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Oct 3,1946-
Filgd Dec. 4, 1943
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Patented Oct. 8, 1946
Charles Gillings and Lawrence. John- Murray, Liv-i
erpool, England, assi gnors to Automatic Elece
tric Laboratories, Inc, Chicago, 111., a corpora
tion of Delaware
Application December 4, 1943, Serial No. 5125888
In Great Britain January 8, 1943
8 Claims.
The present invention relates‘ to switching
equipment for use in telephone and like systems,
and is. more particularly concerned with selecting
switches of the cross-bar type having sets of con
(Cl. 179-22)
crossbar group selector and associated common
equipment which is assumed, to be located in the
?rst numerical group selecting stageof an auto
matic telephone system such as is described in
tacts arranged to form both rows and columns at Ul
the above-mentioned application. Fig. 5, which
right angles to one another.
is located on the same sheet as Fig. 4, shows the
In our application Serial No. 513,370, ?led De
group selector trunking diagram.
cember I8, 1943, we have described a crossbar
Forconvenience the designations in the present
switching system in which each of a number of
circuits have been made to line up as far as, is
switching stages is controlled by equipment in ii; possible
with those of- the circuits in the prior
dividual to each stage and the object of the pres
and-the group selector shown is there;
ent invention is to provide a crossbar selector
having improved arrangements for outlet test
ing whereby the amount of apparatus in the in
dividual control equipment is reduced.
On, say, a ZOO-point crossbar group selector
having ten levels and twenty outlets per level
there will be provided ten horizontal bar level
fore assumed to be designated» GSUI, while its
associated» common group is designated GCG,
In the circuits the number of contact units-can
ried by each- relay is shown beneath its designa
tion, as for instance
selecting relays and twenty vertical bar holding
relays whereby connection may be made via the 20 (Fig. 3) andt-hese are designated individually in
crossbar switch contact springs with any one of
the two hundred outlets.
In the above-mentioned application, testing
over a group selector level of twenty outgoing
small letters which in this instance-will be bl, 112,
etc. A slow-to-release relay is shown with a
hatched portion at one end of the rectangle in
dicative thereof, while a slow-to-operate relay is
links to subsequent selectors was performed by 25 shown
with‘ a crossat one end, such a relay being
testing directly from the common control group‘
on to the associated outgoing P conductors, there‘
being provided in the control group one or more
hunter uniselectors together having ten levels
with twenty outlets per level, the particular level
involved being selected by'a digit receiving switch‘
in accordance with the particular group select
ing digit dialled.
According to the invention a crossbar selector
switching unit has control equipment associated
with it which equipment comprises a selector
adapted to connect with and test a number of
leads corresponding to the number of lines in a
group each of said leads being connected to cor
in some instancesislow-tosrelease as well as slow
As- regards the crossbar vertical and horizontal
relays, these are each indicated by a hatched reci
tangle, the contact units individual thereto‘ being
indicated‘ in the same manner'as for ordinary
relays. The sets of crossbar switch contacts
proper which are closed- at the intersection of any
given pair of horizontal and“ vertical bars, for in
stance the contacts controlled by relays IGSP
(Fig. 1) and EGSH (Fig. 2'), are designated
responding leads of the group required by ele 40 and. so. on for each set of contacts‘ involved;
ments of the crossbar switching unit itself such
Off the various uni-selectors such as the‘ con
elements being selected in accordance with the
trol group hunter switch which is designated
number of impulses by which the operation of the
OCSi, the various; sets of wipers: and‘ banks are!
unit is initially controlled.
designated, OCSI', 0082; etc. The driving mag-~
Conveniently the control. equipment is individ
net. which is indicated by a hatched square will
ual to the unit which it controls although it will
in this instance be designated OCM, and? the
be appreciated that circumstances may make it
magnet interrupter contacts will be designated
desirable fora single unit. to control more than
0cm. In‘ the case of the‘ digit switch uniselector‘
one crossbar selector switching unit.
TDS, since the‘ numberv of positions required is
The invention will be better understood from 50 considerably less‘ than the twenty-?ve available
the following description of one method of carry
they are arranged to make two appearances
ing it into effect, reference being had to the ac
thereon so that this’ switch will have two home
companying drawings comprising Figs. 1-5.
Figs, 1-4 when arranged in the manner indi
cated in Fig. 40 show circuits of a 200-point‘ 5
positions I and ‘I2.
Referring now‘ to-Fig; 5‘,_.the group ‘selector com
prises twov crossbar switching‘ units with their
vertical bars in e?ect coupled together as shown
to form a group selecting unit. More speci?cal
ly, the coupling will be e?ected electrically by
the connection or” each column of vertically com
moned contact springs of the spring sets in one
unit with a corresponding column of vertically
commoned contact springs 0n the other unit of
the pair.
The selector is of the 10-level 20-outlet-per-'
level type and is capable of handling ten connec
tions, and for this purpose the ten incoming links
will connect with the horizontal bar relays
lGSP-—l UGSP. The horizontal bars provided for
the purpose of determining the selected one of
the ten possible levels are controlled by the re
lays IGTP—IUGTP and the two sets of 20 vertical
holding relays lGSI-I—2BGSH and ,lGTH
ZEIGTI-I when operated in pairs such as lGSI-I
and lGTI-I or ZGSI-I and ZGTH, and so on, and
in conjunction with one incoming and one level -
selecting relay, enable the two units of the pair
forming the group selector switch proper to func-v
tion to connect an incoming external link via a
free internal link within the selector to. a free
one of the twenty outgoing links accessible from
aselected level of the selector.
Referring now to the circuits of Figs. 1-4, cir
cuits of the group selector GSUI are shown in
the upper parts of Figs. 1 and 2, while circuits
contacts lnf3, lgspll, and |gsr3 to battery via the
winding of relay IGSP. This relay at contacts
lgspll and 'lgsp5 extends the calling loop through
via common leads 34 and 35 to relay A in the
control group GCG and although at these con
tacts it disconnects its own operating circuit it
remains locked via make-?rst contacts lgspl
and contacts lnf5 to lead 36 which is earthed
via contacts gsl of relay GS which will have been
operated over the incoming P lead from the outlet
testing relay in the preceding stage before the
loop is extended forward to the group selector.
Relay A in operating at contacts al (Fig. 3)
operates relay B in series with recti?er MRD in a
conductive direction to battery via resistance YP.
Relay B in operating, at contacts bl (Fig. 1)
extends earth over common lead 32 and then via
contacts lgspZ to operate relay IGSR in series
with resistance YH, at contacts b2 brings up relay
BB (Fig. 3), while an alternative locking circuit
for relay IGSP (Fig. 1) is completed at contacts
b4. At contacts bl (Fig. 3) an energising circuit
is completed for relay C on its series-connected
windings in series with resistance YQ and switch
magnet TDM (non-operative in this condition),
while at contacts b8 relay B is locked up inde
pendently of the operated contacts al.
group selector relay IGSR in operating at con
tacts lgsrl extends the earthed lead 32 through
to the incoming P lead and this earth extends
of the control group GCG are .shown in the lower 30 back to hold the relays in the preceding stage
parts of these ?gures and in Figs. 3 and 4.
In the group selector circuit there is shown only
the, horizontal prepare relay IGSP together with
the auxiliary relays IGSR and INF associated
with the ?rst out of the ten possible incoming
internal links to the selector, which relays, in
common with the corresponding relays of the nine
other incoming links have access over common
which are connected to the P wire; contacts
lgsrl also disconnect the operating circuit for
relay GS which commences to release slowly.
At contacts lgsr3‘ it prevents relay IGSP from be
ing re-connected to the incoming negative lead on
any subsequent release of this latter relay, while
at contacts Igsrd it prevents earth from being
connected to the positive lead on the above condi
leads 3l—3l to group GCG. In addition, the
tion. At contacts lgsr5 the continued hold
vertical hold relays IGSH and IGTH of the ?rst
ing of relay IGSP is rendered independent of
vertical internal link and the horizontal pre
contacts Inf5. In the control group relay BB
pare relay IGTP associated with the ?rst of the
in operating at contacts bbl (Fig. l) disconnects
ten possible outgoing levels are also shown which
the relay GS from all the incoming P leads to
are operable from group GOG over leads 40—43.
the selector so as to mark the group selector as
The control group GCG comprises a set of re
busy. At contacts bb2 a dial tone source is con
lays and two uni-selectors of the 25-point reverse
nected up over lead DTE to the centre winding of
drive electro-magnetically-operated type, the
relay A from whence it extends by induction into
thousands dialled digit being received on switch
the outer windings and then on to the speaking
TDS, whereupon one of the level selecting relays
leads and back to the calling party. Relay C
lGTP-l UGTP is operated in accordance with the
in operating at contacts 02 (Fig. 3) prepares for
digit dialled. All the vertical hold relays IGTH
the reception of the thousands dialled digit on to
ZUGTH not already in use are thereupon operated,
magnet TDM of the switch TDS from contacts
while theuhunter switch OCS is set in operation
and is caused to test over the selected outgoing
level, connection between the contacts of switch
OCS and the lines connected to this level being
effected via the crossbar contacts at the inter
section of the actuated level selecting horizontal
al of relay A (Fig. 1) which is operated from
the calling loop.
The calling subscriber on hearing the dial tone
should now proceed to dial the thousands digit
of the required number, but in case he should
neglect to dial and so hold common equipment
bar and the vertical bars. When switch OCS
GCG unnecessarily, arrangements are made to
?nds a free outlet, the corresponding GSH relay
release this equipment and to return busy tone to
is operated and this maintains a holding circuit
the calling subscriber if dialling does not take
for the relevant GTH relay on to the P conductor
place within a predetermined period after seizure.
of the selected outlet when the control group is
This is effected in the following manner by the
subsequently released and becomes available for
use of the pair of relays TA and TZ (Fig. 3) in.
piloting a further call through the same group 65 conjunction with a delay set (not shown) which
is common to the exchange and which is arranged
; When the group selector is taken into use, the
to supply earth-pulses bearing a de?nite time re
calling subscriber’s loop is extended on to the
lation to two common leads S and Z. On opera
left-hand incoming negative and positive leads
tion of relay B when the control group GCG is
(Fig. l), which leads will relate to the ?rst of
taken in use, contacts b3 (Fig. 3) connect the
theten possible incoming external links to the
right-hand winding of relay TA to the S lead and
selector switch, and the terminating crossbar re
if or when the delay set is in its normal position
lay IGSP will operate over the following circuit:
an earth will be encountered on this lead and
earth, contacts Igsrd, Igsp5 and ln?l, positive
conductor, subscriber’s loop, negative conductor, 75 relay TA will operate. At contacts tal it locks to
earth on to the left-hand. winding, at contacts m2
it connects its middle. winding and the lower
winding of relay TZ to the Z lead, while at con
tacts me it extends earth on to the delay set
start lead ST. After the predetermined period
an earth pulse is applied from the delay set to. the
Z lead, whereupon relay TZ operates and at con
tacts 2523 removes the short-circuit from its upper
winding over which it looks to the earthed con
tacts b2 via resistance YJ. At contacts is! and
tz? the initial operating and locking circuits for
relay TA are opened but this relay remains held
in the circuit including its middle winding and.
the lower winding of relay TZ. At contacts tel
earth is extended over lead 33 to short-circuit 15
and initiate the release of relay lGSR in the
group selector, while at contacts tea (Fig. 2) earth
is extended over lead 3'] to bring up relay lNF in
the group selector. At the end of the Z pulse,
relay TZ remains held and relay TA releases. In
the group selector relay tNF in operating at contacts lnfl maintains earth on the incoming P
lead and disconnects any circuit therefrom to
relay IGSR, while at contacts infi a locking cir
cult is completed for relay iGSR but in this in‘
stance this circuit is ine?ective owing
short-circuiting over lead
At contacts mill
and mill the incoming speaking leads arev trans
ferred from relay A to relay lNF,-whereupon
relay A releases. At contacts inf? number-um .
obtainable tone is, on release of relay GGSR, con
nected up over common lead NTE to the centre
winding of relay lNF from whence it returns to
the calling party; relay IGSR {in releasing re»
leases relay EGSP. In the control group, relay A.
in releasing at contacts at short-circuits and re
leases relay B, whereupon relays BB and TZ are
released, while the TDS switch is stepped off
normal on the release of relay C and is then
horned as is described later and the control group 40
GOG is then ready to handle a subsequent call
through the group selector.
If the calling party commences to dial within
the allowable predetermined period after receipt
of dial tone, then on the ?rst release of relay A its
an energisin.Cr circuit is completed for magnet
TDM as follows: earth, contacts b3, a! and c2,
the direct connection of a comparatively low value
non-inductive resistance such as YP in parallel
with its winding; neither magnet TDM nor relay
0 moreover. will hold operated in series with relay
At the end of the digit, relay A remains operated and holds relay B, while relay C commences
to release slowly. On release of relay C,- contacts
ci (Fig. 2.) extend earth over operated contacts
114'; and b9 and wiper TDSZ which will be in posi
tion 2 or ‘£3 if say digit’ 1 has been dialled; where
upon‘ the level I crossbar selecting relay IGTP
will be operated to actuate the horizontal bar as
sociated with the ?rst one of the ten levels of out
lets. Contacts 03 complete an operating circuit
for ‘relay NR and this relay in operating at con-'
tacts m‘!- (Flg. 1) further disconnects any circuit
to relay GS, and at contacts m2 (Fig. 3) com
pletes a self—interrupted driving circuit for mag
net OCM of switch 003 via bank and wiper
OCSl, contacts 7cr2 and lei-r4, magnet interrupter
contacts 0cm, magnet OCM to battery, the driv
lrig circuit being subsequently maintained by the
low resistance winding of relay N. Contacts m3
(Fig. 2) extend earth over lead 43‘ which is com
mon to all the relays iGTH-NGTH on the
group selector, whereupon assuming that none
of these relays are already in use, they will allbe
operated. Since the level I selecting relay IGTP
is already operated, the sets of crossbar contacts
on thislevel will be operated and will connect the
control group GOG through to the P conductors
of all twenty of the outgoing links on level I in
the following manner. For instance, as regards
‘relay lGTI-l shown, with this relay operated in
addition to relay IGTP, then the set of contacts
IGTP 1-3
shown in Fig, 2 will be operated and the P lead
of the ?rst outgoing link on level I will be con
nected through over contacts lgsh? and lead 42
tocontact 2 on bank OCS3 of switch OCS. Relay
in operating will effect the operation of
left-hand low resistance winding of relay C, mag~
net rl‘DlVl to battery; the winding of relay B is
(not shown) and contacts
short-circuited during this time, while the right 50
hand winding of relay C is similarly short-cir
- 2GTH3
cuited in series with resistance YQ. On re-oper
ation of relay A at the end of the ?rst impulse of
the dialled train, an energising circuit is re-corn
pleted for relay B and relay C now holds operated
on both its windings in series with magnet TDM
which will not hold in this condition and which
thereupon releases to advance its wipers to con
tacts 2 or it according to'which half of the banks
is being used. An operating circuit is now com
pleted for relay N via wiper and bank TDS! , oper
ated contacts Z7123 and contacts n2 to battery via
will connect the second F lead on level I through,
via contacts 2gsh2 (not shown) to contact 3 on
bank 0083 and so on. By this means the twenty
P leads on level I are connected through to con
tacts 2-125 inclusive on bank OCS3.j On the}
operation of relay B when the control group was
taken into use, contacts 115 and b6 will have con
nected up the dual testing cut-drive relay KR to
wiper 0083, and hence during the rotation of the
wipers of switch 008 relay KR will be succes
resistance YO. This relay in operating, at its
contacts 11! opens the holding circuit for relay
sively connected to the twenty outgoing Pleads
C and at the same time short-circuits its right?
hand winding, at contact 112 prepares for the
If the P lead connecting with contact 3 of
operation of relay NR and at contacts n3 (Fig.
l) disconnects the dial tone circuit.
Succeeding impulses of the train are delivered
of level ,I in turn.
bank OCS3 is already engaged _from another
group selector, wiper OCS3 will encounter ‘an
earth potential and relayKR will not ‘operate.
The switch 008 will then proceed to step on to
to magnet TDM and relays B and C hold oper- 70 the next position and test the second P lead
and if this also proves to be busy the self-inter
atedv during this time. It may be mentioned here
rupted driving operation of switch 0083 will con
that the presence of the metal recti?er MRD in
tinue until a free outletis encountered which will
the initial energising circuit for relay B serves to
be marked by an idle marking resistance battery .
prevent the slowing up of the operation of the
such as that normally extended on to the incom- '
magnet TDM which would otherwise result from 75 ing P leads of the group selector GSUI and‘ relay '
KR will thereupon operate and at contacts krZ
(Fig. 3) will open the magnet OCM driving cir
and OCSI and this relay proceeds to release
slowly. When it does so, contacts 112 open the
holding circuit for relay NR which commences
to release slowly and on the release of this relay
For the purpose of the description it Will be
assumed that the ?rst of the twenty outlets on 5 contacts nrl (Fig. 1) replace the idle marking re
sistance battery comprising resistance YK and
the winding of relay GS on the common test lead
3| of the control group GCG to indicate that this
Relay KR in operating at its contacts krl (Fig. 4)
group is now ready to set up any further call
extends earth forward over its upper low resist
the associated group selector GSU l , while
ance winding to guard the outlet seized, and at
at contacts nr3 the earth is removed from com
the same time to hold itself operated. At con
mon lead 43, whereupon all the vertical hold re
tacts kr2 (Fig. 3) an operating circuit is com
lays which have been operated therefrom with
pleted for relay KRR over wiper and bank OCSI
the exception of relay lGTH, which in this in
to earth via the low resistance winding of relay
N. This relay in operating at contacts Icrrl and 15 stance remains held from the P lead of the seized
outlet, are restored to normal.
krrZ (Fig. l) disconnects the operating circuit
level I is free in which case relay KR will oper
ate as soon as wiper OCS3 reaches position 2.
‘for relay A, at contacts krr3 (Fig. 4) prepares
for the dual testing function of relay KR in case
it should be required as will be described later,
In case the OCS switches in two or more con
trol groups should happen to test on the same
outgoing link simultaneously. then both of the
KR relays will operate over their windings in
and at contacts krr4 (Fig. 3) further disconnects
series to the same idle marking resistance bat
the magnet OCM driving circuit. At contacts
tery and will operate their respective relief re
krr5 (Fig.v 4) earth is extended via wiper OCSZ in
lays KRR, while at the same time earth will be
position 2 and over lead 41 to operate relay IGSH
extended forward over their upper low resistance
in the group selector, this relay corresponding to
the ?rst outlet which has been seized, while con 25 windings. In control group GCG relay KRR in
operating at contacts krr3 extends a battery po
tacts krrS (Fig. 4) prepare to maintain relay KR
tential via resistances YL and YM, and thence
operated independently of the idle marking re
via contacts b5 to energize the lower winding in
sistance battery on the selected P lead,
opposition to the upper Winding, similar remarks
Relay IGSH (Fig. 2) in operating in addition
to operating the horizontal selecting relay IGSP 30 applying to the KR relay in the other control
initiates the actuation of the set of contacts
Now in the case of a single connection from
one KR relay to the outgoing P lead the opposing
?ux produced in the lower winding on operation
and at its own make-?rst light contacts lgshl 35 of relay KRR will not be su?icient to overcome
the holding ?ux in the low resistance upper wind
(Fig. 4) completes a local locking circuit for relay
ing and the relay will therefore hold. In the
KR via bank and wiper OCS4 to battery over
case of a dual connection the holding ?ux pro
contacts lam-6 and resistance YHA, while at con
duced in each due to the current through their
tacts lgshz it extends its own operating earth
through to the P lead of the outgoing link taken 40 low resistance upper windings will be halved,
while the opposing ?uxes due to their lower wind
into use and also via contacts lgsh3 to maintain
ings will remain the same. In these circum
relay IGTI-I independently of the contacts nr3.
stances both the KR relays release and cause the
The calling subscriber’s loop is therefore now
associated hunting switches to continue search
extended through the group selector and out over
the ?rst of the twenty outgoing links on level 45 ing. Due to the difference in the speed of any
two switches, after a few steps one will reach
I to the succeeding switch, and relays IGTH,
a free outlet before the other, whereupon the
IGSH and IGSR will be held from the earthed
associated KR relay will operate to guard the
lead 4|; in the meantime the control group will
outlet seized and to disconnect the magnet driv
be proceeding to free itself in the following man
50 ing circuit.
ner to be available for further use.
In connection with the operation of the GTH
On release of relay A, contacts al (Fig. 3)
relays when the OCS switch is about to hunt,
short-circuit relay B and this relay commences
it will be appreciated that in case a vertical in
to release slowly. Before it releases an earth
ternal link within the group selector GSUI is
will have been returned over the P lead from
the succeeding switch so that relays IGSR, (Fig. 55 already engaged, then it is necessary to busy the
corresponding outlet on all levels of the switch.
1) [GSH and IGTH (Fig. 2) are no longer de
Assuming that, say, the ?rst internal link within
pendent for their holding on an earth supplied
the switch is already engaged, then relays IGTH
from the control group. On release of relay B,
and IGSH will already be operated when relay
relays BB, KR and KRR release in turn. At con
tacts M (Fig. l) and b9 (Fig. 2), the group se 60 NR in the control group operates. Relay NR will
operate the other nineteen relays ZGTH-Z DGTH
lector prepare relays IGSP and IGTP are re
and the switch OCS will then commence to hunt.
leased but the pins or their equivalents which are
When it reaches contact 2, since relay IGSH is
engaged by the vertical bars actuated by relays
operated in addition to relay lGTI-I, the test cir
“381-1 and IGTH remain held. At contacts bb3,
R12, and Icrrll (Fig. 3), homing circuits are com 65 cuit will be broken at contacts lgshZ (Fig. 2)
so that relay KR will be unable to operate and
pleted for switches TDS and OCS via the low
the OCS switch will therefore proceed to advance
resistance winding of relay N, the circuit for
to the next position.
switch TDS extending over wiper and bank TDSI,
If all the outlets prove to be busy, the switch
contacts b123, interrupter contacts tdm, magnet
TDM to battery while the circuit for switch OCS 70 OCS will rotate its wipers to contacts 22 when a
battery potential via resistance YR will be en
is completed via bank and wiper OCSI, contacts
countered by wiper OCS3 and relay KR will there
kr2 and MM, interrupter contacts com and mag
upon operate and will bring in relay KRR. Re
net OCM to battery. When both these switches
lay KRR functions as before described with the
reach their home positions, the holding circuit
for relay N is opened at wipers and banks TDS! 75 exception that contacts krr5 (Fig. 4) now extend
earth over wiper OCSZ in position 22 and then
over lead 31 to operate relay INF over its left
conductors at di?‘erent times, thereby to deter
hand winding. Relay INF in operating, at its
mine whether the di?erent ones of the lines in
contacts lnfl maintains a guarding and holding
earth on the incoming P lead and at its contacts
[M3 and In?l (Fig. 1) connects itself across the
incoming speaking conductors to which it locks
and at contacts lnj2 (Fig. 1) completes a locking
having a plurality of incoming lines, a second
circuit for relay IGSR. At contacts lgsrG (Fig.
the selected group are idle or busy.
5. In a switching system, a ?rst crossbar switch
crossbar switch having a plurality of groups of
outgoing lines, means for seizing any one of said
incoming lines, means thereafter controlled by
impulses over the seized line for selecting any one
3) busy tone is connected up over common lead 10 of said groups of outgoing lines and operating
BTE' to the centre winding of relay INF from
said second crossbar switch to complete connec
whence it returns to the calling party. During
this time the common control proceeds to release
tions simultaneously from all of the outgoing lines
of the selected group to said ?rst crossbar switch,
in normal manner so as to be available for use
for testing each of said connections in turn,
in setting up further calls in the group selector. 15 means
thereby to ?nd a connection whose associated
What we claim as new and desire to secure by
outgoing line is idle, and means operated respon
Letters Patent is:
sive to the ?nding of a connection whose associ
1. In a switching system, a, plurality of groups
ated outgoing line is idle for operating said ?rst
of lines, a numerical switch, means for operating
crossbar switch to extend such connection to the
said switch directively to select any one of said 20 seized incoming line.
groups, a crossbar switch thereupon operated :by
6. In a switching system, a ?rst crossbar switch
said numerical switch to complete connections
having a plurality of incoming lines, a second
simultaneously to all of the lines of the selected
crossbar switch having a plurality of groups of
group, means for testing the lines of the selected
outgoing lines, means for seizing any one of said
group successively over the connections completed -
to the respective ones of said lines by said cross
bar switch, and means operated responsive to said
testing means ?nding a line having a predeter
incoming lines, means thereafter controlled by
impulses over the seized line for selecting any
one of said groups of outgoing lines and operat
ing said second crossbar switch to connect with
mined condition on it fOr causing said crossbar
the outgoing lines of the selected group, means
switch to interrupt all of said connections except 30 for testing the outgoing lines in the selected group
the one completed to the line having such condi
successively over the connections completed to
tion on it.
those lines by said second switch, thereby to ?nd
2. In a switching system, a plurality of groups
of lines, means for establishing a predetermined
an idle outgoing line in the selected group, and
means operated responsive to the ?nding of an
idle outgoing line to complete a connection from
condition upon any one of said lines, a numerical
switch, means for operating said switch direc
the seized incoming line to said idle outgoing line
tively to select any one of said groups, a cross
over said two crossbar switches in series.
'7. In a switching system, a plurality of primary
bar switch thereupon operated by said numerical
switch to complete a connection to each line in
lines, a plurality of groups of secondary lines,
the selected group, and sequence means for test 40 control equipment common to said lines, means
ing each line in the selected group in turn over
for seizing said equipment over any one of said
the connection completed to that line by said
crossbar switch, thus to determine whether such
line has said predetermined condition upon it.
3. In a switching system, a plurality of groups
of lines, a plurality of conductors common to said
groups, the different ones of said conductors cor
responding respectively to the different lines in
each group, impulse operated means for selecting
any one of said groups, a crossbar switch there
upon operated to connect all of said conductors
to the respectively corresponding lines of the
selected group, and means including a hunting
switch operated to connect with said conductors
successively for ?nding an idle line in the selected
4. In a switching system, a crossbar switch hav
ing a plurality of groups of lines, a plurality of
conductors common to said groups, the di?’erent
ones of said conductors corresponding respectively
to the different lines in each of said groups, im
primary lines, means in said equipment operated
by impulses over said one primary line to select
any one of said groups of secondary lines, a cross
: bar switch thereupon operated by said equip
ment to complete a connection to each of the
secondary lines in the selected group, means for
testing each of said connections in turn to deter
mine whether the secondary line associated there
with is idle, and means controlled by said test
ing means responsive to ?nding a connection
whose associated secondary line is idle for extend
ing that particular connection to said one pri
mary line, thereby to interconnect said one pri
55 mary line with said idle secondary line in the
pulse operated means for selecting any one of
said groups and operating said crossbar switch
to connect each line of the selected group to the
respectively corresponding one of said conductors, 65
testing means, and a switch operated to connect
said testing means to the different ones of said
selected group.
8. In a switching system as claimed in claim 7,
equipment individual to said one primary line,
and time controlled means for connecting said
individual equipment to said one line and releas
ing said control equipment in the event that said
impulses are not received within a predetermined
interval of time after seizure of said control equip
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