Patent GB-719085-A (GB)
Title: Electronic telephone systems
IPC: H04Q3/52
Filed: 1951-10-15
Abstract: 719,085. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Oct. 15, 1951, [Feb. 20, 1951], No. 24008/51. Class 40 (4). In an automatic exchange in which each circuit of a first group of circuits is individually associated with a particular column of tubes in an electron tube matrix, and each circuit of a second group of circuits is individually associated with a particular row, a sequentially operating circuit selects one circuit of the first group and prepares the tubes of the associated column for operation, and one of the circuits of the second group then operates that tube of its associated row which also forms part of the prepared column, thus completing a connection over the matrix between the selected circuit of the first group and the said circuit of the second group. In the embodiment described, the circuits of the first group are link circuits, e.g. 16, 17 (Fig. 1), the sequentially operating circuit is an electronic distributer 27 which allots an idle link circuit for use in a call, the circuits of the second group are line circuits 14, and the matrix 15 serves as both line switch and final selector. The exchange is assumed to serve one hundred subscribers. The subsets 10, 11, are of conventional type except in so far as the impulse springs of the dials are shunted by a resistor in order that the line relay of a calling line may be maintained during impulsing. Each line is associated with a row of "calling" tubes, e.g. C10, C11, ... Cln; and each link circuit, such as 16, with a column of "calling" tubes, e.g. C10, C20, .... Another row of "called" tubes, e.g. A10, All, ... Aln, is associated with each line; and a column, e.g. A10, A20, ... , with each link circuit. The "calling" tubes are used for extending calls from calling lines to link circuits, and the "called" tubes for extending link circuits to called lines. Operation of electronic distributer 27 as allotter. -The next idle link is pre-selected by the distributer 27 shown in detail in Fig. 4. When the power is switched on, + 150V is extended over the back contact of relay 520 to fire tube 503 of a ring counting chain comprising tubes 503-507. Relay 520 thereupon operates, rectifier 522 ensures that the anode potential does not fall below + 120V, and with a 70V drop across the tube, the cathode rises to +50V. This fires tube 508, thus raising the potential of lead SC-1 from-50V to +25V. If the first link is busy, the busy potential on its guard lead 101 (Fig. 2) fires tube 513 (with 503 fired), thus raising its cathode potential from -50V to -30V. This change of potential difference across resistor 523 causes tube 501 to conduct, thus reducing the anode potential of tube 508 to approximately that of ground. Tube 508 is extinguished and the potential of SC-1 drops to - 50V. Tube 501 also triggers the pair 500, whereupon the tube 502 generates a short positive pulse across resistor 525, which advances the counting chain by one step (i.e. 504 fires, 503 and 513 are extinguished), and if the second link is busy 514 fires. Assuming that the third link is idle, 515 will not fire when 505 does; and, after 514 has been extinguished, its cathode potential again becomes -50V, so that 501 is cut off. Condenser 527 discharges quickly to stop further stepping of the counting chain, and condenser 529 discharges slowly until 510 fires. Seizure of idle link.-Assuming the first link 16 to be idle, then +60V is extended to the anodes of the associated tubes such as C - 10 over lead CA-1 and relay 110 (Fig. 2). When the subscriber 1 (Fig. 1) initiates a call, the operation of his line relay 20 applies -100V to the cathodes of C10, C11, ... Cln, disables A10, All, ... A1n, and applies ground to marker 26. Tube C10 fires, reducing its cathode potential to -65V, and the potential on lead CA-1 thus drops from +60V to +5V. Operation of relay 110 in the link (Fig. 2) marks that link busy over lead 101, and the allotter 27 steps on to the next idle link. The caller then dials the wanted number, the impulses containing an A.C. component of rectangular waveform with a fundamental frequency of 10 c.p.s. The lower secondary terminal of transformer 28 (Fig. 1) and the centre tap of choke 114 (Fig. 2) are maintained at ground for A.C. signals by condensers 36 and 114A, respectively, and the variations in potential across transformer 28 are thus transmitted via tube C10 to the link 16. To avoid using a large line transformer 28, the link circuit is arranged to respond to the higher frequency components in the impulse wave. Thus, when the fundamental impulse frequency is well below the lowest frequency passed by the transformer, a short pulse of one polarity appears in the secondary at the start of each impulse, and one of the opposite polarity at its end; and the link circuit responds to these pulses. Registration of called number.-The operation of relay 110 (Fig. 2) transmits a positive pulse via condenser 129 to the binary counting chains 130-137, and 138-145 (Fig. 3), thus causing all the right-hand triodes to conduct, and brings up slow-to-operate relay 120. The pulse repeating circuit of tube 157 (Fig. 2) is triggered by the positive pulse at the beginning of each dialled impulse, and is restored by the negative pulse at its end. Hence, at the beginning of each impulse a short positive pulse is delivered to the left-hand triode of the pulse shaping circuit of tube 158, and the resulting rectangular pulse is applied to the grid of tube 159, from the cathode of which it is repeated over back 150 and front 120 to the counting chain 130-137 (Fig. 3). These pulses also render tube 161<SP>1</SP> (Fig. 2) conducting, and condenser 173 maintains it so for the duration of the train; so that relay 170 comes up during the reception of the digit. Relay 180 is operated by 170, and on the relapse of the latter, two-step relay 150 operates and locks under control of 110, thus transferring the pulsing circuit to the second counting chain 138-145 (Fig. 3). Relays 170, 180 (Fig. 2) re-operate to the second digit, and when 170 relapses, 180 locks up over front 150, and 190 (Fig. 3) and 200 (Fig. 5) operate to battery in the marker (Fig. 5) over a contact chain of the relays corresponding to 190 in the other links, provided no other link has its relay 190 operated. All links busy.-In this event all the relays 120 (Fig. 2) will be operated and the normally-operated relay 60 (Fig. 1) released, so that the common electrode of the diodes 37, 38, ... goes positive. With relay 20 operated, negative potential is applied to the left-hand electrode of diode 37 which therefore fires, thus connecting all-links-busy tone to line 1. The caller hangs up, relay 20 relapses, and tube 37 is extinguished. Operation of marker 26 (Fig. 5).- The link seizes the marker by operating relay 200, which connects anode voltages to tubes 203-210. The starter electrodes of these tubes are connected over leads A1-D1 and A2-D2 to the counting chains of the link (Fig. 3) and those which extend to ionized tubes in the counting chains fire. The corresponding relays 220-250 and 270-300 (Fig. 5) pull up in accordance with the binary equivalents of the tens and units digits, respectively. The relay of group 310-400 which corresponds to the decimal equivalent of the tens digits is thus operated and -24V is extended via relay 420 and contacts of the units relays 270-300 to the lead of group L1-L100 (Fig. 1) corresponding to the called line and thence to negative battery via a relay (e.g. 50 of line 2) if the line is idle; or to direct ground if it is busy. Called line busy.- Relay 420 operates to the busy ground and grounds the busy lead to operate 180<SP>1</SP> in the link (Fig. 2), which connects busy tone to lead CA-1. Relays 180, 190 (Fig. 3), and 200 (Fig. 5) relapse and the marker is released. Called line being rung by another caller.-Relay 420 (Fig. 5) stays down, and slow-to-operate 430 pulls up to bring up 180<SP>1</SP> in the link. Called line Idle.-Relay 420 stays down, but ringing relay 50 (Fig. 1) operates and applies -100V to the cathodes of answer tubes A20, A21 . . . A2n. The SA lead of the link connected to the marker is grounded by relay 190 (Fig. 3) and thus the tube A20 associated with that link fires. Operation of relay 50 also shortcircuits the transformer 46 and applies ringing current to the called line and ringing tone to the caller. Relay 170<SP>1</SP> (Fig. 2) pulls up in series with A20 and operates 160 which opens the input circuits to tube 157 and connects lead AN-1 to lead CA-1 through a coupling condenser. Relays 150, 180, 190 and 200 relapse. On the reply of the called party, the operation of his line relay 30 transfers the cathodes of A20, ... A2n to the line transformer 46, grounds lead L2 to mark line 2 busy, and releases relay 50. Release.-When the called party hangs up, relay 30 restores, thus grounding, the cathode of A20, and when the calling party hangs up, the release of relay 20 extinguishes C10 and A20. The link is then released.