Manual / Guide · 1958
AE Training Bulletin 807: The Connector
AE connector switch operation and circuit; key for a small PBX.
Manual / Guide · 1958
AE connector switch operation and circuit; key for a small PBX.
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 800 Electrical Principles of Telephony 801 Mechanical Principles of Telephony 802 F u n d a m e n t a l s of Apparatus and Trunking 8 0 3 Distributing F r r.z m e s 805 The Plunger L i n e s w i t c h and A s s o c i a t e d Master-Switeb 3 8 0 6 Rotary L i n e s w i t c h 807 The Connector 808 The Selector Figure 1. Typical single-frequency local connector. THE CONNECTOR 1. WHAT THE CONNECTOR DOES The connector is t h e only switch which can do n e a r l y e v e r y job i n e s t a b l i s h i n g a telephone connection. It is just about the most important switch i n a switchtrain. The connector is analogous to a manual-switchboard operator's arm, front plug, ringing key, etc. Typically, the connector has access to 100 lines, and the last 2 digits the caller dials control the connector. Because automatic switchboards a r e inherently "multiple " switchboards, the connector t e s t s whether t h e called line is busy. If t h e called line is idle, the connector rings out on the line. When the called p a r t y a n s w e r s , the connector cuts off the ringing, and supplies t r a n s m i t t e r current to both the calling and the called parties. When both parties hang up, the connector releases itself a n d o t h e r e q u i p m e n t u s e d d u r i n g the conversation. The c o n n e c t o r , supplying b u s y tone, ringing current, transmitter current, disconnect control, etc., is virtually a self-sufficient switch. If the exchange h a s l e s s than 100 l i n e s and does not require selectors, a complete central offike can be built of just l i n e f i n d e r s and connectors.* 2. SCOPE OF BULLETIN 807; BIBLIOGFLAPHY T h i s bulletin 807 d e s c r i b e s a typical 8 - r e l a y connector in i t s simplest f o r m but complete with everything necessary to s e r v e individual*" line s ... . * P l u s outside-line p r o t e c t n r s , power equipment, etc. **Also, in a terminal-per-station c e n t r a l office, (a) it c a n s e r v e 2 - p a r t y divided-ringing p a r t y lines. (b) with single-frequency s e m i - s e l e c t i v e ringing on 4-party l i n e s , i t can s e r v e "1-ring" p a r t i e s . (c) with h a r m o n i c ringing, i t can s e r v e p a r t y l i n e s on the "frequency-per -shelf1' basis. Automatic E l e c t r i c Company m a k e s many connectors, all slightly different, to meet local needs. Other publications*** describe features of some of these. 3. TYPICAL CONNECTOR (figure 1) The operating e l e m e n t s of this connector a r e eight r e l a y s , a shaft with r a t c h e t m e c h a n i s m and w i p e r s , m a g n e t s to r a i s e and r o t a t e the shaft, v e r t i c a l - o f f - n o r m a l s p r i n g s , a magnet to r e l e a s e t h e s h a f t , and a h e l i c a l s p r i n g t o r e s t o r e the shaft. Each connector is mounted above two contact b a n k s w h i c h a r e p a r t of the s h e l f on which connectors a r e mounted. A s shown in figures 1 and 4 , t h e c o n t a c t b a n k s a r e b o l t e d t o t h e connector. In r e s p o n s e to signals f r o m the c a l l e r ' s dial, the c o n n e c t o r r a i s e s i t s s h a f t t o the l e v e l corresponding to one dialed digit, and r o t a t e s the s h a f t u n t i l t h e w i p e r s r e a c h t h e r o t a r y position corresponding to the next dialed digit. Thus the wipers come to r e s t on bank contacts connected to the called p a r t y ' s telephone line. 4. CONTACT BANKS (figure 2 ) Each connector h a s one upper a n d one lower bank (figure 2). In the lower bank ("line b a n k J J )a r e 200 b r a s s contacts 100 p a i r s t e r m i n a l s f o r the wires of 100 telephone lines. ... ***For example: ... .. .......... .......... ............... ............... .... .... Terminal-per-line party-line connectors Bulletin 813 Trunk-hunting connectors Bulletin 813 Level-hunting connectors Bulletin 813 Bulletin 815 Test connectors Bulletin 816 Toll connectors Terminal-per-station plan Engineering notes 2030 Individual ringing control Engineering notes 2037 Engineering notes 2037 is based on a terminal-per-station connector with 4-conductor banks (+, -,C, and EC f o r each station), sometimes called the "frequency-per-terminal" system. Figure 2. Banics and wipers. Figure 3 . Bank-contact position numbering. In t h e u p p e r b a n k ( " c o n t r o l bank") a r e 100 s i n g l e c o n t a c t s , t e r m i n a l s of a t h i r d w i r e , c o n t r o l l e a d C, f o r e a c h line. C o n t r o l l e a d C (analogous to the manual- switchboard ' 'sleeve " ) i s a n i n t r a - o f f i c e w i r e ; i t does not go outside the central- office building. The connector u s e s l e a d C: 100 telephones. Shelves a r e m a d e i n s e v e r a l sizes, to hold 11, 16, o r 21 connectors. One is a t e s t connector, not available f o r subscriber calls. (a) T o t e s t w h e t h e r the c a l l e d l i n e is busy. (b) T o cut off (during a call tothe l i n e ) equipm e n t u s e d when the s u b s c r i b e r m a k e s a call f r o m h i s telephone. ( c ) T o m a r k the called line "busy". The positions of the contacts of e a c h bank a r e numbered with 2-digit numbers. T h e t e n s digit r e p r e s e n t s the level in which the contact l i e s ; the u n i t s digit r e p r e s e n t s the r o t a r y position of the contact i n the level. When i t o c c u r s as a t e n s digit (e.g., 03), ''0" represents the tenth o r top l e v e l , a n d when i t o c c u r s a s a u n i t s digit (e.g., 30) "0" represents the tenth o r last r o t a r y position. The f i r s t level's f i r s t r o t a r y position i s p o s i t i o n 1 1 ; the f i r s t l e v e l ' s l a s t r o t a r y position is position 10. Figure 3 shows position numbering as s e e n f r o m the f r o n t of a contact bank. The number assigned to each position i s the n u m b e r t h a t m u s t b e d i a l e d t o b r i n g t h e connector w i p e r s to that position. Figure 4 shows a shelf of nine connectors with room for expansion* to eleven connectors. The connector on the left, with only t h r e e relays, is the t e s t connector. The w i r e s of all 100 l i n e s a p p e a r i n the banks below e a c h connector. A l l banks on the shelf a r e "multipled" together, and then the 300 wires f r o m the banks come to the terminal block at the right-hand end of the shelf. T h e r e the switchboard i n s t a l l e r s o l d e r s cables which c a r r y the wires thru other central-office equipment (linefinder shelf, distributing f r a m e ( s ) , etc.) and finally (2 w i r e s only) to the s u b s c r i b e r lines. S o m e t i m e s a n o t h e r s m a l l e r t e r m i n a l block is used for leads into the shelf; i t would be mounted on the end opposite the bank t e r m i n a l block. If (as in figure 4) there i s no such terminal block, the cables bringing leads into the connectors a r e soldered d i r e c t l y to the shelf jacks. On the fuse panel a r e 2 s u p e r v i s o r y lamps, the release-alarm lamp, the fuse-alarm lamp, and a fuse f o r e a c h connector. If e i t h e r p a r t y fails to hang up a f t e r a c a l l is completed, one of the white s u p e r v i s o r y l a m p s will light. If a connector release magnet drew current too long, 5. A CONNECTOR S H E L F (figure 4 ) 100 t e l e p h o n e s a r e s e r v e d by a s h e l f of c o n - n e c t o r s . T h e n u m b e r of c o n n e c t o r s on the shelf will b e t h e m a x i m u m n u m b e r of s i m u l taneous c a l l s expected t o b e m a d e often to t h e *When the t i m e c o m e s to do s o , i t is a s i m p l e m a t t e r t o add a connector in one of the vacant positions on tae shelf: Just jack the connector into the shelf, bolt i t s banks ( a l r e a d y on the shelf) t o the connector, check t h e wipers for alignment with t h e banks, and add a f u s e t o the f u s e panel. Local connectors Combination Figure 4. Connector shelf. indicating the s h a f t had f a i l e d to r e s t o r e , the green release-alarm lamp would light. If trouble in any switch on the shelf blew a fuse, the r e d f u s e - a l a r m lamp would light. I m m e d i a t e l y t o t h e r i g h t of t h e f u s e p a n e l i n figure 4 a r e toggle switches f o r t h e l e a d s f r o m the r i n g i n g m a c h i n e a n d t h e t o n e e q u i p m e n t . Below the toggle switches a r e the r e l e a s e - a l a r m r e l a y and the busy-tone capacitor, which s e r v e a l l switches on the shelf. On different shelves, these s h e l f a c c e s s o r i e s m a y b e a r r a n g e d differently. The f i r s t f i v e c o n n e c t o r s on t h e r i g h t of the t e s t c o n n e c t o r i n f i g u r e 4 a r e t h e l o c a l type described in this bulletin. T h e t h r e e connectors a t t h e r i g h t of t h e v a c a n t p o s i t i o n s c a n s e r v e toll c a l l s a s w e l l a s l o c a l c a l l s , and have a n e x t r a relay in their circuit. Local c a l l s choose f i r s t t h e local connectors; when a l l local conn e c t o r s a r e i n u s e , l o c a l c a l l s c a n u s e the combination connectors. T o l l c a l l s can u s e only t h e combination l o c a l and-toll connectors, however. Thus, five local and t h r e e t o l l c a l l s , e i g h t l o c a l calls,, o r a n y intermediate combination can be handled simultaneously by the connector shelf shown in figure 4. Each connector has i t s own 3-terminal* position in the local-selector-shelf contact banks. Thus, a shelf of 10 connectors r e q u i r e s 30 l e a d s f r o m local selector shelves, plus a few other leads for battery, ground, ringing current, busy tone, etc. "ombination selector banks. 'connectors require 4 terminals in the toll 6. MECHANICAL OPERATION The d i a l b r e a k s and quickly r e - c l o s e s the line circuit. Each number on the dial b r e a k s the Line c i r c u i t that number of t i m e s , except of c o u r s e "O", which interrupts the line 10 t i m e s . After previous digits have operated o t h e r equipment to find a n idle connector, the tens-digit pulses control the connector vertical magnet. The vertical magnet operates the ratchet mechanism to r a i s e the shaft one s t e p f o r each pulse. The pause between the tens digit and the units digit allows a relay to t r a n s f e r the stepping c i r c u i t f r o m t h e v e r t i c a l to t h e r o t a r y m a g n e t . T h e pulses f r o m the units digit then cause the shaft to b e r o t a t e d , one s t e p f o r e a c h p u l s e , to the d e s i r e d p o s i t i o n in the c o n t a c t b a n k s . A f t e r rotation, the shaft r e s t s on a fixed detent to the left of the shaft, called the stationary dog, and the rotary tooth of a detent called the "double dogJ' holds it i n position with the wipers on the calledline contacts. If the line is not busy, connection will b e m a d e and the called l i n e will be rung. At the end of a call, the r e l e a s e magnet operates an a r m a t u r e which disengages t h e double-dog and releases the shaft. The stationary dog holds the shaft on the level while the r e s t o r i n g spring at the top of the shaft rotates the shaft to remove the wipers from the contact banks; then the shaft falls by i t s own weight. At t6e f i r s t v e r t i c a l s t e p , the c o n n e c t o r shaft r e l e a s e s a l e v e r which allows the vertical-offnormal springs to r e s t o r e . When the connector releases and the shaft falls, the lever is depressed and reoperates the vertical-off-normal springs. T h i s o p e n s t h e r e l e a s e - m a g n e t c i r c u i t and p r e p a r e s t h e c o n n e c t o r f o r t h e next call. 7. CONNECTOR RELAYS Interaction of the connector's 8 relays direct i t s o p e r a t i o n s . Relays A, D, and G a r e o r d i n a r y f a s t - a c t i n g r e l a y s . Relay A , often called the pulsing relay, supplies t r a n s m i t t e r c u r r e n t t o the caller, and receives dial pulses and transmits them t o o t h e r relays and to t h e v e r t i c a l o r the rotary magnet. Relay D, the back-bridge relay, is s o c a l l e d b e c a u s e i t p r o v i d e s t r a n s m i t t e r c u r r e n t to the called party bridged a c r o s s t h e "back" end of the connection. Relay G is the busy-test relay. R e l a y s B, C , and E a l l have c o p p e r s l e e v e s around their cores to make them slow to release.* Holding-relay B grounds the connector's control lead t o m a r k t h a t s q i t c h b u s y and hold a l l p r e c e d i n g s w i t c h e s i n t h e t r a i n . It is slow to r e l e a s e s o t h a t i t w i l l n o t r e l e a s e while relay A momentarily interrupts the relay B c i r c u i t t o s e n d pulses to t h e magnets. Thus, relay B can dis!inguish between a short duration b r e a k i n t h e loop c i r c u i t a t the d i a l s p r i n g s , and a l o n g e r b r e a k a t t h e hookswitch caused by hanging up. R e l a y s C a n d E , t h e v e r t i c a l sequence r e l a y and t h e r o t a r y sequence r e l a y , a r e s l s w - t o release s o that they will remain operated during a s e r i e s of pulses f r o m relay A. T h e s e relays distinguish the separately dialed digits, remaining o p e r a t e d when relay A b r e a k s t h e i r circuit in short rapid sequence duririg a digit, and releasing when relay A breaks their circuit f o r the longer interval between two s e p a r a t e digits. Relay C is o p e r a t e d during v e r t i c a l stepping, and then r e l e a s e s to prepare the rotary stepping circuit. During r o t a r y stepping, relay E operates; a f t e r the w i p e r s r e a c h t h e c a l l e d l i n e , d u r i n g t h e relay E r e l e a s e delay, the line is busy-tested. Relay K, the wiper-closing relay, h a s a copper s l u g o n i t s a r m a t u r e end to m a k e i t slow t o o p e r a t e . Wiper-closing r e l a y K connects the connector relays, etc., to the wipers resting on the called party's line-bank contacts. It is slowt o - o p e r a t e s o the called p a r t y ' s cut-off r e l a y will have t i m e to r e m o v e t h e line equipment f r o m t h e called line before ringing c u r r e n t is connected to t h e line. A n o t h e r r e l a y with a n a r m a t u r e - e n d s l u g is ringing cut-off relay F i n the path f o r alternating current f r o m the ringing machine to the calledtelephone r i n g e r . It m u s t b e slow to o p e r a t e *A slow r e l a y ' s r e l e a s e delay is only a fraction of a second f o r example a third 0f.a second f o r r e l a y B, and a tenth of a second for relays C and E. If these sound like s h o r t amounts of t i m e about which to make a fuss, .. . r e m e m b e r : a c a m e r a often does i t s work in only 1/50 second! Utilization of these delays of a tenth o r a third of a second makes possible most of the marvels of dialcontrolled telephone switching. so t h a t i t w i l l not be o p e r a t e d by $ c y c l e s of alternating (ringing) current. Besides the copper slug, relay F has a copper sleeve around i t s c o r e t o l o w e r i t s inductive r e a c t a n c e t o alternating c u r r e n t f r o m the ringing machine. The winding of relay C is connected somewhat d i f f e r e n t f r o m t h e o r d i n a r y , with battery rather than ground connected to the "inside " o r start-of-winding t e r m i n a l s . This causes the magnetic fields of adjacent r e l a y s A and C t o augment one another. Thus, when relay A receives short pulses (and so sends long pulses to relay C ) f r o m a high-resistance line, magnetic flux f r o m relay C aids relay A. When relay A receives long pulses (and s o s e n d s s h o r t p u l s e s to relay C ) f r o m a short low-resistance line, flux f r o m r e l a y A h e l p s k e e p r e l a y C operated between pulses. 8. LINE EQUIPMENT Altho it is usually part of a linefinder shelf ( s e e bulletin 821 especially [perhaps also bulletins 805 and 8061 ) and is never part of the connector, line equipment affects and is affected by the connector. Line equipment serves a s a gate thru which calls made from the line a r e channeled differently than calls made @the line. A call from the line s t a r t s a linefinder which picks up the call and routes i t to dial tone and to dial-controlled equipment. A c a l l to the l i n e - r e q u i r e s a c l e a r path which will not s t a r t a linefinder nor bring in dial tone. Each line h a s a line r e l a y bridged a c r o s s the line, and, on the control lead, a cut-off relay to disconnect the line relay. When a c a l l e r lifts h i s handset to make a call, the line relay brings in a linefinder and a selector (with dial tone). When the calling line has been found, ground on the control lead operates the cut-off relay, which disconnects the line relay, r e l e a s i n g i t . t h e r e b y doing away with the "linefinder start" signal. Thus, once a calling line has been found, we want the line r e l a y out of t h e way s o i t won't t r y t o s t a r t a n y m o r e linefinders. F o r t h i s reason,, a s soon a s t h e call is extended to the connector, the connector holds the c a l l e r ' s cut-off relay. .. the telephone-subscriber Likewise, on a call line, we want the line relay out of the way because we won't want i t to s t a r t a linefinder. F o r this reason, the connector operates the called line's cut -of£ r e l a y , a n d i t c u t s off t h e l i n e r e l a y . The c o n t r o l - l e a d g r o u n d which o p e r a t e s a calling o r called l i n e ' s cut-off relay, a p p e a r s on t h a t l i n e ' s l e a d C m u l t i p l e d t h r u o u t t h e connector-shelf b a n k s ( f i g u r e 4);and m a r k s the line."busy" in the banks of every connector which could have a c c e s s to it. 9. SUMMARY O F FUNCTIONS (f) if the line is idle, connect calling and called lines a n d m a r k t h e m busy t o o t h e r calls The connector is designed to: (a) hold the- p r e c e d i n g s w i t c h e s i n the t r a i n operated (b) direct and connect the wipers to the terrninals of the called line (g) c l e a r the line equipment f r o m the called line (h) connect ringing c u r r e n t to the called line and s u p p l y r i n g b a c k t o n e t o t h e calling line (c) keep line wipers dis connected during rotation to prevent interference with other lines (i) remove ringing c u r r e n t and ringback tone (d) apply a busy t e s t t o the called line (j) supply t r a n s m i t t e r current to both parties (e) if the line is busy, give the busy signal and prevent connection (k) r e l e a s e a l l s w i t c h e s when t h e c a l l is when the called p a r t y a n s w e r s concluded. LOCAL-COh NECTOR C 10. SEIZURE (figure 5) connector ahead, and opens the circuit of selector slow-to-release relay B . Meanwhile, connector relay A closes contacts 2-3, operating connector relay B. Relay B contacts 8-9 ground lead C to hold s e l e c t o r r e l a y F a n d o t h e r p r e c e d i n g switches, and to mark this connector busy. Relay B contacts 4-5 and relay C contacts 2 - 3 p r e p a r e the circuit to the vertical magnet. The connector, marked busy to other selectors by the ground on lead C , is now r e a d y to r e c e i v e p u l s e s f r o m the dial. When a c a l l e r l i f t s h i s h a n d s e t , h e c l o s e s a c i r c u i t to t h e c e n t r a l office a n d o p e r a t e s h i s line e q u i p m e n t to c a l l f o r a l i n e f i n d e r . T h e l i n e f i n d e r c o n n e c t s h i m to a s e l e c t o r which provides dial tone. A s the caller dials the f i r s t digits of the called party's number, one o r more s e l e c t o r s a r e operated. T h e l a s t s e l e c t o r will find and connect the c a l l e r to an idle connector having a c c e s s t o the called line. E i t h e r a battery- s e a r c h i n g o r a n absence-of-groundsearching selector could precede this connector. If an absence-of-ground-searching s e l e c t o r is used with this connector, selector relay F will have only one winding, and will operate unless lead C is grounded and short-circuits relay F. Relay F operates a s above, closes a c i r c u i t t h r u c o n n e c t o r r e l a y A , and connects preceding-switch lead C to lead C of the connector ahead. In this case, battery f o r operation of relay F comes f r o m within the selector, and connector relay C does not operate simultaneously with s e l e c t o r r e l a y F, b u t is o p e r a t e d b y g r o u n d f r o m the selector immediately after relay F operates. When a b a t t e r y - s e a r c h i n g s e l e c t o r b r i n g s i t s w i p e r s t o t h e t e r m i n a l s of l i n e s t o a n i d l e c o n n e c t o r ( f i g u r e 5), b a t t e r y t h r u c o n n e c t o r relay C operates relay C and energizes selector relay F winding #1, closing r e l a y F contacts X. Contacts X close a circuit thru relay F batteryconnected winding #2, which operates a l l relay F contacts. Relay F now closes a circuit f r o m the calling telephone thru the line wires to connector r e l a y A, c o n n e c t s t o g e t h e r p r e c e d i n g - s w i t c h lead C with wiper C which r e s t s on lead C of the CALLING TELEPHONE 1 I I PRECEOlNG SWITCHES I I BATTERY-SEARCHING SELECTOR 'I CONNECTOR I I I I I I I Figure 5 . Seizure. Solid armatures show initial conditions when relay F contacts "2"' close. Dotted armatures show final conditions. CONNECTOR Figure 6. Vertical stepping. 11. VERTICAL STEPPING (figure 6 ) A s the c a l l e r d i a l s the t e n s digit of the called number, h i s d i a l a l t e r n a t e l y opens and c l o s e s the c i r c u i t of r e l a y A . T h e n u m b e r of t i m e s the c i r c u i t is i n t e r r u p t e d c o r r e s p o n d s to t h e digit d i a l e d . R e l a y A r e l e a s e s d u r i n g e a c h interruption, but slow -to-release relay B r e m a i n s o p e r a t e d continuously. E a c h t i m e relay A r e l e a s e s , its contacts 1-2 close a c i r c u i t t h r u the v e r t i c a l magnet, operating the v e r t i c a l magnet and r a i s i n g the shaft one step. E a c h t i m e r e l a y A r e - o p e r a t e s * , the v e r t i c a l magnet r e l e a s e s , p r e p a r i n g i t s a r m a t u r e and pawl m e c h a n i s m f o r a n o t h e r s t e p . During t h e f i r s t s t e p , V.O.N. s p r i n g s 3-4 open th.e c i r c u i t *Each time r e l a y A contacts 1-2 open, the capacitor connected to relay B contact 5 charges, and tends to absorb the high voltage induced in the stepping magnet when the stepping-magnet c i r c u i t is opened. T h i s s u p p r e s s e s s p a r k i n g a t r e l a y A contacts 1-2. Each t i m e r e l a y A contacts 1-2 re-close, the r e s i s t o r limits the capacitor discharge current, so there'll be no possibility that relay A contacts 1-2 might be spot-welded together. , + I 3 ,I-*<$:, I of r e l a y C winding #2.** H o w e v e r , r e l a y C winding #1, in parallel with the v e r t i c a l magnet, e n e r g i z e s during the f i r s t pulse, and keeps slow-to-release r e l a y C o p e r a t e d until p u l s e s f r o m the tens digit stop. Then the interval between the tens digit and the units digit will be s o long that relay C will release. The dial pulses p r i n g s a r e closed, a n d r e l a y A holds r e l a y B d u r i n g t h e i n t e r v a l b e t y e e n t h e two d i g i t s . 12. ROTARY STEPPING ( f i g u r e 7) The r e l e a s e of r e l a y C p r e p a r e d the circuit f o r the r o t a r y m a g n e t . W h e n t h e u n i t s d i g i t i s dialed, r e l a y A again r e l e a s e s and r e o p e r a t e s quickly several times, and a t contacts 1-2 sends pulses t o the r o t a r y magnet and r e l a y E . The r o t a r y magnet rotates the shaft and wipers one s t e p f o r e a c h pulse. S l o w - t o - r e l e a s e r e l a y E 1 **Also uring the first step, the vertical magnet unlatches the "rele se link", which allows the double dog to drop into the shaft hub and hold the shaft a t each level to which it i s raised. (Compare the footnote on page 14.) H ' 7 f -2 2 I ) Figwe 7. Rotary stepping. ROT. A B G K Busy Tone E - Another Connector Figwe 8. R e connector finds the called line i s busy. Relay E i s about to release. operates on the first pulse and remains operated until a f t e r pulsing stops. Relay E contacts 2-4 connect wiper C to relay G t o p r e p a r e f o r the busy t e s t . Relay E contacts 5-6 prevent interruption of the rotary-magnet circuit i f wiper C s w e e p s o v e r a g r o u n d e d ( b u s y ) contact and momentarily operates relay G. 13. TESTING THE CALLED LINE a moment, relay E (figure 8) releases, contacts 5-6 prevent further stepping, contacts 3-4 make before contacts 2-4 break, permitting r e l a y G to lock. Relay G contacts 3-4 prevent r e l a y K o p e r a t i n g i f the called l i n e w e r e to b e f r e e d before the c a l l e r hangs up. Altho the w i p e r s r e s t on bank contacts of the called line, they stand "dead" at relay G contact 3 and at relay K contacts 7B and 5B; notice that t h e r e is really no connection to called line. 13.1 C a l l e d l i n e b u s y ( f i g u r e 8 ) . T h e l a s t r o t a r y s t e p puts the wipers a t the called line. At a busy line, wiper C finds ground from another c o n n e c t o r , and r e l a y G o p e r a t e s . R e l a y G c o n t a c t s 4 - 5 p r e p a r e a locking c i r c u i t , and c o n t a c t s 6 - 7 s e n d the c a l l e r busy tone. (The f i r s t selector has already started the busy-tone g e n e r a t o r - a n d - i n t e r r u p t e r , f i g u r e 11.) A f t e r 13.2 Called line idle (figure 9). If the called line is i d l e , wiper C encounters b a t t e r y f r o m the called p a r t y ' s cut-off relay. Relay G does not operate. After a moment, relay E releases, and c l o s e s a c i r c u i t f r o m b a t t e r y t h r u r e l a y CO, wiper C, relay E contacts 2-1, relay K winding #1, relay G contacts 3-4 to relay B contacts 9-8 and ground. Figure 9. fie connector finds the called line i s idle. Relay E i s about to release. Figwe 10. Seizure of the called line. Relay K winding # I has just closed contacts "X". 14. SEIZURE OF THE CALLED LINE (figure 10) The c u r r e n t t h r u winding #1 e n e r g i z e s r e l a y K enough to close only "X" contacts I T - 2 T . F o r just a moment, they connect r e l a y K winding #2 in p a r a l l e l with r e l a y CO and i n s e r i e s with relay K winding # l . The circuit . . . i n figure 10 the h e a v y l i n e . . . is f r o m b a t t e r y t h r u t h e r o t a r y magnet, r e l a y K winding #2 and contacts 2T-IT, r e l a y B contacts 7-6, r e l a y E contacts 2- 1, r e l a y K winding #I., r e l a y G c o n t a c t s 3-4, and r e l a y B contacts 9-8, to ground. T h e high r e s i s t a n c e of r e l a y K winding # 2 allows only a s m a l l c u r r e n t flow t h r u the r o t a r y magnet; the r o t a r y m a g n e t d o e s not o p e r a t e . Winding # 2 operates relay K fully, and contacts 5T-6T shortc i r c u i t winding # 1 and connect s o l i d ground to winding #2 and r e l a y CO. About 1.2 s e c o n d s out of 6, the r i n g i n g - i n t e r r u p t e r c a m c o n n e c t s the r i n g i n g g e n e r a t o r to the c a l l e d l i n e as s h o w n b y f i g u r e 12 h e a v y line, and rings the r i n g e r (bell). T h e capacitor in s e r i e s with the called-telephone r i n g e r allows only a l t e r n a t i n g c u r r e n t t o flow t h r u r e l a y F. Relay F is slow to operate s o that it will not be operated by alternating c u r r e n t . 15. RINGING If t h i s c o n n e c t o r is in a s m a l l c e n t r a l office where the ringing machine does not run continuously, r e l a y K (figure 12) contacts 7T-8T s t a r t the ringing machine. F i g u r e 11 s h o w s a t y p i c a l s i n g l e - f r e q u e n c y ringing machine. It c o n s i s t s of duplicate s e t s of e q u i p m e n t , s o t h e r e ' l l a l w a y s b e a s p a r e for emergencies. The motor-driven r ~ n g i n g generator to the left produces alternating current of about 90 v o l t s and 20%. You recall from your own experience, a telephone bell o r "ringer" does not ring continuously, but r a t h e r b r i e f l y , with a f e w s g c o n d s ' s i l e n c e between rings. T h i s is timed by an i n t e r r u p t e r . T h e i n t e r m p t e r m a y be a group of slow-acting r e l a y s , etc., o r i t m a y b e m o t o r - d r i v e n as in f i g u r e 11 l o w e r r i g h t c o r n e r . T y p i c a l l y , t h e ringing i n t e r r u p t e r might w o r k on a 6-second cycle, ringing 1.2 seconds, silent 4.8 s e c o n d s . Relay K c o n t a c t s 5B-6B and 7B-8B s e t up the ringing c i r c u i t . . in f i g u r e 12 the h e a v y line. . Figure 11. Ty ical single-frequency ringing machine. h the lower !!eft comer i s a 20-rin ing generator, driven by the 60-a-c motor a%ove it. The machine in the lower right corner generates dial tone, interrupts dial tone into busy tone, interrupts ringing current to provide the silent periods, etc. The 2 up er right machines are s t a d b y units to operate rom centrueoffice battery during commercial- ower failures. d t the upper left is an isolating transformer w l i c h keeps the trip-battery d.c, (51 9.1) out of the ringing-generator windings. I R.M. START - I 11 -----.--I \ Figure 12. Ringing and ringback-tone circuits. Relay K contacts 9T- 10T close the ringback-tone c i r c u i t . R i n g b a c k t o n e is t a p p e d f r o m the ringing-current circuit, taken thru a smallcapacitance capacitor, sent thru the calling telephone, and returned thru relay A, etc., to ground. capacitor blocks the battery d.c., no d.c. flows, and s l o w - t o - o p e r a t e relay F cannot o p e r a t e . In f i g u r e 1 2 , a t t h e r i n g i n g i n t e r r u p t e r , t h e central-office battery voltage is offered out on the l i n e , b o t h d u r i n g t h e r i n g i n g i n t e r v a l s (thru the generator and relay F), and during the s i l e n t i n t e r v a l s ( t h r u r e l a y F). I n f i g u r e 12, with the called telephone on the hook, the ringer When the called party answers (figure 13), his hookswitch removes the a - c path thru capacitor and ringer, and replaces it with a direct-current circuit thru transmitter, induction coil, etc., for relay F winding # l . Relay F winding #1 closes "X" c o n t a c t s 1 - 2 , e n e r g i z i n g winding #2. 16. CALLED PARTY ANSWERS; RINGING C U T O F F F 3 - CALLED TELEPHONE 4: t6 --------+I' Thru r~ngingInterrupter 1 IIHII~---- + 9 eP+ = GRD Figure 13. Called party answers. 1 Relay F has just closed contacts 'cX". I RING BACK TONE I TNGING CURRENT GEN. GRD. 111 7 c' R.M. START 10 8T Figure 14. Relay F has operated fully. Ringing cut off. Relay F o p e r a t e s fully ( f i g u r e 1 4 ) ; c o n t a c t s 3-4 - 5- 6 cut off ringing c u r r e n t and ringback tone, and complete one side of the transmission line; contacts 7-8- 9 disconnect generator ground and complete the o t h e r side of t h e t r a n s m i s sion line; and contacts 1 0 - 1 1 stop the ringing ma chine. The c a l l e d p a r t y d r a w s t r a n s m i t t e r c u r r e n t t h r u r e l a y D ( f i g u r e 1 4 ) . Relay D o p e r a t e s , and (figure 15) i t s make-before-break contacts 8-9-10 and 11- 12 -13 r e v e r s e the polarity* of the transmitter current which relay A supplies toward the caller. *For most calls, this battery reversal is of no significance. It h a s a useful function in these cases: (1) If the call i s f r o m a paystation, i t results in collection of the charge for t h e call. In a measured-service o r message-rate exchange, it causes the completed call to be counted. If the call is f r o m an operator, it gives h e r "off-hook" (3) (dark) supervision. (2) Figwe 15. Caller's transmitter-current polarity reversed. CALLING PARTY LINE EQUIPMENT LINEFINDER SELECTOR CONNECTOR LlNE EQUIPMENT CALLED PARTY Figwe 16. Conversation thru local switch train in a 1000-line central office. 17. CONVERSATION (figure 16) to t h e c a l l e d p a r t y . R e l a y A h o l d s r e l a y B, which k e e p s ground on c o n t r o l lead C t o hold: Figure 16 shows conditions during conversation, and s h o w s t h e p o s i t i o n of t h e c o n n e c t o r i n a t y p i c a l 10 00 - l i n e s w i t c h t r a i n . C a p a c i t o r s (between r e l a y s A a n d D ) couple c a l l e r and c a l l e d p a r t y f o r v o i c e t r a n s m i s s i o n . Notice that c o n n e c t o r r e l a y s A a n d D a r e t h e o n l y r e l a y s connected a c r o s s t h e t r a n s m i s s i o n path. T h e c a l l e r ' s line-equipment cut -off r e l a y Linefinder and to m a r k the c a l l e r ' s line b u s y a t t h e banks of a l l connectors on t h e shelf which s e r v e s h i s 100-line group. Relay A s u p p l i e s t r a n s m i t t e r c u r r e n t t o the caller, and r e l a y D supplies t r a n s m i t t e r c u r r e n t From preceding switches - c Busy II -~--I/tHI~ ,: ? I - Figure 17. Control lead and connector relays held during conversation. , Remaved when called party releases I+ --- 1 8 c -- - - +IIHII Figure 18. Connector circuits for dropping preceding switches. R e l a y K k e e p s ground on w i p e r C t o hold t h e c a l l e d l i n e ' s cut-off r e l a y , a n d to m a r k t h e called line busy. ; F i g u r e 17 shows holding-circuit d e t a i l s within the c o n n e c t o r i t s e l f . R e l a y A h o l d s r e l a y B. Thru r e l a y K c o n t a c t s 5 T - 6 T and r e l a y B contacts 6-7, t h e c a l l e r holds r e l a y s F a n d K to keep the transmission path closed thru. This, like most connectors, is a '"last-party- r e l e a s e ' ' connector: t h r u r e l a y K c o n t a c t s 7T - 8 T a n d r e l a y D c o n t a c t s 4 - 5 , t h e c a l l e d p a r t y , too, holds r e l a y s F and K t o keep t h e t r a n s m i s s i o n path c l o s e d t h r u . T h u s , t h e two c o n v e r s i n g p a r t i e s h a v e joint c o n t r o l of t h e c o n n e c t o r . E i t h e r o r both can hold it. It holds i t s w i p e r s a t the called line until t h e l a s t of the 2 p a r t i e s to hang up h a s hung up. 18. RELEASE 18.1 If c a l l e r hangs up f i r s t . T h e c a l l e r may have called about more than one thing, so, to be s u r e h e c a n complete a l l p u r p o s e s of h i s call, etiquette r e c o m m e n d s that the called p a r t y should wait and allow t h e c a l l e r t o b e the f i r s t to hang up. When t h e c a l l e r h a n g s u p , h i s h o o k s w i t c h (figure 16) opens the c i r c u i t of r e l a y A (figure 18). R e l a y A r e l e a s e s , o p e n s t h e c i r c u i t of slow-to-release relay B, and o p e r a t e s r e l a y E. When relay B releases, i t removes ground f r o m lead C , and opens the c i r c u i t of s l o w - r e l e a s e relay E. The preceding switches release. Slowto-release relay E remains operated a moment. Then i t releases, and connects ground f r o m relay Busy Tone 2 F-1- - - ---/I, V.O.N. - Figure 19. Release from a call to a busy line. RLS. G RD. -2 4 1 48 Hi..,x"k~s THROUGH RELEPSE ALARM RELAY GRD .c, I Figure 20. Release-magnet circuit open dwing conversation. K c o n t a c t s 5 T - 6 T t h r u r e l a y E c o n t a c t s 2-1, r e l a y K l o w - r e s i s t a n c e (12 5 a ) winding #1, (and [figure 251 relay G contacts 3-4), to lead C . . not a b l e yet to m a r k the connector "busy" to a c c e p t a n o t h e r call. r e l a y F w i l l not h a v e o p e r a t e d . R e l e a s e of r e l a y K o p e n s t h e r i n g i n g c i r c u i t , s t o p s the ringing i n a c h i n e , o p e n s t h e r i n g b a c k - t o n e circuit, a n d o p e r a t e s t h e r e l e a s e m a g n e t . See S18.5. Next, t h e c a l l e d p a r t y h a n g s u p , r e l e a s i n g relay D. Relay D contacts 4-5 (figure 17) release r e l a y s F and K . Relay K opens the wipers ( s o that during r e l e a s e they will b e e l e c t r i c a l l y "dead" when they rotate o v e r other lines), and r e l a y K c o n t a c t s 3B-4B o p e r a t e t h e r e l e a s e magnet. See $18.5. 18.5 M e c h a n i c a l r e s t o r a t i o n . R e f e r r i n g t o f i g u r e 2 0 , when t h e c a l l e r ' s phone "on hook" hLs released relay B, the called phone "on hookJ' h a s r e l e a s e d r e l a y D , both "on hook" h a v e r e l e a s e d relay K, and r e l a y K h a s disconnected the w i p e r s , the r e l e a s e m a g n e t withdraws the "double dog", and latches it under the " r e l e a s e link ' '* . 18.2 If c a l l e d p a r t y h a n g s up f i r s t , r e l a y D r e l e a s e s , opening i t s c o n t a c t s 4 - 5 ( f i g u r e 17) a s i n t h e p a r a g r a p h a b o v e ... but t h i s t i m e r e l a y B c o n t a c t s 6 - 7 continue to hold r e l a y s F a n d K. T h e r e is no f u r t h e r action u n t i l the c a l l e r h a n g s u p , r e s t o r i n g r e l a y A. R e l a y E o p e r a t e s again, but h a s no function. R e l a y B releases, r e m o v e s ground f r o m lead C to r e l e a s e the switch t r a i n , and opens the c i r c u i t s of r e l a y s E, K, and F. Relay K disconnects the w i p e r s , a n d ( f i g u r e 25) o p e r a t e s the r e l e a s e magnet. See $18.5. . 18.3 Release after calling a busy line (figure 19). If the called line w a s busy, r e l a y s K, F, a n d D did not operate, s o only relays A,. B, and G must be r e l e a s e d (figure 19). When the c g l l e r hangs up, r e l a y A r e l e a s e s , opening the c i r c u i t t h r u relay B. Relay B removes ground f r o m lead C to r e l e a s e t h e p r e c e d i n g s w i t c h e s , r e l e a s e s relay G , and o p e r a t e s the r e l e a s e magnet. See S18.5. 18.4 R e l e a s e f r o m a n unanswered c a l l . If the call is unanswered, release is the s a m e a s when the c a l l e r h a n g s u p l a s t ( $ 18.2), e x c e p t t h a t . Tension in the helical s p r i n g atop the shaft r o t a t e s shaft and w i p e r s t o the left and off the banks. Then g r a v i t y t a k e s o v e r , and pulls the shaft down t o i t s n o r m a l position. When the s w i t c h s h a f t d r o p s to i t s n o r m a l position, it operates vertical off-normal springs V.0 .N .: s p r i n g s 1- 2 open t h e r e l e a s e - m a g n e t c i r c u i t , a n d s p r i n g s 3-4 connect b a t t e r y t h r u r e l a y C 500S2 w i n d i n g # 2 t o l e a d C t o t e l l b a t t e r y - s e a r c h i n g s e l e c t o r s t h i s connector is r e a d y to handle a n o t h e r call. *When the connector is preceded by a b s e n c e - o f - g r o u n d - s e a r c h i n g s e l e c t o r s , a f t e r figure 2 0 r e l e a s e m a g n e t c i r c u i t is closed, i t i s not i m p o s s i b l e t h a t a new c a l l might s e i z e the connector, o p e r a t e r e l a y B , and open the release-magnet circuit before the shaft has restored to n o r m a l . With r e l e a s e link R L having latched double dog DD, the shaft will r e s t o r e completely nevert h e l e s s . (Compare the fobtnote on page 7 ) . 19. GENERATOR CONNE,CTIONS RINGING 19.1 We need battery f o r , ringing cut-off. Page 10 mentions the r i n ~ i nc i~r c u i t n e e d s c e n t r a l office b a t t e r y t o o p e r a t e t h e r i n g i n g cut-off r e l a y . T h e r e a r e 2 w a y s to connect c e n t r a l office b a t t e r y into the ringing c i r c u i t . 0 Advantages a r e simplicity, and th