US1556474A - Automatic switching system - Google Patents

Description

Oct. 6, 1925. 1,556,474

A. BARNAY AUTOMATI C SWITCHING SYSTEM 5 Sheets-Sheet l Filed July 24, 1923 F I F191 Oct. 6, 1925.

A. BARNAY AUTOMATIC SWITCHING SYSTEM 1104 July 24, 1923 5 Sheets-Sheet 2 fiw e/w or r4. 567/7767 fly y mflww 'W r flf/ji Ev movfl o i I mm 1,556,474 A. BARNAY AUTOMATIC SWITCHING SYSTEM Oct 6, 1925.

Filed July 24, 1925 5 Sheets-Sheet 5 Oct. 6, 1925.

A. BARNAY AUTOMATIC SWITCHING SYSTEM mea gg zx, 133 J Sheets-Sheet 4 xuxunwzww 3 5 mmm wxvxw w E SKAQ uto mwmm Oct. 6, 1925.

A. BARNAY AUTOMATIC SWITCHING SYS TEM 5 O m 5 H r g m A M m 2* W/ Patented Oct. 6, 1925.

UNITED STATES PATENT OFFICE.

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Application filed July 24, 1923. Serial No. 653,568.

To all whom it may concern:

Be it known that I, ANTOINE BARNAY, a citizen of the French Republic, residing at 126 Avenue de Valenton a Villeneuve St. Georges, Seine and Oise, France, have. invented certain hew and useful Improvements in Automatic Switching Systems, of which the following is a specification.

The present invention relates in general to an automatic switching system of the kind generally known as a step by step system, employed particularl in telephony, but capable to be employe generally in any system of intercommunication either electrical or electromagnetic.

The main object of the inventlon is to produce a new and improved system of selec tion'whereby the operation of the selectors,

in response to impulses of a calling device is realized in the same way as the trunk hunting movement these two movements being produced by the same means.

Another object of the invention is to employ only one type of switch, of simple mechanical construction, robust, having very little inertia, for the difi'erent series of I switches such as preselectors, finder switches and selectors.-

A further object of the invention is to pro vide an auxiliary organ individual to a selector or common to a number of selectors of the same category of very little inertia which is operated by the impulses of the calling device and which in turn directs the group hunting movement of theselector or selectors i Lastly, another object of the invention is to provide means for grouping the lines connected to the banks of the different switches in the mosteconomical manner according to the needs of the trafiic. Referring to the drawing which represents a preferred form of the invention,-

Fig. 1 is a diagram of the; different organs used to establish a connection.

Figs. 2, 3 and 4. are circuit diagrams of the'organs represented "in, Fig. 1 and should I diflerentconnections between i the auxillarv control switches and the selector switches.

Fig. 8 isanother circuit diagram in which the, control switches are common to acertaln number of selectors.

1 etc.

.. and anauxiliary or control switch (1,.

The organs employed to establish a con nectlon and represented in Fig. 1 consist of the calling subscribers'telephone P, a line and cut oil relay R, a finder switch A, a preselector B, a undreds selector D, a line selector E,the line and cut off relay of the called line R and the called 'subscribers telephone P. 'The system represented, is a three digit system, for a four digit system, there would be another selector, the thousand selector, similar to the selector D, introduced between the calling'line and the line selector E, for 5 digits two selectors between the calling line and the connector, and finally, for a two digit system the selector D would be omitted. A finder switch A and a preselector B areshown but according to the trafiic to be handled it might be economical to use only one or the other of these two organs. I The progression of tliecall is. the same, excepting for the transmission mechanically and electrically of the impulses sent out by the calling device, as in the best known step by step systems.

The subscribers stations P and? may be one of anyof the well known types having a calling device which opens and closes the line circuit a number of times equal to the digit to be sent. Q

The line and cut off relays R are individual to each line, and each line is multipled on the banks of a group of finder switches and also on the banks of the line selectors which have access to the group of one hundred lines, in which is located the 'line considered. t

The finder switch A' and the preselector B consist of agroup of relays and two rotary switches K and i of a group of relays and a rotar switch K similar to the rotary switches 1 and K The switches represented at K K K and K are step by step rotary switches of the type in which the-wipers move in a forward direction only. In further explanation of these switches it should be stated that they are of the type in which the wipers are the selector D consists advanced when the stepping magnet retracts its armature ratherthan when the rows of contacts to'which may be connected either the subscribers or trunk lines, and on' the selectors an extra row or two of auxiliary awa contacts are "bank, these wipers being either double or single;'in the first case when one end of the wipers quits the last contact of a row, the other and engages the first contact of the same row. In the second case, the wipers are in contact with the bank only during half a revolution, one set of wipers being secured to the shaft at 180 degrees from the other, and only one set of wipers is in contactwith the banks at the same time.

For a 50 line rotary switch, the bank consistsof tliree rows of 50 contacts each and 3 double wipers, fora 100 line switch the bank consists of 6 rows of 50 contacts each and either six single wipers or 6 double wipers, and a relay associated with the wipers to select one of the two sets of wipers. This latter arrangement is preferable as it diminishes by half the rotation of the switch. For a 200 line switch the bank consists of 12 rows of 50 contacts each and 12 single wipers are used with a wiper choosing relay.- For the selectors, in all case'san extra row of contacts on the bank and an extra wiper are provided to control the rotation of the switch.

Each selector is provided with a set of off normal sprin s which are operated as soon as the wipers save their normal position.

In Fig. 2 the line finder A. is a 100 line rotary switch having two sets of three double wipers, the preselector B is a 50 line rotary switch with 3 double wi ers and the selector D. has two sets of t ree double wipers and an extra wiper with its associated row of bank contacts. The control switches such as C, associated with the selectors, are of the same general construction as the previously described rotary switch K K K and operates in the same manner. They are much smaller than. the rotary switch K K K and are provided with two or more rows of 11 contacts each, and have a set of 03 normal springs which are operated when the wipers leave their normal position.

The control switch C, Fig. 52, associated with the selector D is provided with two rows of 11; contacts each, arranged in such that the contacts occupying correspon ing positions in the two rows, are connected electrically by the wiper.

The mechanical construction of these rotaryswitches is not an object of the present invention.

The Fig. 3 is the circuit diagram of the line selector E with its two associated control switches C and C and its rotary switch K These organs are similar to those of the hundreds selectors shown in Fig. 2; the only difference between the line selector and the hundreds selector is the arrangement of the circuits.

The Fig. 4 represents arotaryline selector, i. e. a selector which after being directed to a group of lines by two trains of impulses is capable to select and connect with an idle line in the group, the selection of an idle line in a group being automatic and each group of lines being determined and limited by the resistance of the cut 05 relay of the last line of the group which is less than that of the other cut off relays associated with the other lines of the same group. To facilitate the grouping of the lines, the cut off relays such as R,, R and R of the lines, which are served by a rotary line selector, are provided with an extra terminal connected to the left hand end of the winding of the cut off relays. The test wire is connected to this middle terminal when there is only one line, or to the middle contact of the last line when there are several lines listed under one number. The test wire is connected to the end terminal on all the other lines of the group.

Fig. 5 is a diagram showing the connections between the control switch and the row of control contacts of a thousands or hundreds selector which has access to ten different groups of trunk lines and each group of trunk lines having ten trunks. Supposing that the selector is a hundreds selector; in this case the control wires for the 1st. and 2nd. hundreds, 3rd. and 4th. hundreds, 5th. and 6th. hundreds, 7th. and 8th. hundreds, 9th. and 0 hundreds, are connected together on the bank of the control switch. These five control wires are connected to five series of 10 contacts on the row of control contacts in the bank of the rotary switch K, in such a way that when the digit 1 or 2 is dialled, the selector only rotates to find an idle line, when the digit- 3 or 4 is dialled, it rotates over ten contacts before beginning the trunk hunting movement and so on. For the digits 9 or 0, the selector rotates over 40 contacts before beginning the trunk hunting movement. The selection between the odd or even digit is obtained by a wiper selecting rela as will be described in the de tailed circuit description further on. After the wipers are directed to the first set of contacts of a group of trunks by the control switch which is operated by the impulses of the calling device, an ldle trunk in the'group may be selected by the automatic rotation of the wipers the control wire for the group being connected to the ten confacts of the control bank in the chosen group.

Fig. 6 is a diagram representing. an uneven grouping on a ten thousand selector in a multi-oflice telephone system. It is assumed that there are 60,000 subscribers lines in the system, distributed amongst six dif necessitate 750 trunks between the two ofiices in one group, this groupment may be obtained by employing secondary line switches each having a capacity of 50 trunks and the trunks from the selector banks in groups of 15. i If it were necessary to have only 650 or 700 trunks, the trunks from the selectors banks would be arranged in groups of 13 or 14.

It is assumed that the traflic with the 4th and 5th ten thousand is not very heavy and instead of employing secondary line switches, it is more economical to have the trunks from the selector bank in groups of 25.

It is further assumed the 6th and 7th ten thousand are two oflices in the same building and as the cost of the inter oflice trunk lines is not preponderating, the trunk from the selector banks will be arranged in groups of 10.

This simple example is chosen to show I the advantages to be gained by varying the size of the different trunk groups when it can be done easily without too many comlications, which is the case in this system.

t is not necessary to have any two groups alike, for example, in providing two rows of control 'contacts,10 groups of trunks each having a different numberof trunks may be obtained. I

In general there may be 50, 100, 150 or 200 trunks in a selector bank and these trunks may be arranged in any number of group between 1 and 10.

Likewise, in another oflice of the supposed multi office system, the traffic may be distributed in an entirely different way than in the oflice considered and an arrangement of the trunk groups entirely different would be moreeconomical;

Fig. 7 is a diagram showing the connections between the control switches and the control contacts of a line selector. The

tens control switch 0 has five wires (one for two tens consecutive) connected to the first contact ofeach group of ten contacts in the row of control contacts of the bank of the rotary switch K the selection of the odd or even tens being obtained by ,a relay.

The units control switch G is connected by 9 wires (the first contact is not connected as it does not require the rotation of the selector) to the nine remaining contacts in each one of the 5 groups of tens control contacts. Normally the line selector has a capacity for 100 lines but its capacity may be doubled when it connects with subscribers having several lines listed under one number. In this case, a second row of control contacts on the bank of the rotary switch is necessary.

Before entering into the detailed circuit" description a general outline of the operation is as follows: 7

When the receiver is removed at the calling station, the calling line is extended to a selector (hundreds selector in a 3 digit sys tem, thousands selector in a 4 digit system, etc. by means of a finder switch or a preselector or the two organs acting together.

Responsive to the first train of impulses sentby the calling device, the control switch takes a position corresponding to the impulses received and places a battery potential on a control contact of the bank of the main rotary switch so as to stop the'latter on the first trunk of the group determined by the first train of impulses. The main rotary switch does not wait until the end of the train of impulses before commenc in to operate. Assoon as the control switch reaches a'position that determines a movement, the main. rotary switch commences to operate and continues until the control wiper reaches the contact which is connected to the control switch. After reaching the aforementioned contact, the

automatic trunk hunting movement begins. When an idle trunk is found, the calling line is extended to the next serially'related selector and the same operation is repeated. When the final or line selector is reached, the operation-is a little different from the other series of selectors, as in the line selector two trains of impulses are necessaryto determine the final position of the wipers. For this purpose, two control switches are provided, one for the tens digits the other for the units digit. The first'control switch directs the wipers to the tens group corresponding to the impulses received for the tens digit and the second, operated by the unit digit impulses directs the wipers on to the particular line of the tens group al-' ready chosen In the case of a rotarydine selector, after finding the, first line of a group of lines having the same number, the line selector selects an idle line in the group,- if-there is one, and in case all the lines are busy, gives a busy signal to the calling subscriber.

In the present system, an idle line is identified by the presence of negative battery on the test wire, and a line tests busy if the negative is not connected to the test wire, therefore the so called dead lines i. e. the lines not in service give automati-j cally the busy test when an attempt is made to connect with them.

be described more in detail and for this purpose, it will be assumed first that the subscriber at station P, Fig. 2, desires to establish a connection with the subscriber at station P, whose telephone number is 903. When the receiver is removed at station a circuit is completed for the relay 2, flour Md, contact 6, the line and the st" scribers station in series, the contact 7, the winding oi? relays 2 to battery. Relay 2 is energized and a contact t places ground on the starting wire of the tinder switches by the contact 9; and at the contact 3 connects the low resistance winding oi" relay 5 to the test contacts of the line finder banks.

The relay 33 of the finder A is energized by the gIUUfiMl on the starting wire, over the circuit ground. contact 4, contact 9, contact 45, winding of relay 33 to battery. Relay 33 energiz d closes the circuit of the rotary magnet over the path; ground, contact 41, contact 30, contact 21. contact 58, winding of the electro magnet 59 to battery. By the contact 37, ground is placed on the test wiper 10 in series with the winding of relay 16 in passing by the contact 25. At contact 36, ground is connected to test wiper 13 by way of the contact 18 and the winding of rela 24. lit the wipers of the finder switch are not on the set of contacts of the calling line. neither one of the relays 16 or Qt is energized and the rotary magnet is energized over the aforementioned circuit. Near the end of its stroke, the armature 58 opens the circuit of rotary magnet 59 and when the armature 58 is retracted h its spring, the wipers will be advanced into engagement. with the next set oiv bank contacts. This operation is repeated until one of the test wipers encounters a test contact connected to battery in series with a low resistance which is the condition of a calling line. Supposing that the test wiper 10 is on the test contact ot the calling line, relays 5 and 16 energize in series over the circuit. ground contact 37, contact 25, winding of relay 16, test wiper 10, test contact of the line finders bank, contact 3, the low resistance winding of relay 5 to battery. The cut oti relay 5 opens the circuit of relay 2 at contact 7, removes the ground from the calling line contact 6, and at the front contact of armature 8, establishes its holding circuit, with its two windings in series. The second *inding of relay 5 is oi high e ou h resistance to prevei e energization stop relay such as 16 or 24% of tinder switch and cons quently to another tinder switch to stopon line.

Y hen 1 ea ers circuit of the rotary magnet 59 at contact 21 and the wipers are stopped on the set of contacts of the calling line. Furthermore, the relay 16 prepares its holding circuit at contact 17, opens the circuit'ofrelay 24 at contact 18 and at contacts 22 and 23 connects the line wipers 11 and 12 to the contacts 50 and 52.

At the same time thatthe finder switch K, starts its line hunting movement, the pre selector K starts hunting for an idle hundred selector. When the relay 33 energizes as has been explained, it closes the circuit of the rotary magnet 57 by the following path: ground, contacts 43, 38, 56, winding of the magnet 57, contact 119 to battery. At the same time at contact 40 the low resistance winding of relay 4:2 is connected to the test wiper 53. The rotary magnet 57 operates as has been explained for the rotary magnet 59 to advance the wipers 53 to inclusive.

- Vhen the wipers encounter the contacts of an idle hundreds selector, such as the selector D Fig. 2 which is identified by battery on the test wire, the relay a2 is energized over the circuit: battery, winding of the magnet 93 of the control switch C the first contacts of the two rows of contacts of the control switch, which are connected together by the wiper 100, contacts 80, 71, test contact of the bank of the preseleotor, test wiper 53, contact 40, upper Winding of relay 42, to ground. Relay 42'011 energizing, opens the circuit of the magnet 57 at contact 43 and. the wipers are stopped on the idle hundreds selector. Furthermore, at contact 47, the lower high resistance winding of relay s9, is connected to the test wiper and at contacts 49 and 51, the calling line is extended to the relay of the selector by Way of the wipers 54 and 55 and the contacts 112 and 11 i. Relay 65 is energized in series with the calling line and by the contact 66 closes the circuit otrelay 68 to ground at contact at. On energizing relay 68 replaces the hattery potential on the test Wire at contact 71 by ground at contact 72, to complete the holding circuit of relay 42 in the preselector and to busy the hundreds selector to the other preselectors.

Returning now to the finder switch and the preselector. As explained the said switch and preselector begin their operation at the same time. If the preselector finds an idle hundreds selector before the switch has found the calling line, the circuit as described for the relay 33 is opened contact i when relay 4&- is energized hu iinmed established by the contacts he winding of relay a slow relay do 0 s time that its cii 4-2 0' ates. When circuit of the relay 33 at either the contact 19 or the contact 28 and after an instance the slow relay 33 falls back. Onthe "other hand, if the finder switch connects with the calling line before the preselectors finds an idle hundreds selector, if there are no other lines of the group in the calling position, when the relay 2 falls back at the energization of relay 5, groundwill be removed from the starting wire. But at the same time, the calling line has been extended to the contacts 50 and 52 by one of thestop relays 16 and 24 and the relay 33 remains energized in series with the calling line until the relay 42 operates. In any case, the relay 33 does notf-all backuntil the calling line is extended to an idle hundreds selector.

As a further result of theenergization of relay 42, ground is" placed on relay 5 by thecircuit, ground, contacts 44, 26,17, winding of relay 16, test wiper 10, test contact front contact of armature 8 andthe said armature,

and the two windings of relay 5 to battery. g

"tenth contact of Its bank, ground is placed Relays 5 and 16 remain energized over this circuit, when relay 33 falls back and opens the contact 37. At the contact 45 the circuit of relay 33 is opened and the starting wire is extended to the contact/35, but this has no effect at this time as relay 16 is energized and the contact 19 open. An instant after its circuit is open, relay 33 falls back and the starting wire is extended to the next finder switch by the contact 34.

Inthe hundreds selector as a further result of the energization of relay 68, by the contact 75, ground is placed on the contacts 2, 4, 6, 8 and 10 of the first row of bank contacts of the control switch 0,, and on the contacts 3, 5, 7, 9 and 11 of the same row of contacts in series with the upper'winding of relay 90. At contact 73, relay 68 prepares the impulse circuit for the magnet 98 of the control switch, at contacts 70 and 76 prepares the circuit of the magnet 115- and opens at contacts 69 and 74the release circuits'of the control switch C and the rotary switch K When the calling line is extended to the hundreds selector, the subscriber hears a special tone induced in the induction coil 109 that indicates that he can begin to dial his number, r

The calling subscriber will now operate his calling device dial in accordance with the first digit 9, of the called number as are-- sult of which nine interruptions will be produced in the circuit of his line and the line relay 65 of the selector D will be'deenergized nine times. At each deenergization, the relay 65 transmits an impulse of current to the magnet 98 of the control switch ,over a path which extends from ground by way of contacts 64, 67, the winding of relay 77, contact 7 3, the first contact in the first row ofcontacts in the bank, of the control switch, the wiper 100, the-first contact in the second row of contacts in the bank of the con.- trol switch, the winding of magnet 98 to battery. By the operation ofthe magnet 98, responsive to these impulses, the wiper 100 is advanced stepby step and is brought to rest on the -te'nthQQontact of the bank. Relay 77 is ener'gizedin series with, the magnet 98 and since it is slow acting, it-holds its armaturejattracted during the series of impulses. Also the relay 68, on account of its slow action does" not fall back during the impulses. After the first impulse, the wiper 100 leaves its normal position and the circuit of the magnet 98 is opened at this point but a new circuit for the eight succeeding impulses has already been established by the relay 77 at the contact 81. At the contact 79, relay '77 short circuits the upper windingof relay .90 and at contact 82 opens a When the wiper 100 comes to rest on the I on the control wire that is connected to the control contacts in the bank of the rotary switch. K thatv occupies the same positions as the trunklinesto the line selectors of the.

9 and '0 hundreds.

After the first step 'of'the control switch the off normal springs are shifted and-fa circuit is completed ,for the magnet 115 to ground by-the contacts 64, 106, 70,89, 76,

' 83, 116 the winding of the magnet 115 to bat+ tery. As the control wiper 125 of the rotary switch K whenin 1 normal position, is on IOU a contact connected. to the second and third contacts in the second row of contactsof the control switchs'bank (see Fig. 5) and fsince the wiper placesground on these con} tacts as it passes them, after the first impulse relay 84 isenergized before the magnet 115 has time to operate,'over,the circuit,

ground, contact 75, 2nd. contact of the first. row of contacts wiper 100, 2nd. contact of the 2nd. row of contacts in the bankof'the control switch,.the control wire 101, the first contact of the 1st. group"(not shown) of control contacts in the .bank of the rotary switch K the control wiper 125, winding of relay 84 to battery. Relay 84 opens the circuit of the magnet 115 at the contact 89 before it hastimeto-operate. After the 2nd. impulse the wiper 100 laces ground in serieswith the upper win ing of relay 90- on the same control wire as for the 1st. impulse but this winding is short circuited by relay 7 7 so no circuit changes'takes place and relay 84 remains energized. After the 3rd. impulse,

the wiper 100 removes the ground from the control wire 101 and places it on the control wire 102. This control wire is connected to the contacts on the control bank of the rotary switch K,- that occupies the same position as the trunks to the 3rd. and 4th. hundreds. lVhen the ground is removed from the Wire 101, relay 84 falls back and at contact 89 closes the circuit of the magnet 115. This magnet operates in the same way as the magnets of the finder and preselector to advance the wipers 125 to 131 inclusive. The operation of the magnet 1.15 continues until the wiper 125 finds a grounded contact, which causes relay 84 to operate again and opens the circuit of the magnet 115 at contact 89. As the advancement of the wipers begins during the impulses and that for each two impulses received by the control switch C, the magnet 115 only advances, its wipers ten contacts, the wipers 125 to 131 inclusive are brought to rest in a very short time after the ninth impulse on the contacts of the first trunk connected to the ninth and zero hundreds. An instant after the ninth impulse relay 77 falls back and when the relay 84 energizes to stop the wipers on the 9th. group of trunks, the circuits of the automatic trunk hunting operation are completed. With relay 77 at rest and relay 84 energized ground is connected to the test wiper 129 in series with the lower winding of relay 61'by way of the path, ground, contacts 78, 87, lowerwinding of relay 61, contacts 91 and test wiper 129. At the same time, ground is placed on the magnet- 115 by the circuit: ground, contacts 64, 88, 76, 83, 116 the winding of the magnet. 115, to battery. It the first set of contacts "in the 9th. group is busy there will not be a battery potential on the test contact and the relay 61 will not be energized and the magnet 115 advances the wipers 'in the same manner as when hunting for the group of trunks. When the wipers are on an idle set of contacts, the test wiper 129 will find battery and the relay 61 is energized by the circuit; ground, contacts 78, 87, lower wind ing of relay 61, contact 91, test wiper 129, test contact, test conductor 134, resistance 204 (Fig. to battery. The circuit of the magnet 115 is opened at contact 64 and the wipers brought to rest on the contacts of an idle line selector in the 9th. hundred. As a further result of the energization of the relay 61, the upper winding of relay 61'is connected at contact 62 to the test conductor; at contact 63 ground is placed on the test conductor of the preselector and at the contacts 112 and 114 the circuit of the line relay 65 is opened and by the contacts 111 and 113 the line is extended to the relay 145 of the line selector (Fig. 3) by way of the contacts 95 and 97, the wipers 130 and 131 and the conductors 132 and 133.

The relay 145 energizes in series with the calling line and closes a circuit for the slow acting relay 153 to ground by way of the contacts 146 and182. Relay 153 on energizing, causes a considerable number of circuit changes. At contacts 155 battery is removed from the test conductor and ground is placed on the same to complete the holding circuit o1 relay G1 in the hundreds selector and to busy the line selector to all other hundreds selectors. Returning now to the hundreds selector. when the relay (35 falls back, it opens the circuit of relay 68, which on account 01 its slow action does not fall back but an instant later in order that the holding circuit furnished by relay. 153 or the line selector is assured hetore the contacts 72 and are opened. hen the contact 75 is opened, relay 34 falls back and opens the circuit of the lower winding of relay 61, but this relay now has a holding circuit by the high resistance winding, the contact 62 and the grounded test conductor.

Should all of the line selectors in the 9th. hundred be busy. the magnet 115 would drive the wipers 125 to 131 inclusive on the first contact of the following group of trunks and as on this group of trunks the control contacts are not grounded. relay 84 would fall back permitting the magnet 115 to drive the wipers to their normal position. ln this position, the contact 117 is opened and the circuit of the magnet 115 is opened as relay 7'? has fallen back. In this position, the calling subscriber would receive the busy signal induced on the induction coil 110, as the ground for the line relay is fed through this coil by way of the contacts and 107. When the calling subscriber hangs up his receiver, the release would take place as will be described further on.

Returning now to the line selector, the relay 153 besides placing ground on the test conductor 13. as already explained, prepares the ini 'iulse circuits of the control switches C, and C, at contact 157; the ground at contact 159 is extended to the relay 161 by way of the wiper 207 and the first contacts in the two rows of contacts or" the tens control switch by way of contacts 159 and 186. ground is'placed on the first row of contacts of the control switch C, and by the wiper 214 and the first contact of the second row of contacts of the said bank. the ground is extended directly to the contacts 2. 4. 6. 8 and 10 of the first row of contacts of the tens control switch (1, and in series with the lower winding of relay 1% to the contacts 3, 5. 7, 9 and 11 of the same row of contacts. ll hen the relay 161 energizes, it connects at the contact 163 the impulse cir cuit to the magnet 205 of the tens control switch and prepares its holding circuit at contact 164.

The calling subscriber now operates the dial of his calling device in accordance with the second figure 0 of the called number, as a result ten interruptions will be produced in the circuit of his line and relay. 145 will be deenergized 10 times. At each deenergiill) zation an impulse of current will be sent to the magnet 205 over a circuit which extends from ground by way of contacts 182,147,

at the end of the ten impulses, the wiper 207 will come to rest on the 11th. contact of its bank with theresult that ground in series with the lower winding of relay 196 is placed on thecontrol conductor 222 which is connected to the control contacts of the 9th. and 10th. tens groups of lines in the bank of the rotary switch K Relay 148 is energized in series with the magnet 205 and since it is slow acting it holds its armature attracted during the train of impulses. After the first impulse the wiper 207 leaves its normal position and the first circuit of the relay 161 is opened but a second circuit is established by way of the contacts 164, 150, 186 and 159 to ground. At contact 151 relay 148 short circuits the lower winding of relay 196. Contact 209 is closed after the first step of the magnet 205 and a circuit is completed for the magnet 215 to ground by the contacts 216, 179, 209, 186 and 159. As the control wiper 224 of the rotary switch K when in normal position, is on a contact connected to the 2nd. and 3rd: contacts of the second row of contacts of the control switch C (see Figure 7) and since the wiper 207 places ground on these contacts as it passes them, after the first impulse, relay 177 is energized before the magnet 115 has time to operate and opens the circuit of the said magnet at contact 179. After the third impulse the ground on the 2nd. and 3rd. contacts of the second row of contacts of the control switch C is removed and the relay 177 in falling back permits the magnet 215 to operate in the same manner as the magnet 115 of the hundreds selector. and .to advance the wipers 224 to 230 step by step. When the control wiper 224 reaches a grounded contact the relay 177 is energized and opens the circuit of the magnet 215, at contact 17 9. On account of the high speed of operation of the magnet 215, and that for each two impulses received by the control switch C the magnet 215 only advances its wipers ten contacts. and that the advancement of the wipers begins during the impulses, the wipers 224 -to 230 inclusive arebrough-t to rest in a veryshort time after the 10th. impulse on the first line in the 9th. and 10th. tens groups of lines. An instant: after the last impulse slow relay 148 falls back and removesthe short circuit: on the lower winding of the relay 196. This relay now energizes in series with. the relay 177 over,;-the circuit, ground, contacts 159, 186, first. contact of the first row of contacts in the bank of control switch C the wiper 214 the second-contact in the first row of contacts of the said bank, the lower winding of relay196, the 11th. contact of the first row 01 contacts, the wipers 207, the 11th. contact of the second row of contacts of the control switch C the first contact in the 5th. group of tens contacts in the row'of control contacts in the bank of K the control wiper 224, the winding of relay 177 to battery. The relay 196 connects up the wipers 225 to 227 inclusive as they have access to the even numbered groups of ten lines, and at contact 199 closes its holding circuit to ground by way of contact 159.

' When the relay .148 falls back it opens the holding circuit of relay 161 at contact 150 and relay 161 falls back also. In falling back relay 161 closes the impulse circuit to the magnet 210 of the unit control switch C by way of the contact 162.

The calling subscriber will now operate the dial of his calling device in accordance with the last digit 3 of the called number, as a result of which three interruptions will be produced in the calling subscribers line circuit and the line relay 145 will be deenergized three times. At each deenergization relay 145 transmits an impulse of current to the magnet 210 of the units control switch over a path which extends from ground by way of contacts 182. 147, winding of relay 148, contacts 157, 170, 162, the winding of the magnet 210 to battery. For each impulse, the magnet 210 advances its wiper 214 one contact and at the end of the three impulses the wiper 214 will come to rest on the fourth contact of its bank. with the result that ground is placed on the control conductor 223, multiplied on the 3rd. contact in each of the ten groups of control contacts of the-bank of the rotary switch K, (see Fig. 7 V

As long as the wiper 214 is in contact with the first or second contact of its bank, relay 17 7 remains energized but when it leaves the second contact, relay 177 falls back and closes the circuit of the magnet 215. Magnet,

215 operates to advance the wipers, until the wiper 224 finds a grounded contact, in this case the third contact in the tenth group of ten lines. Relay 17 7is reenergized, opens the circuit of magnet 215 at contact 179 and the wipers come to rest on the third line of the tenth tens group of lines. After the first impulse the ofi normal springs of the control switch C are shifted and the contacts 212, 213 are closed. When the relay 148 falls back after the last impulse, the circuit of relay 169 is closed by the path, ground, contacts 159. 186, 149, 180. 213, the upper winding of 169 to battery.- Relay 169 establishes its holding circuit to ground. by way of contacts 159, 186-. 172, the upper winding of relay 169 to battery. By the contact 171 this same ground is connected to armature 164. At contact 174 relays 161 and 189 are connected in series and by the contact 175, the test wiper 225 is connected at a point midway between the windings of relays 161 and 189, by way of the path, test wiper 225, contacts 198, 185, 167 and 175. At contact 170 the impulse circuit is opened.

It the called subscriber is busy, the test contact is grounded, and this ground on the test wiper 225 short circuits relay 189 and energizes relay 161. As a result, of the energization of relay 161, a locking circuit is established at contact 164 (this contact is adjusted to make before the others are operated) at contact 165, the connection of the test wiper to relay 161 is opened: at contact 167 the connection of the test wiper 225 to the relay 189 is opened and at the contact 166 ground is placed on the magnet by way of the circuit: ground, contacts 159, 186. 172 166, 217, 216 and the winding of magnet 215 to battery. The magnet 215 operates and drives the wipers 224 to 230 inclusive to their normal position. At normal position the ofinormal contact 217 is opened and the magnet 215 comes to rest. As a further result of the energization of relay 161, a busy signal is placed on the calling line in series with the condenser 142, by the contacts 168 and 176 to inform the calling subscriber that the called line is busy and that the connec tion cannot be completed. The calling sub scriber on restoring the receiver causes the connection to be released as will be explained further on. T1 the called line is idle when the wipers come to rest, the test wiper will find battery on the test contact in series with the right winding of the cut off relay 234; of the called line. This winding is 01 low resistance and practically short circuits relay 161 when relay 169 is energized. As a result, relay 189 is energized by its two windings in series but it only has enough ampere-turns to close the contact 187 without operating the others and on account of. the resistance of these two windings the cut 06 relay is not energized. At contact 187, the test wiper 225 is connected to the upper low resistance winding of relay 189 and the relays 189 and 2341 are completely energized. Relay 2341 removes the line line relay 232 from the line at contact 237, at contact 238 removes the ground from the called line and at contact 236 removes the short circuit from around its left winding. The relay 2341 remains energized with its two windings in series. Returning to relay 189, a considerable number of circuit changes takes place when it is energized. At contact 188, the connection of the test wiper 225 to relay 161 is opened; contact 186 the ground is removed from the holding circuits of relays 169 and 177 and by the contacts 194: and 195 it connects up the line wipers 226 and 227 to the contacts 191 and 198 of the ring out on? relay 181. Relay 177, on Tallnoses-re ing back, closed the circuit of the ringing current on to the called line at contact 178 and the called subscribers bell is rung over the circuit: ground, the ringing generator 221, the ringing interrupter 220, 219, contacts 178, 193, 195, 202, the wiper 227, the line conductor 233, the subscriber s bell 2 13 and the condenser, 242 line conductor 232, line wiper 226, contacts 200, 1941, 191, the lower winding of relay 181 to battery. A small capacity condenser is bridged across the contact 190 to permit a small part of the ringing current to pass out on the calling line each time that the called subscriber is rung. The slow relay 181 is not energized by the ringing current, but when the called subscriber answers, a path for direct current is completed at the called subscribers station in series with the transmitter and receiver and the relay 181 is energized. 11s a result of the energization of relay 181, a holcing circuit is established at contact 181; at contacts 190 and 192, the calling line is extended to the battery teed relay 135. Relay energizes in series with the called line and the called subscribers station. As a result of the energization of relay 135, the battery to the calling line is reversed at the contacts -141 and 138139 for supervisory purposes. As a further result of the energization of relay 181, the ground on the winding of relay 153 is opened at contact 182 but is immediately reestablished by the contact 136, when relay 135 is energized. The two subscribers are now in communication and the circuit of the voice currents is shown by the heavy lines.

At the end of the conversation, when either the called or the calling subscriber replaces his receiver, the relay 153 falls back. Tr" the calling subscriber replaces his receiver first, the relay 115 in falling back opens the circuit of relay 153 at contact 1 16 and, it itis the called subscriber who hangs up his receiver first, the relay 135 falls back and removes th ground on the winding of relay 153 at contact 136. ltelay 153 in falling back removes the ground on the test conductor 13 1 and relay 61 oi the hundreds selector, Fig. 2, is deenergized, and in falling baclr the connection of the calling line to relay 115 of the line selector is opened at contacts 111 and 113, and relay 1 15 falls back. As another result or the deenergization of relay 153 contact 159 opens and removes the ground from the holding circuits of relays 181, 189 and 196. When relay 189 restores the wipers are disconnected at contacts 194iand 195. When relay 181 falls back, ground is connected to the magnet 215 over the circuit; ground, contacts 182, 117, the winding of. relay 118, contacts 158, 217, 216, the winding of magnet 215 to battery. Magnet 215 operates and drives the wiper 22 1 to 236 inclusive to their normal posi= the wipers come to rest.

- normal position.

tion. In this position contact 217 is opened and the wipers are brought to rest.

As another result of the deenergization of relay 153 at contact 154, ground is placed on the magnet 205 of the control switch O and at contact 160 the circuit of magnet 210 of the control switch C is closed. Magnet 205 operates to drive wiper 207 to normal position. In this position, the off normal springs are shifted, contact 205 is opened and wiper 207 comes to rest. In a similar manner, magnet 210 drives the wiper 214 to normal position and the circuit of the magnet 210 is opened at contact 212.

During the operation of the magnet 215, relay 148 is energized and opens the test conductor at contact 152 thus causing the test line selector to test busy until the wipers are in normal position. An instant after the contact 217 is opened, relay 148 falls back and the lineselector is in position to receive another call.

In the hundreds selector, when relay 61 falls back! the ground is removed fromv the test conductor leading to the preselector, and from the holding circuit of relay 90 at contact 63, and at contact 64, the cir cuit of magnet 115 is closed to ground by the path, ground contacts 64, 67 winding of relay 7 7-, contacts 74, 117, 116, the winding of magnet 115 to battery. Magnet 115 operates to drive the wipers 125 to 131 inclusive to their normal position. In the normal position contact 117 is opened and Relay 77 energizes during the operation of the magnet 105, and opens at contact 80 the test conductor leading to the bank contacts of the preselectors, thus causing the hundreds selector to test busy until the wipers are in At the same time that ground is placed on magnet 115, the circuit of the magnet 98 is closed by the path, ground, contacts 64, 106, 69, 99 and the winding of the magnet 98 to battery. The magnet 98 operates and drives the wiper 100 to its .normal position. In this position, the off normal springs are shifted contact 106 is opened, and the wiper 100 comes to rest. In normal position, the wiper 100 connects battery to the test conductor and when the relay 77 falls back after the operation of magnet 115, the hundreds selector is in position to be taken for another call.

In thepreselector, when ground is removed from the test conductor, the relay 42 i'alls back, and the wipers 53 to 55 inclusive, having no normal position, remain on the contacts'ot the selector last used. As a result of the deenergizationof relay 42, ground is removed from the cut off .relay 5 of the calling line in series'with relay 16 and relays 5 and 16 fall back. Asthe wipers 10 to 15 inclusive of the finder at contact 269.

ergization of relay 266. the impulse circuit switch have no normal position they remain on the contacts ofathe line last connected. When the calling line out otl' relay 5 falls back the line relay is again connected to the line and the calling line is free to receive or initiate another call.

The operation of the system having been described when the call is for a subscriber with only one line, its operation when the call is for a subscriber having several lines listed under one number will be explained. For this purpose, it will be assumed that the subscriber at station P desires to establish a connection with the subscriber whose telephone number is 016 and that this subscriber has three lines.

When the receiver is removed at station P the calling line is extended to a hundreds selector as explained in theprevious case, assuming that the selector D; (Fig. 2) is again used for the connection, when the calling subscriber operates his dial in accordance with the first digit 0 of the .desired number, ten interruptions will be pro duced in his line circuit and the line relay will send ten impulses of current to the magnet 98 and the wiper 100 will come to rest on the 11th. contact of its bank, the selector will operate as previously explained with the exception that, since the wiper 100 is "on the 11th. contact of the control switches bank, relay 90- will energize in series with relay 84 when the relay '7 7 falls back after the last impulse over the circuit; round, contact 75 the upper winding 0 relay. 90,. 11th. contact of the first row of contacts, wiper 100, 11th. contact of the second row of contacts of the control switch G control conductor 105, 1st. contact of the 5th.lgroup of control contacts in the bank of ,control wiper 125, the winding of relay 84 to battery. At contact 93, relay 90,establishes its holding circuit by its lower winding to ground at contact- 72 and at contact 63 when relay 61 is en-- ergized.

The wipers 126 to 128 inclusive are connected up at contacts 92, 94 and 96 and will be used in establishing the connection. The selector proceeds to hunt an idle line selector as previously explained and will extend the calling line tothe samewhen it is found. Assume that the line selector F (Fig. 4) is used for the connection.

When the relay 61 of the hundreds selector extends the lines to F (Fig. 4) relay 258 energizes inseries with the calling line and at contact 259 closes ground, on to relay 266. Relay 266 on energizing discon nects the battery from the test conductor at contact 268 and places ground on the same Another result of the enis prepared at contact 270. As a further result of the energization of relay 266, ground bank.

is placed on the first row of contacts of the control switch C and on the 2nd. 4th. 6th. 8th and 10th. of the first row contacts of control switch (3' by way of the contacts 272 and 312.

Byway of the 1st. contact in row 1, wiper 335, 1st. contact in row 2 of the control switch (3' upper winding 318 the same ground is placed on the 3rd. 5th. 7th. 9th. and 11th. contacts of the first row of contacts of the same control switch C Furthermore, the circuit of relay 274 is closed to ground by the path, ground, contact 272, the 1st. contact of the 1st row, wiper 328, the 1st. contact of the 2nd. row of control switch (1' the upper winding of relay 274 to battery. As a result of the energization of relay 274. the impulse circuit is connected to magnet 326 at contact 276 and at contact 277 a holding circuit for relay 274 is prepared.

The calling subscriber will now operate his calling device in accordance with the second digit 1 of the desired number. as a result of which, four interruptions will be produced in the circuit of his line, and the line 'relay 253 of the line selector l will be deenergized once, and one impulse of current will be sent to the magnet 326 over the circuit. ground, contacts 302, 260. the winding of relay 261, contacts 270, 315. 283. 276, the winding of magnet 326 to battery. The magnet 326 operates and advances the wiper 328 on to the 2nd. contact of the Relay 261 energizes in series with the magnet 326 and at contact 263 completes the holding circuit of relay 274. and at contact 264 short circuits the upper winding of relay 318. This latter operation has no effect in this case as the wiper 328 is at rest on the 2nd. contact of its bank. and ground is placed on the 1st. control contact of the first tens group ofcontacts in the bank of the selector switch. and since the control wiper 338, in normal position rests on this contact, the relay 289 is im mediately energized and opens the circuit of the magnet 346 at contact 292 before it has time to operate. by the ground that is placed on its circuit at contact 330 after the first step of the magnet 326. An instant after the impulse of current. relay 261 falls back. causing the deencrgization of relay 274. Relay 274 on falling back closed the impulse circuit to the magnet 331 of the control switch C The calling subscriber will now operate his calling device in accordance with the last digit 6 of the desired number and as a result of which 6 interruptions will be produced in the circuit of his line and the line relay 258 will be deenergized 6 times. At each deenergization. the line relay 258 transmits an impulse of current to the magnet 331 over a path which extends from ground by way of contacts 302. 260, winding of relay 261, contacts 270, 315. 23 27 the winding of magnet 331 to battery. ly the operation of the magnet 331. responsive to these impulses, th wiper is advanced to the 7th. contact of its bank and places a ground on the 6th. control contact; in each group of tens contacts in the bank of the selector switch. Vhen the wi er 32% leaves the 3rd. contact of its bank the circuit ot relay 289 is open. and relay 230 on falling back. closes the circuit of the magnet 346 at contact 292 and the magnet 346 operates and advances the wipers 338 to 344 in lusive. \Vhen the wiper 338 finds a grounded contact. which in this case, is the 6th. contact in the first group of ten lines, the relay 285) is reenergized and opens the circuit of the magnet 346 and the wipers 338 to 344 inclusive come to rest on the first line of the three lines having the same telephone munher, in this case the 016. After the first step of the magnet 331. the contact 334 is closed and when relay 289 is energized after the last train of impulses. it closes the cir cuit of relay 282 over a path extending from ground by the contacts 272, 312, 262. 290, 334. the upper winding of relay 282 to battery. Relay 282 on energizing. establishes its holding circuit at contact 285, to ground by way of the contacts 312 and 262. As a result of the energization of relay 282. the impulse circuit is opened at contact 283: at contact 284. ground for the holding circuitof relay 274 is connected and by contacts 279, and 305. this ground is extended to the lower winding of relay 289 and to the relays 294 and 297 in series by way of contact 348. At the same time, the test wiper is'connec-ted to a point between the windings of relays 294 and 297. by the path. the test wiper 342, contacts 319. 313. 291. 236 and one side of the winding of re lay 294. It the first line of the three lines is busy. there is ground on the test contact in series with a relay such as relay 16 or 24 of the finder sw'itch (Fig. 2). it the line is calling or in series with a resistance such as resistance 363 if the line is busy by being called. In either case. relay 294 is shunted by this resistance to such an extent that it is not energized when the test wiper is on the contact of a line having a resistance such as .360 and 361 connected in series with the winding of the cut off relav. Relay 297 energizes by the ground on the test contact in series with the resistance such as 363 or the relay such as 16 or 24 (Fig. 2). As a result. ground is connected to the magnet 346 over the path ground. contacts 272; 312. 346 to battery. The magnet is energized and at contact 348. disconnects the test wiper 342 from the winding of relay 297v Relay 297 on deenergizing opens the circuit 296. 300. the winding of the magnet the energization of the magnet 346 at contact 300, and the magnet 346 on retracting its armature advances the wipers 338 to 344 inclusive on to the contact of the next line. When the control wiper leaves the.6th. contact of the group of ten lines, the circuit of the upper winding of relay289 is opened but it is held energized by the lower winding over the circuit already described. It the second line is busy the same operation is repeated and the wipers are advanced to the third and last line of the group. On this line, the test conductor is connected directly to the winding of the cut oil relay and'the-resistance 362, similar to the resistances 360 and 361, is excluded from the circuit. If the last line is busy, there is enough current through the winding of relay 294, on account of the comparatively low resistance of the winding of the cut ofi' relay 359, to cause the relay 294 to'operate at the same .time that relay 297 operates. As a result of the energization of relays 294 and 297, the circuit of relay 274 is closed over the path, ground, contacts 272, 312, 295, 298, lower winding of relay 274 to battery. As a result 07 the e'nergization of relay 274, a locking circuit is established at contact 278; at contact 279, the ground extending to relays 289, 294 and 297 is removed; at contact 281, the busy signal is placed on the calling line, in series with the condenser 257. As a further result of the energization of relay 274, a circuit for the magnet 346 is establishedat contact 280 by the path extending from ground by way of contacts 272, 312, 284, 280, 349, 347, the winding of magnet 346 to battery. The magnet 346 operates and drives the wipers 338 to 344 to their normal position. In this position, contact 349 is opened and the wipers come to rest. The calling subscriber on hearing the busy signal will hang up his receiver and the release takes place as will be described further on.

Assuming now that the first line of the group. of three lines is idle, when the wipers are brought to rest on the contacts ot the line, test wiper finds battery 111" series with the right low resistance winding of relay 357, and the relay 297 shunted by the battery in series with the low res stance winding of relay 357 is not energized but relay 294 is energized over the circuit, ground contacts 272, 312, 284, 279, 305, winding of relay 294, contacts 286, 291, 313, 319, test wiper 342, test wire 354 and the right hand winding of relay 357. As a result of of relay 294, the circuit of relay 310 is closed by a; path extending from ground, contacts 272, 312, 295, 299, the winding of relay 310 to battery. Bela-3 .310 energiz es andv at contact 311 establishes a looking circuit to ground by way of" contact 272. As a further result of the energization of relay 310, ground is removed from the banks of the control switches C and C and from the contacts 284, 285 and.295.,

Relays 282, 294 and 297 fall back. As another result of the energization of relay 310, ground is placed on the winding of the cut off relay 357 over the path, ground, resistance 363, contacts 314, 319, test wiper 342, test wire 354 and the right handwinding of relay 357 to battery. Relay 357 energizes in series with the resistance 363 and places its left hand winding and the resistance 360 in series with the right hand wind ing. Furthermore, the relay 357 removes the line relay (not shown) from the called line. i

Furthermore, at the energization of relay 310, the connection of the test wiper to the relay 294 is opened at contact 313; the impulse circuit is opened at contact 315 and the line wipers extended to the contacts 307 and 309 of the ring cut off relay 301 at contacts 316 and 317.

The ringing of the called station (not shown) and the conversation proceed, as explained for the normal line selector, and the release of the connection takes place in the same general way, when either of the subscribers. hangs up his receiver. Relay 266 falls back, it the called subscriber hangs up first, relay 248 in falling. back removes the ground on relay 266 at contact 249 and if the calling subscriber hangs up his receiver first, the relay 256 falls back and opens the circuit of relay 266 at contact 259. Relay 266 on falling back, removes the ground on test conductor 247 at contact 269 and relay 61 in the hundreds selector D (Fig. 2) falls back and disconnects the line conductor at contacts 111 and 113. As a further result of the deenergization of relay 266, ground is placed on the magnet 326 of the control switch (1' bya path extending from ground by contacts 267, 329-, the winding of magnet 326 to battery. Magnet 326 operates and drives wiper 328 to the normal position. In this position, the contact 329 is opened and the wiper 328 is brought to rest. By contact 273, ground is placed on the magnet 331 of the control switch C in series with the contact Magnet 331 drives the wiper 335 to normal position and in this position, the circuit of the-magnet 331 is opened at contact 333 and the wiper is brought to rest. As another result of the deenergization of relay 266, ground is removed from the holding cireuits of relays 301 and 310 at contact 272 and these two relays fall back. Relay 310 on falling back, disconnects ground from the test wiper at 314 and disconnects the line wipers at 316 and 317. The removal of ground from the test wiper 342 causes the cut off relay 357' to fall-back and the called line is free to initiate or receive another call. As a result of the deenergizav tion of relay 301, a. circuit is closed for the magnet 346 which may be traced from ground, contacts 302, 260, winding of relay 261, contacts 271, 349, 347, the winding of magnet 346 to battery. Magnet 346 operates in series with the relay 261 and drives the wipers 338 to 344 totheir normal position. In the normal position contact 349 is opened and the wipers come to rest. During the operation of magnet 346, relay 261 remains energized and the connection of the test conductor to battery is opened at contact 265. As a result of which the line connector is busied to an further calls An instant after, the magne 346 ceases to operate relay 261 falls backand the line selector may be seized for another call.

The release of the liu-ndreds selector, preselector, finder switch and the cut off relay of the calling line is effected as previously described and need not be repeated.

When all the hundreds selectors of a group of-preselectors are busy, the group of preselectors are marked Busy. Referring now to Fig. 2, there is shown for each selector a chain relay such as 118, 118', and 118", which is energized as soon as the selector is taken. When all the selectors of a group are engaged, all the chain relays of the'group are energized, and the circuit of the busying relay 120 is closed. This relay on pulling up, places ground instead of main battery on the magnets of the preselectors. As a result of the changing of the polarity of the magnets, the relay 42 of all the idle preseleetors in the group energize over the circuit: ground, contact 121, mag

net 57 contacts 56 and 39, resistance, contact 48, lower winding of relay 42 and main battery, at contact 45, the circuit of relay 33 is opened, and the starting wire is switched to the following preselector, at contact 46. When a' selector in the group becomes free, the corresponding chain relay falls back, opening the circuit of relay 120, which on falling back makes the busied preselectors available for connections.

A traffic meter 60 is provided for the line finders. When a line finder such as the line finder A finds a calling line, one of the relays 16 or 24 is energized at the same time as the relay 33 and the circuit of the meter is closed by the circuit: ground, oontact41, contact 20 (or 29), the meter 60, and main battery. Whenthe relay 33 falls back the circuit of the meter 60 is opened and it falls back after having registered a call.

Having explained the process of setting up and releasing a typical connection when the circuit arrangements shown in Figs. 2, 3 and 4 are employed, it will be desirable now to consider briefly the establishment of a connection when the circuit arrangement shown in Fig. 8 is used.

In this case, the control switches instead of being individual each to a certain selector, are common to a number of selectors of the same category, the number of selectors associated with each control switch depending on the traffic to be handled and the control switches such as C, C and C, are inserted in the circuit of a selector, only during the time necessary for the operation of the selector, the other selectors which may be connected to the control switch in use being busied during this time, in order that other calls may be directed to other groups of selectors which are free to receive them.

In Fig. 8, the common control switch 0, is connected to its associated hundreds selectors circuit, one of which is represented at D by' the common conductors 434 to 442 inclusive, and the common control switches C" and C", connected to their associated line selectors circuit, one of which is represented at E by the common conductors 525 to 530 inclusive.

Assuming now that the subscriber at station P desires to establish a connection with the subscriber whose telephone number is 733.

When the receiver is removed at station P the calling line is extended to a hundreds selector as previously explained, assuming the selector D (Fig. 8) to be the selector taken. Relay 455 is operated before the relay 33 in the preselector falls back over the following circuit; negative battery, magnet 407 of the control switch C,, the first set of bank contacts of C,, short circuited by the wiper 408, in normal position, contact 419, the common conductor 437, contact 456, upper winding of relay 455, contact 472 established when the rotary switch K is in normal posi'ton, contact 459, test conductor 483, test contact, test wiper 53 ot the proselector B, Fig. 2, contact 40, upper winding of relay 42, to ground. As a result of the energization of relay 455, the calling line is connected to relay 429 by the contacts 453 and 454, at contact 450 a holding circuit for the lower winding is prepared, at contact 448, ground is placed on the 2nd, 4th, 6th, 8th and 10th contacts of the first row of contacts in the bank on the control switch C,; at contact 449, ground is placed on the 3rd, 5th, 7th, 9th and 11th contacts of the same bank in series with the lower winding of relay 464; at contact 444 the control wiper 476 is connected to the control relay 433 by way of the common conductor 442, at contact445 an operating circuit for the mag ing line and by the contact 415 closes the circuit of relay 431. As a result of the energization of relay 431, battery is removed from the conductor 437 and replaced by ground, at contact 418, the holding circuit for relay 455 is colnpleted to ground by way of contacts 418, 456 and 450, and by way of contacts 451 and 459, ground is placed on test conductor483; at contact 413, the impulse circuit for the magnet 407 is pre-' pared and at contact 412, the common operating conductor is connected to an off normal contact 405, of the control switch C Ground is extended to the upper winding of relay 429 in series with the secondary winding of the induction coil 402, which has a vibratory current impressed on its primary winding, and the calling subscriber hears a special tone that indicates that he may begin to operate" his calling device.

The calling subscriber will now operate his calling device in accordance with the first figure 7 of the called number and as a result of which seven interruptions are produced in the circuit of his line, and the relay 429'will be deenergized seven times. At each deenergization, 'relay 429 transmits an impulse of current to the magnet 407 of the control switch C over a circuit which extends from ground by way of the contact 416, winding of the slow relay 430, contacts 413, 414, winding of magnet 407 to battery. By the operation of the magnet 407 respon sivc to these impulses the wiper 408 is rotated into contact with the 8th series of contacts and places ground on the control conductor 443. Relay 430 energizes in series with the magnet 407 and remains in operated position during the series of impulses. Relay 431, also remains in operated position during the impulses. After the first step of magnet 407, the off normal contacts 403 to 405 inclusive are shifted and ground is extended to the magnet 475 of the rotary switch K, by way of the path, ground, contacts 405, 412, 423, 426, common conductor 441. contacts 445, 474, the winding of magnet. 475 to battery. The magnet 475 operates and advances the wipers 47 6 to 482 inclusive. When the wiper 476 comes into contactwith the first contact of the group to which is connected the grounded control conductor 443, relay 433 of the control switch it)", is energized over the circuit extending from ground byway of contact 448, wiper 408, the 8th-contact in the two rows of contacts of control switch C common control conductor 443, wiper 476, contacts 444, the common conductor 442, the winding of relay 433,. to battery.

As a result of the energizationof relay 433. the operating circuit of magnet 475 is opened at contact 426 and the wipers 476 to 482 inclusive come to rest; at contact 425, the circuit of relay 432 is closed (relay 430 restores an instant afterthe last impulse) by a path extending from ground by way of contacts 405, 412, 423, 425, 417, the winding of relay 432 to battery; and at contact 427 ground is connected to the test wiper 480 in series with the lower winding of relay 463 over the path, ground contact 427, contact 424' common conductor 439, contact 452, thelower winding of relay 463, contact 465 and the wiper 480.

As a result of the energization of relay- 432, the impulse circuit of magnet 407 is opened at contact 414; at contact 421, which is closed before the other contacts are actioned, a holding circuit is established'by way of contacts 412 and 405 toground and at contact 422, ground is connected to the magnet 47 5 over the path, ground, contacts .405, 412, 422, the common conductor 440,

contacts 447, 457, 473, 474, the winding of magnet 475 to battery. If the first trunk of the group is busy, test wiper 480 is not connected to battery by the test contact and relay 463 is not energized and as a result magnet 47 5 operates and advances the "wipers 47 6 to 482. When the wipers are on the contacts of an idle trunk line test wiper 480 finds battery on the test contact and relay 463 is energized over the above described circuit. As a result of the energization of relay 463, numerous circuits changes are produced. At contat i. 458, the upper winding of relay 463 is connected to test wiper 480; at contact 457, the operating circuit of magnet 475 is opened and the wipers 476 to 482 come to rest on the idle trunk line; at contact 460, ground is connected to the test conductor 483; at contacts 461 and 462,

the calling line is connected to the line wipers 481, 482; at contact 459, the upper winding of relay 455 is disconnected from the test conductor 483 and finally, at contact 456, the holding circuit of the lower winding of relay 455 is opened. Relay 455 being slow acting remains in its operating position long enough, after its circuit is opened, to permit the relays in the following switch to energize and establish a holding circuit for the relay 463 by its upper winding. When relay 455' falls back, the connections with the common conductors 434 to 442 are opened and as a result, relays 429 and 433 fall back.

lie-lay 429 on restoring opens the circuit of relay 431 at-contact 415 and relay 431 an instant afterwards restores. When relay 431 falls back, thecircuit of the magnet 407 of the control switch C" is closed to ground byway of the path, ground, contacts 405, 411, 406, winding of magnet 407 to battery. The magnet 407 operates and advances its wiper 408 to normal position. In normal position, contact 405 is opened and wiper 408 comes to rest on the first series of contacts and the control switch is free to be connected to another selector.

Since the seizure of the hundreds selector D, the other selector in the same group having access to the control switch C" are busied on account of thefact that on the energization of relay 431, negative battery is removed from the common conductor 437. During the time that the control switch C, restores its wiper, the associated switches are busied until the wiper 408 establishes the connection between the first contact of the two row of contacts of control switch C,.

If all the lines of a group are busy, the wipers of the selector pass on to the contacts of the first line of the following group, but there is no ground on the corresponding control contact and the relay 433 has its circuit open and falls back, preventing the energization of the relay 465, and the wipers are rotated to their normal position, the electromagnet 475 being in the same circuit as previously described, which is opened at the normal position at contact 473. Moreover, the relay 433 by falling back closes at 428 and 424 the circuit of the secondary winding of the induction coil 409, which has a busy tone impressed upon its primary winding thus giving the busy signal to the calling line through the condenser 410.

Returning now to the line selector, assuming that the line selector seized by the hundreds selector D is the line selector E, Fig. 8. I

When the test wiper comes into contact with the test contact connected by the test conductor 486 to battery a. circuit is established, as already described, from ground, contact 427, common conductor 439, contact 452, lower winding of relay 463, contact 465, wiper 480, test conductor 486, contacts 550, 583, upper winding of relay 536, contacts 544, 497, 495, resistance 492 to battery.

Relay 536 energizes in series with the relay 463 of the selector D and there results numerous circuit changes. At contacts 540 and 541, the calling line is connected to the relay 489 by way of the common conductors 525 and 526, at contact 533, the control wiper 591 is connected to the common conductor 530; at contact 534, an operating circuit for magnet 586 is connected to the common conductor 529; at contact 535 relay 546 is connected to the common conductor 527; at contact 537 a holding circuit for relay 536 is prepared; at contact 538, a circuit for grounding test conductor 486 is'prepared and finally, at contact 539, ground is removed from the restoring circuit of magnet 586.

Relay 489 energizes in series with the calling line and by the contact 490 closes the circuit of the slow relay 504 to ground. Helay 504 on energizing, removes battery from the common conductor 528 at contact 497 and all of the line' selectors associated with the control switches C 2 and C" are busied. At contact 498, relay 504' places ground on the common wire 528 to hold the relays in the preceding switches energized. As another result of the encrgization of, relay 504 the impulse circuit for magnet 518 is prepared at contact 507; at contact 499, ground is placed on the first row of contacts of the control switch C" and on the first row of contacts of control switch C by way of the wiper 524 and the first contact of the second row of contacts of C", and at contacts 505 and 506 the restoring circuit of control switches C and C are opened.

The calling subscriber will now operate his calling device in accordance with the second figure 3 of the called line and as a result there will be three interruptions in his line circuit and relay 489 will be deenergized three times. For each deenergization, relay 489 sends an impulse of current to magnet 518 over the circuit ground, contact 491, the winding of relay 493, contacts 507, 508, the winding of magnet 518 to battery. By the operation of the magnet 518 responsive to these impulses, the wiper 519 is rotated into contact with the 4th. contact and connects ground to the tens control conductor 532. Relay 493 energizes in series with the magnet 518 and remains in operated position during the series of impulses. Relay 504 also remains in operated position during the impulses. After the first step of magnet 518, ground is connected to the magnet 586 of the rotary switch K by the circuit, ground contacts 499, 515, 514, common conductor 529, contacts 534, 543, 585, the winding of magnet 586 to battery. The magnet 586 operates and advances the wipers 591 to 594 inclusive. When the wiper 591 comes into contact with the test contact connected to the control conductor 532, relay 599 is energized over the circuit, ground, contact 499. first contacts and wiper 524 of control switch C,, first row of contacts wiper 519, 4th. contact in the second row of control switch C 2 tens control conductor 532, control wiper 591, contact 533, common conductor 530, the winding of relay 599 to battery. As a result of the energization of relay 599, the operating circuit of magnet 586 is opened at contact 514 and the wipers 591 to'594 inclusive come to rest on the first line of the third group of ten lines. At contact 513, a link in the circuit of relay 546 is connected up and the circuit of relay 510 is closed at contact 512, relay-493 having fallen back an instant after the last impulse, and the relay 510 energizes over the circuit ground cone tacts 494, 512, the winding of relay 510 to battery. As a result of the energization of relay 510, at contact 509, the impulse cir-f cuit is connected to the magnet 523 of control switch C",. and at contact 511 alocking circuit is established to ground by the path ground, contacts 499, 511, the Winding of relay 510 to battery. The subscriber will now operate his calling device in accordance with the last figure 3 of the called line and as a result, there will be produced three interruptions in his line circuit; Relay 489 will deenergize three times and for each deenergization will send an impulse of current to magnet 523 of control switch C" over the circuit, ground contact 491, winding of slow relay 493, contacts 507, 509, the winding of magnet 523 to battery. Magnet 523 responsive to the impulses, rotates the wiper 524 on to the 4th. series of contacts and places ground on the units control conductor 531. After the first step of the magnet 523, another linkin the circuit of relay 546 is closed at contact 520, but this is without effect at this time as relay 493 energizes in series with the magnet 523 and opens the circuit of relay 546 at contact 496. After the second impulse ground is removed from the relay 599, by the wiper 524, and relay 599 in restoring again closes the circuit of the magnet 586 of the rotary switch K,. Magnet 586 operates and advances the wipers 591 to 594 inclusive. When the control wiper 591 comes into contact with the control contact connected to the grounded units control conductor 531,-relay 599 energizes again, opens the circuit of magnet 586 and the wipers come to rest 011 the contacts of the called line.

lVhen the relay 493 falls back after the last impulse, with relay 599 operated, the circuit of relay 546 is closed over the path ground, contacts 499, 511, 520, 513, 496. 535 the winding of relay 546 to battery. Relay 546 on energizing establishes a locking circuit at contact 545 to ground by contact 562, the common conductor 528 and contact 498; at contact 543 the operating circuit of the magnet 586 is opened at contact 544, the

.hold'ing circuit of relay 536 is opened; at contact 542, the test wiper is connected to the relay 579; at contact 547 a holding circuit for relay 567 is prepared; at contact 548 relays 567 and 579 are connected in series, at-contact 550 test conductor is disconnected from the upper winding of relay 536 and from the contact 538; at contact 549 ground is placed on the test con-' ductor 486 and at contacts 551 and 552, the calling line is connected in series with the contacts 555 and 557 to the battery feed relay 559. Relay 559 energizes in series with the calling line and closes the circuit of slow acting relay 561. Relay 561 energizing, places ground by the contact 563 on the relay 579, on the locking circuit of relay 546, and prepares the holding circuits for the relays 567 and 568.

An instant after. its circuit is opened, slow acting relay 536 falls back. As a result of the restoring of relay 536, the circuit of .sition.

relay 489 is opened at contacts 540 and 541 t at contact 533 the circuit of relay 599 is opened.

'Relay 489 falls back followed an instant later by the relay 504. When relay 504 restores, the circuit of relay 510 is opened at contact 499 and at contacts 505 and 506 the restoring circuits for the switches and C, are closed to ground in series with the winding of relay 493 and contact 491. Magnets 518 and 523 operate and advance their respective wipers 519 and 524 to normal po- At normal position, the circuit of magnet. 518 is opened at contact 516. and that of magnet 523 at contact During the restoration of wipers 519 and 524 relay 493 is energized and removes the battery from the common conductor 528 in order to busy all'of the associated line selectors while the control switches are restoring. The control switches C". and may now be employed to establish another connection.

Returning now to the line selector E, if the called line is busy, the test wiper 592 finds ground 011 the test contact, relay 579 is shunted out and relay 567 is energized over the circuit, ground, test wiper 592, contacts 565. 542,580, 548, 570, the winding of relay 567 to battery. Relay 567 on energizing closes a locking circuit at contact 569 to ground by way of contacts 547 and 563, opens the energizing circuit at contacts 570 and 565, and at contact 572 places a busy signal on the calling line by way of the path: battery, induction coil 587, contact 572, condenser 597 and the calling line. The calling subscriber on hearing the busy tone -will restore his receiver and the release takes place as will be described further on.

Assuming that the called subscriber is idle, in this case the test wiper 592 finds battery in series with a low resistance winding of the out off relay such as the relay 596, the relay 567 is shunted and relay 579 is energized over the circuit, battery, right hand winding of relay 596, contact 595, test wiper 592, contacts 565, 542, the two windings of relav 579 in series, contact 563, to ground. With its two windings in series relay 579 only has enough ampere turns to close the contact 578. At contact 578 the upper high resistance winding is short cir-', cuited and relays 57 9 and 596 are fully energized. On being fully energized the cut off relay 596 places its left hand high resistance winding in series with its low resistance winding and the relay 579; Belay 579 remains in operated position When in series with the two windings of'relay 596.

At contact 580, the connection between the test wiper 592 and the relay 567 is opened and at contacts 581 and 582, the line wipers 593 and 594 are connected to the ringing machine in series with the contacts 575 and

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