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Патент USA US2408434

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Oct. 1, 1946.
Filed 'Feb. 13, 1943
14 Sheets-Sheet 1
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operated position.
These three relays control
tains to the establishment of local connections,
remains substantially unaltered. The operation
ofthe link, therefore, with respect to the estab
li’sl'i'inent of local connections is not described
herein, reference being made to the above patent
the sequential allotment of an available link to a
calling line, and the function of the relays CHI
and CH2 in the positions shown is to route the
start conductor I to the ?rst available link in
the of?ce. As stated before, in the present em
bodiment of the invention it is assumed that the
quantity of traffic from and between the various
lines of the o?ice, including trunk service to the
central manual o?ice, may be adequately handled 10
for a description of said operation.
We may now assume that station A desires to
establish a connection to the manual central
o?ice. To do so the station attendant removes
the telephone instrument from its cradle and then
waits for “key” tone upon receiving which he
CHI, CH2 and CH3 serve to route a calling line’ 7 keys an arbitrarily assigned digit indicative of
to one of the three links depending upon which
the trunk connected and, thereafter, keys his own
one of them is free in the order-of allotment.
a station line number,'that is, 20. The removal
The operated condition of relay CHI indicates
of the telephone instrument from the cradle com
that the link to which it provides access is in the
pletes a circuit for line relay L20 which extends
idle condition, the relay remaining locked until
from battery,’ over the No. 1 normal contacts
said link is taken into use, the locking circuit of
of the hold magnet H020 associated with versaid relay extending from battery, through the
tical 20, winding of relay L20, ring conductor R,
winding thereof, contacts of key KYI, conductor 20 over the station loop, tip conductor T, No. 3 norby the use of only three links so that the relays’
2, No. l’back'contacts of relay B of link No. 1
mally made contacts of relay L20 to ground on
(Fig. 6), conductor 3, No. 3 front contacts of re
the No. 2 contacts of cut-oil relay C020. Relay
lay CH I to ground. The, locking circuit of relay
L20 operates. Over its‘No. 3 front contacts, the
CH2, which controls access to link No. 2, is traced
ground terminal of its circuit is switched from:
over a path which extends from battery through 25 solid ground on the No. 2 contacts of relay C020‘
the winding of said relay, contacts of key KY2,
to ground through the secondary winding of
conductor 2' in the bracket line 4, the No. 1
transformer LBT to the primary winding of,
Iback contacts of relay B in link No. 2 (said
which is connected a source of distinctive tone
link being conventionally indicated in Fig. 11),
which, as will be shortly described, is transmitted
conductor 3' in the bracket line 4, No. 6 contacts 30 to the calling line in the event that no link is
of relay CH2 to ground.
available for completing the connection.
On the other hand, the operating circuit of re
Over its No. 1 and No. 2 contacts, relay L20
lay CH3, which provides access to link No. 3,
causes a circuit to be completed for'relay L020
while traceable over the contacts of its associated
of the call allotter circuit (there being one relay
key KY3, conductor 2" within the bracket line
LO—; for each line) and ‘relay vST of link No. l
5, through the No. 1 back contact of relay B of
which, since relays CHI and CH2 of the link al
link No. 3 (said link being conventionally indi
lotter are assumed to be operated and relay CH3
cated in Fig. 11), and conductor 3" within the
isassumed to be ‘normal, is thepreferred link in
bracket line 5, terminates in the No. 3 normal
the orderof selection. The circuit for the relays
contacts of relay._CH3 and also in the No. 3 open
ST and L020 is traced as follows: ground
contacts of relay CHI.
In other words, for a calling line to have accessi
bility to link No. 1, relays CHI and CH2 must
bev operated and relay CH3 must be normal.
through the No. 1 contacts of relay EI, winding
of relay L020, conductor 6, No. 1 and No. 2 con
tacts of relay L020, start conductor I, No. 3 con
tacts of 'relay CH2, No. 1 contacts of relay CHI,
will be shown that as each link is allotted in ro~
tation, the circuits of relay CHI, CH2 and CH3
' conductor ‘I. winding .of relay‘ .ST to battery.
Both relays L020 and ST operate in this circuit.
are changed to provide for the advancement or
Relay L02 0, upon operating‘, completes a’circuit
start conductor I from one link to the next in
for‘ relay N, the path of‘ which may be traced
from ground on the N0. 1 contacts, of relay L020,
conductor I 0, No. 1 back contacts of relay M,
the order designated by the numerical indication’
of each of the three links.
Bearing in mind that relays» CHI,‘ CH2 are’
assumed to be operated and that relay CH3 is
No. 4 contacts of relay MS, winding of relay N
to battery. Relay N operates and completes a cir
cuit for relay M which extends from ground on
the No. 2 contacts of relay N, No. 1. contacts of
assumed to be normal, it may now be further as
sumed that a call is originated at station A (line
20) for a trunk connection to the manual cen
55 relay MS, winding of relay M to battery. Relay
tral ofiice. As before stated, the present inven
M operates, opens the circuit of relay N at its
tion is in the nature of an improvement over
No. 1 back contacts and causes thelatter relay
the small capacity oflice disclosed in my Patent
to release. ‘ The release of relay N opens the oper
2,300,951, in which the stations thereof are
ating circuit of relay M but this latter relay,
equipped either with a'dial device or an alternat 60 however, remains‘locked to ground on conductor
ing current generating device, and in which'links
I0 under the control of the No. 1 contacts of re-'
are provided whereby local connections between
lay MS and its own No. 2 contacts. When relay
the several lines may be established over said links‘
MS operates, as described below, relay M re
by the dialing or keying the number of the want
leases. ' This cycle for operating relays M and'N
ed station. In the present invention, each of the
stations is assumed to be provided with an al
ternating current device LG andv that local con
nections between the several stations in the of;
?ce may be established over the links in the mane
ner described in said patent. Although the link
circuit herein shown ‘and used has been modi?ed
in somerespects over the link ‘in ‘said patent to
provide for the performance of functions essen
tial to the operation‘ of_ the features of the Pres-'
ent invention, its structure, is so far' as it per 75
ordinarily performs no useful function, but will
perform an emergency function which will be ex_
plained in due course. At the same time, relay
L020 completes a circuit for relay E which may
be traced from ground on the N0. 1 contact of
relay EI, No. 2 contacts of relay L020, conductor
8, serially through the No. 1 back contacts of the
individual link relays LK3, LKZ, and LKI in
the call allotter, conductor 9, winding of relay E
to battery. Upon operating,‘ relay E locks to
ground on the No. 1 contacts of relay L020 and,
. 2,408,433
5' -
at the same'rtimey-closes a circuit for ‘relays El
and ‘E2 from ground on'itslcontact-s traced there
through from the No. llcontacts of_ relay "L020,
No.2 normally made contacts of relay ‘MS, the I
windings of relay El .and E2‘, in parallel to
oirelays S and Si, .No. 3 contacts of relay L020,
conductor l9,"wind-ingvof r'elayrCO20 to battery.
‘Relay C020, upon operating, closes an obvious
circuit-,for .hold magnet H021! of the Vertical '29
to'which line-zlllstati'on A) is connected and.
because select‘magnet 9 is operatedcnoss-point
' battery. Relays El" and‘EZ operate but relay
9 on verticalyZD is also operated. This cross
L020, which operated from ground'on the No. 1
point 9 remains operated after the circuit of se
contacts of relay E‘l, now holds locked to ground
lect magnet Shae been opened, and since this
on its ‘own No.vv 1 ‘contacts from battery through
relay ‘ST'of the selected ‘link, as previously traced 10 is standard cross vbar switch operation, it will
not be ampli?ed anyfurther; When ‘hold image
to'conduc-tor 6, winding of relay L020 and its ‘No.
2contacts, conductor-8 as traced to conductor 9,
contacts of relay E to ground on the No.‘ 1 con
net H020 operates,>it releases line. relay L28
which, in turn, releases :relayLOZ? and the lat
tacts of relay L020. Hencef-with the operation
and locking of relay ‘L020 individual to the call
ing- stat-ion‘A and with theoperation of relay
El‘ and E2, all otherflines‘may not receive service
ter, upon releasing, opens‘ the circuit of 0020
and‘. further disconnects ground from start ‘con
ductor l which caused the operation of relay ST.
Relay C020 (as well as every other relay 1CO—)~
been taking place in the link as the ‘result of ‘the
this joining of conductors completes an operat
is slow release and slow operate and will holdup .
if'cal-ls are initiated'therea-t during the ‘time’ when
for the nonce ‘until a holding circuit therefor
stati'onA is havinga link assigned to its since,
with relays El and "Elv operateino ground is 20 will have ‘been completed in‘ the link as de
scribed hereinafter.‘ Also, while conductor l is
available for completing the circuit of any other
now‘ opened, the fact that cross-point 9 on ver
relay LO—- individual to a calling line.
tical 28 is closed, relay'ST will not release, it
When relay El "operates, it completes a circuit
havinga locking circuit‘t'hrough across-point
for relay MS,‘ said circuit ibeing traced from
contact,v which circuit may be traced ‘over the
ground on conductor 10, No; 14 contacts of relay
No. 2 contacts ‘of said relay, No. 1 contacts of
El, winding of relay MS to battery. Since relay
relay vT2, conductor-1m, No. ‘5 normally made
MS has slow-operating characteristics, it oper
contacts of relay LCI’, conductor Sl,"No."3 [con
ates after an interval, at which time it opens
tacts of cross-point 9 on vertical 26, resistors RC
the locking path-of relay N, supplies holding
, '
‘ground ‘over its -No. 2 “contacts ‘for-relays E I: and 30 and RCl‘to ground.
Since cross-point 9ron vertical '2!) ‘is closed, the
E2 and,"over iits No. 13 contacts,-applies ground
‘line ‘tip and ring conductors T and‘ Rare joined
‘On ‘conductor ill to‘ conductor ‘If-l; Ground on
to the'linktip and ring conductors LTzand LR,
conductor H is used vIto complete the‘ circuit of
respectively, over the vNo. 6 ‘and No. 5 contacts
the link select magnet-9 ‘in virtue of operations
of ‘the operated cross-point 9, respectively, and
which will be shortly described and ‘which have
operation of lrelayST therein.‘
ing path for relay’ A of’ the link, which circuit
' -
In'the event that, ‘due to some‘trouble cc'ndi- '
. may be traced from battery, vthrough'the lower
winding of s'aid'relay, aNo. 2 back contacts cfre
>tion,'relay LE ~of~>the ‘call allotter' fails to operate,
relay 'MS lcannot "operate andv ground will not 40 lay ‘HS, conductor LT, No, 6 vcontacts of cross
point v9 on'vértioal-Zll, line conductor '1'‘, over the
‘be applied-to 'conductor‘ll *over its No. ‘,3 ‘con
calling line vloop, ring conductor R, No. 5 con
tacts. If possible under‘ these circumstances, it
tacts ~of cross-point 9 on‘ vertical 20, conductor
‘is ‘desirable ‘to "complete v‘the connection-and so
emergency means are
provided ‘for ‘ applying
ground'to'iconductor -I‘| when relay ~MS fails ‘to
operate. lltl‘will be remembered that, upon'the
operation of ‘relay LO20, a circuit "was 'com
pleted for relay N, ‘and'thatprior ‘to the oper
ation of'irelay MS, v‘relay "N ' caused'ithe' operation
for‘ relay M. Now; when relay‘ M operates,*—itgopens
'the1circuit': of relay N, but relayiM‘ remainslocked
LR of the link, ‘No. 3 back contacts of relay HS,
upper winding ‘of relay A to ground. Relay A
operates and completes a circuit ‘for relay B
which extends from ground on conductor S'I,'No.
5 and No. 4 ‘normally made continuity contacts
on relay. LCI’, conductor ‘I02, front contacts of
‘relay‘AfNo. 4 normally made continuity con
"Hi, and it \will ‘be observed that, (with 1relay"~N
!normal and relay M-operated; -~ground-on_con_
tacts of trelayB, :winding of relay vB to battery.
ylRelay l3v operates and looks over its No. 4 front
‘contacts, conductor ‘mi; No. 5 normally made
continuity contacts on relay L'Cl’, to ground on
ductor 1015 applied to conductor ‘l‘l v"viarthe No.
conductor SI. ,At its No. 7 contacts relay B now
"over-tits v'Nol ‘2 - contacts ;to"ground~3on "conductor
‘l’front- contacts 'of relay) M and the No. 1 con
‘tacts of-relay'N. ‘
" '7
completes aiholding circuit for ‘C022 which traces
from battery through the ‘winding of "said relay
’ Returning, now, to "the operation-ofrelay'ST
C020, No. 4 and No. 2 contacts in series of cross
of the allotted link No. 1,'a circuit is'completed
point '9 in vertical 20,;conductor 51, ‘No. »'7 con
for rselect'magnet'y?, the path-'oflwhich maybe
tacts of relay B, front contactsd'f relay Afcon
trace-difrom battery, throughithewinding of said
‘magnet, ‘conductor vFL'No. 2 contacts *of relay‘B,
conductor SI. Relay 0020 thus holds'operated,
‘No. ‘i ‘contacts‘of relay-ST, conductor H, to-the
laioretra‘ced ground lthereon. ‘Select "magnet '9
operates and conditions thegroup o‘f cross-points
in the ninth horizontal 'leve'l'for *-selection,,in
cluding "cross-point "9 " on "vertical 21!] ‘through
‘which the calling loop will’be extended into-the
as ‘shown hereinafter. ‘Select Lmagnet 9,
ductor ‘I02 and thence as traced to ground on
in turn‘ holding magnet H028 ‘which keeps cross
point 9 closed. At its No.’ '2-ccntacts, relay B
opensconductor ’l-1,-thereby causing the release
of select magnet 9. ‘However, since the hold
magnet H026 is being held, across-point 9 on
vertical 20 will ‘likewise’be held. 'Relay'B ‘fur
ther completes ‘a circuit from ‘ground over its
, uponope‘rating, ‘completes a circuitfrom-ground 70 ‘No-'8 contacts to a relay» (not-shown) in the
power charge circuit I00 by means of which,
" over its contact ‘and paralleled "conductor ? I 8, ‘to
when the "relay isvoperated, circuits are ‘closed
the common‘windings of relays '~¥S~and'~‘S!, caus
"in-g isai'drelays' to" operate and complete a circuit
"for "cut-01f relay I CQZ-lktthé -_'circuit of said-relay
“being "traced "from *ground" on * the i No.- 13 ~contacts
thereby that ,willincrease the-chargingrate to
the link-power supply duringfthe time that-the
I lin-kiis'vbeing used 1and, over its "No. '5 tan'd‘uNo. "6
contacts'relay B further applies ground. to hold
conductors 20 and 2I, respectively, for-holding
and operating certain other relays as noted ,be
low. Over its No. 1 contacts, relay B opens the
locking circuit of relay CHI in the allotter cir
cuit, which, upon releasing, advances the com
mon start conductor I over the No. 3 contacts of
relay CH2, No. 2 contacts of relay CHI, No. 1
contacts .of relay CH2 to conductor ‘I’ which fur
ther extends to relay ST of link No. 2 (conven 10
tionally indicated in Fig. 11) .
the next call. If, link 2 becomes available, relay
CH2 operates over a circuit traceable fromv bat
tery, through its winding, thence ‘as traced to
conductor 3' to ground on the No. 3 normally
made contacts of relay CH3.
Returning, now, to the operation of relay ST
of link I, assumed to have been taken into use as
a result of a call having been initiated at station
A, ground on the No. 3 contacts of said relay
completes a circuit for relay LSI of its private
link connector and this circuit is tracedfrom
ground on said contacts, conductor 58, winding
It is now evident that if, at the time a call is
of relay LSI, serially through the No. 2 normally
initiated at station A (or any other station) link
made continuity contacts of relay LS2 and LS3
I is busy or is otherwise made unavailable, its
relay CHI in the link allotter circuit would be 15 (the former being individual to link 2 and the
normal and the start conductor I, with ground
applied thereto, would be connected to conductor
latter individual to link 3), to battery. Relay
LSI operates, connects operating battery to its
busy or otherwise made unavailable, relay CH2
of relay LCI to battery, and the second extend
ing from the same ground, conductor I03, No. 3
winding through its own No. 2 front contacts
1' of link 2 to cause the operation therein of relay
and, over its No. 1 front contacts, closes two cir
ST in the manner described for relay ST of link
I. On the other hand, if both links I and 2 are 20 cuits, the ?rst extending from ground, Winding
as well as relay CHI will be normal since their
contacts of relay DCT, winding of relay LCI’ to
battery. Both relays LCI and LCI’ operate, the
However, as soon as these relays are both nor 25 former to connect the translator and alternating
current receiver shown in Figs. 9 and 10, respec
mal, a circuit is completed for relay CH3 which
tively, to the link and the latter to connect the
extends from battery through its winding, con
trunk marker of Fig. 14 to the link.
tacts of key KY3, conductor 2" within bracket
In connection with the circuit for operating
line 5, No. 1 contacts of relay B of link 3 (con
relay LCI’ (or LC2' or L03’), it should be ob
ventionally indicated in Fig. 11), conductor 3" to
served that the link is designed to control the
ground over the No. 1 normally made contacts of
setting up of two types of connections, namely,
relay CHI. Relay CH3 operates and, with relays
a local connection between two local stations as,
CHI and. CH2 normal, represents the condition
in which links I and 2 are unavailable but link 3
for instance, between stations A and B, and a
respective locking circuits will be opened at the
No. 1 contacts of relay B of their respective links.
is available.
If, now, a call is initiated at a line
trunk connection between a local station as, for
instance, station A and a trunk extending to the
station, as for example, station A, ground on
desired central o?ice. In the case of a local con
start conductor I is extended to conductor 1"
which is connected to the winding of relay ST of
nection no trunk is required and, therefore, the
services of the’ trunk marker (Fig. 14) may be
link 3, the path being from ground on con
ductor I as applied thereto from conductor 6 1.0 dispensed with whereas, on a trunk connection,
through the No. 2 and No. 3 contacts of relay
its services are required and, therefore, connec
tion of the trunk marker to the link is necessary.
L20, No. 4 contacts of relay CH2, No. 2 contacts
Discrimination between the two types of connec
of relay CH3, conductor 1", to the winding of
tions is achieved by the ?rst digit that will be
relay ST of said link, causing the operation of
keyed by the calling subscriber. Since, in the
said relay and the connection of the associated
present embodiment of the invention, the private
link 3 to the calling line.
branch exchange is limited to twenty lines with
If all three links are unavailable, relay CH3
each line having a numerical designation from
will be normal along with relays CHI and CH2.
20 to 39 depending upon the cross bar vertical
The initiation of a call under these circumstances
will cause ground on the start conductor I to be 50 in the cross bar switch to which the designated
line is connected, and since for the establish
applied to conductor 22 via the No. 4 contacts of
ment of a local connection the calling subscriber
relay CH2, No. 1 contacts of relay CH3, No. 2
merely keys the digits of the wanted number as
contacts of relay CHI, No. 2 contacts of relay
set forth in my above-mentioned patent, whereas,
CH2, to conductor 22. This conductor extends
for a trunk connection, he keys the trunk digit
(within bracket line I3) to the power tone and
ahead of the digits of his own station designa
alarm circuit III! and completes a circuit therein
tion, it is obvious that if the ?rst digit keyed by
which causes a distinct “Link busy tone” to be
applied to conductors 23 and 24 which are con
a subscriber is a 2 or 3 and such digits are not
nected to primary winding terminals of busy tone
transformer LBT. Since the secondary winding
of this transformer is connected to ground and
used for trunk digit designations, said digits may
be used to apprise the link that the connection
will be local and, therefore, that the use of the
trunk marker can be dispensed with. As de
scribed in myabove-mentioned patent, the key
iscompleted into a circuit over the winding of
the line relay L- to battery on the upper nor
ing of a digit 2 or 3 as the ?rst digit will cause
mally made contacts of the hold magnet HO—,
the subscriber at the calling station will hear the 65 the operation of relay T2 of the link or relay T3
(if digit 3 is keyed) followed by relay T2 (if digit
tone as an indication that, due to unavailable
3 is keyed), for registering therein the digit 2 or 3,
links, the connection cannot be established.
respectively, whichever digit it may be. Relay
As soon as a link becomes available, say link
T2 completes a circuit for relay CI (as set forth
I, a circuit is completed for relay CHI which ex
tends ‘from battery through‘ its winding, thence 70 in said patent) and the latter, upon operation,
completes a circuit for relay DCT of the trunk
as traced to conductor 3, No. 5 contacts of relay
marker connector. This circuit may be traced
CH2 to ground. Relay CHI operates and locks to
as follows: Battery through the winding of relay
ground over its No. 3 front contacts to reestab
DCT, No. 4 normally'made continuity contacts
lish the path of start conductor I to the winding
of relay ST of link I in readiness for'seizure on 175 of said relay, conductor I04, serially through the
cally therefrom, relays LC! and LCI’ is, as be
fore stated, to connect to the link when taken into
'I‘K6, TK5, and TI“ (assuming that four trunks
are provided between the private branch ex
change and the central office), No. Qbackcon
.tacts of relay RTT, conductor I05, No. 3 front
contacts of relay LCI’, conductor I06, No.5 con
tacts of relay CI, to ground on the No. 5 contacts
of relay B. Relay DCT operates over the above
use to the common alternating current pulsere
'ceiver and translator shown in Figs. 9 and 10
and-tothe trunk marker shown in Fig. 14. When
these circuits are connected to the link (the sig
‘nal ‘for which is the operation of relay LS’! ) , the
receiver and the trunk marker 1must be made
circuit, locks over its No. 4 front contacts, con
unavailable to the, other two links. This is done
.10 by’
removing the operating ground for relays L02,
ductor I08, to ground on the No. 6 contacts of
relay ON which is operated at this time aswill be
shown, and opens the circuit of relayLCl ’ which
releases and, in so doing, disconnects the trunk
marker from the link.
L03, M32’ and L03’ at the No, 1 back'contacts
ofrelay LSI so that, if either relay LS2 or LS3
should have its operating, circuit established by
relay ST of links 2 and ,3, respectively, the cir
In the event of a trunk connection, however,
the subscriber ?rst keys the trunk digit desig
nation 4 and. thereafter, follows this digit by
keying in succession the two digits of his own
I number which, in the case of station A, would
be a 2 and 0, Under these circumstances, relay
T2 will not be operated until the digit 2 is keyed,
cuit'of relays LC2 and LC2’ or L03 and L03’ will
be cut off at the No. 1 back contacts of relay
LSl. Onv the other hand, if the link taken into
use happens to be link 2 or 3, then the corre
sponding operation of relay LS2 or LS3, respec
tively, will out offthe operating circuit of relay
LSI at their respective No. 2 normally made con
and inthe interval, between the‘keying of the
tinuity contacts so that if link I is seizedgthere
after, the failure of relay LSI to operatewill pre
vent the operation of relays LCI and LC!’ and
thereby prevent the connection of the common
alternating current receiver, translator and trunk
marker simultaneously to two calling links.
‘The alternating currentreceiver of Fig. 10 is‘
trunk digit and the keying of the tens digit of
the calling line, the trunk marker remains con
nected to the link.
,, The . object of operating relay LSI and, lo
N0. 8 contacts of the individual trunk relays TKT,
-, {The operation of relay LCI,’ transfers the hold
ing circuitof relay Bqfrom' groundonconductor
,Sl. andconductor l0l; as traced thereto over the
normally made‘ continuity contactsof relay‘ LC] ',
adapted‘ to receive alternating current impulses '
to the same conductor SI as traced thereto from
from a calling station which, ‘as said before, is
equipped with an alternating current generating
conductor l0l, No. 5 front contacts of relay LCI’,
-conductor,84-,'No. 8 back-contacts of relay NC,
conductor 81, No. 6 frontcontacts of relay LCI,’
device LG, and this receiver as well as the trans
lator and trunk marker must be connected to
the link. before the calling subscriber can be ad
to conductor SI. It also transfers over its No. 4
front contacts the holding ground for out off re
' vised, by an appropriate warning tone, to trans
lay CO20 which now holds over conductor IN
to ground on the No. 5 contacts of relay COK.
Relay LCI ' (or relay L02’ or relay L03’ depend
mit the called line or trunk designation.‘
ing upon which of the relays LSI, LS2 or LS3
the‘primary- circuit of a low frequency tone de
rived fr'om the tone oscillator 10 through ad
isv operated) also performs certain other func_- ,
justable resistance pad-62' and transformer v6|.
tions in they progressiveestablishment of the con
The path is traced as'follows: from the lower
terminal of the secondary winding of trans
nection which vare best , described swhengthese
functions comeinto play.
cordingly, when relay ONA operates, it closes
former 6i, ‘conductor [4, serially through the No.
. Relay LCI closes a circuit fromground on its
No. 5 contacts‘over conductor 60 togthe winding K ' 1 contacts of relays TK‘l-‘TKIJ, inclusive in the
order named, conductor 15, No. 3 contacts of
relay RR,.No. 2 contacts of relay RA, No. 2
contacts of relay' ON,v No. 2 contacts of relay
ONA, conductor“, through the low-pass ?lter
6,3 to the upper terminal of the secondary wind
ing of transformer 6|. The tone frequencies pro
of relay ON which operates to complete a circuit
over its No. 1 contacts to a relay (not shown) in
the “Time out’_’ circuit I20, and applies-ground
over its Nos. 3 to 6 contacts, inclusive, to the con-_ I
nected conductors for controlling certain relays ,
of .the circuit as describedhereinafter.v With the
operation of relay ON, a circuit'is alsocompleted
duced by the oscillator 10 are thus induced over
the, circuit above traced.
for relayONA extending from battery through
the winding of said relay, No, 1 contacts of relay
Through a transformer arrangement
HR, No. 3 normally made continuity contacts of
relay ONA, conductor 16, No. 4 contacts of relay "
LCI, conductor .15, No. 1 back contacts of relay
C,.conductor 2| to ground on the No.- 6 contacts
of relay B.> Relay ONA operates, locks over'its
shown) in the low-pass ?lter 63, the low fre
quencies' are induced in the closed circuit com—
prising the transformer 68, a transformer in said
low-pass ?lter 6,3,andfa transformer in high-pass
v?lter?ll. Beyond the secondary winding of the
No. 3 front contacts under the control of the No. 1 60 transformer (not shown) in the ?lter 64 are
contacts of relay HR to ground on conductor 60 " connected suitable'?lter networks V(not;shown)
which are designed to pass only frequencies with
and,.at the appropriate time, performs certain
in the signal frequencyband of the frequencies
functions which arenoted below. The operation
that are produced by the station generator LG
.of the relay in thef‘Time out” circuit I20 initiates
when, operated, Hence the tone frequencies proe
the operation ofa group of relays orsimilar ine
v'duced by‘oscillator 10 will not pass into the vol
strumentalitiesby means of which a predetere
ume limiter, 65 or into the enabler 80. They will,
mined time interval is measured, which interval
however, be induced into the secondary winding
is the time allowed the calling subscriber to com
.plete keying the wanted number which, inthis
oftransformer 68 if said secondary winding forms
own number.
because conductors ‘H and ‘l'2v are but extensions
oftheline conductors T and B into the link and
case, is the trunk digit and the two digits of his 70 part of a closed electrical system, which it is,
When that interval is terminated, ' <
a circuit is completed for relay HR which oper
ates to perform certain functions best described
in connection with the keying of, the wanted
trunk or called number as the case may be," i
alternating currentreceiver connected thereto.
The ‘path of. this circuit is traced as follows:
75 From the left side of the secondary winding of
The alternating current pulse receiver ‘shown
transformer 68, conductor ‘H, No. 2 back con
tacts of relay HR, conductor 78, No. 6 front con
in Fig. 10 is a conventional disclosure of the re
tacts of relay LCI, conductor 54, condenser C2,
No. 2 back contacts of relay HS, conductor LT,
N0. 6 contacts of cross-point 9 on vertical 20,
ceiver shown
Hecht and A.
It comprises
former 68, the
conductor T, over the loop of station A, conductor
R, No. 5 contacts of cross point 1-) on vertical
20, conductor LR, No. 3 back contacts of relay
HS, condenser 03, conductor 55, No. '7 front con
tacts of relay LCI, conductor 14, No. 3 back con 10
tacts'of relay HR, conductor 12 to the right ter
minal of the secondary winding of transformer
68. Inasmuch as the receiver of the telephone
instrument of station A is included in the above
closed circuit, the tone induced thereover is '
heard by the subscriber, which he understands
as a signal to proceed with keying the number
of the wanted subscriber or trunk.
in Patent 2,269,022 issued to G.
A. Lundstroin on January 6, 1942.
the channel composed of trans
high-pass ?lter 64, the volume lim
iter'65,'the transformer 66, the adjustable pad
61, five detector ampli?ers fA-J‘E with relays
F'A-FE in the respective anode circuits thereof
and a suitable ?lter BPF— intermediate the pad
61 and each one of the detector ampli?er tubes
fA-fE, each of said ?lters being designed to pass
only the frequency intended for the particular
channel in which the ?lter is included. Between
the high-pass ?lter 64 and the volume limiter
65 is bridged the primary winding of transformer
H2 to the secondary winding of which is con
nected the enabler 80. This enabler is identical
to that disclosed and described in the above
If the subscriber fails to key the wanted num
ber or trunk (including the digits of his own 20 mentioned patent to G. Hecht and A. A. Lund
stro-in and is shown only in conventional form
number) in the time taken for relay HR to oper
except for polarized relay 11. The enabler re
ate as above set forth, it is presumed that the
'sponds to a portion of the energy in each of
connection so far set up was due .to the tele
the‘ signal pulses that pass through the high
phone instrument at the station being accident
ally removed from its cradle and not restored. 25 pass ?lter 64 and functions to operate polarized
relay 1'! after a predetermined interval. Relay
In any event, the fact that but three links are
1'! "grounds conductor 18 which is connected to
provided to serve twenty lines makes it impera
the cathode of each of the detector tubes J‘A-fE
tive that no link be unduly kept out of service
thereby'activa‘ting‘ them to respond to the por
after key tone is transmitted to the calling line
without performing the necessary connection 30 tion, of the signal energy ‘that’ passes through
the volume limiter 65. Since the operation of
completing functions that follow the transmis
the enabler 80' is‘ completely described in the
sion of the wantedynumber designation. Hence
above-mentioned patent to G. Hecht and A, A.
if the subscriber fails to transmit the number by
Lundstrom, reference is made to said patent for
the time relay I-IR, operates, relay ONA is un
a complete description thereof, only so much of
locked, a circuit is completed from ground over
said description being supplied herein as will be
the No.- 4 contacts of relay HR, No. 4 contacts
necessary to an understanding of the’ present in
of relay ONA to_ a relay (not shown) in the
howler circuit I30 which operates to complete
a sharp howler tone which is applied over the
It will further be noted that the No. 1 con
No. 2 and No. 3 front contacts of relay HR to 40 tacts of relay ONA are bridged across‘the high
conductors ‘I3 and 74, both of said conductors ex
pass ?lter 64 (through conductors H6 and ill)
tending over the‘ calling loop (as previously
traced) including the station telephone instru
ment. The tone is sufficiently loud to be heard
to short-circuit said ?lter when the relay is nor
mal. This is a safety measure to insure that if,
at the time the subscriber initiates the call, the
at a distance from the receiver and is intended 45 Nos‘. 5 and 6 contacts ‘of cross-point 9 on verti
to apprise the subscriber that the telephone in“
strument should be restored, an occurrence that
will cause the link to be disconnected and re
stored to normal as described hereinafter.
cal 20 close last, and should close after the al
ternating current receiver is, connected to the
link, the impulse produced over the line‘ loop will
not ?nd a passage into the high-pass ?lter. For
Assuming, however, that relay HR has not op 50 if it does and this pulse contains frequency com
ponents within the signal frequency band, these
frequencies would falsely operate one or more of
operates the device LG to transmit the wanted
the signal channels. By the time relay ONA has
designation which, since the connection desired
operated, however, the pulse will have been dis
is to a trunk extending to the manual central
office, will consist of the arbitrary digit “4” in 55 sipated, the short circuit is removed and the re
ceiver is connected to the line as above described.
dicating a trunk to said central oi?ce, followed
As said before, each detector ampli?er tube
by the subscriber’s own number “20.” He does
fAeiE is preceded by a ?lter BPF which passes
this by ?rst operating a key in the device LG
only the frequency intended for the channel in
bearing the numeral “4” thereon and then, in
succession, similar keys bearing the numerals “2” 60 which the tube therein is to operate on the en
ergy carried by said frequency. It is assumed
and “0,” respectively. The depression of each
that the device LG is capable of producing ?ve
key causes two out of ?ve reeds to be plucked
erated, the subscriber, upon hearing key tone,
according to a code combination individual to
different frequencies which, for convenience,
may be designated A-E, inclusive, and that, in
the numeral indicated, and the reeds are set
into vibration to produce two alternating cur 65 accordance with the operation of the receiver as
described in the above-mentioned patent to G.
rents of speci?c frequencies which are now
transmitted over a circuit which may be traced
Hecht and A. A. Lundstrom, frequency A will
as previously to conductors ‘l3 and '14 at the No. 2
and No. 3 back contacts, respectively, of relay
cause the operation of tube fA, frequency B will
cause the operation of tube IE and so on up to
HR and, thereafter, to conductors ‘H and 72, re 70 and including frequency E which will cause the
operation of tube IE.
spectively, connecting with the secondary wind
As already mentioned, each detector ampli?er
ing of transformer 68. These frequencies are in
tube has a relay F- connected in its anode cir
duced into the circuit comprising the primary
cuit, and a front contactof this relay is further
winding of said transformer and the high-pass
75 connected to the winding of "one of the five re‘
?lter 64.
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