Improvements in Selective Signal Apparatus for Party Telephone Lines.
Year: 1897

page_text: Date of Application, 25th Mar., 1897-Accepted, 29th May, 1897
COMPLETE. SPECIFICATION.
Improvements in Selective Signal Apparatus for Party Telephone
Lines.
I, JOHN EDWARD KINGSBURY, of 79 Coleman Street, in the City of London,
Manager, do hereby declare the nature of this invention (which has been com-
municated to me from abroad by The Western Electric Company of Chicago,
Illinois, United States of America) 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 selective electrical signals, and more particularly to
that class wherein main line currents of different direction are employed to operate
polarized signal receiving instruments at the subscriber's stations.
The object of the invention is to provide means for selectively signalling the
several subscribers' stations of a party line telephone eirenit, which means shall be
economical and convenient, and so simple that no specially constructed instruments
or complex mechanism shall be required; and that each station may be signalled
by pressing a single key corresponding to and representing such station.
In this invention by placing two relays at each subscriber's station, by utilizing
in signalling both conductors of the metallic telephone circuit, and by transmitting
currents of both directions or polarities from a central station call current
generator over these conductors separately and combined, as many as twelve
different current combinations can be made and usefully employed; so that if
necessary or desirable, twelve stations of the same circuit can selectively be
called.
It is however an unusual practice to place as many as twelve stations on any one
circuit, and thus when any ten or lesser number of these currents or combinations
of currents are employed in selectively operating the signals of a like number of
stations, two of the remaining combinations can be employed to work interruption
preventing apparatus at all stations, except the one which is wanted or which has
been called.
This invention provides that two main conductors (generally the outgoing and
return wires of a telephone circuit), shall extend from the central station to a
number of substations. As many as twelve substations may if desired be
connected with this circuit; but practice has indicated that the connection of a
lesser number is to be preferred. A convenient arrangement is to assign six sub-
stations to one main circuit.
At each substation a local signalling circuit is provided, which contains the
signal receiving device (a call bell being commonly used), and the said local circuit
is normally open, and is capable of being opened and closed at two distinct points,
so that the bell included therein, can only be operated to give the signal when the
circuit is closed at both such points, and when consequently the current of its
Iccal battery is permitted to circulate therein, and through the call bell magnet
coils.
Two relays are also placed at each substation and are connected in derived
circuits such as branches to earth or to a suitable return conductor from the two
main conductors respectively. These jointly control the local circuits; the two
relays of each pair being arranged to govern respectively the two opening and
closing points of their own local circuit. The relays of the several stations may
be associated in a variety of ways with their main conductor derived circuits, and

page_text: while at some stations each one may be arranged in its own earth or return branch;
at others one only may be in the particular branch of the main conductor, and the
other in a common earth or return conductor. formed by the junction of the
branches from both conductors.
The pairs of relays may furthermore be diversely arranged at the several
stations with respect to their character, polarity, and mode of connection with the
circuit main conductors, some stations being provided with a neutral relay, and a
polar relay, and others with two polar relays; and it is obvious that the polar
relays associated with the two main conductors may be arranged or connected to
respond to either plus or minus currents, that is to say, to currents of either
direction.
At all stations, however, the two relays must both be in position to close the
points of the local circuit which they respectively control, in order that the signal
may be given; and when both are in such position, they may be said to co-operate
in closing the local bell circuit.
In accordance with this invention, each of these pairs of relays co-operate to
give the signal for the station where they are located in response to a definite
current combination transmitted from the central station over the main conductors,
and to no other; the combination being different for each station; and they
therefore are necessarily so arranged, that the specific combination of current
which is required to enable the two relays of any particular station to hold the
local circuit closed at both of its controlled points, will at all other stations be
ineffectual to perform that office, or will indeed act to maintain the discontinuity of
the local circuits at the said station, at least at one point.
To produce the appropriate number of current combinations required for the
selective operation of the several pairs of substation relays, and for such other
circuit operations as are desired, there are associated at the central station with
the two main conductor terminals, a suitable source of signalling current, such as a
voltaic battery or magreto electric generator, an earth connection having free
terminals, and a group of circuit changing signalling keys, one key for each of
the several different combinations which are to be produced.
These keys control the connection between the main conductor terminals, the
generator terminals and the earth connection terminal; each key being so
organized that when pressed it will establish a relation between the said terminals;
differing from that which would be established by the operation of any other key;
and will therefore transmit over one or both of the main conductors a particular
current or combination of currents differing from that which would be transmitted
by any other key. By this arrangement the operation of any one key, will result
in the co-operative action of the two relays, the closing of the local circuit, and
the giving of the signal at the substation corresponding to and represented by the
said key, and at no other; so that the operation of any particular key will ring
the bell of one particular and corresponding substation.
It is desirable that when any station is using the main circuit for conversation,
other stations shall not interfere by calling the central station, connecting their
telephones, or by other forms of interruption. To this end we place at each
station, in circuit with the station relays, a polarized electro magnet whose
armature is responsive in one direction to a particular central station key and
current combination, and in the other direction to another key and current
combination; it will be found convenient for this purpose to employ two
neighbouring keys, and like but opposed current combinations.
Thus
The special polarized magnets of all stations are constructed and are arranged
alike, and their armature levers are arranged to carry a visual busy signal,
and to serve as a locking device for the automatic telephone switch.
while the circuit is at rest, the said armature levers are permitted to
occupy a given position where the busy signal is concealed, and where the
movement of the hook switch levers is not opposed; but when the circuit is to
he used at any station, the proper current combination is transmitted, and the

page_text: polarized magnets of the several stations respond, bringing their signals into sight,
and bringing a mechanical stop into the path of the hook switch lever, so that it
cannot bring the station telephones into the main circuit. When the use of the
line is discontinued, an opposed current combination may be transmitted to with-
draw the busy signals, and free the switch levers.
It is often necessary to set the locking devices before the main circuit is finally
switched for conversation, and when this is done, means must be provided for the
release of the apparatus at the particular station which is to be called, or which
has called, and which in either case is to be concerned in the ensuing conversation.
Such means are provided by giving to a portion of the iron core of the special
polarised relay of the several stations, an auxiliary exciting coil or winding, and
by including the same in the local bell circuit, or in a branch thereof. The
current in such local circuit is always of uniform direction which it is easy to
arrange shall be the direction required to operate the release of the locking
device; and it follows, that since the local circuit of the particular station which
is called is alone closed, the instruments at such station only are released; and.
those of the others remain locked, until they are simultaneously freed at the close
of the conversation.
In the drawings which accompany and illustrate this specification:-
Figure 1 is a simple diagram indicating graphically a principle underlying all
applications of the invention;
Figure 2 is a table of the currents and current combinations which will most
frequently be employed; and Figure 10 is also a table showing an extended list
of such combinations, including four additional ones.
"
Figure 3 is a diagram of a metallic circuit of eight substations to which this
invention is applied; and
Figure 4 indicates a convenient form of polarised relay for use in association
therewith.
Figures 5 and 7 are diagrams of a portion of a party line circuit, indicating
modifications which may be made of the relays of four of the substations; and
Figure 6 is a detail exemplifying the principle of the relays indicated in one
of the said modifications.
Figure 8 is a diagram indicating the application of a portion of the invention
to a telephone circuit of six substations, and introducing the locking device and
busy signal and Figures 8A, and 8B, represent details of the special relay used
to operate these appliances.
:
Figure 9 is a diagram more clearly and fully illustrating the calling, locking and
telephone circuit and apparatus arrangements of two substations; and
Figure 11 is a diagram illustrating the invention when applied to a metallic
circuit serving twelve substations.
Referring for the present to Figure 3, A and B represent two main conductors
extending from a central station C to a number of substations S. S², S³, etc., they
may be the, outgoing and return conductors of a metallic telephone circuit. At
each of the eight substations are two relays R and R2, placed in derived circuits
or earth branches m aud g of the two main conductors respectively, which branches
may be united at e, and have a common earth connection E2; or as indicated by
dotted lines, a common return conductor X.
There is also at each station a signal receiving device D, usually an electric bell,
connected with a battery s in a local circuit c which is capable of being opened
and closed at two points 10 and 11, and which stands normally open at either one
or both of such points.
The relays R and R2 control this local circuit and when the armature levers 13
of both, rest on the contact stops 12 the said circuit is closed and the bell will
ring; while if the armature levers of either one be out of contact with its stop
the circuit remains open and no signal is given.
It will be observed that the relays of each station differ in some way, either in
construction or arrangement from those of all other stations. Thus at station S

page_text: the main conductor A is branched through a polarised relay made responsive to a
plus or positive current, and main conductor B through a neutral relay adapted to:
respond to currents of either direction traversing B.
Station S2 also has a neutral relay on B but a polarised relay responsive to a
minus current on A. The third and fourth stations have neutral A relays and
polarised, plus and minus current B relays; the fifth and sixth stations have each
two polarised relays, one of either sign, but reversed at the two stations with
respect to the two conductors; station S7 has two polarised relays of plus sign,
and S8 two polarised relays of minus sign.
The form of polarised relay shown in the diagram is purely conventional, and
it is evident that any form will answer in which a magnetically polarised poised -
armature is capable of being normally drawn towards the core of the actuating
helix to hold the local circuit open; or in which the armature uniformly rests.
while no current is traversing its main circuit, in a position to hold the local
circuit open; and having been moved from such a position by a current of
appropriate direction, resumes the same on the cessation of such current.
Figure 4 represents a convenient form of the latter class of relay, and since it:
is an instrument well known in the art, no further remark concerning it is necessary,
except to say that it can readily be arranged to invariably bring its armature to
rest in the desired position, by adjusting the pole pieces so that one shall be a
little more forward than the other. Such a relay closes the local circuit at the
point it controls, under a line current of direction adapted to create a repulsion
between the said nearest pole-piece and the armature; and with a current of
opposite direction or with no current at all, the local circuit remains open at that
point.
The plus and minus signs of all of the polarised relays of the system, indicate
the direction of the current with reference to the central station end of the con-
ductor, to which the said relays are designed to respond.
The four neutral relays at stations S to S₁ are ordinary relays with non-
magnetized armatures whose circuit changing levers are held against their back
contact stops by a spring or by gravity; and these relays act to open their point
of the local circuits, under any current exciting them, without regard to the
direction of such current. In these relays the local circuit contacts 11 of S
and S2, and 10 of S3 and S4 stand normally closed when no current is passing in
the main conductor, but are opened by current of either sign traversing the main
with which they are connected.
At the central station G is a generator of calling current and E an earth con-
nection or common return conductor complementary to those at the substations.
K is a group of circuit changing signalling keys, each key corresponding with one
substation appliance, and when any particular key is pressed or operated, the
relays at the particular substation represented by it will co-operate to close the
local circuit and give the signal there, but at the other stations no such effect
will take place. Hence in order to give the signal at any desired substation, it
is only necessary to operate the particular key or call-button which represents such
station. For instance, key No. 1 corresponds with substation S, key 2 with
substation S2, key 3 with substation S³, etc.
It will be observed that branch terminals of the main conductor A are brought
to contact springs or points in every key except 3 and 4; that similar branches x
of the main conductor B are brought to like contact points in all keys except 1
and 2; that branches y and z from the plus and minus generator poles are brought
to contact points in every key; and that branch terminals from the earth or
common return connection E are brought to contacts in every key except 5 and 6.
The arrangement however of these terminal contacts in each key is different, the
differences corresponding with those of the substation relay arrangement, and by
organizing the contacts of each key in such a manner that the operation of such
key will transmit a current combination to which some one pair of substation relays
is responsive, one is enabled to signal the several stations selectively.

page_text: .
In key No. 1 the contacts are so disposed that its operation will connect-
conductor A with the plus generator pole at contacts at vand y, the minus pole of
the generator with the earth or common return terminal contacts z and w, and will
leave conductor B disconnected. By this means a plus current is sent over line A.
and is distributed through the A relays at all of the substations in parallel, finding
return through the earth branches at the said stations; but as no current is
transmitted over line conductor B, all of the eight B relays will remain unaffected.
Under these conditions relay R at station S will close the open point 10 of its local.
circuit, and the point 11 being already closed by the normal position of the:
armature of relay K2 which has not been changed, the local circuit c of station S.
will be closed and the bell at this station will be rung.
But station S2 will not be signalled, because plus currents having no effect on
the polarised relay R of minus sign there, its local circuit remains open; station S³.
is not signalled, because the only effect of the plus current on main A is to attract.
the armature of neutral relay R, and thus open the local circuit (which is already
open at point 11), at another point 10; station S* receives no signal for the same
reason; station S' is not signalled because though the plus polarised relay on A
closes the open point 10 of its local circuit, the said circuit remains open at 11,
there being no current on B; station Se because neither relay is acted upon,
R being of minus polarity, and R2 having no current; station S7 because R alone
is operated and station S8 because both relays are of minus polarity.
The operation of key 2 is the same as that of key 1, except that the poles of the
generator are reversed, the minus pole being united to main A, at and v, and the
plus pole to earth or common return at y and w; conductor B being again left
without connection.
This operation transmits a minus current on main conductor A and no current
ou B, and since this is the combination to which the relays of substation S²,
respond and co-operatively close their local circuit the bell at this station will be
rung. The bell at station S will not ring because its local circuit remains open at
the A relay R, and the bells at all other stations will not because their local circuits
remain open at the B relays R².
The operation of keys 3 and 4 duplicates that of 1 and 2, except that the plus
and minus currents are transmitted on .conductor B, conductor A being left
without current ; and the result is that these keys will ring stations S3 and S
respectively.
The fifth key connects the main conductor A with the plus pole of the
generator G, and conductor B with its minus pole, leaving the earth or common
return conductor disconnected; the two mains are thus united in series and in
circuit with the generator, and a current flows in both whose direction in A is plus
and in B minus. The A relay of substation S³, being plus, and the B relay there
being minus, both act to close their local circuit c and the signal is given at this
station only. No other station can respond to this combination. At S, though
relay R acts to close its local, relay R2 acts to open it; at S² relay R continues to
hold its local open; at S3 and S the local will be open at both points; at St it will
be open at contact 10; at S' it will remain open at the point 11 of relay R² and
at S it will remain open at the point 10 of relay R.
Key 6 performs a similar operation but with the generator and consequently the
current in both mains reversed, and since the relays of station Se are arranged to
respond to this combination of a minus current on A and a plus current on B, the
bell at S is rung.
Again the seventh and eighth keys will respectively connect the plus and minus
poles to both mains in parallel, and in either case the earth or common return
connection to the remaining generator pole, and the signal will be given at S7 for
plus currents on both mains, and at S8 for minus currents on both mains accordingly.
It will be seen that every key transmits a definite and different current or current
combination, that each substation call apparatus is responsive to a definite and
different current combination and to no other, and that each call apparatus is paired

page_text: with a corresponding key so that the operation of any particular. key will always
give the call at the corresponding station and at no other.
The principle of the arrangement of the main conductors in this system of
signalling may be illustrated by the diagram Figure 1, and referring thereto it is
noted that currents of both direction may be transmitted between A and E2, as
from keys 1 and 2 which transmit current over A to the several substation earth
or common return connections; between B and E2 as in the cases of keys 3 and 4;
between A and B in both directions as with keys 5 and 6, and over both A and B
to E2 in both directions as with keys 7 and 8.. Four other combinations can be
transmitted if required and as will be hereinafter shown, without departing from
these principles.
The eight combinations of signalling current which so far have been con-
sidered, are graphically indicated in a tabulated form by Figure 2 which is self
explanatory.
An analysis of the relay combinations will indicate the leading importance of
the non-polarized or neutral relays of the first four stations in securing the selective
and non-interfering response of the eight call receiving appliances. The eight
stations are divisible into two groups, one of which comprises the first four stations
which are operated by current on one main only; while the other comprises the
last four stations which are operated selectively by current upon both mains in the
several combinations of polarity shown. So far as the selective operation of
the first four stations mutually is concerned the neutral relays are not required,
but each one of the combinations of current for the last four lines would call one
of the first four stations, were it not for the presence and preventive action of the
neutral relays.
The invention, however can be practiced without such neutral relays, and
Figures 5 and 7 illustrate two alternative plans of preventing the interference of
the last four current combinations with the first four stations. In these alternative
systems no change in the table of current combinations, the calling generator, or
the key arrangement is involved, nor is there any change required in the arrangement
or apparatus of stations 5 to 8 inclusive.
In Figure 5 at each of the first four stations S, S2, S3 and S4 the two relays R, R²
are both of the polarized kind, and have double windings. The direction of
windings is such, that a plus current on line conductor A alone acts upon both
relays at station S in such a way that both swing their armatures 13 into contact
with their stops 12; and thereby close the local circuit at both continuity
controlling points 10 and 11, so that the bell at station S is rung. This current
-closes neither point at S2, the point 11 only at S3, and the point 10 only at S*.
The transmission of a minus current on conductor A only gives the signal at S³,
because the relays there only are arranged to respond to such a current.
In the same way the relays at S3 and S4 are adapted to respond exclusively to
plus and minus call currents transmitted over B alone.
Considering now the effect upon the apparatus of station S, when the current
combination to which station S5 responds, viz.: a current plus in A and minus in B
is transmitted, it will be found that a plus current in A, would if there were no
current in B indeed operate the S bell, but there being an equal current in B,
which opposes that of A in relay R³ the local circuit will not be closed at the
point 11.
Where the connection of either main conductor with its relays is shown in
dotted or broken lines, the fact sought to be indicated is that the coil represented
by such lines is wound oppositely in direction to the other coil of the same relay.
Similar and obvious considerations to those outlined above will therefore show that
the first four stations arranged as in Figure 5, respond selectively to their appro-
priate current combinations which are currents on one main conductor at a time;
that with combinations 5 and 6 which have diversely directed currents in the two
.mains, the effect at stations S to S¹ is neutralized in the relays R³ so these
combinations will only close the points 10 of the local call circuits; and that with

page_text: combinations 7 and 8 which are of like direction in both mains, the effect at
stations S to S* is neutralised in the relays It, so that these combinations will close
only the points 11 of the local call circuits, These double wound polarized relays
at the first four stations therefore effectively protect the bells of these stations
from being actuated by the combinations which operate the remaining four stations,
and the signals of the eight stations are selectively and independently operative.
In this system an essential requirement is that the relays represented by the
neutral relays of the first four substations of the circuit of Figure 3 shall present
closed local contacts when no current is on their respective main conductors, but
shall break the local circuit at such point with a current of either polarity. The
plan illustrated by Figure 7 shows this requirement met by polarized relays which
have double contacts.
Figure 6 shows the essential parts of such a relay. M is the actuating electro-
magnet, having a polarized armature N- S. poised at one pole, and having the other
in the field of the magnet core. A fixed stop 20 has a contact point 21 and held
against this by the spring r, is a contact lever 22, hung on a pivot 25. An armature
extension b is in contact with the said lever at 11. These parts are so adjusted
that the magnetic attraction existing between the armature pole N, and the core of
the electro-magnet M. is sufficiently strong to maintain the contact between the
extension and the lever 22, but is not strong enough to break the contact
between the latter and the point 21, against the pull of the spring r
Now if a
current is passed through M. in such a direction as will create an S pole in the core
opposite to the N armature pole, the attraction will increase and the contact will
at 21 be broken; whereas, if an opposite current passes, the armature will be
repelled and the local circuit c which connects at S with the armature and at c² with
the stop 20 will be broken.
A relay of this kind therefore, will maintain its local circuit closed only when
no current flows through its coils, but opens the said circuit when a current of
either direction passes.
In Figure 7 such a relay is substituted for the neutral relay at sub-
stations S, S2, S3 and S4 and its function is the same; but as the plan does not
otherwise differ from that of Figure 3, no further description or explanation of it
is necessary.
In applying the foregoing principles to a practical multiple station circuit system
it is desirable to reserve two of the current combinations for the operation of
locking devices common to all of the stations.
In the system which so far has been described the seventh and eighth
combinations have been convenient for this purpose, that is a plus current over
both conductors A and B for locking the telephone apparatus at stations, other
than that where the circuit is in use, and a minus current over both lines for
unlocking.
Six combinations are thus left for selective station signalling and unless other
combinations are added, the number of stations is therefore limited to six, which.
generally is a sufficient number to be served by a single circuit.
The telephone locking device and a visual busy signal which has been added
thereto are shown in association with the other station apparatus in Figures 8, 8^,.
8B and 9.
In these an additional electro-magnetic apparatus R³ is shown as being placed in
circuit with the relays R, and R2 at each substation, half of its winding being in.
the earth branch m of relay R, and half in the branch q, of relay R². These
instruments respond at all stations simultaneously to the locking and unlocking
currents; but do not respond (except under conditions presently to be named) to.
any of the call signal combinations.
Figures 8 and 88 indicate the principles of the locking magnet employed.
Two electro-magnetic helices 40 and 41 have the similar ends of their cores joined.
by soft iron yoke-pieces and to form the instrument R³. Two soft iron polar
extensions and project from 72 and 3 respectively. A polarised bar armature
pivotted at 42 bas one of its poles, say N, projecting between the pole-pieces h
I

page_text: n-4/,--༥ བས4བ བས པ Hང་Y༦ Մ
pole-pieces.
UL the other, under
If current is passed through coil 40 only, the magnetic polarity developed will
be short circuited through the yoke-pieces and the core of coil 41, so that very
little will be manifested in the pole-pieces h and f. And if current be applied to
the coil 41 only, the magnetic polarity will be similarly short circuited, and agin
little effect will be manifested in the pole-pieces.
Again, if current be applied to both coils 40 and 41 in coincident or comple-
mentary direction the yoke pieces 2 and 3 will satisfy the magnetic flux with very
little polarity in h and f. But if current be applied to coils 40 and 41, in
inductively opposed direction as will be the case when the seventh and eighth combi-
Dations are transmitted, consequent poles of full strength and opposite polarity will be
formed at hand f. By these means the inductive attraction between the polarized
armature j, and the pole-pieces, will hold the said armature at rest near either
pole-piece or findifferently, and it will not be displaced or moved by current
passing through either coil 40 or 41 alone, or by current through both coils, if the
directions are such that the inductive effects coincide in the magnetic circuit
through the yoke-pieces 2, 3. But if the current in coil 40 opposes in effect the
current in eoil 41, the consequent poles at h and ƒ will move the free end of the
polarized armature j, to the right or left, according as the polarity of either pole is
that which complements or opposes that of the armature.
As indicated in Figure 9 this appliance may serve to actuate the locking detent,
and also a visual signal indicating the occupied condition of the circuit.
There are of course a variety of ways in which it may be applied, but the
arrangement of the drawings is simple and efficient.
the
It shows the free end of the polarized armature j itself adapted to serve as
the said locking detent, and in the figure, the telephone apparatus is shown as being
locked at substation S2 where the said armature has been swung to the left, where
its end is brought in front of a pin j³ mounted on the switch lever L so that the
said lever cannot move even when relieved from the weight of the telephone T.
But as at substation S³ the apparatus is free and is shown as being in use,
armature being swung to the right, where its end is not in line with the stud j³.
The busy signal X. is shown as a disc, bearing the letter B affixed to a rod j carried
by the armature, and a windowed screen j in front thereof. It is so adjusted that
the disc will appear at the window when the armature moves to its locking position,
and will disappear when the armature moves to its release position.
The figures show the circuit connections.
From conductor A at each substation the circuit is through relay R, and one
coil of magnet R³ to earth, and from conductor B, it is through relay R² and the
remaining coil of magnet R³ to earth. Under these conditions the locking
appliance cannot act under the influence of current from either conductor alone,
but is responsive solely to a combination in which there is either a plus or a minus
current in both circuits.
There is also shown in these figures a branch of the local bell circuit which at
each station shunts the call bell, and which leaving the local circuit conductor 16
on one side of said bell passes by wire 26 to the winding of one pole-piece / of the
auxiliary magnet R³ then by wire 28 to the winding of the other pole piece f and
by wire 27, back to conductor 16, but on the other side of the bell.
The direction of the windings of the pole pieces h. f. is such that when in
selectively signalling any particular station, the local circuit c of such station is
closed by the co-operative action of its relays R, R2 a part of the current from the
local battery s passes through the shunt circuit, and round the said pole-pieces
producing in them opposite polarities, independently of the line currents in the
main conductor coils 40, 41 of the magnet R³ and of such direction as to move the
armature j into its release position.
"
By this arrangement it is provided that all the stations of the general circuit
may be simultaneously locked by the application of the prescribed locking current

page_text: combination; and that when the station desired is being signalled, the telephone
apparatus there may be released individually by the operation of the local ringing
current to the pole-pieces h, and f; the local battery at such station serving when
its circuit is complete to ring the bell by the current in one of its branches, and to
unlock its apparatus by the current in the other. And as the local circuits of other
stations are not closed, the apparatus at the said stations is not released.
Figure 8 illustrates diagrammatically the electrical arrangement of a line of six
substations, and a central station, together with the normally connected apparatus
of the latter, and indicates one way in which incoming calls may be transmitted.
P is a switch plug adapted to fit the spring jack J, and having two con-
ductors A2, B2, which are assumed to connect with the signalling keys; I is a
differentially wound annunciator, and G2 is a normally connected current generator.
The annunciator circuit leads from the separable spring-jack contact of main
conductor A through one of the said differential windings 31, then back through
the other 32 to the separable spring jack contact of conductor B. At a point 60
between the two windings is attached a conductor 30 leading from the generator G²
whose other pole is grounded or connected to a common return.
The relative direction of the annunciator windings is such that the current from
the generator G2, circulates round the core in both directions, and divides on equal
terms between the main conductors A and B, finding return by the earth or common
return connections E2 of the several substations.
The current flowing to the two conductors from generator G2, is shown as being
minus. This is so arranged that the said current may correspond with the
unlocking current on both lines, and hence will not disturb the normal conditions
at the stations.
At each substation there is associated with the telephone hook switch lever L, a
contact spring d having an earth connection and so placed that it will not touch the
hock lever, when the same is at either of its range limits; but will be in rubbing
contact therewith and make a momentary ground connection of practically no
resistance for the lever, and consequently for that main conductor with which it is
directly connected as the said lever moves in either direction.
Thus when the circuit is not being used for conversation, and the telephones at
all stations are hung on their respective hooks, the generator G2 sends a minus
current differentially through the annunciator and equally over both mains in
parallel. The removal now of any telephone from its hook brings about a
momentary and direct connection between the main conductor B and the earth,
suddenly reducing the resistance of the said conductor, and causing the portion of
the current which flows through the B winding of the annunciator to greatly
preponderate.
The core of the annunciator will thus be magnetized, its armature will be
attracted and its shutter released, giving the signal.
When a substation is to be signalled the plug P is inserted into the socket of the
spring-jack J, which cuts off the annunciator and connects the keys K with that
particular circuit.
Key 7 or the key which sends a plus current over both mains in parallel is then
operated to lock the apparatus at all stations, without ringing any of the station
bells. Then the key representing the desired station is pressed, which results in
ringing the bell and releasing the telephone apparatus at such station by means of the
local battery there, without affecting the bells or lock devices of any of the other
stations.
At the close of any communication, key 8 or the key controlling the unlocking
current, viz.: a minus current over both mains in parallel is operated to release the
apparatus at all stations.
While, as has been stated, the eight current combinations which so far have been
considered are sufficient for ordinary practice, the invention is not restricted to
these and may add others where required.
The table of Figure 10, shows four additional current combinations, which may
R

page_text: be utilized; and the diagram Figure 11 represents a circuit of twelve substations,
all of which by the aid of these combinations may be selectively signalled.
For the sake of simplicity the locking devices are omitted from Figure 11, but it
is readily to be understood that an alternative circuit would be one of ten stations
each fitted with the locking devices which have deen described.
The four additional current combinations are those which in Figure 10 are the
seventh, eighth, ninth, and tenth of the table; the seventh and eighth combinations
of the original table Figure 2, having here becn advanced to the eleventh and
twelfth positions it being convenient in this arrangement also to employ these
particular combinations in the locking and unlocking arrangements, when such
operations are to be performed.
In Figure 11, however, the locking devices and their connections are not
introduced, as when employed they would not in any respect differ from those
already shown and described; and the drawing simply shows how the call
apparatus of more substations may be added to the eight of Figure 3, and
operated selectively.
Of the additional combinations as indicated by table Figure 10, No. 7 is
produced by depressing key 7 whereby the main conductor A, and the central
station earth connection are both united to the minus pole n and main conductor B
to the plus pole p of the call current generator G. This action connects the
generator in two circuits; one a metallic circuit utilizing both mains, and the other
a grounded or common return circuit extending from the central station earth or
common return connection, to the substation earth or common return connections
in parallel. The calling apparatus of substation S7 is so arranged that its call
apparatus only, will be rnng by this combination. It has a minus relay R in the
earth branch from main conductor A, no relay in the branch q from main B, and
a plus relay R³ in the common earth connection E' formed by the coalition at e of
the two earth branches.
The local circuit c will be closed at the points 10 and 11 governed by both relays,
and the bell D will give the signal.
Combinations 8, 9 and 10, are produced by the operation of keys 8, 9 and 10,
respectively, and give the signal at substations S8, S9, and S10, respectively.
The arrangement of the key apparatus circuits and substation call apparatus
for these combinations, is similar to that for No. 7, but the factors are transposed.
Key 8 for example connects conductor A and the earth E with the plus pole of
the generator, and conductor B with its minus pole, which causes a current of plus
direction in the metallic circuit through the plus polarized relay R, and a current
of minus direction in the earth completed circuit of conductor B alone, which
includes the minus relay R2 at substation S.
For substation S, the operation of key 9 causes a plus current over A and a
minus current over B in the metallic circuit containing the minus relay R² of B;
and a plus current in the grounded circuit over main A which contains the plus
relay R; for in this case the plus generator pole unites with A and the minus pole
with B and the earth. And key 10 connecting the plus generator pole with B
and E, and the minus pole with A, will produce a plus current over B and a minus
current over A in the metallic circuit which includes the plus relay R²; and a
minus current in the earth circuit of which A is the sole main conductor, and
which contains the minus relay R; and the signal is therefore given at sub-
station S¹º
For this arrangement it may be noted that the relay connections at the first four
and last two stations do not differ from those disclosed by Figure 3. At the other
six stations one of the two relays is placed in the main or coalition earth conductor
leading from e to E2; and also that at stations 5 and 6, the relays R² so placed are
neutral relays, or such as will respond to all currents of sufficient strength passing to
earth there without regard to direction.
A balancing resistance Z is provided at each substation in that branch of the
three-way earth connection which is not occupied by one of the two relays, and

page_text: I prefer to make the magnitude of this resistance substantially equal to that of one
relay so that at any station the resistances measured from the junction point to the
mains A and B and the earth E2 shall be alike. The use of the said resistances Z
is to secure a symmetrical distribution of the several currents at all stations.
The local battery s of any substation may if desired, be as indicated in Figure 9,
the same as that furnished to supply current for the telephone transmitter Tr,
which is shown as being placed together with the primary winding 70 of its induction
coil 12, in an alternative circuit of the said battery controlled by the contact 72 of
the telephone switch L.
I am aware that attempts have been made to signal selectively by means of
combinations of line conductors, and also by combinations of currents, and com-
binations of relays; but I am not aware that it has heretofore been proposed to
combine these three features in a homogeneous system whereby a large number of
stations may be signalled selectively; and whereby with an extremely simple
arrangement of both circuits and apparatus, any particular station may be signalled
to the exclusion of all others by a single pressure applied to a single key.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The arrangements substantially as described whereby each subscriber on a
party circuit can be separately called, such arrangements consisting of a series of
keys at the central station serving to connect two line wires and a return with a
battery or other generator; and a series of call circuits at the subscribers stations
each of which can be closed by the co-operation of a pair of relays which receive
the currents transmitted by the keys; the arrangements being such that each key
transmits and each pair of relays responds to a special set of currents in the line
wires and return.
2. The arrangements of keys, circuits relays and other appliances substantially
as described whereby on a party line all the subscribers instruments may be locked
or rendered inoperative, then one subscriber may be called and his instrument
unlocked ready for use and finally all the instruments may be restored to their
normal operative condition.
3. An electric signalling system comprising a metallic or double conductor main
circuit extending between a central station and a number of sub-stations; a selective
sigual apparatus consisting of a signal receiving device in a local circuit controlled
by two relays at each substation, the receiving device at each station being
selectively responsive through the said relays to a definite and separate or different
main circuit current or current combination; and at the central station, a source
of calling current; an earth or return conductor; and a series of keys representing
respectively the said substations, and controlling the connection of the two main
circuit conductors, the call current source, and the said earth or return conductor
terminals, each key being organized to establish a different relation of the said
terminals, and adapted thereby to transmit over one or both of the said main
circuit conductors, the particular current or current combination to which the
receiving device of the substation represented by such key and no other, is
responsive, substantially as herein before specified.
4. In a selective signalling system, the combination of two main line conductors
extending from a central station to a number of substations; a current generator
at the central station; a group of circuit changing keys also at the central station
controlling the ends of the said main line conductors, the poles of the said call
generator, and an earth or return connection, the several keys being organized to
establish different relative arrangements of these factors, for the transmission at
will of plus and minus currents over either main couductor alone, over both at once
in parallel, and over both in series or when formed into a metallic circuit; and a
normally open local circuit containing a call bell at each substation, controlled by
relays, the said two relays of each station being adapted to co-operate, and to close

page_text: their local bell circuit, and so give the call signal, in response to one particular
combination only of main conductor and current, and to the operation of some
definite one of the said keys, substantially as specified herein.
5. The combination in a system of selective signalling, of the two conductors of
a metallic telephone circuit extending between a central station and a number of
substations, each conductor having an earth or return branch at each substation ;
a signal current generator, a complementary earth or return connection, and a
number of signalling keys at the central station, each of said keys being adapted
to establish a different association of the main conductor, generator and earth or
return connection terminals, and thereby to transmit a current combination distinct
from that of any other key; a signal receiving device in a local circuit capable of
being opened and closed at two points, at each substation; and two relays at each
substation connected in the earth or return branches of the main conductors
respectively, and controlling each, one of the said local circuits opening and closing
points, the character, polarity and mode of connection with the main conductors of
the said relays being diverse at each station; whereby the said relays of each
substation are adapted to close their respective local circuit at both points, and to
operate the signal device at such substation, in response to the current combination
transmitted by a particular one only of the said keys, substantially as and for the
purposes specified.
6. In a system of selective signalling the combination of the two conductors of
a metallic party line telephone exchange circuit; two relays at each substation of
the said circuit in derived circuits of the said conductors, the relays of each station
being arranged differently with respect to character, polarity, or circuit connection,
and made thereby responsive to a signalling current or current combination
different for each station; a local circuit at each station having two points
controlled by the said relays respectively, where it may be closed and opened; a
call signal device included in said local circuit, and adapted to operate and give
the signal when the same is closed; and means for transmitting through the said
metallic circuit, or through either or both of its conductors at will, the particular
signalling curient or current combination to which any of the said pairs of sub
station relays is responsive; whereby any of the substation local circuits may be
selectively closed, and the signal given at such substation to the exclusion of the
others.
7. In a system of selective signalling, the combination with the two conductors
of a metallic telephone circuit extending from a central station to a number of
substations; of substation signalling apparatus at four of the several stations
comprising a polarised and a neutral relay, and at the remaining stations comprising
two polarised relays, the relays of each station being connected differently in
derived circuits of the two main conductors, and adapted to each to control a
local circuit including a signal bell; and a current generator and two sets of signal
sending keys at the central station, the keys of one set being adapted to connect
the poles of the generator diversely, to one or the other of the main conductors for
the selective operation of the single polarised relay of the said four stations; and
the keys of the other set being adapted to connect the said generator poles diversely
with both of the said main conductors for the selective operation of the two polarised
relays of the remaining stations substantially as described.
8. In a telephone system the combination of the two conductors of a metallic
telephone circuit; a central station at one end of such circuit; a call current
generator, and a number of signal sending keys at said central station, the said
keys being organized to establish a like number of different permutation connections
of the said circuit conductors and generator, and thereby to transmit over either
or both of the said main conductors a similar number of distinctive currents or
current combinations; a series of substations equal in number to the said keys less
two, connected with the said two main circuit conductors and a selective signalling
apparatus at each of the said substations, controlled by relays in earth branches of
the said two conductors responsive exclusively to the operation of a corresponding

page_text: one of the said keys, and to the particular current combination transmitted thereby ;
with a telephone locking device, and busy signal at each substation, actuated by a
polarized electro-magnet in the circuit of the station earth branches, the sil
locking magnets of all stations being collectively responsive in locking and
unlocking to the operation of the remaining two keys, and the current combinations
respectively, substantially as herein set forth.
9. The combination substantially as hereinbefore described, in a telephone
system, of a metallic telephone circuit; a central station from which such circuit
extends; a source of signalling current supply, and a number of signal sending
keys at said central station, the said keys being adapted to establish a like number
of different permutations of the circuit conductor and generator connections, and
thereby to transmit by means of either or both of the said circuit conductors, a.
similar number of distinctive currents or current combinations; a series of
substations equal in number to the said keys, less two, connected with the said
main circuit conductors; with a selective signalling apparatus at each station,.
consisting of a signal bell in a normally open local circuit, controlled by tw. relays
in earth or return branches of the said main conductors respectively, each pair of
relays being responsive exclusively to the operation of a corresponding one of the
said keys, and to the particular current combination thereof; a series of polarised
electro-magnets (one at each station, in circuit with the relays thereof, controlling
a telephone locking device and busy signal), collectively responsive in locking and
unlocking to the operation of the remaining two keys, and their current com-
binations respectively; and an auxiliary winding on the core of said magnet included
in the local call circuit of the station, to excite the said magnet, and to actuate it.
to unlock the telephones at a called station, independently of the central station.
unlocking current combination; substantially as described and for the purposes.
set forth.
10. The combination in a telephone system, with a number of selective signallin
appliances each at a different substation of the same circuit, and each comprising
two relays, and a normally open local circuit controlled thereby containing a
signal bell, the pairs of relays of the several stations being each adapted to respond
selectively to a different and distinctive current combination transmitted over the
main circuit conductors; of a telephone locking and busy signal device at each
station actuated by an independent polarized electro-magnet in circuit with the
station relays, the said magnets of all stations being collectively responsive both.
in locking and unlocking, to two additional distinctively main line current com-.
binations; and means consisting of an auxiliary exciting helix of the lock actuating
magnet, connected with the local calling circuit, and made operative by the closure
of such circuit to give the signal, for automatically unlocking the telephones at the
called station only substantially as described.
11. The combination in a telephone system, of the two conductors of a metallic
circuit extending from a central station to six substations; with six signalling
keys at the central station, organized and adapted to transmit over the said
conductors a like number of different call current combinations, to wit-plus and
minus currents over each conductor separately, and plus and minus currents over
the two conductors arranged serially as a metallic circuit; a normally open local
signalling circuit at each substation containing a signal bell, and capable of being
opened and closed at two separate points; and two relays differently combined at
each substation connected in earth or return branches of the said two main con-.
ductors respectively, and controlling the said two points in the station local circuit,
each set of relays being adapted to respond to a definite and different one of the
said current combinations, and to no other, and thereupon to close its local circuit,.
and sound its call signal selectively.
12. In a telephone system, a selective signalling circuit comprising the following
elements: the two main conductors of a metallic circuit extending from a central
station to six substations, a group of eight circuit controlling and signalling keys
at the central station, organized and adapted to connect the terminals of the said.

page_text: main conductors with the terminals of a signalling current generator as many
different ways, and to transmit over the said conductors a like number of different
current combinations, to wit:-plus and minus currents over each conductor
separately, plus and minus currents over the two conductors arranged serially as a
metallic circuit, and plus and minus currents over both conductors jointly in
parallel; a normally open local signalling circuit at each substation containing a
signal bell, and capable of being opened and closed at two separate points; a
differently combined pair of relays, at each substation, connected in earth branches
of the said two main conductors respectively, and controlling the said two points
in the station local circuit, each pair being responsive to a different one of the
said keys and current combinations for the selective operation of its own signal
bell; a telephone switch locking device at each substation; and a polarised relay
in circuit with the two signalling relays controlling the same, the said polarised
relays of all stations being of like character and arrangement, and adapted to
respond collectively to the remaining two keys and current combinations, for the
simultaneously setting and releasing of the said locking devices of the several
stations; substantially as set forth.
13. In a telephone signalling system, the combination of the two main conductors
of a metallic circuit connecting a number of substations with a central station;
with a series of local circuits each containing a signal bell, one for each substation;
and a series of relays two for each substation, connected in derived circuits of the
two main conductors respectively; the currents to which said pairs of relays are
responsive differing from each other in direction over both main conductors
severally connected in circuits completed through the earth or through a common
return conductor, in direction over the two conductors connected in series, and in
direction over the two conductors connected in parallel, whereby any pair of
said relays but only one pair at a time, may be operated to close its local circuit,
as set forth.