Improvements in Multiple-switches for Use with Double Telephonic Leads.
Year: 1895

page_text: Date of Application, 25th Mar., 1895-Accepted, 27th Apr., 1895
COMPLETE SPECIFICATION.
Improvements in Multiple-switches for Use with Double
Telephonic Leads.
1, FRANZ STOCK, of 29 Waldemarstrasse, Berlin, Germany, 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 the multiple switches heretofore usually employed with the two wires
constituting the going and return conductors and herein called the double telephone
leads, the switching of the keys into branch circuits is effected only at a
considerable expense for conductors because for each lead three conductors are
necessary for connecting the several keys. Also, the keys themselves are by the
addition of the controlling devices rendered more complicated than in the systems
of switching employed for single leads. As a result not only is the cost of
installation greater, but the switch-boards are not capable of accommodating the
desirable, and in the case of large installations, the necessary number of keys.
Now this invention has for its object to provide a multiple switch arrangement
for double telephone leads in which the above mentioned drawbacks are obviated
in a simple manner but so nevertheless that the keys with two springs usually
employed in single telephone leads can be also employed with the double leads
with the result that the space available for the several switch-boards will be
capable of receiving a large number say 10000 keys, whilst in the case of existing
installations, the change from the single lead system to the double lead system,
which is more and more felt to be an urgent necessity, can be made with ease and
at not too great a cost.
This result is effected in the manner and by the means I will now proceed to
explain by the aid of Figs. 1 and 2 of the accompanying drawings, which are
diagrams illustrating a multiple switching arrangement according to this invention.
The two leads a b (Fig. 1) belonging to a telephone loop, pass directly to the
electro-magnetic device which controls the calling drop or shutter, and which is of
peculiar construction. It comprises an electro-magnet m of high self-induction and
high resistance, and a pair of electro-magnets no of very low resistance.
By this
arrangement if the electro-magnet m be alone traversed by an electric current, it
will attract the armature g pivoted at a and cause the annunciator drop shutter k
previously held by the armature lever p, to fall, but if the electro-magnets n and o be
energized simultaneously with m, the shutter k will not be affected. Fig. 1 shows
the connections between the leads ab the said electro-magnet device, the springs
of the keys, and the casings of the keys, in the position of rest. When the several
parts are in the position shown, a call current sent from a subscriber's instrument
will pass through the lead a and electro-magnet m, and back through 6 to the
subscriber's instrument. By this means the armature will be attracted, and the
shutter k caused to fall. At this time the branch from the loop through the electro-
imagnet n over the springs of the keys, to the controlling battery C B and thence
to earth, remains inoperative obviously without effect.
By inserting a plug S¹ into the calling key A K (Fig. 2) the telephone T will
be brought in circuit with the telephone loop L¹. Telephonic currents can now
flow through the lead a, the casing e of the calling key A K, one lead of the plug
cord, the battery key B T', the switch U, and the point y to the telephone T and
thence through the secondary winding of the microphone coil J, the switch U and
battery key B T', the other lead of the plug cord, the head of the plug S', and a

page_text: spring to the return lead b. The electro-magnet coil m is situated meanwhile in
a bridge or shunt across the leads a b. An interrupting key inay be inserted
between the point y and the earth, for the purpose of preventing any disturbances
due to the earth connection during the calling up.
To ascertain if a second telephone loop L2 is available for use, a plug S' is
placed against the key casing e' corresponding to such loop and then, if the loop
is free at the exchange, and the plug S2 shown inserted in Fig. 2, be assumed to
be partly removed so as to release the spring f shown depressed, a current will pass
from the controlling battery C B₁ through the keys K' K₁ etc., the electro-
magnet n², the electro-magnet m¹ electro-magnet o' into the lead connecting the
key casings c', and thence through the head of the plug S2, battery key B T2,
switch U and coil J, telephone T, and point y to earth. Consequently the
crackling noise then produced in the telephone will serve to indicate that the
desired loop at the exchange is unoccupied. But if on the contrary, it were
occupied, whether by a calling key or other key, no crackling would be heard in
the telephone, because the connection of the key casings with the controlling
battery C B would be interrupted by the moving away of one of the key
springs f, or by the separation of the contacts and from each other. If an
interruption of contact were to occur in this case within the keys, the exchange-
operator will not make the connection, because he would think that the loop was
engaged but if on repeated trials, the loop does not appear to be disengaged, then
this would give rise to the supposition that there must be an interruption in
the keys.
If now the connection of the loop L2 with the loop L¹ be made, and the switch U
be turned or operated, telephonic currents will pass from the subscriber's instrument
through a and through the casing e of the calling switch board key A K, through
the plug S', through B T, B T2, S2, the key casing c¹, through electro-magnet o¹
and leads a to the subscriber called up, and back through ₁, n', 1', ', and f³, to
the head of the plug S2, and thence through the battery keys B T2, B T', the head
of plug S1, spring hand return lead back to the calling up instrument.
The electro-magnets m and m¹ constitute bridges in the loop circuit, and do not
interfere with the telephonic communication.
The arrangement chosen for connecting up or switching the windings of the
electro-magnets n' and o' has for object to equalise the electrical resistance and
self-induction of the two leads of the loop circuit in order to prevent interference
by simultaneous speaking. As will be seen the calling switch board key A K is so
arranged that in making a connection, the electro-magnets no are not included in
the circuit, whilst the electro-magnet m forms a shunt between the two leads a and b.
Therefore on giving an indication that the telephonic conversation has been finished,
the annunciator shutter of the calling up subscriber will fall, but the shutter of the
subscriber called up will not be able to fall, because the electro-magnets m' and n'
and o¹ are being each traversed by a current, and this current will in each case have
a stronger action upon the armature lever p¹ than upon the armature lever g¹.
The connecting-up of the calling battery W B through the battery keys B T¹
and B T2, and also of the microphone M and of the microphone battery M B is
effected in the usual manner.
When the improved telephonic system hereinbefore described is to be employed
also for single leads with earth return, the branches or leads b b¹ etc. are connected
to earth. In such case in order to enable a certain control to be obtained, even on
the occurrence of strong earth currents, automatic current interrupting devices may
be provided between the controlling battery CV and the earth.
In addition to the advantages herein before mentioned, which result from the use
of the system herein described, it may be here mentioned that in consequence of the
ordinary flap indicating that the conversation has been finished being dispensed
with, the construction of the multiple switch is considerably simplified, whilst
greater certainty in calling up is ensured by the fact that the keys k k, k¹ k¹ etc. are
not situated in the ringing up circuit.

page_text: Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed I declare that what I
claim is :-
1. In a multiple switch for double telephone leads in which the ringing up
current returns through the electro-magnetic device of the calling up shutter direct
to the subscriber's instrument, the arrangement of the switch connections in such
a manner that in making a connection by plugging the calling switch board key A K,
the said electro-magnetic device will be included in a branch circuit or shunt and
thus render unnecessary the arrangement of the flap for indicating that the
conversation has been finished.
2. In a multiple switch for double telephone leads in which the ringing up current
returns through the electro-magnetic device of the calling up shutter direct to the
subscriber's instrument, the arrangement of the switch connections in such a manner
that after plugging the keys K K etc., the said electro-magnetic device will be
secured from the action of the ringing up currents by means of electro-magnets n
and connected with the respective telephone leads substantially as herein
described.
3. A switch arrangement of the kind specified in the preceding claims in which
the key lead forming a branch from the corresponding main lead, is carried past the
keys K K through a controlling battery C B to earth, and is thus employed as a
controlling lead, substantially as herein described.
4. In a multiple switch for double leads, constructed as specified in the preceding
claims, the calling switch board key A K, consisting of a fixed spring I and two
key-springs h and i which are connected to but electrically insulated from each
other, and are adapted to be lifted away from the spring substantially as
described.
5. In a multiple switch for double leads, constructed according to the preceding
claims, an electro-magnetic device for the calling up shutter, comprising the
electro-magnet m having great resistance and high self-induction and arranged to
act upon an armature g pivoted at a, and the electro-magnets no having small
resistance and arranged to act upon an armature lever p, fixed to the said armature I,
the electro-magnet n being arranged in a branch from the main lead 6 through the
calling switchboard key A K to the keys K K, and the electro-magneto being
arranged in a branch from the main lead a to the key casings c c, substantially as
herein described.
6. A multiple switch for double telephone leads constructed arranged and
operating substantially as described and shown for the purpose specified.
For the Applicant,
W. LLOYD WISE,
46, Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.