A Method of effecting Multiplex Telegraphic and Telephonic Communication and Apparatus for that Purpose.
Year: 1897

page_text: A Method of effecting Multiplex Telegraphic and Telephonic
Communication and Apparatus for that Purpose.
I, JOHN IMRAY, of No. 28, Southampton Buildings, Chancery Lane, in the
County of London, Consulting Engineer, and Chartered Patent Agent, do hereby
declare the nature of this invention (as communicated to me from abroad by_La
Société Anonyme pour la transmission de la force par l'Electricité, of 13, Rue
Lafayette, Paris, France), to be as follows:-
This invention relates to means of utilising two conducting lines, which connect
two main stations at a distanco apart, for transmitting telegraphic and telephonic
communications simultaneously from a number of branches or subscribers at the
one station to a corresponding number at the other station. For this purpose, at
the two main stations there are provided synchronously revolving commutators,
each having as many segments as there are branches or subscribers, a brush for
each contact being connected to each of the branches or subscribers. These com-
mutators being made to revolve with considerable velocity, the interruption of
each contact at each revolution does not practically interfere with the continuity
of the transmitted communication. The two lines thus constituite a completo
metallic circuit connecting each branch or subscriber at the one station, to a cor-
responding-branch or subscriber at the other station but not to any other than
the particular branch or subscriber for which the commutator contact is arranged:.
The revolution of the commutators may be effected by clockwork rendered
synchronous by being corrected at short intervals by special currents transmitted
along both lines together, operating as a single line with earth return. Or the
two commutators may be driven by synchronous electric motors. By introducing
in the two lines transformers having double oppositely wound primary coils induc-
ing currents in secondary coils connected to the commutators, the currents travers-
ing the two lines as one line for correcting the clock work or working the motors
are neutralised in the primary coils and therefore have no effect on the secondary
coils, whereas the currents transmitted along the one line and back by the other
render both primary coils effective on the secondary coils. The transformers
moreover, being thus arranged; provent interference of call currents or of earth
or accidental currents with the telegraphic or telephonio communications.
As the interruption of communication between any two subscribers during the
greater part of each revolution of the commutators, renders the telephone com-
munications weak, these may be reinforced either by reinforcing the currents sent
into line, or by providing each receiver with a relay. The currents sent into line'
can be reinforced by applying a continuous current dynamo having a double wound
armature to send opposite currents into the two lines.
A relay for a telephone receiver consists of a bundle of iron, bars surrounded
by the receiving coil, outside of which are two other bars connected at the base to
the middle bars and operating as poles on an iron plate which is very near but not

page_text: touching them. On this plate is a microphone forming part of a local circuit in
which the ordinary receiver is included..
Dated this 30th dow of June 1807
ABEL & IMRAY,
Agents for the Applicant.
A Method of effecting, Multiplex Telegraphic and Telephonic
Communication and Apparatus for that Purpose.
I, JOHN IMRAY, of Birkbeck Bank Chambers, Southampton Buildings, Chancery
Lane, in the County of London, Consulting Engineer and Chartered Patent Agent,
but formerly of No. 28, Southampton Buildings, in the County of London, do
hereby declare the nature of this invention (as communicated to me from abroad
by La Société Anonyme pour la transmission de la force par l'Electricité, of 13,
Rue Lafayette, Paris, France), and in what manner the same is to be performed,
to be particularly described and ascertained in and by the following statement:-
This invention relates to means of utilising two conducting lines which connect
two main stations at a distance apart for transmitting telegraphic and telephonic
communications simultaneously from a number of branches or subscribers at the
oue station to a corresponding number at the other station.
For this purpose arrangements and apparatus are employed as will be described
with reference to the accompanying drawings.
In Fig. 1 let X Y and X Y represent the two conducting lines connecting the
distant main stations and A from each of which double lines lead to a number
of subscribers a, b &c. n at the one station and a' b &c. at the other, the inten-
tion being that a may communicate with a, b with b¹ &c. In order to render
explanation more clear let it be assumed that there are 6 subscribers at each end.
In that case there is provided at each station a commutator as shewn in Fig. 2
having 6 segments, a rubber m at A connected to X of the line X Y and a rubber at A¹
connected to Y. Each of the subscribers a, b &c. at A is connected' to X' of the
line X Y, and each of those at A' is connected to Y: The second conductor of
each subscriber can when desired be connected to the corresponding segment of
the commutator a to 1, b to 2 &c. at the one station and a¹ to 1, b¹ to 2¹ &c. at the
other. If the rubbers m m¹ move synchronously over the segments, that is to say
when m is on 1, 2 &c. m¹ is on 11, 2 &c., then obviously a can communicate with
a', b with 6' &o. while the rubbers are on the corresponding segments, but while
any one pair of the subscribers are thus communicating, none of the others are in
communication. The contacts being intermittent when m and m² move over the
segments it might be thought that no distinct telephonic conversation could be
carried on, but experiment has shewn the following results:-
1) Conversation can be well carried on if the contacts succeed each other at
intervals less than 1th of a second.
2) The passage of the rubbers over the segments does not produce any interfer-
ing noises.
3) The loudness is not greatly diminished as the number of simultaneous com-.
munications increase, at least 5 simultaneous conversations can be carried on with
the usual instruments.
Thus the principle of multiple telephony by which existing instruments and
lines can be utilised, has been experimentally established.
Commutators operating as indicated diagrammatically in Fig. 2 have been

page_text: devised to fulfil the required conditions, and means of synchronising them have
been worked out.
As to the commutators, obviously continuous revolution must be better than
reciprocation, and therefore revolving commutators are employed as shewn in
Figs. 3 and 4. On an axis running in bearings P P are fixed 6 insulated
rings 1, 2, 3 &c. and a collector C divided equally into 6 segments with cach of
which one of the rings 1, 2, 3 &c. is connected. On each ring bears a rubber g¹gª
&c. fixed on an insulating base p. Each rubber is connected to a subscribers
contact. On the collector C bears a single rubber which is always in connection
with the end of the line X Y. Obviously, on turning the axis u each of tho
rubbers g g is successively connected to the line X Y, and thus the result set
forth in reference to Fig. 2 is attained. In order to give the required rotation,
the axis has fixed on it the armature K of a continuous current electric motor
having commutator h and brushes G, this being worked by a local source of
electricity at the station. On the axis are fixed two other rings B B having
rubbers which are connected to two opposite segments on the commutator h
so as to obtain alternating currents for effecting synchronism as will be hereafter
described.
Instead of making the number of segments on the commutator correspond with
the number of communications to be made simultaneously, it is generally pre-
ferred to multiply the number by a factor 2 using a construction such as is shewn
in Fig. 5.
If n be the number of simultaneous communications the commutator C has
n groups each of 9 segments each group connected to its ring as before described;
but on the commutator C bear 9 brushes F spaced equally apart, and all con-
nected in parallel to the end of the line.
This arrangement has the advantage of reducing the necessary speed of
revolution.
The mode of synchronising the commutators at the two ends of the line
illustrated as follows:
may be
Let it be assumed that there is a special line for transmitting the synchronising
currents, and let the motor K be considered as also a generator of alternating
ourrents, and let these alternating currents traverse the special line as indicated
in Fig. 6, then a condenser of capacity such that the coefficient of apparent self
induction in the circuit, being introduced, the generator of the alternating currents
will, as is well known, tend to become synchronised. By operating thus no
current of working force has to be transmitted but only a much smaller synchronis
ing current. In order to prevent the pendulous movements which always tend to
become superposed on the motion of synchronously coupled dynamos, the
armature Fig. 4, has arranged all round it a magnetic screen consisting of
copper bolts parallel to the axis and rivetted to a copper disc at each end.
For transmitting the synchronising currents without a special line let there be
as shewn in Fig. 7 a line consisting of two conductors kl and rs connected to
each other at both ends. If these were connected to earth, currents might be
passed either in opposite directions through the two working telephones and tele-
graphs or in the same direction through both lines returning by earth, these
latter being synchronising currents. The generators of the alternating currents
of the motors K K, furnished with condensers are connected to the ends of both
kandrs and to earth t. But in order that these currents any more than
accidental earth currents may not act on the telephonic instruments, the following
arrangement is employed. At both stations A A¹ there are transformers T Ti
each having two primary circuits consisting of two wires wound together, the one
introduced in the line the other in the line rs but in such wise that when two
equal currents traverse these lines in the same direction they have no effect on the
transformer, but when currents traverse k lands in opposite directions they both
act on the transformer. If now a secondary circuit S is wound on the same bobbin
in each case, it will be affected by the telephonic currents but not by the synchronis-

page_text: ing currents, or by earth currents; and reciprocally a current in S will induce a
current closing on itself in the lines and rs but without creating any difference
of potential at their ends.
The conductors X Y and X' Y¹ of Fig. 2 are connected to the secondary S.
This arrangement has the advantage that synchronising currents of high tension
can be used without affecting the subscriber's instrument. Such high tension
currents could be obtained by means of a transformer connected to each motor or
by a separate high tension motor.
Although the synchronous movement of the rubbers m and n may be obtained
as described by currents traversing both telephonic lines, this may be otherwise
effected, as for instance by clockwork synchronised by currents transmitted at
intervals, which may be longer the more perfect the clocks.
In order to reinforce the sounds of the telephones, which are somewhat lessened
in volume by the discontinuity of the currents, and which therefore when more
that 5 communications go on simultaneously, become feeble, two methods may be
employed, either (1) reinforcing all the currents traversing the line between the
main stations, or (2) by providing each telephone with a telephonic relay as in
multiple telegraphy each receiver is provided with a telegraphic relay.
For carrying out the method (1) as shewn in Fig. 8 the line kl, r s connecting
A and A¹ has introduced into it a continuous current machine, its armature M
having two equal windings each connected to a collector with brushes ¹³
connected to the lines as shewn sending currents in opposite directions which close
themselves in these lines without tending to pass to earth to which the lines are
always connected.
The rotation of M can thus act on the telephonic currents but not on the synchron-
ising or earth currents. The magnets of the machine having two windings produc-
ing two inducing circuits V1 V the one introduced into the ether in r s.
The connections are so made that the magnetising forces developed by the telephonic
currents become added together, while those developed by the synchronising cur-
rents neutralise each other. In order to increase sensibly the general self induc-
tion of the system by the introduction of the machine, there should be little wire
on its magnets but much on its armature, its reaction being induced by known
means.
For carrying out method (2) a telephone relay is arranged as shewn in Fig. 9.
EE is a bundle of magnetised bars surrounded by a coil y y which is traversed
by the telephone currents.
External masses of iron z z allow the magnetic circle to close itself through
the narrow air gap between the magnet and a plate ppl which carries a
microphone D D introduced in the circuit of a local battery Q and the receiver R.
The intensities of the currents developed in the receiver circuit are obviously much
greated than those of the currents traversing the coil y y since they derive energy
from the battery Q.
Then the sounds heard at R are much louder than those of a recoivor without
relay would be.
The subscribers can call in the usual way to the official at the central station
who can also call the official at the connected station in the following manner.
The double line connected to earth which transmits the synchronising currents
is utilised for this purpose.
As there is usually a great distance between the stations it is of advantage to
employ induction apparatus, such as those of the Abdank Abakanowitz kind shewn
in Fig. 10. Bobbins N N suspended by vibrating blades vv can vibrate in the
fields of permanent magnets ee. The alternating currents thus produced which
can work bells L L have a certain frequency can be transmitted by the same lines
as the synchronising currents, and are capable of being separated from them at
the ends of the line, for which purpose their frequency is made very different from
that of the synchronising currents. At the two ends of the line two shunt circuits
between the line and earth are arranged, the one comprising the motor M of the

page_text: commutator and the condenser for annulling the self induction of the armature
by currents having the frequency of the synchronising currents. The other
circuit comprises the call appliances, the bell L and an electric resonnator consisting
of a self induction coil J and a condenser jl of capacity such that the coefficient
of apparent self induction of this circuit is sensibly nil for currents of the
frequency of those produced by the vibrating blades.
Obviously in the arrangements described telegraphic instruments can be sub-
stituted for the telephonic instruments, but for telegraphic purposes there is usually
only one line with earth return. The synchronising currents should therefore
have much greater frequency than that of the signalling currents. The two
motors may then be connected between earth and the line having added to them
electric resonators consisting of self induction coils, and condensers suited to the
frequency of the synchronising currents which are stopped by the self induction
of the telegraphic apparatus, but readily traverso the resonators which on the
other hand prevent passage of the signalling currents.
The double line may obviously be employed as above described (1) for trans-
mitting simultaneous telephonic communications by currents closing on themselves
in the two conductors and (2) for transmitting simultaneous telegraphic com-
munications by currents traversing the two conductors in the same direction to
earth. For this it is only necessary to work by the motor in each main station
two separate commutators, the one for telephonic, the other for telegraphic com-
munications.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed I declare that what I
claim is:-
1. For multiple telephonic communication a line consisting of two conductors
connecting two main stations and torminating at these in synchronously moving
commutators arranged to put successively in communication a number of sub-
scribers at the one station respectively with corresponding subscribers at the other,
the commutators revolving so rapidly that the intervals between the contacts for
each subscriber are so short that there is no perceptible discontinuity and the
synchronising of the commutators being determined by electric motors or clock
work electrically synchronised at intervals by currents transmitted by both
conductors.
2. The modification of the arrangements above set forth for the purpose of
multiple telegraphic communications by applying electric resonators in connection
with a single line.
3. The combination of the arrangements above set forth for effecting multiple
telephonic communications by the two lines one of them acting as return, and also
multiple telegraphic communications by both lines with earth return, with pro-
visions substantially as described for synchronising the commutators and for
separating the telephonic from the telegraphic and synchronising currents.
4. A telephonic relay for reinforcing the sounds at the receiver, substantially
as described.
1
L 1000