US2110910A - Telephone system - Google Patents

Description

March 15, 1938. B. A. HENSLER Er AL, 2,110,910

TELEPHONE SYSTEM Filed Aug. 23, 1935 I 4 Sheets-Sheet l Jfrr March 15, 1938. B. A. HENSLER ET AL TELEPHONE SYSTEM Filed Aug. 23, 1935 4 Sheets-Sheet 2 T ll! Arrx March 15, 1938. 'B A HENSLER AL 2,110,910

TELEPHONE SYS TEM Filed, Aug. 25, 1935 4 Sheets-Sheet 3 U QW 41 5 db; :22 i

March 15, 4-938. B. A. HENSLER El AL 2,110,910

TELEPHONE SYSTEM Filed Aug. 25, 1935 4 Sheets-Sheet 4 fizz/wen Amman r 5464015 6%; Xian/4K0 n-519s Patented Mar. 15, 1938 UNITED STATES PATENT osrlcs TELEPHONE SYSTEM Bernard Anthony Peters, London,

mens Brothers & Company England Hensler and Charles Leonard England, assignors to Sie- Limited, London,

'7 Claims.

This invention relates to telephone systems and more particularly to an arrangement suitable for use in a toll or trunk telephone system wherein each incoming call causes a switching apparatus to set itself to a position indicative of the order of arrival of the call with respect to other calls, the several switching apparatus so set being released in the order of arrival of the respective calls and are thereupon caused to search for a free subsequent circuit as these are rendered available. The setting and release of the switching apparatus may be controlled by a chain of relays which are operated and released respectively to control such operations, and the system may be applied to a toll or trunk system wherein calls are set up on demand by operators, i. e. a demand system.

A system of this type has already been suggested in which a distributor switch on being set in motion by an incoming call searches for and tests into an outlet to a display panel and if other calls are awaiting attention the call is added to a queue, the switches stepping on and so moving the call to the head of the queue as earlier display positions become available. If there are no other calls waiting in a queue and a subsequent circuit is available the distributing switch nevertheless tests into the first display position and is immediately released to search for the subsequent circuit.

In the present invention improved call queueing arrangements are provided by arranging that in moving ,a call up the queue the distributing switches do not step but a common switching mechanism associated with the display effects the moving up process by providing for the release of the switches in the display positions in turn as subsequent circuits become available. This arrangement is especially advantageous where the distributing switches are high speed motor driven switches as the step by step action in the queue is avoided. A furtheradvantage is gained by placing the display positions at the end of the distributing switch bank so that if a subsequent circuit is available at a time when there are no calls in the queue a searching distributing switch is not stopped momentarily in a display position but proceeds directly to the outlet to the subsequent circuit.

It is, accordingly one feature of the present invention that switching apparatus taken into use by an incoming call is caused to search for a free subsequent circuit, such as a connecting circuit on an operators position and if this search is unsuccessful to assume a position corresponding to the order of thecall with respect to other calls which have failed to be connected to subsequent circuits. The several switching apparatus are released from such positions in the order of .arrival of the calls as subsequent circuits are rendered available to search for these circuits.

According to another feature of the invention switching apparatus taken into use by incoming calls and formed into a queue remains in the same position during the movement of the call to the head of the queue until it is released to search for a subsequent circuit for the extension of the call.

The arrangements on which the incoming calls are thus queued may consist of a number of relays which are operated seriatim as the calls take a position in the queue, and arrangements maybe provided whereby the relays are picked up in a continuous order of rotation irrespective of the actual relative position of a call in a queue.

In the application of the invention to a normal or semi-automatic system arrangements are provided for giving relief to the demand operators, by signalling a further operator or operators when more than a certain number of calls are queued up. The furtheroperator or operators may normally deal with other types of incoming calls.

In order toeffect a certain economy modifications tothe system of the prior invention may be made whereby incoming lines are connectable to the switching apparatus already referred to over a searching switch, the switching apparatus having full availability ,to the subsequent connecting circuits.

One method of carrying out the invention is described by Way of example in the following description of the. arrangements illustrated in the accompanying drawings, wherein the inven tion is illustrated as applied to a toll or trunk telephone system in which under normal traffic conditions calls are dealt with in the demand basis. It is to be understood that the invention is not confined on its application to such systems, but is capable of utilization in any system of call distribution.

In Fig. l of the drawings are illustrated an incoming line circuit ILC, and a call distributor circuit DD. There is also illustrated a portion of .an operator's cordless. connecting circuit CC, of which there is provided a number on each position, and a portion of an operators position circuitOPC, only those circuit elements of these latter circuits necessary to the understanding of the present invention being shown.

In Fig. 2 is illustrated a lamp display circuit LDC, calling lamps DOP on a demand position and calling lamps OOP demand and incoming on a further or omnibus position. A further portion of an operators position circuit OPC is shown in this figure.

An incoming line circuit ICL Fig. 1 includes a step by step switch or uniselector P having wipers and arcs pl to p5, driving magnet PDM, and interrupter contacts pdm. The line relay is designated LA, the test relay TA and a switching relay H. The incoming line, junction or trunk is designated JCT. The arcs p2 and 103 are concerned with the connection of the speaking wires, the arc pl with the testing circuit, the arc M for determining the type of call, i. e. whether it is an ordinary call or one from a coin box. The arc p5 is a homing arc.

The distributor circuit includes a motor driven switch or uniselector D with wipers and arcs I, la, 4, 4a, and a latch magnet LM. The circuit for and the driving motor of the switch being well known per se is not shown.

Each arc of contacts consists of two rows of 52 contacts each, a double-ended wiper being adapted to traverse the rows in succession. The arcs are associated in pairs, namely, l and la, 2 and 2a, and so on, and it is arranged that during search when the wipers of an arc have traversed the contacts in both rows of the are a switching relay WS is operated to connect the main circuit wire to the wiper of the other are of the pair. The arcs I, and la, and 2, and 2a, are for connecting through the positive and negative wires, and the arcs 3, and 3a, and 4, and 4a, are concerned with testing into the connecting circuits.

The connecting circuits at the several operators positions are connected to the contacts on the several arcs. To the final eleven contacts in the second set of contacts of are 401. are connected the wires 1d, and OF which lead to the lamp display circuit Fig. 2. Connections are also made from certain of the ten contacts in arcs 3a and 2a corresponding to the contacts of arc to to which the wires ld are connected, the purpose of these connections being explained fully hereinafter. The connecting circuits are commoned over the arcs of the distributor switches of the several distributor circuits, the connecting circuits including those on demand positions, omnibus and other relief positions. There is provided a line relay L, a releasing relay B, a testing relay T, and switching relief relays S and SS respectively. The relay TCO is provided for determining the origin of a call, e. g. whether it has been originated over an ordinary line or a call box line. The relay RR is a ringing relay for applying a ringing current back to a calling party. The functions of relay D8 will be best understood from the subsequent detailed description, but generally they are to modify the testing circuit for testing in to the connecting circuits after a call has been released from association with the lamp display circuit.

The portion of the connecting circuit illustrated in Fig. 1 shows contacts SPKI, SPKZ and SPKS of a speaking key and relays SK,.SL, BA, and AS this being the order in which the relays are operated. The functions of the relays Will be best understood from the following detailed description. The elements of the operators circuit CPC Figs. 1 and 2 include contacts CA! and CA2 of a call answering key, and contacts. RA (Fig. l) of a release answering key. 'The functions of the relays CG, CN, and MN will be described in detail hereinafter.

The lamp display circuit Fig. 2 includes step by step switches or uniselectors AB and BA. The arcs abl abB of switch AB are shown, but only the arc ha! of switch BA is shown, the other arcs of the switch BA being associated with the lamp multiple extending over the arcs ab6ab8 and the method of connection of the multiple t0 the arcs will be readily understood from the consideration of the wiring of arcs ab6-ab8. The multiple wiring from the arcs ab6ba8 extends to the display lamps lil on the demand operators positions DOP, and it will be seen that the multiple wires over the arcs are slipped at each are so that the first contact of the arc abB is connected to the wire leading to display lamp l, the first contact in the arc ab! is connected to the wire leading to display lamp 2 whilst the multiple wire to lamp l appears at the second contact in the arc and so on over the remaining arcs. The demand lamps on the omnibus position OOP are connected in parallel with the lamps on the demand position DOP.

The are ab'l is concerned with the stepping and homing of the switch AB, and the object of the arcs c122 and ha! is to ensure that the switches AB and BA are always in alignment, the relay SY controlling the stepping of the switch BA to bring it into alignment with switch AB.

The wires Zdlill from the arc 4a of the distributor switch are connected seriatim to the relays AJ, contacts of the relays AJ being connected seriatim to the wipers of arcs ab6 12118.

The functions of the various relays shown will be best understood from the subsequent detailed description.

An omnibus position normally deals with incoming calls signalled on the incoming lamps quite independently of the traffic on the demand operators position "unless excessive congestion exists on the latter, whereupon the incoming lamps on a particular omnibus position or positions are disconnected and the demand lamps connected up by the operation of relay AA. Such a condition is indicated to a supervisory operator over the lead SP.

The general operations of the arrangements illustrated are as follows: Upon a call being made over a junction or line JCT the switch P in ILC searches for and tests into a free distributor circuit DD.

Normally one or more demand operators will have a position connecting circuit assigned which is brought about by throwing the speaking key SPK associated with the connecting circuit and the call answering key CA in the position circuit. On the seizing of a distributor circuit DD the switch D is caused to hunt for an assigned connecting circuit, and when such is found the calling party is switched through to the operator who then sets up the desired connection.

If the call had originated at a call box or over a line demanding special treatment, the operator would receive a tone on the origination and switching through of the call, and then cause the conversational connection to be set up by throwing a key (not shown) in the connecting circuit which applies earth to the negative wire.

The operator controls the release of the call and can release it by throwing either the key REL in the connecting circuit CC or the key RA in the position circuit OPC.

In the event of a call being made whilst a. connecting circuit is not assigned, the distributor switch hunts until afreecircuit over oneof the display leads Id is found and tests into this to cause a calling lamp to light, and busies the circuit against other searching distributor switches which will test into the other displaycircuit leads. The calls are thus caused to be queued up in the order of origination, and when the display circuit is fu1l,i. e. ten calls arestored," other searching distributor switches test into an overflow circuit over the lead OF to which" the call meter CM is connected at this time to indicate the number of calls so held.

An operator causesthe release of the call from the head of the queue by simply assigning a connecting circuit, the distributor switch associated with this call then being released from the display to search for the assigned connecting circuit whereupon the switches AB and BA step tomove up, in effect, the remaining calls in the queue one in the order of their priority of calling. Calls held on the overflow circuit are released and one of these tests into the lamp circuit just freed which now is so connected as to place the call at the lowest position in the queue, whilst the other calls are again connected to the overflow circuit.

If a call is held in the display circuit for more than a predetermined period a timing circuit comes into operation to cause calling lamps to light on a relief position (over the lead AL Fig.

2) so that a relief operator is signalled. Similarly, in the example described, a relief operator is signalled if the number of calls in the queue areaches seven, the relief operator being held until the number falls below six; If the number of calls in the queue reaches nine then the incoming lamps associated with a particular 10mnibus operators'position are disconnected, and the demand lamps are connected in parallel with the lamps on the demand operators position so that the omnibus operator'can assist the demand operator. The omnibus position is disconnected when the number of calls in the queue falls below eight.

The circuit arrangements illustrated will now a be described in detail.

Assuming that a call is made over an ordinary line, i. e. a:line from an ordinary local subscriber or over a local selector, then a loop'will be applied to the positive and negative wires JCT resulting in the operation of relay LA over contacts -h4 and n5. At contacts lal earth isuapplied tothe P wire-to busy the line at preceding selectors, if the call has been made over a selector, and at contacts Za3 the test relay TA is connected to the wiper of the test are p1. A circuit is closed from earth over contacts tal, M, 1112, pdm to magnet PDM to battery and magnet PDM energizes and opens the contacts pdm whereby the above circuit 'is broken and the magnet deenergized and the wipers of the switch are stepped on to the first outlet in their arcs.

If the outlet is busy the relevant contact in arc -.-.pl will be marked busyby an earth applied from the distributor circuit DD and as a consequence relay TA'will be short circuited and prevented from operating and therefore when the contacts pdm close 'on' the de-energization of themagnet PDM the circuit for the magnet isxagain closed and the wipers stepped on tothe next outlet in the manner before described.

A free outlet will be marked by a battery po-. tent-ial over contacts (m2, ssG and bl in the'distributor. circuit DDflzandx-as a,- consequence when the wiper pl meets a free outlet relay TA operates from the battery potential, over are pl, and contacts ms; The driving circuit for the magnet PDM isopened and an obvious circuit is closed for the right-hand coil of relay H at contacts tal. Relay H operates and at contacts hl locks itself temporarily over its left hand coil to earth over contacts lal, and at contacts hZ prepares a point in a locking and busying circuit over which it locks on the release of relay LA.

At contacts 71.3 a furtherpoint in the driving circuit for magnet PDMis opened. Contacts 116 prepare a circuit for the operation of relay TCO over its coil (I) and arcs p5 and p4, but however as the line calling is an ordinary line no connection is made to the contact in are 124.

At contacts M andn5 relay LA is disconnected, relay LA being slow to release and does not release immediately and the incoming loop is extended to relay L in DD over contacts rrl and W2 and relay L operates. A circuit is closed for relay B from earth over contacts 885 and ll and relay B operates. circuit for relays SS and DS, and, contacts 13 prepare a holding circuit over the arc pl for holding the circuit ILC. Contacts l4 prepare a supervisory circuit for the supervision of the call.

Upon the operation of relay B an earth is applied over contacts M and are pl to short circuit relay TA, hold relay H, and busy the outlet at the preceding selector if such has been employed. Relay LA releases shortly after relay B operates and-disconnects relay TA. Contacts 122 connect a ringing signal tone from lead RS and over contacts as? to the positive wire and thence to the calling party. Contacts b3 close a point in the circuit for the test relay T.

A circuit is closed from earth over contacts tl, sl, i006, b4, latch magnet LM to battery and earth, and the latch magnet operates closing contacts whereby-the circuit of a driving motor is closed, the motor in rotating driving the wipers of the distributor switch in known manner.

Under normal operating conditions, i. e. when calls can be answered on demand, a connecting circuit, a portion of which is shown in the rectangle CC, will be assigned on one or more operators positions, the assignment of a connecting circuit necessitating the throwing of a speaking key SPK associated with the connecting circuit CC and the connect answer key CA in the operators circuit OPC. On the closing of the contacts SPKZ a circuit is closed from battery over a resistance in the operators position circuit OPC, the coils of relay SK in series over the contacts SPKZ, contacts sZl to earth and relay SK operates and at its contacts skl short circuits its left hand coil. A circuit is closed from earth over the left hand coil of relay MN in OPC, contacts bal, SPK3, s7c2, relay SL to battery and earth and relays MN and SL operate in series. Contacts .92! hold relay SK over its right hand coil independ ently of contacts SPKL A battery potential is applied to the contact in the are 4 or M of the distributor D corresponding to the connecting circuit, over relay BA, key contacts REL, contacts s13, 8M, key contacts RA and CAl in. OPC, and contacts s12.

Assuming that an assigned connecting circuit exists in the arcs l, 2, 3, 4 of the distributor switch D then the wipers of the switch are driven until the wiper of are 4 meets the contact marked by battery over the relay BA, whereupon a circuit is closed from earthscontact enl, (also shownin Fig. 2) contacts 120.3, arc and Wiper 3, contacts wsd, s34, ds3, b3, rectifier 7', both coils of relay T in series, contacts ws5 to the marked contacts and relay T operates and at contacts tl opens the circuit for the latch magnet LM, whereby the wipers of the switch D are brought to rest, short circuits the upper coil of relay T, and relays T and BA operate in series. The lower coil of relay T is of low resistance and the earth over it busies the outlet to the connecting circuit against other searching distributors by preventing their T relays from operating. At contacts ba2 relay BA locks itself independently of contacts 812 and CAI, and at contacts bal disconnects the left hand coil of relay MN and connects in its place the right hand coil of this relay in series with relay CG. Relays SL and MN hold and relay CG operates. At contacts 12113 a circuit is prepared for relay AS but this relay cannot operate in series with the upper coil of relay T owing to the disposition of the rectifier 1'. Contacts had close the circuit of the supervisory lamp ASL in front of the operator.

When relay T operates and contacts tl change over, a short circuit is removed from relay S, and this relay operates in series with the latch magnet LM, the latch magnet however not being energized suiliciently in this series circuit to withdraw the latch.

Relay S at contacts sl locks itself independently of the latch magnet and at contacts s2 and s3 prepares to extend the positive and negative conductors to the connecting circuit CC. Contacts s4 prepare a point in a circuit for relay AS in CC. Contacts 85 do not concern us at present.

A circuit is closed from earth over the 0115 normal contacts onl, which as the switch is off normal are closed, contacts s5, coil (I) of relay DS, relay SS, resistance to battery and earth, and relays SS and DS operate.

At contacts es! and over contacts Z2 a locking circuit is closed for relays SS and DS independently of the contacts onl and .95. Contacts ssZ and $33 prepare further points in the positive and negative wires to the connecting circuit CC.

Contacts 334 connect earth over Z4 and s4, and over 10.94, ba3, relay AS to battery and relay AS operates to disconnect and extinguish the supervisory lamp ASL at contacts 6052. A locking circuit is closed for relay AS over contacts as! and SPKl to prevent relay AS being released whilst the speak key is operated. At contacts ss5 an obvious circuit is closed for relay TCO and the circuit for relay B is opened. Contacts $85 perform no function at this stage. Relay TCO operates.

When relay B releases after its slow releasing period the circuit ILC, and the preceding selector if such has been used, are held over contacts bl, $86, and s6 and Z3 in parallel.

On the operation of relay TCO contacts i002 and i003 complete the connection of the positive and negative wires to the connecting circuit. The other contacts of relay TCO will be referred to hereinafter.

The operator may now converse with the calling party and completes the connection to the wanted party. The speak key SPK in CC and the key CA in OPC are restored and relays CG, MN, and SL are released at SPK3. Relay SK is released at contacts sZI, and relays BA and T are held over the contacts ba2 and s13.

When the calling party clears the line, or flashes the operator to call her attention, relay L releases and at contacts 14 opens the circuit for relay AS in CC, the relay releasing to light the supervisory lamp ASL in front of the operator at contacts cs2.

The operator may release the distributor circuit by operating the release key RA in OPC or REL in CC and thereby release relay T which at contacts ti short circuits relay S.

On the release of relays L and S the earth is removed from the private Wire to the circuit ILC, and the preceding selector, and relay H is released which at contacts 716 closes an obvious homing circuit for the switch P.

At contacts 35 the original circuit for relays SS and DS(I) is opened, but these relays remain held over onl, Z2, and ssl, and a homing circuit for the switch D is closed over onl, 85, b4, LM to battery and the switch commences to home and when the home position is reached contacts on! open disconnecting the circuits for the magnet LM and relays SS and DS. Relays SS and DS release, and relay SS releases relay TCO. The testing circuit for the switch P is held open at contacts 0212 until the switch reaches home. The circuits are now at normal in preparation for dealing with further calls.

If the circuit ILC terminates a call box line the connection from the arc M to the coil (I) of relay TCO over contacts too will be completed, and it will be seen that on the operation of relay SS relay TCO will be prevented from operating over this coil as it is short circuited. As a consequence: a tone will be given to the operator over contacts i002 and the positive conductor and the operator on observing such tone throws a key (not shown) in the connecting circuit whereby an earth is applied to the negative wire and relay TCO is operated over its coil (II) and contacts tco 3, ss3, and s3.

Relay TCO operates and performs the functions before described.

In the event of the assigned connecting circuit being connected to the arcs la, 2a, 3a and 4a of the switch D, then when the wipers meet the last contacts in their arcs a circuit is completed from earth last contact in arc 3, contacts ws4, ss l, (183, 123, rectifier r, relay T, ws5, last contact in arc 4, (coil (1) of relay WS to battery and relays T and WS operate. At contacts wsl relay WS locks itself over its coil (II) to contacts on]. At contacts 1082-1085 the arcs I, 2, 3, and 4 are disconnected and'arcs I 11, 2a, 3a, and 4a are connected up. Contacts ws6 prepare to lock relay TCO over its coil (I). The circuit of relayT is opened when contacts ws5 change. over and relay T releases. Relay T is operated only for a very short time which may be insufiicient to allow relay S to operate. Even so, if relay S does operate relay SS and DS cannot operate as they are short circuited at this time by the connection of earth over contacts 882, $2, ws2 and are I a, the earth to the other side of the relays being derived over contacts on! and .95.

The switch now searches over the second half of its arcs for the assigned connecting circuit and when this is found the operations as before described take place.

If it is required to ring a calling subscriber who has left the line the operator throws a ringing key (not shown) in the connecting circuit whereby a battery potential is applied to the positive wire which operates relay RR. At contacts rrl and 772 ringing current over the leads R and RRS is applied to the calling line.

In the event of a connecting circuit not being assigned such as will happen at busy periods the distributor switch D drivesuntil the wiper of arc 4a meets the wires ld leading to the lamp display short circuited over contacts s32, 82, we! and are la. so that they cannot operate.

A circuit is closed from earth over contacts ss3, s3; ws3, arc 2a, coil (II) of relayTCO to battery and relay 'ICO operates and looks over contacts 'wsl and tool.

At contacts i005 a circuit is closed for relay DS over its coil (II) and contacts ss5 and relay DS operates Relay B isheld independently-of contacts ll. at contacts (152 so that relay B cannot be released in the-event of the calling party leaving the line.

'When relay A, Fig. 2, operates it closes a locking circuit for itself at contacts al independently of the arcs'ab3 and M24, and at contacts a2 prepares a circuit for relay B. Contacts 13 prepare a point in the circuit to'the overflow lead OF, but this circuit is not completed until a maximum number of calls arestored on the display. Contacts a4 and all close in parallel and'completea circuit over arc abt for the calling lamp I on the demand operators position DOP. Relay AC operates in parallel with lamp I and over contacts 3% and looks over contacts-ac! independently ofthe former contacts. Contacts (102. prepare to connect an earth to the wire ld leading to the distributor circuit DD to release the relay T thereof when the call is released from the display. Contacts a.c3 prepare anjenergizingcircuit for the magnet BADM,and contacts (104 prepare an energizing circuit for the magnet ABDM. Contacts ac5 prepare a circuit for the upper coil ofrelay ST and contacts act prepare a circuit-for the lower coil of this relay. 'Relay EN also operates over its left hand coil in parallel with lamp I. At

contacts e112 a further point is prepared in the circuit for relay ST. At contacts enl (see CC Fig.

1) the earth for the normal testing operations of the relays .T in' the distributors is removed from all connecting circuits associated with the distributor switches so that distributors searching for a connecting circuit in response to fresh calls are prevented from testing in-whilst callsare waiting on the display lamps.

The distributor switches D and their associated circuits over which succeeding calls are made are caused to test into and associate themselves with the relays BJ which operate in succession as calls arrive and at their respective contacts-4 and 5 close the circuits for the lamps DOP2--O over the arcs ab'l-ab8 and similar arcs of the switch BA, that is, provided meanwhile no calls have been answered. When the maximum number of calls are queued up on the display lamps,

. and therefore relay J operated, further searching switches test into the lead OF which extends to the callmeter CM over contacts 9'3 and arc (1125, the call meter indicating the number of calls so connected. The resistance in the connection from each distributor circuit to the lead OF is individual to the distributor circuit so that the relays T of other searching distributors are not affected and can freely test into the lead OF.

It will-be seen that providing the switches AB and BA arestanding in correspondingpositions a circuit is closed over arcs ab2 and bal for relay SY which at contacts syl opens the self drive circuit for the magnet BADM. Upon an operator assigning a connecting circuit by throwing the speaking key SPK associated with the connecting circuit and by throwing the connect answer key CA.v in the position circuit OPC, a circuit is completed from earth, over contacts CA2, relay CN, contacts cgl, mnl,

(relay MN being operated at this time in series with relay SL Fig. 1), e112, acfi, stl, lower coil of relay ST to battery and relay ST operates and locks itself over its upper coil and contacts st2,;

and ac5. When contacts stl are in the mid position relay CN which is a very fast operating relay :operates in series with the resistance and closes a circuit in serieswith itself for-coil (II) of relay CG over contacts c'nl but this coil is shunted for,

the moment. Relay CG operates when contacts stl change over and at contacts cgl opens a point in the operating circuit for the lower coil of relay ST;

A further point in the operating circuit for the;

lower coil of relay ST is opened at contacts stl and this coil, being shunted, gives the relayslow releasing characteristics. r 7

Thus the signal transmitted from the operators circuit OPC to the relay ST is of very short dura-.:

tion and occupies only a part of the movement of the contacts stl, this minimizing the chances of the simultaneous connection of two operators positions to the'display circuit.

A circuit is closed from earth over-contacts syl, ac3, std, magnet 'BADM' to negative and'the magnet energizes. 'A circuit isalso closed from ,earth overcontacts (104, stE, arc abl, magnet ABDM to battery'and this magnet energizes. I At contacts stB a point in the original operating circuit for relay AC is opened, but this relay holds over contacts acl.

Anearth is extended over contacts (102, $153, col, arc ab3, to relay A short circuiting this relay and also relay T in the distributor-circuit both of which relays release.

magnet LM to battery and the magnet energizes to close the circuit of the driving motor and the wipers of the switch are advanced to the home position where the contacts onl open releasing 'relay WS which in turn releases relay TCO at:

contacts 1086. Upon the relapse of relay TCO the circuit for the magnet LM is completed over contacts tl, sl, tcofi and b4 and the wipers are driven in search of the assigned connecting circuit, and when this is found relay T'operates' from earth over contacts tco'l, ds3, b3, rectifier R, relay T, contacts ws5 and over arc 4 or 4a. Relay T on operation allows relay S to operate and the operations as before described take place.

When relay A in the lamp display circuit Fig. 2

releases the circuit for the lamp DOPI and for :relay AC is opened at contacts at and a5, and

relay AC releases. At contacts act and ac the circuits for the magnets vBADM and. ABDM are opened and the wipers of the switches BA and AB are stepped. The short circuit is removed from relay A at contacts ac2. The holding circuit for the upper coil of relay ST is opened at contacts ac5 but relay ST does not release -im,;

mediately as it is rendered slow to release by virtue of its shunted lower coil so that the circuit to the operators circuit is maintained open at contacts stl for a short period to enable the apparatus in the display circuit to function correctly.

As the call of the first order of priority has been answered it is necessary that the other calls that are queued up on the display lamps should all be moved up one in their order of priority. This is accomplished over the arcs abfi, ab! etc. It will be seen that when the switch AB steps a circuit is closed over contacts b and b5, second contact of arc ab! to lamp DOPI and to relay AC in parallel therewith when relay ST releases. Thus the call of the second order of priority is moved into the first place, whilst the third call lighting the lamp DOP3 is moved into second place and associated with the lamp DOP2 and so on.

When the switch AB steps the circuit to the lead OF is broken at arc ab5 and the wipers are stepped on to the contacts connected to the contacts a3. Thus all of the T relays in the distributors held over the lead OF are released and the associated switches search for the free display lamp circuits, one of the distributors seizing the circuit of the freed relay A whilst the unsuccessful switches continue in operation until they again test into the lead OF over contacts 113, arc'ab5, and the call meter CM.

When the operator has dealt with the call the key CA is restored releasing relays CN and CG and that portion of the position circuit shown in Fig. 2 is restored to normal.

It will be seen that under normal operating conditions when no calls exist on the calling lamps, and relay EN is normal, relay CO is operated on the operation of the key CA and at contacts col opens a point in the test circuit into the display circuit. 7

When seven calls exist on the calling lamps DOP a circuit is closed for relay ON over its right hand coil in parallel with the lamp 1 and relay ON operates and locks over its left hand coil in parallel withlamp 6. An earth is connected over contacts 001122, 0712, to the lead AL leading to the lamp display circuits on one or more relief or omnibus positions whereby the operators on these positions are signalled to assist in the answering of the calls. Relay ON is released when the number of calls falls below six.

In the event of nine calls becoming queued up a circuit is closed for the right hand coil of relay OM in parallel with the calling lamp 9 and relay OM operates and closes at contact cm! a circuit for its left hand coil' in parallel with lamp 8.

At contacts omZ a circuit is closed for relay AA at one or more further relief or omnibus positions, the operating earth being derived over contacts oomZ which are contacts of a relay similar to relay OM but which is associated with the display lamps on an omnibus position, so that if more than a certain number of incoming calls are signalled in this position the omnibus positions cannot be called to assist in handling the traffic on the demand position.

Relay AA operates and at contacts cal to aalfl connects the demand display lamps on the omnibus position OOP in parallel with the display lamps on the demand position so that the, corresponding lamps light. The circuits for the incoming lamps on the omnibus position are disconnected at contacts call to aa20. Thus an omnibus operator is called to assist the demand operators and may answer the calls in an eX- actly similar manner to that previously described, the omnibus operator having connecting circuits associated with the demand distributor circuits.

At contacts aaZl a circuit is closed over the wire SP for a supervisory device to indicate the state of congestion to a supervisory operator. When the number of queued calls fall below eight relay OM is released releasing relay AA, and the demand calling lamps on the omnibus position are disconnected and the incoming lamps reconnected.

If however nine or more incoming calls are queued up on the incoming calling lamp display on the omnibus position a relay, say OOM similar to relay OM in LDC associated with that display will be operated and contacts oomZ will be open. Thus it will not be possible to interrupt the incoming 'traflic to the omnibus operators position until some of the incoming traffic has been dealt with. 7

In order that calls are'not held beyond a certain period during the time that insufiicient calls' are in the queue to signal the omnibus position there is associated with each of the relays AJ of the lamp display circuit LDC two relays, such as relays SA and ZA, only those relays associated with the relay A however being shown, the other pairs being connected and operated in an identical manner.

Two contacts a6 and a1 control the operation of the relays SA and ZA, and as all of the other relays BJ are provided with similar contacts, which however are not shown, the relays are designated as having seven contacts.

Earthed impulses are periodically and alternately delivered over the leads S and Z.

Assuming that a call is held on relay A over a period during which the impulses are delivered to the leads S and Z,then, when the impulse is given over the lead S a circuit is closed for the right hand coil of relay SA over contacts 2112 and a6, and relay SA operates, and looks over its left hand coil, contacts a'!, left hand coil of relay ZA, and contacts sal. Relay ZA will not operate in this circuit. When the impulse occurs over the lead Z relay ZA operates over its right hand coil and contacts 8112. At contacts zal a locking circuit is closed for relay ZA over its left hand coil and the left hand coil of relay SA is short circuited making the relay slightly slow to release. The circuit for the right hand coil of relay SA is opened at contacts zaZ and after a short period relay SA releases. A circuit is closed for relay DL at contacts 203, and relay DL operates.

At contacts all! a circuit is closed for relay AA, and at contacts (H2 an earth is applied to the lead AL to operate similar relays such as AA on the relief positions.

The switches AB and BA are stepped in the manner described to alter the position of the calls in the queue until the switch AB is stepped to the twenty first contact whereupon a circuit is closed from earth over contacts abdm, arc and wiper ab! magnet ABDM to battery and the switch AB is stepped to its normal position under the control of its interrupter contacts. Immediately the wiper of are (1112 steps out of alignment with the wiper of arc bal relay SY releases and at contacts syl closes the circuit for magnet BADM and the switch BA homes whereupon relay SY operates and opens the homing circuit for magnet BADM at contacts syl.

The common relays NA in the lamp display circuits are night alarm relays adapted to operate when any lamp is alight to operate an alarm.

We claim:

1. In a telephone system, a group of connective circuits, a group of hunting switches of the homing type having access to said circuits as first choice, a group of overflow circuits accessible to said switches as second choice, whereby switches operated at times when no connective circuits are available will connect with successive overflow circuits, and controlling means operating on switches connected with overflow circuits in the order in which the connections are established for releasing a connected switch and for causing it to rehunt over said connective circuits each time a connective circuit becomes idle.

2. In a telephone system, a group of individual overflow circuits, automatic switches having access to said circuits if no regular outlets are available, means for making each individual overflow circuit busy when seized, a common overflow circuit which is not made busy when seized and which may therefore be occupied by a number of switches when the individual overflow circuits are all busy, means for successively releasing the switches connected to individual overflow circuits, and means effective whenever an individual overflow circuit is freed for causing the switches connected to the common overflow circuit to hunt for the free individual overflow circuit.

3. In a telephone system, a group of automatic switches, a group of connective circuits accessible to said switches, a group of individual overflow circuits accessible to said switches only if none of said connective circuits are available, a common overflow circuit accessible to said switches only if all said individual overflow circuits are busy, means operative at a time when one or more switches are connected to the common overflow circuit and responsive to a connective circuit becoming available for releasing one switch connected to an individual overflow circuit and for causing it to hunt for the available connective cirr cult, and means for releasing all switches connected to said common overflow circuit and for causing them to hunt for the free individual overflow circuit.

4. In a telephone system, a group of overflow circuits, at corresponding group of lamps, switches having access to said circuits, means for busying each circuit when seized and for lighting the corresponding lamp, means for releasing switches from overflow circuits one at a time, and means intervening between the said circuits and lamps and operative every time a switch is released for changing the relation between said circuits and said lamps to associate each circuit with a different lamp.

5. In a telephone system, a group of relays numbered consecutively, a group of lamps correspondingly numbered, means for energizing said relays in the order of their numbering to light the corresponding lamps, means for releasing said'relays in the same order, and means operative each time a relay is released for shifting each relay into association with the next lower numbered lamp.

6. In a telephone system, a plurality of connective circuits common to a plurality of operators, automatic switches having access to said circuits, circuit arrangements such that the connective circuits are normally unselectable by said switches and are individually made available for selection when the operator handling the calls is ready to take a call, overflow circuits accessible to said switches at times when no connective circuits are available for selection, and means responsive to a predetermined number of overflow circuits becoming occupied for automatically signalling another one of said operators to assist in handling the calls.

'7. In a telephone system, a plurality of connective circuits common to a plurality of operators,

automatic switches having access to said cir- .2.)

cuits, circuit arrangements such that the connective circuits are normally unselectable by said switches and are individually made available for selection when the operator handling the calls is ready to take a call, overflow circuits accessible to said switches at times when no connective circuits are available for selection, means for successively releasing switches from overflow circuits to permit them to hunt for connective circuits as the latter are made available by the operator, and means for automatically signalling another operator if a switch remains connected to an overflow circuit for a predetermined time. BERNARD ANTHONY HENSLER. CHARLES LEONARD PETERS.

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