Patent GB-892248-A (GB)
Title: Improvements in or relating to line-connector circuits for use in automatic telephone systems
Inventor: MUNDY RICHARD CHARLES NORRIS
IPC: H04Q3/00
Filed: 1958-10-15
Abstract: 892,248. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 9, 1959 [Oct. 15, 1958], No. 32866/58. Class 40 (4). In a system including an automatic satellite (non-exchange) the lines at the satellite and the line circuits at the exchange are scanned in synchronism and when a connection is required to be set up between a line and its corresponding line circuit the scanning is stopped and cross-bar switches at the satellite and at the exchange are operated in accordance with the position reached in the scan to complete the desired connection. General arrangements. Fig. 2.-Four junctions J1-J4 are associated with the four bridges of each of the cross-bar switches SE and SR at their exchange and remote (satellite) ends, respectively. Each switch has ten select magnets and two group switching magnets to serve the twenty subscribers. Scanning circuits LSE and LSR are driven in synchronism by the pulse generator PG, synchronism being maintained by the resetting circuit RC which ensures that both scanning circuits commence the cycle at the same instant. Detection of a calling condition at a line or at a line circuit causes a signal to be returned over a lead SSL to stop pulse transmission to the scanning circuits. A select magnet appropriate to the line concerned is operated in SE and SR together with the appropriate group switching magnet in each switch. Off-normal contacts of the operated select magnet of SE initiates operation of a bridge magnet of that switch by means of one of the operating circuits BOE allotted by the junction allotter JA, whereafter a signal over the junction concerned causes the associated operating circuit BOR to operate the relevant bridge magnet of SR. The select and group switching magnets are then released, JA allots the next free junction and the scanning circuits recommence scanning. Release is under control of the line circuit at the exchange end, the release of the bridge magnet of SE applying a signal via BOE and the remote bridge magnet releasing circuit BRR to the appropriate junction to cause BOR to release the bridge magnet of SR. Line scanning circuit, Fig. 4.-Each of these includes a cyclic counter containing ten identical bi-stable circuits BC1 to BC10. Pulses from the pulse generator are applied over lead DPL to a further bi-stable circuit BC11 which directs the pulses alternately to pulse leads PLO and PLE leading to the odd and even-numbered circuits of the counter, respectively. At the beginning of a cycle, the transistor corresponding to TX1 in each circuit BC1 to BC10, TX3 in BC11, and TX6 in a further circuit BC12 are off, viz., non-conductive, having been reset by the momentary switching off of TX5 by a signal over RPL from the resetting circuit RC (Fig. 2). The first pulse over DPL then switches on TX3, whereupon TX4 is switched off and the resulting negative going pulse on PLO switches on TX1 of BC1. The resulting pulse on PL2 switches on TX1 of BC2. The second pulse on DPL produces a negative-going pulse on PLE, which switches on TX2 of BC2, the resulting pulse on PL3 switching on TX1 of BC3. Action continues in this way until the output pulse from BC10 switches off TX1 of BC1, the resulting pulse on PL1 being applied to BC12 to change over this circuit. BC12 thus effects grounding of leads GAL and GBL in alternate cycles of ten scanning pulses to ensure that the "A" or " B " 10-line groups, respectively, shall be scanned. Scanning pulses are delivered over leads SL1 to SL10. Scanning action at remote unit, Fig. 5.- Assuming lead GAL to be grounded, TX10 in the "A" group line circuit LCAR is switched on during the period of the corresponding scanning pulse on lead SL. The normally conductive TX12 is thus switched off, whereupon TX13 conducts and current flows in the winding of the select magnet SMAR associated with the line circuit LCAR. The scan normally moves on to the next line circuit switching off TX10 and TX13 before sufficient flux is built up to operate SMAR. However, if the line is calling, negative potential is applied over the loop to the base of TX14 which, when TX10 is switched on during the scan, conducts. The earth on GAL is then extended via TX10 and TX14 to the common stop scan lead SSL and thence to the pulse generator. This stops the supply of pulses to the lead DPL so that the scan is stopped on the calling line and the appropriate select magnet SMAR can operate. The appropriate group switching magnet is operated in like manner. Scanning at the exchange, Fig. 6.-The arrangements are basically similar to those at the remote unit. When the scan reaches the line circuit LCAE, TX15 is switched on and TX16 off, whereupon TX17 conducts in series with TX18 and current flows in the winding of SMAE. If a call is being made to the subscriber in question the final selector extends ground to the private wire PLA to switch off TX19, whereupon TX21 conducts and the ground on SL is extended to SSL to stop the scanning. SMAE and SMAR then operate. Completion of connection over junction.- Operation of a select magnet at the exchange closes off-normal contacts SMON (Fig. 7) renders TX25 to TX28 non-conductive. The transistor of the group TX29 to TX32 associated with the allotted junction, say TX29, is switched off so that the transistor TX33 associated therewith conducts in series with TX35 and the bridge magnet BME. On the operation of BME its off-normal contacts BMONE1 (Fig. 9) remove -10 volts from the junction, whereupon the ground extended over the K contact switches off TX36 at the remote unit. TX38 then conducts in series with TX40 and bridge magnet BMR. Operation of BME closes contacts BMONE2 (Fig. 7), thus switching on TX41 to maintain BMR operated when TX33 is switched off by the release of the select magnet. Contacts BMONR1 and TX42 (Fig. 9) perform a similar function for BMR. Closure of the first two pairs of contacts at the operated cross-points extend the speech conductors from the line to the line circuit as shown in Fig. 9. The third pair at the exchange applies positive potential to the bases of TX18 and TX22 (Fig. 6) to switch both transistors off. TX20 thereupon conducts, thus switching off TX21 to terminate the stop scan signal on SSL. Select magnet SMAE is released by the switching off of TX18, whereupon TX25 to TX28 (Fig. 7) again conduct, thus switching off TX33 and allowing TX41 to maintain BME energized. TX47 also conducts and switches off TX48, thus removing a ground from the junction allotter drive lead JADL. Contacts BMONE4 apply ground to the emitter of TX43 (appropriate to the junction taken into use) which has its base biased negatively from the junction allotter. TX43 therefore conducts and switches off TX49 to remove the second ground from JADL, thus allowing the pulses on ADL to pass to the junction allotter (Fig. 8, not shown) which is a four-stage counter similar to that of Fig. 4. The fourth pair of contacts at the exchange cross-point connect the private wire PL (Fig. 7) to the base of TX34. Operation of the L relay (not shown) in the line circuit at the exchange grounds PL, but to prevent TX34 from being switched on (and thus releasing BME) in the interval between the operation of the cross-point and that of relay L, a large capacitor C1 is connected between its collector and base. Release.-Removal of ground from PL (Fig. 7) and its replacement by a negative potential causes TX34 to conduct after a short delay, thus switching off TX35 and releasing BME. Off-normal contacts BMONE3 (Fig. 9) apply ground to the input of the mono-stable circuit TX51-TX52 to render TX51 conductive, the resulting conduction of TX53 allowing BRR to operate. Reversion of the mono-stable circuit to normal then releases BRR. While BRR is operated it applies - 200 volts over the junction to fire VK at the remote unit, thus switching on TX39 which switches off TX40 to release BMR.