Improvements in Telephonic Switching Apparatus.
Year: 1891

page_text: Date of Application, 23rd July, 1891
Complete Specification Left, 21st Apr., 1892-Accepted. 21st May. 1892
PROVISIONAL SPECIFICATION.
Improvements in Telephonic Switching Apparatus.
I, ALFRED ROSLING BENNETT, of 22, St. Alban's Road, Harlesden,
London, N.W., Electrical Engineer, do hereby declare the nature of this invention
to be as follows:-
The object of my invention is, in a telephone exchange operated by metallic
circuits and multiple switch-boards constructed conformably to my Specification
No. 19486 of November 29th, 1890, to provide a method by means of which the
operator at any one section of such a multiple switch-board can, by applying a test,
discover whether any particular subscriber's metallic circuit is connected at any
other section.
The test enables the operator to tell whether a connecting cord is in at any
section other than her own.
Each connecting cord for metallic circuit switching necessarily consists of two
insulated conductors. From each conductor of such a cord, preferably from its
centre, I lead a branch wire or conductor to earth through a resistance which may
conveniently consist of a coil of insulated wire wound on a bobbin but it may also
be made up of liquid, carbon or any suitable conductor. The resistance may or may
not be combined with cores, sheaths or condensers for the purpose of increasing the
electro-magnetic inertia and static capacity of the branch to earth. To attain the
best results it is necessary that the branch to earth from each of the conductors in a
cord should be as nearly as possible alike in resistance, magnetic inertia and
capacity. To prevent variations due to changes of temperature the material
employed should be alike in each branch, and to save space when wire is used
both resistances may be wound on the same bobbin. All the connecting cords
used with the switch-board must be so fitted.
Each operator is provided with a testing apparatus consisting of a flexible
conducting cord tipped with metal, which cord is permanently connected to earth
through a source of electricity such as a voltaic battery or magneto generator and
through an instrument capable of indicating visibly or audibly when a current
passes through it.
To test, the operator applies the metal tip of her testing-cord to the metal socket
of the subscriber's metallic circuit which is before her on her section of the switch-
board.
If there is no connecting cord in a socket of the same metallic circuit on any
other section the indicating instrument will not be affected since the current from
the battery contained in the circuit of the cord cannot find an outlet through the
subscriber's metallic circuit which is insulated from the earth at all points. The
absence of a signal will show that the subscriber wanted is not engaged at any
other section and the operator may accordingly connect him on hers.
But if a connecting cord is in a socket on any other section the indicating
instrument will reveal a current the moment the tip of the testing-cord is applied to
the socket, since the battery current will now find an outlet to earth through one of
the branches to earth from the connecting cord that may be in. The operator will
then know that the subscriber wanted is engaged and must not be connected on her
section.
Instead of the source of electricity being in the circuit of the testing-cord it may
be placed in the branches between the connecting cords and earth. In this case the
operator's testing apparatus consists only of a flexible cord, tipped, and connected
through the indicating instrument to earth.
On applying the tip to the socket she obtains a current only when a connecting

page_text: cord is in. This arrangement is necessary when the subscribers' metallic circuits
are, as in the switching system of the Mutual Telephone Company in Manchester,
connected to earth in the subscribers' offices for ringing purposes.
Instead of a flexible cord with a tip the operator may wear a thimble or finger-
stall, wholly or in part made of conducting cloth or other conducting material, ou
one or more fingers, preferably one finger of each hand. These thimbles or finger-
stalls are in connection with flexible conducting cords loosely bound along the
operator's arms and afterwards suitably connected to the testing apparatus. The
test is made by simply touching the socket concerned with one of the fingers so
provided.
The indicating instrument used for testing may consist of a galvanometer, an
electro-magnet, a voltameter, a telephone or any device adapted to respond promptly
to the passage of a current.
As the branches between the connecting cords and earth are of equal resistance,
inertia and capacity, the efficiency of the subscribers' metallic circuits will not be
impaired by the derivations to earth.
The invention may be varied in detail. For instance, instead of connecting each
conductor of a cord to earth through a resistance, as hereinbefore described, each
conductor may be connected to one plate of a condenser, or to one circuit of an
induction coil or of a phonopore, the source of electricity and earth being joined to the
other plate of the condenser or circuit of the induction coil or phonopore. When
either of these plans is adopted the source of electricity employed should preferably
be one capable of furnishing intermittent currents or reversals and the operator's
indicating instrument should be adapted to reveal the passage through it of such
currents.
As in the first plan described, the source of electricity may be placed in circuit
with the testing-cord. In that case the earth is joined direct to the second plate of
the condenser or circuit of induction coil or phonopore.
The condensers, coils or phonopores connected to the conductors of a cord should
be as nearly as possible equal in capacity, resistance and dimensions, otherwise the
efficiency of the subscribers' metallic circuits will be impaired.
Dated this Twenty-second day of July 1891.
COMPLETE SPECIFICATION.
Improvements in Telephonic Switching Apparatus.
I, ALFRED ROSLING BENNETT, of 22, St. Alban's Road, Harlesden,
London, N.W., Electrical Engineer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement :-
The object of any invention is in a telephone exchange operated by metallic
circuits and multiple switch-boards constructed conformably to my Specification
No. 19486 of November 29th, 1890, to provide a method by means of which the
operator at any one section of such a multiple switch-board can, by applying a test,
discover whether any particular metallic circuit is connected at any other section.
The test I provide enables the operator at one section to tell whether a connecting
cord is in at any other section. The test does not necessitate the use of any special
or additional wire and at the same time does not interfere with conversations which
may be proceeding on the metallic circuits to which it is applied. The test is
likewise so contrived as to detect any defect of insulation in the metallic circuits in
connection with which it is used. In this respect it forms an unusual and useful
auxiliary to a telephone exchange since a subscriber's line that falls below any degree
of insulation that may be predetermined by the engineers in charge always tests as
though engaged, so that, until repaired, the operators are automatically warned
against using it.

page_text: Each connecting cord for metallic circuit switching necessarily consists of two
insulated conductors. From each conductor of such a cord, preferably from its
centre, I lead a branch wire or conductor through a resistance which may
conveniently consist of a coil of insulated wire wound on a bobbin, but it may also
be made up of liquid, carbon or any other suitable conductor. The resistance may
or may not be combined with cores, sheaths or condensers for the purpose of
increasing the magnetic inertia and static capacity of the branch wire or conductor.
To attain the best results it is necessary that the branch from each of the conductors
in a cord should be as nearly as possible alike in resistance and other electrical
conditions. To prevent variations due to changes of temperature the material
employed should be alike in each branch and to save space, when wire is used both
resistances may be wound on the same bobbin. All the connecting cords used with
the switch-board should be so fitted.
Each operator is provided with a testing apparatus consisting of a flexible
conducting cord tipped with metal, which cord is permanently connected to a source
of electricity and to an instrument capable of indicating visibly or audibly when a
current of electricity passes through it, substantially in one or other of the various
ways to be hereinafter set forth.
All the branch wires or conductors are joined after passing through the resistances
aforesaid and are then connected to earth as is also the circuit containing the
indicating instrument, testing cord and source of electricity.
To test, the operator applies the metal tip of her testing cord to the metal
socket or other contact device of the metallic circuit wanted which is before her on
her section of the switch-board. If there is no connecting cord in a socket of the
same metallic circuit on any other section the indicating instrument will not be
affected since the circuit of the source of electricity will remain unclosed. The
absence of a signal will show that the metallic circuit wanted is not engaged at any
other section and the operator may accordingly connect it on hers.
But if a connecting cord is in a socket on any other section the indicating instru-
ment will reveal a current the moment the tip of the testing cord is applical to the
socket, since a circuit of the source of electricity will now be closed and a current
will circulate. The operator will then know that the metallic circuit wanted is
engaged and must not be connected on her section.
Instead of the source of electricity being in the circuit of the testing cord it may
be placed in the branches between the connecting cords and earth. In this case the
operator's testing apparatus consists only of a flexible cord tipped with metal
connected through the indicating instrument to earth. On applying the tip to a
socket she, as before, obtains a current only when a connecting cord is in at some
other section.
An effective arrangement of the essential parts of my invention is shown in
Figure 1 of the accompanying drawings in which C' C' represent the two conductors
of the flexible connecting cord; B' B the branch wires or conductors therefrom;
R¹ R' the resistances; the source of electricity; A, A, A, A, the contact pieces
of the switch-pegs or spring-jacks; T' and T the flexible conducting cord and
metal tip of the operator's testing apparatus; I a polarized relay; La local battery
and O the operator's telephone.
Figure 3 of the accompanying drawings shows the general arrangement of the
connections according to one effective method of carrying out my invention. In
this figure, as in all the other figures subsequent to it, five metallic circuits, M¹ to Mo,
are shown each of which has sockets or contact devices represented by small
semi-circles on three sections, S' S' S³, of the switch-board. Two pairs of the
metallic circuits, namely M M and MM, are represented as joined by two pairs
of connecting cords and the fifth, M³, is shown as out of use. A third pair of
connecting cords is shown but not as in use. In all the figures R' R' represent the
balanced resistances; V the source of electricity; I'II³ the indicating instru-
ments; T¹ T' T' the testing cords of which each operator has one; C¹ C³ the

page_text: conductors of the connecting cords and P₁ to P' the subscribers" telephones at the
distant ends of the metallic circuits. The equipment shown is for three operators
but these and the connecting cords may be multiplied to any desired extent.
It is evident that the application of a testing cord to any of the contact devices
of the disengaged metallic circuit, M, will not result in a signal on the indicating
instrument since no circuit would thereby be established. But it is plain that a
similar application to any of the contact devices of the metallic circuits which are
in use, Mi to M', would cause a signal since the circuit would be closed through
one or other of the resistances R₁ R². For instance, an operator testing M
at S with testing cord T would immediately be advised by a signal on the
indicator I.that a connecting cord is already in at some other section, say at S³
as shown.
The same result may be attained by disposing the apparatus in different ways
as represented in Figures 4, 5 and 6. According to these last two plans the
source of electricity is divided and the divisions placed at V1 V2 V3.
For practical purposes the resistances R' R' may each equal 3000 ohms;
the source of electricity V may be a voltaic battery; a revolving magneto or
dynamo generator; a thermo-pile; the secondary of an induction coil with make-
and-break contact, or any torin of vibrator, pole-changer or interruptor; while
the indicating instrument may be a telephone, a voltameter, a galvanometer or
any suitable form of electro-magnet, with resistances of 3000 Ohms as stated
the source of electricity may consist of ten ordinary Leclanché cells joined in
series and the indicating instrument may be a polarized relay, wound to a
resistance of 600 ohms, of the patterns known as the l'ost Office or the Siemens.
The click of the relay armature may be used as the signal but if a louder one
is desired the relay may be made to close the circuit of a local battery consisting
of one or two Leclanché cells and an ordinary electric bell or other suitable
instrument, or of the operator's telephone as shown in Figure 1.
It will be understood that as the branches containing the resistances R¹ R³
are equal in their electrical properties the balance of the metallic circuits will
not be disturbed and their efficiency consequently not impaired by the derivations
they create.
The metallic tip of the operator's flexible testing cord may advantageously be
in the form of a thimble or finger stall wholly or in part made of conducting
material. Such a contrivance is shown in Figure 2. These thimbles or finger-
stalls, two of which may with advantage, although one may be made to do, be
worn by an operator, one on a finger of each hand, are connected to the
indicating instruments by flexible conductors which may be loosely bound along
the operators' arms. The test is made by simply touching the socket concerned
with a finger provided with such a thimble.
My invention may be further modified in the manner indicated in Figure 7 of
the accompanying drawings. With this plan a source of electricity yielding
intermittent, vibratory or alternating currents, such as a rapidly revolving
magneto, a pole-changer, a make-and-break_interruptor or a Rhumkorff induction
coil, may advantageously be employed. The two conductors, C¹ C², of the
connecting cord are bridged by the primary, H', of a phonoporic induction coil,
which may be of 6000 Ohms resistance, superimposed on which is its secondary, H*,
which may be of 300 Ohms resistance. The poles of the source of electricity, V,
being connected respectively to earth and to H the application of the test will,
if a cord is in, yield a click or signal on the indicating instrument, I, which,
with this plan, should be a telephone or some other form of electro-magnet
delicate enough to reveal the currents from the source of electricity, V, that
are induced through the phonoporic coil H' H*. In this modification of my
invention the source of electricity may be divided and its position varied
similarly as shown in Figures 4 and 6 for the plans illustrated in Figures 3
and 5.

page_text: 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. In telephone exchange systems worked with metallic circuits and multiple
switch-boards constructed according to my Specification No. 19486 of 1890, the
system of operators' test, with its several modifications, substantially as herein
described and drawn.
2. In operators' testing systems for use in telephone exchanges with multiple
switch-boards constructed as aforesaid, the application to each connecting cord of a
leak to earth, either direct or through a source of electricity, in such a way as not
to disturb the balance or efficiency of the metallic circuits connected together by
means of such cord. This claim is exemplified in Figures 1, 3, 4, 5 and of the
accompanying drawings.
3. In operators' testing systems for use in telephone exchanges with multiple
switch-boards constructed as aforesaid, the employment of a derivation or bridge,
without earth, between the two conductors of each connecting cord and the application
by induction to such derivation or bridge of currents capable of inducing similar
currents in the conductors of the connecting cord and consequently in the metallic
circuits connected by such cord without destroying the efficiency of the metallic
circuits. This claim is exemplified in Figure 7 of the accompanying drawings.
4. In operators' testing systems for use in telephone exchanges, for the purpose of
facilitating the application of the test by the operators, the use of a thimble or
finger-stall wholly or in part made of conducting material and constructed sub-
stantially as herein described and drawn.
Dated this Tent