US1903211A - Electromagnetic switch - Google Patents

Description

D. A. CHRISTIAN ELECTROMAGNETIC SWITCH March 28, 1933- Filed Sept. 21, 1951 5 Sheets-Sheet l .nm 1% m m i D March 28, 1933. D CHRIS-HAN 1,903,211

' ELECTROMAGNETIC SWITCH Filed Sept. 21, 1931 5 Sheets- -Sheet 2 I'HUEEIEF Dauid Edam mm? March 28 1933'.

D. A. CHRISTIAN ELE CTROMAGNET IC SWITCH Filed Sept. 21, 1931 5 Sheets-Sheet 5 March 8, 1933- D A. CHRISTIAN ELECTROMAGNETIC SWITCH Filed Sept. 21, 1931' 5 Sheets Sheet1 4 km? David Edam Chg-hm March 28, 1933.

D. A. CHRISTIAN ELEGTROMAGNET IG SWITCH 5 Sheets-Sheet 5 Filed Sept. 21, 1831 E 1 l =w I M mm fi 25% a w mm w E E 8 Dru-id Fldlm Christ?! Patented Mar. 28, 1933 UNITED STATES PATENTVQ' OFFICE DAVID ADAM cHEIsrrAN,.oE LoNDoN, ENGLAND, ASSIGNOR T0 srEMENs BROTHERS a COMPANY LIMITED, or LONDON, ENGLAND ELECTROMAGNETIC SWITCH This invention relates to electro-magnetic switches of the kind used automatic tele} phone systems and has in View means whereby any one of a comparatively large number of incoming circuits may be connected to any one of a comparatively large number of outgoing circuits in a simple and economical manner. v

In the present invention we provide a I switch comprising a plurality of sets of wipers and associated contact banks the wipers being movable by a commonmotive means and arranged so that in their stepping the Wipers of the several sets occupy different relative positions as regards one another at each complete passage over a group of contacts in a bank, the corresponding wipers of the several sets being connected together either directly or indirectly.

The invention admits of several embodiments. v I

In one embodiment the wipers of one set are advanced one step for each complete passage by another wiper set over a group of associated bank contacts. For example, the switch may comprise two sets of rotating wipers and associatedbank contacts. Each wiper set may be assembled as a unit, the two units being mounted on rotatable members in line, one of the members being rotated by a pawl and ratchet mechanism as in known arrangements, the other member being driven from the first by any suitable means so that its wipers are advanced one step after the v first set has passed over a given number of fixed contacts.

In another embodiment the wipers of each set are adapted to be stepped simultaneously, the stepping being so arranged that after a complete passage by one Wiper set over a group of associated bank contacts another. wiper set lags behind the first mentioned wiper set by one or more contacts, thelag increasing at each complete passage over a group of contacts by the first mentioned wiper set. As an example of this embodiment the following arrangement may be employed. Two wiper sets are mounted on separate rotatable members as in the previous example, each set having a ratchet, the two 563,953, and in Great Britain October 8,1930.

ratchets being engaged by a common pawl or pawls suitably connected. One ratchet has a different number of teeth to the other whereby afterthe passage by one wiper set over a given number of contacts subtending aparticular angle the other wiper set has passed over a similar number of contacts subtending a different angle. It may be arranged that there is a certain amount of lost motion in the engagement of the pawl with one of the ratchets so that at each step the ratchets are moved through different angular distances. H

The ratchets may be of diflerent diameters in which casethe ratchets will move for the whole stroke of the pawl but at different angular speeds. I

Alternatively the ratchets may be of the same diameter and be engaged by projections on the pawl which make different strokes.

Switches according to the invention may be employed for interconnecting purposes in an automatic telephone system.

A switch of the kind above described may be arranged as a backward and forward hunting pair, one set of wipers being employed for backward hunting and the other set for forward hunting or selecting. A number of such switches may be assembled for backward hunting over the same multiple,v the contacts associated with the forward selecting wipers being connected to directly to outgoing links such as links to different groups of numerical selecting switches or further groups of backward and forward hunting switches may be connected betweengroups of links and the outgoing links to furtherapparatus. The backward hunting switches of these further groups may each operate on a group of links, the outlets of the forward selecting switches of a group being multipled to a group of outlets to further apparatus.

The outlets from the forward selecting switches associated with further apparatus may be graded in a suitable manner and additional pairs of switches may be added for the purpose of increasing the accessibility of any group of outgoing links.

The selection of a particular route for a connection may be accomplished in any convenient manner such as by the use of a common bypath or marking arrangement responsive to impulses and used only during the setting up of a connection.

For the better understanding of the invention reference will now be had to the accompanying drawings in which Figs. 1 and 2 show one form of driving mechanism for a rotary selecting switch embodying the invention, and Fig. 3 a modification. These drawings show only sufiicient of the driving mechanism for the understanding of the invention the assembly of the switch wipers and banks following a well known form. Figs. 4 and 5 show diagrammatically how switches according to the invention may be employed to interconnect any one of a number of inlets to any one of a number of outlets. Figs. 6 and 7 show circuit arrangements for the interconnecting scheme shown in Fig. 4. The switches are of the type in which when one wiper of a set leaves one end of a bank another wiper of the set is stepped into the bank at the other end.

In Fig. 1 a mounting plate 1 is provided with extensions 2 which provide bearings for wiper shafts 3 and 15 and support the bank of contacts indicated in dotted lines at 4. Mounted on plate 1 is the driving magnet 5 having armature 6 carrying extension 7 to which is secured a double pawl member 8 having two pawls 9 and 10. A return spring 11 stretching between a projection on the armature extension 7 and a suitable pin or stop 12 provides for the quick return of the armature when the magnet is de-energized. The pawls 9 and 10 engage respectively ratchets 13 and 14 of different diameters and having different numbers of teeth. Ratchet 13 is mounted on shaft 3 to which is secured a set of wipers co-acting with one bank of contacts and ratchet 14 is mounted on shaft 15 to which is secured another set of wipers co-acting with a different bank of contacts. The number of teeth in the two banks are so arranged that for one complete traverse of the banks one wiper set takes a greater number of steps than the other, there being one more contact position in the bank associated with the wipers on shaft 3 than in the bank associated with the wipers on shaft 15.

IVhen the magnet is energized both pawls engage the ratchets and each ratchet is rotated one step. If there are, for example 10 contact positions in the bank associated with the wipers on shafts 15 and 11 in the bank associated with the wipers on shaft 3 then after the magnet 5 has been energized and de-energized 10 times each wiper set would be in contact with the 10th bank contacts. On the next step the wiper set on shaft 15 is stepped off the 10th contact and again makes contact with the first contact in the bank while the wiper set on shaft 3 is stepped from the 10th to the 11th contacts. The 11th contacts are disconnected so that on the first rotation of the wipers from the position where both wiper sets rest on the first contacts each contact in one bank is put into contact with corresponding contacts in the other bank. WVhen the wipers on shaft 3 are stepped onto contact 11 no connection is made with contact 1 in the other bank but at the next step the wipers on shaft 3 are stepped from the 11th contact and are brought into contact again with contact 1. Contact 2 in one bank is now connected to contact 1 in the other bank and the wipers are rotated again until the wipers on shaft 3 reach the 11th contacts. During this rotation the contacts in one bank are put into connection with the contacts in the other bank but this time the interconnection by the wipers at any moment is between different pairs of contact sets from the interconnection made during the first rotation. When contact 10 is reached by one set of wipers the other set is again on contact 1 so that when the former set steps to contact 11 and then again to 1 the latter set steps to 2 and then to 3 and there is a difierence of two contact positions between the positions of the two wiper sets at any moment. By continued rotation in this manner the number of contact positions between the positions occupied by the wiper sets is increased by one at each complete traverse of the banks and after 10 complete traverses forming a cycle both wipers are stepped onto their contacts 1 at the same time. It will be seen that during this cycle each contact in one bank has been put into connection with each contact in the other bank once.

It will be readily seen that instead of making the ratchets of different diameters I may make them the same diameter but provided with teeth of different pitch so as to produce a different angular displacement between the wiper sets after one complete traverse of the bank. In the case assumed it would be arranged that one wiper set requires one more step to traverse the same angle than does the other wiper set. The magnet armature may be connected to a common member connected to two pawls which engage teeth on the two ratchets. In order to step both ratchets a full step at each operation of the driving magnet the strokes of the pawls must be different and this may be attained by forming one pawl as a projection from and shorter than the other so that as regards the short pawl there is a period of lost motion at each stroke equal to thedifference in pitch of the teeth on the two ratchets.

Fig. 3 shows a modification of the driving arrangements in which one set of wipers is advanced one step after each complete traverse of its bank by the other set. This type of mechanism is well known inconnection with counting mechanisms to produce decimal rotation. In this figure the driving mechanism only is shown diagrammatically. The ratchet 18 is secured to shaft 3 which carries one set of wipers andis stepped by means of the pawl 8. The ratchet 14 is securedto shaft 15 and carries another set of wipers. On a spindle parallel to shaft 15 is mounted a pinion 16 engaging with the teeth of ratchet 14.- and adapted to be rotated by a cam 17 carried by shaft 3. The cam is so arranged that after one complete traverse of its banks by the wipers on shaft 3 the pinion 16 is engagedand rotated a quarter turn thereby rotating ratchet 14 toadvance the wipers on shaft 15 one step. This ratchet is stepped in a similar manner after each complete traverse of its bank by the wiper set on shaft 3 so that each contact in one bank is put into connection once with each contact in the other bank during a complete cycle of operations.

Reference will now be made to the diagram.- matic arrangement shown in Fig. 4. At a switching stage a number of switches form a panel and a numberof panels are provided, links incoming from a preceding switching stage being connected to the multiple of a a panel. In the figure are shown two panels only A and B at a switching stage and three switches per panel. The switches are of the type previously described andwill be referred to as first couplers. A switch comprises two sets of wipers designated a and 7) respectively. A set comprises the speaking and test wipers and a control wiper or wipers as required, each set being associated with a bank of contacts the wipers, or some of them, of a set being adapted to be put into direct electrical contact with corresponding wipers of the other set. The switches associated with panelA are designated AFCl, AFC2 and AFC3; and those associated with panel B are designated BFCl, BFC2 and BFCES. The wipers a of a switch are associated with contacts of the panel multiple while the wipers p are associated with contacts of groups of links multipled over contacts wiped by similar wipers of correspond-- ing switches in other panels. Thus wipers a of switches AFCl, AFC2 and AFC?) are associated with contacts connected to the panel multiple while wipers p of switches'AFCl and. BFGl are associated with contacts con:-

nected. to a group of links LCl. A'coupler hunts in two directions, the switch acting as a backward hunting switch with its wipers a and as a forward hunting switch with its wipers p.

Similar switches to be referred to as sec ond couplers are provided which act in a sim ilar manner; A second coupler acts as a backward hunting switch with its wipers a which co-act with contacts connected to a group of multipled links and as a forward hunting switch with its wipers p which co-act with contacts connected to a group of multipled outlets. Of these second couplers those designated XSCl, XSC2 and XSG3 are associated with a group of outlets X, and groups of multipled links. Similarly those designated YSCl, YSC2 and YSCS are associated with a group of outlets Y and the same groups of multipled links. The wipers a of a second coupler with which it acts as a back-- ward hunting switch'are associated with a group of links and more particularly these wipers of switches XSCl and YSCl are as sociated with contacts connected to a group of links LCI which group is as stated above multipled also over contacts of first couplers, while wipers p with which a second coupler acts as a forward hunting switch are associated with the groups of outlets and more particularly these wipers of switches XSC'l, XSC2 and XSC3 are associated with contacts connected to outlets multipled over other switches in the group X. The corresponding wipers p of couplers YSCl, YSCQ and YSC3 co-act with contacts similarly connected and multipled over the group of outlets Y.

In order to set up a connection from an incoming link, such as, for example, one connected in panel A to an outlet, such as, for example, one connected in the group Y, a first coupler is first taken into use. This may be the coupler AFCl and it is rotated in search of the calling'incoining link. When this is found a test is made at the same time for a free link in the group LCI and rotation continues until the switch is stepped on tothe calling link with one set of wipers and at the same time the other set is stepped on to contacts connected to a free link. A second coupler having access to the group Y which may be that designated YSCl isthen started to hunt with one set of wipers for the link in the group LCl seized by the coupler AFCl and with the other set for a free outlet in the group Y, rotation of the switch continuing until both the marked link and a free outlet have been found. The couplers are taken into use b a control'switch not shown in this figure which selects a free second coupler having access to the desired group of outlets which latter is determined by impulses reccived by the control switch. A further requirement has to be met in that a free group of links over which the couplers are. to be connected must be found. This may be done by marking a link from the control switch or arranging that links in a group are marked free and available one at a time by suitable means. Circuit arrangements for setting up a connection over switches diagrammatically represented to this figure are shown in Figs. 6 and 7 and will be referred to later.

As even distribution of trafiic over the links is unlikely grading of the outlets of the second coupler may be resorted to in order to increase the availability.

In Fig. 5 is shown an arrangement of first couplers and links similar to that shown in Fig. 4 but no second couplers are provided. In this case the links in a group are connected directly to outlets. In the example shown outlets of group 1 are connected to the first links in each group of links, outlets of group 2 to the second links of each group of links and so on, the links in the group LCl being connected to outlets in different groups. In this case the control switch receives impulses for determining the group of outlets in which connection is to be made and searches for a coupler having access to the calling incoming link and for a tree link to the desired group.

In order to deal with unevenly distributed trafiic it may be arranged that couplers serving a panel are taken into use in a definite order and that the first choice couplers give access to first choice links. Grading may be employed whereby the earlier choice couplers have access to individual links and later choice couplers have common access to links.

Figs. 6 and 7 will now be referred to. Fig. 6 shows a first coupler FC, adapted to connect incoming links in a panel A to a link in a group of links LC and a second coupler SC adapted to connect linits in the group LC to outlets in the group X, while Fig. 7 which is intended to be placed below Fig. 6, shows a control switch CS available in common to a panel adapted to select, in response to impulses, couplers having access to the calling line and to the desired group of outlets.

The control switch CS is of the ordinary two motion type with G wipers and corresponding contact banks. It is controlled by an impulse relay A, dialling relay 1) and test relay TC. Its magnets are designated VM, RM and Zlii for the vertical, rotary and release magnets respectively. The couplers are unidirectional rotary switches, each being provided with 8 wipers and corresponding contact banks. The first coupler magnet is designated DFM and the switching relay TF, and the seconl coupler magnet and switching relay are designated DSM and TS respectively. A coupler in its function as a backward hunt-ing switch employs wipers a, b, 0, d and in its function as a forward hunting switch employs Wipers p, g, 7', 8.

The arrangement shown is assumed to be connected in a system in which the dialled impulses are recorded on a register which retransmits them over the 7) wire to the several switching stages and in which retransmission from the register may be held up by the connection at a switching stage of battery on the a wire.

A preceding switch tests in over wire 0, contact k2 of relay K and if the control switch is free contact 002 will be open. VJ hen the link is seized earth is connected to wire 10 at the preceding switching stage and relay T operates from earth on wire 2) over contact 704:, winding of relay T, contacts $1, 031 to battery. Contact t1 which is of the make before break type connects winding (1) of relay X in series with relay T and contact t2 connects earth on wire 0 to contact a2 which on operation of relay A extends this earth over vertical oil-normal contact n1 of control switch CS to slow releasing dialling relay D. Contact t5 marks the bank of wiper (Z of the coupler FC; contacts ta and t6 connect the incoming a and Z) wires to the control switch circuit, the circuit over wire 6 including relay A of the control switch, and contact t3 connects the wire 0 to the contacts in the bank of wiper 0.

Relay A now operates from battery connected to the 6 wire in the register circuit and opens its contact al to guard vertical magnet VM against a false impulse. Contact a2 closes the circuit for relay D, contact a3 opens a point in the circuit of the release magnet and closes a point in that of the rotary magnet, and contact at prepares the test circuit for relay TC. Relay 1) operates and at contact (Z1 prepares a holding circuit for itself during impulsing, and at contact d2 prepares the vertical magnet circuit for impulses.

Relay X, which operates after relay T, prepares a holding circuit for itself at contact :03 and at contact m2 connects earth to all the wires 0 incoming to the panel to prevent any other link incoming to the panel being seized until the control switch has been restored and is available to deal with another call. Contact ml opens the operating circuit of relay T. The train of impulses for extending the con nection at this switching stage is now received from the register and relay A responds to it, repeating the impulses at contact al to vertical magnet VM which steps the wipers of switch CS to a level containing outlets in the desired group denoted by the number of impulses transmitted to it. This group contains the outlets X multipled to second couplers SC. At the {first vertical step the vertical of"- normal contacts are operated, contact n1 opening the operating circuit of relay D and completing the holding circuit for that relay, contact n2 preparing the rotary magnet circuit, and contact 723 closing the holding circuit for relay X over its winding (11). At the end of the impulse train relay A remains steadily operated and relay D releases. Contact (21 opens to prevent re-operation of relay D and contact 0Z2 closes the circuit for the rotary magnet RM which is intermittently energized by means of the interrupter in its circuit. The wipers are rotated around the level opposite to which they have been stepped in search of a free first coupler denoted by earth over contacts gp, tft and wiper 1 of switch CS and of a free second coupler denoted by absence of earth over wiper 2 of switch CS, the'coupler searched for being associated with the same group of links. These correspond for example to couplers AFCl and XSCl associated with links LCl in Fig. 4. V

It should be explained that a relay GP is provided common to all first couplers having access to a group of links such as for example the couplers AFCl andBFCl in Fig. 4 and the relay has a contact g7) in each coupler circuit F C. As-soon as a first coupler is taken into use relay GP is operated and by opening its contacts 9 ensures that only one link in a group such as LCl (Fig. 4) is marked for search at a time, other control switches being prevented at this time from taking into use couplers having access to this particular group of links. This will be readily understood by inspection of Fig. 4.

It being assumed that the coupler FC is free and that relay GP is not operated relay TC will operate if the cou ler SC is likewise free. Search by switch G continues until a pair of couplers connected to the same group of links is free whereupon relay TC not being short circuited by earth over wiper 2 but finding earthover wiper 1 operates and opens the circuit of. magnet RM at contact 2503. Contact tc2 connects earth to wiper 2 to mark the second coupler SC engaged and contacttc connects earth to wiper 3'to operate relay RF in the first coupler FC and the relay GP. Relay GP operates and opens the test circuits of all the couplers having access to the link LC at its contacts 9 but relay TC continues to hold by means of its winding (II) over contacts tel, t2 and wire 0. ates relay. TD and contact. t06 disconnects relay A. Relay TD operating contact toll connects battery over contact t6 to the incoming a wire to hold up impulsingat the register, contact M2 prepares a circuit for relay K and contacts tcl3, tdetand tcl5 connect up wipers 4, 5 and 6 of switch CS.

In the first coupler relay RF has operated. Contacts rfl and 17 2 connect up the test circuit of relay TF and contact H3 closes the circuit of the coupler magnet DFM. Mag net DFM is now intermittently energized by means of the interrupter and drives the wipers round until wipers p, g, r, s are stepped on to a free link LC at the same time as wipers a, b, e, (Z are stepped on to contacts, of the marked incoming link. A

Contact 75-05 oper-' free link LC is denoted by absence of earth on the contact in the bank of wiper 1', and the marked incoming line by the connection of earth over contact $5 to the bank of wiper d. When these conditions are met relay TF. operates over its winding (I) and locks up over its winding (II) and contact tfl, wiper a, contact t3 and wire 0 to earth. Contact tf2 opens the circuit of magnet DFM, contacts #3, #5 and #6 connect wipers a, b and 0 through to wipers p, g and r, and contact if?) disconnects winding (I) of relay TF from Wiper 9'. Contact #4 opens in the test circuit of switch CS against release of relay GP and contact #7 connects earth over wiper 5 and contact Z034: to relay EF. Relay EF operates and at contact efl connects earth over contact M3 and wiper 4 to relay RS. Relay RS operates and at contacts 1'81 and 7'82 prepares testing circuits for relay TS and at contact r83 closes the circuit of magnet DSM of the second coupler. The magnet is operated intermittently by means of the interrupter in its circuit and rotates the wipers of the second coupler until its wipers p, g, r, s are stepped on to contacts of a free outlet at the sametime as its-wipers a, b, 0, (l are stepped on to contacts of the link seized by the first coupler. The test for a free outlet is absence of earth over wiper 1" and contacts ts3 and T81 while the link seized by the first coupler is marked by earth over contact 77% and wiper s of coupler FC.. When the above conditions are met relay TS operates over its winding (I) wiper (Z of coupler SC, the link:

LC, wiper s of coupler FC, contact 17% to earth. Relay TS locks up over its winding (II) contact tsl, wiper c of coupler SC, the link LC, to the 0 wire and opens the circuit of magnet DSM at contact ts2. Contact ts?) disconnects winding (I) of relay TS from wiper 1" of coupler SC, contacts ts5 and ts6 switch the a and 6 wires through, contact 2584 connects earth to the contact in the bank of wiper 2 of switch CS to mark the coupler encontact 002 in the control circuit from the incoming wire 0, contact 703 closes in parallel with contact t3 which will shortly be opened, and contact 704 opens the circuit of relay T and winding (I) of relay X. Relay T releases and disconnects the control circuit from the incoming link, contact t2 opening the locking circuit of relay TC, contact t4 opening the circuit of relay A, contact 156 disconnecting battery from wire a thereby allowing impulsing from the register to recommence, and contact t7 opening the operating circuit of relay K. Relays A, TO and TD release. A circuit is nod closed from earth over contacts Z03, 0Z2, a2, a3, magnet ZM to battery. The magnet operates and releases the switch OS to normal whereupon the off-normal contacts are restored and the release magnet circuit opened at contact n2. 10 Contact 72?) opening, relay X releases and battery is again connected to the other incoming wires p of the panel and the busy marking on other incoming wires 0 is removed by the opening of contact 002. The release of relay TD releases relays EF and ES and by the opening of contacts 2504 and id?) relays RF and RS are released.

The remainder of the connection is set up by further trains of impulses received at subsequent switching stages which may be similar to that shown in Figs. 6 and 7.

The connection is released by the disconnection of earth from wire a at the point where the feeding bridge is situated result- 25 ing in the release of relays TF and TS and, by the disconnection of earth from wire 79 by a contact similar to 88, relay K is released. The opening of contact 2588 disconnects earth from wiper s thereby releasing relay K in the next switching stage.

In an alternative arrangement that may be employed the control switch in addition to searching for a pair of couplers having access to the calling line and the wanted group searches for a free link between two couplers. Vhen the link and a pair of free couplers are found the control switch is brought to rest and marks the link for which the two couplers may then search simultaneously, the whole group of links being marked busy to other control switches while the couplers are searching for the marked link. In order to avoid complicated group control arrangements and to simplify the control switch a distributor switch may be provided for each group of links which is always set on contacts of a free link. A number of distributor switches, each having access to a different group of links could be provided and would be available in common to all the control switches having access to the groups of links. A control switch would then search for a free distributor switch which on being found is seized and applies a busy marking on the link on which it is standing which link is then searched for by the couplers seized by the control switch.

In aswitch of the kind described it will be clear that if the number of contact positions in one bank exceeds that in the other bank by one each contact in one bank will be put into connection once with each contact in the other bank during a cycle of transverses of the switch banks. The number of contact positions in the two banks may however dif- 65 for by more than one provided the difference is not a sub-multiple of the number of contacts in the smaller bank.

I claim:

1. In an automatic switch, two sets of wipers, two banks associated with said two sets of wipers, respectively, each bank comprising a plurality of sets of bank contacts, common driving means for said wiper sets, and means controlled by said driving means for moving said wiper sets to connect each set of contacts in one bank to every set of contacts in the other bank.

2. In an automatic switch, two sets of wipers, two banks associated with said two sets of wipers, respectively, each bank comprising a plurality of sets of bank contacts, a stepping magnet common to both sets of wipers, and means controlled by said stepping magnet for rotating said wiper sets over their respective bank contacts, said means including separate rotating arrangements for each wiper set so that by continued operation of said stepping magnet each contact set in one bank will be connected to every contact set in the other bank through said wiper sets.

3. In an automatic switch, two wiper sets, two banks associated with said two wiper sets, respectively, each bank comprising a plurality of contact sets, one bank containing a greater number of contact sets than the other, a stepping magnet, and separate means controlled by said stepping magnet for moving said wiper sets over their respective bank contacts step by step, whereby each contact set in one bank is connected to every contact set in the other bank through said wipers by continued operation of said magnet.

4:. In an automatic switch, two sets of wipers and associated banks, a common operating magnet, and a separate ratchet and pawl for each wiper set controlled by said magnet whereby one wiper set is rotated through a greater angle than the other for each operation of said magnet.

5. In an automatic switch, two shafts each mounting a set of wipers, a bank associated with each set of wipers, a ratchet on each shaft, one ratchet having a greater number of teeth than the other, two pawls for engaging said ratchets, respectively, and a common driving magnet for operating said two pawls.

6. In an automatic stepping switch, two sets of wipers, two banks associated with said two sets of wipers, respectively, a magnet, means controlled by said magnet for rotating one set of wipers over its bank, and means for rotating the other set of wipers one step each time said first set has completely traversed its bank.

7. In an automatic stepping switch, two sets of wipers, two banks associated with said two sets of wipers, respectively, a magnet, means controlled by said magnet for rotating one set of wipers step by step over its bank, and means controlled by the rotation of said first set of wipers for rotating the other set of wipers one step each time said first set has been rotated a predetermined plurality of steps.

8. In a telephone system, a plurality of stepping switches, each switch having two sets of wipers and two banks respectively associated therewith, a plurality of incoming trunks connected in multiple to one bank of each of said switches, and a plurality of groups of outgoing links, each group being connected to the other bank of different one of said switches.

9. In a telephone system, two groups of stepping switches, each switch having two sets of wipers and two banks respectively associated therewith, two groups of incoming trunks, one group multipled to the first banks of one group of switches and the other group multipled to the first banks of the other group of switches, and a plurality of groups of outgoing links equal in number to the number of switches in each of said groups of switches, each group of links being multipled to the second banks of aswitch in each group of switches.

10. In a telephone system, a stepping switch having two sets of wipers and two banks respectively associated therewith, a plurality of incoming trunks connected to one bank and a plurality of outgoing trunks connected to the other bank, means for marking one of said incoming trunks to indicate a calling condition on said trunk, common driving means for said sets of wipers, and means for controlling said driving means to rotate said sets of wipers until the first set connects with the marked trunk and the second set simultaneously connects with an idle outgoing trunk.

11. In a telephone system, a stepping switch having two sets of wipers operated by the same driving means, one set of wipers having access to incoming trunks and the other set having access to outgoing trunks, means for marking one of said incoming trunks, a relay in said switch for rendering said driving means inoperative, and means for operating said relay responsive only to the simultaneous connection of the first set of wipers with said marked trunkand of the second set of wipers with an idle one of said outgoing trunks.

12. In a telephone system, a plurality of stepping switches each having two sets of wipers, the first set of each switch having access to the same group of incoming trunks and the second set of each switch having access to a difi'erent group of outgoing trunks, a control switch common to'said incoming trunks, means responsive to the operation of sa d control switch by a dialled digit received over one of said incoming trunks for seizing an idle stepping switch having access to the desired group of outgoing trunks as I indicated by the value of the received digit, a single driving magnet rotating both sets of wipers of the seized stepping switch, and means for stopping said switch responsive to the simultaneous connection of one set of wipers with the calling incoming trunk and of the other set of wipers with an idle outgoing trunk in the desired group.

13. In a telephone system, a plurality of incoming trunks, a plurality of groups of outgoing trunks, a plurality of switches having two sets of wipers for interconnecting incoming and outgoing trunks, means common to said incoming trunks and controlled over a calling one of said trunks for selecting an idle switch having access to the calling trunk and to the desired group of outgoing trunks, and means for operating the selected switch 'to connect the calling trunk with an idle outgoing trunk in the desired group by means of said sets of wipers, said means including a single driving magnet for operating both sets of wipers.

' 14. In a telephone system, a group of incoming trunks, a plurality of groups of outgoing trunks, a plurality of groups of links, a group of switches having access to said group of incoming trunks and said groups of links, a second group of switches having access to said groups of links and to said groups of outgoing trunks, means controlled over a calling incoming trunk for simultaneously selecting a switch in the first group having access to the calling trunk and to one group of links and a switch in the second group having access to the same group of links and to the desired group of outgoing trunks, and means for automatically operating the selected switches to complete a connection from the calling trunk to an idle trunk in the desired group of outgoing trunks.

15. In a telephone system, a group of incoming trunks, a plurality of groups of outgoing trunks, a plurality of groups of links, a group of switches having access to said group of incoming trunks and to said groups of links, a second group of switches having access to said groups of links and said groups of outgoing trunks, means responsive to a digit received over a calling one of said incoming trunks for selecting an idle switch in the first group having access to the calling trunk and to one group of links and an idle switch in the second group having access to the same group of links and to the desired grouppf outgoing trunks as indicated by the value of the received digit, and means for automatically operating said first switch to connect the calling trunk with an idle link and for automatically operating said second switch to connect the link seized by said first switch with an idle trunk in the desired group of outgoing trunks.

In testimony whereof I atfix my signature.

DAVID ADAM CHRISTIAN.

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