Inductor devices – Core surrounding linear conductor
Patent
1992-11-19
1995-12-05
Wong, Peter S.
Inductor devices
Core surrounding linear conductor
H01F 1706
Patent
active
054733006
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a coupling transformer for a multi-core electrical conductor such as a twin core cable.
According to the present invention there is provided a coupling transformer for a pair of spaced electrical conductors bearing substantially equal and opposite currents, comprising a relatively high permeability member disposed in electromagnetic relationship with the conductors; the member, in use, defining a pair of flux paths and sharing a further portion, extending between the conductors, of relatively lower permeability; and a pair of electrically connected secondary elements each also disposed in electromagnetic relationship with a portion of the flux path defined by the high permeability member.
The transformer can be used to pick up or induce energy on a two or more core cable, such as a telephone cable, without making electrical contact with the cable provided the core conductors are spaced to permit the passage of flux between them. Thus, the invention provides a very simple tap into a multi-core cable without having to break the insulation or otherwise disturb the line.
When the transformer is used to pick up energy, e.g. signals, from the electrical conductors the secondary elements are arranged to provide antiphase outputs related to the current in the conductors. Conveniently, the secondary elements are connected together to provide an addition of the outputs. Commonly, the secondary elements are simply connected together so that the antiphase outputs are additively combined.
The device has many applications, for example, it could be used as a coupling for a plurality of burglar or fire alarm sensors to a common cable. Each sensor could be added to the common cable without having to break into it. Thus, sensors could be added or taken away as circumstances require.
A particularly useful application of this invention is as an extension tap on a telephone line or any signals around the audio frequency range up to high frequency and even radio frequency. The electromagnetic relationship between the flux path and the secondary elements can be according to conventional transformer coupling or by the Hall effect or a combination of both.
A particularly advantageous aspect of the invention is the fact that the arrangement of the two core cable effectively cancels noise picked up in the cable itself. The reason for this is that the opposed currents in the two cable cores induce a flux in the flux paths which result in a voltage induced in the secondary member, whereas noise picked up in both cores is substantially cancelled out.
The electromagnetic relationship between the flux path and the secondary elements is arranged to be by means of electromagnetic coupling, magnetoresistive coupling (the Early effect), the Hall effect or the like as will be apparent to the skilled person.
The cable coupling transformer according to the present invention can take many different forms while adhering to this general principle.
In one form of the invention the high permeability member may be an enclosure in the form of a frame or tunnel or an open channel having opposed limbs about which the electrical elements are wound in opposite senses. Ends of the windings may be connected such that an induced potential difference between the free ends is the addition of the voltages induced in both windings. In this, or any other embodiment, the windings may be equal, but this is not a strict requirement. For balance, the added outputs of the elements may be amplified appropriately if the outputs are initially unbalanced. Of course, the transformer works equally well in the opposite mode in which an electrical current in the windings induces a flux in each flux path and thence equal and opposite voltages in the cores of the cable. This is true of the invention as it is as a principle of transformers in general.
The enclosure or channel may be straight sided, i.e. rectangular in section, in which case the windings embrace opposed limbs. A tunnel arrangement of high permeability member is preferred to a simple fram
REFERENCES:
patent: 4021729 (1977-05-01), Hudson, Jr.
patent: 4833337 (1989-05-01), Kelley et al.
patent: 5220297 (1993-06-01), Crowhurst
patent: 5233318 (1993-08-01), Sasaki et al.
Berhang Adolf
Wong Peter S.
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