Manual / Guide · 1957

AE Training Bulletin 806: The Rotary Line Switch

Rotary line switch (preselector) operation.

Author: Automatic Electric Co.
Year: 1957
Type: Manual / Guide
Credit: Telephone Collectors International (TCI) Library, telephonecollectors.info (retrieved via Internet Archive Wayback Machine)

T h e ROTARY TCH O R l 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 i s on2 of t h e helpful booklets ir, the AUTOWIATIG .ELECTRIC TEAIMP?$@ SERIES SpE STROWGER AUTOMATIC TELEPHONE SYSTEMS Electrical Principles of 'relephony Mechanical Principles of Telephony Fundamentals o f Apparatus and Truwkilmg The Plunger Lineswitch and Associated -M;zster -Sx-.vitcB? Rotary EP9aeswitc:h The Connector The Selector 818 81% 820 821 Pulse Repeaters Trunking Power and Supervisary Equipment Epa?%~-LineConnector 8 and Trunk- Wanking Gsnnectocra Re.sferting-Call Tai:e.th~ds The T e a t and V e r i f i c a t i o n Switch T r a i n Toll Switch Train Sr?r;it~hi~bg Se4ec tol--Regeater Private Automatic Exchanges with PABX Api;endix Community il%u%omatic Exchanges &Ian.eea! $wi"rrhboards Linefinder Switche_a CONTENTS Page . GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2 . 25-POINT LINESWITCH iMECHANISM . . . . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . . . . . . . . . . . .1 2.2 R o t a r y switch mechanism . . . . . . . . . . . . . . . . . . . . . 2 2.1 Relay a s s e m b l y 3 . 11-POINT AND 16-POINT LINESWITCH MECHANISM . . . . . . . . . . 3 4 . . . . . . . . . . . . . . . . . . . . . . . . .3 3.1 Relay a s s e m b l y 3.2 R o t a r y switch mechdriism . . . . . . . . . . . . . . . . . . . . .3 . ROTARY LINESWITCH FUNCTIONS . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . . .3 4.2 Incoming c a l l s . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4.1 5 Outgoing c a l l s . NONHOMING LINESWITCIl CIRCUIT . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . . . . . . . . . . . . . .3 5.1.1 Seizure . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5.1.2 Seeking a n idle trunk . . . . . . . . . . . . . . . . . . . . 3 5.1.3 Engaging an idle trunk . . . . . . . . . . . . . . . . . . . 4 5.1.4 Switching through . . . . . . . . . . . . . . . . . . . . . . 4 5.1.5 Releasing . . . . . . . . . . . . . . . . . . . . . . . . . 4 5.2 Incoming c a l l s . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.3 Supervision . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1 Outgoing c a l l s 6 . HOMING LINESWITCH CIRCUIT . . . . . . . . . . . . . . . . . . . . 5 . . . . . . . . . . . . . . . . . . . . . . . . . . .6 6.1.1 Seizure . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1.2 Engaging a n idle trunk . . . . . . . . . . . . . . . . . . . 6 6.1.3 Switching through . . . . . . . . . . . . . . . . . . . . . . 6 6.1.4 Releasing . . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.1 Outgoing c a l l s 6.2 Incoming c a l l s ..........................6 THE ROTARY LINESWITCH 1. GENERAL The r o t a r y lineswitch, instead of the plunger lineswitch, may be used in Strowger dial systems as individual line equipment. It is well adapted for certain traffic and service conditions. The rotary lineswitch is a single-motion (rotary) "non-numerical" switching device; i t s operation requires no digit in the call number nor any movement of the dial. A r o t a r y lineswitch is associated lnrith each telephone line and, in operation, is independent of all other lineswitches It requires no m a s t e r switching mechanism. This lineswitch auto matically connects the associated telephone line, a t the initiation of a call, to an idle trunk terminating in a connector (100-line system) o r a selector (in a larger system). . With r e s p e c t to circuit operation, rotary lineswitches a r e divided into two general types: homing and nonhoming . A homing-type r o t a r y lineswitch is one which normally r e s t s in an off-trunk position. At the termination of a connection, the wipers rotate to this home position (generally the first 'position of bank contacts). The homing-type lineswitch is "post-selectingv--the selection of the idle trunk o c c u r s after the call is initiated. This r o t a r y lineswitch is used with a "graded" trunk arrangement. Trunk selection s t a r t s with the f i r s t position, permitting tkie use of individual trunks, if desired. Graded multiple is a method of trunking where a small. number of trunks of a group a r e individual to a number of lines, and the remaining trunks a r e common t o a number of groups of lines. In the nonhoming-type lineswitch, the position of the selecting wipers does not depend on the condition of the trunk (whether idle o r engaged). The wipers remain in the position of the trunk previously used by them. Another call from the s a m e line engages the same trunk, i f idle. When another lineswitch occupies the trunk, the wipers rotate to the next idle trunk. In theory, the nonhoming-type rotary lineswitch is post-selecting; in practice, the lineswitch engages the trunk with which i t s wipers a r e in contact for a large percentage of initiated calls. The nonhoming-type rotary lineswitch i s available in four different trunk capacities: 11, 16, 25, and 50 trunks, known a s the 11-point, 16 -point, 25-point, and 50-point r o t a r y line switch. The latter has been used only under special conditions. When the- 25-point rotary lineswitch is used a s individual line eqyipment (primary lineswitches), the outgoing trunks generally terminate directly in connectors o r selectors. A common group of twenty-five trunks is very efficient with respect to the traffic which can be handled by the group during the busy periods. The homing-type rotary lineswitch is available only in the 10 -trunk and 16 -trunk capacities. 2. 25-POINT LINESWITCH MECHANISM The rotary lineswitch, shown in figure 1, consists of two major parts: the relay assernbly and the rotary switching mechanism with associated bank. The line and the cut-off relays, composing the relay assembly, a r e built into a compact group which may be either directly associated with o r disassociated from the rotary switch mechanism. The rotary switch is a simple but sturdilyconstructed selecting mechanism, comprising essentially a semi-cylindrical bankof contacts over which a s e t of wipers rotate by means of a ratchet mechanism actuated by a motor magnet . 2.1 Relay assembly. The relay assembly consists of two relays: the line relay (slowacting), and the cut-off, o r B.c,o,, .relay (quick-acting) A mechanical interlocking de vice, shown in figure 2, interconnects the armatures of the two relays. . On ineoming call$, with the line relay a t normal, a finger on the cut-off relay a r m a ture strikes the end of the interlocking spring. The cut-off relay a r m a t u r e will move only endugh to open all break contacts but not sufficiently to close any of i t s make contacts, When the line relay is energized on an outgoing call, a finger on the line r e l a y engages Figure 1. 25-point lineswitch. Figure 2. Construction details. an inclined plane a t the end of the interlocking spring, moving the end of this spring out of engagement with the finger of the cut-off relay armature. In this case, when energized, the cut-off relay armature operates completely, closing a l l make contacts. The control wipers, which test for an idle trunk, have more wiping surface than the others, so that while rotating from one trunk to the other they a r e always in contact with a t least one control bank contact. This pres e r v e s the continuity of the circuit if successive contacts a r e grounded (busy trunks). 2.2 Rotary switch mechanism. The rotary switch mechanism uses a semi-cylindrical bank having three o r four levels, each containing twenty-five contacts. A pair of doubleended wipers rotates over each level of contacts. When one end of a wiper is on the bank corrtacts, the other end is free from the bank. This arrangement and the unidirectional motion of the switch maintain a s e t of wipers in contact with the bank t e r minals a t all times. When one end of the wipers is leaving contact twenty-five, the other end is approaching contact number one. By rotating through a half circle, the wipers successively step over a l l contacts. The electrical circuit to each wiper is maintained through a brush spring which makes contact with the wiper, a t the hub of the assembly. Figure 2 shows the driving mechanism of the rotary switch. A ratchet wheel mounted on the wiper shaft is engaged by a pawl pivoted to the a r m of the motor -magnet a r m a t u r e . When the motor magnet is energized, this pawl is withdrawn from the ratchet wheel. It engages the next tooth when the motor magnet is de-energized. A drive spring causes the pawl to engage the ratchet tooth, stepping the wipers one step ahead when the motor magnet r e l e a s e s . At the end of the driving stroke, the pawl strikes a stationary stop which p r e s s e s the pawl against the ratchet wheel, locking the latter to prevent "overthrow." A stationary detent also engages the ratchet wheel, preventing any backward movement of the wipers when the pawl is released. i 2 3 . 11-POINT AND 16 -POINT LINESWITCH MECHANISM e m Figure 3 is a view of the 11-point, homing- ) type rotary lineswitch showing the relative ? positions in which the relays and the mechanism a r e mounted. The 16 -point rotary lineswitch is s i m i l a r to the 11-point lineswitch except for the trunk capacity. 3 . 1 Relay assembly. The relay assembly except for the mounting bracket is similar to that used with the 25-point r o t a r y lineswitch. The bracket of the 11-point and the 16 -point switch permits mounting the relay assembly directly on the r o t a r y switch frame. The homing-type rotary lineswitch requires no mechanical interlocking device since the line can be seized only when the wipers a r e on the home position. 3.2 Rotary switch mechanism. While the 11point and 16 -point rotary switch mechanisms a r e smaller and different in construction, the mechanical functions a r e similar to those of the 25-point rotary switch and, therefore, will not be repeated. As shown in figure 3, the pawl, a f1a.t flexible spring, is fastened directly to the a r m of the motor magnet armature. The s p i r a l drive spring, secured to the a r m a t u r e proper, is f used for restoring the pawl. f Figure 3. 11 -point lineswitch. 4.2 Incoming calls. On calls to the telephone, the functions of the lineswitch a r e : (a) To prevent the lineswitch f r o m engaging a connector o r selector trunk. A s e t of cam (off-normal) springs, normally open when the wipers a r e in the home position, is required with this type of rotarylineswitch, (b) To f r e e the line.of all bridges o r attachments. 4. ROTARY LINESWITCH FUNCTIONS - 5. NONHOMING LINESWITCH CIRCUIT 4.1 Outgoing calls. On calls originating from the telephone, the functions of the lineswitch are: A schematic circuit for the nonhoming-type primary rotary lineswitch (in this c a s e , 25point) is shown in figure 4. The 16-point and 11-point switches use the s a m e circuit. The only difference is in the number of trunks accessed. (a) To busy the line a t the connector bank terminals against intrusion by incoming calls, immediately upon operation of the lineswitch line relay. (b) To automatically hunt and seize an idle trunk. ( c ) To extend the line through to the selected connector o r selector. (d) To c l e a r the line of a l l bridges o r attachments. - (e) To connect the subscriber's m e t e r to the trunk m e t e r lead, when message register i. a service is provided. (f) To restore to normal when the calling telephone disconnects. 5.1 O u t e o i n ~calls. 5.1.1 Seizure. When the handset of the calling telephone is removed from the cradle, a circuit is established from ground through the winding of the common supervisory-ground relay, a break contact on the B.C .O. relay B, over the (+) line, through the telephone, back over the (-1 line, through another break contact of relay B, and the 8003 winding of relay A to battery. Relay A operates. 5.1.2 Seeking an idle trunk. Relay A operates and closes i t s "X" contaots. If the wipers a r e resting on a busy trunk, ground from the control bank contact is connected to the 953 winding of the motor magnet through COMMON 1 76 SIGNAL WIPERS RLY. -0' WHEN GROUNDED AT C.tJOR. BREAKS ALL BACK CONTACTS, BUT DOES NOT C ~ O S E THG MAKE CONTACTS DUE T O A MGCHANlCAL L O C K I N G DEVICE. Figure 4. Rotary lineswitch circuit, nonhoming type. the control wiper, a break contact on relay B, the "X" contacts on relay A and the interrupter springs, csusing the motor magnet to operate. Ground from the control lead is a l s o connected to one terminal of the 1200S2 winding of relay B through the "X" contacts of relay A. Ground is also connected to the other terminal of this winding when the "Y" contacts of relay A close. This shunting of the relay B coil prevents i t from operating when the wipers engage a busy trunk. Ground is also connected to the control normal, through the "Y" contacts of relay A to busy this line to incoming calls. The operation of relay A moves the locking spring out of alignment with the locking finger, on the armature of the cut-off relay. Relay B operates fully. When the motor magnet operates, i t s circuit is opened a t the interrupter springs. The motor magnet de-energizes and i t s armature and pawl, , r e s t o r i n g to normal under the power of the drive spring, step the wipers ahead one step. This is repeated a s long a s the control wiper encounters busy (grounded) control bank contacts. When an idle trunk is found, the coptrol wiper will not encounter ground and, therefore, the shunt around the 1200f2 winding of the cut-off relay B is removed. 5.1 - 3 Engaging an idle trunk. When an idle trunk is found. a circuit i s established from ground, through the "Y" contacts of relay A, the 1200a winding of relay B, the interrupter springs, the 95f2 motor magnet coil to ( - ) battery operating relay B. The high resistance of relay B coil prevents the motor magnet from operating in s e r i e s with i t . 5.1.4 Switching through. Relay B operates and extends the telephone line and the control lead through the 'wipers and bank contacts to the switch ahead. The operation of relay 33 also opens the operating circuit for relay A and c l e a r s the line of attachments. Relay A is slow-acting, keeping the ground circuit connected to relay B until ground is returned over the control lead from the succeeding switch. Relay B is held operated until the connection is released. , * . No stepping occurs when the rotary switch is seized, if i t s wipers a r e resting on an idle trunk. d 5.1.5 Releasing. When the handset is replaced, the loop to the telephone is opened and the TO SIGNAL COMMON TO UEXT -.I SWITCH 5 M.F. 5 M.F. - 100"' TI-' .l <k C A M SPG. I I a ? 2 +(TI ,' UI U) e C (S) / TO SIGNAL CAM SPRINGS CLOSE ON FIRST ROTARY STEP. WIPERS Figure 5. Rotary lineswitch circuit, homing type. switch ahead disconnects ground from the control lead. Relay B r e s t o r e s , disconnects the line and control leads from the trunk, and r e -establishes the circuit for relay A. The switch is now normal ready for another call. ground to the (+) line through a make contact on relay B. This relay operates and sounds an alarm when any rotary switch in the group fails to extend the telephone line to the switch ahead within a reasonable length of time after it is seized. 5.2 Incoming calls. On incoming calls the connector places ground on the control normal lead. A circuit from this ground through the 1200Q winding of cut-off relay B, the interrupter springs and the 95Q winding of the motor magnet to ( - ) battery operates relay B. When relay B operates, the locking finger on i t s armature engages the end of the locking spring. This prevents full operation of its armature. The N.I. resistance, connected in parallel with the winding of this supervised ground relay, prevents excessive sparking a t the break contact of relay B. Spark suppression for the motor-magnet interrupter springs is shown in figure 4. A .2 M.F. condenser is supplied for each lineswitch. One terminal is connected to the motor-magnet winding. The other (center) terminal is connected to ground through a common relay, having its 200Q winding shunted by a lOOQ N.I. resistance. This relay causes an alarm to sound should any condenser become short-circuited. The movement of the armature, however, is sufficient to open the circuit t o relay A and clear the line of attachments. Thismechanical interlocking device prevents the armature of relay B from closing its make contacts and the telephone line is not extended through to a primary trunk. % 5.3 Supervision. In figure 4 a relay, having its -$/ 30Q winding shunted by a lOOQ N .I. resistance, is connected in the common lead supplying 6 . HOMING LINESWITCH CIRCUIT. - A homing -type primary lineswitch circuit is shown in figure 5. The line bank contacts, in the home position, a r e unwired. Therefore, a mechanical interlocking device is not ueed since the cut-off relay B may be fully operated on the incoming calls. 5 6.1 Outaoing calls. 6.1.1 Seizure. When the handset is removed from the cradle, relay A is operated over the calling party's loop. A circuit to the motor magnet is closed from ground at the "Y" contacts of relay A, the control bank contact and wiper, a t the home position, a break contact of relay B, the "X" contacts of relay A, and the interrupter springs, to the 10051 winding of the motor magnet and (-) battery. Ground is also connected to the control normal lead to prevent intrusion bjr incoming calls. ground a t t h e "Y" contacts of relay A in s e r i e s with the motor magnet. The high resistance of relay B prevents the motor magnet from functioning a t this time. 6 .1.3 Switching through. The operation of relay B extends the telephone line and the con&ol lead to the switch ahead. It also opens the circuit to relay A and clears the line of attachments. Relay A is slow acting and does not release before ground is returned over the control lead, from the switch ahead. Relay B is held operated by this ground until the connection is released. The motor magnet operates, interrupts i t s own circuit and releases. This causes the drive spring to act upon the armature and pawl to step the wipers off the home position and onto the f i r s t s e t of bank contacts. When the control wiper leaves the home bank contact, i t disconnects ground from the winding of the motor magnet. If the f i r s t trunkis busy, ground on the control bank contact will re-operate the motor magnet to step the wipers to the next s e t of contacts. This stepping action will continue a s long a s busy trunks a r e encountered. When the wipers step from the home position, a part of an incomplete restoring circuit for the motor magnet is closed through the cam springs. 6.1.4 Releasing. When the handset i s returned to the cradle, the switch ahead releases and removes ground from the cpntrol lead, causing relay B to r e s t o r e . This completes a circuit from ground through the break contacts of relay A and B, the cam springs (which closed when the switch stepped off the home position), the interrupter springs, and the motor magnet to ( - ) battery. The motor magnet will step the switch wipers to the home position. At this point the cam springs open the motor magnet circuit to prevent further rotary stepping. The switch has now restored to i t s normal position ready for another call. The ground on the control lead of a busy trunk a l s o shunts the B.C.O. relay B. This prevents i t from operating when the wipers a r e engaging a busy trunk. 6.2 Incoming calls. On incoming calls the connector places ground on the control normal lead operating B .C .O. relay B . 6.1.2 Engaging an idle trunk. When the switch wipers find an idle trunk no ground is encountered on the control bank contact. Therefore, the motor magnet does not reoperate and the shunt is removed from the winding of the relay B coil. Relay B now operates from Relay B operates, opens the relay A circuit and, c l e a r s the line of attachments. When the handset is returned to the cradle, relay B releases and recloses the relay A operating circuit. The switch has now restored to normal ready for another call. i i 6 R i G I N A T G R S O F D I A L T H E Makers of Telephone, Signaling, and Cornrnunication &paratus T E L E P H O N E . .. Electrical Engineers, LPesigne~s,and Consultants Factory and General OiPices: Northlake, Illinois, U. S, A. 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