems much of the equipment is in the form of racks of electrical equipment in wich the circuitry is on slide-in units. Such a slide-in unit supports electrical and electronic components, often including integrated circuit units, which are interconnected by wiring, usually in the form of printed circuit tracks. The unit has also a connector element at its inner end which mates with a corresponding connector element in the rack, these connector elements providing access to the rest of the equipment.

With such systems it is often required to be able to test or fault-find at the slide-in units for test purposes, i.e. without having to take the equipment out of service To enable this to be done a slide-in unit to be tested in withdrawn, and a slide-in unit extender. also known as an outrigger is plugged into the connector element on the rack. The unit to be tested is then plugged into the extender, which is a board with wiring, usually printed wiring between the connector elements on its two edges. The extender may be hinged to allow access to both sidi > -)f the unit for testing, and it may also provide isolation facilities and access points for test leads. Unfortunately the extender adds a considerable length of connection due to the depth . )f the rack into whic h it is plugged. and this additional length of connection mtroduces unwanted cross-laik An .)bject of this invention is to provide an extender for use as indicated above in which the disadvantage referred to is minimized.

According to the present invention there is provided an extender unit which includes a generally rectangular printed-circuit board unit with connectors at two of its parallel edges and with printed circuit tracks connected between the contacts of its said connectors, in which when in use for testing slide-in unit of an electrical equipment the extender unit is plugged into the equipment in place of the unit to be tested and the latter unit is plugged into the extender, and in which to reduce crosstalk due to the con ductor on the extender unit each of those conductors which carries signals when the extender unit is in use is parallelled by a grounded screening conductor Embodiments of the present invention will now be described with reference to the accompanying drawings, in which Fig. 1 is a perspective view to explain the use of an extender to which the invention is applicable, and Figs. 2, 3, 4 and 5 are cross-sections of printed circuit conductor arrangements embodying the invention.

Fig. 1 is highly schematic, and shows the shelf structure in skeletal form. The shelf assembly 1 has along its rear face a number of shelf connectors such as 2, these usually being socket connectors. The extender unit (also known as an outrigger) is shown at 3 and this is plug-connector ended at one end to plug into a shelf connector such as 2. At its outer end the extender unit has a connector 4 into which the slide-in unit 5 to be tested is plugged.

It will be seen. as mentioned in the opening paragraphs, that because of the printed wiring between the two connectors of the extender unit, trouble has been experienced in the past due to the crosstalk introduced by the additional conductor lengths brought in by the extender unit. The present invention overcomes this by the provision on the board of the extender unit of grounded screens for the signal bearing ones of the printed circuit tracks on the extender unit's printed circuit board.

In Fig. 2, we see in cross section the printed circuit board 10 of an extender unit on which there is a printed track 11 which carries a signal when the unit is in use, adjacent to which are grounded tracks 12, 13 and 14. Hence the signal-carrying track is screened on three out of four sides, which substantially reduces the cross talk due to or involving the track 11.

In many cases the signals are conveyed on balanced highways, and here we use the arrangement shown in Fig. 3, where 16 and 17 are printed tracks which form a pair of balanced highways, tracks 18, 19, 20 and 21 are the grounded tracks which provide the screening.

It is desirable that a single extender unit should be provided with a number of different slide-in units of the same height and depth, so the allocation of signals to be printed wiring is made variable. This is achieved by providing manually settable switches on the printed board at one or both of its ends. The number of such switches provided depends on the number of different ways needed by the shelf connector.

Fig: 4 shows an arrangement of signal-bearing and grounded tracks which, when provided with switching between the tracks and one or both of the extender unit's connectors enables all required combinations to be provided with minimum crosstalk. In this arrangement tracks 25, 26, 27 and 28 are signal-bearing tracks and tracks 29, 30, 31, 32, 33 and 34 are grounded screening tracks. Of these tracks, tracks 25 and 26 relate to one signal port of the equipment and tracks 27 and 28 relate to another signal port. These arrangements are repeated as often as needed to provide the necessary connections across the extender unit.

In the case of balanced highways we have an arrangement such as shown in Fig. 5.

Here tracks 40 and 41 relate to a first balanced highway and tracks 42 and 43 relate to a second balanced highway. The other tracks are screening tracks: note that between adjacent signal tracks on one face of the board there are screening tracks. This track pattern is also repeated as often as is needed.

The track patterns indicated above repeat across the width of the board and in the preferred arrangement there is a set of manually-operable switches at each end of the extender units' printed circuit board.

Each such set of switches varies the pattern of connection between the printed tracks at its end of the board. Hence with the use of two such switches, and careful design of the track pattern one extender unit can be used in conjunction with a wide variety of slide-in units, perhaps with all such units of the equipment which have the same height and depth.

WHAT WE CLAIM IS: 1. An extender unit which includes a generally rectangular printed-circuit board unit with connectors at two of its parallel edges and with printed circuit tracks connected between the contacts of its said connectors, in which when in use for testing a slide-in unit of an electrical equipment the extender unit is plugged into the equipment in place of the unit to be tested and the latter unit is plugged into the extender, and in which to reduce crosstalk due to the conductor on the extender unit each of those conductors which carries signals when the extender unit is in use is paralleled by a grounding screening conductor.

2. An extender unit as claimed in claim 1, and in which for a signal-bearing conductor track on one face of the board there are three screening conductors, one aligned with the signal-bearing conductor but on the other face of the extender unit and the other two on the same face as the signal-bearing conductor, one on each side thereof.

3. An extender unit as claimed in claim 1 or 2, in which for a balanced pair of signal highways the two conductors thereof are aligned with each other but on opposite faces of the extender unit, and in which the screening conductors are four in number, two on each face of the extender unit with each signal-bearing conductor between two of the screening conductors.

4. An extender unit as claimed in claim 1, 2 or 3, and which includes switches at one or both ends of the extender unit for varying the pattern of connections between the conductors and the connectors of the extender unit.

5. An extender unit as claimed in claim 1, 2, 3 or 4 and in which the conductors are printed circuit tracks.

6. An extender unit substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of grounded screens for the signal bearing ones of the printed circuit tracks on the extender unit's printed circuit board. In Fig. 2, we see in cross section the printed circuit board 10 of an extender unit on which there is a printed track 11 which carries a signal when the unit is in use, adjacent to which are grounded tracks 12, 13 and 14. Hence the signal-carrying track is screened on three out of four sides, which substantially reduces the cross talk due to or involving the track 11. In many cases the signals are conveyed on balanced highways, and here we use the arrangement shown in Fig. 3, where 16 and 17 are printed tracks which form a pair of balanced highways, tracks 18, 19, 20 and 21 are the grounded tracks which provide the screening. It is desirable that a single extender unit should be provided with a number of different slide-in units of the same height and depth, so the allocation of signals to be printed wiring is made variable. This is achieved by providing manually settable switches on the printed board at one or both of its ends. The number of such switches provided depends on the number of different ways needed by the shelf connector. Fig: 4 shows an arrangement of signal-bearing and grounded tracks which, when provided with switching between the tracks and one or both of the extender unit's connectors enables all required combinations to be provided with minimum crosstalk. In this arrangement tracks 25, 26, 27 and 28 are signal-bearing tracks and tracks 29, 30, 31, 32, 33 and 34 are grounded screening tracks. Of these tracks, tracks 25 and 26 relate to one signal port of the equipment and tracks 27 and 28 relate to another signal port. These arrangements are repeated as often as needed to provide the necessary connections across the extender unit. In the case of balanced highways we have an arrangement such as shown in Fig. 5. Here tracks 40 and 41 relate to a first balanced highway and tracks 42 and 43 relate to a second balanced highway. The other tracks are screening tracks: note that between adjacent signal tracks on one face of the board there are screening tracks. This track pattern is also repeated as often as is needed. The track patterns indicated above repeat across the width of the board and in the preferred arrangement there is a set of manually-operable switches at each end of the extender units' printed circuit board. Each such set of switches varies the pattern of connection between the printed tracks at its end of the board. Hence with the use of two such switches, and careful design of the track pattern one extender unit can be used in conjunction with a wide variety of slide-in units, perhaps with all such units of the equipment which have the same height and depth. WHAT WE CLAIM IS:

1. An extender unit which includes a generally rectangular printed-circuit board unit with connectors at two of its parallel edges and with printed circuit tracks connected between the contacts of its said connectors, in which when in use for testing a slide-in unit of an electrical equipment the extender unit is plugged into the equipment in place of the unit to be tested and the latter unit is plugged into the extender, and in which to reduce crosstalk due to the conductor on the extender unit each of those conductors which carries signals when the extender unit is in use is paralleled by a grounding screening conductor.