Patent GB-822306-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: ALLUM ROBERT DEVENISH
IPC: H04Q3/00
Filed: 1956-11-05
Abstract: 822,306. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Oct. 15, 1957 [Nov. 5, 1956], No. 33631/56. Class 40 (4). In a circuit arrangement for indicating when two multi-stage synchronously-operating coldcathode tube potential distributing circuits become out of step two pairs of cold-cathode tubes are provided which are so interconnected that the striking of the first tube of a pair biases the second tube of that pair and extinguishes the first tube of the other pair and potentials are applied to the tubes of the pairs from the distributing circuits in such a manner that if the two circuits are in step a striking potential is applied to the second tube of a pair when the first tube of that pair is non-conducting so that the second tube cannot strike, but if the two circuits are out of step the striking potential is applied to the second tube of a pair when the first tube of that pair is conducting whereupon the second strikes to give an indication, the particular second tube which strikes being determined by the sense in which the two distributing circuits are out of step. As shown, two ten-stage distributing circuits OS and ES, each consisting of ten count tubes VKCA1 to VKCA0 and VKCB1 to VKCB0 and ten pulse repeating tubes VKRA1 to VKRA0 and VKRB1 to VKRB0, are driven by the pulse sources PSA and PSB controlled by common equipment (not shown) to provide synchronous outputs. H.T. is permanently connected to all the tubes except the pulse repeating tubes to which switched H.T. is applied over lead SHT so that they conduct only for a short period beginning at approximately the same time as a pulse is delivered from the pulse sources. When the H.T. is switched on, tubes VKAL and VKBL both strike and the alarm relay AL pulls up. Operation of key KAR opens the anode circuits of these two tubes and the circuit of relay AL, and also strikes the start tubes VKAST and VKBST. The pulse sources PSA and PSB are inhibited (by means not shown) during the time KAR is operated, but thereafter the first pulse strikes the stage 9 pulse repeating tubes VKRA9 and VKRB9, biased by the striking of VKAST and VKBST, which apply scanning pulses to leads VA9 and VB9 and to the permanently biased stage 0 count tubes VKCA0 and VKCB0 which strike. VKRA9 and VKRB9 are extinguished on the disconnection of the H.T. from SHT. VKRA0 and VKRBO strike to the next pulse and the two distributing circuits continue to be driven in like manner. Operation of checking circuit.-This circuit consists of the two pairs of tubes VKUCA and VKUPA, and VKUCB and VKUPB, pulse potentials being applied from stage 0 and stage 7 of OS to the trigger electrodes of VKUCA and VKUCB, respectively, and from stage 1 and stage 6 of ES to those of VKUPA and VKUPB, respectively. When the two distributing circuits are in step the sequence of operations is that VKRA0 conducts, striking VKUCA which biases VKUPA, and on the next step VKRB1 conducts and pulses VKUPB which not being biased, does not strike. When stage 6 is reached, VKRB6 conducts, striking VKUCB, thus extinguishing VKUCA and biasing VKUPB. The bias is thus removed from VKUPA so that when it is pulsed from VKRA7, VKUPA does not strike. When stage 0 is again reached, VKUCA strikes and extinguishes VKUCB. If, due to a fault, one distributing circuit misses one or more steps, either VKUPA or VKUPB will strike, followed by VKLA which brings up relay AL. If circuit OS is lagging on ES, then VKRAO will strike at the same time or later than VKRB1, and, since the potential at the cathode of VKUCB and hence the bias on VKUPB does not disappear instantaneously, VKUPB will strike. If OS is leading ES, VKRA7 will strike at the same tune or earlier than VKRB6, in which case VKUPA is still biased and will strike. At the initial switch on of the equipment or if an interruption of the H.T. supply occurs, the count tubes of both OS and ES may be extinguished. To give an indication of this condition the resistors R10, R13 (connected to ground) and R11, R14 (connected to - 50 volts) are provided, their values being such that the potential drop across R10 and R13 due to the connection of R11 and R14 is approximately equal and opposite to that due to the striking of a count tube. The current in R11 and R13 is therefore normally negligible and the grids of VA and VB are at ground potential. Both these tubes therefore conduct and the potential drop across R12 and R15 holds the trigger electrodes of VKAL and VKBL below the striking voltage. However, if no count tube is fired in one or both distributing circuits, the junction of R10 and R11 and/or that of R13 and R14 becomes negative by at least 1 volt and the resultant drop in the anode current of VA and/or VB allows VKAL and/or VKBL to strike. The consequent operation of AL gives an alarm. Operation of the reset key KAR restarts the two circuits at stage 9 as at the initial switch on.