Improvements in Telephone Exchange Apparatus.
Year: 1890

page_text: Date of Application, 9th Dec., 1890-Accepted, 7th Feb., 1891
COMPLETE SPECIFICATION.
Improvements in Telephone Exchange Apparatus.
I, JOHN EDWARD KINGSBURY, of 79 Coleman Street, in the City of London,
Manager, (a communication to ine from abroad by the Western Electric Company,
of Chicago, Illinois, United States of America,) 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:-
This invention relates to telephone exchange systems in which metallic circuits
are employed and its object is to provide for uniting any two circuits together
without including in the united circuit thus formed any electro-magnetic device or
devices other than the telephones of the subscribers who are thus connected together.
while at the same time means are provided for signalling between the central office
and the different subscribers for the connections and disconnections as occasion may
require.
a
The telephone lines each consist of two limbs or branches, one limb of each telephone
line being normally grounded at the subscriber's station and open at the central
office, the other limb being normally open at the subscriber's station and grounded
at the central office through an annunciator and battery, a different annunciator
being provided for each telephone line and the battery being preferably common to
large number of lines. Each limb of the circuit is provided with a different
terminal upon the switch board, or in case of multiple switch boards upon each of
the switch boards at the central office and double stranded cords provided with
terminal plugs are employed for uniting any two of said telephone lines together,
the plugs being each provided with two terminals adapted to close upon different
terminals of the telephone lines respectively. The strands of said cords are recipro-
cally connected from the terminal of one plug to the opposite terminal of the other
plug of the pair.
The arrangements are such that when two subscribers are connected the two
telephone lines are united in metallic circuit and are also provided with a branch
connection through a different self induction coil on opposite sides of said metallic
circuit. A condenser is provided in one of the strands of the connecting cords.
Also a condenser in the operator's telephone circuit and also a high resistance
ground test circuit including one coil of an induction coil, the other coil of the
induction coil including the operator's telephone as hereinafter described.
When only one switch board is required the condensers and test currents are
dispensed with.
In the accompanying drawings which are illustrative of the invention :-
Figure 1 is a view illustrative of three telephone lines extending from the
subscriber's stations thereon to the central office, each telephone line consisting of
two branches one branch of each being connected with a different portion or terminal
of a socket on each of the three different switch boards and the other limb being
connected through the other side or portion of each of said sockets and extending
thence through an individual annunciator to a common ground line, including a
battery together with the operator's apparatus at two of the switch boards.
Figure 2 is a detailed view of a pair of loop plugs having their opposite terminals
reciprocally connected together.
Figure 3 is a detailed longitudinal section of the preferable form of socket.
Figure 4 is a detailed view of a modified form of loop plug.
Figure 5 is an end elevation of the loop plug shown in Figure 4.
Figure 6 it a detailed sectional view of a modification of the line terminals, the
socket being divided horizontally and adapted to receive a plug of the form illustrated
in Figures 4 and 5.
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page_text: board it represents three subscribers' stations each connected with the switch
board at the central office with a pair of loop plugs and their cords and the
operator's telephone and calling apparatus upon the switch board, the metallic
circuits of two of said stations being looped together by means of plugs and cords.
Figure 8 is an illustrative diagram of the circuits of four subscribers' stations,
each connected through its individual annunciator at the central office and through a
common ground wire containing a battery, two of said stations being shown looped
together.
Referring to Figure 1 subscriber's station 1 is connected with the switch
boards 1, 2 and 3 at the central office by a metallic circuit a consisting of two
branches a¹ and a²; the normal circuit of branch a' may be traced from ground at
subscriber's station 1 through the bell at said station and thence to the central
office; the normal circuit of the branch a² may be traced from the normally open
grounding key a³ at station 1 to the central office. At the central office each branch
is provided on each of the switch boards with a different terminal, the corresponding
terminals of the two branches on each board being preferably different insulated
parts of the same socket. Thus the sockets bed of the line a on each of the boards
consist each of two parts, that is to say, socket consists of the insulated parts;
socket e consists of the insulated parts ce², while socket d consists of the insulated
parts d²; branch a' is connected with the portions c¹ d', while branch a² is
connected with the portions 22 d. The branch a' is normally open at the central
office, while the other branch a² extends through an individual annunciator e con-
stricted to act also as a self induction coil and thence to wire to ground, a battery g
being included in the ground wire f
Subscriber's station 2 is connected in the same manner with the switch boards 1,
2, 3 by the line ; branch of said line being normally grounded at station 2 and
normally open at the central office while branch is normally open at station 2
and normally grounded through an individual annunciator i connected with the
ground wire through battery u.
Station 3 it will be understood is provided with subscribers' apparatus similar to
the apparatus shown at stations 1 and 2, and is connected in the same manner by
wire with the central office apparatus, branch k¹ being normally open and branch k
being connected through individual annunciator and thence to the wire f which
includes the common battery g as shown.
As shown in Figure 2, m is the answering loop plug consisting of two insulated
parts or terminals m² m²; the other plug n which may be termed the connecting
plug is provided with two insulated parts or terminals n' n².
It will be observed that the strand o connects terminal m' of plug m with
terminal n² of plug n while strand o' connects terminal of plug n with terminal n²
of plug m; that is to say, the opposite terminals of the pair of plugs are reciprocally
connected together.
-
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In the strand o¹ is placed a condenser and the usual calling key pl, the condenser
being nearest to the plug n. The connections 2p from the different strands o o'
respectively, extend to the operator's telephone contact points, the condenser p
being placed in the circuit with the telephone.
The several parts of the operator's apparatus illustrated in Figure 2 are marked
with corresponding letters of reference at board 3 of Figure 1. The test plug q
shown at board 3 Figure 1 is connected through one coil of a converter and
thence through resistance q² to ground, the other coil of the converter being included
in circuit with the operator's telephone. Similar operator's apparatus may be
provided at each of the boards as shown at board 1 Figure 1.
I will now describe the operation of the apparatus. We will suppose subscriber
at station 2 desires a connection with the subscriber at station 13 subscriber at
station 2, by pressing on his key y³ at station 2, closes the branch ² to ground, and
thus current from battery g is sent through annunciator i. The operator at
board 3 seeing shutter of annunciator i fall inserts her answering plug m as shown
in the switch or socket of line upon board 3 and the subscriber takes down his

page_text: 9
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telephone. The ground connection of branch ' at station 2 is thus taken off and
the telephone looped into the line in metallic circuit. As soon as the telephone
is thus taken down the circuit of battery is connected over branch through
station 2 to branch and hence to the terminals of the different sockets with which
said branch A is connected. The test consists in determining the presence or
absence of battery at any of the said terminals in the manner hereinafter explained
or otherwise. The operator at the same time throws down the cam lever g of her
listening in key, thus looping her telephone into the circuit. The operator is thus
brought into connection with subscriber of station 2 and receives the order; she
next proceeds to test the line called for; this test is made by touching the point of
the test plug g to the outer portion d' of the socket or contact d; that is to say,
the portion of the socket or contact connected with the branch a' of the telephone
line whatever may be the particular form of the sockets or contacts or the position
of the different terminals thereof. If the telephone at station 1 is on the telephone
switch and the line is not connected with any other line, no current from battery
will be found present when the tip of test plug 7 is applied to the terminal d'; if,
however, the telephone is removed from the telephone switch or if the line has been
called for and connected by a connecting plug with any other line upon either of
the boards, current from battery will be sent through the test plug 7 and the
induction coil and the telephone of the operator being included in the circuit of
the other coil of the induction coil g; the operator listening and hearing the sound
caused by the induced currents will know that the line is in use. If the line thus
tested has been connected with another line by means of the connecting plug n
battery will be present at the test pieces b, c, etc. without regard to the position
of the subscriber's telephone; thus as shewn at board 1 test plug is shewn
applied to the test piece of switch of line a and the telephone at station 1 of
line a is on the hook. The line will, however, test busy since the battery g will be
found connected with said terminal or test piece b'. The circuit may be traced as
follows: From battery g by wire and branch to the terminal m² of answering
plug and thence by strand o' to the terminal' of plug n which terminal n' is in
contact with the test piece d¹ of plug d and thence over the branch a¹ to test
piece of switch b. The resistance included in circuit with the test plug should
be such that the current from battery g thus closed through the test plug will not
be sufficient to throw down the shutter when the test plug is thus made.
The object of the condenser p is to prevent the annunciator of the called sub-
scriber from being thrown down when the subscribers are through talking and hang
up their telephones; the condenser p has the same function in case the operator
should be listening in at the time the calling subscriber hangs up his telephone.
When the subscriber called hangs up his telephone the calling subscriber's
individual annunciator is thrown down thus notifying the operator to disconnect.
Thus suppose subscriber at station 1 hangs up his telephone as shewn, while the
lines a and are connected as shewn at board 3, the subscriber at station 1 in this
instance would be the "called or answering subscriber" and the subscriber of
station 2 would be the "calling subscriber." The telephone of the answering
subscriber at station 1 being hung up, branch a' is connected to ground at station 1
and thence to terminal d' of the socket and thence to terminal n¹ of plug n and
thence to the tip m² of plug n and thence by wire through the annunciator i and
thence to wire and through battery to ground. Annunciator i of the calling
subscriber is thus thrown down when the answering subscriber hangs up his
telephone.
When the calling subscriber hangs up his telephone as shewn at station 2 current
from battery g will not be sent through individual annunciator e of the answering
subscriber since the condenser p will be found included in the circuit. The circuit
formed through the condenser p and annunciator e may be traced from ground at
station over branch to terminal m' of the plug m and thence over strand o to
condenser P and thence to the tip 'n' of plug n and thence over a portion of branch
wire a² through the answering subscriber's annunciator e and thence through

page_text: battery to ground. The annunciator e will not be operated therefore when the
calling subscriber hangs up his telephone.
In case the operator's telephone were connected into the circuit, still the
condenser would prevent battery current from battery g from flowing through
the annunciator e.
It is well known in the art that a condenser in a telephone circuit is not
objectionable. Though the line is thus made open as to ordinary battery currents
still the circuit is complete as to voice currents, that is to say, the two connected
subscribers can telephone over a circuit including a condenser the same as if the
condenser were not present.
As shewn in Figures 4 and 5 the loop plug has its two terminals on opposite
sides thereof; these terminals being insulated by suitable insulating material. The
socket shewn in Figure 6 is divided longitudinally instead of transversely as shewn
in Figure 3; this plug socket or contact Figure 6, is especially designed to receive
a loop plug of the form shewn in Figures 4 and 5.
In Figure 7 which shews the simplified arrangement for a single switch board the
circuits of station 3 are shown in their normal condition, the telephone resting
upon the switch; the circuit of branch A may be traced from ground through the
bell to the telephone switch and thence to socket or terminal 13 of the switch board;
the branch A being shewn open at terminal B; branch C is shewn open at the
upper contact of the switch and may be traced through the telephone and
transmitter to terminal E upon the switch board and thence through the
annunciator F and thence to the ground wire G including the battery H. By
means of a key I at station 3, branch C may be closed to ground thus closing
battery H through the annunciator F to operate said annunciator, thus notifying
the central office of the call. The operator may call up any subscriber by
inserting one of the loop plugs in the socket or connecting device of the subscriber
wanted and connecting the generator K with the branch which is normally closed
at the subscriber's station, that is to say, in case of station 3, the operator, by
inserting a plug in the socket consisting of terminals or equivalent contacts B, E
would close the sleeve of the plug to terminal B and thus by depressing key K
or K, as the case might be, would send current through the bell at station 3.
Stations 1 and 2 are shewn connected together for conversation by means of the
loop plugs L, M, and the cords connecting said plugs together. The sleeve of the
plug when inserted as shewn in a socket or connecting device of any line makes
connection with the normally open terminal of the socket or contact, while the tip
is closed to the terminal of the socket or contact which is provided with a branch
connection through the annunciator and battery to ground; thus as more clearly
shewn in Figure 8 the normally open branch P of the line of station 1 is connected
with the normally closed branch Q of station 2 through strand N while the
normally closed branch Q1 of the line of station 1 is connected through strand O
with the normally open branch P¹ of the line of station 2; that is to say, the open
branches of any two lines are reciprocally connected respectively with the closed
branches or limbs of said lines, that is to say as before stated, open branch P is
connected with closed branch Q and closed branch Q' is connected with open
branch P.
The talking circuit thus formed includes only the telephones of the respective
subscribers. Moreover, the two sides of the metallic circuit thus formed will be
found branched each through a different coil to a common line including battery
and thence to ground at the central office. By means of a loop switch R the
operator's telephone may be bridged in to the circuit between the strands N, O, when
desired. When the subscribers are through talking each one on hanging up his
telephone or otherwise operates the individual annunciator of the other, thus
indicating that the conversation is finished.
The invention as thus described admits of various modifications which would
readily suggest themselves to those skilled in the art and I therefore do not limit
myself to the constructions shewn.

page_text: Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what I
claim is :-
1. The combination with two subscriber's stations, of their metallic circuit
telephone lines looped together to form a single metallic circuit for conversation,
free of resistance, except the telephones, the different sides of said metallic circuit
being provided with a branch circuit to ground, said branch of each line containing
the individual annunciator thereof, each constructed to operate as a self induction
coil and a ground branch including a battery, substantially as and for the purpose
specified.
2. A metallic telephone line circuit consisting of two branches, one branch being
normally connected with ground at the subscriber's station and thence through the
subscriber's bell to the telephone switch and thence to the central office, said branch
being connected with the test portion of a socket or contact on each of two or more
switch boards and being normally open, while the other branch being normally open
at the subscriber's station extends to the other terminals of the same sockets or
contacts on said switch boards and thence through an annunciator and a battery to
ground in combination with the telephone switch and a ground key at the
subscriber's station whereby on depressing the grounding key current from the
battery is sent through the individual annunciator while on operating the telephone
switch the two branches are united in metallic circuit.
3. The combination with a switch board of telephone lines connected therewith
said telephone lines each consisting of two branches one branch being normally
closed at the subscriber's station and connected through the bell and switch of the
station and extending to one terminal of the line upon the switch board while the
other branch is normally open at the subscriber's station and extends through the
telephone at said station to the corresponding terminal upon the switch board from
which terminal it is connected through an annunciator and a battery to ground, and
switching apparatus at the central office adapted to loop together any two of said
telephone lines, the open terminals of the two lines being reciprocally connected
with the grounded terminals of the other, whereby a talking circuit is formed
which includes the resistance of no electro magnet coils except those of the
telephone while the different sides of said circuits are balanced through ground
branches including respectively the individual annunciators of the lines.
4. The loop plugs connected with flexible cords the two strands of said cords
being each connected diagonally with the different terminals of said plugs a
switching device and a telephone adapted to be bridged across said strands substan-
tially as and for the purpose specified.
5. A pair of loop plugs and connecting cords the strands of said cords being
connected respectively from one terminal of one of the plugs to the opposite
terminal of the other plug reciprocally in combination with a condenser included
in one of said strands substantially as and for the purpose specified.
6. Two metallic circuit telephone lines looped together at the central station each
of said lines being provided with a ground branch through its individual annunciator
and a battery to ground the looping device consisting of a pair of plugs each having
two terminals and different strands, each of the terminals of one plug being
connected with the opposite terminals respectively of the other plug and a condenser
included in the circuit between two of said opposite terminals substantially as and
for the purpose specified.
7. Two telephone lines each consisting of two branches one branch of each being
normally grounded at the central office through an annunciator and battery and
the other branch of each being normally open, of a looping device connecting
reciprocally the normally open branches with the closed branches and a condenser
included between two of said connected terminals and switching apparatus at the
different subscriber's stations operated by the telephones whereby on hanging up
the telephone of one station the annunciator of the line is operated as a clearing

page_text: out signal while on hanging up the telephone of the other station the current is
prevented from flowing through the annunciator of the line of the first station
substantially as and for the purpose specified.
8. The combination with the telephone line extending from ground at the central
office through a battery to terminals one on each switch board and thence to the
subscriber's station and thence back to test terminals one on each switch board of
switching apparatus at the subscriber's station for forming a ground connection for
the battery, or uniting the telephone line through the subscriber's station in metallic
circuit to connect the battery to the said test terminals.
9. The combination with the telephone line extending from ground at the central
office through a battery to terminals one on each switch board and thence to the
subscriber's station and thence back to test terminals, one on each switch board, of
switching apparatus at the subscriber's station for forming a ground connection for
the battery, or uniting the telephone line through the subscriber's station in
metallic circuit to connect the battery to the said test terminals and testing
apparatus for determining the presence or absence of battery current at said test
terminals at the different boards to determine whether the line is in use.
10. The combination with a pair of loop plugs having different terminals recipro-
cally connected together by different strands or wires diagonally or oppositely of a
condenser included in one of said strands and a telephone in a bridge between the
cords, a condenser being included also in the bridge substantially as and for the
purpose specified.
11. The combination with a pair of loop plugs having different terminals recipro-
cally connected together by different strands or wires diagonally or oppositely of a
condenser included in one of said strands and a telephone in a bridge between the
cords a condenser being included also in the bridge a converter having one coil
including the said telephone and the other coil including a branch ground circuit of
high resistance provided with a test plug or moveable terminal adapted to close
upon any one of several test pieces provided upon a telephone switch board.
12. A telephone line consisting of two branches one branch as branch A (see
Figure 7) extending through the signal bell and telephone switch of the subscriber's
station and thence to a normally open terminal as terminal B upon the switch board
the other branch as branch C being normally open at the subscriber's station and
extending through the telephone to a terminal E corresponding with terminal B
said terminal E being connected through an individual annunciator F to a ground
branch G including battery and a key I connected with branch C at the
subscriber's station and switching and signalling apparatus at the central office
whereby the subscriber may call the central office or the central office the subscriber
at will substantially as and for the purpose specified.
13. Two telephone lines a and (see Figure 1) each consisting of two branches,
branches a' and ' of the said lines being each normally grounded through the bell
of its subscriber's station and each extending to different test terminals one for each
line on each board the branches a² and 2 being each permanently grounded at the
central office and each extending through a battery and a different individual
annunciator and to different terminals one for each of said branches a² ² on each
board the test piece and terminal of each line on each board forming a divided
socket or contacts adapted to receive a loop plug, said branches continuing to a
normally open grounding key at the respective subscriber's stations thereof, the
telephone and telephone switch at each subscriber's station and operator's calling
testing and connecting apparatus at the different boards, whereby the lines may be
united for conversation at one board and tests made at any of the other boards
substantially as and for the purpose specified.
Dated this 8th day of December 1890
J. E. KINGSBURY.