Improvements in Switch Board Systems for Telephone Exchanges.
Year: 1892

page_text: Date of Application. 5th Mar., 1892
Complete Specification Left. 3rd Dec., 1892-Accepted, 14th Jan., 1893
PROVISIONAL SPECIFICATION.
Improvements in Switch Board Systems for Telephone Exchanges.
I, JOHN EDWARD KINGSBURY, of 79 Coleman Street, in the City of London,
Manager, (a communication to me from abroad by The Western Electric Company,
of Chicago, Illinois, United States of America,) do hereby declare the nature of
this invention to be as follows:-
This invention relates to multiple switch board systems for telephone exchanges;
its object is to provide means whereby it may be certainly determined at any
board whether a line is already in use at some other board or not, said means
being distinct and separate from the line circuite.
The invention comprises, contact-pieces upon the different jacks of the line
adapted to be crossed together by a suitable contact-piece upon the connecting
plug, corresponding contact pieces upon the different jacks being connected together,
and novel means for determining at any spring jack when the said contact pieces
are short circuited at some other jack. Said means consist of a testing plug
having two contact-pieces which are adapted to make contact with the said
contact-pieces of the spring-jack, a telephone receiver in a circuit between the two
contact-pieces of the testing plug, and a source of telephonic undulatory current
in a parallel circuit with the telephone. This source of telephonic undulatory
current will then normally create a continuous and preferably slight disturbance in
the telephone receiver; but the current will be wholly shunted from the telephone
when the testing-plug is inserted into the spring-jack of a line already in use,
through the contact-pieces of the testing-plug, corresponding contact-pieces of the
spring jack tested, and the cross connection between the contact pieces of the jack
in which a connecting plug is present.
This improved testing system is especially adapted for use in connection with a
multiple switch board system in which contacts upon the spring jacks are provided
adapted to be short circuited to shunt or otherwise render inoperative the individual
annunciator of the line. In such a case the same contacts which perform the
function of rendering the individual annunciator unresponsive when a connection is
made to line, will perform the additional function of indicating the idle or busy
condition of the line, when tested with the testing apparatus of this invention.
The testing plug may be one of the regular connecting plugs of an operator's
telephone outfit. The source of telephonic current may be the secondary coil of
an induction coil whose primary is in circuit with a battery and a microphone
lightly adjusted and kept in continuous slight vibration; the induced current in
the secondary of the induction coil then finds circuit through the telephone
receiver in parallel with it and produces a continuous rustling noise therein.
Thus to an operator testing a line the cessation of the sound in her telephone
indicates that the line is already in use at some other switch board.
The invention is illustrated in the accompanying drawings; therein I have
shown it in connection with a multiple switch board system in which a retardation
coil is included with the individual annunciator in a branch circuit between the
two sides of the telephone line, the annunciator being short circuited when a
connection is made to a line.
In the drawing two telephone substations 1 and 2 are shown each connected
with two spring-jacks upon two sections of switch-board and with individual
annunciator upon one of the boards; the two lines are shown in connection for
communication, through a cord circuit of well known type, equipped with my
testing apparatus. A second cord circuit is shown, one of its connecting plugs
being placed in position for testing one of the lines. .

page_text: The apparatus at the substation 1 is of the ordinary character, consisting of a
calling generator a and a call bell a' in a branch from one side of line b, a
telephone transmitter a³ and a receiver a³ in another branch from the same side
of line, and a gravity switch a connected to the other side of line 6, adapted to
connect either the calling apparatus or the telephone apparatus in the line circuit
according to the position of the switch. The lines ', extend to an exchange
where they are connected to line-springs c c respectively of the two spring
jacks dd upon two sections of multiple switch board e e; an individual
annunciator of ordinary construction and a retardation coil g also of well known
character are included in a loop joining the two sides of line bb'.
The spring-jacks are provided with additional contact-pieces or test-rings h,
which are connected together, and by a conductor to a loop including the retarda-
tion coil and the individual annunciator at a point midway between them. The
connecting plug i is of the ordinary two-part type, having tip k making connection
with the line spring c and sleeve . making contact with the line spring e', which
is made longer for that purpose. The extra contact piece h also makes contact
with the sleeve of plug i whereby longer line spring cand the piece h are crossed
together when the plug is inserted into the spring-jack. The circuit connections
are so disposed that the individual annunciator is short circuited when the line
spring and the piece are thus crossed together.
•
The apparatus and disposition of the circuits of substation 2 is similar to that
of substation 1, and the line being continued through earth instead of a complete
metallic conductor. Its individual annunciator is placed upon another switch
board e.
Like contact pieces of the two plugs of a pair are connected together by con-
ductors in the usual way, calling keys being included in these conductors each
adapted to disconnect both contact pieces of one of the plugs from those of the
other, and to connect them to wires m m¹ forming the terminals of a calling
generator n, whereby call signals may be sent to any line. A clearing out
annunciator is placed in a bridge connection between the different conductors
joining the two plugs; a listening key p is provided, adapted to connect the
terminals of a telephone sety to the different conductors or cord strands in the
usual manner when its plunger is depressed. The secondary of the induction
coil is placed in a parallel circuit with the telephone set ; the primary of
this induction coil is included in circuit with a battery s and a microphone t which
is adjusted lightly and kept in continuous slight vibration.
I will now explain the operation of the system shown, giving special attention
to the operation of testing by this invention to determine whether a line is already
in use or not.
Suppose, for example, that subscriber at substation 1 wishes to communicate
with subscriber at substation 2. He operates his calling generator a, and the
switch a being down, sends a current over the lines bb, which finds circuit, at the
central station, through the retardation coil g and the individual annunciator f.
The annunciator is thus operated, attracting the attention of the operator at the
board e', whereon it is situated to the call. The operator then inserts one connecting
plug i of her pair into the jack d¹. A local short circuit is now closed about the
individual annunciator f which may be traced from one side of that annunciator by
the branch of line to the line spring c of jack d' thence to the sleeve ¹ of the
plug i, thence to the extra contact piece or test ring of the jack, thence returning
to the annunciator : hence any subsequent calling current sent over the lines b
will be wholly shunted from the annunciatori, which will therefore be unresponsive.
The telephonic current of lines will not, however, be shunted through the coil g
on account of its high self-induction.
The operator having thus established a connection between her cord circuit and
the calling line, depresses the plunger of her listening key p, as is shown in the
upper cord circuit, at board e, thereby connecting her telephone set in a loop with
the lines bb. Having learned the connection desired, she proceeds to test the line.

page_text: called for. This she does by inserting the other connecting plug of her pair a
slight distance into the jack d' of the line called for at her board, until the tip of
the plug makes contact with the longer line spring of that jack, at the same time
fixing her attention upon the faint rustling noise in her telephone. The plug at
her board e is shown in position for making such a test of the jack d² of lines to
station 2.
h
If now; the line tested be in use, as is actually the case in the drawing, the
secondary of induction coil will be provided with a short circuit through one
side of the listening key p, one cord strand to the tip of the testing plug thence to
the line spring c of the jack d², thence to conductor 63, to the line spring c¹ of
jack to the sleeve ¹ of the plug in that jack, thence to the test ring returning
to test ring of jack thence to the sleeve of plug through the other side of
listening key p to the other terminal of coil r. The telephonic current from the
induction coil is thus thus wholly shunted from the telephone set q, producing
complete silence therein, thus indicating to the operator testing that the line tested
is already in use at some other switch board.
•
If the line tested were not in use, a circuit would still exist from the tip to the
sleeve of the test plug but would contain the coil of the electro-magnet of the
annunciator of the line tested, which being of high resistance and self-induction,
would not form any appreciable shunt to the telephone set, and hence would not
materially reduce the noise in the telephone.
Thus a complete disappearance of noise in the telephone of the testing operator
is a certain indication that the line tested is already in use.
It will be noted that this test is effected without disturbing the condition of the
line tested, and without at any time attaching a ground or common connection to
either the line or the operator's outfit.
Assume that the operator at board e¹ finds lines to station 2 not in use; she then
inserts the other plug of her pair into the jack d³. The two substations are
thus looped into a continuous circuit which may be traced from station 1 over the
lines to the line springs cc' of jack d', thence to the corresponding contacts of
plug i thence through the ringing keys to the similar contacts of the plug,
thence to the corresponding contacts of the jack d³ and over the lines to sub-
station 2. The operator's telephone is in a bridge connection between the two
sides of this circuit.
The operator now depresses the plunger of ringing key, thus connecting the
two contact pieces of the plug it to the two poles m m' of the calling generator n
thereby sending a calling signal to the substation 2.
Having assured herself that the subscribers at station 1 and 2 are in communi-
cation, she allows the plunger of listening key p to rise, thus disconnecting her
telephone set.
When the communicating subscribers have completed their conversation, one of
them, for example subscriber at station 1, may send a clearing-out or disconnection
signal; this current will find circuit to the line springs c c of jack, thence
through the cord circuit to the clearing out annunciator o, which will thus be
operated and will indicate the disconnection signal to the attendant. An incon-
siderable portion of the signalling current will find circuit through the retardation'
coily, but none can by any possibility operate the individual annunciator f of either
of the connected lines.
Many other circuits for multiple switch boards have been devised to which this
invention is equally applicable. I do not deem it necessary to describe these.
systems further, since the application of this invention thereto may be readily made'
by any one skilled in the art.
I do not limit myself to the employment of an induction coil as a source of
undulatory current, or to the vibrating microphone t to induce such current. Any
other source of slight telephonic current or current of rapid pulsation or alternation
may be employed in connection with the operator's telephone set in the manner I
have described.

page_text: Moreover it is not essential that the operator's telephone be employed as a
responsive device; other appliances adapted to give an audible or visual respouse
upon the cessation of current through them may be employed in place of the
telephone set 7, and a source of current suitable to the particular responsive device
may be employed. Many modifications of the invention may thus be constructed
without departing from the spirit thereof.
Dated this 5th day of March 1892.
Improvements in Switch Board Systems for Telephone Exchanges.
1, JOHN EDWARD KINGSBURY, of 79 Coleman Street, in the City of London,
Manager, (a communication to me 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 multiple switch board systems for telephone exchanges;
its object is to provide means whereby it may be certainly determined at any board
whether a line is already in use at some other board or not said means being
distinct and separate from the line circuits.
The invention comprises contact-pieces upon the different jacks of the line
adapted to be crossed together by a suitable contact piece upon the connecting
plug, corresponding contact pieces upon the different jacks being connected together
and novel means for determining at any spring jack when the said contact pieces
are short circuited at some other jack. Said nieans consists of a testing plug
having two contact pieces which are adapted to make contact with the said contact
pieces of the spring jack, a telephone receiver in a circuit between the two contact-
pieces of the testing plug, and a source of telephonic undulatory current in a parallel
circuit with the telephone. This source of telephonic undulatory current will then
normally create a continuous and preferably slight disturbance in the telephone
receiver; but the current will be wholly shunted from the telephone when the
testing-plug is inserted into the spring-jack of a line already in use, through the
contact-pieces of the testing-plug, corresponding contact-pieces of the spring jack
tested, and the cross connection between the contact pieces of the jack in which a
connecting plug is present.
This improved testing system is especially adapted for use in connection with a
multiple switch board system in which contacts upon the spring jacks are provided
adapted to be short circuited to shunt or otherwise render inoperative the individual
annunciator of the line. In such a case the same contacts which perform the
function of rendering the individual annunciator unresponsive when a connection is
made to line, will perform the additional function of indicating the idle or busy
condition of the line, when tested with the testing apparatus of this invention.
The testing plug may be one of the regular connecting plugs of an operator's
telephone outfit. The source of telephonic current may be the secondary coil of
an induction coil whose primary is in circuit with a battery and a microphone
lightly adjusted and kept in continuous slight vibration; the induced current in the
secondary of the induction coil then finds circuit through the telephone receiver in
parallel with it and produces a continuous rustling noise therein.
Thus to an operator testing a line the cessation of the sound in her telephone
indicates that the line is already in use at some other switch board.
The invention is illustrated in the drawings left with the Provisional Specification;
therein I have shown it in connection with a multiple switch board system in which
a retardation coil is included with the individual annunciator in a branch circuit

page_text: ULIC
when a connection is made to a line.
ities of the telephone me, the annunciator being short circuited
In the drawing two telephone substations 1 and 2 are shown each connected with
two spring-jacks upon two sections of switch board and with individual annunciator
upon one of the boards; the two lines are shown in connection for communication,
through a cord circuit of well known type, equipped with my testing apparatus.
A second cord circuit is shown, one of its connecting plugs being placed in position
for testing one of the lines.
The apparatus at the substation 1 is of the ordinary character, consisting of a
calling generator a and a call bell a' in a branch from one side of line b, a telephone
transmitter a² and a receiver a³ in another branch from the same side of line, and a
gravity switch a connected to the other side of line ', adapted to connect either
the calling apparatus or the telephone apparatus in the line circuit according to the
position of the switch. The lines extend to an exchange where they are con-
nected to line springs e respectively of the two spring jacks d d upon two
sections of multiple switch board e e¹; an individual annunciator f of ordinary
construction and a retardation coil y also of well known character are included in a
loop joining the two sides of line bb.
The spring jacks are provided with additional contact-pieces or test rings 1,
which are connected together, and by a conductor to a loop including the retardation
coil and the individual annunciator at a point midway between them. The con-
necting plug is of the ordinary two-part type, having tip k making connection
with the line spring c and sleeve making contact with the line spring e¹ which is
made longer for that purpose. The extra contact piece also makes contact with
the sleeve of plug i whereby longer line spring c¹ and the piece h are crossed
together when the plug is inserted into the spring jack. The circuit connections
are so disposed that the individual annunciator is short circuited when the line
spring c and the piece are thus crossed together.
"
The apparatus and disposition of the circuits of substation 2 is similar to that of
substation 1, the line 62 being continued through earth instead of a complete
metallic conductor. Its individual annunciator is placed upon another switch
board e.
Like contact pieces of the two plugs of a pair are connected together by
conductors in the usual way, calling keys being included in these conductors each
adapted to disconnect both contact pieces of one of the plugs from those of the
other, and to connect them to wires m m forming the terminals of a calling
generator n, whereby call signals may be sent to any line. A clearing out
annunciator o is placed in a bridge connection between the different conductors
joining the two plugs; a listening key p is provided, adapted to connect the
terminals of a telephone set to the different conductors or cord strands in the
usual manner when its plunger is depressed. The secondary of the induction
coil is placed in a parallel circuit with the telephone set 7; the primary 2 of
this induction coil is included in circuit with a battery s and a microphone t which
is adjusted lightly and kept in continuous slight vibration.
I will now explain the operation of the system shown, giving special attention to
the operation of testing by this invention to determine whether a line is already in
use or not.
Suppose, for example, that subscriber at substation 1 wishes to communicate
with subscriber at substation 2. He operates his calling generator a, and the
switch a being down, sends a current over the lines which finds circuit at the
central station, through the retardation coil g and the individual annunciator f.
The annunciator fis thus operated, attracting the attention of the operator at the
board el, whereon it is situated; to the call. The operator then inserts one con-
necting plug i of her pair into the jack d³. A local short circuit is now closed
about the individual annunciator f which may be traced from one side of that
annunciator by the branch of line 6' to the line spring c¹ of jack d' thence to the
sleeve k' of the plug i, thence to the extra contact piece or test ring / of the jack,

page_text: thence returning to the annunciator f; hence any subsequent calling current sent
over the lines will be wholly shunted from the annunciator, which will
therefore be unresponsive. The telephonic current of lines will not, however,
be shunted through the coil g on account of its high self-induction.
The operator having thus established a connection between her cord circuit and
the calling line depresses the plunger of her listening key p, as is shown in the
upper cord circuit, at board e, thereby connecting her telephone set in a loop with
the lines b. Having learned the connection desired, she proceeds to test the line
called for. This she does by inserting the other connecting plug of her pair a
slight distance into the jack d³ of the line called for at her board, until the tip of
the plug makes contact with the longer line spring of that jack, at the same time
fixing her attention upon the faint rustling noise in her telephone. The plug at
her board e is shown in position for making such a test of the jack d² of lines to
.station 2.
If now,
the line tested he in use, as is actually the case in the drawing the
secondary of induction coil will be provided with a short circuit through one
side of the listening key p, one cord strand to the tip of the testing plug thence to
the line spring c¹ of the jack d, thence to conductor 63, to the line spring of
jack d³ to the sleeve of the plug in that jack, thence to the test ring returning
to test ring of jack thence to the sleeve of plug 3 through the other side of
listening key p to the other terminal of coil r. The telephonic current from the
induction coil is thus wholly shunted from the telephone set 2. producing
complete silence therein, thus indicating to the operator testing that the line
tested is already in use at some other switch board.
If the line tested were not in use, a circuit would still exist from the tip to the
sleeve of the test plug but would contain the coil of the electro-magnet of the
annunciator of the line tested, which being of high resistance and self induction,
would not form any appreciable shunt to the telephone set, and hence would not
materially reduce the noise in the telephone.
Thus a complete disappearance of noise in the telephone of the testing operator
is a certain indication that the line tested is already in use.
It will be noted that this test is effected without disturbing the condition of the
line tested, and without at any time attaching a ground or common connection to
either the line or the operator's outfit.
Assume that the operator at board e¹ finds lines to station 2 not in use; she then
inserts the other plug of her pair into the jack d³. The two substations are thus
looped into a continuous circuit which may be traced from station 1 over the
lines to the line springs c c of jack d', thence to the corresponding contacts of
plug thence through the ringing keys to the similar contacts of the plug i,
thence to the corresponding contacts of the jack 3 and over the lines to
substation 2. The operator's telephone 7 is in a bridge connection between the two
sides of this circuit.
The operator now depresses the plunger of ringing key , thus connecting the
two contact pieces of the plug i¹ to the two poles m m' of the calling generator n
thereby sending a calling signal to the substation 2.
Having assured herself that the subscribers at station 1 and 2 are in communi-
cation, she allows the plunger of listening key p to rise, thus disconnecting her
telephone set.
5
When the communicating subscribers have completed their conversation, one of
them, for example subscriber at station 1, may send a clearing out or disconnection
sigual this current will find circuit to the line springs of jack d', thence
through the cord circuit to the clearing out annunciator o, which will thus be
operated and will indicate the disconnection signal to the attendant. An incon-
siderable portion of the signalling current will find circuit through the retardation
.coil 9, but none can by any possibility operate the individual annunciator f of
either of the connected lines.
Many other circuits for multiple switch boards have been devised to which this

page_text: invention is equally applicable. I do not deem it necessary to describe these
systems further, since the application of this invention thereto may be readily made
by any one skilled in the art.
I do not limit myself to the employment of an induction coil as a source of
undulatory current, or to the vibrating microphone t to induce such current. Any
other source of slight telephonic current or current of rapid pulsation or alternation
may be employed in connection with the operator's telephone set in the manner
I have described.
Morcover it is not essential that the operator's telephone be employed as a
responsive device; other appliances adapted to give an audible or visual response
upon the cessation of current through them may be employed in place of the
telephone sety, and a source of current suitable to the particular responsive device
may be employed. Many modifications of the invention may thus be constructed
without departing from the spirit thereof.
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 1
claim is :-
:-
1. In a testing system for multiple switch boards, the combination with a device
adapted to give a suitable response upon cessation of current through it, of a source
of electricity in a parallel circuit therewith, and contact pieces constituting
terminals of said parallel branch circuits adapted to be applied to the contact-
pieces of a spring-jack whereby it may be determined whether the said contact
pieces of the spring-jack are short circuited or not, substantially as described.
2. The combination with a group of spring-jacks each having two contact-pieces
adapted to be crossed together by a connecting plug placed therein, like contact
pieces of all the spring-jacks being connected together, of a testing plug having
two contact pieces adapted to be applied to the two contact-pieces of a spring jack,
and a source of electric current and a responsive device adapted to give a response
upon the cessation of current therethrough, in parallel circuits between the two
contact pieces of the plug, substantially as described.
3. The combination with spring-jacks each having two contact-pieces adapted to
be crossed together when connection is made thereto, like contacts of the different
spring-jacks being connected together, of a testing plug having contacts adapted to
be applied to the contact-pieces of a spring-jack, and a source of telephonic
undulatory current and a telephone receiver in parallel circuits, whose terminals
are connected to the two contact-pieces of the testing plug respectively, sub-
stantially as described.
4. In combination with a telephone line circuit extending from a substation to a
central station and connected with spring jacks at the central station, each having
two line-springs and a test ring, a connecting plug adapted to be inserted into any
spring jack, having two contact pieces, one adapted to make contact with one of
the line-springs, and the other adapted to cross together the other line-spring and
the test ring of the jack, a testing plug having two contact-pieces adapted to be
applied to the test ring and to that line-spring which is adapted to be crossed with
the test ring respectively, and a source of telephonic undulatory current and a
telephone receiver in parallel branches, whose terminals are connected to the two
contact pieces of the testing plug respectively, substantially as described.
Ai 2nd day of December 1905
J. E. KINGSBURY.