Year: 1885

page_text: We SEBASTIAN ZIANI DE FERRANTI of St Benet Chambers Fenchurch Street
in the City of London Electrician and GEORGE LEONARD ADDENBROOKE of
9 Mecklenburgh Street in the County of Middlesex Electrical Engineer do hereby
declare the nature of this invention to be as follows:-
In telephone circuits at the present time it is common to use induced currents in
the receiver or line circuit obtained by coupling up a battery the transmitter and
the primary of an ordinary induction coil in a local circuit at each station and the
receiving instruments at each station on a wire coupled with one end of the
secondary coils whilst the other ends of the coils are placed to earth or coupled to
another return wire.
According to our invention in place of using an ordinary induction coil that is
an induction coil in which the primary and secondary coils are wound on to a
straight iron core as has heretofore been the case on telephone lines we use
converters or translators in which there is a closed magnetic circuit as for example
a Gramme ring wound with primary and secondary coils or in which a closer
approximation to a closed magnetic circuit is obtained than is the case with
induction coils having straight magnetic cores as at present in use.
Any induction coil in which by virtue of its being a nearer approximation to a
closed magnetic circuit than the ordinary straight form gives a sensibly higher
efficiency.
a return
It is usual also in telephonic systems to have main or trunk line wires to which
branch lines at either end passing to subscribers can be coupled using the earth as
In some cases these main or trunk wires have been duplicated and
connected at their ends to the ends of a secondary coil of induction coils the core
of which is of the usual straight form. Whilst one end of the primary coil of the
induction coil at each end has been coupled to the branch telephone wire and the
other end to earth.
When trunk lines worked with induced currents are so used we employ.
convertors or translators formed with closed magnetic circuits or approximately
closed circuits in place of induction coils of the usual straight form and in this
way we are enabled to obtain a far higher efficiency making the transmission of
speech through long lines easier than heretofore and transmitting currents with
comparatively so small a loss that it is possible with a battery or magneto in the

page_text: earthed circuit at one end of the line to ring a bell through both translators the
bell being placed in the earthed circuit at the other end of the line. This enables
us to obtain practically the efficiency of a double wire system without doubling the
branch subscribers lines.
For telegraphic purposes likewise we use convertors or translators of the kind
herein before mentioned to enable a battery of low electro motive force to generate
a secondary current of sufficiently high electro motive force to work the instru-
ments at the receiving end of the line.
In an office in which more than one instrument is used it is sufficient to place
the number of convertors required with their primaries in series or parallel in
circuit with one generating source the secondaries being wound in such a manner
as to give the required electro motive force for working each line. The transmitting
instruments would be placed on the primary circuit.
1
CARPMAEL & Co.,
Agents for the Applicants.
Improvements in Telephony and Telegraphy.
We, SEBASTIAN ZIANI DE FERRANTI of St Benet Chambers Fenchurch Street
in the City of London Electrician and GEORGE LEONARD ADDENBROOKE of
9 Mecklenburgh Street in the County of Middlesex Electrical Engineer do hereby
declare the nature of this invention and in what manner the same is to be
performed to be particularly described and ascertained in and by the following
statement:-
In telephone circuits it is usual to employ induction coils, the primary forming
part of a local circuit including a battery and a transmitter whilst the secondary
is in the line circuit which also includes the receiver.
According to our invention in place of using an ordinary induction coil that is
an induction coil in which the primary and secondary coils are wound on to a
straight iron core as has heretofore been the case on telephone lines we use con-
verters or translators in which there is a closed magnetic circuit as for example a
Gramme ring wound with primary and secondary coils-or in which a closer
approximation to a closed magnetic circuit is obtained than is the case with
induction coils having straight magnetic cores as at present in use.
Any induction coil in which by virtue of its being a nearer approximation to a
closed magnetic circuit than the ordinary straight form gives a sensibly higher
efficiency.
It is usual also in telephonic systems to have main or trunk line wires to which
branch lines at either end passing to subscribers can be coupled using the earth as

page_text: end a coupling piece in form like an armature is applied; or even some amount of
advantage is obtained if the armature piece be not employed. In ordinary
induction coils such as are now employed in telephony the core being straight the
lines of force to complete the magnetic circuit have to pass for a long distance through
air and this greatly interferes with the effective magnetization of the core and the
efficiency of the coil. Where the ends of the core are brought together and into
contact as represented in the drawing the magnetic circuit is complete through the
iron of the core. But where the ends of the core are not brought into contact
but only approximated to each other some advantage to the efficiency of the coil is
obtained and the advantage increases as the air space between the ends of the core
is lessened.
A suitable induction apparatus to be employed to couple subscribers lines on to
a main line wire we construct as follows:
Several thin sheets of soft iron are laid together with some insulating medium
such as paper between each and round the centre third of their length are wrapped
the primary and secondary circuits which for example may consist each of from
200 to 400 yards of No 36 copper insulated wire which will be found about the
most suitable lengths for ordinary purposes though for special purposes the absolute
and relative lengths may be largely departed from. The dimensions of the iron
sheets may be 6 inches by 2 inches. After the wire has been wound on, the iron
sheets are turned back upon the wire alternately. Thus each piece of iron makes
up a complete magnetic circuit within itself but is insulated from its neighbours.
An equal number of iron sheets are turned over on each side of the wire thus
making the coils symmetrical in every way. The whole may then be bound.
tightly with wire to compress and keep. together the coil.
The arrangement of the telephone circuit is as follows:-
Two induction coils or convertors are employed; one of the windings of each of
these is in a main circuit which usually (in order to avoid the effects of induction)
is completely metallic that is to say, has a return wire.
The other windings of the induction coils or convertors form parts of local
circuits at each end of the main line one end of the winding in each case being to
earth and the other end connected to suitable switching apparatus which may be
of the usual description for single line working. The subscribers lines and
apparatus may be of the ordinary character but preferably with magneto machine
and bell for signalling.
*
With such an arrangement by means of a magneto or small dynamo machine or
other form of alternate or intermittent or rapidly varying currents one exchange
can signal another or call up a subscriber connected to the local circuit at the
further end of the trunk line. The indicator or bell in the distant exchange or
subscribers circuit responds with complete efficiency although it is not in the same
circuit with the generator but in a distant circuit having no metallic or conductive
connection with it and although the main circuit is interposed and has no metallic
or conductive connection with either.
Just in the same way as a local line is coupled with a double main line one part
of a main line may be coupled with another, as in the case where it may be judged
unnecessary to double the whole of the main line but only a part is doubled where
from special causes interference by induction is likely to be experienced as for
example in the vicinity of an electric lighting installation.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that what
we claim is :—
1. Our improvements in telephony consisting in the use therein of an induction
apparatus of which the primary forms part of a local circuit including a battery
and a telephone transmitter; and the secondary forms part of a line circuit, such
primary and secondary coils being wound upon an iron core which is either formed
into a complete ring or rings or which has its ends approximated. so that the

page_text: magnetic circuit in the core is completed through. metal or more nearly so than
when a straight core is employed.
2. Our improvement in telephony consisting in the use therein of an induction
apparatus of which the primary forms part of a subscribers line or local circuit and
the secondary forms part of a main circuit; such primary and secondary coils being
wound upon an iron core which is either a complete ring or rings or which has its
ends approximated so that the magnetic circuit in the core is completed through
metal or move nearly so than when a straight core is employed.
3. The combination of a line circuit with at each end of the same, induction
apparatus having as stated above a magnetic circuit closed or partially closed
through metal; such induction apparatus serving to couple the line circuit
inductively with two other circuits one including an electric bell or mechanical
indicator and the other a magneto electric machine or other source of rapidly
alternating or varying currents; the whole forming a mechanism by which a bell
may be rung or indication given on one circuit by varying currents originated in
another and this through the intervention of a third circuit.
4. The arrangement and combination of telephonic mechanism substantially as
herein.described.