Central Battery Telephone Exchange System.
Year: 1896

page_text: Date of Application, 25th June, 1895
Complete Specification Left 25th Mar.. 1897-Accepted. 19th June, 1897
PROVISIONAL SPECIFICATION.
Central Battery Telephone Exchange System.
We, DANIEL SINCLAIR, Engineer-in-Chief to the National Telephone Company,
Limited, Oxford Court, Cannon Street, in the City of London, and WILLIAM AITKEN,
Engineer with said Company at above address, do hereby declare the nature of this
invention to be as follows:
The object of this invention is to improve the efficiency of an exchange system
generally and particularly to simplify the operating both for the subscriber, and the
operator at the exchange, so that as a result the latter will be enabled to attend to
about twice the number of lines that she does with the systems at present in use,
and consequently the cost of the multiple switch boards will be reduced, as only half
the present amount of jacks and cable will be required. Any of the forms of metallic
circuit multiple jacks at present in use may be employed, but preferably the 5-point
branching jack-two line springs, and test spring that breaks contact with the barrel,
and nakes contact with earth strip when plug is inserted-is used. These jacks are
connected to the cable in the ordinary way. Across each metallic circuit line a
special indicator is bridged. This indicator may be of either of two forms-
a. It may consist of two parallel bobbins, each wound in the same direction, or
differentially to 500 ohms-or other resistance, the inside end of each coil being.
brought to a tag for connection to battery. Both coils are sheathed in the usual way
for self induction. The vibrating arm has a light aluminium shutter with black and
white strips. In front a fixed plate is cut with similar spaces through which these
strips show. When the line is clear the indicator shows, black, when the subscriber
calls it shows white.
b. It may consist of two parallel. bobbins, one wound to 1000 ohms-or other
resistance, either differentially or otherwise, with centre point brought out to
soldering tag, the other wound to 100 ohms--or other resistance,-this second coil.
only being used as the indicator with shutter, &c., as before described, the centre
point of the first coil being joined to one side of the second, the other side to battery...
Both coils are sheathed for self induction. The first described coil is placed in bridge
across the metallic circuit. The connecting cords are of the usual type with a
special indicator as before described bridged across. These indicators may be of
higher resistance than the line indicators. The centre point is joined to earth. A
listening key is also inserted by which the subscriber is answered, and the wanted line
tested. The engaged test. is got in the ordinary way but no test battery is necessary.
Accumulators or other source of electricity, may be used for the permanent current,
and these are grouped as required.
The subscriber's instrument is, similar to the form at present in use, but the
connections are modified, so that when the switch is down the bell only is in circuit,
with centre point to earth. When the switch is up the earth and bell are out of
circuit, and the receiver and secondary only in circuit, with the generator armature
short circuited. When the crank is turned the receiver, &c., is short circuited, and
the armature brought into circuit.
In the operation of the system the battery is normally connected to line, and line
indicators thereby held down.
1. Subscriber lifts receiver off switch, and indicator in exchange shows white.

page_text: 2. Operator inserts answering plug in subscriber's line jack and subscriber gives
number of line wanted.
3. Operator tests line wanted by touching front of jack with tip of calling plug, and
if there is no click in receiver, inserts plug. If engaged she can reply in usual way by
voice, or she can insert plug into a special jack connected with vibrator which will
give a definite sound to subscriber, which shall be known as the engaged reply.
When subscriber hangs receiver on switch the line is to be cleared. The insertion of
the plug into the jack of the subscriber wanted, gives the current through the line
indicator another path to earth, through the clearing indicator, so that this line
indicator does not move when the called subscriber lifts his receiver off the switch.
The current through the line indicators to earth through the clearing indicator, also
sets the latter, causing it to show white.
4. Calling subscriber rings subscriber wanted. This does not indicate in the
exchange.
5. When conversation is finished either subscriber putting receiver on switch
indicates "finished" in the exchange, the current being shunted from the clearing
indicator to earth through subscriber's instrument, and the current now passing
through being insufficient to hold it down it therefore shows black.
. 6. Operator pulls out plugs.
The operator's instrument need not be differentially wound.
Part of this system can be used in conjunction with existing exchanges, the present
ring-off indicator being removed, and the pattern clearing indicator substituted and
connected to an earthed battery. The centre of bell at subscriber's instrument should
be earthed. The subscribers can then call each other without affecting the exchange,
and either subscriber putting receiver on switch can give the signal to clear the lines.
In the exchange system described arrangements may be made for charging
subscriber's local batteries from the central battery used for holding down the
indicators, the switch held down by the receiver having the connections so altered
that when the telephone is not in use for speaking the current from the central
battery passes through the local battery. When the switch is up the earth could be
cut off and the circuit so arranged that the local battery would be discharging through
the microphone circuit. The local battery may be a simple form of secondary call or
accumulator made to suit the requirements.
Dated this 24th day of June 1896.
WALLACE FAIRWEATHER,
Chartered Patent Agent, 62 St. Vincent Street, Glasgow,
Agent for the Applicants.
Central Battery Telephone Exchange System.
We, DANIEL SINCLAIR, Engineer-in-Chief to the National Telephone Company,
Limited, Oxford Court, Cannon Street, in the City of London, and WILLIAM AITKEN,
Engineer with said Company at above address, 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 this invention is to improve the efficiency of an exchange system
generally and particularly to simplify the operating both for the subscriber, and the
operator at the exchange, so that as a result the latter will be enabled to attend to
about twice the number of lines that she does with the systems at present in use, and
consequently the cost of the multiple switch boards will be reduced, as only half the
present amount of jacks and cable will be required.

page_text: The object of the invention is attained by the following means:-
Firstly. By arranging the apparatus at the sub station and the central station in
such a manner that signals are automatically transmitted from the sub station to the
central station, in a novel manner, when the subscriber wishes to attract the attention
of the central station, either to obtain a connection, or a disconnection from .a
connection already obtained, each of these signals being distinct from the other.
Secondly. By so arranging the apparatus in the central station that one subscriber
may ring the other subscriber without disturbing the indicators at the central
station.
Thirdly. By so arranging the circuits at the central and sub stations that the
magneto generators usually provided at the subscribers' instruments are unnecessary.
Fourthly. By so arranging the apparatus at the central and sub station that the
central battery will not be discharging normally, but only during conversation.
Fifthly. By providing means whereby the secondary batteries for working the
transmitters at the sub stations may be continuously charged during such time as the
instruments are not in use.
The invention is illustrated by the accompanying drawings,
Fig. 1 of which is a diagrammatic representation of the circuits and apparatus at the
central and sub stations according to our invention, whereby the sub station is enabled
to automatically signal to the central station by the removal or replacement of the
receiver on the switch-hook.
Fig. 2 is a similar view showing the arrangement of the circuit at the sub-station
and central station when the magneto generator at the sub-station is dispensed with.
Fig. 3 is a diagram of modified connections of our invention as applied to multiple
switchboards in which make-and-break or series jacks of any of the well known'
patterns are used.
Fig. 4 shows the modification of the circuits and apparatus at the sub-stations when
the local circuit batteries are charged from the central station during such times as
the instruments are not in use.
In the various modifications of our central battery telephone exchange system
illustrated by Figs. 1, 2 and 3, we preferably use metallic circuits between the. sub
station and the central station, extended through the switchboard on what is commonly
known as the 5-point branching jack (although any of the well known forms of
branching or make-and-break jacks may be used) composed of two line springs a, b,
and test spring c, the latter normally making contact with the bush or barrel d, of
the jack, but when the plug is inserted is lifted by means of a vulcanite stud, placed
on the line spring b, against the earth or common return strip e.
At a convenient point in the central station and across each metallic circuit a special
This indicator may be
indicator g may be bridged between the line springs a and b.
of either of two forms, viz., a differentially wound coil of suitable resistance and high
self-induction, or two separate coils of suitable resistance and high self-induction.
These coils may be used as the line indicators or part thereof, although preferably we
use them only as bridging coils, and they may consist of two parallel bobbins, each
wound in the same direction, or differentially to 00 ohms or other resistance, the
5 inside end of each coil being brought to a tag for connection to battery. Both coils
are sheathed in the usual way for self induction. The vibrating arm has a light
aluminium shutter with black and white stripes. In front a fixed plate is cut with
similar spaces through which these stripes show. When the line is clear the indicator
shows black, when the subscriber calls it shows white.
As an alternative to the indicator or bridging coil above described we may use an
indicator which consists of two parallel bobbins, one wound to 1000 ohms-or other
resistance, either differentially or otherwise, with centre point brought out to soldering
tag, the other wound to 100 obms or other resistance, this second coil only being
used as the indicator with shutter, &c., as before described, the centre point of the
Both coils
first coil being joined to one side of the second, the other side to battery.
are sheathed for self induction. The first described coil is placed in bridge across the
metallic circuit, and a connection is taken from the centre-point to a suitable

page_text: indicator ', adapted to respond to a battery current (the said indicator may be of any
well known patterns, such as the grid, suspended or balanced shutter, needle, or a non-
inductive indicating device) thence to a battery or other suitable source of electricity J
the other pole of which is connected to earth. The apparatus provided at the central
station for connecting two subscribers' lines together consists of the usual 2-way
plugs and k² joined together by flexible conductors, a bridging coil or coils of
suitable resistance and high self-induction being joined across, and a connection being
taken from the centre point to a battery indicator m of any of the well known forms,
this in turn being joined to earth. A connection is also taken.from each conductor of
the connecting cord to a switch or listening key n, of any of the well known patterns,
so as to allow of the operator answering a calling subscriber, and testing the line of
the wanted subscriber in the ordinary way but without the necessity of using a test
battery. A socket contact q is fitted in the plug hole of the answering plug k', and
so connected that when the answering plug is in its position of rest a current from the
central battery finds a path through a suitable resistance p, (preferably the average
resistance of the subscriber's circuit) through the contact q, through the clearing
indicator m, and so to earth.
At the sub station the apparatus provided preferably consists of what is known as
the magneto generator and call bell with the connections of the usual automatic
switch so arranged that when the receiver s is on the hook of this switch, the bell
(preferably of low resistance) is joined to the two lines, and the centre-point of the
bell is connected to earth, through the spring t. On the receiver being removed from
the automatic switchhook the local circuit is closed in the well known manner, and the
bell and earth are cut out of circuit. The secondary coil y' of the induction coil, and the
receivers are joined in the circuit, the armature of the generator w at the same time
being short circuited. When the generator handle is turned the armature is thrown
into circuit, and the secondary coil of the induction coil y' and the receiver s are short
circuited in the usual well known manner.
We will now describe the operation of our invention with reference especially
to Fig. 1.
In the operation of the system the battery is normally connected to line, and line
indicators thereby held down. Normally the current from the central battery or
other source of electricity passes through connection, through line
indicators and 2 to the centre of the bridging coil or coils and g² over the
lines a and b, through the bell coils u, and from the centre point to the spring,
and so to earth. This current energises the line indicators and 2. Subscriber A
wishing to be put in connection with subscriber B lifts his telephone receiver s from
the switch-hook; this closes his local circuit, cuts the bell and earth from circuit
with lines a' and ', and joins up the secondary coil y' of the induction coil and the
receiver s in circuit with lines a', 6'. The current from battery j now finds no path
"to earth, consequently the line indicator is no longer energised, which indicates
to the operator by the indicator showing white that subscriber A desires attention.
The operator then lifts the answering plug from its socket and inserts it into
subscriber A's springjack, and replies in the usual manner. The insertion of the
plug into A's spring jack again energises the line indicator ', and restores it to its
normal condition. On receipt of A's order to connect him with B the operator
touches the barrel or bush d of the nearest jack of B's line with the tip of the calling
plug. If the line is not engaged at any other section of the board her receiver o
will remain silent, if engaged a current will flow from the main battery j, through
indicator ', bridging coil g, and the line springs a and b of the answering jack,
through the tip and sleeve of the answering plug k¹, part finding a path to earth
through bridging coil and indicator m, and part through listening key n to operator's
receiver o, and through the tip of the calling plug k, through the barrel d of the
springjack of B's line, through spring c, to earth at the line jack in which a plug is
inserted. The operator will then so inform the subscriber either by voice, or by
inserting the calling plug 2 in a jack with (1) a battery and vibrator, or (2) a
phonograph in circuit which will send over the line to the calling subscriber (1) a

page_text: "
definite sound which shall be known as the busy or engaged signal, or (2) repeat
busy or other similar word which will indicate the condition of the line wanted.
Supposing B's line tests free, the operator inserts the calling plug k³, depresses
the plunger of listening key n, and thereby cuts her receiver o out of circuit.
The insertion of the calling plug into the jack of B's line, provides another path for
the current from the battery i, through the line springs a and b, through the tip and
sleeve of the calling plug through bridging coil or coils l, and through clearing
indicator m, (thereby energising it) to earth. This causes the line indicator to
remain energised, and therefore inoperative to any changes in the condition of the
circuit; e.g., when subscriber B lifts his receiver off the switch hook to reply.
The subscribers are now in a position to ring (with receiver off hook), and
communicate with each other without disturbing the line indicators and 2.
On completion of the conversation the placing of one or both receivers on the
switch-hooks at sub-stations A and B indicates "finished" to the exchange and
shunts some of the current from central battery j over the two subscribers' lines
to earth at the sub stations A and B, thus depriving the clearing indicator m of a
large proportion of the current, the remainder of the current then being
insufficient to effectively energise the clearing indicator, said indicator shows white,
thus giving a distinct signal that the two subscribers' A and B have completed their
conversation.
It will readily be observed that the apparatus and circuits shown at Fig. 2, are
a modification of Fig. 1, and we will now proceed to describe the variations and
the object of the same. At the central station the variation consists of the
provision of a suitable listening key and ringing key, and these may be of any of
the well known patterns, and also of a source of ringing current either continuous or
alternating according to the class of bell used at the sub-station.
At the sub station the apparatus provided preferably consists of a call bell (which
may be either of the trembling or polarized pattern) with the connections of the usual
automatic switch r (Fig. 2) so arranged that when the receiver s is on the hook of
this switch, the bell (preferably of low resistance) is joined to the two lines, and the
centre point of the bell is connected to earth, through the spring t. On the receiver
being removed from the automatic switch-hook the local circuit is closed in the well
known manner, and the bell and earth are cut out of circuit. The secondary coil y'
of the induction coil and the receivers are joined in the circuit.
We will now describe the operation of our invention with reference especially
to Fig. 2.
In the operation of the system the battery is normally connected to line, and the
line indicators thereby held down. Normally the current from the central battery
or other source of electricity. j passes through connection, through line
indicators and to the centre of the bridging coil or coils and 3 over the
lines a and b, through the hell coils u, and from the centre point of the spring t,
and so to earth. This current energises the line indicators and A. Subscriber A
wishing to be put in connection with subscriber B. lifts his telephone receiver s from
the switchhook; this closes his local circuit, cuts the bell u and earth from circuit
with lines a' and b', and joins up the secondary coil y' of the induction coil and the
receivers in circuit with the lines a', 6'. The current from battery j now finds no
path to earth, consequently the line indicator is no longer energised, which
indicates to the operator by the indicator showing white that subscriber A desires
attention. The operator then lifts the answering plug k¹ from its socket and
inserts it into subscriber A's springjack, and replies in the usual manner.
insertion of the plug into A's springjack again energises the line indicator ¹,
and restores it to its normal condition. On receipt of A's order to connect him
with B the operator touches the barrel or bush d of the nearest jack of B's line with
the tip of the calling plug 2. If the line is not engaged at any other section of the
board her receiver o will remain silent; if engaged a current will flow from the main
battery j, through indicator h³, bridging coil g', and the line springs a and b of the
answering jack, through the tip and sleeve of the answering plug k¹, part finding a
The

page_text: path to earth through bridging coil and indicator m, and part through listening
key to operator's receiver o, and through the tip of the calling plug 2, through the
harrel of the springjack of B's line, through spring r, to earth at the line jack in
which a plug is inserted. The operator will then so inform the subscriber either by
voice, or by inserting the calling plug 2 in a jack with (1) a battery and vibrator, or
(2) a phonograph in circuit which will send over the line to the calling subscriber
(1) a definite sound which shall be known as the busy or engaged signal, or (2) repeat
"busy" or other similar word which will indicate the condition of the line wanted.
Supposing B's line tests free, the operator inserts the calling plug 2, and with the
listening key n in the position shown in Fig. 2, depresses the plunger of the ringing
key in connection with plug 2, thereby sending a current to line which rings the
subscriber wanted, thus rendering the use of a magneto-generator unnecessary.
After subscriber B has answered, the operator throws up the key thereby cutting her
telephone out of circuit. The insertion of the calling plug into the jack of B's line,
provides another path for the current from the battery j. through the line
springs a and b, through the tip and sleeve of the calling plng k through brilging
coil or coils, and through clearing indicator m, (thereby energising it) to earth.
"This causes the line indicator 2 to remain energised, and therefore inoperative to
any changes in the condition of the circuit; e.g., when subscriber: B lifts his
receiver off the switchhook to reply. On completion of the conversation the
placing of one or both receivers of the switchhooks at sub stations A and B
indicates "finished" to the exchange, and shunts' some of the current from central
battery over the two subscribers' lines to earth at the sub stations A and B, thus
depriving the clearing indicator m of a large proportion of the current, the
remainder of the current then being insufficient to effectively energise the clearing
indicator, said indicator shows white, thus giving a distinct signal that the two
subscribers' A and B have completed their conversation.
We will now proceed to describe our invention as adapted for central stations
where make-and-break jacks are used, as shown in Fig. 3. Any of the forms of
metallic circuit multiple jacks at present in use may be employed, and the connections
on the subscriber's switch hook modified so that the centre of the subscriber's
instrument is put to earth when the receiver is off the hook, which is the reverse
of that described with reference to Fig. 2 of the drawings.
The apparatus necessary at the central station for the line circuits is as before
described in connection with Fig. 1, with the exception of the jacks. The apparatus
for connecting two sub-stations together is as before described for Fig. 1, with the
exception that the indicating device m in the cord circuit instead of being connected
direct to earth, is joined to the central source of electricity j.
At the sub-station the apparatus may be of either of the patterns described in
connection with Figs. 1 and 2, with the exception that the secondary circuit of the
transmitter induction coil y and also the receiver s are differentially wound, the two
main terminals of the receiver being connected to the two inside ends of the
differentially wound secondary coil, and the centre point of the receiver being joined
to spring t so that an earth may be joined to the centre point of the receiver on
the same being removed from the switchbook.
Normally the central source of electricity, although in connection with the lines,
finds no path until such time as the receiver is taken off the switchhook, the path
then being through indicator ', bridging coil or coils g', inner contacts a and b,
jacks spring a and b, through both circuits of the differentially wound secondary coil,
through the receiver to earth, energising indicator, and thus attracting the attention
of the operator who then proceeds to answer, tests the jack of the line wanted, and if
free connects and rings in the manner previously described in connection with Fig. 2.
The insertion of the plugs k¹ and k into the line jack lifts the springs a and b from
the inner contacts a² and 62, thus cutting the bridging coils g' and g², and line
indicators and 2, out of circuit, and the clearing indicator m is energised by
the current from the central source of electricity, finding a path through the
bridging coil, the lines of A and B subscribers and the secondary coils and

page_text: receivers of both sub-stations to earth. On one or both of the subscribers A and B
replacing the receiver in the switch-hook the clearing out indicator m is no longer-
effectively energised and gives the signal to the operator that the subscribers have
completed their conversation.
Part of this system can be used in conjunction with existing exchanges, the present.
ring-off indicator being removed, and the alternative form of indicator already
described, substituted and connected to an earthed battery. The centre of bell at.
subscriber's instrument should be earthed, the instrument circuit being as shown on
Fig. 1. The subscribers can then call each other without affecting the exchange, and
either subscriber putting receiver on switch gives the signal to clear the lines.
In the exchange system described arrangements may be made for charging
subscriber's local batteries from the central battery used for holding down the
indicators, the switch held down by the receiver having the connections so altered
that when the telephone is not in use for speaking the current from the central
battery passes through the local battery. When the switch is up, the earth could be.
cut off and the circuit so arranged that the local battery would be discharging through
the microphone circuit. The local battery may be a simple form of secondary cell or-
accumulator made to suit the requirements.
Fig. 4 shows method of charging the secondary cells of the primary circuit at.
the sub-station from a central source of electricity. This may be used in conjunction
with the system and its modifications previously described, the addition to the
sub-station instrument being a switching device on the automatic switch-hook for
connecting the local circuit battery to the line wires and earth when the receiver is on the-
switch-hook, and disconnecting the lines and earth from the local circuit battery and
connecting the battery to primary circuit of the transmitter on the removal of the-
receiver. To enable the circuit to be clearly understood we have lettered the various.
connections. The current from the central source of electricity when the receiver is.
on the switch-hook finds a path through the line indicator, bridging coils g¹, and
the lines a and b, through the calling bell a (which may be specially wound) to-
the central point 2, through the local battery », connection 2, through spring t to.
earth. When the receiver is off the switch-hook, there is no current over the lines,
as the earth has been cut off at spring t. The local circuit battery v is joined up.
to the primary y of the induction coil, through 2, contact 3, microphone 2, and
contact v, and connection v.
This invention admits of modifications in the arrangements which would readily
suggest themselves to those skilled in the art. We therefore do not limit ourselves.
to the precise arrangements shown or described herein.
Having now particularly described and ascertained the nature of our said inven--
tion, and in what manner the same is to be performed, we declare that what we-
claim is :-
1. The improved system of automatic signalling on telephonic systems substantially-
as herein before described under several modifications with reference to the annexed.
diagrams.
2. The combination of the hereinbefore described circuits of automatic signalling on
telephonic systems in conjunction with a central source of electricity for charging the-
local circuit battery substantially as set forth.
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather,
Chartered Patent Agents,
62 St. Vincent Street, Glasgow, Agent for the Applicants..
WALLACE FAIRWEATHER,
Of the Firm of Cruikshank & Fairweather,
Chartered Patent Agents,
Vincent Street, Glasgow, Agent for the Applicants..