Electricity: conductors and insulators – Anti-inductive structures – Conductor transposition
Reexamination Certificate
1998-10-01
2001-02-13
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Anti-inductive structures
Conductor transposition
C174S034000, C174S034000, C361S827000
Reexamination Certificate
active
06188016
ABSTRACT:
FIELD OF INVENTION
The present invention relates to an arrangement for mutually coupling electrically two pieces of electronic equipment, each having good EMC properties and retaining said properties.
DESCRIPTION OF THE BACKGROUND ART
It is known to enclose sensitive electronic equipment in an electrically conductive cage, a Faraday cage, to obtain good electromagnetic compatibility (EMC) with respect to said equipment, e.g. protection against electrostatic discharges (ESD).
In those situations when duplicate systems are used, two such pieces of equipment, will normally stand side-by-side so that the first piece of equipment is able to take over the functions of the second piece of equipment should this second piece of equipment malfunction or require inspection. It is, of course, possible to enclose both pieces of equipment in one and the same cage, thereby protecting both pieces of equipment. However, problems arise when the first piece of equipment needs to be repaired or serviced. In order to obtain access to this equipment, it is necessary to open the cage, which will impair the EMC properties with respect to the second piece of equipment, therewith risking disablement of the second piece of equipment and therewith a total breakdown. It is therefore necessary to enclose each piece of equipment in its respective cage.
In order for equipment that has good EMC properties in general to communicate with other equipment via cables for instance, it is necessary to provide holes in the cage that encloses the equipment and that constitutes the actual basis for said good EMC properties. Such holes enable radiation to leak into and out of the cage, resulting in poorer EMC properties.
When two cages stand side-by-side, electrical discharges, ESD, from one piece of equipment in the first cage are able to pass out through the hole therein and wander through the air or along electric conductors and in through the hole in the second cage and there disable the equipment enclosed by this second cage. This is, of course, highly unfortunate and presents a specific problem to the application of duplicated systems.
There are many different causes of electrostatic discharges, ESD. For instance, the equipment may be subjected to such discharge by a person coming into contact with the equipment or solely being present in the proximity thereof. In order to prevent such an occurrence, there are often provided special grounding or earthing points at which a person is able to connect up an electrically conductive arm band and therewith obtain the same ground, or earth, as the equipment, thereby preventing an ESD. Unfortunately, an ESD will sometimes occur before the person concerned has been able to ground his body at a grounding point, which may have catastrophic consequences in the case of sensitive equipment. A second person can cause an ESD, even though the first person is grounded or earthed. If the first person has had time to open the cage, the EMC properties of the equipment enclosed therein will be greatly impaired, and even if the actual discharge does not cause problems, the electromagnetic radiation caused by the discharge may play havoc and create problems with respect to nearby equipment, by passing through holes that carry electric cables.
Computers that are used for switching purposes in telephony are often duplicated, so that if the first computer is disabled, the other computer will take over. When repairing the first computer, it is extremely important that no electrostatic discharges caused by a careless technician will also disable the other computer, which would result in a total breakdown in operations. The problem is particularly serious in respect of new types of IC circuits that are extremely sensitive to static discharges.
SUMMARY OF THE INVENTION
The invention solves the aforesaid problem of enabling part of a duplicated system to be serviced without impairing EMC properties, e.g. without impairing ESD protection, of the other part of the system, by minimising the open hole area and sealingly enclosing the shield of the connection cables with a grounded electric conductor, and electrically connecting said conductor to the cages.
More specifically, the solution is achieved with the aid of a tube-like element which connects the two cages. The inner diameter of the tube-like element is adapted to the diameter of the cables received in the hole so as to obtain a sealed joint. The holes provided in the sides of the cages are sufficiently large to accommodate an electric contact element of reasonable size, meaning that the holes may be substantially larger than the thickness of the cables received therein. These holes are covered with an electrically conductive member, for instance a steel plate, such as to adapt the hole opening to the diameter of the cables.
The object of the invention is to prevent an electrostatic discharge occurring in one cage or the equipment encased thereby from wandering through the air or through electric conductors to the other cage or the equipment encased thereby, so that the EMC properties of one part of a duplicated system will be retained even when the protection in the other part is partially non-existent, so as to be able to pass cables effectively from one piece of equipment to another while retaining EMC properties, e.g. ESD protection, and to be able to carry out repairs and servicing on one side of a duplicated system without impairing the EMC properties of the other side.
The advantages thus afforded are good EMC properties between the two parts of a duplicated system, minimisation of the risk of disabling both sides of duplicated equipment as a result of an electrostatic discharge. Other advantages are that the solution is simple and inexpensive, that the solution enables cables having large electric contact devices in relation to cable thickness to be passed from one piece of equipment to other pieces of equipment, that ESD spikes will not wander from one piece of equipment to the other, and that the one cage will still provide good EMC properties and be protected against radiation caused by ESD, for instance, even when the other cage is open and has lost its ESD protection.
REFERENCES:
patent: 4547623 (1985-10-01), Van Brunt et al.
patent: 5081326 (1992-01-01), Usui
patent: 5091604 (1992-02-01), Kirma
patent: 5329066 (1994-07-01), Hansson
patent: 5717576 (1998-02-01), Van Doeselaar et al.
patent: 0 219 639 (1987-04-01), None
patent: 94/20968 (1994-09-01), None
Enström Kent
Essland Hans-Olov
Kassman Björn
Svensson Anders
Torhage Erik
Burns Doane Swecker & Mathis L.L.P.
Kincaid Kristine
Telefonaktiebolaget LM Ericcsson (publ)
Walkenhorst W. David
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