Manual / Guide · 1969
2000 and SE.50 Type Group Selectors (ETP 0258) — Australian Post Office, TPH 1836 (1969)
21 pp
Manual / Guide · 1969
21 pp
TPH 1836 Engineering Training Publication 2000 and SE.50 Type Group Selectors - ETP 0258 Issue = 1, 1969 Prepared by: Engineering Training Authorised by: Manager, Operations Planning & Programming Branch, HQ. Distribution Code: Selective Filing Category: K Telecom Australia AUSTRALIAN POST OFFICE TECHNICAL TRAINING Engineering Training Group, ETP 0258 PUBLICATION 6 Flinders Street, Melbourne, Victoria, 3000 2000 AND SE.50 TYPE GROUP SELECTORS PUBLISHED 1969 PREVIOUSLY HXS 510 1. INTRODUCTION .. 1 2. OPERATIONAL FUNCTIONS 2 3. 2000 TYPE GROUP SELECTOR 3 (CE 65) 12 4. SE.50 TYPE GROUP SELECTOR (CE 11030) 1. INTRODUCTION. 1.1 In the technical training publication "Internal Trunking", it was shown that to extend the range of a step-by-step exchange beyond 100 lines, add one or more additional switching stages. stages - direct the setting up of the call, it is necessary to These additional stages - group selector each selector stage in turn responding to one digit of the dialled number until the call is finally directed to the final selector associated with the group of lines (100 or 200, depending upon the selector type) containing the desired number. 1.2 The main functions of a bimotional group selector are:• To step vertically under the control of the appropriate dialled digit . • To "cut in" (rotate horizontally) to the bank contacts of the dialled level and select a free circuit to the next selector stage. 1.3 • To remain in the "switched through" condition for the duration of the call. • To release itself at the end of the call. The 2000 type selector became the standard bimotional switching mechanism for Australia during the 1930's. Since that time, earlier varieties of bimotional selector have been commonly referred to as pre-2000 type equipment. Shortly after 1950 the SE.50 type of bimotional equipment was introduced into the Australlan network. The SE.50 mechanism occupies the same mounting as the 2000 type, and group selectors of both types can work side by side in the same shelf. principle of the 2000 type mechanism is described in Paper 1 of Telephony SE.50 type mechanism 1.4 The 4, and the is described in the publication "SE.50 Type Selector Mechanism". This publication lists the general operational functions of group selectors and describes the main features of the circuit operation of both the 2000 and SE.50 type group selectors. 2000 AND SE.50 TYPE GROUP SELECTORS 1.5 While reading the circuit descriptions in this publication, you should study the small explanatory diagrams included with the text and relate them to the complete Also attached is a cha.rt or operational diagram which outlines circuits attached. the sequence of operation of the selector relays and magnets. 2. OPERATIONAL FUNCTIONS. 2.1 The main operational fUnctions of the SE.50 and 2000 type group selectors are:(a) When the loop is extended from the previous selector, • Returns earth on the private to hold and guard the connection. • Provides dial tone when used as a first selector. • On first and incoming selectors, provides a P.G. alarm should the 6 minutes without dialling. selector be held for longer than (b) Steps vertically under the control of the pulses received. (c) "Cuts in" (Steps horizontally) on the level reached at the end of the vertical pulses, hunts for and seizes the first free outlet in the level. Two outlets are tested at each rotary step - one in the lower bank in the upper bank (odd) and one (even). (d) Switches the calling loop through to the selected outlet. • If both upper and lower outlets are free, the odd outlet (lower bank) is selected. (e) After switching, maintains a holding earth on the private for a time sufficient to permit an earth to be returned on the private from the selector or circuit connected to the seized outlet. (f) SE.50 only. wire. Steps off an outlet which fails to return an earth on the P (g) Maintains the selector in the "switched through" condition until release conditions a.re applied. earth is removed from the (This is normally at the end of the call when P wire). (h) Releases itself when release conditions are applied. • Provides a guarding circuit for itself during release. • Provides a release alarm should the selector fail to release due to a mechanical defect. • In the event of release a�er no progress or all outlets busy, provides a release unguard period to allow the simultaneous release of all previous selectors. (i) When all outlets on the dialled level a.re busy • the selector steps to the llth rotary contact and operates llth step 'S' mechanically operated springs. • busy tone is transmitted to the calling subscr iber . • the overflow meter is operated . 2 2000 AND SE.50 TYPE GROUP SELECTORS 2.2 Two additional facilities provided by the SE.50 type group selector are "pre busying" and "Junction guard". Pre-busying. When a selector required for maintenance is in use on a call, the technician, by transferring a link in the test jack, can prevent the switch from being taken for another call, while still allowing all the previous switches to release in the normal way at the end of the call. Junction guard. During release, the negative lead to the selector is opened. If the switch is an incoming selector this indicates a busy condition on the junction if the repeater relay set at the originating exchange is equipped for back busying. • 3. 2000 TYPE GROUP SELECTOR (CE 65). 3.1 LOOP SEIZURE. When the calling loop is extended from the previous selector on the positive and negative wires of the selected trunk, the loop operates the A Test jacks 3 and 4 permit a maintenance relay of the group selector (Fig. 1). technician to monitor a call or to loop a selector for testing purposes. COJ � NR2 BU.SV FROM PREVIOUS SEL. TJ TO 0 o----�- ·I� N SlfBb 0 o---....---� ·I DIAL TONE N NR3 COE> FIG. 3.2 GUARDING AND HOLDING. 1. LOOP SEIZURE. When a selector is seized, it is essential that an Application of earth potential is quickly applied to the incoming private wire. this earth causes the selector to test busy to other testing circuits. It is also fed back to the previous selector of this call to hold the switching relay operated. For normal selectors, earth is applied to the private by B3 contact after Al extends This means that there is the the earth from CD5 to operate the B relay (Fig. 2). combined operate lags of relays A and B before the guarding and holding earth is applied. In the case of subscriber's uniselectQr circuits connected to long lines, there is a possibility of the switching relay releasing before a holding earth is For this reason, selectors used as first selectors may be strapped returned from B3. between U8 and U9. With this strapping added, earth from CD5 is applied to the private immediately relay A operates, and it is then reinforced by earth from The earth from CD5 is disconnected when relay CD is operated on contacts Bl and B3. its 700 ohm winding by contact B2. 3 2000 AND SE.50 TYPE GROUP SELECTORS T ,J'. J: •i _ - FAST: GUARD, ONLY 8 �°!::. N2 Al _. .....,___ N4 FIG. 2. GUARD AND PULSING PREPARATION. When it is necessary to busy a selector strapped for the fast guard feature, it m::>st important that the test link is t ransferred from TJ 13/14 to TJ 7/8. is Opening the circuit at TJ 13/14 prevents a current drain via resistor R4 and the vertical magnet. 3.3 DIAL TONE TO CALLER. W hen the selector is a first selector, connects dial tone to the this winding into the two 570 ohm winding of relay A, contact B6 (Fig. 1) The tone is induced from 200 ohm windings and so to the caller, If the selector is not a first selector, the dial tone connection is replaced by earth. 3.4 P.G. SUPERVISORY. When contact applying earth to the private, supervisory lamp to a P.G. switch lights, delayed Al operates relay B, contact B3, as well as also extends earth via B4 contact and a alarm circuit. The supervisory lamp on the 6 minutes without any vertical N and if the switch remains looped for stepping, an alarm condition is given. If the switch is stepped vertically, springs are operated, the lamp is extinguished and the alarm condition is removed (Fig. 3). per iods. In many exchanges this alarm is disconnected except for certain specified t I BJ "" �..__"rs_2 l 4---ll• /.01t RI SUPY. 2/6V 100 P.C. ALARM FIG. 3. BATT P.G. SUPERVISORY ALARM. 4 2000 AND SE.SO TYPE GROUP SELECTORS 3.5 VERTICAL PULSING. When the selector is first seized, contact B to the battery behind the vertical magnet. operate in series with B. 700 ohm winding. Al operates relay The vertical magnet does not Relay B holds via Bl and at B2 operates relay CD on its CDl prepares a low resistance operating circuit magnet and CD2 prepares a circuit for relays for the vertical HA and RB (Fig. 4). HB6 CD I H B ...__i�.:.L-.J �BJ NRI. J C02� HA .___,_;.:.;:c.i._1 l _L (b) (a) FIG. 4. VERTICAL PULSING, When the caller dials the digit appropriate to this r ank of switching, relay A releases with each pulse and the Al contact short circuits relay B, allowing sufficient current to flow to completely operate the vertical magnet. Relay B is short circuited each time the Al contact restores and is re-energised each time Al The B relay holds during pulsing because of the slow release effect operates. caused by the inductive current circulating in its short circuited winding. The vertical magnet is energised each time Al contact short circuits relay B, and releases each time the resistance of the B relay is included in series with the magnet. dialled. The wiper carriage is raised a number of steps according to the digit At the first vertical step, the vertical off-nonnal Nl operates relays HA and HB on their circuit the 550 ohm windings. 700 ohm winding of relay CD. the short-circuited Relay CD releases, springs operate and HA3 and HB6 short Relay CD remains operated during the pulse train as it receives a high value current pulse through the the vertical magnet is operated, (N) Contacts 5 ohm winding each time and the magnetic flux is maintained by the effect of 700 ohm winding. after a delay period, at the end of the pulse train as the A relay is held operated by the calling loop and the current through the 5 ohm winding of CD in series with relay B and the vertical magnet is not sufficient ta hold relay CD operated. 5 2000 AND SE.50 TYPE GROUP SELECTORS SUMMARY OF FLUX BEHAVIOUR DURING PULSING. Before pulsing commences, relays A, B and CV are all operated and the vertical magnet is energised to a slight As the vertical degree by the current through the magnet in series with relay B. magnet normally operates on current values approximating lA, and the current through 3.6 relay B is in the region of 40mA, the vertical magnet flux is at this stage only slight. During pulsing, the A relay releases at each break period of the dial. short circuits relay B so that the flux commences to fall in relay B. The Al contact At the same time the vertical magnet is energised and relay CD receives a high value pulse through its 5 ohm winding, causing a build up of the flux in relay CD. When the A relay re-operates at each make period of the dial, relay B is energised again and th� flux value of relay CD falls, while the vertical magnet releases. If the operate and release times of relay A are in accordance with the dial ratios, the pulsing circuit relays will perform satisfactorily. A longer than normal operated time for relay A could result in relay CD releasing, which results in the A longer than normal released time for relay selector switching to the wrong level. A could result in relay B releasing and causing the selector to release. At the end of the vertical pulse train, AUTOMATIC CUT-IN. 3.7 relay CD releases slowly and at CD4 operates the rotary magnet from earth at B3 via operated HB ( Fig. and HA contacts and the rotary interrupter springs 5). The rotary magnet steps the wipers to the first contact of the dialled level. NRI CD 2 ).!HAI rtlf.'°'-------<1>---11• HB2 NI RMI ... ..r-t-• 4�--Q. T FIG. 5. F igs. 200 OUTLETS-BANKS ASSEMBLY. 3.8 AUTOMATIC CUT-IN. 1, 2 and 3 in the paper "Internal Trunking" show the make up of bimotional selector banks. The standard 2000 type group selector is a 200 outlet selector, which means that each level has an availability of 20 circuits or trunks. To obtain this availability, the group selector is associated with three 220 point banks, The lower bank contains the positive and negative connections for the "odd" numbered outlets on each level -10 circuits numbered 1,3,5 . . . • . • . 19; the m iddle bank contains the positive and negative connections for the even numbered outlets 2,4,6 . . . • . • . wire connections for both line groups. 20, while the upper bank contains the private This enables the group selector to test simultaneously via the private or top set of wipers the condition or potential existing on one odd and even private contact. 6 2000 AND SE.50 TYPE GROUP SELECTORS 2000 The method of outlet testing used on OUTLET TESTING-CUT DRIVE PRINCIPLE. 3.9 type group selectors employs a system known as the "cut-drive" principle. When the selector "cuts in" at the end of the vertical stepping, a self interrupted drive circuit for the rotary magnet is completed via operated HA and HB contacts and the Once this circuit is established, it is rotary magnet interrupter springs. maintained until it is "cut" by the release of either HA or HB relay when a free outlet is tested. As the rotary magnet steps the wipers to the first contact, the rotary interrupter springs open the circuit to the rotary magnet and also to the operate windings ohms) of the HA and releasing, HB relays (Fig. 6). the HA and HB relays test with their 400 ohm windings the condition on the private contacts of that pair of odd and even circuits. circuits are busy, there is hold operated the HA and an (550 During the period that the rotary magnet is When both the odd and even earth potential on each private contact which will HB relays. When the rotary magnet and its interrupter springs restore, the self interrupted rotary circuit is once more completed, wipers are stepped to the next set of contacts. and the This action is repeated if the next odd and even circuits are both busy. When either the odd or even circuit is free, there is no earth potential on the private contact, the associated HA or opened at the HA or HB contact. HB relay releases, and the drive circuit is -·� RMI NI ·iH B� CD 4 RM FIG. 3.10 6. OUTLRI' TESTING. OUTLET TESTING-ODD FREE, EVEN BUSY. contacts, relays HA and drive is maintained. While the selector is testing over busy HB remain operated and the self interrupted rotary When a free odd outlet is encountered, absence of earth on the HB to release. HB2 cuts the rotary drive circuit to prevent any further stepping. Earth from B3 via HB5 normal is extended via the Pl wiper to busy the free outlet. HB4 releases relay HA and HB6 and HA4 remove the short circuit Relay CD operates and at CDl from the 700 ohm winding of relay CD (fig. 7). CD3 and CD6 disconnect relay A and re-operates relay HA on its 1500 ohm winding. Pl wiper allows relay together with contacts HA2 and HA6 extend the calling loop to the selected outlet. HA7 prepares a circuit to hold relay CD after relay B which releases slowly. B2 restores. circuit returns an earth on the private to hold relay HA. call, relay HA remains operated on its CD operated on its Al contact short circuits During the slow release of relay 700 ohm winding. B, the seized For the remainder of the 1500 ohm winding and contact HA7 holds relay 7 2000 AND SE.50 TYPE GROUP SELECTORS p 163 ����-t�+--- HB 2 HA3 HB6 HA7 CD v CDI ODD OUTLET FREE - RE-OPERATION OF HA. FIG. 7. 3.11 BOTH OUTLETS FREE. When both odd and even circuits test free, HA and HB relays both release and a guarding earth from B 3 is applied via HB5 normal and B4 operated contacts to busy the odd outlet, Relay CD operates, the call is switched to the odd outlet as described in para. 3.12 The pair of conta cts is tested with relays HA EVEN OUTLET FREE - ODD BUSY. and HB operated. If the even outlet is free, there is no earth at the P2 wiper, relay HA releases and at HAl cuts the rotary drive circuit. busy, HA re-operates and 3.10. If the odd outlet is relay HB remains operated on its 400 ohm winding via B4 contact and the Pl wiper to the earth at the busy odd contact. When HA relay releases, HA5 extends earth from B3 to guard the seized outlet, and HA3 operates relay CD by removing the short circuit from the 7 00 ohm winding. CD re-operates, magnet, relay HB holds on its 1500 ohm winding 5 ohm winding of CD, operated and HAl normal, CDl and NR4 to earth on the P wire from B3 via HB2 Contacts CD3, through to the selected even outlet, B which releases slowly. When relay from battery via the vertical During CD6 and HBl, HB3 switch the calling loop Relay A releases and at Al short circuits relay the slow release of relay B, the next selector is seized and earth is returned on the private of the selected even outlet to maintain relay HB operated on its 1500 ohm winding, on its 700 ohm winding. Contact HB6 maintains relay CD operated HB7 prepares a circuit for the operation of a test bell when a test link is inserted in TJ9 and 10. This circuit allows a technician to determine whether a call is connected to the lower bank upper bank (even outlet, (odd outlet , HA operated) HB operated) without removing the switch cover -=- T s/c "'\��.� BELL RINGS - UPPER BANK CALL BELL DOES NOT RING - LOWER BANK CALL + T. T. !\ELL FIG. 8. USE OF TRUNK TEST BELL. 8 or to the (Fig. 8). 2000 AND SE.50 TYPE GROUP SELECTORS 3.13 THROUGH CONDITIONS. F igs. 9 and 10 show the respective through conditions when switched to an odd or an even outlet. relays private (HA or HB) In each case, one of the switching 1500 ohm winding by earth fed back on the is held operated on its wjre from the selector connected to the seized outlet. operated switching relay hold the HA�••\ CD3 �....: ---<1.1�· ------Q,.f · lHAb l ----o i - . .: - ODD O U TLET s PI HA4 • 1 •� �-,><,---<:r _.__ _.., _ HBJ ·· ••• �� HB3i + Contacts of the 700 ohm winding. .. · .• .___, . ; --'- �-crHA� l ii· ,.._._,._., _ I FIG. 9. THROUGH CONDITIONS - ODD CD3 OUTLET. HA2 l---Q. ,,.-c_D_.b.)� HB3 + _ _ ___ ..:.. .I ..:.. VM CD s I. , : , ·••H_B_I_-_,l.. • • ••• •• _,, •� + •• · 100 · =- EVEN OUTLET __ + ..______ ...· HAI HB2 i •• i HA 5 P---< :H"'.B•:"-- _:..:P21 ..ti •:•• p- -- 41 •••• p __..._________. FIG. 10. THROUGH CONDITIONS - EVEN OUTLET. 9 • 2000 AND SE.50 TYPE GROUP SELECTORS 3.14 ALL OUTLETS BUSY. When all outlets on a dialled level are busy, relays HA and HB remain operated and the rotary drive is ma intained until eleven rotary steps are ta.ken, when the llth step or S springs operate. As the eleventh contacts are not connected to working trunks, there is normally no earth on the P contacts and relays HA and HB both release, cutting the rotary drive circuit. Relays CD and HA re-operate as described in para. 3.11 and the caller is switched to the odd bank. At each switch, the llth positive and negative contacts on all levels of the odd bank are commoned and wired back via U jacks 4 and 7 to the A relay. Because of this wiring, the calling loop is still connected to the A relay and earth from B3 holds relay HA operated. Fig. 11 shows the conditions while the caller is receiving busy tone. _ ����� BUSY TONE 1 a...-·;:���A• \: .. i HA2 CD3 --l-, _, + \ WIRING FROM llTli OOO CONTACT ON ALL · .i; " '' l + � ���� � . : � HAb ..· j ..::. TO �--1�•0VEllFlDW METER FIG. 11. ALL OUTLETS BUSY CONDITION. RELEASE OF CONNECTION. The 2000 type g roup selector releases by rotating to the 12th step, where it falls to below the first level and rotates backwards The release after a normal call occurs under spring tension to the normal position. when the holding earth is removed from the P wire by the switch ahead. The switching relay HA or HB releases, followed by the release of relay CD. Contact CD4 completes a self drive circuit for the rotary m agnet from the release alarm earth via TJ 11/12, B7, rotary interrupters DMl and vertical off-normals Nl. The switch drives to the 12th step, where it falls and restores as previously described. When the carriage reaches the normal position, the Nl contacts open the release circuit. If, due to some mechanical defect, the carriage does not restore to normal within 9 seconds of the release circuit being completed, a release alarm is given. During the release of the selector, there is a guarding earth connected to the incoming private wire via CD5 and N2. This earth is removed at N2 when the switch fully restores to normal. lbwever, there is an unguarded period from the time that the earth is first removed from the P wire by the switch ahead until the release of HA (or HB) followed by relay CD. The total unguard period, consisting of the combined release lags of these two relays, is approximately 20 milliseconds. If the switch is seized during the unguarded period, the release circuit is still maintained, and the switch restores normally. Relay B cannot be re-operated until the switch is f'ully restored, as its operating path is via N2 normal. 3.15 10 2000 AND SE.50 TYPE GROUP SELECTORS p RMI NI N2 11 M TJ I RELEASE ALARM EARTH FIG. 12, When the release takes place from the RELEASE CIRCUIT. "all outlets busy" condition, the earth on the private and the holding of the HA relay is from c ontact B3, and not from any earth returned from a switch ahead, When the caller replaces the handset, and Al short circuits relay B which releases slowly. relay A releases Contact B3 removes the earth from the incoming private and releases relay HA, which in turn releases relay CD, During the combined release lags of relays HA and CD, earth is removed from the incoming private to allow the release of holding relays in any previous selectors used on the call. 3.16 The remainder of the release is the same as for a normal call. EFFECT OF FAULTY (OPEN) OUTLET. negative or private wire, releases, If the seized outlet is open on the positive, no earth will be returned on the P wire. When relay B the switching relay will release and in turn release relay CD, completing Contacts CD3 and CD6 re-connect the 3.15. A relay re-operates, but relay B cannot operate until the switch restores completely to normal. The release of relay B removes earth the release circuit as described in para. A relay across the calling loop. from the incoming private and releases all of the previous switches, so that the call is lost. NOTES 11 4. SE.50 TYPE GROUP SELECTOR (CE 11030). 4.1 The following description is based upon drawing applied to the selector to drawing CE-900, CE-11030, but it can be equally there are only minor differences as between the two circuits. 4.2 SEIZURE. When the calling loop is extended from the previous selector, relay A Al operates relay B from battery behind the vertical magnet to earth operates, at CD on its 600 ohm winding from earth at NR3 ( Fig. 13). N5 and B7 operates relay On first and incoming selectors the switch supervisory lamp lights from earth at El or N5 via CD2 operated contact. private wire by B3, A guarding earth is normally applied to the incoming U8 and U9 may be strapped, but if a fast guard is required N5 to be applied to the private wire immediately the Al contact On first selectors, contact CD4 connects dial tone to the 570 ohm winding allowing earth from operates. of relay A, where it is induced into the two 200 ohm windings and so to the calling line. � I• � + B3 p T/- L CDI 11· �4 I -- I ' CD 11 8 TJ B NR4 N2 •I ·1H 'I 24 VM Hi · :1 N� P.G. ALARM BATTERY FIG. 13. SEIZURE. 12 0 \/L--" H f--'VB7 NR3 2000 AND SE.50 TYPE GROUP SELECTORS 4.3 VERTICAL STEPPING. Before pulsing co=ences, relays A, Relay CD is operated on its Band CD are operated . 600 ohm winding and a 510 ohm shunt path around the 500 ohm winding is prepared at CDl. Contact CD5 prepares the vertical magnet pulsing circuit by short circuiting the 430 ohm resistor in series with relay B. shows a simplified version of the vertical pulsing circuit. Fig. 14 When pulses are received, the A relay releases at each break and re-operates each time the loop circuit is remade. Each time the A relay rele ases, contact Al short circuits relay Band operates the vertical magnet from earth at B l. When the A relay re-operates, the short circuit is removed from relay B which is energised again in series with the vertical magnet. The additional resistance of relay B causes the vertical magnet to release each time relay B is connected in series. At the first vertical step the vertical off normal (N) springs place a shunt across the 500 ohm winding of relay CD (N4) and connect an ohm winding (N5). intermittent short circuiting earth via Al operated for the 600 After the first vertical step, the 500 ohm winding of CD is shunted for the remainder of the pulse train and the 600 ohm winding is short circuited each time relay A operates. Relays B and CD both hold during vertical stepping . B BI (OP) VM NR4 CD 510 FIG. 4.4 ROTARY "CUT-IN". SIMPLIFIED VERTICAL PULSING CIRCUIT. 14. At the end of the vertical pulse train, relay A :r:emains operated, relay Bis held in series with the vertical magnet and relay releases after a delay period of 90-135 milliseconds. CD Contact CD3 extends the magnet alarm earth to operate the rotary magnet, moving the wipers to the first row of bank contacts on the dialled level. RM 52 RM I CD •l�A1 �. rJN:CDJ 02 ___/. - HBI FIG. N3 15. } ��:��T T EARTH N'.> FIG. ROTARY CUT-IN. 13 16. RE-OPERATION OF CD. 2000 AND SE.50 TYPE GROUP SELECTORS 4.5 RE-OPERATION OF RELAY CD. At the first rotary step, rotary off-normal (NR) At NR5, the earth via Bl and Al which was previously short springs operate. circuiting relay CD now re-operates CD on its 600 ohm w inding. 4.6 When NRl and CD3 operate at the first rotary step, a self- CUT-DRIVE PRINCIPLE. interrupted rotary drive circuit from the magnet alarm earth via HBl and HAl contacts is established. The rotary interrupter springs operate when the rotary magnet armature is almost fully operated and restore when the magnet is almost fully released. Each time RMl springs are operated, the magnet alarm earth is extended to The opposite side of each winding has the 85 ohm windings of both HA and HB relays. a negative potential connected and tests via the Pl and P2 wipers the condition on the private contacts. While both odd and even private contacts are busy, the busying earth potential shunts the HA and HB r elays and prevents their operation. The drive circuit is maintained and when the interrupter springs restore the rotary magnet is operated and pteps the wipers to the next contact. outlet is found. The drive continues until a free On a free outlet there is no shunting earth and HA or HB relay (or both) operates from the magnet alarm earth to negative potential via a 390 ohm resistor. The rotary drive circuit is "cut" at either HAl or HBl (Fig. 17). Earth from CD7 operated is extended via HA2 or HB2 to guard the seized outlet . •• HA2 PI • • : ODD • NR •• • • (OP) •I Hi• CD (OP) ·I � RM RMI Hi· HBI B6(0PJ MAG.ALARM P2 EARTH •• • • : EVEN H B2 • • FIG. 4.7 17. CUT-DRIVE P RINCIPLE - SE.50 SELE CTOR. During the f irst rotary step, ODD OUTLET FREE, EVEN OUTLET BUSY. re-operate relay CD. I • NR springs The rotary magnet operating earth is transferred via CD3 and NRl to the rotary interrupter springs RMl. During the period that the RMl springs are operated, relays HA and HB test the Pl and P2 outlets via the 85 ohm windings. As the even outlet is assumed busy, earth on the P2 contact short circuits relay HB and prevents its operation. If the odd contact is free, there is no short circuiting earth and relay HA operates on its 85 ohm winding from the magnet alarm earth to negative behind the 390 ohm resistor. The rotary magnet drive circuit is disconnected at HAl, the HA relay holds on its 750 ohm winding via HA4, and the negative, and private wires are extended to the selected outlet via HA3, respectively. The calling loop is extended through to next selector. switched selector releases and at Al releases relays CD and B. positive HA5 and HA2 Relay A in the During the slow release of these relays contact B3 maintains an earth on the incoming private and CD7 holds relay HA. A guarding and holding earth is returned on the private wire from the next selector to hold this and previous selectors after the final release of relays B and CD. When contact CD6 restores, inserted in the holding circuit of relay HA. an additi�nal resistance of 2000 ohms is This reduces the holding current to approx. 20mA and ensures a fast release at the end of the call. the only relay operated is relay HA. Fig. During conversation, 18 shows the switched through condition. 14 2000 AND SE.50 TYPE GROUP SELECTORS FROM CALLER A3 >-- -----------�r·• ���TH/ : : • •• · ----<�""'�----------+--1--0 ··: ( HA5 : • •• ••• ;,.R 2 : • •••• S3 VIA PREVIOUS SELECTOR _+ _____ p TO ODD NUMBERED OUTLET LOWER BANK ) r-1�---<Hl.A. �p .. � I Rb 2000 so as HA HA4 ..._....-0-... CDb FIG. 18. 4.8 THROUGH CONDITION - ODD OUTLET SELE �TED. EVEN OUTLET FREE, ODD OUTLET BUSY. The outlet testing circuit is prepared as described in para. 4.7. If the odd outlet is busy, the 85 ohm winding of short circuited and relay HA does not operate. HA is If the even outlet is free, the alarm earth via the operated interrupter springs operates relay HB on its 85 ohm winding. Relay HB holds on its 750 ohm winding via HB4, disconnects the rotary magnet operating earth at HBl and switches the negative, selected outlet via HB3, and B. positive and private wires through to the HB5 and HB2 respectively. Relay A releases, followed by CD An earth is returned on the private wire from the next selector during the release time of relays B and CD. After the release of relay CD, a 2000 ohm resistor is included in the hold circuit of relay HB in the same manner as shown for the odd outlet in Fig. 18. 4.9 BOTH OUTLETS FREE. Relay HA and HB both operate on their 85 ohm windings. the holding circuit for relay HB is opened at HA4, relay HB releases. As Relay HA remains oper ated on its 750 ohm winding and the call is switched to the odd outlet as described in para. 4.10 4.7. "STEP-ON" FROM FAULTY OUTLET. If an earth is not returned on the seized outlet the switching relay (HA or HB) 40-80mS release lag of relay CD. P wire of a is released at CD7 after the This is a much shorter release lag than that obtained at the end of the vertical stepping as on this occasion the 600 ohm winding is not short-circuited and the principal delaying feature is the 510 ohm shunt across the 500 ohm winding of CD. The restoration of contacts CD3 and HAl (or HBl ) re operates the rotary magnet and the wipers are stepped to the next set of contacts. Relay A, which was placed back across the circuit by the release of the switching relay, re-operates to the calling loop and at Al extends earth from the still operated Bl contact to operate relay CD on its 600 ohm winding. Contact CD3 transfers the magnet earth via RMl operated so that relays HA and HB can re-commenct testing outlets in the usual manner. 15 2000 AND SE.50 TYPE GROUP SELECTORS 4.11 ALL OUTLETS BUSY. When all outlets on the dialled level are busy, steps to the llth rotary step and operates "S" the overflow meter, springs. S2 opens the rotary magnet drive circuit, the selector Sl applies an earth to S3 opens the hold circuit via 2000 ohms for the switching relays and s4 applies busy tone to the 5TO ohm winding of relay A. HB operates on its 85 winding via HB4 and CD6 to earth at CDT. ohm winding and holds on its T50 ohm HB3 and HB5 releases relay CD after a release lag of 40-80mS. disconnect relay A, which at Al Relay HB is released by CD contacts and places relay A back across the line to re-operate to the calling loop. operates relay CD on its 600 ohm winding. winding of relay A into the two 200 ohm windings and fed to the caller. time that the caller is receiving busy tone Fig. Al Busy tone is induced from the 5TO re ohm During the relays A, B and CD are held operated. 19 shows the conditions while the caller is receiving busy tone. �--� �+����������������-H_B_S�HAS .::. J NS FIG. 4.12 19. H � �: ..__ ._' _ -2-40.. � N ol !co CALLER RECEIVES BUSY TONE - ALL OUTLETS BUSY. RELEASE FROM NORMAL CALL. The release of the selector after the completion of a matured call is initiated by the removal of the holding earth from the P wire of the selected outlet. the negative, The switching relay HA or HB releases and disconnects positive and private incoming wires from the outlet. extends the magnet alarm applies the magnet alarm earth to operate CDl earth to operate the release magnet and CDT applies a gua rding earth to the private during the release of the selector. shunted by CDl, HAl or HBl relay CD on its 500 ohm winding. Relay CD is but the delay effect of this shunt enables relay CD to hold operated during the selector r elease. When the selector has fully restored, N3 disconnects the magnet alarm earth and N4 removes the shunt from the 500 ohm winding of CD so that it can release quickly. incoming selector private wire is unguarded from the time that the holding removed from the P wire until earth is re -applied by CDT. presents the release of the switching relay HA relay CD. 16 The earth is This unguard period re or HB followed by the operation of 2000 AND SE.50 TYPE GROUP SELECTORS If the circuit is seized during the unguard period, relay A cannot operate as the negative line is opened at Nl. This feature also supplies a junction guard if the selector is an incoming selector and the repeater relay set at the originating exchange is fitted with back busying facilities, Fig. 20 shows the release conditions after a matured call. •• BJ p .- --- 'tv---1' co1 J TJ oi H�-" HA --c:i.. - SJ � . .. �I ) I 2000 ...._-�-....-� � � �H HA I 510 MAO NET ALARM EARTH .. FIG. 20. RELEASE CONDITIONS. RELEASE FROM ALL OUTLETS BUSY CONDITION. While the caller is receiving busy tone after an all outlets busy condition, relays A, B and CD are operated. When the calling subscribers handset is restored, relay A releases and Al contact short Earth is re circuits relay B and opens the circuit to the 600 ohm winding of CD. moved from the incoming private at B3 to allow all preceding selectors to release. Because the B2 connects the magnet alarm earth to the 500 ohm winding of relay CD. two windings of CD are reverse connected, the flux in CD must completely restore to zero and then build up in the reverse direction to operate relay CD on its 500 ohm winding. CDl extends the magnet earth to operate the release magnet and CD7 applies earth to re-guard the incoming private. 4.13 RELEASE ALARM. If , due to a mechanical defect, the selector does not release when release conditions are applied, a release alarm is given after a 9 second delay period. 4.14 PRE-BUSYING. When the selector is required for maintenance and a call is in progress, a technician may "pre-busy" the selector by removing the release link from between test jacks 11 and 12 and inserting it between test jacks 10 and 11. 4.15 At the end of the call, when the switching relay releases, the magnet alarm earth does not operate the release magnet, but is diverted to test jack 10 and operates the T.T. bell. Relay CD operates on its 500 ohm winding from the magnet alarm earth and at CD7 places a guarding earth on the incoming P wire. All other previous selectors release when the holding earth is first removed from the private at the conclusion of the call. The release alarm is given after 9 seconds to ensure prompt attention. 17 2000 I. -- - L.OOP EXTENDED FROM · ----- ·- IMPULSING. AND ROTARY CUT IN" SEARCH. - %--;;. �� OUTL �� , W•-� - LO . - · : -- - -- --- ----;�� OU I. 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JL . -- ··1· ·-: . · .. ·---··---·-- ··--.----. · · : .. _ · - · --:u_L·ou:Tli,:$-r. u_s_v-. .. UPPE.R I TOMI v1A OPl.RAT[D. ' I I I I I I el (ALTltRNA V T E TO I I I I -·· -- --·· · L --L -- -���{ �-�-,.-:i�-�---.1�� -- -I I I I 1 RE-GUA"D. I i---- _...._ _ -- __ ___ _ _ _ A LOWER.. 6 . . - -- - _ _ . I• 3 AaOVE�. - - _ _ ··---· · • � � -- - ---t-- - T + t 1 --. . .. --·- - --··· ·- ----· · ---- 1• ausv OVEU'LOW A RELAY Ml'TIUl - · -- . --7 ".. .... ·- -- - - I I CD I - I I I MB -- I RM - - - -- -- - . --11-- ·· -- •• - i--- - >--1- R£L£4Sl I I I suiv. L"- I II 11 N NR I s • . UN-GUARD. >--1- IPW.tv. l/C. 2l. OPERATIONAL DIAGRAM GROUP SELECTOR (2000 TYPE). FIG. 19 2000 AND SE.50 TYPE GROUP SELECTORS TCF o{G. WOF (VCCH. SIOI:) OA TDF TAGS ON � MUU'. 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