Manual / Guide · 1955
AE Training Bulletin 805: The Plunger Line Switch and Associated Master Switch
Keith plunger line switch and master switch operation.
Manual / Guide · 1955
Keith plunger line switch and master switch operation.
a AUTOMATIC ELECTRIC TRAINING SERIES Bulletin The PLUNGER B and ASSOC ATEQ MASTER-SW O R I G I N A T O R S O F T H E D I A L T E L E P H O N E This is one of the helpful booklets in the AUTOMATIC ELECTRIC TRAINING SERIES on STROWGER AUTOMATIC TELEPHONE SYSTEMS E l e c t r i c a l Principles of Telephony Mechanical Principles of Telephony Fundamentals of Apparatus and Trunking The Plunger Lineswitch and Associated Master-Switch Rotary Lineswitch The Connector The Selector P u l s e Repeaters Trunking Power and Supervisory Equipment Party-Line Connectors and Trunk-Hunting Connectors Reverting-Call Methods The Test and Verification Switch T r a i n Toll Switch T r a i n Switching Selector-Repeater P r i v a t e Automatic Exchanges with PABX Appendix Community Automatic Exchanges Manual Switchboards Linef inder Switches - May we send you o t h e r s pertaining to equipment in your exchange? THE PLUNGER LINESWITCH AND ASSOCIATED MASTER-SWITCH 1. LINE -EQUIPMENT FUNCTIONS 1.1 Calls FROM a line When a c a l l e r t a k e s h i s handset "off hook", h i s line equipment s i g n a l s the c e n t r a l office that he wishes a connection s e t up. When the central office responds with "Number, please? " (for a manual office) o r with "dial tone" (for an automatic office), the line signal's w o r k i s done and the signal i s cut off. 1.2 Calls TO a line ! Apparatus used only to get attention ("Number, please? " o r "dial tone") for calls from a line m u s t b e c u t off by t h e l i n e equipment when s o m e o n e m a k e s a c a l l to t h e line. (If the attention-getting a p p a r a t u s w e r e not cut off, it would remain bridged a c r o s s the line and (a) would i n t e r f e r e with ringing and (b) when the called p a r t y a n s w e r e d , his "off-hook" would call in a n o p e r a t o r o r bring in a selector with dial tone,) In t h e f i r s t a u t o m a t i c s w i t c h b o a r d s , each subscriber's line had i t s own connector switch. in larger switchboards, each subscriber's line h a d a s e l e c t o r s w i t c h . E a c h connector o r selector had several relays and 300 bank contacts and was used only a few minutes each day; i t stood idle most of the time. The time-efficiency of the s u b s c r i b e r ' s telephone line and of the switching equipment associated therewith is very low; therefore, i t i s more economical from the standpoint 'of initial cost and maintenance to provide individual line equipment of simpler d e s i g n and with f e w e r functions. In,1906, a s m a l l e r and l e s s expensive switch, t h e "lineswitch", was introduced. In a lineswitch system, each subscriber's line has a lineswitch. When the caller lifts his handset to make a call, the lineswitch automatically connects the line to an idle s e l e c t o r o r connector. Fewer expensive selectors and connectors a r e required. Since each selector o r connector i s used by more than one line, i t i s in use for a l a r g e r percentage of the time; therefore, the more expensive equipment i s used more efficiently. 1.3 Summary, T h e line equipment s e r v e s a s a gate through w h i c h c a l l s c a n b e m a d e both f r o m and to the line: c a l l s f r o m the line either signal an o p e r a t o r o r a r e r o u t e d t o the d i a l tone and dial-controlled equipment; and calls 2 the line a r e routed d i r e c t l y out onto the line (with the a t t e n t i o n - g e t t i n g - a p p a r a t u s -bridge cut off). 2 . LINE EQUIPMENT In a magneto s y s t e m the line equipment is the drop and the jack with cut-off springs. In manual common-battery* systems the line equipment is the line lamp, line relay, cut-off relay, and jack(s) . In modern Strowger automatic systems, the line equipment is a line r e l a y and a cut-off relay either (a) with a lineswitch o r (b) with starting and marking leads to linefinders. 3. LINESWITCHES There a r e two basic kinds of lineswitch: ,(a) the plunger lineswitch, described in this bulletin 80 5; and ( b ) the r o t a r y l i n e s w i t c h , d e s c r i b e d in A u t o m a t i c E l e c t r i c Company bulletin 806-. 4. PLUNGER LINESWITCH 1 *The f i r s t manual common-battery central office was not put in operation until December 1893. More than a year e a r l i e r , November 3, 1892, the f i r s t Strowger automatic central office was cut over. Plunger lineswitches a r e found in Strow e r main and private plants a s line equipment. hey a r e often referred to a s the "Keith" type lineswitch a f t e r the inventor, Alexander E . Keith. The 5 Guide shaf U- spring, Solenoid Locking , segment Locking-arm roller Plunger Figure 1. Master-switch and self-aligning plunger lineswitches. (Vertica L mounting, usual for pub 1 ic main exchanges. ) PLUNGER LINESWITCH F i e r e 2. Master-swl. t c h and self-aligning plunger 1 ineswi tches. (florizontal mounting, usual for private automatic exchanges and for private automatic branch exchanges,) plunger lineswitch is a n ingenious mechanism which c a n connect t h e associated telephone line t o a n y o n e of 1 0 t r u n k s * e a c h l e a d i n g to a S t r o w g e r n u m e r i c a l switch. F i g u r e 1 shows v e r t i c a l l y - m o u n t e d p l u n g e r lineswitches and their associated master-switch, found in central o f f i c e s r e n d e r i n g r e g u l a r public telephone service. F i g u r e 2 shows horizontally-mounted p l u n g e r l i n e s w i t c h e s and t h e i r associated m a s t e r - s w i t c h , u s e d i n p r i v a t e automatic exchanges (P-A-X). The plunger lineswitch consists of a line relay and an operating magnet which actuates an a r m a t u r e carrying a pivoted plunger. This magnet has two windings: one called the "pull-down coil" (PDC), and the other the "bridge cut-off" (BCO) winding. The bank contacts a r e visible in both photographs a n d a r e a r r a n g e d i n s u c h a m a n n e r that the plunger can engage any one of the ten sets of bank contacts. ' *American Institute of Electrical Engineers "American S t a n d a r d Definitions of E l e c t r i c a l T e r m s " 165.55.100 defines a trunk as "a telephone line or channel between two c e n t r a l offices o r switching devices, which is used in providing telephone connections between s u b s c r i b e r s generally." W h e n t h e c a l l e r r e s t o r e s h i s h a n d s e t , the connection releases, and i n the " self -aligningr' ** lineswitch (type 27), the plunger a l i g n s automatically with the i d l e lineswitch plungers on the master-switch guide shaft. P l u n g e r l i n e s w i t c h e s a r e grouped u n d e r the control of master-switches. Lineswitch groups a r e mechanically linked when they a r e served by one master-switch. One master-switch usually s e r v e s up t o one hundred lineswitches. Each l i n e s w i t c h g r o u p u s u a l l y c o n s i s t s of f r o m twenty-five to one hundred l i n e s w i t c h e s p e r master-switch, and has access to a maximum of ten trunks. **Earlier, t h e fan-tail lineswitch (sometimes known a s type 26) w a s i n w i d e s p r e a d use. T h i s s w i t c h is s t i l l in production f o r replacements and additions. T h e fan-tail type differs from the self-aligning type in the construction of t h e p l u n g e r which ( i n t h e fan-tail type) h a s a slotted fan-shaped tail that engages the spline of the master-switch guide shaft. T h e fan-tail is entirely withdrawn f r o m the spline when the plunger engages one of the s e t of ten bank c o n t a c t s . J u s t a f t e r t h e c a l l e r h a n g s up, t h e plunger releases, but does not align with the other idle lineswitch plungers until the master-switch in i t s cycle of oscillations passes the trunk previously used by that lineswitch. Then the spline of the master-switch will engage the plunger, and will move i t along with the other idle lineswitch plungers. FUNCTIONS When t h e s t a t i o n loop is closed, the plunger is t h r u s t into t h e bank, and the insulated r o l l e r s attached n e a r t h e end of t h e plunger p r e s s the bank springs associated with the.line into contact w i t h t h o s e of t h e t r u n k which t h e plunger has engaged. Trun kr to numerical switches Lines I 2 3 4 5 6 7 8 9 10 3 2 1 Of the t h r e e s u b s c r i b e r s ' lines r e p r e s e n t e d in f i g u r e 3, l i n e s w i t c h No. 3 is shown a s having o r i g i n a t e d a c a l l , c a u s i n g t h e p l u n g e r of t h i s lineswitch to b e t h r u s t into the bank, thus con- f necting line No. 3 with trunk No. 8. The remaining plungers have been moved away by the guide shaft a n d a r e a l i g n e d o p p o s i t e t r u n k No. 7 which i s a s s u m e d t o b e idle. . , 5. FUNCTIONS OF THE PLUNGER LINESWITCH 5.1 Outgoing c a l l s On c a l l s originating a t the telephone (outgoing c ' a l l s ) , t h e f u n c t i o n s of t h e l i n e s w i t c h a r e : (a) To extend the line through to an idle selector ( o r connector) trunk. (b) To busy the line a t connector bank terminals against intrusion by incoming calls, i m m e d i a t e l y u p o n o p e r a t i o n of t h e l i n e s w i t c h line relay. - (c) T o " c u t off" o r d i s c o n n e c t t h e b a t t e r y connected line relay and ground from the line. 5.2 Incoming c a l l s On c a l l s to t h e telephone (incoming calls), the functions of t h e lineswitch a r e : (a) T o " c u t off" o r d i s c o n n e c t t h e b a t t e r y connected line relay and ground from the line. (b) T o p r e v e n t t h e l i n e s w i t c h p l u n g e r f r o m e n g a g i n g a s e l e c t o r o r c o n n e c t o r trunk. 6. ASSOCIATED MASTER-SWITCH Trunk multiple Figure 3 . -6earing Relation of plunger lineswitches and trunks. Figure 3 is a schematic layout showing a p a r t i a l g r o u p of s e l f - a l i g n i n g p l u n g e r l i n e s w i t c h e s . Only t h r e e lineswitches of the group a r e r e p r e sented, although i n practice there a r e from t w e n t y - f i v e to o n e h u n d r e d l i n e s w i t c h e s i n a group. All t h e lineswitch plungers comprising any one group a r e controlled by a master-switch a n d i t s r e s p e c t i v e guide shaft; t h e r e f o r e , t h e position of the plungers with relation to the t r u n k s is determined by the guide shaft. Each lineswitch plunger of t h e group will have a c c e s s to t h e t e n s e t s of c o n t a c t s i n i t s a s s o c i a t e d bank, thus providing each line with the possibility of seizing a n y o n e of t h e a v a i l a b l e t r u n k s leading t o the n u m e r i c a l s w i t c h e s . T h e a r r a n g e m e n t of t h e b a n k m u l t i p l e a n d t h e i n d i v i d u a l l i n e is a l s o s h o w n i n F i g u r e 3 . E a c h s i n g l e l i n e i n the i l l u s t r a t i o n r e p r e s e n t s e i t h e r a t r u n k o r subs c r i b e r ' s line. T h e position of t h e p l u n g e r s of e a c h group of l i n e s w i t c h e s is c o n t r o l l e d by a m e c h a n i s m t e r m e d the "master-switch." This control is through the movement of the plunger guide shaft. T h e p r i m e function of the m a s t e r - s w i t c h is to k e e p t h e p l u n g e r s of a l l l i n e s w i t c h e s r e s t i n g opposite the bank contacts of an idle trunk. Each t i m e a t r u n k is e n g a g e d , t h e m a s t e r - s w i t c h immediately moves, o r steps, a l l the remaining idle lineswitch plungers to a position opposite a n available trunk. The plunger type lineswitch is thus preselecting i n operation; that is, the idle trunk is selected p r i o r to the initiation of a call. T h e f u n c t i o n s of t h e m a s t e r - s w i t c h m a y b e s u m m a r i z e d a s follows: (a) To provide "supervised" ground (+ battery) to the associated lineswitches. (b) To seek an idle trunk whenever a lineswitch engages the preselected trunk. f *< -% (c) T o p r e v e n t a n y l i n e s w i t c h f r o m plunging while the master-switch is seeking a n i d l e trunk. SELF-ALIGNING LINESWITCH (d) To lock the plunger guide shaft in the trunk position chosen. (e) T o control the self-aligning lineswitches on rapid recalls. The power for moving the master-switch from trunk No, 1 to No. 10 is supplied by a solenoid type magnet. During the movement from trunk No. 10 to No. 1 the master-switch selects trunks, and a "U" shaped spring furnishes the motive power for this stepping movement. The speed a t which the plunger guide shaft and the associated l i n e s w i t c h p l u n g e r s m o v e is controlled by a governor, and is generally between the limits of 104 and 112 oscillations per minute. The masterswitch bank wipers a r e s o fastened to the plunger guide shaft that when the lineswitch plungers a r e opposite trunk No. 10, the master-switch wiper is r e s t i n g on m a s t e r - s w i t c h bank contact No. 10, etc. 7. SELF-ALIGNING LINESWITCH CIRCUIT F i g u r e 4 is a t y p i c a l s c h e m a t i c c i r c u i t of a self - a l i g n i n g linesw i t c h and t h e a s s o c i a t e d master-switch. This figure includes the essential p a r t s of the n u m e r i c a l s w i t c h to which the p r i m a r y l i n e s w i t c h t r u n k connects. In this example a selector is assumed. Connections f o r a c o n n e c t o r would b e establi.shed i n a like manner, connecting the "+" , "-' ' , and "C' ' leads. 7.1 Chain circuit When the lineswitch and master-switch circuit is normal, a s shown, a local circuit is maintained f r o m ground (+ b a t t e r y ) a t the double break contacts of start relay A-1, through the 2200-ohm winding of delay relay E- 1, through the double b r e a k c o n t a c t s of chain r e l a y F-1, s e r i a l l y through the double b r e a k contacts of a l l line r e l a y s of the lineswitches associated with the master-switch, and thence through the 12,000-ahm winding of open-chain relay B-1 to " battery. Open-chain relay B-1 is thus held operated a s long a s no line relays a r e operated. At this time, the current flow through the 2200-ohm winding of delay relay E-1 is not sufficient to cause i t s a r m a t u r e to operate, due to the high resistance (12,000 ohms) of the winding of open-chain relay B-1 i n s e r i e s with it. -" The double-break contacts of this chain circuit, through all the lineswitches of the group, insures continuity of the chain, a s both contacts must be open b e f o r e the chain c i r c u i t is interrupted. 7.2 Line and o ~ e r a t i n pcircuit --- On originating calls, when the calling person removes the handset f r o m the cradle, a circuit is established f r o m battery, through the 800-ohm winding of line relay A, break contacts "-" of the B.C.O. relay, over the line, through t h e t e l e p h o n e , b a c k o v e r t h e "+" l i n e , and through the break contacts on the B.C.O. relay to ground (+ battery) .* The line relay A operates, interrupting the chain circuit at its double-break contacts which permits the open chain relay B-1 to r e s t o r e t o n o r m a l and in t u r n complete a c i r c u i t f r o m ground (+ b a t t e r y ) , through the supervisory lamp and over the common tell-tale l e a d to d e l a y r e l a y e q u i p m e n t , not shown. ' I - ' * The operation of the line relay (A) also establishes a c i r c u i t f r o m ground (+ battery) a t the break contacts of start relay A-1, through the 2200-ohm winding of delay relay E-1, through the doublebreak contacts of chain control relay F-1, through the make contact of line relay A, and through the 240-ohm "pull-down" winding of the operating r e l a y (B) to "-" battery. Ground (+ battery), through make contacts on relay A, is connected to the control normal lead (C) to protect the line against intrusion by other calls via the connector. 7 . 3 Delay circuit The 2200-ohm winding of the delay relay (E-1) is now energized in s e r i e s with the "pull down" coil of relay B. Relay B does not operate a t this time, due to the high resistance of delay relay E-1. This delay relay is slow in operating, due to the counter magnetic effect produced by i t s short-circuited 8 -ohm winding. Upon operating, 8-ohm winding i n parallel relay E-1 connects ~ t s with the 2200-ohm winding, thus reducing the r e s i s t a n c e i n s e r i e s with the 240-ohm P.D.C. (pull-down coil) of r e l a y B. The c u r r e n t flow through the 240-ohm "pull down" coil of relay B is now sufficient to operate both the plunger and the B.C.O. a r m a t u r e s . 7.4 Operation of B.C.O. Armature The B.C.0, a r m a t u r e operating, interrupts the circuit to line relay A, but this relay does not release immediately, due to the magnetic effect produced by the copper slug. The operation of the plunger a r m a t u r e closes s p r i n g contacts associated with it, establishing a circuit f r o m ground (+ b a t t e r y ) a t a m a k e contact of line r e l a y A, through t h e contacts of t h e plunger a r m a t u r e springs,, and through the 1200-ohm winding of r e l a y B to t h e "-" b a t t e r y . The B.C.O. winding when energized will hold the plunger and t h e B.C.O. a r m a t u r e s operated. *Line relay "A" i s a slow acting type r e l a y due to the copper slug o r collar attached on the a r m a t u r e end of the core. It is not generally known that the slow-to-operate feature of the relay i s a s necessary a s the slow-to-release f e a t u r e . When t h e c i r c u i t is closed, t h e copper slug prevents the magnetic field from reaching the a r m a t u r e until the core of the relay i s fully saturated. This delay in t h e a t t r a c t i o n of the a r m a t u r e becomes important a moment later when relay B operates and opens the circuit to relay A. If the induced current were insufficiently strong, t h e a r m a t u r e of r e l a y A would r e l e a s e before selector relay B-2 could operate to ground control lead C. Thus the full saturation of the core must precede the attraction of the armature. MASTER 7.5 Operation of plunger T h e p l u n g e r engaging the bank, establishes simultaneoilsly two connections; one f r o m ground (+ b a t t e r y ) a t l i n e r e l a y (A), via t h e c o n t r o l lead (C), through t h e lineswitch bank contacts, t h r o u g h a m a s t e r - s w i t c h bank contact and t h e master-switch wiper, and through the 1075-ohm winding of s t a r t r e l a y A-1 to " -" b a t t e r y ; the o t h e r e x t e n d s t h e " -" l i n e and t h e "+" l i n e t h r o u g h t o t h e s e l e c t o r . I t should b e r e c a l l e d that the c i r c u i t to r e l a y A of the lineswitch h a s b e e n o p e n e d b u t t h e l i n e r e l a y A h a s not y e t released. S t a r t relay A-1 operating, i n t e r r u p t s t h e c i r c u i t t o t h e pull-down c o i l of lineswitch r e l a y B. T h e plunger and the B.C.O. a r m a t u r e s a r e now held operated by the 1200-ohm B.C.0. winding which is still supplied ground (+ battery) f r o m a m a k e c o n t a c t of l i n e r e l a y A. T h e s u b s c r i b e r ' s line circuit extended through to t h e selector by the plunger engaging the bank may b e t r a c e d f r o m t h e " -" battery, through the upper 200-ohm winding of line relay A-2 of the selector, o v e r the "-" trunk, through t h e lineswitch bank c o n t a c t s , o u t o v e r t h e "-" l i n e , t h r o u g h t h e telephone, b a c k o v e r t h e "+" line, through t h e l i n e s w i t c h b a n k c o n t a c t s , o v e r the "+" trunk, and through the lower 200-ohm winding of r e l a y A-2 to ground (+ battery) . A f t e r t h e f o r e g o i n g operation h a s t a k e n place, line relay A of the lineswitch will r e l e a s e . It is a p p a r e n t f r o m the d e s c r i p t i o n that i n o r d e r to prevent the r e l e a s e of the lineswitch, relay B-2 of the s e l e c t o r m u s t o p e r a t e and r e t u r n ground (+ battery) over the control lead (C) to the B.C.O. winding of t h e lineswitch b e f o r e line r e l a y A of the lineswitch has released. T h e a d j u s t h e n t of l i n e r e l a y A, which is of t h e slow-acting type, c a r e s f o r t h i s t i m e interval. Line relay A-2 of the s e l e c t o r operating, establ i s h e s a l o c a l c i r c u i t t h r o u g h t h e 800-ohm w i n d i n g of r e l e a s e r e l a y B - 2 . R e l a y B-2 o p e r a t i n g , c o n n e c t s ground (+ b a t t e r y ) to t h e control lead (C). This connection may b e t r a c e d f r o m ground (+ battery), through m a k e contacts on r e l e a s e r e l a y B-2 of t h e s e l e c t o r , through the lineswitch bank contacts, through the plunger a r m a t u r e s p r i n g c o n t a c t s , and through the 1200-ohm B.C.O. winding of r e l a y B, t o "-" b a t t e r y , t h u s m a i n t a i n i n g t h e B.C.O. winding e n e r g i z e d a n d p r e v e n t i n g t h e r e l e a s e of the plunger a r m a t u r e a t t h i s time. Ground (+ battery) a t the make contacts of r e l e a s e r e l a y B-2 of the s e l e c t o r is a l s o maintained on t h e m a s t e r - s w i t c h bank contact, preventing the seizure of the selector by another lineswitch. T h i s s a m e g r o u n d (+ b a t t e r y ) c o n n e c t i o n is m a i n t a i n e d on t h e c o n t r o l n o r m a l ( C ) t o the connector banks. 8. MASTER-SWITCH OPERATION As p r e v i o u s l y mentioned, when t h e lineswitch p l u n g e r f i r s t e n g a g e s t h e bank, a connection is completed f r o m ground (+ battery) a t a m a k e contact of r e l a y A of the lineswitch, through the l i n e s w i t c h bank contacts, through t h e m a s t e r s w i t c h b a n k contact and a s s o c i a t e d wiper, and through the 1075-ohm winding of s t a r t relay A- 1 to " - * * battery. The s t a r t relay (A-1) operating, opens the c i r c u i t of the P.D.C. (pull-down coil) of relay B, and establishes a circuit f r o m ground (+ b a t t e r y ) , through the m a k e contacts of r e l a y A-1, and t h r o u g h t h e 105-ohm winding of t h e locking magnet D-1 to "-" battery. The locking magnet operating, disengages the lock l e v e r f r o m the locking segment, and allows the "U" s p r i n g to move the guide shaft, thus moving all lineswitch p l u n g e r s i n a counter-clockwise direction. When t h e m a s t e r - s w i t c h w i p e r is disengaged f r o m t h e m a s t e r - s w i t c h bank contact position No. 10, t h e circuit to the s t a r t relay A-1 will b e opened, causing t h i s relay to r e s t o r e t o n o r m a l and r e l e a s e locking magnet D-1. The operations j u s t d e s c r i b e d w i l l p e r m i t t h e l o c k l e v e r to engage t h e next notch of the locking s e g m e n t , w h i c h w i l l h o l d all i d l e l i n e s w i t c h p l u n g e r s o p p o s i t e t r u n k No. 9 . D u r i n g t h e p e r i o d t h e l o c k i n g m a g n e t D - 1 is o p e r a t e d , a c i r c u i t is c l o s e d f r o m ground (+ b a t t e r y ) a t t h e locking magnet springs, through the 800-ohm winding of c h a i n c o n t r o l r e l a y F-1 t o "-" b a t t e r y which o p e r a t e s a n d o p e n s t h e c h a i n c i r c u i t of t h e l i n e s w i t c h e s to p r e v e n t a n y l i n e s w i t c h f r o m plunging while the master-switch is seeking a n idle trunk. In moving f r o m trunk No. 10, should trunk No. 9 be i n use, ground (+ battery) will b e maintained on master-switch bank No. 9, and i n this c a s e the s t a r t relay (A-1) will b e prevented f r o m releasing. The "U" spring will then move the locking segment and the guide shaft to trunk No. 8. Similarly, i f trunk No. 8 t e s t s busy, the locking segment and guide shaft will continue to s t e p i n s u c c e s s i o n to trunks 7, 6, 5, etc., until the f i r s t i d l e t r u n k is found. 8.1 R e t u r n motion of m a s t e r - s w i i c h S e a r c h i n g f o r a n i d l e t r u n k will continue until trunk No. 1 is reached, at which point a r m No. 1 on the locking segment will push the a r m springs into contact. When t r u n k No. 1 b e c o m e s busy, s t a r t r e l a y A-1 w i l l o p e r a t e a s previously described. The s t a r t relay (A-1) operating, will c l o s e a c i r c u i t to locking m a g n e t D-1 which, i n t u r n , w i l l c o m p l e t e a c i r c u i t t h r o u g h the 8 0 0 - o h m w i n d i n g of chain c o n t r o l r e l a y F - 1 causing i t to operate. Since the a r m springs a r e closed,when the locking segment is in trunk No. 1 position, the operation of the start relay (A-1) a t t h i s t i m e e s t a b l i s h e s a c i r c u i t f r o m ground (+ battery) a t a make contact on s t a r t r e l a y A-1, t h r o u g h t h e c o n t a c t s of t h e a r m s p r i n g s , and MISCELLANEOUS through the 500-ohm winding of t r i p relay C-1 to 1 s -13 battery. The trip relay (C-1) operating, will mechanically lock i t s armature, by the extension of the armature spring on this relay engaging the catch on the locking spring. This mechanical lock i s t o m a i n t a i n the t r i p r e l a y s p r i n g s in an operated position a f t e r the t r i p relay (C- 1) has b e e n d e - e n e r g i z e d by t h e i n t e r r u p t i o n of ifs circuit a t the contacts of the a r m springs; these a r m springs break contact immediately after t h e master-switch moves from trunk No. 1. A circuit is now maintained from ground (+ battery) through make contacts of the trip relay (C-1), and through the widing of the solenoid magnet to "-" battery. The solenoid energizing will pull its plunger into t h e coil, thus moving t h e locking s e g m e n t and the guide shaft in a clockwise direction, and also the lineswitch plungers from a positlon opposite trunk No. 1 to a position opposite trunk No. 10. When the t r u n k position No. 10 is reached, the locking segment will be s o positioned that a r m No. 10 w i l l d i s e n g a g e t h e m e c h a n i c a l lock thereby releasing the trip-relay armature. This will open the circuits to locking magnet D-1 and c h a i n c o n t r o l r e l a y F - 1 p e r m i t t i n g t h e m to restore to normal. The trip relay (C-1) releasing also interrupts the circuit to the solenoid magnet, stopping i t s movement. 8.2 Delav and chain control r e l a v s Because t h e 8-ohm winding of delay relay E - 1 normally is short-circuited, the operation of the plunger of t h e lineswitch associated with a line w h i c h is o r i g i n a t i n g a c a l l is m o m e n t a r i l y delayed. This is to c a r e for a condition arising w h e n a s u b s c r i b e r , a f t e r o r i g i n a t i n g a call, r e l e a s e s t h e lineswitch and then r e c a l l s before t h e lineswitch plunger has had t i m e to realign itself with the other idle lineswitch plungers. By slightly delaying the reoperation of the lineswitch plunger, the possibility of the lineswitch engaging a busy trunk is eliminated. m o r e than one lineswitch f r o m operating at precisely the s a m e instant, which might permit m o r e than one lineswitch plunger t o engage the same trunk. In case more than one line relay (A) in the same group of lineswitches operates a t the same instant, the operated line relay (A) nearest t h e g r o u n d (+ b a t t e r y ) end of t h e c h a i n will function f i r s t and connect ground (+ battery) to i t s associated pull-down coil (P.D.C.). At the s a m e t i m e i t will disconnect ground (+ battery) f r o m that portion of the chain circuit leading to t h e pull-down c o i l a s s o c i a t e d with t h e other operated lineswitch A relay, The plunger of the operated lineswitch located in the chain circuit nearest to the ground (+ battery) terminal of t h e c i r c u i t , t h e r e f o r e , will be the f i r s t to plunge into the lineswitch bank. The plungers of the other lineswitches located f a r t h e r along in the chain cannot plunge until the master-switch has moved to an idle trunk and the line relay (A) of t h e lineswitch n e a r e s t the ground (+ battery) t e r m i n u s of t h e chain c i r c u i t has r e s t o r e d to n o r m a l , thus r e e s t a b l i s h i n g continuity of the chain circuit. 8.4 Self -aligning f e a t u r e If a c a l l is originated when the plungers of a l l i d l e lineswitches a r e resting opposite a trunk which, due to s o m e fault, is open circui'ted, the plunger will engage the lineswitch bank contacts a s s o c i a t e d with t h i s t r u n k , but s i n c e ground (+ battery) cannot be returned o v e r the control lead (C) from the selector to energize the B.C.O. w i d i n g and there hold the plunger i n engagement with the bank contacts, the plunger armature will r e l e a s e almost immediately. The plunger will instantly realign with the other i d l e lineswitch plungers opposite the next unoccupied trunk (the master-switch having meanwhile sought the idle trunk), and then plunge again, engaging the good f r e e trunk. 8.5 Incoming calls When t h e 2-ohm winding is s h o r t - c i r c u i t e d , c h a i n r e l a y F - 1 will be slow to r e l e a s e (just a s if the relay had a copper slug). In this case, h o w e v e r , t h e quick operation of r e l a y F-1 i s not a f f e c t e d , s i n c e t h e 2-ohm winding is not s h o r t - c i r c u i t e d until r e l a y F- 1 has operated. T h i s s l o w - r e l e a s e f e a t u r e of r e l a y F-1 is p r o v i d e d t o hold t h e chain c i r c u i t open until line r e l a y A of a lineswitch (which h a s engaged a trunk) has released, This feature prevents the delay relay f r o m reoperating and causing false operation of the peg-count m e t e r , not shown in figure 3, in case the master-switch completes i t s stepping motion f r o m t h e engaged trunk to a n idle trunk before the lineswitch has disconnected the P.D.C. f r o m the chain circuit. 8.3 P u r p o s e of t h e chain contacts The purpose of the chain circuit, through make contacts of all switches in the group, is to prevent Figure 1 shows each B.C.O. armature and plunger a r m a t u r e independently centered on a common pivot. The B.C.O. armature, which is outside the p l u n g e r a r m a t u r e , h a s i t s tip bent a t a right a n g l e , s o i t c a n p r o j e c t through a s l o t in the plunger armature, Because of this, the a i r gap between the c o r e and t h e B.C.O. a r m a t u r e is s h o r t e r than the a i r gap between the c o r e and the plunger armature. Thus, a smaller reluctance is offered the magnetic flux passing f r o m t h e c o r e to thg B.C.O. a r m a t u r e . On a n incoming call, the connector engages the line, and grounds control lead (C) which completes a circuit through the B.C.O. coil. The c u r r e n t flow through the B.C.O. coil produces a magnetic f i e l d s t r o n g e n o u g h to o p e r a t e t h e B.C.O. armature, but insufficiently strong to pull down the plunger armature. The B.C.O. a r m a t u r e i n operating disconnects ground (+ battery) f r o m CALLS TO THE TELEPHONE t h e + l i n e and c u t s off o r d i s c o n n e c t s t h e line r e l a y f r o m t h e - l i n e . T h e c o n n e c t o r then r i n g s t h e c a l l e d line. When t h e c a l l e d p a r t y a n s w e r s , t h e connector s u p p l i e s t r a n s m i s s i o n c u r r e n t to the called line. The above explanation of the B.C.O. and plunger armatures must not be confused with t h e i r action on a n outgoing call, w h e r e the B.C.O. c o i l has enough magnetic pull to hold both a r m a t u r e s once they a r e operated. Revised December 1955 P r i n t e d in U.S.A. 8 by John S. Swift Co., Inc. 2,000 9-57 i i i i I I To connector banks s i $ I 1 i i I / i 1 i I 10 e II i f i ! I I f i j i I t i i i ! i i O R I G I N A T O R S O F T H E D I A L Makers of Telephone, Signaling, arul Communication Apparatus T E L E P H O N E .. . Electrical Engineers, Designers, and Consultunts Factory and General Offices: Northlake, Illinois, U. S.-4. ASSQCIATED RESEARCH A N D MANUFACTURING COMPANIES - - - - - - - - - - General Telephone Lahoratories, Incorporated Northlake, Illinois, U. S. A. Automatic Electric (Canada) Lirnitetl - - - - - Rrockville, Ontario, Canada Automatique Elec~riq~re, S.A. - - - - - - - - - - - - Antwerp, Belgiurn Antomatic Electric, S.A.T.A.P. - - - - - - - - - - - - Milan, Italy - - - - - - AUTOMATIC ELECTRIC SALES CORPORATION Northlake, Illinois, U. S. A. Sales Ofices in All Principal Cities GENERAL EXPORT BlSTRlBUTOR AUTOMATIC ELECTRIC INTERNATIQN.4L INCORPORATED Northlake, Illinois, U. S. A. REGIONAL DlSTRfBUYlNC CQMPAEBlES A N D REPRESENTATIVES AKGEDITINA, URUGUAY, PARAGUAY, CHILE, AND BOLIVIA D. C. Clegg Sala 61 Rua Conselheil-o Crispiniano No. 69 Sao Paulo, Brazil AUSTRALIA Automatic Electric Telephones Limited 86 Holdsworth Street, Woollahra Sydney, Australia BELGIUM AND LUXEMBOURG Automatique Electrique, S. A. 22 Rue du Verger Antwerp, Belgium BRAZIL Automatic Electric do Brasil, S. A. Sala 61 Kua Conselheiro Crispiniano No. 69 Sao Paulo, Brazil CANADA Automatic Electric Sales (Canada) Limited 185 Bartley Drive Toronto 16, Ontario, Canada CENTRAL AMERICA L. Pitigliani Apartado Postal 21327 Mexico 7, D. F., Mexico COLOMBIA Automatic Electric de Colombia, S.A. Apartado Aereo 3968 Uogo~a,Colombia EUROPE, NORTH AFRICA, AND NEAR EAST Automatic Electric International, Incorporated P. 0.Box 15 Geiieva Montbrillant Geneva, Switzerland ITALY Automatic Electric S.A.T.A.P. Via Bernina 12 Milan, Italy Rf EXTCO Automatic EIec~ricde Mexico, S.A. Apartado Postal 21327 Mexico 7, D.F., Mexico NETHERLANDS Automatique Electrique, S.A. Huygenstraat 6 's-Gravenhage, Netherlands PERU AND ECUADOR J. P. Maclaren Apartado Aereo 3968 Bogota, Colombia VENEZUELA Automatic Electric De Venezuela, Compaiiia Anonima Apartado 6362, Est. Caracas, Venezuela Other Sales Representatives and Agents Throughout the Forld . Automatic Electric Company . . A member of the General Telephone System