Patent GB-935331-A (GB)
Title: Improvements relating to line concentration arrangements for telephone systems, and to remote power supply arrangements suitable for use in such line concentration arrangements
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/58
Filed: 1959-11-27
Abstract: 935,331. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Nov. 18, 1960 [Nov. 27, 1959], No. 40459/59. Class 40 (4). In a telephone line concentration arrangement for connecting a plurality of subscribers' lines to their line circuits over a smaller number of junctions, direct current power for the concentrator apparatus is derived from the exchange over all idle junctions, the latter being connected effectively in parallel. In the event of all the junctions being busy, the concentrator arrangement is such that no incorrect operation results since the apparatus therein is left in a relaxed condition. General description of the arrangement.-Each junction 18 is connected between a concentration point junction-terminating circuit (Fig. 2), and an exchange-end junction-terminating circuit (Fig. 4), these circuits being multipled on the banks of uniselectors individual to the subscribers' lines 11 (Fig. 1), and the subscribers' line circuits (Fig. 6) respectively, in the latter case there being an individual concentration link circuit (Fig. 5) associated with each line circuit. Assuming that junction 18 is not in use on a call, then a relay TL (Fig. 2) is operated and negative exchange battery 69 (Fig. 7A) is connected over the simplex of the junction and those of other idle junctions via the primary windings of transformers TXE (Fig. 7A) and TXC (Fig. 3C), and thence over wire 19 to a power supply unit PSU (Fig. 3F) in the concentrator. Under normal conditions, i.e. at least one junction idle, condenser C1 will be charged and power will be available for the operation of the concentration point apparatus. The condition of the lines and the line circuits (through the intermediary of the link circuits, Fig. 5), i.e. idle, busy, &c., is checked periodically by scanning circuits SCC (Fig. 3E), and SCCE (Fig. 7E) respectively, and depending upon the conditions which these scanning circuits find, appropriate control pulses of X (500 c.p.s.), Y (800 c.p.s.) or Z (1100 c.p.s.) tone are sent in both directions over idle junctions. The scanning circuits are controlled by sets of bi-stable circuits 1-6 (Fig. 3G), and 1E-7E (Fig. 7G), corresponding operations of each set being performed virtually in synchronism by the receipt of the abovementioned pulses and each bi-stable circuit being responsible for causing the scanning circuits to search for a particular condition of the lines. Thus a sequence of operations is performed by the sequential triggering of the bistable circuits, although some of the stages of the sequence may be omitted depending upon what the line scanners find, and this sequence is repeated continuously as long as at least one of the junctions is idle and condenser C1 is being charged. Power supply arrangements.-As mentioned above, the power supply unit receives power over wire 19 as long as at least one junction is idle. This unit comprises two storage capacitors C1 and C2 the former being connected over lead 20 to all points in the concentrator marked " - " and the latter feeding all points marked "-25V." A charge on C1 is mantained in preference to one on C2 by making the breakdown voltage (15V) of Zener diode Z1 lower than that (25V) of Z2 so that transistor T1 is normally conducting and in the event of a heavy current drain on C1, the potential across Z1 falls below the breakdown value, i.e. its impedance increases; the emitter of transistor T2 becomes more positive and T2 diverts more charging current to C1, transistor T3 therefore cuts off, hence cutting off transistor T4, since the Zener diode Z2 in its emitter circuit is no longer receiving sufficient current to operate in the breakdown region, i.e. C2 ceases to receive charging current. A constant check is maintained on the voltage level on lead 20 by a checking circuit VLC and in case the level should fall, e.g. all junctions busy, Zener diode Z3 ceases to conduct and so cuts-off transistor T7. In so doing, transistor T5 is cut-off and transistor T6 is made conducting (or put into a condition ready to conduct when power is restored). When the voltage subsequently rises, re-operation of T7 cuts-off T6 and causes T5 to conduct and thus over lead 66 a positive pulse is sent to a " Z " timer 36 which opens a gate on the Z-tone transmitter 35 momentarily, so that a burst of Z-tone can pass over transformer TXC to the junction and hence to the exchange, where bi-stable circuit 2E is reset so that the sequence of operations can recommence; the cutting-off of T6 sends a negative pulse to the base of transistor T8, causing the latter to conduct and hence operate a blocking oscillator T9, TXT. This operation causes a " resetting " pulse to be applied to all the cores of the line scanning circuit SCC, the cores of a pulse repeating circuit PRC (Fig. 3D) (which initiates the operation of SCC) and also over lead 65 applies a resetting pulse to the bistable circuits 1-6 and three further bi-stable circuits AB1, AB2, AB3 so that the sequence of operations referred to above can be recommenced on the receipt of a " start " signal from the exchange. Operations of the line-scanning circuits.- The following operations take place: (a) Initially, bi-stable circuit IE (Fig. 7G), is reset to its " set " condition so that its righthand transistor conducts and applies a positive pulse to Z timer 52. The latter opens a gate to allow a pulse of Z tone to be transmitted to line and closes a further gate for blocking the Z tone receiver 43. Receipt of the Z tone at the Z receiver 27 (Fig. 3C) causes operation of the blocking oscillator T9, TXT with subsequent resetting of the concentration point apparatus and the transmission of a Z tone pulse to the exchange. This pulse is applied to Z receiver 43 (Fig. 7C), causing conduction of transistor T17 and consequently, over lead 76, resetting of bi-stable circuit 2E. The last-mentioned Z tone pulse is only sent to the exchange if the voltage level checking circuit operates at this time, i.e. condenser C1 discharged, but under normal conditions, i.e. " resetting " at the exchange end when at least one junction is idle, the resetting operation initiated by the action of the blocking oscillator causes a pulse of Y tone to be sent by resetting bi-stable circuit 1 to its " set " condition. Thus, whether a pulse of Z tone is sent or not, the resetting of bi-stable circuit 1 (Fig. 3G) causes a positive pulse to be applied over lead 77 to the Y timer 33-causing the latter to open a Y tone transmission gate and to close a Y tone reception gate-the subsequent pulse of Y tone received by the exchange making transistor T99 conduct so as to trigger bi-stable circuit IE to its " unset " condition, i.e. left-hand transistor conducting. (b) This " sets " circuit 2E, i.e. right-hand transistor conducting, and consequently multivibrator MVE is triggered-off to start a scanning sequence due to the negative condition appearing on the base of transistor T20. Each core of the scanning chain SCCE is connected to a concentration link circuit by a wire, e.g. 68 and if the link is free no further action occurs when its particular core is energized, but when each core is energized in turn a positive pulse from the collector of transistor T100 is sent to the X timer 46 to cause a pulse of X tone to be transmitted. If the link circuit had been in a condition signifying that it needed clearing down, bi-stable circuit AB2E would be in a " set " condition, i.e. left-hand transistor conducting, and the above mentioned positive pulse would have been applied to the Y timer 49, because gate C25, MR18, R32 would then be open. The pulses of X tone received at the concentrator are applied, via X-receiver 23, to transistors T33 (T34 conducting since circuit 1 is in the unset, i.e. normal, condition) T32, T31 and T30 so as to cause synchronous scanning of the line terminating circuits by the scanning chain SCC. Assuming that none of the junctions requires clearing down, the energization of a checking counting stage FCCE at the exchange causes a pulse of Y tone to be sent over the free junctions (transistors T14, T13, Fig. 7E, conducting) which tone brings about the conduction of transistors T10, T11 (Fig. 3E). The latter return bi-stable circuit 1 to its " unset " condition and cause a pulse of Z tone to be sent to the exchange in order to restore bi-stable circuit 2E to normal. The resetting of these circuits automatically " sets " circuits 2 and 3E or 3 and 4E depending upon the open or shut condition of gates associated with the left-hand transistors of the bi-stable circuits. In the case under consideration bi-stable circuits 3 and 4E are " set," since bi-stable circuits AB1 and AB1E are both in their normal states. The operation of circuits 2 and 3E which only occurs when a junction requires to be freed will be dealt with in the paragraph on " release." (c) The setting of bi-stable circuit 4E again initiates the operation of a link-scanning sequence and the synchronous stepping of the line scanner SCC, by the transmission of X pulses. Assuming that none of the links are found to be in a condition signifying that they are involved in a connection requiring to be extended over a junction for the setting up of an incoming call to the subscriber, then a pulse of Y tone is sent to the concentrator when the checking counting stage FCCE is reached in order to cause the resetting of circuit 3 and the subsequent " setting " of circuit 5. Circuit 4E is reset and subsequently circuit 6E is " set " by the pulse of Z tone produced at the resetting of circuit 3. The operation of circuits 4 and 5E which occurs when a junction is required for an incoming call will be described in the paragraph on " incoming calls." (d) The setting of bi-stable circuit 5 (Fig. 3G), causes the negative condition on the base of transistor T25 to be removed with consequential cutting-off of this transistor and hence operation of m