Signals in Telephonic Communication, Permitting of a Direct
Year: 1884

page_text: Signals in Telephonic Communication, Permitting of a Direct
I, CHARLES DENTON ABEL of No 28 Southampton Buildings, Chancery Lane in
the County of Middlesex, Consulting Engineer and Patent Agent, do hereby
declare the nature of the said Invention for "AN IMPROVED MODE OF AND
APPARATUS FOR WORKING THE CALL SIGNALS IN TELEPHONIC COMMUNICATION,
PERMITTING OF A DIRECT CALL BETWEEN THE SUBSCRIBERS" and in what manner
the same is to be performed to be particularly described and ascertained in and by
the following statement :—
This Invention has for its object to permit two subscribers of a telephonic
exchange, after their wires have been put in communication through one or more
central stations, to signal to each other by a bell by means of a special key, without
requiring for this purpose to actuate the signals of the central station or stations
hence, the term "direct" has been given to this system.
On the other hand a subscriber can, by means of another key, call the central
station without acting upon the signal bell of the subscriber with whom he has
been put in communication.
For carrying out this doublo system of signalling, each subscriber is provided
with two keys whereby the current of the signalling battery can be sent into the
line wire in two different ways, enabling him either to actuate the call signals of
the central offices, or the signal bell of another subscriber.
The construction and mode of operation of apparatus for this purpose will be
readily understood on reference to the accompanying Drawings.
I. Sheet 1 shews diagrammatically the arrangement for signalling direct on lines
with double wires. The following cases may occur:
1, Simple call of the station B' by the subscriber A. The current in this case
passes as follows. On pressing upon the key C B, the current of the battery PA
passes from the copper pole C through contact c b, key C B, key C A through mh,
and reaches the central station B' through the line L', passes to the back plate Pl
of the jack, traverses the relay R¹ of the signal bell, which is actuated and closes a
ID 71

page_text: .
local bell circuit. The attendant is thus called by subscriber A. The current
passes from the relay R' back to plate p¹ of the jack by the moveable contact v, qu
passes to line arrives at station A, traverses key CA, through g n, and key C B
(which is depressed) through a e, and arrives at the zinc pole Z, thus completing
the circuit.
2, Call of the subscriber A by the station B¹. Copper pole c of the battery Pi B¹
(the zinc pole Z of which is always to earth) is put in communication with the two
wires of the line ₁ L, by pressing key C, B, and introducing the plug f¹ in the
right hand hole of the jack P¹ p¹ of subscriber A, so as to send the current of the
battery P¹ B¹ into the relay R of the signal bell at the subscriber and thence to
earth.
Two operations have to be performed. a, Introduction of stopper f, into the right
hand hole of the jack P¹ p¹ to which are connected the two wires of the line L¹ and
of subscriber A, so as to put in communication the two wires t¹ and v' of the
flexible conductor with the two plates P1 p¹ and thereby with the wires of the
line L, . In order to make the diagram clearer, the two plates of the jack have
been shewn one below the other, while in reality they are on top of but insulated
from each other. The introduction of the stopper in the right hand hole has
also the effect of depressing the contact spring q' by means of the pin u¹ fixed
thereon; so that, the contact v' q¹ being broken, there can be no derivation through
the relay R¹.
b, In pressing upon key C₁ B₁, the stopper ƒ, being in place in the right hand
hole of the jack, the current is made to pass as follows: From earth T¹ to zinc Z
of battery P B¹, thence to contact b¹, through the two springs c and d', thence
parallel through wires t¹¹ to line wires L¹ through the plates p¹ P¹ of the jack.
Following out the two parallel currents through L' to r, it will be seen that
they here join again. In L' the current passes the spring h to the bridge m; from
spring b to bridge d and thence to r. In the current traverses key CA from g
_to_n.and key C.B.from-a-to-fi-passes-from-x-to-y-and-arrives-at-.-From--the-
combined current passes into the relay R and thence to earth T, through the
contact q P which only made when the lever ✓ is lowered as indicated in the
Drawing. The circuit starting from earth T at the central station B', thus arrives
at earth T at the station of A, actuating the relay R. The armature v of the
relay R, in touching the contact t closes the local circuit t, v, P S, S, of the
subscribers signal bell, and he is thus signalled.
3, Call of central station B' by station B¹. The stopper fi is introduced into
the jack p P and the key C₁ B₁ is pressed upon, in order to send through the
entire circuit the current of the battery P, B₁ into the relay situated at the
central station B². This call is however not peculiar to the system under
consideration.
4, Direct call between the subscribers. To enable this to be effected, the calling
subscriber A, for instance, first requires the two intermediate central stations B¹
and B to connect his two line wires with those of the subscriber A¹. For this
purpose, the lines L' and L' and the lines and 12 will have been connected at B¹
by means of a flexible conductor having similar stoppers f¹. At B L₂, L¦
and, are connected in the same manner, cutting the relays R¹ and r² out of
the circuit and leaving 1 and R2 in derivation, so that subscriber A in pressing on
key CB can call A' and in the same manner A¹ can call A.
The connections being thus established in order that A' can be called by A it is
sufficient at A to press a key CA in order to put zinc Z of battery PA to earth T;
to then connect the two wires of line L¹ so that if these two wires have the same
resistance the difference of potential will be nil in the central stations B' and B² at
the connections V² and v², V' and v¹ of each of the relays R¹ and r¹, and which
which consequently will not be actuated by the passage of the current thus sent,
while the relay R¹ at subscriber A¹ will be actuated and will close the local bell
circuit S¹

page_text: The course of the current is as follows:-In pressing on key CA at A the current
passes from the copper pole of the battery PA, through key CA at 2, through
springs h and g, thence into line wires L' . The double current traverses
station B' by means of a flexible conductor connecting the plates p¹p and P¹ P
of the two jacks. Thence the current passes to the line wires L, L, traverses
station B like B', the relay r' being out of action as before stated, and R² being
left in derivation. The current arrives through L and at the station A'. The
current passes along the wires L and to their junction at r¹ as follows: For L¦:
spring g bridge n' through key C'B' through spring a¹ and bridge f¹, through
contact ytor. For : key C₁ A' through spring h¹, to m¹; key C¹ B¹
through spring b' and bridge d' and to junction where it joins L. From r¹ the
combined current passes to the relay R¹ which it actuates. Its armature v', making
contact with t, closes the circuit of the battery P¹ S¹ and signal bell S¹ and thus
signals the subscriber A'. Passing from R¹, the current passes through the
contact qp to earth. The zinc pole Z of the call battery PA of the subscriber A¹
is also to earth because in pressing on the key CA the contact K is put in
communication with the spring j which is put to earth through the contact p q.
It will be evident that if the two subscribers A A¹ were put in communication
through a single central station B¹, the same action as above described would take
place; there would only be one operation less, namely the calling of the station B³
by the station B¹.
5, Apparatus Sheet II. The special apparatus employed for this method of
operating are of two kinds: the keys and the relays. The keys have either two or
three contact springs, separated from each other by metallic or insulating pieces.
In pressing on a single button the springs are simultaneously caused either to make
contact with each other or with other contact pieces while at the same time they
are made to break other contacts that are made in the "rest" position.
Fig. 1 is a plan shewing, arranged on one and the same board, the direct calling
key CA with three contact springs as shown in the side view at Fig. 2, and
the calling key CB of the central station having two contact springs, as shewn in
the side view at Fig. 3.
Figs. 4 and 5 shew a plan and an elevation of the keys C, B, and C, B, which
nre identical in construction, that serve at the central stations to call subscribers
provided with apparatus for direct signalling. The relays situated at the
subscriber's are of a peculiar construction; they are of two different types and
they can be interpolated in the line in two different ways for effecting the same
object, which is to close a local signalling circuit by means of the same currents.
According to one arrangement the inner ends of the wires of the subscribers
relays R R (Sheet I) are coiled round each bobbin of the relay and connected
with each other, as shewn in the diagram at Fig. 6, and the outer ends of the same
wires are connected, the one to the point B and the other to earth.
This is an ordinary relay with two bobbins, shewn in elevation at Fig. 7 and in
plan at Fig. 8 Sheet II. It is interpolated between the point B and earth, and is
worked by a current produced by the union of the two other currents passing
simultaneously from the two line wires L¹. An ordinary relay with two bobbins
arranged on the wire that passes from the point B of the junction of the lines L'
and to earth permits of the direct signalling between two subscribers. There
are however circumstances in which the relay placed in this manner may give rise
to inconvenience, namely when two subscribers, having direct call, are connected
by a single central station with very short line wires.
The greater part of the calling current to the central station, finding no
resistance to its passage through the circuit L' B ", will pass that way, while
only a very small part of the current will pass to the station through the relay in
derivation, this relay offering a tolerably high resistance (200 Ohms). This relay
will therefore not be actuated, and the subscriber will be unable to call the central
station.

page_text: signalling to the central station while the other serves for signalling directly to
another subscriber with whom he has been put in communication, substantially as
herein described.
Third. The herein described method of direct signalling on telephonic circuits
with double wires, wherein the circuit is so modified as to cause the current to
pass in the same direction along both line wires, the return current being obtained
through earth.
Fourth. In the method of telephonic signalling on a double wire circuit referred
to in the preceding claim, the combination of two calling keys at the subscribers
station, the calling key at the central station being provided with two contact
springs acted upon by a single button, whereby the metallic circuit can be closed,
firstly, in the "rest" position, in the subscribers telephonic apparatus, and secondly,
when the subscriber calls, in the battery of his station, substantially as herein
described.
Fifth. The herein described construction of key for direct signalling, having
three contact springs two of which are made on pressing the button to effect first the
connection of the two line wires, and second the connection of the circuit thus
formed with one of the poles of the subscribers battery, the other pole of which is
put to earth by the third contact spring.
Sixth. The combination with the key referred to in the preceding claim of a
signal bell apparatus or relay situated at the subscriber's station on the earth wire
leading from the junction of the two line wires, such relay serving to close the
local circuit for actuating one or more signal bell apparatus, substantially as herein
described.
Seventh. The herein described construction of relay with two bobbins, with
coils running in contrary directions, connected to the two line wires, the earth
wire being connected to the union of these two wires between the bobbins of the
relay, such relay being made to produce at the subscribers station, a supplemental
resistance in the metallic circuit, for the purposes set forth.
°
ABEL & IMRAY,
Agents for the Applicant,
28, Southampton Buildings,
London, W.C.