US1550769A - Telephone-exchange system - Google Patents

Description

TELEPHONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 Sheets-Sheet 1 s. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 Sheets-Sheet 2 www NW NW MNN NNN Aug. 25, 1925.

\N QN 3N I Aug. 25, 1925. 1,550,769

s. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM Filed Sept. 26, 1923 i4 Sheets-Sheet 5 //7/ e/7f0r." Ju/m/e/ 15. W/W/d/m;

Aug. 25, 1925.

s. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 Sheets-Sheet 4 wg mwm wwm.

wk wk w? Aug 25, W25. 3,550,769

S. B. WILLIAMS TELEfl-IONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 Sheets-Sheet 5 Aug. 25, 1925; 1,559,769

s. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 sheets-sheet a Aug, 25, m5 1,550,769

S. B. WILLIAMS TELEPHONE EXCHANGE SYS TEM Filed Sept. 26. 1923 14 Sheets-Sheet '7 Aug. 25, wzsu 1,550,769

S. B. VJILLIAMS TELEPHONE EXCHANGE, SYSTEM Filed Sept.-26, 1923 14 sheets-sheets Aug. 25, 1925. 155G369 S. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM Filed Sept. 26, 1923' 14 sheets-sheet 9 @4/ WWW A??? L M M 3m "L HHL Mm Q k a; T T a M v m fimml 0 III! w AL -||.L $9 I MR B L M H 1 I- L H M H m w m m m HILW H fl 1. B! H u H ;|.|i! F .WmF |i!H m TELEPHONE EXCHANGE SYSTEM Filed Sept. 26. 1923 14 sheets-sheet 10 Aug. 5, 1925.

S. B. WILLIAMS TELEPHONE EXCHANGE SYSTEM 9 h S t e e h S 4 1 Filed Sept.

S. B. WILLIAMS TELEPHONE EXCHANGE SYS TEM 14 Sheets-Sheet 12 Filed Sept. 26, 1923 Awe/72w": Jamz/a/ 5. W/W/d/w 4 7} Aug. 25, 1925,

5 B. WILLIAMS TELEPHONE EXCHANGE SYS 'IEM Filed Sept. 26, 1923 14 Sheets-Sheet 14 Wye/12W" Ja/m/e/A? W/m'a/ms Patented Aug. 25,

UNITED sra 'rss SAMUEL nwrnmms, or BROOKLYN, NEW YORK, Assisi Ion T0 WESTERN mam.

PATENT- orricz.

COMPANY, INCORPORATED, OF NEW YORK, N. Y'., A CORPORATION NEW YORK.

urnnnrnonn-nxomen SYSTEM.

Application iiled September 26, 1928. Serial No. 664,825.

To all whom it may} canoe-m:

Be it known that I, SAMUEL B. WILLIAMS,

a citizen of the United States of America,

residing at Brooklyn, in the county of Kings and State of New York, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, andexact description.

ihis invention relates in general to telephone exchangesystems and more particularly to exchange systems of the class wherein automatic switching apparatus is used for setting up conversational connections. r v

i The principal object of the invention is to improve the organization of recording and controlling equipment for exercising a quick and reliable control over the selective switches in a telephone system.

A feature of the invention is to provide a plurality of equivalent switch controlling mechanisms, each associable with common recording devices, and also with any of anumber of selectorswitches at a switching stage for selectively operating such switches.

Another feature relates to the provision, in a system of the foregoing character, of a plurality of switch controlling mechanism each associable with the selector switches at a numberof stages for selectively operating a switch at each stage.

A further feature consists in so arranging the switch controlling mechanisms that when one of them is unserviceable another will handle its share of the calls until the disabled mechanism is restored to service.

Other features and advantages of the invention will be more clearly understood from the following detailed description and also from the appended claims.

Referring to the drawing, Figs. '1- to 13, inclusive, when arranged in the order illustrated in Fig. 15, disclose an automatic telephone exchange system embodying the features of the present invention.

Fig. 1 illustrates aline switch ordinate type v lines to'tr'unksl Fig. 2 shows one of the trunk circuits in full leading from the line switch to the first group selector. s Fig. 3 illustrates a portion. of one'of a of the conumber of first switch controlling markers.

orv extending subscribers the coordinate type.

Fig. 4 illustrates one of a number of coordlnate connector switches which serves to group selector switches of complete connections to the called subscribers lines. s F1g.'5 illustrates a special circuit em.-

ployed for reverting calls.

- Fig. 9 shows amulticontact relay connecting device for associating the register senders with the switch controlling mechanlsms or markers. V

Fig. 10 illustrates a controlling circuit arrangement common toa number of the Figs. 11, 12 and 13 disclose one of the. switch controlling mechanisms or'markers. Fig. 14; is a schematic diagram of the system.

The line switch 100, the selector and con-v nector switches 300 and 4:00 and the sender selector switch 600 are coordinate switches .in which incoming circuits are connected to outgoing circuits through the medium ofhorizontal links. The operating contacts are actuated by means of coordinate ve'rti- I cal and horizontalbars. For a clear understanding of the construction and the operation of switches of this character refer- No, 1,517,331, issued Dec. 2, 1924.

1' General arrangement of the system. I

It is believed that a better understanding may be had of the system and of the features of invention embodied therein by first considering the general plan illustrated in the diagram of Fig. 14. In this diagram the subscribers lines, two of which,

14.00. and 1401, are illustrated, enter the ex-.

change and terminate in vertical rows .of contacts on the line swith 1402. The line switch 1402 operating in response to the initiation of the call extends the calling next call.

- to th called subscribers line.

line over an idle trunk 1403 to the first selector switch 1404. At the same time the trunk 1403 is extended through a sender selector switch 1405 to one of a plurality of senders 1406, 1407, etc.

The subscriber now manipulates hls sendin}; transmitter and stores up in the selected sender, the record of the called subscribers line. Thereafter, the sender through a connecting device 1408 is associated with on of two equivalent markers 1409 and 1410. The markers are arranged to be taken for use in alternation. If both are idle the marker 1409 will be taken for use when a call arrives. Thereupon, the switching device 1411'is adjusted to render the second marker 1410 available for the If, While the second marker 1410 is in use, the first marker is released, the device 1411 will be readjusted so that the next succeeding call is handled by the first marker 1409. Should either of the markers become disabled for any reason, the switching device 1411 would throw the other marker into service permanently so that all incoming calls thereafter will be handled by the available marker until such time as the disabled marker is restored to service.

Following the attachment of the senderto the marker as aboveoutlined, the record of the called subscrib'ers line is transferred from the sender into the, associated marker.

The marker, thereupon determines the selection of the vertical row of contacts which represents the group of called subscribers lines containing the desired line. These called subscribers lines appear. in a number of coordinate connector switches 1413, 1414, etc. and each such switch accommodates a plurality. of the groups of lines. Therefore, it is necessary for the marker not only to determine which of the connectors shall be taken for use, but also to determine the particular vertical group of contacts in that connector in which appears the called line. Having fixed the vertical row of contacts containing the called line in the connector switch 1413, th marker determines the selection of a group of trunks 1412 outgoing from the selector switch 1404 and terminating in the switch 1413.

Following this the marker determines the selection of an idle trunk in the group 1412 and also determines an idle horizontal link in each of the switches 1404 and 1413 and then operates the horizontal magnets to extend the calling line through the switches Upon the completion of the connection the marker is released and immediately thereafter the register sender is also disconnected.

Should the calling subscriber desire connection with a party line the marker is arranged to receive information as soon as connection has progressed to a point where the called lin is ascertained in the connector switch. This information in the marker is then transferred through the first selector switch 1404 to the trunk circuit incoming from the line switch 1402 where it serves to determine the selection of the proper code of ringing current to be applied to the party line. As will be seen hereinafter for four party lines a semi-selective ringing arrangement is employed in the present system. Each party line has four appearances in the connector switch, two of which are reversed as regards the tip and ring conductors. The ringing equipment in the trunk circuit is adapted to apply a code consisting of either one ring or two rings with the usual intervening intervals. By selecting one of two different codes by use of the marker and by reversing the tip and ring conductors of the connector switch terminals, two bells on the party line may be rung at a time either with one short ring or with two short rings. The parties at these two substations will differentiate their bells by means of the codes.

In the event that the subscriber on a party line wishes to make a reverting call, namely, one to another substation on the same line, the marker receives special information from the recording sender. By the use of this information the marker determines the operation of the first sector switch 1404 to select one of a number of special trunks 1415, each including a reverting ringing equipment 1416. In this case the connector switch 1413 is dispensed with entirely. Having selected a reverting ringing equipment 1416, the proper ringing condition is ascertained from the marker and is applied to the party line to ring both the called and calling subscribers bells.-

Detailed description of establishment of a connection-Local ofiice call.

It will first be considered that the subscriber of line 101 wishes to converse with another subscriber whose call number is When the calling subscriber removes his receiver from the switchhook a circuit is closed from battery, through the winding of relay 102, outer back contact of relay 103, through the subscribers loop, inner back contact of relay 108 to ground. Relay 102 operates and closes a circuit from battery through relay 104, left back contact of relay 105, conductor 106, outer contact of relay 102, conductor 107 to ground. Relays 104, 105 and 108 enclosed within the broken rectangle pertain to the vertical group of lines in the row 110 of switch 100. These relays are brought into action whenever one of the ill) Inn

outer left back contact of relay 1 11. Relay 108 energizes and looks over its inner right front contact, windin of relay 109 to ground at relay 111. clay 109 energizes and closes an obvious circuit for slow re- I lease relay 125. Relay 109 also closes a circuit from battery through the vertical operating magnet 113, outer right front contact of relay 108, left front contact of relay 109 to ground at relay 111.

Relay 108 closes a circuit for relay 105. which energizes. Relay 112 was operated over the left front contact of relay 104, conductor 107 to ground. Relay 105 now opens the circuit for relay 104 which releases and opens the operating circuit for relay 112, but this circuit was previously replaced by a multiple path over the left front. contact of relay 105 and outer front contact ofrelay 102. I Relay 112 closes a holding ground for relay 105.

'Relay 109 also closes a circuit from battery through vertical operating magnet 114, terminal and switch arm 116' of allotter switch 115, back contact of relay 119, right contact of relay 111 to ground at outer right front contact of relay 109. The allotter switch 115 has a position for each of the several trunks which lead out from the line switch 100 to succeeding selector switches.

The allotter switch ,115 is operated by magnet 118 and will always take a position of rest corresponding to an idle trunk. Switch 115 is assumed to have been previously op-' erated to find the idle trunk 121. Uonsequently, vertical operating magnet 114 is now operated and locks itself over the winding of relay 111 to ground at relay 109. Relay 111 being shunted at this time does not operate.

The magnets 113 and 114 operate and pre pare the contacts in vertical rows 110 and 120, respectively. Magnet 114 closes a circuit which may be traced from battery through the winding of relay 602, left back contacts of relays 202 and 203, conductor 124 to ground at magnet 114. Relay 602 operates and at this time starts a series of operations in the circuit provided for the sender selector 600 in a manner similar to the op erations described for the line switch 100. Magnet 114 also closes a circuit traceable from battery, winding of relay 119, contact and winding of stepping magnet 118, switch arm 117 and test-terminal of switch 115, conductor 124 to ground at magnet 114.

Relay 119 is slow to release and keeps the circuit for switch arm 116 open during the stepping operation of switch 115. Magnet 'in operating, opens the shunt around the winding of relay 111.- Relay 111, therefore. operates in series with the winding of magnet 114. Relay 111 opens the circuit for relay 125 which is made slow to release in order to permit certain operations to take place before its armature is completely retracted.

When magnet 113 operated it closed a circuit which may be traced from battery, right-hand windingof relay 126, inner left front contact of relay 102, conductor 127, outer left contact of relay 108, contact of 'relay 128 to ground at magnet 113. Relay 126 is common to a group of horizontal operating magnets 144, 132, any one ofwhich is able to connect the calling line to an outgoing trunk. With each horizontal operating magnet is associated a relay 133, 134 which will cause an incoming call to be extended to an idle link in the line switch 100. It will be assumed that the first link 130 of the'group associated with the calling line is idle. Relay 126, in operating, closes a locking circuit for itself through the winding of relay 128 to ground at magnet 113.

ing of magnet 144, left back contact of relay 133, right front contact of relay 126, front contact of relay 128 to ground at relay 111 when relay 111 operates as above described. Horizontal opera-ting magnet 144 now opcrates and causes the connection to be established between the link 130 and a set of contacts in vertical row and also with aset of contacts in vertical row 120. The subscribers line is thereby extended through to the trunk 121.

Ground at magnet 114 now is extended through the winding of relay 131, conductor 134, contact in vertical row and wire of link 130, through the right winding of relay [33, both windings in series of magnet 144 to battery, thus providing a holding circuitfor magnet 144-. The ground at magnet 114 is also extended from the wire of link 130, through contact in vertical row 110 and through the winding of cut-off relay 103 which now operates. Relay -102 deenergizes and causes the release of relay 112, provided that no other call is waiting.

Relay 602 in operating closed a locking circuit for itself over its outer right contact, conductor 236 to ground at the inner back contact of relay 204. Relay 602 also connects ground to conductor 235 through relay 203 to battery. Belay 208 energizes relay 111 and magnet 114. The release of relay 128 opens the operating circuit for horizontal magnet l44'which now holds up through the winding of relay 133 as previously traced to ground on conductor 124. The shunt is now removed from the operating winding of relay 133 and this relay energizes and in so doing shifts the operating circuit for magnet 144 on to magnet 132, which now will be ready to take the next call in the same horizontal group. With the magnets 113 and 114 deenergized and the allotter switch 115 at rest the line switch 100 is in readiness to extend another call.

Tuning now to the operation of the sender selector 600, the operation of relay 602 closes circuits for relays 604, 605, 608 and 609, in the same manner as described for relay 102 in the line switch circuit. Vertical magnet 613 is operated over a circuit from battery through its own winding, outer right front contact of relay 608, left front contact of relay 609 to ground at relay 611. Vertical magnet 614 is operated from battery througlrits own winding, terminal and brush arm of the allotter switch 615, contacts of relays 619 and 611 to ground at relay 609. Vertical magnet 613 connect-s ground to horizontal group relay 626, which operates and locks in series with relay 628 and'the operation of the horizontal magnet 631 takes place as soon as relay 611 energizes in the holding circuit for magnet 614. The vertical magnet 614 connects ground to the test bank of allotter switch 615 which will step forward to the set of terminals corresponding to the next idle vertical operating magnet. Relay 625 energized at the time relay 609 was energized and its release was subsequently started when relay 611 operated. Relay 625 is slow to release in order to provide time for certain operations to take place before its complete release.

With horizontal magnet 631 and vertical magnets 613 and 614 operated, contacts in vertical rows 610 and 620 will now close with the wires in horizontal link 630 and the connection is thus established between the circuit of trunk 121 and the sender shown in Figs. 7 and 8. Ground from magnet 614 is extended to hold horizontal magnet 631 in a manner similar to that described for magnet 144 of line switch 100.

The ground at the right contacts of magductor 143, subscribers loop, conductor 142,.

contacts and'wire of link 130, conductor 122,

upper frontcontact of relay 204, conductor 232, contacts and wire of link 630, conductor 652, inner left contact of relay'7'15, left winding of coil 713 to groundjzit-relay 714.

Relay 700 operates in thiscircu'it and connects ground to relay709. Relay 709, in turn, operates relay 710 and a holding ground is now extended from the second outer front contact of relay 710 to conductor 624. Slow-to-release relay 625 can now complete its release and the release of vertical magnets 613 and 614 of the sender selector will take place in a manner similar to the release of the vertical magnets of the line switch 100 as described above. Horizontal magnet 631 will be held energized b the holding ground just described on con uctor 624. Relay 602 was released at the time relay 204 operated and the release of the remaining relays related to the sender selector will take place as described above for similar relays associated with the line switch 100, so that the sender selector 600 will again be in a position to extend a connection from another trunk to another sender.

The operations so far described were caused by the removal from the switchhook of the subscribers receiver. At the time relay 710 operated a circuit was completed from ground at its innermost front contact, conductor 730, through the right winding of coil 713, conductor 7 53, outer left back contact of relay 861 to a source of dial tone. This tone is transferred by induction from the right to the left winding of coil 713, and may thus be heard by the subscriber who then will set his dial for the sending of the first digit. The circuit is in a condition to receive the first series of two impulses.

The first break in the line circuit causes relay 700 to release and open a short circuit across the right winding of relay 711 which will operate in a circuit from battery, through coil 716, right winding of relay 711 and right front contact of relay 709.v Relay 711 energizes and operates relay 712 which looks over its inner left contact to conductor 730 which is grounded at relay I the winding of relay 717, left back contact of relay 718, inner right back contact of relay 719 to ground on conductor 730. Another circuit is now closed from battery through the winding of relay 717-, middle left contactof relay 711 to grounded conductor 730. A circuit is also closed from battery through the winding of rela 718,

outer left contact of relay 711 to con uctor 730. Relay 718 energizes and locks over its inner left contact and inner right contact of relay 719 to conductor 7 Relay 712, in operating, extends a' circuit from ground at right contact of relay 711, over the right contact of relay 712, left middle back.

contacts of relays 704,. 703, 702 and 701:, winding of relay 701, outer left back contact of relay 702 to the holding conductor 750, outer right contact of relay 719, outer left contact of relay 711' to grounded conductor 7 30. The winding of relay 701 is thus short circuited.

When the line circuit is again completed relay 700 energizes and again shunts the operating winding of relay 711 which, there fore, releases its holding circuit having been opened by the operation of relay 712. The

ground at right contact of relay 711 is thereby removed from the circuit described for relay 701, which circuit now includes the right winding of relay 712 and battery.

The first counting relay 7 01 therefore oper ates and locks itself to battery over its inner left contact, and thereby places a ;shunt around relay 712. Relay 712 "is dlfl'erentially wound and the current in the right-' hand winding is now so much reduced that the relay will release, the release being ac-- celerated by the left-hand winding. It will be noted that relays 709 and 717 are slow to release and,therefore, are maintained energized' during the reception of impulses. Upon the second break in the line circuit. relay 700' again deenergizes. Relays 711 and 712 again energize as just described.'

Ground from the right contact of relay 711 is now extended over the right contact of relay 712, middle left back contacts of relays 704, 703 and 702, middle left front contact of relay 701 through the winding of rewinding of relay 712. Relay 702 locks to battery and shunts the winding of relay 712 which again releases. Relay 702 also opens the holding circuit for relay 701 at its outer left front contact and relay 701 releases. It

should be noted that'the inner left contacts of the counting relays 701 to 706 are made to close slightly before the middle left front 7 contacts open so that the holding circuits for these relays are sure to be closedbefore thelr operating circuits are opened.

The first series of impulses now having been completed an interval occurs, during winding of relay 811 to battery. elay 811 energizes and locks over its lower front contact to conductor 752, through'winding of relay 719, left outer contact of rela 718,

contact of relay 717 to grounded con ucto'r, 730. Relay 719 does not operate in this circuit being shunted by the previously descri circuit. Relay 811 in energlzing establishes a connection at its upper front cont-actsfrom the counting relays to the relays Th. 1n the thousands register over conductors 721, 722, 723 and 724. For the present setting of the counting relays a ground will be extended from the grounded conductor 750, over the outer left front contact of relay 02, conductor 722, contact of relay 811, winding of relay B of the thousands reg1ster Th. to battery. 'Relay B locks to conductor 830 which is grounded at relay 710. Relay B further closes a circuit from conductor 830, outer I left contact of. relay 3, throughthe winding of relay 812 to battery, causing relay 812 to operate and lock over its inner leftc'ontact, back contact of relay 862 to conductor 830. Relay 812 closes a circuit for relay 861 which now removes the dial tone from the line circuit and prepares a circuit for the application of busy tone. Relay 812. also opens the energizing circuit for relay 811 and thus removes the short around relay 719 which therefore operates. Relay 719 opens the holding circuit of the counting relays at its outer right contact and at its right inner contact relay 719 opens the holding circuit of relay' 718., The counting relay 702 releases andalso relay 718, which in turn,

opens the circuit for relays 719 and 811 at its outer left contact and relays 719 and 811 release.

lay 702, outer left contact of relay 703 to the holding conductor 750. The second countfirstdigit as described above, but since only one impulse is sent out, relay 701 will remain energized at the time slow release relay 717 completes its release in the time interval between the second and third digit. Relay 717 now extends the ground from conductor 7 30, over its own contact, left outer contact of relay 718, left contact of relay 719, conductor 751, right front contact of relay 812, right back contact of relay 822, through the winding of relay 821 to battery. Relay 821 connects the counting relays to the H relays in the hundreds register and locks itself to conductor 752, through winding of relay 719, contact of relays 718 and 717 to conductor 730. Relay 719 is again shunted as described above. A circuit is now extended from conductor 750, inner right front contact of relay 701, right back contact of relay 706, conductor 721, contact of relay 821, winding of relay A of the hundreds register. Relay A energizes, locks to conductor 830 and closes a circuit at its outer left contact to relay 822 which, therefore, operates and locks. The operating circuit for relay 821 is now open and the shunt removed from relay 719, which operates and causes the release of the counting relay 701 and relay 718. Relays 719 and 821 release and, slow release relay 717 energizes as described for the first digit.

The setting of the hundreds register is thus completed and the circuit is ready to receive the third digit which, in this case, is assumed to consist of three impulses. The operations for the first two pulses will be the same as for the first digit. At the end of the third impulse when relay 711 deenergizes and the shunt is removed from relay 703, this relay energizes over a circuit traced from battery right winding and right front contact of relay 712, middle left back contact'of relays 704 and 703, middle left front contact of relay 702, winding of relay 7 03, outer left contact of relay 704 to ground at conductor 750. Relay 703 operates and opens the circuit for relay 702 and in looking places a shunt around the winding of relay 712 which deenergizes as previously described. When new slow-to-release relay 717 completes its release, ground from conductor 730 is extended over its own contact, outer left front contact of relay 718, left contact of relay 719, conductor 751, right front contact of relays 812 and 822 and right back contact of relay 832, through the winding of relay 831 to battery. This circuit also extends from the right back contact of relay 832, through winding of relay 863. These two relays energize. Relay 863 temporarily removes ground from its armature for purposes as will be described later. Relay 831, in operating, connects the counting relays to the relays T of the tens register and two circuits are new extended. by the counting relay 703, from the conductor 750, one to be traced over its outer left front contact, conductor 722, contact of relay 831, winding of relay B to battery. The other circuit and the shunt removed from relay 719. The

subsequent release of relay 718, 719 and 831 takes place as previously described and slowto-release relay 717 again energizes.

The'circuit is now ready to receive the units digit, which in the case assumed, consists of two impulses. The operations in response to these two impulses are the same as described for the first digit and when relay 717 releases, a circuit is extended from conductor 730, contact of relays 717, 718 and 719, conductor 751, right front contacts of relays 812, 822, 832, right back contact of relay 842, winding of relay 841 to battery. Relay 841 now connects the counting relays to the relays U in the units register and the circuit from the second counting relay 702 will be extended through the winding of relay B which locks and furthermore operates the relay 842. This latter relay also looks and opens the shunt around the winding of relay 19 which operates. The operation of relay 719 and the subsequent release of relays 718, 719 and 841 take place, whereupon relay 717 energizes.

When relay 842 operated a circuit was completed from battery left winding of relay 731, conductor 732, outer left front contact of relay 842, inner left back contact of relay 864 to ground at contact of relay 863. Relay 731 energizes and locks over its own right contact, inner left back contact of relay 718, inner right back contact of relay 719 to conductor 730. Ground is now extended from the inner left front contact of relay 731, middle left contacts of relays 733 and 734, outer right back contact of relay 735, left back contact of relay 736, conductor 901, through relay 911 to battery. Relay 911 energizes and closes a circuit from battery through winding of relay 921, right back contact of relay 922, lower front contact of relay 911, conductor 925, through relay 1001 to ground. Relay 921 operates in this circuit and locks at its left front contact over back contacts of relays 1003 and 1002, through the winding of relay 1001' to ground. A circuit is now completed for the lower winding of relay 912 from battery over the upper front contact of relay 911, upper back contact of relay 914, right front contact of relay 921, through grounded conductor 1010. Relay 912 energizes and extends ground to relay 922 which energizes and closes a holding circuit for itself at its

Images