Manual / Guide · 1958
AE Training Bulletin 808: The Selector
AE selector switch operation and circuit.
Manual / Guide · 1958
AE selector switch operation and circuit.
T h i s is one of the helpful booklets in the AeLlrfOiLliATPkC ELECTRZC TRAINING SERIES on STR0VJC.EE3: AUTOMATIC TELEPHONE SYSTEMS 80C E l e c t r i c a l P r i n c i p l e s of Telephony 8 0 % Mechanical P r i n c i p l e s of Telephony 802 Fundamentals of Apparatus and Triknking 805 The P l u n g e r Lineswitch and Associated Master-Switch 806 R o t a r y Lineswitch 80'7 The Connector 808 The Selector 81 8 P ~ l s eR e p e a t e r s 81 1 Trunking 81 2 P o w e r and Supervisory Equipment 81 3 Party - Line Connectors ax=d Trunk-Hunting Connectors 814 Reverting-C a l l Methods 81 5 The T e s t and Verification Switch T r a i n 816 T o l l S i ~ j t c hTrain 81 4 "%witching Selector -Repeater 81 8 Private Autamatic Exchanges with P A B X Appendix 81 9 Community A:_rtomatic Exchanges 320 Manual Switchboards 82 1 Linefinder Svrltcfies May we s e n d yc.u e t h e r s pertaining t o equipmet?: i n -your exchange ? CONTENTS Page GENERAL .................................................. 3 ................................................... 4 SELECTOR TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 BATTERY-SEARCHING SELECTOR .................................. 4 5.1 S e i z u r e . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.2 V e r t i c a l stepping ............................................ 4 5.3 R o t a r y motion .............................................. 5 .............................................. 5.4 Switch.through 6 5.5 A l l t r u n k s b u s y ............................................. 6 5.6 R e l e a s e ................................................... 6 ABSENCE-OF-GROUND-SEARCHING SELECTOR ......................... 6 6.1 S e i z u r e ................................................... 6 6 -2 V e r t i c a l stepping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.3 R o t a r y stepping ............................................. 7 6.4 Switch.through .............................................. 8 6.5 A l l t r u n k s b u s y ............................................. 8 6.6 R e l e a s e ................................................... 8 DIGIT-ABSORBING SELECTOR ..................................... 8 7.1 S e i z u r e and v e r t i c a l stepping ..................................... 8 FUNCTIONS .................................. 8 ..................................... 8 7.4 Digit-absorbing l e v e l need not b e wasted (optional .figure 5 wiring F) . . . . . . . . 1 0 7.5 Digit a b s o r b e d repeatedly (optional .figure 5 wiring E ) .................. 10 7.6 V e r t i c a l stepping a f t e r digit absorption ............................. 10 SUPERVISORY LEAD ............................................ 10 TONE START LEAD ............................................. 10 SPARK PROTECTION ............................................ 10 7.2 Non-digit-absorbing l e v e l dialed 7.3 Digit-absorbing l e v e l dialed Figure 1. Typical selector. ( T h e one illustrated is the absence-of -ground-searching s e l e c t o r the circuit of which is shown in figure 3.) THE SELECTOR 1. GENERAL When the total number of terminals to be served by a Strowger Automatic exchange is greater than the t e r m i n a l capacity of the connectors used, one o r m o r e selectors must be employed in the switch train by which each connection is s e t up. Assuming that 100-terminal connectors a r e used, a single rank of selectors is required in a 1000terminal system. The first digit dialed operates a s e l e c t o r to select the desired hundred-group of connectors. The selection of the particular t e r m i n a l i n the hundred-group of connectors (tens and units selections) is the function of the connector switch. In a 1 0 , 0 0 0 - t e r m i n a l s y s t e m , two r a n k s of s e l e c t o r s a r e required: the f i r s t i s operated by the first digit dialed, and selects the thousandgroup of trunks* which terminates in the second rank of selectors; the second rank of selectors is operated by the second digit, and selects the d e s i r e d hundred-group of connectors i n the thousand-group previously selected. Similarly, in a 100,000-terminal system, the f i r s t selector in the train will select the desired office unit (comprising 10,000 terminals ultimate); the second selector, the desired thousand-group in t h a t o f f i c e u n i t ; and the t h i r d s e l e c t o r , the d e s i r e d hundred-group in the thousand-group previously selected. T h e s e l e c t o r is a n u m e r i c a l type of groupselecting, trunk-hunting switch which requires but one digit for its operation. It is a two-motion switch employing a shaft which f i r s t is raised vertically and then is rotated horizontally. The pulses created by the dial control the vertical motion, which is the movement that selects the desired trunk group. The rotary motion is autom a t i c , and i s the trunk-hunting movement of the s e l e c t o r . 2. MECHANICAL ARRANGEMENT A typical s e l e c t o r is shown in f i g u r e 1. The s e l e c t o r c o m p r i s e s a group of control r e l a y s mounted on a base on which a r e mounted also a frame supporting a shaft and a ratchet mechanism f o r raising and rotating the shaft. Affixed to the lower portion of the shaft a r e two sets of wipers, t e r m e d t h e "line" and "control" w i p e r s . Mounted within the switch frarne a r e the vertical and r o t a r y stepping magnets, and the magnet which r e l e a s e s t h e r a t c h e t m e c h a n i s m and permits the shaft to return to normal when the connection is released. The number of vertical steps the wipers r i s e depends upon the number of pulses in the digit dialed, and the number of rotary steps the wipers take to the right depends upon the n m b e r of "busy" trunks encountered in the selected bank level. The pulses f o r v e r t i c a l stepping energize the vertical magnet, causing the vertical a r m a t u r e to operate and r a i s e the shaft a corresponding number of steps, by means of a pawl affixed to the end of the a r m a t u r e engaging a toothed hub known as the "vertical hub". As soon a s vertical stepping i s completed, the rotary magnet automatically rotates the shaft until an idle trunk is found in the selected ba* level. The auxomatic s t e p p i n g m o t i o n o f t h e r o t a r y a r m a t u r e is transmitted to the shaft by means of the rotary p a w l e n g a g i n g a toothed hub known as the " r o t a r y hub". T h e s e stepping motions c a u s e the w i p e r s to e n g a g e c o n t a c t s of a s e m i - c y l i n d r i c a l bank secured to the bottom of the selector. Referring to F i g u r e 1, i t will be observed that the bank contacts a r e arranged in two groups; the upper of the two is t e r m e d the "control" bank, and the lower, the "line" bank. A latch with two detents, t e r m e d the "double dog", holds the shaft and wipers in the position to which they have been stepped by the v e r t i c a l and r o t a r y movements. The shaft is released by the r e l e a s e magnet, which, when energized, o p e r a t e s the r e l e a s e armature. This armature, striking a projection of the double dog, disengages both the vertical and rotary dogs f r o m t h e i r respective toothed hubs, which permit the helical restoring spring to return the shaft counterclockwise to disengage the wipers f r a m the bank contacts, and f r e e the shaft hub f r o m the stationary dog, whereupon the shaft d r o p s to i t s n o r m a l position. Except for the vertical and releasing actions, controlled by the telephone station, the operations of the selector a r e entirely automatic. : * A m e n c a n Institute of E l e c t r i c a l Engineers "Amerlcan 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 " $65.55.100 defines a t r u n k 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'.' The banks shown in figure 1 really are part of the shelf on which t h e s e l e c t o r mounts. If a selector is to be removed from the shelf, remove the selector bank-rod nuts. BULLETIN 808 3. FUNCTIONS 5. BATTERY-SEARCHING SELECTOR The major functions of the selector, in the order in which they take place, a r e : Figure 2 shows the circuit of a basic batterysearching selector for use in any selector rank. Dial tone is connected to f i r s t s e l e c t o r s only. 3.1 I m m e d i a f e l y upon s e i z u r e , to hold a l l p r e c e d i n g switches in the t r a i n operated and guarded until the holding (control) circuit is completed t o the next (succeeding) switch in the t r a i n . 3.4 To find and connect with an idle trunk in the selected bank-level (rotary motion), This rotary motion comprises seven functions: 5.1 Seizure. When a battery-searching selector is seized, the preceding switch grounds lead C and c o n n e c t s t h e calling line and telephone a c r o s s leads -LINE and +LINE. When the preceding switch i s a linefinder, a s soon a s the f i n d e r s t a r t s hunting it c o n n e c t s a 5000 non-inductive bridge a c r o s s -LINE and +LINE t o s e i z e the s e l e c t o r until the calling line is found. As soon as the calling line is found, the finder removes the 5000 bridge, and the calling line and telephone hold the selector. (a) To rotate the shaft automatically. (b) To keep the line wipers disconnected during rotation. (c) To test the trunks successively. (d) To stop the rotary movement at the first idle trunk. (e) To protect the trunk selected until the holding (control) circuit is completed by the next (succeeding) switch in the train. (f) T o extend t h e l i n e t h r o u g h to the next (succeeding) switch in the train. (g) To disconnect a l l bridges o r attachments from the transmission circuit. The ground on lead C operates relay C, which, if this i s a f i r s t selector, at make-before-break c o n t a c t s 5-6-7 r e p l a c e s d i r e c t ground with ground through a dial-tone transformer winding (not shown). Dial tone, induced into the winding, indicates to the calling line that the linefinder (or line switch) has finished i t s work and dialing may proceed. Dial tone is not provided in subsequent switches since the interdigital pause ( t i m e taken to pull a d i a l to the next desired digit) i s long enough to allow a selector to hunt a c r o s s and seize one of ten trunks on a level ($5.3). 3 . 5 If a l l t r u n k s i n t h e s e l e c t e d l e v e l a r e engaged, t o r e t u r n a n audible busy signal to the caller. Relay A operates through a circuit that includes a d-c loop and both i t s windings in s e r i e s , and at contacts 2-3 completes a circuit to relay B. 3.6 When the caller hangs up, to release without interfering with other trunks. Relay B operates, a t contacts 6-7 closes what for the moment is an additional ground on lead C to hold the preceding equipment when it ,switches through (S5.4) and, i f i t is o t h e r than a f i r s t s e l e c t o r , to m a r k t h e s w i t c h busy to other s e a r c h i n g s e l e c t o r s . T h e ' s a m e ground also holds relay C through i t s winding No. 2. 3.2 If i t is a unit in a first-selector group, to connect dial tone to the calling line. 3.3 To r a i s e the shaft and wipers in response t o pulses from the dial. 4. SELECTOR TYPES Two basic types of selector circuits have been used widely for many years. The older is spoken of a s t h e " 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 , a t e r m which r e f e r s to the means of m a r k i n g trunks idle to the switch a s it hunts a c r o s s a selected bank level. The newer type is known a s the "battery-searching" selector, a term which also refers to the means of marking trunks idle to the switch. An absence-of -ground-searching selector searches the trunk control-leads for absence-ofground which marks a trunk idle and allows the selector to stop ($6.3 and $6.6). 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 s e e k s negative battery on the trunk control-leads (95.3 and $5.4). Busy trunks in both types of switchtrains a r e marked by ground on the control leads. Because it i s easier to understand, the batterys e a r c h i n g switch will b e discussed first ($5). By addition of one relay and normal-post springs ( F i g u r e 4), either type can be made to absorb digits a s discussed in §7. 5.2 Vertical stepping. The caller pulls the dial off normal and releases it. During the return to normal, the dial pulse springs open the loop the number of times indicated by the dialed digit. Relay A r e l e a s e s during each open period, at contacts 2-1 completes a circuit through relay B contacts 2-3 and r e l a y C contacts 3-4 to the v e r t i c a l magnet and to r e l a y C. The copper sleeve on relay B keeps relay B operated even though r e l a y A contacts 2-3 open i t s circuit momentarily. The vertical magnet operates, elevates the shaft one s t e p , and the w i p e r s a r e in line with the fisst level of bank contacts. For each succeeding p u l s e , t h e v e r t i c a l m a g n e t r e o p e r a t e s and raises the shaft and wipers one step o r bank level. While the shaft is being elevated the f i r s t step, the vertical-off-normal springs are released mechanically.' Vertical-off-normal springs 3-4 complete a c i r c u i t through r e l a y B contacts 11-10, relay F contacts 2T-IT, cam springs 2-1, 2 3 -"' BATTERY-SEARCHING SELECTOR F A B C D uent selectors. Marking circuit of next switch. To bartery through common time-delay relays that light lamp ~H,I I - Figure 2 . Battery-searching selector circuit. and rotary-magnet i n t e r r u p t e r springs 2-1 to r e l a y D. R e l a y D o p e r a t e s , a t contacts 2-1 short-circuits cam springs 2 - 1 to i n s u r e that a n e l e v e n t h r o t a r y s t e p (if r e q u i r e d ) can be completed (§5.5), and at contacts 4 - 3 prepares a circuit f o r the rotary magnet. Vertical-offnormal springs 5-6 open the circuit of relay C winding No. 2. The c o p p e r s l e e v e on r e l a y C keeps r e l a y C operated throughout pulsing, even though relay A contacts 2-1 open i t s circuit between pulses. If the calling line is relatively long (and h a s few p a r t i e s ) high l i n e r e s i s t a n c e limits current flow. Relay A when magnetized may be magnetized only weakly, r e l e a s e s quickly when t h e d i a l pulsesprings open, and reoperates slowly when they reclose. This gives relay C an extralong pulse. On t h e o t h e r hand, if the calling line is relatively short, relay A when magnetized is magnetized strongly, releases slowly, and reoperates quickly, giving relay C a short pulse. Because relay A and relay C mount adjacent to each other, their magnetic fields interact. The other-than-usual connection of relay C (not ground, but negative battery connected to "in" terminals) causes the magnetic fields of relays A and C to augment each other. Thus when a long line magnetizes relay A only moderately, flux from relay C a s s i s t s relay A. And when a short line magnetizes relay A so strongly that the pulse to relay C is short, the strong flux from nearby relay A adds to the magnet;--+ion from the Lem' -law sleeve currents _..relay C to help keep relay C operated between pulses. 5.3 Rotary motion. After relay A seoperates Tollowing the last open period, relay C releases, at conticts 5-6-7 r e m o v e s dial tone f r o m the calling line, and a t contacts 2 - 1 completes a circuit through relay D make contacts 3-4 to the BULLETIN 808 r o t a r y magnet. The rotary magnet operates, rotating the shaft and wipers to the f i r s t s e t of bank contacts (trunk No. 1 of the level selected). Just a s the rotary-magnet armature completes i t s stroke, i t opens rotary-interrupter contacts 1-2, to release relay D. If the first trunk of the level selected i s in use, ground ( o r open) will b e encountered while s e l e c t o r control wiper C r e s t s on the control bank contact, and switch-through relay F cannot operate. Relay D releases, opening the circuit of the r o t a r y magnet. A s the r o t a r y magnet s t a r t s t o r e l e a s e , i n t e r r u p t e r contacts 1-2 reclose the circuit of relay D and the stepping c y c l e i s repeated until an idle trunk is found ($5.4) o r all trunks test busy ($5.5). 5.4 Switch-through. Negative battery m a r k s an idle trunk, completing a circuit to switchthrough relay F wh& wiper C engages the control bank contact. Relay F operates, a t contacts IT-2T opens f u r t h e r the circuit of relay D to p r event additional r o t a r y stepping, at "X" make contacts 2T-3T locks through its winding No. 2 through vertical-off -normal springs 4 -3 and r e l a y B contacts 10 -1 1 to ground at r e l a y B contacts 6-7, at make contacts 8T-7T and 7B-8B prepares a locking circuit over wiper C that will be completed when relay I3 in the next switch operates and returns holding ground, at contacts 1B-2B-3B and 4B-5B-6B disconnects relay A and extends the calling loop through to the next s w i t c h o v e r w i p e r s (-) and (+), and a t b r e a k contacts 4T-5T opens the circuit of slow-release r e l a y B. Note that "X" contacts (make that closes before all others) insure a locking circuit before ground a t relay B contacts 6-7 s h o r t circuits winding No. 1 through contacts 7B-8B. The*combined operate times of relays A and B in the next switch is much less than the release time of relay B in this circuit, thus insuring that ground will be returned over wiper C to hold relay F before the circuit is broken at relay B contacts 6 -7. Relays A and B release in this switch, and the next digit dialed s t e p s the succeeding switch. 5.5 All trunks busy. If all ten trunks test busy, an eleventh rotary step is taken, at the s t a r t of which a cam attached to the shaft operates cam springs 1-2 to prevent relay D from reoperating after the eleventh step. Cam springs 3-5 make and 4-5 b r e a k to r e p l a c e d i r e c t ground with ground through a busy-tone transformer winding. 5.6 Release. Before switch-through relay F o p e r a t e s , the release-magnet circuit is held open a t r e l a y A contacts 2 - 1 and a t r e l a y J 3 c o n t a c t s 2-1. If the c a l l e r hangs up before r e l a y F o p e r a t e s , r e l a y A and then r e l a y B r e l e a s e , thereby completing the circuit of the release magnet. The releas e-magnet armature s t r i k e s t h e double-dog, disengaging i t s two detents from the vertical and rotary ratchets, thus permitting the shaft and wipers to return to their normal position. When the selector has switched through, relays A and B a r e n o r m a l and the release-magnet circuit is open at relay F break contacts 5T-4T. When t h e calling p a r t y disconnects with the selector in this position, the open calling loop releases relay A in the last switch of the train (usually a connector if the call has been completed). The corresponding relay B releases, removing ground from control lead C to release all switches in the train. Switch-through relay F releases, and at contacts 5T-4T completes the circuit of the release magnet. Notice that make contacts 7T-8T open b e f o r e contacts 2T-1T close, to prevent battery through relay D f r o m marking the selector idle before i t is completely released. Although when the final switch f i r s t removes holding ground from the control lead, battery through t&-1300~2 of relay F winding No. 2 is connected through make contacts 2T-3T and 7T-8T to lead C, a switch-through relay in a switch hunting a c r o s s lead C is not sensitive enough to o p e r a t e f r o m t h i s 13003 battery. Finally, notice that r e l a y F contacts 7T-8T disconnect relay F quickly f r o m lead C even before "X" contacts 2T-3T open. This minimizes the possibility for relay F to reoperate if another s e l e c t o r , hunting, momentarily extends 10052 ground to lead C. Just before the shaft reaches its normal position, the v e r t i c a l - o f f - n o r m a l Springs r e o p e r a t e . Springs 1-2 open t h e release-magnet circuit. Springs 5-6 re-connect battery through relay C winding No. 2 to lead C to mark the switch idle. 6. ABSENCE-OF -GROUND-SEARCHING SELECTOR Another local selector is the absence-of-groundsearching switch shown in figure 3. It is similar to the battery-searching selector, in that it also has five relays, uses relay-interrupted rotary stepping, and has almost identical A, B, and C relays. It differs in that the switch-through relay has a single winding and is designed to operate from battery through the interrupter relay when not short-circuited by ground marking a busy tMmk, the release magnet has contacts that ground lead C during release to give positive guarding, and relay C i s not pre-energized over lead C. The m e c h a n i c a l a r r a n g e m e n t s a r e practically identical except that this absence -of -groundsearching switch has release-magnet springs. 6.1 S e i z u r e . When an absence-of-groundsearching selector is seized, the seizing switch c l o s e s a d-c c i r c u i t a c r o s s l e a d s -LINE and +LINE. Note t h a t , when idle, t h e switch i s marked by neither ground nor battery on lead C axxi that even though the seizing switch (linefinder H-75311 o r similar) does ground lead C, relay C is not operated thereby. Relay A operates, and at contacts 2-3 completes t h e c i r c u i t of r e l a y B. Relay B operates, at contacts 4-5 grounds lead C to mark the switch busy and to hold the preceding switches, at contacts 6-7 completes the circuit I I J 1 .* ABSENCE -OF-GROUND-SEARCHING SELECTOR F A B C D ; 3 -3 Marking c i r c u i t 3 5 bD B U k P 8 2 Simplified c i r c u i t f o r relay F. Figure 3. Absence-of-ground-searching selector circuit. of relay C winding No. 2, at contacts 8-9 prepares a c i r c u i t f o r r e l a y D, and a t c o n t a c t s 10-11 grounds lead SUPY to s t a r t dial-tone equipment ($8). Relay C operates, at contacts 4-6 supplies dial tone (if this is a f i r s t selector), and a t contacts 1-3 short-circuits unoperated relay F. --,' 6.2 Vertical stepping. Relay A follows the dial pulses* releasing during each o ~ e n - l O o ~ period pulse relay C winding No. and the vertical magnet. The vertical off-normal springs release d u r i n g t h e f i r s t v e r t i c a l s t e p . V e r t i c a l offn o r m a l s p r i n g s 5-6 open t h e c i r c u i t of relay C winding No. 2 (but pulses through winding No. 1 k e e p r e l a y C operated throughout vertical stepping). Vertical off -normal springs 3-4 close a c i r c u i t a s follows: f r o m ground a t relay B contacts 4 -5, through release-magnet springs 2 -3, r e l a y C s p r i n g s 3-1, r e l a y B s p r i n g s 9-8, r o t a r y - m a g n e t i n t e r r u p t e r s p r i n g s 2 - 1 , and v e r t i c a l off-normal s p r i n g s 3-4, t o r e l a y D. Relay D operates, locks, and places a n additional short circuit around relay F. After the l a s t vertical step, relay C releases, removes one short circuit from around relay F, ground and completes a circuit as follows: a t relay Bcontacts 4-5, through release-magnet springs2 - 3, relay C springs 3-2, and relay D spfings 3-4 to the rotary magnet. 6.3 R o t a r y s t e p p i n g . T h e r o t a r y magnet operates, and rotates the shaft and wipers to the f i r s t set of bank contacts. After the wipers a r e on these f i r s t contacts, and just a s the rotarymagnet armature completes its stroke, rotary- 7 BULLETIN 808 magnet interrupter springs 1-2 open the circuit of relay D. Relay D releases, removes its short circuit from relay F, and opens the circuit of the r o t a r y magnet. If the first trunk is busy, ground encountered by wiper C keeps relay F short-circuited. Also, a s the rotary magnet releases, rotary-interrupter s p r i n g s 2-1 connect t h e w i p e r - C ground to r e l a y D. R e l a y D o p e r a t e s , l o c k s , puts an additional s h o r t c i r c u i t a c r o s s r e l a y F, and operates the rotary magnet, stepping the wipers to the next trunk. 6.4 Switch-through. Absence-of -ground marks an idle trunk. When the rotary magnet s t a r t s to release after rotating the wipers tosuch a trunk, interrupter contacts 1-2 close battery from the winding of relay D to relay F. The only ground c o m p l e t i n g a c i r c u i t to r e l a y D now c o m e s through the 1300Q of relay F, and the resultant c u r r e n t is enough t o o p e r a t e only r e l a y F. Relay F operates, a t contacts 7T-8T provides i t s e l f a n additional path through r e l a y D to negative battery for use when relay B release s, at contacts 5B-4B opens the circuit of relay B, at contacts 1B-2B-3B and IT-2T-3T disconnects relay A and extends the calling loop through to the next switch, and at contacts 5T-6T connects w i p e r C to lead C s o t h a t t h e next switch, returning ground w e r wiper C, can hold this and preceding switches. Relays A and B in this switch release. 6.5 All trunks busy. If all ten trunks test busy, an eleventh rotary step is taken, at the s t a r t of which a cam attached io the shaft operates cam springs 1-2 to prevent relay F f r o m operating a s soon a s relay D r e l e a s e s a t the end of the Figure 4. Normal-post springs. Arrows show cam lugs bent 90' to operate l e f t n o r m a l - p o s t s p r i n g s when wiper-shaft is opposite o r cut in on level 2 o r 3. eleventh step. The wipers a r e off the banks and r e l a y D cannot r e o p e r a t e . Cam s p r i n g s 3-5 connect busy tone to the calling line. 6.6 Release. Release is s i m i l a r t o that of a battery-searching selector (S5.6) except that in an absence-of -ground-searching switch, releasemagnet s p r i n g s 2-3 disconnect r e l a y F f r o m lead C and springs 1-2 ground lead C to m a r k the switch busy. 7 . DIGIT-ABSORBING SELECTOR When two neighboring automatic exchanges a r e interconnected by free-service dialing trunks, i t is d e s i r a b l e to uoe "universal numbering" a n d h a v e t h e f i r s t s e l e c t o r s in e a c h office "absorb" the f i r s t digit dialed when i t indicates the local exchange to save a rank of selectors i n each office (see bulletin 819). Figure 5 shows a digit-absorbing selector. The switch shown is an absence-of -ground-searching selector but the digit-absorption feature is available a l s o for battery-searching selectors. Notice that another o r s i x t h r e l a y , F, is used; that normal-post s p r i n g s (figure 4) a r e added and a r e adjusted to o p e r a t e w h e n a d i g i t - a b s o r b i ng l e v e l is reached during vertical stepping; and that the release magnet is equipped with contact springs. 7.1 Seizure and vertical stepping. Seizure arid vertical stepping take place essentially the same a s w a s d e s c r i b e d in $6.1 and $6.2, During vertical stepping, vertical-off-normal springs 3-4 operate relay C, which locks. 7.2 Non-digit -absorbing level dialed. If the digit is to be permitted to select and gain access to-the level (that is, i s not to be "absorbed"), when v e r t i c a l stepping ends, the normal-post s p r i n g s a r e n o r m a l (unoperated). Relay D releases, closing a circuit from ground at relay E contacts 5B-4B ard relay A contacts 2-3 (wiring E) o r at relay B contacts 8-9 and relay E contacts 8B-7B (wiring F),vertical off-normal springs 6-5, relay D contacts 2-1, relay F contacts 6-5, and left normal-post springs 2-1, to relay F winding No. 2. Relay F operates, locks, disconnects d i a l t o n e ( i f t h i s is a first s e l e c t o r ) , and at contacts 7-8 completes the circuit of the rotary magnet. Rotary hunting proceeds a s in $6.3. 7.3 Dipit-absorbing level dialed. If the digit dialed is to be ineffective in selection of and is to be denied a c c e s s to the level (that is, if the digit is t o be "absorbed", and the switch shaft is to r e t u r n to normal, to s t a r t o v e r when the next digit is dialed), when vertical stepping ends, the switch wiper shaft comes to r e s t operating the normal-post springs. Relay D Eeleases, and c l o s e s a c i r c u i t from ground* through vertical off -normal springs 6-5, relay D contacts 2-1, relay F contacts 6-5, and left n o r m a l - p o s t s p r i n g s 2-3, to the r e l e a s e 'with wiring F, ground i s supplied f r o m relay B contacts 8-9 through relay E contacts 8B-7B; with wiring E, ground i s supplied from relay E contacts 5B-4B through relay A contacts 2-1. DIGIT -ABSORBING SELECTOR 4 Busy llf 1 (- c . I 7 --- Simplified circuit for relay F 1- ' NOTE 1. When switch i s to releaseevery time digit absorbing level i s dialed, use wiring E. When switch i s to release time the digit absorbing only the level is dialed. use wiring F. elease Left normal-post spnngs - $ Figure 5. Digit-absorbing selector circuit (absence-of -ground searching). magnet. At i t s contacts 1-2 the release magnet locks, and also short-circuits unoperated relay j FwindingNo.1. Atcontacts3-4therelease ---* magnet unlocks and r e l e a s e s r e l a y C. A s the shaft f a l l s away f r o m the level dialed, the left normal-post springs r e t u r n to normal, and (unless level "1" was dialed) close a circuit f r o m g r o u n d * t h r o u g h v e r t i c a l off-normal springs6-5,relayDcontacts2-1,relayF contacts 6-5, and left normal-~osts u r i n ~ s2-1. to r e l a y F winding No. 2. ~ k l @a ~ opgratesi l o c k s , and disconnects d i a l tone (if t h i s is a f i r s t s e l e c t o r ) , When the shaft r e a c h e s its normal position, vertical off -normal springs 6 - 7 r e o p e r a t e r e l a y D, and v e r t i c a l off-normal s p r i n g s 1-2 open the release-magnet circuit. If level "1" was dialed, during release vertical off-normal springs 5-6 a r e likely to open before left normal-post springs 1-2 close, Relay F must be operated nevertheless, but a different technique is used. When the shaft reaches its normal position, vertical off-normal springs 6-7 reoperate relay D, and vertical off -normal springs 1- 2 r e m o v e the s h o r t circuit f r o m relay F winding No. 1. C u r r e n t flowing from ground at relay B contacts 10-11, through r e l e a s e - m a g n e t s p r i n g s 2-1, r e l a y F contacts 3-4, relay B contacts 7-6, relay F winding No. 1, and t h e r e l e a s e magnet, causes relay F winding No. 1 to operate i t s contacts "X", closing the circuit of relay F winding No. 2. Relay F operates fully, disconnects dial tone (if this is a f i r s t selector), and at contacts 3-4 opens the circuit of the release magnet. 7.4 Digit-absorbing level need not be wasted optional - figure 5 wiring F). Notice that, with lrelay F o p e r a t e d and locked (9'7.2 o r $7.3). relay F contacts 5-6 make the 1e'f;c normal-post springs ineffective and prevent further release. T k s , the level to which access was denied when d i a l e d o n t h e f i r s t digit can, if d e s i r e d , be accessed (cut in on and used) when dialed on the second digit; digit absorption need not waste the level. 7.5 Digit a b s o r b e d r e p e a t e d l y (optional f i m r e 5 wiring E ) . If when r e l a y F operates and l o c k s ($7.2 o r $7.31 it l o c k s t o r e l a v A spring 3, t h e relay ~ - 1 o c k i n ~ circuit i s opehed e a c h t i m e an additional digit i s dialed. This p e r m i t s digit absorption ($7.3) to r e c u r every time the switch i s dialed to the level where the normal-post c a m lug is bent. In this case, a given digit can be a b s o r b e d repeatedly a s in $7.3, and $ 7.4 and 57.6 do not apply. 7.6 V e r t i c a l stepping a f t e r digit absorption. With the s h a f t r e t u r n e d to n o r m a l and with. relay F having operated ($7.3) and having closed i t s c o n t a c t s 7 -8, the r e s p o n s e of t h e digitabsorbing selector to a second dialed vertical digit will b e like that of a n o r d i n a r y selector ($ 6.2), namely: At the f i r s t vertical step, vertical off-normal springs 3-4 operate relay C which locks. At the end of vertical stepping, relay D releases, and closes the circuit of the rotary magnet. Rotary stepping, testing, hunting, and switch-through follow a s i n $6.3 and 96.4. 8. SUPERVISORY LEAD T o s t a r t dial and busy tone for the selectors, and to give a visual indication when a selector is being held by a ' 'permanent" o r grounded line, a supervisory lead is provided on both selector types and is grounded by selector relay Q. The s u p e r v i s o r y l e a d (SUPY) is c o m m o n t o a l l selectors on a shelf and terminates in a relay (figure 2) which s t a r t s the tone equipment and lights a shelf supervisory lamp. Another s u p e r v i s o r y r e l a y (figure 2), in the r e l e a s e b a t t e r y lead, g i v e s an a l a r m if any r e l e a s e magnet on the shelf remains operated longer than is normal. 9. TONE START LEAD T h e s e l e c t o r switch-through r e l a y (figure 2 r e l a y F f o r example) grounds lead TONE ST (tone s t a r t ) t o s t a r t the busy-tone s o u r c e for the connectors. 10. SPARK PROTECTION The non -inductive windings connected in parallel with the operating windings of the interrupter r e l a y s a n d t h e r e l e a s e m a g n e t s offer lowimpedance paths f o r current s u r g e s when the associated circuits a r e opened, thus reducing sparking at the contacts which open the circuits. T o p r o t e c t c o n t a c t s in the highly-inductive vertical and rotary magnet circuits, the contacts a r e b r i d g e d by c a p a c i t o r s which a b s o r b the s u r g e when the contacts open the circuit. The capacitors are connected in series with a resistor which l i m i t s t h e discharge c u r r e n t when the contacts first reclose. For example, in figure 2, capacitor S and t h e associated 2000 r e s i s t o r b r i d g e r e l a y A contacts 2-1 during vertical s t e p p i n g . C a p a c i t o r S1 and t h e s a m e 200R r e s i s t o r b r i d g e r e l a y D contacts 3-4 during rotary stepping. Special precious-metal contacts, labeled N on the circuit diagrams, a r e used for interrupter contacts and f o r contacts, such a s figure 2 vertical off-normal springs 1 - 2 , that b r e a k the release-magnet circuit. ? MEMORANDA Revision March 1958 P r i n t e d i n U.S.A. by John S. Swift Co., Inc. 2000 3-58 o a ~ c r ~ a ~ o a~ a TsH E D I A L T E L E P H O N E . . i"laX~rsof T~lephon~. Signaling, and Corazmunicntion rtJp-nnragus . Ebr-rriraE Engineers, Des'ign~W,and i;?ns:~Iea~ts. Factory and B'atnrral O&ces: Korthlahe, Illinois, U. 3. 4, ASb6CIAYBD RESEARCH AND MANUB.&C%UWIMGCOMPANIES - - - - - - - Xnrthiake, Tllinti;~,tT. S. h. - - - - - - - - - - lirockviiie, Ontario, C a n a i i a in~rtornatiqoeElectricfur, S.A. . - - . - - . . - - - - - - - - - rlniwerp, Belgii~rrr Autornatie: Electric, S.A.T,A.T9. - - - - - - - - - - - - - - - - - - - - MiLan, Itaiy <',tbnerai Teiephiane H,aboratories, Pncorpnrateci Autnmatir: Pi,ia:ctric (Canada) 1,itnited D45TWBIUTQR iiN U,B, AND P0SSESS1BNS SUTOhiATIC ELECTRIC SALES CORPORATIOX KosthlaBe, dliinsns, U. S. A, Sales Ofices in AU 63i-incipul Cizaes _iU_iTObIt4TlCF:LECTRHC: hN%ERNhTlO"P(%Ed INCORPORATED Diorthjakr, Illinrris, U. S. 4. REGiiOWAL DISTRIBUTING COMPANltS AND WEPRI%BWMABBVEB ARGEhTINPh. IjRUGlJAY, PAR-k@TJ'AYI CHILE, ANIb BOLIVIA D. C. Clegg Sula 51 Rua C O ~ S P ~ ~ P ~ ~ Crisplniano F C I No. ti9 Sao Pm~rlo,Brazil AUSTRALIA GC)L,f9MISiA Automatic EEertrir de Colon~l-iia,S.B. Apartatlo Aareo 39613 Bogma, C:olo~nbia EUROPE, NOKTIr" AFRfd:_$., /B&P> NEAR EAST Electric Interneii<:nal, Incorporated 1%1~8nmaric Automatic Electric Teiephorres L i m i t e d 86 Holdsworth Sweet, Wmllahrs Sydney, Australia BELGIUM A S D LUXE&ISZO'I;RG Wutomatiq~eElesctrique, S. -4. 22 Rere did Verger Anawerp, Belgiur~z P. O. Box 15 Geiiava hloa?thri:!s:ri G e n e ~ a ,Switzerland I T A LY Automatic Electric S.A.T.A.P, Via Bernina 12 btilrnl, I$al>- BRAZIL MEXICO At~tomatbeZlecrric 140 B r a d r S.A * Autonlatic FGectrir cie $ l e x i c ~ ,5.4. Apartaslo Postal 2 i327 klenico 7 , H1.F.: hliexiro Sala 62 Rua C.'oilseibeiro Criepbninno No. 6') Seo Pauio, B r a ~ i i CAl+ADA Autoinatic Electric SaIes (Casraba) Lieni3;ed 185 Barite.; Drive T o r o i ~ t o16, Ontario, Canada CENTRAL AMERXCIA NFTWRRL.&T4IfS :Il;soiimatiq~;eEiec:~rii~itc~ $.A. tluygenetraat 6 's-Gravoirhag~,3eilterfanc!rs PER:_JAxa Ec:J-kl>QR J. P, hlaclaren 2.Pitiglimi Ahjartsdo Bcsrai 'Pf 327 Mexico 7 , U: F., ?$'?rxiv$: Apartado Aerru 3963 fhgo?a, s i ~ ' i ~ m ? ~ i a VEyEZi JEl,& -. i[nitnims ;ttztcslzatii: Electric De gieneziteie, iJi>m;bsrrra Ajzarbodo i;3b2? Est. Caracaii, venezraeja > . 7